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FEBRUARY 2022 ISSN 1030-2662 02 The VERY BEST DIY Projects! 9 771030 266001 $ 50* NZ $1290 11 INC GST INC GST 12 24 All About How Batteries Work, Part 2 Dual-Tracking Hybrid 25V DC Power Supply 70 44 TL866II Universal Programmer Review Triple Fan Controller With Speaker Protector 76 Super-Reliable Remote Gate Controller Solid-State Tesla Coil with Flame-like siliconchip.com.au Discharge Australia's electronics magazine February 2022  1 Build your own Fridge Door Alarm This useful and simple project may save you the cost of throwing out good food that went off, because someone forgets to close the fridge door. The alarm will sound and alert you if the door is not properly closed within a specified time. The display and keypad helps make it really easy to set-up. SKILL LEVEL: BEGINNER CLUB OFFER BUNDLE DEAL 3995 $ SAVE 30% For step-by-step instructions & materials scan the QR code. KIT VALUED AT $61.05 www.jaycar.com.au/fridge-door-alarm See other projects at www.jaycar.com.au/arduino Improve your project ONLY ONLY 4 $ ADD A STATUS INDICATOR RGB LED Module $ Add a status LED module to display different states, i.e. armed, tripped, alarm, triggered. XC4428 100 $ gift card OnSSale 24 January ilicon Chip to 23 February 2022 695 95 PLAY A MELODY 76mm Replacement Speaker Upgrade the buzzer to a speaker and play musical melodies instead. AS3006 Got a great project or kit idea? $ ADD A SENSOR Digital Temperature Sensor Module Use this sensor to show the temperature of the fridge along with the latch alarm. XC3700 If we produce or publish your electronics, Arduino or Pi project, we’ll give you a complimentary $100 gift card. Upload your idea at projects.jaycar.com Looking for your next build? Silicon Chip projects: jaycar.com.au/c/silicon-chip-kits Kit back catalogue: jaycar.com.au/kitbackcatalogue 1800 022 888 www.jaycar.com.au Awesome projects by 2 ONLY 4 95 Australia's electronics magazine Shop online and enjoy 1 hour click & collect or free delivery on orders over $99* siliconchip.com.au Exclusions apply - see website for full T&Cs. * Contents Vol.35, No.2 February 2022 11 Book Review: Radio Girl 24 David Dufty’s book is a biography of Violet McKenzie, Australia’s first female engineer and one of the founders of Wireless Weekly magazine. That magazine was eventually renamed to “Electronics Australia”. By Nicholas Vinen Review 12 All About Batteries – Part 2 The second article in our series on batteries covers upcoming technologies being researched, as well as detailing the ‘tried and true’ lead-acid battery and some other unusual battery types. By Dr David Maddison Science 44 41 Low-noise HF-UHF Amplifiers These three wideband HF-UHF amplifier modules are said to provide 20dB of gain with frequency ranges of 1MHz-3GHz, 5MHz-6GHz and 50MHz4GHz respectively. By Jim Rowe Low-cost electronic modules 70 70 TL866II Universal Programmer The TL866II can program over 16,000 parts, including many of the popular Atmel and Microchip microcontrollers. It is relatively inexpensive and will even program PLDs (programmable logic devices). By Tim Blythman Review 24 Dual Hybrid Power Supply – Pt1 This Supply has two separate outputs, which can deliver up to 25V DC at 5A. They can be connected in series and ganged up to form a dual-tracking supply. It uses an LCD screen, and rotary encoders/pushbuttons for control. By Phil Prosser Power supply project 44 Fan Controller & Loudspeaker Protector Controlling up to three fans, switching them on at preset temperatures and adjusting their speed via PWM is only part of what this project does. It also functions as a loudspeaker protector for mono or stereo amplifiers. By John Clarke Audio project 62 Solid-State Tesla Coil By generating extremely high voltages, this Tesla Coil will form a ‘flame’ discharge using only discrete components, making it easy to assemble and perfect to show off to your friends. By Flavio Spedalieri Home science project 76 Remote Gate Controller If the controller for your sliding or swinging electric gate fails, replace it with this very reliable Gate Controller. It can be triggered remotely or via a local button, and it even stops the gate if it encounters an obstacle. By Dr Hugo Holden Remote control project 2 Editorial Viewpoint 4 Mailbag 6 Subscriptions 61 Product Showcase 85 Serviceman’s Log 92 Vintage Radio 101 Tasma 305 ‘rat radio’ by Fred Lever Online Shop 102 Circuit Notebook 108 Ask Silicon Chip 1. Resistor-Mite auto-ranging ohmmeter 2. A capacitive soil moisture meter 3. Musical bicycle horn 111 Market Centre 112 Advertising Index SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke – B.E.(Elec.) Technical Staff Jim Rowe – B.A., B.Sc. Bao Smith – B.Sc. Tim Blythman – B.E., B.Sc. Nicolas Hannekum – Dip.Elec.Tech. Advertising Enquiries Glyn Smith Phone (02) 9939 3295 Mobile 0431 792 293 glyn<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 Phil Prosser – B.Sc., B.E.(Elec.) Cartoonist Brendan Akhurst 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 For overseas rates, see our website or email silicon<at>siliconchip.com.au Recommended & maximum price only. Editorial office: Unit 1 (up ramp), 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9939 3295. ISSN 1030-2662 Printing and Distribution: 24-26 Lilian Fowler Pl, Marrickville 2204 2 Silicon Chip Editorial Viewpoint Be wary of devices that require apps to work Devices controlled by mobile phone/tablet apps might seem convenient on initial inspection. But they can suffer from a range of problems that often make them inferior choices. The first problem is that many of these apps are buggy (sometimes to the point of being useless) and can also have compatibility problems. It’s incredible how apps from multi-billion-dollar companies can be so flaky. For example, many aircons now have apps to control them, and these can be very hit-andmiss in operation, even though the unit itself might cost thousands of dollars. Then there are those compatibility problems that might mean that the operating system on your phone or tablet is too old or too new to work with the app. I’ve run into this on more than one occasion, being able to install and use the app on some devices but not others. Worse, after a few years (possibly not even that long), the company will inevitably decide that they no longer want to update/support the app, so you will be unable to use it on the latest mobile operating systems. This leaves you with the unpalatable choice of either sticking with an older operating system version, resulting in a range of severe security problems, or upgrading and losing support for the app. One member of our staff previously bought a Belkin remote-controlled power point controlled by an app on his iPhone. Belkin decided to stop updating the app, and now the device is a useless piece of eWaste. You might expect that from brands you haven’t heard of, but I thought that Belkin was a more ‘upmarket’ brand. This is a huge problem for iPhone users because the only way to install apps (unless “jailbroken”) is via the App Store. So there’s no way to get a suitable app on your phone once the manufacturer decides to drop support. With Android devices, you can install a .apk file if one is available – but the compatibility concerns still apply. And now there is news that the company (MyGnar Inc.) behind the expensive product called the GNARBOX has gone bust. This is a device costing upwards of US$500 that is used to back up photos and videos from your phone without you needing to carry around a computer. Guess what? It works via an app, and now that the company has gone under, it has been pulled from the App Store. So even though you can still buy a GNARBOX, you can’t use it if you have an iPhone or iPad! Louis Rossmann* posted a video on this at https://youtu.be/Elsbcoyk6jA This puts retailers in a precarious position; presumably, they have already paid for their stock of GNARBOXes, but now they will be in legal trouble if they sell them because the marketing claims for that product are no longer valid. Similarly, many GNARBOX owners now effectively possess expensive bricks. This will have to give anyone pause in future when they consider purchasing a device that can’t be used without a specific app. All hardware devices should be able to be used in a ‘standalone’ mode, and I also think they should stick to using ‘standard’ access protocols such as HTTP over WiFi, avoiding the need for device-specific apps and all the problems described above. * While his electronics knowledge seems a bit limited, Louis is very skilled at computer repair. His YouTube videos on Macbook repairs are often fascinating and entertaining. He also makes some excellent arguments in favour of the Right to Repair, a subject we reported on in detail in the June 2021 issue (siliconchip.com.au/Article/14881). by Nicholas Vinen Australia's electronics magazine siliconchip.com.au siliconchip.com.au Australia's electronics magazine February 2022  3 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”. Australia’s history of manufacturing electronic components Many people may not be aware of the extent of electronic component manufacturing that once occurred in Australia. We made just about everything necessary at the time, such as valves (vacuum tubes), resistors, transistors, transformers, etc – even solar cells. I recently tried to donate some examples of discrete Australian made electronic components to Victorian museums (some pictured), but sadly, they weren’t interested. Perhaps a collection should be established somewhere, including a museum collection, as a repository of Australia’s former manufacturing past. Dr David Maddison, Toorak, Vic. Comment: We welcome comments from readers suggesting a museum that would be interested in such items. Perhaps the Powerhouse Museum in Sydney would want them. Modifying RF signal generators for better performance I am writing regarding the El Cheapo Modules article on the 35MHz-4.4GHz Signal Generator in the December 2021 issue of Silicon Chip (siliconchip.com. au/Article/15139). I have bought several similar modules from sellers in China – some standalone synthesizer boards and 4 Silicon Chip other boards with an onboard microcontroller and an LCD screen. Some use the ADF4351 or the ADF5355 synthesizer chips, while others use the MAX2870. I recommend using the standalone boards as shown in the photograph below. There is a mountain of information on interfacing these boards to an Arduino Uno/Arduino LCD shield or a PIC microcontroller. Free Arduino sketches are available to control the frequency output, or a HEX file in the case of the PIC microcontroller. This approach gives you a considerable amount of freedom to tailor the Arduino sketch or HEX file to your own needs. I am currently working on the ADF5355 standalone board depicted with an Arduino Uno/Arduino LCD shield. I have greatly improved the board’s performance by replacing the LT1763 power supply chips with the ADM7150 series (5V/3.3V), which have dramatically lower noise (1μV RMS compared to 20μV RMS). The 5V rail is the one where noise really matters. Cleaning up the 3.3V rails had much less influence on the quality of the RF output. I am planning to use the improved board to extend the range of my RSA3030-TG when examining some of the higher frequencies, around 4-6GHz. It is noteworthy that Analog Devices’ very expensive ADF5355 development board also uses the ultra-low-noise ADM7150 voltage regulators. The result is a very low noise synthesizer – as good as the ADF5355 can deliver. I would avoid using the ADF5355 Board with GLCD that you can buy online. Sadly, these boards are just junk. The outputs look like they have been modulated with another frequency source – they are extremely noisy. The ADF5355 ‘black’ boards are better in noise performance, but you Australia's electronics magazine can only realize their full potential by modifying the power supply. I am planning to make a control board using just an ATmega328 chip. I will use shielded containers for both the ADF5355 board and the ADM7150 power board (5V and two 3.3V outputs), with a very precise (GPS-­ disciplined) frequency standard and perhaps some wideband RF amplifier modules to make a low-noise frequency synthesizer that covers the 54MHz to 14GHz region. This should not be too expensive to build – probably less than $300. I have a home workshop complete with a lathe, vertical milling machine, metrological instruments and an assortment of metal cutting tools. I will be using these to make RF enclosures for the ADM7150 power board and the ADF535X frequency synthesizer. Making quality RF enclosures out of aluminium stock is not hard, just time-consuming. However, in retirement, time is what I have in great abundance. Samuel Evans, Hackham West, SA. R80 Aviation Receiver kit changes I enjoyed the article on the R80 Aviation Receiver (November 2021; siliconchip.com.au/Article/15101) so much that I ordered one through AliExpress. On arrival, I was surprised to find the receiver, although very similar siliconchip.com.au Subscribe to JANUARY 2022 ISSN 1030-2662 01 The VERY BEST DIY Projects! Batteries 9 771030 266001 $ 50* NZ $1290 11 INC GST INC GST imagine life without them MetronoMes wi th Australia’s top electronics 8 or 10 LeDs protect to six amplifier modules up with our Multi-Channel Sp ea ke magazine r Protector Silicon Chip is one of the best DIY electronics magazines in the world. Each month is filled with a variety of projects that you can build yourself, along with features on a wide range of topics from in-depth electronics articles to general tech overviews. Published in Silicon Chip If you have an active subscription you receive 10% OFF orders from our Online Shop (siliconchip.com.au/Shop/)* Rest of World New Zealand Australia * does not include the cost of postage Length Print Combined Online 6 months $65 $75 $50 1 year $120 $140 $95 2 years $230 $265 $185 6 months $80 $90 1 year $145 $165 2 years $275 $310 6 months $100 $110 1 year $195 $215 2 years $380 $415 All prices are in Australian dollars (AUD). Combined subscriptions include both the printed magazine and online access. Try our Online Subscription – now with PDF downloads! All About Batteries; January 2022 The PicoMite BASIC Interpreter; January 2022 Hummingbird Amp; December 2021 Raspberry Pi Pico; December 2021 An online issue is perfect for those who don’t want too much clutter around the house and is the same price worldwide. Issues can be viewed online, or downloaded as a PDF. To start your subscription go to siliconchip.com.au/Shop/Subscribe to that in the article, is now at version seven, not six as described in the magazine. The circuit has undergone a major revision with the NE5204 and NE602 front-end replaced with TA2003 AM/ FM receiver chips and other chip changes making a simpler circuit diagram. The PIC controller has also been moved to the PLL board. The modifications to the squelch are no longer necessary as the TA2003 chip implements this. The receiver also includes mono coverage of the FM Broadcast band for those times you get tired of the endless aircraft movement calls. All in all, a good kit and easy to put together for someone with moderate skills and knowledge of circuits. The instructions, supplied on request, are in Chinese, and you have to work out from the circuit diagram where the ICs go, as they are different both in type and layout to the article featured in Silicon Chip. Nigel Dudley, Denmark, WA. Comment: see also the letter in the Ask Silicon Chip section of the January issue and Andrew Woodfield’s response to it. He has provided a translated instruction manual which we’ve made available from our website. TV sound levels are all over the place Thank you for printing my letter titled “Historical articles enjoyed” in the July 2021 issue. I got a great kick out of finding that you have printed one of my letters in your very popular magazine. But reason I am writing in this time is that I’m finding the sound levels are all over the place in the general television programming. I have a reasonable sound system that has been built up over the years in my loungeroom. While we have the level quite low and at a normal listening level, when ads or a news break comes on, the sudden increase in loudness is quite disturbing. I know that every television station uses compression to make the sound level sound ‘the same’ and give it ‘more punch’, but despite that, the sudden increase in level can be quite bothersome! It might not be as noticeable on a lot of televisions, even with a sound bar installed to increase sound quality. Changing from channel to channel often brings up problems with mismatched levels, and one has to readjust the volume then too. Many of the HD channels are down in level and need adjustment as they are lower in level than other programming. I think this is to do with the amount of channels that are transmitted on the one frequency. Stephen Gorin, Bracknell, Tas. Comment: We have noticed the same thing and it is infuriating. There is a simple solution but it would require all broadcasters and streaming services to adhere to the standard, which would probably be hard to achieve. Every stream/broadcast/video should have a dB offset encoded within it; just a simple number, so it should not be hard to do. This is the dB offset (positive or negative) needed to be applied to the volume level in a reference system (representing a decent sound system) to get the dialog in that program to a certain reference level. That way, they can still get more dynamic range by making the dialog quieter, so they can have louder music or effects or whatever, but then that number will siliconchip.com.au Helping to put you in Control ECO PID Temperature Control Unit RS485 ECO PID from Emko Elektronik is a compact sized PID Temperature Controller with auto tuning PID 230 VAC powered. Input accepts thermocouples J, K,R,S, T and Pt100 sensors. Pulse and 2 Relay outputs. Modbus RTU RS485 communications. SKU: EEC-022 Price: $104.45 ea Mini Temperature and Humidity Sensor Panel mount Temperature (-20 to 80degc) and Humidity (0 to 100% non condensing) sensor, linear 0 to 10V output. Cable length 3 meters. SKU: EES-001V Price: $164.95 ea ESM-3723 Temperature and RH Controller 230 VAC Panel mount temperature & relative humidity controller with sensor probe on 3 metres of cable. It can be configured as a PID controller or ON-OFF controller. 230 VAC powered. Includes ProNem Mini PMI-P sensor. SKU: EEC-101 Price: $619.95 ea PTC Digital ON/OFF Temp Controller DIN rail mount thermostat with included PTC sensor on 1.5m m lead. Configurable for a huge range of heating and cooling applications. 230 VAC powered. SKU: EEC-010 Price: $98.95 ea Ursalink 4G SMS Controller The UC1414 has 2 digit inputs and 2 relay outputs. SMS messages can be sent to up to 6 phone numbers on change of state of an input and the operation of the relays can be controlled by sending SMS messages from your mobile phone. SKU: ULC-005 Price: $228.76 ea 20% off! 4 Digit Large 100mm Display Accepts 4~20mA, 0~10Vdc, is visible 50m away with configurable engineering units. 10cm High digits. Alarm relay and 230VAC Powered with full IP65 protection SKU: FMI-100 Price: $1099.95 ea Touchscreen Room Controller SRI-70-BAC Touchscreen Room Controller are attractive flush mounted BACnet MS/TP controllers with a large colour intuitive 3.5” touchscreen for viewing the system status and modifying the settings. SKU: SXS-240 Price: $306.90 ea For Wholesale prices Contact Ocean Controls Ph: (03) 9708 2390 oceancontrols.com.au Prices are subjected to change without notice. Australia's electronics magazine February 2022  7 increase. You would then be able to enable a feature in your TV to automatically apply an offset to the volume level based off that number. So the dialog in all programs would be at the same level, regardless of how it is recorded or processed. This might need to be combined with some sort of compression technique to limit the maximum volume level (perhaps via a second coefficient). But we believe this would be much better than the current situation with each program having an arbitrarily different loudness level. Another amusing old magazine I have never replaced any components in it, and it still gives a perfect picture (from analog signals, of course) with a slight frame buzz, no doubt due to some of the electrolytics drying out. It is a hybrid valve/transistor set. Some time ago, I made a Heath Robinson modification so that I could receive the US Armed Forces TV, which was broadcast in NTSC. I only needed to adjust the vertical hold for the different number of lines and switch in the ceramic capacitor to change the sound carrier frequency. The simple modification worked perfectly! Christopher Ross, Tuebingen, Germany. What a surprise to open the November issue and see the image I sent in of the portable radio from 1936 (page 8). I recently came across a 1937 issue with the cover shown adjacent. With COVID-19 travel restrictions now lifting and caravans coming out again for the summer break, please do not leave the wife in the caravan cooking bacon and eggs while motoring to the next comfort stop! Graham Street, Auckland, New Zealand. Ultra-LD Mk.4 alternative transistor Vintage TV is still going strong My subscription copies of Silicon Chip (it’s a great magazine) seem to be arriving regularly in Germany now, albeit around the middle of the month. I was very interested in your Vintage section on the Sony TV. I thought it might be interesting to mention the TV I bought in 1970 (shown in the photo at the end of this item). 8 Silicon Chip Your response to the letter from I.P.V. of Karrinyup, WA (Ask SILICON CHIP, August 2021, pages 109-110) suggesting the IMX8-7-F as a replacement for the now unobtainable HN3C51F got me searching for a closer match. I found the HN4C51J, which appears to be identical to the HN3C51F except that the two transistor bases are tied together (hence it comes in a five-pin package rather than six), and the pinout is different. To accommodate the new pinout, the PCB will require slight modification. First, cut the PCB track between pins 5 and 6 of where the HN3C51F was originally located. Next, install a jumper between pins 6 and 2 in the original configuration. The HN4C51J may now be installed with pin 4 of the HN4C51J placed where pin 1 of the HN3C51F was to go. Cutting the track between the original pins 5 and 6 should be straightforward. The jumper between the original pins 6 and 2 might be more challenging. The easiest solution might be to fit the HN4C51J first, then install a ‘bodge wire’ from pin 3 of the HN4C51J directly to the pad of the nearby 68W emitter resistor. Mark Fort, Brassall, Qld. Comments: that should work. We agree that it will be easier to solder a wire after fitting the part. If doing this, make sure to cut the track thoroughly. If we revisit the design, we will adjust it to use this transistor. Having said that, we think substituting the IMX8-7-F will not affect performance, and it is a direct replacement with no PCB modifications required. More on Digital TV standards This email was prompted by Bryce Cherry’s letter, published in the November 2021 issue (page 6), regarding Australia's electronics magazine siliconchip.com.au DVB-T2 digital TV and MPEG-4 for Ultra HD TV and better spectrum utilisation (ie, more TV channels in the same bandwidth). I wrote to the Household Assistance Scheme administrators and requested MPEG-4 capability be compulsory, but also to not pay any antenna installer who used an antenna designed to receive any channel in the range 0-5A, pointing out that there will be no broadcasts on those channels and the antenna will produce less reliable reception due to noise. Now you cannot buy a new band 1/3 antenna. I also have made submissions to Standards Australia to make MPEG-4 compulsory, not optional. Examining the specifications for current TVs, it is difficult to see if they support both DVB-T2 and HEVC, which are needed for broadcasters to transmit Ultra High Definition TV, in competition with the video-on-demand companies. UHD from the internet requires HEVC, but DVBT2 is only needed for over-the-air broadcasts. If DVB-T2 is used for broadcasting, all receivers must be capable of receiving it or, a DVB-T2 set-top box will be required. They are used in some overseas countries. This is how we converted from analog to digital TV. Initially, HDTV used MPEG-2, but it was too data-­ hungry, so MPEG-4 had to be used. If Australian Standard AS 4933 in 2010 had made MPEG-4 compulsory, in 2015, all programs could then have switched to MPEG4, allowing most programs to go high definition. SD programs on TV are still using MPEG-2. We need an update to AS 4933 and AS 4599.1:2015 to include UHD and other new developments. In 2014, TV channels were restacked to allocate a block of consecutive channels to each transmitter site. Except for Darwin, all capital cities have their main transmitters in VHF’s channels 6-8, 10-12 (Block A). All other sites use one of these blocks: B (28-33), C (34-39), D (40-45), and E (46-51). Notice there is a spare channel in each channel block. The only exceptions are Alice Springs, Melbourne and Adelaide. These are for Community TV, which the Government is trying to push online, so they are only giving 12-months extensions to their licences. The other community stations went bankrupt under these conditions. Some remote towns have VHF and UHF, but the transmitters are in different locations. Why are Australian antenna manufacturers selling VHF/UHF antennas except for caravans? Alan Hughes, Hamersley, WA. Praise for Voice Modulator I just completed building Warwick Talbot’s “voice modulator” circuit from page 91 of the August 2019 issue of Silicon Chip (siliconchip.com.au/Article/11777), and it didn’t work. The carrier was audible at the output and the input signal was distorted. I noticed on the circuit diagram that the diodes are arranged in a bridge rectifier configuration. I then read that the diodes are meant to be wired in a circular layout, ie, anode to cathode to anode etc. I subsequently changed both the germanium and silicon diode orientation, and wow, what an amazing instrument! My circuit uses a cheap (about $15) square/sine/triangle generator board containing an ICL8038 IC, and I added siliconchip.com.au Australia's electronics magazine February 2022  9 Warwick’s circuit on Veroboard. I want to build another on one PCB to minimise the mess of wires! Was the error drawn by Warwick or the Silicon Chip graphics department, either thinking “bridge rectifier”? Ian Horacek, Essendon, Vic. Comment: Sorry about the drafting error which was introduced when we redrew the circuit. It was mentioned in the Notes & Errata section of the October 2019 issue and also on page two of our 2019 Errata Sheet. October issue enjoyed You have excelled again with your October 2021 issue. Congratulations to all involved. The article on Gravitational Waves is a beauty and the 2/3-way Active Crossover looks like it will be useful. I have already ordered the cute SMD Test Tweezers kit from your shop. David Humrich, Perth, WA. Comment: you weren’t the only reader who ordered that kit! We expected it to be popular but were still overwhelmed. We only caught up with demand in early November. The USB V Cable Tester project, which debuted in November, has also been extremely popular, again beating our expectations. While we were better prepared for that, it still took us a few weeks to catch up. Documenting old switchboards Last year, I got to visit a location I had visited several times in the 1980s when I was a kid. Last year it was wet, so I only packed my DSLR camera. However, a few days ago, another opportunity to visit arose, low wind and dry weather, airspace classification checked etc. The people who let me in were amazed that I could see the site from the air. While there, I was asked if I wanted to see anything else, so being me, I said “the main switchboard”. What a beauty it was, 1960s vintage, looking far more impressive than the main switchboards for a large major metropolitan supermarket. Needless to say, I took photos of it (and of the drawings that were with it). It has multiple boxes, each with a lever switch on the side and a small door on the front that took cartridge style fuses (a bit like a giant version of a 3AG or M205 fuse). Each area of the then-new buildings had two threephase cables going to two small cabinets with circuit breakers (one for off-peak night store heating and hot water, the other general power and lighting). That main switchboard also fed five existing buildings as well as outdoor lighting, swimming pool stuff and the caretaker’s house. The site had its own transformer outside as well. I didn’t touch anything as I knew that parts of it (quite possibly all of it) are still live. It’s definitely more interesting to look at than the switchboards at work, which are a mix of 1993 and 2018 vintage beige cabinets with boring rows of circuit breakers. Even the main distribution boards look boring. I have access to the plant room, being the in-store maintenance assistant. I suggest, if it is safe to do so, take photos of the older gear. It makes great visual references for drawings and other arts and also helps to record our built/industrial heritage. Darcy Waters, SC Wellington, New Zealand. 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. $50 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. 10 Silicon Chip Australia's electronics magazine siliconchip.com.au Radio Girl I n 2020, the now late Gary Johnston, owner of Jaycar Electronics, sent me this book along with a letter that reads, in part: I really loved the book and read it in one sitting. It really touches the history of hobby electronics and Amateur Radio in Australia. Mrs Mac as she was known was not only a technical person, she was an entrepreneur. She opened a hobby electronics shop and started Wireless Weekly – the precursor of “Radio & Hobbies” and [its later manifestations]. That’s a pretty resounding endorsement from Mr Johnston. His ex-Boss, Dick Smith, also clearly enjoyed it very much, based on his published comments. I regret not having time to read the book until recently. It is essentially a biography of Violet McKenzie, née Wallace, pieced together from historical documentation and interviews with her friends. David Dufty has done a good job of that. One aspect of this book that surprised me is that I thought it would concentrate more on the story surrounding how Violet became Australia’s first female engineer. I also wanted to read about how she started Wireless Weekly (along with three others), ran probably the first ‘hobbyist’ electronics store in Sydney and so on. It does describe those events, but it concentrates more on her role in the formation of the WRENS, among the first women allowed to serve in Australia’s armed forces. That is certainly interesting in its own right. In retrospect, it makes sense that there would be far more information available on that aspect of her life than her earlier (and less ‘official’) activities. Besides telling the story of this remarkable woman’s life, the book also contains lots of fascinating history. I was amazed by the contortions that went on in the first half of last century trying to justify why women should not be engineers, serve in the armed forces or (one gets the impression) even leave the kitchen. That is all in the past now, especially given the drive to get more women to take up “STEM” subjects (science, technology, engineering & mathematics) – coincidentally, a movement that Gary Johnston was part of. In Australia, this can arguably all be traced back to Violet, and her fascination with radios and electricity in general. I was a little disappointed to reach the end of the main part of the book after about 250 pages. Still, that’s understandable given that a limited amount of information is available, especially regarding the early years of Violet’s life, up to the 1930s. Perhaps a technical person perusing some very early copies of Wireless Weekly could have dug up some technical facts that would have spiced up the book for the more switched-on (ahem) readers. But while that would be interesting to me, I suppose it might turn casual readers off. Of the 250 pages in the main part of the book, about 150 are dedicated to the wartime period of 1940-1945 or so. That isn’t surprising given the momentous events that occurred. Still, I wish enough information were available for Mr Dufty to have written a bit more about those fascinating early years. I also note that the book doesn’t really contain any criticisms of Mrs McKenzie. I suppose you would not expect to hear many negatives in interviewing her friends and family, and perhaps there was very little about her not to like. But it does seem a little one-sided as surely, nobody is perfect. Having said that, I don’t want to cast any aspersions on anyone as I prefer to look at things on the bright side myself. siliconchip.com.au Book Review by Nicholas Vinen “The story of the extraordinary Mrs Mac, pioneering engineer and wartime legend” written by David Dufty. The book has extensive information regarding the sources used to piece Mrs Mac’s life story together. That undoubtedly makes it an excellent resource for anyone who wants to investigate further. So the bottom line is: should you read this book? It is well-written and well-researched. If you are into Amateur Radio, Vintage Radio or are interested in the history of electronics, I would say yes. Or perhaps you want to read a story about how one very clever woman overcame much resistance to live a life that we would take for granted these days. In that case, you would also enjoy it. In fact, if all you are looking for is an interesting but true story about a unique individual who became a pioneer, you could do far worse than to read this book. Most readers, young and old, would get something out of it. Radio Girl is published by Allen & Unwin with an RRP of $29.99 (softcover/paperback). It is sold by most book retailers, in-store and online, and is also available as an eBook. SC Australia's electronics magazine February 2022  11 A ll A bout Part 2: by Dr David Maddison Batteries Battery technology is being actively researched worldwide in an attempt to find a better way to store energy from solar panels and wind generators and for powering the latest generation of technology. This article will look at some of that upcoming tech, and will also describe the ‘tried and true’ lead-acid battery in more detail. I n the first article in this series, we gave the history of cell and battery technology, listed some common battery types and explained some of the theory behind them. This article will describe lead-acid batteries in more detail (as they are still in widespread use) and discuss some of the more obscure battery types. A third and final part, to be published next month, will cover electric vehicle batteries, how to characterise batteries and take certain measurements. It will conclude with some miscellaneous battery facts. More about lead-acid batteries Lead-acid batteries might seem ‘primitive’, but they are still very useful. A major reason for this is that they are inexpensive compared to their capabilities, especially capacity and current delivery. Many decades of research has led to them being almost perfected, and many different sub-types are available to suit various applications. Lead-acid car batteries, in particular, are subject to many myths because they need to be replaced regularly (sometimes at a relatively high cost), and when they fail, it is usually at the most inconvenient time. 12 Silicon Chip How a lead-acid battery works Let’s start by considering just one cell of a standard ‘flooded’ lead-acid battery. A typical “12V” battery has six cells in series, each developing about 2V. The essential components of such a battery are (see Figs.31-33): • A spongy, porous lead plate anode that provides a large surface area to assist in the dissolution of the lead (negative) • A lead dioxide plate for the cathode (positive) • Sulfuric acid electrolyte The lead plate is usually alloyed with antimony or calcium for strength. The two plates are kept apart with a porous non-conductive membrane such as fibreglass. In a fully charged state, a lead-acid battery has one lead plate, one lead dioxide plate and a high concentration of aqueous sulfuric acid. Both plates develop a lead sulfate (PbSO4) layer as the battery discharges, and the aqueous sulfuric acid becomes very weak, almost like water. It is essential to realise that, unlike most metal oxides, lead dioxide is electrically conductive. However, lead sulfate is a poor conductor and that is why a discharged lead-acid battery has a higher internal resistance than a fully charged one. During discharge, the following Fig.31: the basic layout of a lead-acid battery. The positive and negative plates are supported by grids made of lead alloyed with calcium or antimony for strength. The active material that fills the grid of a charged positive plate is red-brown lead dioxide, while on a charged negative plate, the grid is filled with sponge lead. Original source: Jorge Omar Gil Posada, CC BY 4.0 Australia's electronics magazine siliconchip.com.au Assures reserve electrolyte capacity. To protect against leakage and corrosion. Safety Valve Relieves excess pressure. Sealed Terminal Post Prevents acid leakage. Reduces corrosion; extends battery life. ► Hi-Impact Case and Cover Fig.32; a cutaway of a lead-acid battery (in this case, an AGM or absorbed glass mat type) showing the internal plate structure. Note how multiple pairs of plates are interleaved to increase the battery’s current capacity, both for charging and discharging. AGM means that the electrolyte is absorbed into a glass mat separator between each pair of plates, making them spill-proof and more robust. Cast On Strap Using auto welding system to weld plate group; to ensure the stability of the product. Special Grid Design Withstands severe vibration. Assures maximum conductivity. Absorbed Glass Mat Separator Makes the battery spill-proof. Valve regulated design eliminates fluid loss. Special Active Material Using exclusive materials to prolong battery life and dependability. reaction occurs at the negative (anode) plate. The PbSO4 formed sticks to the lead electrode and coats it. Two electrons are produced in this reaction (2e-). Pb(s) + HSO4(aq) → PbSO4(s) + H+(aq) + 2e− During discharge, the following reaction occurs at the positive (cathode) plate. The PbO2 of the plate is reduced to Pb metal and then reacts with the SO42- of the acid to produce PbSO4 (lead sulfate) which coats the electrode. Two electrons from the above reaction are consumed. The overall reaction at the cathode is: PbO2(s) + HSO4(aq) + 3H+(aq) + 2e− → PbSO4(s) + 2H2O(l) Combining the two ‘half reactions’ above into one chemical equation we get: Pb(s) + PbO2(aq) + 2H2SO4(aq) → 2PbSO4(s) + 2H2O(l) In other words, both the lead and lead dioxide become lead sulfate, while at the same time, the sulfuric acid becomes watery. This reaction produces a cell siliconchip.com.au potential of 2.05V. The actual voltage in a real battery will be slightly different depending on several factors. The above reactions are reversed during the charging process, and the lead sulfate is converted to the lead or lead dioxide of the original electrode. At the same time, the weak watery acid reverts to a strong acid. Most of the energy in a lead-acid battery is stored as the potential energy of the sulfuric acid. More precisely, most of the energy comes from the H+ (free protons) in the acid reacting with the O2 (oxygen ions) of the PbO2 to form water, H2O. One way to judge the quality of a lead-acid battery Arguably, you can judge the quality of a lead-acid battery by its weight. The heavier it is compared to another of similar capacity, the more lead has been used and the longer the expected life of the plates. Batteries from one manufacturer are often sold in multiple grades, perhaps three. Those of the cheapest grade have a short warranty, while the more expensive types come with longer warranties. The difference is due to the more robust construction and more materials Australia's electronics magazine Fig.33: lead plates for manufacturing lead-acid batteries. You can see the grid structure (which appears to be hexagonal), and the brown colour of the lead oxide is also apparent, in contrast to the grey metallic lead. in the more expensive battery, especially more lead. However, for a counterpoint to this, see Fig.34 on the next page! The efficiency of lead-acid batteries This can vary according to the construction method. Flooded batteries are around 70% energy efficient, meaning that only about 70% of the electricity used to charge them is recovered during discharge. Sealed lead-acid batteries (‘gel cells’) can be 95% efficient. Charging efficiency also depends on the temperature and the charging current/rate. Also, a lower discharge rate will achieve more of the rated capacity than a higher rate, because of losses from heating and gas formation. Lead-acid batteries are one of the world’s most recycled items, especially car batteries. Lead-acid battery life Battery life is shortened by high temperatures (hence many batteries these days being relocated from the engine bay to the boot, or under the seat), a high rate of discharge, a high depth of discharge or storing the battery at too low a voltage. February 2022  13 A special deep-cycle battery should be used to achieve a long life if the battery will frequently be deeply discharged. Utilising a lead-acid battery’s full rated capacity (Ah) will shorten its life. In general, a standard lead-acid battery should not be discharged more than 50% of its rated capacity, preferably less – see Table 1. If more capacity is needed, use a bigger battery. A deep cycle battery can tolerate a higher depth of discharge, but shallower discharging is still better. Over-discharge or excessive temperatures cause ‘battery sulfation’ and degradation of the plates (hence thicker, heavier lead plates lasting longer). When excessive sulfation occurs, it is usually permanent, although some claim it can be reversed if the battery has only been excessively sulfated for a short time. This is the subject of endless debates. (We have published multiple “battery zappers” which intend to fix sulfation; some swear by them.) Stored batteries should be maintained on a float charge at the voltage recommended by the manufacturer, or at least their voltage checked periodically and recharged as necessary. A typical float charge voltage is in the range of 13.2-13.8V, but check the manufacturer’s recommendation. The problem with silvercalcium batteries The silver-calcium lead-acid battery is a relatively new type of lead-acid battery with a much longer life than other types. The author had one in a car that lasted about ten years, more than three times the life of a typical car battery. The problem with these batteries is that they require a higher than typical charging voltage of 14.4V to 14.8V (the standard lead-acid charging range is more like 14-14.4V). Unless a vehicle’s charging system is designed (or modified) to be used with these batteries, they will be inadequately charged and will eventually sulfate and have a short life. Because of the silver content, these batteries are more expensive than others, but the author’s opinion is that they will be cheaper in the long run because of their extended life as long as they are charged to the correct voltage. Problems with swapping batteries For certain car brands and models, 14 Silicon Chip Fig.34: contrary to what we said elsewhere, a heavier lead-acid battery is not always a sign of a better battery. This unfortunate person found a small battery inside their big battery case, with the empty space filled with concrete... especially those made in the last ten years, replacing the battery isn’t as simple as disconnecting the old one and connecting the new one. When the battery of a modern car is changed, many settings can be lost and have to be reprogrammed, and certain systems such as power windows might need to be resynchronised. For example, here is the procedure required when changing the battery on some Mercedes models. You might save a small fortune doing this yourself compared to getting a dealer to do it! siliconchip.com.au/link/abc6 You can also maintain settings in various cars by carefully jumpering power to the battery leads during replacement to avoid complete power loss. See the YouTube video titled “How to change your car battery without losing your radio code and dashboard setting. HD” at https://youtu. be/9HREVVZAqNI In certain post-2002 BMWs, a new battery requires registration with the car engine control module so that the charging system knows about the new battery and its capacity, type and charging voltage. This even has to be done if the new battery is the same type as the old one. See: siliconchip. com.au/link/abc7 In modern cars, there is some controversy as to whether the negative or positive lead should be removed first when replacing a battery (or if it even matters). In old cars, it used to be negative first. Some say positive first on modern vehicles to avoid a voltage spike through the car’s electronics. We don’t think it makes any Australia's electronics magazine difference. However, there is an advantage when jumping a car or charging its battery to making the final (negative) connection to an exposed area of the chassis or engine, rather than directly to the battery. Besides making it easier to make solid contact, this has the advantage that any spark generated during connection or (probably more importantly) disconnection is away from the battery and therefore unlikely to ignite any hydrogen gas which might have evolved from the battery. Note that car batteries have gotten quite a lot more expensive as the demands placed on them have multiplied. Modern cars have electric power steering, stop/start systems, high-compression engines and many electrical accessories. As a result, they need higher-capacity batteries that can be discharged and recharged faster, deeper and more frequently. Automotive battery parameters (lead-acid) The primary purpose of an automotive battery is to start the engine, which requires a very high current for a short time (usually many hundreds of amps for a few seconds). Once the engine starts, the alternator keeps the battery charged and provides power for functions such as ignition, engine and vehicle management, radio and lighting. Car batteries are not designed to be deeply discharged; this will degrade battery life. They also generally aren’t intended to run accessories for long periods with the engine off, although siliconchip.com.au Table 1 – Regular Wet Lead Acid Battery Voltage (12V nominal) 100% 12.70V 95% 12.60V 90% 12.50V 80% 12.42V 70% 12.32V 60% 12.20V 50% 12.06V 40% 11.90V 30% 11.75V 20% 11.58V 10% 11.31V <10% (fully discharged) 10.50V or less special deep-cycle/starting ‘hybrid’ batteries can do that without significantly shortening their life. When buying an automotive leadacid battery, you will see various specifications quoted, as follows: CCA (cold cranking amperes) The current that a battery can deliver at about -18°C (0°F) for 30 seconds while supplying at least 7.2V. Current delivery drops with temperature, which is why this is measured at such a low temperature. Under more temperate conditions, current delivery will be significantly higher than this. CA (cranking amperes) As for CCA but at 0°C (32°F). HCA (hot cranking amperes) As for CCA but at 26.7°C (80°F). Group size Refers to standard battery sizes established by the (American) Battery Council International and specifies the terminal size, location, and polarity, but not the current rating or capacity. ETN (European type number) A numbering scheme for car batteries (replacing the DIN number) that specifies the voltage, capacity, CCA and dimensions. The first digit is voltage: 1 or 2 is 6V while 5, 6 or 7 is 12V; the second and third digits are the nominal 20hr continuous discharge capacity; the fourth, fifth and six digits are a unique code that gives details such as physical size, endurance, terminal configuration and clamping parts; the seventh, eighth and ninth digits give the CCA rating. For example, 536-040-030 refers to a 12V 36Ah battery with a unique code number of 040 rated at 300 CCA (the siliconchip.com.au Comments Cycling in this zone gives a reasonable battery life expectancy. Occasionally dropping into this zone is OK but will shorten battery life if done repeatedly. Avoid discharging this deeply as permanent damage will occur. 030). Confusingly, if the Ah capacity is 100 or more, its leading digit (‘1’ for ratings ≥ 100Ah, or ‘2’ for ≥ 200Ah) gets added to the first digit of the ETN, so 660 in the first three digits would mean 12V and 160Ah. JIS (Japanese Industrial Standard) A sizing standard used for Japanese and Korean cars. It is simpler than group size (US) or ETN (Europe) and consists of four groups of characters. For example, a 55 B 24 L battery has a 55 performance rating for starting and capacity (higher is better), B refers to 129mm width and 203mm total height, 24 is the length in cm and L means that the negative terminal is on the left side with the terminals closest to you. RC (reserve capacity) The time in minutes that a battery ► State of Charge (SoC) Notes: Readings are taken with no load using a voltmeter after resting for more than two hours. Battery temperature is held steady at 25°C. Batteries just taken off charger will have a significantly higher voltage until the surface charge decays over two hours or more. will deliver 25A continuously at 26.7°C (80°F) before its voltage drops below 10.5V. Amp-hours (Ah) The constant current a battery can produce over a 20hr period (current × hours) at 26.7°C (80°F). Charging a lead-acid battery Lead-acid batteries are charged in various stages of constant current or voltage (see Fig.35). The voltage used depends on multiple factors such as construction method and exact chemistry but is usually 2.30V-2.45V per cell. Even very similar batteries from different manufacturers can have slightly different charging requirements. The charging voltage is a compromise, as too low a voltage will result in slow charging and sulfation, and too high a voltage will result in gassing and plate corrosion. Manufacturers recommend a specific float charge to maintain stationary batteries at around 2.25V-2.27V for flooded leadacid batteries at 25°C. Lead-acid batteries should be stored fully charged. Note that common float chargers Fig.35: a typical charging cycle for a lead-acid battery. The curve shape is generally the same for different lead-acid variations, but the voltages, currents, and times will vary. Larger batteries will have a higher initial current; the end of the bulk charge stage is when it draws less than about 5% of the initial constant current. Australia's electronics magazine February 2022  15 maintain 2.3V/cell or 13.8V for a typical battery. A car battery is called “12V” since the nominal cell voltage from electrochemistry is 2.05V and six cells give 12.3V. However, the charging voltage is usually from 13.8V to 14.7V (but generally closer to 14.4V). An attempt to charge a lead-acid battery at 12.3V will not work; it must be at the manufacturer’s (higher) recommended voltage. Note that charging voltages are usually specified at room temperature (25°C). Manufacturers also typically specify a temperature coefficient in mV/°C. It is negative for lead-acid batteries, so the charge voltage reduces at higher temperatures and increases at lower temperatures (charging usually stops at 0°C). What liquid should you add to a lead-acid battery? Only distilled water should ever be added to a car battery. The sulfuric acid is not consumed and more does not need to be added. An exception to adding acid is in ‘dry’ lead-acid batteries that, for reasons of safer shipping and longer storage life, have no acid or other liquid in them at all. When you buy these, you get a special container of acid to go with them and add it before use. Such batteries are available in the USA and UK, among other countries. A YouTube video about doing this titled “How to fill a dry battery with sulfuric acid (Yuasa)” – https://youtu. be/89Nf3IJcFJQ The author has not Fig.36: a drawing of a lead-acid “B” radio battery, circa 1920, in a rubber box and with glass cells. Moisture could be absorbed into the porous rubber, and leaking acid could also establish conductive pathways that drain the battery. This one was made by the Willard Storage Battery Co. 16 Silicon Chip seen such batteries in Australia, and sadly, in Victoria (possibly other states as well), sulfuric acid is a restricted chemical. The author has such a battery and was unable to buy acid to fill it. The myth of leaving a car battery on concrete The myth is that a car battery will go flat quickly if stored on a concrete floor. There is no truth to this for modern car batteries. What flattens these batteries in storage is gradual self-­ discharge. Lead-acid batteries have low self-discharge rates, but they can still lose around 5% of their capacity per month, more at higher temperatures. Lead-acid batteries should be connected to a trickle charger for storage or regularly topped up to the recommended storage voltage. The problem with storing them on a concrete floor happened with much older generations of car batteries. Early batteries had glass cell cases encased in a timber box (see Fig.36). Water or moisture that gathered on a concrete floor caused the timber case to warp, possibly breaking the glass. Later generations of car batteries utilised porous rubber cases with added carbon, and moisture or leaking acid could create unwanted conductive pathways between cells. For comparison, other battery chemistry self-discharge rates are: ● Lithium-metal primary cells: 10% in 5 years ● Alkaline cells: 2%-3% per year ● Nickel-based batteries: 10%-15% per month after 10%-15% in the first 24 hours ● Lithium-ion: 1-2% per month after 5% in the first 24 hours Typically, the self-discharge rate doubles for every 10°C increase in temperature, so keep stored batteries cool (small batteries can be kept in a refrigerator). In Western countries, this is the point at which the battery is recycled. But in some places, you can take your old battery to a battery rebuilder, and they will reform it into a new battery, perhaps while you wait. See the videos titled “Dead Car Battery Restoration” at https://youtu.be/UvtsBuqLC1g and “How Battery Plates are Made & Restoration of an Old Battery” at https:// youtu.be/VEvPjOKkPyE Lithium-ion car starter batteries Lithium-ion batteries are available as direct replacements for lead-acid batteries in conventional cars. They are lighter in weight (eg, a 120Ah leadacid battery weighs about 30kg compared to 8kg for lithium-ion) and will tolerate a deeper discharge without damage than conventional batteries. Some of these batteries require special charging compared with leadacid types and normally could not be directly replaced; however, some versions contain internal electronics to make them compatible with conventional charging systems. They are also claimed to last longer, say 2000 complete discharge cycles for lithium starter battery compared to 500 for lead-acid. The self-discharge rate can also be lower. However, we recommend that you take caution if you are considering replacing your car battery with a lithium-­ion type, as we have heard stories of vehicle fires started by such batteries. The safest type to use would be LiFePO4 as they generally do not catch fire if abused. You can see a teardown of a lithium-­ ion starter battery at siliconchip.com. au/link/abbq Note that small lithium-ion battery packs are also available for emergency jump-starting, and these generally work very well (but you have to charge them every few months). Other car battery myths Unusual battery types Numerous online videos purport to show how to restore a failed car battery and chemical additives are available that claim to do this. These will generally not work, as the typical reason for failure is the physical destruction of the battery plates. There is no way to restore disintegrated plates without disassembling the battery, melting the lead, recasting it and making it into a new battery. Here we describe some other interesting or important types of batteries not already covered, although there are too many types to cover them all. Australia's electronics magazine Aluminium-air batteries Aluminium-air batteries have occasionally been in the news, typically promoted as the “1000 mile (1600km) car battery”. These batteries are not rechargeable. siliconchip.com.au What can you salvage from used batteries? They are similar to zinc-air batteries as a current is produced by reacting aluminium with atmospheric oxygen. This results in aluminium oxide (Al2O3), and when depleted, this would be collected and converted back to Al2O3 by the input of energy. You can make your own aluminium-­ air battery; several videos show how. For example, see the one titled “Aluminum Air Battery Build 2.0” at https://youtu.be/8wEmjwfHqRI You can recover useful items from certain batteries and cells. For example, in non-alkaline carbon-zinc batteries, there is a carbon rod that can be reused for various projects (see below). It can be used as an electrode for electrochemical experiments or even for making a carbon arc lamp. The best carbon rods are obtained from D cells or 6V lantern batteries. These batteries also have a zinc case and manganese dioxide filling, both useful in many amateur chemical experiments. Brand new lithium disposable batteries have a coiled-up sheet of lithium metal in them; see the video titled “Get Lithium Metal From an Energizer Battery” at https://youtu.be/BliWUHSOalU Used laptop battery packs are a good source of 18650 (18mm diameter, 65mm tall) lithium cells for torches or other uses. Battery packs often fail due to just one or two bad cells, so the rest can be reused. Older laptop battery packs used 18650 cells, and many of these packs are still in service. When they inevitably fail, they can be a good source of 18650 cells. Take care during disassembly; there are many online tutorials about how to get the cells out. Warning: the contents of many batteries, including lithium metal, are hazardous. Take appropriate precautions when dealing with chemicals and look at numerous web pages or videos dealing with battery salvage. Ambri liquid metal battery According to Ambri (https://ambri. com), “the liquid metal battery [comprises] a liquid calcium-alloy anode, a molten salt electrolyte and a cathode comprised of solid particles of antimony, enabling the use of low-cost materials and a low number of steps in the cell assembly process”. Fig.37 shows the reactions involved in this type of battery. We described this type of battery in the April 2020 article on Grid-scale Energy Storage (siliconchip.com.au/Article/13801). The battery system is tolerant of over-charging and over-discharging and is not subject to thermal runaway, electrolyte decomposition or outgassing. The batteries have to be started using heaters. They are packaged in 3m (10ft) shipping containers. The battery system is intolerant of movement, as this causes unwanted mixing of the liquid layers. So they are only suitable for stationary applications such as grid-scale storage. The batteries need to stay hot; once heaters start them, the ongoing charge/ discharge cycles will keep them hot as they are kept in insulated containers. The operating temperature of the battery is over 240°C. Left: carbon rods salvaged from zinccarbon batteries (non-alkaline types). Source: W. Oelen (CC BY-SA 3.0) Future developments of liquid metal batteries include those with lower operating temperatures, possibly using a gallium-based liquid metal cathode and a sodium-potassium liquid metal anode. Gallium is liquid at room temperature but very expensive. The dissolving battery Scientists at Iowa State University have developed a battery that dissolves in water (see Fig.38). It is part of the emerging field of “transient electronics”, devices that are designed to have just a short life and then dispose of themselves after their function has been performed. The 1mm x 5mm x 6mm battery pictured provides 2.5V and dissipates after 30 minutes of immersion in water. It uses a lithium-ion chemistry and would power a calculator for 15 minutes. Flow batteries Flow batteries are a type of battery (strictly, a rechargeable fuel cell) in which the electroactive chemicals are a liquid that flows through an electrochemical cell. The electrolyte is stored 1. Charged State Ca and Sb separated Liquid Metal Calcium (Ca) alloy (negative electrode) Ca Solid antimony (Sb) particles (positive electrode) Sb 2. Discharging 4. Charging Batteries absorb power from the grid e− Half-reactions (3) CaSbx → Ca2+ + Sbx + 2e− (4) Ca2+ + 2e− → Ca Overall charge reaction CaSbx + Energy → Ca + Sbx e− siliconchip.com.au Half-reactions Ca Ca²+ Sb Ca Ca²+ Sb Fig.37: the charging and discharging reactions for the Ambri liquid metal battery. Batteries provide power to the grid CaCl2-based salt electrolyte e− CaSb (1) Ca → Ca2+ + 2e− (2) Ca2+ + Sbx + 2e− → CaSbx e− Overall discharge reaction Ca + Sbx → CaSbx + Energy 3. Discharged State Ca and Sb form an intermetallic alloy Australia's electronics magazine Fig.38: the Iowa State University “transient battery” provides a voltage and current while it dissolves in water. February 2022  17 Fig.40: images and diagrams showing the operation of the alkaline fuel cells used on Apollo spacecraft and the Space Shuttle. They generate electricity from the reaction of hydrogen and oxygen gases. in tanks and continuously supplied to the cell to generate electricity or be recharged. In contrast, a traditional cell has the electrolyte permanently stored around the cell instead of in external tanks. Advantages include scalability, deep discharge capability, low self-­ discharge, relatively low cost and long cycle life. Disadvantages include complexity, added failure points (eg, pumps), difficulties with handling possibly toxic liquids, low energy density and low charge and discharge rates. Flow batteries were mentioned in our article on Grid-scale Energy Storage (April 2020). A vanadium redox flow battery was unsuccessfully tested in Australia as Fig.39: an Australian-made Gelion zinc-bromide cell using non-flow technology. 18 Silicon Chip Fig.41: a cross-section of the Licerion lithium-metal battery, which works similarly to a lithium-ion battery, but with several significant benefits claimed. part of the King Island (Tas) Renewable Energy Integration Project. The Federal Government is now backing the world’s largest vanadium flow battery in the Flinders Ranges, of 8MWh capacity. Redflow (https://redflow.com) is an Australian manufacturer of zinc-­ bromine flow batteries. They make batteries of all sizes, from residential to grid-scale (also mentioned and shown in the April 2020 article). Gelion (https://gelion.com) is another Australian manufacturer of zinc-bromide cells but uses a non-flow technology, shown in Fig.39. They are also developing Li-Si, Li-S and Li-Si-S battery systems. is an example of a molten salt battery. They use a molten salt electrolyte such as LiCl-rich LiCl-LiBr-KBr, operating at a temperature of 375-500°C. The negative electrode is a lithium alloy with aluminium or silicon, while the positive electrode is a sulfide of iron (such as FeS or FeS2), nickel, cobalt or other metals. These batteries have high power and energy density, are tolerant of overcharge, overdischarge and freezing, and are relatively safe. The downside is their high operating temperature and the thermal management that goes with that. Sodium-sulfur and sodium-­ nickel chloride batteries are further examples of this type. Fuel cells Lithium-metal “Licerion” batteries Fuel cells are not strictly batteries, although they have a similar function and may be subject to a separate article in future. Unlike batteries, they do not run flat or need recharging as their fuel is continuously supplied. Like batteries, they are electrochemical cells. Fuel cells were used on Apollo Spacecraft and the Space Shuttle (see Fig.40). We published a three-part series on fuel cell technology in the May, June & July 2002 issues, so for more details, refer to those articles (siliconchip.com. au/Series/226). Lithium alloy-iron / metal batteries A lithium alloy/metal sulfide battery Australia's electronics magazine Licerion is a trademark of Sion Power for their lithium-metal batteries. They are stated to have increased charge density, increased cycle life, better safety and fast charging capability compared to other batteries used in electric vehicles. They are still under development (see Fig.41). According to Sion Power, they have solved many of the problems with lithium-ion, lithium-sulfur and early lithium-metal batteries. “The solution was to pair a proprietary lithium metal anode technology with conventional lithium-ion cathodes. By eliminating the cathode graphite, Sion Power achieved the combination of siliconchip.com.au Fig.42: the movement of ions in a Li-S cell during discharge. Original source: Wikimedia user Egibe (CC BYSA 4.0) Fig.43: this experimental lithiumsulfur cell from Monash University in Melbourne looks similar to a typical lithium-polymer cell. ultra-high energy with long cycle life.” Lithium-sulfur battery Lithium-sulfur (Li-S) batteries are seen as a replacement for lithium-ion batteries because they theoretically have a much higher energy density and do not use expensive cobalt, most of which comes from politically unstable areas (see Figs.42-44). Serious problems with Li-S batteries are the low conductivity of the sulfur electrode, a large volume change of 80% during charging and discharging (leading to the eventual destruction of the electrode) and the permanent loss of sulfur in the electrolyte due to unwanted reactions (the “polysulfide shuttle” effect). In Australia, research is underway on these types of batteries at both Deakin University and Monash University. Deakin is working with Australian company Li-S Energy Ltd (www.lis.energy), using boron nitride nanotubes to enhance cell performance. At Monash, work is underway to use ordinary sugar to stabilise and improve the performance of Li-S batteries. Sion Power was a world leader in commercial Li-S technology, and in 2014 their cells were used to power the Airbus Defence and Space Zephyr 7 HAPS flight which set a record for continuous unrefuelled flight of over 14 days. During that flight, solar cells on the wings recharged the batteries. siliconchip.com.au They have now announced they are moving on to lithium metal technology with batteries they call “Licerion”. US company Lyten (https://lyten. com) is another company working on developing Li-S batteries. They are developing batteries for electric vehicles that also use graphene. See our September 2013 article on graphene at siliconchip.com.au/Article/4393 They are using a technique they call “Sulfur-Caging” to improve the stability of cell components to overcome problems with existing Li-S batteries. They see this as a major breakthrough. Lyten says their batteries will have three times the gravimetric energy density of Li-ion batteries and a life of 1400 charge/discharge cycles. The batteries do not suffer from thermal runaway or combust when damaged and have no critical metals like nickel and cobalt that originate in conflicted countries. A wide variety of battery form factors are possible, as well as a high charge rate: up to 3C, meaning the charge current is three times the Ah rating of the battery (eg, charging a 10Ah battery at 30A). They have an operating temperature range of -30°C to 60°C, and up to 100% depth of discharge is possible. See the YouTube video titled “This Startup Says Its Lithium Sulfur Batteries Have No Rival!” at https://youtu. be/9LfaIppP1Us Mercury batteries Mercury batteries (Fig.45) are now banned in many regions due to the toxicity of mercury (and the cadmium used in some types). Nevertheless, they were important battery types from 1942 to the 1990s, especially in military equipment during the second world war. They had the advantage of a long shelf life and a constant voltage of 1.35V during discharge. Note: Since 1990, IUPAC (which names chemical elements) has stated that sulfur should be spelled with an ‘f’ worldwide. Fig.44: several Lyten Li-S batteries, including 18650 (18mm diameter, 65mm tall) cells at right. Australia's electronics magazine February 2022  19 Fig.45: the cross-section of a typical (obsolete) mercury cell. Original source: Ted Ankara College Library and Information Center A special version containing cadmium had a voltage of 0.9V and was usable at temperatures as high as 180°C. Many cameras, hearing aids, cardiac pacemakers and early electronic watches used mercury batteries, while large mercury battery packs for industrial applications were also available. For devices that still require mercury batteries, there are a few options. Cameras designed before 1975 often used cadmium sulfide photoresistors for light metering, powered by mercury batteries, commonly a 1.35V PX625 type. Light meters designed for mercury batteries often did not have voltage regulation as the battery voltage remained so constant. This poses a problem for substitute batteries which are unlikely to have such a stable voltage. For light meters that included voltage regulation, a 1.5V alkaline PX625A can be used, or a 1.66V silver-oxide S625PX. If the device has no voltage regulation, a 1.35V zinc-air battery can be used, but it will run flat in weeks once the battery is unsealed. Of course, the battery must fit physically. Some vendors make mechanical adaptors for alkaline or silver oxide, including voltage regulation circuitry (see Fig.46). Wein makes a zinc-air cell converted to the same shape as Fig.46: a Kanto MR-9 adaptor in the shape of a PX625 mercury cell (left), which accepts an SR43 silver oxide cell (right). Source: Wikimedia user huzu1959 (CC BY 2.0) the original PX625. Mercury PX625 cells are still made in Russia and sold online. PX640 is another type of mercury battery that was used in cameras. Two (2.7V total) were used in cameras such as the Yashica TL Electro. Adaptors are made to use two SR44 batteries with a total voltage of 3.1V. A diode is used to lower the voltage delivered to 2.7V. Older “insect eye” type of exposure meters are likely to be selenium cells that don’t require a battery. Zinc-air batteries Zinc-air batteries rely on the chemical reaction between oxygen in the air and a zinc electrode to create a current. They have a very high energy density but must be kept sealed to exclude oxygen before use. They are available in sizes from hearing aid batteries to electric vehicles and even grid-scale energy storage (see Fig.47). They produce 1.35V-1.40V. The batteries can be either rechargeable or non-rechargeable. Rechargeable types rely on replacing the zinc oxide with fresh zinc, or electrolytically converting the oxide back to zinc. Other metal-air batteries Fig.47: the zinc-air regenerative fuel cell system for large scale energy storage by Zinc8 (www.zinc8energy.com). Zinc oxide particles are converted to zinc in the regenerator and put in the storage tank until needed, whereupon they are delivered to the fuel stack. Oxidised particles are returned to the storage tank for later regeneration. 20 Silicon Chip Australia's electronics magazine We already mentioned aluminium-­ air and zinc-air batteries. There are also air batteries based on lithium, sodium, potassium, magnesium, calcium and iron. These other types are proposed and of possible future interest only; they have no present commercial applications. The US military used BA-4286 non-rechargeable magnesium-air batteries from 1968 to 1984 until lithium thionyl chloride batteries replaced them. The cost of the magnesium siliconchip.com.au Fig.48: “reversible rusting”, the basis of Form Energy’s iron-air battery. battery was comparable to a zinc-air battery, and they were superior to zinc-carbon batteries. Iron-air batteries are being investigated for grid-scale energy storage. US company Form Energy (website: https://formenergy.com) is developing this technology. Their batteries use “reversible rusting” of iron in combination with oxygen and water to produce or store electricity (see Fig.48). During discharge, atmospheric oxygen causes the iron to rust, while during charging, the rust is converted back to iron and oxygen is released. Form Energy has not supplied specific details of the electrochemistry involved. Advantages claimed are extremely low cost (one-tenth that of lithium-ion for large scale batteries), safety and scalability to grid size. For more information, see the video at https://vimeo.com/575943459 Microbial fuel cells Microbial fuel cells use biological materials as “fuel”, digested by special bacteria. This process involves oxidation or reduction of the biological material, and electrons are collected and used to power a circuit. The idea was conceived in 1911 by Michael Cressé Potter but attracted little interest at the time. Then in 1931, Barnett Cohen made a cell that produced 35V at 2mA. In 2007, the University of Queensland and Foster’s Brewing used wastewater from brewing to power a microbial fuel cell, or a “beer battery”, as one might call it [remember Dick Smith’s Beer-Powered Radio? – Editor]. Although plans called for a 2kW fuel cell to be produced, we could not find any results published for this siliconchip.com.au Fig.49: a No.6 dry cell on a 7mm grid with a AA cell for comparison. Source: Wikipedia user Militoy (CC BY-SA 3.0) experiment. There are online plans about building your own microbial fuel cell, at Instructables: siliconchip. com.au/link/abbr – PDF – siliconchip. com.au/link/abbs The No.6 dry cell I have fond childhood memories of these large 1.5V cells – see Fig.49. They were typically used in bell ringing systems, telephone systems, alarms, ignition systems, some clocks and school science experiments. My late father was a bank manager and the bank alarm system, which would be regarded as primitive by modern standards, used these cells in backup batteries. They were replaced every few months and the old ones discarded, and he would bring them home to me. They were ideal for my experiments, such as making electromagnets or making wire glow red hot. They conveniently had screw terminals which made it very easy to attach wires. These cells are no longer available, although apparently, there are some copies on eBay that produce the wrong voltage. They are still used in certain vintage products such as “self-winding” clocks from the Self Winding Clock Company (1886-1970) – see https://w. wiki/4NaT A US seller makes authentic-looking replacements with modern innards, available from siliconchip.com.au/ link/abbt The original cells were 67mm in diameter and 172mm tall, with a capacity of 35-40Ah. There are original used cells on eBay; they are almost certainly depleted, but they attract good money from collectors. Nuclear batteries During the 1960s, nuclear batteries utilising plutonium-238 were seriously considered for powering artificial hearts (see Fig.50). However, no such hearts were ever implanted. Fig.50: the operating principle of a betavoltaic device. The beta represents an electron or positron emission via nuclear decay. The spontaneously created electron-hole pairs in the semiconductor and the loss of the beta particle from the emitter cause a current to flow through the load. Australia's electronics magazine February 2022  21 Fig.51: a rendering of the proposed nuclear diamond battery. Many people are sceptical about its viability. Fig.52: the operational scheme of sodium-sulfur cell. Note the use of a solid polymer electrolyte and the test tube shaped design. Nuclear powered pacemakers were made but have been discontinued. They would still operate after 88 years, compared to a conventional lithium battery at 10-15 years. We discussed this in our October 2016 article on “Implantable Medical Devices” (page 31; siliconchip.com. au/Article/10329). The nuclear pacemaker battery is a betavoltaic device. It is essentially like a solar cell, but instead of being struck by photons from the sun, it is struck by beta particles (electrons or positrons) from a radioactive source. Radioactive sources can produce some combination of alpha (helium-4 nucleus), beta (electron/positron) or gamma (electromagnetic) radiation, so not all radioactive substances are suitable. A different type of nuclear “battery” used on spacecraft is the radioisotope thermoelectric generator (RTG). These were used on the Pioneer and Voyager spacecraft (December 2018; siliconchip.com.au/Article/11329), Mars rovers (July 2021; siliconchip. com.au/Article/14916) and many other spacecraft. A “diamond” nuclear battery is a recent development (Fig.51). It is a betavoltaic device made of irradiated graphite nuclear waste. The graphite waste containing radioactive carbon14 is converted to a diamond-like coating and acts as the beta particle source, producing a tiny current for thousands of years. Australian YouTuber David L. Jones has stated this battery is not viable in his video titled “EEVblog #1333 - Nano Diamond Self-Charging Battery DEBUNKED!” at https://youtu.be/ 22 Silicon Chip uzV_uzSTCTM and so has YouTuber Thunderf00t in the video “NUCLEAR Diamond Battery: BUSTED!” at https:// youtu.be/JDFlV0OEK5E Sodium-sulfur batteries The sodium-sulfur battery uses molten sulfur as the positive electrode and molten sodium as the negative, with solid sodium alumina as the electrolyte (see Figs.52 & 53). The battery operates at over 300°C. These batteries are used at over 190 sites in Japan for large-scale energy storage, plus some sites in Europe, North America and the UAE. NGK Insulators Ltd commercially produces these batteries in Japan. A 200kW/1200kWh battery fits into a 6m/20ft shipping container and has a life of 15 years or 4500 charge/discharge cycles. + terminal − terminal This type of battery was an early candidate for electric cars and was also tested on a Space Shuttle flight. It is a candidate for a Venus landing mission due to its high-temperature operation. Silver-oxide batteries Silver-oxide primary cells comprise a silver oxide cathode and zinc anode. They are primarily sold in the form of button cells to power watches and other small devices where the cost of the silver is not excessive. There is also a silver-zinc battery that is rechargeable and had the highest energy density before the development of lithium-ion batteries. They are mostly restricted to military and aerospace applications because of their expense. The Lunar Rover used in the Apollo missions used two 36V silver-oxide 192 battery cells fuse − pole (sodium) safety tube solid electrolyte (Beta alumina) + pole (sulfur) sand thermally insulated lid radiated heat duct main pole heater Battery Module Battery Cell 6 NAS battery moldules containerised NAS battery units (800kW) power conversion system container controller Battery Container Battery System Fig.53: this shows how sodium-sulfur batteries are configured for large-scale storage, such as in power grids. NAS is the trade name for this battery. Australia's electronics magazine siliconchip.com.au non-rechargeable batteries of 121Ah capacity each, giving a range of 92km. Sodium-ion batteries Sodium-ion batteries are under development. They are similar to lithium-­ion batteries but without the supply or cost problems of lithium, cobalt, copper and nickel. However, they currently have a low energy density and a short life. Sodium-ion batteries were initially developed alongside lithium-ion batteries until it became apparent that lithium-ion batteries were superior. But there has been a resurgence of interest due to the aforementioned supply and cost problems. Solid-state batteries Solid-state batteries use solid electrodes and solid electrolytes instead of a liquid or gel (see Fig.54). They were first experimented with in the 19th century but were not practical until recent developments in solid electrolyte materials and electrodes. They have a higher energy density than conventional Li-ion batteries and are of particular interest for electric vehicles as they use non-­flammable electrolytes. Experiments with Li-S as a cathode material and a solid lithium anode are looking promising. The Weston Cell The Weston Cell was invented in 1893 and was used as a calibration standard for EMF and voltmeters from 1911 until 1990 (see Figs.55 & 56). It uses cadmium and mercury to produce a stable voltage of 1.018638V for an “unsaturated” cell design. The Fig.55: a Weston Cell from NIST, the National Institute of Standards and Technology in the USA. voltage produced is very slightly temperature-­dependent, according to a known formula. “Saturated” Weston Cells are less temperature-dependent, but they lose about 80μV per year, so they need to be calibrated regularly. Today the Josephson voltage standard, a superconducting integrated circuit, has mostly replaced the Weston Cell. Electrolytic cells The inverse of a battery/cell is an electrolytic cell. They consume energy rather than produce it and are typically used to decompose chemical compounds. Common examples are the decomposition of water into hydrogen and oxygen (“electrolysis”), the electrolytic refining of aluminium by the Fig.56: how a Weston Cell is constructed. Cd is cadmium, Hg is mercury, SO4 is sulfate and H2O is water. Original source: Paweł Grzywocz (CC BY-SA 2.5) Hall–Héroult process and electrolytic rust removal (see our article on “How To Remove Rust By Electrolysis” from October 2014 – siliconchip.com.au/ Article/8041). Recharging a battery is also an electrolytic process; essentially, a rechargeable cell switches between being a regular cell and an electrolytic cell depending on the direction of current flow. Next month In the third and final part of the series next month, we’ll cover electric vehicle batteries in more detail. We’ll also describe concepts like battery internal resistance, depth of discharge, lifespan, storage charge and temperature, battery protection and have some battery trivia. SC Fig.54: a solid-state battery is much like a conventional battery but with a solid electrolyte. Original source: Wikimedia user Luca Bertoli (CC BY-SA 4.0) Fig.57: a Diesel-powered electric car charging station on the Nullarbor. “Range anxiety” is a concern for many EV owners. We’ll have more details on electric vehicle batteries in the third and final part of this series next month. siliconchip.com.au Australia's electronics magazine February 2022  23 Intelligent Dual Hybrid Power Supply PART 1: BY PHIL PROSSER This power supply has two separate outputs, each capable of delivering up to 25V DC at 5A.They can be connected in series and ganged up to form a dual tracking supply, and both outputs are controlled and monitored using a graphical LCD screen, two rotary encoder knobs and two pushbuttons. B oth outputs are powered by a single transformer, and they can be used independently or ganged up to form a dual-tracking (positive and negative) or higher current single-ended supply. This design uses a hybrid switchmode/linear approach for decent efficiency and low output ripple and noise. Due to its high efficiency, it doesn’t need fans, so there is no fan noise or associated dust buildup. Much audio and analog work demands a bench power supply with decent voltage and current capability, plus dual tracking outputs, so this supply fits the bill. We received some questions on the practicality of building a pair of our 45V, 8A linear supplies (October & November 2019; siliconchip.com.au/ Series/339) and hooking them together. You certainly could do that, but this supply is a much more compact and lower cost solution. It adds valuable 24 Silicon Chip features like monitoring the voltages and currents on one screen, and switching off or reducing the voltage of both outputs if either current limit is exceeded. The slightly lower voltage and current capabilities (25V instead of 45V and 5A instead of 8A) will still suit most applications. For example, while this supply won’t allow you to test a 100W power amplifier module at full power, it would be good enough to test it at lower power levels, to verify that it works before hooking up its normal power supply. And when you aren’t using it as a tracking supply, you can make the two outputs completely independent and control them separately. Another advantage of the digital controls is that the internal wiring for this supply is quite straightforward and neat, consisting mainly of some ribbon cables that carry control Australia's electronics magazine signals, plus a handful of wires that carry DC power. Using a microcontroller to control the power supply and drive the user interface allows us to be smart in how we control the limits. It can work out voltage and current limits based on the transformer’s VA rating and secondary voltage. This allows a wide variety of transformers to be used. Dig through your parts bin and recycle! The supply uses two alike regulator boards for dual rails. It can be built with a single board if you only need one rail – the user interface can handle single-/ dual-rail implementations. If you’re dead set against using a microcontroller, the regulator board has been designed so that it can operate with just two pots. You would need to organise your own voltage and current monitoring, but you can build it that way, and leave out quite a few of the more expensive parts, like the siliconchip.com.au Fig.1: the blue trace shows a 2A load step with the supply set to deliver 15V. The yellow trace is a close-up of the output voltage, showing how it varies. The vertical scale is 50mV/ div, and the output voltage only varies by a small amount when the load changes. analog/digital conversion chips, isolators, CPU and display. The microcontroller interface is simple to use, though. There are just two controls you will use day-to-day: the output voltage and current limit. If you need it, there is more detail accessible in setup menus, including calibration and configuration screens. The interface is controlled using two rotary encoders with integrated pushbuttons, plus two extra pushbuttons. The encoders adjust the voltage and current limits, while pressing either swaps between controlling the two outputs. One of the extra switches lets you go into setup mode, while the second button is an ‘emergency stop’ button that shuts down the power supply output immediately. This is useful if the magic smoke starts leaking from something! Pressing it again restores the output. Fig.2: this is a similar view to Fig.1 but with a much faster timebase (100μs per division). The initial 100mV step is characteristic of the LM1084. The LM1084 and the overall loop feedback response brings the output back to 15V within 100μs. Performance When measured using an oscilloscope, mains-related hum and buzz is not detectable (see Fig.1), nor is switchmode noise. Output noise is typically less than 20mV peak-to-peak, and less than 5mV RMS. This is pretty much constant across the full range of load variations. The response of the power supply to load change is good. Figs.2 & 3 show that the output voltage recoves within 100μs with a 5A load step, with a maximum offset of just 200mV over 40μs. Fig.4 shows how the unit behaves when it goes into and out of current limiting, with the current limit set to 5A. In response to a short circuit on the output, the voltage falls to achieve the programmed current limit almost immediately, and remains stable. Recovery takes around 5-10ms and has very little overshoot. The supply has no thermal problems when short circuited. With both channels delivering 5A continuous into a short circuit, the heatsink will get quite hot to touch, but settles at about 60°C. Fig.3: the same scenario as in Fig. 2 except this time, the output voltage has been set to 18V and the load step is 4A. The change in output voltage is slightly greater at 200mV peak drop, recovering within 100μs. On the trailing edge, the output changes by 75mV and it recovers within 2ms. This peak is small for such a large load step with minimal output capacitance. Fig.4: this shows how the unit behaves going into and out of current limiting. Ideally, its reaction should be swift and with little overshoot. In response to a short circuit, the output voltage is rapidly reduced. When the short is removed, the output voltage recovers in about 20ms, with no overshoot visible. Hybrid design This supply uses both switchmode and linear regulators, like our Switchmode/Linear Bench Power Supply (April-June 2014; siliconchip.com. au/Series/241) and the more recent Hybrid Lab Power Supply with WiFi (May & June 2021; siliconchip.com. au/Series/364). siliconchip.com.au Australia's electronics magazine February 2022  25 A few quick sums show that a purely linear power supply delivering ±25V and 5A would demand a huge heatsink, dissipating over 125W per rail or 250W total. This is greatly reduced by using a switchmode pre-regulator, which generates just a little more voltage than the linear regulator needs at its input. We aimed for about 5V of headroom in this design. If we can achieve this, then the linear regulator dissipation is a maximum of 5V × 5A = 25W for regular operation per rail, totalling 50W in the worst case. That is still a reasonable amount of heat to dissipate, but eminently doable. The pre-regulator and bridge rectifier dissipate some power too, which will add in the region of 10W. The downside is that switchmode power supplies have a reputation of being hard to design, and because of how they work, a bad rap for introducing noise into circuits. Our goal was a product that could be built from standard components, which would ‘just work’. We tried and rejected two alternative pre-regulator designs before settling on the one presented here. The result meets the above design brief, and neatly fits two independent regulators in the same case. It can deliver 5A over the range of 2-25V continuously per rail, without the need for fans and cutouts. Implementation The Intelligent Power Supply comprises four main parts: the main transformer, one or two regulator modules and a controller, as shown in Fig.5. This allows either single or dual rail power supplies to be built. We expect that most constructors will build the power supply as a dual unit. Each regulator module can operate independently, and its outputs are floating with respect to the other. So for a dual-tracking power supply, you connect the “+” of the negative rail to the “-” of the positive rail and select “Dual Tracking” in the setup. You can also set the mode to “independent” in the user interface, and independently set voltage and current limits for each rail. To keep construction simple, we have built a +5V DC power supply for the control interface into the regulator modules. So, the control microcontroller can be powered without the need for separate boards or transformers. 26 Silicon Chip Fig.5: the basic arrangement of the Intelligent PSU. Two separate secondaries on the transformer power the two regulator modules. One of these also provides 5V to the control interface, which uses a serial peripheral interface (SPI) bus to control and monitor both regulator boards. Fig.6: here is how each regulator module is arranged. The incoming AC is rectified, filtered and regulated to provide three supply rails for the rest of the circuitry on the regulator board. The raw DC is also fed to a switchmode pre-regulator which provides 5V more than the selected output voltage to the LM1084-based final linear regulator stage. The output voltage and current are set by a dual-channel DAC, and monitored via a dual-channel ADC. Only one of these needs to be installed and enabled. Refer to Fig.6, the functional block diagram of the regulator module. The regulator takes a nominal 24-25V AC input and control input, and produces regulated DC as commanded. Our software controls one or two of the regulator modules via a single 10-pin header on each. You could theoretically build more than two, provided you modified our code or wrote your own user interface. We’ll explain how to do that later. As shown in the photos, the module’s size (built on a 116 x 133mm PCB) is quite modest for a power supply of this sort. Two of these modules fit sideby-side in the proposed case. The main heatsink runs across the back of the regulator module(s). Attached to it are two linear regulators, Australia's electronics magazine the bridge rectifier and switchmode pre-regulator. Circuit description Let’s start at the output and work backwards. The complete circuit of one regulator module is shown in Fig.7, and the output regulators are just to the right of the diagram’s centre. The output stage is based on one or two LM1084IT-3.3 regulators. This is a 3.3V low-dropout linear regulator in a TO-220 package. At 5A load, it has a dropout of 1.5V. This low dropout voltage is required to allow the small pre-regulation difference, and get 25V DC from this unit when using a 24-25V AC transformer. The Texas Instruments LM1084IT-3.3 handles a maximum input-output voltage differential of 25V, although, in this application, the differential will siliconchip.com.au This is what the finished project looks like when mounted in its case. typically be about 5V. The exception is when the current limit kicks in, and while the pre-regulator capacitors discharge, the LM1084 will see an increased input voltage. We have specified two LM1084IT-3.3 devices in parallel, with 0.05W current-sharing resistors, to ensure that there are no limitations on the output current and to optimise the thermal design. The output voltage is set with the help of LM358 op amps IC3a & IC3b. IC3b monitors the output voltage, divided by the 15kW and 1kW resistors, and compares this to the voltage from pin 14 of IC4, a digital-to-analog converter (DAC), labelled Vset. If the output falls below Vset, it turns off NPN transistor Q6, which allows the voltage at the “GND” pin of the LM1084s (not connected to GND…) to increase. The opposite occurs if the output voltage is too high. This operational amplifier operates siliconchip.com.au as an integrator, reacting slowly to establish the overall output voltage. The high-speed aspect of regulation is dealt with by the LM1084 regulators. Current control is implemented in the same manner, but instead of monitoring the output voltage, we monitor the output of the INA282 current sense amplifier and compare this to the Iset DAC output (from pin 10 of IC4). If the measured current exceeds the set current limit, NPN transistor Q5 is switched on, pulling the “GND” pin of the LM1084s down. How do we achieve a 0V output given the minimum voltage an LM1084IT-3.3 can output is 3.3V? This design connects the op amp negative rail and emitters of transistors Q5 & Q6 to a -4.5V rail, allowing the GND pins of the LM1084IT-3.3s to be pulled negative. As a result, the output voltage goes down to 0V. This part of the circuit is very similar to that published in the 45V Linear Australia's electronics magazine Bench Supply project from November 2019. As in the original article, we have a constant current source comprising two NPN transistors to ensure a minimum load on the LM1084s. The pre-regulator We have selected the MC34167 chip as the pre-regulator. This is a switchmode ‘buck regulator’ (step-down) which operates at about 72kHz. A buck regulator switches the input voltage (pin 4) through to the output inductor (pin 2) on and off rapidly. There are two distinct phases of operation in a buck regulator: When the regulator switch is on, current flows from the input rail (34V DC), building up the inductor current and charging the output capacitor. The inductor stores energy in its magnetic field as a function of the current passing through it. When the regulator switch is off, current continues to flow through the February 2022  27 28 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.7: this shows the entire regulator module circuit. The rectifier, filter and regulators that provide the +12V, +5V & -4.5V rails are at upper left. The ADC, DAC, and isolating circuitry are at lower left. The switchmode pre-regulator is at upper right, and the final linear regulator stage and current monitoring circuitry are at middle/lower right. siliconchip.com.au Australia's electronics magazine February 2022  29 Parts List – Dual Hybrid Power Supply 1 metal instrument case, minimum 305 x 280 x 88mm [eg, Jaycar HB5556] 1 CPU board assembly (see below) 1 LCD assembly (see below) 1 front panel interface assembly (see below) 2 regulator assemblies (see below) 1 230V AC to 24-0-24 or 25-0-25 160-300VA toroidal transformer (T1) [eg, Altronics M5325C or M5525C] 1 chassis-mount 10A IEC mains input socket [eg, Altronics P8320B] 1 10A-rated safety 3AG panel-mount fuseholder [eg, Altronics S6000] 1 10A fast-blow 3AG fuse 1 300 x 75 x 46mm diecast aluminium heatsink [Altronics H0545] 24 M3 x 16mm panhead machine screws 16 M3 x 6mm panhead machine screws 14 M3 hex nuts 12 flat washers, ~3.2mm ID (to suit M3 screws) 22 shakeproof washers, ~3.2mm ID (to suit M3 screws) 12 fibre or Nylon washers, ~3.2mm ID (to suit M3 screws) 3 ~3.2mm inner diameter solder lugs (to suit M3 screws) 2 20-way IDC line sockets [eg, Altronics P5320] 5 10-way IDC line sockets [eg, Altronics P5310] 1 4-way 17.5A mains-rated terminal block [eg, cut from Altronics P2135A] 2 100nF 63V MKT capacitors 2 10nF 63V MKT capacitors Wire, cable etc 1 2m length of red 7.5A hookup wire 1 1m length of black 7.5A hookup wire 1 1m length of yellow 7.5A mains-rated hookup wire 1 1m length of green/yellow striped 7.5A mains-rated hookup wire ★ 1 1m length of brown 7.5A mains-rated hookup wire ★ 1 1m length of light blue 7.5A mains-rated hookup wire ★ 1 200mm length of 20-way ribbon cable 1 600mm length of 10-way ribbon cable 1 45 x 50mm sheet Presspahn or similar insulating material 1 40 x 45mm sheet of aluminium, 1.5-2.5mm thick 2 10 x 20mm sheets of aluminium, 1.5-2.5mm thick 1 90 x 70mm x 3mm thick sheet of clear acrylic/Perspex ★ all can be stripped from a 1m length of mains flex or a discarded mains cord Parts list for CPU assembly 1 double-sided PCB coded 01106193, 60.5 x 62.5mm 1 2-way mini terminal block, 5.08mm spacing (CON5; optional) 2 5x2 pin headers (CON7,CON9-CON11,CON23) 1 10x2 pin header (CON8) 2 3-pin headers (LK1,LK2) 1 2-pin header (JP5) 3 shorting blocks (LK1,LK2,JP5) 1 ferrite bead (FB12) 1 miniature 8MHz crystal (X2) OR 1 standard 8MHz crystal with insulating washer (X2) 1 10kW vertical trimpot (VR1) Semiconductors 1 PIC32MZ2048EFH064-250I/PT 32-bit microcontroller programmed with 0110619A.HEX, TQFP-64 (IC11) 30 Silicon Chip 1 25AA128-I/SN I2C EEPROM, SOIC-8 (IC12) # 1 LD1117V adjustable 800mA low-dropout regulator, TO-220 (REG2) # 1 LM317T adjustable 1A regulator, TO-220 (REG3) 1 blue SMD LED, SMA or SMB (LED2) 3 SGL41-40/BTM13-40 or similar 1A schottky diodes, MELF (MLB) (D14-D16) Capacitors 1 470µF 10V electrolytic 5 10µF 50V electrolytic 11 100nF SMD 2012/0805 50V X7R 4 20pF SMD 2012/0805 50V C0G/NP0 Resistors (all SMD 2012/0805 1%) 1 10kW 1 1.2kW 2 1kW 1 560W 2 470W 1 390W 2 330W 1 100W 3 47W Parts list for LCD assembly 1 128 x 64 pixel graphical LCD with a KS0107/KS0108 controller and 20-pin connector 1 double-sided PCB, coded 01106196, 51 x 13mm 1 10x2 pin header 1 20-pin header Parts list for front panel interface 1 double-sided PCB coded 18107212, 74.5 x 23mm 2 right-angle PCB-mount rotary encoders with inbuilt pushbuttons (RE1,RE2) [Altronics S3352 or Mouser 858-EN11-VSM1BQ20] 2 right-angle PCB-mount sub-miniature momentary pushbutton switches (S1,S2) [Altronics S1498] 1 5x2-pin IDC box header (CON1) 7 22nF 50V ceramic capacitors 2 10kW 1/4W 1% thin film axial resistors Parts list for one regulator assembly (double the quantities for two) 1 double-sided PCB coded 18107211, 116 x 133mm 1 220μH 5A ferrite-cored toroidal inductor (L1) 1 10μH 6.6A ferrite-cored toroidal inductor (L2) [Bourns 2000-100-V-RC] 1 330μH 3A ferrite-cored toroidal inductor (L3) (only needed for one module) 1 10A slow-blow M205 fuse (F1) 2 M205 PCB-mount fuse clips (for F1) 3 2-way screw terminals, 5.08mm pitch (CON1,CON2,CON4) 1 5x2-pin vertical header (CON3) 2 3-pin vertical polarised headers with matching plugs housings and pins (optional – for manual control) (CON5,CON6) 1 2-way vertical polarised header (CON7) 2 3-way pin headers with jumper shunts (JP1,JP2) 2 micro-U flag heatsinks (for REG1 & REG2) [eg, Altronics H0627] 6 TO-220 silicone insulating kits (washers and bushes) 4 15mm-long M3-tapped Nylon spacers 9 M3 x 16mm panhead machine screws 4 M3 x 6mm panhead machine screws 9 M3 hex nuts 13 flat washers, ~3.2mm ID (to suit M3 screws) 13 shakeproof washers, ~3.2mm ID (to suit M3 screws) Australia's electronics magazine siliconchip.com.au Semiconductors 1 INA282AIDR bidirectional current shunt monitor, SOIC-8 (IC2) # 1 LM358 dual single-supply op amp, DIP-8 (IC3) 1 MCP4922-E/P dual 12-bit DAC, DIP-14 (IC4) # 1 MCP3202-BI/P dual 12-bit ADC, DIP-8 (IC5) # 2 MAX14930EASE+ 4-channel isolators, SOIC-16 (IC6,IC7) # 2 LM317 1.5A adjustable regulators, TO-220 (REG1,REG2) 1 LM2575T-5.0V 5V 1A buck regulator, TO-220-5 (REG3) [Altronics Z0587] (only needed for one module) 1 LM337 1.5A adjustable negative regulator, TO-220 (REG4) 1 MC34167TV 0-40V 5A integrated buck regulator, TO-220-5 (REG5) # 2 LM1084IT-3.3 5A low-dropout regulators, TO-220 (REG6,REG7) # 2 BD139 80V 1A NPN transistors, TO-126 (Q3,Q10) 7 BC546 80V 100mA NPN transistors, TO-92 (Q4-Q8,Q11,Q13) 2 BC556 80V 100mA PNP transistors, TO-92 (Q9,Q12) 1 400V 10A bridge rectifier with metal base (BR1) [eg, Compchip MP1004G-G] # 9 1N4004 400V 1A diodes (D1,D2,D5,D6,D9,D10,D13,D17,D19) 1 6TQ045-M3 45V 6A schottky diode, TO-220AC (D3) # 1 P600K (or -M) 6A 800V diode (D8) [Altronics Z0121] 1 1N5819 40V 1A schottky diode (D12) 1 1N4148 signal diode (D14) 1 6.8V 400mW zener diode (ZD2) [eg, 1N754] Capacitors 3 4700µF 50V 105°C electrolytic, 10mm pitch, ≤20mm diameter [eg, Nichicon UVZ1H472MRD] 1 3300µF 50V electrolytic [Altronics R4917] 3 1000µF 50V low-ESR electrolytic 1 1000µF 50V electrolytic ≤13mm dia [Altronics R4887] 1 470µF 25V low-ESR electrolytic 2 220µF 50V low-ESR electrolytic 5 100µF 50V low-ESR electrolytic 2 15µF 50V solid tantalum, SMD E-case [eg, Mouser 581-TPSE156M050H0250 or 80-T495X156M50ATE200] 7 10µF 50V 105°C electrolytic 1 1µF 63V MKT 3 470nF 50V X7R SMD ceramic, M3216/1206-size 12 100nF 63V MKT 10 100nF 50V X7R multi-layer ceramic [Altronics R2931] 2 100nF 50V X7R SMD ceramic, M2012/0805-size 1 1nF 50V X7R multi-layer ceramic [eg, Altronics R2900A] Resistors (1/4W 1% thin film axial unless otherwise stated) 2 180kΩ 5 1.8kΩ 1 15kW 1 1.2kΩ 1 12kΩ 3 1kΩ 12 10kΩ 2 680Ω 1 6.8kΩ 2 220Ω 1 4.7kΩ 1 100Ω 2 3.3kΩ 2 68Ω 2 0.05Ω (50mΩ) 1% 1W shunts [TT Electronics OAR1R050FLF] # 1 0.01Ω (10mΩ) 1% 1W shunt [TT Electronics OAR1R010JLF] # 2 0Ω resistors or lengths of 0.7mm diameter tinned copper wire (LK1,LK2) (only needed for one module) # [Mouser, Digi-Key etc] siliconchip.com.au inductor, as is required because there is energy stored in the inductor. The ‘input side’ of the inductor, the node where the MC34167 output connects to it, still has current flowing into it. But the MC34167 switch is off. As a result, this node tries to go negative. The ‘catch’ diode (D3) clamps this to about -0.5V as it is a schottky type. During this phase, current continues to flow into the output capacitor, but the energy is supplied from the inductor’s collapsing magnetic field. There are a few important things to keep in mind when designing a buck regulator: • The switching nodes (input, output, diode, input capacitors and ground traces between these) all see current switching at 72kHz. These pulses have very fast rise and fall times, which means we need to be conscious of induced voltages across pins and tracks and the potential for these pulses being coupled into other parts of the circuit and indeed itself. • The switchmode regulator’s output pin is switching between the full input rail and -0.5V very rapidly and is a significant source of EMI. • The catch diode carries substantial current; the duty cycle depends on the output voltage and current. The worst case is with a low output voltage and high current, where this device carries much of the load. • The output ripple is heavily influenced by the inductor and capacitor values. The principal losses in a switchmode regulator of this sort are in the switch. The MC34167 has a maximum voltage drop of 1.5V at full current. The catch diode will drop 0.5V when it is conducting, and there are resistive and core losses in the inductor. These losses add to a few watts, representing more than 70% efficiency in the worst case, and closer to 90% for higher currents. So the pre-regulator’s function in this circuit is to efficiently drop the unregulated input voltage, ensuring that the linear regulators only ever need to drop about 5V. This way, we can draw 5A from the power supply without excessive dissipation in the final regulator stage. The circuit around the pre-regulator (REG4) is very similar to an ON Semiconductor (OnSemi) application note, but with a couple of important differences. The output voltage of the MC34167 is set by the feedback pin (pin 1). If this is below 5V, the device’s duty cycle increases to drive the output voltage up. Conversely, if this is above 5V, the duty cycle decreases. We have used 6.8kW and 1.2kW resistors in the feedback divider, which would normally set the output to 33V. (5.05V × [6.8kW + 1.2kW] ÷ 1.2kW). This is more than we need, and we need to drop this to keep it 5V above the linear regulator output. This is done by Q9, a BC556 PNP transistor across the 6.8kW feedback resistor, in conjunction with the 4.7kW and 1kW resistors providing feedback from the overall power supply output. The 4.7kW and 1kW resistors divide the voltage difference between the pre-regulator and linear regulator, and this voltage drives the BC556 transistor to act as a feedback amplifier. When the pre-regulator’s output is too low, the base-emitter voltage on the BC556 is less than 0.6V. The current source turns off, and the feedback to the MC34167 is reduced. When the pre-regulator’s output is too high, Australia's electronics magazine February 2022  31 the base-emitter voltage of the BC556 is more than 0.6V, and the current source turns on, generating 5V across the 1.2kW resistor and increasing feedback to the MC34167. The 68W resistor sets the maximum current from this current source, limiting the current we inject into the MC34167 sense pin, so that under fault conditions, we do not damage it. Note how we are using the 0.6V typical Vbe of the BC556 as the voltage reference to achieve a nominal 5V drop for the output regulator. This does vary a little with temperature and overall output voltage, but that does not matter. The pre-regulator will always deliver about 5V more than the linear regulator. The MC34167 is well within spec being fed from rectified 25V AC (about 33V after BR1) with margin for an unloaded transformer and mains voltage variation, without asking the device to work beyond its specified range. A bonus of using a switchmode pre-regulator is that at lower output voltages, the system will be able to deliver more current than it demands at its input. Our software allows for this. Control and monitoring Control and monitoring of the Intelligent PSU are via an SPI serial interface to each board. This allows access to the optically-isolated DAC and ADC chips. These are both two-channel devices that allow programming of the output voltage and output current limit (via the DAC), and monitoring of the actual output voltage and current (via the ADC). These digital signals are carried over a 10-wire interface back to the control board, with the pinout shown in Table 1. To increase versatility for situations where microprocessor control is not required, we have made provision for external potentiometers to set the voltage and current limit (via CON5 & CON6). If you choose to use this, simply leave off all components in the optically isolated section and also leave off the ADC and DAC chips. The protocol for this interface is straightforward. Digital values are written to the DAC to set the voltage and current output and limits, and digital values are read from the ADC. If “rolling your own” interface, the panel opposite will be helpful. ADC and DAC The dual 12-bit ADC and dual 12-bit DAC are Microchip MCP4922 and MCP3202 devices respectively. Their very simple digital interfaces are described in their data sheets. Calibration is required to convert the digital values, to and from voltages and currents. Our supplied control code handles this. The isolation devices allow one microcontroller module to control and monitor multiple independent regulator modules, which could have their grounds connected to different potentials (via the output connectors). There are two links, LK1 & LK2, that allow power to be fed back from one of the regulator modules to the control interface. If you are using the recommended microcontroller, then you install these on one, and only one, regulator module. It does not matter Table 1 – control connector pinout Function Comment 1 DAC #1 chip select Active Low 2 SPI SDO (to micro) Also known as MISO 3 ADC #1 chip select Active Low 4 SPI SDI (from micro) Also known as MOSI 5 DAC #2 chip select Active Low 6 SPI SCK (from micro) Micro is SPI master 7 ADC #2 chip select Active Low 8 SPARE 9 GND 10 Vdd Silicon Chip The remainder of the circuit The AC from the transformer is rectified by 10A bridge rectifier BR1. Above 3A, this will need heatsinking, so it is mounted on the heatsink via flying leads. There is the provision to mount it on the PCB for lower-current applications. There is also a negative rail generator comprising diodes D5 & D6 and two capacitors, 3300μF & 1000μF. Using these values avoids output transients after switch-off. This generates Table 2: resistor colour codes Pin 32 which. This allows the LM2575 regulator on that board to power the micro. It also connects the microcontroller to the ground of this regulator module, but that is fine, as both will float together, but separately from the other regulator module. The 12-bit devices have 4096 voltage steps. The linear output regulator compares the DAC voltage to the output voltage divided by 16 (15kW ÷ 1kW + 1). This means that the output voltage is controlled in 19.5mV steps (5.0V × 16 ÷ 4095). The INA282 IC which monitors the output current through the 10mW resistor includes 50 times amplification. So the full-scale output of the INA282 is 2.5V (5A × 0.01W × 50), and this translates into an ADC measurement resolution of 2.4mA (1A × 0.01W × 50 × [5V ÷ 2.5V] ÷ 4095). For setting the current limit, the DAC will have the same notional current per bit. The user interface software includes calibration for all these settings and measurements, so you do not need to install precision parts when building this. Either from micro or supplied to micro – see text Australia's electronics magazine siliconchip.com.au a negative rail for the op amps, so that the output voltage can go down to 0V, as described earlier. That negative rail is then fed to REG4 to produce the regulated -4.5V supply. There are three 4700μF 50V capacitors for bulk storage, close to the switch-mode regulator. This is required to support the expected ripple current and to provide a very low-impedance supply to that regulator. Lower value capacitors can be used, but the maximum output voltage will be reduced. There are two 15μF surface-mount tantalum capacitors on the top side of the board, and 470nF and 100nF SMD ceramics on the underside. These are located near the power and ground pins of the MC34167, to ensure that the MC34167 supply has a low source impedance at high frequencies. This minimises the chance of voltage spikes being induced in the power supply tracks. The 50V ratings on these parts are for a good reason; as we’ve written previously, ceramic capacitors with higher voltage ratings perform better even when charged to lower voltages. We have three 1000μF 50V low-ESR electrolytic capacitors in the output filter, in parallel with 470nF ceramic capacitors; these must handle the ripple current at 5A output. The output voltage is filtered again with a 10μH inductor & a 100μF low-ESR capacitor. There are four other ancillary regulators on the board, none of which are configured unusually: • +12V (11.5V actual) rail generated by REG1 (LM317), for the op amps. • +5V (5.1V actual) rail, generated by REG2 (LM317) from the +12V rail, for the ADC and DAC chips. • -4.5V (-4.5V actual) rail, generated by REG4 (LM337), for the op amps. • +5V rail generated by REG3 (LM2575-5), a second switchmode regulator which supplies the control interface, and optionally the microcontroller/user interface. An efficient switchmode regulator is used here to allow the control interface to draw several hundred milliamps without creating much extra heat. secondary windings. We used the Altronics M5525C, a 25+25V AC, 300VA transformer. This design is very versatile and will happily operate from anything above 15V. The only essential feature is that the secondary windings are not internally joined. Note that the Altronics transformer is wound for 240V AC mains. Our lab sees 230V AC most of the time, in line with current Australian mains standards. So the output voltage is about a volt lower than spec under ‘normal’ conditions. As a result, at very high currents (above 4.7A), the power supply loses regulation at 24.5V. If you want to avoid this you can wind a few extra turns on the transformer to boost the output a volt or so, or choose a different transformer. For most uses, this limitation will never affect you. We have set a current limit for the power supply at 5A per rail and a maximum output voltage of 25V DC. It is important that when you set up the controller that you enter the correct VA rating for the transformer, and its nominal AC voltage. These are used to calculate current limits that are used to protect the transformer from being overloaded. Transformer selection Control circuit The ideal transformer is a 300VA unit with two independent 25V AC This control circuit has been used in several previous projects, starting siliconchip.com.au Controlling the Regulator Module via SPI A DAC write is used to set the output voltage (channel 1) and the current limit (channel 2). First, drive chip select (CS) low for the selected DAC. Then write 0x7000 (28,672 decimal) + 0x0 to 0xFFF (4095 decimal) as the DAC value for the desired voltage. Or write 0x9000 + 0x0 to 0xFFF to set the current limit. After the write, bring CS high again. For example, to set the output to 5.1V: drive the DAC’s CS low, send 601 to channel 1 (so write 0x7259), then take CS high again. Remember that many microcontrollers require you to read the SPI buffer after you write an SPI word. To read the actual voltage and current for each channel, you need to query the ADC. Keep write speeds reasonable; we have used 100kHz, which allows good accuracy on the ADC, and provides easy setup and hold times. Drive CS low for the selected ADC, then send the read command byte: 0x01. Make sure you wait until the whole SPI byte has been sent from your micro to the ADC, then read a byte and discard it. Next, send the read command 0xA0 for voltage, or 0xE0 for current. Make sure you wait until the whole SPI byte has been sent from your micro to the ADC, then read and store the next byte. Write 0x00 to the ADC, wait until the whole SPI byte has been from your micro to the ADC, then read another byte. The last byte read contains the lower 8 bits of the result, while the upper 4 bits of the 12-bit result are in the lower 4 bits of the previous byte read. So, for example, in the C language you can compute the read value as: unsigned short value = (byte1 & 0x0F)*256 + byte2; Australia's electronics magazine with the DSP Active Crossover & 8-channel Parametric Equaliser (MayJuly 2019 issues; siliconchip.com.au/ Series/335). As in that project, the interface is displayed on a monochrome graphical LCD. That LCD, the front panel control board and the regulator boards are wired back to the control board via ribbon cables and multi-pin headers. The control circuit is reproduced here; see Fig.8. Microcontroller IC11 is a PIC32MZ2048 32-bit processor with 2MB flash and 512KB RAM, which can run up to 252MHz. It has a USB interface brought out to a micro type-B socket, CON6, although we haven’t used it in this project – it’s there ‘just in case’ for other projects. The PIC is also fitted with an 8MHz crystal for its primary clock signal (X2). Provision is made on the PCB (and shown in the circuit) for a 32.768kHz crystal for possible future expansion, but it is not used in this project and can be left out. There is also a serial EEPROM which is used to store the calibration values, voltage and current settings. This must be fitted. The front panel controls are wired back to 10-pin header CON11 (and on to PORT E of the micro). The regulator board(s) connect to 10-pin header CON7. The other headers and connectors are unused in this project. 5V February 2022  33 A partial kit will be available Despite the current component shortages, we will be offering a partial kit for this design along with the PCBs – see page 101 for details. 34 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.8: this CPU control circuit has been used in several projects. It includes a powerful 32-bit PIC32MZ processor, an 8MHz core crystal, an optional 32768Hz timekeeping crystal, 5V & 3.3V regulators, an SPI EEPROM, plus numerous connectors. The timekeeping crystal and 5V regulator are not needed for this project. CON7 connects to the regulator boards, CON11 to the front panel control board and CON12 to the LCD; the other connectors are unused. siliconchip.com.au Australia's electronics magazine February 2022  35 power for this board is applied across pins 10 & 9 of CON7 from one of the regulator boards. The user interface is displayed on a graphical LCD, wired up to CON8 on the micro board via a ribbon cable. This provides a reasonably standard 8-bit parallel LCD drive interface. The eight LCD data lines (DB0-DB7) are driven from a contiguous set of digital outputs of IC11 (RB8-RB15). This allows a byte of data to be transferred to the display with just a few lines of code and minimal delay. The other LCD control lines are driven by digital outputs RB4, RB5, RB6, RD5, RF4 and RF5 and the screen is powered from the 5V rail, with the backlight brightness set with a 47W resistor. The LCD contrast is adjusted using trimpot VR1, which connects to CON8 via LK2. CON23 is a somewhat unusual in-circuit serial programming (ICSP) header. It has a similar pinout to a PICkit 3/4 but not directly compatible; it’s designed to work over a longer cable. Since each signal line has at least one ground wire between it, signal integrity should be better. Jumper leads could be used to make a quick connection to a PICkit to program the microcontroller the first time. Or you could attach a 10-pin IDC connector to the end of a ribbon cable and then solder the appropriate wires at the other end of the cable to a 5-way SIL header as a more permanent programming adaptor for development use. There are two regulators on the board, but REG3 is not needed in this case because the 5V rail is generated on the regulator board. REG2 is required, though, to produce a +3.3V rail from the 5V rail via schottky diode D15, powering microcontroller IC11. LED2 is connected from LCD data line LCD0 to ground, with a 330W current limiting resistor, so it will flash when the LCD screen is being updated. The front panel for this power supply (shown enlarged for clarity) is built on a PCB measuring 74.5 x 23mm and is populated with passive components, plus two rotary encoders and two buttons. All these switch contacts have 22nF debouncing capacitors across them; there might not appear to be one across switch integrated into RE2, but it is in parallel with the other one, so they share one debouncing cap. The Gray code outputs of rotary encoder RE2 have pull-up resistors, while those of RE1 do not, because the micro can provide pull-up currents on those pins. All the switch contacts are wired either between a micro pin and GND, or a micro pin and the +3.3V rail, depending on what’s most convenient for the software to deal with. Those connections go back to the micro pins via CON1. Next month We have finished describing how the Intelligent PSU operates. Next month, we will present the details of the three main PCBs, describe how to assemble them, mount them in the case, and wire up and test the unit. We’ll also show you how to use the device and control it via the LCD graphical interface and front panel SC controls. Front panel board Fig.9 shows the circuit of the front panel board specific to this project, and there isn’t a whole lot to it. Rotary encoders RE1 & RE2 generate “Gray codes” by closing switch contacts between pins 1 & 3 and pin 2 (common). They also have integrated pushbutton switches that connect pins 4 & 5 when pressed, plus there are two separate momentary pushbutton switches, S1 & S2. 36 Silicon Chip Fig.9: the front panel circuit includes two rotary encoders with integrated pushbutton switches, plus two extra buttons and a handful of debouncing capacitors. 10-pin header CON1 on this board is wired back to CON11 (in Fig.8), so the micro can sense when the encoders are rotated and buttons are pressed. Australia's electronics magazine siliconchip.com.au Prices end February 28th. Make Build It Yourself Electronics Centres® & Build D 0874 NEW! All the gear you need to keep powered up & creating. 275 $ prints! Ideal for small, precise SafeGuard 1000VA UPS New model from PowerShield featuring 8 protected sockets and 4 with power backup from the internal battery. Ideal for safe shutdown of office equipment, POS machines, NAS boxes and PCs. Up to 135aH st capacity. Ju 65mm thick! 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B 0092 Find a local reseller at: altronics.com.au/storelocations/dealers/ Using Cheap Asian Electronic Modules By Jim Rowe Three low-noise HF-UHF Amplifiers Left-to-right: module one (1MHz-3GHz), module two (5MHz-6GHz), module three (50MHz-4GHz) All three of these low-cost wideband HF-UHF amplifier modules claim to provide 20dB of gain, over frequency ranges of 1MHz to 3GHz, 5MHz to 6GHz and 50MHz to 4GHz. They vary mainly in terms of size, shielding, supply voltage and price. T he 1MHz to 3GHz module is the largest, with a PCB measuring 50 x 50mm. It has SMA input and output connectors at each end and a mini 2-way terminal block for the power connections at the rear. The amplifier circuitry is inside a 32 x 30 x 6.5mm shielding box in the centre of the PCB, visible in the photos. There’s also a small power indicator LED at upper right (D2). This module is currently available online from Banggood (code 1238137; siliconchip.com.au/link/ab8q) for around $15, plus $7.50 for postage. That makes it the cheapest of the three modules we’re describing. It has been designed to run from a 12V DC supply, with a stated current drain of 75mA. It has a maximum input level of 0dBm, and the maximum output power is said to be +19.5dBm (approximately 100mW). While it’s described on the PCB as a low-noise amplifier (LNA), no noise figure (NF) is given. I could find no information regarding its internal circuit, or the active devices inside. But when I powered it up and checked its gain with my Signal Hound SA44B spectrum analyser and TG44A tracking generator (controlled using their Spike software), the results were quite impressive, as you can see from the red trace in Fig.1. The gain measured about 21dB at the low end, drooping fairly smoothly siliconchip.com.au to 13.5dB at 3GHz, and then wobbling up and down a bit before falling to 3dB at about 4GHz. That’s not bad for a lowcost module with a rated frequency range of 1MHz to 3GHz. I don’t have the equipment to measure the NF, but I was able to use the SA44B with Spike to measure the module’s DANL (distortion & noise level) at 1GHz and 3GHz with a 50W input termination. I then compared these measurements with the DANL of the SA44B alone (50W input termination) at the same frequencies. The results showed a rise in the DANL from -153dBm to -138dBm at 1GHz (+15dB), and a rise in DANL from -149dBm to -139dBm at 3GHz (+10dB). This is perhaps not good enough to qualify the module as an LNA, but quite acceptable for many applications. I also checked the module’s current drain from the 12V supply, and it measured precisely 75mA. So overall, this module is a good choice if you only need to amplify signals at frequencies up to about 3GHz, and would be happy with the gain curve shown in red in Fig.1, the maximum output of 100mW and the modest noise performance. It would likely provide a good way to boost the output from a drone control transmitter, for example. The second module The next amplifier module is physically smaller, with a PCB measuring 33 x 24.5mm and again with SMA input and output connectors at each end. This module doesn’t come with a mini two-way terminal block fitted to the PCB for power, but there are two Module one is the largest of the three measuring 50 x 50mm, it uses a twoway screw terminal block for the power connection. Australia's electronics magazine February 2022  41 Fig.1: the gain curve for the three modules – red (1MHz-3GHz), blue (5MHz6GHz), green (50MHz-4GHz). pads at top centre ready to mount such a block (on either side of the PCB). The amplifier circuitry is again inside a shielding box in the centre of the PCB, measuring 18.5 x 14.5 x 3.5mm. There is no power indicator LED. This module is available from Banggood (code 1119141; siliconchip.com. au/link/ab8s) for around $21.50, plus $7.50 for direct mail shipping from China. It is designed to operate from a 5V DC supply, with a nominal current drain of 85mA, so it can be powered from a standard USB power pack. Again, it is claimed to provide a nominal gain of 20dB, this time from 5MHz to 6GHz, with a maximum input level of 0dBm. The maximum output power is stated to be +21dBm (around 120mW) at the 1dB compression point. This module isn’t claimed to be an LNA. I could find very little information regarding this module’s internal circuitry, apart from the suggestion that it’s based on a Qorvo SBB5089Z InGaP MMIC (monolithic microwave integrated circuit) amplifier device. This comes in a 3- or 4-pin SOT-89 package, and in the data sheet, Qorvo gives the circuit for an evaluation board which I have redrawn in Fig.2. That is a pretty standard MMIC circuit, and probably close to what is inside this module. When I powered it up, the first thing I checked was its current drain from a 5V power pack. This turned out to be 36mA, less than half the claimed nominal value of 85mA. However, the current might increase when the module is delivering its maximum output power of +21dBm. Next, I checked its gain with my Spike test setup. This combination only goes up to 4.4GHz, but the result is shown in blue in Fig.1. As you can see, it was pretty respectable over this range, varying between about 13.5dB and 16.5dB with an average value of around 15dB. The Qorvo data sheet for the SBB5089Z suggests that it probably extends to provide at least 14.5dB of gain at 6.0GHz, but I can’t confirm that. After this, I used the SA44B with Spike to measure this module’s DANL at 1GHz and 4GHz with a 50W input termination, and again compare them with the figures for the SA44B alone, at the same frequencies. The results this time showed a rise in the DANL from -153dBm to -140dBm at 1GHz (+13dB), and a rise from -140dBm to -132dBm at 4.0GHz (+8dB). The second module is the smallest and most sparse of the three. It only has two unused pads for the power connection. 42 Silicon Chip Australia's electronics magazine This is a little better than the results for the first module, but still perhaps not good enough to be regarded as an LNA, even though it would be quite acceptable for many applications. So this module would probably be a good choice if you want to amplify signals at frequencies above 3GHz, up to about 6GHz, and would be happy with the gain curve shown in Fig.1 (blue trace) and its ability to deliver up to approximately 120mW. The noise performance is not too bad, either. On the down side, this module will cost you about $6 more than the first one, and doesn’t come with a terminal block already fitted. But its smaller size might make it easier to fit into equipment like a drone control transmitter. The third module The final amplifier module we’re looking at differs from the other two as it is completely housed in a cast aluminium case, so it’s fully shielded. The case measures 42 x 32 x 12mm, with the SMA input and output connectors at each end and an insulated feed-through pin fitted to the rear of the case for its power input. A small solder lug held by the feedthrough pin’s external body allows for the connection of the negative power lead. This module is available from Banggood (code 1443559; siliconchip.com. au/link/ab8t) for around $31 plus $7.50 for shipping from China, which makes it the dearest of the three. Like the second module, this one operates from a 5V DC, with a nominal current drain of 90mA. So again, it can be powered from a standard USB power pack. The nominal bandwidth is 50MHz to 4.0GHz, with a typical gain of 19dB and a maximum output power of +22dBm (about 150mW) for 1dB compression at 2GHz. The maximum input signal level is stated as less than +10dBm, or 10mW. The noise figure is quoted as typically 0.6dB, suggesting that this module is intended for use as an LNA to boost the sensitivity of receivers and test equipment like spectrum analysers. I measured its current draw at 82mA, just a little lower than the claimed value, but as before, this was when the module’s input was terminated with 50W. It will likely rise when the module is handling an RF signal. siliconchip.com.au Fig.2: little information is given on the 5MHz-6GHz module, so the circuit shown is based on a Qorvo SBB5089Z-based evaluation board. It should be close to what the module is comprised of. Next, I checked its gain, as before with the SA44B/TG44A/Spike test setup. The result is shown in green in Fig.1. The gain is highest at around 50MHz (27dB), drooping down to around 15dB at 1.32GHz, 10dB at 2.2GHz and 2dB at around 4.0GHz. This is a little disappointing, considering the amplifier is claimed to have a gain of 18dB and a bandwidth of 50MHz to 4.0GHz, but it would still be quite useful if you are mainly dealing with signals below 1.8GHz. As noted earlier, I don’t have the equipment to measure the NF directly. But when I used the SA44B spectrum analyser with Spike to compare the amplifier’s DANL at 1GHz and 4GHz against that of the SA44B alone (in each case with a 50W input termination), the results were noticeably better than for the other two modules. At 1GHz, the DANL rose from -153dBm to -143dBm (+10dB), while at 4GHz the DANL rose from -140dBm to -135dBm; a rise of only 5dB. So it might be a bit lacking in terms of gain and bandwidth, but it probably does qualify as an LNA. The bottom line Based on these test results, each module has strengths and weaknesses. The best choice depends on the gain and bandwidth you need, the kind of application you want to use the amplifier for and how much you can pay. For example, the second module offers the best gain/bandwidth performance, coupled with a reasonable noise performance and the ability to provide an output of around 100mW. It’s also not that much more expensive than the cheapest (first) module, so it is probably the best choice for applications like boosting the output of a drone control transmitter. But the first module provides much the same performance at frequencies below 3GHz, so with its lower price, it is an attractive choice for the same kind of application. siliconchip.com.au Suppose you are mainly interested in signals below about 1.8GHz and noise performance is critical, such as boosting the signals going into a receiver or spectrum analyser. In that case, the third module is probably the best choice, despite its significantly higher price. Using these amps with the LTDZ V5.0 spectrum analyser You might recall that towards the end of my review of the low-cost LTDZ V5.0 spectrum analyser (January 2022; siliconchip.com.au/Article/15178), I mentioned that I would be testing this type of amplifier module to see whether they could be used to improve that device’s sensitivity. That’s because the LTDZ analyser has a relatively high noise floor of about -77dBm, meaning that any signals lower than this (or possibly even slightly higher) would essentially be ‘lost in the noise’. An LNA could be used to boost these signals well above the noise floor, allowing them to be distinguished and measured. After checking out the three modules reviewed here, I decided that the second and third (LNA) modules would be the best candidates for this job, so I tested both. First, I inserted the amplifier modules in front of the LTDZ analyser, with their inputs terminated with 50W, and ran some plots to see if their noise affected its noise floor. They did not; the noise floor measured -77dBm with or without both amplifiers. The next set of tests involved feeding a -80dBm CW signal from my signal generator through the relevant amplifier module and into the LTDZ analyser at four frequencies: 1GHz, 2GHz, 3GHz and 4GHz. Without the amplifier, I would expect a flat line at -77dBm. Any peaks above this would mean that the amplifier was providing some benefit. With the second (cheaper) module, I saw two bumps of about 7.5dB on either side of 1GHz in the first test, about 7dB on either side of 2GHz, about 4dB on either side of 3GHz, and about 2.5dB on either side of 4GHz. So this module does give the LTDZ analyser a modest increase in sensitivity up to 4GHz, without affecting its noise floor. The reason why there were two bumps rather than one peak is explained in the main body of the article linked above. It’s a property of the analyser’s unnecessarily broad resolution bandwidth, not a failing of the amplifier module. I also tested the more expensive LNA and got two bumps about 8dB high on either side of 1GHz, two much smaller bumps (<1dB) on either side of 2GHz, two similarly small bumps on either side of 3GHz, and no discernible bumps at all around 4GHz. I must conclude then that the second, less-expensive amplifier module with a stated frequency range of 5MHz to 6GHz is the best option for improving the sensitivity of the LTDZ analyser, and does give a helpful improvement in sensitivity, of about 10.5dB at 1GHz, 10dB at 2GHz, 7dB at 3GHz SC and 6.5dB at 4GHz. The last amplifier module is housed inside a cast aluminium case. There’s an insulated pin fitted to the edge of the case which is used for power, along with a solder lug adjacent for the negative power lead. Australia's electronics magazine February 2022  43 Cooling Fan Controller M This board controls up to three cooling fans, switching them on at a preset temperature and ramping their speed up as it increases, preventing overheating while minimising noise. It can also protect loudspeakers from damage while also preventing power switch-on and switch-off thumps. It isn’t just useful for amplifiers; this board is ideal for any device that needs cooling fans. SPECIFICATIONS & any devices need forced-air cooling when working hard but do not need fans to be running (or perhaps only running slowly) when they are idle or under light load conditions. This includes large power supplies, audio amplifiers, motor speed controllers – just about anything that gets hot under load. Even devices for which passive convection cooling is adequate can have their lifespans extended if they are fitted with fans that switch on once things start heating up. Those fans might only need to run during summer, when ambient temperatures are high. Ideally, the fans stop or spin slowly when only a bit of cooling is required, to prevent the annoyance of constant fan noise (and dust collection). One simple method to provide cooling fans is to have a thermostat connected to the heatsink that switches on the fan(s) whenever the temperature exceeds a certain threshold. But, when switched on, the fan(s) run at full speed and make considerable noise. That is especially bad for an audio amplifier as it can ruin the listening experience. A less obtrusive method is to adjust the speed of the fan(s) so that there is a gradual rise in speed as temperature rises. Once the heatsink passes a certain temperature, the fan(s) run slowly to start with; this usually provides DC offset reaction time: 75ms Temperature setting range: 0-100°C (273-373K) Fan PWM control frequency: 25kHz Over-temperature hysteresis: 4°C (4K) Amplifier DC offset detection: < -2V or > +2V AC loss detection threshold: 9V AC Relay power-up delay: typically 6s after fans are detected Fan disconnect/failure audible alarm: 264ms burst of 3.875kHz at 1Hz Trimpot voltage/temperature conversion: 10mV/K (2.73V = 273K = 0°C) Over-temperature or DC fault audible alarm: 264ms burst of 3.875kHz at 0.5Hz NTC thermistor range: 0-100°C (responds to highest temperature when two are used) Trimpot adjustments: three – fan switch-on threshold, fan speed range & over-temperature alarm 44 Silicon Chip Australia's electronics magazine siliconchip.com.au Loudspeaker Protector By John Clarke sufficient air movement to bring the amplifier back to a lower temperature. If the temperature continues to rise, the fan will run at a progressively faster rate, up to full speed. By choosing the right fans, they will be extremely quiet at slow speeds, and the temperature can usually be controlled without making noise. Here, we’re using PWM-controlled computer fans with brushless motors. They are readily available at a range of prices, start at just a few dollars each, and generally are silent at low speeds. Some can still move a lot of air at full speed, though. As this board is especially suitable for power amplifiers, we’ve added several extra features to it. Power amplifiers should include loudspeaker protection to disconnect the speakers if the amplifier fails. Power amplifier failures can destroy the speakers and even start a fire, especially if it’s a highpower amplifier. That’s because one common failure mode involves one or more of the output transistors failing short-circuit, possibly resulting in the entire supply rail DC voltage (up to perhaps 80V) being applied to the speaker. Given their low DC resistance, any loudspeaker connected will be quickly destroyed by this. At best, the loudspeaker coil will burn out without any further damage. But a worse scenario is that the speaker cone could catch fire, burning the speaker box and anything else that’s in the vicinity. The built-in Loudspeaker Protector Controller averts speaker damage by disconnecting the loudspeaker from the amplifier should the amplifier exhibit this type of fault. Since there is the ability to disconnect the loudspeaker from the amplifier, we can provide de-thumping features. At power-up, an amplifier can generate a brief, uncontrolled voltage excursion until its power supply stabilises. This will produce a thump sound from the loudspeaker(s). We eliminated it by adding a delay from power-up before connecting the loudspeaker. A similar thump can occur at switch-off. Therefore, we disconnect the loudspeaker as soon as the AC supply is lost, before any voltage excursions from the amplifier can cause a thump sound. PWM fan control Our Controller works with 4-pin PWM fans. These fans have internal pulse-width modulation (PWM) speed control, where the duty cycle of the waveform at a control pin is adjusted to change the fan speed. At low duty cycles, the fan runs slowly and increases in speed as the duty is increased. Our Controller can drive up to three fans. PWM fans have four connections: two for power (+12V and 0V), one for speed adjustment and one for speed feedback (RPM sensing). These are labelled as the Control and Sense terminals. The sense terminal produces two pulses per fan revolution when the terminal has a pull-up resistor connected to a 5V supply. These pulses provide information about the speed of the fan, and in particular, whether the fan is running. If the pull-up resistor is not included, the fan will always run at full speed when power is applied. The fourth pin is the Control terminal and is for the PWM signal to set the fan speed. The applied PWM signal only needs to supply a small amount of current as it does not directly drive the fan motor. Internally, each fan includes a motor driver circuit that operates based on the PWM signal applied. Scope 1 shows the 25kHz PWM signal that is applied to the fan. The top yellow trace is a low duty cycle (16.7%) waveform, and when this is applied, the fan runs slowly. The lower white trace shows the PWM waveform when the duty cycle is increased to around 70%. With this higher duty FEATURES Suits mono & stereo audio amplifiers, or any other device which needs thermal fan control Onboard loudspeaker protector controller with de-thumping at switch on & off Loudspeakers are disconnected with over-temperature fault One or two thermistors for temperature sensing PWM control for one to three cooling fans Over-temperature and fan failure alarms Temperature control range of 0-100°C Fan detect and relay-on LED indicators siliconchip.com.au Australia's electronics magazine February 2022  45 cycle, the fan runs faster but still not at full speed. That requires a continuously high signal. You can find more details on this style of PWM fan control in the PDF document at siliconchip.com.au/link/ abc3 Features As we wrote earlier, this board is applicable to a wide range of situations, but as it’s ideal for audio amplifiers, the following description will concentrate on that usage. The Controller can be used with a mono or stereo amplifier with one or two heatsinks. The loudspeaker switching relay is selected to suit the amplifier power rating; it will need a high current rating for use with highpower amplifiers (100W or more). This is discussed in a section below titled “Relay choices”. Any relay that is used must have a double-throw contact (ie, SPDT or DPDT). We will describe why that is necessary a bit later. The Controller is presented as a bare board and is designed to be housed within the amplifier enclosure. It runs from a 12V DC supply, with a current draw possibly approaching 750mA depending on the type of fan and how many are used. While this 12V could be derived from an existing amplifier supply, a separate supply is probably warranted, especially when more than one fan is used. Note that you can use the Controller without using all the features. You can leave one thermistor disconnected if you don’t need both, or both can be disconnected if you are only using the loudspeaker protection and dethumping features. If you don’t want to connect the AC detection input for dethumping, it can be connected instead to the 12V DC input. If you aren’t using the loudspeaker protection features or only have a single channel to protect, connect the unused sense inputs to the 0V terminal. Finally, if you want to use the speaker protection/dethumping features but not the fan control, use a jumper shunt to bridge pins 3 and 4 of one of the fan connectors. That prevents the Controller from showing a ‘fan disconnection/failure’ error that would otherwise prevent operation. Circuit details The entire circuit of the Controller is shown in Fig.1; it is based around microcontroller IC1. It monitors several inputs, including two NTC thermistors for temperature measurement, two amplifier output voltages and an AC input from a power transformer. The AC input is used to sense when the amplifier is switched on or off. It also has three analog inputs connected to the wipers of trimpots to set the temperature control parameters, plus three frequency-sensing digital inputs for monitoring the fan speeds (RPMs). IC1 produces output signals for driving the alarm piezo, LED indicators for each fan and a relay driver/ LED indicator. Under normal circumstances, the relay will switch on after about six seconds from power-up. This connects the amplifier output(s) to the loudspeaker(s). In more detail, the NTC thermistor inputs are at CON5. Thermistor TH1 connects to the analog input at pin 7 of IC1 and pin 8 for TH2. Each thermistor connects between ground (the 0V rail) and the input pin with a 10kW pull-up resistor to the +5V supply. As the name suggests, negative temperature coefficient (NTC) thermistors decrease in resistance with increasing temperature. For the thermistors used, the resistance at 25°C is 10kW, so in conjunction with the 10kW pull-up resistor, they give 2.5V DC at 25°C. As temperature rises, this voltage falls. The resistance and hence voltage-versus-­ temperature is not linear; it follows an exponential curve. The thermistor beta value is 3970, which allows us to calculate the expected resistance and thus voltage at various temperatures. You can use an online calculator like the one at siliconchip.com.au/link/ aaj1 to calculate the expected values at any temperature. We have stored a pre-calculated table of values from 0 to 100°C within the memory of microcontroller IC1. IC1 converts the voltages to 8-bit digital values using its internal analog-­ to-digital converter (ADC) and then Scope 1: two PWM fan control waveforms, with a low duty cycle at the top in yellow (so the fan runs slowly) and a high duty cycle below in white, for a higher fan RPM, but short of full speed. Fig.1: there isn’t a great deal to the ► Controller circuit since most of the functions are handled by the firmware (software) loaded into microcontroller IC1. At upper right there is signal conditioning so the amplifier output signals can be fed into the micro’s ADC, with the relay driving circuitry below. The components at lower right are for the PWM fan interface while the thermistor inputs, adjustment trimpots and indicator LEDs at left. 46 Silicon Chip Australia's electronics magazine siliconchip.com.au uses the lookup table to convert them to temperatures. Temperatures below 0°C are treated as 0°C and similarly, temperatures over 100°C are treated as 100°C. When two thermistors are connected, the highest temperature of either thermistor is used. That way, for a stereo amplifier with two heatsinks, the fan speed and other aspects will be determined by whichever is hotter. If only one thermistor is used, the unused input is left open, and the pull-up resistor holds the input at 5V. That ensures that the unused input will have a lower temperature reading. Trimpot adjustments Trimpots VR1, VR2 and VR3 are for setting how you want the fans to be controlled. The voltage setting at siliconchip.com.au the wiper of each trimpot is directly related to temperature in Kelvin (K). A difference in 1K is equivalent to 1°C, but 0°C = 273.15K. So to convert °C to K, simply add 273.15 and to convert K to °C, you subtract that same value. The conversion from voltage to temperature in our circuit is 10mV/K. So a voltage setting of 2.73V sets a temperature of 273K, which is 0°C. For other temperatures, add the °C value required to 273, divide by 100, then adjust for that voltage. For example, for a 50°C setting, you need to achieve 3.23V ([273 + 50] ÷ 100) at TP1, TP2 or TP3. VR1 adjusts the threshold setting, which is the lowest temperature where the fans start running. Test point TP1 can be used to check this setting. The voltage at pin 9 of IC1 is converted Australia's electronics magazine to a 10-bit digital value and then to a temperature value in °C. VR2 sets the temperature range over which the fans run from minimum through to maximum duty cycle. For example, if you set a threshold of 50°C and a range of 10°C (VR2 adjusted for 2.83V at TP2), the fans will start to run at the minimum duty cycle when the thermistor temperature reaches 50°C. The duty cycle will increase linearly as temperature increases, up to and above 60°C, where they will be running at full speed. As VR2 sets a temperature range, you don’t need to readjust VR2 if you change the threshold temperature setting with VR1. VR3 sets the over-temperature alarm threshold, and you can monitor this setting at TP3. Whenever the measured February 2022  47 temperature is above this setting, it will set off the piezo alarm and switch off the relay(s) that connect the loudspeaker(s). The speaker disconnection allows the amplifier to cool off as it is no longer loaded. When this alarm goes off, the fans are set at maximum speed (if they aren’t already) to cool down the amplifier, and regular operation does not resume until the temperature drops by 4°C. Typically, this over-temperature setting would be set at least as high as the threshold temperature plus the speed range. Amplifier connections The Controller monitors the AC side of the amplifier power supply as well as amplifier output offset voltage. These are wired to CON4; the AC supply voltage goes to IC1’s AN4 analog input at pin 16, while the amplifier outputs go to AN5 (pin 15) and AN6 (pin 14). AC detection is done by half-wave rectifying the voltage from the transformer’s secondary. Diode D5 rectifies the AC, and the resulting voltage is fed through a low-pass filter comprising a 47kW resistor and 2.2μF capacitor. Without any AC voltage, the AN4 analog input at pin 16 of IC1 is held at 0V via the 47kW pull-down resistor. When at least 9V AC is applied, the voltage at pin 16 will exceed 2.5V. This voltage is limited to 4.7V by zener diode ZD3. The time constant for the filtering has been chosen to ensure sufficient ripple voltage is removed from the rectified AC while minimising the detection period for loss of AC. The amplifier outputs are monitored via pairs of 47kW resistors which limit the current fed into the circuit. They also act to level-shift the output signals from the amplifier to an average DC level of 2.5V. Two 10μF capacitors, in combination with these resistors, filter out the AC signal from the amplifier, leaving only the DC level. We have set the speaker output over-voltage detection threshold to be 2V on either side of 0V. Since the pairs of 47kW resistors divide the signal level by two and add 2.5V, the normal range of voltages at pins 14 & 15 of IC1 is between 1.5V and 3.5V. Anything outside this indicates a DC fault in the amplifier. Note that the 10μF capacitors are only truly effective at removing the AC for signal frequencies above about 100Hz. Below that, more and more of the AC voltage will be present at the micro inputs. The AC voltage level is also dependent on the amplifier output level, so at low frequencies close Scope 2: the yellow trace shows a high-level 20Hz signal from a 500W amplifier and the cyan trace below shows the signal at pin 14 of IC1. While this is an extreme case, it demonstrates how the signal can go outside the 2V detection window (dashed lines) even without a DC fault. Therefore, the software has been designed to detect and ignore this case and only respond to genuine DC faults. 48 Silicon Chip Australia's electronics magazine to 20Hz, it can exceed the offset detection threshold, especially with a highpower amplifier. This is shown in Scope 2. The top yellow trace is the output from a 500W amplifier at 20Hz, with an RMS voltage of about 49.1V and 142V peakto-peak. The lower blue trace is the waveform as presented to the AN5 input of IC1. The AC voltage is 2.36V peak-to-peak, riding on a half-supply DC level of 2.56V. The horizontal lines represent the 1.5V and 3.5V thresholds. This shows that at low frequencies and high amplifier output levels, the waveform can exceed the offset threshold limits at the waveform peaks. Any standard offset detector circuit using transistors to detect the offset will switch off the relay whenever the AC signal exceeds the limits. To circumvent this, the filtering would need to be increased by using a capacitor larger than 10μF. However, increasing the filter capacitor will also increase the delay from the initial detection of offset from the amplifier and the relay switching off. This is not ideal as the speakers need to be disconnected by the relay as quickly as possible if there is a fault. Instead, we use software logic to determine whether there is a DC fault or just a high-level AC voltage. The waveform is sampled about 1000 times per second, and whenever the offset voltage threshold is exceeded, a 75ms timer is started. If the detected offset voltage drops to within the offset voltage threshold boundaries during this period, there is no DC offset, so the relay is not switched off. A genuine DC offset would continue being detected as exceeding the offset threshold. If DC offset is still seen at the end of the timeout period, it will switch the relay off and the alarm will sound. Zener diodes ZD1 & ZD2 limit the voltages across the possibly 16V-rated capacitors. This can happen if the circuit is connected to an amplifier when IC1 is not inserted into its socket. When IC1 is in-circuit, the internal protection diodes will limit the voltage at the input to 0.3V above the 5V supply and 0.3V below 0V. ZD1 & ZD2 provide extra protection by limiting the voltages across the capacitors to a maximum of 15V and -0.6V. The 2.2kW series resistors further limit the current to the protection diodes within IC1. siliconchip.com.au We are using a 15V zener rather than 4.7V despite the supply being 5V due to the leakage current. A 15V zener diode with up to 5V applied will only conduct about 0.05μA compared to 100μA or more for a 4.7V zener diode at only 1V. That leakage current would drastically affect the half-supply voltage set by the pairs of 47kW resistors that only cause a 53μA current flow under quiescent conditions. Note that if one of these two inputs is not connected to an amplifier (eg, your amplifier has a single channel), that input must be tied to 0V or else it will be detected as a DC fault. Piezo alarm The external piezo transducer for the alarm is driven via the RB6 output of IC1 (pin 11) via a 220W resistor. This resistor is part of a low-pass filter to reduce the harshness and volume to a less piercing level. The filtering utilises the capacitance of the transducer to filter out some of the harmonics from the square wave. The driving frequency is around 3.9kHz and is produced in bursts of 264ms every two seconds for both the over temperature and amplifier offset alarms. The fan fault alarm rate is 1Hz. Relays There is the option to connect two relays, RLY1 and RLY2. These are driven in parallel and via transistor Q1. A high level from the RB7 output of IC1 applied to the base of this transistor switches on the relay or relays. Diode D6 prevents high-voltage backEMF excursion when the relay coil switches off, thus preventing damage to the transistor. The amplifier’s positive speaker output connects to the normally open (NO) relay contact of the relay while the plus side of the speaker connects to the relay wiper or common (COM) with the normally closed (NC) contact connecting to the negative speaker output (usually Earth) on the amplifier – see Fig.3. When the relay switches on, the amplifier output is connected to the speaker’s positive terminal. If the amplifier is working correctly, the contacts will disconnect the speaker without any problems when the relay is switched off. However, it is not so easy when there is an amplifier fault and the speaker output from the amplifier has a high positive or negative DC voltage. siliconchip.com.au Parts List – Fan & Loudspeaker Protector 1 double-sided plated-through PCB coded 01102221, 95 x 74mm 1-3 4-pin PWM fans to suit heatsink dissipation requirements● 1-2 lug-mount NTC thermistors, 10kW at 25°C, beta 3970 (TH1, TH2) [Altronics R4112] OR 1-2 dipped NTC thermistors with separate securing clamps (TH1, TH2) [Jaycar RN3440] 1-2 high-current 12V SPDT or DPDT relays (see text) 1 piezo transducer (PIEZO1) [Jaycar AB3442, Altronics S6109] 3 4-way polarised PWM fan headers, 2.54mm pitch (CON1-CON3) [SC6071, Digi-Key WM4330-ND, Mouser 538-47053-1000] OR 3 4-way polarised headers, 2.54mm pitch, modified (CON1-CON3; see text) [Jaycar HM3414, Altronics P5494] 4 3-way screw terminals, 5.08mm pitch (CON4) 2 2-way screw terminals, 5.08mm pitch (CON5) 4 6mm-long M3-tapped spacers 5 M3 x 6mm panhead machine screws 1 M3 hex nut 4 PCB stakes/pins (optional) 1 20-pin DIL IC socket (optional; for IC1) ● We used EZDIY 120mm PWM fans purchased from Amazon for our prototype (search for B07X25CJT5). These are inexpensive (we paid $23 for three) and quiet, although they are not the most powerful we’ve tested. Try Corsair ‘maglev’, Noctua or BeQuiet 4-pin PWM fans for applications that require faster air movement or higher pressure. All computer stores should sell suitable fans. Semiconductors 1 PIC16F1459-I/P programmed with 0110222A.HEX, DIP-20 (IC1) 1 7805 5V 1A linear regulator, TO-220 (REG1) 1 BC337 500mA NPN transistor, TO-92 (Q1) 4 3mm high brightness red LEDs (LED1-LED4) 3 1N5819 40V 1A schottky diodes (D1-D3) 3 1N4004 400V 1A diodes (D4-D6) 2 15V 1W zener diodes (ZD1,ZD2) 1 4.7V 1W zener diode (ZD3) Capacitors Resistor Colour Codes 2 100μF 16V PC electrolytic 2 10uF 16V PC electrolytic 1 2.2μF 16V PC electrolytic 6 100nF MKT polyester Resistors (all 1% 0.5W axial metal film) 6 47kW 5 10kW 3 2.2kW 3 1kW 1 470W 1 220W 3 10W 3 10kW top adjust multi-turn trimpots (VR1-VR3) Because of the high DC voltage, trying to break the speaker connection by opening the contacts can cause an arc to develop, and current continues to flow through the speaker. This is where the NC contact comes into play. This contact closes to short out the speaker, typically breaking any arc. If the arc remains and current continues to flow through the relay, the amplifier DC supply fuse will blow. Fan control There is considerable logic involved Australia's electronics magazine in driving the fans. This is because many PWM fans require a minimum duty cycle to be applied before they spin. Specifications for these fans give a minimum figure of 20% duty cycle, although most will run at lower duty cycles than that. In fact, the fans we used to test our prototype run at a slow 540rpm when the duty cycle is 0%. We believe this is a feature to improve the LED backlighting on the fan blades, so they become a blended wall of light as the blades spin. February 2022  49 Non-LED-lit fans are likely to stop at 0% duty cycle. (We didn’t look specifically for the LED lighting feature, it was just ‘part of the package’ for these low-cost but otherwise good fans.) The fan(s) connect to CON1-CON3, and at least one fan needs to be connected for the circuit to work. However, the circuit can be tricked into believing a fan is connected with a bridging shunt between the Control and Sense terminals (pins 3 & 4). Power for each fan is supplied from the 12V supply via a Schottky diode (D1, D2 or D3), and their 12V rails are bypassed with 100nF capacitors. The diodes are for reverse supply polarity protection. The common PWM output from pin 5 of IC1 is applied to each fan’s Control input via a 10W resistor. Pull-up resistors are provided for the Sense pin on each fan, and these pins connect to the RA3, RA0 and RA1 inputs on IC1 so it can check if each fan is running. Indicator LEDs driven via the RC4, RA4 and RA5 digital outputs of IC1 via 1kW resistors show which fan is connected and flash if no fans are connected. The micro determines the minimum duty cycle for the PWM signal that will cause all connected fans to run the first time the circuit is powered up. Once found, this minimum duty and the number and positions of connected fans are stored in flash memory, so the Controller starts up faster subsequently. The stored settings are used, provided the fans run at the stored minimum duty cycle on each power-up. A check to find the minimum duty where all the fans will run is only done again if the number of fans connected changes, the connection position for the fans changes or if one of the fans does not run when the stored minimum duty cycle is applied. The setup procedure first applies PWM signals at about 80% duty cycle to the fans for 10 seconds, then checks which fans register as spinning. At this stage, all fan LEDs will flash at 1Hz. If no fans are detected, an error is indicated by all fan LEDs flashing and the piezo alarm sounds. The relay(s) stay off until a working fan is connected. If fans are found, it determines the minimum duty cycle that will cause all fans to spin. After that, the LEDs associated with any connected fans are lit. The number of fans, their positions 50 Silicon Chip and the minimum duty cycle are stored in memory, and this is indicated by all the lit fan LEDs briefly blinking off. The program then continues with the usual six-second delay before switching the relay(s) on, but only if the checks for temperature, amplifier offset and AC power all pass. Subsequently, when the circuit is powered up, it will start the six-second delay almost immediately, provided the fan connections have not changed. The connected fan or fans are usually detected within one second. Power supply The circuit requires a 12V DC supply which is applied to the fans via reverse polarity protection diodes D1-D3. The supply also goes to 5V for IC1 by regulator REG1 via diode D4, also for reverse polarity protection. The 5V supply also functions as a 5V reference for the trimpots. Construction The Controller is built on a double-­ sided, plated-through PCB coded 01102221 that measures 95 x 74mm. Fig.2 shows the assembly details. Begin by fitting the resistors. There is a resistor colour code table in the parts list, but you should also check each lot using a digital multimeter (DMM) before installation, as the colour bands can be misleading. With these parts in place, mount the diodes, taking care to orientate these as shown in Fig.2. D1, D2 and D3 are 1N5819 schottky types, while D4, D5 and D6 are standard 1N4004 diodes. Zener diodes ZD1-ZD2 are 15V 1W types while ZD3 is 4.7V, 1W. You can fit the optional socket for IC1 now; be sure it is orientated correctly before soldering. Next, insert the capacitors, taking care with the electrolytic types that must be positioned with the longer leads towards the + symbols. Follow assembly with the trimpots. These are all multi-turn types and should be orientated with the screw adjuster positioned as shown. Then install transistor Q1. The four 3-way screw terminal blocks making up CON4 need to be joined first by fitting each side-byside by sliding the dovetail mouldings together. Make sure the wire entry side is toward the nearest edge of the PCB before soldering. Similarly, the two 2-way screw terminals for CON5 must Australia's electronics magazine be connected and mounted with the wire entry to the edge. If you are using standard 4-way polarised headers to connect the fans, rather than the special Molex parts listed, they need to be modified so that you can insert the fan plugs. This involves cutting the polarising backing tab to remove the section behind pins 3 and 4. We used side cutters to snip the plastic out. When mounting CON1-CON3, be sure to orientate these headers correctly, with the polarising tab piece away from the PCB edge. The LEDs can now be fitted, with the longer leads inserted into the anode (A) holes. Mount them such that the tops are about the same level as the adjacent header for LED1-LED3, and the screw terminal for LED4. You can now install PCB stakes/pins at test points TP1-TP3 and TP GND, or simply leave them off and use the multimeter probes directly to the PCB pads. We used a PCB pin at the GND test point but left them off TP1-TP3. Regulator REG1 is mounted horizontally on the board. First, bend its leads to pass through their mounting holes, then secure its tab to the PCB using the M3 x 6mm machine screw and nut, after which the leads can be soldered. Before installing IC1, check the regulator output voltage by applying 12V to CON4’s +12V and 0V terminals. Check that the voltage between the regulator metal tab and the right-hand output pin is close to 5V. Typically, these regulators are well within 100mV of 5V. If the voltage is incorrect, check that the input voltage at the left lead of REG1 is at least 6V. If you got your PIC from our Online Shop, it will come programmed. Otherwise, if you have a blank PIC, download the HEX file (0110222A.HEX) from our website and load it into the chip using a PIC programmer. Now switch off power and mount or plug in IC1, after checking its orientation. Setting up With power applied, adjust VR1, VR2 and VR3 for suitable temperature settings while monitoring the voltages TP1, TP2 and TP3 respectively. We recommend starting by adjusting VR1 to get 3.03V at TP1, giving a 30°C (303K) fan starting temperature. Then set VR2 (Range) for 2.83V at TP2, providing a 10°C ramp range. That way, siliconchip.com.au the fans will be at full speed by 40°C. You can initially set the over-temperature setting for VR3 to 50°C. That’s 323K, so adjust VR3 for 3.23V at TP3. These settings may need adjusting to optimise the way the fan speed varies with temperature. Consider that with a starting temperature of 30°C, the fans will start to run as soon as you power the device up on a hot day if the device is not in an air-conditioned room. On a sweltering day where it reaches 40°C, the fans will run at full speed all the time (which might be necessary!). It depends on the device you are cooling and how sensitive it is to temperature. Keep in mind that, as it’s an external device, the thermistor will be measuring a lower temperature than the semiconductor junctions that are presumably generating the heat. You could raise the switch-on threshold temperature considerably if the device adequately cools via convection when it isn’t running at maximum power; the fans would then only need to run at higher loads and temperatures. When adjusting the range, we don’t suggest you go too much lower than 10°C as the fans will appear to operate in an on/off manner, particularly with a range setting below 2°C. If the temperature cannot be controlled using these settings, or if the fans run at full speed most of the time, you might need more fans (up to three maximum for this Controller), larger fans or fans that run at a higher speed at 100% duty cycle. Keep in mind that there are flow-optimised fans and pressure-optimised fans (with different blade shapes). Fig.2: assembly of the Controller is straightforward; fit the components as shown here, starting with the lower-profile axial parts and working your way up to the taller devices. Watch the orientations of IC1, the diodes (including LEDs), trimpots and electrolytic capacitors. Accuracy Note that temperature setting accuracy is dependent on the 5V supply rail being close to 5.00V. If it is only a few tens of millivolts different, the setting accuracy will not be affected too much. If you need precise temperature settings, you can multiply the required temperature voltage (ie, the 10mV/K value) by the actual supply voltage, then divide by 5. Then adjust the trimpot to get that calculated voltage. For example, if the supply is 4.95V, multiply the required temperature voltage by 4.95 and divide by 5 (or multiply by 0.99 [4.95 ÷ 5]). For example, if you want to set the threshold to 330K (57°C) but the supply voltage siliconchip.com.au Fig.3: here’s a guide on how to connect one of the speaker protection relays. If you have two amplifier channels, you can use a DPDT relay, in which case the wiring is similar but you duplicate the speaker & amp wiring for the second set of relay contacts, and connect the second SPEAKER + terminal to the other AMP1/AMP2 terminal. For two separate SPST relays, do the same but connect the second relay coil back to the other pair of relay terminals on the controller board. Australia's electronics magazine February 2022  51 are also available in smaller sizes like 80 x 80mm or 92 x 92mm, as well as larger sizes like 140 x 140mm. If your device requires lots of cooling, use the largest fans that will fit into its case and check their air movement specification in litres per minute (L/ min) or CFM (cubic feet per minute). Make sure there are ventilation holes in the case so that the air movement is not restricted going past the heatsink fins. Note that if you are not using the fan control section of the Controller, pins 3 and 4 of either CON1, CON2 or CON3 must be bridged with a shorting block. Only one such shunt is required. A single Protector board can control up to three fans, as used in our upcoming 500W Amplifier. is 4.95V, set it to 3.267V (330 × 0.99) instead to get it spot-on. Relay choices The choice of relay depends on the amplifier power and whether you are using the circuit with a mono or stereo amplifier. In all cases, the relay must be a double-throw type. That means having a normally open and a normally closed contact for each pole. For stereo amplifiers up to 200W, you could use the Altronics S4310 12V coil, 10A DPDT contacts cradle relay with their S4318A base, or the Jaycar SY4065 12V coil 10A DPDT contacts cradle relay and SY4064 base. For a mono amplifier up to 200W, you could still use the DPDT relay but parallel the contacts or just use one set. For higher power amplifiers, up to about 600W, you can use the Altronics S4211 12V 30A SPDT relay for a mono amplifier, or use two of them for a stereo amplifier (you can also use the Altronics S4335A). analog electronics like amplifier input stages and preamps, as it may radiate some EMI (although it shouldn’t be too bad as it is shielded). Fan choices There are many 4-pin PWM fans available (mainly designed for cooling computers), and you can choose to use up to three with our Controller, even mixing different types if desired. Typically, larger diameter fans move more air with less noise, as do multiple fans when compared to a single fan. See the parts list for some suggestions. These fans are often available in multi-packs at quite reasonable prices. The most common size for PWM fans is 120 x 120mm, although they Finishing up Mount the board in a suitable spot in your amplifier case using threaded standoffs and machine screws (we’ve specified 6mm spacers to keep it compact, but you could use other lengths). Wire up the power supply, including the AC sense line from the transformer secondary, or short the AC input to +12V if you are not using that feature. Next, wire up the thermistor(s) to CON5 (they are not polarised so can be wired either way around) and the relay(s), piezo transducer and amplifier outputs (if present) to CON4. Plug the fans in, power up the board and check that it behaves as expected. You can heat a thermistor with a hot air gun and verify that the fans start, spin faster, then slow down and stop someSC time after you stop heating it. Power supply choices If your amplifier supply already has a 12V DC rail, you could consider powering this board from it. You need to test how much current it draws with the fan(s) at maximum speed and verify that the amplifier supply can safely deliver that much current. A good alternative is to use a separate enclosed switchmode supply such as the Jaycar MP3296 (or Altronics M8728), rated at 12V and 1.3A (shown above). This is mains-powered, and it should be switched on and off with the same power switch as the amplifier itself. Keep it away from sensitive 52 Silicon Chip Fig.4: if you only need the fan speed control, you can leave off some components as shown. The insulated red wire link is needed so that the AC detection circuitry will allow normal operation whenever power is applied. Australia's electronics magazine siliconchip.com.au Back to work. Think Jaycar. On Sale 24 January - 23 February 2022 449 $ STURDY ALUMINIUM PANEL JUST COLLECT ALL 5! 2995 $ CLUB OFFER GREAT VALUE SAVE $50 Entry Level 3D Printer Large build volume of 220Lx220Wx250Hmm. Resume printing function. Filament auto feeding. Support PLA, ABS, & PETG type filament. TL4432 Jaycar 40th Anniversary Auto-ranging Hobbyist DMM THIS MONTH'S CLUB OFFER: Pocket sized 2000 count auto-ranging multimeter. 600V AC/DC, 200mA AC/DC, continuity & diode tester. Leads included. Cat III 300V / Cat II 600V. QM1528 FREE* Pocket Protector & Pencil In-store only. CONTROL PANEL WITH 4.3" COLOUR SCREEN CELEBRATE WITH THIS RETRO JAYCAR POCKET PROTECTOR AND 5 ESSENTIAL POCKET TOOLS. WHILE STOCKS LAST. Just spend $50 on any hardcore product and receive the pocket protector and a different tool FREE each month. There are 5 tools to collect. Pencil, Screwdriver, Ruler, Trim Tool and Torch. COLLECT THEM ALL! * Available for Club members only on purchases made in-store, limit 1 per customer, other T&C’s apply pls see our website for details. MORE 3D PRINTERS ON PAGE 2 NOW 24 $ 95 SAVE $5 NOW 89 $ 95 VERY QUICK & EASY SET-UP SAVE $10 Front Back Arduino® Compatible Nano Development Board Fully compatible with all the features of the full Duinotech boards but on a tiny DIP-style form. Powered by a mini-B cable or 7-14VDC. ATMega328P microcontroller. 46Lx18Wx18Hmm. XC4414 Bluetooth® 5.0 Audio Transmitter & Receiver with Optical WEATHERPROOF 1080P 1080p Battery Powered Xtreem® Wi-Fi Cameras WI-FI Wire-free to place around the house/ office to watch live or recorded video remotely. Heat & motion sensing, night vision, 2 way talk and more. Multi-directional. Can stream audio to or from your Bluetooth® device to play on your stereo, speaker etc. TOSLINK Optical input & output. AA2112 SINGLE SINGLE+SOLAR QC9120 QC9122 199 $ 269 $ $ UP TO 6 MONTHS BATTERY LIFE (FROM A SINGLE CHARGE) TWIN 399 QC9121 12VDC - 230VAC Pure Sine Wave Inverters FROM 9995 $ To power devices such as power tools, laptops, battery chargers etc. MI5732-MI5740 300W up to 2000W models available from $99.95 to $499 Gas Soldering Tool Kits Adjustable tip temperature. Includes 3 x tips, cleaning sponge & case. Pro Piezo TS1318 NOW $129 SAVE $16 Super Pro TS1328 NOW $149 SAVE $20 Shop the catalogue online! NOW FROM 129 IDEAL FOR SENSITIVE EQUIPMENT $ SAVE<at>$20 Free delivery on online orders over $99* Exclusions apply - see website for full T&Cs. * GREAT VALUE INFO ONLINE SCAN TO WATCH VIDEO & SEE FULL RANGE www.jaycar.com.au 1800 022 888 Model Makers CLUB OFFER: FREE* $100 DUAL COLOUR PRINTING BUILT-IN HD CAMERA & WI-FI SUPPORT GIFTCARD When you purchase any of these 3D printers 4.3” TOUCHSCREEN 4.3” COLOUR TOUCH SCREEN PRINTS LARGER SIZES ONLY 1149 $ ONLY 1299 $ Anycubic 4K Resin 3D Printer Larger print volume of 192Lx120Wx245Hmm. 8.9” 4K LCD. Fast printing speed (3 x faster than previous models). More detailed prints compared to filament-type printers. Uses Anycubic App to remotely control print operations, monitor printing progress etc. TL4421 ALSO AVAILABLE: Anycubic 2-in-1 Wash and Cure Machine TL4423 $499 Scan to view range Flashforge Adventurer 4 3D Printer Fixers & Technicians JUST 2000W Heat Gun Keep your fridge at the right temperature. Min & max alarm. Temp range -50°C to 70°C. QM7209 NOW SAVE $10 48W Soldering Station Lightweight. Anti-slip grip. Temp range from 150°C to 450°C. Mains powered. TS1620 NOW FROM 19 $ 95 SAVE 10% Quick Connect Crimp Connector Pack PIECES Bullet, ring, fork, spade and joiners in various sizes and colours. 160-pce PT4530 NOW $19.95 SAVE $3 300-pce PT4536 NOW $39.95 SAVE $5 More ways to pay: NOW 795 $ 6 PIECES SAVE 20% SAVE 25% Glue Lined Pre-cut Heatshrink Tubing A box of six common sizes (4.0mm, 6.0mm, 8.0mm, 12mm, 16mm & 19mm) in a clear plastic case. WH5521 3495 $ 110 PIECES Drill, saw, sand, polish, carve or grind. 12V <at> 12,000RPM. TD2451 NOW 24 NOW 12V Rotary Tool Kit Set of 6. Slotted and Phillips. Metal precision. TD2023 95 Remove paint, shrink heatshrink and more. 2 Speed settings. 4 nozzles. Mains powered. TH1609 SAVE $5 Jeweller’s Screwdriver Set $ 160/300 JUST 2995 Digital Thermometer for Fridge or Freezer 4995 LOTS OF FILAMENT AND RESIN COLOURS & STYLES AVAILABLE FROM $19.95 $ 2495 $ Creality Dual Filament 3D Printer CR-X Create amazing high-quality prints with two colours or materials. Dual cooling fans. SD memory card slot. Prints up to: 300Lx300Wx400Hmm. TL4410 Large print volume of 220Wx200Dx250Hmm. Features include a levelling-free removable print bed, quick release nozzles & a HEPA13 air filter. TL4431 $ ONLY 1299 $ 60 PIECES NOW 2995 $ SAVE 25% Solder Splice Heatshrink Pack 42 PIECES Quickly create sealed soldered joint in one go. Includes assorted colours and sizes to suit various cable size. WH5668 Tools of the Trade JUST 29 $ 95 JUST THIS MONTH'S CLUB OFFER: FREE* Pocket Protector & Pencil 32 $ 48 Piece Screwdriver Set In-store only. T&C's Apply. 95 * Heavy Duty Wire Stripper, Cutter & Crimper Great tool to repair phone, game consoles and other electronic gadgets. Made from S2 tool steel. Magnetic storage for bits. TD2134 BEST SELLER Strip all types of cable from 10-24 AWG (0.13-6.0mm). 204mm long. TH1827 CURES UNDER UV JUST 3995 $ Supplied with a transparent practice padlock so you can see how the various mechanisms operate. 20 Different picks. 3 Torsion wrenches. Automatic tension tool. TH2200 Jaycar will not accept responsibility for any inlawful use of this item. It is intended for private (personal security) and hobby (locksport) use only. Tradies Off Site NOW 99 SAVE $30 $ Bondic Liquid Plastic Welding Kit Bond, build, fix & fill virtually anything in seconds. Solvent-free. Stays liquid until cured with the included UV LED Light. NA1530 Ultra-high current 1000A AC and DC current measurement. CAT III, 6000 count. Data hold, backlight, non contact voltage, relative measurement and more. QM1634 BEST SELLER JUST Measures voltage, resistance, capacitance, temperature and more. CATIII 600V 10A. 4000 count display. QM1323 GREEN & RED LED INDICATORS 4995 Ideal for finding dropped screws/bolts or locating objects in tight spaces. Easily connects to your laptop, Smartphone or tablet. Includes hook, a magnet and a 45° mirror. QC3373 JUST 2495 $ USB Inspection Camera Non-contact AC Voltage Detector Detects AC voltages from 200 to 1000V. Flashlight function. QP2268 FOR THE WORKSITE OR CAMPSITE 199 15L Brass Monkey Portable Fridge or Freezer Full function car fridge in a compact size. Ideal for tradies out and about. GH1623 Spring-loaded, comfortable handles. Suits 14-18 & 22-26 AWG lugs. Built-in wire cutter. 185mm long. TH1834 Digital Multimeter with Temperature JUST $ Crimping Tool for Non-Insulated Lugs 4995 $ 1000A True RMS AC/DC Clamp Meter JUST JUST 1695 95 EASY TO USE AUTORANGING METER $ $ JUST 44 $ 24 Piece Lock Picking Kit COLD DRINKS OR ICE TREATS NOW 95 5995 $ SAVE10% NOW 4995 $ SAVE $10 SAVE $10 1W 80 Channel UHF Radios Rechargeable. Hands-free function. Scrambler voice encryption. LED torch. DC1108 Looking for more product information? Visit your local store or our website jaycar.com.au NOW FROM Robust cases with stainless steel pins, waterproof seals and very solid catches. Ideal for your test or scientific equipment. Medium 330Wx280Dx120Hmm HB6381 $59.95 Large 430Wx380Dx154Hmm HB6383 $89.95 X-Large 515Wx415Dx200Hmm HB6385 $114 STAY IN TOUCH 79 $ ABS Instrument Cases with Purge Valves 12V Portable Stove Cook and warm up food whilst on the road or off site. YS2811 HOT PIES We reward our industry professionals Office Upgrades NOW FROM 4995 $ SAVE $10 NOW 4995 $ PC Monitor Desk Brackets SAVE $20 Dual PC USB Keyboard/Mouse Switch VESA compliant. Metal frame with scratch-resistant, powder-coat finish. Single CW2874 NOW $49.95 Double CW2875 NOW $69.95 Scan for more info Share up to four USB devices between two computers. USB 3.0 compliant, supports speeds up to 5Gbps. XC4925 NOW 99 6995 NOW 2495 $ $ SAVE $10 GREAT VALUE SAVE $10 Active Noise Cancelling Headphones 15W Wireless Qi Fast Charging Stand USB powered. Fast 15W/10W and standard 7.5W/5W charging. MB3673 USB 3.0 Converter to HDMI 1080p Add another monitor or projector to your PC via USB. Full HD 1080p. XC4973 CLUB OFFER 169 $ 4 X USB 3.0 PORTS • USB TYPE-C • 3.5MM AUDIO SOCKET with Bluetooth® 5.1 Absolutely superb sound. Built-in controls and microphone. Rechargeable battery. AA2170 9 DIFFERENT ADAPTORS INCLUDED ETHERNET UP TO 1000MBPS SAVE $30 TYPE-C • HDMI PORT • DISPLAYPORT • VGA PORT SD & MICROSD CARD SLOTS 4K 13-in-1 Multifunction USB Type-C Hub ONLY 2495 SAVE 15% Connect to a monitor via VGA from a DisplayPort. 1080p resolution. WQ7431 $ USB Type-C to HDMI Lead Connect your USB Type-C enabled device such as a smartphone, tablet or laptop directly to a HDMI TV or monitor. 1m long. WC7950 NOW FROM NOW FROM 21 $ 95 SAVE 10% $ 95 SAVE 25% SAVE 15% USB 3.0 Extension Leads USB A plug to socket. Suitable for high speed USB3.0 application. 5m and 10m available. XC4126-XC4128 4 FOR 2985 29 $ JUST 4995 95 Allows a computer with a USB port to use any RS-232C serial device via the USB port. Over 1Mbps data transfer rate. 1.5m long. XC4834 EASY SET-UP, NO SCREWS! Ultra portable storage solution, fits any M.2 NVMe or SATA SSD drive and supports ultra high speeds up to 10Gbps(NVMe) via USB3.1 USB-C. XC5908 JUST USB to DB9M RS-232 Converter DisplayPort to VGA Converter USB Type-C External M.2 SATA/NVME SSD Case 29 $ NOW ACMA approved. 10m YN8297 NOW $21.95 20m YN8298 NOW $32.95 30m YN8299 NOW $44.95 79 $ High Output Laptop Power Supply Leads, Adaptors, Converters Extra Long Cat6a Patch Leads ONLY 129 $ 132W power output. Includes connectors for a wide range of laptop brands. 12/24VDC 8.5A max. MP3346 Connects via a USB type-C connector. Add just about any port and even more devices to your laptop. XC5907 $ JUST $ Lightning® to USB Lead Charge or sync your Lightning® socket equipped iPhone®, iPad® or other Apple® devices. WC7728 $9.95 EA TERMS AND CONDITIONS: REWARDS / CLUB MEMBERS FREE GIFT, % SAVING DEALS, & MEMBERS OFFERS requires ACTIVE Jaycar Rewards / membership at time of purchase. Refer to website for Rewards / membership T&Cs. IN-STORE ONLY refers to company owned stores and not available to Resellers. Page 1: CLUB OFFER: SAVE $50 on Entry Level 3D Printer (TL4432). Page 1: CLUB OFFER: FREE Pocket Protector (HP1800) & Mechanical Pencil (TD2540) for purchases of $50 or more on Test & Measurement, Tools & Soldering, Service Aids, Kits, Science & Learning, Passive & Active Components, Electromechanical & Enclosures. Page 2: CLUB OFFER: FREE $100 Gift Card with purchase of 3D Printers TL4421, TL4431 and TL4410. Page 4: CLUB OFFER: SAVE $30 on XC5907. Page 4: MULTIBUYS: 4 x WC7728 for $29.85. Page 6: MULTIBUYS: Any 2 for $18 applies to NA1002, NA1012 or any combination. Page 7: MULTIBUYS: 2 x XC4514 for $12. 2 x XC4419 for $9. Page 7: MULTIBUYS: Any 2 for $20 applies to TH1890, TH1893 or any combination. Page 8: CLUB OFFER: SAVE $50 on MB3767 or MB3768. SUPPLY CHAIN DISRUPTION. We apologise for factors out of control which may result in some items may not being available on the advertised on-sale date of the catalogue. Audio Production Maonocaster All-in-One Production Studio NOW 3995 $ SAVE $10 ONLY 199 $ CREATE STUDIO-QUALITY SOUNDING PODCASTS, LIVE STREAMS & RECORDINGS with Microphone Easy to use. Features 2 mic inputs, 4ch mixer, noise reduction, 8 sound effects, built-in battery for portable use, and more. Includes: Mixer, Mic, Tripod, Audio Leads, USB Lead & XLR Lead. AM4224 3 Channel Stereo DJ Mixer Headphone socket. Coloured LED output display. RCA input sockets. Photo / Line and CD inputs. 12VAC <at> 300mA mains adaptor included. AM4207 In Store Only NOW 2495 $ SAVE $5 USB MIDI Interface Connects your older MIDI equipped musical instrument that has 5-pin DIN to your computer via USB. XC4934 Audio Mixer with Bluetooth® Technology NOW 1995 $ Compact & rechargeable. 3.5mm Auxiliary input & output. 6.5mm microphone input. 1500mAh rechargeable battery. AM4230 SAVE $10 Front Back NOW 149 $ 1080P Front SAVE $30 1080p HDMI Cat5e/Cat6 Over IP Extender Extend HDMI connections over IP extender up to 150m*. AC1752 *Cat6 cable up to 150m, Cat5e up to 100m. Additional Receiver AC1753 $89.95 HDMI cable doesn’t reach? No problem, use this handy extender! NOW 119 $ SAVE $20 Concord 4-Way 4K HDMI Splitter Connects a single HDMI source to up to four HDMI displays. Support High-Dynamic-Range (HDR) video. AC5002 Multiple HDMI devices but your TV or Display has only 1 HDMI port? A Splitter is your answer. HELPFUL HINT Update your Home Theatre 10% OFF SELECTED TV MOUNTING BRACKETS Wi-Fi HDMI Miracast Dongles Plug into your TV via HDMI port and begin streaming content from your smartphone, tablet or PC to your TV. 1080p AR1922 NOW $29.95 4K AR1924 NOW $59.95 NOW FROM 2695 SAVE 10% TV Mounting Brackets 95 Multiple TV’s but only 1 cable box? No problem. Split the signal and watch TV in different rooms with this easy switcher. Universal remotes to suit popular makes. AR1952-AR1964 Huge range of high quality brackets to suit virtually all TV screens. CW2805-CW2883 Looking for more product information? Visit your local store or our website jaycar.com.au HELPFUL HINT Front 29 95 NOW 5995 $ SAVE $10 4K Android Media Player FROM 79 $ Back Browse the web, run Android games and apps, or watch your favourite media. Wi-Fi or ethernet input. XC6012 4K SAVE 10% Replacement Remote Controls Back Switch HDMI signals from multiple sources to a single output. Supports 3D video. Remote control included. AC1705 SAVE<at>$20 26 $ 3 Way HDMI Switcher NOW FROM $ NOW FROM $ HELPFUL HINT JUST 4295 $ 95 Concord 4K HDMI 2.0 Amplified Cables IDEAL FOR LONG RUNS Amplified transmission. Avoids signal loss. Extra long; 10m, 15m, 20m & 30m long available. WQ7437-WQ7439 FROM 595 $ TV Flyleads RG-59U coaxial cable. Plug to plug. 1.5, 3, 5 & 10m long. WV7350-WV7354 We reward our industry professionals BEST SELLER Mini Sized Computers UNO R3 Development Board THIS MONTH'S CLUB OFFER: FREE* Stackable design makes adding shields easy. Powered by a USB-B cable or 7-14VDC. ATmega16U2 USB-Serial chipset. 53Lx75Wx13Hmm. XC4410 UNO UNO + WI-FI XC4410 XC4411 2995 $ Raspberry Pi 4B 4GB Single Board Computer $ 3995 Pocket Protector & Pencil In-store only. UNO + ACC 5995 $ XC3900 BEST SELLER Tiny credit card size computer. Quad Core Processor. Powered via USB Type-C. Wi-Fi, Bluetooth® 5 & USB ports. XC9100 RASPBERRY PI 4B 4GB INSIDE ONLY 109 $ THESE ARE SELLING FAST. CHECK WEBSITE FOR STOCK AVAILABILITY. ORDER NOW TO AVOID DISAPPOINTMENT. Raspberry Pi 400 Keyboard Desktop Computer JUST 135 $ All-in-one Pi computer integrated into a keyboard. Quad-core 64 bit processor. 2 x USB 3.0 and 1 x USB 2.0 ports. Gigabit Ethernet, HDMI, USB Type-C ports and more. XC9115 Prototyping Accessories FROM 3 $ 45 Jiffy Boxes ABS plastic. Industry standards sizes from 83x54x31mm to 197x113x63mm available. HB6011-HB6015 FROM 495 $ Prototyping Breadboards Ideal for electronic prototyping and Arduino® projects. 170, 400 & 830 tie points available. PB8815-PB8820 ANY 2 FOR 18 $ SAVE 20% ONLY 4 $ 95 EA FROM 550 $ Vero Type PC Boards Alphanumeric grid, pre-drilled 0.9mm, 2.5mm spacing. 95mm wide. 75mm, 152mm, 305mm lengths available. HP9540-HP9544 ONLY 1495 $ Aerosol Service Aids Circuit Board Lacquer NA1002 Contact Cleaner NA1012 $11.50EA NOW FROM 9 $ 95 SAVE 20% 0.25W 5% Carbon Film Resistor Packs 300 Pieces RR1680 NOW $9.95 SAVE $3 850 Pieces RR1697 NOW $17.95 SAVE $5 1700 Pieces RR2000 NOW $31.95 SAVE $8 SPST IP67 Pushbutton Switches Momentary action. 12mm mounting hole. Black or red. SP0656-SP0657 NOW 14 $ 95 SAVE 25% Jumper Lead Mixed Pack 30 Plug-Plug. 40 Plug-Socket. 30 Socket-Socket. 150mm long. WC6027 NOW 1995 $ SAVE 20% JST Connectors Kit Includes the popular JST XHP 2.54mm and PH 2.0mm housings & headers. Used for prototyping, repairs, and hobby applications. PT4457 100 PIECES Assorted LED Pack 100 PIECES Contains 3mm and 5mm LEDs of mixed colours. ZD1694 Not sure what to build next? Here's some inspiration: jaycar.com.au/projects Maker Essentials BEST SELLER Touchscreens for Raspberry Pi Add a user interface to your RPi project. Connect directly to your Pi. Resistive touch. 2.8" 320X240 5" 800X480 XC9022 XC9024 $ 2 FOR 12 $ SAVE 20% 39 9995 95 $ 7" 1024X600 139 $ DC Voltage Regulator Module Accepts voltage from 4.5- 35VDC, and outputs from 3-34VDC. 2.5A max output current. XC4514 $7.95EA XC9026 2.5" 240x320 LCD Touchscreen Large, colourful touch display shield which piggybacks straight onto your UNO or MEGA. microSD card slot. 77Lx52Wx19Hmm. XC4630 2 FOR 9 $ 5V Relay Board Operates directly from 5V. SPDT relays. 10A rated. XC4419 $5.45EA. NOW 240V Soldering Irons ANY 2 FOR 14 $ JUST 2995 $ SAVE 15% 95 20 $ 3 PIECES SAVE 25% Stainless Steel Tweezer Set Angled & duckbill 120mm. Superfine 135mm. ESD safe. TH1760 SAVE 25% Stainless Steel Cutters & Pliers 115mm Side Cutters TH1890 145mm Long Nose Pliers TH1893 $13.95EA Stainless steel barrel. Impact resistant handle. Electrically safety approved. 25W TS1465 $14.95 40W TS1475 $19.95 DON’T FORGET YOUR SOLDER! 1495 $ 15g, 200g, 500g & 1kg available. FROM $2.95 NS3092 FROM NOW JUST 2995 $ FITS OVER PRESCRIPTION OR SAFETY GLASSES LED Headband Magnifier Adjustable head strap. 1.5x, 3x, 8.5x or 10x magnification. QM3511 2 x AAA Batteries SB2426 $1.95 NOW 34 $ 95 995 $ SAVE $20 Third Hand PCB Holder Ideal aid for PCB assembly, soldering work etc. Heavy cast iron base. Movable arms. TH1982 25M ON EACH ROLL SAVE 10% Light Duty Hook-up Wire Pack 99 $ JUST Quality 13 x 0.12mm tinned hook-up wire on plastic spools. 8 different colour rolls included.WH3009 Adjustable arm. High/low light setting. Includes 125mm dia. 3 dioptre. 1.75x lens. QM3554 NOW 12 $ $ EA SAVE 15% EA SAVE 25% 15A Tinned Handy Packs For winding chokes, crossover coils etc. 0.5mm-1.25mm available. WW4016-WW4024 ARDUINO® COMPATIBLE This icon indicates that the product will work in your Arduino® based project. NOW 995 95 100g Enamelled Copper Wire INTERCHANGEABLE LED Illuminated LENSES Clamp Mount Magnifier Flexible power cable suitable for general purpose, automotive and marine applications. 10m roll length. 3 colours available. WH3054-WH3056 RASPBERRY PI COMPATIBLE This icon indicates that the product will work in your Raspberry Pi project. What's CLUB OFFER NOW FROM 549 $ 4.5A OUTPUT SAVE $50 BUILT-IN CIGARETTE LIGHTER SOCKET BUTTON SWITCHES ONLY 9995 $ MASSIVE CAPACITY UP TO 140,400MAH ONLY 2995 $ 90W Mains to USB Power Supply Power the latest laptops or quickly charge all of your mobile devices. Massive 90W of power, auto voltage and current selection on the Type-C PD socket. Features 2 x USB Type-C (PD3.0/QC4.0+) and USB Type-A (QC3.0). MP3416 Dual Car Cigarette Lighter Adaptor with 3 x USB Charging Ports + Voltmeter Versatile adaptor to expand your existing 12V socket and add the latest high power USB charging to your vehicle. LCD voltmeter to keep an eye on your car battery voltage. PP2119 Smart Wi-Fi Multi-Channel Weather Station 4 USB PORTS Multi-function Portable Power Centres with Pure Sine Wave Inverter Compact and lightweight. Features a battery, inverter, charging management system, multiple output ports.Use it during blackouts or to power small appliances around the work or campsite. Due Early February. 78,000mAh 300W Pure Sine Inverter MB3767 NOW $549 140,400mAh 500W Pure Sine Inverter MB3768 NOW $699 Features weather trend, comfort level indicator, min/max temp & humidity, synchronised internet local time & date, alarm with snooze and more. The included sensor has up to 150m range. XC0438 Wireless Thermo-Moisture Soil Sensor to suit XC0439 $34.95 INTRO SPECIAL 109 $ 249 $ Portable HD LED Projector OUTDOOR SENSOR SAVE $20 ONLY Accepts up to 1080p video input via HDMI/ VGA, can also play movies from your SD card or USB drive via the built-in media player. Projection distance 1m-7m. 32"-210" viewable size. Remote control included. AP4010 ACCESS FROM SMARTPHONE VIA WI-FI BUILT-IN SPEAKER NEW LOW PRICE NEW LOW PRICE NEW LOW PRICE JUST JUST 39 $ 49 95 2-In-1 Laser Measuring Tape NEW LOW PRICE $ Measure up to 30m using the laser or up to 5m with the retractable tape. USB rechargeable. QM1627 ORRP $59.95 JUST 799 $ Sparkle Stitch Kit Learn simple sewing and electronics and make spectacular light-up wearable technology. KM1080 ORRP $79 In-store Only. 100MHz Dual Channel Oscilloscope 7" colour LCD. Built-in waveform generator. PC connection via USB. SD card support. Lightweight and compact. Includes 2 probes & USB cable. QC1936 ORRP $899 Scan QR Code for your nearest store & opening hours 1800 022 888 www.jaycar.com.au Over 100 stores & 130 resellers nationwide HEAD OFFICE 320 Victoria Road, Rydalmere NSW 2116 Ph: (02) 8832 3100 Fax: (02) 8832 3169 ONLINE ORDERS www.jaycar.com.au techstore<at>jaycar.com.au Arrival dates of new products in this flyer confirmed at the time of print. Call your local store to check stock. Occasionally discontinued items advertised on a special / lower price in this flyer have limited to nil stock in certain stores, including Jaycar Authorised Resellers, and cannot be ordered or transferred. No rainchecks. Savings off Original RRP. Prices and special offers are valid from 24.01.2022 - 23.02.2022. PRODUCT SHOWCASE KCS sells 500,000 TraceME LoRa units KCS BV is proud to announce that a new milestone was reached in Q3 2021 – over 500,000 ‘TraceME’ LoRa and other tracking units have been sold. Since KCS have integrated new LPWAN (Low-Power Wide Area Network) technologies, new use cases and massive IoT deployments became possible. Switching from traditional GPS/ GPRS systems to LPWAN based systems resulted in reduced costs and increased battery lifespans to more than 10 years in some cases. It has now become feasible for countless industries and businesses to implement IoT. Some examples of how to use it include smart waste management, temperature-controlled transport, smart road signs and large-scale asset tracking such as E-bikes. In 2022 and beyond, KCS will continue to build on its existing TraceME products to enable new use cases and provide further enhancements. KCS remains dedicated to showing why it is a safe choice for any large-scale IoT deployment. Please visit www.trace.me for more information. KCS TraceME Kuipershaven 22, 3311AL Dordrecht Netherlands www.trace.me New automotive boost controller from Analog Devices Analog Devices (Maxim) have introduced a highly efficient multi-phase synchronous boost controller that regulates high-power Class-D amplifiers in automotive infotainment systems. The MAX25203 features both programmable gate drive voltage and current limit blanking time, as well as accurate current balancing, and operates at a high switching frequency, all while shrinking PCB space by 36%. The MAX25203 joins ADI’s family of automotive boost controllers that include the MAX25201 and MAX25202 single/dual boost controllers, both designed for lower power applications. You can buy evaluation boards, view the data sheet and order samples from Maxim’s website at: https://bit.ly/ MAX25203Product The MAX25203 controller starts with a battery input voltage from 4.542V, and operates down to 1.8V after start-up. It sustains an absolute maximum output voltage of up to 70V and features a low shutdown supply current of 5µA. The Max25203 is useful to generate backlight and Class-D audio amplifier voltages and also offers I2C bus diagnostics including die temperature, phase current monitoring and optional true shutdown to improve system reliability. Output voltage is scalable via the PWM input or I2C interface and a syncout feature supports additional phases for higher power systems. The MAX25203 synchronous boost controller features: • Factory programmable gate drive voltage from 5.5-10V increases power density by reducing MOSFET Rds(on) loss for higher efficiency and lower cost. • Programmable current limit blanking time supports short peak current events without power supply overdesign for lower solution cost. • ±5% current share accuracy from phase-to-phase reduces inductor size. • Resistor programmable switching frequency up to 2.1MHz improves EMI and reduces external components’ size and number. Maxim Integrated 160 Rio Robles, San Jose CA 95134 USA Phone: 408 601 1000 www.maximintegrated.com Microchip further expands Gallium Nitride (GaN) RF Power portfolio Microchip has announced a significant expansion of its GaN RF power device portfolio with new MMICs and discrete transistors that cover frequencies up to 20GHz. The devices combine high power-­ added efficiency (PAE) and high linearity to deliver new levels of performance in applications ranging from 5G to electronic warfare, satellite communications, commercial & defense radar systems, and test equipment. Microchip’s portfolio of RF semiconductors in addition to GaN devices siliconchip.com.au ranges from gallium arsenide (GaAs) RF amplifiers and modules, to lownoise amplifiers, front-end modules, varactor, schottky & PIN diodes, RF switches and voltage variable attenuators. In addition, the company provides high-performance surface acoustic wave (SAW) sensors and microelectromechanical systems (MEMS) oscillators and highly integrated modules that combine microcos with RF transceivers that support major short-range wireless communications protocols Australia's electronics magazine from Bluetooth, Wi-Fi & LoRa. The power devices announced include the ICP0349PP7-1-300I and ICP1543-1-110I, as well as other Microchip RF products, which are available in volume production. For more information, visit siliconchip. com.au/link/abcd Microchip Technology 2355 West Chandler Blvd, Chandler Arizona 85224-6199 USA Phone: (480) 792 7200 www.microchip.com February 2022  61 Flavio Spedalieri’s Solid-State Flame Discharge Tesla Coil This relatively small and simple device generates extremely high voltages, enough to form a ‘flame discharge’ resembling a candle flame. It can also demonstrate wireless power transmission by lighting up neon globes and fluorescent lamps at some distance. T he inspiration for this project came from a YouTube video by Jay Bowles of Plasma Channel in January 2021 of a Plasma Flame Generator. I loved the simplicity of the circuit (tuning and operation is a challenge, though), its unique output, and the fact that the resulting device is relatively small. In this design, a solid-state oscillator drives a primary coil which excites the resonator (secondary) coil, producing a high-frequency, continuous-wave output. The discharge produced by the Coil is a very interesting “flame discharge” resembling a candle flame. The Coil can be used to demonstrate wireless power transmission by lighting up neon globes and fluorescent lamps. In the lead photo, you can see a matrix I made using 100 neon lamps, sections of which light up when placed 62 Silicon Chip in proximity to a strong electromagnetic (EM) field (such as generated by this Tesla coil). Depending on the panel’s orientation, it can display the amplitude of the EM field or the relative shape. I think this is a really interesting way to observe such fields. The first thing you might think of looking at photos of this device is: “is it safe?” Yes, and no. It generates about 150kV, and given its operating frequency of around 10MHz, it can cause RF burns. Clearly, you need to be meticulous in building, testing and operating such a device. But we won’t tell you “don’t try this at home”. Still, we don’t recommend that beginners assemble such a device. It is more suitable for someone who, for example, has built several mains-powered devices and is used to the safety precautions involved Australia's electronics magazine in working with 230V AC. That’s because such people normally have the required mindset of ‘hands off when power is applied’, double-­ checking everything before switching power on and thoroughly insulating all high-voltage conductors. So without further ado, let’s get into it. Tesla Coils This Tesla Coil is based on a Class-E RF power amplifier that’s tuned to oscillate at around 10MHz. It drives a tap on an auto-transformer; the transformer’s secondary is excited by the oscillator to produce a high-frequency, continuous-wave output. You might be used to seeing Tesla Coils with a doughnut-like metal toroid on top, from which the discharge emanates. This one is simpler, with a dome instead, but it’s still a siliconchip.com.au This device generates hazardous voltages! Although the unit operates from a low-voltage DC supply, its high-voltage output will cause RF burns if you come close to or contact the discharge terminal, even when no discharge is apparent. The flame produced is a plasma, which is extremely hot and capable of melting copper wire (not to mention flesh!). Without the brass/stainless steel breakout point, it can begin to melt the wire at the discharge point. Always ensure that you are nowhere near the breakout point when powering the unit up. Keep all parts of your body (or anyone else’s) clear of it until power has been switched off and the discharge stops. And remember that a high voltage can still be present even when no discharge is visible. The potentiometer specified has a plastic shaft; use caution if substituting a pot with a metal shaft. At a minimum, you would need to use a plastic knob and ensure that the knob fully covers the shaft. For added safety, the coils (L2 & L3) and the breakout point can be encased in a 150mm diameter transparent plastic film or Perspex surround, with an open top 50mm higher than the breakout point. Electromagnetic interference warning This Tesla Coil is an RF generator. The input power can be up to 240W (48V <at> 5A) and the Class-E amplifier is very efficient, converting a considerable amount of input power to RF energy. That said, when breakout is occurring, most of that energy is converted into light and heat. Be aware that it can cause RF interference when operating, mainly in the HF (3-30MHz) band. That includes shortwave radio, multiple amateur radio bands, aviation and maritime communications and CB radio. The operating frequency of this unit is very close to the amateur 40m band, so be careful, or you might make some radio hams very unhappy! Tesla Coil (we’ll describe a larger and somewhat more complicated Tesla Coil with a toroid in a later article). The Tesla Coil is a loosely coupled resonant transformer invented by Nikola Tesla in 1899. It is capable of producing high-voltage, low-current, high-frequency alternating current. The voltages produced by Tesla Coils result from resonant voltage rise in the secondary and are not proportional to the turns ratio between primary and secondary windings as with traditional, tightly-coupled transformers. That allows exceptionally high voltages to be produced with a practical circuit; in some cases, over 1MV! The Tesla Coil comprises two L-C resonant tuned circuits. The primary tank circuit consists of the primary capacitor and a coil. The secondary coil (and often, high-voltage toroid) and the surrounding air form the secondary L-C circuit. The two circuits are connected in series and tuned to resonate at the same frequency for efficient energy transfer. The classical Tesla coil uses a spark gap arrangement to switch the energy stored in the primary capacitor into the primary coil. The energy in the primary circuit, moving back and forth between the capacitor and primary coil, transfers (couples) some of the energy to the secondary circuit. The voltage in the siliconchip.com.au The Tesla Coil when operating can produce a flame discharge which loosely resembles a candle. Care should be taken when operating the Coil as the flame produced is extremely hot and it produces very high voltages! Australia's electronics magazine February 2022  63 secondary continues to rise until the electrical field strength exceeds that of the insulating property of air surrounding the large surface areas of the top load and breaks out as an arc. Tesla coils can be scaled up to produce many millions of volts. Currently, the world’s largest Tesla coil is the “Electrum” designed by Eric Orr in New Zealand (see www.gibbsfarm. org.nz/orr.php) and built by Greg Leyh of Lightning on Demand (www. lod.org). Excitation methods The excitation methods for Tesla coils fall under three main types. Spark gap Tesla coil (SGTC) Includes static gap, triggered gap and rotary gap types. This type of excitation may also be referred to as “disruptive”. A high-voltage source is typically used. Solid-state Tesla coil (SSTC) Includes single resonant and dual resonant solid-state (DRSSTC) types. A DC power supply is used to charge the capacitor, with a power semiconductor such as a Mosfet or IGBT replacing the spark gap. Vacuum tube Tesla coil (VTTC) A similar topology to that used in radio transmitters. The main difference is that VTTCs operate in continuous-­ wave mode instead of the pulsed output of the previous excitation methods. The VTTC also requires a high-voltage supply such as specially configured microwave oven transformers. The Tesla Coil described in this article is interesting, as it falls within the solid-state coil (SSTC) category. However, it operates in continuous mode, not dissimilar to a VTTC, but at a much higher frequency of around 10MHz (rather than several hundred kHz to several MHz). We call this an HFSSTC. The main advantages of the HFSSTC are that it can be powered from a low-voltage DC supply, it doesn’t make much noise and you don’t need to deal with high-voltage primary power supplies. A continuous-wave coil operates at 100% duty cycle, resulting in silent operation. An interesting property of high-frequency, high-voltage output is its ability to produce a flame discharge, in which the ionised air (plasma) takes on the appearance of a candle flame. However, producing 64 Silicon Chip a stable flame is tricky and requires a fair bit of tuning. 5-10V signal at the gate of IRFP260N Mosfet Q1 to start the circuit oscillating. Feedback via capacitor C1 triggers and sustains the oscillation. The 4.7nF shunt capacitor and TVS diode provide some protection for the Mosfet; however, be prepared to lose a few Mosfets during testing and operation. ZD1 and TVS both aim to prevent the voltage at the gate from exceeding the gate-source voltage specification of the device, which is 20V. A 15V zener diode may also be used. L1 (10μH) is hand-wound with 24 turns of 0.5mm diameter enamelled copper wire on a cylindrical former. A 10μF capacitor is used for supply filtering, rated so that the circuit can be driven from a supply up to 63V (although 36-48V is sufficient). The primary coil (L2) consists of five turns of 1.32mm diameter enamelled copper wire wound on a 35mm high, 57mm diameter former. The resonator coil is installed inside the primary and is modular, so it can be easily removed. In my Coil, the 150pF and the primary inductance of 2.4μH gives a Circuit description As shown in Fig.1, the circuit uses a simple Class-E RF power amplifier to provide an RF drive current for the oscillator. This amplifier design dates back to the mid-1960s. Unlike a typical RF amplifier which drives a 50W resistive load, the Tesla Coil (secondary resonator) is a high-Q filter network. This type of circuit can achieve highly efficient switching using a Mosfet with zero-current switching (ZCS). This high efficiency is required to produce enough output power for a sustained discharge. ZCS means that the Mosfet is switched when the current flowing through it is at a minimum. The heart of the circuit is the LC oscillator formed by L2 (2.4μH) and C1 (150pF). The values of these components determine the oscillator’s frequency. In this case, around 10MHz (give or take). The voltage divider formed by VR1 and its 1kW series resistor generates a DOME COIL WINDING DETAILS L1: 24 TURNS OF 0.5mm DIAM. ECW ON A 22mm DIAM. FORMER L2: 5 TURNS OF 1.32mm DIAM. ECW ON A 57mm DIAM. FORMER L3 SECONDARY L3: 150 TURNS OF 0.5mm DIAM. ECW ON A 27mm DIAM. FORMER IRFP260N ZD1 A G K F1 12–63V DC (4A LIMITED) + – 10A D D PTC1 150pF q RXE250 10 m F 80V 4kV (C1) 1kW 2W ZD1 12V K A SC L2 2.4mH PRIMARY L1 1 0 m H 1W Ó2022 S D 1k W 2 W VR1 10kW G 4.7nF 2kV 0.5W 15V TVS Q1 IRFP260N S HF SOLID STATE TESLA COIL Fig.1: the circuit of the Solid-state Tesla coil is simple and elegant, with 150pF feedback capacitor C1 causing Mosfet Q1 to drive C1 and L2 at resonance. The inductances are chosen so that C1/L2 resonate at the same frequency as L3 and the stray capacitances around it (including the breakout point at its top). This results in extremely high voltages being efficiently generated at the top of L3, creating a flame discharge. Australia's electronics magazine siliconchip.com.au theoretical primary resonator frequency of approximately 8.34MHz. However, the interconnecting wires will increase inductance. The measured frequency of my oscillator is 7.42MHz, dropping slightly when the discharge is ignited, to 7.37MHz. The voltage rating on the 150pF capacitor needs to be a minimum of 4kV, so four 2kV capacitors are used in a series/parallel arrangement to double the voltage rating while maintaining the same capacitance. Mosfets have a fair bit of parasitic capacitance and non-zero switching time, and therefore ‘dislike’ operating at high frequencies. However, the use of zero-current switching (ZCS) operation helps in this respect. Secondary resonator The second resonant circuit is based around the secondary coil, L3. This develops a high voltage at the top of the Coil when it is excited at the same resonant frequency. The secondary comprises approximately 150 turns of 0.5mm diameter enamelled copper wire wound on a 25mm (ID) x 106mm tall PVC pipe former. An M4 x 12mm stainless steel bolt and a brass acorn nut is used as the breakout point or “top load”; it also influences the overall resonant frequency of the Coil. Another important reason for having this sort of discharge point is that the temperature produced by the discharge is enough to melt copper wire! Before constructing the secondary coil, I modelled the coil parameters in a Tesla Coil design software tool, “JavaTC” (shown below). This calculated the resonant frequency of the Coil and allowed me to make adjustments as required. Tuning Dealing with such a high frequency, it is surprising how minimal changes can affect the operation of the Coil. A slight tweak may mean that it doesn’t work at all, produces more of a corona discharge (rather than a flame) or blows the Mosfet. Tuning the Coil properly is therefore critical. I was fortunate enough that after I built my Coil, I managed to get it operating in the desired manner. But this was not without its challenges. Initially, I was cooking inductor L1. I was originally using a 12V SLA battery. I later learned that at a particular setting of the control potentiometer, there was a momentary current surge of more than 20A, which turned L1 into a fuse and it took the Mosfet with it. Therefore, I recommended using a current-limited supply to run the Coil. In case you still want to use a battery, I have added a PTC thermistor and fuse at the input of the final circuit, which will hopefully prevent damage under these conditions. Still, it’s best to use some form of supply current limiting if possible. In a pinch, this can be done with a wirewound series resistor of a few ohms, although that will reduce the overall efficiency of the circuit. Once you have achieved stable operation, tuning can be accomplished by adjusting the number of turns of the primary coil (L2), the interwinding spacing and its overall position (height) with reference to the secondary coil. The most significant effect that I found was the use of the stainless-steel bolt and acorn nut. This “top load” lowers the Coil’s resonant frequency, and adjusting its position has a significant effect. In my case, the final resonant frequency of the secondary is 8.12MHz. The calculated inductance for L3 is 168mH, which in theory should give a resonant frequency very close to 10MHz. It’s likely 20% lower than this due to stray capacitance. Input current limiting As mentioned earlier, I added the PTC ‘fuse’ (PTC1) because I found that it is possible to make the circuit draw so much power that it blows up the Mosfet and burns out L1. PTC1 goes high resistance if it conducts more than about 5A. Once you switch power off and let it cool, it should then work normally the next time. I have also added a 10A fast-blow fuse in case the PTC can’t act fast enough. There’s no guarantee that it will save the other components, but it’s cheap insurance. Neither of these components should do much other than provide peace of mind if you are using a 3.5A to 5A current-­limited supply as suggested. But I expect many people will not Output from the software JavaTC, which is used for designing Tesla coils. siliconchip.com.au Australia's electronics magazine February 2022  65 have such a supply. In theory, with this final circuit, you can power it from something like a battery that can supply many amps, and it should hopefully survive. The secondary coil was wound with the assistance of a hand drill, but it can be done by hand. Construction The first task is to prepare and wind the secondary resonator coil. The former is made from standard 25mm inner diameter PVC pipe available from Bunnings or any plumbing supply store. I cut it to a length of 106mm, which was based on my calculated winding data from JavaTC and allowed for extra material at each end for mounting. The outer diameter of the PVC tube is 26.9mm, and the winding itself is 82.2mm high. I gave the surface a light sanding, followed by a light coating with electrical-­grade varnish; however, this is not critical. As mentioned earlier, the secondary coil is wound using 0.5mm diameter enamelled copper wire, available from Jaycar, Cat WW4016 or Altronics, Cat W0405. The secondary coil can be wound by hand or with the assistance of a hand drill. Once finished, apply several coats of clear polyurethane varnish to seal the coil. Another option is “Ultimeg” electrical varnish, which I have used; it is available from Blackburn Electric Wires in Kingsgrove, NSW (see www.bew.com.au/varnish and also www.bew.com.au/wire). I built the base of the unit around a large heatsink, Jaycar Cat SY4085. As well as cooling the Mosfet, it’s heavy enough that the Coil won’t fall over easily. The central channel provides a space to mount the driving electronics. Also, it has flanges to act as feet, with holes to attach spacers for holding the upper structure. The base plate supporting the primary and secondary coils is made from an off-cut of 3mm FR-4 substrate (basically a PCB without copper). I obtained this from a transformer manufacturer in Wollongong, NSW but it can be purchased through Blackburn Electric Wires (see links above). Alternatively, you can also use an acrylic (Plexiglas/ PMMA) sheet. The heatsink needs holes to be drilled and tapped for the mounting points, as well as the Mosfet. I mounted the driving components on a cut piece of unclad, punched laminate, 56mm x 107mm. Silicon Chip has produced a PCB design to make assembly easier. I cut the board so that it fit snugly inside the heatsink channel. Our driver PCB is coded 26102221 and also measures 56 x 107mm. Mount the parts on that now, using the overlay diagram (Fig.2) as a guide to see which parts go where. The control potentiometer is mounted on a PCB measuring 56 x 30mm. This is mounted at 90° on the end of the main PCB using tinned copper wire braces to produce a robust mechanical support. L1 is a 10μH inductor. In my design, this is 24 turns of 0.5mm diameter enamelled copper wire on a length of 20mm diameter PVC pipe. However, I had to rewind this three times during initial testing due to it burning up. 0.5mm wire will not handle 20A, which I discovered during troubleshooting. However, after moving to a current-limited power supply, I have not had any problems with it. If doing it all over again, I would consider using larger diameter wire. To connect the base of the secondary back to the driver, I used a 2mm banana plug and socket so that I could remove and disconnect the secondary to work on the device. The connections to the Mosfet are terminated on the underside of the board (the solder side). The wires pass through holes drilled in the heatsink and are terminated to a three-pole pluggable screw terminal. The Mosfet is connected via the plug. I highly recommend this approach, as it is reasonably likely that you will blow up a Mosfet at some point during testing. Fig.2: we designed this driver board based on Flavio’s, which he made on a piece of unclad, punched FR4 fibreglass insulation. It’s pretty straightforward as there aren’t that many components, but we have kept the tracks well spaced apart to prevent arcing. 66 Silicon Chip Australia's electronics magazine siliconchip.com.au I also recommend purchasing a bulk quantity (eg, 10 pieces) to ensure you can continue to experiment. I glued the primary coil (L2) former and secondary (L3) plastic coupling to the FR-4 fibreglass base using two-part epoxy. I began to use the Loctite brand (see parts list) over Araldite and have not looked back. It works very well and is also cheaper. Mosfet choice I recommend using the IRFP260N Mosfet but I have also tested the IRFP460N. This is a 500V, 20A device (compared to 200V, 50A for the 260N). So far, it has been working well. In total, I have blown up three IRFP260N and two IRFP460N Mosfets and burnt out L1 twice in the process of building and experimenting with this device. Testing Before proceeding, make sure to keep your body away from the secondary coil at all times, especially the exposed metal at the top. This sort of voltage at such a high frequency can cause severe RF burns. Always power the unit up with the potentiometer would fully anti-clockwise. As mentioned earlier, the recommended power supply is a current-­ limited power supply delivering around 32V DC. 3.0-3.5A should be sufficient. You can test the unit initially without the secondary coil. Place a small neon lamp near the primary (not connected electrically) and power up the circuit. The electromagnetic field will cause the neon to light up if it is siliconchip.com.au While this Tesla Coil prototype was built on a veroboard, a manufactured PCB will be available from the Silicon Chip Online Shop. The finished board is then mounted comfortably inside the heatsink. The adjacent photo shows the mounting arrangement for the Mosfet, which is located on the other side of the heatsink underneath the main board. Australia's electronics magazine February 2022  67 Parts List – Tesla Coil 1 double-sided PCB coded 26102221, 56 x 107mm 1 double-sided PCB coded 26102222, 56 x 25.5mm 1 12-60V DC 3-8A current-limited supply 1 5A trip PTC thermistor (PTC1) [eg, RXE250] 2 M205 fuse clips (F1) 1 10A fast-blow ceramic fuse (F1) 1 heatsink with flanges [Jaycar SY4085 recommended] 1 plastic knob to suit potentiometer VR1 [Jaycar HK7010] 1 pair of red & black cables with inline bullet connectors [Jaycar WC6018] 1 2-way screw terminal with 5.08mm spacing (CON1) [Jaycar HM3172] 1 3-way vertical pluggable header [Jaycar HM3113, Altronics P2533] 1 3-way pluggable terminal block and vertical socket [Jaycar HM3113+HM3123, Altronics P2533+P2513] 1 120 x 100 x 3mm sheet of unclad PCB material (FR-4) or acrylic sheet (for coil base) 1 25mm length of 20mm inner diameter PVC pipe (former for L1) 1 35mm length of 55mm inner diameter PVC pipe (former for L2) 1 106mm length of 25mm inner diameter PVC pipe (former for L3) 1 25mm PVC coupling (to mount L3) 4 6mm-long untapped Nylon Spacers [Jaycar HP0930] 4 32mm-long untapped Nylon spacers (tap with M4 threads) [Jaycar HP0988] 4 M4 x 10mm Nylon machine screws [Jaycar HP0160] 4 4mm ID Nylon washers [Jaycar HP0166] 4 M4 x 10mm panhead machine screws 1 M3 x 10mm panhead machine screw and flat washer 1 M4 x 12mm stainless steel machine screw (for breakout point) 1 M4 brass acorn nut (for breakout point) 1 15m length of 0.5mm diameter enamelled copper wire (for winding L1 & L3) [Jaycar WW4016, Altronics W0405] 1 1m length of 1.3mm ◉ diameter enamelled copper wire (for winding L2) 1 150mm length of cable tie (for mounting L1) various lengths and colours of insulated hookup wire epoxy glue (Loctite brand recommended, available from Bunnings 1210127) clear polyurethane varnish (for coating the secondary coil) nail & paddle pop sticks (to make breakout starting tool) ◉ 1.25mm diameter ECW could be used, but some adjustments might need to be made to the design [Jaycar WW4024, Altronics W0409] Semiconductors 1 IRFP260N ▣ 200V 50A N-Channel Mosfet, TO-427AC (Q1) [Digi-Key IRFP260NPBF-ND, Mouser 942-IRFP260NPBF] 1 12V 1W zener diode (ZD1) [Jaycar ZR1412, Altronics Z0632, Digi-Key 1727-1946-1-ND, Mouser 512-1N4742A] 1 1.5KE15CA 15V 1500W transient voltage suppressor (TVS) [Digi-Key 1.5KE15CALFCT-ND, Mouser 603-1.5KE15CA/B] ▣ It’s a good idea to buy a few, so you have spares in case they fail during testing, the IRFP460N rated at 500V, 20A also works Capacitors 1 10μF 80V+ electrolytic [Jaycar RE6078, Digi-Key 493-4781-1-ND, Mouser 647-UCA2W100MHD1TO] 1 4.7nF 2kV plastic film [Digi-Key 399-12555-ND, Mouser 80-R73UN14704000J] 4 150pF 2kV plastic film [Digi-Key 1928-1172-ND, Mouser 505-FKP1150/2000/10] Resistors 2 1kΩ 2W * 5% [Digi-Key A138277CT-ND, Mouser 279-RR02J1K0TB] 1 10kΩ 24mm ½W potentiometer with plastic shaft (VR1) [Digi-Key 450D103-3-ND] * Increase the power rating for supply voltages greater than 48V 68 Silicon Chip Australia's electronics magazine oscillating correctly, as shown in the lead photo. Remember that you will need to wind the potentiometer clockwise a bit before anything happens. Power it down and place the secondary inside the primary. When powered back up, you may be able to observe a discharge. If you have a compact fluorescent lamp (CFL), bringing it near the secondary should cause it to light up, again due to the EM field. Operation I have found my Tesla Coil to have relatively stable performance. I am driving my Coil from a dedicated 48V 5A Mean Well switchmode power supply. To start the Coil, you slowly rotate the control pot until the circuit starts to pull current, then tap the acorn nut with an insulated metal tip. The Coil will not establish the discharge on its own; the arc must be established using a small metal tip quickly tapped on the acorn nut. I made a simple little tool from paddle-pop sticks and a nail for this purpose. The tool is simply made by sandwiching a nail between two paddle-­pop sticks, with the assembly held together by epoxy glue. For a nice touch, cover the sticks with heatshrink tubing. Start the breakout by turning the control pot to about halfway and tap the breakout point with the tool. One advantage of this approach is that it minimises the loading on the Coil, siliconchip.com.au which can cause the arc to go out. I was able to get a ‘flame’ just over 5cm long by supplying 32V DC at 3A (96W). If you have an oscilloscope, you can carefully probe the gate of the Mosfet to check the oscillation frequency. It should be around 7MHz. Scope 1 shows what you can expect to see when probing the Mosfet gate (in this case, during discharge). Note how the waveform is not a square wave or a sinewave. You might expect it to be a square wave, but there are all sorts of resonances plus parasitic capacitances and inductances in the system that conspire to make it look a bit messy. At this sort of frequency, Mosfet switch-on/off waveforms generally have edges that look like ramps with a step in them due to capacitive feedback within the Mosfet. So, a waveform like that shown in Scope 1 is not unusual for high-frequency switching. It is possible to run the Coil at higher voltages and power levels, up to 60V/8A. I recommend you experiment with care as it’s pretty easy to blow it up at high power levels. Experimentation One interesting experiment that can be performed is placing a tiny amount of elemental salt on the electrode. This will cause the flame to burn with vivid colours. I found that the best salt is simply a tiny amount of common sodium The coupling arrangement for the two inductors (L2 & L3) as viewed from the top of the Coil. Adding some sodium bicarbonate makes an especially interesting looking flame. bicarbonate (baking powder). This generates a very aggressive flame that is very yellow (Sodium-D lines). Finally, I would like to thank the engineers at Coast Electric Industries (http://coastelectrical.com.au) and Illawarra Transformers in Wollongong. They have helped me immensely with this and other related projects. You can download a copy from www. classictesla.com/java/javatc/javatc. html The theory of tuning a Tesla coil is covered at www.hvtesla.com/tuning. html (more so for classic coils, but it’s still relevant to measuring the secondary resonant frequency in this design). My website is www.nightlase. com.au and the page for this specific project is www.nightlase.com.au/ ?pg=hfsstc A video of my Tesla Coil working can be downloaded at: www.nightlase.com. SC au/?pg=hfsstc#HFSSTC-Videos References For more reading about Tesla coils, see https://w.wiki/4Mt6 JavaTC is an excellent and free piece of software used in Tesla Coil Design. A front view of the mounting arrangement of the Coil’s main circuit board gives a better perspective of how snug a fit it is in the heatsink. Scope 1: the waveform measured at the gate of Mosfet Q1 relative to ground. This is during discharge, and you can see the resonant frequency in this condition is 7.37MHz. The gate waveform is roughly trapezoidal; parasitic circuit capacitances (and especially those within Mosfet Q1) are pretty significant at this sort of frequency, so you can’t expect a clean-looking waveform. siliconchip.com.au Australia's electronics magazine February 2022  69 Review by Tim Blythman XGECU TL866II Universal Programmer We like the Microchip PICkit 4 for programming PICs and many Atmel parts (eg, AVRs). But there are times when you might need to program something else, and you don’t want to end up having to buy a different programmer for every type of chip you might come across. A low-cost universal programmer like the TL866 is the answer. T he PICkit range of programmers is indispensable when working with Microchip (and now Atmel) parts. The PICkit 4 is fast and versatile, while the Snap programmer is inexpensive and can program many chips that don’t need a high programming voltage. But if your interests span a broader range of chips, including EEPROMs as well as micros, there is an alternative. It is an excellent choice if you want to tinker with older components. You might have heard of the so-called “MiniPro” programmers; this is a common nickname for a range of programmers produced by a Chinese company called XGecu. We sourced our unit from what appears to be the official eBay XGecu store (user xgecupro; www.ebay.com.au/usr/xgecupro). The unit we are reviewing is the TL866II model. There are also the older TL866A and TL866CS models, plus the higher-performance T56 model. The one we ordered cost around $75 and took about three weeks to arrive. At the time of writing, the T56 costs around $220, while the TL866A and TL866CS are no longer available from XGecu. Other companies have cloned these older models, so any that are available are likely clones. Since the clones depend on XGecu’s control program (XGPro) to operate, XGecu’s fix appears simply to be ending support for these older programmers. Indeed, the control program can apparently detect and disable some of these clones. Thus, we can’t recommend the TL866A or TL866CS. 70 Silicon Chip The TL866II The TL866II consists of a grey box around 10cm long with a 40-pin ZIF (zero insertion force) socket at the top. Two LEDs indicate power (POW, red) and operation (RUN, yellow). The top of the case is notched for the ZIF socket handle, and a USB socket is opposite. A six-way header is available on one edge. This is for attaching an ICSP (in-circuit serial programming) header lead, to connect to a matching header on a PCB. Thus, the TL866II can be used to program DIP chips out-of-circuit, or just about any chip in-circuit, as long as an appropriate onboard header is present. The case is also marked with a notched IC outline to show the orientation of parts going into the ZIF socket. The unit feels weighty, and you can see two stacked PCBs through the hole for the header. All in all, it appears to be a well-made and compact piece of equipment, no larger than it needs to be. Just four screws hold the case together, so we whipped them off to take a peek inside. The two boards are sparsely but neatly laid out with surface-mounted components. Each pin on the ZIF socket is accompanied by a diode and transistor. This is necessary to cater for the variety of pin layouts that can be accepted. Different logic voltage settings are available, so presumably, these parts also handle level conversion. The two PCBs are joined by several socketed pin headers, and secured together by two soldered wire pins. The ZIF socket’s ability to work with such various chips with different pinouts depends on being able to drive any pin with the correct signal. This array of diodes and transistors help to do that. Australia's electronics magazine siliconchip.com.au Many components need a higher voltage (typically 9V-15V) to perform their programming sequences. These large inductors are part of the circuitry to generate these voltages. Two small TSSOP parts on the top PCB appear to be 16-channel LED drivers. The rear PCB has a large 100-pin QFP chip with its markings sanded off. Presumably, this is the microcontroller, the identity of which is being hidden to avoid being cloned. The rear PCB also sports an array of circuitry that also appears to be tied to each ZIF socket pin. There is also an AMS1117 3.3V regulator and a pair of MC34063 switchmode regulators. They are backed by several solid-looking inductors and surface-mounted electrolytic capacitors. This is evidently the boost circuitry used to generate the higher Vpp programming voltage used to program some PICs and EEPROMs. The microcontroller appears to have enough pins to drive any of the ZIF socket pins, giving the unit its flexibility and ease of use. Our unit arrived in a small cardboard box and included a 1m-long USB cable. Various kits are available; ours came with a six-way cable to suit the ICSP header, a PLCC IC extraction tool and a pair of IC adaptors for PLCC32 and SOIC16/SOP8 parts. Other packages are available with a variety of IC adaptors. These vary from the simple PCB-based DIP/SOIC and DIP/SOP adaptors (similar to what we stock in the Silicon Chip Online Shop, at siliconchip.com.au/Shop/18), through to those with PLCC sockets and even ZIF sockets that accept surface-mounting parts directly. What chips can it program? You can find the complete list of supported parts at www.xgecu.com/ MiniPro/TL866II_List.txt and over 16,000 parts are listed. Many of these include different package variants of the same chip, so the number is slightly inflated. But this list does include chips from over 150 manufacturers. In contrast, the device support list for MPLAB X 5.40 has around 3000 parts, including some devices which are not supported by any of the listed Microchip programmers. The TL866II (and other MiniPro devices) appears to focus on reading and writing various flash memories, EEPROMs, and similar parts. So it is a handy tool for backing up and restoring such devices. Almost 1000 Microchip microcontrollers are listed as supported, but most are quite old. For example, the list includes the PIC16C56, which dates back to the early 1990s. It doesn’t include many of the newer, enhanced core 8-bit Microchip parts, or even any PIC24s or PIC32s. So the TL866II is not the best way to program the latest microcontrollers. Over 1000 Atmel parts are listed, although this includes a majority of memory and EEPROM chips. The list includes favourites like the ATmega328, as used in the Arduino Uno, but not the slightly newer ATmega32u4, as used on the Leonardo board. Again, the list cannot be said to be up-to-date with recent parts. The Atmel list also includes several ATF-series PLDs (programmable logic devices), which are functionally equivalent to similar (GAL series) devices earlier produced by Lattice Semiconductor Corporation. Some of the Lattice GALs are also listed. PLDs can be considered to be smaller, simpler versions of FPGAs (field-programmable gate arrays). We reviewed Lattice’s iCEstick FPGA development board in April 2019 (see siliconchip.com.au/Article/11521). While FPGAs can be quite complex devices, PLDs are typically used for ‘glue logic’ functions, where one PLD can replace a handful of logic gate chips to save space. Such PLDs were used in early microcomputer designs, so this programmer may appeal to those interested in recreating and restoring such devices. We published an article by Dr Hugo Holden about restoring the graphics cards used with these early computers (see siliconchip.com.au/Series/352). The TL866II can also test many 74and 4000-series logic chips; a total of 226 parts are listed. There is even an auto-detect utility, which can identify logic chips based on their response to stimuli. It had no trouble identifying a 74HC86 XOR gate in our testing, but listed several options for a 74HC14 hex schmitt trigger inverter. This list included some hex inverter gates, including open-collector variants; enough to nail down the basic functionality. XGPro software More components on the bottom, corresponding to the pins in the ZIF socket. The many pins of the onboard microcontroller are routed to these components. siliconchip.com.au Australia's electronics magazine The control program for the TL866II and T56 is called XGPro, and it is regularly updated. We started by using version 10.61, but at the time of writing, version 10.75 was current. This February 2022  71 can be downloaded from www.xgecu. com/MiniPro/xgproV1075_setup.rar Only Windows operating systems are supported, and the manual notes that this includes versions from Windows XP through to Windows 10. There are some reports of operation under Linux using WINE, a framework for launching Windows executables. However, there is a free, open source version of the software which is actively maintained and is primarily for Linux and macOS. It can be downloaded from https://gitlab.com/ DavidGriffith/minipro/ but do note that it’s a command-line program. Screen 1 shows the overall layout. It’s not dissimilar to interfaces like the MPLAB X IPE or even the older PICkit 3 control program, with most of the window filled with a memory layout display. An array of functions are accessible just below the main menu bar, including all the most common actions such as blank check, verify, read, erase and program. The small AND gate symbol at the top right opens the window for identifying logic chips. Screen 2 shows the Logic Test window. Here we’ve selected a 4017 decade counter; the test vectors are shown at the bottom of the window, with the key above. The NEW/EDIT/ DELETE/COPY buttons indicate that it is possible to define further tests by creating a different set of test vectors. The 4017’s sequential nature means that its state depends on both current and previous inputs; the test can handle these sort of chips, plus simple combinational logic. The TEST button runs the test vector for that specific chip, which completes almost instantly. The Auto Find feature runs through the full list of test vectors and takes a few seconds to complete. It lists any matches in the lower panel, and as we noted, it can find multiple matches. Screen 1: most of the XGPro application window is taken up by a tabbed memory view, with assorted function buttons along the top and options along the bottom. The search can be refined by chip type and manufacturer. Various packages are identified separately, even though they could have the same pinout. Even SRAM chips are listed; these cannot be programmed (as their contents would be lost when power is removed), but can be subjected to a quick test sequence. We picked the PIC16F84A in a DIL package to run the program through its paces. The main panel shows tabs for the flash memory (arranged as the 14-bit words that this part uses), EEPROM and configuration bits. A fourth tab shows some part and wiring information (see Screen 4). This includes the connections for using the ICSP header, which matches the standard PICkit layout. So if you have an existing header made up for a Chip selection The Select IC button (upper left of Screen 1) allows the chip type to be selected, while the arrow at right gives a recent history of 10 items. Screen 3 shows a blank search window. The search entry does not do exact matching, but appears to match the sequence of characters entered regardless of any intervening characters. This may be a blessing or a curse, depending on how well you know the part number you are searching for! 72 Silicon Chip Screen 2: the Logic Test window shows the test vectors for a good number of parts. Support for new devices can be added by editing these vectors, while the AUTO FIND function helps identify unknown parts. Australia's electronics magazine siliconchip.com.au the experience is not too different (for PICs) from the older PICkit 2 and PICkit 3 programmers. Other devices Screen 3: the Device selection window gives a few options for narrowing down to a specific part, including type, manufacturer and even package. This is handy due to the vast number of devices that are supported. PICkit, it should work with the TL866II as well. This pinout is also shown if the ICSP option is chosen (see grey inset in Screen 4). Most of the options are similar to other programming applications, but there is a pin detect checkbox. This will alert you if no device is detected in the ZIF socket, although it doesn’t appear to work when connecting via the ICSP header. The read process is shown in Screen 5. The chip ID was detected and the process finished in around half a second. We fitted a PIC16F88 to test that the chip ID was being checked, and it reported an error, so the process is quite robust. Device erasure took a similar amount of time, while a program sequence took around five seconds, including rereading/verification. So We tried a few other compatible devices that we had around the Silicon Chip office. A 32Mbit (4-megabyte) W25Q32JV serial flash memory chip took around seven seconds to read. Assuming the chip is read with a single sequential read command, the serial clock runs just under 5MHz. Writing took about 30 seconds, consisting of eight seconds to erase, 15 seconds to program and seven seconds to verify. This device’s data sheet shows typical erase times of ten seconds while writing the entire memory is expected to take 6.5 seconds. That the erase time is lower than typical is probably due to the chip exceeding its specifications. The specified write time does not account for the data transmission overhead, which we expect would take about at least as long as reading the chip. A 1Mbit (128-kilobyte) SST39SF040 parallel flash memory chip took about four seconds to read, half a second to erase and around 25 seconds to program (so approximately 30 seconds for an erase/program/verify cycle). This is a bit slower than the typical Screen 4: the parts we tested all included a Device Info panel, which shows memory and pinout information. A guide to hooking up the programmer using the ICSP header is available (if it is supported for that part), but not shown in this image. siliconchip.com.au Australia's electronics magazine February 2022  73 The bundle we purchased includes a TL866II programmer, USB cable, an ICSP cable and the adaptors and PLCC chip extractor seen here. Various combinations are available with an assortment of different adaptors. Screen 5: the TL866II works very fast with parts like the PIC16F84A, and appears to complete a read almost instantaneously. Other parts with larger memories can take longer. times shown in the data sheet, but that does not include overheads such as entering programming mode (which on this device needs to be done for each byte written, and requires four bytes to be transmitted). A 256kbit (32-kilobyte) 24LC256 I2C EEPROM took just over four seconds to read and 15 seconds to program, including verification. That isn’t far off the expected reading time, assuming a 100kHz I2C clock and sequential reading, or a 400kHz clock and random reading. The writing appears to have some extra overhead, with around 2.5 seconds of write time expected (512 page writes at 5ms each). So the TL866II appears to be nearly as fast as possible with serial (SPI) devices, but perhaps slower with parallel and I2C devices, depending on protocol overhead. Programming PLDs We got hold of some ATF16V8 PLD parts (specifically the ATF16V8B15PU, from Digi-Key for around $1.70 each) to see how easy it would be to use these parts with the TL866II. We found a binary to 7-segment hexadecimal project online at http://39k.ca/ hex-to-7-segment-decoder-pld/ for this part. Helpfully, it also has a precompiled JED file that we could use to program the chip. JED files are the PLD equivalent of HEX files, but they hold a list of 74 Silicon Chip bits rather than hexadecimal nybbles (also known as nibbles). XGPro will load and save JED files when a PLD is selected as the active part. Reading and verifying the chip took less than a second, while writing this image took around five seconds. There is also an encryption option; we found we had to clear this to allow correct verification. Presumably, the chip cannot be read when encryption is enabled. When rigged up on a breadboard, the ATF16V8 produced the correct signals to drive a 7-segment LED display. While we haven’t worked with PLDs much before, it appears to be quite simple with the TL866II programmer. Program features Each device has separate tabs for its individual memory spaces. For example, a PIC16F84A has tabs for program memory, EEPROM and configuration bits. Any of these can be modified, so it can be used as a basic chip flash memory editor. The file menu offers the option to save and load to either binary or Intel HEX files, so it should be compatible with the output from most compilers. Interestingly, we found that on hand-editing some HEX files, XGPro did not complain if there were checksum mismatches. This could be to your advantage if you don’t like manually calculating checksum data, and wish to edit your Australia's electronics magazine files manually. However, it is concerning that the programmer will apparently happily program corrupted data into a chip without warning you. It also has the ability to load and save the system state as a project, including part numbers and settings, and projects can be password protected. This would be a good way to manage flashing various firmwares to a variety of devices. There is also the facility to control up to four programmers by using the Multi Programming interface. This is accessed by pressing the icon of the chip with four red arrows, shown in Screen 6. This uses the current settings to start a programming sequence with a single keystroke. It is intended to be used in a production environment where multiple identical chips are being processed. Since we only have one programmer, we couldn’t test this out. Conclusion The TL866II is a versatile piece of equipment and, after pulling out the drawers looking for old parts, we were pleasantly surprised by the number it could program. It seems solid, and the interface is simple to use. That it can program a multitude of parts in a ZIF socket without worrying about pinouts and programming adaptors is a feature that we almost immediately took for granted; it’s just that easy to use. siliconchip.com.au If you have stock of older devices or want to dabble with building a microcomputer (or experiment with some of the chips that this entails), it will be a handy tool, and it is one that we will continue to use at Silicon Chip. ► But it cannot work with many newer parts, although there is the option to add definitions to supplement its range. If you’re working with modern parts, then it is probably not going to be very useful. Screen 6: you can use the XGPro control program to program up to four chips in four programmers, all connected to one computer. A single SC keystroke triggers each one. Radio TV & Hobbies The Complete Collection on USB Every issue from April 1939 to March 1965 If you're into anything vintage it doesn't get any better than this scanned collection of every single issue of Radio & Hobbies, and Radio TV & Hobbies magazines before they became Electronics Australia. It provides an extraordinary insight into the innovations in radio and electronics from the start of WW2 to the early transistor era! PDF Download $50 SC2950: siliconchip.com.au/Shop/3/2950 USB + Download $70 SC6142: siliconchip.com.au/Shop/3/6142 Postage is $10 within Australia for the USB. See our website for overseas & express post rates. siliconchip.com.au Australia's electronics magazine February 2022  75 Driveway Gate Remote Control for sliding and swinging electric Gates Sliding/swinging gate controllers inevitably fail after some years of service. The more poorly made models will die after just a few years, so you will end up repairing or replacing them frequently. The solution is to replace the controller with this much more robust design, and as you build it yourself, it’s easy to fix if it does go wrong. By Dr Hugo Holden W hen I moved into my current home some 20 years ago, I enjoyed the fact that the front fence had a sliding electric driveway gate. However, after about a year, the gate started to malfunction, initially with intermittent behaviour and then total failure. I inspected the gate control module, which was based around a controller CPU. The motor switching relays looked somewhat small for the task, and I could see significant contact burning through their transparent covers. I called the manufacturers for a schematic, but they did not want to provide any assistance. Instead, they directed me to their local repair agents. A fellow at the company seemed quite sympathetic, but it was apparent he ‘wasn’t allowed’ to help a customer to effect their own repairs. As is often the case, the repair agents were unable to make PCB-level repairs and could only replace the whole 76 Silicon Chip control board for hundreds of dollars. Initially, I accepted this. It failed again a year later, and again, I had to buy a new PCB. Further failures appeared after lightning storms on two occasions. After repeated episodes of the system failing, I was getting fed up. I took one of the original boards and replaced the relays, to good effect. I also replaced some aged electrolytic capacitors, but the writing was on the wall. Fortunately, the radio receiver board (a generic third-party product) had always been very reliable, so I kept that and decided to design a new controller board to connect to it. My solution I decided to throw the original controller PCB in the bin and design my own from scratch. Looking around at the parts in my workshop, I had a good supply of 74-series vintage TTL logic ICs (some of which were were used Australia's electronics magazine in a Pong system; see the June 2021 issue) . These are rugged and reliable, also highly resistant to damage from electrostatic discharge (ESD). The task of an electric driveway gate appears simple on its face. But like many automation systems, the devil is in the detail. My sliding gate is powered by a 24V DC bidirectional brush motor. It has two standard micro-switches as motion limit switches. These are mounted close together in the motor drive unit and are mechanically activated at each end of the gate travel, via a spring arm, when the gate is fully closed or fully open. A swinging gate is likely to have a similar arrangement, so my controller could be suitable for that type of gate. However, I have not tested it as such. You would have to check how your gate system works before deciding to use my controller. The controller logic needs to take account of the states of these limit siliconchip.com.au Easy to service; no software and all through-hole parts Triggered by a single remote or local button (or both) High long-term reliability and EMI tolerance Stops the gate if it hits an obstacle Safe power-on reset Power input: 24V AC Motor current limit: adjustable from 0A to 8.33A Power for remote control board: 5V DC or 24V DC Motor drive: 24V DC or rectified AC at up to 8.33A (200W) switches during the use of the gate. It must then control the motor direction appropriately when the gate starts from a fully closed or fully open, or perhaps intermediate position. It also needs to detect the motor current in case the gate strikes an obstacle, to stop the gate motor. The gate is controlled by a handheld remote via a radio receiver board, its output being a momentary closed contact from a small relay on the radio receiver board. But it could also be controlled by a manual pushbutton. Finally, the control logic requires a very effective reset function to ensure that the gate remains in its stopped position with any kind of rapid, slow, or variable mains power cycling. Otherwise, a brownout, blackout or other event could trigger the gate’s motion and maybe open up the gate when you are not home. there are four fundamental modes of operation, cycled through by a button press. Initially ignoring the two limit switches, the remote control needs to cycle the gate through four operational states, shown in Fig.1. Therefore, a two-bit counter is needed, giving four logic states. I achieved that using a 7474 dual D-type flip-flop IC. These flip flops can be preset or cleared, which is required to take account of the gate limit switch conditions. Fig.1: the gate is controlled using a ‘state machine’ with four states: fully open, fully closed, opening or closing. The remote button cycles to the next state in the loop, while the limit switches on the gate force the machine into one of the stopped states. The state machine Considering these requirements, siliconchip.com.au Australia's electronics magazine February 2022  77 Fig.2 shows how the state machine is controlled by a combination of the limit switches and the remote control. For example, when the gate is opening and it reaches the limit switch, a 100ms pulse is gated via the OR gate and the lower AND gate, the state machine changes to the ‘stop before forward’ state, and the gate motor stops. If the control button is then pressed on the remote, upon the button initially being pressed, the ‘stop before forward’ state is reset to be 100% sure the state machine is in the correct condition according to the now-static switch data. On the trailing edge of the pulse, the state machine is then clocked to the ‘forward’ state, and the gate begins to close. The closed switch is triggered when it is shut, and the machine is set to the ‘stop before reverse’ state. If the button is pressed again, the state machine is reset to this condition on the leading edge of the pulse, then clocked to the ‘reverse’ state on the trailing edge, and the gate starts to open. The stopped states are applied on the leading edge of the control pulse to ensure that, whatever state the This is the type of universal motor typically used to drive a sliding or swinging gate. They are typically powered from 24-48V DC or rectified AC although some run from as little as 12V. controller was in before, the motor stops before it starts moving. This way, the gate always starts in the correct direction and doesn’t attempt to run itself past the stops set by the two limit switches. Circuit details The circuit is shown in Fig.3. Either power-cycling or gate over-current is designed to set the gate into the ‘stop before reverse’ condition. This does not cause a problem even if the gate is power cycled in the fully reversed condition, as with the next activation of the remote control, the state machine is forced into the correct condition (ie, ‘stop before forward’) before the gate starts its motion. One important feature of the design is that the limit switches are debounced. The cross-coupled Fig.2: more detail on how the state machine is implemented using digital logic chips. When either the remote button is pressed or a limit switch is activated, a pulse is generated. These pulses are ORed to create a pulse that advances the state machine to the next state. The pulses are also ANDed with the limit switch signals to force the machine into either the fully closed or fully opened states when needed. 78 Silicon Chip Australia's electronics magazine siliconchip.com.au inverter gates (IC1a, IC1b, IC1e & IC1f) very effectively debounce a changeover switch, unlike other methods using RC networks, Schmitt triggers, delay timers etc. This method is mainly time-domain independent, and the 7404 logic ICs are not harmed because their outputs are only forced low for the very brief propagation time of the inverter gate. 74-series ICs, while good at sinking current, only weakly source it. One interesting consideration is whether to regard the two limit switches as independent items, or two items acting together. The two limit switches are entirely isolated from the mechanical perspective, and it is essentially impossible to activate them simultaneously. After all, the gate cannot physically be in two places at once (open and closed), and the spring arm that activates the switch can only be pushed in one direction at a time. However, the switches are mounted close together, and the cables to them are in one bunch. So very heavy RFI (eg, from a nearby lightning strike) could possibly fool the electronics that both switches are activated at once. Therefore, I concluded it was best to XOR the signals from the two gate microswitches using gate IC2d as a form of ‘digital common-mode noise pulse immunity’ because an XOR only responds if its inputs are complimentary. In other words, if both switches are seen as closed at once, it is treated as if neither is closed. The debounced and XORed limit switch outputs are then strobed into the state machine’s clear & preset terminals, with approx 100ms pulses from 555 timers IC7 & IC8. These are triggered by a command from the remote control (or pushbutton) or a state change when a limit switch is activated. This arrangement ensures that the limit switch states set the correct state machine state (via the CLR and preset inputs of the two 7474 flip flops, IC6a & IC6b), while the remote control can also cycle through the sequence by clocking the first flip-flop, which in turn clocks the second flip-flop. The outputs of the state machine (labelled A & B) are uniquely decoded into two simple control signals, forward and reverse by another XOR gate (IC2a) and a pair of NAND gates (IC4c siliconchip.com.au Parts List – Remote Gate Controller 1 double-sided PCB coded 11009121, 209.5 x 134.5mm 1 sealed ABS enclosure, 222 x 146 x 75mm [Jaycar HB6132 ➊] 1 24V AC power supply (plugpack or mains transformer, sufficient to handle the full motor current) 1 radio receiver board with relay output, plus one or more matching keyfobs 2 3-way terminal blocks (CON1, CON2) 1 2-way terminal block (CON3) 1 6-way PCB-mount barrier terminal (CON4) [Altronics P2106] 1 3-way pin header with jumper shunt (JP1) 2 24V DC coil 24V/30A SPDT relays (RLY1, RLY2) [Jaycar SY4047] 2 M205 PCB fuse clips (F1) 1 M205 4A slow-blow fuse (F1) 1 5kW mini horizontal trimpot (VR1) 2 6073B-type 19x19mm TO-220 mini flag heatsinks (for REG1 & D8) [Jaycar HH8502, Altronics H0630] 4 M3 x 8-10mm panhead machine screws 4 M3 flat washers 4 M3 star washers 4 M3 hex nuts 4 M3 x 6mm self-tapping screws 1 or more cable glands (to suit installation) ➊ it will fit in Altronics H0312A or H0313 boxes, but the mounting holes will not line up with the plastic posts in the base Semiconductors 1 7404 or 74LS04 hex inverter, DIP-14 (IC1) 1 7486 or 74LS86 quad 2-input XOR gate, DIP-14 (IC2) 1 7408 or 74LS08 quad 2-input AND gate, DIP-14 (IC3) 1 7400 or 74LS00 quad 2-input NAND gate, DIP-14 (IC4) 1 7402 or 74LS02 quad 2-input NOR gate, DIP-14 (IC5) 1 7474 or 74LS74 dual D-type flip-flop (IC6) 3 555 timer ICs, DIP-8 (IC7-9) 1 7805 5V 1A linear regulator (REG1) 2 BC639 60V 1A NPN transistors (Q1, Q2) 2 BC548 30V 100mA NPN transistors (Q3, Q4) 1 BS270 P-channel small signal Mosfet (Q5) [Digi-Key, Mouser element14] 3 1N4148 signal diodes (D1-D3) 4 1N4004 400V 1A diodes (D4-D6, D8) 1 30A rectifier diode, TO-220-2 (D7) [eg, SDUR30Q60 or STTH30R04W] Capacitors 1 4700μF 63V snap-in radial electrolytic (optional) 1 1000μF 63V radial electrolytic 2 100μF 50V radial electrolytic 4 10μF 50V radial electrolytic 1 2.2μF 50V multi-layer ceramic 15 100nF 63V MKT 5 10nF 63V MKT Resistors (all 1/4W 1% metal film unless otherwise stated) 1 1MW 1 120kW 3 47kW 2 9.1kW 1 4.7kW 6 1.5kW 1 1kW 2 620W 2 430W 2 100W 3 68W 5W 10% wirewound 1 0.68W 50W 10% wirewound [element14 Cat 2478215 or 2946343] Australia's electronics magazine February 2022  79 & IC4d). These signals are inverted by two 7404 gates (IC1c & IC1d) and used to drive two BC639 transistors (Q1 & Q2) that switch the two 24V relays, driving the gate motor forward or in reverse. Current sensing resistor (R1), in series with the motor, develops a voltage proportional to the motor current. 80 Silicon Chip The commutator noise is filtered out by an RC-low pass filter comprising a 1kW series resistor and a 100μF capacitor to ground. If the gate collides with an obstacle, the output voltage of the filter increases and this forward-biases the base-emitter junction of transistor Q4, generating the OVR signal. Australia's electronics magazine This stops the gate and sets the state machine to ‘stop before reverse’. However, when the gate starts up and accelerates from a stopped position, there is a motor current surge. To ensure the current detector is deactivated when the motor starts in either the forward or reverse direction, timer IC9 generates a pulse of around 1.3s siliconchip.com.au Fig.3: the full circuit for the Gate Controller is somewhat complex but you can compare it to Fig.2 to get an idea of which section does what. The three timers, IC7-IC9, each act as pulse stretchers to ensure that brief events such as a short button press are not missed. duration, which causes Q3 to inhibit the charging of the 100μF filter capacitor. The motor can be powered by halfwave pulsed DC using just the power rectifier, but you can speed it up with the addition of the 4700μF capacitor. I used an IXYS 30A rectifier to ensure that it would not fail. siliconchip.com.au Pull-up resistors One subtlety of the design that isn’t immediately obvious is the need for the 1.5kW pull-up resistor at the output of IC5a. The 74xx TTL logic device outputs only go up to about +3V when high, despite running from a 5V supply. That isn’t a problem when they feed the inputs of other 74xx devices, Australia's electronics magazine as the inputs are designed to handle this. Note that 3V is above the ~1.7V trigger threshold of a 555 with a 5V supply. But given the weak pull-up current from a 74xx device (around 0.4mA), it’s much better to have an external pull-up resistor so that the 555 is reliably triggered, especially February 2022  81 since the trigger signal is capacitively coupled. Construction The Gate Controller is built on a double-sided PCB coded 11009121, which measures 209.5 x 134.5mm. Refer to the PCB overlay diagram, Fig.4, as a guide during construction. There is nothing particularly difficult about assembling this board, so the usual technique of starting with the lowest profile components and working your way up should work well. Start with the small resistors, checking the value of each lot with a DMM before fitting them. Then mount the diodes, ensuring that the striped cathode ends are orientated as shown in Fig.4. Next, install the ICs, taking care that their pin 1 ends are located as shown. I don’t recommend using sockets as they are a potential failure point, and as mentioned earlier, all the ICs used in this design are very reliable. We only fitted them to the board shown for development reasons. Follow with the sole trimpot. Then fit the smaller transistors, being careful not to get the different types mixed up, followed by the smaller MKT and ceramic capacitors, which are not polarised. Next, mount the larger resistors, spacing them off the PCB by a few millimetres to allow cooling air to circulate. Follow with the fuse clips, ensuring the retaining tabs are towards the outside so you can insert the fuse later. Bend the leads of REG1 and D8 to fit their respective pads, with the device tab holes located over the matching mounting holes on the PCB. Slip the heatsinks between the PCB and the device’s tabs, then attach the tabs securely using M3 machine screws, nuts and washers on either side. Ensure they are secure and the bodies and heatsinks are straight before soldering and trimming the leads. The large 50W resistor is held to the board using two M3 screws, nuts and washers on either side. Once you’ve mounted it in place, bend a lead offcut from one of the 5W resistors so that it reaches from the pad towards the centre of the PCB to the 50W resistor lead, then solder it in place. The tabs of the relays should drop right into the slots provided on the PCB. Make sure they’re pressed all the way down, and use a generous amount of solder on each pin to hold them securely to the PCB. Now mount the terminal blocks (wire entries towards the outer edge of the PCB), barrier terminal strip and the larger electrolytic capacitors, ensuring the latter are orientated with the longer positive leads to the pads marked + on the PCB. Bend another off-cut to go from the other lead to the AC terminal as shown in Fig.4 and the photo, then solder it to the other end of the resistor and clamp it down in the screw terminal. Wiring it up Before mounting the PCB in the case, you will need to figure out where the radio receiver module will be mounted (it might be possible to fit it to the inside of the enclosure lid), which wires need to enter the box and where the best place is for them to enter. The wire entry will need to be waterproof if the unit will live outside, which can be done either using one or more cable glands (as mentioned in the parts list) or seal the holes with neutral cure silicone sealant after running the wires through. Most likely, you will have ten wires to run in two twin leads and two multicore cables: two for the low-voltage AC power input, two wires going to the motor and five or six wires going to the limit switches. Ideally, use cables with a round profile and run each through its own cable gland. You could use a four-core screened cable for the limit switches and twocore round cable for the others, meaning you need three glands and thus three holes in the case. If you can’t fit the radio receiver in The finished Driveway Gate Controller is located in a plastic enclosure near my gate with a liberal amount of waterproof tape applied (shown on the lead image). This means I can still open it up to access the board (however unlikely that is now) while still keeping the water out. I certainly wouldn’t want water getting in and corroding away all my hard work! 82 Silicon Chip Australia's electronics magazine siliconchip.com.au the case, you will need to run some additional wires to the outside. These are two wires to power the receiver board (assuming you aren’t supplying it with power externally) and two which run from the receiver’s relay contacts to input connector CON3. They could be run together using three- or fourcore screened cable. Note that, as there is no room in the box for a mains transformer, you will either need to use an AC plugpack or (more likely) mount a mains transformer, mains input socket (or captive cord), fuseholder and wiring in a separate insulated box. We won’t give any instructions on how to do this, except to say that you need to use correctly-coloured mainsrated wire where appropriate (Active = brown, Neutral = light blue and Earth = green/yellow striped). You will also need to ensure that all exposed mains conductors are insulated (eg, with heatshrink tubing) and tied up neatly with cable ties so they can’t float around in the box if they break loose. If you aren’t experienced with building mains-powered equipment, you will be better off finding a suitable plugpack instead. Drill holes for these glands (or the bare wires, if using silicone) near where the relevant connectors will be once the PCB is mounted in the case. Mount the glands securely, then install the PCB, insert the wires, attach them to the relevant terminals (as shown in Fig.4), pull out most of the slack and tighten the gland nuts. If you have room to fit the receiver in the box, you could attach it to the inside of the lid using neutral cure silicone sealant – make sure it isn’t going to foul any components on the main PCB when the cover is in place. Another option is to use tapped spacers and screws (assuming it has mounting holes), but if you do that, make sure you seal the screw holes through the lid so moisture can’t get in. If mounting it on the lid, that also siliconchip.com.au Fig.4: assembling the PCB is straightforward. Fit the parts in the locations and orientations shown here. Note how the large resistor is attached to the PCB using machine screws, then two wires are soldered to its exposed terminals. One goes straight down to a pad on the PCB, while the other end connects to one of the low-voltage AC input terminals on CON4. Australia's electronics magazine February 2022  83 The electrolytic capacitor sandwiched between Q3 and VR1 should be 100μF as shown in the circuit and overlay not 10μF as shown in silkscreen of the photos. Our first batch of PCB that we are selling have this listed incorrectly, so keep an eye out when assembling! Subsequent PCB batches will have this problem fixed. allows you to run the receiver antenna around the inside of the lid, assuming it is using a length of wire as a whip. Testing, setup & use There isn’t much to go wrong, but since the motor will not be running initially, you could connect a safety resistor (say 10W 5W) in series with the AC supply the first time you set it up. Check the AC voltage across that resistor; it should be well under 1V. If it’s more, switch off and check the board and wiring for faults. Assuming it’s OK, measure the voltage between pins 1 and 14 of IC6 (or just about any of the 74xx ICs). You should get a reading close to 5V. Next, check the voltage at the 68W 5W resistor leads right near the edge of the PCB relative to the tab of REG1. This reading should be between about 22V and 28V if a radio receiver board is connected, but it could be somewhat higher than that (up to about 35V) if there is no radio receiver board drawing power from the unit. If that all checks out, remove the safety resistor and connect the low-voltage AC supply directly to the board. Now is also a good time to fit the onboard fuse, which protects the motor. The remainder of testing assumes 84 Silicon Chip you have the unit wired up to your gate. Double-check that the connections to the limit switches and motor are correct before proceeding. We’ll assume the gate is initially closed, although it would be best if you could manually open it slightly. It is ideal if you are near the gate and can manually activate the limit switches easily. Set VR1 to its midpoint, then power the controller up. It should reset in a state where it’s ready to open. Press the button on the remote or short the terminals of CON3. The gate should start to open. If it tries to close instead, remove the power and swap the wires to the motor terminals. If it simply doesn’t budge, or move a tiny amount then stops, you might need to wind VR1 up to allow more motor current. Assuming it starts to open, actuate the fully open limit switch and verify that it stops. Then press the remote button again and check that it starts to close. Actuate the fully closed limit switch and verify that it stops, and that if you press the button again, it begins to open. Assuming it does that, check that it opens and closes all the way. If it stops partway, turn VR1 slightly clockwise and try again. Australia's electronics magazine If it opens and closes all the way the first time, try winding VR1 anti-clockwise a bit and repeat. Continue until it stops working reliably, then turn VR1 clockwise slightly and verify that it works reliably again. The idea is to set VR1 just far enough clockwise that it opens and closes every time, but not too much further than the minimum setting to achieve this. That way, it will stop quickly if something gets in its way. All that’s left is to seal it up and tuck it away. Your Gate Controller should work reliably for many years to come! Conclusion One great advantage of this gate controller is that it uses standard garden-­ variety 74 or 74LS series TTL digital logic ICs. These are rugged and generally very reliable. Many commercial gate controller manufacturers will not release their firmware or schematics; even if they did, it would require the specific programming hardware and utilities to re-program a new microcontroller if needed. On the other hand, this design can be repaired easily and at minimal cost if it goes wrong. Mine has been running for over 15 years now and has proven to be very reliable and trouble-free. SC siliconchip.com.au SERVICEMAN’S LOG The accordion job Dave Thompson An unusual job turned up at the workshop the other day. Well, it didn’t just walk in; the owner brought it in after discovering it at an estate sale. The inheritors were going to throw it away, but my client saved it. It was a piano accordion, probably at least 50 years old, and this guy couldn’t bear to see it chucked into the bin. This client had played the instrument in various bands over the years and was always looking for a decent model to replace his existing ones because they eventually wear out with all that squeezing. Back in the ‘90s, when I was playing in a folk-rock band, the accordion player was always on the lookout for good working models, perusing second-­hand shops in towns we played because it was increasingly difficult to find a good working instrument. Life on the road is very hard on them. When we did find one, it was pressed into use, and as soon as the bellows blew out or the reeds went west, it would go in the skip because repairing or restoring them was just an exercise in frustration. There were no spare parts to be found, so it was just easier to get another one and put it into service. Now I know what you’re thinking: “did he fire six shots or only five?” Oops, sorry, wrong script. I meant to say: there’s nothing very electronic about a piano accordion. And usually you’d be correct, but this one had a unique feature. At some stage, someone had mounted a couple of microphones on the outside near the grille (where the treble sound comes out). These feed via some not-so-neat cables into a small Jiffy box, which I assume housed a preamp of some description, making it ready to be plugged in and amplified. Back when I played in the band, I was forever struggling to mic up the accordion properly. For one, the guy siliconchip.com.au who played it liked to move around a bit, and two, the microphones we were using (Shure SM57s) were very awkward to mount onto the instrument itself, so we inevitably ended up just gaffer-taping the mic in place. Not very elegant, but it worked reasonably well for what we liked to call “folk and roll”. One of the main issues is that the sound grille on an accordion is quite long, typically the entire length of the instrument and a single microphone is naturally going to pick up sound loudest from where it is placed on the grille. The other notes at the extreme ends of the scale will not be ‘heard’ as well by the mic. This created a headache for the sound guy because it would be very loud in the middle notes and buried in noise for the rest of the reeds placed farthest from the microphone. To work around this, we tried adding shrouds (usually made of folded and shaped stiff card) in an attempt to even out the audio, but with only partial success. Eventually, we settled on using two mics spaced out along the grille, and when mixed together, this provided the best solution. But it looked a right mess with the mics taped to the body and inconvenient cables dragging everywhere, making it a bit of a nightmare to play for the accordionist. Whoever modified this one had crafted two small ‘stands’ for the microphones, but they had ditched the bulky mic bodies and used only the dynamic capsule still mounted in its housing. It was a bit rough around the edges, but the mics were pretty sturdy and solidly mounted to the body. Australia's electronics magazine Items Covered This Month • • • • • The accordion job Brightening up a clock radio Unorthodox Porsche parts Mobility scooter repair The misattraction of a nuclear magnetic resonance machine Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz We apologise for the lack of cartoons in this issue. Our cartoonist, Brendan Akhurst, is currently trekking in the mountains of Nepal searching for evidence of past alien civilisations after their presence was revealed to him in a dream. Each capsule was permanently wired with shielded cables for the short run to the Jiffy box, which was taped onto one of the shoulder straps. There was an XLR connector mounted in the back end of the Jiffy box, and a single standard microphone cable would connect the whole shebang to the snake and off to the mixing desk. Apparently, this part of it was not working, nor were several of the bass buttons, which are mechanically operated by the player to open and close bass reeds on that side of the instrument. So there was a lot going on, and I decided to tackle the non-electronic part first. That was relatively easy; opening a hatch on the bottom of the accordion revealed all the mechanics of the bass buttons, a complicated system of springs, levers, actuators and pushrods. It was ‘literally’ choked with dust, grime, what looked like animal hairs and other detritus picked up over decades of being played in dingy lounges and smoky bars. A good going-over with a decent brush, a bit of low-pressure compressed air and a good lube job with February 2022  85 some light sewing machine oil soon had everything freely moving and ready to go. Now for the electronics The Jiffy box had simply been taped to the strap, and it had likely been there a long time. While the tape’s fabric came away easily enough, most of the adhesive stayed behind. Great, that was one more thing for me to take care of. The bottom of the box was held on by four screws that were easy enough to remove. Inside was what appeared to be a preamp built onto a piece of veroboard. Several small trimmer-type pots were mounted on the board, along with the usual arrays of transistors, capacitors and resistors. I’ve made many preamps like this over the years, so I wasn’t too fazed by it; I’d simply reverse-engineer it to see what I was dealing with, and if I couldn’t get it working, I’d just make another one using one of my existing circuits. The interesting thing is that it had a 9V battery connector fitted, but no battery was present, so it might well be phantom powered. I’d know more once I had it out and under the light and magnifying glass. Once on the bench, I could see there were two channels involved – one for each mic presumably, and each one was identical, with the signals being mixed at the final stage. It was a relatively advanced preamp and appeared to be set up for phantom power, where 48V is sent along the XLR/microphone cable from the mixing desk to power the circuit. However, I thought I’d start things off by applying 9V from my bench power supply to the battery connector to see if there was any life in this thing at all. With power on, nothing happened. I used a signal generator at the mic input and listened to the output with my bench amp. Nothing. Zip. Nada. I drew up a circuit based on what I was seeing. The preamp used JFETs at the input stages, the classic MPF-102 types. With reasonably low noise figures and high input impedances, they were the go-to JFET for quite a few years. There was also a simple tone control circuit, which appeared to be of the Baxandall type, controlled by the trimpots. The output was buffered by a single transistor stage fed by both ‘halves’ of the preamp where the signal was mixed together; overall, it was a relatively straightforward preamp. Its gain and impedance could probably be changed by altering a few bias resistors here and there, but as it had obviously worked in the past, I thought I’d stick with the same values where possible. I used a similar design in a preamp I made many, many moons ago for my acoustic guitar. I’d modified the guitar for live use by including a so-called ‘thinline’ piezo pickup mounted under the bridge. Vibrations from the individual stings are detected by the pickup, and after piping it through to a preamp, the signal is fed to the outside world via a standard 6.3mm stereo output jack that doubles as both an on/off switch and the rear strap-fixing point. On my acoustic, the rear strap holder was on the centreline at the back of the main part of the body. Simply plugging a cable in switched on the electronics using one of the two contacts in the stereo socket, with the inserted plug shorting out the contacts like a switch. 86 Silicon Chip I mounted the preamp inside the guitar on the back side, near a handy timber strip brace, using stick-on Velcro, making it solid but easy enough to remove if I had to. I clipped a 9V battery into a holder using the same Velcro just under and inside the sound hole for easy access; while space was tight, I could change the battery without loosening any strings. The current draw was so low that a battery lasted me at least a year of regular live use. So I decided to use something similar here. All goes accordion to plan What I wouldn’t do is add the complexity of onboard tone controls. Not only is it pointless with them being inaccessible from the outside of the Jiffy box, but they are also redundant because the tone could be controlled by using the much more functional tone controls on the mixing desk itself. Someone can adjust these until the sound is pleasing and then leave them, or they can be adjusted in real-time if a sound engineer is present. I would also stick with the existing XLR output connecter, which would allow me to balance the output signal, with the downside being I couldn’t use the connector as a switch. As I mentioned, it appeared that the old preamp had been at least partly set up for using phantom power, which again complicates the circuit and requires extra components to step the supply voltage down from 48V to 9V. Since the phantom power function is controlled by a switch on the mixing desk, there would be no problem omitting it entirely and simply using a battery, which would last this client several years given the number of live gigs he plays. Then, it would merely be a matter of opening the Jiffy box and replacing the battery when required. The client was happy with all that, so I set about recreating the best parts of the original circuit. Finding components was not difficult, as I have plenty of new-oldstock transistors and FETs. I suppose I could have simply upgraded everything to modern parts, but this job was already eating into my time, and I didn’t want to have to research new values for different transistor types. The 2N3904 output transistor was modern enough, and I had dozens of MPF-102s that I’d likely not use in years, so I chose to use them. I assembled it on a piece of veroboard – designing and making a PCB for something this simple was beyond the scope of the job, but I gave the usual clearances for signal and power lines to minimise hum and RF pickup. Due to the size of the Jiffy box, I had plenty of room to play with. I could have used a new box with a battery compartment and all the usual conveniences, but that would mean lots of marking out and drilling holes and essentially redesigning the wheel, so I left it all that as-was. What I did add was a low-profile toggle switch for turning the thing on and off. I mounted it next to the XLR socket, where it would be unlikely to be bumped but still handy to access. He’d just have to turn it on manually if he wanted to amplify the instrument through a PA system. I won’t bore you with the build, other than to say it is always the best part of the job for me, working out where stuff goes and what tracks to cut on the veroboard. Once it was done, I triple-checked it and powered it up on the bench using my power supply and fed in a signal. I was Australia's electronics magazine siliconchip.com.au greeted with a nice strong output signal in my ‘phones, so it was obviously working. The next step was to plug in the two mics and the output to my test amplifier and see what happened. I had a very clear output from the mics, with quite low noise, so I was pleased enough with that. The wires coming from the mic capsules were shielded but routed awkwardly over the accordion and simply held in place with strips of tape. As this wasn’t very elegant, I looked to see if I could improve on that somehow. As usual, getting the old gaffer tape adhesive off was a mission in itself, but some liberal use of isopropyl alcohol soon had it back to a natural finish. I wasn’t about to start drilling holes in the instrument’s body, and the only feasible way was along the edges of the moving parts and off up the strap to the Jiffy box. I’ve collected lots of those little square cable clips over the years – they used to come with some motherboards or computer cases, and I always ended up with way too many. They have a very low profile, with a small slot for a cable tie to pass through. I have both black and white versions, so I put each one on the bright red body to compare looks. I decided to go with the black ones since the cables were also black. I (literally) pressed them into service along the cable run, about every 60mm, using double-sided tape applied to the bottom of each holder. Once in place, it was a simple matter of running the smallest cable ties I could find in my drawer through the slot, around the cable and pinching them down snugly without the cut-off part of the tie being exposed. This can rip skin if that part sticks out and one rubs against it the wrong way. I also used longer Velcro straps to mount the Jiffy box to the accordion strap, in the position it was before, making it easier to remove to change the battery. I was pretty pleased with the result. It was not ideal, but a lot tidier than before and likely more robust as well. The only thing left to do was unclip the bellow straps and have a play through a proper amp. I’m no keyboard or piano player, so this test would just involve a lot of noise. Due to a few years of piano lessons, which ended about 50 years ago, I know a few scales, but that’s about it. And hefting accordions around, squeezing and pulling and hitting buttons and keys all at the same time is more complicated than drumming! While I couldn’t do it justice, it sounded pretty decent through the mic input on my guitar amp, and tone control was also broad and workable. I called the client, and he came around and put me to shame playing it but was very happy with the result. I hope he gets many good years of use out of it now. Brightening up a digital clock radio display B. P., of Dundathu, Qld is one of our most prolific contributors, and he hasn’t stopped yet. He doesn’t want a repairable device to be thrown away if he can help it... We have had this digital clock radio in our lounge room for longer than I can remember. I’m not even sure where we obtained it, but I think we bought it second-hand from one of the local op shops around the time we moved into our new home, in 1992. The clock has worked well over the years but lately, the siliconchip.com.au Australia's electronics magazine February 2022  87 time would start flashing even though it was still correct. I fixed this by incrementing the hours until I got it back to the right time. At first, I suspected it was caused by a power supply glitch, but it kept happening. After a while, the clock started going haywire and showing all sorts of random times. I ignored it for a few days, but then when I tried to reset the time, it was stuck flashing 12:00. I decided to replace the clock initially and have a look at it later. However, the replacement clock had a dull red display which was harder to see and is more suitable for a bedroom, whereas the original clock has a bright yellow display that was much better with the bright light in the lounge room. So it was time to have a look at the original clock to see what the problem was. I already had an idea what was causing the problem, as some years ago I’d encountered weird behaviour from a digital clock. I was unable to diagnose the problem until I built an ESR meter. I was then able to determine that the filter capacitor was faulty. Replacing it fixed that clock, and it’s still working well now. Suspecting that this clock had the same problem, I proceeded to dismantle it. This was quite tricky as, being a clock radio, it has the cable for the front radio display needle under the circuit board. That meant that I couldn’t take the circuit board out of the clock to work on it without making reassembly very difficult. After removing the three screws securing the board, I managed to lift one side of the board high enough to test the filter capacitor with my ESR meter, but I couldn’t get any reading from it. So the capacitor was basically open-circuit. I then managed to get my 25W soldering iron under the board and removed the capacitor. I re-tested the capacitor with the ESR meter while it was still warm from desoldering, and I got a reading of 88W. I tested it again later after it was cold and once again, I got no reading. This is one of the worst capacitors I have ever encountered that hadn’t blown its top; it looked like it was still good. This ESR meter has helped me greatly over the years to identify seemingly good capacitors as bad. It was marked as 470μF 16V, but a compact size. I hunted through my container of salvaged capacitors and I found a few around the same size. After testing them with my ESR meter, I selected the one with the lowest reading and installed it. This was quite tricky, trying to solder under the board with minimal room, but I managed to do it. Before reassembling the clock, I tested it to make sure that the repair had been successful. I set the clock up safely so that I was able to see the display and access the buttons on top of the top case. After plugging the clock in, it flashed 12:00, so I changed it to the correct time. This was successful, so I had obviously solved the problem. I unplugged the clock and then reassembled it carefully, ensuring that the power cable correctly looped around the post that acted as a cable restraint. I then returned it to its place in the entertainment unit, and it’s now working perfectly again with its usual nice bright display. This was another win for the environment and also my pocket. Classically unorthodox car parts D. T., of Sylvania, NSW ran into the bane of the classic car collector, non-standard parts that are hard to find (and often expensive). Thankfully, this one could be disassembled and fixed at a component level... This digital clock/radio had a few problem capacitors. 88 Silicon Chip Australia's electronics magazine During my spare time in COVID-19 lockdown, I’ve been restoring a 1982 Porsche 928. This is a nearly 40-yearold car, and parts are becoming scarce (read: expensive). I’ve been working my way through the car and came to the rear demister. Having resoldered the terminal to the back window (not as hard as it sounds), I connected the battery and switched it on, only to find no warmth at all. A quick check of the fuse box found the relay missing. The 928 is a complicated car by 1980 standards (not today’s, though!). The rear demister provides two power levels. A high heat ‘Boost’ mode operates for about 15 minutes when you push the (momentary) switch. A lower power ‘Maintenance’ mode runs continuously when the switch is on. Boost mode also activates the rear-view mirror heaters. The demister itself is the typical resistive type but is split into two halves – the halves run in series in Maintenance mode and parallel in Boost mode. When this car was designed, they didn’t have the integrated electronics systems that cars have now, so the timing and switching functionality was provided in a special double-width relay that plugs into the fuse panel. This relay also has start and ignition inputs to disable the demister during starting or when the engine isn’t running, and an output to drive the indicator light in the switch. I found a used relay online, and it wasn’t too expensive, so I bought it. It arrived a week later but, after plugging it in, I was disappointed to find Maintenance mode worked OK but Boost mode didn’t. I was about to contact the seller, but a check of the ad showed it was “for parts or not working” – I had missed that point. I decided to try to fix it myself. I thought it probably had a dried out electro. It wasn’t hard to open – I used a screwdriver to bend the aluminium case around the edge and removed the phenolic base. The base was part of an assembly that included the two relays and a phenolic PCB. The circuit consisted of two relays and three transistors plus quite a few resistors and diodes. It all looked pretty good – the tracks and soldering were OK with no apparent faults, nothing was scorched, and the electros hadn’t leaked or were siliconchip.com.au A redrawn circuit diagram of the demister from a Porsche 928, with the actual module shown in the photo below. bulging. I set it up on a bench supply and confirmed the Maintenance relay operated correctly but the Boost didn’t. I measured the relay coils and found the Maintenance coil to be about 60W but the Boost coil was way higher – in the kilohms range. I had a good look at the PCB – most of the soldering still looked OK, but the relay coil windings were very fine wire (0.1mm) and where they joined onto the PCB looked a bit sus, so I cleaned and resoldered them. It was tough to tell if the joint was OK because the wire was so fine, but now I measured something more reasonable for the Boost relay coil. Testing now showed it would latch for about three minutes, but nothing like the expected 15. To make matters worse, the time would get shorter each time I tried it, and after a couple of runs, it would only pull in while the Boost line was active (ie, while the button was being pressed). There were two electros – one of them was 470μF (clearly the main timing capacitor), so I measured voltage across it while I held the relay engaged. It discharged very slowly, as expected, but I didn’t know what the trip point was. I replaced it anyway, but it didn’t make any difference. I then started changing other parts – the other electro and the transistors siliconchip.com.au – all to no avail. I saw another solder joint that I didn’t like the look of, so I resoldered it, then decided to resolder them all. It still didn’t work. Next, I decided to trace out the circuit. This sounds easy, but the combination of non-standard part pin spacing, no overlay and some factory modifications meant it took a few hours before I had something that I thought was right. I’m quite amazed by electronic design engineers of these old eras – they did so much with minimal parts. Like old valve TVs – 10 or so valves to Australia's electronics magazine make a whole TV! These days you’d just pop in a microcontroller and be done with it, but that’d be a couple of hundred thousand transistors on its own. A 555 could do the timing, but that’s probably a hundred transistors, plus you’d need other logic. I tried monitoring voltage levels, but due to the very analog nature of the design and the pre-existing fault, I struggled to rationalise what was happening with what was on the schematic. In desperation, I measured the relay coil winding resistance again and found the Boost relay coil was February 2022  89 back where it was when I started, way too high. Thinking I still hadn’t made a decent connection, I fiddled around with it – sometimes it would measure OK and sometimes not. I couldn’t see anything wrong with the coil but nothing I was doing was working, so I decided to bodge in a temporary replacement. I grabbed a relay from an old motorised car antenna and wired it in place. Success! This worked for around 15 minutes every time. The next thing was to fix it properly. The antenna relay was too big, so I either needed a new, smaller version or had to fix the old coil. From the load resistance, I worked out it needed 20A contacts but I couldn’t find anything small enough, so I started looking inside old car relays. I found one with a coil similar in size and resistance to the faulty one, and with a bit of trimming, I got it to fit. My guess is the old relay coil has a break somewhere with the wire ends rubbing against each other to make a high-resistance joint. When I moved it around or some heat accumulated in it, the ‘joint’ would fail. Unfortunately, I’ll have to wait for a while before I actually use it as the car needs a lot more work. Mobility scooter repair B. G., of St Helens, Tas wasn’t content to simply swap a failed board. He decided to investigate and figure out why it failed. It turned out to be a simple but unexpected fault... My wife has a large second-hand four-wheel mobility scooter (she calls it her tractor). One morning when she went to power it up, it was dead; when switched on with the key, a small meter usually shows the relative battery condition and a power LED lights. I could see a bunch of cables running up the steering column, disappearing behind a cover. Removing that cover exposed a circuit board. This was easily removed by unplugging the cables. Close inspection showed a mixture of parts and no sign of heat or damage. We had the original operating manual with the agent’s number in Hobart. We rang him, and he very helpfully agreed to send several boards after paying a deposit. He suggested measuring the battery voltage and shorting the key switch, which I did to no avail. Starting with the easiest part to access, I decided to replace the control 90 Silicon Chip board on the steering column and was rewarded by the machine coming to life. I returned the remainder to the agent. He was surprised at the failure, saying they had never had a control board failure before. But the story doesn’t end there. When our family arrived for Christmas from the mainland some months later, lo and behold, the scooter failed again with the same symptoms. My son-in-law, a medical electrical engineer, decided to remove all covers and trace and check all the looms while I traced as much as possible on the new control board. There was no obvious damage on this board either, but the key switch track went through a plated-through via to a socket pin to the motor controller. The trouble was that there was no continuity from one side of the board to the other, so we used a small drill to open up the via and soldered a wire to the tracks on both sides. That fixed the continuity problem, and the scooter came back to life. For the other failed board, a simple wire link soldered between the socket contacts was an easier and quicker repair. So I now have a serviceable spare. I contacted the agent again. He seemed impressed, saying that they would not be able to fault-find to that extent, and they would email the manufacturer in Israel. Some weeks later, the agent rang again to say that they had agreed with our diagnosis and that they would modify all their boards with a wire link. I hope the brain keeps working; it’s satisfying when it does. Editor’s note: it seems that the via was too small and fused due to inrush current at switch-on. Larger vias or more vias in parallel would likely solve the problem, although a through-wire is a very robust solution. The misattraction of a nuclear magnetic resonance machine D. D., of Coogee, NSW recalls a servicing problem he encountered many years ago. At first, it seemed that something was wrong with the electronics, but the fault was traced to another nearby source... Two articles in the August 2021 issue prompted me to write to you: Advanced Medical & Biometric Imaging (siliconchip.com.au/Series/369) and the History of Op Amps article (siliconchip.com.au/Article/14987). Both brought back fond memories of my long-lost youth and reminded me of a story that might amuse your readers. The top and underside of the control board of a mobility scooter. A simple wire link as shown on the underside fixed the continuity problem that was found. Australia's electronics magazine siliconchip.com.au In the mid-1960s, I worked at a university chemistry department in the UK, looking after electronic equipment. The story involves NMR (nuclear magnetic resonance) machines and valve-based op amps. NMR machines were highly prized (and very expensive) in those days, and the chemists loved them because they could get a beautiful paper chart output showing the exact chemical composition of a sample. Not long after I started, we got an NMR machine. It was installed during a holiday period when the university was very quiet, in a small room on the lower ground floor of the building. One of the lab technicians, Archie, was ‘promoted’ to work as the machine operator and given the necessary training to use it. All went well for a few weeks; academics and researchers brought samples down to be analysed, and Archie duly provided the relevant chart outputs. However, it was not long before things started to go awry. One day, I got a call from a harassed Archie asking if I could go and see what was going wrong with his machine. He showed me charts where the trace had started normally and then suddenly disappeared. “It happens at random,” he said, “and usually when I am just doing something very critical, it is driving me mad. Do you think you can fix it?” I was a bit dubious as it was a very complex machine, and I only had the vaguest idea how it worked, but I took the manuals back to my workshop to study and promised to come back the next day. I could see that it had a huge magnet, and the manual made it clear that the stability of this magnet was of paramount importance, within a few parts per million. I also saw that the output peaks could be integrated to indicate the quantity of each element in the sample. This was done using a valve-based op amp integrator. My first thoughts were that either the magnet or the integrator were drifting randomly. I wasn’t game to go anywhere near the magnet as the manual had lots of dire warnings, but I thought I could have a look at the integrator. This was a plug-in module; I pulled it out and saw it had a row of valves and an impressive looking feedback capacitor, among other components. I could see no obvious signs of a fault. Ordinarily, I would have suspected the feedback capacitor and replaced it, but I could not find a suitable part, and I was reluctant to ‘hack into’ this new and expensive machine. So I admitted defeat and said I would call the company. Soon, the rep turned up and of course, Murphy being alive and well, the machine behaved perfectly. He said that the problem was probably caused by large metallic objects moving in the magnet’s fringe field. Maybe it was cars passing by in the car park, right outside the wall, or the lift next door. He said the magnet fringe field could extend several metres, and the solution was to install steel sheets in the walls of the room to screen the magnet. The estimated cost was thousands of pounds. At this point, the Professor was called, and a discussion ensued as to what to do. As a true academic, he decided that an experiment must be conducted to find the actual cause of the problem. One of the junior lab techs was summoned and asked to drive his car past the NMR room, jump in the lift, go up to the top floor, then come back down. Archie started a scan, and we all waited to see the results. Sure enough, both things caused the machine to go haywire. The Professor was very annoyed and puzzled, and demanded to know why this had not been observed when the machine was first installed. Of course, it was now term time, and hordes of students were around, going up and down in the lift and driving in and out of the car park. The Professor said he was not going to pay thousands for screening the room. His solution was to paint an exclusion zone outside on the car park tarmac and instigate times when the lift could not be used. Poor old Archie then had to put ‘out of service’ signs on the lift whenever he quickly did a batch of scans. The situation still exists with modern NMR and MRI machines, but proper installation planning involving medical physicists can eliminate the problems (see www.aapm.org/ SC pubs/reports/RPT_20.pdf). 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 siliconchip.com.au Australia's electronics magazine February 2022  91 Vintage Radio Tasma 305 ‘rat radio’ from 1936 By Fred Lever Manufactured by Thorn & Smith (Tasma) in Mascot NSW, the Lawrence 305 is a superhet console radio. It was purchased in a slipshod initial condition, with missing components or oddball replacements. A full rework was needed, of course keeping to the time period. I purchased a derelict Tasma radio chassis from eBay, shown in Fig.1. The chassis was rusted, missing parts and in sad condition. Over its life, it had acquired replacements such as the odd IF coils, but one nice original item was the Tasma dial (Fig.2). I refurbished the radio using the gang and dial, and as many of the original parts as I sensibly could. The chassis took some sorting out, with some engineering to fit later-­ series front-end valves; as part of this process, I needed to fabricate bits and pieces such as coils and shield cans. I arrived at a working chassis and used a 12-inch 1960s Rola permanent magnet speaker fitted with an output transformer and a choke to replace the original electrodynamic type. The set was then a working radio, just waiting for a cabinet to live in. The chassis and speaker sat around for ages waiting for me to make my mind up on what cabinet I would make. I sketched some ideas based on photos of a model 305 and other similar Tasma sets. My thinking then swung around to making what someone in the 1950s or 60s might have made if they needed a second or ‘shed’ radio using a chassis from an old wrecked pre-war console radio. I considered using distressed timber pieces from the scrap pile with old nail holes, warts and all, just like a “rat rod” vintage car where a modified engine and transmission are fitted to a fresh chassis but with a faded body, showing the patina of 80 years or so of use. Thus, my hotted-up Tasma 1936 model 305 chassis and speaker became a “rat radio”. I have plenty of old scrap timber pieces. Most fit the technical description of firewood, having patina in spades! I set to and made up a small console cabinet. The whole process of chassis refurbishment and cabinet construction stretched over a long period. This article picks out just a few of the essential steps in the journey. Refurbishing the chassis The chassis is serial number 305141, ARTS&P rego B52187. The rust had set into the horizontal surfaces with deep pits; I removed the top parts (Fig.3) and discovered some very rough metalwork. Some butcher had chiselled out the original IF cutouts to put in an odd pair of 175kHz coils, one Kingsley KIF4 and one unknown type. Fig.1: the chassis was in an abysmal state when I received it. Fig.2: the dial didn’t look too bad (besides the discolouration from the lamp’s heat at the top), but it was pretty brittle. I added a protective layer to preserve it. 92 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.3: the chassis after removing all the parts but before rust treatment. I profiled and drilled the IF cutouts to accept a matched pair of 1950s 455kHz units labelled “24-7” and “242”. I added a hole in the rear to accept a mains power cord gland. With drilling and cutting completed, I brushed off the loose rust but did not attempt to smooth the chassis out any further. Then I masked up the parts on the chassis underneath and sprayed one coat of etch primer on the top and, before that set, one thick coat of Mission Brown enamel (Fig.4). The brown then crinkle dried, effectively hiding the pockmarked steel. Editor’s note: if you’re going to paint over rust, after removing any loose rust, you should apply a ‘rust converter’ or a primer that does a similar job, like Rustoleum Stops Rust Rusty Metal Primer. Otherwise, it can Fig.4: with the worst of the rust gone and a coat of primer plus a thick coat of paint, it’s now ready to rebuild. continue to rust under the paint. The electronic parts I stripped the electronic parts out from under the chassis. The set had a preassembled tagboard (Fig.5) with most of the IF and AF resistors and capacitors on it. The capacitors were hidden underneath (see Fig.6). A wiring loom was laced around the edge of the chassis with all the supplies like the heater wiring, transformer connections and B+ feeder wires. Some bodgy plastic wires had been added at some point. I pulled the plastic-coated wiring out and used some spare period-­ correct cloth-covered wire to make up the missing connections. The electronic parts were in terrible condition, with many of the capacitors leaky and Fig.5: the original wiring; note the tag strips on which pretty much all the smaller parts were mounted. siliconchip.com.au Australia's electronics magazine the resistors way out of tolerance. I replaced all the out-of-spec parts with 600V-rated polyester capacitors and 1W resistors from Jaycar, except for the back-bias and voltage droppers, where I used either PW3 or 2W types. I did not need to put any parts under the tag strip. That allowed the strip to be re-mounted lower in the chassis. The chassis had a four-pin socket for a type 80 rectifier, with the rest being 6-pin valves. I kept the type 80 rectifier and type 42 output valves as in the original but put a fresh set of octal sockets for the first three valves: a 6K8 mixer, 6U7-G IF amplifier and a 6B6-G demodulator/AF amplifier. The last two needed external shields. I fabricated these from soup cans – see Fig.17 for the result. Fig.7 shows the original circuit Fig.6: some of the larger capacitors were hiding under the central tag strip. February 2022  93 Fig.7: the Tasma 305 radio’s original circuit. I would have liked to restore it to its original condition, but too many of the original parts had gone bad and exact replacements are very difficult to get. Fig.8: this is the ‘rat radio’ circuit I came up with; it brought the radio ‘up to date’ if one were living in the 1950s. Parts from that era are much easier to get, and in fact, I already had most of them. 94 Silicon Chip Fig.9: the two matched 1950s era intermediate frequency transformers I found in my collection that turned out to work pretty well. Fig.11: the wobbulator output with the known-good, pre-tuned IFT I used as a reference. I aimed for a similar result when testing the ‘new’ IFTs. Fig.12: the output using the 24-7 IFT after adjustment. It’s more or less as expected. while Fig.8 is my final ‘rat’ circuit. The arrangement is a typical superhet of the 1950s with AGC control on the first two valves, to keep a level output for a range of radio stations. The front end covers the broadcast band only, and has a curious twin-coil and three-gang tuning arrangement, like a poor man’s RF stage without a valve. I considered inserting an extra 6U7 RF amplifier and making it a six-valve set but I refrained from that and just wired the 6K8 and 6U7 as usual. The 6B6 has a set of diodes that perform the detection and AGC functions. I tested and have marked the circuit with the optional part to use a higher-­ gain 6B8 pentode. However, the lower-­gain 6B6 triode was sufficient to drive the type 42 to full output. If a 6B8 were used, the plate-toplate feedback resistor from the type 42 would help reduce the excess gain and calm any instability. When testing unknown IF coils, one puzzle is to determine which is the primary and secondary, and which ends go the plate, B+, grid, and bias. This can make a difference in some cases as the coils may not be symmetrical and will work inefficiently if connected backwards. On most old IFTs, one can find a flying grid top cap wire, allowing you to determine the grid and secondary connections. I connect the transformers both ways around to my tester to see if the response was better one way or another. With these IFTs, there was a definite ‘good’ and ‘bad’ way of connecting the primary, so that defined the P and B+ pins for me. The intermediate frequency transformers (IFTs) are marked 24-7 455KC and 24-2 455KC (Fig.9). I wanted to test them first, so I dug out the valve IF ‘wobbulator’ tester I made years ago. This tester puts the IFTs into a valve environment with full HT and circuit capacitances. It quickly shows if a coil is not working correctly. The tester is virtually a radio, with a local oscillator using a 6SN7 tunable oscillator, a 6SK7 IF stage and a 6H6 detector. Breakout terminals at appropriate circuit points are provided to clip on meters or an oscilloscope. A 6AC7 sawtooth sweep generator and a 6AC7 reactance valve ‘wobbles’ the 6SN7 tank oscillator to sweep the frequency and thus provide a response curve. The sweeper was still connected to an IFT I had been tested previously, so I powered the unit up and verified that it still worked. With a bit of fiddling, I obtained a sweep response shown in Fig.11. I set the centre frequency at 455kHz and peaked the cores to get maximum response. I then swapped in the transformer marked 24-7 and got the result shown in Fig.12 with the slugs adjusted to their centre peaks. That looked good, so I tried the other unit and got the trace shown in Fig.13, then peaked it and got a pretty good-looking response, shown in Fig.14. Fig.13: the output with the 24-2 IFT before adjustment. Fig.14: the output with the 24-2 IFT after adjustment. Also fine. Testing the IFTs The oscillator coil While I had sorted out the IFTs and was using the original air-cored aerial coils, I had no oscillator coil. I needed a coil to produce the tuning range, say 500-1700kHz, plus 455kHz, meaning it needed to operate from about 950kHz to 2150kHz. Delving into the coil box, I found an air-cored coil the same diameter as the Tasma tuning coils. This was a single three-terminal tapped coil meant for Fig.15: the oscillator coil after I’d finished making my modifications to suit the set under construction. siliconchip.com.au Australia's electronics magazine February 2022  95 Fig.16: the oscillator plate waveform looks bizarre and mangled. Fig.17: ahh, much better. The top of the chassis after restoration. The soup can shields are a ‘love it or hate it’ affair. I happen to think they look pretty decent. a different type of oscillator circuit. I unwound turns from the main winding and then drilled an extra hole in the former to make the coil a four-­ terminal unit, suitable for the 6K8 frequency changer. I reduced the turns until it measured 1.4mH, the inductance I have used in previous 455kHz superhet builds (see Fig.15). I hooked it up to a tuning gang on the bench and checked the frequency range with a fixed and variable padder capacitor. The best way of testing a coil is to put it in the same electrical surroundings as it would be in the set. I wired up a 6SN7 triode to the gang and coil to form an oscillator and checked the result. Depending on the gang trimmer and padder settings, I could get frequencies from 900kHz to 2400kHz, which was close enough to try. I also cut up a scrap Philips IF aluminium shield can in the lathe to suit and tested with the coil inside that; the can’s presence alters the coil’s inductance. I added a ferrite core so I can vary the inductance a bit in the chassis. That gave me three things to tweak: the core, the padder and the gang trimmer. I fitted the cut-down can with threaded feet pinched from another can to hold it to the chassis. The coil worked a treat. The oscillator plate wave is a bit mangled (Fig.16), something there is a bit non-linear! However, the tuned tank wave, the one that matters, was clean with regular 96 Silicon Chip amplitude all over the tuning range. Odds and ends There was a broken mains voltage selector switch on the rear of the chassis. I removed that and fitted the three-core mains lead and gland. That allowed me to provide a solid Earth wire connection to the chassis. I cleaned the dial (shown in Fig.2) by drilling out the rivets, taking it apart and treating each part separately. The celluloid front piece has a dark blemish at the top from lamp heat, and the painting inside was in a fragile condition. The lettering would flake off if touched. I left the blemish as a ‘beauty spot’ and sprayed some clear fixative over the surface. Some white paint spruced up the inside of the metal casing. I fashioned a vintage-looking pointer from a piece of alloy sheet and tapped the spindle so I could use a tiny BA-size screw to hold the pointer on. I cleaned or re-painted other parts to freshen them up. The final circuit My final circuit is not all that different from the original. My IF transformers are 455kHz, differing from the original 164kHz, hence the need for a new oscillator coil. There were some challenges in making the tuning, oscillator and IF coils track in harmony and getting the call sign markings on the dial to match roughly where the stations were. But Australia's electronics magazine it was nothing that a spot of trimmer, core and padder setting tweaks could not handle. I did not use the wire-wound “Candohm” voltage divider resistor shown as item 20 in Fig.7 (and visible in Fig.5) as the end of that was burnt out. I simply used individual dropping resistors to provide the various screen and oscillator voltages needed. Using the smaller modern parts simplified the look of the under-chassis and gave better access to the valve sockets, as shown in Fig.18. The old electrolytic cans with most of the original transfers still intact looked great. I bolted the dead cans back on the chassis with the decal surfaces sealed with clear spray and fitted some modern replacements on a tag strip mounted onto the ends. The speaker choke The speaker was originally an electrodynamic type where the magnet-­ exciting coil was also the smoothing choke for the HT supply, having a DC resistance of 1650W. I had an old Rola 2W 12in type 12O permanent magnet speaker spare, so I bolted it to a plywood off-cut, as shown in Fig.19. I had a 30H choke with 22W resistance to replace the function of the magnetising coil. After experimentation, I finished with a 2kW 30W wirewound resistor connected in series with this choke. That combination gave me a 250V DC HT with minimal ripple in the working chassis. Then I siliconchip.com.au Fig.18: the bottom of the chassis after restoration. The smaller modern components make it look much neater, and it’s also considerably easier to work on, especially as there are no more capacitors hidden under the central tag strip. Fig.19: the Rola 12O loudspeaker I selected for the radio. rewound a 30VA power transformer to work as an output transformer and fitted both to the panel (Fig.20). The output transformer With a 2W coil impedance, it’s best to keep the transformer adjacent to the speaker so the connecting leads are short. I needed a pretty ‘lazy’ transformer for 5W audio with plenty of iron, a secondary delivering about 3V and a turns ratio to reflect 7kW load to the type 42 plate. I used a Jaycar MM2150 (30VA) with a 60W mains primary and a tapped secondary of 6, 9, 12 and 15V. The primary inductance is 5H, and it uses an interleaved lamination stack. The primary handles at least 30mA of DC plate current, and this will add permanently to the iron magnetisation, so I wanted to air gap the stack. The secondary was wound with just the right size wire for a 2A speaker coil current rating (3V at 4W) and had plenty of taps to play with. The primary was the problem; its turn count was not high enough to give a reasonable inductance with the air gap, and it was also too low to get a ratio to reflect 7kW from 2W. The solution was to strip the primary and see how many more turns of a smaller wire I could put back on. I have some eight thou (0.2mm) diameter enamelled wire rated at 80mA, so I used that. I managed to cram 2150 turns into the former, about twice the original number. With 230V AC applied, that gave me 1.6V, 3.4V, 5.1V and 8.6V at the output. I used the 3.4V tap, a ratio of about 70:1. The reflected impedance would be 9.8kW (702 × 2W) , a tad high for a type 42 valve. I restacked the laminations and now had a primary with 200W resistance and 6.1H inductance. Fig.21 shows the primary coil bobbin with a dreaded thermal fuse and Fig.20: the rear of the speaker showing how I mounted the output transformer I made by modifying a mains transformer, plus the filter choke and series resistor for the HT supply (replacing the field coil of the original electrodynamic speaker). Fig.21. I removed the thermal fuse from the transformer while modifying it as it will no longer be a mains transformer. siliconchip.com.au Australia's electronics magazine February 2022  97 Fig.22: the modified transformer after reassembly. Note the red tape providing the ‘air gap’ in the core to prevent saturation from the unavoidable direct current flow. Fig.23: the Bakelite speaker plug I fabricated from a discarded valve base and a scrap dome. Fig.24: the simple cradle I made to hold the chassis. It’s strong and fits the chassis nicely. original winding, both of which were removed. I taped the core “I” pieces together with red insulating tape that defined the size of the air gap (Fig.22). I wired the speaker assembly to the chassis using a discarded valve base as a 5-pin plug. A scrap Bakelite dome fitted neatly into the valve base, so I glued that in (Fig.23). For a starting point, I made up a flat bar cradle for the chassis to sit on and bolt to, shown in Fig.24. This cradle sits at an angle in the chassis, sloping backwards so that the dial is tilted more on an eye-line (see Fig.25). I cut up two five-ply sheets to form the sides, 914mm high and 254mm deep. The cradle sits between these, far enough from the floor to leave room for the speaker plate (Fig.26). This bit of guesswork caused trouble as the dial wound up not being in the centre of the space it occupied and ruined the theory of ‘proportions in design’ when viewed from the front! The set should have been further up. Oh well, this was just another challenge to solve later. Then it was a matter of putting enough timber into the structure to make a frame that would take the weight of the set (Fig.27). That structure is the bones of the set and functional as-is. The set could be considered finished at that point, but it looked a bit bare! A hint to amateurs like me for using timber to build cabinets: build the structure on a level, flat workbench. Shim the bench legs using a bubble level on the top. My bench is a slab of 25mm chipboard sheet sitting on trestles, level to bubble all ways. The sheet itself is flat to about 1mm. Your right-angle square and bubble level are your best friends in keeping the assembly square as you build! I like to get the corner foot weights as even as possible, so the set sits naturally square on the floor. This basic assembly was a bit back-heavy, mainly from the weight of the power transformer. I also put the speaker transformers at the bottom to get the mass as low down as possible. It is preferable to have the set back heavy for safety, so if wobbled, it favours falling toward the wall. All of the interior beams are good Fig.25: you can see how the chassis cradle sits at an angle so that the dial appears straight-on when you look down at it. Fig.26: I mounted the chassis just high enough so that the speaker board would fit below it. This turned out to be a mistake – I could easily have mounted it higher, but I didn’t think of it at the time! By the time I realised this, it was too late... Making the cabinet 98 Silicon Chip Australia's electronics magazine Fig.27: I added bracing to the frame so it would not fall apart if moved with the chassis inside. siliconchip.com.au Fig.28: I added some profiled pieces of timber at the top to resolve the shape. You can also clearly see the frame I made from the speaker grille in this shot. structural timber. The outside timbers are in various stages of aging with random wastage, splits and nail holes. eBay provided a genuine period round Bakelite dial bezel to frame the dial scale plate hole. I dressed the frame, trying not to have too much of a boxy look by adding some curves here and there. There was a problem resolving the look of the top of the set with the side shoulders merging with the dial panel sloping back. I used a piece of quad to roll the front to the top, and a skirting board with a rolled edge for the side plates. Then it was a matter of profiling bits of ply to fit around the top and shoulders and glue the whole thing together. While the glue was drying at the top, I attacked the speaker grille design and made a frame from tomato stakes with the three vertical bars and two sidebars, shown in Fig.28. That gives the speaker some protection and a frame to tack a rectangle of brownish speaker cloth on the inside. I made the frame a push-fit between the shoulders. I trimmed the rough ply edges on the cabinet with a saw, then sanded them smooth. The inside of the cabinet received a spray job top to bottom with matte black paint, along with the speaker grille. Then I brushed the outside of the cabinet and the grille with clear varnish. Three coats of varnish were enough to seal all the rough bits up and highlight the wood grain, nail holes and all the blemishes. Control knobs The set needed three control knobs. These could have been the typical Bakelite types, but while walking down the kitchen aisle at Bunnings, I saw all sorts of cabinet doorknobs. I randomly chose some faceted ballshaped items and, in my innocence, imagined they were plastic. That would be easy to chuck in the lathe and re-profile to look like radio knobs. Unfortunately, they were glass! I never have much luck machining glass in my lathe, so I left them ballshaped, drilled the alloy bases to ¼in to suit the pot shafts, machined the bases to cylinders, then cross-drilled and tapped them for grub screws. Those I made by cutting the heads off 5/32in screws and slotting them with a hacksaw. The resulting knobs (Fig.29) look a bit odd on the set (Fig.30), but you have to try these things. siliconchip.com.au Fig.29: the original Bunnings (left) and modified (right) knobs. The modified knobs were made using a lathe to better suit a 1950s style. Fig.30: this shows how the knobs look mounted below the original dial. This isn’t quite what I was going for, but I think they turned out OK. Fig.31: a close-up of the finished chassis mounted in the cabinet. Australia's electronics magazine February 2022  99 Fig.32: the rear view of the completed ‘rat radio’. I’m pleased with how tidy it is. Fig.33: I solved the blank space by adding a badge. Once again, it didn’t turn out quite the way I intended, but it still looks reasonable. Finishing it Fig.34: this diagram, taken from the service manual, is used in conjunction with the original circuit diagram. It labels the points of interest on the underside of the Tasma 305 chassis, with the numbers relating to the those shown in Fig.7. 100 Silicon Chip Australia's electronics magazine I do not mind rough textures and chunks missing out of surfaces and even odd colours, but I do mind bad proportions. The open area above the dial was just wrong. It needed some optical filling to ‘centre’ the dial bezel. Concocting a winged “Tasma” logo from ply scrap and mounting this to split the distance between the bezel and the cabinet top achieved that – see Fig.33. The detail of the logo was a disaster. I had a bright script style “TASMA” centre icon in yellow to match the front panel. When I varnished the surface, the varnish leached the yellow ink out and faded the icon almost to nothing. You win some and you lose some! [It looks like a purposefully ‘distressed’ detail – Editor] Another detail that I could have done better is that the chassis bolts to the baseboard using Whitworth set screws and wing nuts. The set has that mellow 40s sound and needs an external antenna wire to pick up any stations. Job done! I decided the project had finally arrived at the destination as a ‘rat radio’. Beauty is in the eye of the beholder! SC siliconchip.com.au ONLINESHOP SILICON CHIP .com.au/shop PCBs, CASE PIECES AND PANELS 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 JUN21 JUL21 JUL21 JUL21 AUG21 AUG21 AUG21 AUG21 AUG21 AUG21 SEP21 SEP21 OCT21 OCT21 OCT21 NOV21 NOV21 NOV21 08105211 CSE210301C 11006211 09108211 07108211 11104211 11104212 08105212 23101213 23101214 01103191 01103192 01109211 12110121 04106211/2 04108211 04108212 09109211 Subscribers get a 10% discount on all orders for parts $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 HUMMINGBIRD AMPLIFIER 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 NEW PCBs 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 DEC21 DEC21 DEC21 JAN22 JAN22 JAN22 JAN22 JAN22 JAN22 01111211 16110206 29106211 23111211 23111212 15109211 15109212 01101221 01101222 $5.00 $5.00 $5.00 $5.00 $7.50 $2.50 $2.50 $7.50 $5.00 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 01102221 26112211/2 11009121 SC6204 18107211 18107212 01106193 01106196 $5.00 $7.50 $20.00 $25.00 $7.50 $2.50 $5.00 $2.50 PRE-PROGRAMMED MICROS As a service to readers, Silicon Chip Online Shop stocks microcontrollers and microprocessors used in new projects (from 2012 on) and some selected older projects – pre-programmed and ready to fly! Some micros from copyrighted and/or contributed projects may not be available. $10 MICROS 24LC32A-I/SN ATmega328P ATmega328P-AUR ATtiny85V-10PU ATtiny816 PIC10F202-E/OT PIC10LF322-I/OT PIC12F1572-I/SN PIC12F617-I/P PIC12F617-I/SN PIC12F675-I/P PIC16F1455-I/P PIC16F1455-I/SL PIC16F1459-I/P PIC16F1705-I/P PIC16F88-I/P $15 MICROS Digital FX Unit (Apr21) RF Signal Generator (Jun19), Si473x FM/AM/SW Digital Radio (Jul21) RGB Stackable LED Christmas Star (Nov20) Shirt Pocket Audio Oscillator (Sep20) ATtiny816 Development/Breakout Board (Jan19) Ultrabrite LED Driver (with free TC6502P095VCT IC, Sep19) Range Extender IR-to-UHF (Jan22) Nano TV Pong (Aug21), SMD Test Tweezers (Oct21) Range Extender UHF-to-IR (Jan22) Model Railway Carriage Lights (Nov21) Useless Box IC3 (Dec18) Digital Lighting Controller LED Slave (Dec20) Ol’ Timer II (Jul20), Battery Multi Logger (Feb21) Fan Controller & Loudspeaker Protector (Feb22) Digital Lighting Controller Translator (Dec21) Universal Battery Charge Controller (Dec19) ATSAML10E16A-AUT High-Current Battery Balancer (Mar21) PIC16F1459-I/SO Four-Channel DC Fan & Pump Controller (Dec18) PIC16F18877-I/P USB Cable Tester (Nov21) PIC32MM0256GPM028-I/SS Super Digital Sound Effects (Aug18) PIC32MX170F256D-501P/T 44-pin Micromite Mk2 (Aug14), 4DoF Simulation Seat (Sep19) PIC32MX170F256B-50I/SP Micromite LCD BackPack V1-V3 (Feb16 / May17 / Aug19) Touchscreen Digital Preamp [2.8in/3.5in version] (Sep21) PIC32MX170F256B-I/SO Battery Multi Logger (Feb21), Battery Manager BackPack (Aug21) $20 MICROS PIC32MX470F512H-I/PT Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) PIC32MX470F512H-120/PT Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) PIC32MX470F512L-120/PT Micromite Explore 100 (Sep16) $30 MICROS PIC32MX695F512L-80I/PF Colour MaxiMite (Sep12) PIC32MZ2048EFH064-I/PT DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) DIY Reflow Oven Controller (Apr20), Dual Hybrid Supply (Feb22) KITS & SPECIALISED COMPONENTS INTELLIGENT DUAL HYBRID POWER SUPPLY (FEB 22) Hard-to-get parts for the regulator module – all the ICs & regulators ◉ needed to build one module, plus the schottky diode, 10μH inductor, 4700μF 50V capacitors, 1W shunts and SMD capacitors – does not include PCB (Cat SC6096) $125.00 ◉ does not include the LM2575T as it comes with the CPU module parts Hard-to-get parts for the CPU module – most of the required parts, including programmed PIC32MZ, EEPROM, LM2575T, LM317 & LD1117V regulators etc. You just need the PCB, headers, a ferrite bead, trimpot and electrolytic capacitors (Cat SC6121) $60.00 VARIOUS MODULES & PARTS - 4-pin PWM fan header (Fan Controller, Feb22) - 64x32 pixel white 0.49in OLED (SMD Test Tweezers, Oct21) - pair of AD8403ARZ10 (Touchscreen Digital Preamp, Sep21) - Si4732 radio IC (Si473x FM/AM/SW Radio, Jul21) - EA2-5NU relay (PIC Programming Helper, Jun21) - VK2828U7G5LF GPS module (Advanced GPS Computer, Jun21) $1.00 $10.00 $35.00 $15.00 $3.00 $25.00 IR-TO-UHF MODULE FOR RANGE EXTENDER (CAT SC5993) (JAN 22) SMD TRAINER KIT (CAT SC5260) (DEC 21) PCB and all SMDs (including the programmed micro) for the IR-to-UHF module Complete kit includes the PCB and all on-board components, except for a TQFP-64 footprint device $25.00 $20.00 HUMMINGBIRD AMPLIFIER (CAT SC6021) (DEC 21) USB CABLE TESTER KIT (CAT SC5966) (NOV 21) MODEL RAILWAY CARRIAGE LIGHTS KIT (CAT SC6027) (NOV 21) SMD TEST TWEEZERS KIT (CAT SC5934) (OCT 21) NANO TV PONG SHORT FORM KIT (CAT SC5885) (AUG 21) MODEL RAILWAY LEVEL CROSSING (JUL 21) MINI ISOLATED SERIAL LINK COMPLETE KIT (CAT SC5750) (MAR 21) Hard-to-get parts includes: two 0.22W 5W resistors; plus one each of an MJE15034G, MJE15035G, KSC3503DS & 220pF 250V C0G ceramic capacitor Short form kit with everything except case and AA cells Includes PCB, IC1 (programmed), IC2, D1, L1, SMD capacitors and resistors. Does not include reed switch, magnet, LEDs or through-hole parts PCBs, micro, other onboard parts and heatshrink (no cell or brass tips) PCB and all onboard parts only (does not include controllers) - Pair of programmed PIC12F617-I/Ps - ISD1820P-based audio recording and playback module All parts required to build the project including the PCB $15.00 $110.00 $25.00 $35.00 $17.50 $15.00 $5.00 $10.00 $10 flat rate for postage within Australia. Overseas? Place an order via our website for a quote. All items subect to availability. Prices valid for month of magazine issue only. All prices in Australian dollars and included GST where applicable. To Place Your Order: INTERNET (24/7) siliconchip.com.au/Shop PAYPAL (24/7) eMAIL (24/7) Use your PayPal account silicon<at>siliconchip.com.au Australia's electronics magazine silicon<at>siliconchip.com.au MAIL (24/7) PHONE – (9-5:00, Mon-Fri) Your order to PO Box 139 Collaroy NSW 2097 Call (02) 9939 3295 with with order & credit card details You can also order and pay by cheque/money order (Orders by mail only). Make cheques payable to Silicon Chip Publications. 02/22 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. Resistor-Mite auto-ranging ohmmeter To verify that resistors are good, you could measure their values using a DMM, then convert the colour bands to resistance values and compare them. But it’s much quicker if you connect each resistor to the Resistor-Mite as it shows the expected colour bands, and you just have to compare them to the ones printed on the resistor. It uses a Micromite LCD BackPack with some extra components to convert a resistance value to its closest standard equivalent set of colour bands, then shows them on the LCD screen. So that it can measure a wide range of resistor values accurately, it can switch in multiple different value resistors to form a voltage divider with the resistor under test (RUT). By knowing which resistor has been switched in and measuring the resulting voltage, it can figure out the unknown resistor value to a fair degree of accuracy. While the PIC32 used in the Micromite has a built-in analog-to-digital converter (ADC), it only has 10 bits of resolution. This circuit uses an 18-bit MCP3421 external ADC chip controlled via an I2C serial interface to provide more accurate results. With a 3.3V reference, a 10-bit ADC can measure in 806μV steps. As the MCP3421 is being used here in single-ended mode, it has an effective resolution of 17 bits, giving 131,072 steps and a resolution of 15.625μV (in combination with its internal precision 2.048V reference). The switched resistor values are 100W, 1kW, 10kW, 100kW and 1MW. The lower values are used to measure low-value resistors. If the reading it gets is near the end of its range, it switches to the next higher resistor. It continues until it either gets a reasonable reading, or runs out of higher-value resistors to use as part of the divider. To cover for any variable fluctuation in the voltage and reading, both the ADC digital output code and the voltage divider supply voltage are read eight times by the Micromite and averaged. Also, although both the Mosfets and the ADC have negligible impedance values, these still affect the accuracy of the results, so the software compensates for them. To avoid possible high currents when measuring very low-value resistors, an additional resistor (Rfix) is added in series to the tested resistor end of the voltage divider circuit. The resulting calculation to determine the value of the RUT is: Vin ÷ Vadc - 1 Rrut = − Rfix 1 ÷ (Rref + Rmosfet) + 1 ÷ Radc When a test resistor is placed in the ZIF socket at left it will, after a short time, display the closest value for that resistor. 102 Silicon Chip This gives a result accurate to within a fraction of a percent for values from below 1W to at least 10MW. The RUT, connected across the ZIF socket, forms the upper resistor in the divider while the switched resistor is at the bottom, connected to ground. The switching is done by activating one of Mosfets Q1-Q5, wired between the ‘bottom’ end of the divider resistor and ground. Rather than using a BackPack PCB for this design, I created a custom PCB that includes the BackPack circuitry plus the extra components needed, mainly using SMDs. The board also has provision for using a prebuilt MCP3421 ADC module and a 5V to 3.3V AMS1117 linear regulator module. The PCB supports either the 2.4in or a 2.8in LCD touchscreen. The EAGLE PCB file, top/bottom copper etching patterns and Gerber files are available for download from siliconchip.com.au/Shop/6/6231 along with the Micromite software. When an unknown resistor is placed in the 28 pin ZIF socket and the TEST button (S1) is pressed, each resistor is activated one at a time by switching on Mosfets Q1 to Q5 in turn. The voltage from the divider is then This menu is used to set the values of the five fixed resistors on the PCB connected to Q1-5. It can be accessed by touching the large resistor on the adjacent screen. Australia's electronics magazine siliconchip.com.au read by activating the ADC in 18-bit ‘one-shot’ mode (by sending I2C data &H68,0,1,&H8C). At the same time, the supply voltage is read via pin 24 of the PIC32 chip. This is repeated eight times, with a short pause after each count to discharge the ADC sampling capacitor fully, then averaged. If the voltage reading is below 0.4V, the next Mosfet is activated, and so on until the read voltage value is above this threshold. If a full-scale reading remains at the end of the process, a message is shown which reads “NO siliconchip.com.au RESISTOR FOUND OR OUT OF RANGE”. The Micromite then shows the resistor colour codes for the closest match to the value determined. The values of the five switched resistors on the PCB can be calibrated by touching the large resistor pattern on the screen. When selecting a new value using the touchscreen input, press the selected box for few seconds to allow for correct readings. Gianni Pallotti, North Rocks, NSW. ($150) Australia's electronics magazine This AMS1117 regulator module can be used instead of the BackPack’s on-board LD1117A (REG1) and respective capacitors. February 2022  103 Using a capacitive soil moisture meter There are several types of lowcost soil moisture meters available from eBay and similar outlets. These measure the voltage created between two electrodes of different materials when the probe is inserted into wet soil. Unfortunately, these electrodes quickly oxidise, giving false readings. This design uses a capacitive moisture probe which is shielded from the environment with a protective coating. It does not suffer from the disadvantage of the cheap probes. These probes are readily available on eBay. They are advertised as containing a 3.3V onboard regulator, but I found that on mine, it was replaced with a wire link. They seem to work fine regardless of that. The probe is connected to a PIC32MX170F256B-50I/SP microprocessor programmed with the Micromite software. The micro drives a 1.8-inch (45mm) diagonal TFT ST7735S-based LCD module with 128 x 160 pixels. 104 Silicon Chip A pushbutton activates the moisture meter which capacitively measures the proportion of water in the soil, from 0% (bone dry) to 100% (saturated). The result is displayed on the LCD screen. The unit switches off automatically eight seconds later. It’s powered from a standard 9V battery, and the battery voltage is monitored and a warning displayed when the battery level gets low. So that the battery lasts a long time, the unit is completely powered down when off. Pressing the button attached via CON3 forward biases the base-emitter junction of NPN transistor Q1, which sinks current from PNP transistor Q2. Q2 supplies current from the 9V battery to the inputs of regulators REG1 (3.3V, powering IC1) and REG2 (5V, powering the LCD screen & sensor). When IC1 boots up, it brings its RA0 digital output (pin 2) high, holding Q1 and thus Q2 on, so power continues to flow after the pushbutton is Australia's electronics magazine released. After displaying the reading for eight seconds, IC1 brings its pin 2 low, switching off Q1 & Q2 and thus powering the whole unit down. Getting a reading from the sensor is simple. It produces a voltage at its Vout terminal that’s proportional to the soil moisture content. The 100kW resistor to ground ensures this voltage stays within the 0-3.3V range that IC1 can handle. This is converted to a digital value by IC1 using its internal analog-to-digital converter and the pin 4 analog input (AN2). Analog input AN3 at pin 5 is used to sense the 5V supply rail voltage to determine when the battery is low. That’s because the battery can power the circuit as long as the 5V rail can be regulated. Once this rail starts to drop compared to the 3.3V rail (which will not sag as readily), the unit determines that the battery is exhausted. The display is connected using the SPI interface of the microprocessor and the backlight is powered via a siliconchip.com.au 100-120W resistor. The backlight takes a significant proportion of the overall current, thus this range of values is a compromise between display readability and battery life. In an indoor setting, this value could be increased significantly. To fit the probe into the 3D printed case, I desoldered the plug and soldered wires directly to the probe. I then fixed it to the case using hot melt glue. On the first prototype (pictured), the probe was mounted component side down, but the case is now designed for the opposite orientation. On the two prototypes, the start pushbutton was protected from moisture by repurposing a section of the rubber overlay from a multi-button keypad. Software & calibration The ST7735 LCD display driver was written and is maintained by Peter Mather on The Back Shed forum. This must be loaded into the Micromite first, then saved as a library. To do this, load “moisturelib.bas” into Musical bicycle horn Human powered vehicle racing in Australia generally requires an “electronic warning device” to be fitted to each vehicle to be used when overtaking. Usually, a piezo siren is used, but those are boring! This design uses a piezo siren to play simple tunes, and with the right software, it can also act as a very loud MIDI synthesiser. The horn is powered by two AAA cells and is controlled by an Arduino Nano. Its circuit is shown in Fig.1. Sound is generated by a piezo transducer salvaged from an old smoke alarm. In general, the older the smoke alarm, the larger the piezo diameter siliconchip.com.au the Micromite and then type “library save”. Next, load “moisture.bas”. The Micromite will need to be reset before the first time it is run so the display driver is initialised. After that, the software will run automatically. Calibration is straightforward. Short the pins of CON5, then press the start button until the display says “Reset”, then release it. Remove the short from CON5, then power the unit up with a completely dry probe. Wait until the display switches off, then submerge the probe in water and power it back up again. Keep it submerged until it switches off. The prototype is housed in a custom 3D-printed case. The STL files and Micromite BASIC software code are available to download: siliconchip. com.au/Shop/6/6232 Editor’s note: a BC547 can be used for Q1 and a BC639 for Q2 if you have trouble finding the recommended ones. Kenneth Horton, Woolston, UK. ($120) The moisture meter in its 3D-printed case. Once calibrated, the unit displays the moisture content of the soil that the probe is inserted into as soon as the start button (on top) is pressed. It will then automatically switch off after eight seconds. and thus lower the resonant frequency, hence better performance for lower notes. The best transducers are separate from the smoke alarm case so that a separate resonance chamber does not need to be created. To generate a high voltage for the piezo to be loud enough, a two-stage system is used. One stage boosts the battery voltage to an intermediate level, and the second stage drives the transducer. This is inspired by but implemented differently from the Hornit bike horn. The first stage uses a PWM signal generated by the Arduino to switch Q1 on and off at 62.5kHz, drawing current through L1 so that when Q1 is switched off, the voltage across Q1 rises above the supply voltage. This forward-biases diode D1 and charges the 47μF capacitor. As there is no feedback, zener diode ZD1 clamps the maximum voltage to 22V for safety. The second stage consists of autotransformer L2, designed for piezo sirens and some smoke alarms, pulsed by Q2 to generate each note. The autotransformer has an approximate inductance of 3mH on the primary and 90mH on the secondary, and produces over 100V peak-to-peak for driving the transducer depending on the frequency. The autotransformer is the hardest part to source. I found the easiest Australia's electronics magazine February 2022  105 Fig.1 method of obtaining one was to buy a small piezo siren such as Jaycar LA5141 and disassemble it. The smoke alarm the piezo transducer was salvaged from may also have one. Two buttons are connected to header CON2, one for making the horn go off and one for changing the tune that is played. A double-throw momentary centre-off switch could also be used. LED1 indicates the status. The microcontroller spends most of its time in power-down mode, using virtually no power, waking only when a button triggers an interrupt or the chip is reset. A couple of modifications need to be made to the Arduino Nano to reduce the power requirements and avoid charging the batteries when plugged into a computer. Fig.2 shows the changes on the circuit of a standard Nano. 106 Silicon Chip The modifications involve disconnecting the positive USB power rail from the ATmega328P and removing unnecessary components that use power. This means removing the diode between the USB +5V rail and the 5V rail, cutting a track to disconnect the 5V pin of the CH340 USB to serial converter, adding a wire to connect the 5V pin of the CH340 to the USB +5V rail and removing the RX, TX and power LEDs. I also removed the built-in voltage regulator for good measure. The brownout detection fuses on the ATmega328P need to be changed to reset the microcontroller at 1.8V instead of the default 2.7V, so that it will operate reliably with partially discharged cells. To do this, the extended fuse needs to be set to 0xFE from its default value of 0xFD. You need an external Atmel programmer to do this, Australia's electronics magazine although you can use another Arduino. See these links: siliconchip.com.au/link/abb2 siliconchip.com.au/link/abb3 siliconchip.com.au/link/abaw I have designed a PCB for the horn. It is single-sided and has fairly generous tolerances for home manufacturing, although wire links are needed if two layers aren’t available. I also designed a 3D-printed case to house the unit. It might need to be modified to suit your piezo siren. The software, PCB patterns and 3D printer STL files can be downloaded from the GitHub link below. The battery and PCB are screwed to a tray that can be slid in and out of the housing for access when the front is removed. The USB connector of the Arduino, LED and button connector are accessible from the back. As the unit isn’t fully waterproof, I siliconchip.com.au Fig.2 recommend that the circuit board be conformally coated to protect against moisture. Large components such as the autotransformer and capacitors should be glued down for vibration resistance. Optimising the volume I noticed that the volume was unpredictable for each note. To get the best performance, I wrote a Python script and corresponding Arduino sketch to try many different duty cycles. When left with a computer with a microphone in a quiet room, the computer will measure which parameters give the loudest results. After a bit of cleaning up, the program will produce code that can be pasted into the main BikeHorn sketch. See the Tuning subfolder in the source siliconchip.com.au code for more information on this. Generating & uploading tunes I wrote a plugin for the sheet music editing software Musescore3 that can take suitable sheet music and MIDI files and generate an array that can be copied and pasted into the sketch. Note that the “Loop endlessly” checkbox should be ticked and musical rests at the start and end of the tune removed for continuous operation. See the Musescore Plugin page, which can be found at https://github. com/jgOhYeah/TunePlayer Tunes need to be pasted into tunes.h in the main BikeHorn sketch and the tune’s name included in the array at the bottom of the file. The Arduino IDE can be used to upload the sketch to the Arduino. Australia's electronics magazine If the ‘change tune’ button is pressed on resetting the microcontroller, the Arduino will go into MIDI synthesiser mode. This listens for MIDI messages on the serial port and attempts to play them. It can only play one note at a time, though, and by default, it listens on MIDI channel 1. On the computer side, a program such as Hairless MIDI Serial is suitable. Turning the MIDI to serial bridge on in Hairless MIDI Serial is enough to reset the microcontroller without taking the siren apart. You can find source code and related files for this project at https://github. com/jgOhYeah/BikeHorn and a video of it in operation at siliconchip.com. au/Videos/Bike+Horn Jotham Gates, Notting Hill, Vic. ($150) February 2022  107 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 Decoding USB Cable Tester messages I have just completed the USB Cable Tester (November & December 2021; siliconchip.com.au/Series/374). What a great little gadget. I found a few high-resistance cables, which I disposed of. The ability to distinguish between power-only vs data cables allowed me to exercise my label maker. However, even after re-reading both articles again, as well as the June 2021 USB expose, I remain confused about the meaning of several displayed messages. I wonder whether you can explain what these messages mean. For example, when I plug both ends of a particular cable in, it is reported as “POWER ONLY”. On the next line, the message “CHECK UFP” is present. But the meaning of that is unclear, and I am not sure what to do about it. When the DFP (USB-A) is unplugged, it now reports what appears to be a single-ended UFP analysis: “UFP: DP ,DM ,” What do “DP” and “DM” mean, and what can be inferred from the blank field following each? (R. M., Ivanhoe, Vic) ● You are correct that the display size sometimes limits the amount of information that can be displayed, but we thought we struck a reasonable balance. The DM and DP designation refer to specific conductors in the USB cable (also known as D- and D+). These can be seen in the Fig.1 schematic in the first article, where they connect to the various USB sockets. As noted on page 93 of the second article, “Check DFP” (or UFP) is a prompt that you can get more detailed results by testing one end only. You appear to have realised this. The resulting “UFP: DP ,DM ,” message indicates that the DM and DP wires of the upstream-facing port (UFP) are connected together. That they are not shown elsewhere means they are not detected at the other end of the cable. We didn’t see this type of cable in 108 Silicon Chip our testing, but it is consistent with some non-standard cables made for charging only. The shorted pins are detected by some chargers or power supplies to produce a specific charging current, usually more than 500mA. So that cable is only suitable for power. The blank fields simply make the display more legible by aligning the listed items. In general, any DFP or UFP indication apart from GND and SHLD being connected (in anything but a power-­ only cable) is not a good sign. The specifics of that message will only be helpful if you intend to repair the cable. USB Cable Tester is only for passive cables I have built the USB Cable Tester and have a question about USB-C cables containing an E-Marker chip. Does the Tester work with these cables? I have a USB-C to USB-C cable with a chip in it, and the Tester tells me it is Power Only and 0+ 0-. Both ends of the cable are right-angle connectors, making it difficult to try all the combinations as the USB-C sockets are close together. Thank you for another excellent project. The SMD Test Tweezers are useful for SMDs and also through-hole resistors, with their tiny colour code bands. (J. B., Blackwood, SA) ● We don’t have many cables with chips, so we weren’t confident in advising what the USB Cable Tester would do when connected to one, especially as different brands would probably implement different features. The Tester only applies a minuscule current, probably not enough to activate any electronics in the cable. If power is needed to allow the data lines to work, they may not be detected at all, as appears to be the case with your cable. Testing USB 2.0 Micro-B cables Regarding the Micro-B connector on the USB Cable Tester, I have some Australia's electronics magazine equipment that uses the USB 1.1-2.0 Micro-B plug. Will that fit into part of the USB 3.x Micro-B socket? (A. F., Salamander Bay, NSW) ● As far as we know, all USB plugs/ sockets are backwards compatible. The USB 3.x Micro-B socket is basically a USB 2.0 Micro-B socket with an extra socket (with more pins) alongside it. So you would just plug the USB 1.12.0 Micro-B plug into that portion of the socket and ignore the rest. The USB Cable Tester can check just about any passive cable. The only thing it can’t do is verify signal integrity for high-speed transfers – that would be hard to do without making it much more expensive and complicated. Finding an amplifier kit for a beginner I’ve read your magazine for a long time, but I’m only at a beginner level with electronics. I want to build an amplifier project from your magazine that I can buy in kit form from Jaycar or Altronics. Ideally, I would like to build a stereo amplifier with a bit of power, but one that is not overly complex to build. I was thinking of building the Compact 12V 20W Stereo Amplifier (May 2010; siliconchip.com.au/Article/152) using the Altronics kit, Cat K5136. I don’t particularly need the 12V option, but I thought this might be easy enough to build. Do you have any other recommendations for amplifier kits that I can buy off the shelf? (E. M., Hawthorn, Vic) ● We agree that this kit is an excellent amplifier for beginners to build. Most other kits would involve mains wiring, whereas this one runs from a safe, low voltage, but is still very useful. 20W per channel can be plenty depending on the speakers and the room. If you ‘graduate’ to a more experienced level and want to build a mains-powered amplifier, the recent Hummingbird miniature power amplifier is easy to assemble and can siliconchip.com.au deliver up to 100W. See the December 2021 issue (siliconchip.com.au/ Article/15126). SMD Tweezers drawing too much current I ordered one of your Christmas Ornament kits & the SMD Tester Tweezers kit (Cat SC5934, October 2021; siliconchip.com.au/Article/15057). I built the Test Tweezers kit first to check I had the LEDs around the correct way on the Ornament. I have noticed that SMD Test Tweezers have a thirst for batteries. When the display is on, the current draw is about 6mA, but when it is idle, it only drops to 3mA! That drains button cells in just a few hours. I can run it off an external 3V battery pack with no problems. I built it partly for the novelty, and to test SMD parts before trying to solder them in future kits. Still, it’s a fun testing toy to have. Thanks for all the hard work selling these kits. (M. A., Artarmon, NSW) ● That definitely doesn’t sound right. The expected sleep current is a few microamps. We’ve built a few prototypes, and they all sit happily idle for weeks at a time and wake up when needed, which they wouldn’t do if they were drawing that much current all the time. We suspect that either the OLED is misbehaving or the micro is not going to sleep. Check that the display is completely blank after the five second timeout. The 6mA drain during use sounds quite high, so we think something is continuously drawing an extra 3mA. That would also explain the high sleep current. While faulty PICs are rare, we have come across them occasionally, so that is possible. But we think more likely it is the screen, and you should be able to confirm that by unplugging/ desoldering it. Spot welder for making Li-ion batteries Have you published any articles/ projects on spot welders for making Li-ion battery packs? (Tom, via email) ● We haven’t, although we will be publishing one in the near future. While you can find many designs for spot welders online. Do not make one that uses direct mains power – they are not safe. siliconchip.com.au Errors programming newer PICs I am trying to convert from the older PIC series that I am used to, such as the PIC16F88, to the more modern (and lower-cost) devices such as the PIC16F1455, but I have run into a problem trying to program them. In July 2010, you published an article on using the PICkit 3 to program micros which I have followed since. In my setup, I use the PICkit 3 to power the PIC. When I went to program the PIC16F1455, the programming software said that I would have to download new firmware for the programmer, which it did automatically. I then followed the standard procedure for programming in the past, and received a message saying: PK3Err0045: You must connect to a target device to use PICkit 3. PK3Err0035: Failed to get Device ID I had definitely ticked the box saying power device from PICkit 3. I repeated the process and received the same result, this time using a DVM to confirm that I had 5V on the device. I changed back to a PIC12F617 that I programmed before, and received the same error message. So now I can’t program at all. I am using MPLAB IDE V8.91. Have you come across similar problems and can you help me solve my problem? (L. K., Ashby, NSW) ● We have run into problems like this, especially programming newer PICs with older programmers like the PICkit 3. The PICkit 4 seems to handle this a bit better (although the PIC16F1455 is supported by the PICkit 3). We usually use MPLAB X these days since we need the latest version to work with the latest parts. We tested programming a PIC16F1455 using MPLAB v8.91 (one of the versions just before they switched to the X series), and we also couldn’t get it to connect to or read from the part (although it updated the programmer firmware as expected). Retrying with MPLABX v5.05, it worked straight away. MPLAB v8.91 is from 2013, and the PIC16F1455 is about the same age, so it’s a bit of a ‘bleeding edge’ combination (that’s now about eight years old). The Microchip Archive has at least one newer MPLAB version pre-X Australia's electronics magazine (v8.92) and all the older MPLABX versions, which you can download from siliconchip.com.au/link/abcc We recommend that you try using a newer version of the IDE. Even if you insist on using the pre-X IDE for development, you could still install MPLAB X and use the programming software (IPE) that comes with it to flash the chips. Universal Dimmer has limited IR angle I have been using John Clarke’s Universal Dimmer with Remote Control since it was published in February & March 2019 (siliconchip.com.au/ Series/332). I recently converted a large room into a home cinema and installed the dimmer in place of an existing wall switch beside the screen. The switch controls four LED lamps and works fine if not using the remote. But I find that unless the remote faces the switch directly (ie, perpendicular to the touchplate at 5m), it is not recognised, implying a very narrow angle of sensitivity. The problem is that it does not respond at my preferred seating position approximately 6m away from and 30° to the face of the touchplate. What, if anything, can be done to enable me to allow the remote/touchplate combination to work from my preferred seating? (N. H., Sanctuary Point, NSW) ● You could use an infrared remote control extender. This receives and retransmits the infrared signal from an infrared LED closer to the receiver and from a different direction. Alternatively, use an infraredto-433MHz transceiver. This eliminates the need for a wire between the receiver and the IR retransmitting LED. We described such a device in the January 2022 issue (siliconchip.com. au/Article/15182). Sourcing 9mm pots from overseas I bought all your parts to make the 3-Way Active Crossover (September & October 2017; siliconchip.com. au/Series/318), including the SMD pack and potentiometers VR3-6. Now I am having difficulty sourcing 10kW potentiometers VR1, VR2 and VR7-VR10. February 2022  109 I am based in Canada, and I don’t want to order from Jaycar; I would prefer to find a local distributor. I am guessing that these are Alpha units. Do you have the part numbers? (N. M., North Saanich, BC, Canada) ● Digi-Key or Mouser should be able to help you. They are both based in the USA and have Bourns potentiometers that are equivalent to the Alpha pots that we used. Search for the following Bourns part numbers on either website: PTD902-2015F-A103 10kW dual logarithmic, one required PTD901-1015K-B103 10kW single linear, one required PTD902-2015K-B103 10kW dual linear, four required Inconsistency in SC200 current measurements I just read the letter from R. S. in the Ask Silicon Chip section of the October 2021 issue regarding an imbalance in the quiescent current of the SC200 audio amplifier (January-March 2017; siliconchip.com.au/Series/308). I was wondering if this was sorted out because I built four modules and all had exactly the same difference in the positive and negative rail. I presumed it was OK as the modules seem to work fine. I’ve just purchased the parts to build two Hummingbird amplifier modules for my tweeters, and I’ll be following that with the Three-way active crossovers. Thanks for the great work. (T. B., Bumberrah, Vic) ● While looking into this enquiry, we re-read the original letter and discovered a discrepancy. The SC200 articles state that the safety resistors should be 68W 5W types, but R. S. noted that they were 6.8W, and we took his word for it. Now that we think about it, they probably were 68W, meaning the imbalance was only 5mA, not 50mA. There is a slight imbalance in the current drawn by the SC200 amplifier, on the order a couple of milliamps, which is swamped by the module’s quiescent current once the bias has been set. But before the bias is set, the difference would be apparent. The difference has to do with 4mA flowing from the positive rail to ground, though the two 6.8kW series resistors at the collector of Q6, and the 2mA or so through the 22kW resistor at the collector of Q7 between the 110 Silicon Chip negative rail and ground. The result is an imbalance of about 2mA, so the positive rail safety resistor can be expected to have a voltage drop about 140mV higher than the other. We aren’t sure why R. S. noted a drop of roughly double that, but it might come down to resistor tolerances, capacitor leakage or something else we hadn’t considered. As long as the imbalance equates to just a few milliamps, the output sits near 0V and the bias control responds as expected, we think the amplifier modules should work fine. Trouble getting LCD BackPack to work I have built your Advanced GPS Computer kit, but the LCD screen does not light up. It has 3.3V power to it. I note in the August 2019 article on the Micromite LCD BackPack V3 that there is a section on driving the 3.5-inch touchscreen; is this software incorporated in the pre-programmed software for the processor? The LCD Touchscreen still doesn’t work if I remove the GPS board. I assume that the V3 Backpack should work without the GPS board. Without the GPS board plugged in, I am using the USB to power the Backpack. The LCD still does not illuminate. The only change I made on the GPS board was because I could not source the IRLML2244 P-Channel Mosfet. I have an IRLML2244 on order from RS Components with delivery due on the 23rd of December, but the date keeps slipping; I ordered it in August. So I used an IRF9540N P-channel Mosfet instead. (J. L., Tauranga, NZ) ● You cannot replace the IRLML2244 with an IRF9540N as it is not a logic-­ level Mosfet (it’s also in a totally different package). The -3.3V gate drive voltage will not be sufficient to switch it on to any significant extent. The parts situation is extremely frustrating, but element14 and RS both have suitable parts in stock, such as the BSS308PEH6327XTSA1 (element14 Cat 2432719, RS Cat 823-5500). You mention that the screen has 3.3V power. Where are you measuring this? The LCD panel is only fed 5V (from the USB socket) and has its own 3.3V regulator. The separate backlight supply is also 5V. If you have some photos of your assembled PCBs, that may help us diagnose further. Australia's electronics magazine With the BackPack powered via the USB socket, a quick way to test the backlight is to short the two leftmost pins of VR1 (MANUAL BACKLIGHT) on the V3 BackPack PCB. You could solder a jumper header for testing. This should power the backlight directly, even if the LCD is not initialised. The pre-programmed PIC is set up to initialise the LCD, however. The fact that it is not lighting up points to a problem somewhere on the BackPack PCB. Check around Mosfets Q1 and Q2. Q1’s gate should be at +3.3V due to the pull-up resistor, while Q2’s gate should be at 0V, being pulled down by Q1. Sourcing parts for CDI project from overseas Greetings from France. Some time ago, I purchased components from you for the Multi-Spark Capacitor Discharge Ignition (CDI) project (December 2014 & January 2015; siliconchip. com.au/Series/279), including the PCB, transformer components, ICs, Mosfets etc. It’s now wintertime in France, so I wanted to assemble the kit and purchase the rest of the needed parts locally. I’m looking for the S14K275 VAC metal oxide varistor (Jaycar RN3400, Altronics R4408), but I can’t find that exact part here. Same for the Vishay BCC23922105 100nF class X2 275V AC capacitor. Are there any alternatives to these, or can you suggest where I can purchase them? (P. H., Saint-Pierre-surOrthe, France) ● The S14K275VAC is a metal oxide varistor (MOV) with the following specifications: • Disc diameter: 14mm • Lead pitch: 7.50mm • Operating voltage: 275V AC • Clamping voltage: 710V AC • Peak current: 4500A • Maximum energy: 115J Farnell in France (fr.farnell.com) sell the EPCOS B72220S0271K101 (catalog code 1004363), which should be a suitable replacement. The 100nF 275V AC capacitor is an X2-rated metallised polypropylene (MKP) capacitor with a 15mm lead pitch. Farnell also has an equivalent to this, the EPCOS B32922C3104M000 (catalog code 1112840). continued on page 112 siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip FOR SALE FOR SALE KIT ASSEMBLY & REPAIR LEDsales VINTAGE RADIO REPAIRS: electrical mechanical fitter with 36 years ex­ perience and extensive knowledge of valve and transistor radios. Professional and reliable repairs. All workmanship guaranteed. $17 inspection fee plus charges for parts and labour as required. Labour fees $38 p/h. Pensioner discounts available on application. Contact Alan, VK2FALW on 0425 122 415 or email bigalradioshack<at>gmail. com LEDs and accessories for the DIY enthusiast PMD WAY offers (almost) everything for the electronics enthusiast – with full warranty, technical support and free delivery worldwide. Visit pmdway.com to get started. SILICON CHIP ASSORTED BOOKS FOR $5 EACH Selling assorted books on electronics and other related subjects – condition varies. Some of the books may have already been sold, but most are still available. Bulk discount available; post or pickup. All books can be viewed at: siliconchip.com.au/link/aawx Email for a postage quote, quote the number directly below the photo when referring to a book: silicon<at>siliconchip.com.au LEDs, BRAND NAME AND GENERIC LEDs. Heatsinks, LED drivers, power supplies, LED ribbon, kits, components, hardware – www.ledsales.com.au TRONIXLABS PTY LTD would like to thank all of our customers for their support and feedback. For any enquiries or customer technical support, please email support<at>tronixlabs.com PCB PRODUCTION PCB MANUFACTURE: single to multilayer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www.ldelectronics.com.au DAVE THOMPSON (the Serviceman from 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, NZ but service available Australia/NZ wide. Email dave<at>davethompson.co.nz KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, address & credit card details, or phone Glyn (02) 9939 3295 or 0431 792 293. WARNING! Silicon Chip magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of Silicon Chip magazine. Devices or circuits described in Silicon Chip may be covered by patents. Silicon Chip disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. Silicon Chip also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. siliconchip.com.au Australia's electronics magazine February 2022  111 Obsolete parts in older projects Could you please tell me whether any hard-to-get parts are required to build the Constant High-Current Source from June 2002 (siliconchip. com.au/Article/4065) or the 50W DC Electronic Load from September 2002 (siliconchip.com.au/Article/4029)? I realise that you probably don’t have PCBs for these projects. (R. M., Melville, WA) ● For the Constant High-Current Source from June 2002, the heatsinking arrangements might need to be changed to suit available heatsinks. The remaining parts are commonly available. For the 50W DC Electronic Load Advertising Index Altronics.................................37-40 Dave Thompson........................ 111 Digi-Key Electronics...................... 3 Emona Instruments.................. IBC Jaycar.............................. IFC,53-60 Keith Rippon Kit Assembly....... 111 LD Electronics........................... 111 LEDsales................................... 111 Microchip Technology.................. 5 Mouser Electronics..................OBC Ocean Controls............................. 7 PMD Way................................... 111 SC RTV&H on USB...................... 75 SC USB Cable Tester.................. 91 SC Vintage Radio Collection...... 10 Silicon Chip Subscriptions.......... 6 Silicon Chip Shop.................... 101 The Loudspeaker Kit.com............ 9 Tronixlabs.................................. 111 Vintage Radio Repairs.............. 111 Wagner Electronics..................... 87 112 Silicon Chip from September 2002, the STW34NB20 200V, 34A N-channel Mosfet is obsolete, so an alternative will be required. Suitable parts that are currently available include the IRFP240PBF, IRFP250(N)PBF, IRFP260(N/M)PBF and IXTH26P20P. Searching for another discontinued part I am trying to build the Sound Level Meter from your Electronics Test Bench book but I am having difficulty finding a three-position, two-pole switch with the correct pin placement. This project is probably over 20 years old. Is there some way I can mimic what the switch does with jumper pins, perhaps? Failing that, where would I get such a switch? (S. N., Clayton North, Vic) ● You are right that switches with the contact arrangement used in that project are no longer available. Switches are available with a similar layout, but you will have to wire it to the board using flying leads. You could use a DP4T slide switch from Altronics (Cat S2040) and wire the switch terminals to the PCB, with the third and fourth positions wired in parallel. You could also use the Altronics S2033 (4P3T) slide switch and ignore the third pole. It would also be possible to wire up a rotary switch like Altronics S3008 or S3022, or Jaycar SR1212. The PreChamp is an old design I am building several PreChamp pre-amplifiers (July 1994; siliconchip. com.au/Article/5252) to increase the signal output from the line output jack (not the headphone jack) on a TV, and plugging the resulting increased signal into a Bluetooth transmitter then to Bluetooth headphones. It works OK, but I’m not happy with the resulting audio quality when compared to another pair of wireless headphones that I have. Using a signal generator and a Hantek USB scope, I have discovered that the frequency response of the PreChamp is not flat. With a constant input level at all frequencies, I found that at 100Hz the output level was 85mV but at 10kHz, the output level climbed to 200mV, and at 15kHz, the level was 225mV. Australia's electronics magazine I have altered the Preamp’s gain by changing the two resistors to 1500W and 150W using the formula printed in the magazine, giving a gain of approximately 11 times, which is around 21dB. Would this have altered the frequency response of the PreChamp? I suspect not. Can you suggest any components that I can change the value of to get the frequency response flatter? (N. L., Christchurch, NZ) ● The PreChamp is quite an old design and we would not design something like that today. As a result, it has relatively poor frequency response flatness. Still, it should not be behaving in the manner you have described. Our circuit analysis of the original design shows that it has a plateau-type response with -3dB points at around 60Hz and 100kHz, and -1dB points at around 115Hz and 37kHz. So it suffers a fair bit at the lower frequency end, but should be pretty flat at the high end, up to about 20kHz. Changing the gain-setting resistors doesn’t have much effect on the calculated response. Note that we published a new design in January 2013 – the Champion (and Pre-Champion). That circuit has a much flatter frequency response. We even published frequency response and distortion graphs in that article, unlike the original Champ/PreChamp. Still, we aren’t sure why you are getting an increased response at higher frequencies. That points to an increase in feedback impedance with frequency, but the only non-resistive element in the feedback network is the 1.5nF capacitor, which should have the opposite effect. The only explanations we can come up with are that your input coupling capacitor is too low in value or faulty, which would cause lower frequencies to have more attenuation and thus give you a rising response with frequency. It could also be a similar problem with the output coupling capacitor. SC The March 2022 issue is due on sale in newsagents by Monday, February 28th. Expect postal delivery of subscription copies in Australia between February 28th and March 11th. siliconchip.com.au “Rigol Offer Australia’s Best Value Test Instruments” Oscilloscopes NEW 200MHz $649! New Product! 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