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APRIL 2023 ISSN 1030-2662 04 9 771030 266001 $ 50* NZ $1290 11 INC GST INC GST WIDEBAND Fuel Mixture DISPLAY SYourilicon C hirp own pet cricket 500 class-d amplifier use two inexpensive pre-built modules to make the W A T T Stay connected with our 4G Antennas & adaptors Compatible with 2.4GHz & 4/5G networks for cross-compatibility 1 5dBi Antenna • Magnetic mount • Suitable for LTE, AMPS, GSM, PCS, UMTS and Wi-Fi • 2m lead with FME connector • 337mm long AR3340 ONLY $59.95 4 5m SMA Extension Lead 5 SMA to Induction 3G Plug 6 SMA to Modem Leads • Low loss • 50Ω coax • Flexible lead WC7824 ONLY $49.95 7dBi Antenna • Magnetic mount • 3m lead with FME connector • 435mm long AR3344 ONLY $74.95 2 • Adhesive backing AR3330 ONLY $24.95 7dBi Spring Mount Antenna • ½ wavelength design • 5m lead with FME connector • 740mm long AR3342 ONLY $149 3 3dBi Glass Mount Antenna • ¼ wavelength design • 3m lead with FME connector AR3338 ONLY $49.95 Range of leads that plug into the antenna socket on your USB modem. AR3332-AR3336 ONLY $24.95 EA SMA to Huawei E160/618 Plug AR3332 1 2 SMA to Sierra TS9 Plug AR3334 Telstra 4G USB Modem AR3336 We stock a great selection of Networking Antennas, Leads, Plugs, Sockets and Adaptors to improve the range and reliability of your wireless network. Explore our wide range of wireless networking products, in stock on our website, or at over 110 stores or 130 resellers nationwide. jaycar.com.au/4gwireless 1800 022 888 Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. Contents Vol.36, No.04 April 2023 16 Underground Communications Like underwater communication (covered last month), communicating underground such as in mines or tunnels can be quite tricky. There are various techniques like using repeaters, mesh networks or groundpenetrating low-frequency radios. This article covers all that and more. By Dr David Maddison Technology feature 54 T48 Universal Programmer The T48 programmer by XGecu is the latest revision to the popular TL866II line (often called the ‘MiniPro’). XGecu sent us one to review and we wound up pleasantly surprised, although there are some newer chips it cannot (yet) program. By Tim Blythman Programmer review 80 Using TestController TestController is a free software program that can be used to automate much of the logging and analysis required when operating multiple test instruments. Data can be received via serial, USB, Bluetooth, WiFi, LXI and GPIB connections, making it versatile. By Richard Palmer Software guide 26 500W Class-D Mono Amplifier This 500W Class-D single-channel (monoblock) amplifier is for those who want serious power on a budget. Construction is made simple by utilising two pre-built modules and not much else. By Phil Prosser Amplifier project 40 Wideband Fuel Mixture Display, Pt1 Measure your engine’s full range of air/fuel ratios in real-time to make sure it’s running optimally. The Fuel Mixture Display is capable of conveniently showing the value on a computer, smartphone or tablet via Bluetooth. By John Clarke Automotive project 60 Automated Test Bench Our veritable ‘Swiss Army Knife’ Test Bench can provide test voltages, test signals, vary a resistance, switch a component in or out of circuit and even measure some voltages. You can then run all these tasks using automation software such as TestController. By Richard Palmer Test & measurement project 72 Silicon Chirp – the pet cricket This pet cricket will keep you company, only needing to be occasionally ‘fed’. It sounds just like the real thing, and can be set to only make a sound in the dark, using just a single lithium coin cell. It’s even able to mimic other animals like a frog or bird! By John Clarke Toy project Page 26 5 0 0 WATT class - d amplifier WIDEBAND Fuel Mixture Display Page 40 Silicon Chirp the pet cricket Page 72 2 Editorial Viewpoint 5 Mailbag 53 Subscriptions 84 Serviceman’s Log 92 Product Showcase 94 Vintage Radio Browning-Drake 6A by Dennis Jackson 100 Circuit Notebook 104 Online Shop 106 Ask Silicon Chip 111 Market Centre 112 Advertising Index 112 Notes & Errata 1. Lithium battery & case for Arduino Uno 2. Three-phase sinewave generator 3. LC resonance bands graph for Q Meter 4. Cell under-voltage protection circuit 5. ESP32-based millisecond clock 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. Advertising Enquiries (02) 9939 3295 adverts<at>siliconchip.com.au Regular Contributors Allan Linton-Smith Dave Thompson David Maddison – B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Geoff Graham Associate Professor Graham Parslow Dr Hugo Holden – B.H.B, MB.ChB., FRANZCO Ian Batty – M.Ed. Phil Prosser – B.Sc., B.E.(Elec.) Cartoonist Louis Decrevel loueee.com Founding Editor (retired) Leo Simpson – B.Bus., FAICD 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) 6 issues (6 months): $65 12 issues (1 year): $120 24 issues (2 years): $230 Online subscription (Worldwide) 6 issues (6 months): $50 12 issues (1 year): $95 24 issues (2 years): $185 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 194, Matraville, NSW 2036. Phone: (02) 9939 3295. ISSN: 1030-2662 Printing and Distribution: 24-26 Lilian Fowler Pl, Marrickville 2204 2 Silicon Chip Editorial Viewpoint Renewable energy costs are seriously understated by the media If you have read Dick Smith’s autobiography (that I reviewed in the January 2022 issue) or know much about the founder of Australian Geographic, you would know he is definitely an environmentalist. However, he has also been known to heap scorn on renewable energy policy, and he has a point. The costs and difficulties involved with renewable energy generation are grossly understated in the media, so much so that the public and policymakers are likely being misled. This isn’t helped by the somewhat vague “GenCost” reports from the CSIRO and AEMO, producing headlines like “Renewables cheaper than coal, says CSIRO” and “CSIRO/AEMO study says wind, solar and storage clearly cheaper than coal”. Having read the latest GenCost report (you can, too; see the link below), I think it’s hard to come to that conclusion without ignoring important facts. Firstly, I’m not sure exactly who the report is written for, but I don’t see how a journalist or politician could understand it. You would have to be an expert in the field, except that experts probably don’t need to read such a report. Also, I might have missed it, but I couldn’t find a proper comparison of the long-term costs of the different generation methods. Graphics and tables show capital costs per MWh for various generator types, but while they have a comparison of the “levelised cost of electricity” (LCOE) for various technologies, they do not have such a comparison that includes the cost of storage for renewables. Calculating such costs for coal, natural gas or nuclear power generation is relatively straightforward. Choose a reasonable lifetime for a power plant (say, 50 years). Take the cost of building the plant, add the expected maintenance, upgrade and fuel costs, then divide by the power rating in MW and lifespan in years. That gives you the dollars per MW per year. It’s harder to calculate that for renewables, though. For a start, you have to decide how much storage (realistically, batteries) you need for them to act as a base-load power source. The report implies that the cost of those batteries will be the largest single expense by far. They give a capital cost figure of around $2,859,000 per MW for 8-hour battery storage. You also need to determine how many times the batteries (and possibly generators) will need to be replaced in the period of interest. Most current battery technologies are unlikely to last 50 years, so they might have to be replaced several times. Multiply $2,859,000/MW by the number of megawatts and number of times it will need to be replaced, and the cost of batteries alone could easily exceed the cost of a traditional power plant. We aren’t even sure if the figures include the cost of recycling the battery at the end of its life etc. It all comes down to what assumptions you make about the need for batteries. However, it’s evident that neither wind nor solar power can always be relied on to deliver power when needed (especially at night!). The report discusses scenarios with up to 90% “variable renewable energy” generators. I question the stability of a grid with anything like that sort of percentage without enormous battery banks. Given the modest cost increase figures being presented, I doubt they have accounted for that fully. Read it for yourself and see if you think it is a helpful document for our policymakers. CSIRO report: https://publications.csiro.au/publications/ publication/PIcsiro:EP2022-2576 I would like renewables to be a viable source of large-scale power generation. However, wanting something to be the case doesn’t make it true. Policymakers can only make the right decisions with honest and transparent information on all the costs involved. by Nicholas Vinen Australia's electronics magazine siliconchip.com.au Widest selection of electronic components™ In stock and ready to ship au.mouser.com australia<at>mouser.com 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 has the right to edit, reproduce in electronic form, and communicate these letters. This also applies to submissions to “Ask Silicon Chip”, “Circuit Notebook” and “Serviceman’s Log”. Another test equipment giveaway Like some of your older readers, I also have several pieces of test equipment available to readers for pickup at no cost. All are working, and I have full service manuals for most items (service manuals are not giveaways), but the information is available: 1. Goodwill GVT-417 audio millivoltmeter 2. Sound Technology 1700B noise/distortion analyser – automatic (the extra low distortion oscillator isn’t working properly, but the standard oscillator is working) 3. HP3581 wave analyser to 50kHz; tuneable, can track an input 4. B&K 1623 tracking audio filter 5. Genrad GR1982 Class 1 Sound level meter with octave filter 31Hz-16kHz, includes microphone and calibrator (31Hz-4kHz) 6. Rigol 815 Spectrum analyser with tracking generator – the front end preamp (chip) and RF switch (chip) are damaged, but I have the parts for a reader with good SMT soldering skills. The items are located in Sydney, approximately 5km from the city centre. Please email Silicon Chip (silicon<at> siliconchip.com.au) if you are interested and they can pass the enquiry on to me. Braham Bloom, EmiSolutions. Also, a Silicon Chip magazine giveaway Many thanks for a great magazine, but the time has come for a spring clean (in the summer). I now have over 100 magazines to give away to a good home. My start was back in the days of Radio, Television & Hobbies and I haven’t missed a copy of Silicon Chip since you started. They will need to be collected from Yarra Glen in Victoria. Please email Silicon Chip if you are interested and they will pass it on to me. Ray Lopez, Glenray Electronics. Source code for WiFi DC Load is now available I have had requests for the source code for the WiFi-­ Controlled Programmable DC Load (September & October 2022; siliconchip.au/Series/388), so I placed it on GitHub at https://github.com/palmerr23/ESP32-DCLOAD/ This source has also been added to the download on the Silicon Chip website: siliconchip.au/Shop/6/6518 Note that the code is quite extensive and requires multiple libraries from various locations in addition to the files in the repository. I’ve put a “readme.md” in the source folder that briefly outlines the requirements. I recommend using Arduino v1.8 rather than v2.x due siliconchip.com.au to its better ESP32 support. Otherwise, my ESP32-OTAand-File-Manager fills most of the gap with V2 (except that there’s still no exception decoder). Another constructor and I are currently working on some upgrades – mainly improvements to the battery test function, which currently exits early sometimes, and to keep the result screen in view until there’s user action, rather than having it disappear after a few seconds. If you have a wish list, we’d be happy to look at them. Richard Palmer, Murrumbeena, Vic. Offset drivers predated Duntech I have been subscribing to Silicon Chip magazine for many years and still enjoy reading every article, and I have built numerous kits over the years. I started with Electronics Australia in the early seventies and found Leo Simpson’s articles on EA and Silicon Chip very interesting. In the November 2022 project article on the Active Monitor Speakers (siliconchip.au/Series/390), Phil Prosser mentions offsetting the drivers and cites Duntech speakers from the nineties as an example. British company B & W used this approach well before that in the seventies, with their model DM6 speakers that were reviewed in EA, August 1976, page 22. I purchased a set of these soon after reading that, and they are still going strong. They are why I have not built any of the many excellent speaker designs published in Silicon Chip, although I am tempted to try the Active Monitors. If I do, I have to decide which ones are better and use them on my hifi system, relegating the others to the TV sound system. Lee Cockram, Dianella, WA. Phil Prosser comments: B&W certainly did use offset drivers. I hope I didn’t make it seem like Duntech were the first, but they certainly took the concept to extremes and leaned heavily on it in their branding and design philosophy. I don’t own any B&W speakers, but I certainly do rate them highly. I have found the quality of drivers such as those B&W use, even from the ‘60s and ‘70s, to be excellent. If you have an inkling to build some speakers, give the Active Monitor Speakers a try. They are very fine and you can tune them to your personal taste. GPS Clock project is inspiring I am currently restoring a tower clock with a 1.8m face, with geared movement and gearbox. It originally used an old-school 1 RPM synchronous motor that is beyond repair. Your GPS Analog Clock Driver has inspired me in modernising my 50-year-old clock. Chad Roberts, Auckland, NZ. Australia's electronics magazine April 2023  5 Making ESP8266 work with AU/NZ WiFi networks I built Geoff Graham’s excellent GPS-synchronised Analog Clock (September 2022; siliconchip.au/Article/15466) only to discover that the GPS coverage inside my home is poor. So I modified the circuit to use a WeMos D1 Mini following the description in the November 2022 issue. However, I ran into some problems with the precompiled firmware, eventually solving them all. My home WiFi network is provided by a mesh based on routers from one of Australia’s largest broadband providers. I found that the D1 Mini would never connect to the WiFi access point nearest the clock. However, if I moved the clock to a different part of the home, it would always connect to those other access points. Because my access points are meshed, they all have the same SSID. I discovered that the problem access point always auto-configures itself onto WiFi channel 13, with the other access points on channels between 1 and 11. A web search suggested that many other folks outside North America have encountered problems with Arduino ESP8266 designs and WiFi channels 12-14. By forcing the troublesome access point onto a channel between 1 and 11, the problem went away. I was then able to ‘fix’ the Arduino to connect to channel 13 by downloading all the latest required libraries into the Arduino IDE and recompiling the software from its source code. Unfortunately, while it then connected to channel 13, I noticed that the clock would occasionally lose time. After investigating the logs, I found that the Arduino was not reliably connecting to my WiFi – it sometimes failed to connect. My WiFi mesh publishes two SSIDs: my regular network name and a ‘guest’ network, both on the same WiFi channel. I wondered if the Arduino might be confused by the presence of a guest network from the same access point. Lo and behold, disabling the guest solved the unreliable connection problem. I modified the source code slightly, adding debugging statements to list the visible SSIDs, channels and signal strengths of all the visible access points. I noticed that the D1 Mini was poor at estimating signal strength. I consistently saw a variation of up to 10dB of signal strength between the guest and the ‘real’ SSIDs for all my access points and the neighbours’ access points. That seemed strange because the same hardware transmits both guest and ‘real’ SSIDs, so the signal strength should be the same. I speculated that when the guest signal 6 Silicon Chip strength appears greater, the Arduino may fail to connect to the ‘real’ SSID for some reason. By changing the Arduino WiFi library to the “wifiMulti” library (which supports more than one SSID) and configuring both the guest as well as the ‘real’ SSIDs into the Arduino, the WiFi connections were rock-solid every time, and my clock has been accurately keeping time for the past month. In addition to supporting more than one SSID, I made some other minor changes to the source code: adding comments, support for the backspace character in configuration data, a change to the LED behaviour to reduce power consumption a little, and adding SSID and WiFi channel number into the dummy ESP82 sentences that are written to the serial port. That last change makes it easier to see what is happening as you watch the Arduino connect to your access point – and you can watch the signal strengths apparently vary in real time! Because of the added configuration options, I had to relabel the configuration menu to accommodate the new settings. I hope this information and the software modifications are of interest and useful for others too. Stefan Keller-Tuberg, Fadden, ACT. Comment: WiFi channel incompatibility between regions has been a problem for a long time; it’s great that you came up with a solution. We’ll make the revised software (including source code) available for download. We are also going to publish a new WiFi/NTP-based ‘GPS’ time source in the near future that uses the Raspberry Pi Pico W. We think it will be more reliable than the D1 Mini version. Soundbar built with modifications I thought that you and your readers might be interested in the soundbar project that my friend and I built from the design in the August 2022 edition of Silicon Chip magazine (siliconchip.au/Article/15426). We followed your design except for using a different amplifier and mounting it on the front of the soundbar. We used a Fosi Audio BT30D 2.1 channel Bluetooth 5.0 power amplifier. We could not obtain the amplifier suggested by Allan Linton-Smith, so we opted for this one instead. The only other modification we made was using cedar for the end cheeks. It makes installing the speaker cloth a lot easier because you can tuck it under the end cheeks, as you can see from the photos. Chris Sebastian, Coffs Harbour, NSW. Australia's electronics magazine siliconchip.com.au LEADING DISTRIBUTOR OF 37,000+ TEST AND TOOLS PRODUCTS Meeting your requirements as always Contact us: https://au.element14.com/test-and-tools-range Dual voltage supply is not a new idea On page 91 of the December 2022 issue, you published a circuit that gives two different positive output voltages using a transformer and bridge rectifier. You might like to know that the same circuit appears on page 184 of the Radio Amateur’s Handbook, 1946 edition, where it is referred to as a duplex power supply. The circuit used valve rectifiers and choke input filtering but is otherwise the same. It appears in several later editions, and may well have appeared in earlier editions. Robert Bennett, Auckland, NZ. Comment: the person who submitted that item told us that the concept didn’t originate with him, so we are not surprised that it was initially published quite some time ago. Tesla Coil article enjoyed This is just a quick note to say how much I enjoy Flavio Spedalieri’s articles (eg, the 30mm Spark Gap Tesla Coil from February 2023; siliconchip.au/Article/15657). I always purchase the paper version of the magazine when his articles are featured. I especially appreciate his inclusion of what went wrong and what he did to improve his designs. Unfortunately, modern media frequently only presents the successes and not the satisfying journey that actually gets you there. Mark Whitehead, Hawthorn, Vic. Another Tesla Coil story Back in about 1980, I built a fairly large Tesla Coil, as shown in the adjacent photo. To give you an indication of the size, the former for the secondary winding was made from four-inch (10cm) diameter drain pipe. Like the one in your recent article, it was fed from a neon tube transformer. Due to its size, the resonant frequency was much lower, and the resultant spark was fatter and longer. Initially, I used a ball-handle spark gap but achieved a much better result by wiring six automobile spark plugs in series, as shown in the photo at lower left. I thought this might be of interest to your readers. Les Kerr, Ashby, NSW. Update on 30mm Tesla Coil My article on the Tesla Coil has come up well, and I have been receiving positive feedback. I wanted to share something I learned recently. In Photo 14, on page 59 of the February issue, the arcs have distinctive striations and patterns. This is only visible due to the slower camera shutter speed I used. These striations are colloquially referred to as “The Banjo Effect” because it visually resembles a swinging banjo string. Each striation correlates to a single firing of the spark gap. Flavio Spedalieri, Frenchs Forest, NSW. Australian success story – Rode Microphones Many of your readers are unlikely to know that Rode microphones are designed and manufactured in Australia for a worldwide market. Their factory is at 107 Carnarvon Street, Silverwater, NSW. What triggered my interest in this company was visiting a camera shop that carried their products; I noticed they were made in Australia. Subsequently, I was listening to a news report recorded in the field by the ABC and received on a DAB+ receiver, and the sound made me feel as if I was where the reporter was. It was in stereo. They must have been using one of those. I have no connection to the company, which is 3300km away from me. One of your authors might like to go and interview the company as I think we should promote the success of Australian electronics companies. Alan Hughes, Hamersley, WA. Giving old computers a new life I thoroughly agree with your Editorial Viewpoint regarding serviceability and planned obsolescence in the February 2023 issue. I no longer buy multi-functional items such as TVs with built-in DVD players, preferring separate components which can be individually replaced. Over the last few years, I have also been buying ex-­ government laptops from Australian Computer Traders (ACT) in Queensland, for myself, friends and family. Other businesses also sell these on eBay, both locally and from the USA. I’ve gotten excellent service from ACT. 8 Silicon Chip Australia's electronics magazine siliconchip.com.au I concentrate on Lenovo laptops up to seven or so years old. These are relatively cheap; you can put the model and/or serial number into the support page on the Lenovo website and get all the specs of that particular computer and all the supporting documentation, including the hardware maintenance manual. The units have also had the BIOS unlocked. Lenovo supports Linux, and I put the latest version of Ubuntu Linux onto these computers with ease. Even though they can be several years old, they’re super fast with Linux. The latest version of Ubuntu (22.04) even updates the BIOS in the Software Centre. These units usually come with Windows 10 installed; I used to update the BIOS using Windows update or the Lenovo update software before installing Ubuntu, but this is no longer necessary since Lenovo started selling laptops with Linux pre-installed. They undoubtedly contribute to the kernel to ensure their product plays happily with the OS. Printers used to be a huge problem, but the better printer manufacturers now also have Linux printer software available. Epson is one, and I recently installed a Brother printer software suite onto a friend’s Lenovo T470s (six years old), running the latest Ubuntu. Proprietary printer software still needs to be installed via the terminal, but this is a printer manufacturer’s decision. Ubuntu does have its own printer software already installed that works with almost all known printers, and detects the printer the moment it is plugged in. I learn more with every computer I work on, and yes, I did brick the odd one early on. I have now learned to stop and take a break if I encounter a problem I don’t understand. Have a coffee, take a walk, enter the situation into Lenovo or Linux support sites and, so far, solutions have always come up. This may even take a week of research, but well worth the knowledge gained. I don’t work for Canonical, Lenovo, Epson, Brother or ACT, but I don’t mind acknowledging good service when I receive it. Jacob Westerhoff, via email. Did early computers have error correction? In the article on Computer Memory in the February 2023 issue (siliconchip.au/Series/393), there was a sidebar on page 15 titled “Early programs that were run more than once?” on the apparent practice of running programs several times to ensure correct output. At age 70, I have seen all sorts of architectures, and early computers are a hobby of mine; I find it hard to believe that computers capable of running complex programs did not have parity checking, but I’ll pass this along to a mailing list dedicated to early computing and let you know the consensus. Dave Horsfall, North Gosford, NSW. Comments: Looking into this a little deeper, we found the following on Wikipedia: Seymour Cray famously said “parity is for farmers” when asked why he left this out of the CDC 6600. Later, he included parity in the CDC 7600, which caused pundits to remark that “apparently a lot of farmers buy computers”. The original IBM PC and all PCs until the early 1990s used parity checking. Later ones mostly did not. 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Shop at Jaycar for: • Over 13 Arduino® Compatible Development Boards • 4 x Great Value Starter Kits • Plethora of Shields, Modules, and Sensors • Great range of Breadboards and Prototyping Accessories Explore our great range of Arduino® compatible products, in stock on our website, or at over 110 stores or 130 resellers nationwide. jaycar.com.au/devboards 1800 022 888 Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. So, some early computers had parity checking, but not all. We suspect that pre-1960, not many did. It likely depended on how critical the intended role of the computer was and whether technology realistically permitted it at the time. James Webb & RCA TV articles enjoyed I enjoyed some ‘holiday reading’ with your December issue. There were two outstanding articles in particular. The 13-page description of the amazing James Webb Space Telescope by Dr David Maddison was very informative (siliconchip.au/Article/15575). Surely, it is the most complicated piece of space hardware ever built and so well described by Dr Maddison. Ten thousand million US dollars certainly buys you a nice little telescope! I look forward to further updates on its findings. The second excellent article was Dr Hugo Holden’s 1946 RCA TV receiver restoration (siliconchip.au/Article/15593). It is a gold-medal standard restoration if I ever saw one. His meticulous attention to detail is unlike any I’ve read about before, with some very informative circuit information as a bonus. It was very much enjoyed. Timothy Ball, Kogarah, NSW. More on thermistor measurements and ECAD software I really like the idea of the Digital Boost Regulator made using internal PIC modules (December 2022; siliconchip. au/Article/15588). I think I can use that idea. On p108 of the same issue, regarding difficulties getting consistent resistance measurements of thermistors, 0.27mA through 2kW is actually much lower power than 150mW – more like 150μW. However, you could be correct that the problem is the meter test current since it’s the only variable. Luckily it’s fairly easy to measure: Get a known value resistor, ideally one close to the value of the resistance you expect for the thermistor. In this case, 2.2kW would work. Connect it to a meter and set it to measure ohms. While that meter is connected, use another meter to measure the voltage across the test resistor. You can then calculate the test current from the voltage and resistance. It’s also possible the change in resistance was caused by the way the thermistor was held, ie, in a hand or free with alligator clips. Holding it in your hand might increase the temperature to around 30°C, which could be enough to change its resistance significantly, depending on the thermistor curve. Regarding ECAD software, like many designers my age, I learned how to design PCBs with Protel years ago at work, progressing through the versions, ultimately purchasing and using Altium Designer. Having left that job and no longer with access to Altium, I started using KiCad. I’ve been quite happy with it. Don’t get me wrong – Altium Designer is very good, but it’s way more complicated than I need for the relatively simple PCBs I design. KiCad has a reasonably comprehensive library of schematic and physical parts, supports netlist transfer between the circuit and PCB, and has a Gerber plotter with a separate viewer and a handy calculator specifically for PCB design. It even supports differential pairs. It definitely has some problems, but nothing I haven’t been able to work around. The best part is it’s free – truly free, unlike some other software that’s only free until you 12 Silicon Chip Australia's electronics magazine siliconchip.com.au Discover New Technologies in Electronics and High-Tech Manufacturing See, test and compare the latest technology, products and turnkey solutions for your business SMCBA CONFERENCE The Electronics Design and Manufacturing Conference delivers the latest critical information for design and assembly. Industry experts will present technical workshops with the latest innovations and solutions. Details at www.smcba.asn.au In Association with Supporting Publication Organised by Co-located with reach some arbitrary limitation on design complexity (PCB size, part count, pin count etc). Once you reprogram all of your muscle memory for a new set of shortcuts, you can get pretty quick with it. Anyone who needs a half-decent PCB design program should try it out. David Timmins, Sylvania, NSW. Hybrid Tracking Bench Supply component failure As detailed in the Ask Silicon Chip pages of the March 2023 issue (pp100-101), I had trouble with my Hybrid Power Supply with analog controls. Phil Prosser kindly helped me troubleshoot my power supply and we found that the MC33167 switch-mode regulator had failed open-circuit. We tracked its failure down to a fault in zener diode ZD2 that had apparently caused it to go open-circuit, so it was no longer protecting the VFB pin of REG5 from excessive voltage. Phil said that he thinks the slip of a meter probe from the output of the switching regulator to the feedback pin might have led to the untimely demise of both components. Colin O’Donnell, Glenside, SA. In defence of the slashed zero As a long-time reader and subscriber to Silicon Chip magazine, I often see something in the magazine that deserves an answer. However, I only occasionally put my fingers on a keyboard to reply. Mark Hallinan’s letter to the Mailbag was one such occasion (January 2023, page 5). In his letter, Mr Hallinan argues that the slashed zero is obsolete technology and is more difficult to read than the capital O. I contend that if he finds it more difficult to read, that is probably due to the slashed zero not being used enough rather than being used too much. In most advanced European countries, the use of the slashed zero is commonplace, and I’m sure most people there would have become very familiar with reading it. Mr Hallinan admits that the slashed zero is entirely appropriate when used in alphanumeric strings. If it’s OK to use it there, surely it would be better to use it all the time so that people get used to it and find it just as easy to use as people do in Europe. The numeric zero written as a capital O is described as unambiguous, but that is only in certain instances. My amateur radio call-sign contains the letter O and it is also part of my email address. When I give my email address verbally, I have to explain that the character following the figure 5 (for South Australia) is a letter O and not a zero. That would be less of a problem if all instances of a zero were written as a slashed zero. Finally, Mr Hallinan describes the slash zero as being “so 1970s”. Does that mean that everything about that decade was inferior? To me, the years of the 1970s were the best of the 20th century. I lived and worked in four Australian capitals, spent two years working in Antarctica, and had working visits to Papua New Guinea and Norfolk Island. Let us use the slashed zero more rather than less, and there will be less ambiguity, not more. Keith Gooley, Yattalunga, SA. Comment: it’s also good practice to avoid saying “oh” when you mean “zero”, as they are two distinct characters. However, we note that some older typewriters had single keys SC for O/0 and even I/l! Silicon Chip as PDFs on USB ¯ A treasure trove of Silicon Chip magazines on a 32GB custom-made USB. ¯ Each USB is filled with a set of issues as PDFs – fully searchable and with a separate index – you just need a PDF viewer. ¯ 10% off your order (not including postage cost) if you are currently subscribed to the magazine. ¯ Receive an extra discount If you already own digital copies of the magazine (in the block you are ordering). The USB also comes with its own case EACH BLOCK OF ISSUES COSTS $100 OR PAY $500 FOR ALL SIX (+POSTAGE) NOVEMBER 1987 – DECEMBER 1994 JANUARY 1995 – DECEMBER 1999 JANUARY 2000 – DECEMBER 2004 JANUARY 2005 – DECEMBER 2009 JANUARY 2010 – DECEMBER 2014 JANUARY 2015 – DECEMBER 2019 WWW.SILICONCHIP.COM.AU/SHOP/DIGITAL_PDFS Ordering the USB also provides you with download access for the relevant PDFs, once your order has been processed 14 Silicon Chip Australia's electronics magazine siliconchip.com.au Prototyping Accessories GREAT RANGE. GREAT VALUE. 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JUST 4495 $ HG9980 Shop at Jaycar for: • Soldering & Accessories • Components, Cables and Connectors • Magnifiers and Inspection Aids • Tools, Service Aids and Chemicals Explore our full range of prototyping accessories, in stock at over 110 stores, or 130 resellers or on our website. jaycar.com.au/prototyping 1800 022 888 Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. Dr David Maddison UNDERGROUND communications Communicating between people underground, or below and above ground, is challenging because rock and soil usually absorb the radio waves used to carry voice signals. In this article, we investigate the Image Source: https://unsplash.com/photos/5p-3r7kBhKc solutions to these problems. T he underwater communications discussed last month primarily concentrated on submarines and other submersibles. Underground, there are a wider variety of locations, including mines, tunnels and cave systems where people might need to communicate with each other or with the surface world. There are also cases like avalanches where people might be buried in snow, creating similar challenges. Even the seemingly unrelated issue of radio communications in aircraft cabins shares some of the same technology and solutions. We’ll start by describing some of the concepts used in all of these scenarios. Radiating feedlines Radiating feedlines, also known as ‘leaky coax’ or ‘leaky feeders’, are important for communications underground or in any enclosed area shielded from radio transmitters. They can be used in caves, tunnels, mines, car parks and even inside aircraft or ships. A radiating feeder is like an 16 Silicon Chip imperfect coaxial cable with slots or gaps fabricated into the shield (outer) wire, allowing electromagnetic radiation to escape – see Fig.30. This is the opposite of a regular coaxial cable, which is designed to contain or block as much electromagnetic radiation as possible. Because signal strength is lost in a signal conducted along a radiating feeder, the signal needs to be boosted with an amplifier at regular intervals, every 350-500m or so. An application of radiating feedlines that most readers would be familiar with is in road tunnels such as the Sydney Harbour Tunnel, Lane Cove Tunnel, Burnley Tunnel, AirportlinkM7, Northbridge Tunnel etc. In most of these tunnels (and others in our capital cities), radio and mobile reception operate normally, even when you’re a kilometre or more from either end of the tunnel. Road and rail tunnel communication Radio signals do not travel very far into tunnels. AM broadcast signals Australia's electronics magazine have wavelengths between 175m and 555m, so they will not travel far into a tunnel, given that its diameter will be much smaller than those wavelengths. FM broadcast signals with wavelengths between 2.8m and 3.4m can travel through a sufficiently wide tunnel, but for the signal to enter the tunnel cleanly, it would need to be line-of-sight from inside the tunnel; a reflected signal from outside would be much weaker. The signal would also be largely absorbed as it bounced off the tunnel surfaces multiple times unless the tunnel was perfectly straight and had a clear ‘view’ of the transmitter. DAB frequencies range from 1.3m to 1.6m and behave similarly to FM broadcast signals. Mobile phone telephone signals have even smaller wavelengths, from 43cm down to millimetres for 5G. They could travel some distance through a tunnel provided it had line-of-sight to the transmitter and the tunnel was perfectly straight. Those conditions are rarely met, so radio contact is usually maintained inside a tunnel via ‘rebroadcasting’. siliconchip.com.au Rebroadcasting commercial AM, FM and DAB channels improves driver satisfaction and reduces distraction by not having their favourite radio program interrupted. Given the expensive tolls we pay to use these tunnels, it’s the least they could do! Such rebroadcast systems generally also have a feature called ‘audio break-in’ so that emergency or service announcements can be made over all radio programs being rebroadcast, regardless of which channel the vehicle’s radio is tuned to. In an emergency, signs will usually come on overhead that read “turn on your radio” (or similar) so drivers can be advised of the best course of action. Passive versus active rebroadcasting Radio signals can be rebroadcast either passively or actively. Passive rebroadcast (see Fig.31) involves connecting an external antenna to one or more internal antennas to rebroadcast the signal in a different direction; in this case, through the tunnel. For shorter wavelengths, like FM or DAB, this could be Yagi antennas mounted at intervals in the tunnel. For longer wavelengths, it could be a leaky feeder. Passive rebroadcasting is only suitable for straight tunnels with line-ofsight to the rebroadcasting antenna(s); signal splitters are required for more than one antenna, in which case the signal would be excessively weakened. However, such a signal could be amplified in the same way it is in, say, an apartment block with one antenna and many outlets. More commonly, active rebroadcasting is used. Receivers pick up and decode the signals using antennas outside the tunnel. They then feed the decoded signals (eg, audio) through audio break-in electronics to amplifiers and transmitters that re-radiate it at the original frequencies using antennas throughout the tunnel. See Fig.32 for a typical setup. Depending on the rebroadcast unit(s) and setup, it is possible to have AM and FM broadcast, DAB, VHF/ UHF/800MHz paging and two-way radio access in a tunnel. For mobile phones, it’s usually easier to install small mobile cell ‘towers’ throughout the tunnel linked back to the backhaul network rather than trying to preserve two-way siliconchip.com.au Fig.30: cutaway views of various radiating cables offered by Exlanta (http:// exlanta.com). Fig.31: a passive repeater as used in some tunnel installations. An outside signal is picked up by a Yagi antenna, connected to another Yagi antenna that redirects the signal into the tunnel. No electronics or power is required. For this type of installation to work, the tunnel would have to be straight with line-ofsight to the rebroadcasting antenna. Fig.32: an example of a tunnel with radiating feedline and ancillary equipment. Original source: https://alliancecorporation.ca/manufacturer/rfs-radiofrequency-systems/ Australia's electronics magazine April 2023  17 Fig.33: the radiation pattern of an EION Tunnel WiFi access point with a helical antenna. Original source: www.eionwireless.com/ assets/images/documents/datasheets/Tunnel-WiFi-Oct-14.pdf EION Tunnel WiFi Antenna Coverage Pattern Fig.34: the HeyPhone uses a ground dipole antenna and transmits 87kHz USB at ~10W. Source: https://bcra.org.uk/creg/ heyphone/pdf/heyphone-usermanual.pdf communications between phones in the tunnel and towers outside it. The phones are ‘handed off’ between the towers inside and outside the tunnel, just like they would be when moving between standard towers. Apart from tunnels, such systems can be used in other underground structures such as car parks, mines, and inside buildings where reception might be poor due to metal film on the windows or for other reasons. WiFi in tunnels WiFi can be installed in tunnels and other underground spaces. The most efficient way to do this in tunnels is to use WiFi access points with specially-­ designed helical antennas that have an extended radiation pattern in the direction of the tunnel, rather than a traditional circular pattern. Purpose-built access points are available for this usage from EION Inc – see Fig.33. Cave communications For cave radio, radio is transmitted through the earth (TtE) or via direct line-of-sight (LoS) with relays or multiple ever-weakening reflections. Regular radios can be used in caves for short hops with line-of-sight, but they are rarely suitable as caves rarely have many long and straight passages. Radio can also be transmitted and received via radiating feedlines but, of course, that involves running a wire, as does conventional one-wire (with earth return circuit) or two-wire telephony. The Molefone (TtE) The Molefone (Fig.35) was a radio developed for cave rescue and general use by Bob Mackin of Lancaster University in the 1970s, and used extensively in the 1980s and beyond. It used a multi-turn loop antenna of about 41cm diameter and could achieve a range of about 150m-200m through rock at 10W. It operated on 87kHz USB (upper side-band). No circuit diagrams are available. 87kHz became standard for other cave communications systems, such as the HeyPhone and System Nicola (both mentioned below), to retain compatibility. They are not being made now due to the unavailability of certain components and the resulting inability to repair failed units. The HeyPhone (TtE) Fig.35: operating a Molefone in the Matienzo Caves, Spain. Note the loop antenna made of computer ribbon cable. Source: http://matienzocaves.org.uk/ ugpics/2366-2007e-molep.htm 18 Silicon Chip Australia's electronics magazine The HeyPhone (https://bcra.org.uk/ creg/heyphone/ & Fig.34) was designed by John Hey and is something of a replacement for the Molefone. The British Cave Rescue Council (BCRC) initiated the project in conjunction with John Hey after a meeting in 1999. Unlike the Molefone, the HeyPhone uses a ground dipole as its primary antenna rather than a loop, although it is also capable of utilising loops. The ground dipole comprises two earthed electrodes 25-100m apart. Ground dipole antennas have greater siliconchip.com.au penetration than the loop antennas used by the Molefone. Like the Molefone, the HeyPhone used 87kHz USB at about 10W, and the two radios were compatible. This project is now no longer active or supported, but if you are an experimenter, you can obtain circuit diagrams and other documentation to build your own: https://bcra.org.uk/creg/heyphone/ documentation.html You can also get a user manual for the device at: https://bcra.org.uk/creg/heyphone/ pdf/heyphone-usermanual.pdf HeyPhones were said to be used in the Tham Luang cave rescue (Thailand; June-July 2018), along with Maxtech mesh radio units (see below). System Nicola (TtE) Following the death of Nicola Dollimore in a caving accident in 1996, funds were collected to make the “ultimate cave radio”. It was a collaborative effort between the French, Swiss and British and based on the HeyPhone. The Mk2 was released in 1998 and is the system used throughout France. The Mk3 digital version was developed in the early 2000s, while the Mk4 is currently under development; see Fig.36. The Mk2 radio operates at about 87kHz & 3W with USB modulation. The ground dipole antenna uses two electrodes in the earth about 40m80m apart. The through-rock transmission distance is about 500m-1200m, depending on conditions. Unfortunately, there is little information on this radio. System Nicola does not have a website, but they do have a Facebook page, www.facebook. com/AssociationNicola/ Cave-Link (TtE) Cave-Link (www.cavelink.com/ cl3x_neu/index.php/en/) is a throughthe-earth cave communications system that uses VLF frequencies to conduct text data transfer, not voice, to a depth of 1300m or possibly more. The above-ground part of the system, which the manufacturer calls an ‘earth current modem’ (see Fig.37), can also be connected to the mobile phone system to transfer SMS messages. Some European cave rescue organisations use Cave-Link and it is also used for data logging from sensors located inside caves (eg, water flow, siliconchip.com.au water depth, temperature, CO2 level, pH, pressure etc). It operates between 20kHz and 140kHz using 4PSK (quadrature phase shift keying) modulation and the ARQ (automatic repeat request) error correction protocol. The antennas on the surface and in the cave consist of two metal plates, each connected to one conductor of the feedline from the transmitter or receiver, buried in the ground connected by a cable. This forms an antenna known as a ground dipole (see Fig.16 from last month). The distance between the plates corresponds to a vertical depth of transmission approximately ten times the horizontal distance between the plates. Fig.36: two Nicola Mk4 radios (stacked on each other), which are currently under development. Source: System Nicola Facebook page HF Radio (TtE) HF radio has some capability of penetrating the earth, primarily through dry rock in arid regions. Some experiments have been done at 1.8750MHz using an Elecraft KX3 transceiver (see https://youtu.be/WTnrDwIPKrI). Other experiments reported are: 1. Paul Jorgensen, KE7HR, with an FT817ND transceiver on 3.9MHz SSB and 5W, demonstrated voice communication to a depth of 238m in Carlsbad Cavern, New Mexico, USA. 2. In 2015, the UK Cave Radio and Electronics Group communicated to a depth of 100m with a slant distance of 692m using 20W at 7.135MHz SSB with an IC-706 transceiver. 3. The BCRA Cave Radio and Electronics Group Journal 97, March 2017, reported the reception of 7MHz WSPR signals (weak signal propagation reporter, described in our article on Digital Radio Modes) 100m underground in the UK from nine countries. Fig.37: a Cave-link terminal for sending text data via VLF through the earth. Source: https://expo.survex. com/expofiles/documents/hardware/ Cavelink2.13_en_2014-3.pdf Two-wire telephones (wired) Cavers used surplus army two-wire field telephones in the past. However, they have mostly been replaced by single-­wire telephones or Michiephones. Single-wire telephone (wired) A single-wire cave telephone, also known as a Michiephone, uses only one wire instead of the two used by classic analog telephones. The return circuit is through the earth (see Fig.38). With one wire, the spool weighs less and it is easier to deploy the wire. They work for days on batteries; see www.speleonics.com.au/business/ michiephones/ Australia's electronics magazine Fig.38: Jill Rowling from Speleonics using a single-wire Michiephone. Source: www.speleonics.com. au/business/ (reproduced with permission) April 2023  19 Fig.40 shows the classic circuit for a typical device, designed by Australian Neville Michie in the 1970s. They are very simple, the main component being an operational amplifier. Speleonics is an Australian manufacturer of these devices, although they do not appear to be making any at the moment. The main difference between the device they manufacture and the original design is that theirs also has a filter to remove 50Hz mains hum. VHF & UHF Mesh Radio (LoS) Fig.39: the Entel/Maxtech MaxMesh SDR radio, as used in the Thai cave rescue. Source: www.entelkorea. com/assets/resources/brochures/ HT786-MaxMesh.pdf During the 2018 rescue of a Thai youth soccer team trapped in a cave, rescuers established communications with equipment flown from Israel, made by Maxtech Networks (https:// max-mesh.com/). The equipment fit in one suitcase and comprised walkie-­ talkie-like software-defined radios (SDRs). Either 17 or 19 radios were brought (depending on which report you read) but only 11 were ultimately used to establish a communications link 4km into the cave by forming a mesh network. Maxtech produced the mesh software, while UK-based firm Entel produced the radio platform (Fig.39). The radios operate in the VHF and UHF ranges (225MHz-470MHz). Without a mesh network, communications in a cave between two radios at these frequencies would be line-of-sight or via a limited number of reflections around corners. However, in a mesh network, each radio can act as a relay station for the next one. Individual radios still communicate with each other via line-of-sight or reflections. Despite this, a radio at the start of the network of radios (eg, at the tunnel entrance) can seamlessly communicate with a radio at the far end. Each consecutive radio in the mesh network passes the message on to the next, even though there is no direct link between the communicating radios (first and last). Audio and video communications were established for the cave rescue using 11 radios (siliconchip.au/link/ abir), each with a battery life of 10 hours. In certain places, the only path was through water, so they laid underwater data cables to connect pairs of software-defined radios. The mesh network established by the radios was self-forming, self-­ routing, self-healing and required no other infrastructure. It was a ‘mobile ad hoc network’ (MANET) and used a time division multiple access (TDMA) Media Access Control (MAC) scheme with an innovative routing algorithm. Note that these radios are not explicitly designed for cave rescues; they would be helpful in any hostile environment, such as in collapsed buildings after an earthquake. Fig.40: the Michiephone circuit as produced by Speleonics. The microphone used is extremely hard to get; it is from an old-style telephone handset, and there is no modern replacement. Original source: www.speleonics.com.au/ business/ 20 Silicon Chip Australia's electronics magazine siliconchip.com.au The system can also establish gateways to 3G and 4G phones, analog radios and other networks. For more information, see the video at siliconchip.au/link/abis and the one titled “Maxtech networks video over radio” on YouTube at https://youtu.be/ C2q9L8iAOyA UHF Mesh Radio (LoS) The video “Underground & ThroughThe-Earth Communications” at https:// youtu.be/WTnrDwIPKrI describes an experimental mesh network made of Ubiquity M2 (2.4GHz) and M900 (900Mhz) MIMO (multiple-input and multiple-output) wireless bridges using custom firmware from http:// hsmm-mesh.org/ The result was an IEEE 802.148 mesh network for cave communications. Voice entered the cave via an HF radio link and then was digitised and transmitted through the cave. Fig.41: the results of an APRS UHF radio test in Mammoth Cave, USA, showing the location of radios (numbered in blue) in the cave system, the communications path in red and distances in feet (700ft = 213m). Source: www.aprs.org/cave-link.html APRS (LoS) Using APRS (Automatic Packet Reporting System) radios in caves is also possible. APRS is an amateur radio protocol, so it is not currently available for general cave use, but ham operators who are also cavers are exploring its use. As per mesh radio networks discussed above, the VHF and UHF frequencies are line-of-sight only or via limited reflections. Unlike the Maxtech radios, only data can be transmitted with APRS. Like Maxtech, individual radios can act as repeater stations (‘digipeaters’) for several radios in a chain. An experiment was performed with APRS radios on the 2nd-3rd of March 2013 in Mammoth Cave, Kentucky, USA, the world’s longest known cave system (Fig.41). It was found that for VHF radios, the average hop length was 119m with a maximum of 162m. For UHF, the average hop length was 134m with a maximum of 207m. Fig.42: a MagneLink unit alongside a miner. Source: www.teslasociety.ch/info/ magnetlink/2.pdf They also found that signals would go around a 90° bend in the cave passage without a significant difference in range compared to a straight section. Increasing the power to 50W did not make much difference compared to 5W or less; even ½W was satisfactory. The cave passages were reasonably large, about 9m to 15m wide and 3m to 6m tall. Radiating feedline in caves (wired) Like mines and tunnels, a radiating feedline can be used in caves to enable Using 87kHz through-the-earth comms in Australia Even though 87kHz through-the-earth communications has been established as an international standard for cave rescue communications, it is apparently not approved by ACMA (the Australian Communications and Media Authority) and would be illegal to use in Australia for that purpose. That is why Speleonics only produces the wired Michiephone device and not wireless devices. As it is an international standard and the risk of interference is low-to-nonexistent, ACMA should revisit their objection to such usage and make an exception, at least for cave rescue or exploration purposes. siliconchip.com.au Australia's electronics magazine normal radio operation within line-ofsight of the wire. Such an arrangement would typically be used in tourist caves; however, feedlines have been used experimentally in other caves. Due to the high cost of purpose-made radiating cable, with the experiment described in the PDF at siliconchip. au/link/abit, the objective was to find a cheap substitute for the expensive purpose-made cable. They discovered that low-cost domestic satellite cable was sufficiently leaky (unintentionally) to be useful for this application. Communications in mines Wireless radio communications in mines may be through the earth, via radiating feed lines or wired telephone systems. MagneLink (wireless, through the earth) Magnetic Communication System (MCS) by Lockheed Martin (see Fig.42) is an emergency communications system used in mines to communicate April 2023  21 Mine Emergency Responder Loop antenna on surface MCS Rescue Team Loop antenna in mine entry MCS MCS – strategically positioned along escape routes or with emergency refuge shelters Fig.43: the MagneLink Magnetic Communications System (MCS) in a rescue scenario. Source: www.teslasociety.ch/info/magnetlink/2.pdf with trapped miners and rescue teams that provides two-way voice and text. Trapped miners with access to a MagneLink can activate it to send out a beacon signal, helping emergency teams find the trapped miners. It can be used either vertically between the ground and the mine, or horizontally along a mine tunnel with a blockage – see Fig.43. The system uses loop antennas, so communication is via the magnetic field component of a radio signal rather than the electric field component (see Fig.44). This allows much smaller antennas to be used rather than the alternative type, the ground dipole, which might need to be tens or hundreds of metres long. The part of the system installed in the mine is intended to be kept in designated locations such as ‘refuge areas’. The loop antenna is wrapped horizontally around a mine structure, such as a support pillar (an unexcavated area for roof support). In tests, the MagneLink system has achieved communication depths of radio signal 457m for voice and 610m for text. Radiating feedlines in mines (wired + wireless) Radiating feedlines (leaky feeders) work in mines much as they do in other locations such as tunnels. They are designed for bidirectional communications using handheld devices. On the surface or at some other command centre, a base station is responsible for sending and receiving transmissions (see Figs.45 & 46). There are also amplifiers about every 350-500m, and power for these can be carried by the feedline itself, typically at 12V. Frequencies used are usually in the VHF and UHF bands. The basic building block of a radiating feedline in a mine is a power cell, with one cell per section of a mine. Many power cells may be connected together. Having many cells provides redundancy in case of damage to one section – see Fig.48. Nodes/mesh (wireless) Another way handheld radios can Fig.44: how MagneLink and other through-the-earth communications systems that use loop antennas work. Source: www.cdc.gov/niosh/mining/ UserFiles/Works/pdfs/2013-105.pdf be used in a mine is as part of a nodebased system. While the range of radios underground is generally limited, small repeater stations or nodes can significantly extend radio range – see Fig.47. These nodes and the radios used with them are microprocessor controlled. As discussed earlier, the system forms a mesh network when many nodes are used. The mesh network routes signals between nodes as it deems appropriate (Fig.49). If one node is out of action, an alternate path is established. Medium-frequency system (wired + wireless) Medium-frequency radio waves in enclosed underground spaces will couple into any existing conductors such as power lines, data cables or a radiating feedline. Unlike VHF and UHF radio, medium frequencies can use any existing conductor. So if a suitable conductor is present, MF radios can be used over an extended distance inside a mine, and no repeater is needed. Fig.45: the basic architecture of radiating feedline inside a mine. 22 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.46: how a section of radiating feedline might be laid out in a mine. The dots show the signal between two miners. The downside is that handheld MF radios are considerably larger than VHF and UHF radios. A solution is to use VHF/UHF to MF converters. This enables a small handheld radio to be used within range of a converter which then retransmits the signal at MF, coupling it into nearby conductors. At the other end of the link, the MF is upconverted to VHF/UHF to allow another miner to receive the transmission. Avalanche beacons Avalanches occur when an unstable layer of snow breaks free and slides down a mountain, burying any unfortunate skiers or snowshoe walkers in its path. They are common in areas of Europe and North America. People in avalanche risk zones often carry a form of emergency locator beacon called an avalanche transceiver. Avalanche emergency locator beacons were first invented in 1968, and commercial units were first sold in 1971. They operated at 2.275kHz (ULF). In 1986, 457kHz (MF) was adopted as the standard frequency. The 457kHz (656m) frequency was adopted because it is not subject to significant attenuation by snow, rocks, trees, debris or people, and is less prone to problems resulting from multipath reflections compared to the much lower 2.275kHz frequency. Fig.47: repeater nodes can be used to communicate between two radios that are otherwise out of range of each other. Extending this concept results in a mesh network. Fig.48: example of how a radiating feedline, with above- and below-ground redundancy, can continue to operate after a disaster. Original source: www.technowired.net/wp-content/uploads/2017/02/4.-Sistema-MCA1000-Digital-en.pdf siliconchip.com.au Australia's electronics magazine April 2023  23 Fig.49: multiple repeater nodes can be used to communicate between two radios in a range of locations that would otherwise be out of range of each other. Together, these nodes comprise a mesh network. By necessity, the antenna length can only be a small portion of the wavelength, making transmission very inefficient. Still, the effective electrical length can be increased by using a ferrite core loop antenna with many turns. In use, when each party member heads out into the avalanche-prone area, they turn on their transceiver, and it emits a beep over the radio once per second. If any party members become buried in an avalanche, the remaining members switch their units from transmit to receive to pick up signals from the buried members. The range of the beacons is 40-80m. Due to the shape of the radiated signal, there is a specific technique for finding someone buried in the snow; practice is required to refine the technique, as time is of the essence. Fig.50 shows the radiation pattern, and there are various YouTube videos that explain the required search technique. More modern beacons use digital transmission modes and some use W-Link in addition to the standard 457kHz signal. W-Link operates on either 869.8MHz or 916-926MHz, depending upon the region. W-Link transmits additional information, such as device ID and allows signals Fig.50: the shape of the radiated signal affects the search pattern during avalanche rescues. Practice is required to quickly locate people buried under the snow using their beacons. Original source: https://youtu.be/tXpEUBDzbu0 24 Silicon Chip Australia's electronics magazine of people already rescued to be ignored. Modern beacons (Fig.51) also employ two or three 457kHz antennas in receive mode to make the receiver more sensitive in certain directions depending on the relative alignment of the transmitter and receiver. If you wear one, keep it under your outer clothing to prevent the batteries from freezing and to stop the device from being torn off if you are caught in an avalanche. Many people are not aware that avalanches can occur in Australia. Although rare and not as large as overseas, they occur in certain alpine Fig.51: the Mammut Barryvox S Avalanche beacon for finding buried victims. It has a feature to assist in the search pattern, W-Link and three antennas. Source: https:// varuste.net/p77030/mammutbarryvox-s siliconchip.com.au Related Silicon Chip articles Fig.52: a pipeline pig can be located through steel, soil and concrete by picking up the 22Hz signal transmitted from the pig. regions, although not typically in areas frequented by skiers and are not as dangerous as the ones that occur in the Americas, Asia or Europe. Australia’s Mountain Safety Collective (https:// mountainsafetycollective.org/) conducts training and has rescue teams for avalanche incidents. Pigging communications (pipelines) Pigging involves inserting a ‘pig’ into a pipeline for cleaning or inspection (see Figs.52 & 53). The pig is a device that tightly fills the internal diameter of the pipe and is pushed along by fluid or gas pressure behind it. Some are equipped with electronics to communicate their position or other data to the world above. We have discussed various aspects of VLF and ELF frequencies and comms before and aspects of underground communications in the following articles: ● Radio Time Signals throughout the World (February 2021; siliconchip.au/ Article/14736) ● Underground mapping, leak detection & pipe inspection (February 2020; siliconchip.au/Article/12334) ● Atmospheric Electricity: Nature’s Spectacular Fireworks (May 2016; siliconchip.au/Article/9922) ● How Omega Ruled The World Before GPS (September 2014; siliconchip. au/Article/8002) ● HAARP: Researching The Ionosphere (October 2012; siliconchip.au/ Article/492) ● Digital Radio Modes (April & May 2021; siliconchip.au/Series/360) The industry standard frequency for pig communication is 22Hz. Such signals penetrate the metal of a pipeline and soil or reinforced concrete above it. Leaky feedlines on aircraft Aircraft are not exactly underground [I’m sure the passengers are relieved to hear that! – Editor], but some of the same problems apply to radio reception onboard planes as inside tunnels. Leaky feed line systems have been developed by companies like W. L. Gore & Associates for use in the cabins of widebody and single-aisle aircraft – see the PDF at siliconchip.au/link/abiq These airborne systems provide ‘picocells’ for mobile phone coverage, Fig.53: a pipeline cleaning pig on display in a cutaway length of pipe. Some have electronics and communicate at 22Hz. Source: https://w.wiki/6Exp (CC BY-SA 2.0) siliconchip.com.au Australia's electronics magazine access points for WiFi and support Bluetooth, DECT, DECT2, Globalstar, GSM, IRIDIUM Sat, MMS, PDC and TETRA protocols. They reduce dead zones and reduce the weight of the required equipment. The antennas are suitable for frequencies from 400MHz to 6GHz. See the YouTube video titled: “GORE Leaky Feeder Antennas” at https:// youtu.be/ZK7wBCfJJa0 Conclusion In summary, there are two main techniques for underground communications without having to run wires throughout the enclosed space: the use of low frequencies (typically VLF or LF, 3kHz to 300kHz) for better penetration of rock and soil, or the use of repeaters (possibly in a mesh) to overcome line-of-sight difficulties in curved tunnels or a series of cave/ mine chambers. The main advantage of the VLF/ LF approach is that only two radios are required; however, the low frequencies involved generally require the use of relatively large antennas (somewhat mitigated by using loops). In cases like tunnels or mines where there is frequency activity and significant infrastructure already exists, mesh networks or leaky feeders allow for greater flexibility. For rescue situations, likely a mix of the two approaches will be required. VLF/LF radios can be used initially until a mesh network can be built, allowing rescuers to communicate with small hand-held radios. Given the low cost of powerful RF chips these days, it probably won’t be long before low-cost mesh radios are widely available; possibly even open-source designs. SC April 2023  25 DESIGN BY PHIL PROSSER 485W into 4Ω (single channel) Operates with loads between 4-8Ω Very high efficiency (typically >80% at moderate power levels) Very low in cost and easy-to-build with minimal soldering required Typically, 0.02% distortion over most power levels at 1kHz Frequency response from <5Hz to 20kHz, +0,-1.5dB Built-in speaker protection 5 MONOBLOCK 0 class-d amplifier 0 If you need a serious amount of audio power, are on a budget, and are not after ‘high fidelity’, this is for you! It uses two prebuilt modules and not much else, mounted in a compact metal chassis, WATT to deliver heaps of audio power all day long. B uilding a 500W+ amplifier is a serious undertaking. To make sense, a high-power Class-D amplifier would need a switch-mode power supply. After all, why bother with a Class-D amplifier if you need a 1kVA transformer and bank of capacitors, making the thing half the weight of a VW Beetle? DANGER – LIVE COMPONENTS Do not consider touching the heatsinks or anything on the PCBs when the amplifier is powered or for several minutes afterwards. Assume that contact will be lethal! Never, ever touch the PCBs if the amplifier is even plugged in. If you want to measure the heatsink temperature, use a noncontact IR thermometer. 26 Silicon Chip So we came up with the idea of using some of the relatively cheap modules available on sites like eBay and AliExpress. There were three questions on our minds: were they safe, would they even work, and would the performance be acceptable? So we started surfing online shops and came across two promising modules (see the adjacent panel). Deciding on the modules All the modules we purchased for evaluation have reasonably good availability and have been on sale for many months. Some things that drove us to choose them were: Table 1 – Measured performance into a 4W W resistive load Voltage Freq (RMS) Load Power THD+N Notes 8V 1kHz 4W 16W 0.026% Warm up test, heatsinks 36°C 20V 1kHz 4W 100W 0.017% Heatsinks 40°C after a few minutes 30V 1kHz 4W 225W 0.019% Heatsinks 49°C after a few minutes 40V 1kHz 4W 400W 0.03% 44V 400Hz 4W 484W Output started clipping 44V 1kHz 484W Output started clipping 4W Australia's electronics magazine siliconchip.com.au ● The power supply modules have decent mains-to-secondary isolation. ● They have decent heatsinking and quality capacitors. ● They are common/available parts sold in a range of voltages, ie, a moderately mature and supported design. ● The prices are neither too cheap to be true nor overly expensive. So we placed orders for one of each to test out (plus the modules listed in the panel overleaf that we didn’t end up using). The cost of each module was in the region of $100. $200 for a power supply and amplifier module is bonkers for this sort of power level. If you have built a 500W amplifier using discrete parts and a linear power supply, you will know that this would barely pay for the transformer, let alone the rest. So is this still too cheap to be true? Our greatest concern with purchasing this sort of equipment online is safety and electrical standards. In choosing these modules, we spent a lot of time downloading photos and trying to see how they were laid out, if there were slots milled between feedback opto-isolators and suchlike. Once we had received them, we inspected them to see if they matched the pictures – they did. We then tested them to the best of our ability using our old-school megger (500V) and found no measurable leakage from primary to secondary on both power supplies during a 60-second test. We are not promoting these power supplies as being compliant with any standard, mind you! But there is visible isolation built into the design and measurable isolation on test, which was enough for us to work with them. The power supplies purchased both claim to be capable of “1000W”, although the smaller of the two owns up to being more like a 500W continuous unit. We think it reasonable to rate both power supplies under 1kW continuous, given the parts used, especially the smaller one. Of the two sets of modules, we chose to proceed with the larger, black modules. We have provided some information on the ‘also-ran’ modules for interest but recommend that you stick with the two shown opposite. Performance Table 1 shows some spot measurements of distortion at various power levels. These agree with the claims siliconchip.com.au #1 Large Class-D Amplifier IRS2092S 1000W Class-D Mono Amplifier (see Photo 1): siliconchip.au/link/abic siliconchip.au/link/abid siliconchip.au/link/abie Claims Speaker protection operating from an independent power supply Supply voltage: ±65V to ±80V Photo 1: this Maximum output power: 1000W 500W+ Class-D amplifier module Efficiency: ≥90% was under $100 and includes a speaker Signal-to-noise ratio (SNR): 90dB protection relay. The control circuitry is Dimensions: 157 × 101 × 44mm mounted on a vertical sub-PCB. Net weight: 0.45kg This has four onboard 1000µF 100V supply bypass capacitors per rail labelled Nichicon HE(M), 18mm in diameter and 42mm high. The Nichicon data sheet we found did not list a 1000µF, 100V cap in this range, 820µF being the largest. The size of this capacitor is consistent with the ratings. The main switching transistors are both labelled IRFP4227. The output bobbin is wound on a substantial toroid (35mm diameter) using 1.2mm enamelled copper wire. This amplifier incorporates a speaker protection circuit with a substantial relay. It is more of a high-power AC relay, rated at 30A, but the DC voltage rating is only 30V. Still, we would rather have this in the circuit than not! #2 Large Switch-Mode Supply 1000W LLC Soft-Switching Power Supply (see Photo 2): siliconchip.au/link/abif siliconchip.au/link/abig Claims Output power: 1000W Input voltage: 220V AC (nominal) Output voltage options: ±24V, ±36V, Photo 2: this inexpensive “1000W” ±48V, ±60V, ±70V or ±80V (±70V switch-mode power supply seems to use in our case) reasonable quality components and, as far Efficiency: 88-93.7% as we can tell, is sufficiently safe. We were Standby power: 2W pleased that it passed a 500V insulation Size: 156 × 100 × 50mm breakdown test. Net weight: 350g It has four input filter capacitors rated at 180μF and 400V, which should provide sufficient headroom at 220-240V AC. The CapXon brand capacitors have a ripple current rating of 700mA each. When delivering 1kW, the ripple current will be just over that. So their ratings are marginal if we use this to its full rated capacity. The output capacitors are labelled Nichicon 1000μF 80V. These are low-­ impedance capacitors made for switch-mode power supplies that are the right size and look OK. The mains rectifier is a GBK2510, rated at 1000V & 25A. The output diodes are MURF2040CT 20A ultrafast rectifiers. The mains-side switching transistors have their part numbers ground off! As shown in Photo 3, the clearance on this module between Neutral and the mounting screw (which will be Earthed via the chassis) is just over the minimum allowable. However, it is better than the other one we bought and considered (see “The also-ran modules” panel overleaf), so it is OK. Photo 3: the distance between this component lead that connects to the incoming mains Neutral and the mounting hole is smaller than we would prefer, but is just enough to meet separation standards if Neutral & Active are swapped. That is more common than you might think, especially in old houses. Australia's electronics magazine April 2023  27 Fig.1: the frequency response of the 500W Class-D module is very flat, dropping by only 0.4dB at 10kHz and 1.4dB by 20kHz. It’s definitely suitable for driving an LFE (low-frequency effects) channel, given that there is no such roll-off at the low end. made by the module suppliers. A distortion level of around 0.02% at 1kHz is not exactly hifi, but it isn’t terrible either. It is certainly acceptable for many tasks, especially PA, sound reinforcement, or driving a subwoofer in a hifi or home theatre system. The frequency response into a 4W load is shown in Fig.1. There is a bit of a drop-off at the upper end, but it isn’t terrible. It is, however, totally flat down to 10Hz, making it perfect for driving a subwoofer. The slight rise at 5Hz is irrelevant as it is minimal. LFE (low-frequency effects) channel content might go down to 3Hz, at which point it will still be very close to 0dB. Maximum power testing Scope 1: the amplifier output (yellow) into a 4W load near clipping, close to 500W. As it approaches clipping, the Class-D switching frequency drops from 225kHz to about 56kHz, allowing it to deliver a lot of power with some distortion. The ‘choppy’ appearance of the waveform is normal for Class-D. Scope 2: the amplifier pulsed output at around 1kW peak into a 2W load. There’s something nasty going on near the zero-crossings that would lead to very high distortion (if you can see it on a ‘scope, it’s bad!). Still, it is capable of driving 2W as long as the signal dynamic range is high enough. 28 Silicon Chip Australia's electronics magazine Using a 1kHz waveform, the amplifier ran for an extended period delivering 500W into a 4W resistive load. When loaded, the 15V rail voltage increases, almost certainly a result of this rail being an unregulated winding on the switch-mode transformer. The dummy load was a set of 1W resistors made from very heavy duty Nichrome wire. At full load, they were just short of red hot, and the heat generated was enough to make it uncomfortable to hold your hand 20cm above the dummy load. The amplifier sustained this on a continuous basis throughout a 20 minute test – see Scope 1. Reducing the output to about 30V RMS and the load to 2W, the protection relay immediately switched off. Assuming this was overload protection, we switched to using a pulsed signal that is more typical of music, with six cycles at 1000Hz followed by 100 cycles of silence and then it repeats. The amplifier was able to generate this waveform at clipping into 2W. The output voltage was about 60V peak, consistent with a claim of close to 1kW – noting that they specify 10% distortion and the tests here were below clipping. The fact that the amplifier shut down for continuous duty but was capable of brief bursts of output is important. We doubt this amplifier would drive a 2W subwoofer with modern music, which can have significant content at low frequencies. The amplifier was happy with a continuous waveform into 4W, though. The distortion into 2W was visible on the scope (see Scope 2), so we would dread to think of the actual distortion level. siliconchip.com.au The ‘also-ran’ modules___________________________________________________ We considered other amplifier & power supply modules when designing this amplifier. The following modules looked OK, but we decided they were not as good as the ones we went with. Some readers might still be interested in using them in different scenarios, although note that the safety of the alternative switch-mode supply is concerning. #3 Small Class-D amplifier IRS2092S 1000W Mono Digital Amplifier (see Photo 4) siliconchip.au/link/abih Claims Supply voltage: ±58V to ±70V Output power: 1000W (±70V power supply, 2Ω load, 10% THD) Efficiency: ≥90% SNR: 90dB THD+N (±70V, 2Ω): 1% <at> 900W, 0.1% <at> 750W Frequency response: 20Hz ~ 20KHz Speaker load impedance: 2-8Ω Voltage gain: 36 times Input Sensitivity: 1.5V RMS Protection: output short circuit, speaker protection (no relay, though!), over-temperature Dimensions: 132 × 68 × 45mm Weight: 260g The output filter capacitors are two 470μF 100V units per rail, labelled Fulkon CD288H. Data sheets were not obvious on the internet, but they look about the right size for the job. The main switching transistors are both labelled IRFP4227, but the labelling is quite different between them. The output bobbin is wound on an E-core using Litz wire, which is reassuring. Photo 4: we also tested this Class-D amplifier module which could deliver a similar amount of power. We didn’t choose this one because we’d be running it right at the upper limit of its specified voltage range, whereas the other module has another 10V of headroom and also seems a bit better designed. #4 Small Switch-Mode Power Supply LLC Soft-Switching 1000W Power Supply (see Photo 5) http://siliconchip.au/link/abii Claims Input voltage: 200-240V AC Output voltage: ±35 to ±80V (±70V in our case) Other output voltages: independent 12V, auxiliary ±12V Voltage regulation: main ±3% with no load or ±10% with load; independent, ±15% with no load Output current/power: 880W for main, 0.5A each for independent and auxiliary Continuous power: 500W <at> 25°C Rated power: 880W for about 5 minutes at 25°C. A cooling fan should be added for long-term operation. Peak power: 1200W (less than 100ms) Efficiency: up to 95% Weight: 400g There are four input filter capacitors rated at 120μF and 400V, sufficient for running this from 220-240V AC with headroom. The input capacitors are smaller both physically and in capacitance than the preferred unit. At 1kW, their ripple current will be more than 800mA. The data sheet on the installed parts does not specify this parameter, but looking at similar parts, this will likely exceed their rating. The output capacitors are labelled SLF 1000μF, 100V in the CD288H range, specified for high-frequency and low-impedance. These look right for the job. The mains rectifier is a KBL608 unit rated at 800V, 6A unit. That is marginal. Somewhat disconcertingly, the clearance from the mounting hole (to an Earthed standoff) and Neutral on this PCB is closer than desirable – see Photo 6. With a shakeproof washer, it is a touch over 2.5mm, right on the edge of acceptability. A solution might be to use no washer or a smaller washer. Photo 5: the alternative power supply. It can’t deliver quite as much continuous power as the one we ended up using and seemed to use inferior components that are operated too close to their ratings for our liking (in some cases, beyond!). Photo 6: the power supply shown in Photo 5 also has too little clearance between the Earthed mounting hole and the nearest Neutral conductor. siliconchip.com.au Australia's electronics magazine April 2023  29 So in summary, the amplifier ‘does what it says on the box’ aside from delivering that kilowatt into 2W. Design So, let’s look at what it takes to turn these into a very powerful amplifier. The basic arrangement is shown in Fig.2. It is very much about the appropriate connection of the modules and the provision of some cooling. This is a ‘monoblock’ amplifier with no volume control. We expect you would feed it from a preamplifier that provides volume control, input switching etc. For stereo use, you would need to build two of these, although if you want to power a subwoofer, one should be fine by itself. In terms of a preamp as part of a stereo system, you could use our Digital Preamp with Tone Controls from September & October 2021 (siliconchip. au/Series/370) or our Ultra Low Distortion Preamplifier with Tone Controls from March & April 2019 (siliconchip. au/Series/333). You could, in theory, add a volume/ level control pot on the front panel and route the signal wiring to the amplifier module via that pot. We’ll leave that as an exercise for our readers as we expect most constructors will use a separate preamp. Build and testing We first had to work out how to house this safely and at a reasonable cost. We chose the Jaycar HB5556 chassis as it is just right in size, of good Fig.2: thanks to the prebuilt modules, the ‘circuit’ of this amplifier is dead simple. The power supply generates three rails: -70V, +70V and +15V, which are fed to the amplifier module. The 15V rail also powers the 12V fan via a 39W 1W dropper resistor. build quality and at a great price. This case also lent itself to us implementing some forced air cooling. There are three main baffles to keep things cool, as shown in Fig.3. We are striving to achieve forced airflow over the heatsinks for the power supply and Class-D amplifier. Even though these are better than 90% efficient, if you are driving 1000W into Speaker power handling Speaker power ratings are a bit of a vexing topic. Those who were around in the 1980s and 1990s will have seen the outlandish Peak Music Power Output or “PMPO” numbers that ran into the thousands of watts, often from a 10W IC amplifier chip! At a more pragmatic level, the power rating of a loudspeaker is primarily defined by the capacity of the voice coil to dissipate energy and, at a mechanical level, the excursion limit of the cone. For example, a tweeter typically has a 25mm coil weighing a small fraction of a gram. Many are rated at 100W or more, but the actual continuous power they can handle is only a couple of watts. They rely on the crossover and the nature of music signals to reduce “100W” to only a few watts seen by the tweeter. Woofers have a much tougher life. AES2-1984 defines the power handling test. Power handling is measured with pink noise with a 6dB peak-to-RMS ratio. For example, the BEYMA 21LEX1600Nd driver has a 3200W “program power” rating and a 1600W continuous power rating, equating to a 400W RMS sinewave power rating. Be warned that this amplifier could be very bad for the health of your domestic speakers! We have not recently produced a speaker design that can handle 500W continuously, although the Majestic Loudspeakers (June & September 2014 issues; siliconchip.au/Series/275) are somewhat close, at 300W (tested). 30 Silicon Chip Australia's electronics magazine a load, that is 50-100W being dissipated in each module, mainly via their heatsinks. They will get very hot running this way without air moving over them. Of course, this will not normally be the case. Typical music has a crest factor over 10dB (depending heavily on the type of music), which means that on average, with full-range music not being driven heavily into clipping, the output power would rarely be over 100W for very long. But consider the realistic use case for a 500W (or 1000W) amplifier; its niche is in subwoofer duty, where, with modern music, all bets are off. Modern music has periods of close-to-continuous bass output. So keeping everything cool is essential. With modest output, say, averaging up to 100W or so, these amplifier modules are fine in a case with passive cooling. If that is your application, you can avoid manufacturing the plenum presented here. If you intend to play loud music for extended periods, you need to bolster the cooling. Our plenum is made from three folded sheets of aluminium and uses the case’s lid as the top. This allows us to add a fan and force air over the heatsinks, increasing their efficiency. siliconchip.com.au Fig.3: the case is reasonably compact yet more than large enough to fit the two modules. A series of baffles direct air sucked in through the rear panel (by an 80mm fan) across the heatsinks of the amplifier module and power supply, then out through vents on the left side. The top vents are blocked off to prevent air from escaping before it has completed this route. Without getting too much into the details of heat removal, consider that heatsinks dissipate energy through convection (hot air rising from the heatsink being replaced by cooler air), radiation (mainly IR energy being emitted) and conduction from the heatsink into thermally connected materials. Without running our amp so hot that it’s about to melt, radiation is not a significant factor. Convection is an important means of heat removal, but the case stifles this somewhat, and even in free air, heat will only be removed by convection siliconchip.com.au so fast. By forcing air from outside through the case, over the heatsinks and then exhausting it from the case, we can increase the transfer rate between the heatsinks and the air, picking the heat up off the heatsink and dumping it outside the case. Making the baffles We folded aluminium sheets to form a labyrinth, with a fan forcing air in from the rear of the enclosure and using the perforations along the sides of the case for exhaust. The panels are all securely Earthed for safety. The Australia's electronics magazine cutting and folding details are shown in Figs.4-6, with instructions to follow. We made ours from three sheets of 1.2mm-thick aluminium, although a thickness between 1.0mm and 1.5mm will be fine. You could alternatively use polycarbonate sheets and glue or tap and screw them, or if you have the gear, 3D print it. Use our plan as a guide and follow the principles of forcing air across the heatsinks and out of the box. Assuming you’re making the panels as we did, first cut the metal sheets to size. We used a jigsaw. An angle April 2023  31 Fig.4: the plenum baseplate is bent up on either side to form the ends of the chamber. The cut-out in the upper left corner is for air to exit into the left-hand side of the case, where it escapes via side vents. Fig.5: this panel, also made from a bent aluminium plate, seals off the section of the plenum chamber closest to the case’s front panel. grinder with 1.6mm metal cutting discs also works but requires caution. Drill the holes as shown before bending. If you do not have a pan brake, 1.2mm aluminium can be successfully bent by clamping it to a workbench with a tight 90° edge and using a hammer and piece of timber to ‘panel beat’ the corners into the metal sheet. Go slowly and gently. Make sure the end panel is a good fit for the base. We achieved this by 32 Silicon Chip making the base piece first, then, once it was folded, adjusting the folded ends of the rear panel to achieve an acceptable fit. This does not need to be perfect; there will be a fair bit of airflow, so a leak here and there really does not matter. If you choose to paint your metalwork, make sure to mask off around the Earth lug, as you need a good electrical connection there. With the baffles made, cut the holes in the rear panel for the fan, Australia's electronics magazine input, output and power connectors, as shown in Fig.7. This is an inside view, so if you are cutting from the outside, make sure to mirror it. The final result from the outside (once all the components are mounted) is shown in Fig.8. Cutting the fan hole is a bit fiddly. We used the ‘drill and file’ method, in which you drill many 4-5mm holes around the inside of the final cut line to remove the bulk of the material, then use a file to smooth the edges. An siliconchip.com.au Fig.6: this baffle divides the plenum chamber into two halves, one side for the power supply and one for the amplifier module. The rectangular cut-out allows air to pass from one side to the other. Fig.7: this shows the cut-outs needed in the rear panel but note that the large hole at bottom centre, with two smaller holes near it, is for the Speakon terminal that constructors might opt to leave out. The RCA socket hole has been moved since we built the prototype, as it interfered with the fan. Fig.8: this shows how the rear panel should look once completed. The Speakon terminal is wired in parallel with the binding posts; only one is required, depending on the speaker connector you plan to use. alternative method is to use a jigsaw with a metal cutting blade. To make the holes in the base of the case, present the plenum base to the rear panel with the rear panel in the case, then mark the mounting holes. These are shown marked on the siliconchip.com.au drawing; there are six of them between the folds. This will ensure these are in exactly the right spot. Once marked, drill these, then the mounting holes for the PSU and amplifier modules. These holes need to be countersunk on the underside. Photo Australia's electronics magazine 7 shows how we aligned the plenum in the case to drill the mounting holes. Mount the amplifier and PSU modules now, as shown in Photo 9. Use countersunk M3 machine screws to secure the eight 15mm threaded PCB standoffs to the base. This will allow April 2023  33 Photo 7: once you’ve made the plenum base, you can fiddle with the baffle separating the two halves, so it’s a good fit and not too much air will leak past. Fig.9: cut a sheet of Presspahn or similar insulating material (thick cardboard will do) and mount it on the power supply to ensure sufficient airflow over both the heatsinks and transformer. the plenum assembly to sit flat in the case when assembled. Then use 6mm M3 machine screws and star shakeproof washers to secure the boards. Optimising the airflow We made an extra baffle for the power supply module to force more air over the heatsinks, shown in Fig.9, made from Presspahn. Unfortunately, Presspahn insulating card is becoming hard to get, although we did find an equivalent material (see the parts list). If you can’t get that, use thick cardboard, as we are not relying on its insulating properties too heavily here. Under no circumstances use metal. This is secured with two M3 machine screws and star shakeproof washers to the tapped holes in the top of the heatsink. Use Loctite to ensure these screws do not come loose over time. You should also stick a piece of card to the inside the top panel to cover the vent holes over the plenum. This way, the air does not escape through there and has to flow past all the heatsinks on the way out. Once that’s in place, cut and stick lengths of weather-stripping foam along all the top edges of the plenum chamber and baffles, as shown in the photos. This will make a seal with the case’s lid so that too much air doesn’t flow over the panels and mess up the airflow pattern. Wiring it up With the modules installed, mount the internal baffle. This is important as it controls airflow, as shown in Fig.3. You can see how this sits in Photo 8. Photo 8: the rear view of the 500W Class-D Amplifier’s chassis. 34 Silicon Chip Australia's electronics magazine siliconchip.com.au SILICONE SEALANT OVER EXPOSED METAL HEATSHRINK SLEEVES OVER SPADE LUGS & CONNECTORS N L +15V GND CABLE TIES 12V FAN V+ GND V– OUT GND 39W 1W RESISTOR POWER SUPPLY MODULE AMPLIFIER MODULE IN GND +15V GND V– GND V+ PRESSPAHN BAFFLE (NOT FULL HEIGHT) HEATSHRINK SLEEVES OVER ALL SPADE LUGS & CONNECTORS Fig.10: all the wiring for the amplifier is shown here, except that the Speakon connector has been left off. If fitting it, wire it in parallel with the binding posts. You could use the spare output terminals on the amplifier module for that if you wanted to. Don’t leave off the insulation or cable ties for the mains wiring (also see the photos) and ensure the Earth lug makes good contact with the chassis base. Once it is screwed in, install 10A mains-rated red, green and black wire between the ±70V outputs from the PSU to the amplifier module’s power inputs, referring to Fig.10. This rating is essential as there is 140V DC between these conductors and they can carry significant current. Use medium-duty hookup wire to connect the independent 15V power rail to the amplifier module. Add lengths of 6mm heatshrink siliconchip.com.au tubing over much of these two sets of wires because we will run these cables through the hole in the internal baffle, and we will be tying these to the very top of this opening. This will control where these cables sit, and the heatshrink adds a level of protection and ruggedness to this cabling. Fan connection Next, connect the power to the fan. The fan is a 12V type, but the closest Australia's electronics magazine rail we have is 15V DC, so a 39W 1W resistor connected in series with the fan drops about 3V. The fan is wired to the 15V connector on the amplifier board. Use light-duty or medium-duty hookup wire. Mains wiring The mains wiring is also shown in Fig.10. There is not a lot of it; however, you must take caution with all wiring as most is either mains potential or April 2023  35 Photo 9: this shows how the two modules fit inside the plenum chamber within the case. The wiring between the two modules has been run along with the input and fan wiring, but the output and mains connections have not been made yet. high voltage DC or AC (the output). Ensure all wiring is secured with zip ties to keep it tidy and controlled if anything comes loose. Install the power switch on the front panel as shown in Fig.11. Then take two lengths of brown and blue mainsrated 10A wire and connect from the IEC mains connector to the switch as shown. Connect the topmost terminals on the switch to the IEC mains input, and then run a second pair of wires from the central switch terminals back to 36 Silicon Chip the mains input on the power supply. We used insulated crimp connectors on the IEC connector and switch. If you wish to solder these connections instead, insulate the joints with 10mm diameter heatshrink tubing. Keep these wires twisted and tidy, and zip-tie them such that they cannot come loose in the case. We found it handy to label the unswitched and switched input wires. Using a length of yellow/green striped 10A mains-rated wire, connect the Earth pin on the IEC connector to Australia's electronics magazine the M3 Earth screw that runs through the case and plenum metalwork. Before assembling this, take a utility knife and scrape the paint from the case around this bolt. Use a star shakeproof washer on the bottom and top of the case and attach a 3.2mm solder lug to this. Connect the Earth wiring and check continuity with a multimeter. Install an 8A or 10A ceramic fuse in the IEC mains input/fuseholder assembly. Remember to insulate the exposed metal strip on the back of this siliconchip.com.au Fig.11: just one hole is needed in the front panel for the power toggle switch. That is unless you elect to add a volume control pot or a power-on indicator (an illuminated switch could be used instead). connector with neutral-cure silicone sealant, as it will otherwise be live whenever the mains cord is plugged in. this to the top of the plenum with a cable tie and want this as extra abrasion protection. Output wiring Input wiring Use mains-rated 10A rated wire for the amplifier output connections. We used 400mm of green and red wire twisted together from the amplifier output to the output connectors. We included both Speakon and binding posts outputs; you may only need the binding posts. We sleeved the output wiring in a 250mm length of 6mm diameter heatshrink tubing. We did this firstly to ensure there could be no confusion between this and the power wiring and also because we will be securing Take 300mm of shielded cable and connect the RCA connector on the rear panel to the screw terminal header on the amplifier board. Use a short length of sleeving to insulate the exposed ground braid and 20mm of 3mm diameter heatshrink to form nice terminations. Caution At this point, you should have a standalone chassis with the amplifier modules installed and wired up. First and foremost: safety. If you are not totally comfortable working with high voltages then do not proceed without help. It’s also safest to do the first power up with the lid secured. This amplifier can generate a lot of power. To do this, it uses high supply rails of ±70V DC. It could easily stop your heart if you make contact with these two rails. Also, the switch-mode power supply operates from the mains and has close to 400V DC in parts of the circuit. This is also lethal. Second: danger to your possessions. The amplifier generates 44V RMS continuously into a 4W load. This is close to 500W. If you feed this into your speakers as a sinewave, we can guarantee you will destroy them. See the panel on “Speaker power handling”. This view shows how we wired up the output connectors and gives you a good view of the Presspahn baffle that optimises airflow over the power supply module. You can also see how the mains input wiring has been insulated. Also note how the output wiring and ±70V rail wiring is cable tied to the top of the plenum, just behind the Presspahn baffle. siliconchip.com.au Australia's electronics magazine April 2023  37 Similar cautions apply for test equipment; make sure that if you connect this to a distortion analyser, it is on a 50V or 100V RMS range. Testing First, check that the mains power switch is on, then with it unplugged, do a final check with a DVM on its 20MW range (or similar) and check for any measurable resistance between the Active and Neutral inputs and the output ground connector. If there is, then you need to stop and find the problem. Also perform a final check of your Parts List – 500W Monoblock Amplifier 1 1000W Class-D amplifier module (see links at the start of the article) 1 1000W 70V split-rail switch-mode power supply (see above) 1 vented metal bench enclosure, 304 × 279 × 88mm [Jaycar HB5556] 1 dual binding post for speakers [Altronics P9257A] 1 panel-mount insulated RCA socket [Altronics P0220] 1 fused IEC mains input socket [Altronics P8324] 1 10A+ mains-rated chassis-mount DPST/DPDT toggle switch [Altronics S1052 or Jaycar ST0585] 1 8-10A fast blow sand-filled or ceramic M205 fuse [Altronics S5934] 1 Speakon chassis-mount speaker connector (optional) [Altronics P0792] 1 quiet 80mm 12V fan [Altronics F1150] 1 80mm fan guard [Altronics F1022] 1 2-way 2.54mm-pitch vertical polarised header [Altronics P5472, Jaycar HM3412] 1 2-way 2.54mm-pitch polarised header plug [Altronics P5492 + 2 × P5470A, Jaycar HM3402] 1 39W 1W resistor Hardware 1 428 × 225 × 1.0-1.5mm aluminium sheet (for base) 1 225 × 103 × 1.0-1.5mm aluminium sheet (for baffle) 1 259 × 100 × 1.0-1.5mm aluminium sheet (for plenum end) 1 115 × 65mm sheet of Presspahn or similar insulating card [www.ebay.com.au/itm/293254125529] 9 M3 × 16mm panhead machine screws 12 M3 × 10mm countersunk head machine screws 16 M3 × 6mm panhead machine screws 12 M3 hex nuts 32 M3 star shakeproof washers 8 15mm M3-tapped spacers 1 3.2mm solder lug [Altronics H1503] 9 blue insulated 6.3mm female spade crimp lugs for 1.5-2.5mm2 wire [Altronics H2006B] 1 1.2m length of 9-10mm wide adhesive foam weather stripping [Bunnings 3970353] 1 1.5m length of 5-10mm wide adhesive foam weather stripping [Bunnings 3970353] 1 pack of small Nylon cable ties Wire & cable 1 1.5m length of brown mains-rated 10A hookup wire 1 1.5m length of blue mains-rated 10A hookup wire 1 0.5m length of green/yellow striped mains-rated 10A hookup wire (eg, stripped from a length of 10A three-wire mains flex) 1 1m length of red mains-rated 10A hookup wire 1 1m length of green mains-rated 10A hookup wire 1 1m length of black mains-rated 10A hookup wire 1 0.5m length of red medium-duty hookup wire 1 0.5m length of black medium-duty hookup wire 1 300mm length of single-core shielded audio cable [Altronics W3010] 1 1m length of 6mm diameter clear heatshrink tubing 1 200mm length of 3mm diameter clear heatshrink tubing 38 Silicon Chip Australia's electronics magazine wiring. A fault here will be both spectacular and dangerous. Plug the amplifier in, switch it on and listen for the speaker protection relay switching in after a couple of seconds. Carefully measure the voltage between ground, V+ and V− on the power supply output using some properly insulated DMM probes and a suitably rated meter. The rails should both be within 5V of 70V but with different polarities. Carefully measure the voltage on the +15V input to the amplifier and ensure it is close to expected. If any of the above fails, unplug the amplifier and leave it off for 10 minutes. After verifying that the mains plug is still out, disconnect the power amplifier from the power supply so you can check the PSU by itself. If you can’t see the right voltages at its outputs with no load, you have a faulty PSU. If the PSU measures OK, rebuild it and check your wiring carefully. Now plug in a signal generator to the input and a CRO with a 10:1 probe set to measure up to 70V peak to the output. Power up and look for the sinewave on the output. Increase the signal level until you see clipping; check that this is about 40-44V RMS. Connect a load and start the input signal at a low volume level, increasing to a manageable level. Only use a loudspeaker for this if you have no other choice and are happy to test at moderate levels only. If you have a dummy load, run the amplifier at as high a power as is safe for your load for 5-10 minutes. If you are using a speaker for the test, play some moderately loud music. At this point, we are really just checking that nothing goes wrong – no puff of magic smoke etc. After testing as hard as you feel safe, unplug everything and open the amplifier. Use an IR thermometer to measure the temperature of the PSU heatsinks, the E-core transformer on the PSU (in our tests, this was the hottest part) and the amplifier heatsink. If these are all below 65°C, everything is fine and you are all set! Otherwise, check the airflow management components (baffles, seals etc) to verify that there are no massive air leaks and confirm that you haven’t skipped any of the steps listed above. SC siliconchip.com.au Laboratory Power Supplies A GREAT RANGE of fixed and variable output power supplies at GREAT PRICES for hobbyist or industrial workbenches. AFFORDABLE PRECISE VOLTAGE SOLUTION AFFORDABLE HIGH CURRENT SOLUTION Variable Voltage & Current $ Precise voltage level and JUST 209 current limiting. • Adjustable 0 to 30VDC • Adjustable 0 to 5A • <1mVRMS Ripple Voltage MP3840 POWER TWO CIRCUITS SIMULTANEOUSLY Variable Voltage & High Current $ High current range with current limiting. • Adjustable 0 to 15VDC • Adjustable 0 to 40A • 100mV Peak-Peak Ripple MP3091 ENTRY LEVEL Dual Output, Dual Tracking JUST 399 Automatic constant-voltage/ constant-current. • 2 x 0 to 30VDC, 2 x 0 to 3A • Independent outputs & displays • <1mVRMS Ripple Voltage MP3087 MID LEVEL JUST 439 $ PROFESSIONAL Model no. MP3079 MP3078 MP3089 MP3096 MP3097 MP3800 MP3098 MP3802 MP3842 MP3840 MP3091 MP3087 Type Fixed Fixed Fixed Fixed Fixed Variable Fixed Variable Variable Variable Variable Variable Output Single Single Single Single Single Single Single Single Single Voltage DC 13.8V 13.8V 13.8V 13.8V 13.8V 0 to 24V 13.8V Current 12A 20A 40A 5A 10A 15A 20A Backlit Analogue Recommended Retail Price (RRP) $79.95 $119 $219 $129 $169 $179 $249 Single • • • • Backlit Analogue Backlit LCD LED Backlit LCD Backlit LCD $259 $169 $209 $399 $439 Shop at Jaycar for: • Isolated Stepdown Transformers • AC/DC Power Supplies • Auto Transformer (VARIAC) • Plugpacks & Desktop • Power Leads & Boards Power Supplies Explore our full range of power supplies, in stock at over 110 stores or 130 resellers or on our website. Dual 0 to 16V 0 to 16V 0 to 5A 0 to 30V 0 to 15V 2 x 0 to 32V 0 to 27V 0 to 3A 0 to 36V 0 to 2.2A 0 to 5A 0 to 40A 2 x 0 to 3A 25A Current Limiting Display Single jaycar.com.au/laboratory-psu 1800 022 888 Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. Switch between displaying air/fuel ratios for two different fuels ◀ Accurate air/fuel ratio and lambda measurement and display ◀ Wideband and narrowband O2 sensor compatible outputs ◀ Several display options, including wireless via Bluetooth ◀ Optional exhaust pressure correction for readings ◀ Correct sensor heat-up procedure implemented ◀ Compact size, fitting in a 120 x 70mm case ◀ Factory-calibrated oxygen sensor ◀ Part 1 of John Clarke’s WIDEBAND Fuel Mixture Display Measure your engine’s full range of air/fuel ratios using our Display, along with the latest wideband oxygen sensor from Bosch. It even includes Bluetooth, so you can display the lambda value or air:fuel ratio on a computer, smartphone or tablet! W hether you are driving a vehicle that uses a carburettor to mix air and fuel or with fuel injection, being able to monitor that the air/fuel ratios are correct ensures your car engine is running in prime condition. That’s especially important if it is a high-­ performance vehicle that has been heavily tuned since running lean can quickly destroy an engine under load. The air/fuel ratio can be measured in real-time using our Wideband Fuel Mixture Display (called the WFMD from now on). This is invaluable if you are involved in carburettor tuning in older engines or with car modifications. Anything that can affect air or fuel flow or with engine management remapping can cause an engine to run too lean or too rich. Most modern vehicles include at least one oxygen sensor near the engine on the exhaust pipe to monitor 40 Silicon Chip the exhaust gas. Vehicles made since about 2010 will usually have two or more, with at least one to verify that the catalytic converters are doing their job, converting any excess fuel or oxygen to inert gases. The primary oxygen sensor(s) near the engine allow the engine control unit (ECU) to control the air/fuel ratio being burned. Typically, they are narrowband sensors that can only accurately detect a nearly stoichiometric mixture or air/fuel ratio. A stoichiometric mixture is when there is complete fuel combustion and all the oxygen is used up with no fuel left over. The engine control unit (ECU) usually adjusts the amount of fuel injected per volume of air to maintain a mixture close to stoichiometric. This is called ‘closed-loop’ operation; the ECU controls the fuel mixture with feedback from the oxygen sensor. The ECU will Australia's electronics magazine increase the amount of fuel delivered if the exhaust is lean or reduce fuel if it is too rich. During acceleration or cruising, the mixture may go beyond stoichiometric and become rich or lean, beyond the measurement range of the narrowband oxygen sensor. In these cases, the ECU operates in open-loop mode, using predetermined mixture information stored within the ECU. In this case, it is not using the air/fuel ratio as a feedback parameter (at least, not immediately). The narrowband sensor has a very sharp voltage change around the stoichiometric mixture point, rising above 450mV if the mixture becomes rich and falling below 450mV if it becomes lean. To maintain a stoichiometric air/ fuel, the ECU constantly adjusts the mixture from slightly rich to slightly lean and vice versa, as the narrowband siliconchip.com.au SPECIFICATIONS — Supply voltage: 11-15V — Start-up current: 1.6A (~20W), typically dropping to 0.6A (7.5W) when up to temperature — Reading accuracy: typically ±1% plus 1 digit — Lambda measurement range: 0.7 (rich) to 1.84 (lean) — Air/fuel ratio range: 10.29 to 27.05 for petrol (stoichiometric 14.7:1) and 10.85 to 28.52 for LPG (stoichiometric 15.5:1) Status indication: warming up, operational, error via LED flashing Engine start voltage detection threshold: adjustable from 0-15V; 13V typical Heat-up period: typically <10s from cold Heater maximum effective voltage (Veff): 12Veff after initial preheat and 13Veff for <30s Heater over-current protection threshold: 4A Heater drive frequency. 122Hz during warm-up and >100Hz during operation Other protection: 5A fuse, heater open-circuit detection Sensor temperature: regulated to 780°C Exhaust pressure correction: up to 900hPa above standard atmospheric pressure of 1013hPa Sensor cell temperature/impedance measurement: AC drive at 1.953kHz and 243μA Sensor cell DC loading: <4.5μA Reference current: 20μA — — — — — — — — — — — — OUTPUTS — MM: 0.7-1.84V corresponding to 0.7-1.84 lambda — MV+: 10.29-27.05V representing air/fuel ratios of 10.29:1 to 27.05:1 for petrol OR 10.85-28.52V representing air/fuel ratios of 10.85:1 to 28.52:1 for LPG — MI: 0.7-1.84 lambda — Narrowband output: simulates the 0.8-1.17 lambda S-curve of the Bosch LSM11 narrowband sensor — Narrowband response time: 100ms time constant — Wideband response time: 100ms for a 5% change in oxygen content — Bluetooth: 9600 baud ASCII serial stream (8-N-1) — Bluetooth display works with Windows, macOS, Linux and Android devices sensor voltage swings above and below 450mV at around 1Hz. Fig.1 shows the typical output from a narrowband oxygen sensor. It has a very sharp response on either side of the stoichiometric point (lambda of 1), ranging from about 300mV up to 600mV. For rich mixtures, it ranges from around 600mV to almost 900mV (lambda up to 0.8), is quite non-linear and varies markedly with temperature. It is similarly non-linear for lean mixtures, ranging from around 300mV down to a few mV (lambda of about 1.15). The overall sensor response follows what is called an S-curve. To learn about lambda, refer to the explanatory panel later in this article. If you haven’t changed anything on your vehicle, there is little reason to worry about the fuel mixture since the ECU takes care of it. But if you have made any changes to improve siliconchip.com.au its performance, especially if you’ve tuned it or added/changed something like a turbo, you need to check that the mixture is OK. Part changes that can affect the mixture include the inlet air filter, throttle body, injectors, manifold absolute pressure (MAP) or mass airflow (MAF) sensors, custom ECU chips, adding a supercharger or turbocharger, catalytic converters, exhaust manifolds, mufflers and resonators, or anything resulting in changes to fuel mixtures and oxygen sensor readings. Note that if your vehicle already has a wideband oxygen sensor, you won’t be able to replace that with this one. The narrowband output on the wideband fuel mixture display unit can only be used if the vehicle has a narrowband oxygen sensor; in that case, the original narrowband sensor can be replaced by the wideband sensor Australia's electronics magazine via the WMFD’s narrowband output. Suppose your vehicle already has a wideband sensor. In that case, you can add the sensor to another bung (threaded hole) in the exhaust near the original sensor to monitor the air/ fuel ratio separately with the WFMD. Alternatively, the sensor can be placed in the tailpipe for temporary use. The Bosch LSU4.9 sensor Our new controller is designed to work with a Bosch LSU4.9 wideband oxygen sensor. This type of sensor (or a similar type from another manufacturer) is used in some late-model cars to measure and control the mixtures over the full range of engine operation. When combined with the WFMD, mixture readings cover the range of air/fuel ratios from lambda values of 0.7 (very rich) to 1.84 (very lean). Our WFMD is housed in a small plastic case, as shown in the accompanying photo. It includes an 8-pin socket for the wideband oxygen sensor connection plus cable glands for the power input leads, pressure sensor leads and the panel meter or a connection to a multimeter. It has an output that simulates a narrowband sensor. This enables the vehicle’s existing narrowband sensor to be replaced with the Bosch LSU4.9 and still provide for normal engine Fig.1: the output of a typical narrowband O2 sensor like the LSM11, known as an ‘S-curve’. The lambda value varies rapidly beyond about 50mV and 800mV on either side of the stoichiometric point (450mV), so it can’t accurately measure very rich or lean mixtures. April 2023  41 Fig.2: in contrast with Fig.1 for a narrowband sensor, the output of a wideband sensor after processing (here from the MM output), is a nice straight line over a wide range of lambda values (lambda is the measured air/fuel ratio divided by stoichiometric ratio). operation by connecting the narrowband signal to the ECU. The simulated narrowband signal is the same as it would receive from the original narrowband sensor, so ECU and engine operation are normal. The narrowband output from the WFMD is as shown in Fig.1. If your engine uses a carburettor or does not have an oxygen sensor, the wideband sensor can be installed in the exhaust pipe near the engine. You can also use the wideband sensor by temporarily installing it into the end of the exhaust pipe. You might want to do this for easy monitoring of different vehicles. More details on this will be given in a later article in this series. Improvements Our last O2 sensor controller was published in the June, July & August 2012 issues (siliconchip.au/Series/23). While it used the same sensor and worked well, this new version has some clear improvements. Firstly, this version fits in a more compact box measuring 120 x 70mm compared to 155 x 90mm. That can be important in a car where there often is little room to add new hardware. Secondly, the new version can show lambda and the air:fuel ratio simultaneously, and the air:fuel ratio scaling can be switched between two different fuel types, eg, petrol and LPG. The new version also has the Bluetooth feature lacking in the older one. This revised unit can also deliver a voltage directly proportional to the air:fuel ratio, not just a voltage derived from the lambda. This version can also handle compensation 42 Silicon Chip for higher exhaust pressures, up to 900hPa above 1013hPa rather than just 587hPa. We’ve also switched to using a commonly available automotive pressure sensor. Due to packing more features into an even smaller PCB, this version uses more SMDs than the last one, including a 44-pin micro, compared to the 18-pin DIP chip used in the 2012 design. Display options The WFMD includes several ways to view the air/fuel ratio and lambda. In its most basic form, a multimeter can be used to read off either value. A second option is to use a panel meter that includes both a voltage and current display. The lambda value is shown on the current display, while the voltage display shows the air/ fuel ratio. To do this, the current measurement section of the panel meter is modified to increase the shunt resistance. That’s so that the WFMD only needs to provide milliamps of current instead of amps. A third display method is via a Bluetooth connection, where the air/fuel or lambda value is shown on a phone, tablet or computer screen. This method avoids having any wired connection between the WFMD and the actual readout and would be especially useful if the WFMD needs to be mounted at the rear of the vehicle but monitored from the front. Fig.2 shows the WFMD controller lambda output over the range of air/ fuel ratios from 0.7 to 1.84 lambda. Two lambda outputs are available. The multimeter (MM) output is shown as a voltage on the left Y axis, while the V/A meter output (MI) is shown on the right Y axis as a current. Both these outputs are linear with respect to lambda values from 0.7-1.84. There is another output labelled MV+ for the V/A meter or a multimeter that provides a direct air/fuel ratio to voltage scale, ranging from 10.29V to 27.05V for petrol, when set for a 14.7:1 stoichiometric mixture, or 10.85V to 28.52V when set for a 15.5:1 stoichiometric mixture for LPG. These values can be set to other air/ fuel ratios if desired; you can even switch between two different scaling factors using a jumper shunt or external switch. Effectively, the voltage from the MV+ output is the same as from the MM output but multiplied by the air/ fuel ratio at stoichiometric for your type of fuel so that a voltmeter will give Air/fuel ratio & lambda The air/fuel ratio (or air:fuel ratio) is the ratio of the mass of air to the mass of fuel being burned. Lambda is the ratio of the actual air/fuel ratio to the stoichiometric air/fuel ratio. A stoichiometric mixture is when the air/fuel ratio is such that there is the exact mass of air required to completely burn the exposed mass of fuel. By definition, a stoichiometric mixture has a lambda of 1. For petrol, the stoichiometric air/fuel ratio (lambda of 1) is 14.7:1. This can drop to 13.8:1 when 10% ethanol is added and even further for E85 (85% ethanol), to 9.7:1. The stoichiometric air/fuel ratio is typically 15.5:1 for LPG. These values can differ depending on the exact fuel composition. For petrol, a lambda of 0.7 is equivalent to an air/fuel ratio of 0.7 × 14.7:1 = 10.29:1. Similarly, a lambda of 1.84 is equivalent to an air/fuel ratio of 27.05:1. Lambda is a universal measure of air/fuel mixtures since it is not dependent on the specific fuel. More details on the LSU4.9 wideband sensor Comprehensive data for the LSU4.9 sensor is available in a PDF file at: www.ecotrons.com/files/Bosch_LSU49_Tech_Info.pdf Australia's electronics magazine siliconchip.com.au a direct reading of the air/fuel ratio. Status indication A red status LED inside the controller, seen through the transparent lid, indicates when the controller is heating the sensor to its operating temperature. This occurs each time the controller is switched on, and it takes less than 10 seconds for the operating temperature to be reached. Once the sensor is at operating temperature, this LED flashes rapidly. From that point on, the wideband controller monitors the oxygen sensor signal and feeds a simulated narrowband signal to the ECU. By contrast, the LED flashes more slowly if there is a sensor error. Wideband oxygen sensor operation The wideband sensor operates very differently from a narrowband sensor. In its most basic form, a narrowband sensor has only one wire carrying the sensor output voltage. The common connection is via another wire or the sensor body connection to the chassis (ground). Many narrowband sensors also have an internal heater, and these units will have more wires for the heater element. Still, there are usually at most four wires on a narrowband sensor. By contrast, the wideband sensor has eight connections up to the sensor socket, with six wires connecting from the sensor socket to the controller. This is because the wideband sensor includes a narrowband oxygen sensor, an oxygen ion pump and a heater. The heater and oxygen ion pump need to be controlled, which is where the WFMD is required. Before we describe how a wideband sensor and its associated controller work, it’s necessary to explain the characteristics of a narrowband sensor. Fig.3 shows a cross-section of a typical narrowband sensor. It’s about the same size as a spark plug and is threaded into the exhaust system so the sensor is exposed to exhaust gases. The assembly is protected by a shield that includes slots so exhaust gas can pass into the sensor. The sensor is made from a zirconia ceramic material with a thin layer of porous platinum on both sides. These platinum coatings form electrodes to monitor the voltage produced by the zirconia sensor as the exhaust gas siliconchip.com.au Fig.3: this shows the structure of a typical narrowband sensor. Exhaust gasses coming in contact with the zirconia ceramic sensor generate a voltage between the interior and exterior platinum electrodes that’s related to the concentration of oxygen in the exhaust compared to the outside air. passes through it. The sensor is called a Nernst or fuel cell and produces a voltage when exposed to air/fuel mixtures. The device operates by measuring the difference in oxygen content between the exhaust gas and outside air. The oxygen content of air (about 20.95%) serves as the reference oxygen concentration. A voltage is produced between the electrodes because the zirconia sensor has a high conductivity for oxygen ions at high temperatures. When a narrowband sensor includes a resistive heating element, this heater quickly brings the sensor up to its operating temperature. It thereby allows the ECU to run in closed-loop mode sooner than without the heater. The arrangement of the wideband sensor is shown on the left side of Fig.4. It also includes a narrowband sensor (the sensor cell), but there are major differences in how it is used. Instead of obtaining reference oxygen from the outside air, it uses a pseudo oxygen reference chamber. This chamber obtains oxygen ions from the exhaust gases. When burning a lean mixture, oxygen is available from the unused oxygen in the exhaust gas. When the air/ fuel ratio is rich, oxygen is extracted from gases such as CO2 and H2O (the latter in the form of steam). Oxygen ions are maintained in this chamber by applying a small reference current to the sensor. Australia's electronics magazine The Bluetooth module is on the left, while the microcontroller is in the middle. April 2023  43 Fig.4: a wideband sensor (left) is similar to a narrowband sensor but needs the more complex control electronics shown on the right. Those electronics drive an oxygen ion pump in a negative feedback loop. By measuring the current required to run that ion pump, we can determine the air:fuel ratio of the exhaust gas entering the measurement chamber. A pseudo reference chamber is used to provide an oxygen reference instead of from the outside air because, when using outside air, the reference chamber needs to be constantly replenished with oxygen. The only pathway for the gas is via the sensor leads between the copper wire and the insulation. Any contamination of the sensor leads from oils, tars and fuels can affect the oxygen flow to the sensor. The leads are also susceptible to damage if the sensor lead connections are soldered during wiring maintenance (instead of crimped). Soldering will melt the plastic insulation sufficiently to seal the wire against oxygen flow. Conversely, for a pseudo reference, oxygen replenishment is not affected by sensor lead contamination since it derives its oxygen from a different source. The pseudo reference chamber needs to be continuously replenished to avoid being depleted of oxygen. That is because any oxygen in the reference chamber will diffuse into the measurement chamber to balance out the partial pressure of oxygen that is higher in the reference chamber, due to Fick’s First Law. Exhaust gas is sampled within a small measurement chamber (that is separate from and much smaller than the volume within the exhaust pipe), enabling a pump cell to move sufficient oxygen ions into or out of this chamber. The pump cell is driven with pump current to maintain a stoichiometric measurement within the sensor cell (the narrowband sensor). If the measured mixture is lean, the sensor cell detects excess oxygen. The pump cell then drives oxygen ions out of the measurement chamber until the sensor cell produces a stoichiometric Fig.5: the ion pump current plotted against lambda. It is not linear, but by storing a copy of this curve, we can easily perform a look-up and do a little interpolation to determine the actual lambda value from the pump current. 44 Silicon Chip Australia's electronics magazine lambda value, as detected by the narrowband sensor. Conversely, if the mixture is rich, oxygen ions are pumped from the surrounding exhaust gas into the measurement chamber gap until the sensor cell again reaches its stoichiometric lambda value. Current is applied to the pump cell in either direction, depending on whether oxygen needs to be pumped into or out of the measurement chamber. The oxygen pump is used to maintain a stoichiometric lambda value within the measurement chamber. So while the narrowband sensor (sensor cell) is used to ‘look for’ a stoichiometric mixture, it doesn’t provide the air/fuel mixture information. Instead, the amount of current applied to the pump cell required to achieve a stoichiometric mixture provides the necessary information to determine the air/fuel ratio accurately. Fig.4 shows how the wideband sensor is controlled. Vs is the output voltage from the oxygen sensor cell, while Ip is the current into or out of the pump cell. Vs is 450mV for a stoichiometric mixture and this is compared against a 450mV reference. If Vs is higher than the 450mV reference, the mixture is deemed rich and the Vs sense comparator (IC4a) output goes high. The controller then adjusts the Ip current to pump oxygen ions into the measurement chamber to produce a stoichiometric measurement. Similarly, if Vs is lower than the 450mV reference, the mixture is deemed lean and the comparator output goes low. As a result, the controller adjusts Ip to pump oxygen out of the measurement chamber. The pump current (Ip) indicates whether the mixture is actually rich siliconchip.com.au Parts List – Wideband Fuel Mixture Display 1 double-sided, plated-through PCB coded 05104231, 103.5 × 63.5mm 1 120 × 70 × 30mm plastic enclosure [Jaycar HB6082] 1 cable gland to suit 3-6.5mm or 4-8mm cables 1 inline 3AG, blade or mini-blade fuse holder (F1) [Altronics S6001, Jaycar SZ2015] 1 5A fast-blow fuse to suit fuse holder (F1) 1 6-way pin header, 2.54mm pitch (CON1; optional; for programming IC1 in-circuit) 3 2-way pin headers, 2.54mm pitch, with jumper shunts (JP1-JP3) 4 M3 × 15mm panhead machine screws and hex nuts 5 50mm lengths of light-duty hookup wire (red, black, yellow, green & light green; for circular connector to PCB) 2 150mm lengths of 7.5A hookup wire (blue and red; for circular connector to PCB) 2 200mm lengths heatshrink tubing (3mm & 5mm diameter) 2 2m lengths of 7.5A hookup wire (red and black; for power connection) Semiconductors 1 PIC16F18877-I/PT 8-bit microcontroller programmed with 0510423A.hex, TQFP-44 (IC1) 1 OPA2171AID dual rail-to-rail op amp, SOIC-8 (IC2) 1 LMC6482AIM or OPA2171AID dual rail-to-rail op amp, SOIC-8 (IC3) 1 LMC6484AIM quad rail-to-rail op amp, SOIC-14 (IC4) 1 LM317T adjustable linear regulator, TO-220 (REG1) 1 LM2940CT-12 low-dropout 12V automotive linear regulator, TO-220 (REG2) 1 STP16NF06L or IPP80N06S4L 60V 60A logic-level N-channel Mosfet, TO-220 (Q1) 2 BC817 NPN transistors, SOT-23 (Q2, Q5) 1 BC807 PNP transistors, SOT-23 (Q3) 1 BC847 NPN transistor, SOT-23 (Q4) 1 1N4004 400V 1A axial diode (D1) 3 1N4148WS 150mA switching diodes, SOD-323 (D2-D4) 5 SS14 40V 1A schottky diodes, DO-214AC (D5-D9) 1 BZV55-C16 ½W zener diode, SOD-80C (ZD1) 1 BZV55-C33 ½W zener diode, SOD-80C (ZD2) 1 BZV55-C15 ½W zener diode, SOD-80C (ZD3) 1 3mm high-brightness red LED (LED1) Capacitors (SMD M2012/0805 or M3216/1206 size) 5 100μF 16V PC radial electrolytic 1 10μF 16V PC radial electrolytic 3 10μF 50V SMD X5R/X7R ceramic or lean. A negative Ip indicates a rich mixture, while a positive Ip current indicates a lean mixture. The amount of current indicates the deviation of the lambda value from 1.0. Fig.5 shows a graph of Ip versus lambda for the wideband sensor. The lean region curve (up to 1.84) was developed from a graph of Ip versus oxygen concentration provided in the Bosch LSU4.9 data and the equation: siliconchip.com.au 5 1μF 50V SMD X5R/X7R ceramic 1 470nF 63V MKT polyester 1 220nF 63V MKT polyester 6 100nF 63V MKT polyester 2 100nF 50V SMD X7R ceramic 1 3.3nF 50V SMD X7R ceramic 1 22pF SMD NP0/C0G ceramic Resistors (SMD 0805 or 1206 size, 1% metal film) 1 1MW 1 15kW 1 330W 2 560kW 8 10kW 1 150W 2 470kW 1 5.1kW 1 120W 4 100kW 1 2.2kW 1 62W 1 62kW 1 1.1kW 2 10W 3 22kW 1 1kW 1 1W (optional; 1 20kW 1 470W for meter display) 0.1W 3W (2512 package) Trimpots (3296W-style multi-turn top adjust) 2 500W (VR1, VR10) 1 1kW (VR3) 9 10kW (VR2, VR4-8, VR11-13) 1 50kW (VR9) Sensor parts (Tech Edge – http://wbo2.com/) 1 LSU4.9 wideband oxygen sensor [Tech Edge 017123] 1 2.6m sensor extension cable [Tech Edge DIY26CBL] 1 8-pin circular panel socket (male) [Tech Edge S8PIN] 1 8-pin circular line plug (female) [Tech Edge P8PIN] 1 6-pin LSU4.9 sensor connector plug [Tech Edge CNK17025] Optional pressure sensor (recommended) 1 diesel particulate filter differential sensor [VW 076906051A or similar] 1 3-way plug or similar for sensor connection [EFI Hardware C03F-0007] 1 3-way cable rated at 1A or more 1 cable gland to suit 3-6.5mm or 4-8mm cables Optional Bluetooth interface 1 HC-05 Bluetooth module [Core Electronics CE00021] 1 4-pin tactile pushbutton switch (S1) [Altronics S1120, Jaycar SP0600] Optional dual meter display 1 dual digital DC voltmeter and ammeter [Core Electronics 018-05-VAM-100V10A-BL] 1 UB5 Jiffy box with mounting flange [Jaycar HB6016] 1 4-way extension cable rated at 1A or more 2 cable glands to suit 3-6.5mm or 4-8mm cables Lambda (λ) = (1 + Oxygen% ÷ 3) ÷ (1 − 4.77 × Oxygen%) For the rich region, a four-step graph provided in the LSU4.9 Bosch data sheet is used with linear interpolation for values between those steps. A function is applied to the lambda value to produce an S-curve response for the simulated narrowband (S-curve) output shown in Fig.1. Ip is sensed by measuring the voltage Australia's electronics magazine across a 62W ±1% resistor (in parallel with Rcal). During the manufacturing of each sensor, it is calibrated at the Bosch factory using a 61.9W ±0.1% resistor from the E96 range. Rcal is trimmed so that the voltage across this resistor, measured against lambda, is the same for each sensor. Rcal can be a value ranging between 30W and 300W, depending on the characteristics of the individual sensor. April 2023  45 The value for Ip shown on the vertical axis of Fig.5 is therefore not the total pump current; Ip is actually the current through the 62W resistor. So while Fig.5 shows Ip varying between -1.85mA and +1.07mA, the actual current could vary from -2.23mA to +1.29mA if Rcal is the maximum value of 300W, -5.67mA to +3.28mA if Rcal is the minimum of 30W or somewhere in between. This current needs to be supplied by the wideband controller circuit. Pump cell control and sensor measurement Fig.6 shows the general arrangement for the pump cell and sensor cell measurement. A filtered pulse-width modulated (PWM) signal from the microcontroller (IC1, PWM5) is applied to buffer stage IC3a. This supplies current to one side of the pump cell via trimpot VR3 to the Rcal resistance (inside the wideband sensor’s socket) and the 62W resistor. The other side of the pump cell connects to a 3.3V supply at Vs/Ip. When the output of IC3a is at 3.3V, there is no current through the pump cell. For positive current through the pump cell, IC3a’s output goes above 3.3V; when IC3a’s output is below 3.3V, the pump cell current is negative. IC3a’s output can swing between 0V and 5V to allow for the current range required for the lambda extremes of measurement (0.7 to 1.84). The pump Fig.6: the general arrangement of the wideband controller. The PWM5 output of the micro is filtered and then buffered by IC3a to provide a controllable ion pump current. Since the other end of the ion pump is held at +3.3V, the pump current can flow in either direction. It’s monitored via IC4d, while IC4a measures the sensor cell voltage. Fig.7: the percentage difference in ion pump current at various exhaust pressure values. The error also depends on the lambda value, with the effect greater for lean mixtures, so the measured exhaust pressure and lambda are considered when correcting this error. 46 Silicon Chip Australia's electronics magazine cell current (Ip) is monitored using op amp IC4d, which amplifies the voltage across the 62W resistor by 25.45. Its output is fed to the ANA6 analog input of microcontroller IC1. Simultaneously, op amp IC4a amplifies the sensor cell voltage (Vs) by 4.7 times. A 20μA reference current is also applied to the sensor cell at this point. While this is called a reference current, it is not a critical value; the word ‘reference’ indicates that the current is to maintain oxygen ions for the pseudo oxygen reference. The reference current does not flow through the 62W and Rcal resistances, so it does not affect the calibration of the wideband sensor when it comes to accurately measuring the oxygen content in the measurement chamber. Trimpot VR4 provides an offset voltage that is buffered by IC4b so that IC4a’s output is 2.5V when the sensor cell voltage is 450mV. The microcontroller monitors IC4a’s output at its ANA7 input and varies the pump current to maintain a 2.5V reading. This effectively keeps the sensor cell at its stoichiometric point. When the sensor cell is measuring stoichiometric, the Ip value determines the actual lambda value. One complication with Ip is that it depends on exhaust pressure, which is always above atmospheric pressure. Fig.7 shows the change in Ip versus pressure. Our Wideband Oxygen Sensor Controller provides pressure correction for up to 900hPa above standard atmospheric pressure (1013hPa). At 900hPa above atmospheric pressure, the Ip required for a given lambda value is about 15% higher for lean mixtures and 10.5% for rich mixtures. So the microcontroller can correct for this, an air hose connects from the exhaust manifold to a pressure sensor in the WFMD. However, this is optional if you are not overly concerned about the reading error. Note that the exhaust pressure does not affect stoichiometric mixture readings because Ip is zero. Ip also depends on temperature, so any variation in the sensor cell temperature will affect the Ip readings. Fig.8 shows how the sensor cell resistance varies with temperature; the change in Ip with temperature is around 4% per 100°C. There are two ways to ensure the lambda readings remain accurate. One is to correct for the effect siliconchip.com.au of temperature using the graph and the 4% change per 100°C. The better option is to maintain a constant sensor temperature by driving the heater and monitoring the sensor cell resistance. Fig.8: to make accurate measurements, we need to keep the sensor cell at 780°C. As its resistance varies with temperature, we can determine its temperature by measuring that resistance and use feedback via the heating element to maintain it at the correct temperature. Heater element control By maintaining the sensor at 780°C, the lambda versus Ip graph can be followed to determine the required display values without needing temperature compensation. The sensor cell temperature is measured by monitoring the impedance of the sensor cell, which is high at room temperature, falling to 300W at 780°C. The impedance of the sensor cell is measured by applying an AC signal to it, as shown in Fig.9. A 5V peak-topeak (p-p) AC signal from IC1’s RC0 digital output is applied to the sensor cell via a 220nF capacitor and 10kW resistor. The capacitor blocks DC and the resistor forms a voltage divider with the impedance of the sensor cell. When the sensor cell has an impedance of 300W, the voltage across it is 145.6mV peak-to-peak. IC4a has a gain of 4.7, so its output is 684mV peakpeak. The microcontroller measures this signal at its analog input ANA7 and maintains the 300W sensor impedance by varying the heater current. The sensor cell would need to vary by 25°C to produce a 1% variation, equating to about a 100mV shift in the measured voltage at ANA7. Since we maintain the voltage to within much less than that, the resulting lambda error is minimal. Controlling the heater current Fig.10 shows the heater control circuit. Mosfet Q1 is connected in series with the heater element across the 12V supply and driven by a PWM signal from IC1 (PWM6). The heater current is monitored via a 0.1W series resistor; the voltage across this resistor is lowpass filtered by a 22kW resistor and 10μF capacitor and fed to the microcontroller’s AND6 analog input. If the heater is disconnected or goes open-circuit, the lack of current will be detected and the WFMD will shut down. Similarly, if the heater current becomes excessive, the controller will switch off Q1 and the heater. Heating the sensor from a cold start requires a special procedure with a slow increase of heater power. This eliminates moisture buildup in the sensor and prevents thermal shock, siliconchip.com.au Fig.9: the sensor cell impedance is measured by superimposing a small AC signal on the DC sensor cell voltage with a fixed source impedance. The lower the cell’s impedance, the more heavily this AC signal will be attenuated. SC6721 Kit ($120 + postage) Includes the PCB and all the parts that mount directly on it; the microcontroller comes preprogrammed (the Bluetooth module is also included). You need to separately purchase the oxygen sensor, case, wiring, fuse holder, off-board connectors (including those for the O2 sensor) and optional parts like the pressure sensor and LED display. Fig.10: the average heater voltage is controlled by applying a PWM signal to the gate of a Mosfet to switch the heating element on and off rapidly. The current it draws passes through a 0.1W shunt resistor and the resulting voltage is fed to the micro via a low-pass filter to get an average voltage. Australia's electronics magazine April 2023  47 Fig.11: This simple divide-by-three circuit changes the battery voltage of 10-15V into a 3.3-5V range that’s suitable for measurement by 5V-powered microcontroller IC1. The Windows/Mac/Linux software (above) and Android App (below) both show the AFR and Lambda values so you can just read off whichever one suits you. The stoichiometric setting for the AFR reading is set with a trimpot on the main unit. Why is there no iOS App? We tried to create an iOS App similar to our Android App using both Processing and the MIT App Inventor. However, there seems to be an underlying limitation in iOS when it comes to handling Bluetooth serial streams. The problem is that iOS does not seem to support the Bluetooth SPP (serial port profile) that the HC-05 Bluetooth module uses. See: https ://developer.apple.com/ forums/thread/95083 The WFMD might work with an iOS device over Bluetooth if you can find a Bluetooth module similar to the HC-05 that uses a different Bluetooth protocol supported by iOS. We have found modules with the model designation AT-09 or HM-10 to be widely available with claimed iOS support and they appear to be pincompatible with the HC-05. However, it is unclear what that really means. If we can make them work with iOS devices, we will provide an update in one of the upcoming articles in this series. 48 Silicon Chip which could damage the ceramic sensor. The sensor is not heated until the engine starts so that exhaust flow can blow any condensation out of the sensor. A preheat period then begins with an effective 2V applied to the heating element for two seconds. The heater voltage then increases to an effective 7.2V and ramps up by 73.3mV every 187.5ms. This is equivalent to 0.39V/s, just under the maximum 0.4V/s rate specified by Bosch. The effective heater voltage is based on the battery voltage and the duty cycle of the PWM waveform. So the battery voltage is monitored to calculate the required duty cycle to achieve the desired average voltage. The battery voltage is also monitored to detect when the engine starts and stops. When the engine starts and the alternator begins charging the battery, its voltage rises above the resting level. In practice, the battery voltage varies from around 12.5V with the engine off to more than 14V with the engine running when the battery is charged. The battery voltage is measured using a voltage divider comprising 20kW and 10kW resistors, shown in Fig.11. While the sensor cell is heated, the impedance of the sensor cell is constantly monitored and as soon as it reaches 300W, the preheat is complete, and power to the heater is controlled to maintain this value. The pump cell control circuit then starts to operate. Next month There isn’t enough room to fit the full circuit diagram and remaining description in this issue, so we’ll have all those details next month. The construction, wiring, set-up and calibration details will also follow. 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To start your subscription go to siliconchip.com.au/Shop/Subscribe Review by Tim Blythman The T48 universal programmer is the latest revision of the popular TL866II, often referred to as the ‘MiniPro’ . Chinese company XGecu sent us one to try out and we found it a worthy successor. XGecu T48 Universal Programmer L ast year, we purchased an XGecu TL866II Universal Programmer, having heard that they could program a wide range of chips. We subsequently published a review of it in the February 2022 issue (siliconchip. au/Article/15209). We found that the TL866II is wellmade and easy to use. The accompanying software is straightforward and familiar enough to those who have used other programming software, such as the MPLAB X IPE from Microchip. The ZIF (zero insertion force) socket in the top means that you can use it on a wide variety of parts without worrying about pinouts and programming adaptors. The programmer configures its connections to go to the correct pins. We remarked that the TL866II supports many parts and is relatively fast at programming. There is a Multi Programming interface, making it easy to use up to four programmers. With the ZIF socket, it could be a handy tool in a small production environment. It can read from devices and output to HEX and binary files, so it is a handy tool for saving and backing up chips too. However, for most of our purposes, typically involving modern PIC devices, the TL866II was not helpful as it does not support the newer microcontrollers we use. Nevertheless, we use it for chips that it supports (such as AVRs and EEPROMs), as the integrated ZIF socket makes it easy to operate and fast enough for our volumes. It has The unit they sent us for testing was accompanied by a pair of TSOP-48 adaptors, one for NAND flash and one for NOR flash. The NOR flash adaptor uses the 16-way IDC cable to plug into a socket on the programmer so it can provide the extra pins needed beyond the 40 on the ZIF socket. A USB cable is also included. 54 Silicon Chip Australia's electronics magazine excellent support for older chips, so it is definitely handy if you are working with legacy devices. The new T48 The latest variant in the TL866 series is the T48, also known as the TL866-3G. We were sent a unit to try out for this review. It can also be found on the XGecu eBay store in various combinations with adaptors for surface mounting parts and socket adaptors for PLCC (plastic leaded chip carrier) components. If you visit their eBay store you will find a range of packages starting at just under $100 for a bare programmer and USB cable (siliconchip.au/link/abjk). Note that there is also a different and more expensive programmer called the T56, which has a similar appearance. The store offers bundles that include other accessories like a PLCC chip puller, IDC breakout cables and even a UV EPROM eraser. The price point of under $100 for the unit with a USB cable only puts it on par price-wise with devices like the PICkit 4. Like the TL866II, the T48 consists of a two-part plastic case with a 40-pin ZIF socket on the top. The T48 is marginally larger and arguably more stylish, with a black case, black ZIF socket and curved corners. The two LEDs are marked the same (POW and RUN), but there is also a 16-way IDC header box instead of the 6-way ICSP header of the TL866II. The unit we were given for testing came with two TSOP-48 socket adaptors, one for NOR flash chips and another for NAND flash chips. siliconchip.com.au Interestingly, the NOR flash adaptor sports a SOIC-8 chip without any discernible markings and features a 16-way IDC header that is clearly meant to be connected to the matching header on the programmer with a supplied IDC cable. This is the simple way to get around programming chips with more pins than are available on the ZIF socket. The more expensive T56 programmer has a 48-pin ZIF socket. You can find the complete supported parts list for the T48 at www. xgecu.com/MiniPro/T48_List.txt In the time between receiving the T48 and completing the review, the supported parts list had increased by around 4000 parts and was nearly double the size of the corresponding list for the TL866II. Hardware Like the TL866II, the case of the T48 is held together by four screws, so we opened it up to see what makes it tick. Like its predecessor, the internals consists of two PCBs connected by a straightforward dual-row header pin and socket arrangement. This runs parallel to the ZIF socket, making for a simple PCB layout. The upper PCB is smaller than the lower one and has numerous transistors and resistors on both sides. The top features four 74HC595 shift registers, and more chips are underneath. We didn’t separate the two boards as they are also locked together by soldered wires. The lower board has a large QFP (quad flat pack) chip which is probably the main microcontroller. Like the TL866II, we could not see which specific part is used, although it would need to be a part that can support the advertised 480MHz (high speed) USB. There are also some relatively large (compared to the smaller resistors and transistors) inductors, which we expect are part of the circuitry to generate the higher voltages (up to 25V) needed to program certain devices. Table 1 – main differences between the TL866II and T48 TL866II T48 (TL866-3G) 16-bit, 32MHz 32-bit, 120MHz Microcontroller Full speed (12MHz) High speed (480MHz) USB Interface 1.8-6.5V in 32 steps 1.8-6.5V in 64 steps Target supply voltage 9-18V in 32 steps 9-25V in 64 steps Target prog. voltage Fixed at 3.3V 1.8-3.6V in 16 steps Target I/O voltage 17,000+ 32,000+ Supported parts and has a positive snap action. Interestingly, the markings on the T48 indicate that the target IC is inserted at the opposite end of the socket to the TL866II. We can see why this might be preferred from an ergonomic point of view. It means that the lever is at the opposite end of the socket to the chip, which gives more clearance. It isn’t really a problem for most chips under 40 pins but could help if you are using 40-pin chips or an adaptor socket that needs to slot into the ZIF socket. Some TSOP adaptors even have a notch at one end to allow for the swing of the ZIF socket handle. The ZIF socket is the only moving part on either programmer, so it could suffer wear-and-tear over time and eventually break. Still, we have yet to have a failure on either programmer (more than we can say for some of the cheap ZIF sockets we use in our own programming ‘jury-rigs’!). Overall, there are no big surprises inside the T48; it is an evolution of the TL866II design, although there has clearly been some development on the software and firmware too. With their common features and shared heritage, much of this review will reflect the differences between the T48 and its predecessor. The general comments we made on the TL866II will apply to the T48. XGecu provides information comparing the TL866II and the T48; an excerpt of some characteristics is seen in Table 1. Many of the remaining comparisons are related to speed, so we will perform our own tests later to compare the speed of the TL866II and the T48. We’ve tried to test with much the same parts as our previous review. The range of supported parts also differs. The comparison documentation generally indicates that the T48 supports all those supported by the TL866II and more. Software Both programmers depend on the Windows-based XGPro software for operation. At the time of writing, we are testing with version 12.39 of the software; this version supports the TL866II as well as the T48. We also tried version 12.45 of the software but did not notice any substantial Comparison Since the TL866II can only provide up to 18V for programming, rather than the 25V of the T48, the T48 can clearly support a broader range of parts. The T48 documentation notes that it incorporates a better ZIF socket than the TL866II. It does feel more robust siliconchip.com.au The T48 shares heritage with the TL866II. A microcontroller with many pins on the bottom PCB interfaces to the 40-pin ZIF socket on the top PCB via an array of passive devices. The 16-way IDC socket can be seen at right; this allows connection to a breakout board and thus parts with more than 40 pins. Australia's electronics magazine April 2023  55 Screen 1: most of the XGPro window is taken up by the memory contents, with a status log at right and numerous function buttons along the top. You can adjust the SPI clock frequency for some chips that use an SPI interface, such as the flash chip shown here. differences. Screen 1 shows the main window of the XGPro software. This software updates the firmware in the programmer, adding features and support for a greater range of parts. So it’s likely that even more target devices will be supported in the future. We noted the existence of the thirdparty “minipro” software for driving the TL866II during our previous review, but at this stage, it does not appear to support the T48, and there is no indication that it might. The overall layout and functionality of the newer 12.39 version of XGPro are much the same as the older 10.75 version we used for our tests of the TL866II, but we found a few differences. Firstly, the software picked up on an error we made at one point: placing the chip at the wrong end of the ZIF socket. We expect we were not the first and will not be the last to do so! Screen 2 shows the specific warning that is given in that case, remarking on the difference in markings between the T48 and TL866II. Software features Screen 2: one subtle difference between the T48 and its predecessor is the location of the lever for the ZIF socket; fortunately, the software designers have included a check and error message that picks up this particular error that we (and no doubt many others) had made. Screen 3: the XGPro software provides clear and simple diagrams for interfacing with ICs via the 16-way IDC header socket. This typical diagram for parts that use an SPI interface makes it easy to build custom adaptors for programming parts in-circuit. 56 Silicon Chip Australia's electronics magazine We found several new features and improvements in the XGPro software. Many of these features appear to work with the TL866II as well as the T48, although we didn’t check them all. For example, there is now the option to set the clock speed for some chips that use an SPI interface. Screen 1 shows the speed option at the bottom. We did not run into any situations requiring running at lower than maximum speed, but it could be handy if you use the T48 via the IDC header cable or on parts already fitted to a PCB. Editor’s note: some AVR chips require low-speed programming when their fuses are set to run at a low clock speed. Screen 3 shows a wiring diagram for a chip that uses SPI. This is provided from the Device.Info tab inside the XGPro program. Each part has at least a diagram showing how it should be fitted in the ZIF socket, plus arrangements for using the IDC header, if appropriate. Screen 4 shows the wiring diagram of a DIP adaptor for a PLCC socket that will allow it to be fitted to the ZIF socket. Such an adaptor is typical of what can be purchased with the siliconchip.com.au programmer, although the information here makes it easy to build your own. One small catch we noticed when trying to program an ATF16V8 PLD (programmable logic device) with the older TL866II and version 10.61 software was that verification would fail if we enabled “Encryption”. It appears that the newer versions allow this now. The data is now programmed and verified, and only then is the security bit programmed to prevent read access. Speed tests Using version 12.39 of the XGPro software, we ran comparative speed tests between the T48 and TL866II. The way that the software versions relate to the firmware versions of the programmer means that it is not possible to revert to older versions, so we were unable to do comparative tests with the older versions of the software or compare the performance of the different firmware versions. XGPro allows basic editing of memory spaces and can also fill regions with certain data bytes or even random data. Our test data involved reading the memory and then changing it to random data. We then saved these random data files to ensure consistency between tests. Screen 5 shows the window used for editing data; it is straightforward enough. It’s also possible to edit data directly in the main window by clicking on a value and typing over it. Performing a program operation on the main memory space of these chips typically involves bulk erasing the device (if necessary), programming the data and then verifying it (by reading it back and comparing it to the original file). The results of the speed tests are shown in Table 2. Unsurprisingly, the T48 is as fast, if not faster, in nearly all cases; only the programming of an FM25640 SPI FRAM chip was slower. Still, that difference was a fraction of a second and probably would not be noticeable to the user. For comparison with the T48, a Snap programmer can program the entire 14kiB memory space of a PIC16F1705 in less than a second. The Microchip IPE only provides timestamps with one-second resolution, so comparing read and erase times is difficult (and perhaps pointless). We also performed some tests on siliconchip.com.au Table 2 – time (ms) for operations on the entire main memory space Operation TL866II T48 Read/Verify 6891 1563 Erase 8609 7547 Program 14172 8172 Read/Verify 4032 2438 Erase 407 391 Program 25172 21859 Read/Verify 140 47 Erase 31 31 Program 1641 1328 Read/Verify 125 109 Erase 828 828 Program 3500 3407 24LC256 32kiB I2C EEPROM Read/Verify 4343 2937 Program 10250 8578 24LC512 64kiB I2C EEPROM Read/Verify 8734 5813 Program 12594 9328 FM25640 8kiB SPI FRAM Read/Verify 172 62 Program 312 469 Read/Verify N/S 23860 Erase N/S 1188 Program N/S 35937 Read/Verify N/S 453 Erase N/S 31 Program N/S W25Q32 4MiB SPI flash chip SST39SF040 512kiB parallel flash chip AT28C64 8kiB parallel EEPROM AT16V8B 2194 bit PLD MT29F1G08ABAEAWP 128MiB NAND flash PIC16F1705 14kiB flash memory microcontroller 33141 N/S = not supported. Screen 4: the PLCC32 to DIP-32 adaptor shown here was included with our TL866II and can be purchased as part of the deal. Still, the pinout diagram makes it easy to design and assemble your own and troubleshoot those connections. Screen 5: the main memory window allows values to be directly edited, but if you need to set a large block of memory to a particular value, it can be done in the Fill Block dialog box. It can also fill a block with random data, which is what we did for our tests. Australia's electronics magazine April 2023  57 parts that are only supported by the T48, including one that requires the use of a TSOP-48 adaptor. The MT29F1G08ABAEAWP 128MiB NAND flash chip was the highest-capacity part we could quickly and easily acquire. Its capacity is large enough that the log noted that we had sufficient hard drive space to store the image! The time taken to program this chip is the same order of magnitude as expected from the data sheet, considering communication overheads. Programming PICs Since we often use PIC microcontrollers in our designs and also sell programmed microcontrollers in the Silicon Chip Online Shop, we were interested to see how handy the T48 would be for our purposes. The supported devices list for the T48 shows several 8-bit (PIC10, PIC12, PIC16 and PIC18) parts but no 16-bit (PIC24/dsPIC33) or 32-bit (PIC32) Microchip parts. Also listed are some of the older AVR parts, such as the ATmega328, as found in the Arduino Uno. Such AVR parts now fall under Microchip’s purview since their takeover of Atmel in 2016. The PIC16F1705 is one of the newer 8-bit ‘mid-range enhanced core’ PIC microcontrollers and is supported by the T48. We used this chip in the Flexible Digital Lighting Controller from October -December 2020 (siliconchip. au/Series/351) In our review of the TL866II, we noted that support for modern parts was lacking, so it is good to see that some newer parts are now supported. The PIC16F1709 (which is similar to the PIC16F1705 but has 20 instead of 14 pins) is also supported. You can also see from Table 2 that programming the PIC16F1705 is relatively slow at 30 seconds. Microchip’s Snap programmer (driven from the Microchip IPE program) can program this part in around a second, and a PICkit 4 is similar. For now, our advice for newer Microchip parts is to continue using their programmers. Support for more PICs The XGPro software has a feature to “Add IC by user”, which is ideal for parts like Microchip microcontrollers. It is intended for parts with the same programming interface as a listed part but a different device ID. The PIC16F1455 is a microcontroller we use frequently; it’s one of a handful of 8-bit PICs with a USB peripheral. It is pretty similar to the PIC16F1705, but unfortunately, different pins are allocated for programming on these two chips, so we couldn’t use this feature to add the PIC16F1455. Using the PIC16F1709 settings, we also tried communicating with some of the newer 20-pin PICs (October 2022; siliconchip.au/Article/15505). Parts like the PIC16F18146, PIC16F17146 and PIC16F18045 have the same pinout for their programming pins, so they might be expected to work. Unfortunately, we could not even retrieve a device ID, so we could not use this feature to work with other chips as we hoped we might. There may be some variations in the programming protocol for these newer PICs. Editor’s note: even Microchip’s older programming hardware & software won’t work with those chips, so that’s likely to be the case. Since different devices often have different flash memory sizes and configuration fuses, adding support in GPS-Synchronised Analog Clock with long battery life ➡ Convert an ordinary wall clock into a highlyaccurate time keeping device (within seconds). ➡ Nearly eight years of battery life with a pair of C cells! ➡ Automatically adjusts for daylight saving time. ➡ Track time with a VK2828U7G5LF GPS or D1 Mini WiFi module (select one as an option with the kit; D1 Mini requires programming). ➡ Learn how to build it from the article in the September 2022 issue of Silicon Chip (siliconchip. au/Article/15466). Check out the article in the November 2022 issue for how to use the D1 Mini WiFi module with the Driver (siliconchip.au/Article/15550). Complete kit available from $55 + postage (batteries & clock not included) siliconchip.com.au/Shop/20/6472 – Catalog SC6472 58 Silicon Chip Australia's electronics magazine siliconchip.com.au Here is a side-by-side comparison of the T48 (right) with the TL866II (left). The T48 is only slightly larger and has a black case with curved corners. A similar case is used for the more expensive T56 programmer, although this (confusingly) sports a 48-pin ZIF socket, unlike the T48, which has a 40-pin socket. this way may be tricky as there will be other factors to consider. Interestingly, you can select the PIC16F1705 in the newer version of the XGPro software while a TL866II is connected, but it will not work and an error message indicates that it is not supported. We have contacted the XGecu company about adding support for some of the newer Microchip parts, and they responded that it should be possible. We hope to see this support in a future software version. memory spaces and thus take some time to program. Conclusion The T48 is superior in just about every way to its predecessor, the TL866II. It supports a greater range of parts and, handily for us, this includes some of the newer PIC microcontrollers. The XGPro software is also being updated and, even in the time we have been reviewing it, we have seen a substantial increase in the number of supported parts. It does cost a bit more than the TL866II, but you would be hardpressed to find a case where the extra cost is not worth the extra capabilities. We’d have no hesitation in recommending the T48 over the TL866II. If you work with many older parts, such as reading ROM chips to preserve their contents or dabbling with recreations of older designs, then the T48 is well suited. We hope that support for modern PIC microcontrollers continues to expand, ideally including the newer parts we reviewed last year, such as the PIC16F18146. The T48 is available from various online stores. Prices start at just under $100 and go up from there depending on which adaptors you wish to bundle into your purchase. Still, given the proliferation of clones of this type of device, it’d be safer to stick with one of the XGecu official stores: eBay official store ebay.com/str/xgecuofficialstore AliExpress official store xgecu.aliexpress.com Amazon store www.amazon.com/xgecu SC Multi Programming We mentioned the Multi Programming feature of the XGPro software in the previous review, but since we only had one programmer, we couldn’t try it out. With two (albeit different) programmers, we were now able to do so. Screen 6 shows this, with the two programmers each programming a 24LC512 EEPROM chip. As you can see, both have run to successful completion in their own time. We did need to plug each programmer directly into the computer as we did not have a powered USB hub; note the warning text at the top of the window. Otherwise, the programmers complained about insufficient power when connected via an unpowered hub. Multi Programming is a handy feature, but not one that we’re likely to use except for chips that have large siliconchip.com.au Screen 6: now that we had two programmers, we could try out the Multi Programming feature. XGecu recommends using the same programmers, but we had no trouble with two different models. Make sure that each device has sufficient power by, for example, using a powered hub. Australia's electronics magazine April 2023  59 This handy device can provide test voltages, test signals, vary a resistance, switch a component in or out of circuit and even measure some voltages. It ties into automation software so it performs tests automatically and records input and output values for analysis. Swiss Army Knife An Automated Test Bench by Richard Palmer W hen testing something on the bench, I often need to fish around in the parts drawer for some control component, like a switch or a pot. That’s so I can test some circuitry across a range of voltages, with different component values or with some element in and out of circuit. I’m usually also measuring the impact of changes at one or two places in the circuit. It’s remarkable how often I reach for the same components: a switch, a 100kW pot, a sinewave generator and a 0-10V control voltage source being among the most frequent. A collection of these most-used elements would be like a ‘Swiss Army Knife’ for the test bench. Most pocket knives don’t pretend to have all the tools you’ll ever need or even the absolute best of each kind of tool. Still, they offer a set of robust, basic tools that will get the job done when the perfect tool isn’t at hand or isn’t needed. The cost and complexity of the project have been kept down by controlling it via WiFi using a web interface rather than an LCD screen. That also means it can be teamed up with test automation software, such as TestController, to automate many test bench tasks. Features and performance Pocket knives range from a single blade to monsters with more than thirty functions. We’ve settled on nine functions for this project, and focused on making them simple to use while 60 Silicon Chip designing them to tolerate moderate abuse. The input and output connections are made with spring-loaded or cam-operated terminals and multiple ground connections are provided. Two 16-bit analog inputs with over-voltage protection can measure ±10V DC to within a few millivolts with excellent linearity. As long as both input terminals are kept within that range, it can measure differentials up to 20V. The input range can be extended by adding series resistance to the inputs. The 0-10V DC analog output has 256 steps of approximately 40mV (see Screen 1). While the accuracy isn’t at the same level as the analog inputs, 256 individual test values should be enough for most purposes. The sinewave generator operates from 133Hz to 55kHz. The generator has two output voltages: 6V peak-topeak (2.1V RMS) and 775mV peak-topeak (0.27V RMS). The available frequencies are multiples of 133.33 Hz, and the software rounds settings down to the nearest available value. Despite being driven by an 8-bit digital-to-analog converter (DAC), the noise and distortion total less than 1.5% across the range (see Scope 1 & 2) after low-pass filtering. Major contributors to this are the sine generator DAC’s voltage steps and a jump of Features & Specifications ∎ 256-step, 0-10V output (from a DAC) ∎ 133Hz-55kHz sinewave generator ∎ Two ±10V fully-differential analog inputs (16-bit ADC) ∎ Analog inverter with ±10V input and output ranges ∎ Two 3.3V digital outputs ∎ Two 5V-tolerant digital inputs ∎ 100kΩ digital pot with ±15V terminal ranges ∎ One 10A SPDT relay ∎ One 350mA SPST reed relay ∎ ±15V and +5V power supply rails ∎ Remote control via serial terminal and WiFi telnet SCPI commands ∎ Web interface ∎ TestController integration (see the article starting on page 80) ∎ Powered by a 5V plugpack ∎ Open-source code (excluding web interface) Australia's electronics magazine siliconchip.com.au Screen 1: here, the DAC output has been fed to both ADC inputs, and we are plotting the desired voltage (mauve) against the actual voltage read by a multimeter (red) and ADC channels one (blue) and two (dark grey) over the range of 0-250mV. The ADC2 plot tracks the external multimeter almost exactly; ADC1 has a slight offset error due to using 5% resistors in the prototype. several steps at the zero-crossing point. These artefacts are much less visible on the high output range, making that the range of choice. When finer voltage control is desired, the sinewave generator can be teamed up with the digital pot to provide 256 voltage attenuation steps for either of the basic output voltages. A general-purpose op amp based inverter is included to provide additional flexibility in handling negative input or output voltages. We’ve included two different relays: RLY1 is a 350mA SPST reed relay, useful for switching signals, while RLY2 is a 10A SPDT type that can switch power supplies and similar. Both have LED indicators. The maximum recommended voltage across both relays is limited to 50V by safety considerations for breadboard-style operation, rather than the relays themselves. Both can switch in less than 10ms. The digital inputs and outputs connect to ESP32 3.3V GPIO pins with series resistances to limit current if they are misconnected. The inputs have zener diode protection, will correctly read 5V logic and are tolerant of up to 20V. The inputs and outputs all have LED indicators. A 256-step 100kΩ digital potentiometer completes the feature set. We have specified a high-voltage type, which allows the pot terminals to be at any voltage within the ±15V analog supply rails. If your preference is for a different resistance (or you simply can’t get the 100kΩ type), you can substitute any of the other MCP45HV Scope 1: the direct sine output from the DAC at 400Hz (blue trace) on the low-level output range shows some noise and a zero-crossing discontinuity. The filtered output (yellow trace) shows a significant reduction in noise at the cost of a slight overshoot at each step change. siliconchip.com.au values (5kΩ, 10kΩ and 50kΩ). The project is housed in a UB1 Jiffy box and powered by a 5V plugpack. A readily available switching boost converter module is used to provide ±15V supplies for the op amps and digital pot. The ±15V and +5V supply rails are available to power external circuitry. The specified boost converter can supply 500mA at +15V and 200mA at -15V. At idle, the unit draws less than 100mA from the 5V supply and around 200mA with both relays energised and all the LEDs lit. While a 1A plug pack is more than adequate to power the unit itself, we recommend a 1.5A model if you will be powering much in the way of external circuitry. Even with relatively high conversion Scope 2: the distortion artefacts from the sinewave output are much less prominent on the filtered output at 5kHz as it spends much less time on each step. Australia's electronics magazine April 2023  61 Fig.1: the Swiss Army Knife is based around an ESP32 WiFi microcontroller module. Besides its digital inputs and outputs, its internal DAC at pin 9 (IO25) is used. Because the ESP32 ADC is poor, an external two-channel differential I2C ADC chip (IC1) is used, along with a digital pot IC for that function (IC2) and a quad op amp to buffer and filter the DAC signal plus provide an externally accessible voltage inverter (IC3b). efficiency, the 5V supply current draw will be around three times that drawn from either the +15V or -15V rails, and more than six times that drawn by a device across those rails. 62 Silicon Chip While the project can be USB-­ powered for commissioning, the USB cable voltage drop during operation might cause the brownout detector on the ESP32 to trigger, resulting in a Australia's electronics magazine potentially endless reboot cycle. The unit features a flexible suite of remote control functions, which is fortunate as there are no controls on the unit itself! It has been specifically siliconchip.com.au Keeping with our pocket knife theme, we’ve specified critical resistors as readily available 1% values to provide a full-scale accuracy of a few percent ‘out of the box’. With a simple calibration process that only requires a multimeter, you can make the analog accuracy better than 1%. While this isn’t a highly calibrated instrument, it has sufficient flexibility, accuracy and connectivity to make life on the test bench far more productive. Circuit details designed to be compatible with TestController, or via its web interface. You can also control it via SCPI text commands from the USB serial monitor in Arduino or via Telnet from a siliconchip.com.au terminal program like PuTTY. The manual included in the project downloads has full details of the SCPI command set and communication parameters. Australia's electronics magazine As shown in Fig.1, the heart of the project is an ESP32 WiFi microcontroller module. The ESP32 handles the digital inputs and outputs directly via its GPIO pins, plus it has a DAC and sinewave generator. It also manages WiFi and serial communications. The nominally 3.3V digital inputs have 4.7kΩ series resistors and 3.3V zener clamping diodes ZD1 and ZD2 to make them reasonably fault tolerant. They draw minimal current from 3.3V logic and around 0.3mA from a 5V source. The inputs will register ‘high’ for any voltage above 2.5V at pins 5 & 6 (IO34 & IO35) and are weakly pulled down by 50kΩ resistors within the ESP32. The input LED indicators are driven by pins 29 & 30 (IO5 & IO18) to avoid loading the digital inputs. Pins 24 & 26 (IO2 & IO4) drive the digital outputs. When low, they will be below 0.3V, and when high, above 2.7V. 220Ω series resistors limit the output current and, with zener clamping diodes ZD3 and ZD4, provide a measure of protection against misconnection. Op amp IC3a amplifies the output from the DAC line (pin 9) that’s nominally 0-3.3V to 0-10V full scale. The feedback resistor has been chosen to provide a little more than the required three times gain so that component variations can be corrected by calibration. The 10kΩ resistor and 100pF capacitor form a low-pass filter to reduce the noise from the DAC. IC3d is an amplifying Sallen-Key low-pass filter for the sinewave output, with a -3dB frequency of around 70kHz. The op amp gain is set to two, as Sallen-Key filters with gains of more than three are unstable. The MC33079 op amps can drive their outputs within 1.5V of the supply rails and have a 175kΩ input April 2023  63 impedance. They can source and sink up to 30mA and feature short-circuit current limiting. 100Ω resistors in series with the outputs provide an extra margin of safety if they are misconnected. As the op amps use an industry-­ standard footprint, substitution should be possible if the specified devices aren’t available. While the MC33079 is a more modern op amp with better specifications, for most jobs the Swiss Army Knife will be used for, the venerable LM324 will work fine. While the ESP32 has in-built analog-­ to-digital converter (ADC) channels, they are not linear enough for even basic measurements. Analog voltages fed in via CON4 & CON5 are measured by a two-channel, 16-bit differential ADS1115 ADC (IC1) which is set to have a 2.048V input range. 91kΩ/10kΩ resistive dividers on the inputs reduce 10V signals to just under 1V, allowing for excess input voltages to be sensed and some component variation to be corrected by calibration. As it is desired to measure both positive and negative voltages, both divider chains are referenced to the 1.1V bias supply (VREF) rather than ground. resistors to filter noise from the input, with a corner frequency of 160kHz (1 ÷ [2π × 10kW × 100pF]). Digital potentiometer The pins on this dual-supply boost converter (5V to ±15V) match those on the PCB (MOD2). Other 5V to ±15V modules could be used but would need to be wired to the PCB appropriately. The ADS1115 has inbuilt over-voltage and negative voltage protection for input currents of less than 10mA, which are limited by the upper resistors in the dividers. If the ADS1115 isn’t available, an ADS1015 can be substituted with a slight drop in accuracy. The bias voltage for the ADC is provided by IC3c, which amplifies D1’s 0.65V forward voltage to the required 1.1V. This diode is biased with 1mA from the 3.3V rail via a 2.7kW current-­ limiting resistor. Inverting amplifier IC3b completes the analog functions. Its gain is set to -1 and input impedance to 10kW by the pair of 10kW resistors. The 100pF capacitor combines with those The terminal voltages of digital pots are generally limited to the device’s digital supply rails. The MCP45HV51 (IC2) is a somewhat unusual high-­ voltage component with an extended analog-­ side voltage range. Its ±15V analog power rails allow the pot terminal voltages to be anywhere within that range. While we chose the 100kW model for our prototype, the MCP45HV series also has 5kW, 10kW and 50kW variants, any of which may be substituted without any circuit changes. Both the ADS1115 ADC and MCP45HV digital pot are controlled over an I2C serial bus by the ESP32. Both devices have their additional address pins tied low. Two relays are provided, driven by NPN transistors Q1 and Q2, with diodes D2 & D3 to quench back-EMF of the coils at switch-off. RLY1 is a 350mA SPST reed relay with a 15mA coil, while RLY2 is a heavy-duty, 10A model with SPDT contacts and a 5V 85mA coil. The indicator LEDs light when a coil is energised. Fig.2: the Swiss Army Knife board can be used bare, or housed in a plastic UB1 Jiffy box. Just with four holes and one large rectangular cut-out need to be made on the lid, plus one hole on the side for access to the DC power input socket. 64 Silicon Chip Australia's electronics magazine siliconchip.com.au Power comes from a 5V plugpack and a boost converter module (MOD2) that supplies ±15V. All three supply rails are brought out to a terminal block for breadboard use. Case preparation If you aren’t using our laser-cut lid replacement, start by marking out and cutting the holes in the lid as shown in Fig.2. There are just the four corner mounting holes to drill to 3mm, plus the rectangular cut-out to make. You can do that by drilling a series of holes just inside the rectangular outline, cutting between the holes to remove the plastic inside and then filing the edges smooth and to full size. We’re doing this before assembling the PCB because, to assist you in locating the holes, you can place the blank PCB on the underside of the Jiffy box lid with the component side showing. It should sit neatly inside the locating ridges. Mark and drill the four mounting holes, then make the cutout, which should be 3mm outside the terminal block outlines. While not necessary, it would be nice to countersink those four mounting holes and use countersunk screws, so they are flush with the lid. PCB assembly Given the current global supply shortage of electronic components, some substitution of the active components may be required. Alternatives are noted in the circuit details above and in the parts list. Our kit (mentioned in the parts list) should make getting the critical parts a lot easier. The 142 × 83.5mm double-sided PCB is coded 04110221 and the component locations are shown in Figs.3 & 4. Most of the components and the ESP32 are on one side, with just the connectors and LEDs on the other side. It’s best to fit the three SMD ICs first. Locate their pin 1 indicators and line them up with the pin 1 indicators on the PCB or Fig.3. Spread flux paste on the IC pads, then tack one pin of the IC to a corner pad. Figs.3 & 4: fit the components to the board as shown here, paying particular attention to the orientations of the ICs, LEDs, zener diodes, relay RLY1 and the boost module. Also, don’t get the transistors (Q1 & Q2) and small signal diodes (D1 & D2) mixed up. The resistors and capacitors are not polarised; while the resistors will be marked with coded values, the capacitors won’t. While the boost module is shown mounted vertically here, using a straight header, you can mount it horizontally as shown in the photo overleaf. siliconchip.com.au Australia's electronics magazine April 2023  65 that the wire entries face the outside of the board, as that will be the most convenient way to use it. Final assembly The underside of the PCB is where most of the components are mounted. This prototype differs from the final version, hence the added wires and components. Check that the part is flat on the PCB and all the leads line up with the pads, re-check the orientation of pin 1, then tack a diagonally opposite pin. Solder the remaining pins with minimal solder on the iron and clean up any bridges between pins with more flux paste and some solder wick. Once you’ve finished, clean off all the flux residue and scrutinise the pins under magnification to ensure all solder joints have formed properly. Move on to the four SOT-23 devices and solder them using a similar technique. Note that there are two devices using this package, so don’t get them mixed up. Then solder the four zener diodes, ensuring their cathode stripes face as shown. Follow with the SMD capacitors and resistors; the resistors will be marked with codes indicating their values, but you’ll have to refer to the ceramic capacitor packages to see their values (or measure them if unsure). Now flip the board over and solder the six SMD LEDs using a similar technique. Their cathodes are usually marked, and they go opposite the + markings in Fig.4 and on the PCB (+ indicates the anodes, not cathodes). You can check their polarity using a DMM set on diode test mode; they should light up with the red lead touching the anode and the black lead touching the cathode. With all the SMDs on the board, clean off any remaining flux residue before fitting the through-hole parts. We have specified header sockets for the ESP32 and the boost module so you can make those items pluggable. While it might be possible to solder them directly, we don’t advise that as it will interfere with the testing and programming sequence. On the side with most of the components, fit the DC socket (CON1), ESP32 (MOD1), boost module (MOD2) and relays. When fitting the boost module, refer to Fig.3 and the photo above. There is an extra row of pins for the ESP32 on the PCB, as some variants of the ESP32 DevkitC come with narrower spacing. You only need to populate the row that matches your module. Mount the terminals (CON2-CON12) on the other side of the board. You’ll probably want to orientate them so The PCB mounts under the lid of a UB1 jiffy box with a hole cut in its top, exposing the rectangular area shown in Fig.4. It is a tight fit; some trimming of the PCB locating slots on the case’s side walls may be required. There is no need for a decal or cover plate as the critical information is silk-screened directly onto the PCB. Clip or file off any pins protruding more than 1.5mm from the silkscreened side of the board, and mount it on the lid using 2mm spacers (eg, two 1mm-thick washers stacked) to provide clearance for the component pins. Mark and drill the hole in the case for the coaxial power socket, as shown in Fig.2, if you haven’t already. Loading the software You should now program the ESP32 separated from the PCB. As well as programs being compiled and loaded via an integrated development environment (IDE) such as the Arduino IDE, the ESP32 can load binary files using an over-the-air (OTA) update program. That has the convenience of being able to update its firmware away from your computer. The first step is to load the OTA program, which also conducts validation of the PCB. Install the Arduino ESP32 board files, following the instructions at siliconchip.au/link/abh9 Next, install the ESP32 exception decoder and file uploader plug-in (Releases: https://github.com/me-nodev/EspExceptionDecoder). Select “ESP32 Dev Module” as the board in the Tools menu of the Arduino IDE and edit the “OTA-Test.ino” file from the project download package (available on the Silicon Chip website) to include your WiFi credentials. Compile and run the program; the Serial Monitor will display the IP OTA loader and Swiss Army Knife basic tests. Starting with WiFi with SSID = [MYSSID], password = [MYPASSWD] ....... Connected to MYSSID IP address: 192.168.1.XX OTA loader at http://SwissArmy.local or the IP address above. ADC NOT found at I2C address 0x48 Digital pot NOT found at I2C address 0x3C Setup done. Now toggling relays and digital outputs, DAC staircases. Screen 2: the expected output of the OTA-Test program on the serial monitor, before the ESP32 is plugged into the main PCB. 66 Silicon Chip Australia's electronics magazine Screen 3: the Over The Air (OTA) login page displays when first accessing the ESP32 via a browser. siliconchip.com.au Address of the ESP32. You should get an output similar to Screen 2 with the Arduino Serial Monitor baud rate set to 115,200. As expected, the program has failed to find the ADC and digital pot. If you miss the messages on the Serial Monitor, simply push the boot (EN) button on the ESP32 module, and it will restart. Power down the ESP32 and plug it into the PCB sockets with the USB socket near the power input barrel socket, leaving off the boost module for now. Re-connect its USB cable to the computer. The two I2C devices should now show as available. All six LEDs and the two relays should turn on and off at two-second intervals. Now connect the boost converter (with power briefly removed) and check the ±15V rails while still operating on USB power. The DAC output should vary slowly between 0 and 10V at the terminal block. The sinewave output should be a series of pulses at the terminal block, as its buffer is AC-coupled, and we’re feeding it a staircase signal. Connect the DAC signal to the inverter input and check that the inverter’s output varies inversely with its input voltage. You can fully test the digital pot and ADC once the main program is loaded. For now, we have confirmed that they are responding to I2C messages. In the Data folder that is associated with the OTA-Test program, edit the profile.json file, find the section that looks like the following and replace the placeholder “ssid” and “pass” values with those for your WiFi network: { } “ssid” : “your SSID”, “pass” : “WiFi password”, “hostname” : “SwissArmy” Next, close the Serial Monitor window. In the Arduino Tools menu, click “ESP32 Sketch Data Upload” to copy the files in the Data folder to the ESP32’s local file system. The rest of the files in this folder are needed for the web interface. This uploaded file system will remain intact when new programs are uploaded. Open up a web page using the IP address or URL indicated by the Serial Monitor. On the OTA-Test program’s web interface, log in using “admin” and “admin” as the credentials (see Screen 3). siliconchip.com.au Parts List – Test Bench ‘Swiss Army Knife’ 1 double-sided PCB coded 04110221, 142mm × 83.5mm 1 UB1 Jiffy box [Altronics H0201 or H0151, Jaycar HB6011] 1 laser-cut UB1 Jiffy box lid (optional; 3mm acrylic) [Silicon Chip SC6337] 1 5V 1A or 1.5A plugpack with 2.1mm inner diameter coaxial plug [Altronics M8903A, Jaycar MP3144] 1 Espressif ESP32-DEVKITC-32D (MOD1) [Silicon Chip SC4447, Altronics Z6385A, Jaycar XC3800] 1 +5V to ±15V boost regulator module (MOD2) [Silicon Chip SC6587] 1 micro-USB cable (to program MOD1) 1 5V SIP reed relay (RLY1) [Pan Chang SIP-1A05, Littelfuse HE3621A0510, Teledyne SIP-1A05-D] 1 5V DC coil 10A SPDT relay (RLY2) [Altronics Z6325, Jaycar XC4419] 2 19-pin female 2.54mm headers (for MOD1) 1 5-pin female 2.54mm header (for MOD2) (can be cut from longer header) 1 2.1mm inner diameter PCB-mount DC barrel socket (CON1) [Altronics P0620, Jaycar PS0519] 7 2-pole, 5mm pitch ‘Euro’ type spring terminal blocks (CON2, CON4, CON5, CON10-CON12) [Altronics P2068, Jaycar HM3140, DECA MX722-500M or Eaton EM278502] 5 3-pole, 5mm pitch ‘Euro’ type spring- or cam-operated terminal blocks (CON3, CON6-CON9) [Altronics P2070, Jaycar HM3142, DECA MX732-500M or Eaton EM278503] 4 M3 × 12mm countersunk machine screws and hex nuts 8 M3 x 1mm Nylon washers Semiconductors 1 ADS1115IDGST or ADS1115IDGSR ADC, MSOP-10 (IC1) 1 MCP45HV51-x0xE/ST 8-bit I2C digital potentiometer, TSSOP-14 (IC2) (x0x = 502 [5kΩ], 103 [10kΩ], 503 [50kΩ] or 104 [100kΩ]) 1 LM324D or MC33079 quad op amp, SOIC-14 (IC3) [Altronics Y2523, Jaycar ZL3342] 2 BC817 or BC846-BC850 SMD NPN transistors, SOT-23 (Q1, Q2) [Altronics Y1312, Jaycar ZT2118] 6 SMD LEDs, M2012/0805 or gull-wing [Altronics Y1107, Jaycar ZD2000] 4 3.3V 1/2W+ zener diodes, DO-214AC or DO-213AA/SOD-80/MiniMELF (ZD1-ZD4) [eg, BZG05C3V3 or MLL5226B] 3 BAS16, BAV99 or similar signal diode, SOT-23 (D1-D3) [Altronics Y0089] Capacitors (all 50V SMD ceramic M2012/0805 size) 4 1μF X7R 8 100nF X7R 2 270pF NP0 2 100pF NP0 Resistors (all 1% SMD metal film, M2012/0805 size) 1 100kΩ 5 91kΩ 1 22kΩ 1 15kΩ 1 12kΩ 15 10kΩ 2 4.7kΩ 1 2.7kΩ 2 1.8kΩ 2 1.5kΩ 4 1kΩ 2 220Ω 3 100Ω SC6589 Kit ($50 + P&P) This short-form kit includes the PCB, lid, all the SMDs, the 5V to ±15V boost module and the SIP reed relay. All the other parts such as the case, connectors, 10A relay etc should be available from local retailers – see above. After logging in, select the downloaded project BIN file with the “Choose file” button, and then press the Update button. The web page will track the upload progress, and after a short delay, the ESP32 will reboot. Re-open the Arduino Serial Monitor, and start-up commands should be displayed, ending with an “SCPI Command?” prompt. If you type “*IDN?” (without quotes) into the command Australia's electronics magazine field on the Serial Monitor and click Send, the software should respond with something like “Platy,SwissArmy,00,v0.1”. The unit can now be sealed up in the Jiffy box, powered via the plugpack and remotely controlled via the web interface. If using a USB connection from this point on, we strongly recommend that a USB isolator be used to avoid April 2023  67 Screen 4: the Swiss Army Knife web interface main page. ADC1 and ADC2 are reading 5.10V and 5.11V respectively, while digital inputs D1 and D2 are both low. On the Settings panel, relay RLY2 is on, and digital output D1 is high. The digital pot is set at 128 steps (50%). The sinewave is currently being adjusted (setting highlighted) to 5.09V; turning the dial will result in 0.1V steps (radio buttons under the dial). Screen 5: the calibration page. If the external multimeter reads 9.61V, DAC1’s output voltage reading would need to be boosted by 0.1V. Changes are not stored until the Save button is clicked but calibration values are saved between sessions. The source code and other software files are available from GitHub at: https://github. com/palmerr23/ SwissArmyKnife damage to the ESP32 in the event of a misconnection. Changing the WiFi credentials If you have difficulty connecting to your local WiFi or need to change the settings, you can issue the following commands from a terminal program or the Arduino Serial Monitor: :SYST:SSID your-WiFi-SSIDwithout-quote-marks :SYST:PASS your-WiFi-Passwordwithout-quote-marks You can also change the WiFi credentials by editing the profile.json file on your computer and uploading it again, using the instructions above. You only need to open the OTA-Test program and re-upload the sketch data. The OTA-Test program does not need 68 Silicon Chip to be compiled or uploaded, but the unit will need to be re-calibrated after the profile upload. Remote control & calibration The unit has been primarily designed to work with the open source software TestController (siliconchip.com.au/ link/abev) or via its web interface. SCPI commands can also be issued via an isolated USB serial connection or over WiFi, using a terminal program such as PuTTy or TeraTerm. TestController uses SCPI commands to control all functions besides calibration and communication settings. Further details of the remote control modes and SCPI commands are available in the manual included in the download for this project: siliconchip. com.au/Shop/6/58 Australia's electronics magazine The web interface can control all the outputs and display all the input readings on its Main tab (Screen 4). It also offers calibration functions on its Cal tab (Screen 5). It’s best if only one of the remote control options is active at any time, as settings made on one interface may not seamlessly update on all the others. Web interface The Main tab of the web interface is accessible via http://swissarmy.local and has the input readings on the left and settings on the right. To set a numeric value, click on the setting to be changed and wind the knob. The radio buttons under the knob determine the size of the increment, from 0.1 to 100 units. Under the sinewave generator siliconchip.com.au Screen 6: adding the Swiss Army Knife via TestController’s “Load devices” screen. The option won’t be available until you’ve installed the device definition file and restarted TestController. frequency setting are buttons to select the low and high output ranges. The digital pot has two linked scales, one in counts (0 to 255) and the other in percent of rotation. Either may be used, and the other will change synchronously. The relay and digital output buttons are on the far right. Calibration The analog inputs and outputs can be calibrated using a multimeter on the Cal tab. Connect the analog output to both analog inputs, set the DAC value to around 9.5V on the Main tab then move to the Cal tab. Measure the analog input voltage with your multimeter and set the difference between the external multimeter’s reading and the analog input in the ‘difference’ column for each input (positive if the multimeter reading is higher than shown). Once that is done, set the difference value for the DAC, then click the Save button. DAC calibration is somewhat less accurate than for the ADCs, given that it only has 256 steps to cover the entire 10V range. You don’t need to calibrate all the inputs and outputs at once as the calibration for any input or output, where the difference value is zero, will remain unchanged when Save is clicked. needs to be loaded into the Devices folder wherever you have installed TestController; the default location is “C:\TestController\Devices”. Restart TestController and add the device on the Load devices tab in TestController (Screen 6), using the address “swissarmy.local” rather than its IP number, which could change if the unit hasn’t been used for some time. Then click the Reconnect button. On the TestController command screen, click the Setup button, and the pop-up window in Screen 7 should appear. The input values displayed at the top of the window will update once Conclusion While this is a relatively simple project, it has the potential to improve both the productivity and flexibility of your test bench. That’s particularly true when coupled with other remote-controlled instruments such as the Programmable Hybrid Lab Power Supply (May & June 2021; siliconchip.au/Series/364) and the WiFi-controlled Programmable DC Load (September & October 2022; siliconchip.au/Series/388). ...continued on page 70 Screen 7: the TestController Setup pop-up window shows the readings and allows most functions to be controlled. Input values are updated every second. TestController integration The TestController interface can control all functions other than calibration and communication parameters. The device definition file included in the downloads (“SwissArmyKnife.txt”) siliconchip.com.au a second, and you can set all output values in the lower sections. Australia's electronics magazine April 2023  69 Using the Swiss Army Knife to test itself The performance graphs in Screen 1 and Screen 8 were created by connecting the analog output to an analog input on the unit, then using TestController to control the analog output. The values were logged by TestController, along with voltage measurements from a Bluetooth-connected multimeter. TestController was used to create the charts. The results could also have been exported to Excel for analysis. While I wrote a script (shown adjacent) to do this, TestController has a built-in step generator function that would have worked equally well. I ran the script several times with different parameters. The first iteration tested the basic linearity of the device before calibration, using 0.25V steps to ramp the control value (Math.sVal) from 0 to 10V. The analog input (blue) line in Screen 8 is almost hidden behind the multimeter results (red), indicating excellent linearity. The analog output (grey) had not been calibrated before the test run and shows a fullscale error of around 300mV. The second test (Screen 1), using increments of 10mV, tested behaviour close to 0V and how the floating-point control value mapped to the 256-step DAC output voltage. As the analog output has a step size of 40mV, the output voltage stays the same for four 10mV control variable increments, allowing time for each output level to be sampled four times pre-step. The ADC1 input has a negative offset of -10mV. This was traced to a mismatch between the divider resistors R2 and R4, as 5% 10kW resistors were used in the prototype. The second analog input (dark grey trace) shows almost no offset voltage and tracks the multimeter reading accurately across the entire range. The code averages 16 samples per reading to reduce the variation between readings. The ADS1115 is capable of 860 samples per second. Over the two ADC channels, averaging sixteen samples gives 25 readings per second, more than fast enough for our purposes. To demonstrate how much this helps, compare Screen 1 to Screen 9, which is the same measurement without the averaging. The analog input measurement (blue trace) also has some unevenness, representing a variation of a few counts between ADC readings. These scripts were run many times during the project’s development, saving time and avoiding transcription errors. Even at a modest hourly rate, the time saved more than equalled the entire cost of the Swiss Army Knife’s components. SC 70 Silicon Chip ; ADC & DAC voltage tracking test ; create a control variable that can be logged =globalvar sVal=0 ; set initial value, let it settle and wait until value is logged =sVal=0.0 PlatyKnife::SOUR:A1 0.00 #delay 3 ; don’t log commands and log values every 3 seconds #logcmds 0 #log 3 #hasLogged ; each iteration: update analogue output and wait for logging #while (sVal<10.2) PlatyKnife::SOUR:A1 (sVal) #hasLogged =sVal=(sVal+0.25) #endwhile #hasLogged #log 0 A TestController script I used to test the Swiss Army Knife. After setting up the initial values, the analog output value is incremented by 0.25V until the limit is reached. Each cycle waits for the log entry to be written before updating to the next value. Screen 8: the tracking of the analogs input and output against the value measured on a B41T multimeter over the complete output range of 0-10V. Note that while the analog input and multimeter readings track well, the analog output had not yet been calibrated and is low (Math.sVal is the analog output setting). Screen 9: the performance at the low end of the analog scale without input sample averaging. You can see the DAC steps of just over 40mV. The ADC’s offset is around -1mV and tracks the multimeter well at low voltages. The 1 LSB jitter seen here is all but eliminated by the averaging done by the firmware. Australia's electronics magazine siliconchip.com.au Design, service or repair with our 100MHz Dual Channel Digital Oscilloscope Need more info than your DMM can display? Upgrade to this new and affordable feature-rich oscilloscope to get an accurate picture of your circuit's operation. 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Jaycar reserves the right to change prices if and when required. Silicon Chirp the pet cricket By John Clarke This pet cricket will keep you company; it only needs to be fed occasionally and won’t run away. Keep it for yourself or play a prank on a family member or friend by hiding it in their room. When they switch the lights off, they will get a bit of a surprise! C rickets, frogs and canaries tend to be organic, made from tried-and-tested construction materials such as DNA and proteins. Until now, that is. Silicon Chirp, the electronic cricket, sounds like a real cricket. Not only is this project fun, it totally (and unexpectedly for a cricket) mimics frog and canary sounds. With very few parts, it is easy and fun to build. Silicon Chirp loves to sing in the dark and happily chirps away, much to the annoyance of others. When disturbed by light, (s)he ceases, thus hiding their whereabouts until darkness falls again. But (s)he does not immediately begin to chirp again when darkness falls. That could take up to 40 seconds. And as you enjoy the peace and when all thoughts of an annoying cricket drift away...chirping starts. And so begins the hunt for that pesky critter. Catching its glinting eyes in the dark, you are faced with a predicament: remain petrified and unable to move, or face that terrifying sight! When the novelty of cricket sounds wears off, it can be changed to a frog, croaking in the dark. Or, for something completely different, change the sound to a singing canary to brighten your day. You might think that the name bears a remarkable resemblance to our magazine, but we assure you, it is purely coincidental. The name comes from the fact that the workings to produce the cricket sound are based upon silicon DNA. Also, it produces a chirping sound. Hence the name: Silicon Chirp. As mentioned, Silicon Chirp can produce the sound of a frog or canaries and, of course, a cricket shape is inappropriate when making these alternative sounds. We considered having three separate PCBs with different shapes, but swapping parts from one to the other seemed impractical. Then again, the Bower Bird still looks like a bird, even when making sounds like a chainsaw or a car alarm. So, this cricket is a keen ventriloquist, mimicking the sounds of other animals while remaining in the cricket shape. It’s so talented that its legs and mouth don’t even move while making those sounds! You could place a frog or bird toy near Silicon Chirp to make the ventriloquism seem all the more real. Features & Specifications ] Looks and sounds like a cricket ] Also has the option to produce frog or canary sounds ] Flashing red eyes ] Can be set to only operate in the dark (or light, in canary mode) ] Low current draw from 3V lithium coin cell ] Current draw: 0.4μA while dormant, 0.48-1.7mA during chirps 72 Silicon Chip Australia's electronics magazine For the cricket, most components are mounted on Silicon Chirp’s back, with its eyes being 3mm red LEDs. The piezo transducer that produces the sounds is slung under the PCB abdomen. Six legs are fashioned from thick 1.25mm copper wire, while the two antennae and ovipositor (tail) are made from a thinner gauge wire. Cricket sounds Crickets produce chirping sounds by rubbing a coarse section of one wing against a scraper on the other. This process is called stridulation; it’s a bit like running a stick along a picket fence or old-fashioned washboard. Typically, the sound a cricket produces comprises three closely spaced chirps, followed by a longer gap, then another three and so on (ie, they have a particular pattern or cadence). A typical cricket chirp comprises four bursts of a 4kHz tone, each lasting for around 50ms. The spacing between each chirp is also about 50ms, while the separation between each triplet is around 250ms. These periods are not precise and do vary a little. However, the tone of the chirp does not appear to vary by any noticeable degree. Silicon Chirp follows the same pattern, with triplets of 4kHz bursts, each separated by a longer gap. However, we found that driving a piezo transducer with three 20ms bursts at 4kHz and with 20ms gaps between them produced the most authentic cricket sound, even though the 20ms siliconchip.com.au Scope 1: cricket-like chirping is simulated by driving the piezo with groups of three signal bursts spaced apart by around 20ms. These groups have much longer silent periods in between them. periods are different from that of an actual cricket. Scope 1 shows Silicon Chirp’s cadence as measured by an oscilloscope. To act like a real cricket, the chirp rate must vary slightly rather than being at precise intervals. So Silicon Chirp’s chirping periods vary randomly over a limited range. In other words, they aren’t always exactly 20ms long or spaced apart by precisely 20ms. The variations in the periods provide a more natural cadence and prevent the simulated cricket chirp from sounding artificial. Frog sounds are produced similarly but with a different cadence to the cricket. For Silicon Chirp, frog sounds comprise a set of 10 chirps, 10ms long with 2ms gaps. This is followed by a 30ms gap and then another set of three chirps. The ten and three groups are separated by a delay of 200-1200ms that varies irregularly. The frequency of the chirps is set at around 2kHz. The canary sounds have been divided into three types, designated A, B and C. Song A sounds like a typical canary, while Song B simulates a Fife canary. Song C is a selection that comprises various single phrases produced by these birds. The canary sings at random. Each song is repeated between two and 27 times with a 2.4 to 17 second gap between them. There is an extended gap between each series of repeated songs, between 80 seconds and nine siliconchip.com.au Scope 2: a close-up of the drive to the piezo, showing how the 3V peak-to-peak square wave signals from the RA0 & RA1 outputs (yellow and cyan traces) combine to produce a 6V peak-to-peak square wave across the transducer (red trace). minutes. Like the cricket and frog, the bird songs are produced by varying the frequency, volume and length of bursts of pulse trains applied to the piezo. The sound volume is varied by changing the pulse width of the signals applied to the piezo transducers. Narrow pulses give a low volume, while wider pulses make more sound. Maximum pulse width equates to a duty cycle of 50%. Each chirp starts at the minimum pulse width, increasing to the required volume level over time. Similarly, the pulse width is reduced to zero over a short interval when a chirp or tweet is about to end. This avoids clicks from the piezo transducers, which would otherwise spoil the effect. Unlike crickets and frogs, which tend to make noise when it’s dark, bird sounds occur mainly when it is light. So the light/dark detection is inverted for the canary. Circuit description The complete Silicon Chirp circuit is shown in Fig.1. It’s based around microcontroller IC1, a PIC16F15214-I/ SN, powered by a 3V lithium cell, switched via slide switch S1. IC1 does not draw much current, typically only about 400nA while it is dormant. This rises to between around 480μA to 1.7mA while making noise. Diode D1 is included as a safety measure to prevent damage to IC1 should the cell be inserted incorrectly. The correct polarity is with the positive side up, but the cell holder will accept the cell in either orientation. With the positive side down, the cell will be shorted out by contact with the sides and top spring contacts. The underside of Silicon Chirp, showing the large piezo transducer. Feel free to customise the board to suit your taste. Note the on/off slide switch near the ‘tail’. April 2023  73 However, during insertion, there could be a brief period when there is no contact with the cell holder sides, so the circuit could be supplied with a reversed voltage polarity that could damage IC1. Diode D1 clamps any reverse voltage to a low level. The cell will lose some capacity if left connected in reverse for more than a few seconds, but that’s better than damaging the IC. IC1’s power supply is bypassed with a 100nF capacitor and runs using its internal 4MHz oscillator. When dormant, this oscillator is shut down (ie, in ‘sleep mode’) to save power. A ‘watchdog’ timer starts running to wake IC1 periodically (at approximately four-second intervals). During this period, the current consumption is typically less than 1µA. During the waking period, IC1 checks the ambient light level on the light-dependent resistor, LDR1. Most of the time, the RA5 output (pin 2) of IC1 is set high (3V), so there is no current flow through the 470kW resistor and the LDR to minimise the current drain. When IC1 is awake, it sets the RA5 output low (0V) and the LDR forms a voltage divider with the 470kW resistor across the 3V supply. The RA4 digital input (pin 3) monitors the voltage across LDR1. In darkness, the LDR resistance is high (above 5MW), so the voltage at the RA4 input is more than 2.7V due to the voltage divider action of the LDR and the 470kW resistor. This voltage is detected as a high level by IC1. With sufficient light, the LDR resistance drops below 10kW, so the voltage divider produces a low level of 63mV or less at the RA4 input. The thresholds for the RA4 input are 20% of the supply voltage for low and 80% of the supply for high. It is a Schmitt-trigger input, so once it exceeds the high threshold, the voltage must drop below 20% of the supply to switch to low. Similarly, once detecting a low, the voltage must go above 80% of the supply before a high level is indicated. That ensures there is no rapid switching between high/low state detection when the voltage is between these thresholds. Driving the piezo transducer IC1’s RA0 and RA1 digital output pins (pins 7 & 6) drive the piezo transducer that produces the chirps. The piezo is driven in bridge mode, connected across these two outputs, which increases the AC voltage to produce a louder sound. When RA0 is driven high, the RA1 output is taken low; when the RA0 output is low, RA1 is high. In one condition, there is +3V across the piezo transducer and in the other, -3V, producing a 6V peak-to-peak square wave, shown in Scope 2. Scope 2 is a close-up of the 4kHz drive waveform fed to the piezo sounder. Channels 1 & 2 (yellow and cyan traces) are the signals applied at either end of the piezo transducer, while the red trace shows the total. So, while each end of the piezo is driven by a 3.28V peak-to-peak waveform, there is double that voltage produced across the piezo. A 100W resistor limits the peak current into the transducer’s capacitive load immediately after the outputs switch. LED1 and LED2 are driven via the RA2 (pin 5) and RA5 digital outputs with 330W current-limiting resistors. These LEDs are driven alternately on and off while the piezo transducer is driven. When RA5 is low and RA2 high, LED1 is lit, while when RA5 is high and RA2 is low, LED2 lights. Note that RA5 is also used to drive the LDR (LDR1) to monitor the ambient light level. When driving RA5 low for light measurement, RA2 is also set low, so the LEDs are off. Similarly, when the LDR is off (RA5 high), RA2 is also brought high to keep the LEDs off. Pushbutton switch S2 changes the Fig.1: Silicon Chirp is controlled by 8-bit PIC16 microcontroller IC1. Slide switch S1 applies power from the coin cell. It then uses LDR1 to sense the light level and, depending on what it finds, produces sounds by driving the piezo transducer from its pin 6 & 7 digital outputs while flashing the eye LEDs via the pin 2 & pin 5 digital outputs. 74 Silicon Chip Australia's electronics magazine siliconchip.com.au siliconchip.com.au TOP VIEW WITH LEGS, TAIL AND ANTENNAE 100W CON1 SCREW & STANDOFF S2 LED1 K LDR1 + PIC16F15214 CELL CAPTURE CR–3032 Silicon Chirp is built on a double-­ sided, plated-through PCB coded 08101231 that measures 94 × 30.5mm. Wire legs are soldered to this PCB so it ‘stands up’ like a real cricket. These wires and the other parts are shown in Figs.2 & 3. Typically, in-circuit serial programming (ICSP) header CON1 is not installed; if you build it using a PIC supplied by us (by itself or as part of a kit), it will come pre-programmed, so programming will not be required. If you need to program a blank micro, ICSP header CON1 can be installed. Screen printing for this is on the underside of the board (for aesthetic reasons); however, it needs to be installed from the top since only the underside of the PCB has exposed pads for soldering. The top layer pads are masked, also for aesthetic reasons. Ideally, you should remove the ICSP connector after programming, as real crickets do not tend to have a programming connector. Begin by installing the surface-­ mounting microcontroller, IC1. You will need a soldering iron with a fine tip, a magnifier and good lighting. The use of flux paste during soldering is advised, in which case you don’t necessarily need a very fine soldering iron tip. Solder IC1 to its PCB pads by first placing it with the pin 1 locating dot to the top left, positioning the IC leads over their corresponding PCB pads. Then tack-solder a corner pin and check that the IC is still aligned correctly. If it needs to be realigned, remelt the soldered connection and gently nudge the IC into alignment. Once correct, solder all the IC pins and refresh that initial joint. Any solder that runs between the IC pins can be removed with solder paste and the application of solder-wicking braid. Continue construction by installing the resistors. They are printed with a code indicating their values, which is 1 double-sided, plated-through PCB coded 08101231, 94 × 30.5mm 1 CR2032 surface-mounting coin cell holder (CELL1) [BAT-HLD-001] 1 CR2032 3V lithium cell 1 SPDT micro slide switch (S1) [Jaycar SS0834] 1 SPST surface-mounting tactile pushbutton switch (S2) [Altronics S1112A, Jaycar SP0610] 1 30mm diameter 4kHz wired piezo transducer (PIEZO1) [Altronics S6140, Jaycar AB3442] 1 45k-140kW light dependent resistor (LDR1) [Altronics Z1619, Jaycar RD3480] 3 M3 × 10mm panhead machine screws (metal or plastic) 1 M3 × 6.3mm tapped Nylon spacer (or two M3 hex nuts) 2 Nylon or polycarbonate M3 hex nuts 2 TO-220 insulating bushes (eg, from TO-220 insulating kits) [Altronics H7110, Jaycar HP1142] 1 6-way header with 2.54mm pitch (CON1; optional, for programming IC1) 1 200mm length of 1.25mm diameter enamelled copper wire (for legs) 1 100mm length of 1mm diameter enamelled copper wire (for antennae & ovipositor) Semiconductors 1 PIC16F15214-I/SN 8-bit microcontroller programmed with 01810123A.hex, SOIC-8 (IC1) 2 3mm red LEDs (LED1, LED2) 1 LL4148, MM4148 or 1N4148WS (or 1N4148; see text) SMD diode, Mini-MELF (SOD-80) or SOD-323 [Altronics Y0161/Y0164A] Capacitors 1 100nF 50V X7R SMD M3216/1206 size Resistors (all M3216/1206 size 1%) 1 470kW 1 330W 1 100W IC1 LED2 A 100nF BOTTOM VIEW (JUST THE PCB) PIEZO1 470kW S1 D1 PIEZO1 Construction Parts List – Silicon Chirp Cricket CELL1 sound produced from cricket to frog or canary. IC1 detects when S2 is closed by monitoring digital input RA3 (pin 4). When S2 is pressed, the voltage at that pin goes to 0V. When the switch is open, the internal pull-up at RA3 keeps that input level high. The S2 switch closure is only checked during power-up; changing the sound can only be done then. 330W Figs.2 & 3: Silicon Chirp is pretty easy to build. Simply place the components as shown here but note that the piezo transducer is wired and mounted over reverse polarity protection diode D1. That diode, IC1 and the LEDs are polarised and must be soldered the right way around; the other components are not polarised. Australia's electronics magazine April 2023  75 Silicon Chirp should look similar to this when yours is finished, but feel free to customise it to suit your taste. Note that the CR2302 cell is secured using one screw as a preventative measure against tampering, so children can’t get a hold of the cell by itself. likely to be “1000” or “101” for 100W, “3300” or “331” for 330W and “4703” or “474” for 470kW. These are in ‘scientific notation’ where the last digit indicates the number of zeros to add to the first few digits to give a value in ohms. Diode D1 can be installed next, taking care to orientate it correctly, with the cathode stripe facing away from the centre of the PCB. There is sufficient pad area to allow Mini-MELF (SOD-80) or SOD-323 package diodes to be soldered in. Alternatively, an axial-­leaded 1N4148 could be used with the leads at each end bent back by 180° to allow soldering to the PCB pads. The 100nF capacitor can be fitted next, and it can be positioned either way round as it is not a polarised part. We installed slide power switch S1 on the underside of the PCB. You could place this on top if you prefer. The on position for the switch is when the slider is toward the front of the cricket. You can also mount pushbutton switch S2 now by soldering its four pins. The cell holder (CELL1) is a halfshell type and its body makes contact with the positive side of the cell. A tinned copper area on the PCB completes the cell holder and provides for the negative connection to the cell. It must be fitted with the cell entry toward the rear of the cricket so that the cell capture screw prevents small children from removing it. This is to comply with Australian Standard (AS/NZS ISO 8124.1:2002), where toys for children three years and younger must have any batteries (and/ or cells) secured in a compartment by a screw. Alternatively, where there is no compartment screw used, there must be two simultaneous independent movements to open the battery compartment. While Silicon Chirp is not really a project for small children, it could be used in a household with children who could potentially swallow button or coin cells, which poses a serious hazard (see the warning panel for details). For our project, cell removal is blocked by a 10mm M3 machine screw inserted from the PCB’s underside and secured on top with an M3-tapped Nylon spacer. When tightened, the spacer cannot be removed by hand and stops the cell from being removed. An alternative to the standoff is to use two M3 nuts, with the top one used as a lock nut, tightened against the other. Mount LED1 and LED2 so that the top of the dome of each LED is raised off the PCB by about 10mm. This provides enough lead length so they can be bent to about 30° above the PCB plane and outward about 10° from the centre line, as shown in Fig.2 and the SC6620: Silicon Chirp Kit ($25 + postage) A complete kit with all the parts in the parts list except the lithium coin cell & programming header. Available from the Silicon Chip Online Shop. 76 Silicon Chip Australia's electronics magazine photos. Make sure the longer lead of each LED (the anode) is inserted in the “A” position on the PCB. Mount the LDR about 5mm above the PCB surface, with its face sitting horizontally. This component is not polarised and can be installed either way around. The piezo transducer is mounted on the underside of the PCB, supported on TO-220 insulating bushes that are used as spacers to raise the transducer from the PCB. This leaves room for the cell capture screw and diode to fit between the PCB and piezo. The piezo transducer is secured with two 10mm M3 machine screws and two Nylon or polycarbonate nuts. You will need to drill out the mounting holes on the piezo unit to a 3mm diameter to suit the M3 screws. The nuts will not fit in the room provided on the piezo transducer mounting lugs, so the screws need to enter from the piezo transducer side. The insulating bushes can then be slipped onto the screw shafts, followed by the piezo transducer, then the Nylon or polycarbonate nuts. We use plastic nuts because a metal nut will short out the cell if used at the end of the cell nearest to IC1. That’s because the PCB hole and surrounding track are connected to ground, while the metal of the cell holder connects to the cell positive. To avoid confusion and prevent the wrong type of nut from being placed at each point, we specify both piezo-securing nuts as plastic. Note that to remove the cell capture screw when the cell needs to be replaced, one of these piezo mounting screws will need to be removed so that the piezo transducer can be swung out of the way. Solder the piezo wires to the underside of the PCB at the positions marked “PIEZO1”. You could instead bring them to the top of the PCB and solder them through the corresponding top holes, although that will look a bit messy. The wires will need to be shortened, but leave sufficient length for the piezo to swing out of the way to access the cell capture screw. The piezo transducer wires will probably be red and black, although the transducer is not a polarised component. It does not matter which colour wire goes to the two piezo PCB pads. Legs and antennae The legs can be fashioned from siliconchip.com.au 1.25mm diameter enamelled copper wire. Each front leg is 40mm long, while the mid and rear legs are each 30mm. These can be as simple or as fancy as you like. The cricket shape printed at the rear of the PCB shows the general leg shape we used, as do Fig.2 & the photos. Bend the legs so that Silicon Chirp’s PCB is above the platform it sits on. Form the feet into small loops so that the sharp ends of the wires are not exposed. Where the legs are soldered to the PCB, you will need to scrape off the enamel insulation (eg, using a sharp hobby knife or fine sandpaper) before you can solder them. Make up the two antennae using 40mm lengths of 1mm diameter enamelled copper wire and the ovipositor (tail) with a 20mm length of the same. Once in place, curl the two antenna wires into shape by running a thumbnail along the inside of the radius, with your index finger on the outside. Now install the CR2032 cell in its holder and switch on power with S1. If all is well, the LEDs will momentarily flash after about three seconds to acknowledge that power has been connected. An acknowledgement by a brief flashing of the LEDs also occurs when a low light level is detected for the cricket and frog, or when a high light level is detected for the canary. Low light can be simulated by covering over the LDR, or a higher light level by shining light onto the LDR. Silicon Chirp will begin chirping after a delay of about 10 seconds, providing the low light level remains for the whole time. If you need to program the PIC yourself, you can download the firmware Warning: small cell This design uses a small lithium cell that can cause severe problems if swallowed, including burns and possible perforation of the oesophagus, stomach or intestines. Young children are most at risk. Read the information sheet at www.schn.health.nsw.gov.au/fact-sheets/buttonbatteries on the dangers of button cells. Ensure that the cell is kept secure using the cell capture screw and Nylon spacer as specified, tightened sufficiently so they cannot be undone by hand. Keep unused cells in a safe place away from children, such as a locked medicine cupboard. New cells should be kept within the original secure packaging until use. Unfortunately, some older button cell powered devices not intended for children under three provide easy access to the cells. Keep these away from children or devise a method to make cell access more difficult (eg, by gluing the compartment shut). (01810123A.hex) from the Silicon Chip website. Additionally, as mentioned previously, ICSP (in-circuit serial programming) header CON1 will need to be installed. One of the piezo transducer leads may need to be disconnected, or one end of the 100W resistor, to allow programming. expressed with the piezo transducer close to a flat surface to emphasise lower frequencies. The canary sounds run through a repertoire before switching off when darkness is detected, so they won’t necessarily stop as soon as the light goes away. Changing the sound Silicon Chirp has a loud chirp, which can be pretty annoying! (But maybe you want that...) To reduce the volume, increase the value of the 100W resistor in series with the piezo transducer. Increasing it to, say, 10kW will reduce the apparent volume by about 50%. Higher values will provide an even lower volume, to the point where it won’t chirp at all. The light sensitivity can also be altered by changing the 470kW resistor value between the positive supply and the PIC’s RA4 input. Increasing the resistance value (say to 1MW) will make the light threshold level darker. By contrast, reducing the resistance value will mean more light is required SC to detect daytime. Changing from cricket to frog to canary and back is performed by holding switch S2 while switching power on via S1. Continue to hold S2 until you see the eyes flashing. They will flash once for the cricket, twice for the frog and three times for the canary. To change to the next selection, continue holding S2 for two seconds until the eyes flash to show the next selection. When you see the selection you want, release S2. The selected sound is stored in flash memory, so that selection remains even if powered off and on again. It only changes when S2 is pressed during power-up. Note that the frog sounds are best Modifications Raspberry Pi Pico W BackPack The new Raspberry Pi Pico W provides WiFi functionality, adding to the long list of features. This easy-to-build device includes a 3.5-inch touchscreen LCD and is programmable in BASIC, C or MicroPython, making it a good general-purpose controller. This kit comes with everything needed to build a Pico W BackPack module, including components for the optional microSD card, IR receiver and stereo audio output. $85 + Postage ∎ Complete Kit (SC6625) siliconchip.com.au/Shop/20/6625 The circuit and assembly instructions were published in the January 2023 issue: siliconchip.au/Article/15616 siliconchip.com.au Australia's electronics magazine April 2023  77 IDEAL FOR STUDENT OR HOBBYIST ON A BUDGET • DATA HOLD • SQUARE WAVE OUTPUT • BACKLIGHT • AUDIBLE CONTINUITY Don't pay 2-3 times as much for similar brand name models when you don't have to. 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ENTRY LEVEL * QM1500 QM1517 QM1527 MID LEVEL QM1529 QM1321 QM1020 QM1446 Display (Count) 2000 2000 2000 2000 4000 Analogue Security Category Cat II 500V Cat III 600V Cat III 500V Cat III 600V Cat III 1000V Cat II 1000V • • Autorange True RMS PROFESSIONAL QM1323 QM1552 2000 4000 2000 4000 4000 2000 4000 6000 4000 Cat III 600V Cat III 600V Cat IV 600V Cat III 600V Cat IV 600V Cat III 600V Cat IV 600V Cat IV 600V Cat III 1000V • • • • • • QM1551 QM1549 • • • • • XC5078 QM1594 QM1578 • Voltage 1000VDC/ 750VAC 500V AC/DC 500V AC/DC 600V AC/DC 1000VDC/ 750VAC 1000V AC/DC 1000VDC/ 700VAC 600V AC/DC 1000VDC/ 750VAC 600V AC/DC 1000V AC/DC 600V AC/DC 600V AC/DC 1000V AC/DC Current 10A DC 10A DC 10A DC 10A AC/DC 10A AC/DC 10A DC 10A AC/DC 10A AC/DC 10A AC/DC 10A AC/DC 10A AC/DC 200mA AC/DC 10A AC/DC 10A AC/DC Resistance 2MΩ 2MΩ 2MΩ 20MΩ 40MΩ 20MΩ 20MΩ Capacitance 100mF Frequency 10MHz Temperature Duty Cycle 20MΩ 40MΩ 200MΩ 40MΩ 40MΩ 40MΩ 60MΩ 100μF 100µF 100mF 100µF 100µF 100µF 6000µF 10MHz 10MHz 10MHz 10MHz 10MHz 10MHz 10kHz 1000°C 760°C 1000°C 760°C 750°C 760°C • Continuinty • • • • • • Relative Min/Max/Hold • Non Contact Voltage • • • $26.95 $32.95 $49.95 • • • • • • • • • • Max Hold • • • $59.95 $74.95 $74.95 IP Rated Price • • • • $20.95 *Lifetime warranty excluded on models: QM1500/QM1517/QM1527 $32.95 $59.95 4000MΩ • • IP67 $11.95 1000VDC/ 750VAC • • Max Hold • QM1493 $109 IP67 $99.95 $149 $199 $289 Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. Integrate your Test Bench with TestController When working on the bench, there’s often a need to synchronise readings on several test instruments, log and analyse the results. A handy piece of free software called TestController can automate much of this process for almost any instrument with remote control features. by Richard Palmer W hile developing my many different projects, there were numerous occassions when I wanted to run through a sequence of settings across one or more pieces of test equipment, log and analyse the results. I’ve found that the free software TestController can remote control, read and analyse just about any device that can connect to a computer and communicate via text or SCPI commands. TestController can be downloaded from https://lygte-info.dk/ I have set up TestController to work with my most recent projects: • Programmable Hybrid Lab Supply (May & June 2021; siliconchip. au/Series/364) • WiFi DC Load (September & October 2022; siliconchip.au/Series/388) • Test Bench Swiss Army Knife (see page 60) As well as those three Silicon Chip projects being WiFi enabled and SCPI controlled, my digital oscilloscope, DDS signal generator and one of my Features ∎ Supports serial, USB, Bluetooth, WiFi, LXI and GPIB connections ∎ SCPI and text-based command protocols ∎ Powerful test automation tools ∎ Comprehensive logging, graphing and mathematical functions ∎ Command scripting across multiple instruments ∎ Over 100 common instrument definitions (including our WiFi Hybrid Lab Supply, DC Load and Swiss Army Knife) ∎ Compatible with Windows and Linux 80 Silicon Chip multimeters also have remote control and reading features. Installation Installing TestController is straightforward. Download the zip file from the website – the link is at the bottom of the main page. Unpack the downloaded archive file into a convenient location, install Oracle Java or the Open JDK and run the executable .bat file. Silicon Chip instrument definition files go into the Devices folder; TestController needs to be restarted for the new devices to become available. Using TestController TestController’s main screen is a Screen 1: TestController’s main screen after two devices have connected and several immediate commands to the DC load have been executed. The font size has been increased via the Configuration menu for improved readability. As a result, there are two rows of screen tabs. Screen 2: the Current values tab shows the most recent readings from the enabled instruments. Australia's electronics magazine siliconchip.com.au good place to begin exploring its features (Screen 1). The tabs across the top provide access to the main functions. The top text window in the Commands tab shows the log of responses from commands sent to the instruments. Automation scripts are also written in this window. The command line text box in the middle of the tab can be used to send commands to any connected instrument. In Screen 1, I’ve right-clicked on the command line prompt, which displays the currently selected instrument. A selection box pops up, facilitating quick changes between connected devices. At the bottom is the help window, which displays all the available commands for the current instrument. It dynamically updates as commands are typed. The Current values tab (Screen 2) provides an integrated view of all the settings and measurements registered for each connected instrument. Any calculated values from the Math tab are also shown here. Table view (Screen 3) contains similar information but as a sequence. Data can be saved for later analysis within TestController or exported for external analysis. Table data can also be plotted on the Chart (Screen 4) and Histogram screens. The Math tab (Screen 5) makes values available as readings for logging, charting or histograms. The remaining tabs configure TestController. On the Commands tab, the Popups button provides access to a range of useful widgets, including graphical control interfaces for the enabled instruments (Screen 6). While the device popups can get hidden behind the main window, they are readily brought back to the front by clicking the Setup button. Screen 7 shows the WiFi DC Load’s device control popup, which mirrors most of the functions on the instrument’s screen. As TestController has powerful logging functions inbuilt, those functions are not duplicated by the popup. Instruments are connected using the Load Devices tab (Screen 8). TestController maintains a list of all the instruments you’ve registered and only connects to the ones that are enabled for this test session. I’ve registered my Owon multimeter, via its Bluetooth serial dongle, three WiFi siliconchip.com.au Screen 3: the Table screen shows logged values. Calculated values from the Math tab are also listed. Screen 4: the Chart tab graphs the information from the Table view and any calculated values from the Math tab. Here, the output of the virtual ramp generator is shown along with an almost constant voltage across the DC load. Screen 5: the Math tab creates calculated values. Here we’ve recalculated the power sunk by the DC load. instruments using their IP addresses or their DNS names, and the internal LF sine generator. Automating test procedures TestController has a range of inbuilt Australia's electronics magazine automation functions that require no scripting. The first example below uses the Param Sweeper tool to create a staircase voltage on the Programmable Hybrid Lab Supply. The second example is a script using April 2023  81 ► Screen 6: the Popups button provides access to control and readings widgets. Screen 7: the WiFi DC Load device popup (see the project in the September & October 2022 issues; siliconchip. au/Series/388). ► one of TestController’s virtual instruments to control a power supply. Testing a range of values TestController’s Param Sweeper popup is very useful in automating tests where a control needs to be stepped through a range of values. It can generate linear, logarithmic or stepped sweeps without any scripting. The following example sets a five-step ramp for the Hybrid lab Supply’s output voltage, logs and charts the results. Pop up the Param Sweeper. On the Main tab (Screen 9), ensure the logging and charting options are selected in the bottom row of checkboxes. You may need to widen the popup window a little so that the Start button is visible. On the Primary tab, fill in the desired parameters for the sweep (Screen 10). Set the parameter to be swept from the drop-down list (PlatyPSU Primary Voltage in this case). Press Start and wait for the sweep to be completed. In the main TestController Chart tab, make sure all the variables you want to be charted are selected, and do the same for log data in the Table tab. The resulting chart and log file are shown in Screens 11 & 12. I varied the load resistance during the test, creating variations in the current readings. Otherwise, the current graph would have simply mirrored the voltage steps. Scripting for complex tasks Screen 8: after enabling the virtual sine or ramp generator, click the Reconnect button to ‘connect’ to them. The final component, and perhaps the most powerful, is scripting. Where the test required isn’t already provided by TestController, scripts are straightforward to create. When creating the script, commands are entered directly into the log window on the Commands tab. You can include any connected instrument in Screen 9: a single (Primary) sweep is selected, with logging and charting at onesecond intervals. I set the chart to be saved as xps.png and the log as xps.csv in the “documents\TestController folder”. The test run was underway when this image was captured. Screen 10: the Param Sweeper’s Primary parameters menu. It is set for five steps of one second each with one-second delays before the sweep starts and after it ends. Baseline values are recorded in the log and chart during these pauses. 82 Silicon Chip Australia's electronics magazine Screen 11: all values shown in TestController’s main window Table tab are logged, whether selected or not. Some columns have been hidden for clarity. siliconchip.com.au the script by using its handle at the start of the command. TestController system actions are preceded with a # and include functions like delays, looping and waiting for a condition to become true. Calculations can also be made, data logged, and plotted from scripts. Adding to the power of its scripting capabilities is the ability to send calculated values to connected instruments, simply by enclosing values in parentheses – ( ). Scripts can be saved and reused. We’ve included a simple scripting example (Script 1); there are more on the TestController website (siliconchip.com.au/link/abev). This example script sets up the Virtual Sine Generator to create a very low frequency (0.033Hz) sinewave for one complete cycle, then uses that to control the output of the Hybrid Lab Supply (PlatyPSU). A chart of the resulting output is shown in Screen 13. The #while and #endwhile commands bracket the loop, and logInterval is a system variable that counts down the remaining time for the test. Any mathematical function, or a reading from an instrument, could also be used to control the loop or set the power supply’s output voltage. Screen 12: this is the chart that was saved at the end of the ParamSweeper test cycle. The load resistance was varied during the test to produce the jagged current line. Only the parameters selected in the Chart tab on the main TestController window are shown. I had to do some fiddling in the Scales for Chart tab to expand the current scale so I could get this display. Conclusion This article only touches on a few of TestController’s features – it can automate most of the testing done on the lab bench. The key requirement is that the test gear must have some form of remote control available. TestController has definitions and remote control interfaces for over 100 different instruments, and more are appearing every week. They range from multimeters through power supplies, signal generators and DC loads to oscilloscopes. If your instrument isn’t listed, adding your own is relatively straightforward. It took me a few hours to create my first definition file for the WiFi-Controlled Lab Supply, but only an hour or so to build the one for the WiFi DC Load as I already understood the basics. The TestController website has regular updates (siliconchip.com.au/ link/abev), and there is an active user forum on EEVblog (siliconchip.au/ link/abhh). We look forward to hearing how readers have automated their test benches in the Mailbag column. SC siliconchip.com.au Screen 13: the sinewave produced by the PSU using commands from TestController. The PSU trace is delayed because the power supply’s output voltage is only measured in the following one-second log window. The actual delay is much shorter. #logcmds 0 VSG:PERIOD 30 ; 30 seconds per complete sine cycle VSG:RANGE 10 ; 10 V p-p VSG:OFFSET 5 ; offset so that all values are positive VSG:ON 1 #log 1 ; log readings every second PlatyPSU::SOUR:OUTP ON ; PSU on #while logInterval>0 ; start the loop PlatyPSU::SOUR:VOLT (VSG.Sine) ; set the PSU voltage to the sine value #haslogged ; wait until log entry has been created #endwhile PlatyPSU::SOUR:OUTP OFF ; note the double :: Script 1: the script for the power supply sinewave generator is relatively simple. The semicolon delimited comments are not part of the TestController script; they are just there to explain how it works. Australia's electronics magazine April 2023  83 SERVICEMAN’S LOG Tips on kits and bits Dave Thompson I’ve fixed so many faulty kits that I now have a pretty good idea of the pitfalls of kit and PCB assembly. Often, the fix is quite simple once I’ve spent a while poring over the board and located the fault, but it’s so much easier if you don’t make a mistake in the first place. So pull up a chair, dear reader, and let Uncle Dave tell you all about the ins, outs, dos and don’ts of PCB and kit assembly. I’ve been building electronic kits and projects since I was eight years old. How do I remember this age so precisely? Because dad, on one of his many travels, bought my brother and me what was then called a 10-in-1 electronics ‘Lab Kit’. These are still sold, with larger 50-in-1 and 100in-1 versions also available. This was the late 1960s, though, and that lab kit was my first real introduction to electronics as a hobby. It enabled me to clip in components and make a simple amplifier, oscillator, lamp flasher and similar projects. I was already an inquisitive child and soaked up as much knowledge as I could. Luckily, dad was doing a wide range of engineering, electrical and electronic jobs, and I often tagged along for the ride. I wasn’t always up with the play, though; for some time, I couldn’t figure out how noise came from a radio or a TV. Like many kids, I assumed there was someone in there somehow. Silly, I know! On my seventh birthday, I was given an eight-transistor radio. I wish I had it now, but it is long gone. I have similar models in my ‘collection’, but not the original one. At the time, I recall promptly pulling it apart to see how it worked. What I saw inside didn’t really clue me in much – but I could see that there were no tiny people in it! In that case, dad had to put it all back together because, like all good servicemen, I am better at taking stuff apart than I am at putting it back together. I worked for years to gain the skills required to put things back together again; it takes even longer if I wanted them to still work afterwards! Items Covered This Month • • • • • • The pitfalls of kit and PCB assembly Louvre rain sensor repair A dual-purpose intercom and ant colony unlocker Converting a torch to use Li-ion cells Repairing a Miele clothes dryer Three blind mice and an aircon Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz Cartoonist – Louis Decrevel Website: loueee.com 84 Silicon Chip An inauspicious start to a career, then. But that’s how I learned to do things; by actually doing, making mistakes, rectifying them, and then making some more. I make no claims of expertise, or even being the best electronics guy on my street; I just read and learned as much as possible from those around me. More projects than I’ve had meat pies In the intervening years, I have made literally thousands of projects – some from scratch and some from kits. Most worked straight out of the box, often because the project came with a PCB layout that could be replicated by the home constructor. In a commercial kit, the designer or kit manufacturer has already done the heavy lifting. We hope that most of the bugs and errors have been ironed out long before a kit is released. In theory, it should be as easy as ABC. While this is typically the case, as anybody who has ever purchased and built kits will tell you, that isn’t always how it works out. It stands to reason that the more complicated the circuit and the project, the more chances a constructor will do something wrong when assembling it, or when configuring it after the build. In many cases, this just means the project won’t work as intended. Still, in some cases (for example, in mains-powered projects), this can be a spectacular showstopper, and especially catastrophic if the PCB gets fried in the process. I’ve also built a lot of kits for many people over the years. It makes sense for someone who wants the device but doesn’t have the confidence to undertake the project. It’s easier to ‘farm’ the build out to someone who is proficient with a soldering iron and already has the mechanical and practical skills necessary to put it together. That said, guys being blokes, many of us take on projects that are obviously above our pay grade. It is no surprise that some of them just don’t work when they come out the other end. As a relatively experienced constructor, if I might be so bold, I’d like to offer some advice for people who might want to take on any of the projects featured within these hallowed pages. One thing to note is you usually don’t need to know much about electronics to build a well-produced kit and have it work. Plenty of people I know – with no previous experience – have built some of the many and varied Australia's electronics magazine siliconchip.com.au valve-based guitar amplifier kits marketed on the web, and they worked out very well. This is a popular way to get into a tube amp without the much-bigger price tag of a commercially produced amplifier. Most of these kits are time-tested and come with excellent documentation, support videos and other resources to ensure the build goes smoothly. Obviously, this isn’t the case for many projects, and it’s a matter of being ‘on our own’ if we decide to try building something a bit more obscure (or even from scratch). Community support can sometimes be available through the circuit designer, kit manufacturer, or even other enthusiasts, but it isn’t always guaranteed. Previous knowledge of electronics is not always a prerequisite. Studiously study soldering for success One skill you do need, however, is to be able to solder properly. Solder is typically how electronic parts are connected to printed circuit boards, terminals and to each other, so it stands to reason that this is a necessary skill constructors must at least be competent at before building anything electronic. Many of the problems I find when given a non-working project to troubleshoot are down to poor soldering, so this is something that shouldn’t be taken lightly, especially with major kit builds like large amplifiers and mains-­ powered devices. There are many tutorials available (including in this magazine) on how to solder correctly, so I won’t go into too many details here, except to say that if someone doesn’t know how to solder, they should learn to do so before starting any kit build. Obviously, there are a range of skill levels regarding soldering; if you are looking at making something that doesn’t require soldering a 100-pin surface-mount component, then there is no burning need (pun not intended) to learn that particular skill. However, people should learn enough to do their proposed job properly. I would say that 25% of the dead projects I get to troubleshoot have simple soldering mistakes. Get yourself a decent iron My number one top tip is to get a decent soldering iron. Using dad’s old plumber’s iron is inappropriate for this kind of work. A decent soldering iron fit for purpose is siliconchip.com.au Australia's electronics magazine April 2023  85 relatively cheap at the likes of Jaycar or Altronics. While it doesn’t have to be anything über fancy, like an expensive soldering station, it is a worthy investment to buy the best one you can afford before getting stuck in. Something in the 25-30W range, with a medium-to-fine tip, is ideal. Some have replaceable tips as well, which can make the iron a lot more versatile; it’s a good idea to have a larger tip, such as a chisel or screwdriver style, on hand in case you need it. Surprisingly, large flat tips can make soldering fine-pitched SMDs easier than the needle-like tips some people think you need for that job. Still, there are times when having a very fine tip is helpful, so you could probably justify having four or so tips to start with: fine, medium, large and flat-edged. Other stuff you’ll need While you’re at it, buy a proper cleaning sponge; never take a file or abrasives to a soldering tip – just a damp sponge will keep the tip in excellent condition. If it gets pitted or wears out (which it will over time), simply replace it (if you can). Keep the tips tinned with solder when you aren’t using them; it helps prevent oxidation. Once you have an iron sorted, the next requirement is some decent solder. The old lead bar granddad left in the shed for fixing a blown copper boiler is obviously not suitable for fine work like this, nor are some of the acidbased flux solders used in golden olden times. If you find a reel of this in the shed, I’d avoid using it on your electronics projects, as the acids in it can corrode PCB tracks and component legs. The best thing is to buy fresh solder while you are down at the store buying a soldering iron. The standard hobby solder available these days is lead-free, which is the best option. Made from copper and tin, with a rosin flux core, a small reel is not expensive, and having a reel in the workshop is always very handy anyway. I use two sizes: 0.5mm diameter for finer work and 0.71mm for larger jobs. While I’m on the subject, do yourself a favour and get a small (or even large) syringe of proper flux paste while you’re at it. Don’t use liquid flux, as it’s only suitable for specific jobs; thicker flux paste can be a real lifesaver, making seemingly impossible tasks possible, especially when working with tiny SMDs. Good soldering is critical because it doesn’t take much in many of today’s designs, kits and projects to cause a device to stop working because of a poorly soldered, high-­ resistance joint. My first port of call in any troubleshooting scenario is to go over all soldered joints one by one with a jeweller’s loupe, or in some cases, a USB microscope. It’s a painstaking job, but one that can nip a potential nightmare in the bud if the rogue joint is spotted earlier rather than later. Generally, if the soldering is good, I don’t have high hopes a dud joint will be the cause of the fault. Still, if the soldering overall is looking a bit dodgy, this is a likely place to find the problem. So it really does pay to learn to solder well before taking on any electronics project. The second most common problem I encounter is components inserted incorrectly. This is such a basic mistake, but even experienced constructors (me included) can put things in backwards. Diodes, electrolytic capacitors, transistors and ICs of all types are the most commonly misplaced components. After checking the soldering, my next step is to check component placement. If the soldering looks pretty good anyway, I might skip straight to this step. This part of the troubleshooting process is much easier if we have a circuit diagram, a PCB layout map and component designations screen-printed on the board itself. Sometimes, this information is not available, but the more information we have, the easier it will be to find the source of the problem. If all the information we have lines up and agrees with each other, the project’s eventual success should be just a matter of assembling it with good solder joints, then checking it and plugging it in to try it. Of course, Murphy and Sod are always testing us. It might be you get a dead component from the factory, or the PCB you are using has a fault in it (multi-layer boards can often have, or develop faults that are invisible to even the keenest eye). Also, many times, I’ve fired something up after building it, and despite checking and re-checking, I find that I have misinterpreted something in the instructions, or installed something backwards only to see the magic smoke coming out. With care, however, assembling a project and getting it working should be fun and rewarding. Attention to detail required When constructing any board assembly, I start with the components that lie flat first, like resistors, diodes and any SMD components. I like to arrange all the resistors with the colour bands facing the same way. This is not some obsessive-­compulsive disorder on my part; I’m just being tidy. It also helps if I (or someone else) need to troubleshoot the board later; constantly flipping it around to check colour bands or read part designations gets tiresome very quickly. 86 Silicon Chip Australia's electronics magazine siliconchip.com.au Editor’s note: it also pays to check resistor values with a DMM. It can be hard to tell black from brown, brown from red, red from orange and grey from white, especially if your lighting isn’t ideal. Once again, there are many tutorials out there on soldering SMD parts, but that is beyond the scope of this article. Needless to say, constructors should check very closely for solder bridges and connections that haven’t been made once they’ve completed soldering in all the SMDs. A decent, lighted magnifying glass or a good jeweller’s loupe will make this task a whole lot easier. Typically, in any reputable kit of parts, the PCB will have a screen print of the component layout depicted on it, which may also include the circuit diagram’s parts references or even the parts’ type numbers or values. This is usually foolproof, because everything should have been carefully worked out beforehand, thus avoiding potential errors. However, there are traps for younger players. Editor’s note: if building one of our PCBs, check the overlay diagram published in the magazine. Sometimes, changes to the PCB silkscreen can be missed after the prototyping stage, and values that were since changed might still be printed there. The overlay in the magazine is usually final and should have all the correct information. Transistors will usually be depicted asymmetrically, indicating they should only be fitted one way. This is all well and good, but it can get confusing if substitute components are used due to supply problems or expense. Kit manufacturers often swap out different types, but usually mention it in any documentation. Some even add a note in the bag with the parts. Pinouts are not always universal among different transistor types. It pays to check that the component you are soldering in has the same lead designation as any original part quoted. Many projects I’ve repaired over the years have had substituted components installed, and as these were inserted as per the instructions and PCB overlay, the project didn’t work. They’d had a different lead configuration. Data sheets for almost every component on the planet are available with a quick Google search, so it doesn’t take much effort and research to make sure you put things in the right way around. This is especially true for many of today’s multi-layer PCB projects; it’s a lot easier soldering something into these PCBs than getting them back out again! Putting components in backward has been a staple error of constructors since project building began. The mantra is to check, double-check, then triple-check before you solder anything in. This tip alone will save a lot of grief and hand-wringing out the other end. Another problem worthy of inclusion here is when working with wound inductors or transformers using enamelled copper wire. This wire is insulated with a very durable coating – it might not actually be enamel anymore, but the theory is the same. This wire is insulated to prevent shorts and flashovers in coils and transformers, so it is quite a thick coating by design. It can also withstand flexing and bending (to a certain extent) without cracking or failing. However, it is not designed to be soldered, and a standard soldering iron will not melt the material, no matter how long you hold the iron on it. This coating must be completely removed, exposing the siliconchip.com.au bare copper wire beneath, before a decent solder joint can be made. I have ‘fixed’ many a project using self-wound inductors where this enamel removal has not been done at all. This means there is no electrical connection between the inductor and the rest of the circuit. Kits and projects usually have specific instructions on the requirements to do this enamel removal, but some constructors don’t get the memo. I’ve found that taking this insulated coating off is best done very carefully with a sharp knife (like a ‘Stanley’ knife or box cutter). Yes, I know people will be eye-rolling and saying they have a better method, but for me, a sharp blade is my go-to tool. Some use sandpaper, or worse, try to ‘burn’ it off with a lighter or blowtorch; this is inefficient and messy, and often leaves soot all over the wire. Careful scraping is the only way to leave a decent, clean wire underneath, ready for soldering. Being too aggressive with the knife could also cut the soft copper wire, so like any task, care and finesse make the difference. With patience and care, even the most complex projects can be constructed and work the first time. By all means, ask questions where possible, and above all, have fun with electronics! Louvre rain sensor repair J. W., of Hillarys, WA is at it again. This time, the louvres on his house were playing up, and it turned out to be some of the usual suspects (but not faulty capacitors for once)... In 2003, I installed a Vergola Louvre Roof System across the rear of my house, which has a North orientation, to let the winter sun in and keep the summer sun out. The system has six separate banks of louvres with a Linak linear actuator for each bank, a rain sensor that shuts the louvres when it rains, an indoor control panel with six buttons and a 7-segment display. You can access each bank by cycling through the number on the 7-segment display and then pressing buttons to open or close it. With cooler weather upon us, it was time to let the sun in and warm the house, but when I activated it, the rain sensor always shut the louvres even though it was not raining. Australia's electronics magazine April 2023  87 I tagged all the wires and took a photo with my phone to ensure I got all the wires back in the correct positions. After disconnecting all the wires, I gave the top a good clean. After finishing the reassembly, I turned the power back on and waited out the required 15-minute delay. I was pleased to see the unserviceable condition go away, and the system worked normally. So now the sun can warm the house again, with the panels closing when it rains. Intercom and ant colony unlocker The louvre control box is shown above, with the rain sensor shown adjacent. The rain sensor consists of two stainless steel combs with teeth that mesh into each other, leaving about a 1mm gap so that a drop of rain will bridge the gap and cause a change in resistance from an open circuit to a few megohms. The control box senses this change and shuts the louvres until 15 minutes after the rain stops. I put the ladder up and examined the sensor and cable, which looked the worse for wear after sitting in the sun for all those years. I decided to remove the sensor and refurbish it with new silicone sealant and paint for the base. I managed to pull an extra 30cm of cable from under the tiles, so I cut off the sun-damaged section. After a final test to see that the sensor showed infinite resistance, I put it all back together and turned on the power. The control panel 7-segment display showed a flashing U for unserviceable. This is normal after a power loss so that if it’s raining, it won’t cause the louvres to open. If the sensor is still dry after the 15-minute delay, the louvres will cycle to open and then close. I waited the required 15 minutes and still had the unserviceable indication. After a further 15 minutes, I decided to disconnect the rain sensor and try again. The unserviceable condition persisted. The next step was to find the control box under the roof tiles in the eaves. After pulling several roof tiles back, I found a large Jiffy box with 16 4mm banana binding posts on the top and a mains transformer. The six linear actuators are connected to 12 high-current binding posts with the reset switch, and the rain sensor connected to four smaller posts. I could see what the problem was straight away. There was 17 years of dust and detritus build-up on the top of the Jiffy box, which looked damp. The separate power transformer must have been providing warmth to some rats by the number of droppings around it. So the dampness was probably rat urine, causing a low enough resistance across the metal base of the binding posts to simulate rain. 88 Silicon Chip P. B. E., of Heathcote, Vic thought he had an easy job as it was ‘probably just’ a dry joint. It turned out to be a few different things, including some unwanted guests... I volunteered to ‘have a look’ at a Fermax intercom and door unlocker. The intercom part worked most of the time, but the unlocker hadn’t worked for years. Intermittent faults are always a bigger problem than simply not working. However, it usually means there is a dry joint or broken wire. I was hoping for an easy fix along those lines. The unit was installed at a property in Melbourne, so I got the whole thing out: master, slave and door strike. That way, I could take it back to the workbench and look at it closer. I left the transformer behind as I knew it was working and it would be easy to supply 12V at home. There were five coloured wires from master to slave and two to the door strike. Strangely, the wire that was used was six-core, similar to alarm wire. I thought five-core trailer wire would have been better. This caused me some confusion as the yellow wire was connected to the slave but not to the master. I tried to get the schematic from Fermax, but it was a dead end. I then spent far too much time trying to find a PDF with the circuit diagram. After about an hour, I managed to find a manual for a similar unit from an intercom place in America. I downloaded the PDF manual and printed the page I needed. It was only then that I found that the yellow wire did nothing. On removing the master unit, I realised it was full of ants. I’m sure they didn’t help the situation. I didn’t have any insecticide, so I sprayed the unit with WD40 – that’s for water displacement, not insect displacement! – Editor. Alas, it turned out that the intercom runs on 12V AC, not DC as I’d assumed. I didn’t have a 12V AC supply, but I did have an old Triang model train transformer that put out 15V AC – close enough. I wired it up on the bench using the same colour codes. I got nothing, not even intermittent operation anymore. Oh dear. It was time to pull this thing apart as far as I dare and clean it. That turned out to be surprisingly easy. It was held together by just two screws and four clips, and once open, the PCB came right out. The speaker was connected with flying leads, so I desoldered them. I cleaned the speaker gently with metho. Knowing the PCB had been subjected to ant acid, I dipped it in a very weak caustic soda solution and washed away all the gunk with a long soft paintbrush. Then I gave it a quick metho bath and dried it using compressed air. I left it in the sun to dry properly. It was time for a coffee! On inspecting the printed side of the PCB, I found what I thought would be the problem, a dry joint. There were a few other joints that, in my opinion, were bad, so they got the resoldering treatment too. On testing the nameplate light, it was blown. A new 12V 5W festoon ‘trailer’ globe Australia's electronics magazine siliconchip.com.au fixed that. I’m not too fond of these festoon globes, but that’s how it’s designed. I then reassembled and wired it back up on the bench. The call button didn’t work very well, so I took it apart and cleaned it again, bending the two metal prongs to make better contact. It then all worked well. I only had to reinstall it in the client’s house back in Melbourne. Easy. After I reinstalled it, no go again. This time, the problem had to be the wiring in the house or underground. I guessed it would be in the hardest location to fix, underground! With a simple multimeter test, I discovered the wire from the master unit to the striker was open-circuit. After digging for only 10 minutes, I found a join in the conduit that I didn’t like. When I took it apart, I found it was full of ants and dirt. The wire was corroded at a three-way join in the conduit (never join wire underground). A new two-core wire had the unit working again. I’d spent about eight hours on this ‘simple’ fix. However, I got more satisfaction from it than many others I’ve done, probably because there were four separate faults. Another success! Converting a torch to use lithium-ion cells B. P., of Dundathu, Qld discovered that it’s pretty easy to convert some torches from using three disposable cells to a single rechargeable lithium-ion cell… Small pocket torches that take three AAA cells are very common. We have several at home, and I always carry one in my pocket. But I was getting a bit sick of replacing the AAA cells. Also, these torches can get a bit touchy with all the connections for the cells and the cell holder. There are eight different connection points; one on each end of each cell and one on each end of the cell holder. Sometimes you have to give the torch a bit of a jiggle before everything makes contact and works. I thought that there must be a better way! I was recently working with 18650 cells and realised that an 18650 cell should be able to power one of these small torches. The only problem is that they are too long to fit inside the torch. I needed a shorter 18650 cell, so I ordered some 18500 cells on eBay. They are 3.7V Li-ion cells like 18650s but are 50mm long instead of 65mm long. The cell holder for the three AAA cells is just over 50mm long, so the 18500 cell will fit inside the torch, but the 18500 cell is smaller in diameter than the threeAAA cell holder. siliconchip.com.au I thought of using 25mm electrical conduit, but it wouldn’t quite fit inside the torch, and the 18500 cell was loose inside it. After cutting a suitable length of conduit, I solved these problems by cutting a slot in the conduit and heating it with my heat gun, then wrapping it around the 18500 cell while it was soft and pliable. Then it was just a matter of assembling the torch with the conduit sleeve and the new 18500 cell. It all fits together nicely and now there are only two connection points instead of eight. With some torches, stretching the spring on the cap end may be necessary, but that was not required in my case. The sleeve can be made from thick cardboard if you do not have 25mm electrical conduit. Although 18500 cells are rated at 3.7V, a fully-charged cell has a similar voltage (4.2V) to three AAA cells in series (3-4.5V), so I didn’t find any need to change anything inside the torch. After converting three of our frequently used torches to 18500 cells, it’s now just a matter of grabbing a charged cell as needed and then re-charging the flat cell instead of having to buy AAA cells continually. Miele clothes dryer repair D. T., of Sylvania Southgate, NSW found out (if he didn’t already know) that buying electrical goods at an auction is a bit of a gamble. Still, that gamble paid off as the faulty device turned out to be relatively straightforward to fix... My wife bought a used Miele T7944C clothes dryer at a local auction. The dryer came with a matching washing machine, which we ran a few loads through, and it worked fine. However, the dryer only worked for about 10 minutes before it stopped with a “Clean out airways” LED illuminated on the front panel. The first thing I did was clean out the obvious filters in the chassis around the door opening. These weren’t too blocked, but it’s hard to know what the problem threshold is when you have a new piece of kit. That didn’t help. Then I found another pull-out filter in the door, which also wasn’t too bad, but cleaning that didn’t help either. Searching the internet revealed this dryer is a ‘condenser’ type, where the moisture from the clothes comes out as liquid in a pipe that you feed into a drain instead of being blown out the exhaust all over your laundry. To achieve this, it has a closed loop where heated air is blown through the clothes like a standard dryer, but instead of exhausting out to the atmosphere, it circulates through a condenser where it is cooled, causing the water in the air to turn into a liquid and drip into a tank/drain. The air is then reheated and passed back through the clothes. All this heating and cooling of air may seem inefficient, but consider that with a regular dryer, fresh air is continuously heated from room temperature and blown out as waste. The internet also revealed that the condenser can be pulled out and cleaned. It too had some accumulated Australia's electronics magazine April 2023  89 fluff, but it wasn’t downright awful. Cleaning it as per the instructions made no noticeable difference. It seemed likely to me that there was a sensor in the air loop somewhere that would show a high temperature if the filters were blocked, so I thought I’d see if I could find it. After passing through the condenser, the air travels up the back through a duct made from galvanised sheet steel that passes under a cover screwed to the back. I removed the cover to reveal a heater, an over-­temperature mains cutout, and something that looked like a sensor. I pulled the connector off and removed the sensor by bending a pair of chassis tabs. On the bench, it measured about 83kW at room temperature. This seemed reasonable for an NTC thermistor, but since I didn’t really know what it should be, I decided to have a go at opening it anyway. The sensor housing was made from two pieces of plastic with four tabs that had been melted over to keep them together. I sliced these off with a scalpel, and the halves came apart to reveal a two-wire sensor that had been spot welded to pair of brass bars – the bars formed the connector pins. Most significantly, there was evident corrosion on one of the joints. Both joints were still physically intact – the pins were still well attached to the sensor wires, but I decided to clean it and re-solder the connections anyway. It wasn’t hard to re-solder after I scraped all the corrosion away. The hard part was fitting it back into the housing with the extra solder. In the end, I cut away some of the plastic housing to make room for the solder, then cable tied it back together and reattached the duct. I didn’t have any washing that needed drying, so I tested it with an old towel I dunked in water. An hour or so later, I had a nice dry towel. I’m not sure if my soldering cured it or if it was the disconnection and reconnection of the plug onto it that ‘cleaned’ the connector (I suspect the latter). Still, I’m glad I removed the corrosion – it was a future failure waiting to happen. 90 Silicon Chip Cable management of an aircon P. B. E., of Heathcote, Vic was asked to ‘have a look’ at a Panasonic CU-624KR air conditioner by a friend. It had been ‘professionally’ repaired, but it turns out that being a professional doesn’t necessarily mean you know what you are doing... This unit was only about 15 years old. The owners said they don’t use it much, so it should be OK. Actually, the opposite is true. Air conditioners, both in homes and cars, should be fired up for about 15 minutes per month to allow the oil to circulate, keeping them in good condition. This Panasonic had been fixed before by ‘professionals’. The problem then was that a mouse (or mice) had decided that the fine control wiring was a good place to sharpen their teeth. The wires were poorly joined back together and insulated with thick tape. It’s amazing it worked at all, but it did for about 12 months. Then nothing again – absolutely nothing. No error codes, lights or relay(s) clicking. I checked the outside unit first, thinking that’s where mice could easily get into. After undoing silly little clips and many screws, it all seemed OK. Nothing obvious was wrong. I gave it a good clean, particularly the fan and evaporator. I then started on the inside unit; this was harder to take apart. The screws are cleverly hidden behind plastic clips. With the screws out, the plastic cover still needs to be un-clipped from the main housing. I couldn’t find the clips for some time due to them being on top and the unit close to the ceiling. After finally getting the plastic cover off, mouse poo and small bits of wire fell out. Oh dear, “there’s your problem”! I made a drawing of the mains wiring that I knew I would need to dismantle. There were two active red wires; I thought that was a bit strange, so I marked them separately. I doubt that it would work if I reversed them. With a lot of wriggling and gentle force up and down, I got the two PCBs out that should be connected with the chewed wire. To make things more of a challenge, Panasonic (bless them) decided to make all these wires the same colour, white. I took the boards home for scrutiny. There were ten wires, with only three still barely connected. What goes to what? All I could think of, and hope for, was that the wires were in the same order on each board. I know one shouldn’t assume, but I had no choice. I set about reconnecting all 10 wires, about 20mm longer than before. That would make it easier to slide the boards back into the plastic housing. I wrapped the new loom in three layers of thick tape, hoping this would discourage future mice attacks. Back on the job, the reassembly was easier than the dismantling. I also packed in some Scotch-Brite pads laced with a good amount of cayenne pepper around both PCBs, hoping that mice aren’t fans of spicy food. I then reassembled the rest of the indoor unit. I went outside to check that I hadn’t forgotten something silly. I turned the unit’s circuit breaker on in the meter box and its separate switch on the wall, then noticed a relay clicked in the outside unit. That sounded encouraging. Back inside, I programmed the remote for cooling at 20°C. I then hit the on button and was greeted with a pretty blue LED. After about one minute, the unit fired up, and it smacked me with cold air. After five minutes, we got too cold and had to turn the temperature up. Another success. SC Australia's electronics magazine siliconchip.com.au Rack Equipment Ideal for IT Networking, Small Offices, Recording Studios, Sound & PA Equipment. GREAT VALUE and IN STOCK at your conveniently located stores nationwide. ALL cabinets feature: • Key lockable front, back & sides • Tempered glass doors • 60kg static loading capacity • Wall mount without brackets Swing frame SWINGS OPEN FOR EASY MAINTENANCE OR INSTALLATION 19" Rack Mount Cabinets 6U Flat Packed HB5170 / Assembled HB5171 12U Flat Packed HB5174 FROM 239 $ Swing Frame 19" Rack Mount Cabinets 6U Assembled HB5180 12U Assembled HB5182 FROM 299 $ Here's just some of our Rack Mount Accessories See our range in-store or online Patch Cables • Cat5e, Cat6a & Cat7 available YN8200-YN8299 FROM $3.75 24 Port Cat6 Patch Panel • Numbered ports • Labelling area • 1U rack height YN8048 JUST 79 $ 95 Patch Lead Management Panel • Keeps leads tidy JUST • Removable cover $ 95 • 1U rack height HB5434 32 Fixed Rack Shelves • Powder coated steel • Supports up to 20kg • 1U and 2U available HB5452 - HB5454 FROM 49 $ 95 Professional 19" Rack Style Enclosures • Metal construction • Supplied flat pack • 1U, 2U and 3U available HB5120 - HB5130 Shop at Jaycar for your Computer Networking gear: • Computer Modems and Routers • Neworking Leads & Adaptors • Ethernet Switches • Keyboards & Mice • Networking Test Equipment • Storage, Docking & HDD Explore our full range of rack mount products, in stock at over 110 stores, or 130 resellers or on our website. jaycar.com.au/rack-mount 1800 022 888 Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. FROM 139 $ PRODUCT SHOWCASE Largest Electronex Expo yet coming to Melbourne this May Electronex – The Electronics Design and Assembly Expo is almost sold out and has been enthusiastically supported by local and international exhibitors. It will be the largest show since the inaugural event in 2010, with over 100 companies represented. Exhibitions are experiencing strong growth post-COVID as businesses welcome the return of face-to-face discussions of their specific requirements with suppliers and industry experts. At the Melbourne Convention and Exhibition Centre on the 10th & 11th of May 2023, Electronex is Australia’s major exhibition for companies using electronics in design, assembly, manufacture and service. In another first, Electronex will be co-located with Australian Manufacturing Week, with trade visitors able to visit both events on either day, to see the entire spectrum of the latest products, technology and turnkey solutions for the electronics and manufacturing sectors. Many of the exhibitors will be launching and showcasing new products and technology. The next issue of Silicon Chip (May 2023) will include a full show feature article with the exhibitor list and new product highlights. The SMCBA Electronics Design and Manufacture Conference will be held concurrently, featuring technical workshops from international and local experts. 98% of visitors to the previous Melbourne event in 2019 said Electronex was beneficial for their industry, so don’t miss it! Visitors can register for free at www.electronex. com.au SMCBA conference topics & speaker overview Keynote Speaker – Cheryl Tulkoff Cheryl is an experienced executive director, teacher and author with over 30 years of experience in electronics manufacturing establishing policies, processes, and procedures aimed at exceeding corporate quality goals. Focusing on reliability and failure analysis, Cheryl is passionate about accelerated product development while improving reliability, optimising resources and improving customer satisfaction. 92 Silicon Chip The keynote “Securing the Electronics Future: Technological Sovereignty Through Innovation & Collaboration” will emphasise the importance of developing secure, reliable and sustainable electronics manufacturing. It will also investigate the need for increased international cooperation between industry, government, and academia to promote innovation. Ultimately, by working together to advance the electronics industry, we can create a more secure and prosperous future for all. Cheryl will also present “The ABCs of DfX in Electronics Manufacturing”. Design for Excellence (DfX) is based on the concept that optimising a product early in the design process is far more effective than addressing problems later. Do some of your design practices limit long-term product success? Is the design process focused solely on meeting a narrow set of defined requirements? Having a broad knowledge of the entire product life cycle – from cradle to grave – dramatically improves productivity, reliability, and sustainability. Common barriers and mistakes will be discussed, along with practices that can be immediately implemented. Phil Zarrow – ITM Consulting In over 30 years of consulting, Phil Zarrow and Jim Hall of ITM Consulting have just about seen it all! You may be familiar with their popular podcast, Board Talk, which addresses industry issues with deep understanding and a sense of humour. Join the “Assembly Brothers” for “SMT Assembly Troubleshooting and Process Optimization”, a journey through troubleshooting the most common defects in SMT with an emphasis on identifying the fundamental root causes and an entertaining overview of SMT assembly process optimisation techniques. Jasbir Bath – Bath Consultancy Jasbir has over 25 years of experience in research, design, development and implementation in the areas of soldering, Australia's electronics magazine siliconchip.com.au surface mount and packaging technologies. He will present “SMT Process Setup”, focusing on the solder paste printer, ensuring correct printing, ensuring the printed paste volume is in the correct range and setting up the reflow oven to ensure the correct reflow profile. Inspection/test equipment during manufacturing will be discussed, including SPI, AOI, X-ray and ICT. Jasbir will also speak on “SMT Process Development”, including the optimisation of printing of solder paste for different components on the board and developing the reflow profile to reduce soldering defects. Audra McCarthy, CEO of Defence Teaming Centre Inc The Defence Teaming Centre Inc is Australia’s peak defence industry body connecting, developing and advocating for Australia’s defence industry. Audra will present “The role of the Australian electronics sector in establishing a sovereign defence industry capability”. She has experience working across the defence industry sector, having previously worked for the Department of Defence, “primes” and small businesses. She has an excellent understanding of the complex challenges impacting the defence sector and its various stakeholders. The full conference program can be viewed at www. smcba.asn.au/conference Australasian Exhibitions and Events Pty Ltd Suite 11, Pier 35-263 Lorimer St, Port Melbourne VIC 3207 Tel: (03) 9676 2133 mail: ngray<at>auexhibitions.com.au www.auexhibitions.com.au | www.electronex.com.au Infineon XENSIV sensor kits Unit 1901-1906, 19/F LU Plaza, 2 Wing Yip Street, Kowloon, Hong Kong Phone: +852 3756 4700 www.mouser.com siliconchip.com.au Microchip’s PolarFire FPGAs and SoCs deliver up to two times the performance per watt compared to competitive devices. The thermal images opposite show the power and heat dissipation when identical designs are run on the PolarFire (top) and a competing FPGA (bottom). PolarFire SoCs and FPGAs demonstrate far superior thermal performance over the operating temperature range. The chart below shows a stable power and thermal performance of PolarFire SoC FPGAs while a competing SoC FPGA demonstrates a thermal runaway at a 60˚C ambient temperature. Failure In Time (FIT) rate grows exponentially over temperature; the low power consumption of PolarFire SoCs and FPGAs delivers superior FIT rates. PolarFire SoCs deliver significant power savings while outperforming SRAM-based SoC FPGAs over the operating temperature range. While consuming 1.3W (dashed yellow vertical line) PolarFire SoCs deliver 6000 CoreMarks whereas competing SRAM based SoC FPGAs deliver 0. Low power advantages of PolarFire SoCs and FPGAs include: • Save up to US$1.5/W (fan-less and heatsink-less designs) • Enable power- and thermal-constrained applications • Create smaller industrial designs • Achieve lower FIT rates with lower thermals Eliminating fans reduces cost and increases system reliability. Total Power Consumption (mW) Power Comparison vs Ambient Temperature 8000 7000 6000 5000 4000 Polarfire 3000 Competitor 2000 1000 0 0 20 40 60 80 100 Ambient Temperature, °C CoreMarks / mW 9000 8000 7000 CoreMarks Mouser Electronics is now stocking the XENSIV KIT CSK PASCO2 and KIT CSK BGT60TR13C 60GHz radar connected sensor kits (CSK) from Infineon Technologies. The XENSIV CSK provide a ready-to-use sensor development platform for IoT devices. The CSK platform enables the creation of new prototype ideas based on Infineon sensors, including radar, environmental sensors and others. Combining sensors, microcontrollers and secure connectivity for a prototype can become a resource-intensive process. The CSK platform solves this by combing XENSIV sensors with power-efficient, high-performance processing based on an Infineon PSoC 6 microcontroller. An OPTIGA Trust M security controller enables secure connectivity. The modular board design of the CSK is compatible with the Adafruit Feather form factor, allowing the user to prototype solutions for various sensor use cases, for example, battery-powered smart home applications. The XENSIV CSK is currently available from Mouser. To learn more about the CSKs, visit: siliconchip.au/link/abjx siliconchip.au/link/abjy Mouser Electronics (HK) Ltd. PolarFire SoC and FPGAs for the lowest total power solution 6000 5000 4000 3000 2000 1000 0 0 500 1000 1500 2000 2500 3000 3500 Power (mW) MPFS095T 2xCortex A9 2xCortex A9 2xCortex A53 Microchip Technology Australia Suite 32, 41 Rawson Street, Epping NSW 2121 Phone: (02) 9868 6733 www.microchip.com Australia's electronics magazine April 2023  93 Vintage Radio Browning-Drake Model 6A from 1927 By Dennis Jackson I’m fascinated by early radio sets, especially regenerative sets from the 1920s. BrowningDrake is a US company that made innovative radios in the 1920s, and this set is one of their later models, which evolved over the years to become solid performers. Shown here is the model 6A with a large Utah horn speaker that came with it. W hen listening to the conversations of older relatives who had made their own wireless receivers during the 1920s, I remember being impressed by the names Browning-­ Drake (B-D) and Radiokes. Browning-Drake made tuned radio frequency (TRF) wireless sets while Radiokes made tuning coil sets. There were none better, according to my father and some of his brothers, who had lived solid physical lives working as farmers and builders and judged things on their merits. Radiokes were a Sydney-based company that manufactured boxed sets of tuning coils for various receiver configurations, plus other desirable components that were mainly aimed at the 94 Silicon Chip amateur constructor. The story of Browning-Drake is well documented. In August 1923, Glen Browning and Fredrick Drake were students at Harvard University in the USA. They were asked to explain theoretical losses in the wireless receivers of the times. Accordingly, after a long detailed mathematical study, they concluded that the major losses were due to unwanted capacitive coupling between the primary and secondary windings and within the windings of the tuning coils between RF stages. The regenaformer Their solution was to develop the “regenaformer” transformer. Australia's electronics magazine The secondary consisted of 74 turns of enamelled copper wire wound on a 75mm Bakelite former that was spiral threaded so the windings were spaced one-half of a wire diameter apart. The primary consisted of 24 turns of 30 AWG (10thou/0.25mm diameter) silk-covered fine wire loosely wound in a slot cut into a ring and placed firmly inside the tube, level with the Earthy end of the secondary. The aim was to reduce capacitive coupling. The feedback or tickler coil is wound on a 60mm former placed in the other end of the secondary former that is free to be rotated 180°. This feedback winding used 20 turns of 26 AWG (16 thou/0.4mm diameter) wire to provide a controllable amount of siliconchip.com.au Opening the front of the model 6A’s case reveals five control knobs and primary tuner. From left-to-right, the knobs control power, variable capacitor C2, station selection, valve filament voltage and feedback coil in the regenaformer. feedback regeneration from the plate of the detector to the grid of the first audio valve. Browning and Drake’s main contribution to the regenaformer was the placement of the primary winding within a slot fitted at the end of the secondary, with a view to reducing unwanted capacitive coupling causing RF losses. Hazeltine’s balancing circuit was used to minimise plateto-grid capacitive effects within the first RF valve. Howard Armstrong had developed the concept of regeneration. To get around his patents, the complete regenaformer, its associated tuning capacitor and tuned aerial coil were initially sold as a boxed kit to people building their own radio. B-D receivers were popular with amateur constructors as they could wind their own regenaformer and the other parts were generally standard items. Interestingly, the variable tuning capacitor used in the first RF stage had a higher capacitance (400pF) than that used to tune the regenaformer (300pF). Maybe this was to compensate for aerial loading. I have noticed a tendency for stations to crowd the lower end of the tuning range on other B-D sets. Complete factory-built B-D receivers were available by the mid-1920s, and I had the good fortune to acquire a B-D model 6A from the USA around 2008 after I saw it advertised on eBay. I rather impulsively placed a bid for $250, which was knocked back due to not meeting the undisclosed reserve. I also had to consider the freight cost of around $200 at the time. I was a bit peeved by missing out on what would have been a once-in-a-­ lifetime chance and set about doing the next best thing, as many an old-time siliconchip.com.au amateur would have done, by building my own. I saved the photos used in the advertisement and whatever other information I could find. I had almost completed the RF section, ready for testing, when an email arrived. The seller had a rethink, and as I was still the highest bidder, I was given a second opportunity. I lost no time paying up through eBay, and the model 6A duly arrived through the back gate to preserve matrimonial bliss. The mid-west USA had been subjected to severe blizzards, and the unfortunate seller needed to buy shakes (wooden shingles) to repair his roof. I upped my payment a bit for the goodwill, and he added his big Utah horn speaker into the bargain. The 1927 model 6A The six-valve model 6A was a complete rethink compared to its basic five-valve predecessor, the model 5R from late 1926. It is a table set built of solid timber, probably poplar, which is light, soft, workable and stains well for an attractive finish. The double doors in front open to display the timber control panel. By 1926, dedicated output valves were becoming available such as the 71A and the CX112A, the latter used in this set. These gave a modest but welcome rise in sound output compared to using more general-purpose valves in the output stage. Still, listeners would have to wait several more years before the moving coil speaker (like we use today) provided a broader range to the audio spectrum. It was common for these pioneering wireless receivers to have all the same types of valves in the line-up. UX201s, UX199s or the Phillips B405, B409 and A609 were the main types. This set uses a bit of a mixture; the UV199 and UX201A were from General Electric (GE), the 200A was a generic type made by several manufacturers, and These coils and associated tuning capacitor make up an original B-D regenaformer sold as a boxed kit (not the one used in the 6A). The rotatable coil which controls feedback regeneration is on top. The secondary is the larger coil while the primary is wound on a slotted former and slid inside the main tube at the bottom, Earthy end. Australia's electronics magazine April 2023  95 Resistance-capacitive coupling is used between all stages, except the first RF amplification stage, which uses an RF choke and coupling capacitor to direct RF to the next stage, the regenaformer. The whole assembly is built on a flat aluminium chassis. That was an expensive metal back then, reflected in the US$85 retail price for the set. Circuit details A close-up of the regenaformer section and the detector valve V2 of the Browning-Drake model 6A. the CX112A and CX340 were made by Cunningham Inc, New Jersey, USA. The first knob to the left is the on/ off switch which disconnects the valve filaments from the A battery. The second is the ‘sensitiser’, claimed to pull in far distant stations, according to one advertisement. This controls a variable capacitor of about 100pF (C2; see Fig.1), which is in parallel with the first RF tuning capacitor (C1) and really adjusts tracking between both ganged tuning capacitors C1 and C5. The third lower centre knob provides single-point tuning, making station selection user-friendly, which was not common with mid-1920s receivers. The fourth to the right is the usual wire-wound rheostat controlling the valve filament voltage, which is adjusted as the ‘A’ battery voltage drops with usage. On the far right is the control for the rotation of the feedback coil within the regenaformer. The model 6A was a well-thoughtout design. It has other cutting-edge innovations for the time, such as the completely separate shielding of the first and second RF sections plus the rear audio sub-assembly, and the use of resistance-capacitive coupling between stages. I could not find a circuit diagram for this set, so I drew my own, shown in Fig.1. B-D receivers used similar first and second RF stages. A UX199 valve was used in the first stage because it was easier to neutralise due to its lower internal capacitance. Hazeltine neutralisation was implemented using C3 at a few picofarads. Medium-size variable capacitor C2 is in parallel with the large ganged variable tuning capacitor C1 and tuning coil L1; its purpose is to adjust tracking as ganged tuning capacitors C1 and C5 tune across the dial. RF choke L5 in the plate circuit blocks RF from the B+ 90V line to redirect through C4, an Aerovox 500pF capacitor, and through L2, the primary of the regenaformer. L2 is wound on a thin former that has been glued and fitted under the Earthy end of the larger tuned winding, L3. L4 is the rotatable feedback coil providing regeneration. The grid leak detector is made using V2, a 200A triode, together with R1 Fig.1: the circuit diagram for the model 6A radio. As there wasn’t any existing circuit online for this radio one was drawn up by tracing and testing the components by hand. 96 Silicon Chip Australia's electronics magazine siliconchip.com.au Viewing the model 6A chassis from above shows the RF and AF shielding partitions. The first RF amplifier is right, while the regenaformer-detector section is left. Four audio valves are shown below (the rear of the set). and C6. R2 blocks RF from the detector B+ 45V battery tap, while R4 and R6 block the audio signal from the B+ 90V to be redirected through coupling capacitors C9 and C10. R3, R5 & R7 are part of the negative grid biasing circuit of the four audio valves. The configuration of C7, C8 & L6 is a bit unusual. That section appears to block and bypass RF from the grid of V3, the first of four audio valves mounted on the sub-assembly to the rear of the shielding cans. There are no audio coupling transformers; instead, resistance-­capacitive coupling is used throughout. The audio sub-assembly is a separate, closely packed unit that was difficult to access while tracing the circuit. Two ‘equalisers’ (made by Amperex) are used to limit the current drawn by the valve filaments (providing a measure of protection similar to an NTC thermistor). After some probing, I determined that the plates of V4 & V5 are connected together, as are both grids; so V4 & V5 are in parallel. Valves are usually connected in series to provide more voltage gain. So my first thought upon seeing this is that they needed more current drive than a single triode could provide. After reassembly, I removed V5 to see what difference it made. There was no difference in the sound output, nor was there any difference when I replaced V5 and removed V4. So the siliconchip.com.au need for the extra valve is a bit of a puzzle. Perhaps some CX340s had weaker drive than others, and this was a ‘crutch’ to allow them to get away with using the weaker valves. Or maybe there is another reason... A bit of a puzzle It had taken almost a century, but the designers were finally caught out. Why weren’t the four audio valves operated in series? I am not sure. All TRF receivers of this general type I have known have had not more than three audio stages, and I can only suggest that adding more could have caused instability. I have another neatly-constructed, home-built TRF set that had an extra valve paralleled experimentally to the audio output valve (both UX201s). Still, from my experience, that does not improve the sound output. Firstly, the human ear has a logarithmic sensitivity; doubling the sound output power would give only The RF section of the model 6A, which incorporates a UV199 valve (V1) and the variable capacitors C1 (ganged tuning), C2 (centre), tuning trimmer and valve balancing trimmer. Australia's electronics magazine April 2023  97 a small increase in the maximum perceived volume level. Secondly, there could be an impedance mismatch to the speaker load when two valves are used in parallel. Further thoughts Unusually, this B-D model 6A will operate well with reduced volume with the first RF valve (a UV199) removed. I have sometimes pondered the actual gains achieved by placing the primary winding in a close-wound slot fitted under the Earthy end of the secondary. I have three examples of factory-­ made regenaformers, and all seem to have the primary turns wound sideby-side on a separate thin former slid inside the main tube at the opposite end to the rotating feedback winding. In each case, all turns are close-wound with fine wire. The problem is that the former cannot easily be removed to check the effect on performance without damaging the unit. This is the technology of 100 years ago and is now part of the history of vintage radio. Battery TRF sets had a short lifespan before becoming redundant by the end of the 1920s due to advances in valve technology and the rise of the superheterodyne set. Conclusion If I were an adult living around 1927 and were given the choice of any of the TRF battery-powered receivers from that period that I have in my collection, I would choose my Browning-Drake The audio side of the model 6A contains valves V3-V6. Clips within the two subpanels hold removable resistors. From left-to-right the valves are: UX201A, CX340, CX340 and CX112A. model 6A. Connected to its original Utah horn speaker, it gives a good sound level from the two remaining AM broadcasters in Hobart. It is lightweight, reasonably easy to set up and tune in once you get the knack, and it is very stable in operation. I now know why those pioneering old-timers working in the bush would get excited when they were talking about their Browning-Drake wireless. Would I remove that extra paralleled audio valve to conserve battery current. Maybe not, would I have known? To power my set, I use the Universal Battery Eliminator designed by Peter Lanksheer from Invercargill, NZ and published in Electronics Australia, March 1990. That design has proven invaluable in powering my battery receivers. After I work out the connections for a particular set, I wire it up to an eight-way connector from Jaycar that matches a connector in the supply lead from the battery eliminator. That enables me to use the one Battery Eliminator for multiple radios, with quick and correct connections to each SC wireless set. U Cable Tester S B Test just about any USB cable! USB-A (2.0/3.2) USB-B (2.0/3.2) USB-C Mini-B Micro-B (2.0/3.2) Reports faults with individual cable ends, short circuits, open circuits, voltage drops and cable resistance etc November & December 2021 issue siliconchip.com.au/Series/374 DIY kit for $110 SC5966 – siliconchip.com.au/Shop/20/5966 Everything included except the case and batteries. Postage is $10 within Australia, see our website for overseas & express post rates 98 Silicon Chip Australia's electronics magazine siliconchip.com.au Refresh your workbench with our GREAT RANGE of essentials at the BEST VALUE. Here's just a small selection of our best selling workbench essentials to suit hobbyists and professionals alike. ALL THE REGULAR OSCILLOSCOPE FUNCTIONS IN A SMALL FORM FACTOR 2 CHANNELS SuperPro Gas Soldering Tool Kit SOLDER ANYTHING, ANYWHERE! 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Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. ONLY jaycar.com.au/workbench 1800 022 888 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. Lithium battery & case for Uno with touchscreen My submission for the Dick Smith Noughts & Crosses competition (October 2021) was published in the January 2023 issue (siliconchip.au/Article/ 15621). It used an Arduino Uno and Adafruit touch-sensitive screen and not much else. It was also featured on page 84 of the April 2022 issue. As I showed it off to friends, I thought it’d look better in a case. So I used OpenSCAD to design a plastic case for it and used a commercial 3D printing service to print it. Then I thought it’d be more convenient if it were battery-powered. Fortunately, battery charging and 3.7V to 5V converter modules are readily available, eg, Jaycar XC4502/XC4512 or Altronics Z6388/Z6366. Although these do most of the work and need little more than the battery and a switch, they look a bit experimental when connected with just wires. So I decided to design another case to hold those parts. I mounted the modules, switch and CON1 on a custom PCB, treating the modules as through-hole parts. The resulting circuit is quite simple, as shown in the diagram. The battery charger is wired to one side of the two-position changeover switch, with the 3.7V to 5V boost converter to the other. The battery is wired to the switch’s middle (common) terminal. If the switch connects the battery to the charger, and 5V is supplied to the input USB connector, the battery will charge. The battery charger will automatically stop when it’s fully charged. If the switch connects the battery to the 3.7V to 5V boost converter instead, 5V is available from the output USB connector. Again, that device is suitably clever and will stop drawing current from the battery when it is flat. To switch the device off, you can put the switch in the charging position but not connect a supply, so the battery doesn’t charge. Gerber files can be download from siliconchip.com.au/Shop/6/146, along with the 3D printer (OpenSCAD & STL) files. There are two versions of the PCB to suit two different switches, Jaycar SS0852 & Altronics S2070. I tried to design one PCB to suit both, but it was too difficult. It is unimportant that the Jaycar switch has two poles and the Altronics switch has only one. The case for the Arduino Uno/ touchscreen combination is in three parts: a body and two ‘floors’, primarily for cosmetic reasons. The floor I call FloorTwo has posts for the PCB and the battery. I decided to tap the holes right through, but that made the other side of the floor messy. FloorOne has only four holes for the four screws that hold everything together, hiding the ugliness of FloorTwo. The case has a cut-out for the touchscreen and holes for the two USB connectors on the Uno. It doesn’t have an on/off switch; if it is supplied with 5V, it is on; otherwise, it is off. FloorOne and FloorTwo have small rebates to fit small ceramic magnets (Jaycar LM1622 or Altronics T1466). They are used to hold it to the battery case. The battery case is similar to that of the Uno. It is a little bigger, and its walls extend beyond FloorOne, so the case for the Uno fits it conveniently. It doesn’t have a ‘window’, but it does have holes for two USB connectors and one on/off switch. In this case, FloorOne and FloorTwo also have recesses for magnets. If the magnet polarities are correct, the Uno case is held securely onto the battery case. Like the PCB, there are two slightly different battery case designs to be 3D printed. One is for the PCB using the Jaycar switch, and the other is for the Altronics switch. Keith Anderson, Kingston, Tas. ($80) The battery case with magnets glued on top to hold the Uno case. The Uno case with the USB & power socket cut-outs and mangets visible. The PCB that holds the switch and two modules. 100 Silicon Chip Australia's electronics magazine siliconchip.com.au Circuit Ideas Wanted Got an interesting original circuit that you have cleverly devised? We will pay good money to feature it in Circuit Notebook. We can pay you by electronic funds transfer, cheque or direct to your PayPal account. Or you can use the funds to purchase anything from the SILICON CHIP Online Store, including PCBs and components, back issues, subscriptions or whatever. Email your circuit and descriptive text to editor<at>siliconchip.com.au Three-phase sinewave generator A device I am designing requires a balanced three-phase sinewave source with an operating frequency in the range of 10-15kHz. The signals must be equal in amplitude and separated by 120° in phase, similar to three-phase mains (but at a higher frequency). I used one of the sinewave oscillators I described in Circuit Notebook of the October 2019 issue as the driver for the three-phase sinewave generator (siliconchip.au/Article/12027). The resulting circuit is based on a quad Norton (current feedback) amplifier such as the LM3900. The phase shifter circuit aims to shift the input signal by 120° while preserving the amplitude. The feedback components (in this case, 20kW & 10nF) determine the frequency at which the desired phase shift is achieved. For unity gain, the feedback resistor must be twice the value of the input resistor (20kW vs 10kW here). Scope 1 siliconchip.com.au A detailed analysis of this circuit, including formulas, can be downloaded from our website: siliconchip. au/Shop/6/144 The oscillator section is the driving source for the three-phase generator. The oscillation frequency of 13.64kHz in this circuit was determined by the phase shift element, which was designed first. For fine-tuning purposes, the 12kW and 5.6kW resistors could be made up of fixed resistors in series with trimpots (eg, 11kW + 2kW trimpot and 5.1kW + 1kW trimpot). There is much more information on how this type of oscillator works in my earlier entry from October 2019. In brief, the 12kW/5.6kW and 2nF/1nF pairs need to have roughly a 2:1 ratio for oscillation, and the oscillation frequency is proportional to the square root of the product of all four of those component values. Scope 2 Australia's electronics magazine The three identical phase-shift elements are connected in series. The third element is optional but useful for monitoring the fine-tuning process to ensure that the input sinewave at TP1 and the output at TP4 are identical. That verifies that each phase shift is 120° as 120° × 3 = 360° and also that the signal amplitudes are being preserved. The three scope grabs (shown below) prove that the circuit works. Scope 1 shows the signals at TP1 (yellow) and TP2 (cyan), Scope 2 shows TP1 (yellow) and TP3 (cyan), while Scope 3 shows TP1 (yellow) and TP4 (cyan). If you connect scope probes to TP1 and TP4 and set the scope to X/Y mode, you will get a straight line at 45° if the circuit has been tuned correctly. Mauri Lampi, Glenroy, Vic ($100). Scope 3 April 2023  101 Graph makes using the Q Meter easier I had the opportunity to use Charles Kosina’s new Q Meter (January 2023; siliconchip.au/Article/15613) for several months, as he sent me a prototype before it was published. I produced the accompanying graph to make using it easier. I’ve gone from not worrying too much about measuring Q (I’ve never had a Q Meter before; I guess I’m an RF barbarian) to it being in frequent use! When using the Q Meter, you must first set the RF signal generator to a frequency that suits the coil’s inductance and the Q Meter’s 40-295pF resonating capacitor range. This frequency can be calculated as the article suggests; however, this log-log graph (based on that equation) is a quicker and easier way to make a ‘first guess’ at this frequency. For example, if you have an 8μH inductor, read up the 8μH grid line to see that it crosses the 10MHz curve at about 35pF (too low to be used), the 7MHz curve at around 72pF and the 5MHz curve at around 140pF. 5MHz is probably the best choice, given that the Q Meter’s 40-295pF variable resonating capacitor will be near mid-range. The capacitor and RF signal generator frequency can then be quickly adjusted to give the highest LED brightness on the Q Meter, giving a reading of the inductor’s Q factor. Andrew Woodfield, Christchurch, New Zealand. ($70) Low-cost cell under-voltage protection To safely use a Li-ion (or LiPo) cell, your device must have an under-­ voltage protection circuit (UVPC). While many cells now have integrated protection, some still don’t. However, adding an UVPC by yourself is easy and should cost very little. This design uses a 6-pin PIC10F220 microcontroller, a P-channel Mosfet and a small passive piezo buzzer, all mounted on a tiny PCB of about 5×5mm! We don’t need to use the GP0 or GP1 pins as analog inputs to measure the cell voltage, as the microcontroller can measure its own supply voltage with respect to an internal 0.6V reference. In this application, the PIC’s Vdd/ Vss power pins are directly connected to either end of the cell. As its supply voltage equals the cell voltage, that’s all it needs to measure. The P-channel Mosfet Q1 acts as a 102 Silicon Chip very fast electronic ‘relay’ driven by IC1’s GP0 digital output (pin 1). Even when the cell voltage is very low, at around 2.7V, this Mosfet should still be able to switch on fully as long as a type with a very low gate-source threshold voltage (Vgs[th]) is used. Suitable types include the AO3401, AO3401A and SSM3J372. These have a low enough on-resistance at 2.7V that the load can draw several amps without the Mosfet overheating. If using this circuit with a load that can draw more than a couple of amps, check the device’s data sheet for its on-resistance at around 3V and maximum dissipation to verify it won’t overheat at the full load current. The piezo is connected to the GP1 pin (pin 3), also configured as a digital output to drive the beeper with one of two distinctive tones for the under-voltage alarm. Australia's electronics magazine The software puts the PIC micro into sleep mode, drawing around 4µA at 3.6V with the watchdog timer activated. The maximum possible delay is used (2.3s), so the PIC wakes up every 2.3 seconds to make one measurement of its supply voltage. If it exceeds the allowable limits, a specific tone is emitted, and Q1 is switched off. After each check, it goes back into sleep mode for another 2.3s. The ratio of run time to sleep time is about 1/2300 (if no tone emitted) or 5/23 (with a tone emitted, for 0.5s in each 2.3s period). During the awake time, it consumes about 0.4mA, so the average current consumed above the 4μA baseline is just a few nanoamps. The voltage limits are 2.7V for the minimum and 4.2V for the maximum. Note that some passive small piezo buzzers don’t work below 3V. In this case, you can add a 1-10mH inductor siliconchip.com.au ESP32-based millisecond clock Clocks fascinate me; I have made clocks with various themes, but never a clock that shows the time to the millisecond. Doing so would require considerable processing power to drive the fast-changing display. That all changed when I realised I could run a 3.5-inch ILI9488-based TFT screen in 8-bit mode with an ESP32 microcontroller module. 12 GPIO pins are required to run the display, but it is very fast. Finally, the display could keep up with the milliseconds! You can see a video of it at siliconchip.au/link/abib The display I used was a “3.5 inch TFT LCD Touch Screen Display Shield for Arduino Uno” and was relatively inexpensive; you can obtain the same screen from sellers on eBay & AliExpress (eg, siliconchip.au/link/abi9 & siliconchip.au/link/abia). Although the TFT display fits easily on an Arduino Uno, this Millisecond Clock is impossible with the Uno as it lacks the required computing power. The connections for the ESP32 are shown in the circuit diagram and table. The time is obtained from the DS3231 real-time clock module. It can measure the temperature, which is also displayed on the TFT. The duration between consecutive seconds from the module is divided by 1000 to calculate the millisecond and displayed on the TFT. You can download the software from siliconchip.com.au/Shop/6/152 Of course, this is a bit of a gimmick as you can’t see the display updating; it’s way too fast. But you can see the tenths of a second changing, and you will be aware of the other digits updating really fast. So it’s still pretty cool and a good conversation starter! Bera Somnath, North Karanpura, India ($100). Touchscreen pin ESP32 pin 5V VIN (pin 19) GND GND D0 IO12 D1 IO13 D2 IO26 D3 IO25 D4 IO17 D5 IO16 D6 IO27 D7 IO14 CS IO33 DC – RST IO32 WR IO4 RD IO2 in parallel with that piezo to make a small resonant circuit. Another option would be to modify the software so that the piezo can be connected between two GPIO configured as digital outputs (eg, GP1 and GP2), driven to opposite levels when the piezo is activated. The software, including HEX file and source code, is available for free from siliconchip.com.au/Shop/6/150 Salim Benabadji, Oran, Algeria. ($100) siliconchip.com.au Australia's electronics magazine April 2023  103 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 194, MATRAVILLE, NSW 2036 (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. 04/23 YES! You can also order or renew your Silicon Chip subscription via any of these methods as well! The best benefit, apart from the magazine? Subscribers get a 10% discount on all orders for parts. PRE-PROGRAMMED MICROS For a complete list, go to siliconchip.com.au/Shop/9 $10 MICROS $15 MICROS Digital FX Unit (Apr21) Si473x FM/AM/SW Digital Radio (Jul21), 110dB RF Attenuator (Jul22) RGB Stackable LED Christmas Star (Nov20) Shirt Pocket Audio Oscillator (Sep20) ATtiny816 Development/Breakout Board (Jan19) Ultrabrite LED Driver (with free TC6502P095VCT IC, Sep19) Range Extender IR-to-UHF (Jan22) LED Christmas Ornaments (Nov20; versions), Nano TV Pong (Aug21) Model Railway Level Crossing (two required – $15/pair) (Jul21) Range Extender UHF-to-IR (Jan22), Active Mains Soft Starter (Feb23) PIC12F617-I/SN Model Railway Carriage Lights (Nov21) PIC12F675-I/P Train Chuff Sound Generator (Oct22) PIC16F1455-I/P Digital Lighting Controller Slave (Dec20), Auto Train Controller (Oct22) PIC16F1455-I/SL Ol’ Timer II (Jul20), Battery Multi Logger (Feb21) PIC16LF1455-I/P New GPS-Synchronised Analog Clock (Sep22) PIC16F1459-I/P Cooling Fan Controller (Feb22), Remote Mains Switch Receiver (Jul22) PIC16F1459-I/SO Multimeter Calibrator (Jul22), Buck/Boost Charger Adaptor (Oct22) PIC16F15214-I/SN Tiny LED Icicle (Nov22), Digital Volume Control Pot (SMD; Mar23) Silicon Chirp Cricket (Apr23) PIC16F15214-I/P Digital Volume Control Pot (through-hole; Mar23) PIC16F1705-I/P Flexible Digital Lighting Controller (Oct20) Digital Lighting Controller Translator (Dec21) PIC16F18146-I/SO Digital Boost Regulator (Dec22) PIC16LF15323-I/SL Remote Mains Switch Transmitter (Jul22) W27C020 Noughts & Crosses Computer (Jan23) ATSAML10E16A-AUT High-Current Battery Balancer (Mar21) PIC16F18877-I/P USB Cable Tester (Nov21) PIC16F18877-I/PT Dual-Channel Breadboard PSU Display Adaptor (Dec22) Wideband Fuel Mixture Display (WFMD; Apr23) PIC16F88-I/P Battery Charge Controller (Jun22), Railway Semaphore (Apr22) PIC24FJ256GA702-I/SS Ohmmeter (Aug22), Advanced SMD Test Tweezers (Feb23) 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) RCL Box (Jun20), Digital Lighting Controller Micromite Master (Nov20) Advanced GPS Computer (Jun21), Touchscreen Digital Preamp (Sep21) PIC32MX170F256B-I/SO Battery Multi Logger (Feb21), Battery Manager BackPack (Aug21) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) 24LC32A-I/SN ATmega328P ATmega328P-AUR ATtiny85V-10PU ATtiny816 PIC10F202-E/OT PIC10LF322-I/OT PIC12F1572-I/SN PIC12F617-I/P $20 MICROS ATmega644PA-AU AM-FM DDS Signal Generator (May22) dsPIC33FJ64MC802-E/SP dsPIC33FJ128GP306-I/PT PIC32MX470F512H-I/PT PIC32MX470F512H-120/PT PIC32MX470F512L-120/PT 1.5kW Induction Motor Speed Controller (Aug13) CLASSiC DAC (Feb13) Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) Micromite Explore 100 (Sep16) $25 MICROS $30 MICROS PIC32MX695F512H-80I/PT Touchscreen Audio Recorder (Jun14) PIC32MZ2048EFH064-I/PT DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) DIY Reflow Oven Controller (Apr20), Dual Hybrid Supply (Feb22) KITS, SPECIALISED COMPONENTS ETC WIDEBAND FUEL MIXTURE DISPLAY (CAT SC6721) (APR 23) Short-form kit: includes the PCB and all onboard parts. Does not include the case, O2 sensor, wiring, connectors etc (see page 47, April 2023) $120.00 TEST BENCH SWISS ARMY KNIFE (APR 23) Short-form kit: includes PCB, all onboard SMDs, boost module, SIP reed relay & UB1 lid. Does not include ESP32 module, case, 10A relay or connectors (Cat SC6589) $50.00 - ESP32 DevKitC module with WiFi and Bluetooth (Cat SC4447) $10.00 - 3mm black laser-cut UB1 Jiffy box lid (Cat SC6337) $10.00 SILICON CHIRP CRICKET (CAT SC6620) (APR 23) DIGITAL VOLUME CONTROL POTENTIOMETER (MAR 23) Complete kit: includes all parts required, except the coin cell & ICSP header SMD version kit: includes all relevant parts except the universal remote control and activity LED (Cat SC6623) Through-hole version kit: includes all relevant parts (with SMD PGA2311) except the universal remote control and activity LED (Cat SC6624) ACTIVE MAINS SOFT STARTER (FEB 23) ADVANCED SMD TEST TWEEZERS KIT (CAT SC6631) (FEB 23) RASPBERRY PI PICO W BACKPACK (JAN 23) $25.00 $60.00 $70.00 Hard-to-get parts: includes the PCB, transformer, relay, thermistor, programmed micro and all other semiconductors (Cat SC6575; see page 41, February 2023) $100.00 siliconchip.com.au/Shop/ DIGITAL BOOST REGULATOR KIT (CAT SC6597) (DEC 22) LC METER MK3 (NOV 22) NEW GPS(/WIFI)-SYNCHRONISED ANALOG CLOCK (SEP & NOV 22) BUCK/BOOST CHARGER ADAPTOR KIT (CAT SC6512) (OCT 22) WiFi PROGRAMMABLE DC LOAD (SEP 22) Complete kit that also includes all optional components (see page 87, Dec22) Short Form Kit: includes the PCB and all non-optional onboard parts, except the case, front panel label and power supply (Cat SC6544) $65.00 GPS-version kit: includes everything in the parts list with the VK2828 GPS module (Cat SC6472; see September 2022 p63) $55.00 WiFi-version kit: includes everything in the parts list with the D1 Mini module instead (Cat SC6472; D1 Mini is supplied not programmed, see November 2022 p76) $55.00 - VK2828U7G5LF GPS module with antenna and cable (Cat SC3362) $25.00 Includes everything in the parts list (see page 64, October 2022) except the Buck/Boost LED Driver (see below; Cat SC6292) $40.00 Short Form Kit: includes all SMDs, the power Mosfets, four 0.02W 3W resistors and the VXO7805 regulator module (Cat SC6399) - laser-cut 3mm clear acrylic side panel (SC6514) - 3.5-inch TFT LCD touchscreen (Cat SC5062) $85.00 $7.50 $35.00 $45.00 WIDE-RANGE OHMMETER (CAT SC4663) (AUG 22) $85.00 $7.50 $10.00 VGA PICOMITE KIT (CAT SC6417) (JUL 22) Includes the PCB, all required onboard parts (excluding optional debug interface) and the front panel. Just add a signal source, case, power supply and wiring $100.00 MULTIMETER CALIBRATOR KIT (CAT SC6406) (JUL 22) DUAL-CHANNEL BREADBOARD PSU BUCK-BOOST LED DRIVER KIT (CAT SC6292) (JUN 22) SPECTRAL SOUND MIDI SYNTH KIT (CAT SC6261) (JUN 22) Includes all parts (except coin cell and CON1) (see page 51, February 2023) Complete kit: includes all parts in the parts list, except the DS3231 real-time clock IC (Cat SC6625; see page 56, January 2023) - DS3231 real-time clock SOIC-16 IC (Cat SC5103) - DS3231MZ real-time clock SOIC-8 IC (Cat SC5779) Q METER SHORT-FORM KIT (CAT SC6585) (JAN 23) (DEC 22) Power Supply kit: complete kit with a choice of red + green, yellow + cyan or orange + white knob colours (Cat SC6571; see page 38, December 2022) Display Adaptor kit: complete kit (Cat SC6572; see page 45, December 2022) $40.00 $50.00 $30.00 Partial Kit: includes the PCB, programmed micro, all SMDs, most semiconductors, PPS capacitors and calibration resistors $75.00 - 16x2 alphanumeric LCD with blue backlighting (Cat SC5759) $10.00 Complete kit with everything needed to assemble the board, you just require a few external parts such as a power supply, keyboard and monitor $35.00 Complete kit with everything needed to assemble the board Complete kit with everything needed to assemble the board Complete kit including all programmed PICs (no case or power supply) *Prices valid for month of magazine issue only. All prices in Australian dollars and include GST where applicable. # Overseas? Place an order on our website for a quote. $45.00 $80.00 $200.00 PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT 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 COLOUR MAXIMITE 2 GEN2 (4 LAYERS) BATTERY MANAGER SWITCH MODULE ↳ I/O EXPANDER NANO TV PONG LINEAR MIDI KEYBOARD (8 KEYS) + 2 JOINERS ↳ JOINER ONLY (1pc) TOUCHSCREEN DIGITAL PREAMP ↳ RIBBON CABLE / IR ADAPTOR 2-/3-WAY ACTIVE CROSSOVER TELE-COM INTERCOM SMD TEST TWEEZERS (3 PCB SET) USB CABLE TESTER MAIN PCB ↳ FRONT PANEL (GREEN) MODEL RAILWAY CARRIAGE LIGHTS HUMMINGBIRD AMPLIFIER DATE 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 AUG21 AUG21 AUG21 AUG21 AUG21 AUG21 SEP21 SEP21 OCT21 OCT21 OCT21 NOV21 NOV21 NOV21 DEC21 PCB CODE 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 07108211 11104211 11104212 08105212 23101213 23101214 01103191 01103192 01109211 12110121 04106211/2 04108211 04108212 09109211 01111211 Price $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 $15.00 $5.00 $2.50 $2.50 $5.00 $1.00 $12.50 $2.50 $15.00 $30.00 $10.00 $7.50 $5.00 $2.50 $5.00 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT DIGITAL LIGHTING CONTROLLER TRANSLATOR SMD TRAINER 8-LED METRONOME 10-LED METRONOME REMOTE CONTROL RANGE EXTENDER UHF-TO-IR ↳ IR-TO-UHF 6-CHANNEL LOUDSPEAKER PROTECTOR ↳ 4-CHANNEL FAN CONTROLLER & LOUDSPEAKER PROTECTOR SOLID STATE TESLA COIL (SET OF 2 PCBs) REMOTE GATE CONTROLLER DUAL HYBRID POWER SUPPLY SET (2 REGULATORS) ↳ REGULATOR ↳ FRONT PANEL ↳ CPU ↳ LCD ADAPTOR ↳ ACRYLIC LCD BEZEL RASPBERRY PI PICO BACKPACK AMPLIFIER CLIPPING DETECTOR CAPACITOR DISCHARGE WELDER POWER SUPPLY ↳ CONTROL PCB ↳ ENERGY STORAGE MODULE (ESM) PCB 500W AMPLIFIER MODEL RAILWAY SEMAPHORE CONTROL PCB ↳ SIGNAL FLAG (RED) AM-FM DDS SIGNAL GENERATOR SLOT MACHINE HIGH-POWER BUCK-BOOST LED DRIVER ARDUINO PROGRAMMABLE LOAD SPECTRAL SOUND MIDI SYNTHESISER REV. UNIVERSAL BATTERY CHARGE CONTROLLER VGA PICOMITE SECURE REMOTE MAINS SWITCH RECEIVER ↳ TRANSMITTER (1.0MM THICKNESS) MULTIMETER CALIBRATOR 110dB RF ATTENUATOR WIDE-RANGE OHMMETER WiFi PROGRAMMABLE DC LOAD MAIN PCB ↳ DAUGHTER BOARD ↳ CONTROL BOARD MINI LED DRIVER NEW GPS-SYNCHRONISED ANALOG CLOCK BUCK/BOOST CHARGER ADAPTOR 30V 2A BENCH SUPPLY MAIN PCB ↳ FRONT PANEL CONTROL PCB AUTO TRAIN CONTROLLER ↳ TRAIN CHUFF SOUND GENERATOR PIC16F18xxx BREAKOUT BOARD (DIP-VERSION) ↳ SOIC-VERSION AVR64DD32 BREAKOUT BOARD LC METER MK3 ↳ ADAPTOR BOARD DC TRANSIENT SUPPLY FILTER TINY LED ICICLE (WHITE) DUAL-CHANNEL BREADBOARD PSU ↳ DISPLAY BOARD DIGITAL BOOST REGULATOR ACTIVE MONITOR SPEAKERS POWER SUPPLY PICO W BACKPACK Q METER MAIN PCB ↳ FRONT PANEL (BLACK) NOUGHTS & CROSSES COMPUTER GAME BOARD ↳ COMPUTE BOARD ACTIVE MAINS SOFT STARTER ADVANCED SMD TEST TWEEZERS SET DIGITAL VOLUME CONTROL POT (SMD VERSION) ↳ THROUGH-HOLE VERSION MODEL RAILWAY TURNTABLE CONTROL PCB ↳ CONTACT PCB (GOLD-PLATED) DATE DEC21 DEC21 JAN22 JAN22 JAN22 JAN22 JAN22 JAN22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 MAR22 MAR22 MAR22 MAR22 MAR22 APR22 APR22 APR22 MAY22 MAY22 JUN22 JUN22 JUN22 JUN22 JUL22 JUL22 JUL22 JUL22 JUL22 AUG22 SEP22 SEP22 SEP22 SEP22 SEP22 OCT22 OCT22 OCT22 OCT22 OCT22 OCT22 OCT22 OCT22 NOV22 NOV22 NOV22 NOV22 DEC22 DEC22 DEC22 DEC22 JAN23 JAN23 JAN23 JAN23 JAN23 FEB23 FEB23 MAR23 MAR23 MAR23 MAR23 PCB CODE 16110206 29106211 23111211 23111212 15109211 15109212 01101221 01101222 01102221 26112211/2 11009121 SC6204 18107211 18107212 01106193 01106196 SC6309 07101221 01112211 29103221 29103222 29103223 01107021 09103221 09103222 CSE211002 08105221 16103221 04105221 01106221 04107192 07107221 10109211 10109212 04107221 CSE211003 04109221 04108221 04108222 18104212 16106221 19109221 14108221 04105221 04105222 09109221 09109222 24110222 24110225 24110223 CSE220503C CSE200603 08108221 16111192 04112221 04112222 24110224 01112221 07101221 CSE220701 CSE220704 08111221 08111222 10110221 04106221/2 01101231 01101232 09103231 09103232 Price $5.00 $5.00 $5.00 $7.50 $2.50 $2.50 $7.50 $5.00 $5.00 $7.50 $20.00 $25.00 $7.50 $2.50 $5.00 $2.50 $5.00 $5.00 $2.50 $5.00 $5.00 $5.00 $25.00 $2.50 $2.50 $7.50 $5.00 $5.00 $5.00 $7.50 $7.50 $5.00 $7.50 $2.50 $5.00 $5.00 $7.50 $7.50 $5.00 $10.00 $2.50 $5.00 $5.00 $7.50 $2.50 $2.50 $2.50 $2.50 $2.50 $2.50 $7.50 $2.50 $5.00 $2.50 $5.00 $5.00 $5.00 $10.00 $5.00 $5.00 $5.00 $12.50 $12.50 $10.00 $10.00 $2.50 $5.00 $5.00 $10.00 WIDEBAND FUEL MIXTURE DISPLAY (BLUE) TEST BENCH SWISS ARMY KNIFE (BLUE) SILICON CHIRP CRICKET APR23 APR23 APR23 05104231 04110221 08101231 $10.00 $10.00 $5.00 NEW PCBs We also sell the Silicon Chip PDFs on USB, RTV&H USB, Vintage Radio USB and more at siliconchip.com.au/Shop/3 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 Advice on electrical safety equipment We are setting up an electrical test bench in a not-for-profit workshop operated by volunteers. Many of the volunteers have some electrical knowledge, but not all. They may be powering up electrical and electronic items that have not been turned on for some time (eg, old radios). We want to make it as safe as possible for everyone. So we’ve obtained the following: a) an RCD. b) a mains isolation transformer rated at 8A, which is easily big enough for anything we have. c) a variac rated at 5A, but it is an autotransformer, ie, the Neutral line goes ‘straight through’. d) a power block with built-in RCD (Bunnings 0135806). It probably trips at 30mA Earth leakage, but it’s not obvious from their website. Would you consider writing an article about setting up a bench to make it as safe as possible? Many (almost all?) of your readers have some kind of bench with power outlets. What’s the safest way to do it? I think the isolation transformer is helpful because the outgoing mains is isolated, but if it’s floating and not referenced to anything, does that make the RCD useless? The variac also has an ammeter so that if the load starts drawing excessive current, even at low voltages, we can switch it off, hopefully before frying anything. Any light you can shine in which ‘order’ (and why) you would connect these three devices would be greatly appreciated. Totally brilliant magazine! We make sure to get every issue. (C. B., Seacombe Heights, SA) ● The RCD from Bunnings would most likely trip at 30mA. Using an RCD is a good safety measure for a laboratory test bench; however, we suggest using a Clipsal or HPM brand RCD to ensure it is of good quality. An isolation transformer does not 106 Silicon Chip necessarily increase safety unless the equipment you are working on has a live chassis, such as some older television sets and radios that had exposed live parts when opened up for servicing. That’s because the isolation transformer does not entirely protect against an electrical shock, although it makes it necessary to contact both sides of the transformer output before a shock can be delivered. While that is less likely than an Active-to-Earth path, we don’t know how much less likely, and it could give a false sense of security. Also, it is true that the RCD does not provide protection when using an isolation transformer, as any current flow from one of its outputs to Earth will not imbalance the incoming Active/ Neutral current. Therefore, we suggest only using the isolation transformer when it is needed. A variac does not provide safety from electrocution. As you mention, it can be helpful to check for excessive current before applying full mains to an appliance. The RCD can be used with the variac. Consider getting a more sensitive (15mA) RCD, as nuisance tripping will be less of a concern in this environment. Ideally, you should have one or more emergency shutdown press-­ buttons around the bench so that the button can be pressed to quickly disconnect power in the event of danger. Power points that switch on and off both the Neutral and Active conductors are safer than those that just switch the Active. These are required for use in caravans. Use quality Clipsal or HPM power points (GPOs) with reliable on/off switches and decent mains contacts within the power point. Rubber floor mats can also reduce the likelihood of current passing through the body to ground, making them worthwhile. Ensure that the workshop has a good Earth via a substantial stake (or several) and that you have a solid Australia's electronics magazine Earth-Neutral link for the multiple earthed neutral (MEN) system used in Australia. This can prevent a floating or high voltage neutral and ensure that the RCD works effectively. Using Soft Starter with 15A loads After reading the articles on the Active Mains Soft Starter (February & March 2023; siliconchip.au/ Series/395), I was wondering how the power limits are derived in the design, as the relay bypasses the control circuit after a preset time. It would be handy to be able to use the Soft Starter to reduce turn-on inrush current for high-power amplifier testing so that the local breakers don’t trip. Professional power amplifiers delivering thousands of watts will often have their own soft start circuitry, but in testing and repair, one might like to bypass this when fault finding. I’m referring to the types of power amps used in professional entertainment systems (Labgruppen, QSC, Quest, Outline, Powersoft & Meyer stage equipment). 3000W at full power is not unusual. You need some special load devices to test these fully. So the Mains Soft Starter would be very useful for testing and repairing this type of equipment in combination with a variac. A large variac can also have quite a high turn-on current from the magnetisation current; it might also help with that. The idea would be to avoid tripping common 16A breakers. If the components for the Soft Starter could be upgraded to 15-16A, it would be quite a handy addition to the test bench. I’m guessing that the current transformer, bridge, main Mosfet and perhaps thermistors might need upgrading, plus proper 15A plug/socket connections. (J. B., Frankston, Vic) ● Assuming you only power up the amplifier with no input signal, the Mains Soft Starter should minimise the power-up current draw and would siliconchip.com.au be suitable with minimal changes. The full power from the amplifier would then only be delivered once the relay switches in and bypasses the thermistor, Mosfet and bridge rectifier. So the wiring, plugs and sockets would only be the changes required. If you want to have the amplifier operating at full power from the start, the components you suggested should be changed, and more heatsinking would be needed for the Mosfet. The transformer would not need to be changed to a 15A type. It is only used for detecting when an appliance is connected; its output is not a calibrated value with respect to the input current for our application. Alternative mid-woofer for Monitor Speakers I have been enjoying Phil Prosser’s articles on the Active Monitor Speakers and Active Subwoofer published over the last few months (November 2022-February 2023; siliconchip.au/ Series/390) and am happily building the cabinets and associated amplifiers. I appreciate the level of individual control that the active crossover setup provides. However, I am a bit torn about making a pair of expensive speakers that cannot be used in a setting with a passive crossover as an alternative. With this in mind, I considered incorporating a switchable two-way passive crossover in each monitor speaker with an alternate set of input terminals. There is a commercially-available high-quality two-way passive crossover (ARA-XORIN) designed for SB speakers in a similar volume cabinet; however, it is designed for a 4W midwoofer (MW16P-4) rather than the 8W version (MW16P-8) that Phil has designed his monitors around. What is the reason for choosing the higher impedance mid-woofer (other than a slightly lower price) in Phil’s design? I’m assuming the 4W driver would work in the active crossover mode with some changes to the calibration, but otherwise would be similar while allowing me to use the passive crossover as an alternative. The tweeter (TW29R-B) is connected with reverse polarity in the passive crossover circuit. I had heard that this was sometimes done in crossover designs but I would be interested 500 to understand why. Many thanks for any info you can give me. (A. J., Marrickville, NSW) ● Phil Prosser responds: on the selection of 4W or 8W drivers, there was no overwhelming reason for the selection. The frequency response is very similar, with the 4W driver being about 3dB more sensitive. I am confident that the phase centres of the drivers are close, if not identical, so the cabinet shaping will be fine. I expect the baffle step tweak to the crossover output to be very close to correct, noting that there is room sensitivity to baffle step correction that you might need to adjust for. The required level will be straightforward to calculate and is something that you can measure relatively easily with a computer and interface card. You will find that the cost of the ARA crossover is substantial. However, if you want a passive crossover as a companion to the active crossover, it would be a wise choice, as there is certainly significant tuning in this crossover to match the drivers. The ARA box design is pretty close to mine in terms of geometry. The tweeter’s flipped polarity POWER WATTS AMPLIFIER Produce big, clear sound with low noise and distortion with our massive 500W Amplifier. It's robust, includes load line protection and if you use two of them together, you can deliver 1000W into a single 8Ω loudspeaker! PARTS FOR BUILDING: 500W Amplifier PCB Set of hard-to-get parts SC6367 SC6019 $25 + postage $180 + postage SC6019 is a set of the critical parts needed to build one 500W Amplifier module (PCB sold separately; SC6367); see the parts list on the website for what’s included. Most other parts can be purchased from Jaycar or Altronics. Read the articles in the April – May 2022 issues of Silicon Chip: siliconchip.com.au/Series/380 siliconchip.com.au Australia's electronics magazine April 2023  107 compensates for the crossover’s phase shift. Our Active Crossover is fourth-­ order and does not require the tweeter to be reversed. The ARA crossover is a mix of third-order and second-­order. I have not fully analysed the circuit, but it is unsurprising that the phase shift at the crossover point requires the tweeter phase to be inverted. It is clear that their designer’s thinking is pretty closely in line with mine, other than our desire for the control and versatility provided by the active crossover. Remember that the subwoofer adds a whole world of dimension to the sound; I cannot recommend it highly enough if you can afford the cost and space. Copper planes don’t always connect to GND Looking at the two Raspberry Pi Pico BackPack projects (March 2022 & January 2023; siliconchip.au/Article/15236 & siliconchip.au/Article/15616), the circuits diagram shows +3.3V from the Pico connected to the SD card socket pin 4, but the actual layout diagram shows pin 4 on the SD socket connected to ground. Is that an error? (S. O., via email) ● The microSD card socket connects to the 3.3V rail at pin 4 via the top layer power plane. You can see that plane also connects to the top of the capacitors to the right of the socket; the capacitors’ lower leads connect to the bottom layer ground plane using vias. There is not a single top layer plane, and the planes do not all connect to the 3.3V rail. For example, looking at the overlay diagram, you can see that CON2’s VIN pin (the VIN5 net on the schematic) also connects to the top layer, as does the 5V pin on the LCD header (also VIN5) and pin 39 of the Pico module. A break in the top layer plane, separating the 3.3V and VIN sections, is just visible under the horizontal line above the Silicon Chip logo. Questions about WiFi DC Load On page 88 of the October 2022 issue, the construction article for the WiFi DC Load (siliconchip.au/ Series/388) says not to install REG1, the 7805 regulator. Without this, the 9-12V input at CON1 goes nowhere 108 Silicon Chip unless you bridge the in and out pad locations on the circuit board (top and bottom). The wiring diagram on page 93 shows 9-12V wires going from the DC socket to both the control board (regulator greyed out) and the main load board. As mentioned in the article, I tested my board using power to the USB connector on the ESP32. From the circuit diagrams in the September issue, the control board is powered by +5V from the main board via CON1 (Main) to CON2 (Control). So, should I bridge the regulator’s in and out pads on the control board, install a 7805, leave out the wires from the DC socket to the control board, or none of these and wire up as indicated on page 93 of the October issue? I also encountered a series of difficulties the programming the ESP32, and the solutions to these may be of interest to your readers: 1) A recent Windows 10 update deleted the USB/Serial drivers from my computer and I had to reinstall them manually. In the case of the ESP32, they are the CP210x drivers from Silicon Labs: siliconchip.au/link/ab59 2) Attempting to program my ESP32 resulted in a timeout error. The solution is to hold down the BOOT button on the ESP32 module when the “Connecting……..” message appears in the Arduino output window just after the compile process has finished. A more permanent solution (which I didn’t try) is also to install a capacitor to the board as outlined here: siliconchip.au/link/abjv 3) On page 92 of the October issue, the instructions are to “Move the Data folder and its contents from the download pack into the same folder as your saved OTAWebUpdater.ino file. … In the Tools menu click ESP32 sketch Data Upload to copy the files in the Data folder to the ESP32’s local file system (SPIFFS).” For the command “ESP32 sketch Data Upload” to appear in the tools menu, you need to download a plugin as instructed here: siliconchip.au/link/abjw This plugin does not work with version 2 or higher of the Arduino IDE, so it’s best to use an earlier version for the whole process. (S. H., Rosanna, Vic) ● Richard Palmer responds: REG1 is required as the load should not be run in production when powered via Australia's electronics magazine the USB cable, as this is directly connected to the negative rail of the load. Any offset voltage (quite likely when testing high-current mains-powered equipment) could damage both the load and the computer. The regulator terminals must not be bridged. The 7805 should be installed with the IN pin toward the 12V power connections and the OUT pin toward the IDC connector (opposite to the silkscreen markings). The reversed 7805 silkscreen occurred as the prototype used a VXO7805 switching regulator, which has the ‘flat side’ opposite that of standard 7805s. A regular 7805 was agreed to be a better choice during the editorial review, as the 5V current draw is low enough not to warrant the more expensive part. I apologise that I didn’t remember to reverse the silkscreen markings. The timeout error, sadly, is endemic to some brands of ESP32 DevKits, which are fine in all other respects, There are published fixes on the internet (add a capacitor), but it hasn’t worked on all the ESP32s I’ve tried. Finally, the file upload issue is a problem with Arduino 2.0. I have suggested the same solution to other readers. For future projects using the ESP32 and requiring file uploads, I have added some code to the download package that allows file uploads via the web browser, similar to the OTA process. The catch-22, of course, is when the WiFi credentials are stored in a file, that needs to be uploaded! Digital GPS LED Clock wanted Many years ago, I bought a Radio Shack digital clock kit. It had six fluorescent green display ‘tubes’ and displayed the time in 24-hour mode with a seconds display. It was mains-­ synchronised. At the time, we were in Queensland, and the area we lived in was not linked to the national grid. I was disappointed as the time could be as much as 15 seconds out compared with the ABC ‘pips’. Returning to Canberra solved that problem! Unfortunately, after many years of service, my soldering started to show up dry joints, and I also grew careless. After one repair, the clock did not restart; it was locked solid at one particular time. siliconchip.com.au I found that I could get replacement chips for less than $2, but there was a catch: I had to order 1000 of them. This was a 24-pin chip without an alarm function, so the chance of reselling enough of them to make the exercise viable was slight. I recently bought a DAB+ clock radio which synchronises the time whenever the radio is used, but it does not show the seconds. It does have a 20mm-high display, readable from a distance. Looking at the GPS-Synchronised Analog Clock by Geoff Graham (September 2022; siliconchip.au/ Series/391), I was wondering if it is possible to use his design’s 1PPS pulse to build a facsimile clock to the old Radio Shack functionality. (B. W., Gowrie, NSW) ● We think that the 6-digit LED GPS Clock from the December 2015 & January 2016 issues (siliconchip.au/ Series/294) is pretty much exactly what you’re after. It’s still a reasonably popular project as we sell PCBs, cases, LED displays etc. That project might be worth updating, although it’s hard to imagine what we would do differently. V Controlling Soundbar input selection I have just fired up my newly built Soundbar (August 2022; siliconchip. au/Article/15426), connected it to my TV, and it works OK, but I have run into a problem. The TPA3116D2 4.1 amplifier is awesome, but I have a Bluetooth transmitter on another audio source nearby. So the sounder defaults to the Bluetooth input instead of the 3.5mm hardwired input from the TV. The TV doesn’t have a Bluetooth output. Can I disable the TPA3116D2 Bluetooth input or give the wired input priority? I could try covering the receiving antenna with aluminium foil to stop it from receiving a signal, or do I have to turn off the other Bluetooth TX, which would be a pain in the proverbial? I’ve searched Google for a solution with no luck. Keep up the good work – the Soundbar article had some errors, but otherwise has been a good project. (I. F., Inglewood, SA) ● Allan Linton-Smith responds: the automatic selection of the input signal is on a first-come, first-served principle. A signal from one or the other source is processed, and the circuitry switches it directly into the input of the amplifiers via a small relay. If you need to disconnect the Bluetooth receiver, you could carefully remove the little aerial from the PCB with a sharp blade, but you will no longer be able to use Bluetooth at all. If you leave a little bit of the aerial metal strip, you can re-invigorate Bluetooth later simply by soldering on a small length of wire the same length as the previous aerial (as if it were stretched out). We don’t recommend using aluminium foil to cover the aerial because it might fall off and cause a short circuit. If you are proficient with a soldering iron, you could remove the selector relay (the little grey box in the middle of the board) and replace it with a DPDT switch mounted externally. Then you can select the input you desire manually. This relay is conventional and has eight pins; two at the very front for the coil and six at the back for switching. Editor’s note: I would be tempted intage Radio Collection March 1988 – December 2019 Updated with over 30 years of content Includes every Vintage Radio article published in Silicon Chip from March 1988 to December 2019. In total it contains 404 (not an error) articles to read, or nearly 150 more articles than before. Supplied as quality PDFs on a 32GB custom USB All articles are supplied at 300DPI, providing a more detailed image over even the print magazine. Physical and digital versions available Buying the USB gives you access to the downloadable copies at no extra charge. Or if you prefer, you can just buy the download version of the Collection. Own the old collection on DVD? If you already purchased the previous Collection on DVD, you can buy this updated version for the discounted price of $30 on USB (plus postage), or $20 for the download version. $60 PDF Download SC4721 siliconchip.com.au/Shop/3/4721 $70 USB + Download SC6139 siliconchip.com.au/Shop/3/6139 Postage is $10 within Australia for the USB. See our website for overseas & express post rates. siliconchip.com.au Australia's electronics magazine April 2023  109 to try to figure out which end of the relay coil is switched, what voltage it is driven at and whether the relay is energised to select Bluetooth or the 3.5mm input. Having worked that out, it should be possible to cut one of the tracks to the relay coil and wire that pin to a 3-position switch, allowing for manual switching of the relay as well as the automatic mode. hfe testing high-power transistors at low amps I decided to test the MJW21195 & MJW21196 that came in my 500W Amplifier kits before assembling them (April-June 2022; siliconchip. au/Series/380). All PNP transistors (MJW21195) measured well, but the seven NPNs (MJW21196) showed strange h fe behaviour. I measured all transistors on three different meters: Atlas DCA55, MK328 and DY294. For these seven PNP transistors, hfe varied from about 30 at 100μA to about 230-250 at 1mA, 290 at 4.8mA for two transistors (430-450 for the other five), all falling to about 80 at 10mA. All the other transistors did not show any significant hfe variation beyond what the data sheet indicates; at 100μA, hfe was 30-40; at 1mA, it was about 50; at about 4.8mA, it was 50-60; and at 10mA, it was about 80-90. Are these faulty? I’d appreciate your advice. (J. P., Wanneroo, WA) ● The DC gain is shown in the data sheets from 100mA to over 10A. That’s a reasonable current range to test power transistor gain. Ideally, you should use the same current to check the gain (eg, 100mA). We suspect that measuring the gain at 10mA and below will give misleading results with such high-power transistors. However, your measurement results show no reason to suspect faulty transistors. Note that all the MJW21195 and MJW21196 transistors we supplied in kits came from either Mouser, RS Components or element14, so we have high confidence they are all genuine parts, and they would have been tested at the factory. We also checked that each kit only got transistors from the same batch. Remember that the design allows for significant variation between individual transistors, with relatively highvalue emitter resistors balancing the 110 Silicon Chip load even for varying gains. Also, we have not had any complaints that the amplifiers did not work from others who bought the kits. Another question on copyright I have a question about the Radio, TV & Hobbies PDFs on DVD that I purchased. I have transferred the RTV&H DVD content to my main SSD as my PC now doesn’t have a fixed CD/DVD drive. I have also used Acrobat to OCR all the PDF files so that I can fairly quickly list and point to searched words for all 320-odd magazine issues using Acrobat’s advanced search tool, which can be very convenient for investigating topics and searching for data. Is this use of the DVD content an acceptable copyright use? (T. R., Endeavour Hills, Vic) ● We don’t have a problem with you making as many copies of this material (that you have paid for) in as many formats as you like, as long as it is for your own use. That would apply to our other digital products, including our Silicon Chip PDFs on USB, PDFs downloaded from our website etc. However, it is a good question since it is a murky area legally, at least in Australia; see the link below, which might or might not help. We don’t think making backups or ‘format shifting’ should be considered an infringement, and we support the proposals to fix our copyright law in terms of ‘fair use’, bringing it in line with that of other countries. ALRC: siliconchip.au/link/abju wanting to play my music via an external media player accessing music files stored on a USB memory stick. How to do it? I’m aware of the availability of FM transmitters that can play through the car’s FM radio, but I would prefer a hard connection via plug and socket. The one thing the car does have is a connector for hands-free operation of a mobile phone, shown in the photo below. There is a mobile App that ‘tricks’ the car’s hands-free system into believing it is receiving an incoming call through which the music can be piped directly into the Bose audio system. It relies on Bluetooth connectivity but will tie my phone up while driving. To achieve what I have in mind would require some sort of interface box between the media player and the connector shown to mimic an incoming call to accomplish the same thing. Is there something available? Has Silicon Chip ever produced such a project? (A. R., Auckland, NZ) ● We don’t have any available project for a purpose this specific, but perhaps a reader knows something about this sort of sound system or connector and can help you. A couple of BackPack problems I’m building the Micromite BackPack V2 (May 2017; siliconchip.au/ Article/10652) as part of the GPS-­ synched Frequency Reference (October & November 2018; siliconchip.au/ Series/326). The installation of components was straightforward, and initial voltage/ current checks indicate that the provided parts were installed correctly. Interfacing with Bose However, I ran into two problems. sound system Firstly, I cannot correctly configure I am wondering if you can help the Micromite for the provided LCD me. My 2007 Nissan has a factory-­ panel. With the Frequency Reference fitted Bose sound system. Incredibly, board (04107181) added to the Backfor this year of manufacture, there is Pack unit, I am powering the BackPack no USB socket nor even an auxiliary unit via 5V USB from the Frequency audio input socket, and certainly no Reference board. Bluetooth connectivity. Since the chip is pre-programmed, This presents the dilemma of the Frequency Reference main page immediately appears on the BackPack touchscreen. But when I touch the button in the lower left of the touchscreen, a button on the right is activated. Similar problems appear on other screens – I push in one place, and a button in another location is activated. continued on page 112 Australia's electronics magazine siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip KIT ASSEMBLY & REPAIR FOR SALE DAVE THOMPSON (the Serviceman from Silicon Chip) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, New Zealand, but service available Australia/NZ wide. Email dave<at>davethompson.co.nz LEDsales KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com LEDs and accessories for the DIY enthusiast LEDs, BRAND NAME AND GENERIC LEDs. Heatsinks, LED drivers, power supplies, LED ribbon, kits, components, hardware – www.ledsales.com.au VISIT THE NEW TRONIXLABS parts clearance store for real savings on new parts at clearance prices, with flat rate express delivery Australia-wide – go to https://tronixlabs.com PCB PRODUCTION PCB MANUFACTURE: single to multilayer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www.ldelectronics.com.au FOR SALE OATLEY ELECTRONICS www.oatleyelectronics.com GET AN APRIL SPECIALS LIST By sending an email to branko<at> oatleyelectronics.com Just mention “April Specials” in the subject. These specials will not appear anywhere else, eg: * 6 x 12V-5W Edison screw bulbs for $18 * 10 x 12V/0.5m LED bars for $22 * Geiger counter kit including a complete military unit for conversion for $80 We will only reply to your enquires and quote you low shipping rates. We will only answer your follow up emails. www.oatleyelectronics.com Phone: 0428600036 ASSORTED BOOKS FOR $5 EACH Electronics and other related subjects – condition varies. Some of the books may have already been sold. See all books at: siliconchip.com.au/link/aawx Email for a quote (bulk discount available), state the number directly below the photo when referring to a book: silicon<at>siliconchip.com.au 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 April 2023  111 It seems like I need to configure the LCD panel, but I can’t get to that via the BackPack’s USB serial port. Using standard Windows serial terminal programs (eg, PuTTY), I can get a basic serial connection at 38400 baud (8-N-1), and when I press a key on my keyboard, the red LED on the BackPack lights up. But there is no reply from the BackPack and no response to any configuration commands. Secondly, at initial power-up, a status page briefly appears before the Frequency Reference main page. After a few seconds, the main page disappears Advertising Index Altronics.................................49-52 Dave Thompson........................ 111 Digi-Key Electronics...................... 3 ElectroneX................................... 13 element14..................................... 7 Emona Instruments.................. IBC Hare & Forbes..........................OBC Jaycar...................... IFC, 11, 15, 39, ..............................71, 78-79, 91, 99 Keith Rippon Kit Assembly....... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology.................. 9 and is replaced by the status page. That cycle repeats 4-6 times before the unit finally ‘settles down’ and remains on the main page. I suspect the problem may be caused by the VK2828U7G5LF GPS module trying to get a good fix, but I’m not sure. I’d appreciate any help you can provide for these issues. (D. P., Enon, Ohio, USA) ● You’re on the right track. The red LED that is flashing is driven by IC2 on the BackPack, so it means that data is being received over the USB link. Some touchscreens have a different touch panel orientation, meaning that the ‘factory’ calibration doesn’t work. To access the BASIC console, you need to send a Ctrl-C (from the serial console) to break out of the running program, after which you can issue commands. Running the “GUI CALIBRATE” procedure is all that is needed once you are in the BASIC console. After that, power-cycle the BackPack to restart the main program. The second problem could be either a power issue causing the Micromite processor to reset or perhaps the (poorly calibrated) touch controller sending commands when touches aren’t occurring. The latter should right itself once the touch controller has been calibrated. If that doesn’t fix it, it could be a problem with either the Micromite V2 PCB or the Frequency Reference PCB. A likely candidate on the Micromite Mouser Electronics....................... 4 Oatley Electronics..................... 111 SC GPS Analog Clock................. 58 SC USB Cable Tester.................. 98 SC Vintage Radio PDFs............ 109 Silicon Chip PDFs on USB......... 14 Silicon Chip Shop............ 104-105 Silicon Chip Subscriptions........ 53 Silicon Chip Test Tweezers....... 10 Silicon Chip 500W Amplifier... 107 The Loudspeaker Kit.com.......... 12 Tronixlabs.................................. 111 Wagner Electronics..................... 85 112 Silicon Chip Errata and Next Issue SC Raspberry Pi Pico W............. 77 is the 47µF tantalum/10µF ceramic capacitor that bypasses IC1’s core regulator. If this capacitor has been mixed up with the other capacitors or is somehow faulty, it can definitely cause stability problems. Why no more Mosfet amplifiers? I have noticed that your amplifier module designs almost never use Mosfets. Why is that? They seemed popular in 1980s kits. I have been pondering lately why your amplifier modules never use switch-mode power supplies. They are cheap now and super lightweight. (J. A., via email) ● We don’t design audio amplifiers using Mosfets because they have few advantages in that role. They produce inherently more distortion and are harder to drive. They are arguably more robust, but a properly designed BJT-based amplifier is reliable enough. For more details, see Douglas Self’s Audio Power Amplifier Design Handbook (reviewed in the March 2010 issue; siliconchip.au/Article/89). We have a Class-D amplifier project in this issue (from page 26) that uses a switch-mode power supply. In a linear amplifier, we would be concerned that switching noise might adversely affect the amplifier’s performance. Still, a Class-D amplifier already has a lot of switching noise, so it’s unlikely to matter in that case. SC Secure Remote Mains Switch, July & August 2022: the paragraph at the end of page 84 in the August 2022 issue says to use 10A-rated mains wire; however, some of the wiring can use 7.5A-rated mains wire, as explained later in the article. Capacitor Discharge Welder, March & April 2022: the front panel drilling diagram, Fig.16, on page 109 of the April 2022 issue has two errors. It is shown as 130mm tall, while the base of the case, where the holes are drilled, is only 105mm tall. Also, the distance between the VOLTS and TIME holes is shown as 60mm but incorrectly drawn as 85mm. A revised diagram/template that fixes these errors can be downloaded from siliconchip.au/Shop/6/6306 Programmable Hybrid Lab Supply with WiFi, May & June 2021: the Altronics ESP32 module specified in the parts list may have rows of pins too widely spaced to fit the control PCB. The revised control PCB used in a later project, code 18104212 (siliconchip.com.au/Shop/8/5826) has an extra row of pins to accommodate different module widths. This can be used with the Hybrid Lab Supply project as long as the correct shorting links are bridged (ie, those indicated with arrows on the silkscreen). Next Issue: the May 2023 issue is due on sale in newsagents by Thursday, April 27th. Expect postal delivery of subscription copies in Australia between April 25th and May 12th. Australia's electronics magazine siliconchip.com.au “Rigol Offer Australia’s Best Value Test Instruments” Oscilloscopes NEW 200MHz $649! New Product! 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