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USB-C Bench PSU Delivering up to 20V at 2A, load switch, automatic thermal switch, ‘circuit breaker’ mode and more Electric Vehicle Charging a practical guide STARTIN G ON PAG E 68 OCTOBER 2026 Programmable USB-PD Modules p38: how to control USB power sources How Motors Work, Part 1 p50: starting with DC motors Audio Spot Frequency Test Generator p60: produce low-distortion test signals Phenomenal Pinball Machine, Part 5 p74: the finishing touches ISSN 1030-2662 10 9 771030 266001 $1500* NZ $1590 INC GST INC GST THE NEW 2026/27 JAYCAR CATALOGUE IS HERE Hot off the press and loaded with our latest products, the new 2026/27 Jaycar Engineering & Scientific Catalogue brings 612 pages of tech, electronics, components and tools together in one place. Keep it on the workbench for easy browsing, comparison and inspiration. Sometimes it’s better to flick than click. O N LY 9 $ 95 ^ The catalogue will be available for purchase from our stores or online. Prefer digital? A convenient flipbook version will also be available online. www.jaycar.com.au | www.jaycar.co.nz Australia New Zealand BJ5000: $9.95 BJ5002: $11.90 Scan the QR Code or visit: AU: jaycar.com.au/p/BJ5000 NZ: jaycar.co.nz/p/BJ5002 Limited print run. Be quick before they sell out! ^Price Shown in $AUD - NZ price is $11.90 Contents Vol.39, No.10 October 2026 12 Improvised Electronics, Part 2 Hobbyists can fabricate valves, transistors and even simple integrated circuits in their own home. So let’s continue looking at how people can make basic and even advanced electronic components. By Dr David Maddison, VK3DSM DIY components 50 Motor Control, Part 1 Improvised Electronics Part 2: Page 12 Page 60 This series will cover many of the different types of motors in depth, looking at how they work and can be controlled. To kick things off, we will start with the common DC motor. By Andrew Levido Electronics theory 68 A guide to EV Charging We describe the most common ways you can charge an electric vehicle, from slow charging at home (Level 1) to fast charging when out and about (Level 3 / DC fast chargers). By Geoff Graham Electric vehicles 90 The Philco Model 38-7 This radio is one of the finest medium-wave and shortwave band domestic receivers to come from the USA before WW2. This is also not the first time I’ve restored the radio, having previously worked on it around 50 years ago. Br Dr Hugo Holden Vintage Radio Audio Spot Frequency Test Generator A practical guide to EV Charging 28 Mighty USB-C Bench Supply Page 68 By using USB Power Delivery (USD-PD), you can build your own adjustable power supply that can deliver up to 20V at 2A. It has an adjustable current limit, software-based fuse emulation, an OLED status display and more. Part 1 by Tim Blythman Power supply project 2 Editorial Viewpoint 4 Mailbag 38 Programmable USB-PD Modules 37 Kits 47 Circuit Notebook 73 Subscriptions 82 Serviceman’s Log 88 Online Shop 101 Ask Silicon Chip 103 Market Centre 104 Advertising Index 104 Notes & Errata In this article we look at the Adafruit HUSB238 USB-PD breakout module and our own-design for a USB-PPS module, which is inspired by the Adafruit design. Either one can be used for our Bench Supply above. By Tim Blythman USB-PD & USB-PPS module 60 Audio Spot Frequency Oscillator With just a few modules and other parts, you can produce low-distortion 1V RMS test signals at specific frequencies between 20Hz and 20kHz. You can also use it for testing RIAA preamps, SSB transmitters and more. By Richard Kabzinski Test equipment project 74 Phenomenal Pinball Machine This series explains how to design and build every part of your own Pinball Machine. In the final part of this series, we finish the deck and integrate the electronics, wiring and electromechanical systems. Part 5 by Phil Prosser Gaming project 1. Stackable button selector panel 2. Busking amplifier 3. Darlington-based amplifier buffer SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke – B.E.(Elec.) A self-made trap for RAM manufacturers Printing and Distribution: Computer memory and storage is incredibly expensive by historical standards at the moment, due largely to extremely high demand from AI companies. That’s a whole can of worms in itself – this could be a huge bubble that eventually pops with disastrous consequences – but that’s not what I want to write about at the moment. Rather, I’d like to discuss the rise of Chinese memory manufacturer ChangXin Memory Technologies (CXMT). You may recall that my March 2026 editorial was titled “Expect more Chinese-brand computer parts”, and it seems I was prescient. The point I want to bring up today, though, is how the current major memory manufacturers such as SK Hynix, Micron and Samsung may be digging themselves into a hole from which they could have difficulty escaping. Right now, they are raking in money thanks to very high RAM prices combined with exceptionally strong demand. But those same conditions have also provided an ideal opportunity for CXMT, based in eastern China, to establish itself as a serious competitor. It is now manufacturing DDR5 memory in volume and, with prices where they are, presumably making very good money doing so. Some people had hoped CXMT’s entry into the market in volume would bring prices down. It probably will... eventually. But that won’t happen until supply catches up with demand. What I think will happen is that, at some point, CXMT – and possibly other Chinese memory manufacturers – will ramp up production to the point that RAM prices start to fall. Alternatively, the extraordinary rate of AI data-centre investment may simply prove unsustainable and demand could drop sharply. When that happens, prices could crash to the point where some manufacturers struggle to remain profitable. RAM has historically been a brutally cyclical business, with periods of shortage and high profits followed by oversupply and collapsing prices. CXMT may be particularly well placed to weather the next downturn. It has access to China’s enormous domestic market, a vast manufacturing ecosystem and substantial state support, while it may also be willing or able to tolerate lower margins for longer as it builds market share. That is where the established manufacturers may be setting a trap for themselves. By enjoying today’s high prices and concentrating increasingly on lucrative server memory and HBM (high bandwidth memory), they are giving CXMT an unusually favourable environment in which to improve its technology, increase production and establish customers. By the time the market turns, CXMT could be a much stronger competitor than it is today. And while CXMT’s technology is not quite world-class yet, it certainly seems to be learning quickly. Its products are already quite usable for many applications. I certainly would not turn up my nose at DDR5 DIMMs fitted with CXMT RAM chips if the price was right. I hope Micron, Samsung and SK Hynix are banking some of the money they’re raking in at the moment because, once the next correction arrives, they may need it. RAM has always been an industry of wild swings, but this time there will be a hungry new competitor waiting when the market swings back the other way. 1 Huntingwood Dr, Huntingwood NSW 2148 54 Park St, Sydney NSW 2000 Cover background image: https://unsplash.com/photos/light-blue-to-purple-gradient-PHtp0cDBJSM Technical Staff Bao Smith – B.Sc. Tim Blythman – B.E., B.Sc. Advertising Enquiries (02) 9939 3295 adverts<at>siliconchip.com.au Regular Contributors Allan Linton-Smith Dave Thompson David Maddison – B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Geoff Graham Associate Professor Graham Parslow Dr Hugo Holden – B.H.B, MB.ChB., FRANZCO Ian Batty – M.Ed. Phil Prosser – B.Sc., B.E.(Elec.) Cartoonist Louis Decrevel loueee.com Founding Editor (retired) Leo Simpson – B.Bus., FAICD Silicon Chip is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 626 922 870. ABN 20 880 526 923. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Subscription rates (Australia only) 6 issues (6 months): $77.50 12 issues (1 year): $145 24 issues (2 years): $270 Online subscription (Worldwide) 6 issues (6 months): $55 12 issues (1 year): $105 24 issues (2 years): $200 For overseas rates, see our website or email silicon<at>siliconchip.com.au * recommended & maximum price only Postal address: PO Box 194, Matraville, NSW 2036. Phone: (02) 9939 3295. ISSN: 1030-2662 2 Editorial Viewpoint Silicon Chip by Nicholas Vinen Australia's electronics magazine siliconchip.com.au 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”. We need Right to Repair laws I thought I would send you a copy of the email I’ve just sent to the Federal Government and the Greens Senator who is the spokesperson for Consumer Affairs – see email below. I know you covered this topic in Silicon Chip back in 2021, and you wrote a submission to the Productivity Commission in response to the draft report. I am wondering what else you might be aware of. I know there is a lot more action on this topic in Europe; I heard recently that France is requiring companies to design durability into the goods they manufacture so that we are not constantly throwing broken devices out. John Louttit, Stafford, Qld. The Hon Andrew Leigh MP – Assistant Minister for Productivity, Competition, Charities and Treasury I am a retired Electronics Technician and I would like to encourage you to establish Right to Repair laws for electronic equipment. I am aware that the Productivity Commission did an investigation into this issue several years ago and issued a report in December 2021. It is now over 4½ years later and I am wondering what progress has been made in relation to the repair of electronic equipment. It is vital that schematic diagrams, service manuals and spare parts are available at a reasonable cost so that electronic devices can be repaired. I note that a lot of work is being done on this in Europe and they are way ahead of Australia. Is the government working on this issue and, if so, when are we likely to see such laws passed? Copies sent to Anika Wells MP – Member for Lilley (my electorate) and Senator Peter Wish-Wilson Comment: new EU electronic device repair rules came into effect in August this year. See siliconchip.au/link/acdb Commentary on Australian standards I am responding to your Editorial Viewpoint regarding Australian Standards in the August issue (siliconchip.au/ Article/20651). I agree with your commentary. Australian Standards must, not should, be available to all persons seeking to understand the minimum requirements to which the Standards apply, at a reasonable cost. I don’t agree that standards should be free; there are man-hours involved in developing and producing these documents, they should be available at a minimal cost. The costs to purchase current Australian Standards are not reasonable; they are ridiculous. I work in the commercial construction industry and have done so for over 4 Silicon Chip 40 years. I primarily deal with building services including electrical, heating, ventilation and air conditioning, hydraulics, fire protection/detection etc. When I need to confirm a particular requirement, I must pay a ridiculous amount of money to access a standard that I might reference once or twice a year. Being a licensed electrician, I begrudgingly purchase AS/NZS3000 when each new revision becomes available, only to then determine the additions or updates that may apply to my work. I am old-school and prefer paper, which is 10% more expensive than the PDF version; the latter is locked down to inhibit distribution. I am yet to understand the reason for the cost. The paper version is not published on Grade 1 clay-coated photography paper, and the PDF version entails no printing or binding costs. I, and many others, completed a survey from the Australian Government about the cost of Australian Standards some time ago, which is the reason they have announced free access to the ‘mandatory’ standards. In Australia, a standard becomes law (mandatory) only when a piece of legislation (such as Work Health and Safety regulations or the National Construction Code) names that exact standard to enforce a legal requirement. One must now be concerned regarding the cost of the ‘user pays’ standards, particularly those that ‘support’ the legal standards, and whether these will elevate in price to support the freebees. Australian Standards were once owned by Australians and available at a reasonable cost until 2003. They are now owned by a private entity. It’s very disappointing. Malcolm Land, Frenchs Forest, NSW. Comment: we agree with you in general, but consider that many things that the government provides to the populace for free still cost money to provide. They are paid from general tax revenue. Standards could be maintained by the government and provided to the people for the benefit of all. Electrical licensing for repair technicians Your August 2026 editorial on open standards has prompted me to offer my experience with electrical licensing in Queensland, albeit some time ago. On leaving the Army in 1991, I decided to establish a small business repairing TVs, VCRs and electronic equipment. I became aware that in Queensland, the electrical rules were such that I had to obtain a Certificate of Competency (license) from the Electrical Workers and Contractors Board if I wished to repair electronic equipment. I queried this with the Board, citing the prevalence of transformer-less (live chassis) TV and similar SMPS-­ powered equipment at that time. A reply informed me Australia's electronics magazine siliconchip.com.au that I required a license to work on any mains-powered equipment with a cord and plug. I sought further information and was advised that I could work on any part of a TV set except the mains power supply. For that, I must have a license. I gave up and went ahead with obtaining a license. I concluded that the Board did not understand the issues with live-chassis TVs. To obtain a license, I had to pay a TAFE college $250 for a test on mains wiring and first aid, mainly CPR. I missed one question on the AC wiring test; namely, in what equipment is a double-pole switch GPO required? The answer was a caravan. I was issued with a Certificate of Competency, Level 1, Restricted (printed in large bold red letters). The Board granted me a certificate restricted to the testing, replacement or repair of mains flexible cords and plugs, and the testing or repair of any electrical article supplied mains by means of a flexible cord and plug. At the time, WA and NT required a similar license. I still have the Certificate of Competency, Board letter and safety guide booklets in my files, all in pristine condition. Peter Johnston, Merimbula, NSW. the Atmel chip in the Simple LC Meter project (May 2026; siliconchip.au/Article/20235). I downloaded it from a website I found using a web search, but it doesn’t allow the use of the AVRisp Mk2 programmer that I have. It assumes USBasp only (I ordered one anyway). AVRDUDESS also doesn’t allow programming/changing individual bytes, so it would probably require me to modify the EEP file using Notepad if the C1 capacitor value is not very close to 1000pF. I have an assortment of ±1% capacitors that I measured with the meter. The readings are about 2% lower than my test caps, likely due to the actual value of my C1 capacitor being out of tolerance. A warning to those who don’t have a copy of Extreme Burner V1.4 and need to download it. As is common, some downloads come with a ‘free’ virus! I got a pop-up window virus after installing it, which I subsequently removed. Glenn Percy, Narre Warren South. Vic. Comment: it’s probably safer to download Extreme Burner from SourceForge (https://sourceforge.net/projects/ bobsienpackages). We have an article on AVR programming software, including AVRDUDESS, coming up later this year. Adjustable Ultrasonic Cleaner works well Dodgy products abound Please pass on my congratulations to John Clarke on another excellent and well-designed project, the Adjustable Ultrasonic Cleaner (siliconchip.au/Series/461). It worked straight away after adjusting the contrast pot VR4 three-quarters of the way anti-clockwise. With 2L of water, I was only managing to deliver around 18W at 10V, but then I noticed some silicone had found its way between the PCB pipe cover and pan. Referring to the project text about not potting the transducer in silicone, I set about removing the silicone seal that had formed between the pipe cover and the pan with a sharp knife. I was then able to achieve 30W at 10V and was somewhat relieved at not needing to add extra windings to the transformer. Having shined up my wife’s jewelry and a number of harmonica reed plates, I can say it works a treat! Stephen Dunn, Wantirna South, Vic. Warning regarding AVR programmer downloads I use AVRDUDESS, which is a little different to the “Extreme Burner” software suggested for programming My Silicon Chip August magazine just arrived and I was reading your article on fake electronic devices. The electricity-­saving device mentioned is pretty widely advertised; I’ve seen it on several sites. Not so much the pest repeller, but it’s also commonly advertised. Regarding rechargeable cells, I bought some 18650 cells on AliExpress and they were total junk. I used them to repack a leaf blower battery and, with the battery fully charged, it lasted about 20 seconds on high. They even weighed significantly less than the original cells; I could feel the big difference in weight. I got a refund on those, then I managed to find some really good Tinker brand 18650 cells from a seller in Australia. There is also a TV aerial advertised with an incredible range (I can’t remember the figure now) but it’s just a stick aerial that plugs into the back of the TV. No way would that even work unless you were on top of the transmitter. Another thing not mentioned is the electronic rust prevention system that is supposed to protect vehicles from rusting. It’s even mentioned in the propaganda that surface rust is normal when the device is fitted to a vehicle. They just admitted that the device doesn’t work, but people still fall for it! The government needs to crack down on this false advertising to stop these scammers ripping people off. With respect to the letter “GPS altimeter wanted” on page 102 of the August issue, we have Garmin GPSs in our vehicles and they show the altitude. We are around 20m above sea level here. The Adjustable Ultrasonic Cleaner built by Stephen Dunn. 6 Silicon Chip Australia's electronics magazine siliconchip.com.au FREE Download Now! 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Free DaVinci Resolve Color Panels ........From $765 DaVinci Resolve is perfect for editing sales or training videos! The familiar track layout makes it easy to learn, while being powerful enough for professional editors. You also get a library full of hundreds of titles, transitions and effects that you can add and animate! Plus, DaVinci Resolve is used on high end work, so you are learning advanced skills used in TV and film. www.blackmagicdesign.com/au Download free on the DaVinci Resolve website Learn the basics for free, then get more creative control with our accessories! Learn More! NO SUBSCRIPTIONS • NO ADS • NO USER TRACKING • NO AI TRAINING The TV reception here is still patchy, but there has been some improvement lately on some channels. ABC and SBS are now permanently off the air. However, Channel 7 and Channel 10 are often on the air during the daytime, less so with Channel 10. However, both 7 and 10 are usually corrupted during news time, with 10 often off the air at this time. Both 7 and 10 have patchy reception at night; some recordings are good, others corrupted or non-existent. Channel 9 is OK most of the time, but some corruption is evident at different times. All these problems started when the TV channels switched from MPEG-2 to MPEG-4. And yes, the Beyonwiz PVRs are MPEG-4 capable, which is evident by the fact that the channels are there sometimes with good reception. The problem is with the transmissions. Finally, I just happened to come across a YouTube channel where this guy swapped over a BGA SSD from a dead motherboard (after he couldn’t repair the motherboard) onto a new motherboard. This is pretty incredible; if anyone is interested in seeing the process, here’s the link: https:// youtu.be/MLMsVX1s77k Bruce Pierson, Dundathu, Qld. Comment: we have mentioned in the past that electronic rust prevention for anything other than boats or buildings cannot work. Don’t waste your money on it. We agree that consumers deserve better protection from scam products. Many of them are still sold openly. Semiconductor date codes Your article on the NE5532 in the August 2026 issue (siliconchip.au/Article/20677) reminded me of an interest- ing point. Most but not all semiconductor packages have a manufacturing date code printed on them. The format is four characters; the first two are the year of manufacture, while the last two are the manufacturing week. This possibly goes back to a JEDEC standard from the 1960s. For example, on page 98, the top-left DIL 8-pin TDA1034B was made in week 37 of 1977. The TO-5 can (Signetics) device shows week 12 of 1982. The DIL Texas Instruments chip, marked Portugal, was made in Week 49 of 1987. Some other device packages have used a fifth letter for day-of-week production traceability; that’s uncommon though. Robert Sebire, Emerald, Vic. Comment: you are right when it comes to older ICs. More recent chips can use different and sometimes more complex schemes that aren’t as easily decoded (or even identified). For example, the chips in that photo marked “835 X 6” and “909XB” aren’t as easily deciphered (they may refer to the 35th week of 1998 or 2008 and the 9th week of 1999 or 2009 but it’s hard to be sure). The YYWW date code is still quite common where there is enough space on the package. However, it is far from universal. Manufacturers also use YWW, year/month codes and alphanumeric schemes in which, for example, a letter may represent the year or month. Some markings combine date information with lot, assembly-site, wafer or revision information. This is particularly common with ICs in small SMD packages, where there may only be four or five characters available. In those cases, the visible code may be partly a device identifier and partly a manufacturing or traceability code TEST MANY COMPONENTS ITH OUR ADVANCED TEST T EEZERS The Advanced Test Tweezers have 10 different modes, so you can measure ☑ Resistance: 1Ω to 40MΩ, ±1% ☑ Capacitance: 10pF to 150μF, ±5% ☑ Diode forward voltage: 0-2.4V, ±2% ☑ Combined resistance/ capacitance/diode display ☑ Voltmeter: 0 to ±30V ±2% ☑ Oscilloscope: ranges ±30V at up to 25kSa/s ☑ Serial UART decoder ☑ I/V curve plotter ☑ Logic probe ☑ Audio tone/square wave generator It runs from a single CR2032 coin cell, ~five years of standby life Has an adjustable sleep timeout Adjustable display brightness The display can be rotated for leftand right-handed use Components can be measured in-circuit under some circumstances Complete kit for $45 (SC6631; siliconchip.com.au/Shop/20/6631) The kit includes everything pictured, except the lithium coin cell and optional programming header. See the series of articles in the February & March 2023 issues for more details (siliconchip.com.au/Series/396). 8 Silicon Chip Australia's electronics magazine siliconchip.com.au SERIOUS STORAGE SOLUTIONS Unlock the full potential of your workspace with HAFCO’s range of storage solution... built to save space, boost productivity, and stand the test of time. PA C K A G E D E A L INDUSTRIAL STORAGE & TOOLING CABINET INDUSTRIAL MOBILE TOOLING CABINET WORKSTATION PROFESSIONAL SERIES MOBILE WORK STATION IBLE INCRED ITY! 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Not all phone cameras are good IR detectors Regarding the comment on p45 of the September issue that smartphone cameras will pick up the flashing from an IR transmitter LED, iPhone cameras haven’t been sensitive to IR remotes for years – I think they now include an IR filter. Either that, or the CCDs are made to be insensitive to IR. I agree it used to be a good way to check the output from a remote control, but I think responding to IR is probably detrimental to picture quality, so it has been filtered out. I just tested my iPhone 13, and it didn’t respond to my TV remote; neither did the previous model iPhone I owned. I tried my son’s Samsung Galaxy S23, probably four years old, and it didn’t work either. D. T., Sylvania, NSW. Comment: it seems to vary a lot between models. Most smartphone/tablet cameras have an IR filter, but some are more effective than others. We tested half a dozen smartphones and tablets from brands including Honor, Huawei, Oppo and Lenovo, and all showed pink/purple flashes when pointed at an active IR transmitter. The bottom line is that you should check your camera can pick up a known-good IR transmitter LED before using it for troubleshooting. Using a VNA to analyse crystals I found your September editorial discussing quartz crystals interesting (“Crystals: more than meets the eye”). Today I was working on a crystal filter for a 50MHz SSB transceiver. This involves selecting crystals from a batch with the same series resonant frequency. A vector network analyser (VNA) is really essential for that. I discovered that one crystal I had on-hand featured a Q just one quarter that of other, similar crystals, making it unsuitable for my application. I managed to get five suitable crystals from a batch of 10, but as they are so cheap, getting 20 is a better option to more closely match the five you select. Anyone doing serious RF work really must have a NanoVNA or equivalent. They’re amazingly inexpensive for what they can do at only about $50. Here are typical values pulled from a 9MHz crystal, measured with the NanoVNA and using the online calculator at www.changpuak.ch/electronics/Quartz_Crystal_Filter_ Designer_1.php (the parallel capacitance was measured with my LC meter that was published in the May issue – I use it all the time!): Fs = 8.996600MHz Fp = 9.015500MHz Cp = 5.7pF Insertion loss at Fs = 4.25dB Series capacitance = 23.5fF Inductance= 13.287mH Reactance = j751,362W Series resistance = 63W Q = 11,926 Charles Kosina, Mooroolbark, Vic. 10 Silicon Chip Australia's electronics magazine SC siliconchip.com.au Improvised Electronics and DIY Components Part 2 by Dr David Maddison, VK3DSM Image source: www.pexels.com/photo/tools-on-a-desktop-7286026 Last month, we explained how components like capacitors, batteries, motors, diodes, resistors or even transistors can be made from scratch, even using scrap. Some people go much further, creating their own valves, integrated circuits and more. We’ll look into how that’s possible in this second and final instalment. A fter we’ve looked at fabricating more advanced components using equipment and techniques available to the general public, we’ll investigate some of the things that can be built using these components. But first, let’s look at making more advanced components and assemblies. Some complex devices or assemblies that can be made in the garage or shed include the following. Others videos that are worth watching are titled “Homemade Cathode Ray Tube, Transconductance Tube Tester, and other stuff” at https://youtu.be/ ZvZXtEbn1Zk and “Video Display On Homemade Cathode Ray Tube” at https://youtu.be/_PzoAReMXOE An old CRT TV can be converted to an oscilloscope, as shown in the GreatScott! video at https://youtu.be/ aScAZReGQc0 A simpler way to do it with no additional electronics is shown in Fig.36 and at https://youtu.be/vHvbCWVtPzY Cathode ray tubes Cathode ray tubes (CRTs) are a form of valve, so they can be made with similar techniques (more on valves later). They used to be common for televisions and oscilloscopes but are now mostly obsolete. A simple CRT is shown in Fig.34, including the basic principle of operation. YouTuber “jdflyback” has been quite successful in making CRTs (see Fig.35 and the associated video). Fig.34: a simplified diagram of a cathode ray tube as formerly used in TVs, oscilloscopes and radar displays. Source: https://w.wiki/Nv7D 12 Australia's electronics magazine Silicon Chip siliconchip.com.au but this is not for beginners due to the extremely high voltages present (typically over 10kV!). Electron beam lithography For the extremely dedicated DIYer, obsolete scanning electron microscopes (SEMs) can often be acquired very cheaply (for scrap value) or even free. They can be used for their original purpose and also modified to draw patterns for electron beam lithography, as shown in Fig.37. You need plenty of space and a means to move these large devices. By adding a pattern generator, such as a Raspberry Pi or FPGA controlling the scan coils via DACs, and disabling or bypassing the raster scan and using a resist-coated sample stage, the SEM can be turned into a basic direct-write electron beam lithography system. Many hobbyists and small labs have successfully patterned features down to about 50-200nm (sometimes smaller) using PMMA (Perspex) or HSQ (hydrogen silsesquioxane) photoresists. For more on this, see the video by Sam Zeloof titled “Making Tiny Things with Electron Microscope - E-beam Lithography” at https://youtu.be/ SB94rQtKlKI and Peter Bosch’s video on “Shooting electrons at plastic to make microscopic features” at https:// youtu.be/HA9p38AnByY Fig.35: an improvised CRT made by jdflyback. Source: https://youtu.be/ESwjVXjDtY Integrated circuit fabrication Home integrated circuit manufacturing is an extreme frontier level of improvised electronics, where dedicated hobbyists attempt to replicate professional semiconductor fabrication processes in garages, sheds or home labs. They are typically working to a late 1960s or early 1970s standard of technology. This is far beyond simple homemade diodes or crystal radios. The most prominent figure in this niche is Sam Zeloof (https://sam. zeloof.xyz), a self-taught engineer who has turned his family’s garage in New Jersey into a functional (though dated) chip fab. As a high school student in 2016-2017, he built his first working Mosfets and logic gates, then progressed to full integrated circuits. His milestones include: the Z1 (2018), a PMOS dual differential amplifier IC with six transistors fabricated using four photolithography masks (see Fig.38). Fig.36: using an old TV as an oscilloscope. Be careful of high voltages! Source: https://youtu.be/vHvbCWVtPzY ▪ siliconchip.com.au Fig.37: modifying a scanning electron microscope for electron beam lithography. Source: https://sam.zeloof.xyz/e-beam-lithography Australia's electronics magazine October 2026  13 Fig.38: Sam Zeelof’s Z1 chip, a PMOS dual differential amplifier with six transistors. Fig.39: Sam Zeelof’s Z1 and Z2 chips compared. There are twelve 100-transistor Z2 chips on the one piece of silicon for a total of 1200 transistors. ▪ the Z2 (2021) is an upgraded silicon chip with 100 transistors, with 12 chips on the same piece of silicon, so 1200 transistors total (see Fig.39). It is almost comparable in complexity to early microprocessors like the Intel 4004 (which had 2300 transistors). It features smaller, faster devices and better yields than the Z1. Zeloof’s work draws inspiration from vintage patents and textbooks, using salvaged or homemade equipment to perform processes like photolithography, oxidation, doping, etching and metal deposition, proving that 1960-70s IC fabrication techniques can be replicated on a tiny budget with persistence and ingenuity. Other notable hobbyists include Jeri Ellsworth (mentioned last month), who pioneered early home semiconductor work in the 2010s, fabricating thumb-sized transistors and basic logic gates using vinyl-cut masks, rust stain remover (for etching) and simple dopants. Her videos directly inspired Zeloof and many others in the community. Recent (2025-2026) developments include hobbyist-developed spin-on glass dopants using TEOS (tetraethyl orthosilicate)/thermal diffusion for safer phosphorus/boron dopant introduction into silicon and small-scale photolithography setups. There are often shared on the ProjectsInFlight website: www.projects­ inflight.com or on their YouTube at: www.youtube.com/<at>projectsinflight While no-one has yet matched Zeloof’s transistor count or IC complexity at home, these efforts show ongoing progress in accessible doping and lithography. Key equipment and materials 14 Silicon Chip needed for a garage-scale fab (based on Zeloof’s documented setup and similar projects) include: Substrates: silicon wafers sliced from ingots or bought pre-cut, often 2-4 inches (50-100mm) in diameter, p-type for PMOS. Photolithography: a UV light source (eg, a modified DLP projector + microscope optics for maskless exposure), photoresist (spin-coated), photomasks (printed or drawn) plus an alignment jig. Furnace/oxidation: a high-temperature tube furnace (up to 10001200°C) for growing gate oxide and diffusion doping. Deposition/etching: Sputtering system or thermal evaporator for metal layers (aluminium), wet etchants (HF-based for oxide, phosphoric acid mixes) and a plasma etcher (optional but helpful). Doping: Spin-on dopants (eg, homemade phosphorus/boron solutions) or gas sources in advanced setups. Inspection: a scanning electron microscope, an optical microscope ▪ ▪ ▪ ▪ ▪ ▪ and a probe station for testing. Safety/cleanliness: fume hood, acid cabinet, HEPA filtration (to minimise dust), gloves/goggles/respirator. HF acid and very high temperatures are extremely hazardous! Other: Vacuum pumps/chambers, chemicals (acids, solvents, photoresist) and wafer-handling tools. The costs for such a setup can be in the tens of thousands of dollars (mostly for the SEM and furnace) but some put together a lab for much less. The process is labour intensive (Zeloof’s runs took around 12 hours per chip) and low-yield, resulting in features in the 5-10 micron range (1000 times the feature size of modern fabs). This level of home fabrication remains a rare, high-commitment pursuit, far from everyday improvisation. Still, it embodies the ultimate in maker ingenuity, turning a garage into a micro-fab and creating working silicon chips from raw wafers. Some related videos are as follows: • “Photolithography on Silicon with PCB Chemicals”: https://youtu. be/Kx1TenvQXTg ▪ ▪ Fig.42: the structure of a TEA laser. Original Source: https://laserkids. sourceforge.net/eng_co2teaLaser.html Australia's electronics magazine siliconchip.com.au • “Making Spin-On-Dopant for DIY Semiconductor Fabrication”: https:// youtu.be/1dFj-tGn8DI • “Metallisation: Making Conductive Traces on Silicon Chips”: https:// youtu.be/Ddd_-4D76do The OpenSilicon Initiative (https:// github.com/RParkerE/OpenSilicon) aims to make it easier for individuals to design and build their own chips. It offers open-source guides, bills of materials, 3D-printable files, firmware and PDKs (process design kits) to help enthusiasts and researchers build semiconductor-related equipment and tools at home. Its current focus is on prototypes for spin coaters, direct-write lithography (405nm laser-based), metrology systems for film thickness measurement, oxidation furnaces and PVD (physical vapour deposition) systems targeting sub-micron resolution in small-batch processing. While this supports DIY experimentation in chip characterisation, testing and basic processing setups, it complements rather than replaces professional fabrication services like Tiny Tapeout or Wafer.Space shuttles (more on them later). The goal is to allow the maker to fabricate more advanced hardware without requiring a full cleanroom. Lasers A transversely excited atmospheric (TEA) laser can be improvised from some basic components (Fig.42) and a 10kV (or so) flyback power supply, as is common in CRTs. This type of laser can be extremely dangerous for a variety of reasons, so such a project is not recommended unless you understand and are trained to deal with the dangers. Laser safety glasses must be used. There are many online sources of Fig.43: one of the many steps in making a Nixie tube (similar to making any valve). Source: https:// youtu.be/wxL4ElboiuA siliconchip.com.au Fig.40: a home-built TEA laser. Source: https://youtu.be/Zv3DFTSs6NQ Fig.41: Nixie tube based artwork. Source: www.daliborfarny.com/project/ omnixie-clock instructions for building such a laser, such as Laser Kids (siliconchip.au/ link/acc5) and see the video at https:// youtu.be/Zv3DFTSs6NQ and Fig.40. Nixie tubes Nixie tubes are very popular ‘retro’ electronic display devices, but they became obsolete in the 1970s as LED and LCD displays became commercially available. Experimenters and restorers could only buy old stock or used devices until Dalibor Farny decided to make them himself and turn his hobby into a business (www.daliborfarny.com), making Nixie tubes. They are essentially artworks, with a price to match Fig.44: purple Nixie tubes made by jdflyback. Source https://youtu.be/ q7I61d27R3E Australia's electronics magazine – see Fig.41 and the video at https:// youtu.be/wxL4ElboiuA All the essential elements of making your own valves are shown in the video; one is shown in Fig.43. “jdflyback” made their own purple Nixie tubes too – see Fig.44 and the video at https://youtu.be/q7I61d27R3E Optical sensors An advanced DIY semiconductor fabricator used a copper oxide semiconductor on a silicon dioxide coated silicon wafer to make a simple optical sensor (Fig.45). Their video, titled “I tried to make a camera sensor”, is at https://youtu.be/O7xH9ZSp_B4 The fabricator used electron-beam Fig.45: an improvised copper-oxide optical sensor. Source: https://youtu. be/O7xH9ZSp_B4 October 2026  15 lithography to draw the pattern. This was accomplished with the aid of an obsolete and modified electron microscope. Valves (also called vacuum tubes) were common in electronic appliances until about the late 1960s or early 1970s, when they were almost exclusively replaced by transistors and ICs. Arguably the most basic type of valve is the incandescent light globe, which can function as a rudimentary thermionic diode due to electron emission from the heated filament under certain circumstances. A valve diode provides a similar function to a solid-state diode, while a triode is the equivalent of a transistor (it’s most similar to a field-effect transistor). Valves are typically fabricated by hobbyists for fun and experimentation, rarely out of necessity. Still, it is conceivable that one day they might need to be fabricated to restore antique electronic equipment if original valves can’t be sourced. The valve diode was invented by Sir John Ambrose Fleming in 1904 (see Fig.46), while the valve triode was invented by Lee de Forest in 1906 (see Fig.47). The latter can amplify signals or act as a switch by using a control grid to modulate the flow of electrons from cathode to anode. Incandescent globes can be used as very poor improvised diodes according to one report on Quora (siliconchip.au/ link/acba). After burning out one filament of a combined brake and indicator automotive lamp, one end becomes the anode and the other heated filament becomes the cathode. They can even be used as valve triode amplifiers, but likely with poor performance – see Fig.48 and the videos at https://youtu.be/LRLtiOMKIA4 and https://youtu.be/JkrrStcYZLk Improvised valves are typically made using a glass envelope, usually soda-lime glass blown and shaped with a torch, with tungsten wire for the filament (cathode), nickel or nickel-­ plated metal for grids and plates, plus Fig.46 & 47: the structure of a diode valve (left) and triode valve (right). Sources: https://w.wiki/Nv7M & https://w.wiki/Nv7N Fig.48: a dual-filament incandescent bulb can be used as a primitive triode by deliberately burning one filament out. Source: https://youtu.be/JkrrStcYZLk Vacuum pumps Vacuum pumps can be made from modified air compressors or refrigerator compressors, but these cannot achieve a sufficiently good vacuum for making valves. A modified refrigerator compressor can reach 10-50 torr, which might be OK for glow discharges and plasma experiments, but not nearly enough for valves, which require a minimum of 10-4 to 10-6 torr. At minimum, a two-stage mechanical vacuum pump with a gauge is needed. These can reach 10-3 to 10-4 torr, which is sufficient for simple diodes and triodes as long as a ‘getter’ is added to increase the vacuum further (more on this later). A torr is a unit of pressure that’s defined as 1/760th of an atmosphere. Such pumps can be purchased on eBay. Traditional quality brands are Welch, Edwards, Alcatel, Leybold, or Varian; and some recommended less costly Chinese brands, including the 2XZ series or similar. Valve fabrication 16 Silicon Chip Australia's electronics magazine getters, which are reactive materials (often barium or barium alloys) placed inside the valve to absorb residual gases after evacuation. Warning: some barium compounds are toxic. The characteristic silver-coloured coating seen on many valves is the getter flash, a thin layer of barium that reacts with stray gases to maintain the vacuum. It is usually a barium-­ aluminium or barium–magnesium alloy. Modern vacuum systems use zirconium alloys instead, which are also activated by heating but don’t vaporise and absorb gases continuously. Construction requires basic equipment like a vacuum pump, as mentioned above, a blowtorch or glass-working torch for shaping and sealing the envelope, and careful assembly of electrodes and leads. While challenging, hobbyists have successfully built simple diodes, triodes and even small amplifiers this way; see Fig.49 and https://youtu.be/-UEfqAWb3fE Here are some basic steps to build a DIY triode valve. Note that this is a rough guide only. The materials needed are: Envelope: Pyrex or soda-lime glass tubing for the envelope. Filament: thoriated tungsten wire (for high emission) or oxidecoated tungsten wire, about 0.6-1mm in diameter Grid: fine stainless steel or nickel wire, or mesh wrapped in a spiral Plate: nickel sheet or a stainless steel cylinder Feed-throughs: tungsten or Dumet wire (the latter is a special composition specifically for glass-to-metal seals) ▪ ▪ ▪ ▪ ▪ siliconchip.com.au ▪ ▪ Internal supports: mica sheets or spacers to centre and insulate elements Chemicals: barium or strontium carbonate slurry for the filament coating and potassium nitrate for cleaning the tungsten. There are restrictions on purchasing the latter in Australia; sodium hydroxide (NaOH) may be an alternative. Tools needed include an LPG/oxygen torch; carbon shaping tools for the glass; a glass lathe (useful but not essential); a vacuum system, as described above, with associated tubing; a spot welder for joining wires (these can be home-made); and a diamond saw or file to cut glass. The steps are: 1. Fabricate the stem – melt tungsten or Dumet wires into the glass to create airtight feed-throughs. 2. Prepare the electrodes – weld the filament, grid and plate to the stem’s internal leads and use mica to maintain spacing between them. 3. Coat the filament – apply a barium carbonate slurry to create an oxide layer on the filament for better electron emission. 4. Seal the envelope – put the assembly into the glass envelope and fuse the stem where the feed-throughs go through, but leave an exhaust port open. 5. Evacuation and bake-out – connect the exhaust port to a vacuum pump and torch the envelope or place it in an oven for a period to remove residual gases. 6. Once a high vacuum is obtained during the bake-out, melt and collapse the exhaust port to seal the unit. 7. Fire the ‘getter’ with an induction heater. 8. Test it to make sure it works. Hazards include heat from the blowtorch or furnace, harmful chemicals during fabrication, and high voltages and possible X-ray production during testing. You can watch an instructional video about making a triode valve at https://youtu.be/hLEYaV_Nl2Q (also see Fig.50). Charles Alexanian (siliconchip.au/ link/acbb) makes their own valves without the use of any especially harmful chemicals. If you decide to make your own, check the material safety data sheets (MSDS) for any substances you will use before starting. One prominent valve fabricator is “Glasslinger” (Ron Soyland), siliconchip.com.au Fig.49: a homemade amplifier by jdflyback with two DIY triode valves. The other components are vintage types. The grey boxes are repurposed doorbell transformers for a choke and the audio output transformer. Source: https://youtu.be/-UEfqAWb3fE Fig.50: a DIY triode valve. Source: https://youtu.be/ hLEYaV_Nl2Q Fig.51: a partially completed Audion valve made by Glasslinger. Source: https://youtu.be/ PxxLPrVbb-A a YouTuber (www.youtube.com/<at> glasslinger) focused on vintage electronics and valve manufacturing to an extremely high professional standard. One of his videos features the manufacture of the de Forest “Audion” spherical triode invented in 1906; see Fig.51 and video https://youtu.be/ mJgEjghVom0 Glasslinger also has a video of a 1912-style radio, which he made using mostly homemade components, including resistors, capacitors and an Audion valve; see https://youtu.be/U6ZVqr0fPo4 and Fig.51. Fig.52 shows a valve made by another constructor. Hobbyists have built X-ray tubes (see Fig.53 and the video at https://youtu.be/yL2RIzlo7W8) but these should be made with caution due to the possibility of radiation exposure. Australia's electronics magazine Other fabricators worth looking up are Claude Paillard (https://youtu.be/ EzyXMEpq4qw), Charles Alexanian (https://youtu.be/bZN735jtikA), Lea Barker (https://youtu.be/3_2n7fpW­ bXE) and Nick Poole (www.youtube. com/live/39-5WgcvaHk). There are several entries on improvised valves in the Nyle Steiner document (PDF) at siliconchip.au/link/ acbc Some additional videos to look at are titled “First Homemade Triode Vacuum Tube” (https:// youtu.be/ajo8SKXBbr8) and “Radio Built With Homemade Fig.52: a very neatly made, nearly complete DIY valve with the base yet to be installed. Source: https:// hackaday.com/2014/11/21/ artisanal-vacuum-tubeshackaday-shows-you-how October 2026  17 Fig.53 (left): an improvised X-ray tube; the light is from the filament. The emitted radiation can be detected with a Geiger counter. Source: https:// youtu.be/yL2RIzlo7W8 Fig.54 (above): the simplest possible crystal radio (left) and a betterperforming crystal radio circuit (right). Triodes” (https://youtu.be/BX7Oy9S7Kdw). The website https://diyvac­ uumtubes.com may also be helpful for would-be valve constructors, although it doesn’t appear to be particularly active. Radios Radios are important in times of crisis or isolation. They become lifelines for news, good morale and even survival. Long before smartphones or internet access, simple radios provided the only connection to the outside world; many of the most remarkable examples were built entirely from improvised or scavenged parts. The crystal radio, one of the earliest and simplest receivers, requires no batteries or external power as it harvests energy directly from the incoming radio waves. It can receive AM broadcast stations from many kilometres away. Its extreme simplicity made it perfect for improvisation. Crystal radios A crystal radio is perhaps one of the simplest possible electronic circuits of practical use you can build. Many have been built for survival by POWs (prisoners of war), or for fun and entertainment. If stranded, you could also listen to the news to see if rescuers are still looking for you! A crystal radio generally consists of a long wire antenna, a diode (which can be a homemade cat’s whisker) for rectification, one or two capacitors (fixed and variable) and a coil to form an LC tuned circuit and a high impedance earpiece – see the right side of Fig.54. Some or all of those components can be fabricated depending on one’s 18 Silicon Chip level of commitment or necessity as described earlier, including the diode, capacitor(s), inductor and earphone. The earliest crystal radios actually lacked a tuned circuit, so they were not selective and just picked up whatever station was strongest, although there were perhaps only one or two radio stations on air in the early days anyway. Such radios consisted only of an antenna, a diode, earphone(s) and Earth, as shown on the left side of Fig.54. This simplest possible radio is likely responsible for the rare examples of radio stations being heard from metal teeth fillings, which could act as an antenna, rectifier and transducer, and causing vibrations that could be felt or heard. Lucille Ball famously claimed to have picked up a radio station with her tooth. While considered scientifically plausible if near a strong transmitter, the TV show Mythbusters was unable to replicate the phenomenon. Regardless, radio signals can be accidentally detected by many electronic circuits. In 1922, the US Bureau of Standards published plans for building a broadcast band crystal set, which you can view at siliconchip.au/link/acbd You could still build one today from those plans using the same or similar components. Admittedly, it is not an absolute ‘minimalist’ design as it has a lot of unnecessary non-electronic hardware. An improvised crystal radio can also use small resistor-sized inductors instead of an air coil, although the performance will be inferior. As we discussed last month, many of the basic components of a crystal Australia's electronics magazine radio or other radios and devices can be made quite easily. Foxhole radios During World War II, Allied soldiers in the field built foxhole radios which were ultra-minimal crystal sets assembled from razor blades, safety pins, wire scraps and headphones, to listen to BBC or Armed Forces Radio broadcasts amid combat (see Figs.55 & 56). Soldiers were not allowed to use powered radios because unintended radio emissions could have given away their location to the enemy. Foxhole radios were built for self-entertainment by deployed soldiers. The terms foxhole radio and POW radio (see below) are sometimes used interchangeably, but POW radios carry the extra layer of secrecy and danger. Some POW radios also acted as transmitters, not just receivers. Improvised battlefield radios “Winnie the War Winner” was built by stranded Australian troops from the Battle of Timor in 1942. It was built using the power pack from a Dutch transmitter, 20m of aerial wire, a broken commercial medium-wave receiving set and a transmitter from another broken radio set. A generator was taken from an old car to charge the batteries. For more on this, see the video at https://youtu.be/r0PCqJyTjAs POW radios POW radios were clandestine crystal (and sometimes valve-based) receivers secretly built by Allied prisoners in German, Japanese and Italian prisoner camps during World War II. Unlike basic foxhole radios improvised in the field, these had to siliconchip.com.au Fig.55: a foxhole radio used by an American soldier on the Italian front. Source: https://w.wiki/Nv7X be completely concealed, often ingeniously hidden in soap dishes, canteens, brooms, fake books, gramophones, table legs, or camp furniture. So it seems the radio hidden in the coffee pot in Hogan’s Heroes isn’t so far-fetched after all. They were built in extreme secrecy, with scavenged or smuggled parts like bed-spring wire for coils/antennas, razor blades or burnt cinnamon bark/ foil for diodes, foil-and-paper capacitors, pilfered headphones, and occasionally smuggled crystals or valves. These sets were more elaborate than foxhole radios, featuring variable tuning (sliding coils or homemade capacitors), better selectivity, and shared listening among trusted prisoners. They received BBC and Allied broadcasts to track war progress, boost morale, distribute censored news summaries and occasionally coordinate escapes. In European camps (near strong signals), crystal sets sufficed; but in distant Japanese camps, valve receivers with batteries were more common. Most documented POW radios were receive-only devices (crystal sets in European camps near BBC signals, or one-valve regenerative receivers in distant Japanese camps powered by batteries or camp electricity). Transmission was highly dangerous because any radiated signal could be easily detected by direction-finding equipment. Borneo camp British Lieutenant Colonel R. G. Wells built a secret transceiver in a Japanese POW camp from scavenged materials like foil from tea chests and burnt cinnamon bark for resistors. He described his efforts in an interview at siliconchip.au/link/acbe Two Queensland brothers, Ernest siliconchip.com.au Fig.56: two diagrams of foxhole radios built by American soldiers on the European Front during World War 2. Source: https://w.wiki/Nv7Y and Charles Hildebrandt, built a POW receiver (strictly speaking they were interned, as it wasn’t a POW camp) which they operated in Java (now Indonesia), which was overrun by the Japanese in 1942. It was constructed from scavenged parts, built into a Dutch gas-mask container and hidden under a piece of concrete. For the last 16 months of the war, they secretly shared news from the ABC, BBC, USA and other stations. A photo of the radio can be seen at siliconchip.au/link/acbf These life-sustaining devices exemplify the ultimate in improvised electronics under duress, with pure ingenuity turning camp scraps into hope and intelligence. Tunnelling diode receivers Early radios that originally incorporated the negative differential resistance (NDR) tunnelling diode previously described were called Crystodynes. The term Crystodyne was coined by Hugo Gernsback, editor of Radio News, in 1924 to describe Oleg Losev’s invention. Gernsback published articles in September 1924’s Radio News detailing the Crystodyne principle, including circuits built in his labs to Losev’s specifications. These Crystodyne radios used the zinc oxide device for amplification, oscillation and detection, enabling regenerative receivers, simple transmitters and oscillators without valves. Tunnelling diode transmitters Using the NDR device described last month, Nyle Steiner demonstrated that he could create audio oscillators, RF oscillators up to 13MHz and even amateur radio transmitters on the 80 metre band (3.5-4MHz) or 40 metre band (7MHz) using crystal control for frequency stability. For example, he built a zinc-based 80m CW (continuous wave) transmitter that reached 8km, all from scavenged or household items, although it only had a power output of 1mW or even far less – see Figs.57 & 58. He also demonstrated the NDR effect with other materials like iron pyrite (fool’s gold). Another NDR device transmitter, by Ashish Derhgawen, is described in the video at https://youtu.be/LfUABN_ HGwU titled “A bizarre transmitter without transistors or tubes”. Improvised spark-gap transmitters Spark-gap transmitters are a very Fig.57: an NDRbased 80m CW (Morse code) transmitter with a range of 8km. Also see Fig.58 overleaf. Source: http:// sparkbangbuzz. com/zinc-osc-2/ zinc-osc3.htm Australia's electronics magazine October 2026  19 early type of radio transmitter that generate extremely broadband radiation. They were used from about 1887 to 1917. They can only transmit Morse code, not voice. A battery, a coil, wire and pieces of steel from wrecked equipment can be used to build a spark gap transmitter even more basic than the early designs. Such a transmitter generates electromagnetic interference that might be detectable by passing aircraft, ships or radio amateurs, although today no one is specifically equipped to detect this type of transmission. Spark-gap transmitters were phased out in 1934, but before that they were used for making distress calls, including from the Titanic; see the videos at https://youtu.be/izCV1WrPFds and https://youtu.be/CtqRwFQE2AM Commercially-made ICs Even if you have the equipment to make ICs and can use it successfully, where do you get designs from? One option is to learn how to design chips yourself, then get a commercial fab to make them. This is usually too expensive for individual but there are options for DIYers or small businesses to dip their toes into IC fabrication. Some possible options are: Tiny Tapeout (tinytapeout. com) provides access to professional silicon by letting individuals, hobbyists, students or small groups submit their digital (and sometimes analog/mixed-signal) designs to be fabricated at a commercial foundry through shared ‘shuttle’ runs. In a shuttle run, multiple user designs are combined onto a single multi-project wafer (MPW), drastically reducing costs compared to a dedicated run. It uses opensource tools such as Wokwi for graphical design/simulation, Verilog/VHDL/Amaranth for HDL (hardware description language) and GitHub-based workflows to reduce costs. No expensive proprietary software is required, nor do you need to sign any non-­ disclosure agreements or have a massive budget. For more details, see the video at https://youtu. be/qVWq_XZko-M which shows the process from idea to fabricated chip, 20 Silicon Chip Fig.58: the circuit diagram for the transmitter shown in Fig.57. including community sharing of designs and interactive demo boards. While Tiny Tapeout is the entry point for anyone to try chip design, wafer.space (https://wafer.space) provides the next step that bridges hobbyist prototyping to small-batch production without losing the open, collaborative spirit. An open-source Z80 clone The Zilog Z80 reached ‘end of life’ (EOL) in June 2024, with Zilog (now owned by Littelfuse) discontinuing production of the classic standalone Z84C00 family CPUs and peripherals after nearly 48 years of continuous manufacturing. In response, the open-source and Fig.59: the open-source Z80 tape-out (the final files that get sent to the IC foundry). Source: https://github.com/ rejunity/z80-open-silicon Australia's electronics magazine hardware preservation community has decided to develop a free and opensource silicon clone of this processor. Functional prototypes have already been made and confirmed working on multiple fabrication processes. Tiny Tapeout infrastructure has played a key role in its early development, enabling low-cost tapeouts on the SkyWater Technology (USA) 130nm process. Additional experimental runs have produced full or near-full pin-compatible chips that run Z80 code, communicate with external RAM, and pass major parts of test suites. Work continues toward a true drop-in 40-pin DIP replacement chip, including a Chip-on-Board (COB) variant on the GF180MCU 180nm process via Wafer.Space (Singapore) shuttles – see Fig.59 and the main project repository at https://github.com/rejunity/ z80-open-silicon Circuit boards Printed circuit board substrates can be fabricated by depositing layers of either insulating or conductive materials layer-by-layer using fused deposition modelling (FDM), a form of additive manufacturing. Insulating substrates include filaments like PLA, ABS, PETG and nylon, while conductive materials include PLA/ABS filaments incorporating graphite, copper or silver to create electrical traces. It should be noted that conductivity with this technique will be less than traditional copper traces. Simple circuits can be fabricated using conductive inks. An inkjet printer can be modified to use silver nanoparticle ink – see Fig.60. Components are held onto the substrate with copper tape. Such techniques are in the early phases of development. Conductive inks and paints can also be made using ingredients such as graphite powder, black iron oxide powder (Fe3O4, magnetite), clear nail polish, polyvinyl acetate (PVA) glue and isopropyl alcohol. Making an iron oxide (magnetite) based conductive ink is shown in the video at https://youtu.be/RjFeeptoilI Making another conductive ink is shown at siliconchip.au/link/acbg W. Wayt Gibbs made a conductive liquid metal that can be used to siliconchip.com.au Fig.60: conductive traces printed with a modified inkjet printer. Components are held on with copper tape. Source: www. instructables. com/PrintConductiveCircuits-WithAn-InkjetPrinter connect components without soldering, described at siliconchip.au/link/ acbh and siliconchip.au/link/acbi plus the video at https://youtu.be/ mF_Z8RUZjJE We don’t suggest you do this, as indium and gallium can be extremely toxic if inhaled or ingested. Light bulbs A DIY light bulb can be made using graphite from a pencil with CO2 as the inert gas; see Fig.61. Doing more with less The following sections demonstrate the use of normal construction techniques but in ways that are not normally considered practical. However, if you were stuck trying to ‘bootstrap’ technology; for example, after a devastating war, with no access to functional computers, some of these techniques might provide a good ‘shortcut’ to making the necessary tools and equipment. CPUs Discrete components can be used to make AND, OR and NOT logic gates to form a basic computer. So, if you could produce or obtain reasonable quantities of transistors and/or logic chips, you could make a relatively simple processing unit from scratch. A small 4-bit processor like the Intel 4004 from 1971 could be built using around 3000-4000 transistors, although if you simplified it as much as possible, it might be possible to make a 4-bit CPU with as few as 900 transistors. An 8-bit CPU like the 6502 could be made with around 5000-8000 transistors, or possibly 2000-3000 if it were stripped back to basics. Clock speeds for these devices would be on the order of a few kilohertz and they would be hard to debug. Debugging such a machine built from discrete or homemade parts would be extremely difficult due to wiring complexity, variability in component performance, noise and the sheer number of connections. By way of comparison, early 4-bit computers often used 800-1500 transistors, depending on the instruction set and register design. 8-bit designs (eg, something like a homebrew 8080 or 68000 clone) easily reach 2,00010,000+ transistors when built with individual gates. ICs require fewer transistors than discrete designs for the same logic siliconchip.com.au Fig.61: an improvised light globe using pencil graphite and CO2 as the inert gas. Source: www. instructables.com/HomemadeLightbulb/?linkId=75697704 Fig.62: the AYTABTU, a computer made of discrete components. Source: https://github.com/mengstr/aytabtu Fig.63: Ben Eater’s 8-bit computer. Source: https:// youtu.be/ HyznrdDSSGM Australia's electronics magazine October 2026  21 Fig.64 (left): the MOnSter 6502, an Mostek 6502 microprocessor clone built from discrete components. Fig.65: a homemade 1024-pixel image sensor. Source: www.instructables.com/DIYImage-Sensor-and-Digital-Camera because they can use tricks to provide multiple functions from a single transistor. They also don’t need to drive (relatively) long wires. Some examples of computers or other digital devices built from discrete parts include: The AYTABTU (All Your Transistors Are Belong To Us) project was an attempt to create “a usable computer built entirely out of discrete components like transistors, diodes, resistors and capacitors just as they did it back in the [1960s]” (Fig.62). See siliconchip.au/link/acbj and https://github.com/mengstr/aytabtu The Ben Eater (Fig.63, https:// eater.net/8bit) is an 8-bit computer built using 74xx logic chips on breadboards. The creator of this computer is offering it as a kit; see https://eater. net/8bit/kits The FACOM 128B is a Japanese-­ designed computer from the 1950s that was made using relays (siliconchip.au/ link/acc6). Since then, many people have designed their own relay-only computers, with memory being a big constraint. The MOnSter 6502 (Fig.64, https://monster6502.com) reproduces the Mostek 6502 microprocessor as used in early consumer computers such as the Apple ][, Commodore PET, Atari 400 & 800 and the BBC Micro (the Commodore 64, Atari 2600 and original Nintendo Entertainment System used close derivatives, like the 6520). There are 4769 components on the ▪ board; 3218 transistors and 1019 resistors comprise the ‘functional’ part of the 6502. Additional components include LEDs to visualise its operation and a variety of other miscellaneous components related to supplying power, driving LEDs, supply filtering etc. Digital cameras Sean Hodgins made a 32 × 32 pixel image sensor and digital camera from parts. Each of the 1024 image sensor pixels was hand-soldered; see Figs.6567 and the YouTube video titled “I Made My Own Image Sensor! (And Digital Camera)” at https://youtu.be/ PaXweP73NT4 If you want to make one, you can download the required files from https://github.com/idlehandsdev/ diycamera Rather than soldering over 1000 parts, you could consider a DIY pickand-place machine to automatically place surface-mount components onto a PCB. One example is OpenPnP (https://openpnp.org) – see Fig.68. Display adaptors Ben Eater made a video graphics array (VGA) display card from ▪ ▪ ▪ 22 Silicon Chip Fig.68: an example of an OpenPnP home-made pick-and-place machine. Source: https://github.com/openpnp/openpnp-openbuilds/blob/develop/Images/ overview_top.jpg Australia's electronics magazine siliconchip.com.au Silicon Chip PDFs on USB Fig.66: the completed DIY digital camera using the sensor in Fig.65. Fig.67: a sample image from the camera shown in Fig.66. standard ICs and prototyping boards – see Fig.69 and the video at https:// youtu.be/l7rce6IQDWs and even basic active elements from scrap. The fundamentals of electronics remain accessible even today. Rediscovering the ‘lost’ knowledge of previous generations can be thrilling, such as adjusting a cat’s-whisker contact to find the sweet spot, building an LC tank that commences self-­ sustained oscillation, or modulating a bias voltage to send a weak signal across a room. Experiments with improvised electronics show that amplification, oscillation and rectification don’t require sophisticated factory-made components but can emerge from your own garage. So grab some galvanised sheet, scavenged wires and a multimeter can allow you to start tinkering and push the boundaries. The next breakthrough in scrap-built semiconductors might even come from your own bench. Conclusion We have provided a window into the world of improvised electronics, where everyday scrap, some ingenuity and a willingness to experiment can yield active devices like homemade negative resistance diodes, liquid rheostats, carbon-rod electrodes, transistors, diodes and oscillators that function without a single off-theshelf part. The home experimenter can still do incredible things, from coaxing quantum tunnelling out of oxidised zinc to building amplifiers, transmitters ¯ A treasure trove of Silicon Chip magazines on a 32GB custom-made USB. ¯ Each USB is filled with a set of issues as PDFs – fully searchable and with a separate index – you just need a PDF viewer. ¯ Ordering the USB also provides you with download access for the relevant PDFs, once your order has been processed ¯ 10% off your order (not including postage cost) if you are currently subscribed to the magazine. ¯ Receive an extra discount If you already own digital copies of the magazine (in the block you are ordering). Further reading and viewing Fig.69: a VGA display adaptor made from standard ICs on a breadboard. Source: https://youtu.be/l7rce6IQDWs siliconchip.com.au • “How to rebuild civilisation. The Ultimate Guide to Rebuilding a Civilization: Dynamic Practices and Core Principles for Building a Sustainable and Ethically Grounded Future”, paperback by Jackson Ridge (2024) • Video: “How long would it take to build a TV in ancient Rome?” (https:// youtu.be/rJAFUu8RcvM) • A 275-page document of Nyle Steiner’s improvised electronics: siliconchip.au/link/acbc • Ben Krasnow’s Applied Science YouTube channel, including a homemade electron microscope, see: www. youtube.com/<at>AppliedScience • Peter Parker’s channel and website with lots of amateur radio DIY content: www.youtube.com/<at>vk3ye SC and https://vk3ye.com Australia's electronics magazine EACH BLOCK OF ISSUES COSTS $100 NOVEMBER 1987 – DECEMBER 1994 JANUARY 1995 – DECEMBER 1999 JANUARY 2000 – DECEMBER 2004 JANUARY 2005 – DECEMBER 2009 JANUARY 2010 – DECEMBER 2014 JANUARY 2015 – DECEMBER 2019 OUR NEWEST BLOCK COSTS $150 JANUARY 2020 – DECEMBER 2024 OR PAY $650 FOR THEM ALL (+ POST) WWW.SILICONCHIP.COM. AU/SHOP/DIGITAL_PDFS October 2026  23 LOOKING TO REFRESH YOUR WORKBENCH? We’ve got the essentials to power up your next project, at the best value. PERFECT FOR COMPACT WORKSPACES $ ADJUSTABLE ARM IDEAL FOR SOLDERING, PLASTIC CUTTING, HEAT SHRINKING, ETC. ONLY 5995 . QM3552 FOR A BETTER VIEW Illuminated Desktop Magnifier • 100mm 3-dioptre glass lens • 30 bright LEDs • Mains powered QM3552 SOLDER ANYTHING, ANYWHERE! $ SuperPro Gas Soldering Tool Kit • Up to 580°C temp range • Up to 120 min run time • Durable case with extra tip storage TS1328 ONLY 209 TS1328 VOLTAGE AND CURRENT DISPLAY $ ONLY 41 50 CONSTANT CURRENT & VOLTAGE IN A SLIMLINE FORM FACTOR . TH1827 CABLE MAKING ONE HANDED! 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TH1981 Explore our great range of 3D Printing gear, in stock on our website, or at over 140 stores or 130 resellers across Australia and New Zealand. jaycar.com.au 1800 022 888 | jaycar.co.nz 0800 452 922 Prices shown in $AUD and correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. $ ONLY 219 MP3842 THIS ISN’T A NORMAL 3D PRINTER. $ JUST 999 CENTAURI CARBON 2 COMBO TL4986 FOUR COLOURS. ONE PRINT. ZERO FUSS. PRINTS WHAT OTHERS WON’T. FAST. QUIET. DIALED IN. CANVAS: AUTOMATIC COLOUR SWITCHING BUILT FOR ADVANCED MATERIALS SMART CALIBRATION. CONSISTENT PRINTS. SEE THE FULL RANGE OF 3D PRINTING ONLINE jaycar.com.au 1800 022 888 jaycar.co.nz 0800 452 922 Prices shown in $AUD, and correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. NEED TOOLS THAT MEASURE UP? We have a GREAT RANGE of multimeters at everyday GREAT JAYCAR VALUE, to suit hobbyists and professionals alike. FOR THE TECH'S TOOLBOX $ $ 3750 QM1020 ONLY 61 95 QM1323 EASY TO READ MEASUREMENTS • Mirror backed scale • Transistor leakage test • Audible continuity AUTORANGING FOR EASE OF USE • Temperature • Duty Cycle • Non-Contact Voltage $ ONLY ONLY 51 95 QM1321 HANDY FOR THE HOME TOOLBOX ACCURACY OF TRUE RMS MEASUREMENT • Capacitance & frequency • Transistor HFE test • Diode & audible continuity • Non-contact voltage $ ONLY 29 95 QM1517 IDEAL FOR STUDENT OR HOBBYIST ON A BUDGET FOR A STUDENT OR APPRENTICE • Data hold • Square wave output • Backlight • Audible continuity Don't pay 2-3 times as much for similar brand name models when you don't have to. Explore our great range of soldering gear, in stock on our website, or at over 140 stores or 130 resellers across Australia and New Zealand. 26 Silicon Chip Australia's electronics magazine jaycar.com.au - 1800 022 888 jaycar.co.nz - 0800 452 922 siliconchip.com.au All prices shown in $AUD, and correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. $ ONLY 119 QM1549 LARGE BACKLIT DISPLAY AND IP67 WATERPROOF RATED 179 ENTRY LEVEL ONLY $ QM1594 219 QM1578 WIRELESS BLUETOOTH FEATURE FOR DATA LOGGING ® • Multimeter functions • Sound level • Light level • Indoor temp • Humidity • True RMS • Capacitance • Frequency • Relative Measurement * $ TAKE EASY ENVIRONMENTAL MEASUREMENT ONLY • Autoranging • True RMS • 6000 count • IP67 Waterproof MID LEVEL PROFESSIONAL QM1500 QM1517 QM1527 QM1529 QM1321 QM1020 QM1446 QM1323 QM1552 QM1551 QM1549 QM1594 QM1578 QM1493 Display (Count) 2000 2000 2000 2000 4000 Analogue 2000 4000 2000 4000 4000 4000 6000 4000 Security Category Cat II 500V Cat III 600V Cat III 500V Cat III 600V Cat III 1000V Cat II 1000V Cat III 600V Cat III 600V Cat IV 600V Cat III 600V Cat IV 600V Cat IV 600V Cat IV 600V Cat III 1000V • • • • • • Autorange • True RMS • • • • • • Voltage 1000VDC/ 750VAC 500V AC/DC 500V AC/DC 600V AC/DC 1000VDC/ 750VAC 1000V AC/DC 1000VDC/ 700VAC 600V AC/DC 1000VDC/ 750VAC 600V AC/DC 1000V AC/DC 600V AC/DC 1000V AC/DC Current 10A DC 10A DC 10A DC 10A AC/DC 10A AC/DC 10A DC 10A AC/DC 10A AC/DC 10A AC/DC 10A AC/DC 10A AC/DC 10A AC/DC 10A AC/DC Resistance 2MΩ 2MΩ 2MΩ 20MΩ 40MΩ 20MΩ Capacitance 100mF Frequency 10MHz Temperature Duty Cycle Continuity 20MΩ 40MΩ 200MΩ 40MΩ 40MΩ 40MΩ 60MΩ 100μF 100µF 100mF 100µF 100µF 100µF 6000µF 10MHz 10MHz 10kHz 750°C 760°C 10MHz 10MHz 10MHz 10MHz 1000°C 760°C 1000°C 760°C • • • • • • • • • • • • • • • • • • • • • • • • • Relative Min/Max/Hold • Non Contact Voltage • • $35.50 $41.50 • Max Hold • • • • • IP Rated Price $10.95 siliconchip.com.au $29.95 *Lifetime warranty excluded on models: QM1500/QM1517/QM1527 $51.95 $37.50 $67.95 magazine $61.95 $90.95 Australia's electronics $90.95 1000VDC/ 750VAC 4000MΩ • • • IP67 IP67 $119 $329 O$179 ctober $219 2026  27 Mighty USB-C Part 1 / 2 Bench PSU By Ti m Bly thm The Mighty USB-C Bench an PSU leverages USB-C’s Power Delivery features to create an efficient adjustable supply that can deliver up to 20V at 2A. It’s extremely portable and has many handy features, including an adjustable current limit. Delivers up to 20V at 2A (if the USB power source is capable) Compact case measures 94 × 83 × 30mm Detailed OLED display plus LED status Rotary encoder for tactile voltage and current control Highly configurable for efficiency or low-noise operation Software features include fuse emulation Detailed USB-PD source information T here is an increasing amount of inexpensive USB-C power supplies from local retailers, which we can use to supply much higher voltages and currents than legacy 5V USB. The original USB-PD (Power Delivery) standards allow a variety of voltages up to 20V at up to 3A; the newer USB-PPS (Programmable Power Supply) offers even more fine-grained control. 28 Silicon Chip So we thought it’d be very convenient to have a light, portable power supply you can plug into a range of USB ports to operate as a simple but useful bench supply. That’s exactly what this project delivers. USB-PD dates back to 2013 and USB-PPS was introduced in 2017, so they are not new standards. It takes time for products to be developed, released and adopted; we have now Australia's electronics magazine reached the point that such power supplies are easy to come by, meaning that a design using these features is practical. In a sense, this project supersedes the Dual-channel Breadboard PSU from December 2022 (siliconchip.au/ Series/401). That small and simple device acted as a basic bench power supply for circuits on a breadboard or in similar prototyping situations. It used a voltage-boosting module to derive up to 15V from a 5V USB input at low currents and could also utilise fixed DC supplies like plugpacks. It was a strictly linear design that could manage 1A output with a DC supply, or much less with a USB input. The Breadboard PSU did not include a microcontroller; it used potentiometers for its setpoints and analog circuitry to drive its outputs. A separate, optional display unit (driven by a microcontroller) monitored the PSU and showed its status on an LCD panel. Despite its simplicity, we use the prototype from time to time; the ubiquity of 5V USB means that there is never any problem finding a suitable power source. This new design can deliver considerably higher voltages and currents than the Breadboard PSU, and it’s very convenient due to the fact it can be powered from a range of USB-C power supplies (including some power banks) and because it’s small, light and highly portable. It also has quite a few new features, like a load switch, automatic thermal shutdown and a ‘circuit breaker’ mode. Hybrid power supplies To understand why a variable supply voltage is so useful (as provided by USB-PD), consider ‘hybrid’ PSU designs. A traditional linear power supply design, like our Breadboard PSU or the 45V/8A Bench PSU from October-December 2019 (siliconchip. au/Series/339) must be capable of dissipating a lot of power. The 45V/8A Bench PSU might need to dump nearly 400W from its heatsink during operation under some conditions. Our design needs to handle this dissipation and ensure the circuitry does not fail from overheating. As a result, the heatsink and fans for that design took up a considerable amount of space in the large enclosure. siliconchip.com.au Fig.1: the requested supply voltage (red area) for DC, USB-PD and USB-PPS sources when a particular output voltage (blue area) is selected. The amount of red visible reflects the voltage that needs to be dropped across the output transistor and thus its dissipation. Less red area is preferable, which is best achieved using a USB-PPS source. The worst-case scenario for such a device is a low output voltage at high current. The circuitry must drop the voltage from the input supply (over 50V for the 45V/8A Bench PSU) to nearly 0V at the maximum current, thus dissipating a lot of power. In contrast, a hybrid PSU includes switch-mode circuitry to provide a variable voltage at the input of the linear section that is high enough to allow proper regulation but no higher. Our Hybrid Bench Supply from April-June 2014 (siliconchip.au/Series/241) can manage about half the output power of the 45V/8A Bench PSU but fits in a case that is about an eighth the size! Pure switch-mode designs are possible, but can suffer from a noisy output, particularly at the switching frequency. The presence of a linear stage after the switch-mode stage in a hybrid design can help to reduce undesirable noise and also speeds up the onset of current limiting in response to a rapidly changing load impedance. The Mighty USB-C Bench PSU is a hybrid design that uses the variable voltage capability of modern USB-PD devices to feed a linear output stage at a level that minimises dissipation. It provides the sort of features that are expected from a bench PSU while using ubiquitous USB power. The Mighty USB-C Bench PSU looks much more polished than the Breadboard PSU and, thanks to the developments in USB power sources, is considerably more powerful too. With much of the circuitry handed off to a separate USB power supply, the Mighty USB-C Bench PSU is tiny, fitting in the palm of the average hand. Its specified output (20V at 2A) is quite modest compared to some of the other units mentioned here, but we siliconchip.com.au are limited by the capabilities of readily available USB-C power supplies. Control algorithm Fig.1 shows graphically how a USB-PD or USB-PPS based power supply can be much more efficient and compact than one running from a fixed DC supply. The red area shows the amount of voltage that must be dropped by the output transistor to achieve the voltage setpoint. This voltage, multiplied by the output current, is the amount of power that the PSU must dissipate during normal operation. So the smaller the red zone, the less power the pass transistor has to manage. A USB-PD power supply can provide one of several discrete voltage output levels. We choose the lowest level that allows enough headroom for the linear regulator to avoid dropout. That provides a significant reduction in the red area. USB-PPS has more fine-grained control (typically steps of 100mV), so it can operate much closer to the ideal level, shrinking the red area even further. Note that a DC supply needs to drop the most voltage at low output voltages, while the USB-PPS supply allows a small but uniform amount of headroom across most of the working range, since it is finely programmable. The USB-PD supply only offers a few discrete steps, but still outperforms the DC supply. In operation, the supply chooses a preferred USB source voltage depending on several settings and live readings. The source is not The Mighty USB-C Bench PSU can be so compact since it outsources the role of AC-DC conversion to an external USB-PD or USB-PPS power supply. Australia's electronics magazine October 2026  29 permitted to supply less than 5V, since that would prevent proper operation of the logic circuitry. Also, the output is capped at whatever maximum the source can supply. You can see these two last behaviours in the horizontal regions of Fig.1(c). The ideal source voltage is based on either the setpoint or output voltage, plus an amount known as the Voltage Headroom. The next highest available PDO (power data object) voltage above this is chosen for USB-PD supplies; you can see this changing behaviour in the stepped shape of Fig.1(b). A USB-PPS supply allows the PDO voltage to be chosen to the nearest 100mV. If no PDO is found, the highest available is chosen, as long as it is at or below 25V. Different PDOs will typically have different current limits, so the achievable current setpoint might change as the voltage setpoint is adjusted. If the Headroom is relative to the setpoint, the PSU will respond quickly to changes, even if current limiting occurs. However, it may dissipate more power while current limiting is active, since the source voltage does not reduce, even if the output voltage drops. Setting the Headroom relative to the output voltage will allow efficient operation (even when limiting is active), but that might result in it being slower to recover from current limiting, since the algorithm then limits the preferred voltage to a lower value than it would with the setpoint. Effectively, the output slowly ramps up on recovery as allowed by the Headroom. Along with numerous other parameters, the Headroom is adjustable, so the behaviour of the USB-C PSU can be optimised for different scenarios and to favour efficiency or response time as needed. Design considerations To interface with a USB-C power supply, we need some circuitry that can request an appropriate voltage from it. There are modules available that can do this, including some based on the HUSB238 USB-C power delivery sink controller IC. Suitable modules include the Adafruit 5807 and Jaycar’s PP2081 (www.jaycar.com. au/p/PP2081). The HUSB238 chip cannot handle USB-PPS, so we have also designed our own compatible module using the 30 Silicon Chip AP33772S USB-C power delivery sink controller IC, which can. Since these modules are quite interesting in their own right, we have described them in a separate article, starting on page 38. You can use our module or one of the commercial modules mentioned above for the USB-C PSU. You can even use a pure DC power source, although you will miss out on the efficiency gains that a hybrid device offers. Because the AP33772S is only available as a QFN (quad flat no-lead) part, which is tricky to hand-solder, we have designed the module for assembly by JLCPCB. In other words, you can purchase the module fully assembled. We recommend you check out that article, if you have not already done so, since it provides more detail on the operation of these power delivery sink controller modules. There is also an explanation of some of the terminology that relates to USB-C Power Delivery (PD) and Programmable Power Supply (PPS) modes. The 2022 Dual-channel Breadboard PSU was intended to be as straightforward and inexpensive as possible. We have the same aim with the USB-C PSU design. There are no obscure parts; the AP33772S IC is the most unusual, but it is readily available from suppliers like DigiKey, Mouser and LCSC (the component supply part of the JLCPCB group). The basic operation is similar to the Breadboard PSU in that a pair of reference voltages are used to set the output voltage and current limit. A dual op amp and some extra circuitry (mostly passives) monitors the voltage and current signals to drive a power transistor as the pass element. The USB-PD modules have an I2C interface, so a microcontroller is necessary. Using a trusty PIC16F18146 8-bit microcontroller adds more than enough smarts to provide a detailed user interface. All the voltage regulation and current limiting happens in the hardware around the op amp, so the core functions are not limited by the software speed. The presence of the PIC16F18146 allows us to provide many other features; for example, a relay can be used to manually switch the USB-C PSU’s output. Combined with a thermistor as a temperature sensor (read by an analog-­ to-digital converter in the micro), the relay can also provide an automatic Australia's electronics magazine safety shut-off if the temperature rises too high or other problems occur. Circuit details Figs.2 & 3 show the complete circuit of the Mighty USB-C Bench PSU. Fig.2 contains all the parts on the main PCB, while the Fig.3 components are on a separate PCB that forms the front panel. The two are connected by a sixway cable from CON1 to CON101. The main voltage control and current limiting is based around IC1, a common LM358 op amp. IC1a performs the voltage control using NPN transistor Q1 (fed from the POWER+ rail) as an emitter-follower to provide current gain. The output from Q1’s emitter passes through a 50mW shunt resistor for current sensing and into the 10kW/1kW divider, which in turn feeds back to IC1a’s inverting input as Vsignal. The control voltage, Vset, is presented to IC1a’s non-inverting input via a 1kW resistor so that the op amp’s inputs see a similar impedance. With the op amp in control, the voltage at the two inputs is the same, meaning that the voltage at the top of the 10kW/1kW divider is 11 times that at the pin 3 non-inverting input. The 50mW shunt resistor is monitored by IC2, a differential amplifier with a gain of 20. Thus, 1A through the shunt resistor results in 1V appearing at IC2’s pin 4. The Isignal line is sent to the non-inverting input of IC1b, which forms the current-limiting part of the circuit. A voltage, Iset, is supplied to IC1b’s inverting input. The output of IC1b connects to NPN transistor Q2 via a 100kW resistor. Q2 has its emitter connected to ground and its collector to the point where the voltage control signal is fed into IC2a. When Q2 switches on, its collector is pulled to ground, reducing the voltage control signal. When the current signal from IC2 rises above the Iset reference, IC1b’s output voltage rises, switching on Q2, reducing the voltage setpoint and thus the output voltage to bring the current under control. The principle of the circuit so far is much the same as the Dual-channel Breadboard PSU, although it only has one channel rather than two. Note that Q2’s base is connected to IC3’s pin 18 via a 10kW resistor. This is primarily so that the microcontroller can monitor the voltage at this point. If siliconchip.com.au Fig.2: this is the part of the circuit on the main PCB; CON1 here connects to CON101 in Fig.3. Two microcontrollers are used; IC3 is the main controller, while IC4 is used mostly for its DAC feature and to control the boost regulator that produces the OA+ op amp supply. The red dotted line from CON5/CON6 to CON2 shows the main current path through the circuit. Q2’s base is near 0.6V then Q2 is conducting and pulling down the voltage reference at IC1’s pin 3, so current limiting is occurring. If Q2’s base is near 0V, there is no current limiting. Relay RLY1 is used to switch the output to screw terminals CON2. RLY1 is in turn controlled by NPN transistor Q4, with back-EMF suppression diode D2 protecting Q4 when the relay switches off. Schottky diodes D4 and D5 protect the circuitry in case the load tries to pull the output below GND or above the positive supply rail. siliconchip.com.au IC1 and IC2 have the necessary supply bypassing capacitors, while the capacitors between the op amp outputs and inverting inputs provide negative feedback to suppress any tendency for the circuit to oscillate. The feedback loop for the current has substantial gain, hence the 10nF feedback capacitor there. LM358 op amp IC1 has some properties that are critical to the operation of the USB-C PSU. Firstly, its inputs and outputs can both operate near its negative rail. Since the signals are Australia's electronics magazine referenced to circuit ground (and will come close to ground at times), these levels must be within the common-­ mode input range of the device. To assist with operation near the negative rail, the feedback voltages are biased slightly upwards via 220kW resistors to the output of 3.3V regulator REG1. A 0V or 0A output actually registers at around 15mV on the Vsignal and Isignal lines. This keeps the op amp away from the limits where the behaviour might become non-ideal. October 2026  31 The output behaviour of IC1 is not so critical, as Q1’s base-emitter voltage drop means that even with a 0V output, the op amp’s output does not need to get close to its negative rail. The op amp’s positive rail is a different matter, as we need enough voltage for IC1 to drive Q1’s emitter near to the POWER+ rail. The positive rail output swing of IC1 is a few volts less than its supply, and we need to compensate for the ~0.7V base-emitter drop of Q1 and the voltage across its 47W base resistor. Thus, a separate OA+ supply is provided, which is above the POWER+ voltage. We will see where the OA+ voltage and the POWER+ rail come from shortly. Main microcontroller IC3 is an 8-bit PIC16F18146 microcontroller with 20 pins. It includes several handy analog and digital peripherals. It is supplied with the usual support circuitry of a 100nF bypass capacitor on its supply rails (+5V and GND), a 10kW resistor pulling up its MCLR pin, with these and the other programming pins (PGD/PGC) connected to header CON3 for programming and debugging. In terms of peripherals, it includes an 8-bit (256-step) digital-to-analog converter (DAC) that we use to provide the Vset voltage. The DAC is referred to an internal 2.048V reference with 8mV steps, meaning that the PSU output can be controlled up to a nominal 22.4V (2.048V × 11) in 88mV steps. This DAC output is available at pin 17. While there are two 8-bit DACs in the PIC16F18146, only one can be connected to an external pin. The other DAC is referred to IC3’s supply voltage and set to code point 32, or ⅛ of the supply. The internal analog-to-digital converter (ADC) is configured to use the internal 4.096V reference, so the chip can measure its own supply voltage without any external components. The ADC is also used to measure a number of other signals, including those relating to the output circuitry, such as Vsignal, Iset and Isense on pins 14, 15 and 16. Pins 10 and 11 (POWER_ SENSE and OA_SENSE rails) also measure other analog voltages. The POWER+ and OA+ rails voltages are monitored via 10kW/1kW dividers in similar fashion to the output voltage. They have 100nF capacitors on their lower legs to provide some low-pass filtering. 32 Silicon Chip Tsense (on pin 8) is another analog signal formed from a divider made of a 10kW NTC (negative temperature coefficient) thermistor and a 2.2kW resistor; this also has a 100nF capacitor for filtering. The lug-type thermistor is mounted on Q1 and connected to the main PCB at CON4, for sensing Q1’s temperature. Second microcontroller As mentioned above, only one of IC3’s DACs can be fed outside the chip. Since that is providing Vset, we need another way to control the Iset current-­ limit determining voltage. External DAC ICs exist, but typically have a 3-wire SPI interface, and we were already running out of pins on IC3. Instead, we have employed IC4, a PIC16F18115 microcontroller, to provide the second DAC channel. The PIC16F18115 is just as cheap as any of the DAC chips we could find and, like IC3, it has an internal 2.048V reference, so it incorporates all the features we need to work as a DAC. IC4 provides the current control voltage ISET_DAC from its pin 5. It is controlled by IC3 via a single-wire asynchronous serial (UART) interface from pin 9 on IC3 to pin 3 on IC4. Like IC3, IC4 is powered from the +5V rail (pin 1, with pin 8 being ground), which is bypassed by a 100nF capacitor. Pins 1, 4, 6, 7 and 8 connect to a second ICSP header, CON7, with pin 4 pulled up by a 10kW resistor. This means both chips can be reprogrammed while on the board, if necessary. IC4 is also responsible for the generation of the OA+ op amp supply rail from the POWER+ rail. This is achieved by the circuitry around NPN transistor Q3 and N-channel Mosfet Q5, connecting to IC4 at its pins 2, 6 and 7. Pins 6 and 7 feed a comparator inside IC4. Pin 6 of IC4 also connects to the POWER_SENSE line to measure the voltage feeding into Q1. Pin 7 (OA_ FB) connects to a similar divider (10kW/1kW) that is in series with a ‘Vbe multiplier’ based on Q3 and the 10kW/1.2kW divider. The Vbe multiplier drops a voltage that is proportional to the transistor’s base-emitter voltage. The multiplier is given by the divider ratio; in this case, 11.2kW (10kW + 1.2kW) divided by 1.2kW = 9.3. At the small currents involved, we measured the base-emitter voltage at 0.55V, so the voltage across the Vbe multiplier is around 5.1V; this is bypassed by a 100nF capacitor. The circuitry around Q5 is a simple boost converter utilising inductor L1 and diode D1. Q5 is driven by pin 2 of IC4, which is fed a PWM signal as long as the pin 7 comparator input is lower than the pin 6 comparator input. This is handled by the configurable logic cell (CLC) peripheral of IC4, so voltage regulation occurs without software intervention. IC4 thus controls the voltage on the output of the boost regulator Fig.3: the front panel has the screen, four pushbuttons (one integral to the encoder), rotary encoder and dual-colour LED. Australia's electronics magazine siliconchip.com.au circuitry. The concept is similar to that used in the Digital Boost Regulator from December 2022 (siliconchip. au/Article/15588), although that used an internal DAC as the control voltage rather than a different signal from within the same circuit. Effectively, the circuit regulates the OA+ rail to 5.1V above the POWER+ rail, which is high enough to allow IC1 to drive Q1. We noted in the Digital Boost Regulator article that the control algorithm is quite crude, so the output passes through a 47W resistor and is bypassed by a 10μF capacitor to provide some filtering at the op amp’s supply pins. If Q1’s collector cannot source enough current, the load will tend to draw from Q1’s base and IC1 instead, because Q1’s base current contributes to the output current. The two 47W resistors help to protect the boost circuit and op amp from exceeding their output current capacity and being damaged. Power delivery Incoming power is supplied via a USB-PD module at CON5, or a pair of screw terminals at CON6. We’ll discuss the operation of the USB-PD module shortly, but we can expect a nominal voltage of 5-20V here, perhaps up to 25V, via 3A fuse F1 to the POWER+ rail. The +5V rail comes from an MCP1804 5V LDO (low-dropout) regulator IC; it has the requisite 10μF bypassing capacitors. The LDO function is vital, as we need to provide near enough to 5V even with a 5V supply. This is necessary so that the 4.096V reference in IC3 can regulate correctly and there is enough voltage to drive the 5V coil of the relay. The practical limit for the incoming supply voltage is about 25V; it must be below op amp IC1’s 30V recommended maximum less the 5V added to the OA+ rail. Current shunt monitor IC2, which runs from the incoming supply, has a maximum supply voltage of 26V. Digital circuitry IC3 is responsible for some other digital signals. Its pin 2 drives Q4 via a 5.1kW resistor, which in turn controls RLY1. There are two I2C serial buses (SDA, SCL, SDA2 and SCL2), which all have 5.1kW pullups to the +5V rail. The RE_A and RE_B lines connect to the quadrature outputs of a siliconchip.com.au Parts List – Mighty USB-C Bench Power Supply 1 main PCB assembly (see below) 1 front panel assembly (see below) 1 USB-C PD or PPS power source (eg, AC to USB-C adaptor or USB-PD battery bank) 1 extruded aluminium enclosure, 94 × 83 × 30mm [Adafruit 2230; DigiKey, Mouser] 1 M3 × 6mm blackened panhead machine screw 1 M3 × 12mm blackened panhead machine screw 2 M3 nuts (solderable; eg, brass or nickel-plated) 2 M3 flat washers 1 TO-3P insulated mounting kit (silicone pad and 3mm plastic bush) 4 small self-adhesive rubber feet wire and connectors to suit usage (eg, 5A cable; optionally, banana sockets) wiring to connect panel to main PCB (approx. 30cm of light-gauge hookup wire) Main PCB assembly 1 73 × 77mm double-sided PCB coded 04107261 1 USB-C PD module [Adafruit 5807, Jaycar PP2081] OR 1 USB-C PPS module [Silicon Chip SC7740] 2 2-way 5mm/0.2in pitch screw terminals (CON2, CON6; optional) 2 5-way 2.54mm/0.1in pitch pin headers (CON3, CON7; optional, for ICSP) 1 2-way JST XH board-mount male connector (CON4; optional) 2 3-way 2.54mm/0.1in pitch pin header (CON5) 1 10kW lug-mount NTC thermistor [Altronics R4112] 2 M205 fuse clips (F1) 1 3A fast-blow M205 fuse (F1) 1 4.7μH 1.3A 120mW SMD inductor, M2520/1008 (L1) [Abracon AIML-1008HC-4R7M, Murata LQM2MPN4R7NG0L] 1 5V/2A DPDT SMD or TH 2A telecom relay (RLY1) [Omron G6K-2F-Y-DC5V] Semiconductors 1 LM358 dual single-supply op amp, SOIC-8 (IC1) 1 INA180B1IDBVT 20× current sense amplifier, SOT-23-5 (IC2) 1 PIC16F18146(T)-I/SO SMD 8-bit microcontroller programmed with 0410726A.HEX, SOIC-20 (IC3) 1 PIC16F18115(T)-I/SN SMD 8-bit microcontroller programmed with 0410726B.HEX, SOIC-8 (IC4) 1 MCP1700(T)-3302 SMD 3.3V LDO regulator, SOT-23 (REG1) 1 MCP1804(T)-5002 SMD 5V LDO regulator, SOT-223 (REG2) 1 FJA4313 or 2SC5242 NPN transistor, TO-3P (Q1) 3 BC817-40 SMD 45V 800mA NPN transistors, SOT-23 (Q2-Q4) 1 2N7002 SMD 60V 115mA N-channel Mosfet, SOT-23 (Q5) 2 1N5819WS 40V 1A SMD schottky diodes, SOD-323 (D1, D2) 2 SS34 40V 3A SMD schottky diodes, DO-214AB/SMC (D4, D5) Capacitors (all SMD M3216/1206 50V X7R MLCC unless noted) 5 10μF X5R 3 1μF 9 100nF 1 10nF 1 1nF Resistors (all SMD M3216/1206 ±1% ⅛W unless noted) 2 220kW 12 10kW 1 2.2kW 7 1kW 1 50mW M6331 3W 1 100kW 5 5.1kW 1 1.2kW 2 47W Front panel assembly 1 double-sided 29 × 89 × 0.8mm black PCB coded 04107264 2 small rubber grommets [Keystone 730] 1 0.91-inch I2C OLED module (MOD101) [SC7484] 1 rotary encoder with pushbutton and 18t spline shaft (RE101) 1 knob to suit RE101 3 reverse-mount SMD tactile switches (S101-S103) [Adafruit 5410] 1 PCF8574 or PCF8574A SMD I2C I/O expander IC, wide SOIC-16 (IC101) 1 back-emitting/reverse red/green bicolour SMD gullwing LED, 3.2×2.8mm (LED101) [Kingbright AAA3528SURKCGKC09] 1 100nF SMD M3216/1206 X7R 50V MLCC capacitor 1 1kW M3216/1206 ±1% ⅛W SMD chip resistor short lengths of solid core wire (eg, component lead offcuts) to connect and secure the OLED Complete Kit (SC7739, $95 + P&P): includes the USB-PPS module, two PCBs, two programmed microcontrollers, the case, and pretty much everything else needed. Preassembled USB-C PPS Control Module (SC7740, $25 + P&P) rotary encoder and also have pullups to +5V and 100nF debounce capacitors to ground. CON1 is the connection to the separate control panel PCB (at CON101). The panel PCB carries OLED module MOD101, which takes in +5V, GND, SDA and SCL signals for power and communication. IC101 is a PCF8574 (or PCF8574A) I2C I/O expander, which also connects to the +5V, GND, SDA and SCL lines. Its pins can act as inputs (with internal pullups) or open-drain outputs, so it is used to read the pushbuttons switches S101, S102 and S103, as well as the pushbutton switch on rotary encoder RE101. IC101 also drives dual red/green LED101 via a single 1kW resistor. To save space on the panel PCB, the resistor is shared, and only one element is driven at a time. If both LED outputs are driven, the lower forward voltage of the red element means that the green element does not illuminate. The quadrature outputs of the rotary encoder (RE_A and RE_B) go directly back to the main PCB. Although IC101 has spare inputs, we don’t expect the I2C interface to be fast enough to keep up with the rotary encoder’s operation. Finally, the second I2C bus (SDA2 and SCL2) connects to CON5 to control the external USB-PD module. Keeping this independent means that the display and controls can still be used even if there is a fault with the second I2C bus. S = Setpoint (target) Mechanical design The main PCB is designed to fit into a small, inexpensive extruded aluminium enclosure, with the intention that Q1 can be affixed to it to add thermal mass and assist with dissipation. The case we have chosen is sold by the Adafruit company and is available from various sellers, including DigiKey and Mouser. The main and front panel PCBs are both sized to be a neat fit to this enclosure, with the front panel PCB replacing the included front panel. The USB-C connection is accessed via a hole cut in the rear panel, and the main PCB is secured to it by means of a nut soldered to the PCB. If you need to resort to a different enclosure, we recommend a similar but larger aluminium case, such as a diecast or extruded design. This will allow Q1 to be heatsinked. The front panel PCB could be used as a bezel and mounted to a larger panel. The holes in the front panel and adjacent to the USB-PD module are suitable for M2.5 hardware. To assist with alternative enclosures, there are mounting holes on the main PCB to allow the use of M3 machine screws and tapped spacers. Two of the holes are adjacent to where the USB socket (on the module) is located, so mechanical strength is supplied where it is most needed. To keep the part count and cost down, we have designed the PCB with strain relief holes adjacent to CON2 Angle brackets <> mark the value that Current setpoint Voltage setpoint can be set with the will flash if it is too rotary encoder high will flash if supply is too low DAC setting (0-255) of the setpoint under user control (output) and CON6 (DC input). This means that wires can be soldered directly to the PCB. The output wires can then be run through the holes in the front panel or be terminated to banana sockets if you wish. You may need to drill out the panel holes to suit banana sockets. Similarly, the thermistor termination and front panel wiring are suitable for 0.1in/2.54mm pitch headers, but the simplest option is to solder the wires directly. There will be little need for strain relief since these parts will not move once the unit is closed up. Firmware for IC4 IC4’s firmware is quite simple. It configures the EUSART peripheral to listen for 9-bit serial data on the SER_ CON line. To avoid problems with spurious data, IC4 waits to receive two identical data words in a row before acting. Using nine bits allows us to send two different sets of 8-bit commands without worrying about data framing. With the ninth bit set low, the remaining eight bits are used to set the DAC level for current control. If the ninth bit is set high, the command uses the other eight bits to set the duty cycle of the PWM peripheral. The PWM peripheral uses a 32MHz internal oscillator with a period of 100 cycles, so it operates at 320kHz, and the value corresponds directly to the duty cycle percentage. Setting the duty cycle to zero effectively disables the PWM signal and thus the boost feature. The software limits the duty cycle to 15% to avoid excessive loads on the boost section. Firmware for IC3 Fig.4: the display is packed with information about the settings and operating conditions of the USB-C PSU. Many of the indicators will flash if improper conditions are detected. At startup, the processor initialises all the necessary peripherals and scans the first I2C bus to determine if there is a PCF8574 (7-bit bus address 0x20) or PCF8574A (0x38) present. After this, the second I2C bus is scanned to determine whether a HUSB238 (0x08) or AP33772S (0x52) is present. If neither is present, a fixed DC source is assumed. This information is displayed on the OLED screen. If present, the module is queried for the USB-C source capabilities, and a summary of this is also displayed. Commands are then sent to IC4 to ensure it is in a known state. Much of the firmware on the main processor is dedicated to providing the Australia's electronics magazine siliconchip.com.au L indicates that current limiting is active A = Actual Thermistor (Q1) temperature will flash if it is approaching the trip limit 34 Silicon Chip Incoming USB-PD supply voltage (or DC voltage) 5V+ supply rail is shown and will flash if below 4.5V user interface. There are numerous settings that can be changed to alter the behaviour of the USB-C PSU, not just the main operating parameters like voltage, current and so forth. A 5Hz timer is used to control updating the display and USB-PD module at a reasonable rate. Various lines are read to measure the voltage and current setpoint and actual value; the thermistor temperature; the OA+, POWER+ and +5V rails; and Q2’s base for current-limiting detection. The monitoring of the nine analog voltages is performed in the background by the ADC peripheral operating continuously in an accumulating mode. This automates oversampling and effectively gives fresh 16-bit results from the 12-bit ADC every 20ms. When a new result is ready, the values are adjusted by calibration constants to provide meaningful values for display and calculation. With the 220kW resistors biasing the voltage and current readings, these are not simply a ratio, but also include an offset adjustment. The remaining values (OA+, POWER+ and +5V rails and Q2’s base) have no offset and are simply scaled. The reason for choosing a 2.2kW resistor as part of the thermistor divider chain is that this value gives a fairly linear relationship (within 1°C) between voltage and temperature over the range of 20°C to 80°C. Thus, the temperature can be estimated using a ratio (slope) and offset calculation, and the same software routines are used to perform the calculations as for the voltages. The main operating screen (Fig.4) allows the two DAC outputs to be adjusted, using the rotary encoder to set the voltage and current setpoints. Pressing the rotary encoder toggles between voltage and current setting. The relay can be controlled with two of the pushbuttons. The raw 8-bit (0-255) DAC value is adjusted, and the calculated voltage and current setpoints are shown. The steps correspond to about 88mV for voltage control and 8mA for current control. With the offset noted above, the DACs need to be at step two or higher to have a non-zero output, which ensures that zero levels can be achieved. In the event that the USB-C PSU detects a fault condition, such as the thermistor going open-circuit or siliconchip.com.au The design uses our APS33772S USB-PPS board (published separately in this issue) to provide the USB-PPS features when powered by a suitable USB power source. Alternatively, you can use a commercial HUSB238 module (such as Jaycar’s PP2081) instead. detecting a high temperature, the relay is opened and the voltage control DAC is set to zero. The fault is displayed and must be cleared before the condition can be reset. The LED on the front panel shows solid red when the relay is off and green when the relay is on and the output is active. A fault will cause the LED to flash. Other data is also shown on the main screen, including the temperature, supply voltage (POWER+) and available current. An “L” is shown if current-limiting is active. In one mode, an overcurrent fault condition will open the relay. The behaviour then is more like a fuse, opening the circuit if the limit is reached. In the brief period before the relay opens, the current limiting is still enforced for safety. Minor faults (not severe enough to cause a trip) are shown on the main page by flashing the appropriate data display. For example, if the temperature is flashing, it is nearing its limit. If the current setpoint is flashing, it might be exceeding the capacity of the power supply. For the current, there is also an option to automatically ramp the setpoint down to a safe level. Settings There are many pages of settings and calibration data. These are entered and cycled through by using the > button on the front panel; this can only be done while the output relay is off. Some calibration settings require an output from the PSU, so the voltage, current and relay are under software control when the settings pages are active. Australia's electronics magazine The first few settings are the ones that might be changed regularly, such as the different operating modes and settings, while the later ones allow adjustment of the calibration parameters. We’ll delve into these later, once construction of the unit is complete. While there are many ways to adjust the settings, we expect that most applications will fall into one of two cases. Firstly, running the boost regulator for the OA+ rail will allow the output to come very close to the incoming supply voltage and offer very efficient operation, since Q1 needs to drop very little voltage. USB-PPS supplies allow the source voltage to be chosen in 100mV steps, and dissipation in Q1 below 1W can easily be achieved across most of the range with this configuration. If necessary, the boost regulator can be shut off. In this case, Q1 will likely be dropping 3V or more depending on the current draw. Due to the loss of headroom, these settings might be better for sensitive applications at lower currents or lower voltages. USB-PD control A critical part of the USB-C PSU’s operation is the need to control the USB-C power source via the module connected at CON5. The aim is to ensure sufficient headroom of the POWER+ rail above the desired output voltage while minimising that headroom, since that is the main contributor to dissipation and heating in Q1. Several parameters and settings that can be used to tweak this behaviour. These are used, along with the source capabilities, to determine the best PDO October 2026  35 (power data object) to request. This is checked and updated multiple times per second; you can see the POWER+ voltage display change as the voltage is changed. Of course, the capabilities of the USB-C PSU are strongly dependent on the features of the USB-C power source that is connected. Most USB power sources provide a slightly higher voltage (than nominal) to compensate for cable resistance. There is tolerance in the voltage specifications for this. For example, a nominally 20V power source powering the USB-C PSU measured at 20.15V and from this, the PSU was able to supply 20.07V into a 200mA load. That does mean that there needs to be some headroom in the current capacity of the supply. During our testing, we sometimes exceeded the power source’s limit (deliberately and accidentally!) and found that the typical supply behaviour was to simply shut down until a power cycle had occurred. Performance The USB-C PSU has been optimised for stability under a very wide range of conditions, so we aren’t making any claims that it has a very fast response to changes. As with similar designs, the ability of the output voltage to decrease due to changes in setpoint is limited by the load and output resistance, since Q1 is only capable of sourcing current. Increasing the output voltage will be as fast as designs like the Breadboard PSU, provided that the USB-PD source does not need to ramp up. The ramp rate under these conditions will depend on things like the headroom setting and source response. Scope 1 shows a typical response to ramping being limited by the behaviour of the source. Since current limiting is handled in hardware, this response is not affected Scope 1: changing the setpoint from 0V to 10V. The blue trace shows the output voltage, while the red trace is the Vset line. The green trace (also 12V scale) shows the USB-C supply voltage. The supply voltage must ramp up to allow the output to meet its setpoint. Although there is a delay due to the supply requiring software control, the output voltage follows the supply quite closely due to the OA+ boost circuitry. by the source’s behaviour. Recovery from current limiting may be slowed if the source voltage has been ramped down. If the USB-C PSU is set to track the setpoint voltage, ramping will not happen except on setpoint changes. Tests with our prototype showed a temperature rise of around 6°C/W, so we expect that the PSU should be able to dissipate around 4W continuously without tripping at normal ambient temperatures. At 50°C, the case is noticeably hot to the touch, so we have chosen this as the trip limit. The electronics can handle this with ease. 4W dissipation should thus allow 2A of continuous current with 2V of headroom, which was achievable over most of the range for the USB-C sources we tested. The continuous SOA (safe operating area) of Q1 goes up to 30V at 4A, so the expected working range is well within these limits. Note that this is dissipation in the PSU and not in the load. With a USB-PPS source and lower headroom, continuous operation at less than 1W dissipation should be Views of both sides of the black front panel PCB. 36 Silicon Chip Australia's electronics magazine achievable, even with a 2A load. Efficiency Fig.1 demonstrates how difficult it would be to give a single efficiency figure for the USB-C PSU. The efficiency and dissipation depend a lot on the voltage and current settings, the headroom settings, and the USB source capabilities. With a USB-PPS power source, the headroom will be close to nominal, especially if the OA+ boost circuit is active. With a USB-PD source, the actual headroom might be much higher due to the spacing of the source voltages, as indicated by the sharp upward steps in Fig.1(b). This is the main reason that we thought it best to design a USB-PPS module. Broadly speaking, efficiency can be improved by tweaking the settings, but this may result in longer response times to setpoint changes or slower recovery from current limiting. We will discuss this in detail in Part 2, along with the settings. Next month As you can see, there is much that has gone into the design of both the hardware and firmware of the USB-C PSU. Since there are so many settings and features to be explained, we will look at the assembly, setup and how to use the PSU next month, including details of the many settings and their SC operation. siliconchip.com.au SOnline ilicon Chip Shop Kits, parts and much more www.siliconchip.com.au/Shop/ Simple USB Power Monitor June 2026 Complete Kit SC7683: $50 siliconchip.au/Article/20365 Includes the PCB, all onboard parts and some clear heatshrink tubing to encase it. This unit is not recommended for USB 3.1 PD above 36V. Dual Mini LED Dice August 2024 SMD LED Complete Kit SC6961: $17.50 TH LED Complete Kit SC6849: $17.50 USB Power Adaptors May 2025 Complete Kit with choice of USB socket SC7433: $10 siliconchip.au/Article/16418 siliconchip.au/Article/18112 Includes either 3mm through-hole or 1206sized SMD LEDs. Choice of either white or black PCB. CR2032 coin cell not included. You can choose from one of four USB sockets (USB-C power only, USB-C power+data, mini-B or micro-B). The kit includes all other parts. DCC Base Station Short-form Kit SC7539: $90 Human Comfort Indicator June 2026 January 2026 siliconchip.au/Article/19558 This kit includes all non-optional components in the parts list (and the RJ45 socket, CON6). It does not include the case, DC power supply, glue, CON4 screw terminal and CON5 locking header. Mic the Mouse Complete Kit SC7508: $37.50 August 2025 siliconchip.au/Article/18637 It includes everything needed to build one Mic the Mouse, except for solder, glue and a CR2032 cell. Complete Kit SC7646: $60 siliconchip.au/Article/20362 Includes everything, except for the case and Li-ion cell. You can either use a 3D printed case (available separately) or a UB3 Jiffy box. → Subscribers receive a 10% discount on all purchases, except for subscriptions (postage is not discounted). → Prices listed do not include postage. Postage rates within Australia start at $12, rates are calculated at the checkout. Programmable USB-PD and USB-PPS Modules We’re starting to see inexpensive power sources that include modern USB-PD and USB-PPS capabilities, making it an ideal time to experiment with compatible modules. This article presents one that is commercially available and another we have designed, both being controlled over an I2C serial bus. By Tim Blythman U SB Power Delivery (USB-PD) is a means for a device to request a specific voltage and negotiate a current limit from a USB-C power source. For example, a USB-PD compatible device might request 12V from a power supply rather than 5V; if the supply doesn’t support that voltage, the device can choose another one that it does. The USB Programmable Power Supply (USB-PPS) protocol goes even further, allowing a USB device to request a voltage from 3.3V to 21V in 20mV steps. As with USB-PD, both the source (eg, a USB charger) and sink (device) need to support this protocol for it to work. These days, more and more USB power supplies support both USB-PD and USB-PPS. We published an article titled “How USB-C Power Delivery Works” by Andrew Levido in our July 2021 issue (siliconchip.au/Article/14919). It describes the electrical interface and communication protocol used by power sources that support USB-PD and USB-PPS. Jim Rowe looked at so-called USB-PD triggers and decoy boards back in August 2021 (siliconchip.au/ Article/14996). These are modules that can be configured to request voltage and current levels from suitable power supplies. They incorporate an IC that manages the signalling needed to communicate with the power supply. They also have an interface that allows a certain voltage (usually) to be directly selected by a user. This might be something simple, like a solder jumper that can be modified, or pushbuttons and a display for interactive operation. One of the modules that we are presenting here has a solder jumper setting, but the main thing we are interested in is an interface (I2C or ‘inter-integrated 38 Silicon Chip circuit’ in this case) that allows them to be controlled programmatically by something like a microcontroller. That means we can build a USB-C powered PSU with a controller that can choose the best supply voltage for efficient operation. The glossary overleaf lists some terminology that is common to USB-PD and USB-PPS. Next, we will review a commercially available module. Then we will follow with our design, which keeps the same physical outline but allows the use of USB-PPS. Using the same outline allows them to be mechanically interchangeable, so either can be used in our USB-C PSU design. Adafruit HUSB238 PD Breakout This module is made by the Adafruit company and can be found on their website at www.adafruit.com/ product/5807 The photo below shows the module and Fig.1 its circuit diagram. This is one of the modules we used for testing our USB-C Power Monitor prototype for the project in the September 2025 issue (siliconchip.au/Series/445). Jaycar sells a module (Cat PP2081) that appears to be identical, and we tested some of these alongside the Adafruit parts. This module also functions as a trigger module, since it can be configured via solder jumpers to provide one of several preset voltages or current settings. Of course, these features depend on the attached power supply being able to provide the requested levels. The module is shipped with settings of 5V and 1A. The jumper settings are used until a different command is received on the I2C bus. Fig.1: like many such modules, the circuit is simple but provides sufficient support circuitry to explore the features of the HUSB238 chip. Original source: https://learn.adafruit.com/assets/124712 Australia's electronics magazine siliconchip.com.au It is based on the Hynetek Semiconductor Company HUSB238 chip (https://en.hynetek.com/2421.html), which is only available in a DFN leadless package. This chip supports USB-PD but not USB-PPS, so it can only supply one of the six voltage levels prescribed by the older USB-PD standards. The voltage levels are 5V, 9V, 12V, 15V, 18V and 20V, which you can see marked on the solder jumpers on the module. Interestingly, none of the USB-C power sources we used for testing these modules supported 18V. Apart from some passive components, there is a P-channel Mosfet that is controlled by an open-drain output on the HUSB238 chip. This version of the chip simply switches on the Mosfet when power is applied, although the data sheet notes that other chip variants may support different behaviours. Module connections The package for the module includes a two-way screw terminal header and a 0.1-inch (2.54mm) pitch pin header; the screw terminal can be fitted to connect the power (VUSB and GND) pads. The header pads break out the I2C bus, power and USB2.0 (D+ and D−) connections, allowing the module to be integrated into a peripheral. There is also a pair of mounting holes near the USB-C socket. The chip is directly powered from the USB supply (which could be up to 20V) and lacks I2C pull-up resistors, requiring these to be fitted externally to suit the desired logic level. The I2C slave address (7-bit) of the HUSB238 is 0x08 (8 in decimal). Interface Internally, the HUSB238 has ten control registers, shown in Table 1. Control and monitoring of the module is achieved by reading from and writing to the registers. Like many such chips, it includes internal resistors to signal an implicit 5V contract when the source is first connected to ensure that the device powers up. The chip appears to automatically make source capability requests to populate the SRC_PDO (0x02-0x07) registers, although this can also be commanded through the I2C bus. After this, the general mode of operation is to read out the SRC_PDO registers to confirm the modes that the power source offers. Register 0x08 can then be written with a value to select a PDO, and the GO command is written to register 0x09. The PD_STATUS0 register can be read to confirm that the new contract is in force. Scope 1 shows a typical timing whilst switching from a 5V PDO to a 9V PDO. The I2C activity consists of writes to registers 0x08 and 0x09. There appear to be numerous HUSB238 libraries available for the Arduino IDE that can be found by searching for “HUSB238”. One of these is developed by Adafruit for this specific module; it can be found at https://github.com/adafruit/Adafruit_ HUSB238 Interestingly, this library was written with the help of an AI agent. The library webpage above has links to the chat sessions, so you can see how it was done. USB-PPS module We found that many of the modern USB-C power sources we tested featured PPS. The finer granularity of PPS means that we can reduce the necessary headroom and thus the dissipation in our USB-C PSU. We discuss these advantages in detail in the project article. We were not able to find a suitably compact prebuilt module that was able to use PPS. The lack of USBPPS support on the HUSB238 is the main reason that we developed our own USB-PPS Module, which we’ll describe now. Our research found the MikroElektronika range of USB-C Sink Click modules, which work with MikroElektronika’s mikroBUS socket; they have a much larger footprint than the Adafruit part. One of these uses the Diodes Incorporated AP33772 USB-PD sink controller IC, which led us to the newer AP33772S chip. Table 1: HUSB238 control registers Just 25mm long, the HUSB238 Power Delivery Breakout (shown enlarged) can be controlled over an I2C interface, making it handy for devices that need to request different voltages from a USB-C source. Source www. adafruit.com/product/5807 siliconchip.com.au Register Notes PD_STATUS0 (0x00) Read-only register with information about the current and voltage available after an explicit contract is established. PD_STATUS1 (0x01) Read-only register with other status information, including that relating to an implicit (5V) contract. SRC_PDO_5V (0x02) Read-only registers with information about capabilities (presence or absence and allowable current) for the indicated voltage. SRC_PDO_9V (0x03) As above SRC_PDO_12V (0x04) As above SRC_PDO_15V (0x05) As above SRC_PDO_18V (0x06) As above SRC_PDO_20V (0x07) As above SRC_PDO (0x08) Read/write register, used to select a PDO for activation by the Go command. GO_COMMAND (0x09) Read/write register, used to request a contract per the Source PDO or issue other commands such as checking source capabilities or resetting. Australia's electronics magazine October 2026  39 Fig.2: similar to the HUSB238 PD Module, our circuit consists of little more than the components required by the data sheet. The external connection at CON2 has been laid out to match the other module, although it lacks the USB data lines due to the limited space available. Like all the other USB-PD chips we investigated, it is in a leadless package; QFN-24 in this case. We would have liked to use a hand-solderable part, but it is available amongst JLC­ PCB’s parts catalog, so we were able to design a PCBA (PCB assembly) for manufacture by JLCPCB. The AP33772S Information about this part can be found at siliconchip.au/link/accy – it can handle VBUS voltages up to 31V and USB-PD modes up to 28V. The circuit for our USB-PPS Module is based on the typical configuration diagram in the data sheet, which you can download from siliconchip.au/link/accz Since we plan to use this module interchangeably with the HUSB238 module, we have adopted the same layout and external connections. While it is electrically and mechanically interchangeable, it requires different communications over the I2C bus. Size restrictions have also limited the features that we have provided. Its operation is otherwise similar to the HUSB238, with reads and writes to the various registers needed to monitor and configure the state of the chip. The AP33772S has 13 PDO registers, seven of which are for SPR mode (up to 20V) and the remaining six are for EPR modes. Support for PPS modes means that there are more options to be selected and configured; for example, checking and setting the voltages and currents for the PPS modes. The AP33772S also has a load switch control, which can be configured to shut off VBUS in the Inspired by the HUSB238 PD module (black PCB), we have created our own USB-PPS Module (green PCB) using the more advanced AP33772S chip. As well as being usable as standalone modules, either can be used in the USB-C PSU we have designed. event of a fault such as a voltage mismatch or overcurrent. USB-PPS Module circuit Fig.2 shows the circuit of our USBPPS Module. CON1 on the left is the standard power-only USB-C socket we use for many applications. We have opted not to add the USB data lines, since the necessary traces would occupy precious space on the small PCB and also necessitate a USB-C socket with more pins to solder. Connections are made directly to IC1, the AP33772S, with the CC lines having external 5.1kW pulldown resistors to ground, required for legacy 5V operation, which is needed to bootstrap the chip. The VBUS line goes via a 5mW shunt resistor that has an upstream tap at the ISENP pin for V 10 8 6 4 2 0 -80 ms -60 -40 -20 0 20 Scope 1: The red and blue traces here show the I2C traffic, while the green trace shows the VBUS level changing after the HUSB238 PD Module receives a command. It’s interesting to note the time taken for the change to occur and the slow ramping applied by the power source. 40 Silicon Chip Australia's electronics magazine One of the advantages of having the module assembled by JLCPCB is that smaller components can be used. Note the use of very small M1608 (imperial 0603) parts. siliconchip.com.au USB-PD and USB-PPS Glossary APDO (Advanced Power Data Object): A PDO that includes variable and programmable modes such as SPR PPS, SPR AVS and EPR AVS. AVS (adjustable voltage supply): The voltage is not fixed but can be varied in 100mV increments EPR (extended power range): Modes that range above 100W – up to 48V and thus 240W when capable of 5A. EPS (external power supply): A device such as a plug pack or battery bank that is used to supply DC voltage. Explicit power contract: A mode that is provided after negotiation between the source and sink. Implicit power contract: The default 5V mode that is provided when a source detects that a sink has connected due to the CC lines being pulled down. PD (Power Delivery): The USB specification that allows compatible devices (sources, Fig.3: since the modules will be offered fully assembled, this overlay diagram is provided for reference only. Note that R2 and R3 at top right are the I2C pull-up resistors, which should be removed if you wish to interface to logic levels other than 5V. current sensing. The downstream tap at VCC provides power to the chip. Downstream power (to the power sink) is switched by dual N-channel Mosfet Q1 in the standard bidirectional blocking configuration, with its sources commoned and gates commoned. The drains provide the external switch connections. In this configuration, the body diodes are back-to-back and prevent current flow in both directions when the Mosfets are off. To control the N-channel Mosfets as a high-side switch, the AP33772S features an internal boost circuit to drive the gate voltage high enough above VBUS; this signal is fed via a 5.1kW resistor. The switched VBUS circuit is taken to the output at CON2, which is laid out to match the output connection on the HUSB238 module. This also breaks out ground and the I2C SDA and SCL lines, which have 5.1kW pull-up resistors to an internally generated 5V rail (V5V). Where possible, 5.1kW resistors have been used in lieu of nearby values. For example, the I2C resistors are usually 4.7kW and the value of the resistor on the gate of Q1 is not critical. This choice was intended to simplify the BoM (bill of materials) for PCB assembly, since each different component reel loaded into the pick and place machine incurs an extra cost. The capacitors are as per the typical system configuration in the data sheet, with these providing bypassing on different power rails. siliconchip.com.au cables and sinks) to deliver higher voltages and currents than previous specifications. PDO (Power Data Object): A configuration of the power source that can be selected by a sink. The PDO will include a voltage level and current capability. PPS (programmable power supply): A mode where the source output voltage can be controlled in 20mV increments up to 21V and current in 50mA increments. SPR (standard power range): The PD mode that supports 5V to 20V. The circuit is quite simple; it just exposes the features of the AP33772S chip. We had originally intended to incorporate the AP33772S directly into the USB-C PSU, but considered that readers may find other uses for it as a separate module. This way it’s also easier to source it pre-soldered to the board. If you need to use the USB-PPS Module with a 3.3V (or lower) I/O voltage microcontroller, we recommend removing the onboard I2C pull-up resistors and using pullups to the logic level being used elsewhere. The I2C pullups are the two 5.1kW resistors marked R2 and R3 near IC1. Fig.3 shows the PCB overlay diagram. Assembly Since the module has been fully assembled by JLCPCB, you only need to fit the requisite headers for your application before use. If you are using it for the USB-C PSU, there are instructions for preparing it in that series. You can test the USB-PPS Module by powering it from a USB-C power source. It should provide a 5V output between the VBUS and ground connections. This test isn’t comprehensive, but at least establishes that the AP33772S chip is requesting 5V and driving the Mosfet switch. Testing and use Scope 2 shows a similar test to Scope 1 but using our AP33772S module and its PPS features. Despite the AP33772S having larger (16-bit) registers, only one packet is needed to request a new PDO from the source, so the transmission is briefer, as is the delay before the voltage change commences. Parts List – USB-PPS Module 1 double-sided 21 × 24mm PCB coded 04107265 1 USB-C socket (CON1) [GCT USB4135 or similar] 1 AP33772S USB-PD interface chip, QFN-24 (IC1) 1 BSO150N03 dual N-channel Mosfet, SOIC-8 (Q1) 2 10μF X5R MLCC M3216/1206 SMD capacitors 1 1μF X7R MLCC M2012/0805 SMD capacitor 2 100nF X7R MLCC M1608/0603 SMD capacitors 5 5.1kW M1608/0603 ±1% 100mW SMD resistors 1 200W M1608/0603 ±1% 100mW SMD resistor 1 5mW M1608/0603 ±1% 100mW SMD resistor Note: the parts listing is provided for reference since the modules will be supplied fully assembled. You just need to supply and solder headers to suit your application. Preassembled USB-C PPS Control Module (SC7740, $25 + P&P) Australia's electronics magazine October 2026  41 Ideal Bridge Rectifiers Choose from six Ideal Diode Bridge Rectifier kits to build: siliconchip. com.au/Shop/?article=16043 28mm spade (SC6850, $30) Compatible with KBPC3504 10A continuous (20A peak), 72V Connectors: 6.3mm spade lugs, 18mm tall IC1 package: MSOP-12 (SMD) Mosfets: TK6R9P08QM,RQ (DPAK) 21mm square pin (SC6851, $30) Compatible with PB1004 10A continuous (20A peak), 72V Connectors: solder pins on a 14mm grid (can be bent to a 13mm grid) IC1 package: MSOP-12 Mosfets: TK6R9P08QM,RQ 5mm pitch SIL (SC6852, $30) Compatible with KBL604 10A continuous (20A peak), 72V Connectors: solder pins at 5mm pitch IC1 package: MSOP-12 Mosfets: TK6R9P08QM,RQ mini SOT-23 (SC6853, $25) Width of W02/W04 2A continuous, 40V Connectors: solder pins 5mm apart at either end IC1 package: MSOP-12 Mosfets: SI2318DS-GE3 (SOT-23) D2PAK standalone (SC6854, $35) 20A continuous, 72V Connectors: 5mm screw terminals at each end IC1 package: MSOP-12 Mosfets: IPB057N06NATMA1 (D2PAK) TO-220 standalone (SC6855, $45) 40A continuous, 72V Connectors: 6.3mm spade lugs, 18mm tall IC1 package: DIP-8 Mosfets: TK5R3E08QM,S1X (TO-220) See our article in the December 2023 issue for more details: siliconchip.au/Article/16043 42 Silicon Chip V 10 8 6 4 2 0 -40 ms -20 0 20 Scope 2: This shows the same as Scope 1, but for our USB-PPS Module. Only one data packet is needed to effect a change and it is initiated much more promptly after the command is given. If you are using the USB-PPS Module in the USB-C PSU, you don’t need to fit any headers until it is time to attach it to the PCB in that project. Otherwise, we found that a pair of three-way socket headers was the best way to experiment with the module, allowing jumper wires to be fitted for breadboarding. Take care when working with this module (and the HUSB238) because it will expose voltages above 5V that should not be directly connected to the pins on a microcontroller. The AP33772S data sheet does not have much detail on the operation of the I2C registers, but we found more information in a user guide for an AP33772S evaluation board (EVB) at siliconchip.au/link/acd0 This guide has more detail on the registers and I2C command format. The AP33772S has a 7-bit I2C address of 0x52. There are also code examples using an Arduino Uno with the EVB (which we expect should also work with the USB-PPS Module). The code can be downloaded from siliconchip.au/ link/acd1 We found that the AP33772S required a slow I2C bus to operate correctly. The data sheet reports a very low requirement for a low-level (logic zero) input of 0.4V, while the I2C specifications allow up to 30% of the logic voltage to be recognised (eg, 1.5V for a 5V system). We suspect this requirement means that extra time is needed for the voltage levels to settle correctly. Table 3 shows a very small subset of the registers available on the AP33772S; these two registers (the ones that we use in the USB-C PSU project) are sufficient to check and select power data objects and thus request different voltages from a connected source. Summary Now we have two different USB-PD modules that we can use with the USB-C PSU, or as standalone parts to be incorporated into other projects. You can find the USB-C PSU project starting on page 28 in this issue. SC Table 2: a subset of AP33772S registers as used by the USB-C PSU Register Size (bytes) Notes Get all 26 source PDOs (0x20) The 26 bytes contain 13 16-bit PDO entries with information about the available voltage, current and whether the PDO is a fixed or PPS type. Select PDO (0x31) The PDO request includes information about the PDO (1-13 from above) to be activated and what voltage is being selected for a PPS PDO. 2 Australia's electronics magazine siliconchip.com.au Techtober Fest! Shop 24/7 <at> altronics.com.au C 0870A SAVE $100 399 $ Sale ends October 31st 2026. Magnetic ‘edge to edge’ grille. Amazing sound for less! Opus One® 2x30W Wi-Fi Ceiling Speakers These high performance speakers offer wireless music streaming by connecting to your home wi-fi for Apple Airplay/casting from any device. 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On its front panel are a series of pushbutton switches known as ‘interlocking ganged switches’. When you press one switch, any other switch that is pressed in pops out, allowing for the selection of one frequency range. Such ganged switches are a rarity nowadays, but they can be handy for things like audio input selection on a preamp, so I have come up with a stackable solid-state version to use in my projects. I have shown three blocks, but it can work with two to however many switches you need, within reason. The detail within the dashed box shows what’s inside each block. Mosfets Q1 and Q2, along with their 220W base resistors, form a bistable latch. Shorting one gate to ground makes the opposite one conduct until you do the same to its gate. This shorting action is performed by Mosfets Q3 and Q4, which allow a positive pulse to control which side is conducting. You can think of this as a set/reset Circuit Ideas Wanted siliconchip.com.au (SR) latch. If we consider LED1 to be the output, activating Q3 is the SET action, while activating Q4 is the RESET action. The SET action is performed by S1, a momentary pushbutton. Reset is the result of pushing the SET button on another block. Simply making each pushbutton also control the RESET option would not work, as the selected block would reset itself and behave unexpectedly. I need to disallow the RESET signal from reaching Q4 when SET is pressed. Q5 solves this problem by shunting the RESET signal to Q4 to ground when the SET button of that block is pushed, making sure that Q3 is allowed to set it, but still resetting any other blocks connected to the reset line labelled on the circuit. Diode D1 stops signals on the reset line from activating any of the latches due to the SET and RESET pins sharing a common connection at S1, ignoring said diode. If you have ever put together such a latch, you would know that you can never predict which of the two transistors will be on when power is applied. To get around this, I added a small RC network with a time constant of around two seconds, connected to Q7, which activates the SET input of the first block at power-on. This arrangement could be moved to any block. It ensures that on power-­ up, only one option is selected and all others are reset. Because these are momentary pushbuttons, there is no indication as to which option is selected, hence the LEDs. The output is from a PNP switching transistor (Q6) that sources current to a load up to 50mA. Q6 inverts its input signal, compensating for the inversion by Q2. The load for each block could be a reed relay coil; in that case, include a back-EMF clamp diode for each coil. I chose Mosfets instead of BJTs because it made the circuit simpler, but also because the inactive blocks draw minimal current (about 5mA per block). Kiran Law, Glenorie, NSW. ($70) Got an interesting original circuit that you have cleverly devised? We will pay good money to feature it in Circuit Notebook. We can pay you by electronic funds transfer, credit or direct to your PayPal account. Or you can use the funds to purchase anything from the Silicon Chip Online Store. Email your circuit and descriptive text to editor<at>siliconchip.com.au Australia's electronics magazine October 2026  47 DIY Busking Amplifier A recent attempt at raising money for charity led me to try my hand at street busking. Filled with enthusiasm after receiving an official busking license, I entered my local music shop in search of a battery-powered amplifier. This ended up being a humbling experience; the cheapest option in the store was $550. My limited talent would be unlikely to offset such a cost! Fortunately, an idea came to mind: could I repurpose an old practice amplifier no longer in use? I had a Pathfinder Bass 10 amplifier that 48 Silicon Chip would work well if it could run on batteries. The power supply section is a typical unregulated supply consisting of a mains step-down transformer, bridge rectifier and filter capacitors. The full Pathfinder Bass 10 circuit is shown here. The +Vs and −Vs rails measured ±18V DC, supplying the TDA2030 power amplifier IC, with ±12V DC rails derived through 820W series dropper resistors for powering the 4558 op amps. I could therefore directly feed the +Vs and −Vs rails with a DC supply from batteries. Australia's electronics magazine I soldered two Makita tool battery adaptors ($8 from AliExpress) to the PCB via heavy-duty wires and tapped off a separate 2.1mm barrel jack socket for supplying an external effects unit. My batteries are rated at a modest 12V and 1.5Ah, giving around 90 minutes of portable amplification. Thankfully, the amplifier still works running from mains power. I just need to remember to disconnect the batteries before plugging it in. Brandon Speedie, Alexandria, NSW. ($80) siliconchip.com.au Darlington-based amplifier buffer I came across a circuit for driving a small 8W speaker with amplified sound from an electret microphone, shown at the top of the accompanying figure. The circuit seemed to lack enough gain to drive an 8W speaker properly. I put the circuit into a simulator with a 10mV peak input signal and the output was a respectable 2.2V peak output with no speaker load. Connecting an 8W load to the output, the voltage across it dropped to about 10mV, equivalent to just 6μW of output power. So the circuit really was not suitable for driving an 8W load. We need to add an emitter-­ follower buffer transistor or, even better, a Darlington pair connected as shown below to produce a large current gain. This prevents the voltage amplifier transistor, Q1, from being loaded by the speaker impedance. The voltage gain of the added buffer (transistors Q2 & Q3) is unity, but siliconchip.com.au we have plenty of voltage gain with the single input transistor, Q1. Simulating this new circuit, after some small adjustments, I achieved 20mW at the speaker (over 3000 times the Australia's electronics magazine power!) with acceptable distortion and a voltage gain of around 110 times. Allan Grant, Karrinyup, WA. ($50) October 2026  49 Motor Control Part 1: DC Motors The focus of this new series of articles is to drill down into how various types of motors work and how they are controlled. In this first part, we’ll start by looking at how DC motors work and how we can control them. By Andrew Levido I n this series, we will look at both the power electronics and the control systems involved. As usual, there will be a little bit of theory, although I will try to keep the mathematics to a minimum and provide plenty of practical examples. Electric motors are truly ubiquitous in our lives today. They are so common that we often don’t even give them a thought. There are probably several motors within a few metres of you wherever you are reading this – whether it is the cooling fan in your PC or laptop, the haptic motor in your smartphone, or the pump in your coffee machine. They are all electric motors of some sort or another, and they almost all have some kind of electronics to control their operation. Electrical machines In electrical engineering circles, motors and generators are classified under the fancy title of “electrical machines”. Electrical machines are any devices that convert electrical energy to mechanical energy (motors) or mechanical energy to electrical energy (generators), or both. The mechanical energy is usually, but not always, transferred by means of a rotating shaft. Most practical electric machines achieve the conversion between electrical and mechanical energy using magnetic fields in some shape or form (one exception is the rare electrostatic motor). For the purposes of this article, I am going to assume the reader has an understanding of the fundamentals of magnetics, including the concepts of magnetic flux, flux density, permeability and the relationships between them. I’m also going to assume a basic familiarity with the concept of magnetic equivalent circuits, where magnetomotive force (mmf) is analogous to voltage, flux is analogous to current, and reluctance is analogous to resistance. If you are not familiar with these concepts, they were all covered in the third article in the Power Electronics series, published in the January 2026 issue (siliconchip.au/Article/19557). I am also going to assume a basic understanding of rotational motion, since this is how most electrical machines transfer mechanical energy. Table 1 contains a summary of the key quantities in rotational motion compared to their linear motion equivalents. You will note that we are using radians to describe angles rather than degrees. You can easily convert between radians and degrees by remembering that there are 2π radians and 360° in a circle. Radians are a bit special because they are actually unitless (or dimensionless in some textbooks). An angle in radians is defined as the ratio of an arc length around a circle to its radius – so a length divided by a length. This technically means the units of angular velocity and angular acceleration are inverse seconds and inverse seconds squared (s-1 and s-2) respectively. The same thing applies if you measure angular velocity in revolutions per minute (RPM) – a “revolution” is a unitless number, so RPM has units of inverse minutes. Since you can convert between radians and degrees, that means degrees is not a true unit either (it is a ‘quantity kind’). Generating torque Now that we have the foundations clear, we can begin to build a picture of how a DC motor works. Fig.1 shows a short piece of conductor with length l suspended in a magnetic field. Ignore for a moment how this field comes about – it could be created by Table 1 – linear vs rotational motion quantities Linear Motion Rotational Motion Displacement s m Angular position θ unitless (radians) Distance Velocity v = ∆s ÷ ∆t m/s Angular velocity ω = ∆θ ÷ ∆t radians/s (1/s) Speed Acceleration a = ∆v ÷ ∆t m/s2 Angular acceleration α = ∆ω ÷ ∆t radians/s2 (1/s2) Acceleration I kg·m2 Inertial Mass T = Jα N·m (kg·m2/s2) Force (Newton’s Law) Work (energy) Power Mass Force m kg F = ma N (kg·m/s2) Moment of inertia Torque Work W = Fs J Work W = Tθ J (kg·m2/s2) Power P = Fv W Power P = Tω W name symbol units name symbol units 50 Silicon Chip Australia's electronics magazine siliconchip.com.au an electromagnet or by a permanent magnet. Suffice it to say that it produces a magnetic flux density of B tesla across the gap. If a current of I amps flows in the conductor, it experiences a force of F = B·I·l newtons in a direction perpendicular to both the current and the field. You can use the right-hand palm rule to remember which direction the force will be. If you place the fingers of your right hand together to represent the magnetic field lines flowing from north to south, and extend your thumb at right angles to represent the direction of the current, your palm will ‘push’ in the direction of the force. It may seem odd that there are no constants of proportionality in the formula for force. This is because, until 2019, this formula formed the basis for the definition of the ampere. Despite this the formula for force has not changed The new definition describes the ampere in terms of charge per unit time, specifically the number of elementary (electron) charges carried by a current of 1A in one second, but originally the amp was defined in terms of force. It is not a huge leap to imagine a loop of wire in the gap that can pivot around a central point, like that shown in Fig.2. You will notice that in the cross-section at the top, the wire on the left has a dot in the centre and that on the right has a cross. The convention (yes, another one) is that the dot represents a current coming out of the page and a cross represents a current going in. You can think of the dot as the point of an arrow coming toward you, and the cross as the fletching at the end of a departing the arrow, if that helps. Each wire in the loop will experience a force in the direction shown by the blue vectors. These forces, acting over the distance from the conductors to the pivot, produce a torque around the pivot. If the wire loops are free to rotate, they will tend to move clockwise until both conductors are outside the magnetic field. If the rotating loop has a meaningful moment of inertia, the left-hand conductor will continue to rotate past the 12 o’clock position and back into the field on the opposite side. Unless we changed the direction of the current, the conductors would experience a force in the opposite siliconchip.com.au direction and be pushed back toward the ‘neutral’ vertical position. Fortunately, it is pretty easy to switch the direction of the current using a commutator and brushes, as shown at the bottom of the figure. The commutator rotates with the shaft and has (in this case) two conductive segments on its surface, each connected to an end of the conductive loop. The brushes are fixed and slide across the surface of the commutator as it rotates, ensuring the current is always maintained in the right direction to produce pulses of torque in the clockwise direction whenever the loop is in the magnetic field. If the polarity of the voltage source connected to the brushes was reversed, the torque pulses would be in the opposite direction. Fig.1: a conductor of length l carrying a current I in a magnetic field with flux density B will experience a force F in a direction perpendicular to both the field and the current. Improvements This simple motor would work, but there are a few things we can do to improve it. The torque is given by the expression T = 2F·r, so we could increase the torque by increasing the force experienced by the conductors or by increasing the radius of the motor. One way to increase the force (from F = B·I·l) would be to increase the length of the motor. The torque is therefore proportional to both the motor’s length and its radius, so its volume, which explains why bigger motors have more torque and therefore more power. But what if we want to optimise the torque for a motor with a fixed volume? We could try to increase the magnetic field density, but we can only take this so far, since the core material will saturate at some point. We are left with only two choices: increase the current through the loop or increase the number of loops, which have the same outcome in practice. If the loop shown in Fig.2 was made up of many turns of wire, the force developed for a given current would be multiplied by the number of turns, since the current loops through the field that many times. This is equivalent to having a single coil and increasing the current by the same factor. If we are going to increase the number of conductors in the field, we could also do it by adding more loops and more commutator sections, as shown at the top of Fig.3. Here, we have four loops in total, which would require eight commutator segments. Australia's electronics magazine Fig.2: a loop of wire that can pivot around a central axis will experience a torque proportional to the forces acting on the conductors and the radius. If the direction of the current is reversed every 180°, continuous rotation is possible. Fig.3: the efficiency of the simple motor in Fig.2 can be improved by increasing the number of conductors subject to the magnetic field, and by reducing the air gap, by filling most of the space with core material. October 2026  51 At any given time, three loops are energised and one is open-circuited. This arrangement will produce a smoother torque, since there are now eight overlapping pulses of torque in each rotation instead of just two. I mentioned above that the upper limit on flux density is dictated by the saturation of the core material. This is true, but it does not speak to how easy (or difficult) it is to create this level of flux density in the first place. The amount of mmf required to create a particular level of flux is proportional to the reluctance of the circuit. This is analogous to the amount of voltage required to push a particular current around an electrical circuit, being proportional to the electrical resistance of the circuit. The reluctance of air is four or more orders of magnitude higher than the reluctance of the transformer steel used in the core. This means that the reluctance of the air gap largely determines the amount of mmf required to produce a given magnetic flux density. The reluctance of the gap is proportional to its length and inversely proportional to its cross-sectional area. The cross-sectional area of the gap is fixed by the motor’s size, so the only way to reduce the reluctance of the gap is to reduce its length. This is why we usually fill the gap with a rotating section of core material and embed the conductors in slots, as shown at the bottom of Fig.3. This rotating core, together with the windings and commutator, is known as the armature. This is just one possible DC motor configuration – some others are described in the accompanying panel. DC motor model We have seen that a current flowing through the armature conductors, switched to be in the right direction by the commutator and brushes, creates a continuous torque. This torque is proportional to the armature current multiplied by a torque constant km, such that T = km·I. This torque constant wraps up the physical dimensions of the motor, the winding arrangement and the field flux density into a single handy number. There is another thing happening at the same time. Faraday’s Law tells us that a voltage is induced in a conductor 52 Silicon Chip Fig.4: the equivalent circuit of a DC motor and the two equations to the right are all that is necessary to characterise any DC motor. If the rotation speed is such that the backEMF exceeds the armature voltage, the current reverses and the motor acts as a generator. that is moving in a magnetic field, and that is certainly what is happening in the DC motor as it rotates. A voltage is therefore induced in the armature conductors in a direction that opposes the voltage applied to the motor’s terminals. This voltage is called the “backEMF” and it is proportional to the speed of the shaft by a speed constant ke such that Eb = ke·ω. These two constants let us construct the very useful DC motor model shown in Fig.4. The model consists of the armature resistance Ra, which takes into account the winding resistance as well as the equivalent resistance of the commutator and brushes, the armature inductance La and the back-EMF source Eb. The formulae to the right relate the electrical quantities to the motor’s torque and speed. Now for the really odd thing: for any given DC motor, the constants ke and km are actually identical. How can this be, given that the torque constant has units of Newton-metres per ampere (Nm/A) and the speed constant has units of volts per radian per second, or volt-seconds (Vs)? These units actually both describe work (energy) per amp, just in different forms. The proof of this is shown in the grey box below the equivalent circuit in Fig.4, if you are interested. Australia's electronics magazine This blew my mind when I first learned it back in the day. You often see different figures for these two constants in motor data sheets, but this will be because one or the other is expressed in some different terms. The speed constant is often given in terms of volts per RPM, for example, and the torque constant may be given in gram-cm (or worse, ounceinches) per ampere. If you convert them to Nm/A and Vs, you will find they are equal. For steady-state operation, we can ignore the inductance, although you may need to consider it under transient conditions, along with the rotor’s moment of inertia. You cannot, however, ignore the motor’s armature resistance, which should be provided in the data sheet. If your motor has carbon brushes, you may not be able to accurately measure the armature resistance from the motor terminals when it is stationary. If your motor has so-called ‘precious metal’ brushes (usually plated with some alloy of silver or palladium), you may have better luck. Nevertheless, I recommend using the value given in the motor’s data sheet. Motors with precious metal brushes are most suitable for light-load, high-performance applications, while those using carbon brushes are most suited for heavy-duty, high-current applications. The brushes on a DC motor in a power tool will almost always be carbon, for example, while those in a model train motor will probably be precious metal types. We can use the DC motor model to understand how the motor will behave under various conditions. If the nominal motor voltage Vn is applied to the motor while the rotor is stationary, the back-EMF will be zero, so the current is limited only by the armature resistance. This stall current, or ‘locked rotor’ current Is will be Vn ÷ Ra, and the corresponding stall or starting torque will be Ts = km·Is. This current and torque will be quite high, and the motor will overheat very quickly if these circumstances are allowed to persist. Fortunately, the back-EMF begins to rise as the rotor accelerates and the current drops as the voltage across the armature resistance decreases. If there was no shaft load and the motor was completely lossless, the current would drop to zero when the motor reached siliconchip.com.au the speed where the back-EMF exactly balanced the terminal voltage. Of course, this does not happen in reality; instead, an unloaded motor reaches an equilibrium speed, called the no-load speed, where the current drops to the level necessary to produce just enough torque to overcome the friction and windage. Torque-speed curve We can plot the torque-speed characteristic of the DC motor as shown in the middle of Fig.4. I have labelled the vertical axis with both shaft torque and armature current, seeing as these are proportional to each other. The red line is the nominal voltage torque-speed characteristic, given by the relationship Ts = km·(V – ke·ω) ÷ Ra. The blue line is the same characteristic at half of the voltage, and the green line is the torque-speed characteristic with zero terminal voltage. There is one very interesting thing to note here. If the shaft’s angular velocity is high enough that the back-EMF exceeds the applied armature voltage, the current flow will reverse and the motor acts as a generator. This can happen when you reduce the voltage on a motor with a high-inertia load, and the resulting reversed torque acts as a brake, slowing it rapidly. That’s the big picture, but it can be a bit misleading because the motor is only rated to operate continuously in a very small area of this graph. I have put some numbers on the chart to demonstrate. I am using data for a relatively large and expensive DC motor about the size of a beer can (65mm in diameter and 125mm long). It is a 24V motor with a nominal speed of 3200RPM (335rad/s). Its stall current is 34A and its stall torque is 2.0Nm. In this condition, the power dissipation in the motor is 816W. The no-load speed of the motor is 387rad/s, at which point it draws 0.45A. A closer look at the data shows that its shaft power is limited to 90W continuously and its electrical input power is limited to 120W. This input power limit puts upper and lower bounds on the continuous current at ±5.0A and therefore a limit on the continuous torque of around ±0.3Nm. The continuous operating region is therefore limited to the space between the two horizontal lines. I have reproduced the torque/speed siliconchip.com.au characteristics of this motor in Fig.5 on the left, focusing on the continuous operating region while motoring. The blue lines represent the motor’s torquespeed characteristic for increasing steps of armature voltage. The red dot is the point where the motor is at its maximum continuous power (24V at 5A = 120W). The black and green lines represent the torque-speed characteristics of two possible loads: a constant-torque load, like a hoist, and a square-law load, like a fan. The dots represent the operating points for the loads at each armature voltage. The main takeaway is that you can control the speed of a DC motor by controlling the armature voltage, but the speed regulation will not be perfect – the actual operating point will depend on the load. Field weakening The motor I used in the example above is a permanent-magnet type, so the value of ke (and km) that relates back-EMF to rotor speed is fixed. It turns out that ke is inversely proportional to the field strength, which makes sense when you consider that the back-EMF is produced by the movement of the armature conductors in the magnetic field and reducing the field strength should reduce the back-EMF. The result is the slightly counterintuitive idea that reducing the field excitation increases the shaft speed for a given armature voltage – but at the expense of torque. This is obviously only possible in wound-field motors where you can reduce the field strength by reducing the field current. By doing this, we can increase the shaft speed of a woundfield DC motor beyond the nominal speed or ‘base speed’ suggested by the nominal voltage/nominal current limit indicated by the red dot in Fig.5. The graph on the right shows how this works. With full flux, the motor can operate at any speed up to the base speed, and any torque (current) up to its rated value by an appropriate choice of the armature voltage. This full-flux region of operation is indicated by the blue torque-speed lines in the chart on the right of Fig.5 and is often referred to as the ‘constant torque’ region. In this context, ‘constant torque’ signifies that the maximum continuous torque is constant. You can increase the speed beyond the base speed by weakening the field. This field-weakening region is indicated in the figure by the green torquespeed lines. Each line represents a step reduction in the field current. This region is also known as the ‘constant power’ region. It is ‘constant power’ in the sense that the continuous power can’t exceed the motor’s maximum rated power. Since power is torque times speed, increasing the speed at a constant power means the torque is reduced. Motor diagrams Before we move on to look at controlling DC motors, I want to show you a typical DC motor operating chart that you will find in most motor data sheets (see Fig.6). These charts can be a bit tricky to read, but have pretty much everything you need on them. This one is for a RS-555PH motor from the Japanese manufacturer Mabuchi. Unlike the torque-speed curves, these graphs have torque on the horizontal axis and speed, current, power and efficiency plotted on the vertical axis. The no-load point is the extreme left of the horizontal axis (zero shaft torque), where you can read the no-load current from the y-intercept of the curve marked I (~150mA) and the no-load speed from the Fig.5: for a wound-field motor, you can reduce the field strength to increase the rotor speed beyond the base speed. Torque falls off quickly in this mode because the motor is operating at a constant power. Australia's electronics magazine October 2026  53 y-intercept of the speed curve marked N (~5500RPM). The stall or locked rotor torque is at the extreme right at around 200mNm. You can read the stall current (a little over 10A) by projecting up to the I curve and across to the vertical axis. The last two curves show the motor power (marked P) and efficiency (marked with the Greek letter eta, η). It’s worth noting that the rated continuous torque of this motor is around 37mNm and the rated current is 2.45A, so continuous operation will be confined to a narrow slice of this graph that I have shaded in cyan. It’s really easy to burn out a DC motor if you don’t control the current carefully! Motor controllers DC motor drives, especially those intended for industrial applications, tend to have a pretty standard control scheme. The diagram at the top of Fig.7 shows the block diagram of a typical DC motor controller. It consists of two nested control loops feeding a modulator; the latter including the power electronics. We’ll look at the modulator in a moment; we will concentrate on the control loops first. The inner loop is a current/torque control loop. This accepts a current demand coming out of the speed controller and compares it to the measured armature current to produce an error signal that is applied to the current controller. This is normally a proportional-­ integral (PI) controller, which can reduce the error to zero. The outer speed control loop accepts a desired speed setpoint and compares it with the rotor speed, as measured by a tachogenerator, or more Fig.6: this extract from a typical motor data sheet shows the curves used by most manufacturers to characterise motor performance. The added shaded area shows the region where continuous operation is possible. 54 Silicon Chip Australia's electronics magazine likely these days, by a digital encoder. The speed error is applied to a speed controller to produce the current/ torque setpoint. The speed controller can be as simple or complex as the application demands. A fan application may be able to get away with a very simple speed controller, while a mine winder or rolling mill will probably incorporate an advanced digital controller. The role of the current control loop is to keep the motor current within the safe operating area to avoid operating the motor outside its continuous ratings for any length of time, and to protect the semiconductors in the modulator. We have seen how important this is, since the locked-rotor current of a DC motor can be 20-50 times its continuous rating. The current control loop is generally fast, typically having a bandwidth in the order of the armature’s L/R time constant. The speed control loop is slower, with a bandwidth dictated by the moment of inertia of the motor’s rotor and the load. The speed control loop is normally in saturation until the motor’s speed gets quite close to the setpoint, so the maximum torque is applied to accelerate or decelerate the load. In low-cost or small drives, it is possible to do away with the need for a speed sensor if you can tolerate a little bit of speed error. In this case, the shaft speed is estimated from the motor voltage and current using a technique known as ‘voltage feedback with IR compensation’. The current feedback is used to estimate the voltage drop across the armature resistance, which is then subtracted from the terminal voltage to get an approximation of the backEMF, which is proportional to shaft speed. You can also sense back-EMF directly in some very specific circumstances that I will demonstrate below. Of course, you can run your DC motor in an open-loop configuration if you don’t care about speed regulation. Still, you should provide some sort of current limit to keep the motor in its continuous operating region. There are many variations of this basic control strategy, two of which are shown in Fig.7. The first is an example where the controller is driving multiple motors that are mechanically coupled. This happens quite a lot in siliconchip.com.au Fig.7: the basic control scheme for driving a DC motor is at the top, plus two variants; one for driving coupled motors and one for servo drives. ▶ Fig.8: the four possible combinations of voltage and current polarity represent four quadrants. Quadrants I and II correspond to driving and braking in one direction of rotation, while quadrants III and IV represent braking and driving in the other. industrial applications, like conveyors and rolling mills. Each motor has its own current/ torque control loop fed by a common speed control loop. This arrangement forces the motors to share the load evenly. The next example is the servo-drive. Servos are capable of precise position control and are used extensively in robotics and automation. The servo controller is identical to the speed controller described above, but has an additional position control loop wrapped around it. The position is measured by some position sensor, like a potentiometer or an absolute digital encoder. You will sometimes see servo controllers implemented without the intermediate speed control loop, such as in hobby servos. Unless the system is very well damped, this approach is prone to overshoot and ringing when a step change in position is requested. Hobby servos have plenty of damping built in, thanks to their multi-element gear train and relatively high friction. Operating quadrants I mentioned above that the DC motor will act as a generator (ie, the armature current will reverse) and power will be siliconchip.com.au exported if the back-EMF exceeds the applied armature voltage. The direction of rotation can also be switched by reversing the polarity of the armature voltage. We therefore have four possible combinations of armature voltage and current polarity, as shown in Fig.8. If this seems familiar, I used a very similar diagram in the AC-to-DC Converter article from the Power Electronics series in the February 2026 issue (siliconchip.au/Article/19657). The quadrants are denoted by Roman numerals counterclockwise from the top right. In quadrants I and III (shaded green), the voltage and the current have the same sign, so positive power is supplied and the motor is driving the load. In quadrants II and IV, the voltage and the current are of opposite polarities, so ‘negative power’ is ‘supplied’ and the motor is being driven by the load. I have called this “braking” since the motor torque acts as a brake on the shaft. Thyristor modulators The ‘meat and potatoes’ of a DC motor drive is the modulator, which consists of the power electronics and its drive circuitry. The classic industrial DC motor controller uses a Australia's electronics magazine thyristor bridge, as shown in Fig.9. I won’t cover the analysis of this topology here, as I did so in the AC-to-DC Converter article mentioned above. The converter can be driven by a single- or three-phase mains supply. I have shown the armature voltage and current waveforms for a single-phase version to the right of the circuit diagram. You will recall that due to the inductive nature of the load, this converter can produce a positive or negative average output voltage, although the current can only ever be positive. This is technically a two-quadrant converter (quadrants I and IV). However, this combination is not really all that useful in motor applications, as the drive can only produce a braking torque if the shaft is rotating in the opposite direction than it rotates when being driven. Active deceleration of the load is not possible, so this two-quadrant circuit is effectively a one-quadrant motor drive. You can achieve four-quadrant operation with this converter if you add a mechanism to reverse the field. This gives you rotation in both directions, but it is difficult to transition smoothly between driving and braking because field reversal is not instantaneous. Field windings tend to have a high inductance, so changing the direction October 2026  55 of the current has to be done with care and takes appreciable time. It is better to use a true four-quadrant converter, as shown at the bottom of Fig.9. This is effectively two two-quadrant converters connected to the motor with opposing polarity. With this circuit, the armature current can reverse smoothly and so the transition from driving to braking and vice versa is much better. This is the arrangement generally used in applications like hoists, mine winders, ski lifts and the like, which require large, high-voltage motors and where the torque can reverse frequently. There is a limit to the braking performance of this type of drive circuit. When driven by the load, the motor terminal voltage must remain lower than the peak voltage of the mains by some margin to ensure the voltage across the thyristors can reverse, to allow them to switch off. ‘Chopper’ modulators Fig.9: the classic two-quadrant and four-quadrant controlled rectifier circuits are commonly used for driving kilowatt or megawatt scale DC motors in industrial applications. The two-quadrant variation cannot provide a braking torque in the direction of rotation, so it is effectively a one-quadrant circuit in motor drive applications. Fig.10: this diagram, extracted from the DRV8874 data sheet, shows that it contains everything necessary to control two motors in two quadrants or one motor in four quadrants. It includes motor current sensing and limiting, making it very easy to implement a safe and effective DC motor drive. 56 Silicon Chip Australia's electronics magazine You can also drive DC motors from a DC source using a ‘chopper’ type drive as shown in Fig.11. If you think the one-quadrant modulator looks a lot like a buck converter, you would be right. That is exactly what it is. If you consider the armature inductance to be the filter inductance and the armature resistance to be the load, and take into account the back-EMF, all of the equations describing a buck converter apply. If the motor current is continuous, the motor voltage is a square wave with an average voltage determined by the duty cycle, as shown in the top chart. If the current is discontinuous, the output voltage has a stepped shape. The motor’s terminal voltage during the zero-current portion of the cycle will be its back-EMF. If you can be sure to always stay in discontinuous current mode, you can sample this voltage to get direct feedback of the motor’s speed. This is generally possible only with small motors that have low inductance and operate over a limited load range. The buck converter is a one-­quadrant drive because neither the motor voltage nor the current can reverse. If the freewheeling diode is replaced with an active switch, as shown in the middle of the figure, this circuit becomes a two-quadrant drive. It behaves like a buck converter in quadrant I, with siliconchip.com.au Q1 as the switch and Q2’s body diode as the freewheeling diode. If you squint, you might be able to see that in quadrant II, it behaves like a boost converter, with the motor’s back-EMF as the voltage source, Q2 as the switch and Q1’s body diode as the output diode. By appropriately driving the two Mosfets (or IGBTs), you can produce a positive or negative motor current, but only with a positive voltage (ie, operating in quadrants I and II). This circuit can therefore provide both driving and braking in one direction of rotation. If you want four-quadrant operation, you have to resort to an H-bridge type driver, like the one at the bottom of the figure. You can think of this as two two-quadrant converters, one connected to each motor terminal. This can produce a driving or a braking torque in either direction of rotation. One thing you need to pay attention to in the two- and four-quadrant circuits shown here is the ability of the source to absorb the energy fed back during braking. It may not be a concern if your source is bidirectional, like a rechargeable battery, but it may well be a problem if your power is coming from a one-quadrant source like a DC-DC converter or a rectifier-­filter. In that case, you can use a capacitor bank to temporarily store the regenerated energy. When driving the motor, the capacitor voltage will be equal to the supply voltage. When the motor is regenerating, the capacitor will charge to some higher voltage. As long as you size the capacitor correctly to limit the voltage rise to something acceptable, this is a good way to manage the regenerative energy, because it can be re-used when the motor is driven again. Sometimes, this approach is just not enough, so a ‘braking resistor’ can be switched in to absorb some or all of the regenerated energy. This energy is obviously lost as heat. Getting practical If you are driving smallish motors (up to a few amps continuous rating), you can get plenty of low-cost chips that implement most of the power electronics of a two-quadrant (halfbridge) or four-quadrant (full-bridge) chopper type controllers that do a lot of the hard work for you. siliconchip.com.au Fig.11: so-called ‘chopper’ style motor drives look like the standard DC-DC converters you may be familiar with. In contrast to the two-quadrant thyristor circuit in Fig.9, the circuit in the middle provides useful two-quadrant operation. The DRV8874 from TI is one such controller I used in a recent project. This chip (Fig.10) has two Mosfet halfbridges capable of switching currents up to 6A. The motor supply voltage can be anywhere from 4.5V to 37V. The half-bridges can be operated separately, to control two single-direction motors in a two-quadrant arrangement, or together to drive one motor in all four quadrants. The chip includes the charge pump and level-shifters necessary to drive the high-side Mosfets, as well as comprehensive safety features including undervoltage lockout on the main supply and the charge pump voltage, overcurrent and over-temperature protection. The logic inputs support 1.8V, 3.3V and 5V logic levels. One very nice feature of this chip is that the lower Mosfet source current is sensed internally and a proportional current (1mA/A) appears at the IPROPI pin. This is really only meaningful for the H-bridge configuration, since the currents from the two half-bridges are summed. An external resistor to ground converts this to a voltage. Australia's electronics magazine Better still, by providing a current reference voltage at the Vref pin, the chip can regulate the Mosfet current to not exceed some desired level. Two regulation modes are available: a cycle-by-cycle mode that works like a typical current-mode controller, or a fixed-off-time mode that holds the Mosfets off for a short period whenever the current exceeds the threshold. The latter has the advantage that it will regulate current even if the PWM frequency is very low or the duty cycle is 100%. As we have seen, current limiting is very important for DC motors, so this feature means the current control loop is effectively done for you. This chip costs just $4.51 in one-off quantities, which is a bargain in my book. There is an even cheaper 3.5A version, the DRV8876, that costs just $2.80. I am out of space, so that’s all I can fit in this month. Next time, I will take a look at externally commutated DC motors, like brushless and stepper motors. ...see overleaf for more October 2026  57 DC Motor Configurations There are literally dozens of DC motor configurations and not enough space to describe them all. I have chosen to describe just a few of the more common ones. Fig.a shows three woundfield motors with the field windings shown in yellow. In all of these figures, the grey areas represent the magnetic path, usually made of laminations of transformer steel. The rotor windings (in blue) are sunk into slots in the rotor steel so that the air gap can be reduced to an absolute minimum. Although it is not shown here, the slots in the rotor do not normally run straight down the length of the rotor. Instead, they are ‘skewed’ or twisted slightly around the motor’s axis. This helps minimise the torque ripple or ‘cogging’ produced as the windings are energised and de-energised as they rotate. Adding more field pole pairs helps to increase the available torque because more of the armature current loops are intersected by the magnetic field. The maximum power of a given-sized motor is fixed, so increasing the torque in this way usually comes at the expense of speed, since power is the product of speed times torque. As you would imagine, every time the brushes slide off a commutator segment, there is the potential for an arc as the commutation is effectively interrupting an inductive circuit. In very small motors, and especially in permanent magnet motors, the inductance is small and a level of sparking can be tolerated. In larger motors, this can be a problem since the sparking can erode the commutator and brushes. Larger motors therefore often have small ‘interpoles’ on the stator positioned between the main field poles. Their purpose is to induce a voltage in the coil undergoing commutation, in such a direction that it speeds up the reversal of current, thereby limiting sparking. The required induced voltage is proportional to the current being commutated, and to the rotor speed, which can be achieved by wiring the interpoles in series with the armature. Fig.b shows two permanent magnet DC motor configurations. In both cases, two-pole field excitation is produced by a pair of permanent magnets attached to the motor’s housing, which serves as the return path for the flux. The motor on the left is typical of high-performance motors and has a slot-wound rotor. The motor on the right is exemplary of a whole family of low-cost motors that have an odd number of ‘salient’ rotor poles. While these salient-pole motors are sometimes designated ‘toy’ motors, they can have very good performance and are often used in battery-operated power tools and other high-demand applications. A salient pole is a magnetic field pole that projects outwards from the rotor toward the stator, creating a non-­ uniform air gap. This type of pole is used in low-cost motors because the armature conductors can be wound directly onto the rotor core by automated machinery. In the case of slot-wound motors, the coils have to be formed first, then inserted into the rotor slots in an interleaved fashion that is difficult to automate. All the motors described so far have a rotor core made from laminated transformer steel. This is great for reducing the air gap, but does mean the rotor inertia is relatively high, limiting the dynamic performance of the motor. Fig.c shows a ‘coreless’ DC motor which, as the name suggests, does not have a rotating magnetic core. Instead, cylindrical permanent magnet poles are fixed in the centre of the motor and the windings rotate about them. A magnetically permeable housing provided the flux return path. The rotating coils are impregnated with varnish or epoxy to form a self-supporting cylinder. The exploded view, extracted from a publication by the German precision motor manufacturer Faulhaber, shows the key components. This particular model has sintered bearings pressed into the ends of the magnet, which has an axial hole in it for the motor shaft. Coreless motors have very low torque ripple because the rotor is comprised of many interleaved turns of skew-wound copper, and very low rotor inertia due to the low rotating mass. They are relatively expensive, but are commonly used in high-performance applications, including servodrives, robotics and medical equipment. Field windings Before the advent of low-cost power Fig.a: the wound-field motor on the left has two field poles, while the other two have four. The motor on the right also has interpoles, which help eliminate commutation sparking. 58 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.c: for very high dynamic performance, it is hard to go past coreless DC motors. These have an armature that is a self-supporting hollow cylinder of conductors that rotates in the air gap between the fixed permanent magnet core and the motor housing. The exploded diagram is taken from a publication by Faulhaber. electronics, it was common practice to power the armature and the field of wound-field DC motors from a common (often fixed) DC supply. You could do this in two different ways, as shown at the top and middle of Fig.d. I have shown a separately excited DC motor at the bottom for completeness. In general, shunt-wound motors are better for constant-speed applications and series-wound motors are better for constant-torque applications, but neither configuration is used as often as it once was, with a couple of notable exceptions. There are three main reasons why: 1. A separately excited motor with the right controller can do anything a series or shunt machine can do and a lot more besides. The reduced cost of power electronics means we can easily control the field separately. 2. Permanent magnet DC motors have more-or-less taken over in the sub-kilowatt range as magnetic materials have improved. No field winding to worry about! 3. Series and shunt machines are hard to reverse. You can’t just switch the polarity of the DC supply to reverse them because that reverses both the armature and field at the same time, so torque is still created in the same Fig.d: wound-field motors can be configured with the field winding in parallel with the armature, in series with it, or powered separately. Universal motors, which can operate from AC or DC, are series-wound DC motors. direction. You have to use relays or contactors to reverse either the field or the armature polarity. I mentioned that there were a couple of exceptions where series-wound motors are still used. The first is in railway traction, where the very high starting torque of series-wound DC motors is important to get heavy rolling stock moving. Having said that, I observe that induction motors with advanced inverter drives are starting to make inroads into this application because of their lower purchase and maintenance costs. The other area where you still see series-wound brushed DC motors is the ‘universal’ motors used in corded power tools and some home appliances. These are actually DC motors that take advantage of the polarity agnosticism mentioned to run directly off the AC mains. The rapidly changing polarity of the mains switches the direction of the current in the armature and field at the same time, leaving the torque direction unchanged from one half-cycle to the next. Universal motors exhibit a bit of 100Hz torque ripple due to the zero crossings in the current waveform, but that isn’t usually a problem for an application like a power drill or a washing SC machine. Fig.b: many smaller DC motors use permanent magnets to provide the field excitation. The motor on the left has a slot-wound rotor, while the one on the right has salient poles. The latter are easier to wind and so are often seen on low-cost motors. siliconchip.com.au Australia's electronics magazine October 2026  59 Image source: https://unsplash.com/photos/blue-and-white-spiral-illustration-UnkJXtHKlsc Audio Spot Frequency Test Generator by Richard Kabzinski Using just a few modules and not much else, this portable device produces 1V RMS test signals at various frequencies with very low distortion. It also has modes for testing RIAA preamplifiers, SSB transmitters and amplifier intermodulation distortion. B eing something of a collector and restorer of old test equipment, I have three classic noise and distortion (N&D) meters in my collection, along with several vintage, retro and homebuilt valve and solid-state hifi amplifiers that I need to test. Two of the N&D meters are AWA units, one a valvebased 3A56068, with the other being a very capable all-transistor F240A. The third unit I have is a Hewlett-­ Packard 334A. At some point, these have all served in a lab or maintenance workshop somewhere in Australia. Since acquiring them, I have carefully checked and restored them to full functionality. The AWA F240 is the highest performing unit, able to measure noise and distortion down to about 0.003%. One thing I have been missing for many decades, though, is a decent low-distortion oscillator. While I have a reasonably late-model digital function generator, with fairly low sinewave distortion of 0.05% or so (measured at 0.025%), I wanted something at least an order of magnitude better, at say 0.0025% or better. This need prompted me to design and build one. It had to be relatively cheap, easy to build and easy to replicate, as I wanted to share the design with my fellow electronics hobbyists and home constructors. There are a few analog designs out there, but they have some drawbacks: • They require special op amps. • They involve a fairly large number of components. • They can typically only produce a single, fixed frequency. • They can suffer from poor frequency stability. • It’s difficult to guarantee that cloning one will give the low distortion results expected, especially if built on a breadboard or Veroboard. The digital design presented here meets my criteria of being cheap and easy to build, with excellent performance, requiring virtually no attention to circuit layout. It’s easy to reproduce and provides excellent performance because it uses a digital-to-analog converter (DAC) to generate the required signals with only a moderate need to worry about circuit layout. The only real downside is that it requires programming. I didn’t want to spend weeks or months designing hardware and writing code, even though I am capable of doing it. This project had to be relatively quick and easy. That means using a software development environment that is widely known and supported, while using off-the-shelf components. I settled on the Arduino ecosystem as there is a plethora of hardware and software support available. The feature list grew a lot during the design phase. I wanted to make the design super useful, easy to use and Screen 1: the splash screen is shown for two seconds at startup. Pressing the FREQUENCY button during this time will show the software license details. Screen 2: it starts in Flat mode at 1kHz but muted. Hold the MODE button for one second to activate it, as shown here. Screen 3: the second mode, Inverse RIAA, adjusts the output level with frequency to aid in testing phono preamplifiers. 60 Silicon Chip Australia's electronics magazine siliconchip.com.au Features & Specifications ▶ Generates sinewaves at 20Hz, 50Hz, 100Hz, 400Hz, 440Hz, 1kHz, 10kHz & 20kHz ▶ 192kHz sampling rate for low distortion ▶ Extra spot frequencies of 50.05Hz, 500.5Hz, 2.122kHz with automatic level adjustments for testing an RIAA preamp/filter ▶ Generates SMPTE intermodulation tones (60Hz & 7kHz with a 4:1 amplitude ratio) ▶ Generates SSB two-tone of 700Hz/1900Hz for transmitter performance testing ▶ Flat mode output level: 1V RMS ▶ RIAA mode output level: 100mV <at> 1kHz after RIAA filter ▶ SMPTE/SSB output level: 2.828V peak-to-peak ▶ Produces DC calibration voltages for easy trimpot adjustment ▶ Simple two-button user interface (MODE & FREQUENCY) ▶ Modes: flat, inverse RIAA, SMPTE test tone, SSB two-tone ▶ Status is shown on a low-cost 128×64-pixel 0.96-inch (24mm) monochrome OLED ▶ Distortion: <0.0025% <at> 1kHz ▶ Frequency accuracy: better than 100ppm ▶ DAC: PCM5102 <at> 192kHz, 16-bit resolution (48kHz for SMPTE/SSB modes) ▶ Output loading: ≥1kΩ recommended (≥600Ω with the NJM5532D op amp) ▶ Power supply: 5V DC <at> 150mA from plugpack or USB (including power banks) set up, and to appeal to a wide audience of users who need audio signals for test purposes. 1. The YD-ESP32-S3-N8R2-DEVMODULE microcontroller board 2. The GY-PCM5102 I2S DAC module Hardware selection 3. A 128×64 OLED display module I had been exposed to the PIC16, The addition of an output buffer op STM32 and ESP32 series of devices amp also means we need a 5V to ±12V and products over the years. Where I converter to power it. work, we use the latter two platforms Apart from these parts, little else is in our products. They are both cost-­ needed. Two pushbutton switches are effective, highly capable and sup- used for mode and frequency selection. ported by the Arduino system. Low- Potentiometers could have been added cost versions of various Arduino-­ for output level control, but I chose to compatible modules are available vir- use trimpots so that a fixed output level tually everywhere. of 1V RMS can be set. I feel this level is I settled on the ESP32-S3 as the con- most suited for amplifier testing. troller because it has good support for This means the generator can also the I2S serial audio interface of the provide an accurate 1V RMS reference DAC I chose. The DAC is a PCM5102 for checking the AC range of digital by Texas Instruments (originally a multimeters and the like. Burr-Brown device) and is available on Resistive dividers can be used on the a small board complete with a voltage buffered output to provide a suitable regulator, filtering, and even a 3.5mm RIAA output level, in my case fed to output jack. separate RCA connectors. The board also provides pads for headers, which was useful for bread- Operating modes boarding. All that was needed to comThe generator has four modes selectplete the design was some kind of able using the MODE button after an display. I chose a 0.96-inch (24mm) initial splash screen (Screen 1): Flat, monochrome OLED screen that’s con- Inverse RIAA, SMPTE and SSB Twotrolled over an I2C two-wire serial bus. tone. The unit starts up in Flat mode; A quick look at the circuit reveals the pressing the MODE button changes the low module count, belying the flexi- mode as shown in Fig.1. bility and features of the design. Three modules form the basis of the Flat mode unit and are available at very low cost On applying power, after two secfrom places like AliExpress: onds at the splash screen, the unit siliconchip.com.au Australia's electronics magazine Fig.1: pressing the MODE button cycles through the four available modes. operates in Flat mode, with the frequency set to 1kHz and the output muted. While in Flat mode, the frequency button cycles through these frequencies on each press: 20Hz, 50Hz, 100Hz, 400Hz, 440Hz, 1kHz, 10kHz, 15kHz and 20Khz. These are all produced at a 192kHz sampling rate from the DAC for the lowest distortion. To unmute the output, press and hold the MODE button for more than one second. The display will show “ACTIVE” (Screen 2). Press and hold it to MUTE again; the output will be set to 0V and the display will show “MUTED”. Since the output of the generator is perfectly flat at all spot frequencies, as well as being used for audio frequency response tests and such, the frequency response of a DMM can be determined up to 20kHz. Normally, lower-cost DMMs don’t have particularly accurate AC ranges, with typical error ratings of ±1% or so. The frequency response is usually limited to a few kilohertz. One of my hand-held DMMs, although True RMS responding, falls off beyond 1kHz. My October 2026  61 Keithley DMM6500 powers on beyond 20kHz with no problem. Inverse RIAA mode These signals are useful for checking the gain and equalisation accuracy of phono preamps. In this mode, the unit will default to a 1kHz reference tone to allow an initial gain check and the measurement of an output reference value from the preamp (Screen 3). Pressing the FREQUENCY button will cycle through the frequencies at the levels listed in Table 1. Note that these levels are far higher than a moving magnet or moving coil cartridge will produce and thus will overload most RIAA preamps if fed directly to them. A resistive divider and/or trimpots will be required to achieve, say, 5-10mV RMS output at 1kHz to better match what a preamp is designed to accept. The calibration to achieve 1V RMS in Flat mode also calibrates this mode. The idea behind the Inverse RIAA test is that the 1kHz tone is used to check the gain of the phono preamp, then the generator is cycled through the other frequencies. A preamp with correct adherence to the RIAA equalisation curve will give equal output voltages at each frequency. For typical phono stages, the variation would be in the order of ±1-2dB. The 50.5Hz, 500.5Hz and 2.122kHz tones correspond to the 3180μs, 318μs and 75μs RIAA filter time constants, respectively. Table 2 provides a means to gauge the deviation of a phono preamp from the RIAA curve relative to a 100mV output. If the phono preamp under test exhibits a higher or lower gain, the voltage ratios in the table can be used to calculate the expected output voltage once the reference point has been measured. Many classic consumer-grade amplifiers were specified to be within ±2dB, with higher-end units giving Screen 4: the intermodulation distortion test mode produces two signals at different frequencies mixed in specific ratios. 62 Silicon Chip Table 1 – Inverse RIAA mode output levels at specific frequencies Frequency Gain Ratio Output level (RMS) 20Hz -19.27dB 0.1087 11.4mV 50.05Hz -16.94dB 0.1422 14.9mV 500.5Hz -2.64dB 0.7377 77.5mV 1000Hz 0dB 1.0 100mV 2122Hz +2.87dB 1.3910 146mV 10kHz +13.73dB 4.8609 510mV 20kHz +19.63dB 9.5723 1.05V Table 2 – phono preamp output variation Output relative to 100mV dB variance Voltage ratio Change 141.3mV +3.0dB 1.4125 +41.3% 125.9mV +2.0dB 1.2589 +25.9% 112.2mV +1.0dB 1.1220 +12.2% 105.9mV +0.5dB 1.0593 +5.9% 101.16mV +0.1dB 1.0116 +1.16% 100.00mV 0dB 1.0000 Baseline 98.86mV -0.1dB 0.9886 -1.14% 94.4mV -0.5dB 0.9441 -5.6% 89.1mV -1.0dB 0.8913 -10.9% 79.4mV -2.0dB 0.7943 -20.6% 70.8mV -3.0dB 0.7079 -29.2% ±1dB. These days, some high-end phono preamplifiers achieve ±0.5dB or even ±0.1dB. However, the very tight component tolerances to achieve this result in a much higher cost. SMPTE Intermodulation Test mode The SMPTE Intermodulation Test tone uses a 60Hz tone combined with a 7kHz tone at an amplitude ratio of 4:1 (Screen 4). This test is one of the accepted tests to measure amplifier intermodulation distortion and is included for the more adventurous among us. This type of distortion produces unwanted signals at 7kHz ± 60Hz, ie, 6940Hz and 7060Hz. A very linear Screen 5: this two-tone test mode is intended for testing single sideband (SSB) radio transmitters. Australia's electronics magazine amplifier will produce less of these additional signals. They can be measured using spectrum analysis or with deep notch filters tuned to 60Hz and 7kHz, allowing the residual signal amplitude to be measured with an audio millivoltmeter or similar. I thought this would be a useful inclusion, but it requires an external audio spectrum analyser or FFT analyser of some kind. The Room EQ Wizard (REW) computer program, combined with a reasonable external audio interface, could fit the bill for some users. SSB Two-Tone mode I’m not a ham, but I spent over a decade in radio communications in my early years and tested many SSB Screen 6: calibration mode produces a DC output with either polarity that can be measured accurately with a DMM. siliconchip.com.au transceivers with a two-tone signal applied (Screen 5). The SSB two-tone signal is well-known, comprising two tones of equal amplitude mixed together. The choice of the two-tone frequencies varies somewhat throughout the world, but the 700Hz & 1900Hz combination generated by this unit is broadly accepted. This unit generates those tones to a high degree of accuracy, unlike many designs out there. The two-tone test provides a means of checking the quality of the modulator and the final output of an SSB transmitter, to arrive at a measure of linearity and the peak envelope power (PEP) output of the transmitter. Further information on these tests can be found on the internet. Circuit details As you can see from Fig.2, there is not much hardware involved. MOD1, an ESP32-S3 module, is the brains. It runs an Arduino sketch to scan the two switches, distinguishing between short, long and dual presses to provide the various functions. It also drives the OLED screen via a two-wire I2C serial interface and sends I2S data (similar to SPI) to MOD2, the PCM5102 DAC. The PCM5102 is used in 16-bit resolution mode, as a cursory glance at the data sheet will reveal there is nothing to be gained from using the higher 24-bit and 32-bit modes. Its distortion and signal-to-noise ratio specifications are limited by the internal DAC architecture. The lower resolution reduces the computational load on the ESP32 chip. This is a stereo DAC, so it provides left and right channel outputs, which are fed via trimpots VR1 and VR2 to op amp IC3, which is used as a buffer to provide low-impedance outputs. The sampling rate is set to 192kHz in Flat and RIAA modes, while SSB and SMPTE modes use 48kHz. This reduction in sampling rate is due The front and underside of the Audio Spot Frequency Oscillator PCB. The PCB mounts to the enclosure via four 30mm standoffs. This provides enough height so that the switches S1 & S2 protude through the front panel by approximately 2.5mm. While most of the components mount on the PCB, the DC power input jack, two RCA output connectors and power switch mount to the enclosure. Screen 7: the DC output calibration mode with the output voltage switched to negative. siliconchip.com.au Australia's electronics magazine October 2026  63 Fig.2: the circuit primarily comprises four modules connected together: the ESP32 microcontroller (MOD1), PCM5102 stereo DAC (MOD2), OLED screen (MOD3) and split-rail generator (MOD4). Added to those is dual buffer op amp IC1, two trimpots, two pushbuttons and a few capacitors. to the complexity of generating and maintaining the phase alignment between the two tones. The 2.828V peak-to-peak output level is the same in this mode as Flat mode, but because of the mixed We have not installed a power switch, as it is optional. 64 Silicon Chip tones, it is no longer equal to 1V RMS. Using the NE5532 as a buffer presented a bit of a challenge, since I wanted to be able to also generate DC voltages for trimming the AC output level, meaning I couldn’t use AC-­ coupling via capacitors. This forced me to use a split supply to power the op amp so I could DC-couple the signals. I decided that a DC-DC converter module was the easiest solution, so I used a 5V DC to ±12V DC converter device. At first, I was concerned about the cost, but the A0512S-1WR3 module does the job nicely at a very modest price. No power supply is complete without a selection of electrolytic and ceramic capacitors scattered around the schematic to filter/bypass the various power Australia's electronics magazine supplies appropriately. The DC-DC converter allows the unit to be powered from a single 5V DC power supply, drawing around 150mA. A word of caution on the OLED display module. There are variants that swap the Vcc and GND pins, so pay attention when wiring it up. The circuit shows the pinout for the version I used. DC calibration A typical multimeter is more accurate on DC ranges than AC, so it’s ideal to be able to use DC measurements to calibrate the unit. The calibration feature provides a DC output from the DAC at nominal levels of +2.828V and -2.828V DC. These levels are fed to the trimpots, allowing the user to set the DC output from the left and right buffered outputs to ±1.414V DC. This trims out DAC variations and also accounts for the 470W resistors (internal to the DAC IC) in series with the DAC outputs on MOD2. Since the AC peak output from the DAC siliconchip.com.au Fig.3: fit the components on both sides of the PCB as shown here. MOD1 and MOD2 should ideally be mounted via headers plugged into sockets; IC1 can also use a DIP socket. The OLED screens can have pin 1 be +3.3V or GND; check yours and use the appropriate header row. The terminal block wire entries face into the middle of the board. precisely tracks the DC values, after this adjustment, the AC output voltage will be very close to 1V RMS. To use this feature, power on the unit and wait until it starts up in Flat mode, then press and hold both the MODE and FREQUENCY switches together for two seconds. The unit will enter CALIBRATE mode with the DAC output set to 0V. Press and hold the MODE switch to unmute the unit. The output voltage will change to a nominal +2.828V (Screen 6). Use a DMM to measure the left and right outputs while adjusting the trimpot to achieve readings of +1.414V. After that, press the MODE switch to switch the polarity of the output to a nominal -2.828V (Screen 7); check that the readings are close to -1.414V. Pressing MODE will toggle the polarity of the output so a fine adjustment can be made to counter the op amp offset voltage if desired. Once you are happy with the settings, press the FREQUENCY button to exit CALIBRATION mode. siliconchip.com.au PCB assembly I initially built my prototype on a breadboard and powered it with 5V from a bench power supply. Even with such a crude setup, the AWA F240 noise and distortion meter yielded a reading of 0.0026%, which is at its noise floor. When I checked the bridge output (null circuitry) of the F240 with a DSO, I could still see a small residual 1kHz signal plus the inherent noise of the F240. This suggests that the theoretical distortion of the PCM5102, specified as 0.0022%, is being achieved or even exceeded. The good thing about this design is that this distortion figure and the output voltage are both constant across all the spot frequencies. The frequency is precise as well, since it is crystal-controlled. Since then, I have designed a 95 × 65mm PCB to make things easier to build and to package up into an enclosure, coded 04111261. The PCB holds the majority of the components, save the DC input jack, RCA Australia's electronics magazine output connectors and optional power switch. The PCB mounts in the enclosure via four 30mm standoffs directly screwed into the bosses. This sets the height of the PCB so that the tactile switch actuators protrude through the front panel/lid by around 2.5mm. The PCB overlay diagram, Fig.3, shows which components to fit on which side. The display and switches are on the opposite side to the other parts. Begin construction by soldering the headers onto the modules if they were supplied unsoldered. Some PCM5102 modules are not supplied with jumpers installed on links on the underside, so it is a good idea to check these and add solder bridges if needed. The links should be 1-L, 2-L, 3-H and 4-L (see Fig.4). I recommend using header sockets for mounting the ESP32-S3 and PCM5102 modules. This allows access to the ESP32-S3 USB COM port for programming in situ, since the screw terminals are normally in the way. This could be useful for the experienced among you to modify the code to add other features. For example, you might want to add a white or pink noise option, or design a WiFi web server interface to control the unit. The op amp can also be socketed, allowing you to try different op amps to see how various types perform if you are so inclined. When fitting components, solder the header sockets first to make aligning them easier. If these are not used, mount the OLED display and tactile switches, then all other components before finally fitting the modules. It generally works best to start with the lowest profile components, working up to the highest. When installing the electrolytic capacitors, pay attention to their polarity. The screw terminals are optional, but they make wiring up easier because wires don’t need to be Fig.4: the black rectangles show the required solder bridges on the bottom of the PCM5102 module if yours doesn’t come with them in place. October 2026  65 directly soldered to the PCB. The terminal blocks result in a much neater result in my view. Putting it all together Fig.5 shows where to drill holes in the lid for the switches and the suggested locations for the DC input socket and RCA sockets. The measurements are referenced to the centre of the lid. Add some masking tape to make it easier to set out the markings and to prevent scratching the clear lid. Use a nail or centre punch to make an indent in the plastic to help keep the drill centred. A step drill is ideal if you have one. Otherwise, start small with a pilot hole of around 2mm and work up to the required hole size in 1mm steps. Take it slow and easy, as plastic can be a challenge to drill with normal drill bits (it tends to ‘grab’ the bit). The placement of the DC jack and output connectors is only a suggestion, as you may want to use the buffered outputs, unbuffered outputs or both. You may also want a separate RIAA output to which divider resistors have been added. I prefer to use a single pair of outputs with inline attenuators I made myself. To mount the PCB, first screw the threaded end of the standoffs into the four outermost corner bosses in the case. The M3 screw section will cut into the plastic bosses well, but it will require firm downward force to ensure that the thread doesn’t strip on the way. A nut driver will help here if you have one; if not, use the screws as a tap to cut the threads first, then screw in the standoffs. The bosses are deep enough to accommodate the full length of the thread. Now you are ready to wire up the PCB to the DC and audio connectors. Light-duty hookup wire is suitable for all the connections since the voltages and currents are low. The common and signal wires of the left and right outputs can be twisted together if desired. Start by connecting the wires to the screw terminals, as that will help to get the lengths uniform when soldering to the connectors later. Don’t tin the wire ends to make them easier to insert into the terminals. Solder ‘creeps’ or ‘cold flows’ and over time, forming bad connections, so it’s a bad habit to get into. For a reliable connection, use the bare stranded wire Fig.5: where to drill the holes in the lid (for the button stalks) and the top end of the case (for the power and output sockets). Since the power/ output sockets are chassis mounting, you can move the holes or come up with a different arrangement as long as they won’t interfere with mounting the assembled board in the case. 66 Silicon Chip Australia's electronics magazine siliconchip.com.au end and twist it before inserting into the terminal. Before soldering to the DC input socket, double-check the polarity on the DC plug to make sure the DC input socket is wired the right way. Most commonly, the centre pin is positive, but that is not always the case, so check using a DMM to be sure. A quick check of the socket pins would not go astray either. This will also verify that the power supply is putting out close to 5V DC before you plug it into the unit, as AC or some other voltage could cause damage. Program the ESP32 if you haven’t already (see the adjacent panel). Once wired up and with the board not mounted, power up the unit. If all is well, once power is connected, red LEDs will light on the ESP32-S3 and PCM5102 modules, and the OLED display will come to life. Check it is functional by pressing the MODE and FREQUENCY buttons. Once you have confirmed everything is working, go through the DC calibration routine to set the buffered outputs to 1V RMS. The PCB can now be screwed down onto the standoffs with four short M3 machine screws. Usually, you can do without washers, but for the purists among us, these can be added – slightly longer screws may be required. If one or more of the standoffs don’t quite align with the PCB holes, a gentle push in the right direction should solve the problem. If you find the buttons are a bit low for your liking, you can either unscrew the standoffs a little to raise them, or add washers under the PCB to raise it. It is possible to mount the PCB to the lid; that may be required if using a different enclosure. You can use offboard momentary switches, wired via CON2 if you prefer. Before fitting the lid, it’s a good idea to power the unit up again and check that it is working as expected. If you want to power the unit from a battery, a USB power bank is ideal; all you need is the appropriate USB to 2.1mm DC plug cable. This unit could have incorporated more functions such as white and pink noise generation, IHF dynamic headroom testing, logarithmic sweeps and others. These could be added by modifying the code if desired. If there is sufficient demand, I may revisit the SC design and add these in future. siliconchip.com.au Programming the ESP32-S3 To program the chip, you will need the Arduino IDE installed on your computer, which can be downloaded from www.arduino. cc/en/software Make sure you have the ESP32-S3 DEV and a USB-A to USB-C cable on hand, or a USB-C to USB-C cable if your computer has a USB-C port. The steps are: Screen 8: the result of the Get Board 1. Install the ESP32 Board Core. If you Info menu item if the ESP32-S3 board have not programmed an ESP32 before, is connected correctly via USB. open the Arduino IDE, go to File → Preferences, and paste “https://espressif.github.io/ arduino-esp32/package_esp32_index.json” into the “Additional Boards Manager URLs” field. Then go to Tools → Board → Boards Manager, search for esp32 by Espressif and click Install. 2. Download the INO file from the Silicon Chip website at siliconchip.au/Shop/6/3651 3. Connect the cable to the ESP32-S3 USB port labelled COM, not the USB OTG port. 4. Connect the other end of the cable to your computer. 5. If using Windows, open Device Manager to find the COM port number that has been assigned to the board. 6. Start the Arduino IDE. 7. Click the File → Open menu and select the downloaded INO file. 8. Select the board type by going to Tools → Board → ESP32 and choosing ESP32-S3 Dev Module, with the COM port identified in step 5. 9. Configure the USB settings: go to Tools and ensure USB CDC On Boot is set to Disabled. 10. Click Tools → Get Board Info to confirm communication is established with the microcontroller hardware (see Screen 8). 11. Install the Adafruit_GFX library by navigating to Tools → Manage Libraries, searching for it by name, then clicking install. 12. Install the Adafruit_SSD1306 library from the same Library Manager window. If the IDE asks to automatically install missing dependencies like “Adafruit BusIO”, select Install All. 13. Click the Upload arrow icon to compile the code and flash it into the ESP32-S3. Parts List – Audio Spot Frequency Oscillator 1 double-sided PCB coded 04111261, 95 × 65mm 1 125 × 85 × 55mm Ritec/Hammond RP1135C plastic enclosure with clear lid [Altronics H0324] 4 3-way terminal blocks, 3.5mm pitch (CON1, CON2) 1 2.1mm ID panel-mount barrel socket (CON3) 2-4 red/white panel-mount RCA sockets 1 ESP32-S3 microcontroller module (MOD1) [AliExpress 1005012092039320] 1 PCM5102A DAC module (MOD2) [AliExpress 1005012157224842] 1 GME12864 or GM009605 0.96-inch OLED display module (MOD3) [AliExpress 32638662748] 1 A0512S-1WR3 DC/DC converter (MOD4) [AliExpress 1005006491073871] 2 6×6×15.3mm tactile pushbutton switches with 12mm-long actuators (S1, S2) 2 5kW 3296-style top-adjust multi-turn trimpots (VR1, VR2) 2 22-pin socket strips (for MOD1) 1 6-pin socket strip (for MOD2) 1 4-pin socket strip (for MOD2) 1 8-pin DIL IC socket (for IC1) 4 M3 × 30mm male/female tapped hex spacers [Würth 971300354] 4 M3 × 6mm panhead machine screws 6 150mm length of light-duty hookup wire Semiconductors 1 NJM5532D or LM833 dual low-noise op amp, DIP-8 (IC1) Capacitors 1 47μF 16V electrolytic 2 10μF 16V electrolytic 2 100nF 50V ceramic Australia's electronics magazine October 2026  67 By Geoff Graham Image source: https://unsplash.com/photos/a-man-ispumping-gas-into-his-car-RI8SyIOg4EM A practical guide to EV Charging vehicles recommend a maximum charge of 80%, in which case they might start at 80%, end at 50%, then recharge back to 80% overnight. Because plugging in an EV only takes a few seconds, many drivers will do this whenever they return home, with the result that their car is always fully charged and ready to go, similar to how many people charge their mobile phones. A Level 1 charger is usually supplied with the car, but if not, it can be purchased for $150-250. Photo 1 shows a typical example. Note that this option requires a GPO near your car; for many apartment dwellers or people with no off-street parking, this is not possible. In that case, your only option is a public charger (described below). Level 2 chargers/adaptors In this guide, we cover the most common methods you can use to charge an electric vehicle (EV) from a slow charge at home to a fast charge on a long road trip. Included are some subtle aspects of EV charging that even a well-versed EV owner may not be aware of. W ith the current popularity of EVs, prospective buyers face a steep learning curve regarding how to “fill up”. For a petrol/diesel vehicle, it is simple: drive to a service station, open the flap, insert the nozzle and squeeze the handle until it clicks off. However, with an EV, you have at least four possibilities, and that can be confusing. Generally, the charging options for an EV are referred to as Level 1, Level 2 or Level 3 charging. These and more were covered in David Maddison’s article on EV Charging in the July 2023 issue (siliconchip.au/Article/15857), but that was more of a technology overview. In these pages, we will consider the more practical aspects for a typical motorist in Australia or New Zealand who is thinking of purchasing a modern EV. Level 1 chargers/adaptors These are the cheapest option. It is simply an adaptor between a standard 68 Silicon Chip home 230V AC mains power socket and the EV. They are called a charger, but they do not actually manage the battery charging; they just contain some safety circuits and a module that communicates with the car, which has an onboard charger. Still, in keeping with common usage, we will also call them chargers. The actual charger is in the EV; all modern EVs have a built-in AC charger that converts the incoming AC power to DC and steps up the voltage to a level suitable for charging the car’s battery. The charge time is dictated by the maximum current that can be drawn from a GPO, which is usually rated at 10A (230V × 10A = 2.3kW). For a typical EV, this means that charging from empty to full takes 30-40 hours. This may sound like an extremely long time, but many people drive less than 120km in a day, and that would only drain the battery to about 70%. An overnight charge will then easily return it to fully charged. Some Australia's electronics magazine These are essentially the same as a Level 1 charger but in a fixed location with a dedicated 32A circuit running back to the switchboard/fuse box. Using a 32A single-phase 230V AC supply, these can provide up to 7.4kW to the car, resulting in a charge time of 10-15 hours, three times faster than a Level 1 charger. Some EVs and Level 2 chargers will accept three-phase power and, if you have access to this, you can charge a little quicker. However, the benefit is small because the onboard charger in most EVs is limited to 11kW or less. For this reason, it is generally not worth the cost of installing a threephase circuit, even if your car and Level 2 charger can support it. In a typical residential installation, a Level 2 charger is a box that is mounted on the wall of a garage. There are also weatherproof versions if it needs to be mounted outside. They usually come with a charging cable (typically 3-7 metres long) and cost from $800 to $2000 or more. To this, you must add the cost of installation, which can easily exceed $1000. Photo 2 shows a typical installation, in this case a Tesla Gen 3 Wall Connector. The more expensive examples will interface with home solar panel controllers so that the vehicle is only charged when there is excess solar power. This means that the “fill up” cost is near-zero. Many people with an EV install a Level 2 charger on the basis that they have paid a lot for the EV anyway and siliconchip.com.au one of these devices is only a proportionally small expense. Obviously, they are also handy if you drive long distances every day. But perhaps their greatest advantage is that they allow you to benefit from the cheap electricity rates that are available at certain times of the day for a limited number of hours. For example, under the Australian government’s Solar Sharer Offer, you can get three hours of free electricity in the middle of the day (in some states and on some plans; note that those plans may [likely will] make electricity more expensive the rest of the time). With a Level 1 charger, you will only get a tiny charge in that time, but with a Level 2 charger, you can get enough to cover a day’s driving, and it is free! Most chargers and EVs allow you to specify a charging window so the car will automatically charge during these cheap times without you having to do anything. Photo 1: a typical Level 1 charger/adaptor for charging an EV from a standard mains GPO. Source: Harvey Norman Photo 2 (above): a typical Level 2 charger/adaptor installation, in this case a Tesla Gen 3 Wall Connector. It is weatherproof, so it can be installed outdoors. Public Level 2 chargers/ adaptors Some businesses and shopping centres have public Level 2 chargers in their car parks. They are also often found in small country towns. Typically, these cost 25-45¢/kWh to use. Sometimes, when a business wants to attract customers, they are free. Usually these chargers are rated at 22kW, but this is misleading because (as mentioned before) the AC charger in your EV will probably be limited to 11kW or less, so it will still take a long time to get a decent charge (typically 6-12 hours). As a result, they are only useful if you want to get a small-top up while shopping, sightseeing, or if you are staying overnight near one. Because of this, they are called Destination Chargers by Tesla. Public Level 2 chargers do not provide the cable between the charger and the EV, so this is something that you need to purchase if you want to use them. Prices vary over a huge range from $40 to $500, so be prepared to shop around and make sure that it is a Type 2 to Type 2 cable as required in Australia and New Zealand. There is a push for public Level 2 chargers to be installed on street power poles. It makes sense when you think about it; there is plenty of power at the top of the pole, and all it needs is a cable running down to the charger/ siliconchip.com.au Photo 3 (left): a public Level 2 charger (Circontrol Evolve Smart T) at the Cockburn Youth Centre in Western Australia. These chargers are often referred to as “BYO cable”, meaning that you must supply your own Type 2 to Type 2 cable to use them. Photo 4: two 350kW chargers, each capable of charging an EV from 10% to 80% in 18 minutes. Source: Chargefox Australia's electronics magazine October 2026  69 Photos 5 & 6: the Type 2 plug used by Level 1 and Level 2 charger/adaptors has seven pins, which include the connections for AC charging (single and three-phase) and communication signals to/from the charger. Photo 7: the CCS2 plug and socket is the standard for charging EVs in Europe, Australia and New Zealand. adaptor fastened to the base of the pole. The intention is to make it easy for EV owners who only have street parking and, if it becomes a thing, this type of charger will be installed in older inner suburbs where there is little offstreet parking. can deliver, with typical capacities of 50kW, 150kW, 250kW and 350kW. The most common are 50kW and 150kW, while Tesla V3 Superchargers are rated at 250kW. Typically, a 150kW charger will charge an EV in 30-45 minutes from almost flat, while a 350kW charger will Level 3 or DC fast chargers charge it in 18 minutes. However, only A Level 3 charger (more usually EVs with 800V batteries can charge called a DC Fast Charger) is a genu- that quickly (more on that below). ine charger because it delivers the Tesla owners can charge using dedhigh-voltage DC directly to the car’s icated Tesla chargers or public DC fast battery, bypassing the onboard AC chargers. However, the reverse is not charger. The vehicle still controls the true, as Tesla only makes a limited charging process by telling the char- number of its chargers available to ger the voltage that it needs, but it is non-Tesla owners. the charger that regulates the charging DC fast chargers are expensive to voltage and current. build and maintain, so you will not High-end chargers can deliver mon- find one in a home. Instead, they are umental amounts of power, up to 500A installed in shopping centres, dediat 1000V via a heavy-duty, liquid-­ cated EV charging stations, and more cooled cable. If your car can take this recently, petrol stations. They include enormous charge rate, you can be back the cable to plug into your car and on the road in as little as 11 minutes, typically cost 50-70¢/kWh. So a full almost as short as the time needed to charge will cost $35-55. fill a petrol/diesel car. You will find most DC fast chargers Admittedly, there are few EVs and in the suburban areas of major citchargers that can reach this speed, but ies and along major highways. If you regardless, all EVs will still get a very are going on a long country trip, you fast charge from a Level 3 charger. need to plan ahead to go from charDC fast chargers are rated accord- ger to charger according to the range ing to the maximum power that they of your EV. 70 Silicon Chip Australia's electronics magazine This is not usually a problem, as there are plenty of route-planning apps for your phone, and the internal GPS mapping function in most EVs will also do that for you. However, in central Australia you are out of luck, as there are almost no public charging facilities out there – that part of the country is dominated by diesel-powered 4WDs. EV battery voltages EVs are categorised by their nominal battery voltage, which can be 400V or 800V. The actual voltage will vary according to the state of charge, temperature and other factors, but 400V and 800V are used as nominal figures. Most EVs have a 400V battery. This includes Teslas and many BYD/VW models, while more premium vehicles like the Porsche Taycan, many Hyundai/Kia EVs and premium BYDs use an 800V architecture. The battery voltage is not important in the driving experience, but it can affect the charging speed when using a DC fast charger. This is because a DC fast charger is limited in the current that it can supply. An 800V EV will get almost twice the energy into its battery compared to a 400V EV when charging at the same charger for the same duration. 350kW chargers are an example of this. They are quite rare, but if you find one and have a 400V EV, your car will request 400V from it, and your charge rate will be limited to about 200kW. This is despite the charger’s 350kW rating, which only an 800V EV can take advantage of. Modern 50kW and 150kW chargers used by big network providers like Chargefox and Evie will deliver over 800V, so an 800V EV will also get a faster charge from them. Older public chargers and most Tesla proprietary chargers are limited to 400V. In this case, an 800V EV will compensate by presenting a 400V load to the charger, but it will not have a speed advantage. Charging rates With a DC fast charger, you don’t get the full power during the whole charging time. Instead, the car will instruct the charger to start at a high power and hold it for a while before reducing it to a lower level based on the battery pack’s temperature. When the car reaches an 80% state of charge (or thereabouts), it will siliconchip.com.au Photo 8: the 2024 model of the Hyundai Ioniq 5. Outside of the luxury brands, this car line typically occupies the higher end of electric vehicles. Source: https://w.wiki/SWAp (CC-SA-3.0) rapidly reduce the charge rate to a fraction of the maximum as the battery nears 100% capacity. This is designed to reduce the stress on the battery as it nears full charge. When using a DC fast charger, the last 20% of slow charging can add a lot to the overall charge time. This is one reason that many manufacturers quote their charge times as being from 10% to 80%, and we used the same convention when quoting charge times above. Protecting the battery from damage is also related to the maximum state of charge that you should use when charging the car. Many (but not all) EVs use lithium-ion batteries. During the charging cycle, lithium ions are transported through the battery’s electrolyte and are embedded into the graphite anode. This embedding causes the anode to swell slightly as it reaches a full charge, causing cracking in the anode, which will eventually reduce the battery’s capacity. For this reason, experts recommend that, as a general rule, you should limit the maximum state of charge to 80%. It is fine to charge to 100% if you need to go on a long trip, and many people always charge to 100% anyway but, for day-to-day running, especially when you charge overnight at home, 80% will help your battery retain its capacity. This advice mostly applies to EVs using lithium-ion nickel-manganese-­ cobalt (NMC) battery chemistry, but it is a good default policy, especially if you don’t know what chemistry your car uses. Some EVs use lithium-­ironphosphate (LiFePO4) batteries, and for many of those, the manufacturers state that it’s fine to charge to 100%. siliconchip.com.au Regardless, due to advanced battery management and modern battery construction, most EV batteries are expected to outlive the car in which they are installed. Battery preconditioning One subject that you might hear about when researching EV fast charging is battery preconditioning. EV batteries charge best at a certain temperature (usually 25-35°C), so when you need a fast charge at a DC charger, it helps to already have the battery near the optimal temperature. Modern EVs will heat or cool the battery for you, and most will even automatically start this process before you arrive at a DC fast charger (when you have selected that as your destination in the car’s navigation system). It is not a problem if you have not preconditioned the battery before you start a fast charge, as the car will regulate the charge rate accordingly, but it might take longer to charge. For most Australians, this is not a concern, as the weather is generally warm. However, if you live in Tasmania or New Zealand, the very cold winter temperatures can make using a DC fast charger rather tedious without preconditioning the battery. Plug types In Europe, Australia and New Zealand, the standard connector for EV charging is the CCS2 (Combined Charging System Type 2) plug/socket. You may see some older standards (such as CHAdeMO) still around, but they are rapidly being phased out. The CCS2 connector (shown in Photo 9) consists of two sockets: the upper socket (with seven pins) carries the connections for AC charging (single Photo 9: the CCS2 socket in a Hyundai Ioniq 5. The upper socket carries the connections for AC charging and communication to/from the charger, while the lower socket has two heavy-duty pins for DC charging at up to 500A and 1000V. Australia's electronics magazine October 2026  71 and three-phase) and communication signals to/from the charger. The lower socket has two heavy-duty pins for DC charging at up to 500A and 1000V. AC chargers (ie, Level 1 and 2) only use the upper socket, as this provides all the connections and signals that are needed, and the lower DC charging socket is ignored. DC fast chargers use both sockets, with the upper socket only used for communicating with the car. In most cars, the DC socket is protected by a removable cover, as it is rarely used. One thing to be aware of is that there are many plug types and standards around the world. For example, China uses GB/T, and North America was using the old CCS1 standard, but is currently migrating to NACS (North American Charging Standard). This can be confusing if you are following foreign reviews. Be careful when purchasing cables and other charging-related items from overseas, as they may not work here. Conclusion Most people with off-street parking and easy access to a GPO socket will find that charging their EV is cheap and simple. An EV differs from a petrol/diesel car, where you typically wait until the tank is almost empty before driving to a service station and filling to the maximum (or refill opportunistically when you pass one). With an EV, it only takes a few seconds to plug it into your home charger, so waiting until empty is not necessary. You just plug in when you return home, and you will always have a ‘full tank’ in the morning. Because of this, many EV drivers with home chargers rarely see their battery charge fall below 70% and range anxiety does not exist. However, drivers who must park on the street do not have it that easy. In this case, you will have to find a local public charger and, because an EV has a similar range to a petrol/diesel car, you will be doing this with roughly the same frequency as visiting a petrol station. It might sound complicated using a DC fast charger on a long country trip, but in reality, they are easy to use – you just rock up and plug in. The car and charger will take care of the complications. Charging can take an extra 30 minutes or more compared to filling a petrol/diesel car, but after a long time behind the wheel, most people will take a break for a coffee or snack, anyway. So it is not a great burden. About the only time a petrol/diesel car has a significant advantage is if you are venturing into outback Australia or if you are doing a very long trip with no breaks, and you do not want to wait the extra 30 minutes or so when SC recharging on the way. Photo 9: this chart illustrates the charging characteristics of an 800V EV on a 350kW charger. The charge time from 9% to 80% was just under 18 minutes. The green trace shows that full power is only drawn for a short time; after it reaches 80%, the charge rate is drastically reduced. This is controlled by the vehicle’s battery management system (BMS). Source: nagapixels on Reddit 72 Silicon Chip Australia's electronics magazine siliconchip.com.au Subscribe to SEPTEMBER 2026 ISSN 1030-2662 09 The VERY BEST DIY Projects ! 9 771030 266001 SEMICONDUCTOR $15 00* NZ $15 90 INC GST INC GST ANALYSER Identifies and tests diodes, transistors & thyristors Measures forward & reverse voltage, Vbe, hfe, Vgs etc Improvised Electronics and DIY Components Battery BackPack Usable in any place that requires an uninterrupted power source; such as our GPS Clock Driver from Co mmodore PET Diagnosing 2022 (shown connected to it) a vintage com puter Australia’s top electronics magazine The Display System 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 $77.50 $87.50 $55 1 year $145 $165 $105 2 years $270 $305 $200 6 months $95 $105 1 year $180 $200 2 years $335 $370 6 months $115 $125 1 year $220 $240 All prices are in Australian dollars (AUD). Combined subscriptions include both the printed magazine and online access. 2 years $410 $445 Semiconductor Analyser; Sept 2026 Battery Backup for GPS Clocks, Sept 2026 Destination Display; August 2026 Prices are valid for the month of issue. Try our Online Subscription – now with PDF downloads! 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 Part 5: final assembly Phil Prosser’s Phenomenal B y now, you should be familiar with the deck, the various parts and the software. We are not going to try to give full constructional details, as they would be very long and complicated. You should be able to figure the rest out with a bit of guidance. We expect you will make your own layout, taking your own approach to the deck and its decoration. Our play surface is 470mm wide. If you are keeping to this, you can use our entire lower section unchanged. You can either copy our middle and upper play area or make your own from scratch, or based on ours. The CAD files on our website can be used as a starting point to make your own deck parts (www.siliconchip.com.au/ Shop/6/3628). Our Machine is shown in Photo 1. This final article will therefore touch on the following: Finishing the deck off Assembly of the ‘back box’ with the controller, power supply, speakers and scoring Final installation of the electromechanical parts on the deck Wiring Decoration Testing We will provide a few pointers on the software in this article, which should set you on the path of being able to change lights, interactions of switches and rollovers to scoring, lights and high current outputs and also sounds. This requires some programming skills but the code is not terribly complicated. 📍 📍 Pinball Machine 📍 📍 📍 📍 Putting parts on the deck For assembly, most parts simply interface with one another. Around the flippers, the ‘inner runways’ and the ‘kicker’ shown in Fig.30 require about 33mm separation to make the alleyways. For the rest of the deck, refer to Photo 23 and the lead photo. Now that you have a deck layout and your game design sorted, let’s get it running. Power supply & controller This final article in this series shows how we went about finishing our pinball machine deck and integrating all the electronics, wiring and electromechanical kit. We will also provide pointers and tips on the wiring, layout considerations and how to test and modify the design. Mount the assembled and tested power supply and controller boards to the back panel of your backboard. We used 10mm-long M3-tapped standoffs (spacers), marking the location of drill holes using the PCB as a stencil. With them mounted, connect the 6-way headers between the Power Supply and Controller boards. These Australia's electronics magazine siliconchip.com.au 74 Silicon Chip are straight across and should be simple. Use heavy-duty wire. Drill a 13mm hole in the rear panel and install the chassis barrel plug. We glued ours in place. Wire this to the Power Supply Board, making sure that the polarity is correct. Use a multimeter to check your connections. We assume that the controller has already been verified as working. Apply power and check that the heartbeat LED flashes. If not, unplug your power supply and check that it is OK. Run the Controller from a USB connection to your computer. If this does not get the LED flashing, reload the software. Check the 5V rail is OK; this really only drives the LEDs. Check for short circuits or parts not installed properly. The back box How you approach the back box is a matter of your style. We assume that, at a minimum, you want to show the score and player number. It’s also a good idea to put a speaker or speakers in there, as well as some form of lighting. Install the score and player PCBs to your backbox first. We have provided bezels that you can print to make these tidy, which you can glue to the backboard. We used 12mm-long 6G wood screws to gently hold the PCBs in place. Install the speakers and the grille(s) of your choice. We painted the interior of the cut holes black, which made our hand-cut holes invisible. ~33mm ~33mm ~3 3m ~3 m Next, work out how you want the lighting installed. You can use LED strip lighting, which is kind of expensive but easy to install, or individual LEDs, which you can install in LED holders. This may form part of your front panel design. Since the strip lighting is designed for a 12V supply, cut it into two strips and wire them in series to suit the 24V DC supply. Wiring it up Now let’s do some cabling. Cut the 1.5mm-thick aluminium bar into 140mm-long and 10mm-wide lengths, then bend them into an 80mm-long, 25mm-tall bracket shape, as seen in Photo 24. Slip large-diameter heatshrink tubing over the brackets and shrink it so that the edges of the metal don’t cut through wires (or wrap them in some kind of flexible plastic). Drill holes in the flanges for screws to mount them. There are other options, but you will need something to keep the cabling under control. Otherwise, the wiring will become a nightmare! Start the wiring with the score and player headers. We pulled the ribbon cable through the brackets to the PCB and cut lengths about 100mm too long. We then installed the crimp connectors on the controller end and reinstalled them to get the lengths right. Pull the cables and install the final crimped connectors. Use a labelling machine to label every cable, otherwise, by the time you finish wiring this up, you will never be able to trace cables through the loom! If you don’t have a labelling machine, you can use small paper labels (ideally laminated) or tags. Make sure the labels are legible and not confusing. Connect the speakers in series to get a 16W impedance. The LM384 is operating from 24V DC and should not drive a 4W load. Measure and install the speaker wire to the Control Board and label it. Now apply power and check that you get sound and the scrolling message on the score display. Remember that the rightmost two characters on Photo 1 (reproduced from part 1): you could create an exact copy of this, using the files and diagrams supplied, or do your own thing. 3m m Fig.30: the arrangement of the inner runways and the kicker. siliconchip.com.au Australia's electronics magazine October 2026  75 the score display are not used except in scoring. If you run into trouble, check the power supply rails. Verify that the heartbeat LED is flashing; if not, unplug the displays and find the short circuit. Hold down the self-test button at power-up and connect your computer running serial terminal software to debug these outputs. Check that the inputs and outputs make sense. Run the LED self-tests and, if you find a problem, check the cabling between the controller and LEDs. Lower deck section There is a fair bit of wiring even in our relatively simple demonstration build. This is shown in Photo 4, reproduced below (from part 1 of this series). We are proud to have kept this under control and avoided the chaos we have seen in many traditional pinball machines. If you use labels and our recommended wiring system, you will get a similar or better result. Install the loader sections as well as the flippers and associated runways. Make sure that the deck sections fit tightly together and double-check that the screws for the solenoids are secured with Loctite or similar; if they come loose, it will be a hassle. You will need to install Switch Input and High-Current Interface boards Photo 23 (left): our deck, shown previously before we got to assembling all the electromechanical parts. The ramp is pretty fun; the ball goes over a rollover as it exits that causes all the lights to flash brightly. You can decide how much of this you want to copy and what you want to change. Photo 4 (right): this view (reproduced from part 2) shows all the wiring under our deck. As you can see, there’s a lot going on, but we kept it all pretty neat and nothing is too difficult. Working on the wiring is actually quite easy. Note our “home made” tilt switch made from fencing wire and a handful of screws in the bottom left. 76 Silicon Chip Australia's electronics magazine siliconchip.com.au under the deck, which is easy to do using 20mm-long 6GA wood screws and the 3D-printed 8mm spacers. The exact location does not matter, provided it does not interfere with your mechanical parts – refer to Photo 25. The Switch Input board has inputs for: The Cascade LED sensor that triggers the triangular cascade LEDs An optional tilt input The Start Game button The Coin button/mechanism The Game Lost sensor input The Player Add button The Left Flipper trigger button The Right Flipper trigger button We used inductive sensors for both the Game Lost and Cascade sensors. This board has 24V supplied to it and can power standard sensors. You could use more conventional microswitch sensors for these if you want to. The inductive sensors are mounted in 3D-printed holders, as shown in Photo 26. The Start Game, Coin and Player Add switches are standard pushbutton switches, while our tilt sensor was made from fencing wire with a simple weight to detect the machine being tilted. SW-200D, SW-420D and SW-520D pre-made tilt sensors are also available inexpensively on websites like AliExpress. Install the Coin, Player Add and Start buttons on your case. Our arrangement is shown in Photo 27. Also install the left and right flipper buttons to your case. We used large 📍 📍 📍 📍 📍 📍 📍 📍 arcade-style switches that have the right ‘clicky’ feel. The Game Lost sensor needs to go right where the ball sits in front of the reloading mechanism, as the software uses this sensor as an input to detect when the ball is lost and needs to be reloaded. All the inputs are labelled on the PCB, and you can neatly wire these inputs through to them. Label the plugs, as all the wires look alike. Later on you won’t remember what each connects to! You need to run heavy-duty speaker wires for the Launch, Reload, Left and Right flipper solenoids from the controller to the High-Current Interface Board. Make very sure that you get the polarities right, as while the solenoids are not polarised, the flyback catch diodes on the High-Current Interface Board certainly are. This board has four identical channels, which are not labelled. Use them however it is convenient – just ensure that you connect the solenoids to the right outputs. We can now test the lower deck section. 01 Apply power to the machine. The system should power up. 02 Run the Self-Test routines and test each part individually. You should be able to push each of the buttons and see the test routine report that they are pressed. 03 Put a steel object on the inductive sensors and verify that this is Photo 25: the power wires from the Controller come in on the left to the High-Current Interface Board, as does the 10-way ribbon cable for I/O lines. They route to your local parts and sensors from here. Photo 24: the control board, power supply, score display and one speaker mounted in the back box. Note the brackets below and to the right of the control board that went from a piece of aluminium and covered in heatshrink tubing. We used several of these to keep the wiring looms neat. siliconchip.com.au Australia's electronics magazine October 2026  77 reported in the test routine. Most sensors also have LEDs on the back that will show you they are working. 04 The self-test routine also has the ability to test the solenoids. Run these tests and check that the flippers and loaders actuate as expected. If not, verify that the inductive sensors are wired correctly, check the ribbon cabling for the inputs, and examine the power wiring to the solenoids. If the polarity is swapped on the power connections, you will damage the flyback diodes and possibly the Mosfet (as we unfortunately found out). Installing the LED lights We have made 3D printable bezels that accommodate 5mm LEDs and are a push-fit into holes drilled in the deck. These use 8mm, 10mm and 12mm diameter bezels that we printed in clear PLA (we liked the 12mm type). We drilled the deck and installed these prior to painting it. These were used for all LEDs on our deck; the files are in the Led_Holder folder. You can use a hammer to get them in if needed (but you must hammer from the top of the deck). Those that are not tight can be secured with a drop of superglue on the rear to hold them in place. During painting, we cut 12mm diameter circles from contact adhesive and stuck these on the bezels so that the paint wouldn’t cover the clear windows. To do this, we sharpened the end of a piece of 12mm copper water pipe and used it as a die. You could also use a 12mm leather punch. The cascade LEDs can fit directly into the bezels if drilled as shown in Fig.19. The cascade LEDs can be jiggled into the bezels and secured with a drop of superglue between a couple of the LEDs and their bezels. The circular LEDs around the bumpers can also be drilled as shown in the diagram, and the target LEDs placed directly in front of each target. The circular bumper LEDs install similarly to the cascade LEDs. Both sets connect to the labelled headers on the controller board using 10-way ribbon cable, which you should run through the cable loom. The target LEDs need to be wired via one of the LED breakout boards. Fig.19 (from part 3): the holes in the deck for our Pinball Machine. Note the rectangular cut-outs for the targets & kickers. You will need to fettle them when installing those parts, but it’s better to start with them too small than too big! 78 Silicon Chip Australia's electronics magazine Installing the targets The cutouts for the targets are shown in Fig.19 (from part 3). These can be siliconchip.com.au Photo 26: there are versions of this 3D print for 8mm and 12mm diameter sensors with two, three or four screw holes, allowing you to get sensors into tight places easily. There is a grub screw hole in the rear of the holder to secure the sensor. Photo 27: our front panel is pretty simple. We used stencils to spray the labels, which are in the download package. You need all three inputs to the Controller for the three buttons. We installed the launcher while we arranged the lower deck sections. cut using a handsaw. We needed to do a little fettling to get the holes to just fit the target assemblies. We drilled 12mm holes for the target LEDs, which light up when you hit a target. The targets screw to the underside of the deck with 16mm-long 6GA wood screws. You need to install the General Input and General LED boards under the deck. We placed ours on one side of the deck, as shown in Photo 28. It is a touch hard to see in the pictures here, but each has a 10-way ribbon cable that runs from the interface board through the wiring loom to the respective input and output connectors on the controller board. Wiring from the target microswitches to the input board is via light-duty hookup wire and polarised header plugs. Label these, but if you get them in the wrong spots, you will simply have the wrong LEDs lighting when you hit the target. We zip-tied these all together to keep things tidy under the deck. Testing the LEDs Apply power to the system with the Self-Test button held down. Run through the tests until you get to the appropriate LED tests. You should have tested the LEDs on the PCBs earlier, which is important if you are gluing them into the deck. If these tests fail, you most likely have a problem with your plugs or crimping. Are both plugs the right way around? Did they crimp properly? Swap them with other LEDs to see if they light up . Are the individual LEDs wired the right way around? Installing bumpers & kickers The kickers need an odd-shaped hole in the deck, as shown in Fig.19. We cut a rectangle using a handsaw, then made the extra notch cutout. As we installed the kicker, we found that we needed to extend the cutout somewhat. We did this using a file and knife, avoiding cutting too large a hole, which would make the deck unsightly. We installed the posts and the top of the kicker, which are 3D-printed from the files “Square Rope Kicker” and “Posts Top L and R” in the Posts Photo 28: the labelling makes this a little messy, but it’s absolutely necessary if you plan to remove or service parts later (and you almost certainly will need to). siliconchip.com.au Australia's electronics magazine October 2026  79 folder. These secured using M4 × 50mm machine screws and hex nuts. We used 5 × 5mm neoprene rubber for the kicker ‘rope’ and superglued this into a rubber band that was tight on the posts. The kicker mounts with its foot just next to the ‘rope’. Screw it into place under the deck using 6G × 16mm wood screws. You need four kicker microswitch brackets in total. These mount under the deck with the microswitch lever touching the rope. Once secured using 16mm wood screws, adjust these by bending the lever with a pair of pliers so that moving the rope a little causes the switch to activate. Getting this right is important, but once set, the adjustment is stable. The bumpers fit through a 25mm hole in the deck that you can drill using a spade bit. The edges of this are hidden by the skirt, so a little tearing on the edge of the drill hole is OK. You need to print and install the bumper shim, which provides extra clearance for 12mm LED holders and makes construction easier. Assemble the upper and lower deck parts of the bumper, as described last month. We set the gap between the ball sensor and deck to about 2mm and ensured that the sensor worked well. If the sensor does not work at some angles, check that the microswitch is square in the recess in the bumper assembly – once located properly, this should operate reliably. Screw the bumper to the deck using 16mm wood screws. Once adjusted, fix the upper and lower sections together using four 9mm self-tapping screws. Put 2.54mm pluggable connectors on the ball sense and LED outputs and two-way terminal block plugs on the solenoid wires. These will need to have sufficient length to reach the interface board. Plug all of these into the labelled locations and you are set. You need to install the Bumper Driver Board, as shown in Photo 29. Like all the under-deck PCBs, we mounted this using the 3D-printed 8mm standoffs and 6G × 20mm wood screws. As with all the power and control interfaces, run labelled 10-way ribbon cables with IDC connectors from this board to the matching connectors on the controller board. Also wire the bumper and kicker switch outputs to the interface board. The kicker microswitches are wired in parallel, so there is only one wire going to the header on the interface. To test the kickers, first double-­ check that the power cabling has the right polarity. Boot the machine in Self-Test mode and you should be able to detect the sensors being pressed for the bumper and kickers. If only some fail, you have a wiring problem. Find it and fix it. If all fail, check that the IDC headers are both on the right way. Then run the power tests. You should see the kicker and bumpers actuate during those tests. Installing the upper deck sensors We installed several rollover sensors on our Pinball Machine, using inductive sensors, as described earlier. We have three between the runways at the top of the deck, one at the exit of the launch runway up the right hand side of the deck, and one at the exit of the tunnel. These all connect to the Rollover Board, which you need to install at the rear underside of the deck. The inductive sensors connect to the rollover board using three-way pluggable headers. On ours, ground was blue, +24V was brown (you could use red) and the open-collector output was black. Use the printable holders for these, which are in the “Sensor Brackets” folder under “Lower Deck Runway”. We used 12mm sensors. These affix under the deck using 16mm wood screws and you can use a small self-­ tapping box screw to secure the sensor into these holders. Get the top of the sensor flush with the deck. We painted over ours. The rollover board connects to the controller with a ribbon cable. To test the sensors, run the controller in Self-Test mode and put a metal object on each sensor in turn to see the input toggle. If you have problems, check that there is 24V supplied to the sensors and verify that the cabling is right. Remainder of the upper deck The remainder of the example upper deck is runways and posts. Yours may differ, but you will surely have some structures and sensors in there. Ours is shown in Photo 23. The 3D-printed parts for our example deck are in the “Runways” folders Photo 29: there’s quite a lot going on in this area including the flippers and their interface, two kickers and many individual LEDs. You can also see one of the bumpers and the bumper/ kicker interface board. We found that labeling things on the underside of the deck helped us navigate our way around during set to work. 80 Silicon Chip Australia's electronics magazine siliconchip.com.au and “Posts” for the posts. We suggest that if you are starting with the example deck, you print these and lay them out on your deck. While we have shown hole locations in the drawing, we would simply place these and screw them down using 16mm wood screws. The posts are placed 43mm apart, which gives room for the thick cloth-covered rubber band we strung between the posts, allowing the 22mm ball to still pass through. With all these in place, you should have everything sorted out and be ready to sand and paint the deck. Painting the deck This author is no artist. After some head-scratching, he came up with some ideas for the theme and deck. We leave the decoration to your imagination and would love to see what you come up with! You can get stickers and decals for pinball machines. While not cheap, these may be worth considering. The pinball surface takes a beating, so if you’re painting the artwork, it needs to be protected with a clear coat. One tip, which I expect every professional painter will know: if using clear coat over a range of different manufacturers’ colour coats, apply many thin layers of clear coat to build a protective layer. Otherwise, you may find the colour coat will bubble or fail. Playing the game We are sure that by this time you have been playing the game in its various states of build; we certainly were. The flow of gameplay is: Boot the machine, which plays the introduction sound clip ‘Insert coins’ by pressing the Coin button. This is announced audibly. Choose the number of players, 1-4, using the Add Player button. Press the Start button, wait for the ball to drop into place, then launch it. Use the flippers to stop it from going into the gutter (if you can). The game will run until each player loses three balls. On Game Over, the player scores are displayed and the system returns to the idle state. 📍 📍 📍 📍 📍 Changing the sounds We have used license-free sound clips as part of the game. These can be changed reasonably simply, but you will need to install the compiler and siliconchip.com.au Pinball Machine Kits Control Board (SC7659, $150) includes the PCB and all non-optional onboard parts Power Supply (SC7680, $50) includes the PCB and all onboard parts Cable & Connector Set (SC7681, $65) includes 17 10-pin box headers, 34 10-pin IDC connectors, 10m of 10-way ribbon cable, 30 2-way pluggable terminal blocks and 20 2-way polarised headers. build new sounds into the application. In the “Sounds” folder (in the download package, under Visual Studio files), you will find the WAV files we used for our sounds, as well as many “.h” files, which we need to copy into the C source folder. There is also a utility called “main.exe” that runs on a PC. This converts a 44.1kHz stereo WAV file into an 8-bit, 11kHz mono header file that you simply copy into the source folder. The syntax for this program is: main.exe INFILE.wav OUTFILE.h This utility puts all the data into the header, including the length of the clip. It can’t be more than a few seconds long. You will need to copy the generated files into the source folder and rebuild the application. The sound files are all stored in the following header files. The names are hopefully self-explanatory: • Runway_1.h • Runway_2.h • Runway_3.h • Pattern_Sensor.h • Launch_Sensor.h • Tunnel_Sensor.h • Bumper_1.h • Bumper_2.h • Bumper_3.h • Kicker_1.h • Kicker_2.h • Targets.h • Start_Runway_Sensor.h • Flipper.h • Coin.h • Player.h • Launch_Are_You_Ready.h • Credit_Needed.h • Player_1_up.h • Player_2_up.h • Player_3_up.h • Player_4_up.h • Ooooh.h • Game_Over.h Changing the software The rest of the source code is also in the Visual Studio folder that’s part Australia's electronics magazine of the download package. We hope it is reasonably self-explanatory. Key aspects of its operation were described in the first article in this series, including a state machine diagram. The state machine calls quite simple functions that update things like the current player number, score and such. The RunGame state is critical in that it repeatedly calls five main functions: 01 Check_Inputs() reads the 32 serial inputs and when they change between calls, triggers either light updates, power updates or game parameters like BallLost. 02 L i g h t s _ U p d a t e ( ) r u n s a sequencer for light patterns. The software is capable of generating multiple complex light patterns and sequences; our example program keeps this simple. You could change this significantly. 03 Power_Update() drives the output Mosfets. There are several defined variables for the on and off times, with the ability to sequence these. Again, our example keeps this simple. 04 set_score_display() updates the score display. 05 set_player_display() updates the player display and moves on to the next player. Conclusion This is a monster project; one of the largest ever presented in this magazine. We hope that if you take it on, you have a lot of fun and make a pinball machine that’s a blast to play. Please send us photos and videos of the finished product! Given its scope, and despite the extensive instructions presented over the last five issues, we wouldn’t be surprised if constructors occasionally need to ask questions. Please email us in that case, via the general Silicon Chip email address, and we’ll do our best to get back to you with a useful answer by the next business day (if SC not sooner). October 2026  81 SERVICEMAN’S LOG ELSEC 764 UV Monitor Repair A friend recently handed me a small handheld humidity, temperature and light meter and asked if I could figure out why it wasn’t working. These meters are typically used in art galleries and museums to monitor environmental conditions, ensuring the best possible conditions for exhibited items. The meter is branded ELSEC model 764 UV + Monitor; it appeared to be a nicely made instrument from the UK and in relatively good external condition. However, on opening the battery compartment, I found the normal 2×AA alkaline batteries were absent and that there had been a fair amount of battery leakage at some stage. I set about cleaning up the terminals and inserting two new cells. The euphoria of having solved a relatively easy problem was short-lived, however. The LCD on the meter sprang to life for a second or so, but then immediately went blank. This repeated over and over every few seconds. The information being displayed on the screen in the short time the display was on gave me some confidence that the microprocessor and sensor circuitry were operational, so it was time to take the back off the meter and explore a bit further. On exposing the main PCB, I found that the alkaline battery paste had spread down one side of the board and engulfed a number of SMDs. I used isopropanol on a cotton bud to carefully clean up the dried paste as best as I could, then used a contact cleaner spray to finish up. After re-inserting the batteries, I was happy to see that the meter’s display was now on and displaying believable numbers for temperature, humidity, UV and light levels. Problem solved, I thought. The meter has a clock function that allows it to display the time and date of minimum and maximum measurement excursions. This is very handy for tracking longer-term environmental variations. For example, you can leave the meter running all night in the gallery and then look to see if there were any out-of-bounds measurements during the night that need further investigation. Perhaps the gallery’s air conditioning system had a hiccup at 4am for some reason. The meter’s time and date are entered using the meter’s front keypad, following the steps of a clock setting function in the main menu screen. Unfortunately, the clock did not begin to advance after being set via the menu. On closer inspection, three of the SMDs affected by the battery paste were a Philips I2C 8583T real-time clock (RTC) chip, an adjoining 32.768kHz quartz crystal oscillator and a very small crystal loading capacitor. Although the meter was allowing me to enter new values for date and time, it appeared that the RTC was not subsequently ‘running’. Under 12× magnification of the chip and crystal, I could see the tracks running between them disappeared under both devices. I could also see what looked like more 82 Silicon Chip solidified battery paste around the bodies of the crystal, the RTC chip and the PCB. I didn’t relish the idea of removing the crystal or RTC from the PCB, so I gently poked around the edges with a fine-gauge stainless steel wire and dislodged a bit more of the paste, especially around the RTC oscillator pins. After another spray with contact cleaner and powering up the meter again, the clock was now advancing. I left the unit running for a few hours and again checked to see if things were OK. The clock had lost a significant amount of time, so the oscillator circuit was still being affected, probably by battery paste lurking out of sight under the RTC chip and/or crystal. Alkaline battery paste is, unsurprisingly, chemically alkaline and thus both reactive (corrosive) and conductive. As a last resort prior to physically removing the chip and crystal, I thought I’d try to dissolve any hidden paste using a mild solution of acidic white vinegar. I shielded adjoining parts of the PCB with soft tissue and applied a few drops of white vinegar to the top row of pins on the RTC chip and crystal while holding the PCB vertically. I could see the vinegar emerging from the lower underside of the RTC chip and crystal, so it was obviously making its way under both devices. I repeated this a couple of times while cleaning it with contact spray in between. After a couple of days now, the RTC is keeping good time, and the meter appears to be working as it should. I was able to compare the meter’s readings with another more modern and more recently calibrated ELSEC 765 meter. All the measurements, including humidity, were almost identical after having sat together for an hour or so. Australia's electronics magazine siliconchip.com.au From the default clock settings at power-up, and from what I can glean from the internet, the meter was made circa 2001 and now, hopefully, will provide a few more years of productive service. Best of all, from my perspective at least, is that a nicely crafted and not inexpensive professional instrument was spared from today’s scrap heap. David Worboys, Baulkham Hills, NSW. Rescuing a muddy Toshiba C665 laptop My son came home from town and presented me with two muddy laptops that he’d picked up at the tip shop for $2. The first one was an HP that was wrecked and covered in mud; it was too bad to save. The second was a Toshiba C665 that appeared to be in good condition, apart from all the mud. It was missing the hard drive, RAM and their covers, but it was otherwise complete. I looked inside the back and it looked clean and dry, so I fitted a RAM module, plugged in a charger, held down the F2 key and pressed the power button. The laptop switched on, and the BIOS screen opened. I could see that the screen had water in it and would need to be replaced. I pressed the right arrow key but it did not work. Some other keys also did not work, so it meant that the keyboard also had water in it and it would need to be replaced as well. But the main thing was that the shell was good and the motherboard worked; everything else that was faulty could be replaced. Now to dismantle it. I removed the keyboard and I could see the CMOS battery (CR2032 cell) there, so if it had just needed the cell replaced, that would have been easy. I removed all the screws on the bottom, then split the top and bottom shells apart. I removed the lid and put it aside, then took out the motherboard, as I wanted to check the heatsink and fan, and clean them. The fins on the heatsink were pretty clogged and the fan was caked in dust. I removed the heatsink from the motherboard, cleaned the fins and cleaned off the old heatsink compound. Then I applied new heatsink compound, refitted the heatsink and cleaned the fan. After that, I cleaned the inside of the bottom shell to remove the dust and mud. Next, I refitted the motherboard and CPU fan, then turned my attention to the lid. I removed the four screws from the corners of the lid, pulled off the front screen surround and removed the last two screws. That got the screen loose. I unplugged the connector on the back and removed the two hinges. It was the standard 40-pin connection that many screens use. I’d recently wrecked a non-working HP Pavilion G6 laptop that had the same screen as this Toshiba C665, so I connected the screen and set things up for a test before I started the reassembly process. I used a USB keyboard so that I could go to the BIOS setup screen and check that the replacement screen was good and free of defects. It’s always a good idea to test any replacement parts with the laptop partly assembled. I always do this whenever I upgrade the CPU as well. The screen was good, so I put the laptop back together, replacing the CR2032 cell with a new one as I did. I got a matched pair of two 2GB PC3 RAM modules and fitted them. I had a 320GB hard drive I could install, but I needed siliconchip.com.au Items Covered This Month • A leaky ELSEC UV monitor • Plus a muddy Toshiba laptop • A signal analyser and smoking transformer • Repairing a Sanwa multimeter • A simple fix for a DigiTech radio • Pfaff sewing machine repair Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz Cartoonist – Louis Decrevel Website: loueee.com A close-up shot of the ELSEC 764 UV monitor’s PCB, showing the SMD ICs that were most affected by battery leakage runoff. Australia's electronics magazine October 2026  83 to find a hard drive bracket. I searched in my box of hard drive brackets, found a suitable one and used it to install the drive. Now I needed a RAM cover and a hard drive cover. I checked my box of covers, hoping that I had suitable ones. I’ve wrecked a lot of laptops over time, and I keep any parts that might be useful. When I was nearly at the bottom of the box, I found a RAM cover, then shortly afterwards, I found a usable hard drive cover. Next, I got out my box of salvaged keyboards, hoping that I could find a good keyboard to replace the faulty one. It didn’t take long to find the right keyboard, which I connected, then I sat it in place to test it before it was finally installed. Now it was time to install Linux. I hadn’t previously installed Debian on a laptop, as I had been using lighter versions on the old laptops that I’d been working on. This laptop was newer, so I thought it would be adequate to run Debian. I downloaded Debian with the KDE Plasma Desktop and burned it to a single-layer DVD. I booted from the DVD and installed Debian. Using Mousepad, a simple text editor similar to Notepad, I tested the keyboard and all the keys worked, so I then reinstalled the top strip. I found that Debian was a bit slow with the i3 processor. I checked the RAM usage and it was only using 2.2GB of RAM out of 4GB for basic tasks, but 8GB would be better for more intensive use. At this stage, I discovered that the battery was not charging, so I checked my box of salvaged batteries. I had two, but one was faulty and the laptop wouldn’t even boot with it in place. The other only held a small amount of charge and it would not charge above 0%, but it would run the laptop long enough to unplug the charger for a few seconds. This was an interesting exercise in saving a piece of junk and turning it into a useful laptop once again. The total cost was under $10, including the $1 my son paid for the laptop itself. I may purchase a new battery in the future, but they are around $40. Maybe a good one will show up in a dead laptop at some point. Bruce Pierson, Dundathu, Qld. Recently, I switched it on and shortly later noticed a tiny wisp of smoke starting to emerge from the ventilation holes! I freaked out and immediately pulled out the IEC connector from the mains, even though the display looked perfect. I thought it must have been burning up in the region of the IEC mains socket. This was a problem I had come across previously in an Agilent 3458A multimeter. In that case, the capacitors and inductors that make up the mains filter in the socket burnt up. The filter box contained cooling oil, which leaked out and allowed the device to overheat and smoke up the whole room! With that instrument, there was no part number listed for the filter assembly, so I replaced it with a Jaycar MS4003 and the instrument worked fine. Back to the 35670A; it is a very depressing moment when smoke appears from an instrument worth thousands of dollars, so I put it away for a later repair. The day arrived; it was time to disassemble the device to confirm that the IEC mains filter was faulty. Four Allen-head machine screws on the rear released the cover to expose the internals. I undid a few more screws, then was able to extract the switch-mode power supply module. I removed the multi-pin connector and placed the power supply on the bench for closer inspection. I held the supply horizontally the whole time because I did not want to have any oil spill all over the works. The smoking analyser This Agilent 35670a dynamic signal analyser is identical to the instrument I reviewed in the June 2012 issue (siliconchip.au/Article/652). I often use it for setting up microphones for testing loudspeakers, infrasound detectors and many other projects. It can analyse audio signals from 290mHz to 102kHz, including frequency response and distortion measurements, but I don’t use it every day. 84 Silicon Chip The very muddy Toshiba C665 laptop that Bruce Pierson needed to clean and refurbish. Australia's electronics magazine siliconchip.com.au The power supply module (left) for Allan Linton-Smith’s Agilent 35670a dynamic signal analyser (right). The device had smoke coming out of it when turned on, which ended up being caused by the floppy drive connector. This SMPS was a separate box totally enclosed by a cage, which I partly removed to inspect the components. The IEC filter looked perfect and there was not a trace of oil... so where had the smoke come from? I put the power supply back in its place, but left the cage open. I switched the instrument back on and watched with a torch to see where the smoke was coming from. It came from a switching transformer – making it seem like it would be an expensive repair! I searched online and found a power supply from a Singapore-­based dealer I know, but it was very different, so I went back online to look for used 35670As. Just about all of those available either had no power supply or were sold as “not working – for parts only”. Possibly because of the same fault. The repair manual refers to the fact that there could be an overload downstream of the power supply, so I removed the connector and then switched it on as before. Bingo – no smoke! All I had to do now to fix it was to work out which module had a problem. I removed the power supply connectors from each module one by one, switching it on at each step to observe if some smoke appeared. I was not too confident that I could disable each module because most of the connectors were hidden amongst a stack of three large circuit boards. On the top of the instrument, exterior to the main circuit boards, there is a floppy drive with a multipin connector that was easily disconnected, so I began there. I switched on the power and waited for a minute. There was absolutely no smoke. What luck! The floppy drive must have jammed and put an enormous load on the power supply feeding it. I left it to soak for a couple of hours, but everything remained normal. siliconchip.com.au I use the floppy drive to save configurations, to avoid the many button presses that would be required to set the instrument up from scratch each time I want to make a measurement. The floppy drive jammed and refused to eject the disk some months ago, so on a subsequent start-up, the electric motor must have been acting like a short circuit, overheating the power supply. Because the power was shut off quickly, the 800414B transformer (shown photographed at upper left) seems to have survived, but a replacement is on my wish list. Fortunately, I had already ordered a brand-new floppy drive, which I will use to replace the damaged one. So it looks like in this case, a little smoking has not resulted in any fatal health problems. Allan Linton-Smith, Turramurra, NSW. Sanwa U-50 DN multimeter repair Back in 1972, I bought a Sanwa U-50 DN multimeter that served me well for over 50 years. Its use declined slightly with the arrival of digital meters, but I always found the old analog meter to have its place in peaking adjustments and monitoring pulse-width modulated signals. Some months back, the old meter developed a loose-­ feeling selector switch and, upon opening the case, I found a small steel ball (of the sort found in ball bearings) rolling around freely. What had happened over the years is that the hole in the spring holding the ball against the detent had worn larger and allowed the ball to escape. The instrument was constructed with the point-to-point wiring scheme used in vintage radios, making it extremely difficult to access anything near the selector switch. I decided that one ball was enough for normal use and simply reassembled the meter in its case. A week later, the other detent ball dropped out the same way! I checked the internet for balls of a slightly bigger diameter, but the next size up was too large. Not to be thwarted, I turned a scrap of nylon rod to form a hemisphere on one Australia's electronics magazine October 2026  85 end, with a short stub and a retaining ring on the other end. This took quite some time to fit due to the poor access to the switch, but I finally got it in. The meter worked perfectly, but several weeks later, I discovered that the AC volts range no longer worked. This range was rarely used, so it may have escaped my attention for quite some time. Opening up the meter again, I found a tiny copper-oxide rectifier that had clearly gone short circuit and was almost certainly not available after so long. I mentioned this to a dear friend of mine who kindly sent me a selection of germanium diodes and transistors to try. A pair of OA5s actually worked extremely well and did not visibly alter the calibration when compared to a digital meter. A month or so later, the meter stopped working on all ranges. I first thought the meter movement had gone open circuit. Applying a few tens of microamperes directly to the movement resulted in a significant deflection, so it looked like the fault should be repairable. Examining the works showed that the selector arm was not lined up with the contacts; in fact, it was halfway between the contacts! The whole switch assembly was quite loose and held in place by only the wiring. It took quite some time to locate a couple of screws that secured the switch assembly to the case because the heads of the screws were largely hidden under the closely packed resistors. With the selector arm correctly positioned, these screws were tightened, but still no meter movement. Tracing out the circuit showed three resistors, one of which might be open circuit, but each tested extremely close to the marked value. Every continuity test failed to reveal the problem, but finally, after turning the meter over many times, I saw a momentary near-full-scale deflection on the Ohms range which, at that moment, had a short applied. I had previously tugged at every solder joint without finding any problems, but there had to be some intermittent connection somewhere. It turned out to be the solder joint on the negative input. A glob of solder had somehow solidified into a tiny hook under the connection lug. It looked like a perfect solder joint from the top, and it resisted pulling, so had escaped further scrutiny. Both the lug and the wire were well-tinned, so it only took a brief touch with a hot iron to finally make a firm connection. Net cost: several days’ labour. Graham Lill, Lindisfarne, Tas. DigiTech DAB+ radio repair Sometimes the cause of a fault can be puzzling, but trivial and obvious in retrospect. A vanishing breed of hifi buffs still goes for ‘component audio’, made up of amplifiers, tuners, CD players, turntables and even preamplifiers. In this case, the offending item was a combined FM/DAB+ radio tuner made by DigiTech (Model AR1753). The problem was that the on/off switch no longer responded to pressure. The switch was mounted on a small circuit board attached to the front panel by four small plastic columns. My plan was to push aside the little projections from the columns and prise off the board, desolder and replace the switch, then replace the board. However, on opening the radio, it became apparent that two of the tabs were already disengaged from the board, such that the push button on the front panel (arrowed in the photo) could no longer reach the switch on the board. Snapping both tabs back in place was all that was needed to restore the switch action. In the photograph, I have restored the left-hand tab to its correct position but kept the right-hand tab as I found it. I suspect that this type of problem is not rare. I surmise that many users apply excessive pressure to pushbuttons. How many switches have been replaced when the problem was mechanical and not electrical? James Goding, Princes Hill, Vic. Pfaff 7550 sewing machine repair This fault is something I have never encountered before or since on any equipment. The story starts over 25 years ago. Sewing is a very serious hobby for my wife; she loved her all-electronic 7550 machine, but she wanted to upgrade to the later 7570 model because it had extra features. A friend asked if she could buy the old machine, paying it off monthly; she got it for a good price. A few years later, she moved to Queensland, and some years later, we visited her. My wife asked if she was still doing much sewing, and she said sadly she was back on her mechanical machine – the Pfaff was consigned to the garage. It had developed an intermittent fault where the The PCB shown here just needed to be pushed further into the locking tabs so that the pushbutton (marked with a white arrow) can properly contact the board. Servicing Stories Wanted Do you have any good servicing stories that you would like to share in The Serviceman column in SILICON CHIP? If so, why not send those stories in to us? It doesn’t matter what the story is about as long as it’s in some way related to the electronics or electrical industries, to computers or even to cars and similar. We pay for all contributions published but please note that your material must be original. Send your contribution by email to: editor<at>siliconchip.com.au Please be sure to include your full name and address details. 86 Silicon Chip Australia's electronics magazine siliconchip.com.au stitching became erratic and slow, eventually coming to a halt with garbled images on the display. The fault could develop after a few minutes, or it could go for more than half an hour. She got three separate repair quotes, all around the $1000 mark (I think one was about $1400) – quite a lot for the time. She couldn’t afford the repairs, all involving main board replacement. We felt a bit obligated, saddling her with a dud, so I said I would take it home and do my best – no guarantees. I knew nothing about sewing machines and would be chasing an intermittent fault without a schematic, but still, it’s just electronics. How hard could it be (famous last words)? I decided to allocate a couple of hours each day to familiarising myself with the board (easily removed through the base), eyeballing it for anything suspicious, looking for bulging caps or discolouration. I checked the voltages, which turned out to be rock solid with no ripple, even when the fault manifested itself – so the power supply was eliminated as a source of the fault. It looked all the world like a heat-related problem, but nothing looked, felt or smelt like it was under any heat stress. I even replaced some electrolytic capacitors and a transistor array, more out of hope than conviction. I got all excited when it went for more than half an hour, but no, the fault returned. I had managed to ascertain that the heart of the system was an Intel processor, but the real-world interface (controlling stepping motors, the display, keyboard etc) was through a large ASIC chip. It looked like, and probably was, a dedicated processor. Since I was getting nowhere with a meter, I decided to check around all the terminals of the ASIC while it was working and see if I could spot anything different when it failed. The chip ran on an internal clock that was presented at one of the terminals. It produced a nice square wave, but I noticed that the negative part of the signal was a little high (about 1V). Still, I didn’t place much significance on it at the time. However, when the fault started manifesting, the clock signal’s negative excursion was now above 2V and slowly rising until everything stopped. I didn’t record any notes at the time, so I can’t recall how high the voltage drifted. Now I was faced with a dilemma. Even in the unlikely event that I could source such a unique component, I would almost certainly destroy the board trying to replace it. Why not try a Hail Mary fix? I ruled out a resistor to ground (it might ruin a high-­ impedance signal). I decided on a low-value ceramic disc capacitor to ground (I can’t remember the value now) and it worked! The signal’s negative extent remained at about 0.5V with no drift. I put it back together and powered it up for two weeks straight, and asked my wife to test it every day, then shipped it off to Queensland. Our friend was recently visiting, and she said it has never missed a beat since. I hadn’t given much thought to it since the fix, but then I read the remarks of one of your contributors in the July 2023 Serviceman’s Log column that a number of people were having main board problems. I would be interested to know if any of your other readers have had a similar problem, or if we just got one unlucky dud. SC Frank Murray, Downer, ACT. siliconchip.com.au Australia's electronics magazine October 2026  87 SILICON CHIP .com.au/shop ONLINESHOP HOW TO ORDER INTERNET (24/7) PAYPAL (24/7) eMAIL (24/7) MAIL (24/7) PHONE – (9-5:00 AET, Mon-Fri) siliconchip.com.au/Shop silicon<at>siliconchip.com.au silicon<at>siliconchip.com.au PO Box 194, MATRAVILLE, NSW 2036 (02) 9939 3295, +612 for international You can also pay by cheque/money order (Orders by mail only) or bank transfer. Make cheques payable to Silicon Chip. 10/26 YES! You can also order or renew your Silicon Chip subscription via any of these methods as well! The best benefit, apart from the magazine? Subscribers get a 10% discount on all orders for parts. PRE-PROGRAMMED MICROS For a complete list, go to siliconchip.com.au/Shop/9 $10 MICROS $15 MICROS ATtiny85-20PU Graphing Thermometer (Mar26), Simple LC Meter (May26) Simple USB Power Monitor (Jun26), Transceiver Test Set (Aug26) ATmega328PB-AU Low-Power FM Transmitter (Sep26) PIC12F617-I/P Active Mains Soft Starter (Feb23), Model Railway Uncoupler (Jul23) Battery-Powered Model Railway Transmitter (Jan25) PIC16F1455-I/P Battery-Powered Model Railway TH Receiver (Jan25) Dual Train Controller (Transmitter / TH Receiver, Oct25) PIC16F1455-I/SL Battery-Powered Model Railway SMD Receiver (Jan25) USB Programmable Frequency Divider (Feb25) Dual Train Controller (SMD Receiver, Oct25) PIC16LF1455-I/P New GPS-Synchronised Analog Clock (Sep22) PIC16F1459-I/P Mains Power-Up Sequencer (Feb24 | repurposed firmware Jul24) 8CH Learning IR Remote (Oct24), Heat Transfer Controller (Aug25) Vacuum Controller (Oct25), Adjustable Ultrasonic Cleaner (Jul26) PIC16F15214-I/SN Silicon Chirp Cricket (Apr23), Mic The Mouse (Aug25) PIC16F15214-I/P Filament Dryer (Oct24), Tool Safety Timer (May25) PIC16F15224-I/SL Multi-Channel Volume Control (OLED Module; Dec23) NFC IR Keyfob Transmitter (Feb25), Rotating Light (Apr25) PIC16F18115-I/SN Model Railway Destination Display (Aug26) Mighty USB-C Bench PSU (Oct26) PIC16F18126-I/SL RGB LED Star (Dec25), DCC/DC Stepper Motor Driver (Apr26) μDCC Decoder (May26; bell [G] or whistle [W]) PIC16F18146-I/SO Versatile Battery Checker (May25), RGB LED ‘Analog’ Clock (May25) USB-C Power Monitor (Aug25), DCC Remote Controller (Feb26) DCC Booster & Reverse Loop Controller (Mar26) DCC Accessory Decoder (Snap / Servo-type, Jul26) Mighty USB-C Bench PSU (Oct26) STM32G030K6T6 Variable Speed Drive Mk2 (Nov24) PIC16F1847-I/P PIC16F18877-I/PT Digital Capacitance Meter (Jan25) Dual-Channel Breadboard PSU Display Adaptor (Dec22) Wideband Fuel Mixture Display (WFMD; Apr23) PIC16F88-I/P Battery Charge Controller (Jun22), Railway Semaphore (Apr22) PIC24FJ256GA702-I/SS Ohmmeter (Aug22), Advanced SMD Test Tweezers (Feb23) ESR Test Tweezers (Jun24), Human Comfort Indicator (Jun26) PIC32MX170F256D-501P/T 44-pin Micromite Mk2 (Aug14), 4DoF Simulation Seat (Sep19) PIC32MX170F256B-50I/SP Micromite LCD BackPack V1-V3 (Feb16 / May17 / Aug19) Advanced GPS Computer (Jun21), Touchscreen Digital Preamp (Sep21) PIC32MX170F256B-I/SO Battery Multi Logger (Feb21), Battery Manager BackPack (Aug21) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) STM32L031F6P6 SmartProbe (Jul25) $20 MICROS ATmega32U4 ATmega644PA-AU PIC32MK0128MCA048 PIC32MX270F256D-50I/PT Wii Nunchuk RGB Light Driver (Mar24) AM-FM DDS Signal Generator (May22) Power LCR Meter (Mar25) Digital Preamplifier (Oct25) $25 MICROS PIC32MX170F256B-50I/SO + PIC16F1455-I/SL Micromite Explore-40 (SC5157, Oct24) PIC32MX470F512H-120/PT Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) PIC32MX470F512L-120/PT Micromite Explore 100 (Sep16) $30 MICROS PIC32MX695F512H-80I/PT Touchscreen Audio Recorder (Jun14) PIC32MZ2048EFH064-I/PT DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) DIY Reflow Oven Controller (Apr20), Dual Hybrid Supply (Feb22) KITS, SPECIALISED COMPONENTS ETC AUDIO SPOT FREQUENCY TEST GENERATOR (OCT 26) MIGHTY USB-C BENCH PSU (SC7739) (OCT 26) - 0.96in OLED display module, white (SC6936) or cyan (SC6176) - PCM5102 DAC module (SC7749) - NJM5532D ($3.50, SC7695) or NJM5532DD ($5.00, SC7694) dual op amp Kit: an almost complete kit which includes the case, PCBs, USB-PPS module and all onboard parts (see p33, Oct26) - pre-assembled USB-C PPS control module (SC7740) - 0.91in OLED screen (SC7484) SEMICONDUCTOR ANALYSER (SC7725) $10.00 $10.00 $95.00 $25.00 $7.50 (SEP 26) Kit: includes an assembled PCB with the top-side components already fitted, plus all other non-optional parts except for the case, battery & label (see p32, Sep26) $95.00 - Hammond 1593XBK plastic case (SC7732) $17.50 LOW-POWER FM TRANSMITTER - Elechouse FM transmitter module (SC7712) - 0.96in OLED display module, white (SC6936) or cyan (SC6176) - ND0205MA 3V-to-5V DC step-up converter module (SC7713) (SEP 26) BATTERY BACKPACK KIT (SC7707) (SEP 26) MODEL RAILWAY DESTINATION DISPLAY (SC7697) (AUG 26) Kit: includes all the parts except for a Li-ion cell (see p82, Sep26) Kit: includes all parts, except for the OLED screen (see p54, Aug26) - 0.32in white OLED screen (SC7698) - 0.50in white OLED screen (SC7699) DCC ACCESSORY DECODERS (JUL 26) I2C CONTROLLER COMPLETE KIT (SC7690) (JUL 26) Snap-type (SC7685): includes the PCB and all non-optional onboard parts Servo-type (SC7686): includes the PCB and all non-optional onboard parts Includes the PCB and all onboard parts (see p83, Jul26) HUMAN COMFORT INDICATOR (SC7646) (JUN 26) Kit: includes all parts, except the case and battery (see p49, Jun26) - white 3D-printed case: portrait (SC7453) or landscape (SC7684) version - 3.3V GY-BME280 module (SC5482) $10.00 $10.00 $5.00 $25.00 $22.50 $5.00 $6.50 $40.00 $40.00 $30.00 $60.00 $12.50 $10.00 siliconchip.com.au/Shop/ PINBALL MACHINE KITS (JUN 26) SIMPLE USB POWER MONITOR (SC7683) (JUN 26) SIMPLE LC METER COMPLETE KIT (SC7657) (MAY 26) μDCC DECODER KIT (SC7617) (MAY 26) POWER AMPLIFIER CLIPPING INDICATOR (SC7649) (MAY 26) STEPPER MOTOR DRIVER KIT (SC7601) (APR 26) CALLIOPE AMPLIFIER PARTS (SC6021) (APR 26) DCC BOOSTER / REVERSE LOOP CONTROLLER KIT (SC7579) (MAR 26) Control Board (SC7659): includes the PCB and all non-optional onboard parts $150.00 Power Supply (SC7680): includes the PCB and all onboard parts $50.00 Cable & Connector Set (SC7681): includes 17 10-pin box headers, 34 10-pin IDC connectors, 10m of 10-way ribbon cable, 30 2-way pluggable terminal blocks and 20 2-way polarised headers $65.00 Includes the PCB and all onboard parts (see p63, Jun26) - 0.96in OLED display module, white (SC6936) or cyan (SC6176) Includes all the parts and the 3D-printed enclosure (see p67, May26) Includes all the parts and the optional piezo (wire not included). Specify if you want a bell or whistle sound for the microcontroller (see p88, May26) $50.00 $10.00 $45.00 $25.00 Short-form kit: includes the PCB and all onboard parts, the case and power supply are not included (see p35, May26) $95.00 - pair of red & white PCB-mounting RCA sockets (SC2615) $4.00 Includes all required parts for DCC or DC mode (see p55, Apr26) Includes some of the harder-to-get transistors, resistors and a capacitor Includes all required parts, except for the Jiffy box, OLED screen (see below), power supply and front panel (see p58, Mar26) - 0.91-inch OLED screen (SC7484) DCC REMOTE CONTROLLER KIT (SC7552) (FEB 26) MAINS HUM NOTCH FILTER (SC7598) (FEB 26) $35.00 $15.00 $45.00 $7.50 Includes all required parts, except for the case and wire/cable (see p63, Feb26) $35.00 Includes everything except for the case and power supply (see p53, Feb26) *Prices valid for month of magazine issue only. All prices in Australian dollars and include GST where applicable. # Overseas? Place an order on our website for a quote. $50.00 PRINTED CIRCUIT BOARDS PRINTED CIRCUIT BOARD TO SUIT PROJECT MICROPHONE PREAMPLIFIER ↳ EMBEDDED VERSION LASER COMMUNICATOR TRANSMITTER ↳ RECEIVER PICO DIGITAL VIDEO TERMINAL ↳ FRONT PANEL FOR ALTRONICS H0190 (BLACK) ↳ FRONT PANEL FOR ALTRONICS H0191 (BLACK) ARDUINO FOR ARDUINIANS (PACK OF SIX PCBS) ↳ PROJECT 27 PCB SKILL TESTER 9000 PICO GAMER ESP32-CAM BACKPACK WIFI DDS FUNCTION GENERATOR 10MHz to 1MHz / 1Hz FREQUENCY DIVIDER (BLUE) FAN SPEED CONTROLLER MK2 ESR TEST TWEEZERS (SET OF FOUR, WHITE) DC SUPPLY PROTECTOR (ADJUSTABLE SMD) ↳ ADJUSTABLE THROUGH-HOLE ↳ FIXED THROUGH-HOLE USB-C SERIAL ADAPTOR (BLACK) AUTOMATIC LQ METER MAIN AUTOMATIC LQ METER FRONT PANEL (BLACK) 180-230V DC MOTOR SPEED CONTROLLER STYLOCLONE (CASE VERSION) ↳ STANDALONE VERSION DUAL MINI LED DICE (THROUGH-HOLE LEDs) ↳ SMD LEDs GUITAR PICKGUARD (FENDER JAZZ BASS) ↳ J&D T-STYLE BASS ↳ MUSIC MAN STINGRAY BASS ↳ FENDER TELECASTER COMPACT OLED CLOCK & TIMER USB MIXED-SIGNAL LOGIC ANALYSER (PicoMSA) DISCRETE IDEAL BRIDGE RECTIFIER (TH) ↳ SMD VERSION MICROMITE EXPLORE-40 (BLUE) PICO BACKPACK AUDIO BREAKOUT (with conns.) 8-CHANNEL LEARNING IR REMOTE (BLUE) 3D PRINTER FILAMENT DRYER DUAL-RAIL LOAD PROTECTOR VARIABLE SPEED DRIVE Mk2 (BLACK) FLEXIDICE (RED, PAIR OF PCBs) SURF SOUND SIMULATOR (BLUE) COMPACT HIFI HEADPHONE AMP (BLUE) CAPACITOR DISCHARGER PICO COMPUTER ↳ FRONT PANEL (BLACK) ↳ PWM AUDIO MODULE DIGITAL CAPACITANCE METER 5MHZ 40A CURRENT PROBE (BLACK) BATTERY MODEL RAILWAY TRANSMITTER ↳ THROUGH-HOLE (TH) RECEIVER ↳ SMD RECEIVER ↳ CHARGER USB PROGRAMMABLE FREQUENCY DIVIDER HIGH-BANDWIDTH DIFFERENTIAL PROBE NFC IR KEYFOB TRANSMITTER POWER LCR METER WAVEFORM GENERATOR PICO 2 AUDIO ANALYSER (BLACK) PICO/2/COMPUTER ↳ FRONT & REAR PANELS (BLACK) ROTATING LIGHT (BLACK) 433MHZ TRANSMITTER VERSATILE BATTERY CHECKER ↳ FRONT PANEL (BLACK, 0.8mm) TOOL SAFETY TIMER RGB LED ANALOG CLOCK (BLACK) USB POWER ADAPTOR (BLACK, 1mm) HWS SOLAR DIVERTER PCB & INSULATING PANELS SSB SHORTWAVE RECEIVER PCB SET ↳ FRONT PANEL (BLACK) 433MHz RECEIVER DATE FEB24 FEB24 MAR24 MAR24 MAR24 MAR24 MAR24 MAR24 MAR24 APR24 APR24 APR24 MAY24 MAY24 MAY24 JUN24 JUN24 JUN24 JUN24 JUN24 JUL24 JUL24 JUL24 AUG24 AUG24 AUG24 AUG24 SEP24 SEP24 SEP24 SEP24 SEP24 SEP24 SEP24 SEP24 OCT24 OCT24 OCT24 OCT24 OCT24 NOV24 NOV24 NOV24 DEC24 DEC24 DEC24 DEC24 DEC24 JAN25 JAN25 JAN25 JAN25 JAN25 JAN25 FEB25 FEB25 FEB25 MAR25 MAR25 MAR25 APR25 APR25 APR25 APR25 MAY25 MAY25 MAY25 MAY25 MAY25 JUN25 JUN25 JUN25 JUN25 For a complete list, go to siliconchip.com.au/Shop/8 PCB CODE Price 01110231 $7.50 01110232 $7.50 16102241 $5.00 16102242 $2.50 07112231 $5.00 07112232 $2.50 07112233 $2.50 SC6903 $20.00 SC6904 $7.50 08101241 $15.00 08104241 $10.00 07102241 $5.00 04104241 $10.00 04112231 $2.50 10104241 $5.00 SC6963 $10.00 08106241 $2.50 08106242 $2.50 08106243 $2.50 24106241 $2.50 CSE240203A $5.00 CSE240204A $5.00 11104241 $15.00 23106241 $10.00 23106242 $12.50 08103241 $2.50 08103242 $2.50 23109241 $10.00 23109242 $10.00 23109243 $10.00 23109244 $5.00 19101231 $5.00 04109241 $7.50 18108241 $5.00 18108242 $2.50 07106241 $2.50 07101222 $2.50 15108241 $7.50 28110241 $7.50 18109241 $5.00 11111241 $15.00 08107241/2 $5.00 01111241 $10.00 01103241 $7.50 9047-01 $5.00 07112234 $5.00 07112235 $2.50 07112238 $2.50 04111241 $5.00 9049-01 $5.00 09110241 $2.50 09110242 $2.50 09110243 $2.50 09110244 $2.50 04108241 $5.00 9015-D $5.00 15109231 $2.50 04103251 $10.00 04104251 $5.00 04107231 $5.00 07104251 $5.00 07104252/3 $10.00 09101251 $2.50 15103251 $2.50 11104251 $5.00 11104252 $7.50 10104251 $5.00 19101251 $15.00 18101251 $2.50 18110241 $20.00 CSE250202-3 $15.00 CSE250204 $7.50 15103252 $2.50 PRINTED CIRCUIT BOARD TO SUIT PROJECT SMARTPROBE ↳ SWD PROGRAMMING ADAPTOR DUCTED HEAT TRANSFER CONTROLLER ↳ TEMPERATURE SENSOR ADAPTOR ↳ CONTROL PANEL MIC THE MOUSE (PCB SET, WHITE) USB-C POWER MONITOR (PCB SET, INCLUDES FFC) HOME AUTOMATION SATELLITE PICKIT BASIC POWER BREAKOUT DUAL TRAIN CONTROLLER TRANSMITTER DIGITAL PREAMPLIFIER MAIN PCB (4 LAYERS) ↳ FRONT PANEL CONTROL ↳ POWER SUPPLY VACUUM CONTROLLER MAIN PCB ↳ BLAST GATE ADAPTOR POWER RAIL PROBE RGB LED STAR EARTH RADIO DCC DECODER DCC BASE STATION MAIN PCB ↳ FRONT PANEL REMOTE SPEAKER SWITCH ↳ CONTROL PANEL DCC REMOTE CONTROLLER MAINS HUM NOTCH FILTER MAINS LED INDICATOR DCC BOOSTER / REVERSE LOOP CONTROLLER ↳ FRONT PANEL SOLAR PANEL PROTECTOR (WHITE) GRAPHING THERMOMETER PICOSDR CONTROL PCB ↳ RF PCB ↳ FRONT PANEL (BLACK) DCC/DC STEPPER MOTOR DRIVER CALLIOPE AMPLIFIER MICROMITE AUDIO PLAYER ADD-ON ↳ ALL-IN-ONE μDCC DECODER SIMPLE LC METER WIFI ALARM MONITOR POWER AMPLIFIER CLIPPING INDICATOR PINBALL MACHINE CONTROL BOARD ↳ POWER SUPPLY ↳ PLAYER LED BOARD ↳ SCORE LED BOARD ↳ LED OUTPUT BOARD ↳ BUMPER LED BOARD ↳ CASCADE LED BOARD ↳ SWITCH INPUT BOARD ↳ GENERAL INPUT BOARD ↳ HIGH-CURRENT INTERFACE ↳ ROLLOVER INTERFACE ↳ BUMPER DRIVER SSB TRANSMITTER (MikeOne/Two/Three) SIMPLE USB POWER MONITOR HUMAN COMFORT INDICATOR ADJUSTABLE ULTRASONIC CLEANER MAIN PCB ↳ FRONT PANEL CONTROL PCB SNAP-TYPE DCC ACCESSORY DECODER ↳ SERVO-TYPE I2C CONTROLLER TRANSCEIVER TEST SET RF/AUDIO PCB ↳ CONTROL PCB MODEL RAILWAY DESTINATION DISPLAY ↳ FLEX ANTENNA PCB SEMICONDUCTOR ANALYSER LOW-POWER FM TRANSMITTER ↳ LID (BLACK, 0.8mm) BATTERY BACKPACK DATE JUL25 JUL25 AUG25 AUG25 AUG25 AUG25 AUG25 SEP25 SEP25 OCT25 OCT25 OCT25 OCT25 OCT25 OCT25 NOV25 DEC25 DEC25 DEC25 JAN26 JAN26 JAN26 JAN26 FEB26 FEB26 FEB26 MAR26 MAR26 MAR26 MAR26 APR26 APR26 APR26 APR26 APR26 APR26 APR26 MAY26 MAY26 MAY26 MAY26 JUN26 JUN26 JUN26 JUN26 JUN26 JUN26 JUN26 JUN26 JUN26 JUN26 JUN26 JUN26 JUN26 JUN26 JUN26 JUL26 JUL26 JUL26 JUL26 JUL26 AUG26 AUG26 AUG26 AUG26 SEP26 SEP26 SEP26 SEP26 PCB CODE P9054-04 P9045-A 17101251 17101252 17101253 SC7528 SC7527 15104251 18106251 09110245 01107251 01107252 01107253 10109251 10109252 P9058-1-C 16112251 06110251 09111241 09111243 09111244 01106251 01106252 09111245 01003261 10111251 09111248 09111249 17112251 04102261 CSE251101 CSE251102 CSE251103 09111242 01111212 01110251 01110252 09111247 04103261 01304261 01104261 08107261 08107262 08107263 08107264 08107265 08107266 08107267 08107268 08107269 08107260 08117261 08117262 06103261 04104261 21105261 04105261 04105262 09111254 09111255 09111256 06104261 06104262 09111252 06101233 P9062-1-C CSE260501C CSE260502 11105261 Price $5.00 $2.50 $10.00 $2.50 $2.50 $7.50 $7.50 $3.50 $2.00 $3.00 $30.00 $2.50 $7.50 $10.00 $2.50 $5.00 $12.50 $5.00 $2.50 $5.00 $5.00 $5.00 $2.50 $5.00 $7.50 $2.50 $5.00 $5.00 $7.50 $3.00 $5.00 $5.00 $7.50 $2.00 $5.00 $2.50 $5.00 $1.50 $2.50 $2.50 $15.00 $25.00 $7.50 $2.50 $5.00 $2.50 $5.00 $5.00 $2.50 $2.50 $2.50 $2.50 $5.00 $2.50 $5.00 $5.00 $7.50 $5.00 $3.00 $3.00 $3.00 $5.00 $5.00 $2.00 $2.00 $7.50 $5.00 $5.00 $3.00 MIGHTY USB-C BENCH PSU MAIN PCB ↳ FRONT PANEL AUDIO SPOT FREQUENCY TEST GENERATOR OCT26 OCT26 OCT26 04107261 04107264 04111261 $5.00 $5.00 $5.00 NEW PCBs We also sell the Silicon Chip PDFs on USB, RTV&H USB, Vintage Radio USB and more at siliconchip.com.au/Shop/3 Vintage Radio Restoring the Philco model 38-7 MW/SW radio from 1938 The Philco model 38-7 radio is one of the finest medium-wave and shortwave band domestic radio receivers to emerge from the USA before World War II. By Dr Hugo Holden T hese radios were shipped to many countries because they had an optional dual-voltage 110/220V power transformer. I acquired my radio in New Zealand during the early 1970s and restored it initially around 1976. I had some help at the time from John W. Stokes, the author of the famous book “70 Years of Radio Tubes and Valves”. John had an excellent radio repair store on Dominion Road in Auckland and helped me with the alignment and some of the repairs. At the time, he explained to me how the 6A8 pentagrid converter valve worked. I soaked up the information like a sponge, being an enthusiastic 18-year-old. John Stokes passed away in August 1999. I will never forget the way he helped me with radio repairs. This radio recently required more work to keep it running. The first restoration was just about 50 years ago now, and the radio is about 88 years old. It has six valves and covers the medium wave (MW) band of 5301720kHz, with a very wide range 90 Silicon Chip shortwave (SW) band specified as 5.718.2MHz but it can actually tune from 5.5MHz to 19.5MHz, as indicated on the dial. The cabinet is an attractive Art déco design, typical of the late 1930s. It has inlaid veneers but is not cluttered. However, from a user’s perspective, the most interesting aspects are the dial and the tuning arrangements. The tuning knob rotates around the outer dial’s perimeter and has a central shaft. The larger of the two knobs mounted on that central shaft and can be pushed inwards, slipping over the outer surface of the shaft. This engages the ridges on the dial glass’s brass retaining ring via a rubber ring on the rear of that larger knob. Rotating the larger knob then acts as a type of reduction gear for fine-tuning. The central shaft and the smaller knob on it can move in and out, providing additional functions. It can engage metal cones mounted on a rear vertical plate behind the dial drum that can be set to preset station positions to lock the variable capacitor’s position and hence the tuned station. This was called “Cone-­ Centric” tuning. This shaft also includes an electrical contact, which can mute the Photo 1: the dial is quite fancy. It’s hard to see here, but there’s a radial embossed pattern in the centre, from the spindle out to the barely visible dark ring that’s just visible inside the inner station labels. siliconchip.com.au audio between the selected cones and at different positions. If not using the cones, that feature is better disabled because if one is not expecting the audio muting, they can be caught out. The central shaft is attached to a diecast metal arm, which attaches to and rotates another shaft on the dial’s central axis that carries the dial pointer. This shaft also passes through the vertical plate carrying the cones and attaches via a flexible coupling to the input shaft and gears of the two-gang variable tuning capacitor. The extra machinery of that rotating arm and its physical mass is counter-­ balanced by a large mass on the central shaft. This imparts the tuning mechanism with a very nice feel in operation. Behind the dial is a closed, drumshaped chamber, painted white inside, into which the dial lamp shines. This lamp diffusely illuminates the dial material, for a welcoming orange glow. The dial is a good size at around 125mm in diameter. It has highly accurate calibration detail and more resembles the type of thing seen on a scientific instrument than any domestic radio dial from 1938. Up close, the dial’s plastic has an embossed surface with an elegant patterning effect. It is visible in Photo 1 but only just. Photo 2 shows the dial drum area and the adjustable cones on the vertical plate. In this case, the central shaft is not pushed in to engage a cone yet. The wire passing into the assembly detects the position of the shaft for muting. When the shaft engages a cone, a separate local mechanism in the rotating arm lifts a contact of a circular track so that the audio is always unmuted. Other features of the tuning mechanism include a variable capacitor with a spring-loaded twin-gear wheel arrangement to prevent backlash, and a special universal rubber coupling. This coupling recently required rebuilding. The laminated rubber discs had become warped under the force of the counter-balance’s mass, and the rubber had become stuck in a stiffened, deformed state. This resulted in a very irregular feel to the tuning mechanism. Also, since the first restoration, the variable capacitor’s rubber mounting feet had degraded. Back in the 1970s, with no parts available, I hand-­ fashioned these replacements from some 5mm-thick red rubber sheet siliconchip.com.au Photo 2: in this side view of the dial assembly, you can see the spring on the small shaft and the cones it engages when pressed to centre on a station. Photo 3: in this photo, the knob has been pressed in and it has engaged one of the cones. Photo 4: this view of the chassis includes the twin-gang variable capacitor and its somewhat unusual flexible coupling arrangement (after I had repaired it with new parts). The variable capacitor mounts and rubber coupling for the input shaft had hardened and were both replaced in this photo. using a scalpel. Over the last 50 years, this red rubber had hardened and cracked. Photo 4 shows an overview of the chassis. Earlier 1970s restoration The chassis underside held up very well over the years since the first restoration. At that time, I replaced all the original wax paper capacitors. The mica capacitors were and are still OK, even today. However, many mica parts become leaky by this age, Australia's electronics magazine and some types suffer from a form of silver migration disease. Back then, I also hollowed out the original wet electrolytic capacitor cans and placed modern electrolytic capacitors inside. I did that by machining a phenolic base and adding solder terminals taken from some 4mm panel banana plugs. The capacitor housings were then re-mounted using capacitor clamps, rather than the original screw and large nut arrangement that they once had. October 2026  91 Fig.1: the Philco model 38-7 radio circuit. It has six valves even though it’s a ‘five valve set’ because it uses an extra envelope for a particularly good delayed AGC implementation; that valve doesn’t improve the set’s sensitivity, unlike a six-valve set with an RF amplification stage. I also renewed the resistors then. Aside from the large wirewound 10kW part, I used modern (at the time) 1W resistors carefully spray-painted with the body-tip-spot colour code. I may have been the only person in the world back in the 1970s who was repainting resistors to make them look age-­ appropriate. I think this has become more of a fashion now with vintage radio and TV restorations. When John Stokes saw those repainted resistors back in the 1970s, he remarked that he could not see the point in doing that, but it made him smile nonetheless. The black rectangular box at upper left in Photo 5, where the mains wires terminate, contains two 15nF 92 Silicon Chip capacitors. These should always be replaced with what we now know as Y capacitors. In the 1930s, ‘Y capacitors’ with modern safety ratings did not exist. The designers simply used 1000V or 1500V rated parts to try to avoid failure. Note the unusual (for today) mains wire colours of red (Active), black (Neutral) & green (Earth). Those are not per today’s standards, but they were correct in the 1970s when I replaced the mains cord. At the time of the original restoration, I removed the valve socket rivets, IF transformers and upper chassis parts. The whole wiring assembly, largely complete, was then removed from the chassis. All the valve sockets Australia's electronics magazine are retained by screws and nuts now. Fortunately, Philco made good wafer sockets, so none required replacing. The chassis was re-plated in the 1970s. However, over the last 50 years or so, some fine pitting and corrosion on the top chassis surface has started to reappear. Electronic design The design here is outstanding, with a number of innovations. The circuit is shown in Fig.1. It uses a 6A8 pentagrid converter valve (Photo 6). The intermediate frequency (IF) amplifier valve is a 6K7, while the detector and AGC generator is a 6J5. The 6K5 audio preamplifier valve feeds a classic 6F6 3W Class-A siliconchip.com.au audio output stage. Finally, the 5Y4 rectifier furnishes the B+ supply. The valve lineup, aside from the 6J5, was very common in 1938. The 6K7 was a fairly standard IF valve used in multiple radios with very similar electrical specifications to the 6U7. These valves are ‘super control pentodes’, meaning that their gain can be well controlled, especially in an RF or IF stage, with the application of a negative AGC voltage. The 6J5 and 6K5 were also common general-utility triodes for detector and audio amplifier uses, as well as other applications. The 6A8 Pentagrid Converter had its origins in April 1933 when RCA released the 2A7, which is the same valve but with a different base and a lower heater voltage. The pentagrid converter valve in the early 1930s was a revolutionary method to combine a superhet radio’s local oscillator and mixer stage into one valve, while at the same time making the mixer amenable to variable mu (μ) for gain control by the AGC voltage. This meant that a very effective overall AGC could be created, with the same AGC voltage controlling both the converter and the IF amplification stages. The 6A8 is a single-cathode valve. All the grid elements are placed concentrically around the cathode, and the electron stream passes by all of them to the anode (plate). The first grid, closest to the cathode, acts as the grid for the oscillator circuit, while the second grid acts as the plate for the oscillator. The G2 grid is a pair of rod-like structures – see Fig.2. The trick to the design of the 6A8 is that G3 acts as a space-charge grid, or a virtual cathode, an effective electron source for G4. This fourth grid acts as the signal input grid, where the received radio station signal is injected from the tuned antenna circuit. The G4 connection is on the 6A8’s top cap. Generally, in most radios, the local oscillator runs above the received frequency by the intermediate frequency. For example, if the received frequency coming into G4 of the 6A8 is 1000kHz, the oscillator will be running at 1470kHz. When these two signals get multiplied by the 6A8, one of the signal components is the difference frequency at 470kHz. Everything but this component of the output is filtered out by the first IF transformer and then passed to the 6K7 IF valve for further amplification and filtering. Although the function of the 6A8 was designed to be multiplication, there will be some non-­linearity, which also aids its mixer function. Shortwave oscillator problems I found that the sensitivity of the radio dropped fairly significantly on the SW band above 12MHz. Some of this is expected because the performance of the 6A8 at the higher Photo 5 (left): the underside of the chassis is neat for a point-to-point wired set. The cotton wire insulation still appears to be in good shape nearly 100 years later! Photo 6 (right): these three versions of the 6A8 share the same base but have different envelope styles. From left-to-right: 6A8GT, metal 6A8 and a 6A8G. siliconchip.com.au Australia's electronics magazine October 2026  93 frequency end in known to be somewhat deficient. Later converter valves such as the 6K8 triode-hexode (released a little late for the 38-7) improved the high SW reception and AGC behaviour. Investigation revealed third harmonic content in the oscillator signal; eg, in the region of 16MHz, the spurious signal was at around 48MHz. This harmonic was very high in level, almost swamping the fundamental wave. It took me a while to discover that this was due to a resonance in the primary of the SW oscillator coil with the capacitance of the G2 grid of the 6A8. This was not a problem with the 6A8 itself, but more related to the proportions of the primary of the oscillator coil and the level of damping in the primary circuit. This was affected by the fact that the 4μF bypass capacitor (11) on the B+ supply is an electrolytic type and poor at bypassing high frequency RF. Bypassing that electrolytic with a 330nF film capacitor suppressed most of the 48MHz oscillation (Photo 7), but then, interestingly a high level fifth harmonic appeared, at around 80MHz. Unrelated to these problems, I also added a 27pF capacitor to trim the value of the fixed 250pF capacitor in the ceramic block (7B) as it was a little low. To damp the very high frequency resonances, I replaced the link wire between the oscillator coil primary and the 6A8 socket pin 6 (grid G2) with a 150W resistor – see Photo 8. This removed nearly all the harmonics and gave a clean oscillator fundamental over the whole tuning range on the Fig.2: the configuration of the 6A8 pentagrid converter valve. It works well, but because the two stages share an electron stream, there is some interaction between them, which can make tuning in to strong SW stations a bit fiddly. SW band, with no practical effect on the MW band. This improved the high-frequency shortwave reception. Probably all the 38-7 radios were affected by this. It wasn’t until I had a 100MHz-capable scope with a very low input capacitance ×100 probe (the Tektronix P6009 – only 2.5pF) that I was able to detect and remedy this problem. In general, it is fair to say that some higher-order harmonics in the local oscillator of a typical radio are not a problem, especially because in the G1 grid circuit, the resonance of the tuned circuit there dominates and a clean sinewave is nearly always seen at that location, even if the tickler winding shows some harmonics and some distortion. Mixer electron stream concern A quirk of the 6A8 is that the AGC control of its RF gain affects the frequency of the oscillator section. Ideally it would not, but it does. The effect of this is more noticeable on the high end of the SW band with a strong enough signal to get the AGC to shift from its normal inactive state of -2V to -6V or more. An increasingly negative AGC voltage increases the oscillator frequency. Since the oscillator part of the 6A8 and the mixer part of the valve depend on the same electron stream from the cathode, they interact. When a strong SW station is tuned in, with the oscillator initially running below the required value to tune in a station, a problem becomes evident on tuning the station. Say the station was on 16MHz, requiring an oscillator frequency of 16.470MHz, and the oscillator is sitting at around 16.300MHz and increasing as the user moves the tuning knob toward the station. As the signal is received and the AGC voltage becomes more negative, there is a rapid increase in the oscillator frequency and an avalanche Added bypass capacitor 150W resistor to replace wire link 27pF added to trimmer and fixed 250pF Photo 7: adding this 330nF capacitor fixed a stability problem at the upper end of the shortwave band that probably affected all of these sets. 94 Silicon Chip Photo 8: this added 150W damping resistor was also required to totally eliminate the HF instability. Australia's electronics magazine siliconchip.com.au Fig.3: RCA’s AN-87 document from 1938, showing how much lower the interaction between the two stages is in the 6K8 compared to the 6A8 due to the shared cathode being in the middle. increase in the negative AGC voltage. The oscillator frequency jumps up, often above 16.470MHz. Therefore, the station appears to abruptly jump into tune and overshoot, requiring extra fine-tuning effort. This undesirable effect is not too noticeable on the low SW band below 10MHz or the MW band at all, as the tuning is less critical for any rotational angle of the variable capacitor. On weak stations (most SW stations are in my locality), the effect is not evident. This effect is more significant with a pentagrid converter such as the 6A8, rather than a triode-hexode converter such as the 6K8 – see Fig.3. The 6A8’s large AGC-dependent frequency shift is because the AGC voltage has more of an effect on the transconductance of the oscillator siliconchip.com.au section as a consequence of the oscillator and mixer sections of the valve sharing the same electron stream. RCA chose to place the 6K8’s anodes on opposite sides of the same cathode, so each plate receives electrons from opposite sides of the cathode – see Figs.4 & 5. This keeps the electron streams separate. Another interesting feature of the 6K8 is that at high frequencies, its G3 input resistance is negative. This acts as a Q multiplier for the resonant circuit feeding it. This was discovered at RCA, where an improvement in selectivity and image rejection was noticed upon testing it. There are other mixer valves with higher conversion transconductances than the 6K8, including the Philips ECH35, introduced in 1939. It appears Australia's electronics magazine to be a further development of the British X41 converter, released in 1936. These valves have an internal architecture where the triode is physically separated from the hexode to reduce interactions between the two sections. Due to the superior performance of converter valves such as the 6K8, ECH35 and X41 compared to the 6A8, I considered fitting one to the Philco radio instead. I selected the ECH35 because it has a higher transconductance than the 6K8 and it can plug directly into the octal socket in place of the 6A8 without having to rewire the socket. However, because there was no pin 1 tag fitted in the socket (to Earth the conductive coating on the ECH35), I linked pins 1 & 8 (the cathode) on the valve base. October 2026  95 Scope 1: the 6J5 anode voltage with no antenna signal. No other significant changes were made except altering the wiring of one resistor (part 10 in Fig.1). I simply moved this 5kW resistor from the junction of part 12 and part 16 to the junction of part 16 and part 22. This was to reduce the anode voltage of the triode section of the ECH35 to remain within its maximum specification. I also shorted out the 22W cathode resistor as the ECH35 is designed to run with a grounded cathode to minimise triode/hexode interactions. I re-aligned the radio because the capacitances of the two converter valves are a little different. The oscillator behaved normally on both bands with the ECH35. On testing the radio, I found improved sensitivity and less noise. From the low MW band up to the 14MHz mark, the sensitivity had improved from 10μV to 5μV. The 5μV figure is almost starting to rival a set with an RF stage, which would have Scope 2: the 6J5 anode voltage with a 50μV RMS signal fed into the antenna. a sensitivity of around 2μV, although with less selectivity. The AGC operation on stronger signals was also improved, with less frequency pulling. Interestingly, the noise with the ECH35 has a different sound to the 6A8, with more low-frequency components. The 6A8 has a preponderance of high-frequency noise. This is likely due to the higher level of phase noise with the 6A8 compared to the ECH35 or 6K8. The sensitivity toward 19MHz improved to around 12μV, about twice as good as it was with the 6A8 at around 24μV in this part of the band. Therefore, I elected to leave the ECH35 in the radio, as the performance improvement was hard to ignore. Delayed AGC circuit with active clamp With the 6J5, the radio had one more valve than the typical five-valve radio. Often, five-valve radios used a 6Q7 or similar, which incorporated two diodes along with the audio amplifier triode. The valve count might have been a marketing feature, but the use of the 6J5 in this case is clever; the valve performs a useful function. To get the AGC to work well, this circuit deployed the 6J5 valve in an unconventional manner. The grid-cathode was used as the AM detector diode, while the anode was tied to a negative potential derived from the “Candohm” resistor (part 43 on the diagram). The Candohm resistor is a three-part wire-wound resistor from the power supply’s negative terminal (the transformer’s centre tap) to ground. A negative bias voltage is developed across it. This is to bias the AGC line, the anode of the 6J5, the grid of the 6K5 and the G1 grid of the 6F6 audio output valve. Fig.4: this shows how the 6K8’s cathode shields the oscillator’s G1 grid to minimise the effect of the AGC voltage on oscillator frequency. Fig.5: the physical configuration of the 6K8 converter valve. Compare this to the Fig.4 schematic. 96 Silicon Chip Australia's electronics magazine siliconchip.com.au Anode voltage 6J5 0V Av = -10V -20Vpp Scope 3: the 6J5 anode voltage with a 50mV RMS signal fed into the antenna. This is fixed bias, rather than having to rely on self-bias with cathode resistors or other bias methods. It is not until the peak positive going IF voltage, coupled by the 110pF capacitor (part 23 on the diagram) to the anode of the 6J5 exceeds the applied negative voltage value of about -2.5V that the 6J5 develops anode current on the IF carrier peaks. This solidly clamps the carrier peaks on the anode close to ground potential, as shown in Scopes 1-3. The initial negative bias on the anode of the 6J5 delays the development of increasing negative AGC voltage until the carrier voltage at the antenna input exceeds about 50μV. Below that, the AGC is kept inactive. As can be seen from Scope 3, the actively driven 6J5 makes for an excellent peak carrier clamp. Any increase in the IF carrier amplitude results in an increasing average Scope 4: the 6J5 anode voltage on a longer time scale, with an unmodulated signal producing a -10V AGC voltage. negative shift in the AGC voltage. Scope 4 shows the 6J5 anode voltage with an unmodulated 470kHz IF signal, coming out of the IF transformer at 20V peak-to-peak. When this signal is time-averaged by the 1MW resistor (part 15) and the 50nF AGC filter capacitor (part 3), this provides about -10V of AGC voltage. Scope 5 shows the situation with modulation added. This does not affect the average AGC voltage. This anode clamp circuit cannot be used as the radio’s detector because of the initial negative voltage applied to the anode, which causes it to stop its action if the voltage from the IF transformer is below about 2.5V peak. Stability problems and IF neutralisation Philco found that in some cases, there could be instability in the 6A8 converter stage of the original Scope 5: the 6J5 anode voltage on a longer time scale, with a modulated signal, still producing a -10V AGC voltage. Anode voltage 6J5 0V Av = -10V -20V siliconchip.com.au Australia's electronics magazine production models at the top end of the SW band. To ameliorate this, they added a 22W resistor between the 6A8’s cathode and ground. This resistor is present in nearly all under-chassis photos of the 38-7 I have seen, but is not on their original schematic. It is handy to have because it is a useful place to monitor the valve’s cathode current and also to detect the oscillator frequency without significantly pulling it. Philco produced very high-quality IF transformers, and the gain of their IF stages was relatively high. Instability could occasionally be a problem there, too. The fundamental problem of instability in an IF stage relates to the fact that the IF valve’s (or transistor’s) input and its output both have high-Q tuned circuits at the same operating frequency. Any electric, magnetic or capacitive interaction between the two resonant circuits results in energy transfer between them, so instability or oscillation can occur. All active amplifying devices have an output-to-input feedback capacitance. Early transistors with high feedback capacitances, in the order of 10pF, always required neutralisation to cancel this effect. Later transistors with feedback capacitances around 1pF or less seldom needed it in a 455kHz IF stage. A screened grid pentode, such as the 6K7, would seldom require neutralisation because the screen grid provides near-total anode to G1 isolation. Still, occasionally, even screened grid pentode IF stages can be unstable. October 2026  97 Close inspection of the 38-7’s schematic shows that there is an additional coil, not often seen, inside the first IF transformer. This is merely a few turns of insulated wire wrapped around the secondary coil, feeding the grid of the 6K7. It took many years and having a good oscilloscope, such as the Tektronix 464, until I was able to examine the effect of this small coil and observe the relative coil polarities, not shown on the schematic. The suppressor grid of the 6K7 that the small coil is connected to acts as a small coupling capacitor to the 6K7’s anode. It is actually a brilliant idea because its capacitance with respect to the anode is a highly controlled parameter due to the valve’s construction, rather than having to create a more temperamental small gimmick capacitance. The phase relationship of the small coil to the coil driving the grid of the 6K7 is such that the feedback provides a small degree of neutralisation to the 6K7 stage. Audio output stage The 6F6 audio output stage can provide 3W, and the sound is enhanced by the well-sized timber cabinet and 8-inch (203mm) electromagnetic speaker. Tone Control and the Fletcher-Munson effect The radio has a three-position tone switch, which is combined with the power switch. Stray hum injection can occur when the on/off switch is mounted on the rear of a volume control; this can be a real problem in some radios. It is much better where Philco put it. With this combined power-on/tone switch, the hum injected into the loudness tap via the 51kW resistor is heavily attenuated. Assuming there was a capacitance between the power and tone switch contacts as high a 60pF, the presence of the 6nF capacitor in two of the tone switch positions would attenuate the hum voltage by about 100:1. In one position, the 6nF capacitor is shorted out, eliminating hum injection by this route completely. The volume control has a loudness tap. This idea was invented in the 1930s to account for a property of human hearing known as 98 Silicon Chip the Fletcher-­ Munson effect. Harvey Fletcher and Wilden Munson published their paper on loudness curves in 1933, only five years before the Philco 38-7 radio was made. It is interesting how quickly this concept got into the electronics designs of the time. Later, more precise filters were added to audio systems with the loudness button. It is hard to determine who first modified the volume control potentiometer in this manner with the loudness tap. Both RCA and Philco were doing it in the late 1930s. In essence, at low volume levels, we perceive reduced bass. The tap normally has a shunt-to-ground RC filter. In the 38-7 radio, it consists of a series 51kW resistor (#32) and a 6nF capacitor (#38). This bypasses the higher-range audio frequencies to ground, resulting in a relative bass boost at low volumes. It is a form of frequency-­shaping that is dependent on the volume control position. In the first position of the tone switch, the 6nF capacitor is shorted out, giving a flat response. Since the 51kW resistor shunts all frequencies equally, it sounds like the bass is cut. In the second position, no frequency shaping is used, but the loudness circuit operates. And in the third, most clockwise position on the control, additional capacitance is added to the anode circuit of the 6F6, cutting the treble. Rewinding the speaker’s field coil When I first got the radio, the field coil was open-circuit and needed rewinding. This required driving out some spiral pins that attached the coil assembly to the speaker’s frame, and some machining to release the coil. I replaced the pins with screws and nuts – see Photo 9. A new bobbin was made of discs of Formica sheet and other materials. This is a common problem with vintage electromagnetic speakers. Other areas it crops up in are vintage valve interstage transformers with very fine wire. This is invariably due to ‘green spot disease’, which is corrosion of the fine copper wire. The vintage enamel did not protect the copper as well as modern enamels. Apart from making the coil go open circuit, this makes it very difficult to count the original number of turns Australia's electronics magazine because the wire breaks so easily in the corroded areas. Re-winding field coils revolves around filling a fixed-volume bobbin with fine wire, similar to the original, to about the same winding height. The DC resistance of the coil that you end up with is inversely proportional to the fourth power of the radius (or diameter) of the wire. This is because the resistance of the wire drops by the square of the radius/diameter, and the number of turns you can fit in the same volume goes up with the inverse square of the radius/diameter. So if you doubled the diameter of the new wire compared to the original, the DC resistance would be about 16 times lower than the original coil! To drop the resistance by a factor of two, the wire size only has to increase by a factor of 1.2 or 20%. The main target value for a field coil rewind on a vintage speaker is the original coil’s DC resistance. The exact inductance is less important, because one wants the B+ voltage to be about the same as it was with the old field coil, and thus a similar voltage drop across the coil with the average supply current. However, the inductance is also affected in a similar manner to resistance with a change in wire size. In a nutshell, it pays to measure the winding height and the original wire diameter very carefully and stick to both those parameters for the rewind. This is not to say that other parameters do not affect the DC resistance of the final result; for example, how Photo 9: the re-wound Philco 38-7 speaker field coil. The spiral rivets were replaced with screws/nuts. siliconchip.com.au Photo 11: the flexible coupling for the tuning shaft had seen better days. Photos 12 & 13: I cut these pieces of Teflon with a circular punch to make a new flexible coupling. The existing rivets were converted into nuts. neatly or scrambled the winding architecture might be. The enamel thickness of the particular wire will also have some effect. If the original bobbin was layer-­ wound with thin paper between the layers, which the re-wound bobbin does not have, the DC resistance could end up 10-15% higher than the original. But this is nothing as extreme as changing the wire’s size. If the new winding turns out to have a slightly higher resistance than the original, some wire can be unwound from the outer surface of the bobbin, so that is not a drama. Replacing cracked and damaged rubber parts Fortunately these days, with interest in vintage radio restorations increasing, reproduction parts are available for this radio. For example, the cloth seen over the speaker is an exact reproduction woven to match Philco’s original cloth, which has long since disintegrated. I also replaced the rubber mounts for the variable capacitor, along with the rubber feet that sit on the chassis corners, used on many other Philco chassis models – see Photo 10. The tricky part was replacing the two hardened rubber discs in the variable capacitor’s coupler. They were riveted in place, and because the casting is a type of pot metal, one must remove them slowly and carefully to avoid damaging it. Photo 11 shows this coupler. The original rubber material was close to 1/8-inch (3.175mm) in thickness. It was a three-layer laminate with a twin fabric layer embedded in it. To make new discs, I used a piece of 1/8-inch thick Teflon plate I had in my hardware collection. It was firm enough for the task but also flexible enough too. It came out of some disassembled medical machine. It was just big enough to cut two discs from; there was no room for error. I bought a hole punch kit specifically for the job. I made a scale drawing on a computer, printed it and used thin double-­ sided sticky paper (called JAC Paper) to stick the paper diagram to the surface of the Teflon plate. The punching was done in a large vise, using an acrylic sheet as the backing for the Teflon, because it was stiff enough to support it for a clean cut, but not so hard that it damaged the sharp cutting edge of the metal punch. Photos 12 & 13 show the reassembly of the coupler. Over time, the counterweight had apparently lost some mass for a perfect balance with the other rotating parts. I cured that by attaching two 5g iron weights (designed for balancing car wheels) to either side of the counterweight – see Photos 10 & 14. I managed to preserve two of the long rivets by drilling them and threading those with 4-40 UNC threads so the removed end could be replaced by screws. I had to preserve these because of their very low-profile heads, required for clearance on the vertical plate holding the cones. The bulge in their body prevented them from sliding through the hole in the casting after the peened-over part was removed. These pins cannot be driven out with that bulge present, or the casting would crack. I applied a thin protective washer and patiently hand-filed them down for clearance, then smoothed them in a lathe. I found four suitable replacement eyelets for the other parts. Alignment & sensitivity testing Photo 10: I replaced the perished rubber variable capacitor mounts with new reproduction types and added some more mass to the counterbalance weight (lower left) as it needed it. The red parts at upper left are the handmade parts from approximately 1976, the black parts below it are the new reproductions. siliconchip.com.au Australia's electronics magazine I am a great believer in having a controlled RF signal source with a good attenuator and accurate frequency counter to test and align vintage radios. It pays to follow the manufacturer’s alignment instructions faithfully. I use the excellent Philips PM5326 solid-state RF signal generator for this task. It has an inbuilt digital frequency counter and was designed for aligning AM and FM radios. It covers 100kHz to 125MHz and has sweep functions October 2026  99 interesting 6J5 detector/AGC stage which adds no gain) and a pentagrid converter. Most of the system noise is in the 6A8 converter valve, which sets the limitation on sensitivity and noise. A tuned RF stage will improve this, and moving to a triode/hexode converter such as the 6K8 or ECH35, as noted earlier, will also improve the S/N ratio. Many communications radios with an RF stage and a threegang variable capacitor have around a 2μV sensitivity for 50mW output. Summary Photo 14: the new flexible coupling installed in the set. to help with the alignment of TV IF stages and AM and FM detectors too. It is always better when the frequency is measured prior to the attenuator inside the generator, because at very low output levels, external frequency counters can struggle even with added amplification. Many manufacturers of radios after the 1960s provided a specific RF input level at the antenna and the associated audio power output level, such as 50mW, into a dummy speaker load. This is very useful for checking the radio’s sensitivity. However, for many domestic valve radios of yesteryear, not only was the sensitivity figure absent, but the alignment instructions were often brief with poor detail. The maximum audio output power was often quoted; for example, for the 38-7 model they stated “Undistorted output: 3 Watts” on the schematic. Of course, the distortion at full output power is not insignificant, and typically in cases like this, on the order of 10% second harmonic distortion. In the case of the radio’s performance with unspecified sensitivity data, I am interested in what the radio can do and what the radio can’t do, at 100 Silicon Chip the threshold of usability of the radio with weak signals. Weak signal performance is where the system noise and the recovered modulation content of the carrier become subjectively equal on a listening test. Any signal level lower than this and the noise starts to corrupt the recovered modulation to the extent that the modulation starts to become unintelligible. In the absence of other specific data, this is the test I deploy after a full alignment to check the radio’s performance. I determine what RF input voltage level at the antenna, using a 30% modulated carrier, results in a 50:50 noise versus recovered modulation on a subjective listening test. Because any RF signal level much lower than the modulation won’t be intelligible. In the properly aligned Philco 38-7 with its usual 6A8 converter, the 50:50 signal & noise equivalence occurs at an RF input voltage close to 10μV at frequencies below 12MHz. In the high SW band area of 14-19MHz, the apparent S/N equivalence is around 24μV. This is a typical value for a radio with a similar five-valve count without an RF stage (not counting the Australia's electronics magazine The Philco model 38-7 radio ticks all of the boxes for a valve radio from the late 1930s. Its industrial design is outstanding for a home appliance, and the mechanical engineering is well above average for any domestic valve radio. The dial and the tuning arrangements are works of art and science. The radio also provides wide-range SW coverage, in one band, plus the standard MW band. The sound quality is excellent, and radio is a sensitive and selective receiver on both the MW and SW bands, where it easily resolves many weak stations with a relatively short wire antenna. There is little evidence of any significant practical defects in the 38-7’s performance in use, except for the AGC pulling problem on strong shortwave stations and somewhat reduced performance in the high SW band area. Using the ECH35 en lieu of the 6A8 improves those problems, but that is not a must. Philco incorporated new ideas and circuit innovations, such as the loudness tap on the volume control. They also incorporated a creative delayedAGC circuit and a unique IF neutralisation method, while avoiding hum coupling problems from the power switch. They were sensible enough to power the radio via a transformer, which avoided any ‘hot chassis’ problems. Importantly, the chassis can be Earthed with a three-wire mains cord. The radio could be supplied in 110V/220V options, making it suitable for export. Overall, this radio has a blend of both form and function, which is very difficult to beat. They appear on eBay from time to time, mainly in the USA, but with the occasional one showing up in New Zealand & Australia. SC siliconchip.com.au ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Send your email to silicon<at>siliconchip.com.au Queries about the Pinball Machine Could you advise me where you obtained the neoprene rubber for the bumpers in this project (siliconchip. com.au/Series/460)? Also, I need some advice regarding the Cascade display. The Cascade PCB I originally received was apparently an early version with 16 LEDs. I now have the correct PCB, as shown in the magazine, but it only has 15 LEDs. There are 16 holes in the deck for the Cascade. As I do not know anything about the installation of the roll over sensors yet, I assumed the 16th hole was for an LED, as it seems to be the only one where a hole is drilled in the playing surface when I was led to believe there will be multiple rollover sensors. What is placed in the hole to keep a smooth surface for the ball to run on and allow the sensor to work? Finally, what about the four LEDs in front of the targets? Do they have a PCB? If not, where are they fed from? I suppose time will answer some of these questions in the next issue. (J. A., Townsville, Qld) ● Phil Prosser responds: I got the neoprene rubber from AliExpress. I searched for “rubber 5x5mm” and “rubber 10x5mm” and looked over the plethora of results. I got a couple of alternative parts and found that the firmest is best. You certainly don’t want foam rubber; it needs to be solid. The material was pretty cheap and came in 2m lengths. It sticks together end-to-end extremely well with superglue. As for the Cascade rollover, there are indeed 15 holes for LEDs and one for the rollover that triggers the cascade LEDs. You drill the rollover hole to the size of the sensor. This is discussed in one of the articles; once you get some sensors, you will see that they work pretty well as roll-over sensors with minimum mucking around. The sensor could simply screw into the hole in the deck, which I did for some initial ones. The top of the sensor siliconchip.com.au is flat and comes out quite flush with the play deck. As an improvement on this, I then made 3D-printed ‘holders’ that screw to the deck underside and hold the sensors. There are three types you can choose from that allow mounting in various locations. Look at the STL files in the download package; their use and function should be self-­evident. All work well. To use these, I screwed the holder onto the sensor, as it is a tight fit, then pushed the sensor into the hole in the deck, which should also be a tight fit. With it all snugged up, I screwed the holder to the deck with a couple of wood screws. This secures the holder and ensures it is truly at 90° to the deck surface. You can carefully adjust the sensor depth by screwing it up and down as required. There is a lock screw hole in the side of the holder, which accepts a small screw. This will hold the sensor securely. If your deck hole is a tad loose on the sensor, the 3D-printed holder will be perfect for keeping everything tight and square. I painted over the sensors. If you have substantial chips or tear-out on your drilled hole, you could use wood filler or epoxy to tidy things up. Still, old-school pinball machines used wires on microswitches through slots in the deck, so resist the urge to get too fussy. I hope the above doesn’t sound too challenging; it really isn’t that hard. This project is big and has a lot going on, which makes condensing it into Using higher-voltage parts for Pinball Machine Just bought the last three magazines to read the articles on the Phenomenal Pinball Machine (siliconchip.com.au/Series/460). I’m keen to build this, but have a few questions first! I have old pinball bumper assemblies, slingshots and solenoid coils lying around, but they are all rated at 50V. Can I use them? I believe, I might have to alter the power supply. Is there anything else I should know? I am looking forward to your reply. (P. B., Bayswater, Vic) ● Phil Prosser responds: The short answer is yes, mostly. The long answer is as follows. There is nothing that stops you from doing this, but some things need to be considered carefully. The IRLZ44NPBF Mosfets are only rated at 55V. I would not use this device for switching 50V. Pretty much all TO-220 package Mosfets have the same pinout, so you have a huge number of choices. Pick one with a Vds rating of 60V or higher and a Vgs(th) of no more than 2V. The Vgs(th) rating is important. It means the Mosfet will switch on properly with the 3.3V logic drive. This is the most important thing for you to check and get right. Pick one with an RDS(on) that is low; say, <0.2W, and a continuous current rating (Id) of at least 30A. That might sound hard, but it isn’t; you will find plenty of suitable devices. Go into the Mouser or DigiKey selection tool and you will see a lot of Mosfets. Currently, the Pinball Machine’s 24V supply is also used for the inductive sensors. 50V is too much for them, so you will need a 6-32V DC supply for the inductive sensors, plus the 50V supply for the bumpers, solenoids etc. You will also need to upgrade all the capacitors that will be on the 50V rail to have a minimum voltage rating of 63V. There is nothing else on the Control Board that uses the high-­voltage supply, so you can safely feed 50V DC into it once you’ve separated the inductive sensor supply. You could actually keep the 24V DC supply exactly as it is on the board, for the inductive sensors and such, and cut the trace on the bottom layer between the power input terminal and the solenoid driver section. Make sure whatever 50V supply you use is beefy enough to supply the peak currents. I would add a big capacitor next to the control board. Australia's electronics magazine October 2026  101 articles a challenge. I trust it will be rewarding as you get it together. As for the target LEDs, simply use the LED interface PCB (coded 01807265) that connects to the medium-­current outputs on the control board via a 10-way ribbon cable. I just made ribbon cable lengths with the LEDs soldered to them that plugged onto the LED breakout board. You could solder them directly, but that would make assembly and maintenance a real hassle. Where to obtain protected Li-ion cells I have ordered the Battery Backpack kit (September 2026; siliconchip.au/ Article/20727), I note that it is recommended to use a protected cell. Perhaps you could advise where you purchased such cells. Jaycar’s AA-size Li-ion cells do not appear to include protection circuitry. (C. W., Leumeah, NSW) ● You seem to be right; Jaycar’s 14500 Li-ion cell (SB2300) states it lacks protection. Compare that to their Cat SB2299 18650 Li-ion cell, which explicitly states it is protected. The cells we used in our prototypes don’t seem to be available any more, but we found the following online, which appear to be suitable. We have not tested them: • Klarus 14GT-92UR (siliconchip. au/link/acc7) • Elemex 14500 (siliconchip.au/ link/acc8) With the apparent scarcity of protected 14500 (AA-size) cells, we are investigating the addition of onboard protection circuitry for future projects. That will mean any AA-size Li-ion cell will be able to be used. LC Meter firmware investigation I recently built the Compact and Simple LC Meter from a kit (May 2026; siliconchip.au/Article/20235). On powering it up, and after the splash screen displayed, I saw the current oscillator frequency displayed and a C value of -1027pF (1027pF was the value of my particular reference capacitor supplied in the kit). Pressing the calibrate button brought the C reading down to 0.0pF. TP2 showed a rock-solid 8.00131MHz. I set about measuring numerous capacitors 102 Silicon Chip from my parts bins, from 10pF up to 470nF. All showed reasonable values. At this stage, I was satisfied the meter was working correctly, and I was suitably impressed. I then started to measure inductors, and this is where things went awry. I recalibrated with the test leads shorted, but everything I measured seemed to measure high from their marked values by about 10%. Repeating the process made no difference. I started wondering if there was something going on with the supplied inductor, or was it my tower of capacitors? Since the capacitance measurements were working fine, the suspicion fell on the inductor. Using the equation L = 1 ÷ C(2πf1)2 from the article, the reference capacitor value of 1027pF, and the calibration frequency displayed on the LC Meter of 520640Hz, I calculated that the supplied inductor (including any stray test lead inductance) was 90.99μH. So it was within tolerance – just. I was still suspicious, though. According to the article, the internal inductor value should be immaterial to the calculation of the unknown inductor. So I performed an experiment. I soldered another 10μH inductor into the test leads of the meter and then recalibrated it. This resulted in a lower calibration value on the meter, as expected. I then re-measured each inductor and compared the results with what I had measured previously. Each new measurement now came in about 9% lower than they had previously. How could this be if the micro is using the formula Lx = (1 ÷ f22 – 1 ÷ f12) ÷ (4π2C) as per the article? The extra inductor shouldn’t have made any difference since I had recalibrated including this extra inductor and the ‘internal’ inductance is immaterial, anyway. I decided it was time to have a look at the Bascom program. I verified that the Bascom program was indeed loading the reference capacitor value correctly. It was also using the formula of Cx = C(f1 ÷ f2)2 – C to calculate unknown capacitor values as expected, but the unknown inductor calculation wasn’t what I was expecting. When calculating Lx, it was using the formula Lx = L(f1 ÷ f2)2 – L. That’s fine if we have an accurate reference value L for the internal inductor, but we don’t. Australia's electronics magazine However, the value of L could be calculated during calibration, as I had manually done above, and then used to subsequently calculate Lx. I went searching again for the setting of this reference value. What I found was that L in this equation (Lref in the program) was a constant and set to 100000 (100μH). That was the source of the problem. It was using a fixed value for L to calculate Lx. So there seems to have been a step missed out in the program, or the wrong formula is being used. Since I didn’t have the ability to change the program without expending a lot of effort, I decided to change the inductor in the meter to one that was as close to 100μH as I could find. I ended up using a bobbin-wound ~100μH inductor that I had to add four extra turns to get the meter to read close to an ideal frequency of 496632Hz during calibration. Once I did this, the meter performed well on both L and C ranges. It has proven to be a very handy device to have around. (M. H., Waiuku, NZ) ● Andrew Woodfield responds: I would like to apologise for the effort you have had to go through over my LC meter. I supplied an incorrect version of the LC meter software. That was one that allowed me to check the inductor temperature drift. Version control on my LC meter software, that’s been written for a variety of platforms over more than a decade, is clearly not a virtue I possess. The correct version (uLCmV2565. zip) is now available from siliconchip. au/Shop/6/3580 and all kits and programmed microcontrollers supplied after the 10th of August have been programmed with the correct firmware. To verify this version works correctly, I substituted a 10nF Mylar capacitor (revising the value stored in EEPROM, of course) and a 47μH choke. The software calculated the inductor value during calibration and correctly measured L/C values across the full range. With this firmware, the readings are calculated without reference to anything except the resonant frequency and the reference capacitor value. These particular component values result in less than desirable resolution, oscillator range changes, and other factors, but the software didn’t care about the large deviation in inductance. continued on page 104 siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip KIT ASSEMBLY & REPAIR FOR SALE DAVE THOMPSON (the Serviceman from Silicon Chip) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, New Zealand, but service available Australia/NZ wide. Email dave<at>davethompson.co.nz LEDsales KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com 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 LEDS, BRAND NAME AND GENERIC LEDs, filament LEDs, LED drivers, heatsinks, power supplies, kits and modules, components, breadboards, hardware, magnets. Please visit www. ledsales.com.au PMD WAY offers (almost) everything for the electronics enthusiast – with full warranty, technical support and free delivery worldwide. Visit pmdway.com to get started. Micromite Explore-40 October 2024 Complete Kit SC6991: $35 siliconchip.au/Article/16677 Includes the PCB and all onboard parts. Audio Breakout board and Pico BackPack are sold separately. Issues Getting Dog-Eared? Keep your copies safe with these handy binders Order online from www.siliconchip.com.au/Shop/4 or call (02) 9939 3295. See website for overseas prices REAL VALUE A T $21.50* PLUS P&P 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 (02) 9939 3295. 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 October 2026  103 Advertising Index Altronics.................................43-46 Blackmagic Design....................... 7 Dave Thompson........................ 103 DigiKey Electronics..................OBC Emona Instruments.................. IBC Hare & Forbes............................... 9 Jaycar............................. IFC, 24-27 Keith Rippon Kit Assembly....... 103 LD Electronics........................... 103 LEDsales................................... 103 Microchip Technology.................. 5 Mouser Electronics....................... 3 PCBWay....................................... 11 PMD Way................................... 103 SC Micromite Explore-40......... 103 SC Ideal Bridge Rectifiers........... 42 Silicon Chip Binders................ 103 Silicon Chip PDFs on USB......... 23 Silicon Chip Kits........................ 37 Silicon Chip Shop.................88-89 Silicon Chip Subscriptions........ 73 Silicon Chip Test Tweezers......... 8 Another test I repeated was to use a fresh, ‘out of the packet’ 100μH choke (actually 110μH) and a 1000pF (1070pF in my case) polystyrene capacitor. Assuming an accurate measurement of the reference capacitor, the software calculated the actual inductor value to about 0.2%. Other factors make the overall measurement accuracy worse. We suggest anyone who has built the kit and can’t reprogram the chip emails Silicon Chip to organise for it to be swapped or reprogrammed. SC200 amplifier questions I have powered up the SC200 Amplifier module I built (January-March 2017; siliconchip.au/Series/308) and measured a 1.2mV output voltage with no input signal. Is that OK? The emitter resistor voltage drops are 0.4mV and 0.47mV. Could you please advise if it is OK to have such a difference between the voltages across the emitter resistors? Nevertheless, I decided to test the amplifier and I did not see sinewave distortion at the output. Then I checked the sound quality, and it was OK as well, with a low supply voltage (about ±20V) and at low volume. I started building the second channel; it will be interesting to see the difference in measurements there. I will test the amplifiers at full power later. I found a possible problem in a footprint on the PCB. Transistor Q19 in the clipping detector seems to be reversed to me. If follow the footprint on the top of the PCB, the emitter is connected to the 100kW resistor and the collector to -56V. (Y. A., Kellyville, NSW) ● 1.2mV is more than an acceptable output offset voltage. Anything less than 20mV is acceptable, but the lower it is, the better. Many amplifiers have an output offset voltage exceeding 10mV unless they are designed for PA use, since output transformers have a low primary impedance and thus demand a low offset. It is normal to have slightly different voltages across the emitter resistors. That’s part of the reason they are there, to help balance out differences in the transistors. No two transistors will be exactly the same, even from the same batch. Your readings under 1mV are quite low and suggest that VR1 (the bias adjustment trimpot) is fully anti-­ clockwise or close to it. You will get slightly better sound quality if you turn the bias up until you see a few millivolts across the emitter resistors. Just make sure they don’t go too high as the transistors warm up. The suggested target is 4.4mV. We don’t see a Q19 in the circuit; we think you mean Q16. Pin 2 is the emitter, and it connects to the -56V rail. Pin 3 (the one by itself) is the collector, and it connects to the resistor. Its pinout is the same as the BC846C shown on the main circuit diagram. So we believe it is wired up correctly on the PCB (the clipping indicator on our prototype passed all testing). Query on RIAA and valve preamps Next Issue: the November 2026 issue is due on sale in newsagents by Monday, October 26th. Expect postal delivery of subscription copies in Australia between October 23rd and November 11th. I am thinking of adding some ‘colour’ to the sound of my transistor-­ based amplifier. I will need a lot of preamplifier gain and RIAA compensation to handle the output from my Shure V15 MkII. Have you published such a project? What about a standalone valve preamp? (J. K., Freshwater, NSW) ● Our latest standalone RIAA preamplifier project was in the August 2006 issue (“Build A Magnetic Cartridge Preamplifier”; siliconchip.au/ Article/2740). It is suitable for use with a valve preamp. The gain is adjustable between 1× and 11×. We have also published a couple of valve preamplifiers: • January & February 2016: Valve Stereo Preamplifier For HiFi Systems (siliconchip.au/Series/295) • November 2003 & February 2004: A 12AX7 Valve Audio Preamplifier SC (siliconchip.au/Series/293) Australia's electronics magazine siliconchip.com.au The Loudspeaker Kit.com.......... 10 Wagner Electronics..................... 87 Errata and on-sale date for the next issue Simple USB Power Monitor, June 2026: the original firmware had a bug that caused it to incorrectly display values with a zero to the left of the decimal point. Updated firmware is now available for download that fixes this error, and all kits and pre-programmed chips we sell have been updated as of 12/08/2026. Simple LC Meter, May 2026: the original firmware had a bug that caused it to assume the onboard inductor L1 had a value of exactly 100μH. That could result in inaccuracy if the inductor’s actual value differs significantly from nominal. 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