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AUGUST 2021 ISSN 1030-2662 08 9 771030 266001 $995* NZ $1290 o n g s INC GST INC GST Im g c ti Dia The VERY BEST DIY Projects! agin Looking Through The Body 26 Second Generation Colour Maximite 2 38 Harold S. Black & the History of Op Amps 46 Nano TV Pong using an 8-pin PIC 68 Multi-purpose Battery Manager Build your own Wi-Fi Relay Controller Easy two-part setup: CONNECT any appliance or device you want to test or activate through the relay module, then use the built-in web-app to CONTROL them via your smartphone or computer. Great for automatic plant watering kits, testing devices, controlling lights, etc. Relays handle up to 10A current and are not suited for mains power. SKILL LEVEL: Beginner CLUB OFFER BUNDLE DEAL 4995 For step-by-step instructions scan the QR code. $ SAVE 20% www.jaycar.com.au/wifi-relay-controller See other projects at KIT VALUED AT $65.85 www.jaycar.com.au/arduino FROM 3 $ 45 Jiffy Boxes ABS plastic. Industry standard sizes from 83x54x31 to 197x113x63mm available. HB6005-HB6025 100 $ gift card Awesome projects by On Sale 24 July to 23 August, 2021 Aerosol Service Aids ONLY 2 $ 95 EA Ferrule Crimp Connectors Pack of 20. Available in 3 types to suit different cable sizes 0.75mm2, 1.50mm2 & 2.5mm2. PT4433-PT4633 20 PCE Must have for all electronic, electrical & field service applications. 175g. Circuit Board Lacquer NA1002 Contact Cleaner Lubricant NA1012 ONLY 1150 $ EA Got a great project or kit idea? If we produce or publish your electronics, Arduino or Pi project, we’ll give you a complimentary $100 gift card. Upload your idea at projects.jaycar.com ONLY 3495 $ 5 Piece Stainless Steel Tool Set Set of 5x115mm cutters & pliers. Soft ergonomic grips. TH1812 Looking for your next build? Silicon Chip projects: jaycar.com.au/c/silicon-chip-kits Kit back catalogue: jaycar.com.au/kitbackcatalogue 1800 022 888 www.jaycar.com.au Shop online and enjoy 1 hour click & collect or free delivery on orders over $99* Exclusions apply - see website for full T&Cs. * Contents Vol.34, No.8 August 2021 SILICON CHIP www.siliconchip.com.au Features & Reviews 12 Advanced Medical & Biometric Imaging – Part 1 The development of non-destructive ways, such as X-rays, to look inside humans and animals has been critical for diagnosing diseases and for performing corrective procedures – by Dr David Maddison 35 Automated PCB Assembly for Home Constructors For a small fee, you can have your own PCBs professionally assembled with dozens, or even hundreds, of SMD components – by Geoff Graham 38 The History of Op Amps Harold S. Black’s discovery of negative feedback paved the way for the development of operational amplifiers, which are widely used in all sorts of electronic devices, especially for audio – by Roderick Wall & Nicholas Vinen 88 El Cheapo Modules: USB-PD Triggers In part one of our two-part series on imaging technologies, we focus on the medical uses of it along with its history. For example: CT scans, MRI, ultrasound etc – Page 12 We look at a series of four different USB-PD trigger/decoy and tester modules. These are used to adjust the voltage and current levels provided by a USB-PD compatible charger or power source – by Jim Rowe Constructional Projects 26 Second Generation Colour Maximite 2 – Part 1 The second generation version of the Colour Maximite 2 is a backwardscompatible, improved version of the first. It has four times as much RAM, support for 1920x1080 video, 24-bit colour and more – by Geoff Graham & Peter Mather 46 Nano Pong using an 8-pin PIC In contrast to the authentic Arcade Pong design from June 2021, our Nano Pong costs just a few dollars to make and fits on a mini PCB measuring 43 x 16.5mm. It simply connects to a TV via an RCA cable – by Tim Blythman The Gen2 Colour Maximite 2 now has the ability to connect a mouse, along with two connectors for Wii controllers. You can even add WiFi via an ESP-01 module – Page 26 68 Multi-Purpose Battery Manager This Battery Manager is an update to our Battery Multi-Logger, and interface to the High-Current Battery Balancer. It can connect or disconnect up to four loads/ chargers, and switch well over 20A at 10-60V – by Tim Blythman 92 Simple Linear MIDI Keyboard This MIDI Keyboard provides an alternative layout to our 64-key MIDI Matrix by letting you join a series of 8-button modules laterally – by Tim Blythman Your Favourite Columns 61 Serviceman’s Log Rocking Raucous Retro Roland Repair – by Dave Thompson 80 Circuit Notebook (1) Portable amplifier built from modules (2) Frequency meter with non-contact mains reading Op amps are used in a huge variety of different circuit configurations, like the inverting amplifier shown above. They rely on the principle of negative feedback, which was discovered by Harold Steven Black in 1927 – Page 38 98 Vintage Radio Bush VTR103 AM/FM radio – by Ian Batty Everything Else 2 Editorial Viewpoint 4 Mailbag – Your Feedback 87 Product Showcase siliconchip.com.au 96 Silicon Chip Online Shop 107 Ask Silicon Chip 111 Market Centre 112 Notes and Errata Australia’s electronicsIndex magazine 112 Advertising Our version of Pong is built on a nano-sized PCB (shown at actual size). It requires just a few discrete components, August 2021  3 a PIC12F1572, the two controllers and an RCA cable – Page 46 SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke, B.E.(Elec.) Technical Staff Jim Rowe, B.A., B.Sc. Bao Smith, B.Sc. Tim Blythman, B.E., B.Sc. Nicolas Hannekum, Dip. Elec. Tech. Technical Contributor Duraid Madina, B.Sc, M.Sc, PhD Reader Services Rhonda Blythman, BSc, LLB, GDLP Advertising Enquiries Glyn Smith Phone (02) 9939 3295 Mobile 0431 792 293 glyn<at>siliconchip.com.au Regular Contributors Dave Thompson David Maddison B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Geoff Graham Associate Professor Graham Parslow Ian Batty Cartoonist Brendan Akhurst Founding Editor (retired) Leo Simpson, B.Bus., FAICD Staff (retired) Ross Tester Ann Morris Greg Swain, B. Sc. (Hons.) Silicon Chip is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 626 922 870. ABN 20 880 526 923. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Subscription rates (Australia only): 12 issues (1 year): $105, post paid 24 issues (2 years): $202, post paid For overseas rates, see our website or email silicon<at>siliconchip.com.au Recommended & maximum price only. Editorial office: Unit 1 (up ramp), 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9939 3295. ISSN 1030-2662 Printing and Distribution: Editorial Viewpoint Productivity Commission report on the Right to Repair T he Productivity Commission has released a draft report on the right to repair, which you can view at www.pc.gov.au/inquiries/current/repair#draft It is open for comments. However, by the time you read this magazine, the comment period will have ended. While the introduction makes it clear that they understand the issues raised by the right to repair movement, I don’t agree with some of their conclusions. For example, they state that “Additional policies to combat premature product obsolescence (in the form of product standards or expanded consumer protection laws to address planned obsolescence) would be unlikely to have net benefits for the community.” I think most Silicon Chip readers will agree that this is wrong. They seem to be conflating the concern that manufacturers purposefully create products with a short lifespan (which I think is generally not true, with some exceptions) with the concern that, by limiting repair options, manufacturers make repairing products so difficult that users have little choice but to replace them when they fail. By legislating to expand those repair options, such as ensuring that spare parts are available beyond the warranty period, consumers could more economically keep devices functional. That would be a net benefit for the community, and I have plenty of anecdotes to support this (many of them are published in our Serviceman’s Log column). For example, I had an air conditioning unit fail after less than ten years due to PCB track corrosion. The serviceman who came out told me that a replacement board was not available, so I would have to replace both the outdoor and indoor units. I was able to fix it by soldering a wire link across the corroded track, which took about two minutes and cost nothing. That unit went on to function for many more years. Consider that the vast majority of consumers in that position would have been forced to shell out perhaps $1000 or more for new units plus the cost of removing the old units and installing the new ones. They might have also had to make some cosmetic repairs due to the new unit not being the same size and shape as the old one. Not to mention all the extra waste generated. All that expense and hassle for a single corroded track that was visually obvious. I’m not knocking the serviceman; I don’t expect air conditioning companies to train technicians to make component-level repairs, and he helped me make the repair which saved me a lot of money and hassles. But that replacement board really should have been available. If it had been, I don’t think it would have cost all that much as it was little more than an infrared receiver and a couple of ICs that relayed commands back to the main control board. And I had already paid for the call-out, so even with the labour to come and swap the modules over, the repair probably would have cost a couple of hundred dollars total; way less than a new aircon. I bet the same story is repeated over and over with washing machines, dishwashers, stoves and all manner of appliances still well within their useful lives. “Sorry, we can’t get a replacement for the module that has failed. You’ll have to buy a new unit.” Or something along those lines. So, while this report seems generally supportive of the right to repair, I don’t think the authors truly understand the situation. While there are costs associated with requiring manufacturers to offer spare parts for a longer period (more in line with the actual useful lives of those products), likely raising the price of those goods slightly, I am confident that the benefits would outweigh those costs. I will be stating this in a submission to the Productivity Commission, and I hope they take it into consideration. by Nicholas Vinen 24-26 Lilian Fowler Pl, Marrickville 2204 2  Silicon Chip Australia’s electronics magazine siliconchip.com.au 100,000+ NEW PRODUCTS ADDED IN PAST 90 DAYS DIGIKEY.COM.AU ENABLING THE WORLD’S IDEAS DIGIKEY.CO.NZ *Australia: A shipping charge of $24.00 AUD will be billed on all orders of less than $60.00 AUD. A shipping charge of $20.00 USD will be billed on all orders of less than $50.00 USD. All orders are shipped via UPS, Federal Express, or DHL for delivery within 3-4 days (dependent on final destination). No handling fees. All prices are in Australian dollar or United States dollar. New Zealand: A shipping charge of $26.00 (NZD) will be billed on all orders of less than $66.00 (NZD). A shipping charge of $20.00 USD will be billed on all orders of less than $50.00 USD. All orders are shipped via UPS for delivery within 3-4 days (dependent on final destination). All prices are in New Zealand dollar or United States dollar. Digi-Key is an authorized distributor for all supplier partners. New product added daily. Digi-Key and Digi-Key Electronics are registered trademarks of Digi-Key Electronics in the U.S. and other countries. siliconchip.com.au Australia’s electronics magazine August 2021  3 © 2021 Digi-Key Electronics, 701 Brooks Ave. South, Thief River Falls, MN 56701, USA MAILBAG your feedback Letters and emails should contain complete name, address and daytime phone number. Letters to the Editor are submitted on the condition that Silicon Chip Publications Pty Ltd may edit and has the right to reproduce in electronic form and communicate these letters. This also applies to submissions to “Ask Silicon Chip”, “Circuit Notebook” and “Serviceman”. FPGA & CPLD based designs desired Some months ago, your editorial spoke of the large number of requests you receive for retrograde articles and projects, and your reasoning for keeping these to a minimum. But those which you include seem quite arbitrary. We have had several issues with a series on videotape and a recent series on the ‘steam-driven internet’, also known as “Digital Radio Modes”. And on top of this, you have a regular column on Vintage Radio. So I scoffed when I saw the project last month about a Pong game built to the original design. But after reading it, I was entranced! Congratulations to Dr Hugo Holden. The detail in the design and the description of the most obscure quirks in, and improvements to, the original was an excellent example of exactly the type of retro project that really interests me; not that I have any intention of building it! I previously built an Arduino-based Pong game. Some people consider PIC or FPGA recreations of old computers to be inferior to pure redesigns like Hugo’s, but this is not necessarily true. For example, take the design behind Grant Searle’s Arduino-based Pong (http://searle.x10host.com/AVRPong/ index.html). It recreates the AY-3-8500 ‘game on a chip’ which was popular in the 1970s. Grant even went to extraordinary lengths to recreate visual artifacts of different versions of the chip. As far as I am concerned, the creative process in producing a design in hardware or software is identical. But for the hardware purists, visit: www. glensstuff.com/videopong/videopong. htm It is an entire pong system built from discrete components (yes, transistors!). It is beautiful, yet totally impractical! So many of your projects are 4  Silicon Chip designed around PICs. But for balance, I would argue for more projects using FPGA and CPLD chips. Last year, you published an article about FPGAs, but I don’t recall any follow-up projects with their practical application. I believe these are particularly suitable for retro projects where the digital logic is relatively simple (by today’s standard), but easy to understand. It could provide a good introduction to the application of these chips, while still engaging with the hobby interests of a large proportion of your subscribers whom I suspect, like me, have an interest in the new and the old, and need to know how these technologies apply in the real world. In fact, the Pong game would be an excellent candidate. Phil Butler, Bentleigh East, Vic. Comments: To some extent, the articles we publish reflect the interests of our contributors and our readers who make suggestions. As you say, some of these articles are pretty impractical but also interesting. That’s the main thing we look for in an article; you don’t need to be sentimental about old technology, as long as the article is interesting enough in its own right. It’s often how the past designers got around the limitations of contemporary technology that makes the articles so fascinating. We will surely use a CPLD or FPGA in a project at some point. We are familiar with these devices and know how to work with them; it’s just a matter of coming up with an idea of something useful to build that requires one. We don’t want to use such a device ‘just because’. Telcos vs TV broadcasters In the document “New rules for a new media landscape - modernising Australia’s electronics magazine television regulation in Australia” at siliconchip.com.au/link/ab6d, there are quite a few facts that the telcos did not mention in their submissions to this consultation: • Every eight years, the telcos switch off their oldest technologies, forcing users to buy new phones. The next planned switchoff is 3G in 2024. • The 3G switch off will leave its spectrum available for 5G. • The telcos are now using the 2G spectrum for low-speed 5G. • On 21st April 2021, the telcos paid $647,642,100 for 2500MHz worth of the 26GHz band (check siliconchip.com.au/link/ab9i). This band allows for very highspeed data transfers. The telcos have been pushing for an increase in their spectrum allocation. They want 610-694MHz (TV channels 40-51). In 2014, the TV channels in use were restacked into six consecutive channels for each transmitter site. This means a channel each for ABC, SBS, the three commercial stations and a spare channel. Channels 40-45 and 46-51 are used to cover many blackspots and for some high-powered regional sites. The telcos want the 84MHz band above when they have just purchased a 2500MHz band, and they will also be able to reuse the spectrum they are currently using for 3G (at 850MHz, 900MHz and 2.1GHz). The telcos are pushing 5G phones, which will reduce the traffic on 4G networks in the busiest areas, primarily metropolitan and surrounding areas. Compare the change in TV standards over time to mobile telephony. Australia started monochrome TV broadcasting in 1956 and backwardscompatible colour broadcasting in 1975, which was not switched off until 2013. That’s over 50 years using much siliconchip.com.au POWER SUPPLIES PTY LTD ELECTRONICS SPECIALISTS TO DEFENCE AVIATION MINING MEDICAL RAIL INDUSTRIAL Our Core Ser vices: Electronic DLM Workshop Repair NATA ISO17025 Calibration 37 Years Repair Specialisation Power Supply Repair to 50KVA Convenient Local Support SWITCHMODE POWER SUPPLIES Pty Ltd ABN 54 003 958 030 Unit 1 /37 Leighton Place Hornsby NSW 2077 (PO Box 606 Hornsby NSW 1630) Tel: 02 9476 0300 Email: service<at>switchmode.com.au Website: www.switchmode.com.au 6  Silicon Chip the same technology and the same channels, compared to the eight-yearly cycle of telcos. Currently, broadcasters do not know what proportion of the operating TVs can decode MPEG4 (H264) video and HE-AAC V2 audio signals, demodulate DVB-T2 signals, decode HEVC (H265) video and xHE AAC sound (used by Netflix) or handle surround sound. In 2015, AS 4933:2015 (Digital television – Requirements for receivers for VHF/UHF DVB-T television broadcasts including ancillary services) finally specified MPEG4 decoding support, despite TVs with this capability being on the Australian market for more than five years. Had this been done earlier and the number of receivers sold tracked, broadcasters would know when to switch to the new standard, allowing all standard-definition transmissions to be replaced by high-definition. By comparison, New Zealand started transmitting all programs using MPEG4 in 2013. In 2018, there was a DVB-T2 trial on the Gold Coast. DVB-T2 and HEVC support could have been required after that completed. From the specifications of currently available TVs, it is difficult to determine if they can receive DVB-T2 and HEVC. Both are needed for Ultra High Definition TV (UHD or 4K), which is not compatible with older TVs. UHD TV is now available via Foxtel using the DVB-S2 satellite and Netflix via NBN. Viewer Accessed Satellite Television (VAST) receivers are all DVB-S2 and MPEG4 capable and can handle UHD if the receiver can decode HEVC-compressed signals. VAST is provided to all telecasters by the government for those outside the coverage area for terrestrial TV. Telcos and streaming companies are always trying to give the illusion that they are the primary method of program delivery by quoting percentage changes in the number of users. But they don’t mention the numbers as a percentage of the total audience. Telcos would like to convey TV programs via their networks, particularly mobile, for profit. The profits can be greater if they restrict the range of programs. Broadcasters need to be technically proactive to fight such threats. I suggest that the sixth spare TV channel should be used to transmit a UHD primary program from each network. This will require 602 additional DVB-T2 transmitters for national coverage. Many would be high-powered transmitters, which would also require electricity supply upgrades to transmitter sites. All broadcasters wish to keep their existing program streams. Suppose they modify their existing transmitters to DVB-T2 and use HEVC video and xHE AAC sound encoders. In that case, they can transmit their primary program in UHD and all other programs in progressive HD. TVs that support DVB-T2 demodulation, HEVC video and xHE AAC sound can receive the older signals; the reverse is untrue. This means that we will need a switchover like the one from analog to digital in 2012. TV set prices have dropped in real terms since then. Proactively, AS 4933:2015 needs to be upgraded to UHD now, so that new TV purchases do not become stranded assets. Alan Hughes, Hamersley, WA. Australia’s electronics magazine siliconchip.com.au Design, Develop, Manufacture with the latest Solutions! Powering New Technologies in Electronics and Hi-Tech Manufacturing Make new connections at Australia’s largest Electronics Expo. See, test and compare the latest technology, products and solutions to future proof your business SMCBA CONFERENCE The Electronics Design and Manufacturing Conference delivers the latest critical information for design and assembly. Industry experts will present the latest innovations and solutions at this year’s conference. Details at www.smcba.asn.au In Association with Supporting Publication Organised by Screw heads and driver bits I found your article on this subject in a recent Silicon Chip magazine very interesting indeed (Right to Repair, June 2021, p13; siliconchip.com.au/ Article/14881). It was remarkable to see so many different styles of screw heads have come out in the past few decades. But I have one that wasn’t mentioned. The screw has a pentagonal head. Recently, I had an electrician work on my solar PV system, originally installed around 2008. The screws used to hold the 60W Kaneka panels down had five-sided heads. He couldn’t work out why his hexagonal sockets wouldn’t undo the screws, and even borrowed some from me to try. Of course, he soon discovered why he couldn’t undo the screws and had to order a driver bit from interstate. The suppliers found one in Melbourne, and it had to come to Adelaide via Brisbane. The electrician left the driver bit with me for when someone else has to move the panels. No doubt the cost of it was added to his invoice. Keith Gooley, One Tree Hill, SA. Comment: talk about reinventing the wheel! Feedback on bugs & updates editorial Your July editorial on “Software: too many bugs, too many updates” was a great viewpoint, and I share your point to perfection. I have to update my Apple devices and also the Windows PCs. A lot of time is spent doing this task, which sometimes results in bricked computers and Apps which no longer work. On the Apple Mac it is not so bad as with any OS upgrade/update, only the Apps are generally affected and will need updating, but some will be deleted if they won’t work under the new OS. Apple generally tells you before that some may not work, but does not advise which ones. You also need to enable the camera before updating as I have it disabled under Kaspersky internet security settings; the update will not work with any device blocked from access – a lesson I had to learn the hard way. The new iOS and iPadOS coming out shortly, version 15, is slated to break a few Apps, but you can keep using OS version 14.x on the devices you currently use. 8  Silicon Chip It is a lot more difficult on Windows machines because, as happened with the Windows 10 upgrades, they brick many PCs. It would no longer run on older but still useful hardware. Much useful software also could not run on that version of Windows. A new version of Windows (11) is about to hit the market, and it too is going to brick newer PCs because of the requirement of having a hardware TPM (trusted platform module) on the system. My latest motherboard, a Gigabyte GA-Z270X-UD3 with an Intel Core i7 processor, has a connector to add the TPM plugin, but it is not available. I am sick of having to upgrade perfectly good, working hardware because Microsoft does not support it. If you have to buy new hardware and software to run the new operating system, it becomes a very expensive exercise. My other bugbear is that Microsoft and Adobe only want to drive subscription software like Photoshop and Office 365. This is fine for companies that use it daily and can tax-deduct this as a business expense. For private users that use the software very infrequently, it is a wasted expense, especially if it stops working if you stop paying the subscription. Also, I have found out that Windows 11 Home version requires you to be online to use it, but not the Pro version, and a Microsoft account is required to use any version of Windows 11. Have you read the long EULA of Windows 10? One needs to read the bit about the online free storage. It appears your data is theirs to use if they so choose, and they don’t actually have to delete all your data at your request. Wolf-Dieter Kuenne, Bayswater, Vic. Comments: The worst part about the forced Windows 10 upgrade was that it worked on older hardware initially, but then it got slower and slower to the point where we had to replace several computers that were perfectly fine previously running Windows 7. The biggest problem was RAM usage. These machines could not be upgraded beyond 4GB, and Windows 10 would allocate around 3GB at boot. Load one or two programs and they started swapping and became uselessly slow. If some of the requirements of Australia’s electronics magazine Windows 11 aren’t changed, we will hold off upgrading as long as possible. Having to log into a Microsoft account to use a computer is simply not on. It’s worth noting for others that while some motherboards have a hardware TPM connector, these are not guaranteed to work for installing Windows 11. This is despite people trying to scalp these TPM modules online. Most newer computers have TPM built-in to the CPU, and only require a change to a BIOS setting to enable it. However, we think the recommended storage and processing requirements for Windows 11 are currently too high, and there are too many computers that aren’t that old which won’t be able to install Windows 11. They fix it once it fails completely You published my letter in the March 2021 issue about the problems I was having with my NBN FTTN connection (on page 9). The FTTN connection finally broke properly; I had no NBN at all. After a couple of days I emailed my provider, and they got the NBN folks to come and fix it. A couple of techs came out in separate trucks, as is apparently required these days. I asked why two were sent and was told that one was a trainee. I was happy about this as I thought that the telcos had given up on training people. Anyway, they fixed it, and I think correctly. The maximum downlink speed is now 80+Mbps. Previously I saw around 40Mbps maximum at best, and towards the end, just before it broke, less than 20Mbps. I am still on a bottom-level plan, so the connection remains slow, but at least now it is very solid. I have a 4G mobile data plan with a different provider for backup, portability, and the rare occasions when I need to upload/ download something large quickly. Apparently, NBNco is enabling/ requiring SOS/ROC (Save Our Showtime/Robust Overhead Channel) on FTTN (and FTTB?), which might make things better with poor lines. Roger Plant, Belgrave Heights, Vic. Comment: How frustrating that telcos often won’t believe there is a problem with your line until it stops working. We’ve repeatedly had that experience in the past (and not just with NBNco). But it’s good to hear that they eventually fixed yours. siliconchip.com.au “Setting the standard for Quality & Value” Established 1930 ’ CHOICE! 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Connectivity tests around all pins of IC2, and the directly connected parts, showed I had a short between two pins, and a close inspection showed it did look suspect. Solder wick fixed that. Both units worked straight off when complete. But I found one ‘bug’ with its operation. If the device is left on and it times out, the PIC micro shuts down the output amp and then goes to sleep. As described in the article, that leaves almost no power being used. But even when you turn off the power from the batteries, the 100µF capacitor stays charged up, with virtually no load. So the micro will stay asleep and not reboot until that capacitor eventually discharges. So, when it has timed out, you need to turn off the power switch for half an hour or more while the 100μF cap slowly discharges. You will not be able to get it to restart till then, and if you do turn it on again too soon, it will just recharge the cap, and you’ll have to wait longer. A fairly easy solution would be to wire the power switch to discharge the cap when it is switched off. The switch would have to be connected the opposite way around, with the common contact being the ‘power out’ to the circuit, and the off switch contact going to ground via a low resistance. Then when you switch it off, it will discharge the cap, and the micro will reboot when you turn it back on. Noel Bachelor, Seven Hills, NSW. Comments: Thanks for your feedback. You are correct that the 100μF capacitor needs to discharge before IC1 comes out of sleep when power is reapplied. The circuit was mainly designed to help an animal pet or baby to sleep, and in that case, the capacitor discharge period is not critical. Your 100μF capacitor must be a good one that it takes so long to discharge; it has approximately 18MW equivalent leakage. Perhaps use a different capacitor or a lower capacitance such as 22μF. Your solution to use the power switch to discharge the capacitor is also effective, but you would need to cut tracks on the PCB. Vintage electronics and electric blanket hazards Thank you for the June edition of Silicon Chip. As usual, it was well worth reading. I won’t comment on the “right to repair” other than to say that I expect a significant response from other readers. My favourite article in that issue was the Better Mousetrap by Bruce Boardman in the Circuit Notebook section. There is not much to the mechanics, but mechanics always brings electronics to life, even if it is the simple releasing of a latch. Please include more simple projects like that one from Mr Boardman. It adds that extra bit of interest to the magazine. The Mini Arcade Pong reproduction by Dr Hugo Holden is a bit of a surprise considering that it is so much easier 10  Silicon Chip Australia’s electronics magazine siliconchip.com.au to use a microcontroller. But then, a layout of TTL chips exposes the workings and complexity needed just to create a simple game like Pong. For those readers who like raw electronics and those who are into retro electronics, this project must be a real pleasure. Even for myself, it had some interest. Before I discovered microcontrollers, I created circuits and PCBs like the Pong game but not with so many ICs. Quite frankly, now I will always use microcontrollers unless there are compelling reasons against them. It is almost winter again, and I have fitted my electric blanket to the bed, and I am reminded of the two occasions when my bed almost caught on fire. Both of the electric blankets had removable leads with plugs that had fake strain reliefs. I had checked the leads from time to time, but unknown to me, the wires were breaking as they entered into those plastic mouldings. Eventually, all the strands broke in one of the wires, resulting in an arc that burned through the insulation. Thankfully, I was in bed in both instances, so I disconnected the power and extinguished the glow with my fingers. There is not much that can be done to correct that problem except replace the designs with better ones. However, there is another problem that is just as serious, and I am guilty of creating the problem. I turn the blanket onto full power and forget that it is turned on. With several ordinary blankets on top, the temperature can rise alarmingly. I would like to suggest another project where a temperature sensor is fitted under the electric blanket and is used to control the temperature. I know it is a simple project, and I could do it myself, but it will be available to everyone if Silicon Chip publishes it as a project. George Ramsay, Holland Park, Qld. Comment: a small, button-cell-powered temperature alarm is a great idea, especially if it is ‘set and forget’. Advanced GPS Computer predecessor I was interested to see the Advanced GPS Computer project in your June 2021 issue (siliconchip.com.au/ Series/366). Some time ago, I built a GPS speed warning device for my ancient Jaguar, which yearns to exceed the local 50km/h limit, whereas I prefer to keep my licence! I used a Micromite fed from a GPS module, displaying the speed on a small SDI display. I have a selectable limit from 40km/h to 110km/h, and have programmed the Micromite to sound a confidence tone from 10km/h below the selected limit, OK double pips from 3km/h below up to the chosen limit, and an alarm if it is exceeded. The alarm flashes a red light and emits a strident warble. When the satellites have not been acquired, there is also a warning. By the way, I note the handsome increase in magazine size. A downside: I’m not sure if I am too rough on it, but my magazine now comes apart too readily. Alan Ford, Salamander Bay, NSW. Comment: We occasionally have problems with the magazine stapling or gluing being insufficient. Please report it to us if that happens, so that we can inform our printers and they can take corrective actions. SC siliconchip.com.au Helping to put you in Control FEMA I4E configurable signal converters These can be configured to measure voltage signals (AC and DC) with ranges from 0 / 50mV up to 0 / 600V, current signals from 0 / 5mA up to 0 / 5A, and frequencies from power lines (up to 100Hz). The output is a standard process signal configurable to 4 / 20mA or 0 / 10Vdc. SKU: FMB-001 Price: $263.95 ea 4-20 mA Loop Powered LP4 Indicator Configurable, 96×48 mm in-loop LED display of process variables. Scale and offset setting allow the value to be displayed in appropriate engineering units. SKU: FMI-010 Price: $171.60 ea ESM-3700-N Process Indicator 230VAC ESM-3700 series Programmable Digital Process Indicators are designed for measuring the process value. 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SKU: AXS-500 Price: $142.95 ea For Wholesale prices Contact Ocean Controls Ph: (03) 9708 2390 oceancontrols.com.au Prices are subjected to change without notice. Australia’s electronics magazine August 2021  11 Advanced medical & Biometric Imaging Part 1: By Dr David Maddison One of the greatest advances of modern times has been the ability to non-destructively look inside people or animals to aid in diagnosing diseases or other conditions. This article describes the history of that technology plus the latest innovations in medical imaging. Image source: www.pexels.com/photo/person-holding-silver-round-coins-4226264/ M any imaging technologies have been developed to date; too many to cover in one article. So this article aims to cover the most important, popular and interesting ones. Next month, we will have a follow up article describing similar imaging systems that look inside machines, vehicles and other objects. X-rays One of the first and most significant medical imaging techniques to be used, still in widespread use today, involved X-rays. Wilhelm Conrad Röntgen is credited with the discovery of X-rays in 1895. However, others had previously noted mysterious rays emanating from various gas discharge tubes such as Crookes tubes, which were used to produce cathode rays (see Figs.1 & 2). It is believed that X-rays were first inadvertently and unknowingly produced by a gas discharge apparatus in 1785 by William Morgan (born 1750). In 1888, Philipp Lenard discovered that something came out of a Crookes tube, causing photographic plates to become exposed. In 1889, Ivan Puluj (Іва́н Пулю́й) published his observation that emanations from a gas discharge tube would darken photographic plates. Then Fernando Sanford described “electric photography” in a letter sent in 1893. Then in 1894, Nikola Tesla observed that his photographic film was damaged by unknown radiation seemingly associated with his Crookes tube experiments (including when he photographed Mark Twain). X-rays were adopted for imaging purposes soon after the first demonstrations by Röntgen (Fig.3). The hazard of over-exposure to X-rays was almost immediately recognised. How X-rays are generated X-rays can be generated by a variety of methods. One common approach is Fig.2: a Crookes tube, shown energised at the bottom. The cathode is at the left and the anode underneath. Source: Wikimedia user D-Kuru. Fig.1: early medical experiments using a Crookes tube to generate X-rays in 1896. The man at the back is examining his hand using a fluoroscope screen while the other is taking a radiograph with a photographic plate under his hand. The tube is powered by an induction coil in the background; its drive pulses are generated by a motor-operated interrupter with a rheostat to vary the coil current and thus the voltage. 12  Silicon Chip Australia’s electronics magazine siliconchip.com.au ► ► Fig.3: one of the first published X-ray images, by Wilhelm Röntgen, of Albert von Kölliker’s hand. It was taken at a public lecture on the 23rd of January 1896. The very first picture was of Röntgen’s wife’s hand, but is of inferior quality. Fig.4: a typical X-ray emission spectrum with a tungsten target. Original source: ARPANSA. releasing high-speed electrons from a hot cathode and colliding them with a target, which is also the anode; in modern X-ray tubes, it is typically made of tungsten. The anode and cathode are housed in an evacuated tube. The energy of the X-rays produced is determined by the voltage by which the electrons are accelerated. X-rays are produced when electrons hit the target by one of two processes: 1) When electrons of a high enough energy knock electrons from the inner orbitals of atoms, and electrons fill such vacancies from higher energy levels, X-rays of a particular frequency are emitted. 2) By the process of Bremsstrahlung (“braking radiation”), where electrons are deflected in the vicinity of charged atomic nuclei of the target, which results in X-ray emission with a continuous range of frequencies. The result of these processes is an X-ray emission spectrum with a continuous range from (2) plus some peaks from (1) – see Fig.4. Crookes tubes were initially used to investigate cathode rays, leading to the development of the cathode ray tube. The production of X-rays was an unintended byproduct of this, leading to their discovery. X-rays are produced when electrons bypass the shadow mask and impinge upon the glass, causing the glass to fluoresce and emit X-rays. X-rays are also produced when the high-speed electrons hit the anode at the bottom. After the discovery of X-rays, siliconchip.com.au specialised Crookes tubes were developed which were optimised to produce X-rays. They had a heavy metal anode made from a metal such as platinum, angled to produce a beam of X-rays from the side of the tube. This is more or less the arrangement for a modern X-ray tube – see Fig.5. Incidentally, the CRTs used in older TVs and oscilloscopes could produce X-rays, although generally not enough to be of concern. Most CRTs had X-ray absorbing glass to minimise the problem. With a Crookes tube, X-rays are generated with the application of 5kV or more; the higher the voltage, the higher the energy of the X-rays produced, leading to greater penetration through targets. Fig.5: X-rays are produced in a tube when high-speed electrons strike the metal target. This is a more efficient method than Crookes tubes. Table 1: X-ray sources for various applications Application Dental Acceleration voltage Source X-ray energy 60kV Tube 30keV General medical 50-140kV Tube 40keV CT scan 80-140kV Tube 60keV Airline bag screening 80-160kV Tube 80keV Shipping container 450kV-20MV Tube or linear accelerator 150keV-9MeV Structural analysis 150kV-450kV Tube 100keV X-ray therapy 10MV-25MV Linear accelerator 3MeV-10MeV Australia’s electronics magazine August 2021  13 linac and are ultimately transferred to the primary storage ring. As the electrons go around the storage ring, they are deflected by magnets, causing them to emit radiation at a range of possible frequencies due to Magnetobremsstrahlung (“synchrotron radiation”; a variation of braking radiation). There are several “beamlines” where different experiments are conducted. One of the beamlines of the Australian Synchotron is the Imaging and Medical Beamline (IMBL). It delivers the world’s widest synchrotron X-ray beam at extremely high resolution, greater even than MRI. How are X-rays recorded? Fig.6: a medical linac (linear accelerator) for producing X-rays for radiotherapy. Original image by The Scientific Sentence. Fig.7: the operation of a linear accelerator. An electron is injected at the left, accelerated to the first “drift tube” and when it gets to the end of that, the polarity changes to the alternating RF current, it is accelerated across the gap to the next one, and so on. The electrons impinge upon a metal target to generate the X-rays. Original image by The Scientific Sentence. Generating X-rays by accelerating electrons onto a target is relatively inefficient, with only about 1% of the electrical energy being converted to X-rays, and the rest into heat. Another way to generate X-rays for imaging purposes is using a linear particle accelerator or ‘linac’ (see Figs.6 & 7 and Table 1). A linac can also be used to produced X-rays for radiotherapy in a medical setting. Linacs generate X-rays by accelerating electrons in a tuned cavity waveguide energised by a radio frequency (RF) electric field. An electron is accelerated through a series of cylindrical electrodes whose polarity is constantly changing due to the RF field; as it gets to the end of one electrode, it is accelerated across the gap into the next one. Another method to generate X-rays is with a synchrotron (Fig.8). The Australian Synchrotron was first discussed in Silicon Chip May 2012 (siliconchip. com.au/Article/671). A synchrotron is another type of particle accelerator, circular rather than linear. Electrons start their journey in a Traditional, two-dimensional planar X-ray images were recorded on film, and many still are. Alternatively, flat-panel sensors can be used. These use ‘scintillating’ materials such as gadolinium oxysulfide (Gd2O2S) or caesium iodide (CsI) to convert X-ray photons into light, which is then detected by an imaging array. Photoconductive materials like amorphous selenium may also be used; these convert X-ray photons into electric charges, which are then read by an electrode array. Fluoroscopy (Fig.9) can be used to produce a two-dimensional “motion X-ray” where the X-rays illuminate a fluorescent screen, or in modern implementations, an X-ray image intensifier and camera or a flat panel sensor, as described above. Fluoroscopy is used for various applications, such as: • Inserting catheters or various electrical leads, such as pacemakers • Investigating the gastrointestinal tract after a “barium meal” has been swallowed (barium blocks X-rays) • Biopsies which require guidance ► Fig.8: the layout of a generic synchrotron showing (1) Electron gun, (2) linac, (3) booster ring, (4) storage ring, (5) beamline (one of many) and (6) end station, where experiments are performed. To give an idea of the size, the main storage ring of the Australian Synchrotron is 216m in circumference. Fig.9: the insertion of pacemaker leads into the heart is a procedure typically done under fluoroscopic guidance, as real-time imagery of the lead is needed. Source: Gregory Marcus, MD, MAS, FACC. 14  Silicon Chip Australia’s electronics magazine siliconchip.com.au • Orthopaedic surgery • Studies of blood vessels such as in the heart, brain and leg • Urology Medical computed tomography (CT) scanning CT scanning, originally known as CAT scanning (computed axial tomography), is a method based on X-rays that can produce cross-sectional slices or three-dimensional images. This is unlike conventional X-ray images, which simply project an X-ray image onto a film or digital sensor. An X-ray beam is passed through an object to be examined, and the intensity of the beam is measured as it exits. Different structures will absorb the beam by different amounts; hard tissue such as bone will absorb more and soft tissue such as brain will absorb less. This gives information about the totality of what the beam has encountered on the way through but no information as to the individual structures encountered. Additional information is gathered by rotating the beam and corresponding sensor to a different angle and repeating the measurement. This is done thousands of times to build up a comprehensive amount of information about many beamlines passing through the object – see Fig.10. This is then transformed into a two dimensional ‘tomographic’ slice by an appropriate mathematical transformation, and by further interpretation of these slices, 3D images can be generated. As with any X-ray procedure, CT scanning exposes the patient to X-rays, although the dose is kept to the minimum possible. Another disadvantage is that certain tissues are not highly visible. To get around this problem, sometimes so-called radiocontrast agents are used, which strongly block X-rays. These are injected to enhance images of specific soft tissues which would otherwise not be sufficiently visible. Substances containing iodine can be used for blood vessels, and substances containing barium for the gastrointestinal tract. Specialised medical uses of CT scanners There are several specialised uses and imaging modes of CT scanning. Two of note are CT coronary angiograms (Fig.11), and the use of CT scans siliconchip.com.au Fig.10: in a CT scanner, the X-ray beam and detectors are rotated about the patient. Three different positions are shown here. The patient also moves through the imaging plane of the beam orthogonal to the page. Original source: Elizabeth Swanson. Fig.11: an image produced by a CT coronary angiogram. Source: Macquarie Medical Imaging (MMI), siliconchip.com.au/link/ab90 in combination with 3D printing to make bone replacement parts to repair bone defects (Fig.12). In a CT coronary angiogram, a highspeed CT scanner is used to image the heart’s arteries. They are made more visible by the injection of a contrast agent. Disease or the location and functional status of stents can be detected. The blood vessels are revealed more clearly this way compared to MRI or ultrasound. Detection of CT X-rays X-ray detectors in CT scanners are generally based on scintillator materials that generate visible light when struck with a charged particle or high energy photon (such as an X-ray photon). Some common materials used are caesium iodide, gadolinium oxysulfide and sodium metatungstate (H2Na6O40W12). This is similar to fluorescence but based on a different physical principle (see Fig.13). The light is coupled to a photodiode matrix or photomultiplier tube to convert it into electrical signals (see Australia’s electronics magazine Fig.12: a titanium skull and facial implant that was created based on a patient CT scan, then 3D printed for implantation. Source: Open Biomedical Initiative (www.openbiomedical.org). llator Scinti ray de Ar dio Photo ut IC Reado trate Subs ector Conn ock ng Bl Cooli Fig.13: a typical X-ray detector array in a modern CT machine. Each element of the photodiode array corresponds to a pixel (picture element). Source: ams (https://ams.com). August 2021  15 The first clinical CT (a brain scan) was performed in 1971 by a scanner invented by Godfrey Hounsfield at EMI Central Research Laboratories in England (see Figs.16-18). It was publicly announced in 1972. Pictures from the original machine had a resolution of only 80x80 pixels. See the YouTube video titled “Radiographer Films Inside of a CT scanner spinning at full speed” at https://youtu.be/pLajmU4TQuI MRI ► Fig.14: a normal CT scan of an abdomen. Source: Dr Ian Bickle, radiopaedia.org Fig.15: an illustration from Oldendorf’s patent for the CT scanner. Fig.14). Gamma-ray detectors as used in scintigraphy; SPECT and PET, discussed later under gamma-ray imaging, work similarly. History of CT The mathematics that was to be later used for computed tomography was introduced in 1917 by Johann Radon and is known as the Radon Transform. It has many uses apart from CT, such as in barcode scanners. Stefan Kaczmarz did additional theoretical work in 1937, followed by Allan McLeod Cormack in 1963-64. This paved the way for the image reconstruction method used by Godfrey Hounsfield (see below). Fig.16: the world’s first commercial CT head scanner, made by EMI in 1971. Image processing was done on a Data General Nova 1200 minicomputer. Source: Wikimedia user Philipcosson. 16  Silicon Chip William H. Oldendorf submitted a patent for a CT scanner in 1960, and it was awarded in 1963. The title is “Radiant energy apparatus for investigating selected areas of interior objects obscured by dense material” and you can view it at siliconchip.com.au/link/ ab91 (see Fig.15). However, his idea was rejected by a manufacturer who said: “Even if it could be made to work as you suggest, we cannot imagine a significant market for such an expensive apparatus which would do nothing but make a radiographic cross-section of a head.” Oldendorf’s work also led to the development of MRI, SPECT and PET imaging. Fig.17: the world’s first clinical CT scan of a human head, at 80x80 pixels resolution, performed in the Atkinson Morley Hospital, England, October 1971. Australia’s electronics magazine MRI stands for Magnetic Resonance Imaging. It uses the principle of Nuclear Magnetic Resonance or NMR. The word “nuclear” was dropped when the technique was introduced because they thought people would be worried that nuclear radiation was involved when that is not the case. In fact, unlike CT scans and X-rays, MRIs do not involve potentially harmful ionising radiation. MRI detects the presence of hydrogen, which is mostly in water (H2O) and fat molecules in the body in abundance. By mapping these molecules and their position within the body, the overall structures within can be imaged (see Fig.19). The position of hydrogen atoms is determined by causing them to emit radio signals and measuring the strength, frequency, phase and timing of those signals, then processing them with a computer. Fig.18: a modern CT image of a stroke victim’s brain. Compare the detail in this image to Fig.17. Source: James Heilman, MD. siliconchip.com.au Fig.19: an MRI image of osteochondroma of the knee. Source: M.R. Carmont, S. Davies, D.G. van Pittius and R. Rees. MRI machines generate a powerful, uniform magnetic field using a superconducting magnet cooled with liquid helium to a temperature of 4K or -269°C. A second magnet is used to impose a gradient over the uniform magnetic field just described. They also contain an RF pulse generator and RF receiver, and a powerful computer to process the data that is produced. The magnetic field strength generated is typically between 1.5T and 3.0T (teslas), compared with the earth’s magnetic field of 0.00006T. As shown in Fig.20, the hydrogen atom of (in this case) a water molecule has a spinning nucleus consisting of one proton, with north and south poles like a magnet. These are randomly oriented under normal circumstances and precess about their axis like a spinning top at a certain frequency. When a powerful and highly uniform magnetic field is applied in the direction indicated in the diagram (the B0 field), all the protons of the hydrogen atoms align along with it, although some are ‘up’ and some are ‘down’. Each of these protons generates a magnetic field, and if the numbers of ‘up’ and ‘down’ protons were even, there would be no net magnetic field as they would cancel each other out. However, it so happens that due to the laws of quantum mechanics, slightly more protons have a preference for the ‘up’ direction, and this means the magnetic fields of the individual protons do not cancel each other, but leave a slight net magnetic field. It is this small net field that is measured in MRI. The magnetic field not only causes siliconchip.com.au Fig.20: hydrogen is found in water and virtually all other molecules in the body. Each nucleus (proton) is randomly aligned with respect to other hydrogen protons. All are aligned by a powerful magnetic field, then are subjected to an RF pulse. Original source: Kathryn Mary Broadhouse. Fig.21: (A) shows the different resonant frequency of protons depending upon the applied magnetic field strength. (B) different structures within organs produce different signal strengths, allowing them to be distinguished. (C) Some of the brain imagery produced. Original source: Kathryn Mary Broadhouse. the protons to align, but the precessional frequency of the protons is also dependent on the strength of the magnetic field. The stronger the magnetic field, the faster the precession. So, once we apply the magnetic field, all the protons align and precess at a specific frequency. A powerful repetitive radio frequency (RF) pulse is applied. That interacts with the small net magnetic field that remains. Suppose that repetitive pulse is Australia’s electronics magazine applied at the same frequency as the precessional frequency of the protons (as determined by the strength of the magnetic field). In that case, they will resonate at that frequency and absorb energy and move their spin axis away from the B0 magnetic field. When the pulse stops, they return to their original position and emit radio waves to release the absorbed energy. These emitted radio waves are recorded (see Fig.21). August 2021  17 Fig.22: cross-sectional and lateral views of an MRI Scanner. Original source: Wikimedia user Fbot. Fig.24: the Siemens MAGNETOM Terra 7T MRI machine, the world’s first 7T machine for clinical applications. Fig.23: the world’s first experimental 10.5T MRI machine with a 110-tonne magnet, designed to image humans. It is at the University of Minnesota. The hole in the middle is where the person goes. Source: www.cmrr.umn.edu Fig.25: an image from the Siemens MAGNETOM Terra, showing small blood vessels in a human brain. Source: Siemens. MRI is used to look at ‘slices’ through the body. If the magnetic field were uniform over the entire body or area of interest, all the resonating protons would emit radio waves at once, and we would not be able to determine their position in the body. As previously mentioned, the resonant frequency of the protons is dependent upon the magnetic field strength. A stronger field means a higher frequency of resonance. This is the reason for the superimposition of the additional magnetic field from the “gradient coils”. The gradient coils are simply loops of wire or metal sheets inside or close to the inner bore of the machine where the patient is located, like those shown in Fig.22. These generate a secondary magnetic field that predictably distorts the uniform electric field, such as shown in Fig.21. There may be other magnetic 10.5T is more than three times stronger than the most powerful commercial machines now in common use, typically 1.5-3.0T. A 3T machine gives a resolution of about 1mm, a 7T machine gives 0.5mm (see Figs.24 & 25) and a 10.5T machine is of course better than that (in this case resolution refers to the smallest feature that is visible). See the YouTube video of a 7T machine titled “Siemens MAGNETOM Terra - 7 Tesla MRI Scanner” at https://youtu.be/PYNGCxQaXrw Hazards involved in high magnetic fields such as 7T or beyond include temporary patient discomfort or overheating. In higher magnetic fields, hydrogen nuclei resonate at a higher frequency, and thus more powerful RF pulses are needed. These are more easily absorbed by the body, which can cause heating if not managed correctly. Small MRI machines are also possible – see Fig.26. 18  Silicon Chip field patterns depending on the specific application. MRI machines usually have three sets of gradient coils corresponding to the X, Y and Z directions. This allows virtually any ‘slice’ of the patient to be imaged by energising some combination of these coils with different intensities. Magnetic field strength With MRI, the more powerful the magnet, the greater the maximum possible image resolution and the faster the image acquisition for a given resolution (due to an improved signalto-noise ratio). Currently, the most powerful fullsize MRI capable of imaging a person is rated at 10.5T with a magnet weighing 110 tonnes and 600 tonnes of iron shielding. It is located at the University of Minnesota’s Center for Magnetic Resonance Research (see Fig.23). Australia’s electronics magazine siliconchip.com.au History of MRI The first clinically useful wholebody MRI scan was obtained in 1980 by a machine developed throughout the 1970s by John Mallard at the University of Aberdeen (see Fig.27). Functional MRI Functional MRI or fMRI machines measure brain activity by detecting blood flow in the brain. Activity is measured based upon the differences in the magnetic response of oxygen-rich arterial blood and oxygen-poor venous blood. Diffusion MRI With this method, MRI parameters are tuned to highlight the movement of certain molecules by looking at the response as a function of time. For example, water molecules that can tumble freely give a different signal to those that are relatively constrained (see Fig.28). Medical gamma-ray imaging Gamma-ray imaging is a medical imaging technique whereby a patient consumes small amounts of radioactively ‘tagged’ chemical agents or ‘radiopharmaceuticals’. These emit gamma rays, and a gamma-ray detector is used to create an image. In a sense, it is like an X-ray but with the radiation source on the inside of the body instead of the outside. The metabolic activity of cells is measured due to the uptake of the radiopharmaceutical by targeted cells. To make the agent, a radioisotope replaces a non-radioactive element in a biologically active chemical compound. Common agents include: • Calcium-47 chloride for investigating bone metabolism • Sodium iodide-123 for thyroid imaging • Krypton-81m for lung ventilation imaging (the m stands for “metastable” since it has a very short half-life of 13s in its isomeric transition form) • The positron emitter fluorine-18 as fluorodeoxyglucose (18F) or 18F FDG for imaging tumours and studies of glucose metabolism in the heart, brain and elsewhere • Rubidium-82 for cardiac imaging Several similar products are made at Australia’s only nuclear reactor in Lucas Heights, Sydney, called OPAL. Certain medical isotopes such as for siliconchip.com.au Fig.26: MRI imagers don’t have to be huge. This is the “Swoop” model of bedside MRI from Hyperfine (https://hyperfine.io). It offers rapid imaging and turnover with minimal patient handling. Fig.27: the first MRI machine to ► produce a clinically useful wholebody image, in 1980. It was called the MRI Scanner Mark One. Source: Wikimedia user AndyGaskell. Fig.28: a diffusion MRI of a human brain; specifically, a diffusion tensor image depicting certain fibre tracts. Source: Wikimedia user Thomas Schultz. Some “fun” MRI videos At the end of its service life, during an emergency or certain maintenance procedures, the very expensive liquid helium that keeps the superconducting magnet coils of the MRI machine cooled to -269°C has to be vented. This is called a magnet quench. Some people have recorded these quenches and also put some objects into the magnet cavity before the decommissioning of these machines. See the video titled “Quenching an MRI Magnet” at https://youtu.be/4dbQxyrhZ2A The liquid dripping from the outside of the metal vent pipe is liquid air that has condensed on the pipe. Also see the video titled “How dangerous are magnetic items near an MRI magnet?” at https://youtu.be/6BBx8BwLhqg Australia’s electronics magazine August 2021  19 Fig.31 (above): a SPECT image showing slices through a normal human brain. The uptake of the radiotracer is greater in regions of higher metabolic activity. Source: Dr Bruno Di Muzio, radiopaedia.org ► Fig.29 (above): a whole-body bone scan using scintigraphy, showing the uptake of radiopharmaceutical in a normal skeletal structure. Source: Wikimedia user Myohan. Fig.30 (above): an Elscint VariCam scintigraphy machine circa 1995. It had a variable-angle dual-head gamma camera and was one of the first machines able to do 2D (planar) scintigraphy, SPECT scanning and PET scanning. GE took over Elscint, and this machine evolved to include CT scanning in the GE Discovery VG with the “Hawkeye option”. Source: Wikimedia user Arturo1299. 20  Silicon Chip ► Fig.32: the imaging principle of PET. A positron is emitted from an atomic nucleus of an injected radioactive compound which is annihilated when it collides with an electron, and two 511keV gamma-ray photons are emitted. These are detected in a coincidence detector ring along a line of response (LOR). An image is assembled from these by tomographic techniques. Source: Herman T. Van Dam (siliconchip.com.au/link/ab97). Fig.33: small PET scanners exist for laboratory animals (microPET). This shows disease progression and regression in response to therapy in a mouse using 18F-FDG as a radiotracer. It appears that the author has transposed scans 4 and 5. Source: University of Iowa, Small Animal Imaging Core Facility. Australia’s electronics magazine siliconchip.com.au PET imaging can also be made in a medical cyclotron. There are about 18 of these in Australia, at various hospitals and imaging centres (there is a list at siliconchip.com.au/link/ ab92). The imaging techniques applicable to gamma-ray imaging are scintigraphy, SPECT (Single-Photon Emission Computed Tomography) and PET (Positron Emission Tomography) Scintigraphy is a two-dimensional or planar technique using a gamma camera (see Figs.29 & 30). It gives an image equivalent to a 2D X-ray. SPECT imaging is much like scintigraphy, but it produces 3D images instead (see Fig.31). To achieve this, the gamma camera(s) are rotated about the patient (tomography) to create a series of 2D slices. The 3D image is generated with the appropriate mathematical transformations in a computer. SPECT scans have a resolution of about 1cm and use the same gammaemitting radiopharmaceuticals as in scintigraphy. PET imaging is similar to SPECT – SPECT radiotracer substances emit gamma rays directly, while those used for PET emit particles known as positrons (see Figs.32 & 33). A positron is the positively-charged antimatter equivalent of an electron. Positron emission occurs when a proton in a nucleus decays to give a neutron, a positron and a neutrino. In PET, gamma rays are emitted when the positron from this decay collides with a nearby electron, causing the annihilation of both particles and the emission of two gamma-ray photons in opposite directions. These are what is detected. The emission of two gamma-ray photons simultaneously in opposite directions and their “coincidence detection” gives more information about the exact location of the emission, and thus a higher image resolution than with SPECT. In coincidence detection, the emission event can be located anywhere along a line between the two detectors. Thus, it is necessary to generate a large set of data from multiple coincidence events with detectors at different angles in a “detector ring” to form an image, as in Fig.32. The data is mathematically filtered to remove likely false coincidences or single instances of emission. siliconchip.com.au Fig.34: the GE Discovery MI Gen 2, an example of a combined CT and PET scanner. Fig.35: a combined CT and PET image showing a lesion of interest in green and a cross-section through the neck on the left. The anatomical detail is captured with CT and the metabolic detail of the lesion with PET. For more information on coincidence detection, see siliconchip.com. au/link/ab93 PET scanners have a resolution of about 4mm-6mm, with dedicated brain scanners going down to about 2.5mm. The fundamental theoretical limit for PET resolution is about 2.4mm for practical devices. This is explained at siliconchip.com.au/ link/ab94 Different radiopharmaceuticals are needed for PET than for scintigraphy and SPECT. The radioisotopes used are short-lived (eg, fluorine-18 with a 110-minute half-life or rubidium-82 at 76 seconds). This means that they must be prepared on-site with a cyclotron. This makes PET scans a very expensive procedure. SPECT is a cheaper imaging method than PET because of the more readilyobtained radioisotopes but gives poorer contrast and resolution. Combined CT, MRI and PET imaging Every method of scanning has inherent advantages and disadvantages. For example, CT and MRI give structural anatomical information while PET gives functional parameters such as metabolism, blood flow and compositional information. Combined images can be helpful to Australia’s electronics magazine relate structure and function. Images from single-mode machines can be combined by overlaying them in an alignment process called image registration. Still, better alignment can be obtained by acquired images using two or more modes from the same machine during the same scanning session. Scans from combined PET and CT (see Figs.34 & 35) have been shown to yield more accurate diagnoses than either type alone. Machines exist that combine PET and CT, or PET and MRI. Both combine structural and functional information; a combined CT and MRI machine has not yet been developed. Combined PET and CT is the more established technology. Medical ultrasonic imaging Ultrasonic imaging (or sonography) uses sound waves beyond the range of human hearing, and is similar to the process that bats and toothed whales use to navigate. The sound waves are typically in the range of 1-6MHz for deeper tissue penetration with less resolution, or 7-18MHz for shallower tissues with greater resolution. Higher frequencies may be used in some applications. Ultrasonic waves are produced by a piezoelectric transducer, which converts an electrical signal into August 2021  21 Fig.38: some of the wide variety of medical ultrasound imaging probes available. From left-to-right we have a linear, curvilinear, phased array, and all-in-one handheld probe. These are from Meraki Enterprises. Fig.36: this diagram shows how a piezoelectric transducer can convert an electrical signal into sound (upper) and also can generate an electrical signal when vibrated by a sound wave (lower). Fig.37: a basic ultrasonic transducer element for medical imaging. The matching layer provides an acoustic impedance match between the transducer and human tissue. Hundreds of such elements can be used in a transducer. Source: Dr Daniel J Bell and Dr Rachael Nightingale et al., radiopaedia.org Fig.39: in phased array ultrasound imaging, each piezoelectric element is fired with a slight delay so that the wavefronts of the individual beams join at an angle dependent upon the delay (θ (θ). T represents the transducer elements, TX is the oscillator signal, C the control system and φ the delay. Source: Wikimedia user Chetvorno. mechanical motion (see Figs.36 & 37). Ultrasonic waves are then transmitted through a sound-conducting medium and reflected back to the transducer. The time delay between the emission of the signal and its return represents the total distance travelled (or twice the distance to the target). It works like sonar (using sound waves) or radar (using radio waves), only on a much smaller scale. The same piezoelectric element used to create ultrasound when a voltage is applied can also generate a voltage signal when a signal is returned. Alternatively, two different transducers may be used. While quartz is a common piezoelectric material, medical devices generally use PZT (lead zirconate titanate) because of its high conversion efficiency. Piezoelectric polymers (plastics) such as PVDF also exist. A typical basic piezoelectric transducer is a disc with electrodes attached. Piezoelectric transducers for medical imaging must be sensitive and have the following properties: a) Good conversion efficiency between electrical and mechanical (sound) energy b) Be acoustically matched to the tissue, much like a radio antenna has to be impedance-matched c) Must be matched to the electronics Materials like PZT are good for (a) and (c) but not (b). Piezoelectric polymers are good for (b) but not (a) or (c). It has therefore been proposed to develop a composite material, having the best properties of both materials. In recent years, composite transducers have been introduced for medical ultrasound consisting of PZT rods embedded into a polymer matrix. Transducers for medical imaging have between 128 and 512 piezoelectric elements in either a linear or phased array (see Fig.38). With a linear array, one individual element is fired, then the next one in sequence and so on, to form a line image. In a phased array, the acoustic beam can be steered electronically by firing each element with a slight delay with respect to the previous ones (see Fig.39). Focusing is also possible by appropriate beam management. Some probes have a mechanically steered transducer array (see Fig.40). While traditionally ultrasound produced two-dimensional images (‘slices’), modern computing power means that ultrasound can now generate 3D images – see Fig.41. 22  Silicon Chip Australia’s electronics magazine Medical ultrasound development in Australia Australia was once a pioneer in medical ultrasound technology. Research began in 1959 with the establishment of an Ultrasound Research Section within the Commonwealth Acoustic Laboratories (CAL). That section became the Ultrasonics Institute in 1975, as a branch of the siliconchip.com.au Probe movement during acquisition of volume Central scan plane Acoustic window Coupling fluid Array Gear Motor Position sensing device Cables Housing Fig.40: an example of a mechanicallyscanned ultrasound transducer for medical imaging. Fig.42: the CAL Mark I Abdominal Echoschope at the Royal Hospital for Women, Sydney, in early 1962. The patient would stand with her abdomen pressed against the water bag on the right. Source: ASUM (www.asum.com.au). Fig.41: a 3D fetal ultrasound with a normal presentation. Source: Dr Servet Kahveci, radiopaedia.org Fig.43: fetal images obtained from Echoscope in 1962, considered the best in the world. The line drawings are manual annotations, not computer renditions; it was an entirely analog system. Source: ASUM. Commonwealth Department of Health. In 1989, the Institute was transferred to the CSIRO, and its staff were eventually integrated elsewhere within the organisation. In 1962, a system designed by CAL called the CAL Mark 1 Abdominal Echoscope (Fig.42) was installed at the Royal Hospital for Women in Sydney. It was designed by George Kossoff and David Robinson. The obstetric pictures obtained from this were acclaimed as possibly the best in the world (see Fig.43). The transducer ran at 2.5MHz and was a 25mm weakly-focused disc. All the original electronics were vacuum tubes, with a Hughes Tonotron storage CRT (as used in radar at the time) for image display using long-persistence phosphors. This was an entirely analog system with no computer (they were not sufficiently advanced at the time). Part of the motivation for developing obstetric ultrasound was the recognition of the hazards of fetal X-rays, the only alternative at the time. Apart from obstetric ultrasound, machines were also developed for the eye, breast and paediatric brain. One of the technical innovations made by the Australian group in 1969 was greyscale imaging, which yielded more and better quality imaging than black-and-white. The greyscales resulted from signal processing to extract more data, such as the distinction between liquid and solid tissue material. Existing Echoscopes were modified to operate in this mode. This development was credited to George Kossoff, David Carpenter, Michael Dadd, Jack Jellins, Kaye Griffiths and Margaret Tabrett. After many successes, in 1975, the work led to the development of siliconchip.com.au Australia’s electronics magazine a machine that was made commercially by Ausonics (part of the Nucleus Group, for whom I used to work) called the UI Octoson. More than 200 were made between 1976 and 1985 and sold in Australia and overseas. The machines sold for $100,000 each (see Fig.44 overleaf). The Octoson could acquire an image in one second. This work was credited to George Kossoff, David Robinson, David Carpenter, Ian Shepherd and George Radovanovich; it became obsolete with the development of realtime scanning. For a more comprehensive history of medical ultrasound in Australia, see siliconchip.com.au/link/ab95 & siliconchip.com.au/link/ab96 Endoscopy A modern endoscope is a flexible, steerable tubular instrument for August 2021  23 Fig.44: the Australian-made Ausonics UI Octoson from 1977. The patient lies on top of a water-filled membrane to conduct the ultrasonic waves. Source: ASUM. Fig.45: a flexible endoscope Source: Wikimedia user de:Benutzer:Kalumet. looking inside certain hollow or otherwise accessible parts of the body such as the colon, oesophagus, bladder, kidney, joints, abdomen and pelvis (see Fig.45). These instruments are usually specialised for the part of the body they are intended for. Inside the flexible tube, there are cables to help steer the instrument and bundles of optical fibres to transmit light into the body cavity as well simpler, safer and cheaper than conventional operations. as conduct light out to a camera. Each fibre optic bundle has about 50,000 individual fibres. Minor procedures can be performed with small instruments attached to the end of the device, to take tissue samples or remove small growths such as polyps. Lasers can also be directed down the tube to destroy diseased tissue. Endoscopic procedures can be much UV imaging of skin Photographing the skin in wavelengths of light other than ordinary visible light such as ultraviolet can reveal damage to the skin or underlying conditions not visible to the naked eye (Fig.46). Thermographic imaging Thermographic imaging is a technology for taking images of the human body in infrared light to examine medical conditions. It primarily reveals temperature anomalies due to variations in blood flow (see Fig.47). It is considered an aid to diagnosis rather than a direct diagnostic tool. It can also be used to measure body temperature in a non-contact manner, as is often done these days on entry to hospitals to ensure a visitor does not have a fever and is possibly infectious. Pill cameras Fig.46: imaging of the skin of a melanoma survivor in ultraviolet wavelengths reveals damage not visible in ordinary light. Source: University of Colorado Cancer Center. Fig.47: thermography of a patient’s legs after exposing the left foot to cold water to examine complex regional pain syndrome (CRPS). Source: Wikimedia user Thermadvocate. ► Fig.48: the PillCam by Given Imaging. It is swallowed and has a tiny camera on board to take pictures as it passes through the body. 24  Silicon Chip Australia’s electronics magazine Tiny ‘pill’ cameras exist which can be swallowed and take pictures throughout the alimentary canal (see Fig.48). This was described in detail in the August 2018 issue, in an article titled “Taking an Epic Voyage through your Alimentary Canal!” (siliconchip. com.au/Article/11187). Next month That’s all we have space for in this issue. Next month’s follow-up article will continue on the theme of imaging technology, but with non-medical applications. That includes investigating delicate archaeological objects, searching for contraband, checking structures for damage or defects and biometric access control. SC siliconchip.com.au Our capabilities CNC Machining UV Colour Printing Enclosure Customisation Cable Assembly *** Box Build *** System Assembly Ampec Technologies Pty Ltd Australia’s siliconchip.com.au Australia’s electronics electronics magazine magazine siliconchip.com.au Tel: (02) 8741 5000 Email: sales<at>ampec.com.au Web: www.ampec.com.au August2021 2021  25 FEBRUARY 37 Second-Generation Colour Maximite 2 The Colour Maximite 2 computer, published about a year ago, has been a huge hit, with thousands built. Now we present the second generation of the Colour Maximite 2. This does not make the first generation obsolete; it is an evolution with several improvements that will be appreciated by enthusiasts who are pushing the boundaries. Part 1: introduction F or readers who missed the introduction of the Colour Maximite 2 (July & August 2020; siliconchip. com.au/Series/348), this computer is inspired by the personal computers of the early 1980s. Computers such as the Apple II, Commodore 64 and the Tandy TRS-80. But thanks to modern technology, it’s way more powerful and costs much less. Like those computers, the Colour Maximite 2 has a built-in BASIC interpreter and boots up instantly, straight into the BASIC prompt. You can immediately enter a command or a program and start doing something useful. The emphasis of the Colour Maximite 2 is on ease of use and having fun. Plug it in, and within seconds, you can be entering a program to draw on the screen, calculate astronomical movements or play music. It is ideal for learning to program, educating children and just exploring what you can do with this small and cheap computer you program yourself. While the concept of the Colour Maximite 2 (CMM2) is borrowed from the computers of the 80s, the technology used is very modern. The CPU is an ARM Cortex-M7 32-bit RISC 26  Silicon Chip Words and MMBasic by Geoff Graham Design and firmware by Peter Mather processor running at 480MHz, hundreds of times faster than the 8-bit CPUs of the 80s. This chip also includes integrated memory, communication systems and its own video controller, capable of generating a VGA output at resolutions of up to 1920x1080 pixels with some resolutions supporting 24-bit ‘true colour’. New features The second-generation CMM2 offers three main improvements over the original Colour Maximite 2. The first is that the random access memory has been boosted to 32MB compared to the original 8MB, and it is also much faster. The revised circuit is shown in Figs.1 & 2. This increased memory capacity and speed have enabled several new features, including a 1920x1080 pixel VGA mode, 24-bit colour and more RAM for BASIC programs to use for arrays, I/O buffers, etc. The second improvement is the video DAC (digital-to-analog converter) which now uses eight bits for each colour channel. That means that this version can generate 24-bit colour, Australia’s electronics magazine supporting over 16 million different colours. This is known as ‘true colour’ and is the same colour range used by PCs. So photographs can now be displayed without noticeable colour banding (eg, in the sky). The third feature is the use of a fourlayer PCB with all components placed on the top side of the PCB. With the first generation, we were able to get away with mainly using through-hole parts, but as we are now mounting the CPU directly on the board (rather than via a module), that is not a viable option. As a result, most vendors will offer this design partially or fully assembled rather than a simple kit of parts. There are a few other minor new features in the Generation 2 design, which we will cover later. These include two Wii game controller connectors, the ability to connect a mouse easily, an optional high-accuracy real-time clock and the ability to mount an ESP-01 WiFi module on the PCB. Circuit description The circuit consists mostly of connectors and ICs surrounding the main processor, IC3, so we’ll just mention siliconchip.com.au some of the more noteworthy aspects of the circuit. The full circuit is shown in Figs.1 & 2. The 24-bit colour VGA output is generated using 24 digital outputs from IC3 arranged in three groups: one for red, one for green and one for blue. Each group drives an R-2R ladder DAC made from discrete resistors. The effect of this is that the 7th output in a group has half the effect on the output voltage as the 8th, the 6th half that of the 7th and so on down the ladder. Almost all components require a 3.3V supply. As the incoming power is 5V DC, the power supply is very simple, consisting mainly of linear regulator REG1 plus many bypassing and filter capacitors. IC4, the RAM chip, connects to IC3 via a 16-bit data bus and 13-bit address bus, plus 10 control lines. Assembly options The new four-layer PCB with mainly SMD components mounted onboard makes scratch-building the CMM2 Gen2 a bit more challenging than the earlier version. If you’re keen to build it yourself, you can still do that, although you might find sourcing the processor somewhat tricky given the severe shortages affecting the semiconductor industry at the time of publishing this article. But it is an option for those who are confident in their SMD assembly skills (or keen for a challenge!). Another option would be to use a PCB fabrication company to populate and solder the surface-mounted components for you, using their pick-and-place machines and reflow ovens. They can do this reasonably cheaply in small quantities. But it will probably be cheaper and easier for you to buy one of the kits that come with a mostly pre-populated PCB, as described below. If you want to solder your own Colour Maximite 2 but are not confident that you can handle the SMDs, especially the 144-pin main CPU, consider building the first-generation design. It primarily uses through-hole parts and offers many of the same features as this revised version. Upgrades to the original In the following discussion, we will describe the second-generation design, including its new features. However, many of its features also apply to the siliconchip.com.au Features & Specifications 480MHz ARM Cortex-M7 32-bit CPU with 2MB of flash and 1MB of RAM Additional 32MB off-chip RAM, used for BASIC variable storage and video pages Colour VGA output with 15 software-selectable resolutions from 240x216 pixels to 1920x1080 pixels, in both standard 4:3 and widescreen 16:9 ratios Four colour modes from 8-bit (256 colours) to 24-bit (16 million colours) Full-featured BASIC interpreter with support for strings, double-precision floating-point and 64-bit integers, long variable names, arrays with up to five dimensions and ‘unlimited’ user-defined subroutines and functions BASIC programs can be up to 516KB (typically 25,000 lines or more) and run at 200,000+ lines per second 24MB storage memory for BASIC programs Seven selectable fonts, user-designed fonts, line drawing, circles, squares and full control over all pixels. Can load image files formatted as BMP, GIF, JPG or PNG from the SD card, positioned anywhere on the screen and scaled and rotated USB keyboard support for US, UK, French, Spanish or German layouts and wireless keyboards with a USB dongle PS/2 mouse support for dual-mode USB mice with a PS/2 adaptor – an optional chip provides support for standard USB mice. SD card support up to 128GB for storing programs and files (FAT16, FAT32 or exFAT) Built-in graphical file manager makes it easier to manage files and directories, along with mouse support Stereo audio output; can play WAV, FLAC and MP3 files, computergenerated music (MOD format), robot speech, synthesised sound effects and sinewave tones Battery-backed real-time clock (RTC) will keep the time even when powered down 28 I/O lines which can be configured as analog inputs, digital inputs/ outputs, for frequency measurement etc; pin layout is compatible with Raspberry Pi HATs Support for communications protocols including serial, I2C, SPI and 1-wire USB socket for connecting to a personal computer (Windows, Mac or Linux) as a terminal or for file transfer Special features for animated games including multiple video layers with selectable levels of transparency, multiple video pages with high-speed copying between pages, BLIT (copy a block of video), SPRITE (animated sprites) and support for Wii game controllers Built-in full-screen editor with colour coded text, up to 255 character line lengths, clipboard for copy and paste, advanced search and replace and mouse support Powered from USB 5V, drawing less than 300mA Firmware upgrades via USB with no special hardware required Compatibility mode for running programs written for the original Colour Maximite Australia’s electronics magazine August 2021  27 REG1 AMS1117-3.3 4 4 2 D– 6 5 3 D+ C ON2 7 8 Vcc V3 RTS DTR R232 DCD IC8 CH340G UD– UD+ RI DSR RXD XI TXD XO GND CTS 12pF 14 10 W 13 10 3 2 +3.3V 9 X3 1 100nF 19 38 37 39 15 21 20 23 24 25 26 4 VDD ST 8MHz OUT XO 3 MODE JP7 GND 3 40 100nF 1mF 10mF 11 + 3 .3 V 16 17 18 12pF 12 1 6x 100nF X1 32768Hz 9 43 49 VDDQ 1 14 27 VDD 53 DQ15 51 DQ14 50 DQ13 48 DQ12 NC 47 DQ11 45 WE DQ10 44 DQ9 CAS 42 RAS DQ8 13 DQ7 CS 11 DQ6 10 DQ5 8 DQ4 CKE IC4 7 CLK MT48LC16M16A2 DQ3 5 DQ2 4 DQ1 DQMH 2 DQ0 DQML 36 A12 35 A11 22 BA1 A10 34 BA0 A9 33 A8 32 A7 A0 31 A6 A1 30 A5 A2 29 A3 A4 VSSQ VSS 6 12 46 52 28 41 54 2 TO NUNCHUK 1 (SEE FIG.2) TO A3 ON CON1 (SEE FIG.2) TO A2 ON CON1 (SEE FIG.2) AUDIO C ON4 SC Ó2021 28 4.7kW 4.7kW 2.2mF COLOUR MAXIMITE 2 GEN2  Silicon Chip 2.2mF 45 10 79 118 117 39 38 157 156 111 120 121 164 152 26 27 29 30 172 159 149 136 103 127 82 91 62 49 72 PE2 PB12 PD3 PD2 PC12 PH4 PB10 PC9 PC8 VDDA VREF+ PG14 PG13 PG7 PA9 PA10 PB6 PG9 MAIN CIRCUIT Australia’s electronics magazine 13 1 92 145 144 141 139 140 89 110 57 32 PC10 PC11 PH12 PG6 PB1 PC0 87 PH10 86 PH9 85 PH8 44 PH3 43 PH2 176 PI7 175 PI6 174 PI5 173 PI4 154 PG11 150 PD6 155 PG12 3 PE4 11 VERT SYNC PI9 12 HORIZ SYNC PI10 PC15/OSC32_OUT PF8 PF9 PH0/OSC_IN PH1/OSC_OUT 151 PD7 45 PA2 80 PB11 98 PD10 97 PD9 96 PD8 78 PE15 77 PE14 76 PE13 75 PE12 74 PE11 73 PE10 70 PE9 69 PE8 68 PE7 143 PD1 142 PD0 105 PD15 104 PD14 106 PG2 67 PG1 66 PG0 65 PF15 64 PF14 63 PF13 60 PF12 21 PF5 20 PF4 19 PF3 18 PF2 17 PF1 16 P F0 108 PG4 109 PG5 169 PE0 170 PE1 112 PG8 84 PH7 58 PB2 101 PD13 100 PD12 99 PD11 83 PH6 59 PF11 160 PG15 46 PH5 123 PA12 122 PA11 50 PA4 51 PA5 125 VCAP 81 VCAP VSSA 80 31 171 +3.3V 2 4 6 COM2:Tx 8 1 16 15 USB TYPE B PWR/CONSOLE 2x 10k W + 3 .3 V PI11 PD4 PA14 PA13 PC14/OSC32_IN 166 107 IC3 STM32H743IIG 1 3 5 7 5 6 100nF PA14 PA13 GND RST C ON8 SDA COM2:Rx 133 132 131 130 153 128 5 4 165 I2C #2 SDA 168 I2C #1 SDA 2 167 I C #1 SCL 33 COUNT1 129 COM2:Rx 34 COUNT2 35 COUNT3 163 SPI1 MOSI PB5 162 SPI1 MISO PB4 161 SPI1 CLK PB3 PWM1C 56 PB0 116 PWM2B PC7 GPIO 134 PI3 SPI2 MISO 94 PB14 41 COM1:DE PA1 SPI2 CLK 93 PB13 95 SPI2 MOSI PB15 115 PWM2A PC6 7 GPIO PI8 2 88 I C #2 SCL PH11 55 GPIO PC5 54 COUNT4 PC4 53 PWM1B PA7 138 FAST COUNT PA15 COM2:Tx 40 PA0 PWM1A 52 PA6 COM1:Rx 47 PA3 COM1:Tx 42 PA2 119 PA8 2 PE3 PI2 PI1 PI0 PH15 PG10 PH13 PE6 PE5 PB7 PB9 PB8 PC1 PH14 PC2_C PC3_C VSS 158 SDA 7 148 RESET PA13 5 SCL SCL 135 4 SQW/INT 126 3 GND 4 100nF RST BOOT0 PG3 PB11 RST PDR_ON 113 PA14 CR1220 BATTERY 6 VBAT VDD VBAT PC13 PF6 PF7 PF10 PD5 102 3 2 Vcc VBAT IC7 DS3231MZ 8 32kHz 8 24 25 28 147 146 137 124 9 71 1 3.3V 1 6 90 100nF ST-LINK 2 61 +3.3V POWER 4.7mF 14x 100nF 48 1m F 22 100mF GND 23 10mF S1 36 PWR +3.3V + 3 .3 V OUT IN 14 +5V 15 JP1 37 TO CON3 PINS 37 & 39 JP3 JP4 TO B3 ON CON1 (SEE FIG.2) TO B2 ON CON1 (SEE FIG.2) siliconchip.com.au BOOT0 + 3 .3 V + 3 .3 V 2.2W ESP_3.3V 100nF 10kW 10kW 100mF 1k W RESET S2 100nF RST 10k W A l JP2 1kW 4.7kW 3 2 A POWER SD CARD K l K 1 IC2 100nF Vcc DS18B20 DQ DIGITAL THERMOMETER 1 TSOP4838 IR SENSOR 3 l GND PROG/RUN IRD1 2 2. 2 W LED1 10 m F 100nF CON6 SD CARD SKT CARD PRESENT CD 240W 240W 120 W 240W 240W 240 W 240W 240 W DATA TO CARD 240W CLOCK TO CARD DATA FROM CARD 120 W 120 W 120 W 120W 120 W 120 W CARD WRITE PROTECT 240W 240W VERT SYNC 240W 120 W HORIZ SYNC 9 1 2 3 4 5 6 7 8 CARD ENABLE 240W 240W 240 W 240 W CON5 VGA CONNECTOR 75 W 240W 240W WP VIDEO – RED 6 11 7 12 8 13 9 14 10 15 1 VIDEO – GREEN 2 120 W 120 W 120 W 120W 120 W 75W 120 W 240W VIDEO – BLUE 3 75W CON9 4 5 (HEADER FOR CONNECTING ESP-01 WIFI MODULE) 240 W 240W 120 W 240 W 120 W 240W 240 W 240W 240W 240 W IC3 PI10 120W 120 W 120W 120W 240W 2 I C #2 SDA IC3 PI9 2 I C #2 SDA 2 I C #1 SDA 2 I C #1 SCL 120 W 10kW VERT SYNC HORIZ SYNC TO NUNCHUK 2 (SEE FIG.2) +3.3V 10k W COUNT1 COM2:Rx COUNT2 COUNT3 SPI1 MOSI SPI1 MISO SPI1 CLK 10kW PWM1C PWM2B GPIO SPI2 MISO +3.3V COM1:DE 2 28 30 32 34 36 38 40 PWM2A GPIO 2 4 6 8 10 12 14 16 18 20 22 24 26 SPI2 CLK SPI2 MOSI GPIO COUNT4 PWM1B FAST COUNT 1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31 33 35 37 39 I C #2 SCL COM2:Tx PWM1A COM1:Rx COM1:Tx 2 I C #2 SDA 2 I C #2 SCL IC5_PIN18 IC5_PIN17 CON3 EXTERNAL I/O +5V 10kW COUNT4 PWM1B FAST COUNT COM2:Tx PWM1A COM1:Rx COM1:Tx Fig.1: the Colour Maximite 2 is centred around the ARM Cortex-M7 processor, IC3. This, along with 32MB (512Mb) RAM chip IC4, does most of the work. The rest of the circuit is mainly concerned with supplying power to those chips and connecting the processor to the outside world. The keyboard & mouse interface didn’t fit in this diagram, so it is shown separately in Fig.2. siliconchip.com.au Australia’s electronics magazine August 2021  29 first generation version via firmware upgrades, for example, mouse support and the 1280x720 pixel display resolution. So, if you have the original Colour Maximite 2, you should upgrade the firmware to the latest version to get these features. The firmware download is available from the Silicon Chip website or the Author’s website at http:// geoffg.net/maximite.html Note that the same firmware file will load and run on both the first- and second-generation designs. The firmware automatically detects the hardware that it is running on and configures itself accordingly. Basic operation summary To use the Colour Maximite 2, all you need to do is plug in a monitor, keyboard and power supply. The computer generates a VGA output with one of 15 different video modes, some widescreen and some that work best with older 4:3 aspect ratio monitors. The highest resolution is 1920x1080 pixels; the 1280x720 resolution works well with a widescreen monitor, and the text is easy to read. The CMM2 defaults to an 800x600 resolution which suits all monitors, but this can be changed using the OPTION DEFAULT MODE command. The keyboard interface accommodates most USB keyboards, including keyboards that use a wireless dongle. Keyboards that have been tested and work well include the Logitech K120, K270, K400+ or K800 models, HP SK2885, Lenovo KU-0225 and Microsoft 600. We have discovered that some keyboards will not work correctly for an unknown reason related to the USB protocol stack. This is rare, but if you run into keyboard problems, try one of the above-listed types. The Logitech K120 works well, is cheap (under $20) and is readily available. The power supply can be any USB source of 5V. The typical power draw of the computer with just a keyboard and monitor is 250mA; however, when you connect external circuitry to the rear I/O connector, this can increase. If you are using a USB charger as a power supply you need to be careful, as many of these struggle when they are anywhere near their limit. So make sure that it is rated for at least 500mA, and preferably at least 1A. Also be careful if you are using a laptop as the 30  Silicon Chip The front view showing the infrared receiver (for remote control), two Wii controller ports for the Wii Nunchuck or the Wii Classic game controllers, status LEDs for power and SD card activity, the SD card slot, the audio output socket and the power switch. power source, as they often limit the current delivered via their USB ports to conserve their battery capacity. With the first generation Colour Maximite 2, we found that most problems encountered by our readers could be traced to the power source, closely followed by the quality of the USB cable used for the power. These are the first things you should investigate if you have strange problems such as failure to boot, errors with the SD card, intermittent crashes, keyboard problems etc. You will need an SD card to hold your programs. The Colour Maximite 2 supports cards up to 128GB formatted with FAT16, FAT32 or exFAT. Generally, you do not need a very large capacity, so an 8GB or 16GB card formatted with FAT32 will provide more than enough space and will be quite cheap (under $10). With a power supply, keyboard and monitor attached, flipping on the power switch will result in the Colour Maximite 2 booting up in under a second, straight into the MMBasic interpreter. It will display the BASIC prompt (a greater than symbol, “>”), and you are ready to enter your first command or program. MMBasic BASIC is a programming language that has been around for a long time. Initially developed in the 1960s by Dartmouth College (USA) for teaching Australia’s electronics magazine programming, it is easy to use and learn. It became popular in the late 70s and early 80s as the default language for early personal computers. MMBasic is the name given to the BASIC interpreter running on the Colour Maximite 2. It is an interpreter, which means that the computer will decode each line of the program as it encounters it. This is different from compiled languages such as C and C++, where code is converted to native machine instructions before execution. Compilers use a series of programs (a compiler, linker and loader) to take your program and convert it into machine code. This is then used to create a program file that the computer can run. This process results in a higher execution speed than an interpreter, but creates certain restrictions in how programs can be written. It also means you need to wait each time you make a change for the code to compile before you can launch it and see what effect that change has had. Many programs don’t need the absolute fastest execution speed, especially with modern processors being quite fast. So interpreted languages are popular with non-professional programmers (and even with professionals for specific tasks). MMBasic in the Colour Maximite 2 is the same as the BASIC interpreter that runs on our popular Micromite series of embedded controller chips. siliconchip.com.au Along the back panel, you can see the VGA output socket, the external I/O socket for a ribbon cable, a Type-B USB connector for power and serial console access and two stacked Type-A USB connectors. The top connector is for the keyboard, while the lower connector is for a mouse. MMBasic has over 500 built-in commands and functions. It is also designed to emulate Microsoft BASIC, the premier programming language for personal computers in the 80s. This means that you can get Micromite programs or programs written for Microsoft BASIC working on the CMM2 with minimal changes. You can type in almost any command at the MMBasic prompt, and the interpreter will execute it immediately. For example, if you type PRINT 2 + 2 and press Enter, it displays “4” on the screen as you would expect. This immediate feedback is one of the benefits of running an interpreter, and it allows you to easily test the commands and functions in the BASIC programming language. ARM Cortex-M7 processor The hardware and firmware of the Colour Maximite 2 are fully covered in the Colour Maximite 2 User Manual, so we will not go into all the details here (there are a lot of details). The computer is centred around the ARM Cortex-M7 processor. This is the large central IC that you can see in the photographs. Along with the 32MB (512Mb) RAM chip, this does most of the work; the other components and connectors supply power and connect the processor to the outside world. When we designed the original Colour Maximite 2, the STMicroelectronics STM32H743IIT6 chip came in siliconchip.com.au two speed types – the older 400MHz version and a later 480MHz version. STMicro was transitioning from the slower to the faster variant, but annoyingly, they used the same part number for both versions. This made it difficult for suppliers and you, the end user, to know what variant you were going to receive. It seems that now the supply chain has flushed out most of the 400MHz chips, as over the past few months, all the chips that we have seen are the 480MHz version. So you can be reasonably sure that the second generation Colour Maximite 2 will run at this speed. But, that is not guaranteed. Regardless, either speed is very fast, and the firmware will automatically support whatever chip is supplied. If you are curious, you can determine the variant you have by using the following command to report the speed: PRINT MM.INFO(CPUSPEED) Oscillator module The ARM processor is clocked by an external 8MHz oscillator module. This signal is multiplied within the processor to generate all the various clocks required, including the instruction clock, USB clock, VGA timing etc. In the original Colour Maximite 2, we used the crystal on the Waveshare CPU module and the oscillator built into the ARM processor to generate this clock. But it turned out that this Australia’s electronics magazine arrangement created a slight jitter in the signal, which sometimes caused a corresponding instability in the VGA video output. Generally, this was not a problem at the standard 800x600 pixel resolution. But as higher resolutions were enabled via firmware upgrades, it became more of a problem. With the second generation design capable of generating a 1920x1080 pixel video output, the requirement for a more stable clock became critical. This is why an external (to the ARM processor) 8MHz oscillator module has been specified. This oscillator is very stable and supports the extended resolutions that many users would like to use. If you have the original Colour Maximite 2 and would like to use the high resolutions provided by the later firmware upgrades, we recommend that you also upgrade the hardware to an external oscillator. The first generation PCB was designed for this possibility, and the second article in this series will have the details of how to perform the upgrade. Usually, video images are stored in the RAM within the ARM Cortex-M7. But for high-resolution images, we needed more RAM than it has. This, in part, is the reason for the external 32MB RAM chip. Using this, the firmware can assemble much larger images. This RAM is also used to support 24-bit graphics modes and provide more memory for BASIC programs. The internal clock/calendar used by MMBasic is derived from the real-time clock built into the ARM Cortex-M7 processor. This is effective, but if you want a much better level of accuracy, you can add an optional DS3231MZ+ to the PCB, and it will typically only lose or gain a second or two in a week. The command to enable this optional feature is: OPTION DS3231 Whichever real-time clock is used, it is powered by the coin battery on the PCB. This is also used to keep alive some static memory within the ARM Cortex-M7 that stores option settings and saved variables so that they are not lost on power down. The current drawn from this battery is tiny, so it should last for many years. The main board now has provision for mounting an ESP-01 WiFi module. August 2021  31 This module uses the ESP8266 chip, a self-contained SOC (system on a chip) that includes the TCP/IP protocol stack, 2.4GHz transmitter/receiver and other features to allow the Colour Maximite 2 to access a WiFi network. Currently, MMBasic does not have Internet features built in, but you can access the ESP8266 using a standard serial interface and the AT commands built into the ESP8266. With special firmware running on the ESP8266, you can extend the BASIC console over WiFi so that you can remotely connect to the Colour Maximite 2 to upload, edit and run programs. Front panel arrangement The two Wii Controller ports dominate the front panel. These will accept either the Wii Nunchuck or the Wii Classic game controllers; MMBasic can work with either. Many games written for the Colour Maximite 2 use such a controller, so they are a useful addition if you plan on playing some games. MMBasic can support up to three controllers, with the third via the rear I/O connector. Positioned between the two game controller connectors are two LEDs. The bottom green LED illuminates when power is applied. The top red LED initially illuminates to indicate that the firmware has successfully found and enumerated the USB keyboard. This is a handy indicator if you are experiencing problems with your keyboard. Following this, the red LED is used to indicate SD card activity. It will illuminate while the SD card is being accessed, and this is a warning: do not remove the card while the LED is lit. The SD card acts as the computer’s “disk drive”, where programs and data are stored. Next to it is the audio socket. The tip is the left channel, the ring is the right channel and the sleeve is ground – the standard configuration. The output is a high-impedance signal at about 1V RMS, suitable for feeding to an amplifier or amplified speakers. Programs can generate audio in many formats, ranging from simple sinewave tones through to playing WAV, FLAC, and MP3 files. Next along the front panel is the power switch, which has a special feature: it can be set to be on when the toggle is down (for Australian and New Zealand readers), or the opposite for 32  Silicon Chip our North American cousins. This is configured via the three jumper pins beside the switch. When the centre pin and the pin to the rear are connected, down will be on. The reverse is true if the centre pin and the pin towards the front panel are connected. Rear panel features Along the back panel (starting from the left) is the VGA connector for your monitor. As described previously, this supports a wide range of resolutions and colour depths. We have been asked why the Colour Maximite 2 does not support HDMI, and the answer is that the ARM CortexM7 does not support this protocol. So an expensive and complicated HDMI controller chip would be required. There are also difficulties associated with HDMI licensing, so this feature was just not practical. VGA to HDMI converters are readily available and inexpensive, so if you want to connect the CMM2 to a monitor via HDMI, that is the best way to do it. These converters cost a lot less than it would cost us to implement onboard HDMI. Next on the back panel is the 40-pin external I/O connector. This supports 28 inputs or outputs, with 12 of these able to be configured as analog inputs. Many of the I/O pins can also be used as PWM outputs or to handle serial communications, including asynchronous serial, I2C, SPI and more. The pin allocations on this connector are inverted compared to the first generation Colour Maximite 2. This is because while the I/O signal allocation on the first generation was compatible with the Raspberry Pi, the pin numbering was inverted, which sometimes caused problems. So the Generation 2 version corrects this by exactly matching the Raspberry Pi configuration, including pin numbering. With the first generation, you had to cut a new key slot in the shroud if you wanted to plug in a device intended for the Raspberry Pi. With the second generation design, this is no longer necessary. Continuing across the back panel, the Type-B USB connector provides both power and a serial console. We covered the power requirements of the Colour Maximite 2 earlier, but the serial console feature needs a little explanation. Australia’s electronics magazine The console is where you enter commands and programs into the computer. Typically, this is done using a keyboard and VGA monitor, but the serial console allows you to connect a PC or laptop to the Colour Maximite 2’s console via a serial interface over USB. You can do everything that can be done via the keyboard and monitor (except graphics) via this interface. You can enter and edit programs, set options, run programs etc. A CH340C USB-to-serial bridge is used. This converts the serial I/O from the ARM Cortex-M7 to USB using the CDC (communication device class) protocol over USB. Support for this chip and the CDC protocol is included in Windows 10 and other operating systems. The first generation Colour Maximite 2 used a different chip for the same task, but the CH340C is cheaper and more readily available, so we have switched to that. Mouse interface The last connector on the back panel consists of two stacked USB Type-A sockets. These are for the keyboard (top connector) and a mouse (lower connector). The second-generation design supports two types of mouse interfaces. The first is a USB-only mouse, which requires a Hobbytronics mouse controller chip (www.hobbytronics.co.uk/ usb-host-soic) to be installed as IC5, along with its supporting components. You can then plug the mouse into the USB mouse socket (the lower socket). This feature is optional, and the circuit for it is shown in Fig.2. Typically, suppliers of the second generation Colour Maximite 2 will not include this chip as it is easier to use a dual USB-PS/2 mouse, which is the second type of mouse interface supported. Most wired mice will automatically switch between USB and PS/2 modes, and many come with a USB to PS/2 adaptor. This adaptor simply signals the mouse to switch to PS/2 mode via a pull-up resistor inside the adaptor. The adaptor also provides the physical PS/2 connector. Even if your wired mouse did not come with this adaptor, it is very likely that it will work as a PS/2 mouse – so it is worth giving it a try. A typical example is the Microsoft Basic Optical Mouse, which is low in cost (under $20), widely available and works well siliconchip.com.au Fig.2: the keyboard & mouse connector, along with the optional USB mouse interface chip, IC5. You generally won’t need this chip as most wired USB mice will work in PS/2 mode, regardless of whether they came with a PS/2 adaptor. as a PS/2 mouse with the Colour Maximite 2. To use a dual USB-PS/2 mouse, IC5 must not be populated, and all four solder jumpers marked PS/2-CLK and PS/2-DAT on the PCB (JP3-JP6) must be joined with solder blobs. You can then plug the mouse into the USB mouse socket (the lower socket). A USB to PS/2 adaptor is not required, as the Colour Maximite 2 will force the mouse into PS/2 mode, even though it is plugged into a USB socket. MMBasic has built-in support for a mouse via the MOUSE() function. The program can query the mouse cursor’s position and detect clicks or double clicks of the mouse buttons using this. Both the file manager and the editor built into MMBasic can also use the mouse for most functions that you might expect. For example, you can use the mouse to point and select a file or line; you can select text with the mouse, scroll using the scroll wheel, double click to open/run a file and so on. While the second-generation design makes it easy to plug a dual-function mouse into the USB socket (without an adaptor), the first generation design running the latest firmware also supports a PS/2 mouse via the rear I/O connector. The only difference is that you will need to solder some wires from the mouse’s connector to the I/O connector, as illustrated in Fig.3. siliconchip.com.au The mouse CLOCK (pin 5) line connects to pin 33 of the I/O connector, and the DATA (pin 1) connects to pin 32. Both must have a 4.7kW pull-up resistor to +5V. This can be assembled on a small piece of perforated stripboard. Where to get it The Colour Maximite 2 is available from several suppliers around the world. Many of these will supply it with all the SMDs already soldered, as building it from scratch requires good soldering skills. Vendors selling kits for the second generation Colour Maximite 2 include Rictech Ltd in New Zealand (www. rictech.nz) and Micromite.org in the UK (https://micromite.org). Both will send kits anywhere in the world. They offer partially assembled kits and, by that, we mean that the PCB is populated with all the small surfacemount components already soldered in place. The larger components (connectors, SD card socket, battery holder, etc) are supplied loose for you to solder yourself. This only takes half an hour or so. These suppliers might also offer fully assembled and tested versions, pre-cut front/rear panels and a suitable case for the completed computer – check the supplier’s website for the details. You will also need USB cables and a 5V supply, as these are generally not included. For brave readers, a construction kit is available from the Author’s website (http://geoffg.net/maximite.html) and this contains the parts list, PCB Fig.3: If you have a first-generation Colour Maximite 2, you can add a PS/2 mouse to it by wiring it to the rear I/O connector as shown here. For the mouse to be recognised by MMBasic, you must upgrade the firmware to version 5.07 or later. Australia’s electronics magazine August 2021  33 Parts List – Colour Maximite Gen2 1 partially assembled PCB module – see below 1 USB 5V power supply or computer with powered USB socket 1 DS18B20+ temperature sensor (IC2; optional) 1 3-pin infrared receiver (IRD1; optional) 1 USB Type-A to Type-B cable (for power) 1 dual horizontal USB Type-A PCB socket (CON1; Amphenol FC1 723098034BLF) ∎ 1 USB2 Type-B right-angle PCB socket (CON2; Amphenol FC1 61729-0010BLF) ∎ 1 40-way DIL right-angle box header, 2.54mm pitch (CON3; Hirose HIF3F-40PA2.54DS(71)) ∎ 1 3.5mm stereo jack socket (CON4; Switchcraft 35RASMT4BHNTRX) ∎ 1 15-pin right-angle HD D-sub PCB socket (CON5) [RS 481-443, element14 2401183/2857990, Digi-Key AE11036-ND, Mouser 523-7HDE15SDH4RHNVGA] 1 SD card socket (CON6; Hirose DM1AA-SF-PEJ(21) or DM1AA-SF-PEJ(82)) ∎ 1 3-pin header (CON7; optional – for serial comms) 1 6-pin header (CON8; optional – for ST-LINK programmer) 1 4x2-pin header (CON9; optional – for connecting an ESP-01 WiFi module) 1 right-angle vertical PCB-mount SPDT toggle switch (S1) [Altronics S1320, RS 734-7107, element14 9473297, Digi-Key EG2364-ND, Mouser 34ASP27T7M2QT] 1 button cell holder for CR1220 (BAT1; Harwin S8411-45R) ∎ 1 CR1220 lithium button cell (BAT1) 1 3mm dual green/red LED assembly (LEDs1a & 1b; Dialight 553-0112F) ∎ 1 3-pin header with jumper shunt (JP2) 1 short length of 0.7mm diameter tinned copper wire, or a component lead offcut (PWR) 1 plastic instrument case, 140 x 110 x 35mm [Jaycar HB5970, Altronics H0472, element14 1526699] 4 5mm untapped spacers ∎ available from [RS, element14, Digi-Key and Mouser] Partially assembled PCB module parts 1 four-layer PCB with plated through holes coded 07108211, 128mm x 107mm 1 32768Hz 12.5pF SMD crystal, 3.2 x 1.5mm two-pin package (X1) [eg, Seiko Epson Q13FC1350000400] 1 8MHz 3.3V SMD crystal oscillator module, 7 x 4mm four-pin package (X3) [eg, Seiko Epson X1G004481001400] 1 5.1 x 5.1mm SMD four-pin tactile switch (S2) [eg, XKB Connectivity TS-1187A-C-C-B] Semiconductors 1 STM32H743IIT6 32-bit microcontroller, LQFP-176 (IC3) 1 Micron MT48LC16M16A2P-6A IT:G 256Mb (32MB) SDRAM, TSOP(II)-54 (IC4) 1 DS3231MZ real-time clock, SOIC-8 (IC7; optional) 1 CH340C USB/serial converter, SOIC-16 (IC8) 1 AMS1117-3.3 3.3V low-dropout linear regulator, SOT-223 (REG1) Capacitors (all SMD 50V X7R ceramic, M3216/1206 size unless otherwise stated) 2 100μF 6.3V SMD tantalum, SMB, SMC or SMD case 4 10μF 16V SMD tantalum, SMA case 1 4.7μF 2 2.2μF 2 1μF 32 100nF 2 6pF C0G/NP0 ceramic, M2012/0805 size 3 1kW 1 10W Resistors (all SMD 1/8W 1% thick film, M2012/0805 size) 5 4.7kW 27 240W 21 120W 3 75W 2 2.2W Optional parts for USB Mouse 1 Hobbytronics USBHOST-SOIC, SOIC-28 (IC5) – www.hobbytronics.co.uk 1 16MHz 10ppm 9pF SMD crystal, 3.2 x 2.5mm four-pin package (X2) [eg, Yangxing Tech X322516MLB4SI] 1 SMD LED, M2012/0805 size (LED2) 2 18pF 50V C0G/NP0 ceramic capacitors, M2012/0805 size 34  Silicon Chip Difficulty obtaining parts When you are purchasing a Colour Maximite 2, be aware that large scale semiconductors such as the ARM Cortex-M7 are in short supply worldwide. It has got so bad that some car manufacturers such as Ford have had to shut down plants and lay off workers because they cannot get the semiconductors needed to finish the vehicles. We have seen this effect with both the ARM Cortex-M7 and the 32MB RAM chip used in the Generation 2 design. So you might experience longer delivery times for your Colour Maximite 2 kit than you would typically expect. This is caused by events outside the control of the supplier, and patience is the only answer. Next month Resistors (all SMD 1/4W 1% thick film, M3216/1206 size) 13 10kW fabrication files, schematic, and the pick-and-place assembly files. You can also get the PCB for the revised Colour Maximite 2 from the Silicon Chip Online Shop, but you will have to gather all the other bits yourself. Note that we still sell a kit for the original CMM2, which includes almost everything you need; it just lacks the case. The design and firmware for the Colour Maximite 2 are in the public domain (free to anyone), and two other vendors have created their own versions of the Generation 2 design. These are compatible with the standard firmware and offer additional features such as a sea-of-holes PCB prototyping area, more Wii Controller ports, etc. These vendors are CircuitGizmos in the USA (https://circuitgizmos.com) and PS Labs in Poland (http://maximite. pslabs.pl). Both of these will ship worldwide, and you should check their websites for the various features of their versions, including the supplied cases. Australia’s electronics magazine In the follow-up article next month, we’ll have PCB layout details, for if you’re planning on building it yourself, debugging/testing, or you just want to see what connection is where. The final construction details will follow that, plus information on loading the firmware into the STM32 chip, a short guide on writing BASIC programs on the CMM2 and some links to external resources that you will find helpful. SC siliconchip.com.au By Geoff Graham Professional PCB Assembly If you aren’t confident soldering small SMDs, don’t have time or don’t want to populate your boards with dozens or hundreds of components, there is another option. For a modest fee, you can have your boards professionally assembled using parts that you specify, and in many cases these components will cost just a pittance! O ur first article on the Second Generation Colour Maximite 2 computer (which you can see on page 26 of this issue) mentioned that you could have the PCB professionally assembled. This includes the PCB fabrication, supply of the components and the soldering of these components onto the board. So, how do you get that done? The process is remarkably cheap and easy, even if you only want a couple of boards assembled. For the home constructor, this is a boon as you can now ‘hire’ a machine to assemble a complex board that would be difficult, if not impossible, to put together yourself. You design your PCB using SMD parts as you would normally do, but instruct your PCB design software to generate two extra files: a Bill Of Materials (BOM) and a Component Placement List (CPL). With these files the fabricator has enough information to supply the components and solder them in their correct positions. For a relatively complicated PCB like the one used in the Second Generation Colour Maximite 2, this saves the effort involved in sourcing then tediously soldering over a hundred tiny components. Furthermore, for someone who is not comfortable soldering SMD components, this avoids that issue entirely. It is worth reflecting on how the times have changed. A little over ten years ago, a typical hobby project would be based on a single-sided PCB etched and drilled at home. Even Silicon Chip projects were based on PCBs The assembled prototype PCB for the Second Generation Colour Maximite 2, exactly as received from JLCPCB. It has about 100 components supplied and soldered, with only the large components (connectors, switch etc) to be fitted. siliconchip.com.au Australia's Australia’s electronics magazine August 2021  35 like that. Now, a fabricator will make you a four-layer PCB for the price of a hamburger and then populate it for the price of a six-pack of VB. How great is that? Designing the board Most PCB design software can generate BOM and CPL files. As an example, the designer of the Second Generation Colour Maximite 2 printed circuit board (Peter Mather in the UK) used DesignSpark. This is a free program from RS Components, and it did a great job. To fabricate the prototype Colour Maximite 2 board, we used a company called JLCPCB (https://jlcpcb.com/) in China. There are other companies (mainly in China; there are some in Australia too) who will do the same, so you are not restricted to JLCPCB. Still, we will use them as an example of how you go about getting your own boards populated. We have covered how to design PCBs before, so we will not go over that again. However, to get the fabricator to populate the board, you need to supply one more bit of information to the PCB design software. This is the unique part code assigned by the fabricator to each component. The fabricator needs these numbers to identify the components to load into their pickand-place machines. If you go into the JLCPCB website, there is a link at the top labelled “Resources”, and if you click on that you can then select “SMT Parts Library”. Then you can browse the various categories (Capacitors, Resistors etc) in their catalog, or you can search using a part code or a value. These are all surface mount components (JLCPCB can assemble some through-hole components by “hand soldering”, at an extra cost). When you select a component, it will list the part code used by the fabricator, which, in the case of JLCPCB, is called the “LCSC Part number”. You must then enter this part code into the properties of the component in the PCB design software. You can also search for parts (and find their numbers) at the LCSC website, which is a Chinese component supplier and the sister company of JLCPCB (http://lcsc.com). This is an example of the Bill Of Materials (BOM) file generated by DesignSpark. The fabricator uses this file to associate a component’s reference designator with their part code. An example of the Component Placement List (CPL) file, used by the pick-andplace robots to place the component on the PCB. It lists the part’s designator, the PCB coordinates of the centre of the component, which side of the board to place the part and the orientation (ie, rotation). 36  Silicon Chip Australia’s electronics magazine It’s important to know the capabilities of the manufacturer; JLCPCB’s can be found at https://jlcpcb.com/ smt-assembly For example, they can only perform PCB assembly on boards between 20 x 20mm and 250 x 250mm in size, with a quantity of no more than 50 PCBs. Parts selection There are a few tricks to selecting parts. If the part is not in their catalog or identified as “Not Stocked”, you will have to source and solder that part yourself after receiving the board. This is true of most non-SMD components, including connectors. But do not be put off if you cannot initially find the component that you need. It might be listed in a different package, different temperature specification etc. An extended search often will get you what you need; JLCPCB says that they stock over 80,000 components. As a last resort, it might be easier to redesign your circuit to use something that they do have in stock, for example, a regulator with a different footprint. If you plan to have the Second Generation Colour Maximite 2 board assembled during 2021, you will probably find that the ARM processor and the 32 megabit memory chips are out of stock. This is due to the current semiconductor shortage; all you can do is wait until they come back into stock, then get in quickly before they run out. JLCPCB lists components as being either “basic” or “extended”. Basic parts are always loaded on their pickand-place robots and are ready to be placed onto your PCB. This primarily applies to items like small resistors and capacitors. The extended components are the less common items that are stored in their warehouse. These must be retrieved and loaded on the pick-andplace robot specially for your build, so they attract an additional charge per item (generally a few dollars each). You need to watch out for the extended fee, as it can add up. For example, the Second Generation Colour Maximite 2 board was initially designed using M3216 (3.2 x 1.6mm, imperial 1206) sized resistors, but most of these are listed by JLCPCB as extended parts. Given the number of different resistor values, that would have added over $40 to the board assembly cost. siliconchip.com.au Redesigning the PCB to use the slightly smaller M2012 (2.0 x 1.2mm, imperial 0805) resistors, listed as basic parts eliminated that cost with no difference in functionality. The components supplied by JLCPCB are generally reasonably priced. For example, an M2012/0805 SMD resistor is less than half a cent. The other factor is that there is no wastage; your project might need (for example) one 10W resistor. If you were assembling that at home, you would likely end up purchasing 10 or even 100 to get that single resistor at a reasonable cost. Component Placement Files With the correct part codes entered into the component properties, you can then get your PCB design software to generate the Bill Of Materials (BOM) and Component Placement List (CPL) files. These are spreadsheets, normally in Excel format. Depending on the software, these files might need some reformatting to suit the fabricator’s specifications (eg, adding headers, swapping columns etc). The BOM file is a list of all components, including their description, the reference designator (R21, C1 etc), the component footprint and the fabricator’s part code. The fabricator is really only interested in their part code and the reference designator. The CPL file lists the reference designator, the X and Y coordinates of the component’s centre on the board, the PCB layer that the component is to be placed on and the rotation of the component in degrees. JLCPCB can only populate one side of a PCB, so in our example CPL file that side is the top layer. The PCB is defined by files in the standard Gerber format, and these are the same as you would use if you were only getting a PCB made without the component assembly. You do need to supply the “paste” file (which is used to create the PCB stencil), which has the outlines of the solder paste stencil that is used to deposit solder paste on the pads as required. Most PCB assemblers will add a separate charge to manufacture the PCB stencil. For a four-layer PCB, as used in the Second Generation Colour Maximite 2, there are a total of ten files required to make the PCB, plus the “paste” file. Placing the order JLCPCB requires that you create a siliconchip.com.au login so that you and they can manage your job. You can then upload your Gerber files defining the PCB. That is easy; just drag and drop the ZIP or RAR file containing all the files onto the web page. Following this are multiple options that you can select (solder mask colour, PCB thickness, copper finish etc), but you can leave these at their defaults for most projects (including the CMM2 Gen2). JLCPCB will auto-fill most of the entries based on the Gerber files which is very convenient – but not all manufacturers do this, so take note. At this point, the website will ask you to select which Gerber files represent the various copper layers on your board and the number of boards that you want to be made. If you just want a PCB (without assembly), you are finished. But at the bottom of the web page, there is a button that allows you to select “SMT assembly”. If you choose that, you will be asked how many you want to assemble and who should add the tooling holes. The tooling holes are small holes in the PCB used in the assembly process, and you usually let JLCPCB add them. Clicking “next” will take you to a web page that asks you to upload the BOM and CPL files. Again, this is a simple drag-and-drop operation. Final checks Clicking “next” again will take you to the summary page. This page lists all the components on the board and provides a ‘preview’ of the assembled board. It is vital that you check this thoroughly as it is easy for a mistake to propagate through, and this is the last checkpoint before sending the board off for assembly. For example, you might find some components listed as being out of stock, and this is where you need to go back to the JLCPCB parts list and select something different. You can either go back to your PCB design software to make the change, or you can just manually edit the BOM file and change the part number there. Either way, you will have to upload your files again and recheck the component listing to ensure that all is OK. The final step is to check the preview provided by JLCPCB of the assembled board. This image is very realistic and shows the PCB with its Australia’s electronics magazine solder mask, vias and silkscreen in great detail. The components are photorealistic, with their markings clearly visible, and they should be positioned in their correct location. This image is almost as good as having the final board in your hand, and provides confidence that you will get what you intended. A detailed check of this image is vital, as it can show all sorts of errors that you did not realise existed when you designed the board. The most common is incorrect component orientation. It is possible that the orientation of the component in your PCB footprint will be different from the footprint used by JLCPCB. That can cause polarised components to be reversed, ICs with pin 1 in the wrong place etc. So check every part thoroughly and, if necessary, edit the CPL file to change the orientation parameter for the offending component, then reload the file. The final result With the component list and image checks completed, JLCPCB will present you with a list of the costs that make up the total price for the assembled board. This includes the price for the board itself, fixed setup charges, extended parts charges, the cost of components etc. Of course, the service is more cost-effective if you are getting a reasonable number of boards made, but it is still worthwhile if you only want two boards assembled (their minimum). The cost of our assembled board for the Second Generation Colour Maximite 2 (as shown in the photo) was about $10 for the four-layer PCB, $59 for the components and $19 for assembly (plus postage). These costs are per board, for two boards and in Australian dollars. Since then, the exchange rates and component prices could have changed, so your experience might vary. Given the complexity of the board, we feel that this is a reasonable price, especially considering that everything is supplied and soldered for you. The actual assembly cost was small, and it makes you wonder why you would be bothered soldering a hundred tiny components when you could have it done professionally for the price of one dish at a restaurant. SC August 2021  37 Harold S. Black, Negative Feedback and the History of Operational Amplifiers Op amps and negative feedback circuits are ubiquitous today, and you would be forgiven for thinking that they have been around forever. But there was a time when electronics was still developing, and such devices had not yet been invented. That changed in 1927 with the bright idea of one clever man… by Roderick Wall & Nicholas Vinen O Fig.1: Harold Black’s original hand-written notes on the principle of using negative feedback for distortion cancellation. 38  Silicon Chip Australia’s electronics magazine ne of the most significant early circuit ideas was Harold Steven Black’s invention of negative feedback. In 1927, Harold S. Black (18981983) was on a ferry heading towards his office in the West Street Labs of Western Electric, the forerunner of Bell Telephone Laboratories in New York City. An idea popped into his head that would dramatically change electronic communications, which continues to be used to the present day. His idea was for a negative feedback amplifier, where the gain is accurately set and distortion limited by feeding part of the output signal back into the amplifier. Black sketched his idea on a misprinted page of his copy of the New York Times, the only paper that he had on him. When Black got to his office, he had a colleague witness and sign it – see Fig.1. Black’s job had been trying to improve three- and four-channel telephone amplifiers based on carrier telephony for the last six years. For long-distance telephone calls, repeaters had to be added to cover the distance. But these repeaters had too much distortion, so by the time the audio signal reached its destination, it was unintelligible. Black realised that amplifier distortion and noise could be reduced using negative feedback, at the expense of reduced amplifier gain. He later said that he did not know what made his idea pop into his head; it just came. siliconchip.com.au Fig.2: a page from one of Harold Black’s many patents regarding negative feedback. This one is from patent 2,102,671, showing some possible ways of building an amplifier with negative feedback using valve(s). Black used his new idea to design low-distortion broadband repeater amplifiers that were finally suitable for long-distance telephone calls. That allowed more channels over a pair of wires. His patents Harold S. Black was granted 62 patents during his career, 18 of which relate to negative feedback; these are listed in Table 1. His most famous patent is number 2,102,671, which you can view at https://patents.google.com/ patent/US2102671A If you replace the number in that link with the other patent numbers (plus the “US” prefix), you can view the relevant PDF. This patent, titled “WAVE TRANSLATION SYSTEM”, was filed in 1932 and granted in 1937. It comes to 87 pages and includes many detailed drawings (including circuits and plots) and plenty of explanatory text. One of the most important sets of circuit diagrams (but far from the only one!) in this patent, appearing on page four, is reproduced in Fig.2. It shows four different ways of implementing his idea using ‘tubes’ or valves, the technology of the day. Other important plots in the patent include gain curves, stability criteria, equivalent circuits and several practical implementations of the technique. control, battery monitoring, instrumentation and sometimes RF too. The principle is used in TVs, radios, computers, medical equipment, control circuits, measuring instruments and mobile phones. You would find it very hard to find an electronic appliance that does not use negative feedback. You will see negative feedback being used with operational amplifiers and in discrete circuits in most issues of Silicon Chip. Operational amplifiers This paved the way to the development of operational amplifiers (op amps); essentially, a monolithic implementation of a circuit which applies negative feedback. Thousands of different types of op amps are available to suit just about any application; low-power types, highspeed types, high-gain types, precision types, singles, doubles, quads etc. The term “operational amplifier” goes back to about 1943, when this name was mentioned in a paper written by R. Ragazinni with the title “Analysis of Problems in Dynamics”. The paper was the work of the US National Defence Research Council (1940), was published by the IRE in May 1947 and is considered a classic work in electronics literature. George A. Philbrick Researches introduced the K2-W valve-based generalpurpose op amp in 1952, more than a decade before the first transistorised version appeared (Figs.3 & 4). The first solid-state transistor was successfully demonstrated on December 23, 1947, but it took a while before transistors were in widespread use. The first series of solid-state op amps were introduced by Burr-Brown Research Corporation and GA Philbrick Researches Inc in 1962. Fig.3: a popular early valve-based op amp, the Philbrick Research K2-W. The importance of negative feedback Almost all analog equipment manufactured today uses negative feedback. This includes circuits that handle audio signals, analog video, motor siliconchip.com.au Australia’s electronics magazine August 2021  39 Table.1: Harold S. Black’s patents relating to negative feedback (patent numbers are hyperlinks) When filed UNKNOWN 8 August 1928 3 December 1929 3 December 1929 26 March 1930 3 April 1931 22 April 1932 30 September 1932 29 December 1932 29 March 1933 29 March 1933 25 September 1934 6 October 1934 5 December 1936 5 December 1936 23 March 1937 10 November 1937 27 May 1938 20 December 1938 30 July 1940 28 February 1942 Serial number UNKNOWN 298,155 411,223 411,224 439,205 527,371 606,871 635,525 649,252 663,316 663,317 745,420 747,117 114,391 114,390 132,559 173,749 210,333 246,791 348,433 432,860 The first solid-state monolithic op amp IC, designed by Bob Widlar and offered to the public in 1963, was the uA702 manufactured by Fairchild Semiconductors. But it required strange supply voltages such as +12V and -6V and had a tendency to burn out. Still, it was the best in its day, and sold for about US$300 (a fortune today!). It was used mainly by the US military due to its high cost. Then the uA709 from Fairchild Semiconductor was released in 1965. It was introduced at about US$70, and was the first to break the $10 barrier, then not much later, the $5 barrier. By 1969, op amps were selling for around $2 each. From then on, multiple manufactures produced op amps in When issued Patent number Title 7 February 1928 CA277770A Wave signalling system Split into serial numbers 411223 & 411224 below 21 December 1937 2,102,670 Wave Translation System 4 June 1935 2,003,282 Wave Translation System NA Not granted Wave Translation System 1 August 1933 1,920,238 Wave Translating System 21 December 1937 2,102,671 Wave Translation System 28 May 1935 2,002,499 Wave Translation System 20 August 1935 2,011,566 Wave Translation System 9 July 1935 2,007,172 Wave Translation System 27 September 1938 2,131,365 Wave Translation System 16 November 1937 2,098,950 Vacuum Tube Circuit 17 March 1936 2,033,917 Electric Wave Amplifying System 27 September 1938 2,131,366 Electric Wave Amplifying System 6 August 1940 2,209,955 Wave Translation System 18 April 1939 2,154,888 Wave Translation System 3 December 1940 2,223,506 Wave Amplification 17 June 1941 2,245,565 Wave Translating System 7 October 1941 2,258,128 Wave Translating System 26 May 1942 2,284,555 Signaling System 20 July 1943 2,324,815 Stabilized Feedback System many varieties, up to the present day. One particularly popular model was the uA741, which has been improved since it was first introduced in 1968. Some variants of it, such as the LM741, are still being produced today! Its equivalent circuit is shown in Fig.5. Modern op amps mostly use the same principles, but differ in some implementation details, such as the method of internal frequency compensation. One big benefit of the op amp is its flexibility. It can perform a wide range of analog ‘functions’ with the addition of a few passive components. These functions include signal mixing, amplification, filtering (low-pass, high-pass, bandpass, notch etc), integration, differentiation, multiplication, simulated inductance and more. Fig.4: the K2-W uses a similar configuration to transistor-based op amps, with an input pair (one 12AX7 twin triode) followed by a voltage amplification/ buffering stage made from another 12AX7 twin triode plus two neon lamps. 40  Silicon Chip Australia’s electronics magazine Pages NA NA 21 12 NA 17 87 10 7 6 12 5 5 5 29 5 7 5 9 8 7 You can think of op amps as the building blocks for most analog circuits. Negative feedback So how is negative feedback used to control an op amp to reduce the distortion and set a fixed gain? The output voltage of an op amp is the non-inverting input voltage minus the inverting input voltage times a large factor (in some cases, over one million). If we say the gain is exactly one million, this means that: • If the + input is 100μV and the − input is 99μV, the output will be +1V. • If the + input is 100μV and the − input is 100μV, the output will be 0V. • If the + input is 100μV and the − input is 101μV, the output will be -1V. From this, you can see that if the difference between the input voltages is more than a few microvolts, the output voltage will be ‘pegged’ at one supply rail or the other. So unless we are using the op amp like a comparator (a possible op amp function), the inputs will almost always be at a very similar voltage. The negative feedback is typically configured to ensure that this is the case. Let’s say we feed 10% of the output voltage back to the inverting input and apply 1V to the non-inverting input. siliconchip.com.au Fig.5: the internal circuitry of perhaps the most ubiquitous op amp, the uA741 (actually, National Semiconductor’s equivalent). It contains 20 transistors, 12 resistors and one ‘Miller’ compensation capacitor for stability. When the output is less than 10V, the voltage difference between the inputs will be positive, so the output voltage increases. When the output is greater than 10V, the voltage difference between the inputs will be negative, so the output voltage will decrease. Thus, the output voltage will tend towards 10V. The only real sources of error in a DC context are the input offset voltage (the output not being exactly 0V with both inputs at the same voltage) and the finite gain, which adds a few additional microvolts of error. But that’s just one part per million or so. So it is pretty close to an ideal amplifier with fixed gain; that is certainly not the case with a typical single-transistor or single-valve amplifier! Due to manufacturing tolerances, it is challenging to set up (bias) a single transistor or valve to provide an exact gain. Even if you achieve it (eg, by trimming), it will likely change with temperature and over time. Note how the exact gain of the op amp is not important; it only affects the (tiny) gain error. The overall gain is set by the feedback divider, usually made of resistors (and sometimes capacitors), so it’s easy to set it close to the desired value. It can be trimmed to be almost exact if required, and it’s unlikely to drift. Negative feedback also gives close siliconchip.com.au to ideal results for AC signals, as long as they are well below the op amp’s bandwidth (usually specified as gain bandwidth, which must be divided by the configured gain). Thus, an op ampbased amplifier can give an essentially flat gain curve across a range of frequencies, whereas a transistor or valve will typically be far from flat unless it is a special type. Here are some basic op amp circuits: 1) Unity-gain buffer Fig.6 shows an op amp arranged as a unity-gain buffer. The output is fed back to the inverting input, so the output voltage tracks the noninverting input. As the output of an op amp has near-zero impedance (due to feedback), but the input has a relatively high impedance, this configuration is useful to avoid the circuit feeding the input from being loaded Fig.6: using an op amp to buffer a signal can be as simple as connecting its output to its inverting input. However, resistor Rf is a good idea to balance the input currents if the source impedance for the noninverting input is relatively high. Australia’s electronics magazine by the circuit the output is driving. Often, the output will be connected directly to the inverting input. But in some cases, the resulting source impedance mismatch between the inputs can cause temperature drift and other problems. Resistor Rf can be chosen to match the non-inverting source impedance to avoid this. 2) Non-inverting amplifier Fig.7 shows an op amp providing non-inverting gain. The output voltage is an AC signal with the same shape as the input signal but an increased magnitude, by a factor of Rf ÷ R1 + 1. As with the buffer, this circuit can be connected to a signal source that has a high impedance, but it still provides a low-impedance output. Capacitor C1 may be omitted, but it’s usually a good idea to keep it. It reduces the circuit’s gain at higher frequencies, thereby increasing stability and preventing the amplification of unwanted high-frequency signals. You might see a high-value capacitor at the bottom of the feedback divider, between the bottom end of R1 and ground, shown as an alternative connection for R1 in Fig.7. This sets the circuit’s DC gain to unity regardless of the AC gain, so it is mostly used when amplifying AC signals; also refer to Fig.19. By reducing the DC gain of the circuit, it prevents the output from pegging at the positive rail on positive signal excursions, and also reduces the amplification of the input offset error voltage. The practical gain limit depends on the op amp’s gain bandwidth and the maximum signal frequency. For example, an op amp with a gain bandwidth Fig.7: you only need two resistors to set up an op amp as a fixed gain voltage amplifier. As the signal is fed directly into the non-inverting input, the input impedance is high. Optional capacitor C1 limits the bandwidth for stability, while C2 can be used to reduce the DC gain to unity while having a higher AC gain. August 2021  41 Fig.8: the inverting amplifier configuration also uses two resistors and one optional capacitor. While it has the advantage that the gain can be less than unity, the disadvantage is that the input impedance is equal to Rin, rather than the usually much higher figure for the op amp’s inputs. Fig.9: the virtual ground mixer is an inverting amplifier with multiple signal sources. As both op amp inputs are held very close to 0V, there is no way that the signals being fed in can interact with each other, except at the output of the mixer. Fig.10: the basic differential amplifier calculates the difference between two voltages, multiplied by a constant, plus an offset. It needs good resistor matching. of 3MHz has a maximum practical gain of 30 times for signals up to 100kHz (3MHz ÷ 100kHz). Noise and distortion in the output increase with gain, as there is less feedback (closed-loop bandwidth) for the op amp to work within. 3) Inverting amplifier By feeding a signal into the inverting input rather than the non-inverting input, via a resistor, the signal is inverted and gain can still be applied, as shown in Fig.8. The gain is -Rf ÷ Rin, so unlike the non-inverting version, gain values less than unity (ie, attenuation) are possible without a separate input attenuator. An unfortunate consequence of this configuration is that the typically high input impedance of the op amp is reduced to the value of Rin, so the circuit feeding the input is loaded more heavily. This can be solved by adding a unity-gain buffer between the signal source and the inverting amplifier. One advantage of this configuration is that both op amp inputs are held at a constant voltage (Vbias), so there is no common-mode signal and therefore no common-mode distortion (often the dominant distortion mechanism). In this circuit, capacitor C1 performs a similar role as in Fig.7, although it is arguably more effective here since it reduces the gain at very high frequencies to zero rather than unity. 4) Virtual ground mixer Fig.9 shows a circuit that is basically an inverting amplifier with multiple resistors feeding different signals into the inverting input. As the inverting input is held at a fixed DC voltage by the negative feedback, there is no possibility of cross-talk between the signals (which might be significant in a mixing console, where they are fed to multiple locations). 5) Differential amplifier This is a very useful circuit used in many different forms. While you can build it using regular op amps, it is probably more widely used in monolithic instrumentation amplifiers (albeit in modified form), difference amplifiers and current shunt monitors. Fig.10 shows the basic version of this circuit. It provides an extremely useful function; it takes the difference between two voltages, multiplies it by a constant (determined by the resistor values) and then possibly adds a positive or negative offset voltage. However, Vref is often set to 0V so the output voltage is referenced to ground. This circuit needs precise resistor matching for a good common-mode rejection ratio (CMRR). Even with 0.1% tolerance resistors, a CMRR of more than 60dB is difficult to guarantee. Trimming can give good results, although the procedure can be tricky. It’s generally better to use lasertrimmed monolithic devices like instrumentation amplifiers (‘inamps’) that can have CMRRs over 100dB. Most instrumentation amplifiers use a slightly different internal circuit that includes three op amps; besides having a very good CMRR, this has the advantage that the gain can be set using a single external resistor. However, the basic principle is the same. A difference amplifier is basically an instrumentation amplifier where the input voltages can be well outside (usually above) the device’s supply range. A current shunt monitor is a specialised version of an instrumentation amplifier. All are based internally on op amps or similar circuits. A shunt monitor allows you to place a low-value shunt resistor in the positive supply to a section of the circuit, Fig.11: this full-wave rectifier circuit uses op amps to effectively cancel out the forward voltage of the diodes. As a result, for positive voltages at Vin, Vout tracks very closely (within microvolts, given sufficiently high precision op amps) while for negative voltages at Vin, Vout = −Vin (again, within microvolts). This is ideal for circuits that need to sense peak signal levels, such as audio clipping meters. ► Fig.12: this Sallen-Key low-pass filter provides ► a reduction in amplitude at -12dB/octave above its -3dB frequency, and multiple stages can be cascaded for an even steeper slope. Changing the resistors to capacitors and capacitors to resistors makes it a high-pass filter instead. 42  Silicon Chip Australia’s electronics magazine siliconchip.com.au ► Fig.14: this active bandpass filter blocks signals outside of a given frequency range, although the slopes are only -6dB/octave. For steeper slopes (eg, -12dB/ octave), one of the active lowpass filters described above can be connected in series with a similar high-pass filter. ► ► Fig.13: this multiple feedback filter does the same job as the Sallen-Key filter, but is more effective at higher frequencies. That’s important for low-pass filters as otherwise, it can pass signals that the filter is supposed to block. As only one extra resistor is needed, it’s a worthwhile upgrade, and the gain can be set without any more resistors (although it does invert the signal). Fig.15: this Twin-T active notch filter attenuates signals at a specific frequency. Both that frequency and the steepness/depth of the notch can be controlled by careful selection of the passive component values. and obtain a ground-referenced voltage to feed to an analog-to-digital converter (ADC) or similar. They have a high CMRR to reject supply ripple. 6) Precision rectifiers A precision rectifier acts like a diode or bridge rectifier, but without the forward voltage drop. This is important for rectifying low-level signals (too low to forward-bias a diode), or for accurately rectifying AC signals in order to measure their magnitude etc. They are commonly employed in devices like VU meters or AC current monitors. Fig.11 shows the full-wave version, similar to a bridge rectifier. The halfwave version is basically just one of the op amp/diode/resistor sections. The op amps reduce the effective forward voltage of the diodes by a factor of their open-loop gain, meaning the ~0.7V drop of a standard silicon diode is effectively less than 1μV for an open-loop gain of around one million. The resistor values shown result in unity gain. This circuit originally came from National Semiconductor who specified R = 100kW, although other values can be used. The values could be changed to give a fixed gain if necessary. 7) Active low-pass filter The simplest way to implement a low-pass filter with an op amp is to combine a basic RC low-pass filter with a unity-gain buffer. However, a more economical arrangement is the Sallen-Key low-pass filter shown in Fig.12. This has a -12dB/octave slope, compared to -6dB/octave for the RC filter, using just one op amp. It also allows gain to be applied. siliconchip.com.au Fig.13 shows a multiple-feedback low-pass filter. This provides precisely the same function as the Sallen-Key filter, but it is less prone to signal feedthrough, which means it performs much closer to an ideal filter at frequencies approaching the op amp’s bandwidth. The only disadvantage is the use of one more resistor. To calculate the required resistor and capacitor values for a given cutoff frequency, go to siliconchip.com. au/link/aajq Note that it is possible to build a third-order Sallen-Key active low-pass filter using a single op amp. This will give you an 18dB/octave roll-off with one op amp, 30dB/octave with two etc. This is shown at siliconchip.com. au/link/ab8v 8) Active high-pass filter To convert the low-pass filters shown in Figs.12 & 13 into high-pass filters, simply transpose the resistors and capacitors. As with the low-pass filters, these will provide a 12dB/ octave slope per op amp. For both the low-pass and high-pass filters, by adjusting the resistances and capacitances, it is possible to design filters with characteristics other than Butterworth. Butterworth has minimal (essentially no) ripple in the passband, but different filter types such as Chebyshev trade off increased passband ripple for a steeper roll-off beyond it. To calculate the required component values, see siliconchip.com.au/ link/ab8w 9) Active bandpass filter A second-order bandpass filter can be created by combining active secondAustralia’s electronics magazine order low-pass and high-pass filters. Alternatively, you can use the configuration shown in Fig.14, where a single op amp can act as a first-order bandpass filter with adjustable gain and a Q of up to 25. This configuration inverts the signal phase; however, if chaining multiple filters, it can be re-inverted by another stage. 10) Active notch filter Fig.15 shows a “Twin-T” active notch filter. One interesting aspect of this design is that the Q, and thus the depth of the notch, changes based on the resistor and capacitor values selected. See the online calculator at siliconchip.com.au/link/ab8x 11) Gyrator Fig.16 shows a ‘gyrator’, an active element that behaves similarly to an ideal inductor at low current values. It does this by using the op amp’s negative feedback to effectively invert the behaviour of capacitor C. This is useful in circuits like graphic Fig.16: the gyrator is a particularly clever circuit. It uses negative feedback to make a capacitor behave like an inductor. It is superior to an actual inductor in many signal processing applications. August 2021  43 equalisers, where resonant (LC) elements are needed with accurate resonance frequencies, low distortion and small size. Inductor tolerances are typically much wider than capacitors, and high-value inductors can be very bulky, so in signal-processing circuits, the gyrator is almost always better than a resonant circuit based on an actual inductor. 12) Baxandall active filter Fig.17 shows a basic version of the widely-used Baxandall active tone control. It has many good properties, such as the ability to have as many or as few bands as you want, with no interaction between the controls, and no special requirements for the potentiometers. This one shows bass and treble pots, but one or two midrange pots can easily be added. Fig.18 is the Baxandall active volume control. The traditional volume control method is a logarithmic potentiometer, but dual versions usually have poor tracking at the low end, so they are not great for stereo circuits. The Baxandall active circuit provides logarithmic-like control with a linear potentiometer for superior tracking. It can also offer significantly better noise performance as the pot adjusts the gain over a wide range, from zero up to many times (as set by the fixed resistors). 13) Audio amplifiers Fig.19 is a simplified version of the circuit from our SC200 audio amplifier. It is essentially a high-power op amp with large output transistors that can source and sink plenty of current (and that are well heatsinked). Most Class-A, Class-AB and similar amplifiers are variations on this theme. Even Class-D amplifiers typically use some form of negative feedback to avoid gross distortion. 14) Other uses for op amps An op amps can be used as a basic comparator by operating it in openloop mode, or with positive feedback (hysteresis). A comparator IC is essentially just an op amp with the frequency compensation component(s) removed for a faster swing at the output. An op amp can also be used to build an ‘integrator’ or ‘differentiator’. An integrator produces an output ramp proportional to its input voltage, while a differentiator produces an output voltage that’s proportional to its input ramp (rate of change). A log amp takes the exponential nature of a bipolar transistor and turns it on its head using negative feedback to provide a logarithmic transfer function. As a result, its output voltage is a constant multiple of the natural logarithm of its input voltage. This can be used as the basis of a multiplier circuit; by taking the natural loge(x) of several voltages, summing or averaging them, then exponentiating the result, the output voltage is the product of the input voltages. Other mathematical functions can be applied to voltages by an op amp, including addition, subtraction, division and inverse logarithm (the exponentiation mentioned above). Op amps can also be used to build controlled current sources/sinks, including constant loads, by combining op amps with large transistors that can handle lots of power with sufficient heatsinking. The generalised impedance con- Fig.17: the Baxandall tone control was initially designed with a valve or transistor as the active element, but it works even better with an op amp. It is elegant and expandable, with virtually no interaction between the stages (in this case, two: bass and treble adjustments). No matter how many bands it has, only one op amp is required per channel (ie, two for stereo). 44  Silicon Chip verter uses two op amps to present a load impedance proportional to another impedance. The ratio can be set using fixed or variable resistors (or even other impedances!). Many op amps are designed to drive relatively low load impedances, such as 600W. These work quite well as basic headphone drivers, with relatively low distortion figures driving typical headphone loads, even as low as 16W. They can’t supply a tremendous amount of power, but enough for most headphones to deliver decent volume, using one low-cost IC. An op amp can also be used as an error amplifier in feedback control. For example, to adjust the drive to a motor to maintain a constant speed despite a varying load. An op amp can form the basis of various oscillators, to generate waveforms at fixed or variable frequencies; primarily sinewaves, but also triangle waves or sawtooth waveforms. An op amp (especially a CMOS type) can be used as a high inputimpedance buffer amplifier or guard ring for monitoring sensors that cannot handle any loading, such as narrowband oxygen sensors and pH sensors. CMOS op amps can have input impedances in the terohms range (more than one trillion ohms)! CMOS op amp buffers can also be combined with analog switches and low-leakage capacitors to form sampleand-hold circuits, often used for sampling voltages over small time windows to feed an ADC or similar. Signal swing limitations For a very long time, the signals at the inputs and outputs of an op amp Fig.18: the Baxandall volume control also places the potentiometer in the negative feedback loop. This gives exponential gain control with a linear potentiometer and a wide range of gain settings with a reasonably constant noise level. Australia’s electronics magazine siliconchip.com.au could only have a considerably smaller swing than the supply range of the op amp. For example, if you had an op amp running from 12V, the inputs and outputs might be limited to a range of 3-9V. Or, with a dual supply like ±15V, you might be limited to a signal swing of ±12V. That’s because the op amp’s internal circuitry needs some voltage ‘headroom’ to operate. But more recently, single-supply and rail-to-rail output op amps started to become available. Single-supply op amps typically allow the inputs and outputs to go down to the negative rail (eg, 0V). So a single-supply op amp running from 12V can handle signals of say 0-9V. Rail-to-rail output op amps generally have the same input limitations as standard op amps, but their output can swing over virtually the entire supply range. This is especially useful when applying gain to AC signals, as in that case, the input swing will never reach the rails anyway (at least, not without ‘saturating’ the op amp). These days, rail-to-rail input/output (RRIO) op amps are very common. Some can even run down to very low supply voltages, like 1.8V! These op amps essentially remove the above limitations, with input and output signals that can range anywhere between the supply rails. Some will even handle input signals outside the rails, although usually only in one direction (eg, positive) and by a limited number of volts. Note that RRIO op amps sometimes compromise performance in other ways, such as having higher noise or distortion, or just costing more than ‘regular’ op amps. Multiple op amps As op amps became cheaper and more versatile, dual and quad op amps became popular. These save money and space; a quad op amp IC often costs less than twice what a single one does, and only requires two power tracks to be routed and one bypass capacitor. Most dual (8-pin) and quad (14-pin) op amp ICs use the same pinout so they can be interchanged. Single op amps are not quite so interchangeable, as these usually come in an 8-pin package. After accounting for the two supply rails, two inputs and one output, the remaining three pins can be used for trimming/balancing, external compensation capacitors or various other functions. Some are interchangeable (even if they don’t have exactly the same features), but not all. These days, single op amps are also available in tiny 5-pin SMD packages for where space is at a premium. Conclusion The op amp is an incredibly flexible device, available these days at very low cost and in a vast range of different versions, optimised for different tasks. While it is possible to process analog signals without op amps, generally, the results will be worse. So most analog designers make extensive use of op amps in their circuitry. They are an essential building brick that most designers would have difficulty doing without. We have Harold S. Black to thank for making our lives SC a lot easier! Fig.19: a slightly simplified version of our SC200 power amplifier circuit. It’s essentially a big op amp; transistors Q1 & Q2 are the differential input pair (the inputs are at their bases), Q8 is the voltage amplification stage, Q11 & Q12 are the output drivers and Q13 and Q15 are the power output transistors. The components highlighted in red form the negative feedback path, from the output at the emitter resistors of Q13 & Q15 back to the base of Q2, which is the inverting input. siliconchip.com.au Australia’s electronics magazine August 2021  45 By Tim Blythman Silicon Chip Nano Pong on your TV Atari’s Pong arcade game is nearly 50 years old and is remarkable for its time, inspiring many of the computer games that followed. Our Nano Pong game is modern and retro at the same time; it replaces the 70-odd discrete logic chips in the original with a single chip that costs about $1! But it still looks and plays much like the original game. I n Dr Hugo Holden’s in-depth article on recreating the original Pong arcade game (June 2021; siliconchip. com.au/Article/14884), he stated that none of the later versions of Pong were as good as the original. He specifically mentioned single-chip solutions as being inferior to the discrete version. This project is an attempt to change that! While this is a complete redesign of the circuitry to implement the Pong game, we have tried to be reasonably faithful to the original in terms of its graphical style, and how the game is played. Another inspiration for this design was our article about new 8-pin PIC microcontrollers (November 2020 issue; siliconchip.com.au/ Article/14648). One of the chips we looked at then was the PIC12F1572 microcontroller. It was about the cheapest 8-pin PIC we could find at the time, and despite that, it had superior features to the PIC12F675 that we have used for many years. As one of the smallest, cheapest microcontrollers around, we decided that it would be an interesting challenge to use it to recreate Pong. corrected a few bugs along the way (all described in the article linked above). But his faithful recreation depends on some parts which are becoming hard to get or expensive. Our version of this classic game is made using not much more than a small microcontroller and some passive components. It’s so tiny that we haven’t even specified a case for it; it can simply be wrapped up in a length of heatshrink tubing and left hanging behind the TV. A pair of controllers (‘paddles’) are built into small enclosures on flying leads, but if you’re interested in creating something more akin to the cabinets and consoles that would have existed at the time, you can do that too. Nano Pong is closely inspired by the original Pong; two players control on-screen bats that vie to keep the ball in play. The winner of the game is the first to win 11 rallies. We say ‘inspired’ as we haven’t attempted to make it identical. No doubt those who played the original game would notice some differences. But we have tried to emulate the style and gameplay of the older game. In doing so, we hope that those building this project can experience the joy of playing a 50-year-old computer game without the hassle of having to locate and solder a multitude of vintage logic chips. Like the original, the two player control paddles are potentiometers that translate the player’s paddle position to a corresponding on-screen paddle. We’ve also added a pushbutton (which isn’t in the original) to allow a player to ‘serve’ the ‘ball’. The PIC chip emulates the gameplay mechanics, and generates analog audio and video signals that can be fed to a PAL television’s AV inputs. Our Nano Pong project fits on a miniature 43 x 16.5mm PCB and relies on a single micro that only costs $1. Nano Pong Dr Hugo Holden’s recreation of Atari’s original Pong arcade game mainly kept with the original design. Still, he made the PCB smaller and 46  Silicon Chip Australia’s electronics magazine siliconchip.com.au Fig.1: this Nano version of Pong doesn’t need much in the way of hardware! A single 8-pin PIC microcontroller and surface-mounted passives are complemented by a handful of off-board parts for the player controls. Hardware Fig.1 shows the complete schematic – there is not much to it! Potentiometers VR1 & VR2 and pushbuttons S1 & S2 are not located on the PCB, but connected via flying leads. CON1 is the first modern flourish. A mini-USB socket provides 5V power to the circuit, significantly simpler than the original mains supply. Since many TVs now have a USB socket, the unit can be powered from the TV that it’s connected to. 5V power goes to pins 8 (GND) and 1 (Vdd) of IC1, a PIC12F1572 microcontroller, bypassed by a 100nF capacitor. IC1’s MCLR pin is pulled up to 5V by a 10kW resistor, so the PIC will run its internal program from flash memory as soon as power is applied. Pins 7 and 6 of IC1 are inputs to the ADC (analog-to-digital converter) peripheral and communicate the Player 1 and Player 2 control inputs to the PIC. Each player has a 1kW potentiometer padded on both track ends by a 470W resistor. The resistors are fitted to the PCB. The potentiometer flying leads connect to pins 1-3 of CON5 for Player 1, and CON4 for Player 2. With the 470W padding resistors in series with the 5V supply, the player paddle wipers vary between 1.25V and 3.75V depending on the potentiometer rotation. siliconchip.com.au We’ve specified standard 24mm potentiometers, but if you think your Nano Pong might be subjected to long periods of vigorous gameplay, you could upgrade them to more robust types. Although it would not be in line with the original, slide (rather than rotary) potentiometers could also be used to make a more intuitive interface, matching the straight-line motion of the bat on the screen. Pins 4 & 5 of CON4 and CON5 connect across normally-open momentary pushbutton switches. By pressing the button, the player pulls pin 2 of CON4/ CON5 (connected to the potentiometer wiper) to 0V. As the lowest voltage the pot can generate is around 1.25V, the microcontroller can distinguish this as a button press. The top padder resistor limits the worst-case current through the switch. Pin 5 of IC1 is the pulse-width modulated (PWM) sound output. It feeds a 1kW/470W divider, reducing the PWM amplitude from 5V peak-to-peak to around 1.6V peak-to-peak or 0.56V RMS. This is AC-coupled by a 1μF capacitor and biased to ground by a 100kW resistor before going to the output RCA plugs that connect to the TV. We’ve chosen these values to keep the sound signal well below 1V, as the audio (as per the original Pong) is a shrill-sounding square wave. The video signal is a standard CVBS (composite video baseband signal) in monochrome PAL format. Many of the differences between PAL and NTSC involve colour transmission, so many NTSC TVs should lock onto this signal. The main remaining difference is in the number of lines that are sent per frame. Modern TVs will usually detect and display the correct format. This signal is formed from digital levels at output pins 2 and 3 of IC1. Pin 2 is designated as luminance (LUM) and pin 3 as synchronisation (SYNC). The TV is assumed to have a 75W terminating impedance, so it Once finished, the PCB and cabling can be covered with heatshrink tubing. Australia’s electronics magazine August 2021  47 the colour picture information; since we are not transmitting such signals, the picture is decoded as monochrome. During the visible video area, the video intensity is determined by the signal voltage, between the black and white levels. A longer sync signal is used to trigger a vertical retrace. Often, the vertical sync signal is mixed with the horizontal sync signal to create a so-called ‘serrated’ sync signal that allows horizontal sync to be detected during the vertical retrace. This improves the TV’s ability to maintain horizontal hold. Thus, a single 1V peak-to-peak analog signal can encode raster intensity and both horizontal and vertical synchronisation to recreate a 2-D TV image. Software Scope 1: a scope grab of the video signal for a typical scan line, along with a portion of the display around that scan line, so you can see how they correspond. Each line is delimited by the dips in the trace to the low sync level (horizontal sync pulses), while the peaks correspond to a white raster on a black background. The red lines indicate that there is a substantial part of the signal outside of the visible area. Fig.2: the way that the screen is laid out makes it very easy to generate in a left-to-right fashion. Each horizontal scan line can display the Player 1 bat, Player 1 score, net, Player 2 score and Player 2 bat. The ball is produced separately by the PWM peripheral so that it can appear at any horizontal position. will see different voltages depending on the pin states. If both LUM and SYNC are low, then the output is 0V, which corresponds to the so-called ‘sync’ level. With SYNC high and LUM low, the TV sees around 300mV. This is known as black level, and corresponds to a black raster being displayed. Finally, with both pins high, a level near 1V is seen, which generates a white raster. Scope 1 shows the voltage generated over time for a typical horizontal scan line, along with several lines of video (including this scan line) above. Note the horizontal sync pulse troughs on either side of the displayed video. 48  Silicon Chip Analog video signal So how does a TV translate this signal to a two-dimensional picture? The TV continually scans its raster in left to right horizontal scan lines from top to bottom of the screen, with each scan line taking around 64μs. A 4-5μs low pulse indicates the start of a new horizontal line. The visible area takes up most, but not all, of the remaining scan line. The actual visible area takes 52μs to transmit, so it is bracketed by periods of black level called the ‘back porch’ and ‘front porch’. Colour transmissions contain signals in the back porch to help decode Australia’s electronics magazine Understanding the following is not necessary for getting Nano Pong to work. Still, it is interesting to compare it with how the original version operates, especially since the original version was purely hardware-based. Accurately emulating the logic chips in Pong would be a better job for an FPGA than a microcontroller, as the former allows everything to happen independently in parallel, a luxury we do not have. Our PIC needs to generate a tightly timed signal to maintain a steady picture. Most older PICs would require a crystal oscillator to provide an accurate enough clock to display a TV image, which would take up two of our eight pins. But here, we get accurate timing by running the PIC’s internal oscillator at 32MHz (requiring the use of the internal PLL), which gives an instruction clock of 8MHz. At 64μs per line, we can distinguish up to 512 horizontal positions per line. By scaling this to use 256 positions, we can use 8-bit bytes to hold pixel locations. In practice, the actual horizontal play area is around 200 positions. If you look closely at our images, there is a bit of horizontal jitter, which would not be present with a more precise crystal oscillator. But we don’t think it looks out of place in our recreation of 50-year-old technology. As PAL TV signals have 312 horizontal lines per field, we conveniently set the play area to be 256 lines, which neatly lines up with the visible area on most TVs. siliconchip.com.au With such tight timing needed, we have fallen back to using assembly language so that we know how long every part of our program will take to execute, ensuring the image quality does not suffer. The initial setup is written in the C language. It then calls our main assembly language subroutine. The main program is a loop of 312 subroutine calls, each corresponding to a horizontal display line variant. These, in turn, consist of numerous direct pin manipulation commands to set the necessary video output levels interspersed with calls to a delay routine to affect the timing. This starts with six vertical sync lines to start the field, followed by 28 blank lines. The blank lines are 5μs at sync level (SYNC and LUM low), followed by 59μs at black level (SYNC high and LUM low). The vertical sync line is serrated by delivering 5μs of black and 59μs of sync instead. After this are 256 active display lines. The counter LINECOUNT is used to keep track of which line is being displayed, and this is compared with the bat and ball positions, then flags are set to indicate whether the bat or ball should be displayed on the current line. These flags are set during the line’s horizontal sync period, so it does not affect the timing of the visible part of the display. The way these flags are set is a bit unusual. To ensure that each line runs for the same amount of time, as needed to maintain a steady picture, we avoid skipping over code we don’t want to run (as usually happens if a condition is false), which would change the program timing. Instead, we use the ‘skip on bit test’ assembler opcodes (BTFSC and BTFSS), which essentially treat the following opcode as a NOP (no operation) if a test is true. These sequences of commands all take the same time regardless of their outcome, retaining the necessary consistent timing. For lines where the ball is visible, we use the PWM peripheral to display it. The PWM peripheral on the PIC12F1572 is quite advanced, with phase and offset parameters. The ball’s horizontal position is determined by the PWM phase and its width by its duty cycle. This means we don’t have to keep track of when to turn the LUM output on and off. siliconchip.com.au Screen 1: a typical game of Nano Pong. The ball is in play after Player 1 has won the first point of the game. Screen 2: with a reasonable amount of program flash memory to spare, we added this splash screen when the unit is powered up. Screen 3: the start of a game, before Player 1 has served the ball. With that taken care of, the remainder of the visible lines can be neatly broken up into sections that can be handled sequentially. From left to right, these are the Player 1 bat, Player 1 score, the net, Player 2 score and Player 2 bat. For the bats and net, we briefly toggle the polarity of the PWM signal, thus getting the XOR effect as the ball passes over, so the ball does not ‘merge’ with them. Fig.2 shows how the horizontal lines are organised, and Screen 1 shows it without the lines. The scores are handled slightly Australia’s electronics magazine differently. These are effectively bitmaps hard-coded as brief assembly language sequences, so the PWM output is turned off while the scores are being displayed. Thus, the ball disappears behind the scores, which could provide an advantage for a canny player. After the 256 active lines, a further 21 blank lines are displayed, followed by a single customised blank line that handles all of the logic that updates the game’s state. The code for this line is two instructions shorter than the other blank lines, to account for the time taken to jump back to the start of the loop. August 2021  49 Most of the time that this final blank line is being generated, the game logic is processed. If it detects that the ball has struck a wall or bat, the ball vector is adjusted. This includes taking into account where it strikes the player’s bat, as this affects the ball’s vertical speed, like the original game. Also like the original game, each strike of the bat can also increase the ball speed. These events also trigger a sound to be played, generated by a different PWM channel playing a tone from pin 5 until it is reset on the next field. This gives a variety of differently toned beeps depending on what the ball has struck. The two ADC channels for the paddles are alternately sampled and allocated to their respective players. The relationship between the ADC value and on-screen position is adjusted to take into account the range set by the resistors. If the ADC value is outside this range, then the bat position is not updated, which also takes care of the case when the ADC pin is pulled low by the button press. Thus, trick serves are not possible. A point is registered whenever the ball reaches the screen edges (ie, missing the player’s bat), which increments the score counter. Flags are set to indicate that the player winning the point is to serve, and if the score has reached 11, that a win has occurred. In this case, a melody is played on the pin 5 PWM channel and the winning score is flashed. Timing for these events comes from different bits in the FIELDCOUNT parameter. Since the main program only uses about 2/3 of the available flash memory, we also added a splash screen, shown in Screen 2. This uses data from the score bitmap sequences in a hard-coded loop. An 8-bit timer counts down over 256 fields at 50Hz, so this screen shows for around five seconds. you can change the 470W resistors connected to the potentiometers at pins 1 and 3 of CON4 and CON5. Increasing their value will create a gap near the top and bottom of the screen that the bats can’t reach, as in the original Pong game. For example, replacing these four 470W resistors with 560W resistors will leave around a 3% gap at the top and bottom of the bat travel. If you have a 5V power source that doesn’t have a USB connector, it can be fed to pins 2 (positive) and 3 (negative) of CON2. We haven’t tested it, but the circuit should run from a 4.5V supply, such as three AA or AAA batteries in series. Construction In keeping with the theme of this being a modernised and miniaturised version of Pong, the PCB uses mainly SMD components. Since these are resistors and capacitors, with one IC in a relatively large 8-pin SOIC package plus the USB socket, assembly is not difficult. The double-sided PCB is coded 08105212 and it measures just 43 x 16.5mm. Refer to the PCB overlay and wiring diagram, Fig.3, during construction. Start by mounting those SMDs. We recommend that you have a temperature adjustable soldering iron, flux paste, tweezers, a magnifier and solder wicking braid, as well as some solder wire. The small PCB can be temporarily secured to your desk with some Blu-Tak or similar, so it doesn’t move around during assembly. Fume removal or ventilation is also recommended, as flux generates more smoke than typical solder wire. Start by fitting IC1 and CON1. Apply flux to the pads and rest CON1 in place, then add a small amount of flux to the top of the pads. Its small plastic pegs should align it to holes in the PCB. Clean the tip of the iron and add some fresh solder. Apply the iron’s tip to the two longer pads on the PCB; the flux should help the solder run up the leads. You only need to solder the two outer leads as this socket only supplies power. If you create a solder bridge, add some more flux and press the solder braid against the bridge until it draws up any excess solder. There should still be enough solder left to make a successful connection. Turn up the iron temperature slightly to solder the four larger pads to the PCB that mechanically secure the connector, then return the iron to its original setting. IC1 needs to be fitted in the correct orientation, with its pin 1 towards the USB socket. There should be corresponding marks on the PCB and the part itself. Apply flux paste to the PCB pads and rest the IC in place. Add a little solder to the iron top and touch it to one pin to tack the part in place. If the IC isn’t flat against the PCB or the pins are not aligned with their pads, carefully apply the iron again and adjust the position. Component notes With such a small PCB, there isn’t a lot that can be modified. If you find that the volume of the sounds doesn’t match your other TV sources, you can adjust the 1kW/470W divider connected to pin 5 of IC1. Reduce the 470W part value (or increase the 1kW part value) to reduce the volume. Alternatively, increase the 470W part value to increase the volume. If you want to make the game harder, 50  Silicon Chip Fig.3: with fewer than 20 onboard parts, the PCB is easy to assemble. Mount SMD parts IC1 & CON1 first, then the passives, then the connectors (if you are using connectors). Australia’s electronics magazine siliconchip.com.au Once it is correctly aligned, solder the remaining pins. Then, if you have bridged pins, use the braid to remove them as described above. The 100nF capacitor sits between IC1 and CON1. Using a similar technique to IC1, tack one lead, adjust and solder the other. Go back to the first lead and add a little flux paste or solder to freshen it up. Don’t be alarmed if your solder joints don’t have compact, concave fillets. The important thing is that the parts are connected firmly, and a large glossy solder joint that isn’t bridging to other parts is fine. Now fit the remaining SMD passives where shown in Fig.3. The resistors usually are marked (see the typical codes in the parts list), while the capacitors will only have their values printed on the packaging. Once all the surface mounted parts are fitted, you can clean the excess flux from the PCB using your preferred flux cleaning solution. Allow the board to dry out thoroughly before continuing. All of the through-hole headers are optional; CON2 is only required if you do not have a pre-programmed microcontroller, while CON3-CON5 can be regular headers or sockets as you need, or you can just solder wires (eg, sections of ribbon cable) directly to the PCB pads. Programming IC1 We expect most constructors will get a pre-programmed PIC from us. Otherwise, you can program the chip after soldering it to the board, but it’s a bit tricky. The problem is that the programming pins, pins 7 (ICSPDAT) and 6 (ICSPCLK) are also connected to the player paddle wipers. So it’s best to program the chip before connecting up those paddles. To do this, plug your programmer Parts List – Nano Pong 1 double-sided PCB coded 08105212, 43 x 16.5mm 1 PIC12F1572-I/SN (SOIC-8) programmed with 0810521B.HEX (IC1) 1 SMD mini Type-B USB socket (CON1) 1 10cm length of 20mm diameter clear heatshrink tubing 3 RCA plugs AND 1 3m length of shielded cable OR 1 triple RCA plug cable [eg, Jaycar WV7316] 1 5-way male pin header (CON2, optional for programming, see text) Capacitors (all 50V X7R SMD ceramic, M3216/1206-size) 1 1μF 1 100nF Resistors (all 1% metal film SMD, M3216/1206-size) 1 100kW (marked “104” or “1003”) 1 10kW (marked “103” or “1002”) 2 1kW (marked “102” or “1001”) 6 470W (marked “471”, “470R” or “4700”) Controller parts 2 small plastic enclosures (eg, UB5 Jiffy boxes) 2 1kW 24mm rotary potentiometers (VR1, VR2) [eg, Jaycar RP3504] 2 large knobs (up to 50mm) to suit potentiometers VR1 & VR2 2 momentary pushbuttons (S1,S2) [eg, Jaycar SP0716] 1 1m length (or longer) of 4-5 core wire for controllers [eg, Jaycar WB1590] 2 100mm cable ties into the ICSP header, CON2. You can solder a header strip to the pads, but we’ve had success by simply resting the header in place and applying gentle force to ensure contact. A PICkit 3 or PICkit 4 can be used, or even a Snap programmer, if you can supply power to the board (which the Snap cannot do by default). The easiest way to do this is using the miniUSB socket, CON1. Use software like Microchip’s MPLAB X IPE to upload the 0810521B. HEX file to the chip. There’s nothing obvious to indicate that the chip is working, apart from using the software option to verify that the file has been transferred correctly. Wiring it up We built the two player controls into plastic UB5 Jiffy boxes, but you could also mount all the parts in a single enclosure to imitate the hardware of the arcade version of Pong. Fig.4 shows the two possible ways that these can be wired. The only difference is that if the controls are wired remotely, one end of the switch can be wired directly to the pot wiper to save having to run an extra wire back to CON4 or CON5. Fig.5 shows the cutting diagram that suits the parts we have used (listed in the parts list). You might need to modify the hole sizes if you are using different parts. Our photos show how we have connected everything, but the design is quite flexible and can be adapted to different parts and enclosures. We’ll describe how we finished our version. This is what our player controls look like, with a separate UB5 box for each controller. Internally it’s very simple, comprising of a 1kW 1kW potentiometer and momentary pushbutton. siliconchip.com.au Australia’s electronics magazine August 2021  51 Fig.4: wiring up the two player paddles/ controllers externally only requires a fourcore cable. Each paddle is wired the same, with Player 1 connecting to CON5 and Player 2 connecting to CON4. If everything is being mounted in the same enclosure, you can run the pot and switch wires back to CON4 & CON5 separately. Drill holes in a pair of UB5 Jiffy boxes according to Fig.5, noting that this should include a hole in the end of the box for the wire. The bottom of the box becomes the top when held in the hand. Doing it this way means that we aren’t trying to juggle wires leading from the lid to the cable entry while mounting the lid. Cut down the potentiometer shafts to suits the knobs you are using, and use a file to tidy up any rough corners or edges. This is most easily done with a hacksaw while holding the end of the potentiometer shaft (rather than the body) in a vice. This avoids straining the potentiometer mechanism. Fit the pushbutton switches and potentiometers to the Jiffy boxes. You can also fit your knobs at this stage. We whipped up some 3D printed knobs to give a bit more grip; the files are available along with the firmware download from the Silicon Chip website. Solder and heatshrink the wires as shown in Fig.3 and our photos. Run the connecting cable out through the hole and secure a cable tie around each cable to prevent it from being pulled off the terminals inside the box. Next, solder the other ends of the wires to their respective pads on CON4 and CON5. If you want to test the paddle operation, apply power and check for 3.75V on the middle lead of each potentiometer in the fully clockwise position, and 1.25V anti-clockwise. This voltage should drop to 0V when the button is pressed. There are normally-closed variants of this switch, so if you find that the action is reversed, you might have this other variant. 52  Silicon Chip Fig.5: we built our paddles into UB5 Jiffy boxes, with holes drilled in their bases as shown. There also needs to be a hole in the side of the box for the cable to pass through. Check that the size of your potentiometers, switches and wires match the hole sizes before drilling. To make the RCA connections for the TV, we simply cut a three-way RCA cable in half. Strip back a good amount of insulation and collect all the braids together. Attach these to pin 1 of CON3 (marked on the back with “G”). We put a short length of heatshrink tubing over the braids for extra protection. Then bare the internal wires by a small amount. The video plug (which will usually be yellow) should be connected to pin 2 of CON3, marked “V”. Pins 3 should go to the left audio lead (white, “L”) lead, and pin 4 should go to the right audio lead (red, “R”). Plug the RCA leads into the AV connections of a television and apply power to CON1. You should see the splash screen followed by the main game screen. Check that everything operates correctly. If so, the main PCB can be sealed up by enclosing it in a length of 20mm diameter heatshrink tubing. Ensure that the CON1 end does not overhang the connector. A 10cm length should ensure that the cables are secure and have some strain relief. Let’s play! At the start of the game, the ball will be in front of one player’s bat. Pressing the button on that controller will cause the ball to be served. Rotate the potentiometer to move the bats on the screen to keep the ball in play. If a player misses the ball, the other player wins a point. Once one player reaches eleven points, the game is over. The winning score will flash and a melody will play. Serving the ball starts SC a new game. This is how we built our Nano Pong setup. It uses a separate controller for each player, and has a composite video connector. 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QC3908 32GB microSDCard XC4992 $36.95 * Pan, Tilt, Zoom INTRO 279 $ SAVE $20 NEW BONUS Swing Arm Wall Bracket with 2 Slide In Locking Plates JUST 89 $ 95 An articulating wall mount for 13"42" flat-panel TVs up to 15kg. Easygrip knobs. Detachable VESA plate. Built-in level adjustment. CW2811 www.jaycar.com.au JUST 5995 $ 1800 022 888 OFFER Buy a Power Supply* to Suit (MP3536) for ONLY $17.95 SAVE $6 Powerful Raspberry Pi *Must buy with XC9001, XC9100 or XC9104 on the same transaction Connect directly to your Pi. Resistive touch. HDMI and USB ports. XC9024 8995 Tiny sized computers for all sorts of powerful projects. Can run Raspbian or Ubuntu Linux, Windows 10 IoT core, dedicated media centre OS, etc. Quad Core. Dual band Wi-Fi & Bluetooth®. BUY 2 FROM 590 $ SAVE 25% Double-sided Mounting Tape 12mm wide x 10m Foam Roll NM2821 $4.95EA OR 2 FOR $7 12mm wide x 25m Tissue Roll NM2823 $3.95EA OR 2 FOR $5.90 95 SAVE $5 ESD Safe Sidecutters High quality Japanese designed. Carbon steel. 135mm long. TH1922 NOW 3995 $ SAVE $10 LED Magnifying Lamp with Third Hand Perfect for PCB assembly & soldering. 3x Magnification. Powered by 4 x AA batteries (sold separately). TH1989 4pk AA Batteries SB2425 $3.25 SAVE $5 4B 4GB 5MP Camera for Raspberry Pi JUST 149 $ Connects directly to your Pi. Supports up to 1080p video. 2592x1944 pixel images. XC9020 ALSO AVAILABLE: 5MP Infrared LED Camera XC9021 NOW $39.95 SAVE $10 Raspberry Pi Starter Kit 4B 8GB 145 Includes Pi 3B board, case, power supply, USB cable, book (Programming the Raspberry Pi: Getting Started with Python), microSD card with NOOBS software, plus starter guide. XC9010 XC9104 NOW WITH BUILT-IN MIC & SPEAKER micro:bit V2 GO Development Board Bundle NEW 24 95 3995 12 95 $ 10% OFF Sensor Shield for micro:bit Enables you to connect multiple sensor modules to your micro:bit. XC4336 EA BBC micro:bit Books Getting Started with BBC micro:bit BM7168 Python Coding on BBC micro:bit BM7170 $ NOW JUST $ Upgraded model! Now with built-in microphone and speaker. Touch sensitive logo. Power indicator. Includes micro:bit board, batteries, JUST battery holder and USB cable. XC4324 NOW 29 $ NOW 1995 SAVE $10 XC9100 $ XC9026 $ 109 $ 7" 139 $ XC9022 5" 8995 $ XC9001 2.8" 2995 $ 3B+ $ Raspberry Pi Single Board Computers 5" Touchscreen for Raspberry Pi NOW 12 $ NOW 1995 95 $ 10% OFF 15% OFF T-Adaptor Shield for micro:bit Prototype Board for micro:bit Easy access to all 23 pins on the micro:bit board. Plug it directly into a breadboard. 80-pin connector. XC4334 Supplied with 400-hole breadboard, designed to break out all IO pins on your micro:bit to create additional circuits and hardware. XC4332 EVERYDAY GREAT JAYCAR VALUE JUST 595 $ EA 150mm Jumper Leads Pack of 40 jumper leads for prototyping. Plug to Plug WC6024 Socket to Socket WC6026 Plug to Socket WC6028 FROM Prototyping Boards 4 $ 95 Transfer your breadboard design without having to rework it. Small 25 Rows/400 Holes HP9570 $4.95 Large 59 Rows/862 Holes HP9572 $9.95 Not sure what to build next? Here's some inspiration: jaycar.com.au/projects JUST 7 $ 95 Breadboard with 400 Tie Points Mid-sized prototyping breadboard 83mm x 55mm. PB8820 Arduino® Compatible Microcontrollers JUST 7995 $ JUST 49 $ JUST 29 95 $ ONLY 2995 95 $ BEST SELLER Arduino® Compatible Learning Kit Includes UNO board, breadboard, plenty of prototying hardware, modules, components and instruction booklet to get you started. XC3900 WITH WI-FI 109 $ Arduino® Compatible MEGA Experimenter's Kit JUST Includes MEGA board, breadboard, jumper wires and plenty of prototyping hardware & peripherals in a plastic organiser. XC4286 95 Arduino Compatible MEGA R3 Board ® WITH WI-FI 59 $ $ XC4421 3995 Arduino® Compatible Nano Board XC4411 Our most powerful Arduino® compatible board. Boasting more IO pins, more memory, more PWM outputs, more analogue inputs and more serial ports. Powered by a USB-B cable or 7–14VDC. ATmegas2560 microcontroller. 53Lx108Wx15Hmm. XC4420 Arduino® Compatible UNO R3 Board Fully compatible with all the features of the full Duinotech boards but on a tiny DIPstyle form. Powered by a mini-B cable or 7– 14VDC. ATmega328P microcontroller. 46Lx18Wx18Hmm. XC4414 Stackable design makes adding shields easy. Powered by a USB-B cable or 7–14VDC. ATmega16u2 USB-Serial chipset. 53Lx75Wx13Hmm. XC4410 SAVE 10% ON THESE POPULAR MODULES NOW NOW FROM 10% OFF 10% OFF 12 $ 95 Stepper Motor Controller Module Allows full control of two DC motors or one stepper-motor. Provides 4A at up to 30V. 3-30VDC. XC4492 NOW 6 $ 95 10% OFF Dual Ultrasonic Sensor Module Measure distances up to 4.5m. Great for obstacle avoidance robotics project. XC4442 JUST 39 $ 95 Light Duty Hook-up Wire Pack Quality 13 x 0.12mm tinned hook-up wire on plastic spools. 8 rolls of different colour included. 25m each roll. WH3009 4 90 $ NOW 2695 $ Relay Modules Switch up to 10A per channel. Includes back-EMF protection and LEDs. One, four and eight channel version available. 1 Channel 5VDC XC4419 NOW $4.90 4 Channel 12VDC XC4440 NOW $11.50 8 Channel 12VDC XC4418 NOW $17.95 10% OFF Temperature & Humidity Sensor Module Measure both temperature and humidity. Features resistive-type humidity sensor. XC4520 FROM 12 $ 95 Prototype Resistor Packs 0.25W 5% Carbon film. 300 pieces RR1680 $12.95 850 pieces RR1697 $22.95 1700 pieces RR2000 $39.95 ARDUINO® COMPATIBLE This icon indicates that the product will work in your Arduino® based project. Arduino® Compatible RGB LED Strip Light NOW 895 $ 10% OFF JUST 4 $ IP65 RATED 95 SPST Rocker Switch 12VDC 30A. LED illuminated. SK0955 Flexible and waterproof LED strip light with 120 addressable WS2812B RGB LEDs (60 LEDs/m) to create amazing lighting displays. 5V. 2m long. XC4390 FROM 350 $ Hobby Motors For hobbies, experimenters, robotics & as replacements. 1.5-4.5VDC. Low Torque YM2706 $3.50 Medium Torque YM2707 $4.95 RASPBERRY PI COMPATIBLE This icon indicates that the product will work in your Raspberry Pi project. $AVE On Testers & Meters NOW 119 $ NOW 5995 99 $ SAVE $10 $ 1000A True RMS AC/DC Digital Sound Level Meter Clamp Meter Ultra-high current 1000A AC and DC current measurement. CAT III, 6000 count. Data hold, backlight, non contact voltage, relative measurement and more. QM1634 4995 SAVE $10 Network Cable Tester with PoE Finder Detect missing or disordered wiring, and open or short circuits. Includes PoE (Power-over-Ethernet) finder to indicate power loss. XC5084 Accurate voltage readout as well as polarity check. Works on 6/12/24V systems. Stainless steel testing probe. 228mm long. QP2216 JUST 14 95 $ 7 $ 95 395 Includes 5m rolls of mixed colours. 19mm wide. NM2806 More ways to pay: NOW SAVE $10 FROM 6 Rolls Insulation Tape Measure temperatures from -50°C up to 600°C in hard to reach places. 12:1 Distance to Spot Ratio. Adjustable emissivity. Large colour LCD display. Powered from 2 x AAA batteries included. QM7424 3995 $ 3-30VDC Tester with Voltage/Polarity Readout Self-Powered LED Voltmeter JUST with Laser Pointer NOW $ $ Non-Contact Thermometer Features a large LCD display, laser pointer, low battery indicator, memory recall and a DC socket for mains power (5VDC at 50mA). Supplied with carry case. QM1449 Measure light in 4 ranges from 0.01 to 50,000 lux. 3.5 Digit LCD display. Auto zeroing. Separate photo detector. QM1587 Super easy to install, simply connect the power you want to monitor. Suitable for use between 4.5V and 30VDC. QP5581 SAVE $10 Digital Tachometer Digital Lightmeter NOW 6995 $ SAVE $10 SAVE $30 Great for car audio installers, clubs and PA. Range: 30 - 130dB. A & C weighted. Data hold & min/max function, backlit. Fast and slow response. QM1589 NOW Jumper Lead Kits Ideal for connecting devices for testing. 10 leads supplied. Standard WC6010 $7.95 Heavy Duty WC6020 $12.95 ONLY 39 $ 95 JUST 19 $ Real-time battery monitoring. Tests battery, cranking, charging, & trip duration. Automatic sync, alerts sent to mobile via free app. QP2265 Digital Stem Thermometer Multi-purpose thermometer. Features fast response, min/max memory and data hold. 205mm long. QM7216 JUST 24 95 $ 95 12V Battery Monitor with Bluetooth® 6 Piece Precision Insulated Screwdriver Set Includes Slotted and Phillips drivers in various sizes. Ergonomic handles. 1000V rated. TD2026 JUST 24 95 $ Professional Cat IV Multimeter Probes Extra long 1200mm. 600V CatIV rated. 20A current rating. WT5338 NOW 24 95 $ SAVE $5 Save On Workbench Equipment NOW 149 $ JUST 1299 SAVE $10 $ BONUS 1 x 1kg Flashforge Filament Valued at $39.95 with purchase of TL4410 (TL4269-TL4276) 60W ESD Safe Soldering Station Powerful 60W heating element. 160-480°C temperature range. Celsius or Fahrenheit temperature display. TS1640 139 3995 $ SAVE $20 SAVE $10 73 PIECE 73 Piece Screwdriver Set Supplied with a transparent practice padlock so you can see how the various mechanisms operate. 20 Different picks. 3 Torsion wrenches. Automatic tension tool. TH2200 0-36VDC 0-5A Slimline 80W Lab Power Supply Powerful and compact design for your workbench. Constant current and voltage options. Includes banana to alligator clamp leads. MP3842 Open all kinds of electronic devices. S2 Steel precision bits. Storage case. TD2136 Lock Picking Kit NOW $ NOW NOW 34 95 $ LOTS OF FILAMENT COLOURS & STYLES AVAILABLE FROM $19.95 Creality Dual Filament 3D Printer CR-X Create amazing high-quality prints with two colours or materials. Dual fan cooling fans. SD memory card slot. Prints up to: 300(L) x 300(W) x 400(H)mm. TL4410 25W 14 95 $ 24 PIECE TS1465 SAVE $5 Jaycar will not accept responsibility for any inlawful use of this item. It is intended for private (personal security) and hobby (locksport) use only. 240V Soldering Irons Stainless steel barrels. Impact resistant handles. Electrically safety approved. JUST 3995 $ 4.3" COLOUR TOUCH SCREEN TS1475 80W 24 95 $ TS1485 CURES UNDER UV NOW 39 $ 40W 1995 $ 95 SAVE $5 Bondic Liquid Plastic Welding Kit Ratchet Crimping Tool For Insulated Terminals Digital Stainless Steel Caliper Bond, build, fix & fill virtually anything in seconds. Solvent-free. Stays liquid until cured with the included UV LED light. NA1530 Heavy duty. Suitable for crimping insulated terminals from 0.5mm to 6.0mm in size. TH1829 0-150mm (0-6") measurement range, metric & imperial. 5-digit LCD. Stainless steel. Case included. TD2082 NOW 2995 $ SAVE $10 J-B Weld Epoxy Two part epoxy resin. Bonds to almost any surface. 25ml. NA1518 JUST 16 $ 95 THE BEST EPOXY GLUE ON THE PLANET JUST 16 $ 95 EA 200g Duratech Solder 60% Tin / 40% Lead. Resin cored. 2 sizes available. 0.71mm NS3005 1.00mm NS3010 Looking for more product information? Visit your local store or our website jaycar.com.au FROM 12 $ FROM 345 95 Rare Earth Magnets with Mounting Holes Super powerful. 4.5mm mounting holes. Round LM1626 $12.95 Rectangle LM1628 $17.95 $ Loom Tubes Keeps wiring in place and suits many other types of applications. 6 sizes available: 7, 10, 19, 25, 40 & 48mm. Comes in 2m or 10m lengths. HP1221-HP1227 We reward our industry professionals Chargers & Storage FROM 1695 $ FROM 3495 $ 4-STAGE 9995 $ MB3611 18650 Li-ion Rechargeable Batteries 2600mAh SB2308 $16.95 2600mAh Unprotected SB2299 $21.95 2500mAh Protected SB2298 $25.95 9-STAGE 189 $ Multi-Stage Battery Chargers MB3613 Intelligent SLA* battery chargers for automotive, marine, motorcycle or workshop use. Suitable for charging as well as maintenance. Safe to leave connected for months. *Sealed Lead Acid 12V SLA Batteries 21 * High quality batteries for standby, emergency and back-up power applications. 7.2Ah SB2486 $34.95 NBN BACKUP BATTERY 9.0Ah SB2487 $44.95 12Ah SB2489 $56.95 18Ah SB2490 $79.95 * Sealed Lead Acid 3 25 /m High Current 2-Core Power Cables 4-Channel Universal Fast Battery Charger Charges any combination of Ni-MH, Ni-Cd, Li-ion, or LiFePO4 cells using Pulse Width Modulation (PWM) at the same time. Powered from a USB Type-C port. MB3703 Interchangeable DC plug and alligator clip. 2m cable. MB3619 7" LCD SAVE $10 Head Up Display Speedometer with GPS & OBDII Data SAVE $30 60A Panel Mount Circuit Breaker 30A Car Battery Type Clips NOW 299 $ JUST 4 75 NOW 4995 $ 2CH 2.4GHz digital. Help see through blind spots. Up to 80m range with crystal clear picture. 12V/24VDC. QM8046 15A Double Insulation WH3079 $3.25/m 25A Single Insulation WH3087 $5.50/m $ 95 12V 1A SLA Battery Charger Wireless Reversing Camera Kit with 7" Display FROM $ $ 120A & 200A ALSO AVAILABLE AT THE SAME PRICE! High quality with multiwire gauge inputs/ outputs, perfect for high powered car audio, automotive or solar installations. SZ2081 JUST 44 95 $ Colour coded handles. Sold as a pair. 70mm long. HM3012 Keep your eyes on the road and read important driving info such as speed, from a head up display reflected off the windscreen. OBD II or GPS operation. Auto brightness adjustment. LA9036 Reversed image reflects correctly onto windscreen. 12 Way Fuse Block with Bus Bar Accepts up to 30A per output with handy fuse-blown indication. Negative bus bar. SZ2032 JUST 5 95 EA Double Blade Fuse Socket Wire Taps Standard SF5115 Mini Blade SF5125 Micro Blade SF5130 FROM 7 $ 95 Weatherproof Deutsch Style Connector Sets Male and female set with housings, wedges, seals and crimp pins. 2, 4 & 6 way available. PP2148-PP2150 Cuts and strips wire. Can also cut bolts with diameter M2.6, M3.0, M3.5, M4.0 & M5.0. TH1828 JUST 9 $ 95 JUST 3995 $ 300 PCE 5 Way Crimping Tool $ JUST 4995 $ JUST JUST 44 95 $ 300 Piece QC Crimp Connector Pack Bullet, ring, fork, spade and joiners in various sizes and colours. PT4536 TERMS AND CONDITIONS: REWARDS / CLUB MEMBERS FREE GIFT, % SAVING DEALS, & MEMBERS OFFERS requires ACTIVE Jaycar Rewards / membership at time of purchase. Refer to website for Rewards / membership T&Cs. INSTORE ONLY refers to company owned stores and not available to Resellers. Page 1: BONUS 1 x Automotive Crimp Tool with Connectors (TH1848) for every purchased of Inspection Camera (QC8718). BONUS 1 x Head Torch (ST3211) for every purchased of 4000 Lumen LED Torch (ST3526). BONUS 1 x Stereo Earphones (AA2156) for every purchased of 20000mAh Power Bank (MB3822). BUNDLE DEAL: 1 x Arduino Sensor Kit (XC9201) + 1 x Arduino Compatible UNO Board for $79.90. Page 2: Buy a Power Supply (MP3536) to suit Raspberry Pi Boards XC9001, XC9100 or XC9104 on the same transaction for $17.95. Page 5: BONUS 1 x kg Flashforge Filament with purchase of Dual Filament 3D Printer (TL4410), select from TL4269-TL4276. SUPPLY CHAIN DISRUPTION. We apologise for factors out of control which may result in some items may not being available on the advertised on-sale date of the catalogue. HDMI Connectivity NOW JUST 9995 99 $ $ SAVE $30 1080p HDMI Cat5e/Cat6 Extender with Infrared 7495 $ 4K Front Front Extend your HDMI signal using CAT5e/6 cable up to 50m*. Ideal for running HDMI signals to new locations or connecting through existing building cables. AC1783 LIMITED STOCK. HURRY! *Depending on cable used & resolution. Rear JUST Concord HDMI Audio Extractor HDMI to Composite AV Converter Extracts audio from a HDMI signal so you can listen to the audio through your home theatre system, amplifier or active speakers. Outputs: TOSLINK, coaxial & analogue 3.5mm stereo audio. AC5030 Convert your digital HDMI signal to a standard composite audio/ video signal. Supports PAL and NTSC standards. USB cable and power supply included. AC1773 4K USB Type-C to HDMI Lead Concord 4K HDMI Leads High quality 24K gold plated connectors. Available in 0.5m, 1.5m, 3m & 5m lengths. WQ7900-WQ7906 FROM 1995 $ USB Connectors USB to DB9M RS-232 Converter 95 Allows a computer to use any RS-232C serial device via the USB port. Suitable for POS systems, digital cameras etc. 1.5m long. XC4834 N300 Wi-Fi Range Extender $ Lightning® Leads Charge, data sync and audio stream from an Apple™ devices that use a Lightning® connector. 1m & 3m available. WC7731-WC7733 Built-in extenders to run your USB devices over long distances. 5m XC4839 $24.95 10m XC4120 $39.95 20m XC4124 $49.95 ONLY 4995 Quickly eliminate dead-spots or provide an access point on your existing wired network. Plug straight into mains power point. N300 300Mbps. YN8370 ALSO AVAILABLE: AC1200 High Power Dual Band Wi-Fi Extender YN8374 $99.95 144W Mains Laptop Power Supply Dual Band USB Wi-Fi Dongle FROM 595 $ 1.5m Quality Leads Video F-Plug to TV Coaxial Plug. WV7384 $5.95 Audio 3.5mm Stereo Plug to 2 x RCA Plugs. WA7014 $6.95 000S SOLD! SAVE $30 65W 64 95 $ JUST 39 95 90W 7995 $ MP3321 Equip your old PC or laptop with ultra fast Wi-Fi. Dual band 2.4GHz and 5GHz. Up to 433Mbps transfer rate. YN8334 Looking for more product information? Visit your local store or our website jaycar.com.au NOW 99 $ Replace your lost or broken laptop charger. Feature short circuit and overload protection. Compatible with most brands. MP3471 $ FROM 1995 95 Extra Long USB Extension Leads REPEATER, ACCESS POINT, OR ROUTER $ FROM 24 JUST Connect your USB Type-C enabled device such as a Smartphone, Tablet or laptop directly to a HDMI TV or monitor. 1m long. WC7950 ONLY 4995 $ $ 29 $ Rear MP3476 FROM 995 $ IEC Leads IEC Male to 3-pin Female 0.15m PS4100 $9.95 Straight IEC Female to 240V Male 1.8m PS4106 $9.95 240V Male to Right Angle IEC Female 1.8m PS4107 $10.95 JUST 1995 $ USB 3.0 4-Port Hub Perfect for connecting all your peripherals to a laptop or portlimited device. No power required, plug and play operation. XC4979 BEST SELLER JUST 995 $ HDMI Adaptors EA Socket to Socket PA3640 Socket to DVI-D Plug PA3644 We reward our industry professionals s ' t a Wh ular Pop INSTALL YOURSELF & SAVE $$$ 4K NOW FROM 1199 $ 2TB HDD SAVE $200 Concord 8Ch 4K NVR Packages Smart viewing and notification. Audio recording. Power-over-Ethernet. Expandable up to 8 cameras. Built-in infrared LEDs for night vision up to 30m. Includes Network Video Recorder, cameras, power & video cables, adaptor, USB mouse, HDMI cable & network cable. With 4 x 4K Cameras QV5700 NOW $1199 SAVE $200 With 6 x 4K Cameras QV5702 NOW $1699 SAVE $200 Limited Stock. In-store Only. 1080p Outdoor Trail Camera NOW 179 $ Monitor local wildlife or use as an outdoor security camera. 10sec-3min motion detection recording onto microSD card up to 32GB (sold separately). Water resistant housing. Time lapse recording. 2.4" LCD. Requires 8 x AA batteries (sold separately). QC8043 32GB microSD Card XC4992 $36.95 12pk AA Batteries SB2333 $7.95 SAVE $20 LED Vehicle Warning Lights* Designed to be mounted onto the roof for maximum visibility. Cigarette lighter plug. Heavy duty magnetic base. 12VDC ST3295 $49.95 12/24VDC with 10 Flashing Options ST3278 $129 *For off-road use only Digital Weather Stations Measure temperature, humidity, wind speed, wind direction and more. Time, day & date display. Up to 150m transmission range. 6" Monochrome XC0432 NOW $169 SAVE $30 7" Colour XC0434 NOW $249 SAVE $50 NOW FROM 169 $ UP SAVE TO $50 JUST 24 $ 95 True RMS Autorange Multimeter Non-contact voltage detection. 1000VDC CATIII rating. 4000 display count. AC/DC current 10A. QM1321 NOW 5995 $ 3995 LCD Monitor Wall Mount Bracket with 10° Tilt Fits 42"- 80" flat panel TVs. Ultra-thin design. VESA standard compliant. CW2867 160 PIECE JUST 9 $ 29 95 Anderson 50A High Power Connectors Compact Ethernet Switches Heatshrink Pack JUST $ SAVE $10 FROM Easily create and expand your wired network. 8 Port 10/100Mbps YN8388 $29.95 5 Port 10/100/1000Mbps YN8395 $39.95 8 Port 10/100/1000Mbps YN8397 $59.95 FROM 4995 $ ST3295 BUILT IN SPIRIT LEVEL with Long Range Sensor $ ST3278 Contains 160 lengths of different sizes in a handy storage case. WH5524 $ EA Used widely in both domestic and industry applications. Supplied as a moulded 2 pole with contacts. 600V (AC or DC). 6, 8, 10-12 Gauges available. PT4420-PT4427 JUST 995 95 Third Hand PCB Holder Tool Ideal aid for PCB assembly, soldering work etc. Heavy cast iron base. Movable arms. TH1982 LEARN, BE INSPIRED, PROJECTS, WORKSHOPS & MORE! 24/7. 1800 022 888 www.jaycar.com.au Over 100 stores & 130 resellers nationwide HEAD OFFICE 320 Victoria Road, Rydalmere NSW 2116 Ph: (02) 8832 3100 Fax: (02) 8832 3169 ONLINE ORDERS www.jaycar.com.au techstore<at>jaycar.com.au Arrival dates of new products in this flyer confirmed at the time of print. Call your local store to check stock. Occasionally discontinued items advertised on a special / lower price in this flyer have limited to nil stock in certain stores, including Jaycar Authorised Resellers, and cannot be ordered or transferred. Savings off Original RRP. Prices and special offers are valid from 24.07.2021 - 23.08.2021. SERVICEMAN'S LOG Rocking Raucous Retro Roland Repair Dave Thompson I’m trying to stay positive despite the world falling apart around my ears. Earthquakes, plagues, waves of misguided activists – they’re all conspiring to ruin what’s left of our idyllic way of life. At least customers still occasionally find their way to me, with devices that sometimes can still be repaired; in this case, a throwback to the 1980s. And that’s just fine with me, because they knew how to build fixable gear back then. Items Covered This Month • Rocking Roland repair • Samsung aircon repair • Fixing LED light fittings • Repairing a water heater and • • • key-fob Multiple LED downlight failures Repairing a TV with constantly decreasing audio levels Fixing outdoor lighting *Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz siliconchip.com.au W e live in ‘interesting times’. The pandemic is disrupting lives, if not directly through infections, then by hammering businesses through the collateral damage of lockdowns, and a drop in people being able to go out and buy goods and services. The economic toll is becoming increasingly apparent and harming us all. There is also significant lobbying going on from all manner of crackpot pressure groups trying to make everyone’s lives worse. They might not see it that way, but there’s no escaping the reality. I get the feeling Australia’s electronics magazine that so many policies these days are not being thought through, especially with politicians now taking advice from school kids rather than listening to the experts. In the electronics world, I’ve been worried about how getting older is affecting my ability to do fine repair work, but I also have all the above in the back of my mind, which doesn’t help my state of mind. Work, while sparse, is still coming in. Recently, a Roland Juno DX2 keyboard came into the shop accompanied by its owner. It had simply stopped August 2021  61 working. Not only were there no dulcet tones one usually associates with a Juno, there was nothing at all. No lights, no power. These vintage 80s-era keyboards are now quite sought after for their genuine ‘analog’ retro sound, so its owner very much wanted it to be fixed. I told him that, in theory, everything was fixable – if not by me then by someone with more experience – and it all really depended on how deep his pockets were. As with many musicians, it turns out his pockets were not very deep at all! Quite shallow, in fact. I advised him that I would assess it and then let him know what was ailing the machine, and it would be up to him as to whether he wanted to carry on. But it was also up to me as to when to pull the pin on any given job, which is part of our serviceman’s creed. He agreed. He had already done some of the work in taking all the screws out from the bottom and cracking the case open, so that saved me some time. He could get this thing apart so easily because he didn’t have any of those stupid security fasteners to deal with. Manufacturers back then were usually sensible, making products that were able and meant to be repaired, with any proprietary spares usually available from dealers (for a good while at least). The electronic components used throughout were often available from any good local electronics store. Access to the circuit boards was usually good as well, with no break-away plastic clips or similar impediments restricting any attempts at repairs. I liked that philosophy then, and I like it now. Dead on arrival Testing this thing was also simple. I plugged in the supplied power lead and hit the “On” button. Result: nada. Zilch. Bupkis. Nothing. The first thing to do was to test the power supply. Many a repair has come unstuck because the serviceman overlooks the patently obvious; that the lead or power supply has failed. It’s easy to do, and I’ve done it myself many times, being too keen to roll up my sleeves and get stuck into a job. One must temper one’s urge to get into it and test the obvious first. In this case, the power lead is likely as old as the machine, and without knowing its history, it could very well have fatigued and failed. The obvious test is to unplug it from the keyboard and stick a couple of multimeter probes into it in a way that I could wiggle it around and ring it out without electrocuting myself. This I did, and I got a healthy 240-odd volts AC no matter what I subjected the cable to. So I was happy that it was OK. The next step was to plug the cable back into the keyboard and test some points in the power supply circuit board. This was separate from the rest of the circuitry and easy to spot, given the transformer, capacitors, diodes and associated leads connecting to it. I love this older hardware; everything is so obvious as to what it does. A quick probe around the board showed that mains potential was going into the transformer but not coming out. This is quite unusual; transformers are one of the most basic of all electronic components and for one to fail is, in my experience, quite rare. I mean, if there’s a 62  Silicon Chip lightning strike or other huge power anomaly, then yes, a transformer can burn out, but in ‘normal’ use, it is unusual. A transformer is essentially just two coils of insulated wire wound onto a soft-iron core; how those coils are arranged determines what type of transformer it is. In the Dominions and other areas where 220-240V is the norm, the primary and secondary windings will be different than in the USA and other territories where the mains voltage is 110-115V. If a device is intended to be used in either location, it will often have two 110-120V primaries that can be connected in series for 220-240V operation or in parallel for 110-120V operation. This is one reason why many modern appliances (computers, printers etc) have a separate power supply; the basic machine runs on the same internal voltages, it is just the supply that differs. Of course, these days, most of those switchmode supplies can run off a wide range of voltages, like 90-250V AC, so they are suitable for use worldwide. Obviously, if there is a frequency-dependent component in the device (that is, it needs the 50Hz or 60Hz signal as a reference to operate), the internal power supply will vary between countries. In this case, however, the Juno was designed to be used in this part of the world, with 220-240V AC mains. I removed the power supply board, a simple operation with only four PK-style screws holding it down, and then desoldered the transformer leads from the board. With the board resting safely on the chassis, I used my non-Variacbranded Variac to slowly apply AC voltage to the circuit downstream from the (now removed) transformer. With my multimeter probes attached to the board’s outputs, I expected to see whatever DC voltages the board was designed to provide. Sadly, I got nothing; perhaps there was more to this than I thought. While I’d need the right transformer, I might also have to see what else was damaged before I could resurrect the Juno. I had hoped I might get lucky, but usually, by the time a transformer blows, there is a lot more collateral damage due to unusually high secondary voltages being produced as it fails. Even though there is a fuse, by the time that blows, a lot of harm can already be done. I might still have many more problems to sort out, but I would have to replace this transformer to find out. The appeals of retro Did I mention I love working on older stuff like this? Each section of the keyboard’s functions sits on a separate circuit board. The VCO (voltage controlled oscillator), VCF (voltage controller filter) and the VCA (voltage controlled amplifier) sections are all separate. The same goes for the keyboard processor, signal processing and audio amplifier sections. If one section fails, a new (or repaired) PCB can simply be installed, and regular operation resumes. This philosophy is unlike how modern instruments are produced, where everything is typically on one big circuit board with propriety COB (chip-on-board) ICs and no spares available from the manufacturer. Even worse, no circuit diagrams generally are provided, whether you are a repair agent or not. If something goes wrong, you usually have to chuck the whole thing away (into a landfill) and pay an exorbitant price for an entire new keyboard, as the cost of repair is Australia’s electronics magazine siliconchip.com.au so high. Nowadays, it seems to be all about IP (‘intellectual property’) protection and making hyper-consumable products with almost zero ability to repair. Back then, for better or worse, they used standard parts and standard (if increasingly clever) circuitry to achieve what they wanted to do. Foreign powers with commercial aspirations often hijacked these designs, calling the resulting device something else, but essentially cloning and copying the original company’s design. Affected manufacturers responded by making it increasingly difficult to reverse-engineer their products, usually by using proprietary parts and making spare parts or components and replacement circuit boards increasingly unavailable, meaning repair was simply not an option. No wonder people are up in arms about huge increases in e-waste and the rise of built-in obsolescence! I’m actually with them. This is just wrong, and while it might be great for IP protection, I don’t think it’s the best way forward. However, as our Juno 2 has discrete components on separate boards, it is a veritable dream for a serviceman like myself to fix. So it seemed that the problem with this machine was in the power supply board. I was hoping that if I could resolve this, the rest of it should still be OK. But like any good mystery, I wouldn’t know until I got the power supply board working. I do know that many of these older analog ICs were pretty hardy devices in their day, so the lack of any obvious burned-black spots on the other PCBs, holes in chips or that distinctive stink of burnt electrical components was a good sign. I was reasonably sure that once I got the power supply board working, the rest of it would start up again and start producing sounds. Fingers crossed! To be thorough, I should test every component on the power supply board. That’s not too onerous a task, to be frank, because there is not much on it. There is a diode rectifier array, two relays, a regulator, a few capacitors and a fuse. The fuse had not blown, so that usually indicates a lack of shorts. The regulator is a standard 78XX type, and the capacitors and diodes are all common components. All are clearly marked, as is the PCB assembly. To really save the planet, modern manufacturers should take a hint from the way this keyboard is manufactured. My first check was to measure the transformer’s output, and I got nothing, indicating that at least one of the windings was open-circuit. Fortunately, the transformer has a part number on it, but a quick Google search found nothing relating to it. The great news is I have a commercial transformer-winding machine. The bad news is that I would have to dig it out of storage in my garage to use it, and that idea wasn’t appealing at all. The good news is that I got about a hundred miscellaneous transformers when I bought the winding machine, but the bad news is I’d have to trawl through those transformers to find a suitable replacement for this one. The good news is that I didn’t have to! I had a Jaycar replacement in the drawer that would not only fit, it would also be suitable electrically. That really is excellent news... This was not so surprising, as all I really needed was a mains transformer with a 12V AC output with a reasonable current capacity, and those are a dollar a dozen. siliconchip.com.au Australia’s electronics magazine August 2021  63 Removing the old one was simple, and replacing it almost too easy. Surely this repair couldn’t be this straightforward. Once I had replaced that, I powered the machine on and... nothing. I knew this was too good to be true. I now had 12V AC, but nothing past the diode array. Out the board came again, and this time I replaced the existing diodes with four 1N4001s. Desoldering these old boards can be tricky, but I have to say I love the smell of that old solder; it brings back many memories. I replaced all the diodes, and for good measure, the regulator as well while everything was out. After reassembly, I hit the power button with expectations of it all working – and it did! The display and all the lights lit up as they should. With an amp plugged in, I hit a few notes and was rewarded with that warm, mellow, smooth, rich, laid-back, melodious, euphonious analog sound. Thank goodness for that! While I likely could have fixed other parts of the circuit if necessary, I was glad that I didn’t have to work my way through it all. The time involved alone would have deterred the owner, and he likely would have bailed on the project. At least now I could tell him that he would probably have many more years of use from this beautiful vintage keyboard. 64  Silicon Chip He was over the moon, and although he said he thought it would be an “easy fix”, he doesn’t know the half of it. Samsung air conditioner repair N. K., of Kedron, Qld likes to wield a soldering iron to repair written-off devices. It’s part of his hobby, and he enjoys the challenge of solving mysteries and saving a lot of money at the same time. In some cases, there is a lot to gain and little to lose... This one was brought to me by my son. His friends, a young couple with small children, had their air conditioner written off by the repairman in the middle of Brisbane’s hot and humid summer. It was an old Samsung split system, and apparently, replacement boards are no longer available. They could ill afford the $2700 quoted for a new system, so my son generously offered to take the boards so he (meaning me) could check them at the component level. So I could not test them in operation. The boards were the indoor and outdoor unit power supplies, the display board and the controller board, hosting the main microcontroller and several other surface-mounted ICs. The repairman said he found dead geckos on both power supply boards and blamed them for the failure. I found evidence of fried gecko on both Australia’s electronics magazine boards, but the marks were confined to the mains areas of the boards. So I doubted that was the real problem. They reported no lights on the indicator panel and the system was completely unresponsive. I figured that if the problem was with the outdoor power supply, or anything else outdoors, the indoor indicator lights should still come on. The outdoor unit is a linear supply with a conventional transformer followed by a four diode rectifier bridge. The fuse was intact. It’s only used to power relays anyway, and the diodes tested OK. There are no Mosfets, so I was confident the problem was elsewhere. I looked briefly at the indoor indicator board and saw nothing visually wrong. There was not much I could have fixed there anyway, so I put it aside. Likewise, the complex controller board looked intact. So I dismissed it as both unlikely and too hard. That left just the indoor power supply board. Its fuse was also intact. It is a switchmode power supply with 230V AC directly rectified to 325V DC. The rectifier bridge checked OK with my multimeter, as did the 400V electrolytic filter capacitor. Tracing the tracks on the board, this fed a TNY266PN offline switcher IC, with Mosfet switches to chop the DC into the primary of the step-down transformer. The secondary, low voltage side of the transformer went to a single half-wave schottky rectifier diode followed by filter capacitors and a small KA78L05AZ linear 5V regulator. There were other components, but they either checked out OK or did not look like suspects. Testing the schottky rectifier diode hit pay dirt. It was short circuit. However, without expensive test gear, I am always suspicious of the black magic lurking in switchmode supplies. You can never tell if something else failed first, damaging the diode, or if the diode failed and took other components with it. In any case, I never trust the Mosfets in a failed switchmode power supply. That TNY266 could have refused to power up due to a sensed low impedance on the primary of the transformer, caused by the shorted diode on the secondary. This, coupled with my overall suspicion about failing Mosfets, led me to replace the TNY266 as well. I could not tell if the KA78L05 5V DC regulator had been damaged by siliconchip.com.au the failed rectifier diode, so I decided to replace it too. The replacement components only cost a few dollars, plus $25 for shipping. I could not find an equivalent axial lead schottky diode, so I used a surface-mount equivalent, soldered to two posts on the board. It was all a gamble, but when my son reinstalled the boards and reconnected the power, the air conditioner sprang to life and started doing its job. So I had the thrill of the hunt, the satisfaction of success, and a suitably impressed son. This also resulted in a very grateful couple and a disappointed air conditioner salesman. Fixing LED light fittings J. N., of Mt Maunganui, New Zealand, had a go at fixing light fittings with failed individual LEDs... I had to replace an outdoor light because it had become too corroded and the housing was letting water in. Fortunately, I had a spare replacement Arlec ABL003 LED unit on hand. After installation, all went well for about three weeks until the light failed. As I am a retired technician and it was out of warranty, I decided to see if it could be repaired. After removing the cover, nothing seemed out of place, so I removed the unit to my workbench. I discovered that it had 18 LEDs in series, powered by an AC-to-DC converter. I applied power and verified that it was producing a reasonable DC voltage. Next, I tested the LEDs and found that two were faulty (marked with red arrows in the photo below). I couldn’t be bothered replacing them even if I could find replacements. Then I realised that I could simply short out the two faulty LEDs by applying solder siliconchip.com.au across them. Upon reapplying power, bingo, the light worked! To be on the safe side, I decided to add a 2.2kW resistor in series with the LEDs to reduce the current through the remaining LEDs to a similar level as it would have been with all of them installed. After a soak test of 48 hours, I reinstalled the light which is still working well after two months. Repairing a small water heater and a faulty key-fob K. D., of Chermside, Qld, had to make two repairs recently, both of which involved fabricating new parts. In both cases, those new parts are far superior to the failed ones that they replaced… I was asked to look at a small unit that heats water to about 40°C and circulates it through a mat. Made thirty years ago, the device had initially been used to keep premature babies warm. It had long been made obsolete from that job and repurposed for use in the laboratory. The complaint was that the unit wasn’t heating the mat. There were four likely points of failure: the element, the control electronics, the pump or the plumbing. Looking at my notes, I had previously replaced the cartridge heater in this unit. The original element was 3/8-inch (9.5mm) in diameter, and the only replacement I could get with suitable electrical ratings was 10mm in diameter. That necessitated the careful reaming of the thin-walled pocket the element fitted into with a chucking reamer. To quickly check the element and control electronics, I measured the power consumption of the unit. I found that the element was clearly Australia’s electronics magazine being cycled on and off by the control electronics. That meant that the failure was most likely in the pump or the plumbing. I disconnected the hoses, and the lack of flow or suction confirmed that the pumping system or plumbing was at fault. Water drained passively from the hose connections, though, indicating that there wasn’t a major blockage in the piping. That left the pump itself as the likely culprit. With the cover removed, I could feel that the rotor of the pump motor was turning, so the impeller had to be the source of the problem. Splitting the integrated pump/heater block required complete disassembly of the unit. All I found in the pump chamber was a protruding shaft. There was simply no impeller to be seen! I did find, however, lots of tiny pieces of Bakelite or phenolic material in the chamber and the water passages. Reassembling these like a jigsaw gave me a flat piece ~40mm x 4.5mm and about 0.8mm thick. It was a very simple impeller that must have been attached to a flat on the shaft with a couple of spots of glue. I thought of various ways to replace the impeller, such as making one from a brass shim or PCB material either glued or soldered to the shaft. Then I realised that I could 3D print a better impeller that would be a press fit and held in position by the flat section on the shaft. I quickly drew a simple design in a 3D modelling package and sent the file off to a colleague for printing. A few days later, I had an impeller ready to fit. It was a snug press fit onto the shaft and turned freely in the pump chamber. When reassembled, the unit pumped far better than anyone remembered. The next repair began when I watched a friend unlock her 2001 Toyota Camry with the key and not the key-fob remote control she usually used. Some questioning led to the explanation that a water bottle had leaked in her bag some days earlier, flooding the remote which had stopped working. It was apparent how the water had gotten in as the rubberised button had perished and fallen out several years ago, leaving a large opening through which the small PCB-mounted switch could be operated directly. Looking into the hole, I could see August 2021  65 several surface-mount components with white corrosion on their leads. I pressed the button a couple of dozen times, and the car responded twice, so I thought it would be worth attempting a repair. The remote was obviously never intended to be serviced, as the case was glued together. Some leverage split the case at the join, revealing an oval PCB containing all the components, including a soldered-in coin cell. Most of the corrosion was near the button and was easily removed with a fibreglass pencil. I then washed the board with isopropyl alcohol. After a couple of days drying in the sun, the car responded to every press of the button. I masked the switch with tape and gave the board a generous coat of Electrolube HPA conformal coating in case of future water ingress. Next, I had to make a new button. I covered the outside of the hole with tape and filled the recess from inside with Dow Corning 3140 conformal silicone. Once cured, and after some trimming with a scalpel, I had a pliable button thoroughly sealed to the case. That left re-joining the case itself. I chose not to glue it, in case I ever had to change the battery. Instead, I used Permatex Form-a-Gasket compound to adhere the case halves together with a watertight joint. The remote has worked for many months, with the homebrew button and case joint still in place. Multiple LED downlight failures R. H., of Ferntree Gully, Vic, must have been busy fixing LED downlights as he has had quite a few fail, as he relates... I was prompted to write this by the LED lamp repair story (Serviceman’s Log; May 2020, page 51). I replaced all our ceiling lights with 12W multi-LED lights of two different brands. Over the last two years we have had sweltering summers, and this appeared to precipitate failures in these lamps. Also, when I installed the first lot of three LED lights in the kitchen, I found that we could not watch TV due to interference. I put about six ferrite rings on each light power cable; that reduced the interference so we could at least watch most TV channels. I ended up shifting the antenna to another side of the house using RG6 quad-shield coax. I then installed another two lights in the dining room, and the second bedroom (my office). I put six or so snap-on ferrite rings on each of the mains power cables again, but still got interference! I can only watch TV with the lights off. As these two rooms were in line with my aerial and the Mt Dandenong transmitter, I had to do another antenna shift; this time positioned so the antenna points away from the house. I also added a masthead amplifier to improve the S/N ratio. We can now watch TV with the lights on. When the weather gets really hot (around 40°C), the roof cavity gets to nearly 60°C, and the LED lamps measure 40°C+ on their faces. Initially, one LED in the group of a dozen or so LEDs in each offending light will flicker annoyingly on/off. Fortunately, at the time of our LED light installation, I purchased an extra spare LED lamp per room. As all the new lights have been fitted with a GPO power point in the roof loft, it was easy enough for me to swap the failing lamp for one of my spares. With multiple lamp failures, rather than throw them away, I have been able to swap good LEDs from a failed unit onto another failed unit to make it work properly again. For our seven installed multi-LED lights, I have changed about 20 individual LEDs on the 120mm aluminium platter. After marking and disassembling the faulty lamp and identifying the LED polarity, I get out my mini gas flame torch. With the 2cm flame burning vertically, I hold the LED platter with pliers and place the faulty LED above the flame. After about five seconds, I can lift off the faulty LED with tweezers and repeat the same to retrieve a good LED from a spare (wrecked) LED light. Again noting the polarity of the replacement LED, I put it where the faulty LED was removed, heat it again with the gas flame (from the reverse side) and the LED will ‘magically slip’ into place using the existing solder. If you look carefully at the LED array photos (mine shown below, and the one published in the May issue), the faulty LED has a black spot. Pretty much every faulty LED I have found suffers from this black arcing spot. The string of series LEDs fails at the point of the weakest LED, and once it has gone open-circuit, the whole string won’t work. The only other fault I have encountered with these LED lights (and with CFLs) is the 2.2µF (sometimes 4.7µF) 400V electrolytic capacitor having a swollen top. Replacing that capacitor usually fixes it. Repairing a TV with persistent lowering of audio levels L. J. C., of Forest Hill, Vic, has a story about an electronic fault that had an unusual cause, leading to a very frustrating intermittent fault... In 1965 my father in law, who lived Burnt spot on faulty LED 66  Silicon Chip Australia’s electronics magazine siliconchip.com.au in a Victorian country town, bought a new TV. I don’t recall the brand, but it was Australian made. It worked well for a few weeks, then developed an annoying fault. While you were watching it, the audio level would slowly decrease, so you would have to get up and turn the volume up. This would continue, so you had to keep turning the volume up periodically until eventually, it was at full volume. After a while, presumably due to a power line spike when a motor turned on or off (eg, a fridge), the fault would disappear, so you had to jump up and turn the volume down! Then, after a few minutes, the cycle repeated; it was most annoying. He had the shop’s TV technician try to fix it a few times, but he never succeeded. Eventually, the set went out of warranty, so I asked him if he would like me to fix it. He agreed. I removed the rear cover; in those days TVs had a circuit diagram conveniently pasted inside. It was essentially a valve TV, but it had transistor audio IF and audio output amps. I was a telephone technician, and my boss had recovered an old TV chassis from the rubbish tip, so I inserted the audio IF and output amp valves in and connected a speaker to use it as a signal tracer. I connected the input of the signal tracer’s audio amp to the input to the set’s audio amp. I then switched the set on, and waited for the volume to decrease. I determined that the fault was in the audio IF stage since the level coming from both speakers decreased. But when I attempted to measure the collector voltage on the first IF transistor, the transient caused the volume to leap back to the original level. Frustrating! I reasoned that the fault might be temperature sensitive, so I put a radiator at the back of the TV to warm up the components (my mother-in-law was not impressed). When the volume eventually reduced, it remained low while I made the measurements. I connected the input of the signal tracer’s IF amp to the collector of the first IF transistor and found that the audio level coming from the signal tracer’s speaker was also low. Looking at the circuit, I noticed that the IF coil was tuned by a 560pF plastic film capacitor. In those days, plastic film capacitors were cylindrical. They siliconchip.com.au The internals of a typical garden LED light. were made by rolling plastic dielectric films with the conducting films, with a pigtail wire emerging from both ends. I concluded that the connection between one of the pigtail wires and the respective metal film was faulty, ie, there was a thin film of oxide between the wire and the metal. When the set was switched on, the transients broke down the insulating film, so the volume was normal. But, as the cap warmed, the insulating film started to reform; thus, the capacitance became smaller, hence gradually detuning the IF stage. But when a transient occurred, either from the mains or me attempting to make a measurement, the insulating film broke down. It became a good Ohmic connection for a while until the insulation started to reform. The gradual detuning by the IF amp reduced the signal level going into the next stage and the FM discriminator, thus reducing the volume. I replaced the capacitor with a new one and thus solved the problem. Fixing simple outdoor lighting F. F. C., of Sydney, NSW likes disassembling broken things and investigating the build quality, finding and fixing problems etc. The subject of this current letter is those cheap outdoor solar lights that are known to fail frequently... These lights are attractive for garden areas, outdoor steps etc because you don’t need to run any wiring to them, and of course, the low cost is the other attraction. The problem is that they never seem Australia’s electronics magazine to last very long. That low cost means that it’s tempting to throw them away when they stop working and buy another one. But often, the fix is quite simple. Opening them up is usually not too difficult, and all you will find inside is a solar panel, a battery, one or more LEDs and a small control board with a handful of components. The ‘battery’ is often a single 18650 Li-ion cell (nominally around 3.7V). If you need a circuit diagram, use your favourite search engine to look up the part code printed or etched into the main chip. As you can see from the photo above, there are only three parts on the tiny PCB. One of the components is a commonly found 4-pin part in a SIL package. If one of these lights fails within the first year or so, the most common cause is corrosion of the battery contacts. While the housing should theoretically be sealed, moisture might still make its way inside, and the contacts will quickly become rusty. That will prevent the battery from charging. Of course, the battery itself can fail over time, but it usually lasts a few years under normal conditions. Another possible failure point is in the wiring to the solar panel, which can be quite fragile. Keep that in mind when you disassemble and reassemble the light to fix it. You could fix the original problem and create a new one if you fracture those connections! The circuitry is so simple that it is unlikely to fail. If it does, you can generally swap the board from another light with a different failure. SC August 2021  67 Multi-Purpose Battery Manager n thma y l B m i T By Our recent Battery Multi Logger is a great tool for monitoring and diagnosing battery problems. But sometimes, you need something which will not just monitor what’s going on but also take action, such as connecting and disconnecting loads based on battery charge state. That’s just part of what this Battery Manager does. O ur Battery Multi Logger (February & March 2021; siliconchip.com. au/Series/355) is a Micromite-based device that monitors the condition and usage of a battery system. It can handle battery systems between 6V and 100V, and it is a convenient tool to keep track of how batteries are being used, ensuring that they are kept healthy. Being heavily discharged or overcharged can greatly reduce a battery’s working life, possibly leading to the need to buy an expensive replacement prematurely. So you want to be sure 68  Silicon Chip that you’re treating them well. Both of these conditions are relatively easy to rectify, as long as you are aware of them happening, by simply disconnecting the load(s) or charger causing the problem. Our recent Battery Multi Logger unit can monitor this but did not have any means to take corrective action until now. The Battery Manager adds switching modules to the Battery Multi Logger, which can connect or disconnect loads and chargers to keep the batteries healthy. Australia’s electronics magazine Part of the design is a new I/O Expander board that provides control signals to allow up to four Switch Modules to independently and automatically connect and disconnect loads as needed. The Battery Manager can also interface with the High Current Four Battery Balancer (March & April 2021; siliconchip.com.au/Series/358) to provide even more detailed information about the state of a multi-cell battery or multi-battery system. The Battery Manager can even be used to program, siliconchip.com.au Features ● ● ● ● ● Compact, flexible and modular addition to the Battery Multi Logger Connect and disconnect up to four loads/sources to protect batteries Low battery drain Can interface with the High Current Four Battery Balancer Capable of switching well over 20A (possibly over 30A) at 10V-60V control and monitor the Battery Balancer. While the Battery Multi Logger hardware remains mostly unchanged from the published design, a new control program adds the interface to configure, control and monitor the Switch Modules and Battery Balancer. The Switch Module and I/O Expander hardware have uses outside the Battery Manager, too. While designed for 3.3V operation, the I/O Expander board will happily work at 5V, so it could be hooked up to an Arduino board or just about any other microcontroller. Similarly, the Switch Module will work with just about anything that can supply a control signal of 3.3-15V. So it can also be driven directly by just about any microcontroller. Switch Module One of the goals of the Battery Multi Logger is to use as little power as possible. So we have designed the new Switch Module to have very low quiescent and operating currents. We are using high-current Mosfets as switches, as these can be controlled with minimal power. The Mosfets are driven by a latching circuit that ‘remembers’ the state of the switch and drives the Mosfet gates on or off as needed. This latch can be toggled in several different ways. A pair of switch contacts connected to the latch circuit can set its state, providing simple pushbutton control. The Switch Module PCB also incorporates a pair of opto-isolators. Their output transistors are in parallel with the switch contacts. Thus, there is also the option to set the latch state and control the Mosfets via an electrically isolated interface. I/O Expander board You might recall from the Battery Multi Logger article that it doesn’t have many free I/O pins left. The two pins that provide the COM1: serial port are not used, though, and are brought out to the Battery Multi Logger PCB edge. But we have earmarked these to interface with other serial devices. A better way to control Switch Module(s) is to use the I2C interface, which is brought out to pins at CON4 of the Battery Multi Logger PCB. We are using a PCF8574 IC, which we described in our article on I/O Expander Modules (November 2019; siliconchip.com.au/Article/12085). This lets us easily add eight I/O ports. In fact, with multiple ICs, we could add up to 128 I/O ports, although that would exceed our requirements. So we have designed a small I/O Expander PCB, which can be controlled using the available I2C bus. It provides eight I/O pins connected to transistors to drive the opto-isolated inputs of Switch Module(s). As noted above, a low quiescent current is important. The PCF8574 draws around 10μA when there is no activity on the I2C bus. Its primary current consumption is the current it supplies to drive the opto-isolators, and they are only active very briefly during switching. Battery Balancer support As we just noted, the COM1: serial port on the Battery Multi Logger is free for us to use. Since the Battery Balancer already has a serial interface, we can simply connect these to allow communication and control between the two. We can also use the Mini Isolated Serial Link (March 2021; siliconchip. com.au/Article/14785) to isolate the different parts of the system. Fig.1 shows an overview of the additions to the Battery Multi Logger to turn it into a Battery Manager. Note the connection from the Battery Balancer to CON6 on the Battery Multi Logger. Fig.1: the Battery Manager consists of the Battery Multi Logger plus the peripherals shown here. Up to four Switch Modules can be added with one I/O Expander; we imagine most constructors will need one or two. It can also interface with the High Current Battery Balancer, allowing cell status and balancing activity to be monitored. siliconchip.com.au Australia’s electronics magazine August 2021  69 Updated software Naturally, these extra features need to be controlled and configured. This is done via extra buttons and pages on the Battery Multi Logger’s Micromite LCD interface, shown in screengrabs later in this article. There is also a more detailed description indicating how to use these new screens along with those images. The first new page controls the Switch Modules; up to eight triggers can be set. These are voltage or current thresholds that result in an action occurring, such as one or more of the Switch Modules being activated. A latch is also set to prevent repeated activation; a trigger can also reset a latch to provide alternate operation. For example, Trigger 1 can be set to activate when the battery voltage falls below 11V. This sets Trigger 1’s latch and, via a Switch Module, also disconnects some non-essential load from the battery, reducing the chance of damage to the battery from deep discharge. Trigger 2 is set to activate when the battery rises to 12.5V and also to reset Trigger 1. Similarly, Trigger 1 can reset Trigger 2. As you might expect, Trigger 2 would be configured to reconnect the load that is disconnected by Trigger 1. Thus these two triggers work to detach a load from the battery except when it has sufficient charge. A similar arrangement in reverse can also work as a crude charge regulator, preventing overcharging. The external switches can also be manually manipulated, either for testing or to override the programming, and you can also manually reset the triggers. Another page shows the current operating state of the Battery Balancer (as reported by the Balancer over its serial port), including which cells are being balanced, in which direction and to what extent. Buttons are also provided to issue commands to the Battery Balancer. Two graph pages are available to show recent data from the Battery Balancer. One page shows the cell and stack balancing activity, while a second page plots the individual cell voltages. I/O Expander operation The circuit diagram of the I/O Expander module is shown in Fig.2. Its CON1 header connects to the Battery Multi Logger’s CON2 for 3.3V power and ground. The I2C bus is present at the Battery Multi Logger’s CON4, which connects to CON2 here. These are situated to align directly, allowing the I/O Expander module to stack onto the existing hardware, using either stackable headers or being directly soldered. Since it is only four wires, it can be run remotely too, although a direct connection is preferable. The Battery Multi Logger hosts the pull-up resistors required for the I2C bus, so these are not present on the I/O Expander board. It’s generally better for pull-ups to be on the master, since only one pair is needed per bus. On the I/O Expander PCB, the 3.3V, ground, SDA and SCL lines from CON1 and CON2 go to IC1’s pins 16, 8, 15 and 14, respectively. A 100nF capacitor bypasses IC1’s supply. There are two more 100nF capacitors to help source current into downstream connectors CON3-CON6. IC1, the PCF8574, has three address pins (1, 2 and 3) that need to be pulled up or down to set its address. We avoid the use of pull-up or pull-down Fig.2: the I/O Expander adds to the modular nature of the Battery Manager, providing extra I/O ports to drive devices like Switch Modules. Each I/O Expander adds eight signals, enough to control four Switch Modules. It uses the PCF8574 addressable I/O Expander IC, which can be configured to respond to eight different addresses, allowing further expansion. 70  Silicon Chip Australia’s electronics magazine siliconchip.com.au resistors as this could increase current consumption. So a group of three jumper pads, JP1-JP3, is provided for this purpose. All pins are pulled low by default, giving a 7-bit address of 0x20 hexadecimal (32 decimal). These jumpers are actually solder pads on the PCB and can be changed by cutting the thin traces and soldering between pads. Since eight I/O pins are ample, we have written the software to simply work with a single I/O Expander board with the default address. The PCF8574 could be replaced by the mostly identical PCF8574A. The only difference is that the PCF8574A uses a different range of addresses; in this case, the default address will be 0x38 (56 decimal), and the software would need to be modified to suit that value. Pin 13 of IC1 provides an active-low input change interrupt signal which is not used in this application. We are using all of the pins as outputs, so we do not need the interrupt function. The remaining pins labelled P0-P7 (pins 4, 5, 6, 7, 9, 10, 11 and 12, respectively) are the I/O pins. They are either weakly pulled up (the default state) or pulled low by a sink capable of around 10mA. Since the opto-isolators on the Soft Switch are active-high devices, we use P-channel Mosfets controlled from these I/O pins to source current from the 3.3V rail. These Mosfets also invert the signals. For example, Q1’s gate is connected to pin 4 of IC1 (P0). The gate is also pulled high by a 10kW resistor. While probably not strictly necessary, we have fitted these so that false triggering does not occur while the Battery Multi Logger is powering up. Q1’s source is connected to the 3.3V rail and is effectively connected to its drain when the gate goes low, The Battery Balancer can be connected to the Battery Manager to provide greater information about the state of the batteries. It connects via our Mini Isolated Serial Link. delivering 3.3V to pin 2 of CON3. A similar arrangement exists for the other seven I/O pins of IC1. The outputs are arranged in pairs, to provide the complementary on/off functions needed for the Switch Module to operate. Each of CON3-CON6 can connect to the input of a Switch Module, and so we can control up to four Switch Modules with one I/O Expander board. In operation, the I2C host (in this case, the Battery Multi Logger) writes a default value of 0xFF (all bits set high) to IC1, which then sits in this idle state, drawing virtually no current. Its output transistors are off, and all pins on CON3-CON6 are not connected to the 3.3V rail. When an output needs to be activated, the Battery Multi Logger sends a data byte with at least one bit set low. This causes the corresponding pin from P0-P7 to go low, turning on its Mosfet and sending its corresponding output high. For the brief period that the I2C bus is active, IC1 draws a modest 100μA, while any of P0-P7 that are active will cause less than 1mA to be sunk through its pull-up resistor. The transistor will also source whatever current is needed to control the connected Switch Module. Switch Module operation Fig.3 shows the circuit diagram of the Switch Module. As mentioned, up to four Switch Modules can be connected to a single I/O Expander board. CON1 and CON2 are large, highcurrent connections to the positive The I/O Expander (also labelled as an I2C Interface) adds another PCB to the Battery Manager stack. If you need multiple I/O Expanders, you could fit them with stackable headers (as used on Arduino Shields). Just be sure to set different I2C addresses on the stacked PCBs. siliconchip.com.au Australia’s electronics magazine August 2021  71 end of a battery and its load or source (eg, a charger). Thus, we perform highside switching, leaving the ground connections uninterrupted. The connections are not polarised, so current can flow in either direction when the switch is on. Across CON1 and CON2 are connected pairs of back-to-back P-channel Mosfets, Q4-Q11. Their sources are connected together, with the drains going to either CON1 or CON2. With the gates held near the source potential, the transistors do not conduct, and the switch is off. If the gates are taken low relative to their sources, then a low-resistance path exists between CON1 and CON2. The Mosfet body diodes pass a positive voltage from either CON1 or CON2 to the remainder of the circuit. CON3 is used to provide a ground connection for the circuit and is wired to the battery system’s common negative terminal. The 10kW resistor in series with the GND connection and the 100nF capacitor across ZD2 provide a filtered logic supply (between LOGIC+ and LOGIC_ GND). Typically, around 90% of the battery voltage is present across the 100nF capacitor and ZD2. Zener diode ZD2 does not conduct under normal conditions; it is not even strictly needed for 12V systems, but will clamp any spikes that might be present. It also allows the switch module to be used with battery voltages over 60V. Q1 and Q2 are configured as a bistable latch, with the 100kW and 220kW resistors connected to their gates providing a mutually exclusive interlock. The gate of Q1 is connected to the drain of Q2 and vice versa. If Q1 is on, then Q2’s gate is pulled to near its source voltage, and it is off. Similarly, if Q2 is on, then Q1 must be off. This latch is what retains the state of the Switch Module. Q1’s gate is also connected to Q3’s gate, so that Q3’s state is generally the same as Q1’s. Q3’s drain is also connected to Q4-Q11’s gates. When Q3 is on, its drain network (consisting of the 100kW and 220kW resistors and 15V zener diode ZD1) drives the gates of Q4-Q11 to 4-15V below their sources. In this state, Q4-Q11 turn on, closing the Switch Module’s connection between CON1 and CON2. Otherwise, their gates are pulled up to their sources by the 220kW resistor and they switch off, opening the Switch Module’s connection between CON1 and CON2. Toggling the Switch Module state involves pulling either of Q1 or Q2’s gates to LOGIC_GND. This can be done by the phototransistor outputs of OPTO1 or OPTO2, respectively. When a voltage is applied at CON4’s pin 2 that is positive with respect to its pin 1, current flows through OPTO1’s LED via the 470W resistor, turning on its phototransistor. Similarly, a positive voltage at pin 3 of CON4 triggers OPTO2, pulling Q2’s gate low. A connection between the pins of CON5 or CON6 will have the same effect. This allows control by something like a pushbutton, in addition to control by the Battery Manager. If both Q1 and Q2 have their gates pulled low, then naturally, Q3’s gate is low too, and the Switch Module is off. Thus the safe ‘off’ state dominates if conflicting signals occur. This is similar to the state that occurs when power is first applied. In this case, capacitor C1 (which will have been discharged by its parallel 100kW resistor) holds Q1’s gate low Fig.3: the Switch Module has two opto-isolated inputs which drive a pair of complementary latching Mosfets. These, in turn, drive a bank of high-current Mosfets for switching loads up to at least 20A. This is useful in its own right, as it can be driven by just about any microcontroller, or even a simple set of contacts such as a pushbutton. Australia’s electronics magazine siliconchip.com.au for a brief period, allowing Q2 to turn on before Q1, and the Switch Module is forced into the off state. The time constant of this RC network is less than 1ms, so as long as external pulses are at least this long, then incoming pulses are latched correctly. If the reverse behaviour is required, then the capacitor is fitted adjacent to Q2, to the pads marked C3 instead of C1. The Switch Module will then power up in the on state. Current consumption When sitting in the latched off state, the current consumption is around 500μA at 60V and proportionally less at lower voltages; around 100μA at 12V. When switched on, extra current flows through Q3, adding around 200μA at 60V, down to 40μA at 12V. The current during switching will be higher than this, with Q1, Q2 and Q3 sinking current, but that occurs only very briefly, as the complementary transistors turn off almost instantaneously. Switch ratings P-channel Mosfets Q4-Q11 are SUP53P06 types with a nominal maximum gate voltage of -20V (with respect to the source) and a maximum drain voltage of -60V. These parameters set the practical working limits of the Switch Module. These Mosfets are specified at around 9A continuous current each (at 25°C), but the PCB track width limits this to about 20A across the four pairs; perhaps up to 30A with ample cooling. This can be increased by supplementing the PCB with extra wires soldered directly to the Mosfets. Alternatively, for very light loads, some Mosfets could be left off. The dividers around Q1, Q2 and Q3 have been set to allow operation up to 60V (respecting their 20V gate limit with the 220kW/100kW divider). Since they have gate thresholds down around 3V, they require a battery voltage of at least 10V to work correctly. ZD1 is provided to clamp the gate voltage to 15V for safety. This is generally not a problem for switching loads, as the maximum voltage seen will be the battery voltage. For charging sources, though, the voltage can be much higher. For example, a 12V solar panel can have a 22V open-circuit voltage. Wind turbines can be even higher; they typically siliconchip.com.au The Battery Soft Switch (or Switch Module) uses highcurrent Mosfets as switches so that the total operating power consumption is low. Four of these Switch Modules can be independently controlled per I/O Expander board. need a shunt regulator to prevent their unloaded voltage from reaching dangerous levels. So care should be taken when using this module with a charging source to ensure that the open-circuit voltage does not exceed the Switch Module’s limits. The Mosfet types can be changed to allow operation at higher voltages, but other parts of the circuit might have to be modified too. For example, the SPP15P10 type Mosfet used in the Burp Charger for NiMH and NiCad Batteries (March 2014; siliconchip. com.au/Article/6730) can handle up to 100V, and is a direct substitute for the SUP53P06. The other change we recommend for higher voltage builds is increasing the value of the 10kW resistor to reduce the quiescent current through it and possibly ZD2. Consider the section in parallel with ZD2 as having a resistance of around 100kW. So for 100V switching, replacing the 10kW resistor with a 220kW resistor will put around 30V across ZD2, allowing the circuit to operate correctly. We have not specified the SPP15P10 Mosfet in our parts list because it has a much higher drain-source resistance. So it will produce more heat at Australia’s electronics magazine the same current level, and we expect most readers will be using the Switch Module below 60V. Handling more current If you find that your current requirements are beyond that of the Switch Module, you can use the Switch Module to operate the coil of a heavy-duty relay. The current when energised will be much higher, but this option allows the Battery Manager to work with just about any load. In this case, just a single pair of Mosfets is sufficient to operate the relay coil (eg, Q4 and Q5). A snubbing diode across the coil is highly recommended, to protect the Mosfets from spikes that the coil might generate when it de-energises. Software updates This is a good point to upgrade the software on the Battery Multi Logger to give it the Battery Manager features, if for no other reason than to get it out of the way before we connect the I/O Expander to the ICSP header (which would make programming trickier). If you have blank chips, follow the original instructions for programming the Battery Multi Logger, including putting the Microbridge firmware on the PIC16F1455. But instead of the August 2021  73 Screen 1: the Battery Multi Logger’s Main screen has been updated to add two new buttons for the Trigger and Balancer functions. At bottom right, the trigger state is shown, and the title has also been changed to reflect the unit’s new capabilities. Battery Multi Logger firmware file (1110620A.HEX), load the newer Battery Manager (1110620B.HEX) file. Don’t forget to set JP2 to the PROG position before using the ICSP interface, and set it back to RUN after programming. For an already-working Battery Multi Logger, you can simply update the MMBasic file. The same library file and LCD OPTIONS are used, so no other changes are needed. The act of loading a program will delete any logged data, so you should export that first, if necessary. The newer software has less space for logged data due to needing more space to store configuration variables for the Soft Switches. Thus, the longterm data is reduced to 10 days, and this allows two Soft Switches (controlled by four triggers) to be fitted. These limits are set by CONST values in the program. We’ve listed some options below regarding how these two values can be changed and still fit within the existing flash memory. But generally, as long as the sum of the number of days stored and the number of triggers is no more than 14, it should work. These are the D_COUNT and TRIG_ COUNT values. Due to the way they are displayed on the page, TRIG_ COUNT should be no higher than eight, as otherwise, the control buttons cannot be seen. You will need to load the ‘crunched’ (with comments and whitespace removed) program, as it does not fit in memory otherwise. The uncrunched version is also available so that you can inspect the fully-commented code and make changes if you like. In general, you should follow the instructions for the Battery Multi Logger but replace the respective HEX and MMBasic files with their Battery Manager equivalents. Run the newly installed program to set the AUTORUN flag. Now it should automatically start when powered up. We’ll go into the software detail later, but you should see the new main page as seen in Screen 1. Construction options An important first step before building the board is to determine what parts are needed. Given the low cost of the parts for the I/O Expander board, we recommend that you build the full version, which can handle four Switch Modules. However, you could leave off some of the parts if you are sure that you will only be connecting one or two Switch Modules. The specifics of your battery installation might also affect how you build it. We’ve designed the Switch Module PCB with holes to suit 8mm screws and thus eyelets suiting up to 8G (3.25mm diameter copper) cable, which should be sufficient for anything that the Switch Module can handle. You will need to consider how many Switch Modules you need. Most people will need one or perhaps two to disable non-critical loads when the battery charge state gets low. There’s always a critical load that can’t be disconnected, and that won’t need a Switch Module; you’d much rather have a flat battery than a submerged boat because the bilge pump wasn’t running! And assuming you have a reputable charge controller, there will be little need to add a Switch Module inline with any connected solar panels. Similarly, you might or might not need to build and connect a Battery Balancer. If you have a 24V, 36V or 48V system composed of 12V batteries wired in series, you can make good use of the Battery Balancer. If the Battery Balancer and Battery Multi Logger can’t share the same ground, you will also need to build the Mini Isolated Serial Link. Regardless, we recommend using the Mini Isolated Serial Link to avoid any potential problems; it’s cheap and easy to build, and safer to isolate the two devices. Building the I/O Expander Let’s start by building the I/O Expander and connecting it to the Battery Multi Logger; you can add switch Modules after that. If you’re just interested in the Battery Balancer related upgrades, you can skip most of the construction (assuming you’ve already built the Battery Multi Logger and Battery Balancer). The I/O Expander is built on a double-sided PCB coded 11104212 which measures 37.5 x 35.5mm. Fig.4 is the PCB overlay diagram; all the components are on one side, but there are some solder pad ‘jumpers’ on the underside, so both sides are shown. Since the I/O Expander will essentially become part of the Battery Multi Logger PCB, we have used Fig.4: assembly of the I/O Expander is straightforward – it uses mostly SMD components, but they are easy to handle. Fit IC1 first, ensuring its pin 1 marking is orientated as shown. All capacitors and resistors are non-polarised and of a single value. You don’t have to use vertical headers, as shown here; you could use right-angle headers, sockets or just solder wires to the pads. 74  Silicon Chip Australia’s electronics magazine siliconchip.com.au surface-mounted parts. We recommend having on hand a fine-tipped soldering iron, flux paste, solder wicking braid, a set of tweezers and a magnifier. Flux paste releases a fair bit of smoke, so good fume extraction or ventilation is important too. Start by fitting IC1, noting that its pin 1 is closest to the mounting hole. We found the marking on this chip difficult to discern; there should be a small circle on the top of the part, and a bevel along the nearest edge. On the chips we have, pin 1 is at lower left when the chip markings are the right way up (with the bevel along the bottom edge). Put some flux on the PCB pads for IC1, rest the chip roughly in place and apply a bit more flux to the top of the pins. It doesn’t hurt to be generous! Load the tip of the iron with a bit of solder and tack one pin in place. Adjust the chip if necessary by melting the solder and nudging the chip with tweezers. Once all the pins are correctly aligned, solder them to the PCB. If there are any bridges between pins, remove them with the braid. Add flux to the bridge and press the braid against it with the iron, carefully pulling it away when the braid has drawn up the solder. Solder the transistors next. They are all the same type and are polarised, but should only fit one way due to their shape. Put some flux on the pads and tack one lead in place, then solder the remaining leads. Despite their small size, the leads are well spread around the part, so they are quite easy to solder. Place the three capacitors next; they are near the top of the PCB. Use a similar technique of soldering one lead at a time. The remaining parts are much easier to solder and have larger pads. Follow with the resistors, then clean up any excess flux with the solution recommended by the flux manufacturer (or your favourite one). Parts List – Battery Manager 1 assembled Battery Multi Logger module (February-March 2021; siliconchip.com.au/Series/355), with IC1 programmed with 1110620B.hex instead of 1110620A.hex 1 assembled Battery Balancer module (optional) (March-April 2021; siliconchip.com.au/Series/358) 1 or more assembled I/O Expander modules (see below) 1 or more assembled Switch Modules (see below) 1 assembled Mini Isolated Serial Link (optional) (March 2021; siliconchip.com.au/Article/14785) various lengths of heavy-duty wire, eyelet lugs etc to suit battery and application various lengths of medium-duty hookup wire (see text) various jumper leads (optional; to connect I/O Expander module[s] to the Battery Manager and Switch Module[s]) I/O Expander module parts (per module) 1 double-sided PCB coded 11104212, 38 x 36mm 1 PCF8574 I2C expander IC, SOIC-16 (IC1) [Digi-Key, Mouser] 8 IRLML2244 P-channel Mosfets (Q1-Q8) [Digi-Key, Mouser] 3 100nF X7R SMD 3216/M1206-size ceramic capacitors 8 10kW 1% SMD 3216/M1206-size resistors 1 5-way header (CON1) 1 2-way header (CON2) 1-4 3-way headers or subminiature screw terminals� (CON3-CON6) 1 untapped 12mm-long spacer, ~3.125mm inner diameter 1 M3 x 20mm panhead machine screw Switch Module (per module) 1 double-sided PCB coded 11104211, 82 x 83mm 1 3-way pin header or subminiature screw terminal� (CON4) 16 M3 x 6mm panhead machine screws 4 M3 x 12mm tapped spacers 8 M3 nuts 8 M3 washers � eg, Digi-Key part number ED10562 Semiconductors 2 4N25 opto-isolators, DIP-6 (OPTO1,OPTO2) 3 2N7000 N-channel small-signal Mosfets, TO-92 (Q1-Q3) 2-8 SUP53P06 P-channel high-current logic-level Mosfets, TO-220 (Q4-Q11) 1 15V zener diode (ZD1) 1 39-60V zener diode (ZD2) (optional; see text) 2 1N4148 small signal diodes (D1,D2) Capacitors 1 100nF 100V MKT 1 1nF 100V MKT Resistors (all 1/4W 1% axial metal film) 3 220kW 3 100kW 1 10kW 2 470W A header can be added to the top of the Logger PCB, as shown, to allow in-circuit programming. This header can also provide power to a Mini Isolated Serial Link for connection to a Battery Balancer (singular red wire). Attaching it to the main board Since the I/O Expander is designed to mount directly to the Battery Multi Logger PCB, shut down the Logger and disassemble it. If you have a header fitted to CON2, remove it and clean up the pads to allow the I/O Expander to be fitted. Take the pairs of header pins and sockets and plug them together. Install siliconchip.com.au Australia’s electronics magazine August 2021  75 them in their respective holes between the two PCBs, with the female headers on the Logger PCB and the male headers on the I/O Expander PCB. This will reduce the chance of exposed connectors if the I/O Expander PCB is removed. You can then clamp the two PCBs together temporarily with a machine screw and nut (or tapped spacer). This will make them easier to solder. Refer to the photos as a guide. Solder the headers in place, remove the temporary screw and reassemble the stack, including the LCD. Instead of fitting the machine screw in the corner where the I/O Expander sits, use the extra spacer and the longer machine screw to secure everything against the tapped spacer fitted to the back of the LCD. Switch Module assembly The Switch Module is built on a PCB coded 11104211 which measures 81.5 x 82.5mm and uses all through-hole parts. Its overlay diagram is shown in Fig.5. Start by fitting the resistors according to the markings on the PCB. It’s best to check their values with a multimeter to ensure you have the correct components. Follow with the two zener diodes. Neither of these are necessary for systems that operate up to around 25V, as there are unlikely to be voltages high enough to cause damage to Mosfets, although it’s a good idea to fit ZD1 to protect the Mosfets. ZD2 is only needed for systems that go over 60V. Keep in mind what we mentioned before about solar panels and windmills producing much higher voltages than their nominal ratings. Next, fit the two 1N4148 diodes near CON4, noting their polarity. Follow with the two adjacent opto-isolators. Take care that their pin 1 markings align as shown in our photos. They both face the same way. Now install the two capacitors. As mentioned earlier, C3 does not need to be fitted unless the default behaviour needs to be changed, so it is not shown in Fig.5. After this, mount the three smaller transistors, Q1-Q3. Ensure that they align to their footprints, and push them down as close to the PCB as possible before soldering. Follow with the larger transistors. If you are not fitting all of them, fit those closest to CON1 and CON2 in matching pairs. For example, if you only need four Mosfets to handle your load current, put them in the spots marked Q4-Q7. For each transistor, bend its leads back 90° around 7mm from where they meet the body. Insert the leads through the PCB and fix the tab in place with the machine screw, washer and nut. Take care not to twist the transistors, which might bend the leads. Once aligned with its footprint, solder and trim the leads. The large copper pour will draw heat from your iron, so use a higher temperature if necessary. We’ve added some thermal relief on the PCB to help with this. Fig.5: the Switch Module uses all through-hole components and is easy to assemble. Watch the orientation of OPTO1 & OPTO2 and the diodes. You can install fewer than eight Mosfets if your load draws less than 20A; just make sure to fit them in pairs (Q4 & Q5; Q6 & Q7 etc). The load can be connected either via the two-way screw terminal, or eye lugs bolted to CON1 & CON2. 76  Silicon Chip Australia’s electronics magazine Basic testing You might like to test the I/O Expander and Switch Module at this point. Connect CON3 on the I/O Expander to CON4 on the Switch Module. Connect G to COM, P0 to OFF and P1 to ON. Now attach a 12V power source between CON1 and CON3 on the Switch Module, with the negative terminal to CON3. Connect a multimeter across the empty C3 pads; it should read about 1/3 of the supply voltage. Shorting the CON6 pads on the Switch Module should cause this to drop to 0V and stay there when released. Similarly, shorting CON5’s pads will cause the voltage to revert to 1/3 supply. Using the SOFT SWITCH page on the Battery Manager, you can press the green button next to TR0 and TR1 to toggle the state via the I/O Expander. Keep in mind that the software has been configured with some defaults to suit a 12V battery, and these will be active when the Battery Manager is first powered up. If all this is correct, then the I/O Expander and Switch Module are working correctly. Your wiring from here will depend on your application, but consider that CON1 and CON2 are the switch terminals. Ideally, you should have a fuse and separate switch to the battery circuit feeding the Switch Module to protect it in the event of a fault. So take care that you don’t connect something that can cause damage or be affected by unplanned switching. You might like to leave this until later, after you have configured the Battery Manager. Note the holes in the corner of the PCB, which are designed to take M3 machine screws, allowing the Soft Switch modules to be mounted in an enclosure. For example, you could fit them to the interior of the same panel as the Battery Manager. Battery Balancer interface You need four wires to connect the Battery Balancer to the Battery Manager if using the Mini Isolated Serial Link, or three if you are not. The fourth wire is to power the isolator. Revision E and later of the Battery Multi Logger PCB has pads breaking out the three connections at CON6. For power, you will need to tap into the 3.3V supply, and the best place siliconchip.com.au for this will be at the Battery Manager’s CON2 (which also connects to the I/O Expander’s CON1). If you have an earlier PCB, then the only way to tap into the serial data pins (Micromite pins 21 and 22) is to solder directly to the pins at the IC. It’s not easy, but it is not much harder than soldering the SOIC parts in the first place. Figs.6 & 7 show the wiring required. Fig.6 depicts how a direct connection would be made, while Fig.7 shows the wiring via a Mini Isolated Serial Link. Note how in both cases, the wires appear to go to two points on the Battery Logger PCB at left. They only need to go to one. If CON6 is present (on Revision E boards or later), then use those connections. Otherwise, use the dashed alternatives. These go to pin 22 of the IC for RX and pin 21 for TX. If CON6 is missing, the ground connection can be taken from pin 2 of the LCD header or the middle pin (pin 3) of CON2, the ICSP header. The preferred arrangement, using the Mini Isolated Serial Link, is shown in Fig.7. Jumpers JP1 and JP2 on the Isolator board are set to the 5V position, which means it takes power from the pin adjacent to ground. Since the Battery Balancer has been designed to have the Mini Isolated Serial Link directly attached, it makes sense to do this, as it matches that configuration. Then run the four wires back to the Battery Multi Logger PCB. If the Mini Isolated Serial Link is fitted upside-down to the Battery Balancer PCB (as in Fig.7), it will not hide the LEDs, although it will slightly overhang the PCB edge. The photo on page 71 shows the Link fitted to the Balancer in this fashion. Due to space constraints, there is no 3.3V connection on CON6, so the best option is to take this from pin 2 of the ICSP header. If you lack CON6, then taking the ground connection from the adjacent pin 3 is a good choice. Similarly, the TX and RX signals are taken from CON6 or the microcontroller pins directly, as shown. While setting up these connections, you might also like to solder a five-way header to either CON2 of the Battery Logger or CON1 of the I/O Expander to regain the in-circuit programming (ICSP) capability. All the things we have hanging from these pins only Fig.6: only one of each colour of wire is needed, but we’ve shown two options for each, so you can choose a suitable way to connect the two boards. The dashed wires are only needed if you have an early revision of the PCB that lacks CON6. While the boards are notionally at the same ground potential, it wouldn’t hurt to add series resistors, but Fig.7 shows an even better option. Fig.7: the preferred method of joining the Battery Multi Logger to our Battery Balancer is via a Mini Isolated Serial Link module. The module needs to be supplied with 3.3V on each side; ensure that the jumper links on the Serial Link are set to the 5V positions, as shown (which actually corresponds to 3.3V in this case). siliconchip.com.au Australia’s electronics magazine August 2021  77 Screen 2: the SOFT SWITCH page shows the trigger states and thresholds. Pressing the buttons allows the triggers’ operation to be tested and triggers to be manually reset, if this form of operation is preferred. take power and ground connections, so they should not affect programming. But you may have to power the board from USB instead of the programmer during ICSP programming, as the programmer might not be able to provide sufficient current. Reassemble anything you have taken apart during this construction. Then power up the Battery Logger and its connected peripherals. Using it Screen 3: each trigger is configured on its EDIT TRIGGER page, including its thresholds. The page displays the switches it drives and the other triggers it will reset. Screen 4: pressing the SWITCHES button on the EDIT TRIGGER page allows the SWITCH OUTPUTs to be set. You can get an idea of the unit’s operation from the example configuration we have provided. Screen 5: the RESET TRIGGERs are set similarly. All the changes made to these (and other triggerrelated) settings are saved on exit from the SOFT SWITCH page. 78  Silicon Chip Australia’s electronics magazine With everything configured, we can explore the new screens. Screen 1 is the updated Main screen, with two new buttons and a display for the status of the triggers. If your battery is above 12.5V, you should see Trigger 1 in red. Or if your battery is below 11V, then Trigger 0 might have tripped. Press the Trigger button to see Screen 2. This is an overview of the triggers, with one displayed on each line. Each trigger has a parameter and threshold that it monitors; these are displayed as in Screen 2. When a parameter reaches its threshold, the trigger is tripped and will show a red TRIP button instead of a green OK button. The trigger cannot trip again until it is reset. On each trip event, any combination of switches can be activated. These switches correspond to Soft Switch inputs, and the software delivers a pulse via the I/O Expander to the corresponding switches. Each trip event can also reset any other trigger, allowing alternate action as two triggers track a variable between the two hysteresis points, as demonstrated by the default settings for TR0 and TR1. This is only one way it can be used. Each trigger could be set to require a manual reset or could even reset multiple triggers. The page shown in Screen 2 lets you manually trip and reset each trigger for testing. Each press toggles between the tripped and reset states. Pressing the button (such as TR0 for Trigger 0) takes you to Screen 3, which has more settings. The TRIP and RESET buttons work as you would expect. The various buttons labelled V and I allow the threshold variable and condition to be set. CLEAR removes any threshold, meaning the trigger will not activate siliconchip.com.au Screen 6: the BALANCER CONTROL page is accessed from the MAIN screen, and shows the current cell voltages and Balancer operating mode. Buttons are provided to issue control commands to the Balancer, assuming it is connected and communicating. automatically. The THRESHOLD+ button sets a positive value, while the THRESHOLD- button is used to set a negative value. This is useful for current thresholds; the Battery Manager cannot measure negative voltages. Finally, the SWITCHES and RESETS buttons allow setting of the actions that result from each trigger. Screen 4 shows the switch controls; these correspond to the P0-P7 outputs on the I/O Expander, while Screen 5 shows the reset controls, which correspond to the triggers. All parameters are saved to flash memory when you press BACK from the Trigger overview page seen in Screen 2. This provides a good compromise between usability and flash wear. Screen 7: the BALANCER HISTORY page shows the recent operation of the Balancer, including which cells are being balanced and in which direction. Balancer menu From the Main page, pressing the Balancer button goes to the BALANCER CONTROL page, as seen in Screen 6. The two columns of buttons at left will send commands to the Battery Balancer to move charge between specific cells and the entire stack. The rate at which this happens is set by the third column, with options of 25%, 50%, 75% and 100%; the currently selected value is highlighted. Similarly, the PAUSE and RESUME buttons send commands to the Battery Balancer to pause or resume balancing. The data displayed at the top of the screen is taken from the Balancer in real time. The GRAPH button goes to the page shown in SCREEN7, which shows the relative flow in and out of each cell. Around 100 data points are stored, and these are updated in time with the logging software’s 10-second cycle. Thus around 15 minutes of balancing data is available. It is only stored in RAM, so it is erased if power loss occurs. The screen does not automatically refresh; you need to press the Refresh button. Pressing the ‘Cell V’ button changes the graph to display the individual cell voltages measured by the Balancer. The chart is centred on the current bottom cell voltage, as this will always be present. The graph spans 1V from top to bottom, allowing cell voltage variations to be easily seen. Battery Manager Thus we have updated the Battery Multi Logger to the Battery Manager. siliconchip.com.au Screen 8: similarly, the CELL V HISTORY shows the relative cell voltages (to Cell 1). The button at bottom left allowing easy toggling between these last two pages. We expect many people will have different requirements regarding what they will control and how they will connect things to the Battery Manager. Indeed we expect many people will be adding the Battery Manager to an existing battery installation, perhaps in a car, caravan or boat. And it becomes a relatively simple addition to such a system. In fact, there are so many features in the improved Battery Manager that readers may not even wish to add all of them. But this is easy, as it is entirely Australia’s electronics magazine modular in construction. We wouldn’t be surprised if some people use the I/O Expander or Switch Module in unrelated projects. Some people may not need the Battery Balancer add-on, especially those with 12V batteries that don't require balancing. Both the I/O Expander and Switch Module will work fine with 3.3V and 5V logic levels, so could be used on their own (or together) with other microcontrollers such as Arduino or Micromite. SC August 2021  79 CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions will be paid for at standard rates. All submissions should include full name, address & phone number. Portable amplifier built from modules One of the things I like about Silicon Chip is that some of the articles published give me ideas for future applications. A good example of this is the El Cheapo article on Class D amplifier modules (May 2019; siliconchip.com. au/Article/11614). Several problems about the particular amplifier described were identified in that article. I searched online for a better unit, and found a TPA3116D2-based 2x50W + 1x100W power amplifier for less than $20, including delivery. The layout of the components on the board was different from the one shown in the article; I suspect it is an improved version. It seems to have none of the problems described in the article. The specifications for this amp quote a working voltage of 12-24V, but the data sheet for the TPA3116D2 IC shows that it will work down to 4.5V. I could 80  Silicon Chip not find a voltage regulator chip on the board, so I tested the amplifier at lower voltages and found that it worked without any apparent problems. With that in mind, I used this amplifier board, in conjunction with two other modules, to make up a radio, Bluetooth and MP3 player that is powered from a nominally 11.1V Li-ion battery pack. The pack I used contains nine 18650 cells arranged in a 3S3P configuration (three sets of three paralleled cells connected in series). I bought this second-hand, and it has built-in cell protection and equalisation modules. It can be charged using a standard 12V DC, 1A regulated plugpack. That charges each cell to 4.0V, which is close enough to full charge voltage (4.2V) for my needs. Australia’s electronics magazine The other two modules I used are a 12V-powered MP3 decoder board with Bluetooth, USB, SD card and FM radio support. It also came with a remote control, and cost just $6. The remote control allows for input selection and volume control. Earlier versions of these MP3 decoder boards were sold as running from 5V, so would need a regulator in my circuit. But later ones are rated to run from a voltage as high as 12V, and still work well at lower voltages. I also bought an 18650/26650 Li-ion battery tester, which shows the battery voltage and load current, for just $10. I decided to incorporate it in my unit to make checking the status of the battery pack easy. I mounted all these components (battery, amplifier, MP3/Bluetooth/FM module and voltage display) inside a large ABS plastic box I bought from Jaycar. I added speaker connectors stripped from a dead amplifier so that external speakers could be easily connected. I sourced some speakers from my local op shop for $2 each, and the sound isn’t too bad. With the battery between 9-11V most of the time, it can be wound up far too loud for an average room. Larger (and better) speakers can be connected to improve the sound quality, making it into a portable outdoor unit with a lot of grunt. I sourced the on/off switch and 5.5mm DC charging socket from Jaycar. The internal wiring is quite straightforward, as you can see from the circuit diagram. I used hot-melt glue and a mixture of nuts and machine screws for a quick and straightforward build. I gave the finished device to my granddaughter as a Christmas present in 2019. It has worked flawlessly for the last eight months, and she has only had to charge the battery four times! She tells me she charges the battery when it stops working. She usually connects her mobile phone using Bluetooth, but occasionally uses other input methods. Sid Lonsdale, Whitfield, Qld. ($100) siliconchip.com.au The MP3 decoder/FM module ► incorporates the display. While most current versions of this module are powered from 12V, earlier versions used 5V and so a separate regulator is needed. The amplifier controls (below the display) are from left-right: left/right channel volume; subwoofer adjustment; total volume control. The amplifier is the smaller device sitting below the twin JVC speakers. Larger speakers (up to 50W) can easily be used if needed. ► A close-up of the display of the ► 18650/26650 Li-ion battery tester module. It displays the battery voltage and load current. The internals of the portable amplifier are shown above at larger than actual size. The power amplifier module measures approximately 100 x 85mm and is sold for about $20 including postage online. Note that this TPA3116D2-based module has a power-on artifact which induces a pop noise on all speakers even when muted. siliconchip.com.au Australia’s electronics magazine August 2021  81 Frequency meter with non-contact mains reading This circuit provides a frequency meter, a non-contact AC mains frequency indicator and a live wire detector in one package. It is helpful for locating the breaks in a wire. It will also identify the phase wire of the mains plugs or switches by flashing a single LED, producing sound on a piezo sounder and displaying its frequency on the LCD. The circuit is based on a 4024 ripple counter used as a sensing element frequency divider, an ATmega8 microcontroller and a 16x2 alphanumeric LCD. After assembling, the circuit must be enclosed in a plastic box with the insulated antenna extending outside. When DPDT switch S2 is in the FREQUENCY INPUT position, it connects pin 6 (digital input PD4) of the micro to the external frequency measurement socket, CON1. The signal fed in will need to have positive peaks of at least 3V to give accurate measurements. The software uses both Timer0 and Timer1 for frequency measurements. Timer0 operates as a counter, while Timer1 is employed as a time reference. The maximum frequency 82  Silicon Chip measured is 6MHz with 16MHz crystal X1 as a reference. When switch S2 is set to MAINS FREQUENCY mode, one of its poles connects output pin 12 (O0) of divider IC1 to the pin 6 (PD4) input of IC2. The other pole connects input pin 5 (PD3) of IC2 to ground. The software configures this pin to have a pull-up current, so it will shift from a high to low voltage when the S2 contacts close. In MAINS FREQUENCY mode, the micro detects this, displaying “Mains Freq.” on the LCD screen. The 150mm-long insulated wire serves as an antenna that is tied to the clock input (pin 1) of IC1 through a 1MW resistor and 1N4148 signal diode. Once the antenna is brought close (within 1-10cm) to an electrical cord or cable, the mains AC signal clocks IC1 and the IC divides the mains frequency by two and produces a signal at output pin 12 (O0). The micro (IC2) measures the frequency and displays the mains frequency on the LCD. At the same time, LED1 flashes and the piezo produces an alarm sound to indicate the Australia’s electronics magazine presence of the live wire while a signal around 50Hz is picked up. Switch S3 is used only in the mains frequency mode, to set the mains pickup sensitivity. With S3 set to low, it only indicates detection at 46-51Hz, while in the “high” position, this is extended to 6-51Hz. The high setting should be used for checking for the presence of mains. The low setting can be used to pinpoint the broken point of a live wire while scanning it, or for detecting the phase wire on a plug or switch. To avoid electric shocks, there should be no physical contact between the antenna (insulated wire) and the live wire, cord or cable while they are being scanned and checked out by this unit. This can be achieved by fully insulating the open end of the wire, or possibly even looping it back into the plastic box housing the unit (but not connecting it anywhere). The unit is powered by a 9V battery, switched by S1 and dropped to 5V by linear regulator REG1 to power the ICs. Mahmood Alimohammadi, Tehran, Iran. ($80) siliconchip.com.au Aug ust Build It Yourself Electronics Centres® t e g d a G Savers NEW! 29.95 $ SAVE $10 65 $ X 4204 3 Dioptre 1.5” screen on rear SAVE $10 70 $ SAVE 50% 99 $ Protect yourself with this feature packed dash cam! 1080p footage and includes high end features such as GPS, wi-fi footage transfer, G-sensor triggering & parking mode. Theft deterrent magnetic bracket. 50 $ Bluetooth® BBQ Temperature Monitor Why pay $300 for a MaggyLamp? The inspect-a-gadget illuminated desk magnifier is an absolute bargain $65, we believe ours is every bit as useful. An incredible visual aid for detailed inspection and work on fine items with full clarity through the lens. Tackle complex miniature tasks with confidence! X 4204 also fitted with 12 dioptre insert. X 7015 Love your slow cooked meats? Cook to perfection with the EasyBBQ dual probe monitor. Makes cooking easy! Android or iOS compatible. 0-300°C range. Requires 2xAAA batteries. Wi-Fi RGB Strip Lighting Kit SAVE $15 59.95 $ Great way to monitor your health at home TGA Approved. Home Blood Pressure Monitor A must have for anyone over 50 years old! Save on doctors visits. This handy meter records your measurements so you can monitor changes over time. Also includes an irregular heartbeat monitor. Stores readings for 2 people. Requires 4xAA batteries. D 2322 Inspect-A-Gadget LED magnifier for micro tasks SAVE $19 X 4003A SAVE 27% P 8149 Build wireless charging into your desk An ultra-slim desk mount 10W wireless fast charger. Requires 60mmØ hole. Includes power adaptor & USB cable. This kit includes 5m of RGB strip lighting, power supply, controller unit and IR remote control allowing you to create colourful lighting effects around your home. Controller features a music sensor input allowing the lighting to trigger to music being played in the room. Great for home entertaining. Works with Alexa and Google Assistant. 60 LEDs per metre. 89 $ D 2323 Automate your appliances with Wi-Fi sockets. Switch any connected appliance on or off remotely from anywhere in the world. Set schedules, monitor and control via your using the Tuya Android/iOS app. Maximum 10A 2400W. Works with Google Home and Alexa 39.95 $ X 3227* 75 $ .95 X 0432A Music sensor can trigger lights to the beat! le version New twist adjustab Get a crisp close up view Adjustable 5x-7x magnifier with LED backlight. Great for reading fine print and hobbies etc. Includes case and batteries. Aluminium case & handle Desk Mount USB Laptop Charger SAVE $40 Charges a laptop, a phone & tablet at the same time! 2 For $ 37 “The most useful present i’ve ever received“ - Mark Edmonds Augusta, WA. Add on an MicroSD card 32GB $10.95 (DA0329). 1080p GPS WiFi Dash Cam SAVE 13% X 4205 5 Dioptre S 9442 50 A must have for any electronics enthusiast. Includes: • Side cutters. • Flat long needle nose pliers. • Flat bent needle nose pliers. • Long nose pliers/cutters. • Bull nose pliers/cutters Say to goodbyein! eye stra great prices! Handy gadgets at 31st. Sale ends August $ T 2758A 5pc Plier & Cutter Set A 96W USB type C charger, plus dual QC 3.0 USB charging in the one compact near flush mount unit. Charges multiple devices at once. Requires 60mmØ mounting hole. Includes power supply. SAVE 20% 27 $ T 2185A 48pc Compact Driver Kit An aluminium driver handle with 48 4mm bits to open and repair all types of devices. Housed in an ultra slimline aluminium casing. Great for field repairs. See web for full kit contents. Order online <at> altronics.com.au | Sale pricing ends August 31st 2021. Upgrade your tool kit. No gas required! Recharges in 3.5hrs SAVE $30 T 2690A 95 $ 30W Lithium ‘Go Anywhere’ Soldering Iron 45 minute run time. 600°C max. Ideal for occasional soldering jobs or light duty repairs and field servicing. Recharge by USB power adaptor in your car or at home - also recharges from a battery bank. Includes replaceable 18650 battery. SAVE 15% 30 $ Hands free, head worn magnifier. Offers 1.5, 2.6 and 5.8x magnification with LED lamp. Requires 2xAAA batteries. T 2555 High Output Blow Torch Super hot 1350°C flame with high output nozzle. Handheld or self standing design for tasks such as heatshrinking, model making, silver soldering! Easy to refill. Add butane gas for $9.35 SAVE 24% FEATURE PACKED SAVE 22% 30 $ 60 All-Rounder Student DMM The perfect beginner, student or enthusiast multimeter. 12 auto ranging test modes with good accuracy and an easy to read jumbo 4000 count screen. Includes test leads. 37 .95 AUTO RANGING 49 $ 19 Range DMM With in-built AC mains detection. Featuring true RMS measurement, transistor and diode testing and backlit display. Rugged casing for added protection in the field. Q 1126A Q 1129 14ea $ Handy Auto Ranging DMM Simplicity & functionality in one compact test device. 10A DC current. 1Hz-30MHz counter. Includes test leads & temp probe. Great for students! Q 1133A 250 gram rolls. T 1100, T 1110, T 1122 READS AC & DC 119 Water & Dustproof True RMS Multimeter 12.95 16.95 $13.95 $ Top of the range! Ideal for marine & mining techs. • True RMS measurement • 40MHz freq. counter with bar graph • Max/min recording • Capacitance to 40mF. • Temperature with thermocouple. 12V Alternator Tester Provides quick and easy way to test alternator/charging system function in 12V vehicles. Provides instantly whether your alternator output is the problem or your battery is in poor condition. Q 3001A Sheath Piercing Q 3000A Standard Handy Automotive Voltage Probes A handy tool for troubleshooting wiring faults in vehicles and wiring looms. 6-24VDC range. Standard probe or sheath piercing versions. 39.95 $ $ 800A AC & DC Clamp Meter Safe and easy measurement of AC & DC voltage/current. In-built non contact voltage detection indicates live AC wiring. Includes test probes, temperature probe & carry case. Q 0965A NEW! $ 99 75 $ Q 1088 Q 3004 FOR THE PRO USER SAVE $26 SAVE 16% $ T 2417 VE! STOCK UP AND SALY. ON TH ON THIS M WATER PROOF! SAVE $50 109 $ An excellent multi purpose soldering iron for service technicians, schools, engineers, R&D, production work etc. Japanese long life ceramic element. 150°-480°C. 0.8mm tip. 2 year warranty. (T 2451) T 2496 SAVE 16% $ Micron® 60W Digital Soldering Station $ 15% OFF 60/40 Leaded Solder Reels IDEAL STUDENT DMM SAVE $60 X 6015 OBD II Bluetooth Scanner Connects your car via Bluetooth to your smartphone to provide a wealth of diagnostic information. Monitor performance in real time! It works with a number of OBDII compatible apps. Do-It-All Multimeter With in-built AC mains detection. This is one of the best DMMs we have evaluated when it comes to build quality and features. Its perfect for the serious enthusiast or tradesperson • LCD bargraph • 3.75 digit display • Mode assistance indicators. • Includes case, temp probe & insulated test leads. Q 1068 Battery Health Analyser Detects and analyses voltage, cold cranking amperes, resistance and cell condition in 12V lead acid cells. Easy connection and operation. Ideal for vehicle servicing or checking 12V SLA cells in backup systems. Order online <at> altronics.com.au | Sale pricing ends August 31st 2021. SAVE $60 139 $ Q 2120 Power up for Spring. M 8193 SAVE $50 Table Lamp With Wireless Charger 199 $ NEW! 39 .95 $ Portable Battery Bank Jump Starter An all round portable charging device - plus vehicle jump starter! Not just for car battery emergencies, this high capacity battery bank also wirelessly charges your phone, powers laptops and other devices. Jumpstarts most 4-6 cylinder vehicles. *Device shown for illustration purposes. A stylish glossy white table lamp with adjustable dimming, colour temperature & wireless charging. Great for the desk or bedside table. Powered by any USB wall charger 2A minimum (M 8862A $13.95). & USB charging! Keeps devices charged with wireless A great bedside or study lamp Don’t get a h caught wit y! flat batterwer Know your po usage. M 8636A SAVE $10 39.95 $ Powerhouse® Watt Meter 130A Perfect for measuring input and output currents and wattage from solar panels or batteries. This digital wattmeter accurately measures DC power usage. Display measures volts, watts and amps in real-time. Peak current 200A. X 4221 N 2023 SAVE 20% 63 $ Pure AC Output Power! SAVE $26 SAVE $65 119 $215 $ 150 $ M 8534A 6/12V 4.5A M 8010A 150VA NEW: M 8536A 12V 10A Multi-Stage Vehicle Battery Chargers Power mains appliances on the road! Now suits LiFePo4, lead acid & calcium type batteries! Each model utilises a microprocessor to ensure your battery is maintained in tip-top condition whenever you need it. Helps to extend battery service life. Suitable for permanent connection. Great for caravans & seldom used vehicles. Weatherproof casing. • Delivers pure AC power from your car battery • Ideal for tricky loads, such as laptops, & game consoles • USB charging output • 12V input • 300W surge rated, 170x108x60mm Get the most from your solar panels with an MPPT regulator This MPPT regulator employs special circuitry to gain up to 20% additional charge from your existing solar panels. Suits 12 or 24V systems. Easy to set up and connect yourself. 42.95 Anderson Style & Car Accessory Plate NEW! IP67 Dust & Water Proof DC Conectors SAVE $54 Part ONLY 2 Pin P 7892 3 Pin P 7893 $8.95 $11.95 $17.95 $19.95 P 7894 6 Pin P 7896 HALF PRICE! Great for automotive wiring - requires no special crimpers to terminate! Use a standard automotive crimper, pliers or solder terminate. 14A rated. DC Power Distribution Posts High current DC power distribution posts with reinforced nylon base (bolt head is encapsulated). 48V DC max. Corner Mounts P 8073 A handy connection for 4WD & NEW! campers. .95 60Wx75Hx $ 42Dmm. NEW! 19 Pins 4 Pin $ P 7811 95 $ Volt & Current Meter for off-grid power. Provides volts and amperes readout for caravans, RVs and off-grid solar remote power installs. A 100A shunt box connects directly between the battery and the load. 12V systems only. Model Type NEW! P 2172 Single M8 Red P 2173 Single M8 Black P 2175 Dual M8 Red P 2176 Dual M8 Black $10.95 $10.95 $12.95 $12.95 $10.95 $10.95 $14.95 $14.95 P 2182 Single M10 Red P 2183 Single M10 Black P 2177 Dual M10 Red P 2179 Dual M10 Black 53.95 $ P 7869 L 1045 NEW! 12 $ .95 Easy Wire Anderson Style Plug Simple screw connection - no need for crimping lugs. 8AWG max cable size. 26.95 $ P 8067 Side Mounts 55cm End Mounts P 8069 ABS ‘No Drill’ Solar Panel Mounts These tough surface mount brackets offer a way to mount solar panels without penetrating the roof of the caravan or boat. They can be attached using a silastic or similar adhesive. NEW! SAVE 22% SAVE 22% 27 23 $ Bar Graph LED Volt Meter P 0693 5-15V DC range. Ideal for monitoring auxiliary batteries. 29mm mounting hole. $ Dual Battery Monitor P 0692 6-30V DC range. Aux & Primary battery displays. 29mm mounting hole. S 2750 59.95 $ 3 Way Breaker & Switch Panel Features 3 x 20A 12V DC rated switches with red illuminated with individual 15A DC breakers. Dimensions: 114W x 96H x 60Dmm. Order online <at> altronics.com.au | Sale pricing ends August 31st 2021. More great gadgets. Attach your camera anywhere! HOT PRICE! D 2038 39.95 $ Go Anywhere Tunes Dynalink® BT5.0 Can Speaker The outdoor entertainer! Pump up the tunes with this nifty little speaker offering 3-4 hours listening time with great audio quality thanks to Bluetooth 5.0. Pairs to a second unit using True Wireless Stereo for even more sound! Water resistant design (IP65 rated) Includes charging cable. USB Travel Charger & Wireless Power Bank S 9843B SAVE $30 169 $ Great for phones, GoPro cameras and small digital cameras, this handy flexible leg tripod can stand on virtually any surface - even wrap itself around a pole! Large version also available D2213 $39.95. D 0507B 36.95 $ Cable Free Wi-Fi Camera ing Includes remote for tak selfies & TikTok videos 34.95 $ D 2212* el Not just for overseas trav rger also a great portable cha This handy 1080p camera can be installed just about anywhere indoors or out and has an in-built battery so you don’t need to run any cables! Offers 4-6 months of motion detect recording. When it’s flat, just take it off the wall & recharge via USB. Suits sheltered outdoor use. Ultra Slim QC3.0/USB C Power Bank Offering both QuickCharge 3.0 charging and 18W USB-C PD output, this pocket size 10,000mAh power bank will keep your devices charged away from mains power. 142x70x11mm SAVE $30 59 $ A do-it-all USB power delivery charger (18W), Qi wireless charger and portable battery bank (6700mAh) for phones and tablets. Includes Australian, US, UK and European adaptors, plus carry case. *Phone for illustration Upgrade your old battery bank to faster charging! 139 $ A 0319 S 9455A SAVE 24% 30 $ HOT PRICE! N 0700A Top up your batteries with solar power. This compact 5W solar panel is designed for keeping your vehicle batteries topped up when parked - ideal for seldom used vehicles. Croc clip or car accessory plug. Suits permanent outdoor install. purposes. Weather resistant! Answer the door when you’re not home! C 9033A Take quick notes while you work 18 $ .50 T 2237 Write a reminder, take a phone message or leave a note for your family with our handy eWriter LCD board. Ultra thin, portable design is also great for kids to draw on. Size: 226x146mm. SAVE 24% 30 $ Bargain True Wireless Earbuds. Quality Bluetooth 5.0 sound and range. Includes charging case with digital power readout. Up to 3 hours listening time per charge. Wi-Fi Video Doorbell with Tuya smartphone app control and 2 way audio. This stylish doorbell connects to your wi-fi and notifies your mobile phone when a person arrives at your doorstep. Great for telling the postie where to put packages. • Security camera mode • Motion detect notification • Includes power supply and indoor doorbell ringer unit. SAVE 20% 40 $ The ultimate camping, fishing, anything light! X 0225A Provides 5 hours use from a high performance lithium battery. Folds flat for easy storage and recharges from any USB mains or car charger. It can even recharge your phone from its battery! 10W, 1000 lumens. ebay.com.au/str/altronicsaustralia Shop with us on + Pay in 4 easy installments with AfterPay® on eBay. Western Australia Build It Yourself Electronics Centres Sale Ends August 31st 2021 Phone: 1300 797 007 Fax: 1300 789 777 Mail Orders: mailorder<at>altronics.com.au » Perth: 174 Roe St » Joondalup: 2/182 Winton Rd » Balcatta: 7/58 Erindale Rd » Cannington: 5/1326 Albany Hwy » Midland: 1/212 Gt Eastern Hwy » Myaree: 5A/116 N Lake Rd Victoria 08 9428 2188 08 9428 2166 08 9428 2167 08 9428 2168 08 9428 2169 08 9428 2170 » Springvale: 891 Princes Hwy » Airport West: 5 Dromana Ave 03 9549 2188 03 9549 2121 New South Wales » Auburn: 15 Short St 02 8748 5388 Queensland » Virginia: 1870 Sandgate Rd 07 3441 2810 South Australia » Prospect: 316 Main Nth Rd 08 8164 3466 Please Note: Resellers have to pay the cost of freight & insurance. Therefore the range of stocked products & prices charged by individual resellers may vary from our catalogue. © Altronics 2021. E&OE. Prices stated herein are only valid until date shown or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. *All smartphone devices pictured in this catalogue are for illustration purposes only. Not included with product. B 0092 Find a local reseller at: altronics.com.au/storelocations/dealers/ PRODUCT SHOWCASE Infrared dynamic gesture sensor from Maxim The MAX25405 optical sensor from Maxim uses infrared to recognise a variety of gestures (swipe, rotation etc). The MAX25405 has a sensing range up to 40cm, which makes it optimal for use in automotive applications such as car head units. Along with integrated optics and a 6x10 infrared sensor array, the MAX25405 includes a glass lens which increases sensitivity and improves the signal-to-noise ratio. The improved performance doubles the sensing range. This allows the other passengers in a car to use gesture-sensing entertainment displays. The MAX25405’s small 20-pin, 4x4x1.35mm QFN package comes together with four discrete LEDs, which ends up 75% smaller than comparable time-of-flight (ToF) camera-based solutions. It replaces multi-IC solutions, saving significant space. The MAX25405 IC and associated MAX25405EVKIT# evaluation kit are available now from Maxim Integrated and authorised distributors. For more information about Maxim Integrated’s MAX25405 gesture sensor, visit http://bit.ly/MAX25405Product Maxim Integrated www.maximintegrated.com/en.html Digi-Key launches myLists management system Digi-Key Electronics announced that it has launched a consolidated list management system, myLists, to streamline customers’ BOM Manager, price and availability, and favourites into one. Digi-Key is introducing myLists to make it easier for customers to manage their lists all in one place. In addition to providing greater convenience, myLists has over 15 features to benefit Digi-Key customers. The most notable features are an attrition calculator to plan for overages that account for parts lost or damaged during manufacturing, upload up to 1000 line items per list, list view customisation, and alternatives suggested in-line for parts when available. Other features also include: • Organise column order and data, and download it in a file • Differentiate lists and those shared with the user into two views • Add tags to assist with list management • Request pricing on six different quantities per part • Update filter options on the parts list • Define list preferences for part packaging: CT/TR or DKR/TR • Set preferences to manage quantities that do not meet requirements • Access to new data such as ECCN, HTSUS, country of origin and environmental information • Add notes to a part New products from Mouser Electronics In April, Mouser launched 3,069 new parts. Some of these new components include: Texas Instruments TMS570LS1227 16/32-Bit RISC flash micro The TI TMS570LS1227 is ideal for high-performance real-time control applications where safety is critical. The microcontroller family provides advanced safety architecture that includes dual CPUs in lockstep, CPU and memory BIST logic, ECC on both the flash and the data SRAM, and many more features. TE Connectivity NTSEAL 20-position connectors TE’s NTSEAL 20-position connectors provide flexible, robust wire-towire connectivity in a compact format for harsh environments with extreme siliconchip.com.au temperatures and vibrations. Applications include wire-to-wire, panel/ bulkhead mount, engine, chassis and automation. ROHM semiconductor BM6437xS-VA 600V IGBT modules The BM6437xS-VA intelligent power modules (IPMs) integrate gate drivers, bootstrap diodes, IGBTs and flywheel diodes. It has a collector current range of 15-35A and works as a 3-phase DC/ AC inverter. To see more of New Product Insider highlights, visit www.mouser.com/ newproductinsider/ Mouser Electronics Inc. Phone: (852) 3756 4700 Web: www.mouser.com Australia’s electronics magazine • Move a part’s position on the list up and down or to a specific row Visit www.digikey.com/en/mylists/ to find out more. Digi-Key Electronics Phone: 1800 285 719 Web: www.digikey.com.au/ Free online courses for embedded control Microchip University offers free online courses for embedded control engineers. Learn about general embedded control topics as well as Microchip, Atmel & Microsemi products. Classes are taught by the same engineers who create the products. Topics covered include: • Using MPLAB® Code Configurator (MCC) • Embedded Linux® • Using Core Independent Peripherals (CIPs) • Motor Control • Power Supply Design • Security • IoT • FPGAs • Analog System Design • Communication (USB, Bluetooth® and TCP/IP) New classes will be added every month. Visit www.microchip.com/ mu to register. Microchip Technology Inc. www.microchip.com August 2021  87 Using Cheap Asian Electronic Modules By Jim Rowe USB-PD Triggers, Decoys & Testers Left-to-right: the FNC88, WITRN UPD005, ZY12PDN-1 & XY-WPDT Following on from the article last month on USB-PD charging modules, we shall now examine some of the many low-cost PD trigger/decoy and tester modules that have appeared recently. These allow you to take full advantage of the USB-PD chargers’ capabilities and use them as versatile and efficient power supplies. A PD trigger is an interface circuit that can manage the negotiating protocols necessary to request the required voltage and current levels from a USB-PD supply, as described last month. As soon as it is connected to a USB-PD compatible host, it engages with the host via the CC1 or CC2 channels to achieve the voltage and current levels that are needed – assuming these are available. Some of these modules are also known as “decoy” or “poll detectors”. These terms all seem to mean much the same thing as PD trigger. Another variant combines the functions of a trigger/decoy module with those of a USB-PD digital meter, so it can display the available or selected voltage(s) and current(s). We’ll start by looking at the smallest, simplest and cheapest of the trigger modules. ZY12PDN-3 “naked” PD trigger The ZY12PDN-3 module is tiny, as you can see from the photos. Everything is mounted on a PCB measuring just 30 x 15mm, with the USB-C input socket at one end and a small two-way screw terminal block at the other end as the power output. The ZY12PDN trigger module is 88  Silicon Chip available in three versions, which differ only in their output connector or lack thereof. Instead of the screw terminal block of the ZY12PDN-3, the ZY12PDN-2 has a USB Type-A socket, while the ZY12PDN-1 has no output connector at all. The trigger circuitry on the PCB uses two main chips: an STM32F030F4P6 microcontroller and a PBAFH device, which is likely the USB physical layer interface. There’s also a small pushbutton switch that can be used to select the voltage and power level required from the USB-C PD host, and an RGB LED to indicate the selected voltage/ power level. When the ZY12PDN is first connected to the PD host, the LED glows red to indicate the default 5V supply voltage. If you then press the button, it will attempt to select a 9V supply. If the PD host has this voltage available, it will switch its output to 9V, and the LED will change to yellow. If you press the pushbutton again, this will attempt to change the supply voltage to 12V. If the PD host has this voltage available, it will switch its The ZY12PDN-3 PD trigger, shown enlarged for clarity. There are two other versions of this module with either a USB Type-A socket or no connector fitted instead of the screw terminal block. Australia’s electronics magazine siliconchip.com.au The WITRN UPD005 is an alternative to the ZY12PDN module. output to 12V, and the LED will change to green. Further button presses will change the voltage to 15V (light blue), then 20V (dark blue) - assuming the host can supply these voltages. If the host doesn’t have one of the voltages you request, the LED will glow purple, and the voltage will stay at the highest voltage which is available. There’s also a ‘demo’ mode, where the LED glows white and the supply voltage cycles through the available levels at approximately 1Hz. If you plug the ZY12PDN into a host port that does not support USB-PD voltage and power negotiation, after about four seconds, the LED will flash blue to warn you that there is no USB-PD support. However, it will still pass through the normal 5V VBUS power. So the ZY12PDN trigger module essentially provides the ability to manually select the voltage from a USB-PD power source. And it does this for a cost of around $11-13, depending on how many you order and from which internet supplier. So it’s a bit limited in terms of the voltages you can request and has no provision for taking advantage of PPS ‘fine tuning’. But if you just need the ability to manually select one of the main PD voltage levels, it is a good choice. For example, you could use it in combination with a computer or USB charger as a very basic bench supply to power something like a breadboard. There are other ‘naked’ trigger modules available that are very similar to the ZY12PDN. One example is the WITRN UPD005 V20, available from suppliers like Banggood for much the same price as the ZY12PDN. I obtained one of these and tried it out, and it did the job just as well as the ZY12PDN. FNC88 PD trigger module & meter The FNC88 PD trigger is slightly larger than the ZY12PDN, but not by much, especially considering that it also includes a digital meter. It measures just 40 x 25 x 10mm, not including the USB-C input plug. And it’s not exactly ‘naked’ either, with a shield PCB mounted 3mm below the main PCB and a protective plastic sheet above the 24mm diagonal colour LCD screen. It’s made by FNIRSI Technology in Shenzhen, China, and is available from quite a few internet suppliers, including Banggood, for around US$25 plus delivery. It comes in a protective case with a clear window, measuring 90 x 62 x 18mm. This should make it sturdy enough for portable use. The FNC88 PD unit has USB-PD bidirectional capability, and this also applies to the built-in digital meter. So PD triggering and measurements can be made using either the USB-C plug at one end or the USB-C socket at the other end as the power source, with the opposite end connected to the ‘sink’ device. This also means that the FNC88 can be connected between a USB-C cable and the USB-C connector of either a host or sink device. On one side of the FNC88’s main PCB, there’s a mini USB-C socket, which extends its capabilities to measuring the current drawn by devices with that type of USB connector. Then on the other (‘top’) side are three tiny pushbutton switches, and an equally small slider switch. The slider switch is to enable or disable the trigger’s USB-PD protocol communicating ability, while the three pushbuttons are used to select the functions of the digital meter. The specified supply voltage range of the FNC88 is 4-24V, and its current range extends from 0 to 5A, so it’s capable of dealing with all devices conforming to the current USB-PD specification. The voltage measurement resolution and accuracy are specified as 0.1mV and ±(0.5% + 2LSD), while the current measurement resolution and accuracy are specified as 0.1mA and ±(1% + 2LSD). Quite impressive! Other features of the FNC88 include measurement and display of: • The power being drawn by the sink device (0-150W, with a resolution of 10mW). • The charge delivered to a battery over a known charging time (0-99,999.9mAh with a resolution of 0.1mAh). • The energy delivered to a battery or other sink device over a known delivery time (0 - 9999.999Wh with a resolution of 1mWh). The front and rear view of the FNC88 module; you can just see the three function buttons at the bottom of the rear view, along with the switch that connects the built-in PD chip to the CC1 pin. siliconchip.com.au Australia’s electronics magazine August 2021  89 This side of the FNC88 module has a micro USB interface which is only used to flash the firmware. • The ability to record measurements over a period of 0-999 hours, 59 minutes and 59 seconds with a resolution of one second and an accuracy of 10 seconds/hour. The PD trigger section of the FNC88 supports these protocols: QC2.0, QC3.0, FCP, SCP, AFC and PD 3.0. Although the FNC88 does not come with any user operating manual, you can download one as a PDF file from the FNIRSI website at siliconchip.com. au/link/ab7n I gave the FNC88 a quick rundown, comparing its voltage and current readings with those from my Agilent U1251B DMM. This showed that the accuracy and resolution of the FNC88’s digital meter were within their claimed figures. So overall, the FNC88 seems to be a very capable and useful device. My only real complaint is that you need either good eyesight or a strong magnifying glass to read the display on its 24mm diagonal LCD screen. There are several other USB-C PD trigger/DM devices available from Banggood and other internet vendors. A good example is the Riden TC66, which is almost precisely the same size as the FNC88 and very similar in its functions and facilities. It’s available for much the same cost as the FNC88. I have seen a suggestion on the internet that the FNC88 might be a knock-off of the TC66, or vice versa. See siliconchip.com.au/link/ab7m The XY-WPDT trigger unit & meter Another USB-PD trigger/meter unit available from many internet suppliers, including Banggood, is the XY-WPDT. At the time of writing, Banggood was selling it as a kit for only $15 including delivery. It is made by the same firm in China which makes the XY-PDS100 ‘quick charger’ we looked at last month. Although the XY-WPDT comes as a kit, assembling it is not difficult and doesn’t involve any soldering – just the use of a very small Philips-head screwdriver, which is included in the kit. The PCB itself is already assembled, so all that remains is fitting the front and rear panels around it using the M2.5 screws and tapped spacers provided. When you complete the assembly, the XY-WPDT measures a modest 61 x 25 x 11mm (not including the USB-C plug protruding from its input end). It’s only a little larger than the FNC88. The main output is via a USB Type-A socket at the opposite end of the unit to the USB-C input plug, and the XY-WPDT comes with a 100mm-long output cable with a Type-A plug at one end and a 2.5mm inner diameter concentric power connector at the other. There are also a couple of USB-C sockets on the unit itself near the USB-C input plug, one on each side, arranged so that the XY-WPDT can measure the voltage and current passing between them. The specifications of the XY-WPDT are not all that different from that of the FNC88. It can negotiate an output voltage between 4V and 20V using either PD 2.0 or PD 3.0 protocols. It can adjust the voltage in either 1V, 100mV or 20mV increments or decrements if the PD host can respond to PPS negotiation (like the XY-PDS100). The meter function can measure the voltage with a rated resolution of 10mV and a precision of 0.3%, and current with a rated resolution of 1mA and a precision of 0.5%. Not quite as good as the FNC88, but still very useful. The readout of the XY-WPDT is a 4-digit 7-segment LED display with 9mm high digits, so although it is not The XY-WPDT is sold as a kit by Banggood, and only requires fitting the components together with a screwdriver to assemble it; no soldering is necessary. 90  Silicon Chip Australia’s electronics magazine siliconchip.com.au as fancy as that of the FNC88, it’s significantly easier to read. Function switching is done via two tiny pushbutton switches (K1 and K2), one on either side of the unit. There are also four indicator LEDs; three indicate the voltage steps in PPS mode (1V/100mV/20mV), with the remaining one indicating current measurement mode. Like the FNC88, the XY-WPDT does not come with any operating manual, nor could I find a manual on the internet. The only information on using it seemed to be in the XY-WPDT follow-up info on the Banggood website, which turned out to be rather terse and not easy to follow. I gave the XY-WPDT a quick checkout coupled to the XY-PDS100 PD charger, and the results were very close to the rated figures for resolution and precision of both voltage and current. Overall then, the XY-WPDT PD trigger/meter is quite a good performer, and very good value for money. My only real complaint is that the method it uses to select the voltage mode using the two tiny pushbuttons K1 and K2 is really tricky, with various short and long presses on each button making it not at all easy to set the XY-WPDT to a particular voltage level, especially in PPS mode. This seems to be because both buttons have different functions according to how long they’re pressed, so you can easily flip things into a different mode without meaning to. In theory, the combination of the XY-WPDT and the XY-PDS100 should make a digitally adjustable DC power supply with its output variable to any voltage between 4V and 20V, but this isn’t all that easy in practice. It would be a lot easier if the two tiny pushbuttons were increased in number, with a smaller number of functions per individual button and less dependence on the time they are pressed. But for applications where you want to ‘set and forget’, it works acceptably well and provides excellent value for SC money. Useful links USB-C: https://w.wiki/nto USB-PD: https://w.wiki/34dT siliconchip.com.au/link/ab7l siliconchip.com.au/link/ab7m Quick Charge: https://w.wiki/34dU siliconchip.com.au The XY-PDS100 quick charger (detailed last month) is shown connected to the XY-WPDT trigger unit, displaying the output voltage. Here’s what the assembled XY-WPDT module looks like. The two extra USB-C sockets on either side allow the unit to operate in pass-through mode. From left-to-right we have the USB-C input, PPS mode LEDs (1V, 100mV & 20mV steps), K1 switch, and current indicator LED. The USB-C input is used with the matching output connector on the opposite side to control and measure voltage or current. Pressing the K1 switch changes between displaying current or voltage, while holding K1 just turns the screen and indicator LED off. Switch K2 is used in conjunction with K1 to change the voltage setting, and is a bit more complicated to set, see: siliconchip.com.au/link/ab7o Australia’s electronics magazine August 2021  91 Simple MIDI Music Keyboard BY TIM BLYTHMAN This MIDI Keyboard is a follow-up to our 64-key MIDI Matrix. It is similarly flexible and offers a way to easily make music, although it can be repurposed for many other uses. W hile MIDI Matrix panels are popular for being a compact way of controlling and interfacing to MIDI equipment, a linear keyboard arrangement like a piano is more ‘standard’ and, for many people, quite intuitive. This is a modular add-on to the MIDI hardware we introduced in April and May this year (siliconchip.com.au/ Series/363). Like the MIDI Matrix, it doesn’t have to be used strictly for MIDI or musical purposes. The MIDI Matrix was designed to be used with an Arduino Leonardo board, as the Leonardo can easily provide a native USB MIDI interface through the versatile Arduino MIDI libraries. We also demonstrated a few different program sketches that can run on the Leonardo to give various features, and showed some ways to interface with software on both a PC and an Android smartphone. At the same time, we presented an Arduino shield that lets you interface the hardware to a great range of MIDI equipment using standard DIN connectors. The Keyboard is intended to replace the Matrix as part of a larger construction, as presented in the earlier parts of this series. Refer to those articles, particularly the first part, to understand how the Matrix (and now Keyboard) can be used. At a minimum, you need an Arduino Leonardo board and some jumper wires to turn the Keyboard presented here into a minimal MIDI Encoder. 92  Silicon Chip The Matrix The original Matrix is basically just an array of pushbuttons that the Leonardo can scan to receive user input. In our MIDI software, each keypress is converted to a musical note. Each row or column of the Matrix is wired to a digital pin on the Leonardo. By using the time-honoured technique of scanning each row in turn, individual button presses can be detected. In our version of the software, the rows are connected to pins configured as inputs with weak pull-ups. Initially, all column pins are set to a high impedance input mode too. Each column is configured as an output in turn, and driven low. If any button connected to that column is pressed, its corresponding row pin is pulled down through the switch contacts. By scanning the columns in turn, we can detect individual button presses. While this system is simple, it cannot detect multiple simultaneous keypresses; for this, each switch needs to be fitted with a diode to prevent ambiguous closures propagating through the Matrix. Our Matrix omits these diodes in favour of simplicity and compactness, and this linear Keyboard is the same in that respect. The new Keyboard We considered a linear keyboard for our original design but could not work out a way of making it both compact and functional. We have now formulated a modular design, so a useful Keyboard can be built that is still compact, or it can be expanded to 64 keys, resulting in a device that’s over a metre long! But it still only needs 16 wires to connect it to the Arduino. The basic unit of the Keyboard is a single PCB with eight keys. Each key is wired to the same row contact as the others and also to one of the eight column contacts. A single Keyboard module is identical to one row of the Matrix. Fig.1 shows the circuit. CON1 is wired to the columns, with each terminal on CON1 wired to one side of each Our prototype uses three of these PCBs, as a keyboard made from a full set of eight PCBs would be well over a metre wide. We’ve retained the CON1 and CON2 pads on some of the boards to demonstrate and test the different options. In practice, only one set is needed; note that connecting to CON3 and CON4 is equivalent. Australia’s electronics magazine siliconchip.com.au Fig.1: this is the simple circuit of a single PCB with eight switches. The offset between CON4 and CON6 is what makes it easily expandable up to eight PCBs and 64 buttons. of the tactile switches, S1-S8. Position 1 of CON2 is connected to the other side of switches S1-S8. At each end of the Keyboard module PCB are connectors CON3-CON6, which can be used to daisy-chain subsequent PCBs to expand the Keyboard. These are eight-way surface-mount pads spaced 2.54mm apart. CON3 and CON5 (on the top side of the PCB) are wired in the same order as, and in parallel with CON1. Thus, the column signals can pass between the PCBs by joining their adjacent CON3 and CON5. These are wired as a parallel bus. Similarly, on the back of the PCB, CON4 on one PCB connects with CON6 on the next. CON4 is wired the same as CON2, but the clever part is how we have wired CON6. Pin 1 of CON6 is wired to pin 2 on CON4, and so forth, all offset by one position. Say we wired up an array of eight of these modules, numbering them 1-8 from left to right, with CON3 and CON4 wired to CON5 and CON6 respectively. Connecting to CON1 & CON2 on the first module, we would have the equivalent of a full 8x8 Matrix only with the keys in a single row. Fig.2 shows how the ‘rows’ are mapped back to CON2 on the first PCB. CON1, CON3 and CON5 are all simply wired in parallel and are not modified by this system. Other configurations If you look closely at the PCB, you can see that the little tab where CON1 and CON2 jut out is scored for removal. This lets you remove these tabs on all but one module. In fact, since CON3 and CON4 are wired identically to CON1 and CON2, you can even remove the tab from all boards and simply take the matrix connections from CON3 and CON4 Fig.2: this shows how multiple 8-button Keyboard PCBs are joined so that the Arduino can tell which key has been pressed. Each PCB along the chain offsets where the connection is ultimately made at CON2, allowing for up to 64 keys to be sensed. siliconchip.com.au Australia’s electronics magazine August 2021  93 of the leftmost board instead. If you don’t mind remapping the pins in software (or changing how they are wired back to the Leonardo board), the CON1 and CON2 connections do not have to be made on the first board. You could even take these connections from the middle of the array. We’ve designed the PCB to use large 12mm tactile switches, as these have a much nicer feel with a larger finger surface. You might find that some smaller switches can be made to fit by bending their leads, although we haven’t tried that. Since there is less space for routing on this PCB than the Matrix, it lacks the option to fit illuminated switches that the Matrix had. Hardware Like the Matrix, the Keyboard we are presenting has quite a basic design, so that you can customise it to your requirements. The switches are placed on 20mm centres, with four M3 mounting holes provided on each PCB. Nominally, the mounting holes will be on 40mm centres, although this depends on the accurate assembly of adjacent boards. The PCBs are 20mm high, not counting the tab for CON1 and CON2; 28mm with the tab in place. We strongly recommend mounting the Keyboard to a sound backing so that the PCBs do not flex when the keys are pressed. The connections for CON3-CON6 will not provide much mechanical strength as they are effectively surface-mounting pads, and are only bonded to the PCB superficially. Construction Most people will want to build a Keyboard with multiple PCBs laid out as a continuous strip, so we will describe what is needed to achieve this. The Keyboard is built on a PCB coded 23101213 that measures 158 x 28mm. Use the PCB overlay diagram, What about the black keys? You might be thinking that pianos actually have two rows of keys, white and black, and you would be right. Also, there are seven white keys per octave, not eight. We have kept this as a linear array of eight keys to make it simple and applicable to a wide range of applications. We plan to produce a 12-key PCB at a later date which has the keys staggered and grouped like a piano. In the meantime, if you’re keen to use this board like a proper piano, you could build it in two rows, with the top row offset horizontally 6mm from the bottom row and with gaps in the keys at the top to give the proper configuration. Both rows could be wired up in series (assuming they contain no more than 8 PCBs total). The software could be modified relatively easily to remap the two rows of keys into the correct sequence so that it can act as a keyboard piano. The restriction of only one keypress being detected at a time would remain, though. Our planned future piano keyboard PCB would remove that restriction. Fig.3, as a guide to fitting the components. Plan and lay out the modules before commencing construction. To keep things compact, the connections between the boards are a little tight, and it will be easier to join them before fitting other components. If you want a different layout, just about any method of wiring CON3 & CON5 and CON4 & CON6 respectively will work. You might even like to use header sockets on one and header pins on the other to allow the units to be unplugged, although this will not achieve a tight spacing. To start the PCB assembly, snap off any CON1/CON2 header tabs that are not needed. Do this by scoring along the line with a sharp knife to cut the copper traces, then carefully flex the PCB with pliers to make a clean break. You might like to clean up the rough edge. As well as our usual warnings about avoiding the inhalation of PCB dust (eg, by working outside and wearing a mask), take care not to file away the traces which run close to the edge of the PCB, especially at the back. Each PCB is 158mm long, meaning that there is 2mm of spare space for a joiner if the key spacing is to be kept even. We used cut-down double-row pin headers. The plastic spacers are very close to 2mm deep, giving the necessary spacing. Start by cutting down the headers to be used for joiners. This is fiddly but necessary, as there is no more than 8mm between adjacent switch bodies on neighbouring PCBs, and typical pin headers are around 11mm tall. You can halve the number of cuts by shifting the pins in the plastic. Place the PCB on a hard flat surface and rest the 2x8 pin header in the CON1/CON2 holes. Push the plastic down firmly with a flat edge that fits between the pins. A steel ruler is ideal for this. This will move the pins such that only 1.6mm (the PCB thickness) of each pin is proud. Now reverse the 2x8 pin header, and use the depth of the PCB as a jig to cut 1.6mm from the other side of the pins. The pin stubs may fly off at speed, so wear safety goggles and aim the header while cutting so that they will fly away from you. See the photos opposite that show what the header should look like after being trimmed and then attached to the PCBs. Soldering these headers is a little tricky as they are not a snug fit. Treat them like a surface-mounted part, applying flux paste to the pads before soldering. We recommend securing the parts during soldering with hightemperature tape (eg, Kapton) so they don’t move around. Tack the ends in place and check that the pins do not foul the tactile switch footprints. You might even like to test-fit the switches to confirm clearances. Solder the remaining pins, and be generous with the flux. It will help the solder to form clean beads that Fig.3: there’s not much to get wrong during assembly, although we recommend fitting the PCB joiners first, as the tactile switches will make access difficult when soldering them. The buttons should snap into place, so soldering them is easy. 94  Silicon Chip Australia’s electronics magazine siliconchip.com.au Parts List – Full 64-key Keyboard 8 Keyboard Modules 7 2x8 male pin headers, trimmed in height (CON3-CON6) 1 2x8 pin header (male or female to suit Leonardo connections, CON1 and CON2) mounting hardware to suit usage (M3 tapped spacers, screws etc) Keyboard Module 1 double-sided Keyboard PCB coded 23101213, 158 x 28mm 8 12mm tactile switches [eg, Diptronics DTS-21N-V or Jaycar SP0608/SP0609, Altronics S1135 + S1138] sit where they need to. Flip the board over and complete the headers on the back of the PCB. Remove any excess flux using a flux cleaner, and test the exposed CON3CON6 pads for continuity between the ends of the strip. As you can see from Fig.2, CON3 is wired straight through to CON5. But CON4 will be offset relative to CON6 (unless you have the full complement of eight PCBs), so check that each pad on CON4 is connected to one and only one pad on CON6. It’s best to do this now, as it can be quite fiddly to rework these connections with the tactile switches in place. Fit the switches next. They should snap neatly into place; just check that they are sitting flush before soldering. Finally, solder headers for CON1 and CON2. We used female headers to match the cables we had made up for the Matrix, but you can use whatever works for your arrangement, even soldering wires directly to the PCB. these are CON3 to CON5 on the front of the PCB. If none of the keys on a PCB work, then it may be a problem with the CON4 to CON6 row connections on the back of the PCB. The cut-down header pins (shown above) measure around 7mm tall so that they will fit between the end switches on adjacent PCBs (shown below). The plastic part is 2mm tall, so uniform board spacing is achieved too. Conclusion Like the Matrix, the Keyboard is designed to work with our MIDI hardware and software. But we think that readers will find other uses, especially in cases where many buttons need to be connected to a microcontroller. SC With the set of Keyboard PCBs wired up to our MIDI shield, we have a linear array of buttons that you can play like a piano. But keep in mind that by default, unlike a piano, multiple keys cannot be played at the same time. Hooking it up We tested our unit with the MIDI_ ENCODER sketch. If you haven’t done so already, we recommend reading the earlier parts of this series of articles, as they describe the software in more detail. Since the Keyboard is effectively equivalent to a Matrix fitted with non-illuminated switches, you can transfer many of the ideas relating to the Matrix to the Keyboard. As with the Matrix, wire CON1 of the Keyboard to CON2 of the MIDI shield (or corresponding Leonardo pins) and CON2 of the Keyboard to CON1 on the MIDI shield, connecting pin 1 to pin 1. Check that all the buttons work as expected, using the key notifications that appear on the Arduino Serial Monitor. If you find that some keys on a PCB don’t work (but not all), check the column connections for continuity; siliconchip.com.au Australia’s electronics magazine August 2021  95 SILICON CHIP .com.au/shop ONLINESHOP HOW TO ORDER INTERNET (24/7) PAYPAL (24/7) eMAIL (24/7) MAIL (24/7) PHONE – (9-5:00 AET, Mon-Fri) siliconchip.com.au/Shop silicon<at>siliconchip.com.au silicon<at>siliconchip.com.au PO Box 139, COLLAROY, NSW 2097 (02) 9939 3295, +612 for international You can also pay by cheque/money order (Orders by mail only) or bank transfer. Make cheques payable to Silicon Chip. 8/21 YES! You can also order or renew your Silicon Chip subscription via any of these methods as well! 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PRE-PROGRAMMED MICROS For a complete list, go to siliconchip.com.au/Shop/9 $10 MICROS 24LC32A-I/SN ATmega328P ATmega328P-AUR ATtiny85V-10PU ATtiny816 PIC10F202-E/OT PIC12F1572-I/SN PIC12F617-I/P PIC12F675-I/P PIC12F675-I/SN PIC16F1455-I/P PIC16F1455-I/SL PIC16F1459-I/P PIC16F1705-I/P PIC16F88-E/P PIC16F88-I/P $15 MICROS Digital FX Unit (Apr21) RF Signal Generator (Jun19), Si473x FM/AM/SW Digital Radio (Jul21) RGB Stackable LED Christmas Star (Nov20) Shirt Pocket Audio Oscillator (Sep20) ATtiny816 Development/Breakout Board (Jan19) Ultrabrite LED Driver (with free TC6502P095VCT IC, Sep19) LED Christmas Ornaments (Nov20; specify variant) Nano TV Pong (Aug21) Car Radio Dimmer (Aug19), MiniHeart Heartbeat Simulator (Jan21) Refined Full-Wave Universal Motor Speed Controller (Apr21) Model Railway Level Crossing (two required – $15/pair) (Jul21) Motor Speed Controller (Mar18), Heater Controller (Apr18) Useless Box IC3 (Dec18) Tiny LED Xmas Tree (Nov19) Microbridge (May17), USB Flexitimer (June18) Digital Interface Module (Nov18), GPS Finesaver (Jun19) Digital Lighting Controller LED Slave (Dec20) Ol’ Timer II (Jul20), Battery Multi Logger (Feb21) 5-Way LCD Panel Meter (Nov19), IR Remote Control Assistant (Jul20) Ultrasonic Cleaner (Sep20), Electronic Wind Chime (Feb21) 20A DC Motor Speed Controller (Jul21) Flexible Digital Lighting Controller Slave (Oct20) Automotive Sensor Modifier (Dec16) Remote-controlled Preamp with Tone Control (Mar19) UHF Repeater (May19), Six Input Audio Selector (Sep19) Universal Battery Charge Controller (Dec19) ATSAML10E16A-AUT High-Current Battery Balancer (Mar21) PIC16F1459-I/SO Four-Channel DC Fan & Pump Controller (Dec18) PIC32MM0256GPM028-I/SS Super Digital Sound Effects (Aug18) PIC32MX170F256D-501P/T 44-pin Micromite Mk2 (Aug14), 4DoF Simulation Seat (Sep19) PIC32MX170F256B-50I/SP Micromite LCD BackPack V1-V3 (Feb16 / May17 / Aug19) Touchscreen Voltage / Current Ref. (Oct16), Deluxe eFuse (Aug17) Micromite DDS for IF Alignment (Sep17), Tariff Clock (Jul18) GPS-Synched Frequency Reference (Nov18), Air Quality Monitor (Feb20) RCL Box (Jun20), Digital Lighting Controller Micromite Master (Nov20) Advanced GPS Computer (Jun21) PIC32MX170F256B-I/SO Battery Multi Logger (Feb21), Battery Manager BackPack (Aug21) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) PIC32MX795F512H-80I/PT Maximite (Mar11), miniMaximite (Nov11), Colour Maximite (Sep12), Touchscreen Audio Recorder (Jun14) $20 MICROS dsPIC33FJ64MC802-E/SP dsPIC33FJ128GP306-I/PT dsPIC33FJ128GP802-I/SP PIC32MX470F512H-I/PT PIC32MX470F512H-120/PT PIC32MX470F512L-120/PT 1.5kW Induction Motor Speed Controller (Aug13) CLASSiC DAC (Feb13) Ultra-LD Preamp (Nov11), LED Musicolour (Oct12) Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) Micromite Explore 100 (Sep16) PIC32MX695F512L-80I/PF PIC32MZ2048EFH064-I/PT Colour MaxiMite (Sep12) DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) DIY Reflow Oven Controller (Apr20) $30 MICROS KITS, SPECIALISED COMPONENTS ETC BATTERY MANAGER $75.00 (AUG 21) $17.50 PCB and all onboard parts only (does not include controllers) MODEL RAILWAY LEVEL CROSSING (JUL 21) $15.00 $5.00 - Pair of programmed PIC12F617-I/Ps - ISD1820P-based audio recording and playback module ADVANCED GPS COMPUTER (JUN 21) $75.00 $25.00 $3.00 - Micromite LCD BackPack V3 kit (SC5082) - VK2828U7G5LF GPS module (SC5135) - MCP4251-502E/P IC (SC5052) ARCADE PONG (CAT SC5834) (JUN 21) $12.50 Pair of Signetics-branded NE555Ns, for critical A9/B9 paddle ICs MINI ISOLATED SERIAL LINK COMPLETE KIT (CAT SC5750) (MAR 21) $10.00 All parts required to build the project including the PCB AM/FM/SW RADIO (JAN 21) $2.50 $3.00 $7.50 - PCB-mount right-angle SMA socket (SC4918) - Pulse-type rotary encoder with integral pushbutton (SC5601) - 16x2 LCD module (does not use I2C module) (SC4198) LED CHRISTMAS ORNAMENTS (CAT SC5579) (NOV 20) Complete kit including micro but no coin cell (specify PCB shape & colour) RGB STACKABLE LED CHRISTMAS STAR (CAT SC5525) $14.00 (NOV 20) $38.50 Complete kit including PCB, micro, diffused RGB LEDs and other parts FLEXIBLE DIGITAL LIGHTING CONTROLLER PARTS MICROMITE LCD BACKPACK V3 KIT (CAT SC5082) (AUG 21) - Micromite LCD BackPack V3 kit (SC5082) NANO TV PONG SHORT FORM KIT (CAT SC5885) siliconchip.com.au/Shop/ (OCT 20) 4 x Si8751AB ICs, 8 x S1HB15N60E-GE3 Mosfets, switchmode converter module, 6N137 opto, high-voltage resistors and capacitors plus SMD LEDs. $100.00 COLOUR MAXIMITE 2 (JUL 20) Short form kit: includes everything except the case, CPU module, power supply, optional parts and cables (Cat SC5478) $80.00 Short Form kit (with CPU module): includes the programmed Waveshare CPU modue and everything included in the short form kit above (Cat SC5508) $140.00 (AUG 19) Includes PCB, programmed micros, 3.5in touchscreen LCD, UB3 lid, mounting hardware, Mosfets for PWM backlight control and all other mandatory on-board parts $75.00 Separate/Optional Components: - 3.5-inch TFT LCD touchscreen (Cat SC5062) $30.00 - DHT22 temp/humidity sensor (Cat SC4150) $7.50 - BMP180 (Cat SC4343) OR BMP280 (Cat SC4595) temp/pressure sensor $5.00 - BME280 temperature/pressure/humidity sensor (Cat SC4608) $10.00 - DS3231 real-time clock SOIC-16 IC (Cat SC5103) $3.00 - 23LC1024 1MB RAM (SOIC-8) (Cat SC5104) $5.00 - AT25SF041 512KB flash (SOIC-8) (Cat SC5105) $1.50 - 10µF 16V X7R through-hole capacitor (Cat SC5106) $2.00 VARIOUS MODULES & PARTS - Si4732 radio IC (Si473x FM/AM/SW Radio, Jul21) $7.50 - EA2-5NU relay (PIC Programming Helper, Jun21) $3.00 - VK2828U7G5LF GPS module (Advanced GPS Computer, Jun21) $25.00 - MCP4251-502E/P (PIC Programming Helper, Jun21) $3.00 - 2.8-inch touchscreen LCD module (Lab Supply, May21) $22.50 - Spin FV-1 (Digital FX Unit, Apr21) $40.00 - 15mW 3W SMD resistor (Battery Multi Logger / Arduino PSU, Feb21) $2.50 - DS3231(M) real-time clock SMD IC (Battery Multi Logger, Feb21) $3.00 - Pair of CSD18534 (Electronic Wind Chimes, Feb21) $6.00 - IPP80P03P4L04 (Dual Battery Lifesaver / Vintage Radio Supply, Dec20) $5.00 - 16x2 LCD module (Digital RF Power Meter, Aug20) $7.50 - WS2812 8x8 RGB LED matrix module (Ol’ Timer II, Jul20) $15.00 - MAX038 function generator IC (H-Field Transanalyser, May20) $25.00 - MC1496P double-balanced mixer (H-Field Transanalyser, May20) $2.50 - AD8495 thermocouple interface (DIY Reflow Oven Controller, Apr20) $10.00 - Si8751AB 2.5kV isolated Mosfet driver IC (Charge Controller, Dec19) $5.00 - I/O expander modules (Nov19): PCA9685 – $6.00 ¦ PCF8574 – $3.00 ¦ MCP23017 – $3.00 - SMD 1206 LEDs, packets of 10 unless stated otherwise (Xmas Ornaments, Nov20): yellow – $0.70 ¦ amber – $0.70 ¦ blue – $0.70 ¦ cyan – $1.00 ¦ pink (1 only) – $0.20 - ISD1820-based voice recorder / playback module (Junk Mail, Aug19) $4.00 - 23LCV1024-I/P SRAM & MCP73831T (UHF Repeater, May19) $11.50 - MCP1700 3.3V LDO regulator (suitable for USB M&K Adapator, Feb19) $1.50 - ESP-01 WiFi Module (El Cheapo Modules, Apr18) $5.00 *Prices valid for month of magazine issue only. All prices in Australian dollars and include GST where applicable. # P&P prices are within Australia. Overseas? Place an order on our website for a quote. PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT BRAINWAVE MONITOR (EEG) SUPER DIGITAL SOUND EFFECTS DOOR ALARM STEAM WHISTLE / DIESEL HORN DCC PROGRAMMER (INC. HEADERS) ↳ WITHOUT HEADERS OPTO-ISOLATED RELAY (INC. EXT. BOARDS) GPS-SYNCHED FREQUENCY REFERENCE LED CHRISTMAS TREE DIGITAL INTERFACE MODULE TINNITUS/INSOMNIA KILLER (JAYCAR VERSION) ↳ ALTRONICS VERSION HIGH-SENSITIVITY MAGNETOMETER USELESS BOX FOUR-CHANNEL DC FAN & PUMP CONTROLLER ATtiny816 DEVELOPMENT/BREAKOUT PCB ISOLATED SERIAL LINK DAB+/FM/AM RADIO ↳ CASE PIECES (CLEAR) REMOTE CONTROL DIMMER MAIN PCB ↳ MOUNTING PLATE ↳ EXTENSION PCB MOTION SENSING SWITCH (SMD) PCB USB MOUSE AND KEYBOARD ADAPTOR PCB LOW-NOISE STEREO PREAMP MAIN PCB ↳ INPUT SELECTOR PCB ↳ PUSHBUTTON PCB DIODE CURVE PLOTTER ↳ UB3 LID (MATTE BLACK) FLIP-DOT (SET OF ALL FOUR PCBs) ↳ COIL PCB ↳ PIXEL PCB (16 PIXELS) ↳ FRAME PCB (8 FRAMES) ↳ DRIVER PCB iCESTICK VGA ADAPTOR UHF DATA REPEATER AMPLIFIER BRIDGE ADAPTOR 3.5-INCH LCD ADAPTOR FOR ARDUINO DSP CROSSOVER (ALL PCBs – TWO DACs) ↳ ADC PCB ↳ DAC PCB ↳ CPU PCB ↳ PSU PCB ↳ CONTROL PCB ↳ LCD ADAPTOR STEERING WHEEL CONTROL IR ADAPTOR GPS SPEEDO/CLOCK/VOLUME CONTROL ↳ CASE PIECES (MATTE BLACK) RF SIGNAL GENERATOR RASPBERRY PI SPEECH SYNTHESIS/AUDIO BATTERY ISOLATOR CONTROL PCB ↳ MOSFET PCB (2oz) MICROMITE LCD BACKPACK V3 CAR RADIO DIMMER ADAPTOR PSEUDO-RANDOM NUMBER GENERATOR 4DoF SIMULATION SEAT CONTROLLER PCB ↳ HIGH-CURRENT H-BRIDGE MOTOR DRIVER MICROMITE EXPLORE-28 (4-LAYERS) SIX INPUT AUDIO SELECTOR MAIN PCB ↳ PUSHBUTTON PCB ULTRABRITE LED DRIVER HIGH RESOLUTION AUDIO MILLIVOLTMETER PRECISION AUDIO SIGNAL AMPLIFIER SUPER-9 FM RADIO PCB SET ↳ CASE PIECES & DIAL TINY LED XMAS TREE (GREEN/RED/WHITE) HIGH POWER LINEAR BENCH SUPPLY ↳ HEATSINK SPACER (BLACK) DIGITAL PANEL METER / USB DISPLAY ↳ ACRYLIC BEZEL (BLACK) UNIVERSAL BATTERY CHARGE CONTROLLER BOOKSHELF SPEAKER PASSIVE CROSSOVER ↳ SUBWOOFER ACTIVE CROSSOVER DATE AUG18 AUG18 AUG18 SEP18 OCT18 OCT18 OCT18 NOV18 NOV18 NOV18 NOV18 NOV18 DEC18 DEC18 DEC18 JAN19 JAN19 JAN19 JAN19 FEB19 FEB19 FEB19 FEB19 FEB19 MAR19 MAR19 MAR19 MAR19 MAR19 APR19 APR19 APR19 APR19 APR19 APR19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 MAY19 JUN19 JUN19 JUN19 JUN19 JUL19 JUL19 JUL19 AUG19 AUG19 AUG19 SEP19 SEP19 SEP19 SEP19 SEP19 SEP19 OCT19 OCT19 NOV19 NOV19 NOV19 NOV19 NOV19 NOV19 NOV19 DEC19 JAN20 JAN20 PCB CODE 25107181 01107181 03107181 09106181 SC4716 09107181 10107181/2 04107181 16107181 16107182 01110181 01110182 04101011 08111181 05108181 24110181 24107181 06112181 SC4849 10111191 10111192 10111193 05102191 24311181 01111119 01111112 01111113 04112181 SC4927 SC4950 19111181 19111182 19111183 19111184 02103191 15004191 01105191 24111181 SC5023 01106191 01106192 01106193 01106194 01106195 01106196 05105191 01104191 SC4987 04106191 01106191 05106191 05106192 07106191 05107191 16106191 11109191 11109192 07108191 01110191 01110192 16109191 04108191 04107191 06109181-5 SC5166 16111191 18111181 SC5168 18111182 SC5167 14107191 01101201 01101202 Price $10.00 $2.50 $5.00 $5.00 $7.50 $5.00 $7.50 $7.50 $5.00 $2.50 $5.00 $5.00 $12.50 $7.50 $5.00 $5.00 $5.00 $15.00 $.00 $10.00 $10.00 $10.00 $2.50 $5.00 $25.00 $15.00 $5.00 $7.50 $5.00 $17.50 $5.00 $5.00 $5.00 $5.00 $2.50 $10.00 $5.00 $5.00 $40.00 $7.50 $7.50 $5.00 $7.50 $5.00 $2.50 $5.00 $7.50 $10.00 $15.00 $5.00 $7.50 $10.00 $7.50 $5.00 $5.00 $7.50 $2.50 $5.00 $7.50 $5.00 $2.50 $10.00 $5.00 $25.00 $25.00 $2.50 $10.00 $5.00 $2.50 $2.50 $10.00 $10.00 $7.50 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT ARDUINO DCC BASE STATION NUTUBE VALVE PREAMPLIFIER TUNEABLE HF PREAMPLIFIER 4G REMOTE MONITORING STATION LOW-DISTORTION DDS (SET OF 5 BOARDS) NUTUBE GUITAR DISTORTION / OVERDRIVE PEDAL THERMAL REGULATOR INTERFACE SHIELD ↳ PELTIER DRIVER SHIELD DIY REFLOW OVEN CONTROLLER (SET OF 3 PCBS) 7-BAND MONO EQUALISER ↳ STEREO EQUALISER REFERENCE SIGNAL DISTRIBUTOR H-FIELD TRANSANALYSER CAR ALTIMETER RCL BOX RESISTOR BOARD ↳ CAPACITOR / INDUCTOR BOARD ROADIES’ TEST GENERATOR SMD VERSION ↳ THROUGH-HOLE VERSION COLOUR MAXIMITE 2 PCB (BLUE) ↳ FRONT & REAR PANELS (BLACK) OL’ TIMER II PCB (RED, BLUE OR BLACK) ↳ ACRYLIC CASE PIECES / SPACER (BLACK) IR REMOTE CONTROL ASSISTANT PCB (JAYCAR) ↳ ALTRONICS VERSION USB SUPERCODEC ↳ BALANCED ATTENUATOR SWITCHMODE 78XX REPLACEMENT WIDEBAND DIGITAL RF POWER METER ULTRASONIC CLEANER MAIN PCB ↳ FRONT PANEL NIGHT KEEPER LIGHTHOUSE SHIRT POCKET AUDIO OSCILLATOR ↳ 8-PIN ATtiny PROGRAMMING ADAPTOR D1 MINI LCD WIFI BACKPACK FLEXIBLE DIGITAL LIGHTING CONTROLLER SLAVE ↳ FRONT PANEL (BLACK) LED XMAS ORNAMENTS 30 LED STACKABLE STAR ↳ RGB VERSION (BLACK) DIGITAL LIGHTING MICROMITE MASTER ↳ CP2102 ADAPTOR BATTERY VINTAGE RADIO POWER SUPPLY DUAL BATTERY LIFESAVER DIGITAL LIGHTING CONTROLLER LED SLAVE BK1198 AM/FM/SW RADIO MINIHEART HEARTBEAT SIMULATOR I’M BUSY GO AWAY (DOOR WARNING) BATTERY MULTI LOGGER ELECTRONIC WIND CHIMES ARDUINO 0-14V POWER SUPPLY SHIELD HIGH-CURRENT BATTERY BALANCER (4-LAYERS) MINI ISOLATED SERIAL LINK REFINED FULL-WAVE MOTOR SPEED CONTROLLER DIGITAL FX UNIT PCB (POTENTIOMETER-BASED) ↳ SWITCH-BASED ARDUINO MIDI SHIELD ↳ 8X8 TACTILE PUSHBUTTON SWITCH MATRIX HYBRID LAB POWER SUPPLY CONTROL PCB ↳ REGULATOR PCB VARIAC MAINS VOLTAGE REGULATION ADVANCED GPS COMPUTER PIC PROGRAMMING HELPER 8-PIN PCB ↳ 8/14/20-PIN PCB ARCADE MINI PONG Si473x FM/AM/SW DIGITAL RADIO 20A DC MOTOR SPEED CONTROLLER MODEL RAILWAY LEVEL CROSSING DATE JAN20 JAN20 JAN20 FEB20 FEB20 MAR20 MAR20 MAR20 APR20 APR20 APR20 APR20 MAY20 MAY20 JUN20 JUN20 JUN20 JUN20 JUL20 JUL20 JUL20 JUL20 JUL20 JUL20 AUG20 NOV20 AUG20 AUG20 SEP20 SEP20 SEP20 SEP20 SEP20 OCT20 OCT20 OCT20 NOV20 NOV20 NOV20 NOV20 NOV20 DEC20 DEC20 DEC20 JAN21 JAN21 JAN21 FEB21 FEB21 FEB21 MAR21 MAR21 APR21 APR21 APR21 APR21 APR21 MAY21 MAY21 MAY21 JUN21 JUN21 JUN21 JUN21 JUL21 JUL21 JUL21 PCB CODE 09207181 01112191 06110191 27111191 01106192-6 01102201 21109181 21109182 01106193/5/6 01104201 01104202 CSE200103 06102201 05105201 04104201 04104202 01005201 01005202 07107201 SC5500 19104201 SC5448 15005201 15005202 01106201 01106202 18105201 04106201 04105201 04105202 08110201 01110201 01110202 24106121 16110202 16110203 16111191-9 16109201 16109202 16110201 16110204 11111201 11111202 16110205 CSE200902A 01109201 16112201 11106201 23011201 18106201 14102211 24102211 10102211 01102211 01102212 23101211 23101212 18104211 18104212 10103211 05102211 24106211 24106212 08105211 CSE210301C 11006211 09108211 Price $5.00 $10.00 $2.50 $5.00 $20.00 $7.50 $5.00 $5.00 $12.50 $7.50 $7.50 $7.50 $10.00 $5.00 $7.50 $7.50 $2.50 $5.00 $10.00 $10.00 $5.00 $7.50 $5.00 $5.00 $12.50 $7.50 $2.50 $5.00 $7.50 $5.00 $5.00 $2.50 $1.50 $5.00 $20.00 $20.00 $3.00 $12.50 $12.50 $5.00 $2.50 $7.50 $2.50 $5.00 $10.00 $5.00 $2.50 $5.00 $10.00 $5.00 $12.50 $2.50 $7.50 $7.50 $7.50 $5.00 $10.00 $10.00 $7.50 $7.50 $7.50 $5.00 $7.50 $35.00 $7.50 $7.50 $5.00 AUG21 AUG21 AUG21 AUG21 AUG21 07108211 11104211 11104212 08105212 23101213 $15.00 $5.00 $2.50 $2.50 $5.00 NEW PCBs COLOUR MAXIMITE 2 GEN2 (4 LAYERS) BATTERY MANAGER SWITCH MODULE ↳ I/O EXPANDER NANO TV PONG LINEAR MIDI KEYBOARD (8 KEYS) We also sell an A2 Reactance Wallchart, RTV&H DVD, Vintage Radio DVD plus various books at siliconchip.com.au/Shop/3 Vintage Radio 1961-65 1961-65 Bush Bush VTR103 VTR103 AM/FM AM/FM Radio Radio By Ian Batty The VTR103 was manufactured by Bush Radio, based in the UK and founded by former employees of Graham Amplion. This set incorporates a complex circuit design, utilising nine transistors to provide the AM and FM bands. The set is shown here with its partly-opaque dial cover removed. Bush Radio began in 1932, becoming part of the Rank empire in 1945. Along with the standout DAC90 and DAC10 valve radios, they released the distinctive TV22 television. The VTR103 case is based on that of the TR82C from the early 1960s (see September 2013; siliconchip.com.au/ Article/4395). The TR82C was itself based on an earlier valve portable, the MB60, released in 1957. Designed by the brilliant young David Ogle, this case just screams ‘retro’ (although it would have been considered very modern at the time!). It is such a popular design that the same case was re-used for the modern Bush TR82DAB radio, also reviewed in our September 2013 issue. You can’t really blame them as it’s such a classic shape, evoking the era of Rock ‘n Roll. The elegant moulded cabinet has clear, bold lines. The large dial dominates the front, its anodised red scale set back in a well behind the tuning knob. The volume, band change and 98  Silicon Chip on/off-tone controls sit in a well at the top of the case. Placing a hand onto the set, one’s fingers easily engage with the controls. The volume and on/off-tone knobs are well-knurled and easy to operate. The band change switches respond positively. Ergonomically, this is one of the most pleasant sets I have in my collection. The dial cover/knobs, regrettably, have hazed with age. That rather dims the bright red anodising of the tuning scale. Face-off: VTR103 vs TR82C Given the visual appeal and easeof-use established by the TR82C, why change anything? That seems to be the approach Bush designers took. Sideby-side on a shelf, differences are the necessary minimum: three pushbutton switches for band changing (LW/ MW/VHF), and a dial with three wavebands. The only other clear difference is the “output to tape recorder” socket at Australia’s electronics magazine the lower right of the case at the back. Bush seems to have anticipated this in the TR82C, which carries a moulded dimple in precisely the same position. The TR82C came in a variety of trims. The metal parts are chromeplated, while the plastics are either in original colours or “flashed” with bright finishes. Control legends are recess-moulded and filled with dark paint. The earlier TR82C used a combination of alloyed-junction OC44/45 transistors in the RF/IF end and OC71/OC81-class transistors in the audio end, offered longwave (LW) and medium wave (MW, ie, broadcast) reception, and was a creditable performer. Frequency modulation (FM) broadcasting was introduced in the United Kingdom by the BBC in 1955, followed by commercial broadcasters in the early 1970s. BBC transmissions were in the range 88~94.6MHz, with commercial stations taking up 94.6~97.6MHz. This explains the VTR103’s restricted FM siliconchip.com.au tuning range of just 88~100MHz. General description The Bush VTR103 is an LW/MW AM/FM radio using nine PNP transistors and three diodes. FM reception is monophonic; there is no provision for FM stereo. The AM sections of the VTR103 are similar to those of the TR82C, including the use of doubletuned IF transformers. The audio section is also much the same. Frequency coverage is 158~280kHz (LW), 526~1605kHz (MW) and 87.5~100MHz (FM). The AM intermediate frequency (IF) is 470kHz, while the FM IF is 10.7MHz. The long wave/medium wave section is a conventional design with a converter, two IF stages and a four-transistor three-stage audio section using a Class-B push-pull audio output stage. All transistors are made of germanium; the RF transistors are alloy-diffused types, while the audio transistors are junction types. Band changing is managed by one of three pushbuttons setting a multi-section rotary switch to the appropriate position. S2A removes power from the two AF114s in the VHF front end for the AM bands, leaving it inactive except for FM operation. The dual-frequency IF design amplifies either IF signal frequency presented to it without needing switching or other intervention. Dual, separate demodulators are used: a peak detector for AM and a ratio detector for FM. Readers may be familiar with the passband characteristics of a typical intermediate frequency amplifier: a single ‘hump’ at the design frequency. The VTR103’s passband responds to signals at both intermediate frequencies, as shown in Fig.1. Would it be possible to receive an AM and an FM broadcast simultaneously? The IF channel is capable of this, but the front end/tuned design ensures that only one signal (either Fig.1: graph of the VTR103’s passband response at the AM (470kHz) and FM (10.7MHz) IF frequencies. siliconchip.com.au It looks fantastic and has fantastic sound quality. The VTR103 is shown at right, next to the LW/MW-only TR82C. The top view of the case shows the volume control (which doubles as the power switch), band change selector, tone control, and the telescopic aerial. The rear of the set has a socket for an external aerial and a connector for a tape recorder. There is a socket on the left-hand (right from this angle) side of the set which is used to connect a pair of earphones. Australia’s electronics magazine August 2021  99 Tuning is by a cord-driven mechanism that adjusts the position of tuning slugs in the RF transformer and LO tuning coil. Both coils are wound from copper straps that provide low RF resistance, and thus high Q and low losses at the operating frequency. Although trimmers CT1 and CT2 are provided, as is an adjustable slug in antenna coil L1/L2, the manufacturer describes all of these as factory-set and advises against user or service adjustment. Aligning of this section is confined to adjusting of the dial mechanism to give correct tuning near midband, at 94MHz. Circuit diagram Celestion speaker The VTR103 uses an aluminium chassis, with the germanium transistors mounted via insulated pins. The chassis is held in placed by four screws along the outside edge, and the tuning knob AM or FM) is converted at a time. The following description will make this clear. Construction Like the TR82, the VTR103 uses a conventional aluminium chassis with transistors mounted to it via insulated pins. The transistors are mounted on the exposed side of the chassis, allowing easy access for measuring electrode voltages, and easy replacement by desoldering/resoldering. The FM VHF tuner sits in a separate metal case. This allows all VHF components to be shielded, reducing the likelihood of radiation interfering with other services. The parts are mounted on a printed circuit board (PCB), making the assembly compact and controlling circuit inductances and capacitances. VHF LO coil 1st FM IFT (IFT1; L6-7) VHF amplifier load coil VHF converter (Q2; AF114) VHF RF amplifier (Q1; AF114) A close-up of the FM VHF tuner which sits in a separate metal case for shielding and is mounted on a PCB. 100  Silicon Chip Australia’s electronics magazine The full circuit of the set is shown in Fig.2. Unusually, the circuit diagram for this set is drawn with a negative ground. Emitters connect to the positive supply and collectors to ground. While this does not affect its operation, most PNP sets were drawn with a positive ground, so you need to be aware of this when reading the circuit diagram. Of course, most modern circuits use a negative ground, so interpreting this one should not be too difficult for most readers. Additionally, the original circuit diagrams show chassis returns either to a common ground rail (thick common bar in the diagram), or to individual earth symbols for illustration clarity. I drew Fig.2 because both schematics I found online were hard to follow. The Trader 1549 version is a dog’s breakfast; the band change switch is broken out into individual make/break contacts, demanding that you get out the pencil and try to work out what is on (or off) for each band. Pity the poor service technician! The Engineering Report’s circuit at least seems to have had the service department looking on, but the erratic and inconsistent placement (for example) of biasing and tuning components in the IF strip is frustrating. I trust that my efforts will be more readily understood. Circuit operation Taking the LW/MW section first, Q3 operates as a self-excited converter with collector-emitter feedback. The ferrite rod antenna receives external signals from the antenna socket via primary winding L8. All band switching is done by just siliconchip.com.au Band change switch Volume control Tone control IFT3 IFT2 IFT4 IFT5 ► IFT7 VHF tuner L13-15 IFT6 AM tuning gang The transistors on the chassis rear have not been labelled due to their small size. You can find an overlay diagram, along with the original circuit, for this set at: www.radiomuseum.org/r/bush_vtr103vtr_10.html Output transformer The front of the chassis doesn’t showcase anything new compared to the rear, apart from the markings on the AM tuning gang and the sockets used by the transistors. You can also see the two OA79 diodes, used for FM demodulation, at the bottom in clear tubes with a white stripe. ► FM demodulator diodes (D2-3) siliconchip.com.au Australia’s electronics magazine AM tuning gang August 2021  101 one switch assembly. The original diagram labels it as S1A, S1B, S2A, S2B, S3A and S3B, according to the positions of the three separate wafer sections on the common shaft. I have omitted the usual dotted “common control” lines (such as those I have used for the tuning capacitors and inductors) to avoid cluttering the drawing. For LW operation, the antenna section of the LW/MW gang (CV1/CV2) connects to the LW antenna tuned winding L9 on the ferrite rod. The signal is derived from antenna secondary winding L10 and fed to the base of the converter via band change switch S3A and coupling capacitor C14. Antenna padder capacitor C13 and LW trimmer CT4 are connected in parallel with CV1 via band change switch S1A. Converter Q3’s emitter connects to the positive supply via oscillator coil feedback winding L13, then emitter resistor R9 (bypassed by C15). The oscillator coil’s L15 tuned winding 102  Silicon Chip connects, via band change switch S3B, to LW padder C17 and LW oscillator trimmer CT5. Capacitor C17 adds enough capacitance to the oscillator tuned circuit to force it to cover the lower LO frequency range of 628~750kHz for longwave reception. Q3’s collector connects, via band change switch S2B, to oscillator coil L14’s primary, and thence to the L16 primary of the first AM IF transformer (IFT2) primary, then to signal and supply ground. This primary is tuned and tapped. IFT2’s secondary L17 is tuned and tapped, with the tap feeding signal to first IF amplifier, Q4. Band change switch S1B shorts the primary of the first FM IF transformer (IFT3) to ground, preventing IFT3 from affecting AM operation. MW converter operation Returning to the converter, for MW Australia’s electronics magazine operation, S1A connects the MW tuned winding L11 and associated trimmer CT3 in parallel with the LW tuned winding L9 and antenna tuning capacitor CV1. Paralleling L11 and L9 reduces the total circuit inductance, allowing the circuit to tune over the 535~1605 kHz broadcast band range. Signal pickup from the ferrite antenna is derived from the MW secondary L12, and switched to the converter base via S3A and C14. In the oscillator circuit, S3B disconnects the LW capacitors C17 and trimmer CT5, connecting MW trimmer CT6 and damping resistor R11 into the circuit, in parallel with oscillator tuning capacitor CV2 and the L15 tuned winding of the oscillator coil. Note that, for both AM bands, 556pF capacitor C22 is in series with gang section CV2; you could call C22 the “master” padder. Band change section S2B maintains the connection from the converter’s siliconchip.com.au Fig.2: the relatively complex circuit diagram for the Bush VTR103 AM/FM radio. The switches have been marked in red for clarity. RF voltages 30% modulated, audio 400Hz, 50mW output. DC voltage with VTVM, no signal thus ○ except max signal this ◇ RF/audio signal injections □. Frame GND signal used for convenience is supply negative. collector to the L14 primary of the oscillator coil. S1B maintains the short across the L18 primary of first FM IF transformer IFT3 to prevent it affecting LW/MW operation. As with LW operation, S2B connects the output from the converter (via L14 oscillator coil primary) to the L16 tuned, tapped primary of AM IF transformer IFT2 and thence to ground. FM tuner operation FM tuning is done using movable slugs. This method is more compact than capacitor tuning (as we need the coils anyway), and less liable to deterioration over time due to vibration or contamination. siliconchip.com.au In the FM position, S2A connects power to the VHF tuner module. This uses Q1 as a common-base RF amplifier. The input circuit is broadly fixedtuned, with capacitive voltage divider C2/C3 tuning antenna secondary L2 and matching the tuned circuit to the low input impedance of Q1’s emitter. Q1 uses combination bias. Since this is a common-base stage, Q1’s emitter is unbypassed (to allow signal coupling), but C4 bypasses its base to RF ground. As with the rest of the set, Q1’s emitter returns (via emitter resistor R1) to the positive supply/ RF ground, while its collector returns, via RF tuned circuit L3/CT1, to DC ground (the negative supply). Australia’s electronics magazine The amplified signal from Q1’s collector is coupled to the converter’s input via C5. Converter Q2 uses a self-oscillating design, and operates in common-base mode both for conversion and for oscillation. Like the RF amplifier, Q2’s unbypassed emitter returns to the positive supply via RF choke L4 and emitter resistor R4. L4’s high reactance improves the converter stage’s input impedance, to ensure successful oscillator operation. Local oscillator (LO) feedback, from Q2’s collector to emitter, is provided via capacitor C7. Notice that there is no phase inversion in this circuit: since a common-base circuit ideally creates no signal inversion between emitter and collector, any collector-emitter feedback has a 0° phase shift, and this is positive feedback that will provoke oscillation. Converter Q2’s collector connects, via the first FM IF transformer primary August 2021  103 L6, to ground. The converter’s FM IF signal is picked off via the primary circuit of first FM IF L6/L7. The primary of the first IFT appears to be in parallel (via C11) with the local oscillator L5/CT2/C10 tuned circuit. L5 is in series with the first FM IF transformer’s tuning capacitor C11. But L5 (just a few turns of copper strap) has such low inductance that it’s a short-circuit at 10.7 MHz. In effect, C11’s ‘bottom’ end is at ground for the 10.7 MHz IF signal, and in parallel with first IFT primary L6. The converter function ‘sees’ a conventional parallel-tuned circuit (C11/L6) at 10.7 MHz. Simultaneously, C11 has a very low reactance at the LO frequency of 98.2~110.7 MHz, so Q2’s collector is effectively connected directly to the LO tank circuit CT2/C10/L5. As well, the first IFT primary (L6) has a very high reactance over the LO tuning range, and is effectively open-circuit to LO signals. The local oscillator function ‘sees’ only the variable-inductor-tuned circuit CT2/C10/L5 at 98.2~110.7 MHz. This ‘dual-tuned’ circuit allows Q2 to act as a converter: simultaneous local oscillation and extraction of the 10.7MHz IF signal from converter Q2’s collector. L7’s secondary tap connects to switch S3A. This disconnects the AM tuned circuits from the converter circuitry and conveys the 10.7MHz FM IF signal to the base of Q3. Band change switch S3B disconnects some of the AM tuning circuitry from AM LO coil set L13~L15. More importantly, S2B disconnects Q3’s collector from AM LO primary L14, while S1B removes the short across the second FM IF transformer IFT3 and allows signals from converter Q3’s collector to pass directly to second IFT3’s tuned, untapped primary L18. Thus, Q3 acts as the first FM IF amplifier. Q3’s AM LO circuitry is disabled by S3C’s shorting of the AM LO transformer’s L13 feedback winding. IF operation for AM For AM operation, IF signals are fed to first AM IF transformer IFT2 from the converter’s collector into tapped, tuned primary L16, and are coupled to tapped, tuned secondary L17. L17’s tapped winding feeds the 470kHz AM IF signal to the base of first AM IF amplifier Q4; however, this 104  Silicon Chip winding is (for DC) in series with second FM IF transformer IFT3’s secondary, L19. Since L19 and C21 resonate at 10.7MHz, they present very little impedance at 470kHz, thus allowing the 470kHz AM IF signal from L17’s tap to be conveyed to the base of Q4. At 10.7MHz, we also have the 10.7MHz tuned circuit in RF series with IFT2’s secondary. A quick calculation shows that C20’s reactance at 10.7MHz is around 50W, creating signal loss at 10.7MHz. The solution is 3.3nF capacitor C23; at 10.7MHz, its reactance is only about 4.5W, putting the ‘cold’ end of L19 close to IF ground. It may appear that C23, with a 470kHz reactance of only about 105W, would severely shunt the AM signal at Q4’s base to emitter, ie, to IF ground. This would severely limit the AM IF channel’s potential gain. However, C23, connected to a tapping on L17, forms a tuned circuit with L17’s tapped section, and thus develops maximum AM IF signal. This is confirmed by the VTR103’s stage-bystage AM gains being pretty much the same as its predecessor, the TR82. In AM operation, Q4’s bias is supplied by series resistor R21 from the negative supply; more on that below. Ground is negative with respect to Q4’s base, and thus it acts as a conventional series-bias circuit. This bias is also acted on by the AM automatic gain control (AGC) circuit, which will be described shortly. Q4’s emitter returns, via bypassed emitter resistor R12, to the positive supply, and its collector connects via the primaries of third FM IF transformer ITF5 and second AM IF transformer IFT4 to ground. As these two windings are in DC and RF series, it’s vital that neither affects the resonance of the other; interaction would compromise the stage gain. Considering the third FM IF transformer IFT4’s primary L20, its reactance at 470kHz is very low, and thus it appears as a near short-circuit, allowing maximum AM IF signal to develop across the tuned, tapped primary L22 of second AM IF transformer IFT5. Its tapped, tuned secondary L23 connects, via the third FM IFT4’s tapped tuned secondary L21, to the base of second AM IF amplifier Q5. Second AM IF amplifier Q5 operates with fixed combination bias via R16/R17 and bypassed emitter resistor R15. The emitter returns to the positive Australia’s electronics magazine supply while its collector returns via fourth FM IF transformer IFT6’s coil L24 and third AM IF transformer IFT7’s coil L27 to ground. As with previous stages, the FM IF transformer’s inductance is low enough to appear as a near short-circuit at 470kHz, allowing the AM IF signal at Q5’s collector to develop across IFT7’s tuned, tapped primary L27. Q5 would usually operate with “starvation” bias so that it would easily overload in FM operation. This is a limiting action, and is the principal reason for FM’s outstanding impulse noise rejection (of car ignition noise, lightning etc). The designers have not taken this course though, relying instead on the noise rejection inherent to the ratio detector (described below). As with Q4’s input circuitry, 3.3nF capacitor C30 resonates with the AM IF transformer’s secondary, allowing the AM circuitry to operate at full gain while (when in FM operation) effectively shorting out the AM circuitry at the FM intermediate frequency of 10.7MHz. Untuned, untapped secondary L28 feeds demodulator diode D1. This develops the demodulated audio across C38 and feeds it, via R19, to band change switch S1C on AM bands. AM band AGC The DC component of the 470kHz AM IF signal, filtered by R20 and C39, is applied to the biasing circuit of first AM IF amplifier Q4 as the AGC control voltage. The AGC voltage is positive, and this counteracts the forward, negative bias applied to Q4 via R21. Stronger signals reduce the forward bias on Q4, reducing its gain and allowing the set to deliver a relatively constant audio output with varying received signal strength. This set does not use an AGC extension diode, despite the provision of dropping resistor R13 in the first AM IF amplifier’s collector circuit. So expect AM AGC to be only moderately effective. FM IF operation AM band converter Q3 is switched to operate as the first FM IF amplifier, as described above. S3A connects the L7 output of the VHF FM tuner module to Q3’s base via C14. S3C and S3B disable the AM LO circuits while S2B and S1B connect Q3’s collector directly to siliconchip.com.au the tuned, untapped primary of second IF transformer IFT3’s primary L18, and thus to ground. Biasing conditions remain unchanged from AM operation. IFT3’s tuned, tapped secondary L19 delivers the 10.7MHz IF signal to the base of second FM IF amplifier Q4. To prevent first AM IF transformer IFT2’s L17 secondary from affecting FM operation, it is bypassed by capacitor C23 as previously stated above. The signal from Q3 is coupled from the second FM IF transformer’s L18 primary to its L19 secondary, and is delivered to the base Q4. Although Q4’s series biasing (R21) is potentially affected by the AM circuitry’s AGC loop (via R20/C39), no AM signal will appear at the cathode of AM demodulator D1 in FM operation. There is no AGC action with this set for FM operation, and Q4 operates at constant, maximum gain without the need to disable the AM AGC circuit. Q4’s collector connects to ground via third FM IF transformer IFT4 and second AM IF transformer IFT5 (L20 and L22 respectively). As with Q3’s collector circuit, the AM IF transformer primary presents very little impedance at 10.7MHz, allowing Q4’s 10.7MHz signal to be developed across L20. Q4’s circuitry is decoupled from other parts of the circuit by dropping resistor R13 and bypass capacitor C27. IFT4’s tuned, tapped secondary L21 couples to the base of third FM IF amplifier Q5. Although this secondary is in series with second AM IF transformer IFT5’s secondary L23, capacitor C30 bypasses L23 for 10.7MHz signals, allowing the FM IF signal from L21 to appear at Q5’s base. Q5 operates with fixed combination bias via R16/ R17, and emitter resistor R15, which returns to the positive supply. Q5’s collector connects to ground via fourth FM IF transformer IFT6’s primary L24 and third AM IF transformer IFT7’s primary, L27. The 10.7MHz IF signal developed across L24 is coupled to centre-tapped secondary L26 and tertiary winding L25. AM IFT7 has no circuit effect at 10.7MHz. The FM demodulator circuit is a conventional ratio detector comprising, mainly, fourth FM IF transformer’s secondary L26/tertiary L25, diodes D2 and D3, resistors R22/R24/RV1 and capacitor C46. siliconchip.com.au At exactly 10.7MHz, signals at the two diodes are of equal amplitude and phase, so they deliver a constant DC voltage to capacitor C46, and the intended audio voltage at C36 is a constant DC value. For an IF signal that deviates above and below 10.7MHz, circuit action delivers unequal signals to D2 and D3. The output voltage at C36 will vary in sympathy with the variations in the IF signal’s frequency above and below 10.7MHz, to produce the demodulated audio signal. But, for a constant amplitude signal, the DC voltage across C46 will remain constant; C46 will neither charge nor discharge. So far, this is a conventional FM demodulator. Should the IF signal amplitude increase or decrease, however, the DC voltage across C46 will decrease or increase correspondingly. This charges or discharges C46 to some extent. The resulting extra loading – or reduction of loading – acts to suppress any AM component in the received signal, such as car ignition noise or other interference. Demodulated audio has deemphasis applied by R18/C40 to remove the preemphasis from the transmitted signal. The resulting audio signal is coupled to band change switch S1C via 250nF capacitor C42. Deemphasised audio is selected by S1C and routed to volume control RV2 and via R23 to the audio section. in this circuit. Q8/Q9 drive push-pull output transformer T2’s centre-tapped primary. T2’s secondary connects, via earphone socket JK1, to the internal speaker. Negative feedback is applied from the collector of Q9, via C53/R32, to the collector of Q6/base of Q7 to reduce audio distortion. Two single-pin jacks (SKT3/4) allow audio pick-off for tape recording. While this is useful, standard practice would see this connection taken off before the output stage, averting the likely crossover and other distortion products common to Class-B output stages. The battery supply is bypassed for stability by C57, and the audio preamp, AM converter and all IF stages are decoupled by R31/C44. The FM section’s VHF tuner module supply is applied via S2A (FM only) and decoupled by R10/C16. Audio section Very good. In a typical British understatement, a 1963 British Broadcasting Corporation Engineering Report stated “the quality of reproduction is pleasing” (see the references below). Its AM performance is as good as its predecessor, the TR82, rivalling Sony’s outstanding TR-712 (see March 2017; siliconchip.com.au/Article/10588). FM performance is also excellent, achieving 40dB of quieting with just over 20µV at the input, as shown in Fig.3, and hitting 60dB+ well before the accepted standard of 500µV. AM performance is also plotted for comparison. Yes, FM radio really is better than AM. The audio section operates identically for all bands. It is a conventional three-stage design with preamplifier, driver and push-pull Class-B output. Preamplifier Q6 operates with combination bias. It amplifies the demodulated audio from volume control RV2 and delivers it to driver stage Q7. Q7 also uses combination bias, and delivers its amplified signal to driver transformer T1’s primary winding. As with all other stages, Q7’s collector connects to ground via its load – in this case, T1’s primary. A variable top-cut tone control (RV3/C52) is connected between Q7’s collector and ground. T1’s secondary provides antiphase signals to the bases of Q8 and Q9. These operate with a small amount of forward bias applied by divider R34/ R35. There is no bias adjustment, and there is no temperature compensation Australia’s electronics magazine Cleaning up the set Despite being sold “as is”, this set was in tip-top working condition. A bit of contact cleaner and a quick tweak of the alignment had it going just fine. The band change pushbuttons had lost much of their labelling, but this was restored using a fine-tipped marker. Oh, for the days of Letraset! The case responded well to polish. As for the electrical restoration, it only needed contact cleaning and a quick alignment. How good is it? Test results AM performance saw the standard 50mW output for 3.4µV at 600kHz, 2.4µV at 1400kHz, but for (signal+ noise)-to-noise (S+N/N) figures of 18dB and 12dB respectively. For the August 2021  105 standard 20dB figures, the input levels were 3.8µV and 5.3µV. Off-air sensitivity was 100µV/m at 600kHz and 90µV/m, for S+N/N ratios of 21dB and 16dB. At 20dB S+N/N, the set needed 120µV/m. Its RF bandwidth was ±1.7kHz for -3dB, ±14kHz at -60dB. Lacking an AGC extension diode (as did the TR82), AGC action is only adequate with a 30dB range. AM audio response is 40Hz~1.8kHz at -3dB from the antenna to the speaker; from the volume control to the speaker, it is 55Hz~4.2kHz. Total harmonic distortion (THD) is commendably low, with less than 0.5% at 50mW and at 10mW (where crossover distortion would usually worsen performance). The set goes into clipping around 150mW. At low battery voltages, it clips at about 35mW, with 2.8% THD, and noticeable crossover distortion. FM performance, as noted above, is excellent. At 88MHz, an input of 7.5µV gives an S+N/N figure of 16dB for 50mW output. More usefully, the VTR103 provides an S+N/N ratio of 40dB with about 30µV at the input, and the standard 60dB with about 60µV at the input. Audio response from the antenna to the speaker is 40Hz to around 8kHz. While it doesn’t meet the full 20Hz to 15kHz broadcast specification, it does sound very good. My preferences, classical music and metal (both of which demand the full audio spectrum for good reproduction) come through well. An external speaker really does show off this set, and points to the outstanding audio performance that FM broadcast offers. Signal-to-noise ratio (SNR) FM broadcasting was introduced as a high-quality service. We expect Fig.3: AM and FM SNR response. (Signal + Noise) to Noise Ratio (S+N)/N +60dB +50dB FM band +40dB AM band +30dB Collectability The one I bought had been used by a video/film production company as set dressing – something to put in the shot for a “sixties vibe”. As it worked just fine, I am pleased with the purchase. As mentioned in the intro, modern reproductions are available. While they look superficially similar, I wouldn’t spend maybe $100 when I could get an original online for less. Let me put it this way: I am not a fan of DAB+ radio. VTR103 versions As with the TR82, the VTR103 came in several different colours. Like my TR82C, my VTR103C has blue trim. There’s also one in brown, and one with an entirely brown case. +20dB +10dB 0dB 5 2 1 10 100 50 20 Special handling 200 Signal Level in microvolts (mV) +10dB Fig.4: FM frequency response. 0 dB OUTPUT (dB ref 50mW) a S+N/N ratio of 60dB or better for a +54dBµV (500µV) signal, and a frequency response of 20Hz~15kHz. Measuring the frequency response is complicated by the receiver’s deemphasis circuitry that compensates the high-frequency preemphasis introduced by the transmitter. Its purpose is to improve the system’s high-frequency noise figures. Fig.4 shows the VTR103’s actual response versus the standard response due to deemphasis. Notice the excess loss of high frequencies after about 5kHz, caused by top cut components such as C56 and confirmed by the “volume control-to-speaker” figures. This drop-off confirms my opinion that the tape recorder output would have given better fidelity if picked off before the speaker connection. Standard –10dB Measured –20dB As with the TR82C, the VTR103’s tuning knob is a press fit. Bush’s servicing manual recommends using a suction cup (such as a “plumber’s helper”) to draw the knob off. The Bush manual clearly advises against attempting to apply pressure “from screwdrivers or other levers”. Sound advice. Another method is to wrap string around the centre boss to make a lifting rig. Take your time. Further reading –30dB –40dB 10Hz 20 40 50 100Hz 200 500 1kHz 2kHz 5kHz 10kHz 20k FREQUENCY 106  Silicon Chip Australia’s electronics magazine As usual, Ernst Erb’s site is the go-to: www.radiomuseum.org/r/bush_ vtr103vtr_10.html Engineering report: www.bbc.co.uk/ rd/publications/rdreport_1963_42 SC siliconchip.com.au ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Send your email to silicon<at>siliconchip.com.au Advanced GPS Computer cable length I am thinking of building the Advanced GPS Computer (June & July 2021; siliconchip.com.au/Series/366). Could you advise whether a 2m length of cable between the GPS module and the Micromite would be possible? I note that your photos only show a cable approximately 50cm long. I also wonder what sort of accuracy one can expect if the unit was in a car doing, say, 100km/h. Keep up the good work. (D. B. S., Artarmon, NSW) • 2m is a bit long for a cable carrying TTL serial signals. It might or might not work; it could be flaky. As the GPS serial is usually only 9600 baud, you might get away with it. Still, you would be better off using a GPS module with an external antenna socket, mounting it near the Advanced GPS Computer and then running a 2m shielded antenna cable to an appropriate antenna mount. If you did want to extend the data cable, we suggest you use a shielded cable. The speed accuracy is down to the GPS module. The data for the VK2828 module we used suggests a speed error of less than 0.1m/s (around 0.3km/h). In our experience, the readings are usually within 1km/h, with the update lag introducing more noticeable errors than the speed accuracy itself. That is because many GPS modules only produce data once per second, plus there is a processing delay. GPS Computer battery charging I built the Advanced GPS Computer, and everything seems to be working OK, but the battery takes forever to charge. Could I lower the value of the 10kW resistor between pin 5 of IC4 and ground to say 4.7kW? It will draw an extra 100mA or so from the power source, but I don’t see why that would matter. (P. C., Balgal Beach, Qld) • The battery we used in our prototype siliconchip.com.au did not have a specified maximum charge current, hence the 100mA setting, which is quite conservative. Lower charging currents will be better for long-term cell longevity too. If you are confident that your battery can handle a higher charging current, then the 10kW PROG resistor can be reduced as far as 2kW. That will give a 500mA nominal charge current, which is the limit of the MCP73831 charge controller IC. A 4.7kW resistor should give around 212mA, as you suggest. USB socket part code query What type of mini USB socket have you used in the Battery Multi Logger (February & March 2021; siliconchip. com.au/Series/355)? The parts list only describes it as an “SMD mini-USB socket”. (B. C., Bray Park, Qld) • We aren’t sure who originated this design but it seems that virtually everyone has copied it. While there are surely incompatible SMD Mini Type-B sockets available, many of the parts you can find will fit this same footprint. One part we know is suitable is the EDAC Inc. 690-005-299043, available from Digi-Key (Cat 1511206-1-ND) and Mouser (Cat 587-690005-299-043). Substitute Mosfet for Ultrasonic Cleaner I’m thinking of building your High Power Ultrasonic Cleaner (September & October 2020; siliconchip.com. au/Series/350), but I’m finding most suppliers of the SUP53P06-20 Mosfet are out of stock. Jaycar seems to still have a few (Cat ZT2464), but if I can’t get those, can I use the IPP80P03P4L-04 that you sell in your Online Shop (siliconchip. com.au/Shop/7/4318)? (E. Z., Turramurra, NSW) • Yes, the IPP80P03P4L-04 should be a suitable substitute for the SUP53P06-20 in this circuit. It has high enough current and voltage Australia’s electronics magazine ratings at 80A and 30V, and its gatesource voltage on-threshold is low enough. Short circuit on Mini BackPack PCB I built your D1 Mini BackPack with WiFi (October 2020; siliconchip.com. au/Article/14599) and was able to load the demo software into it. When I power it up, the screen for entering a location appears on the LCD but the touch function is not working. Can you suggest a solution? (J. L., Tauranga, NZ) • You most likely have a short circuit somewhere on the SD card socket. The SPI pins used to communicate with the touch controller are also used for SD card socket communications. As the screen display is working, most likely, the MISO line is shorted since that line is necessary for the touch controller to work but not the screen displays. Have a close look at the pins on the SD card socket and possibly remove the SD socket if it looks as though something could be shorting out underneath. The reader followed up to confirm that this was the problem. Reflow Oven wiring diagram error I’m building Phil Prosser’s DIY Solder Reflow Oven (April & May 2020; siliconchip.com.au/Series/343). The wiring diagram, Fig.11 on page 90 of the May 2020 issue, shows the ribbon cable arrangement from CON8 to the LCD module, but pin 1 of CON8 appears to go to pin 20 of the LCD. The photo on page 89 appears correct, although I think the ribbon cable cannot be folded neatly. Also, care needs to be taken to prevent the LCD Adaptor board from shorting out on the display cover mounting clips. I’d suggest some stand-offs or insulation here. Could I have some clarification? (I. T., Duncraig, WA) • Phil Prosser responds: You are correct; Fig.11 shows the cable from the August 2021  107 controller to the LCD with pins 1 & 20 swapped. The drawing probably should have had pin 1 indicated on the ribbon cable. I should have picked that up. Yes, the photo is correct. It is possible to fold ribbon cable to ‘neatly’ swap over the pins. It is a little like origami, and it takes a little more cable, but it does work. You need to ‘squish’ it pretty hard, but a clean bend is possible. You bend the cable 90° in the opposite direction you want the corner to go in, then fold it back 180° on top of itself. This error was corrected in the online version, with errata published in the June 2021 issue of Silicon Chip. We have not had trouble with the LCD adaptor board, although thinking of the problem you describe, we wonder if you are trying to mount the adaptor close to flush with the LCD. We generally use standard 2.54mm header pins to connect the LCD adaptor board to the screen, which gives 5mm+ of separation between them. Idea to help the hardof-hearing watch TV Is there an unused audio channel on the Australian TV broadcast standards? I have searched the internet for an answer without success. Recently, TV channels have been broadcasting a secondary audio channel for the vision-impaired. I wonder if another similar facility is vacant and could be made available for the hearing impaired. Such an audio channel could exclude the background or effects sounds that make it so difficult for many hearing-impaired people to understand TV dialog. This would enable Australian programs such as current affairs to be heard with ‘clean’ dialog. It seems that once background and effects audio are mixed in, there is no way of unscrambling the combination. As an afterthought, is the primary TV broadcast audio a multichannel system so that viewers with 5.1 or 7.1 home theatre receivers can produce this effect? If so, maybe a cooperative TV broadcaster could have one audio channel (perhaps the centre channel) free of background/effects so that hardof-hearing viewers could connect to that audio and hear ‘clean’ monaural dialog. Some years ago, one of your readers suggested changing the connections to 108  Silicon Chip one ear of a pair of earphones (causing the ears to hear anti-phase) could produce clean dialog, but I have had no success with this. Any other suggestions would be most welcome. (B. H., Cornubia, Qld) • That is a great idea. While we don’t have the technical details of the Australian TV broadcast standards, channels use either MPEG2/4 digital compression and encapsulation. MPEG2 supports up to 16 audio programs, while MPEG4 supports an essentially unlimited number. So we think there is no technical reason why your suggestion couldn’t be implemented, as long as the TVs decoding the streams can handle more than one or two audio programs (and surely they should). You would have to convince the broadcasters to add those channels, however. Even people with reasonably good hearing can have trouble understanding dialog in TV programs with loud background music or sound effects. Some programs seem to have especially muted-sounding dialog. You are right that 5.1/7.1 encoded transmission usually have the centre channel carrying speech and little else. This is a good reason to have a surround sound system with a centre channel (even if you don’t need the rear channels), as it can make dialog significantly more intelligible. Not all broadcasts have surround sound encoding, though. Ultrasonic Anti-Fouling fault LED flashing I have built your Ultrasonic Anti-Fouling MkII (May & June 2017; siliconchip.com.au/Series/312) from a Jaycar kit. During the testing step, without the transformers installed, I adjusted and measured the following voltages: Input: 14.3V Between pins 5 & 14 of IC1 socket: 4.95V TP1: 1.155V TP2: 0.5V 2200μF capacitor: 0V When power is applied, the green LED comes on for about three seconds, then goes off, and the fault LED flashes. I tested all the resistors with a multimeter before fitting and have now removed and replaced them with new resistors, a new 20MHz crystal and even a couple of the capacitors. No Australia’s electronics magazine change, still the fault light is flashing. I’ve covered each high-voltage part and under the crystal with conformal coating to make sure it does not short on the board. I tried adding a 470W 1W resistor between the drain and source of the Q5 Mosfet, as you’ve suggested in the past to fix similar faults, but that didn’t help either. I also replaced the 2200μF 25V capacitors that came with the kit with Rubycon 25ZLH2200MEFC16X20 capacitors but still get the same fault light. Does it matter that it does not say “low ESR” on the packet? (T. S., United Kingdom) • Those Rubycon caps are suitable; they are listed as low-impedance. As it seems the capacitors are not leaky, we think that Mosfet Q5 isn’t charging the capacitors. Check this Mosfet and whether it is being driven at its gate when power is switched on. There should be a square wave at pin 6 of IC1, and the gate voltage of Q5 should start to increase above the source. Over a few seconds, this voltage should go above 3V, and the 2200μF capacitor should begin to charge. Read the section entitled “Soft start facility” in the instructions, and check if this is happening with your Anti-Fouling unit. Running SC200 from a 35-0-35V transformer I have a quick question concerning the SC200 Power Amplifier modules (January-March 2017; siliconchip. com.au/Series/308). I’ve read in your articles that for the lower power version, using a 160VA transformer with 30-0-30V secondaries, you suggest changing the 22kW resistor between the collector of Q7 and ground to 15kW, and the two 6.8kW resistors at the collector of Q6 to 4.7kW. As I’m using the Ferguson transformers from my old ETI500 with 35-0-35V secondaries, should I change those resistors to 18kW and 5.6kW, respectively? (T. B., Bumberrah, Vic) • The values you have suggested are about right. MMBasic and PRINT USING I have looked in all the MMBasic Manuals (versions 4.5 to 5.05.03) and on Geoff Graham’s Maximite website, but I cannot find any reference to the siliconchip.com.au PRINT USING command. Is there a workaround? I have several BASIC programs I want to convert to MMBasic from the Amiga, Amstrad, Commodore 128 and TRS-80. Also, could you let me know how many articles are in the series “Getting Started with the Maximite”, which I believe started in February 2017? (R. M., Melville, WA) • Geoff Graham responds: As you have discovered, PRINT USING is not implemented in MMBasic. Use the Str$() function instead, which provides a lot of the same functionality (although the syntax is different). The “Getting Started with the Micromite” articles were published in the February, March, May & June 2017 issues. See siliconchip.com.au/ Series/311 Sourcing parts for Ultra-LD Mk.4 Amp I would very much like to build the Ultra-LD Mk.4 200W amplifier, power supply and Mk.3 speaker protector (July-October 2015; siliconchip.com. au/Series/289). I’m starting to investigate the availability of parts before deciding whether to proceed. Are there any parts in those designs that will likely be hard to find? Also, this would be my first Silicon Chip build, and I don’t have any preferred suppliers. I see your references to suppliers such as element14, Rockby, Altronics, Mouser, Digi-Key and Jaycar. I also see that Altronics have a kit for the power supply, and I can obtain the circuit boards plus the SMD parts for the Speaker Protector Mk.3 from Silicon Chip. Does anyone supply more complete kits for the amplifier at all? As you can understand, shipping costs will be significant if I need to source lots of partial shipments (to New Zealand) from different suppliers. Sourcing the correct transformer is a problem. I haven’t found any suppliers that list a version with 2x40V plus 2x15V secondaries. The power supply kit available from Altronics doesn’t appear to include the transformer. I have had discussions with a transformer manufacturer here in Christchurch, but I’d need more detail on its specifications before proceeding. If I need to have a transformer built, can I assume the following? The siliconchip.com.au 40-0-40 secondary will need to handle up to 300VA continuously. It should preferably have a silicone steel core, and the lowest practical winding resistance using copper, not aluminium. (J. G., Christchurch, NZ) • As far as we know, all the parts to build those modules are still available. There are a few parts that you will probably have to order from us. That includes the PCBs plus the frontend transistors for the Ultra-LD Mk.4 amplifier modules, we sell these at: siliconchip.com.au/Shop/7/3400 The PCBs and other parts can be found at: siliconchip.com.au/ Shop/?article=8959 As for the less commonly available parts, it depends on which supplier(s) suit you best. We suggest you try Mouser or Digi-Key first, as they are likely to have the largest proportion of the components you need, and you will be ordering enough to get free delivery. They send out orders pretty fast; usually, we receive parts from those two suppliers within a week of ordering. For the remainder of the components, especially for ‘generic’ things like capacitors and through-hole resistors, try your local Jaycar store. Altronics have a good selection too, and if you will be ordering the power supply kit from them, you can get many of the other parts delivered at the same time. As for the transformer, you are correct that the Altronics part we used has been discontinued and it’s difficult to find a replacement. You could have a transformer made, but also consider using two separate toroidal transformers, one around 300VA with two 40V secondaries and one smaller 2x15V (say 30VA). Both are available off-the-shelf. The only real disadvantage of this configuration is the extra space and a bit more wiring. There are some advantages - you might get a bit more power for the main amplifier modules since you won’t have the preamp draw on that transformer. Your suggestions for the transformer specifications seem sound, although you didn’t mention it being toroidal, which we strongly recommend as they have lower external magnetic fields. If you do have to get one made, see if you can get it with an outer electrostatic shield layer. That helps to reduce the hum field. Australia’s electronics magazine Faulty batch of transistors I purchased several Ultra-LD Mk.4 Amplifier PCBs from your Online Shop, along with the required HN3A51F and HN3C51F transistors. This project was published in the July-October 2015 issues (siliconchip. com.au/Series/289). Following the 12-step setup procedure in the third article, steps 1 to 11 were successful, but I could not achieve the desired offset voltage (step 12) on any of the six amplifiers I assembled. The voltage across the amplifier outputs is far too high. My understanding is that it should be almost 0V. VR2 has practically no effect on the DC level. The voltages across the 68W emitter resistors of Q2a & Q2b measure 60mV rather than the 135mV specified; the voltage across the 12kW resistor in series with LED1 is 20V, not 24V; and the voltage across the 330W resistor at the emitter of Q3a is 580mV rather than 600mV. When I feed a signal generator into the amplifier, the amplifier goes into distortion for all frequencies above 1kHz. Interestingly, all six modules are performing (faulting) precisely the same. I think the fault is with the HN3C51F transistors (Q2). I am confident that the output stage is stable and is operating correctly. (I. P. V., Karrinyup, WA) • We tested several of the HN3C51F transistors that we have in stock, and it seems that we have received a batch of duds. It isn’t that they are out-of-spec transistors; they do not behave like transistors at all, and different samples we tested all behave differently. So it must be a manufacturing failure. Luckily, we were able to find and source a reasonable number of the only compatible substitute part, also now discontinued, the IMX8-7-F. We have tested several of the devices that we received, and they seem to be fine. So from now on, we will supply IMX8-7-F transistors instead of HN3C51F (siliconchip.com.au/ Shop/7/3400) and we will send you replacements for the faulty transistors you received. Luckily, Q2 acts as the current mirror for the input pair, so the performance of these transistors is nowhere near as critical as the HN3A51Fs. We August 2021  109 still have a reasonable number of those in stock. By the way, it looks like the original circuit diagram (Fig.1 on p34-35 of the August 2015 issue) had an error. The 135mV specified for the 68W emitter resistors of Q2a & Q2b should be closer to 68mV as the 2mA from Q3a is split between these two resistors in the quiescent condition. Hence, your voltage measurements were all close enough to be considered correct. Operating hydronic heating during blackout Last Wednesday, a storm broke hundreds of trees near our home, and this is the sixth day without power. We have hydronic heating and plenty of gas, but we can’t run it because the installer says that Bosch boilers are not compatible with generators. They gave no technical explanation for why this is the case, nor any solution. A local electrician said to connect Neutral to the generator ground, which sounds dangerous to me. I have also heard about difficulties powering stationary computers, washing machines and some fridges from generators. Is it possible to run the hydronic heating controller from a generator? (V. K., Mt Dandenong, Vic) • It’s difficult to answer your question without knowing what sort of generator you have. Generator outputs vary considerably depending on whether they are electronically synthesised (inverter generator) or not, and whether they have a pure sinewave output, modified sinewave, square wave etc. If you have an inverter generator with a pure sinewave output, virtually any equipment should be able to run from it the same as it does from the mains. Just make sure that the generator has sufficient peak and continuous current/power capability for the load(s) attached. The pure sinewave output would be cleaner than the typical mains waveforms! The primary power consumption in a hydronic heating system will be the water pump. If the pump is modestly sized, it will probably not draw more than a few amps, so even a modest pure sinewave inverter running from a reasonably-sized lead-acid battery should be able to run it. We do not suggest running sensitive 110  Silicon Chip loads like computers or computercontrolled equipment from a generator without a pure sinewave output. Their waveform can be very distorted, and the amplitude and frequency can vary considerably. That is probably what you are referring to when you mention stationary computers, washing machines and fridges. Easy way to calibrate multimeters I have seven multimeters. Many of them are not used regularly, so I have stored them without batteries in the original boxes, and they remain in good condition. It would be expensive to get them professionally recalibrated, so I am building the Precision 10V DC Reference for Checking DMMs (March 2014; siliconchip.com.au/Article/6729) and have ordered 10W, 100W, 1kW, 10kW & 100kW ±0.1% resistors. I plan to put all these in an enclosure. I know this will not be the same as getting them professional calibrated; it is only to check that they are still within their manufacturer’s specs so that I can use them with confidence. I have ordered the AD587JNZ and the resistors from element14. Do you have any comments on this? (R. M., Melville, WA) • That sounds like a reasonable approach. You will probably find that many of your multimeters are still spot on. They can drift over time, but don’t always do so. You could also use such a setup to calibrate the lower current ranges, in combination with a variable bench supply, ideally with an adjustable current limit. You would need to calibrate one meter’s voltage ranges first. Connect the meter in series with one of the lower-value precision resistors, with the calibrated meter across the resistor. Adjust the supply voltage until you get very close to 10mV across the 10W resistor. You then know that the current is very close to 100mA. The resistor dissipation will be 100mW in this case, so keep in mind the resistor’s power rating. Induction Motor Speed Controller radiates EMI I have built your Induction Motor Speed Controller (April & May 2012; Australia’s electronics magazine siliconchip.com.au/Series/25) from an Altronics kit (Cat K6032) for use on my pool pump, as per the instructions included with the kit. The pump starts and runs as described, but the controller is emitting RFI that interferes with our AM radio reception. The interference is quite evident and disturbing. Our AM radio uses a loop antenna mounted in the ceiling and gives excellent interference-free reception, unless the controller is running. The controller is located in the pool shed, which is about 10 metres from the house in the corner of our yard, so I cannot increase the physical separation. I am also concerned that I will be causing a nuisance to my neighbours. The pump being controlled is an 860W Davey Silensor which, according to my power meter, is drawing around 990W without the controller and about 330W with it. So it should be well within the controller’s capacity. The controller and pump leads are both around 1.8m long and cannot be shortened significantly. The Altronics kit came with a plastic case, as per your article. The pool shed is metal and is not Earthed in any way (I’m not sure if that is required). The radio and pool shed are on the same mains circuit. Please give me suggestions on how I can reduce this interference. (J. M., via email) • We tested whether the IMSC interfered with AM radio reception during the development phase. We did this while it was connected to a pool pump and operating. Bringing a portable AM radio close to the IMSC only resulted in a small amount of hash pickup at a range of about 1m. With the radio more than 2m away from the controller, very little to no interference was apparent. So your controller appears to be creating a great deal more EMI/RFI than our prototype. We therefore suspect that your problem is related to noise coupled onto the mains wiring, rather than direct radiation from the unit or its wiring. First, check your mains Earthing. The effectiveness of the line filtering is only as good as the Earthing. This could be a problem if the controller is at the end of a long cable run, and the Earth impedance is on the high side, or if your domestic Earth connection is not good. You might need to have an electrician install an Earth stake in the pool shed. continued on page 112 siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip FOR SALE FOR SALE KIT ASSEMBLY & REPAIR LEDsales VINTAGE RADIO REPAIRS: electrical mechanical fitter with 36 years ex­ perience and extensive knowledge of valve and transistor radios. Professional and reliable repairs. All workmanship guaranteed. $17 inspection fee plus charges for parts and labour as required. Labour fees $38 p/h. Pensioner discounts available on application. Contact Alan, VK2FALW on 0425 122 415 or email bigalradioshack<at>gmail. com LEDs and accessories for the DIY enthusiast PMD WAY offers (almost) everything for the electronics enthusiast – with full warranty, technical support and free delivery worldwide. Visit pmdway.com to get started. LEDs, BRAND NAME AND GENERIC LEDs. Heatsinks, LED drivers, power supplies, LED ribbon, kits, components, hardware – www.ledsales.com.au Lazer Security For Quality That Counts... QUALITY LED PRODUCTS + MORE Massive parts clearance sale, limited stock. Go to lazer.com.au ASSORTED BOOKS FOR $5 EACH Electronics and other related subjects – condition varies. Some books may have already been sold. Bulk discount available. All books can be viewed at: siliconchip.com.au/link/aawx Email for a postage quote, quote photo numbers when referring to a book: silicon<at>siliconchip.com.au TRONIXLABS PTY LTD would like to thank all of our customers for their support and feedback. For any enquiries or customer technical support, please email support<at>tronixlabs.com PCB PRODUCTION PCB MANUFACTURE: single to multi­ layer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www.ldelectronics.com.au DAVE THOMPSON (the Serviceman from S ilicon C hip ) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, NZ but service available Australia/NZ wide. Email dave<at>davethompson.co.nz KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, address & credit card details, or phone Glyn (02) 9939 3295 or 0431 792 293. WARNING! Silicon Chip magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of Silicon Chip magazine. Devices or circuits described in Silicon Chip may be covered by patents. Silicon Chip disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. Silicon Chip also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. siliconchip.com.au Australia’s electronics magazine August 2021  111 If the Earth is solid, then it would be worthwhile trying a bigger mains filter. This could be as simple as winding the mains wires through a toroidal ferrite core. Speaker Protector not sensing AC I have built the October 2011 Loudspeaker Protector module (siliconchip. com.au/Article/1178) from an Altronics kit (Cat K5167). I configured it for my supply rail voltage and tested it with the prescribed method, and it seemed fine. However, as soon as I connect the AC sense lines from my transformer, it refuses to work. Connecting AC sense to the positive rail as detailed in the instructions and performing all other tests shows the module to be working. Can you enlighten me as to the likely cause of this problem? (D. J., Mandurah, WA) • The first thing to do is check that you have wired up the transformer to the AC sense terminals correctly. Typically, you would have a centre-tapped winding with the centre tap Earthed and the other connections going to both your bridge rectifier AC terminals, and the terminals of CON2 on the Speaker Protector. Assuming the connections are correct, verify that the base voltage of Q2 is low (below 0.2V) when the AC voltage is present at the AC sense input. If that is incorrect, then check diodes D2 and D3 and the transistor Q1 to ensure they are orientated correctly, have good solder joints and are not faulty. That it worked with a DC test suggests transistor Q1 is working OK and that at least one of diodes D2 & D3 is functioning correctly. It could be a problem with the resistor or capacitor values around Q1. If the 470nF capacitor is not soldered correctly or has the wrong value, the circuit will work with DC voltage applied but not AC. Similarly, if the resistor values are wrong, the circuit might not hold up through dips in the AC voltage. Flexitimer with higher supply voltage Many years ago, I built the PICBased Flexitimer Mk.4 (June 2008; siliconchip.com.au/Article/1847) from 112  Silicon Chip a Jaycar kit (Cat KC5464). Can it be modified to run from a 24V supply? (J. S., via email) • You need to change the relay to a compatible type with a 24V DC coil, the 470μF capacitor to a 35V rated type, and the 1kW LED current-limiting resistor to 2.2kW. AEE ElectroneX.......................... 7 Incorrect component in low ohms meter Control Devices..................... OBC Advertising Index Altronics...............................83-86 Ampec Technologies................. 25 I have built the Low Ohms Tester by John Clarke from the June 1996 issue (siliconchip.com.au/Article/4987), but I can’t get it working. The text says that the voltage at pin 2 of IC1 should be the same as pin 3. Adjusting VR1, I can get 2.4V on pin 3, so it appears REF1 is working OK. But the voltage at pin 2 is 1.64V. I have replaced IC1 and Q1 to no avail. (N. L., Christchurch, NZ) • Since you have replaced IC1 and Q1, that seems to rule out either component being faulty (which would explain what you are seeing). However, if Q1 is the wrong type or orientated incorrectly, that would cause this sort of fault. The only other possibilities are a lack of continuity or incorrect value with the 2.4kW resistor, trimpot VR2 or the 200W resistor. Try changing range switch S2 to see if that has any effect; if it does, it is likely one of the latter three components at fault. Note that if this part of the circuit is operating normally, pin 6 of IC1 should be around one diode drop (approximately 0.6V) below the voltage at pins 2 & 3. Dave Thompson...................... 111 Pulse generator circuit wanted Vintage Radio Repairs............ 111 I’m interested in building a pulse generator. I found a pulse generator design in Practical Electronics, February 1979. Can you suggest a circuit as simple as that one, but up to date with similar specifications and features? (R. M., Melville, WA) • We published a pulse generator circuit in the Circuit Notebook section of the November 1997 issue, which has similar features to the one you refer to (siliconchip.com.au/Article/5833). However, there was no PCB design to accompany that circuit. You could also build up the Practical Electronics design as there is nothing wrong with it. All the parts used in that circuit are still available. SC Australia’s electronics magazine Digi-Key Electronics.................... 3 Emona Instruments................. IBC Hare & Forbes............................. 9 Jaycar............................ IFC,53-60 Keith Rippon Kit Assembly...... 111 Lazer Security......................... 111 LD Electronics......................... 111 LEDsales................................. 111 Microchip Technology.................. 5 Ocean Controls......................... 11 PMD Way................................ 111 Silicon Chip Shop...............96-97 Switchmode Power Supplies....... 6 The Loudspeaker Kit.com......... 10 Tronixlabs................................ 111 Wagner Electronics................... 63 Notes & Errata Ultra-LD Mk.4 Amplifier, July-August 2015: the circuit diagram (Fig.1) incorrectly specifies 135mV across the 68W emitter resistors of Q2a & Q2b, the correct value should be around 68mV. The September 2021 issue is due on sale in newsagents by Thursday, August 26th. Expect postal delivery of subscription copies in Australia between August 25th and September 10th. siliconchip.com.au “Rigol Offer Australia’s Best Value Test Instruments” Oscilloscopes NEW 200MHz $649! 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