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JULY 2025 ISSN 1030-2662 07 The VERY BEST DIY Projects! 9 771030 266001 $ 00* NZ $1390 13 INC GST INC GST The SmartProbe The perfect device for troubleshooting circuits. Probe voltages and test continuity with one hand, then put it in your pocket Solar USB Charging Charge your USB devices without paying a cent for electricity Hot Water Solar System Diverter Get the most out of your solar panels – this issue has the assembly and testing instructions ...and much more in this issue! SpaceX THEIR LATEST DEVELOPMENTS, INCLUDING STARSHIP ALL NEW CATALOGUE! It’s Back & PRINTED Exciting news! The Jaycar Engineering & Scientific Catalogue has returned, and it’s our biggest issue yet, with 604 pages packed full of the latest products, components, and tools. IT ’ S B AC K ! 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 Please note: Due to shipping delays, this printed catalogue should be available in New Zealand by late July. Contents Vol.38, No.07 July 2025 14 SpaceX Page 33 SpaceX is the world leader for space launch services (crew transportation, satellite launches etc). They have been responsible for dramatically reducing the cost of access to space. Here is how they have done it. By Dr David Maddison, VK3DSM Aerospace technology 46 Precision Electronics, Part 9 We have now reached the final part of our series on precision electronic systems. We summarise the building blocks that we have already covered and provide an example of how to design a whole system. By Andrew Levido Electronic design 54 Salvaging Parts SmartProbe Precision Electronics Part 9 – Page 46 There’s a lot of useful parts and components that can be harvested from discarded consumer goods like washing machines, printers, photocopiers, drills etc. Here’s what you should look out for. By Julian Edgar Reusing & recycling Page 54 70 8×16 LED Matrix module These LED matrix panels are bright (with just 400mW power consumption), compact and relatively easy to drive. They use an AIP1640 driver IC which can be controlled via a protocol that is similar to I2C. By Tim Blythman Low-cost electronic modules 26 Solar Charging via USB Here’s how to charge and power all your devices from solar power, using a low-cost system. It’s easy to build, and can even be built as a portable system or wired up in your home. By Julian Edgar Simple electronic project 33 The SmartProbe This little device is ideal for taking voltage and continuity measurements. It measures up to ±50V and tests diodes/LEDs/forward voltages. It is powered by a single CR2032 cell. By Andrew Levido Test & measurement project 62 Hot Water System Solar Diverter Using this device can save you a lot of money! It lets you use excess solar power generation to power your electric water heater. The final part in this series covers the construction, setup & testing. Part 2 By Ray Berkelmans & John Clarke Solar energy project 74 SSB Shortwave Receiver, Part 2 Covering the entire shortwave band, this Receiver is digitally tuned and has a bunch of helpful features like squelch, LSB/USB support, good sensitivity and more. We cap things off by showing you how to build, test & align it. By Charles Kosina Radio receiver project SALVAGING PARTS 2 Editorial Viewpoint 5 Mailbag 53 Subscriptions 80 Circuit Notebook 82 Serviceman’s Log 88 Vintage Radio 97 Online Shop 100 Ask Silicon Chip 103 Market Centre 104 Advertising Index 104 Notes & Errata 1. GPS Speedometer 2. Logic level indicator Eddystone EC10 Mk2 by Ian Batty SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke – B.E.(Elec.) 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): $70 12 issues (1 year): $130 24 issues (2 years): $245 Online subscription (Worldwide) 6 issues (6 months): $52.50 12 issues (1 year): $100 24 issues (2 years): $190 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 Printing and Distribution: 9 Kendall Street, Granville NSW 2142 2 Silicon Chip Editorial Viewpoint Confusion between lithium battery types It has become very common for people to refer to lithium-ion batteries as “lithium batteries”, but that is confusing since lithium metal batteries existed before lithium-ion batteries were invented, and they are quite different. The term “lithium battery” used to specifically refer to a disposable battery that used lithium metal as the anode. These have been around since the 1970s and are still widely used in applications where long shelf life and high energy density are important, such as memory backup, smoke alarms and small medical devices. They come in various chemistries, like lithium-manganese dioxide, lithium-­ thionyl chloride, lithium-iron disulfide, and so on. Those all share one critical feature: they are not rechargeable. In contrast, lithium-ion batteries are rechargeable and use a lithium compound rather than metallic lithium. The lithium atoms give up an electron to become positively charged ions, which move between compounds in the electrodes during charging and discharging – hence the name. Though their chemistry is more complex and sensitive than lithium-metal batteries, their energy density and rechargeability have made them the dominant choice for everything from phones to electric vehicles. In fact, what we call “lithium-ion batteries” is a whole family of different chemistries with similar, but not identical, properties. Common lithium-ion chemistry variants include lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt oxide (LiNiMnCoO2), lithium nickel cobalt aluminium oxide (LiNiCoAlO2), lithium manganese oxide (LiMn2O4) and lithium iron phosphate (LiFePO4). You may be familiar with that last one because it has more significantly different properties from most of the others, such as a lower terminal voltage, plus better tolerance for over-charging and over-discharging. Getting back to my main point, why the confusion between lithium-ion and lithium batteries? Somewhere along the line, “lithium-ion battery” got shortened; first in casual conversation, then in journalism, and now even in marketing. The problem is that “lithium battery” still means something else in technical contexts. The distinction especially matters in transport: postal and courier rules, particularly for air freight, can differ significantly between lithium and lithium-ion batteries. It doesn’t help that many consumer devices now include vague labels like “contains lithium battery”, even on products that clearly use lithium-ion cells. This ends up muddying the waters for everyone else. The distinction is especially important when it comes to charging. Try to charge a non-rechargeable lithium battery and you’re asking for trouble. The internal chemistry isn’t designed to handle reverse current, and the result can be catastrophic: swelling, leakage, or even fire. It is not just theoretical; there have been fires caused by consumers mistakenly trying to recharge lithium primary cells, often due to this exact terminological conflation. We all sometimes refer to a cell as “a battery” when (arguably) batteries contain more than one cell, but that’s a minor point. Not so the distinction between lithium and lithium-ion batteries. So let’s make a collective effort to be more precise. Use the term “lithium-­ ion” (or even better, the specific chemistry) to refer to rechargeable batteries. If you’re referring to a lithium-metal primary cell, it’s best to be explicit, but if you must call anything a “lithium battery”, it should be those types only. Cover Image: Steve Jurvetson – www.flickr.com/photos/ jurvetson/8065095602/in/album-72157608597030651/ (CC BY 2.0) Australia's electronics magazine by Nicholas Vinen 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”. The ups and downs of grid-scale solar power I’ve just been reading the articles entitled “The Future of our Power Grid” (March & April 2025; siliconchip.au/ Series/437). I noticed the diagram on page 38 of the April issue, which shows a period in South Australia where it is claimed that 100% of the grid demand was being met 100% by rooftop solar. The article doesn’t mention that on the 10th of September last year, only 2% of the South Australian grid was from renewables – 1% from batteries and 1% from wind. Also, I understand that the South Australian grid is now the most expensive in Australia because of its high levels of renewables. A recent check showed that whereas we are paying about 25¢/kWh here in Sydney for our electricity, my friend with a private home in Adelaide is paying 50¢/ kWh. This is an important issue, and it is one of the reasons that I support nuclear power. I think it is really important that you give the full story in any of these articles. I’m sure you will agree. Dick Smith, Terrey Hills, NSW. The article’s author, Brandon Speedie, replies: Fig.22 was intending to show the value of spinning reserve; with high renewable penetration, some gas is still needed in South Australia for grid stability. Your figure from September 10th illustrates a different but equally important point: there are periods when wind and solar generation are low. This is why dispatchable capacity is so important (see part 1, in the March edition). South Australia’s dispatchable capacity is mainly gas, which is very effective in this role given its speed. Nuclear is well suited to providing spinning reserve, but is of limited value as dispatchable capacity, given its operational constraints. This is the same problem our existing coal generators are struggling with. As for your South Australian friend, I think they are ourPCB LOCAL SERVICE <at> OVERSEAS PRICES AUSTRALIA PCB Manufacturing Full Turnkey Assembly Wiring Harnesses Solder Paste Stencils small or large volume orders premium-grade wiring low cost PCB assembly laser-cut and electropolished Instant Online Buying of Prototype PCBs www.ourpcb.com.au siliconchip.com.au Australia's electronics magazine 0417 264 974 July 2025  5 getting ripped off. The state often has the lowest wholesale prices in the country, so if they are paying more than the national average, they are getting a raw deal on their retail agreement and should look for another plan. Interestingly, the state has long periods of negative wholesale prices, which is spurring interest from industry to build plants previously priced out of the market. BHP is one example; their plans to expand copper production would double the load on the SA grid. Separately, I thought you might enjoy hearing a personal anecdote. My Grandfather, a surveyor, was introduced to electronics by building DIY kits from Dick Smith Electronics. He passed the hobby onto me, a vocation I now call a career. He died recently, but would have enjoyed reading this exchange in the pages of his favourite magazine. Free software for drawing digital waveforms I recently came across WaveDrom, a digital timing diagram (waveform) rendering engine that uses JavaScript to convert a JSON description into an SVG vector image file. I thought this may be of interest to your readers. The software can also run on PC or laptop, although some installation is required. See the following websites: • https://wavedrom.com/ • https://wavedrom.com/tutorial.html • https://github.com/wavedrom/wavedrom The web page says “WaveDrom is a Free and Open Source online digital timing diagram (waveform) rendering engine that uses JavaScript, HTML5 and SVG to convert a WaveJSON input text description into SVG vector graphics.” I have provided a copy of the sample images from the second link (shown below). Joseph Goldburg, Microchip Technology. Probe cases are plastic, not metal Thanks for publishing my letter on the proposal to make cases for the Current & Differential Probes on page 8 of the May 2025 issue. I think there has been a misunderstanding as the proposed boxes are not made from metal. This confusion likely stems from my mentioning heat-treated tool steel jigs in my emails. Shearwater dissuaded me from that as it would be cheaper to get them to mill out the plastic boxes directly. More boxes would mean a better price per box. 6 Silicon Chip Shearwater did a good job of milling the six plastic boxes and end plates. The slide switch opening came out very nice with half-millimetre radius corners. It cost me $450 for the six (three of each project) boxes and end plates that included the CNC programming. Future orders would be cheaper because the program has already been done. The cost per box would basically depend on how many they would do in a batch. It would be nice to know if any readers were interested in plastic boxes, and how many. Michael Vos, Taree, NSW. More on “The future of our power grid” In the second part of this series, on page 38 of the April 2025 issue (siliconchip.au/Series/437), there is a note that I will paraphrase: “100% rooftop solar, all other generators being off aside from a small amount of wind, solar and Torrens Island Gas steam which was providing grid stability.” They are not shown on the Open Electricity data in Fig.22 because the outputs are not metered, but South Australia has four synchronous condensers, two at Davenport (Port Augusta) and two at Robertstown. These were built to cover the loss of grid system strength following the closure of Augusta Power Station in 2016. Each synchronous condenser provides 575MVA nominal 275kV fault capability and 1100MW of inertia. That is equivalent to the inertia created by a 275MW steam-driven synchronous generator. Other states and territories in Australia have built or are building synchronous condensers to cover the shortfalls in system strength as solar, wind and battery inverter-based resources (IBR) replace synchronous generation. Here are some synchronous condenser projects in NSW and Victoria that can be found with a quick internet search: • Victorian Ouyen 600MVA was completed in 2020, while the Ararat synchronous condenser is expected to be in service this year. The AEMO Victorian System Strength Requirement July 2023 report suggests a further eight 250MVA units are required. • NSW Transgrid has forecast a further 14 synchronous condensers are required to provide appropriate system strength. While inverters (IBRs) can contribute to frequency and voltage control, their effectiveness at grid scale is somewhat unknown. AEMO released a technical note in September 2024 titled “Quantifying Synthetic Inertia of a Grid-forming Battery Energy Storage System” (siliconchip.au/link/ac6g) to determine the future role of IBRs in grid stability. A video published by the IEEE in July 2023 titled “Power System Stability With a High Penetration of Inverter-­Based Resources” (https://youtu.be/-hH23MI4Npc) discusses some unique IBR behaviours that, in some cases, adversely affect grid stability. Another consideration is the fault ride-through capability. Fault ride-through is the ability to withstand rapid changes in load, either due to the loss of generation plants or line faults. Synchronous generators and synchronous condensers typically supply 500% more power than their rated nameplate capacities for short periods and 200% for 30 seconds, while an IBR typically supplies 120% of its rated nameplate for short periods. Australia's electronics magazine siliconchip.com.au FREE Download Now! Mac, Windows and Linux Edit and color correct using the same software used by Hollywood, for free! DaVinci Resolve is Hollywood’s most popular software! Now it’s easy to create feature film quality videos by using professional color correction, editing, audio and visual effects. Because DaVinci Resolve is free, you’re not locked into a cloud license so you won’t lose your work if you stop paying a monthly fee. There’s no monthly fee, no embedded ads and no user tracking. Creative Color Correction Editing, Color, Audio and Effects! Designed to Grow With You DaVinci Resolve is the world’s only solution that combines editing, color DaVinci Resolve is designed for collaboration so as you work on larger jobs correction, visual effects, motion graphics and audio post production all in you can add users and all work on the same projects, at the same time. You can one software tool! You can work faster because you don’t have to learn multiple also expand DaVinci Resolve by adding a range of color control panels that apps or switch software for different tasks. For example, just click the color let you create unique looks that are impossible with a mouse and keyboard. page for color, or the edit page for editing! It’s so incredibly fast! There’s also edit keyboards and Fairlight audio consoles for sound studios! Professional Editing DaVinci Resolve 19 ............................................................... Free DaVinci Resolve Micro Color Panel .............Only $809 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 DaVinci Resolve’s color page is Hollywood’s most advanced color corrector and has been used on more feature films and television shows than any other system! It has exciting new features to make it easier to get amazing results, even while learning the more advanced color correction tools. There’s PowerWindows™, qualifiers, tracking, advanced HDR grading tools and more! 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, Learn the basics for free then get more creative control with our accessories! so you are learning advanced skills used in TV and film. Learn more at www.blackmagicdesign.com/au Download free on the DaVinci Resolve website NO SUBSCRIPTIONS • NO ADS • NO USER TRACKING • NO AI TRAINING If the fault ride-through capabilities are insufficient, the grid voltage is likely to fall below the low-voltage trip points of nearby generators during a fault, causing those generators to trip. The remaining generators connected to the grid will then be overwhelmed by the demand and will trip on either under-voltage or low frequency. Low fault ride-through capabilities caused the 2016 South Australia state-wide blackout. The decommissioning of the Augusta Power Station a few months earlier, and the delay of the proposed synchronous condensers project, resulted in the loss of fault ride-through capabilities on the SA grid (siliconchip.au/link/ac6h). The system strength in the NEM is explained in the PDF at: siliconchip.au/link/ac6i The Victorian System Strength Requirement from July 2023 is in the PDF at: siliconchip.au/link/ac6j NSW Transgrid turns to synchronous condensers to safeguard system strength, build 14 synchronous condensers: siliconchip.au/link/ac6k Mathew Prentis, Port Augusta, SA. Simple trick for checking CR2032 cells I was reading the Versatile Battery Tester article in the May 2025 issue (siliconchip.au/Article/18121) and it reminded me of how I worked on computers from time to time, and one problem was flat CMOS batteries (cells). Any time I wrecked an old PC, I tested the CR2032 cell to see if it had enough life left to warrant keeping it. I often found cells that read just over 3V, but that initial test of the voltage did not indicate how charged the cell was. So I would use a 3V LED to check that. If the cell was good, the LED would light up brightly. If the LED lit dimly, then the cell was no good. This was a convenient way of determining the overall condition of the cell. Some time ago, a friend sent me a really good battery (cell) tester that indicates the voltage, internal resistance and the percentage of life the cell has remaining. Last year, our son was overseas, and he left his vehicle with us, for us to take in for a service while he was away. He gave us his spare remote to use. I tried to access the vehicle, but the remote did not work. I suspected that the cell might be flat, but I had to search online to find out how to open the remote. Once I got it open, I tested the button cell with my multimeter and it showed full voltage. I then got out the battery tester and it showed that the cell 8 Silicon Chip was almost dead flat. So, as you pointed out in the article, the terminal voltage of a cell or battery is not an indication of the charge left in the cell or battery. That demonstrates the need for a dedicated tester like the project in Silicon Chip, or the commercial unit that my friend sent me. Bruce Pierson, Dundathu, Qld. Help wanted fixing analog meter movements I am a prolific restorer of valve radios, and my testing equipment ‘arsenal’ consists of several analog meters of various types (mainly multimeters & VTVMs). Unfortunately, many of the meter movements are a bit sticky. I want to find with someone who has the skills to repair these for me – probably one or two at a time. I am very much ‘old school’ and I absolutely love my analog meters. I have been trying to find someone who is able to help for many years, without success. Peter Walsham, Auckland, New Zealand. Feedback on Capacitor Discharger project/kit Thought I would share a photo of the finished Capacitor Discharger (December 2024; siliconchip.au/Article/17310) I made from the kit I bought from you. Even though it’s a simple kit, just the drilling and fitting took me a while. A step drill bit was handy to drill the banana plug socket holes in the ends. My soldering is a little rough; however, it goes together and works. The instructions were pretty good in the magazine. I understand basic operation of the Mosfet and the purpose of the three resistors and bridge rectifier, but it makes me appreciate that learning even the basics of electronics is hard. The red LED comes on at about 8V DC and above. At 10.7V, it draws 19mA from my bench power supply. I guess it will discharge the capacitor down to 8V and then the last 8V you can discharge with a resistor. I just need to make up a label on my laminator at work. I enjoy these simpler kits that are you are selling, as I can’t be bothered buying up all the parts myself as I’m timepoor and they don’t take months to put together. Edward Menzies, Kew, Vic. Comment: you would need to use a resistor or similar if you have to completely discharge the capacitor. The idea is that, once the capacitor is discharged to 8V, it is no longer hazardous to work on the equipment. Australia's electronics magazine siliconchip.com.au siliconchip.com.au Australia's electronics magazine July 2025  9 This is especially useful in cases like switch-mode power supplies where capacitors are charged up to rectified mains voltages (~325V DC) and can retain that charge for hours or even days. The perils of cloud storage I would like to add to what D. T. of Sylvania wrote in the letter titled “Windows’ built-in ‘cloud’ services are a problem”, on page 8 of the May 2025 issue. I stopped using OneDrive some years ago. It was originally another drive on your PC, but then they changed this to synchronise all documents, and that’s when I disconnected it. My new Windows 11 PC came with OneDrive enabled and, after some searching, I disabled it. My PC now shows ‘the cloud’ with a cross through and all greyed out. Of significant concern is that OneDrive is very vulnerable for those users who have had their Microsoft account stolen, as happened to me recently. I noticed that the email address listed in my account wasn’t mine. Trying to recover this resulted in the hacker continuously resetting my Microsoft account address and phone number. I contacted the Microsoft chat line and, after 2.5 hours with an amazing person, they could see the active hacker also at their end. Eventually, they closed my account. The problem is that all the cloud data is wiped immediately when your account is closed. This is the same for Google Cloud services. So never use a ‘cloud’ service for any critical data, unless you have direct access and control of it. Braham Bloom, Russell Lea, NSW. Character Map has a search feature Based on the May 2025 editorial on WinCompose, the Editor obviously doesn’t like using the Windows built-in Character Map program. Did you know it is possible to search for glyphs in Character Map? If you check the “Advanced view” checkbox, you can search for glyphs using the “Search for” field. For instance, if using the Arial font, a search for “greek omega” will result in 46 choices related to the Greek letter Omega. John Elliot V, Blaxland, NSW. Nicholas comments: I have been using Character Map since Windows 3.11 and had no idea that such a feature had been added! Apparently that happened with Windows 2000. It’s baffling that such an important tool is hidden behind an “Advanced view” setting. I still find WinCompose quicker and much more convenient, but this makes Character Map a lot more useful than I thought. A flat battery can cause clocks to speed up On p110 of the May 2025 issue (in Ask Silicon Chip), Geoff Graham replied to a correspondent regarding a GPS Analog Clock gaining time, saying he had not encountered anything that might cause a clock to speed up when the battery voltage dropped. My 40-year-old 1.5V AA cell powered kitchen clock speeds up when the battery voltage drops. It keeps reasonable time when the battery voltage is 1.5V or higher, but speeds up when the battery voltage is 1.4V or lower. That’s how I can tell that it’s time to replace the battery! As a result, I usually replace the cell twice per year. SC John Rajca, Mount Kuring-gai, NSW. 10 Silicon Chip Australia's electronics magazine siliconchip.com.au SORT OUT YOUR STORAGE! 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SpaceX has been responsible for dramatically decreasing the cost of access to space and is aiming to land people on Mars. They’re also behind the Starlink constellation of communications satellites. Part one of two by Dr David Maddison VK3DSM Starship’s seventh test flight Image source: SpaceX / <at> Space_Time3 via X (Twitter). 14 Silicon Chip A size comparison of common rockets from the last few decades. Unlike SpaceX’s, Australia's electronics magazine siliconchip.com.au most are not reusable (exceptions include the Space Shuttle & New Glenn). Sources: Blue Origin, FloraFallenrose (Wikimedia) & public domain sources O f the many achievements of SpaceX, their ability to vertically land and reuse a rocket is particularly notable. Never routinely done before they made it normal, it has enabled a great decrease in space launch costs. Their satellite constellation, Starlink, provides global internet services at a price not too much different from regular wired or wireless services. SpaceX’s Falcon 9 rocket has regular weekly launches (sometimes more frequent) and is usually reused. It can carry a larger payload if its boosters are not reused. It has become a workhorse of the industry for delivering crew and cargo into space. At the time of writing, Falcon 9 rockets have launched 453 times. SpaceX’s competitors like Arianespace (the world’s first commercial launch service), Roscosmos (a Russian stateowned corporation) and ULA (United Launch Alliance, a joint venture of Lockheed Martin and Boeing) cannot currently compete with SpaceX on cost or delivery schedule. As a result, SpaceX dominates the launch services market. According to Space Insider, in the fourth quarter of 2023, SpaceX launched 382,020kg of cargo into space, which was 318 times more than ULA. China’s stateowned launch service, CASC delivered, 40,810kg in the same period. Note that dates provided in this article refer to the local time at the event location, not Australian time. Also, any images that are uncredited are publicity images provided by SpaceX or in the public domain (eg, from NASA). The objectives of SpaceX The chief objectives of SpaceX are stated as: 1. Developing affordable access to space 2. Developing and launching Starlink for global internet access 3. Sending humans back to the Moon 4. Establishing a colony on Mars Successes and failures Like any space agency, SpaceX has had a few failures, especially with its early rockets. Antares Ariane 5 Soyuz Space Shuttle Failure is not treated by SpaceX with despair, but rather as a learning experience. Failures are to be expected, after all; they are pushing the limits of technology and are trying things that have never been done before. Notable events in SpaceX history are: 14th of May 2002 SpaceX was founded. 28th of September 2008 SpaceX’s first rocket launch to reach orbit, the Falcon 1, which was also the first privately developed liquid­fuelled launch vehicle to reach orbit. 8th of December 2010 The first launch, orbit and recovery of a privately developed spacecraft, SpaceX’s Dragon. 25th of May 2012 Dragon was the first commercial spacecraft to dock with the International Space Station (ISS). 3rd of December 201 The SES-8 communications satellite was launched on a Falcon 9. This was the first SpaceX mission to place a spacecraft in a geostationary transfer orbit. 22nd of December 2015 SpaceX achieved the first orbital rocket propulsive landing. 8th of April 2016 The first propulsive landing on an autonomous drone ship. 27th of September 2016 SpaceX’s Interplanetary Transport System was unveiled, comprising the most powerful rocket ever built, to carry 100 passengers to Mars with a view to establishing a self-sustaining Martian colony by 2050. 30th of March 2017 The first re-flight of an orbital rocket (Falcon 9 B1021 was first flown on the 8th of April 2016). It was recovered after its second flight. 3rd of June 2017 A previously used Dragon spacecraft was launched to resupply the ISS. This was the first time Dragon was reused. It was reused a third time, landing on the 7th of June 2020. 6th of September 2017 Starship was announced, then known as Big Falcon Rocket (BFR). It is the largest rocket seriously conceived. 6th of February 2018 Falcon Heavy was launched into solar orbit. 24rd of May 2019 The first 60 operational Starlink satellites were launched. 30th of May 2020 The first launch of the Crew Dragon spacecraft, Demo-2, on a Falcon 9 rocket. The astronauts onboard were transferred to the ISS. It was the first crewed orbital flight conducted by the United States since the cessation of the Space Shuttle program in 2011. 24th of October 2020 The 100th SpaceX rocket was launched, carrying Starlink satellites. 16th of November 2020 The first fully operational flight of Crew Dragon, Crew-1, to the ISS. It was also the first of the Commercial Crew Program flights to the ISS under contract to NASA. 16th of September 2021 The first private fundraising flight on Crew Dragon by Jared Isaacman, founder of the Polaris program, on a Falcon 9 rocket. This was also the first orbital spaceflight with all private citizens. Known as Inspiration4, Energia Atlas Falcon Falcon Delta IV Yenisei New Long Ares I SLS New V Vulcan 9 Heavy Heavy Glenn March 9 Block 1 Glenn 2-Stage 3-Stage N1 Ares V Saturn V SLS Starship Block 2 Cargo the flight obtained an orbital altitude of 585km, the fifth-highest ever orbit for human spaceflight. The mission lasted just under three days. 8th of April 2022 The Axiom Ax-1 mission to the ISS carried four private astronauts, one a professional astronaut and three “space tourists” aboard a Crew Dragon launched by a Falcon 9. This was the first time private citizens visited the ISS as tourists, although they conducted some experiments. The tourists paid US$55 million per seat. 20th of April 2023 The first flight test of Starship atop a Super Heavy booster as an integrated assembly. It became the most powerful rocket ever flown. A lot of damage was done to the launch pad due to the enormous power of the engines. Problems were encountered several minutes into the flight, and the autonomous flight termination system activated to destroy the rocket. 18th of November 2023 The second test flight of Starship. Both the booster and Starship were lost. 15th of February 2024 A Falcon 9 delivered the first American spacecraft to land on the Moon since 1972, the Odysseus lander by Intuitive Machines. of America due to a loss of comms at the landing site caused by damage to an antenna during launch. Starship performed a controlled splashdown in the Indian Ocean as planned. 16th of January 2025 The seventh test flight of Starship. Super Heavy landed successfully but Starship was destroyed. 2nd of March 2025 Blue Ghost Mission 1 by Firefly Aerospace landed on the Moon. It was the first fully successful commercial lunar landing. It was launched on a SpaceX Falcon 9 rocket. 6th of March 2025 The eighth test of Starship. Super Heavy landed successfully but Starship was destroyed. This was the last Starship launch at the time of writing. 6th of March 2025 The PRIME-1 mission landed on the Moon, launched using a Falcon 9. 4th of April 2025 The private space mission Fram2 splashed down. This was the first time astronauts have been in polar orbit. They were in a Dragon capsule, and an Australian was on board. SpaceX’s engines Among the many reasons for the success of SpaceX is the innovative design of its engines and the relatively low cost of their manufacture due to simplicity of design and the extensive use of metal 3D printing to minimise fabrication cost. SpaceX currently uses two families of engine for its boosters: the Merlin and the Raptor. The Merlin is an ‘open cycle’ engine, while the Raptor is ‘closed cycle’. SpaceX also uses two other types of engine for manoeuvring and launch abort, the Draco and the SuperDraco, which are hypergolic engines. Rocket engines contain two propellant components: fuel and oxidiser. Those like the SpaceX Merlin and Raptor engines require turbopumps (similar to jet engines but pumping liquid rather than air) to bring the fuel components together in the combustion chamber (see Fig.1). Hypergolic engines, also used by SpaceX, require no turbopumps; the two fuel components come from pressurised tanks and spontaneously combust when they are brought into contact with each other. They are much simpler than the engines requiring turbopumps (however, some larger hypergolic engines use turbopumps). The pressurising medium is usually helium. 14th of March 2024 The third test of Starship. It completed the second stage burn but broke up during re-entry. The Super Heavy booster was destroyed before landing. 6th of June 2024 The fourth test flight of Starship. Both Starship and Super Heavy successfully performed re-entry and simulated a vertical landing over the ocean (with no recovery tower). 13th of October 2024 The fifth test flight of Starship. The Super Heavy booster landed successfully, while Starship performed a suborbital flight with a soft water landing as planned (it was never intended to be recovered). 19th of November 2024 The sixth test flight of Starship. Super Heavy was planned to land at Starbase, but had to land on water in the Gulf 16 Silicon Chip Fig.1: the Merlin engine is open cycle, while Raptor is closed cycle. Source: https://woosterphysicists.scotblogs.wooster.edu/2022/01/01/merlin-raptor/ Australia's electronics magazine siliconchip.com.au In an open-cycle rocket engine such as the Merlin (Fig.1, left side), some fuel and oxidiser are burned to create gas to run the turbopump and the exhaust from this process is dumped overboard. In closed-cycle rocket engines such as the Raptor (also known as staged combustion engines), the gases from driving the turbine are routed into the combustion chamber, where they contribute to thrust. A closed-cycle engine is more fuel efficient than an open-cycle engine although its design is more complex (see the right side of Fig.1). The Merlin engine The Merlin engine was used on the defunct Falcon 1 and the present Falcon 9 and Falcon Heavy boosters. These engines run on liquid oxygen and RP-1 kerosene fuels. The current versions of the Merlin engine in use is the 1D+, with nine on the Falcon 9 first stage, and 27 on the Falcon Heavy first stage, which is essentially three Falcon 9 boosters joined together. The second stage of the Falcon 9 and the Falcon Heavy both use one Merlin 1C vacuum engine, which is optimised for operation in a vacuum rather than at sea level, with a larger exhaust nozzle. The Raptor engine Fundamental to SpaceX’s desire for high rates of reusability and RAPTOR 1 turnaround of rocket engines is the innovative liquid methane/liquid oxygen fuelled Raptor engine. This engine is so innovative that it has been described as a reinvention of the rocket engine. The fuel comprising liquid methane and liquid oxygen is known as methalox, and it has a higher specific impulse than RP-1 kerosene and liquid oxygen. Specific impulse is a measure of rocket efficiency with units of seconds; it indicates the amount of thrust generated for each unit of fuel used. The higher the number, the more efficient the engine. This means the Raptor can provide more thrust for the same mass of fuel as the Merlin. Methane is commonly available; it is the main constituent of natural gas. Methalox also does not leave much residue in the engines, unlike kerosene. This means the engines don’t have to be cleaned or rebuilt between uses. Thus, they are amenable to reuse and quick turnaround, like aircraft engines, which can be reused immediately after refuelling. Although methalox has a lower specific impulse than liquid hydrogen/liquid oxygen, that fuel is difficult and expensive to use for many reasons. It was used on the 1960s to early 1970s Saturn V Moon rocket for the second RAPTOR 2 Fig.2: 33 Raptor engines power Super Heavy on the IFT-5 test. and third stages, and is used in the first and second stages of NASA’s Space Launch System (SLS) today. The Raptor engine is used on the Starship and Super Heavy booster, for missions to Earth orbit, the Moon and eventually, Mars. The Super Heavy booster has 33 engines; 20 are fixed, while the inner 13 can be gimballed for steering (see Fig.2). Starship has six engines: three regular Raptors and three vacuum variants. The vacuum-­ optimised Raptor variant is named RVac. The Raptor engine has been in a development cycle of constant improvement, simplification and weight and cost reduction; see Fig.3 RAPTOR 3 Fig.3: the Raptor 3 is the current model of the engine. As the development progressed, they were simplified, yet the performance increased. Source: https://x.com/SpaceX/status/1819772716339339664/photo/1 siliconchip.com.au Australia's electronics magazine July 2025  17 and Table 1. For more details on how Merlin and Raptor engines work, see the video at https://youtu.be/ nP9OaYUjvdE The Draco engine The Draco engine is a small rocket thruster used on the Crew Dragon and Cargo Dragon capsule for manoeuvring and attitude control. Each Dragon spacecraft has 16 Dracos. The fuel used is a hypergolic mixture: monomethyl hydrazine and nitrogen tetroxide. Each thruster generates 400N of thrust, or about 40.7kg-force. It is comparable to the Marquardt R-4D thrusters (490N thrust) used on the Apollo Service and Lunar modules, modernised versions of which are still in use today (but which use hydrazine instead of monomethyl hydrazine). Fig.4 shows a Draco operating as the capsule autonomously docks with the ISS. For a video from the same mission of the Dragon later undocking using the Draco thrusters, see https://youtube. com/shorts/AadTz2eqGq4 The SuperDraco engine The SuperDraco (Fig.6) was originally intended for propulsive landing of the Dragon spacecraft as well as being part of the Launch Abort System (LAS), but it was only used on Crew Dragon for emergency escape during a launch – see Fig.5. The Dragons land on water using parachutes for descent, but in the Fig.4: Cargo Dragon firing a Draco thruster (the orange flame) while docking with the ISS. Fig.5: a demonstration of the Crew Dragon launch escape capability using the SuperDraco engine. unlikely event of a complete parachute failure, Crew Dragon can, per a recent enhancement, be propulsively landed using the SuperDracos. There are eight SuperDracos in four pairs on each Crew Dragon. Cargo Dragon does not need this safety feature, so it is deleted to save weight. Each SuperDraco has a thrust of 71kN (7240kg-force), a burn time of 25s and a chamber pressure of 6.9MPa (69 bar). special measures are taken. There is very little written about how SpaceX solves this for the Draco thrusters. Methods that can be used include keeping the fuel in a bladder with the outside of the bladder pressurised; a sliding diaphragm in the tank; the use of surface tension effects to keep a quantity of fuel in place near the tank outlet; a small auxiliary header tank full of fuel; or a small engine with pressurised gas for an ‘ullage’ burn to accelerate the spacecraft and to deposit the fuel at the tank outlet. Only a small amount of acceleration is needed to relocate the fuel, then pumps or pressurisation will push the fuel into the engine. Starting a rocket engine in weightlessness Starting or restarting a rocket engine in the weightlessness of space is difficult, as the fuel in the tanks floats freely and does not settle at the outlet unless Fig.6: SuperDraco engines on Crew Dragon for the launch escape system. 18 Silicon Chip Australia's electronics magazine Fig.7: a Falcon 9 launch. siliconchip.com.au Fig.8: Falcon 9’s first stage landing. Fig.11: the Falcon 9 fairing. Fig.9: the Falcon 9 interstage. Source: Teslarati Fig.10: a Falcon 9 rocket with the Dragon capsule, Trunk and crew access arm. We suspect that Draco and SuperDraco use the bladder method. Both Starship and Super Heavy use residual gas in the tanks for attitude control during descent; Falcon 9 uses nitrogen gas. SpaceX’s rockets SpaceX has three main launch platforms in use: Falcon 9, Falcon Heavy and Super Heavy. Falcon 1 was SpaceX’s first rocket. It made five launches, three being unsuccessful and one with a commercial payload. It was the first privately funded rocket to reach orbit. It operated from 2006 to 2009, but SpaceX decided it was not an economical proposition and started work on Falcon 9. They then rebooked satellite launches from Falcon 1 to Falcon 9. Falcon 9 is SpaceX’s current workhorse rocket for commercial launches (see Fig.7). It first flew on the 4th of June 2010. In 2020, it became the first commercial launch vehicle to put humans into orbit. It is the most launched rocket in US history that has an orbital capability. Falcon 9’s cost per launch in 2024 was US$69.75 million (about $115 million). The total fuelled mass of the FT version is 549,054kg (about 549 tonnes) and it is approximately 70m tall and 3.7m in diameter. A Falcon 9 rocket comprises the first stage (booster), interstage, second stage, payload and fairing. The first stage or booster stage (Fig.8) is the most expensive stage, and is usually recovered. If the booster is optionally not recovered, it allows a higher launch payload, although at greater expense. The first stage has nine Merlin engines. The interstage (Fig.9) is a section connecting the first and second stages. It contains equipment to separate the two stages and the grid fins. The second stage (Fig.12) contains one Merlin vacuum engine and is impractical to recover. The payload is contained within a fairing, which is recovered. It is 13.1m long and 5.2m in diameter (Fig.11). If Dragon or Crew Dragon is launched atop a Falcon 9 rocket, no fairing is necessary (see Fig.10). The FT version of the rocket can launch 22,800kg into low Earth orbit (LEO) if the rocket is expended, or 17,500kg if it is to land. For geosynchronous transfer orbit (GTO), its payload capacity is 8300kg if the rocket is expended, 5500kg if it lands on a drone ship, or 3500kg if the rocket returns to the launch site. Falcon 9 is certified for human spaceflight. Its payload deliverable to Mars is 4020kg. It lands on four legs when it is recovered, and uses its grid fins for guidance. When it is not to be recovered, the legs and grid fins are deleted to save weight and cost. A user guide for the Falcon 9 and Falcon Heavy, intended for mission planning rather than payload design, is available at www.spacex.com/media/ falcon-users-­guide-2021-09.pdf Falcon Heavy comprises a strengthened Falcon 9 core with two Falcon 9 first stages attached as boosters on Table 1 – Raptor engine specifications (sea level variants) Raptor 1 Raptor 2 Raptor 3 Thrust force 185t 230t 280t Specific impulse 350s 347s 350s Engine mass 2080kg 1630kg 1525kg Engine+accessories mass 3630kg 2875kg 1720kg Chamber pressure 250bar 300bar 370bar siliconchip.com.au Australia's electronics magazine Fig.12: an illustration of the Falcon 9’s second stage separating. July 2025  19 Fig.13: the Falcon Heavy rocket. Source: https:// w.wiki/ DkQg Fig.14: grid fins are deployed during re-entry for booster guidance. Fig.16: the simultaneous landing of two boosters from a Falcon Heavy. Fig.15: a Falcon 9 lands on a drone ship off the coast of the Bahamas. either side (see Fig.13). The boosters and the core each have 9 Merlin 1D engines for a total of 27 engines. The core carries a standard Falcon 9 second stage, with the payload attached inside a fairing. It is powered by a single Merlin 1D engine. Apart from carrying cargo, Falcon Heavy was designed to carry humans into space, and has structural safety margins 40% above flight loads compared to 25% on other human-rated rockets. It is capable of taking crewed missions to the Moon or Mars. Its propellant is liquid oxygen/RP-1 (a highly refined kerosene). The first stage burns for 187 seconds and the second stage for 397 seconds. The first flight of the Falcon Heavy was on the 6th of February 2018. Both the boosters and core can be optionally recovered, but if they are, the payload is reduced due to the extra fuel that needs to be carried to power the engines for the descent stage of the flight. The options are to recover boosters and core, just the boosters or none at all. Recovering the boosters and core reduces the cost of the launch. The rocket is 70m tall, while each booster and the core has a diameter of 3.7m for a maximum total width of 12.2m. The mass of the rocket without payload is 1,420,000kg (1420 tonnes). It can carry a payload of up to 63,800kg into low Earth orbit when both the core and boosters are not recovered, or less than 50,000kg when both the core and boosters are recovered. It can carry a payload of 26,700kg into GTO, 16,800kg to Mars or 3,500kg to Pluto if the boosters and core are expended. If the boosters are recovered, the payload to GTO is 16,000kg and if the core is also recovered, the payload to GTO is 8,000kg. The Falcon Heavy has the fourth-­ largest payload capacity of any rocket to ever reach orbit, after NASA’s SLS, the obsolete Soviet Energia (which made two flights) and the US Saturn V, which made 13 flights. Thus, of current rocket systems, it has the second-­highest payload capacity after the SLS. Super Heavy is the booster (first stage) for the Starship spacecraft, which together are the largest rocket ever made, with a combined mass of approximately 5,000,000kg (5000 tonnes) or perhaps more. Both vehicles, Super Heavy and Starship, are designed to be reusable. Fig.17: capturing the Super Heavy booster on the 6th of March 2025. Source: SpaceX & Steve Jurvetson 20 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.18: recovering the payload fairing by parachute. Fig.19: the Dragon capsule (uc.edu). The booster is 71m tall. With the 9m diameter ‘vented interstage”, it has an empty mass of 275,000kg (275 tonnes) and a gross mass, when fuelled, of 3,675,000kg (3675 tonnes). It is powered by 33 Raptor engines with a total thrust of 73,500kN/7,490,000kgforce (Block 1), 80,800kN (Block 2) or 98,100.1kN (Block 3). Block 1 rockets have a burn time of 166 seconds and use methalox propellant. When Starship separates from Super Heavy, the Starship engines ignite while the booster is still attached, thus ‘pushing off’ from Super Heavy. This is the reason for the vented interstage connector; the ‘hot staging’ provides extra thrust. It was stated that this allows for up to 10% more payload to LEO. The payload capacity of Super Heavy into LEO is 100-150 tonnes when the rocket is recovered. The payload might be Starship carrying satellites, up to 100 people going to Mars, cargo, fuel, passengers to the Moon or point-to-point transport on Earth. For an image of Super Heavy landing and being captured by Mechazilla (more on that later), see Fig.17. The Saturn V was the world’s most powerful, successful rocket until the Super Heavy came along. Falcon & Super Heavy re-entry When the Falcon 9 or Falcon Heavy first stage boosters perform re-entry, the engines first slow the booster(s), then the grid fins (Fig.14) help to orientate and guide the booster(s) for a landing on either a drone ship (see Fig.15) or the landing zone on land LZ1 or LZ2 (Fig.16). A landing of Falcon or the side boosters of a Falcon Heavy usually occurs at LZ1 and LZ2, while the core booster lands on a drone ship if it is a full recovery mission. The fairing siliconchip.com.au used to protect the payload is also recovered by parachute and reused where possible (see Fig.18). The second stage is not recovered because it is travelling too fast (27,000km/h) and would require too much fuel to slow down and re-­ enter, unlike the first stage, which is moving much slower. The first stage would eventually fall back to Earth in any case. Grid fins On Falcon 9, Falcon Heavy and Super Heavy, grid fins are used and guide the booster to a landing (Fig.14). For Super Heavy, the landing is in the “Mechazilla” structure. The boosters have four grid fins each. Those on Falcon 9 and Falcon Heavy are made of titanium and measure 2 × 1.2m. They are folded during ascent. On Super Heavy, they remain extended to simplify the design and save weight. In this case, each measures 7 × 3m, is made of stainless steel and weighs three tonnes. When the boosters re-enter, they return enginefirst; the heat-resistant engines act as a de facto heat shield. Super Heavy vs the N1 and Saturn V On the 20th of April 2023, the Super Heavy rocket broke the record for the most powerful rocket. For the 50 years before that, the record was held by the Soviet N1, a competitor to the United States’ Saturn V Moon rocket. However, the N1 never achieved orbit after four attempts. Similar to Super Heavy with 33 engines generating 73,500kN of thrust, the N1 had 30 engines and produced 45,400kN of thrust. The US Saturn V with five engines generated 34,500kN of thrust and successfully took astronauts to the Moon. Australia's electronics magazine Spacecraft SpaceX’s main spacecraft in use or under development now are variants of Dragon and Starship. The Dragon spacecraft are primarily designed for crew and cargo transport to the ISS and Earth orbit. Starship is designed for heavy lifting of crew, cargo and fuel to locations on the Earth’s surface, Earth orbit, the Moon, Mars and elsewhere. Starhopper was a test vehicle built for the purpose of landing and control algorithms for Starship and flown four times in 2019. It used methalox fuel. Dragon 1 flew 23 cargo missions to the ISS from 2010 to 2020. It was not designed to carry astronauts and was the first private spacecraft to dock with the ISS. Dragon 2 (Fig.19) was introduced in 2019, with both Crew Dragon and Cargo Dragon variants. The Crew Dragon carries astronauts to and from the ISS under NASA’s Commercial Resupply Services (CRS) program and also on orbital missions such as the recent Fram2 (Fig.20). Fig.20: recovery of the Fram2 mission Crew Dragon capsule. Note the scorch marks from re-entry. July 2025  21 Fig.21: note how (relatively) spacious the interior of the Crew Dragon capsule is. These are the SpaceX Crew-8 astronauts. The Crew Dragon usually carries four astronauts, but it can be configured to carry seven. The interior is relatively spacious (see Fig.21). Both types of Dragon spacecraft are fully autonomous, but astronauts or Mission Control can take control of Crew Dragon if necessary. Like Dragon 1, Dragon 2s (which are now called Crew Dragon or Cargo Dragon) are reusable. Also see Figs.22, 23 & 24. The Dragon 2 capsules are 8.1m tall, 4m in diameter, with a volume of 9.3m3 and a launch mass of 6,000kg (six tonnes). The return mass is 3,000kg (three tonnes). For landing, Dragon is designed to re-enter the Earth’s atmosphere, where it is initially slowed by its heat shield. Drogue parachutes are then released, Fig.22: The Trunk section at the back of the Dragon 2 capsule is discarded after launch. followed by four main parachutes. Crew Dragon can land safely even if only one of the four parachutes deploy (see https://youtu.be/YDFgFnEVn_o). After landing in the ocean, the main parachutes are disconnected to stop the capsule being dragged by the wind. The capsule is designed to float by itself, but if necessary, extra flotation devices can be deployed in an emergency to prevent the capsule sinking. The Dragon capsules were originally intended to land propulsively using SuperDraco engines, but this idea was abandoned in favour of ocean splashdowns. The Crew Dragon also has SuperDraco engines in case of a launch failure, to remove the capsule from the rocket and move it to safety for a parachute landing (shown earlier in Fig.5). The Cargo Dragon does not need this safety feature, so it does not have the SuperDraco engines installed. In the unlikely event of a total parachute failure, Crew Dragon now has the ability to use the SuperDraco engines to land propulsively. The reason the original plans for Crew Dragon to land propulsively were abandoned was partly due to NASA’s requirement for a parachute landing on water. But now propulsive landing has been reinstated as an emergency measure. The Dragon carries a Trunk module with a 37m3 volume, which is unpressurised and can carry cargo. It is half-covered in solar panels to generate power for the capsule while in flight or docked at the ISS. The other half is covered with a thermal radiator system. Active Vent Valves Emergency Ventilation Fan Dehumidifier Vacuum Isolation Valves Fig.23: a cutaway of Dragon capsule, from the same source as Fig.24. Toilet Dehumidifier Vacuum Lines Fire Extinguisher Valve Panel Cabin Fans Dehumidifier Waste Locker Active LiOH Cartridge Valve Panel Waste Fans Urine Tank Fig.24: some of Dragon’s plumbing and thermal controls. Source: www.uc.edu/content/dam/ refresh/cont-ed-62/olli/fall-23-class-handouts/ SpaceX%205Dragon%20Capsules.pdf 22 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.26: a rendering of the USDV designed for deorbiting the ISS. It is a modified Dragon. Source: https://x.com/ SpaceX/status/1813632705281818671/photo/1 Fig.25: under the skin of the Dragon capsule (uc.edu). The Trunk module is jettisoned before re-entry and is meant to burn up in the atmosphere, but parts of it occasionally survive re-entry. The Trunk provides the mechanical and electrical interface to the Falcon 9. The Trunk also has fins to stabilise the Dragon and Trunk in the event of an aborted launch. Electrical and fluid connections are provided inside the trunk to accommodate various payloads, including small satellites. The Trunk space is almost ‘free’ and represents the utilisation of an area that would otherwise be unused. Fig.25 shows the inner structure of the Dragon, which is made of aluminium, while the outer shell is carbon fibre. Section A is the pressure vessel, which contains the crew couches, while section B contains equipment. The primary heat shield at the bottom is made from PICA-X (more on that later). Dragon 2 communicates by several methods. It connects to satellites via NASA’s Tracking and Data Relay Satellite System; it can communicate with ground stations with a 300kbps Command Uplink and 300Mbps+ telemetry and data downlink. Payloads can be connected to the vehicle via Ethernet, RS-422 and MIL-STD-1553. There are redundant communications systems via telemetry and video transmitters on S-Band and, as of Fram2, connectivity with Starlink via laser. There was once a Red Dragon proposal to propulsively land an uncrewed Dragon capsule on Mars to deliver equipment and a sample return rover. Propulsive landing would be ideal siliconchip.com.au on Mars since the thin atmosphere makes parachute landings difficult. Red Dragon was abandoned when Starship became the focus for trips to Mars. Dragon XL is a planned variant that will be used to supply NASA’s Lunar Gateway, a planned space station in lunar orbit. It will carry cargo and experiments, keeping up to 5,000kg (five tonnes) of supplies in lunar orbit with the Gateway for 6–12 months. The XL is not required to return to Earth; after use, it will be parked in a heliocentric orbit (ie, orbiting the sun). When the ISS is finally deorbited, as planned in the early 2030s, a modified Dragon called the US Deorbit Vehicle (USDV; Fig.26) will dock with the ISS and use 46 Draco engines attached to a larger-than-usual trunk section to guide and push it into the atmosphere at an appropriate place. This will ensure that the structure burns up over the Pacific Ocean and any small remaining debris will fall into the empty ocean after shipping has been cleared from the area. The USDV will have six times the propellant and four times the power of a regular Dragon. It will be a sad ending for the ISS but is necessary for reasons explained in the video at https://youtu. be/cohVHaVMBl8 Starship Starship and its variants (Fig.27) will be a highly versatile workhorse of the future SpaceX fleet, delivering Fig.27: Starship ready for launch. One of the thermal protection tiles has been removed for testing purposes. Australia's electronics magazine July 2025  23 people, cargo and fuel to other locations anywhere on Earth in less than one hour or into Earth orbit, the Moon, Mars and beyond. Starship is the second stage of the Super Heavy booster. Perhaps confusingly, the ‘stacked’ (combined) Super Heavy booster and Starship second stage might also be called Starship together. The depot version of Starship will remain in orbit and so does not require heat shields or control surfaces. The HLS version, which will shuttle between Earth and Moon and will not land on Earth, is similar. Propellant tankers, which can land, can also refuel other Starships. When stacked with Super Heavy and fuelled (Fig.28), Starship has a total mass of approximately 4975 tonnes (Block 1) or 5260 tonnes (Block 2) and a height of 121–123m depending on the version. It is the largest and most powerful rocket ever built and the heaviest object ever flown. Starship can deliver 100–150 tonnes of cargo if reused, or 250 tonnes if the booster is expended. Versions of Starship for landing on the Moon or Mars will have landing legs. One possible use of Starship is for rapid delivery of supplies for military missions or natural disasters on Earth. It will be able to reach anywhere on Earth within one hour. For landing on Earth, Starship will use four flaps for guidance, two forward and two aft, as well as grid fins. It will be caught in the arms of a Mechazilla structure, like Super Heavy. Heat shields protect it during re-entry. The Starship second stage has a height of about 50m (Block 1) or 52m (Block 2), a diameter of 9m, an empty mass of about 85,000kg (85 tonnes) and a fully fuelled mass of 1,500,000kg (1500 tonnes). Starship uses methalox fuel, with three Raptor engines and three Raptor vacuum engines. The versions of Starship optimised for lunar landing will have legs, and possibly engines that are mounted higher up, to avoid kicking up lunar dust. Such versions will shuttle between the Moon and Earth orbit, where they will be refuelled and will not land on Earth. It is estimated that eight Starship launches will be required to get enough fuel into orbit for one refuelling. Why use so many engines? Compared with the Space Shuttle, the Saturn V and other rockets that use relatively few engines, SpaceX rockets use many (see Fig.29). This Fig.28: Starship & Super Heavy booster for Starship’s 8th flight test. 24 Silicon Chip relates to propulsive landing. Large rocket engines have a limited range of thrust in which they will work, and cannot be throttled back to the relatively low thrust levels required for a landing (other rocket designs can’t land this way). Note that while all engines are used for launch, only some are reignited for landing. Smaller engines that can work within the required thrust range are needed. However, because their thrust is relatively low compared to large engines, more are needed for launches. Having many engines also makes the failure of one more tolerable. Another advantage is that standardising on a few engine designs for multiple rocket designs enables greater economies of scale of mass production. SpaceX wants to have a fleet of hundreds or thousands of rockets running continuous missions into Earth orbit and beyond. Next month There is more to this story, but that’s all we can fit in this issue. In the second and final part next month, we will have details of SpaceX’s proposed Mars missions using Starship, more on the rocket recovery methods, their launch sites and some notable missions SpaceX has undertaken. We’ll also have some brief updates on two of their main competitors, Blue Origin and Virgin Galactic. Along with SpaceX, they were both mentioned in our October 2018 article on Reusable Rockets (siliconchip.au/ Article/11257), but much has changed since then. Fig.29: Falcon 9 has nine engines in its first stage, Falcon Heavy has 27, while Starship has 33! This gives redundancy and better control for landing. Australia's electronics magazine siliconchip.com.au Elon Musk: a controversial figure Elon has been somewhat divisive since he became one of the world’s richest people. These days, “controversial” is putting it mildly! Still, as the founder of and visionary behind SpaceX, we can’t tell the story of the company without mentioning him. Whether you love him, hate him, or are totally indifferent, he has been a driving force behind several major technology companies, including PayPal, SpaceX, Twitter/X, OpenAI and Neuralink, among others. Elon Musk’s engineering philosophy These are the distinguishing characteristics of his businesses, as opposed to traditional, more conservatively run ones. He emphasises excellence, high-quality engineering and simplicity of design, as quoted in Walter Isaacson’s biography of Musk: A humourous AI-generated image of Elon Musk and Optimus with Starship on Mars (one wonders how he is breathing with his helmet removed). 1) Question every requirement. Each should come with the name of the person who made it. You should never accept that a requirement came from a department, such as from “the legal department” or “the safety department.” You need to know the name of the real person who made that requirement. Then you should question it, no matter how smart that person is. Requirements from smart people are the most dangerous, because people are less likely to question them. Always do so, even if the requirement came from me. Then make the requirements less dumb. 2) Delete any part or process you can. You may have to add them back later. In fact, if you do not end up adding back at least 10% of them, then you didn’t delete enough. 3) Simplify and optimize. This should come after step two. Common mistake is to simplify and optimize a part or a process that should not exist. 4) Accelerate cycle time. Every process can be speeded up. But only do this after you have followed the first three steps. In the Tesla factory, I mistakenly spent a lot of time accelerating processes that I later realized should have been deleted. 5) Automate. That comes last. The big mistake in Nevada and at Fremont was that I began by trying to automate every step. We should have waited until all the requirements had been questioned, parts and processes deleted, and the bugs were shaken out. Elon is quoted as saying, “the best part is no part”. Another aspect of Musk’s philosophy is that he sees patents as “stifling” and, in 2019, he made Tesla’s entire patent portfolio available under Creative Commons licensing for non-­ commercial purposes. With regards to SpaceX, he said, “If things are not failing you’re not innovating enough.” He wants to see rocket launches become as routine as airline flights, and nearly as cheap, with a similar turnaround time between flights. He wants to ‘democratise space’ and making it accessible to as many people as possible. Musk has said that with SpaceX, he spends more time on government paperwork than rocket development. On the 15th of March 2025, Elon Musk announced on X that “Starship departs for Mars at the end of next year, carrying Optimus. If those landings go well, then human landings may start as soon as 2029, although 2031 is more likely.” (https://x.com/elonmusk/status/1900774290682683612). Optimus is the humanoid robot designed by Tesla. As for the continuing development of Starlink, Elon Musk Tweeted on the 15th of October 2024 that, “The next generation Starlink satellites, which are so big that only Starship can launch them, will allow for a 10X increase in bandwidth and, with the reduced altitude, faster latency” (https://x.com/elonmusk/ status/1845884681050276333). SC siliconchip.com.au Australia's electronics magazine The current Starlink constellation. Source: satellitemap.space July 2025  25 USB Solar Charging System Simple Electronic Projects with Julian Edgar Charge and power all your USB devices from solar with this low-cost system. It’s inexpensive to put together, and once you’ve built it, charging your devices won’t cost a cent! I have lots of solar-powered devices. A solar-powered smart watch, a solar-powered iPhone, solar-powered noise-reducing headphones and a solar-powered mini floodlight. In fact, every one of my devices charged from a USB adaptor is now solar powered. This is achieved very simply and, if you’re careful with your purchasing, very inexpensively too. The parts required Only a few parts are required: a solar panel (Photo 1), a charge controller (Photo 5), a 12V battery and a one or more 12V to 5V USB converters (Photos 2, 3 & 4). You could spend hundreds of dollars on assembling these parts – or you could do as I did, and buy mostly second-hand, via online market places and/or make use of parts that others have thrown away. The solar panel needs to have an output voltage suitable for charging a 12V battery through a charge controller. This means getting a panel that has a maximum open circuit voltage of about 18-30V, depending on the selected controller. The maximum solar panel output power will also be governed largely by the controller you select. Small charge controllers may have a 60W limit, while larger controllers are good for 250W. So selecting the correct panel is done in conjunction with the charge controller you’ve picked. Second-hand solar panels are now ridiculously cheap – expect to pay from about $25 for a suitable used panel. Also remember that, in this application, the panel’s original maximum output power is probably not needed. To put that another way, this is a good project for reusing degraded panels that otherwise would go to scrap. The appropriate charge controller Photo 1: I mounted this 100W solar panel on a disused satellite dish on the roof. The panel can also be wall-mounted, or even just anchored to the ground. Second-hand solar panels are now very cheap. 26 Silicon Chip Australia's electronics magazine will also depend on the battery type you’re going to use. Sealed lead acid (SLA) batteries are ideal for this application as they can be mounted inside without concern for acid spills or venting of gases. However, SLA batteries tend to be expensive – even second-­ hand – so you may wish to use a conventional car battery. A major benefit of using a car battery is that you can get one free of charge. Simply visit a local mechanic or car battery supply shop. There you will find literally dozens of batteries that have been discarded – they’ve been replaced as no longer being suitable for cranking engines. However, starting an engine is very demanding on a battery; the current draw is in hundreds of amps. So these batteries often still have sufficient capacity to work as a storage battery in a solar system of the type being covered here. Photo 2: this 12V-to-USB converter/ charger provides two outputs and a voltmeter to allowing monitoring of system voltage. It cost about $11 from Banggood (similar units can be found on AliExpress & eBay). siliconchip.com.au Solar panel and battery ratings The greater the power of the solar panel, the better it will work through poor weather and the more battery charge you will have to work with. Also, the larger the battery, the longer the system will cope with cloudy days when little solar output is available. To give you a guide, where I live about 100km north of Canberra, in four years I have never gone close to running out of power using a 100W panel and a 26Ah SLA battery – the latter bought as defective and so probably having only half this nominal capacity. That includes charging power tool batteries as well as my phone, watch, camera, etc. Note also that smaller panels and batteries tend to be more expensive second-­hand, so there’s a further advantage in going big. When selecting a battery from the discard pile, use a multimeter to find a battery that still has an open-circuit voltage above 12V. If you are going to use the battery inside, select one that is fully sealed. A battery with flat terminals to which lugs can be bolted will be easier to wire than a battery with round terminal posts. If you have one with round posts, you’ll need to get matching terminals to attach wires to it (eg, Jaycar Cat HC4038), which will be an extra cost. Once you have selected a solar panel and battery, you can pick a charge controller to suit. Here it’s worthwhile buying new. At the time of writing, a 30A (about 400W) 12V charge controller costs around $12, including freight. They can be bought from AliExpress and similar suppliers. Ensure the controller can be configured to suit the battery type you’re using – most can. Many controllers also have built-in USB 5V outputs. If you choose to use these, you don’t need to buy an additional USB converter. However, more for convenience and appearance, I added three USB output converters to my system. Each of these has two USB outputs (giving six in total), on/off switches and an onboard LED display showing the battery voltage. These units are about $11 each. Note that when selecting these, ensure you don’t get ones designed to plug into a cigarette lighter socket – you want wired-in ones. If you want an even cheaper approach, just buy a 12V-to-USB wired converter that comprises a sealed box, USB output socket on a lead, and input power connections. In addition to these parts, you will need assorted cabling, terminals, an inline fuse holder and fuse, and siliconchip.com.au possibly a panel on which to mount the USB outlets. Building the system Before starting to build the system, consider the cabling requirements. I have the charging system working in my home office, so I had to run a cable from the roof-mounted solar panel through the wall of my house. In my case, that was easy but, in many houses, that will be quite hard! If that’s Photo 3: this non-switched panel with two USB outputs costs about $6 from AliExpress. Ensure you get a device that runs from 12V. the situation, consider having the charging system in an outside workshop or shed. It will still be very useful there – for example, most battery-powered tools have 12V car chargers available for their batteries, so the system can be used to charge power tool batteries. Also, consider how the solar panel will be mounted. In my situation, a disused satellite TV dish antenna was on the roof, pointing north. Mounting Photo 4: in my system, three 12V-to-USB adaptors provide six outlets at the desk in my home office. Note the inconsistency in the voltage readouts – at these prices, you can’t expect perfection! This is the charging voltage on a sunny day. Photo 5: this solar panel charge controller from AliExpress incorporates two USB outputs so, if you wish, you can charge your items directly from this module. Australia's electronics magazine July 2025  27 the panel was just a case of attaching the panel to the dish – quick and easy! However, again, that may not be the situation in your case. If roof-­ mounting is difficult, consider mounting the panel on a wall or even on the ground. The panel should face north and be tilted at an angle that approximately corresponds to your latitude, although horizontal panels will generally work OK. We don’t need to squeeze every drop of power out if it! Fig.1 shows the wiring – it is very simple. Ensure you place the fuse close to the battery; it should be rated at the maximum charging current, as dictated by the controller. If you are not used to working with 12V storage batteries, keep in mind that although the voltage is low (so you won’t get a shock), the ability to deliver current is very high and so you must be careful to ensure that the battery is never short-circuited. I have seen this done when someone inadvertently dropped a spanner across the battery terminals... not good! Always take great care when attaching battery connectors; the battery terminals must be insulated when the battery is in use. An easy way to achieve this is to place the battery in a dedicated box. Boxes designed to house car batteries are available from about $15 from local suppliers. First, connect the battery to the solar Parts List – USB Solar Charging System 1 12V solar panel 1 12V charge controller (type to suit panel and battery) 1 12V rechargeable battery 1 pair of battery terminals (may not be required depending on battery type) 1 inline fuse, rated to suit charge controller 1 or more 12V-powered USB chargers various lengths of wire, rated to handle the maximum charging current Fig.1: the wiring is straightforward, but ensure you maintain the correct polarity of all the connections. Don’t insert the fuse until you have wired the battery to the controller. controller, ensuring the polarity of the connections is correct. Once these connections are made and insulated, insert the inline fuse. The controller should then come alive. Set the controller to the correct battery type, and if the controller has these facilities, ensure the settings for float charge and auto-disconnect (that occurs if the battery is discharged too far) are correct – many simpler charge controllers won’t have these functions. Next, connect the solar panel to the controller, again ensuring correct polarity of the wiring. If you’re unsure of which wire is which (an easy confusion to occur if you’ve extended the solar panel wiring), use a multimeter to identify the positive and negative wires – the solar panel will need to be exposed to light when you perform this check. After the solar panel is connected, most controllers will confirm the panel is generating power, either on the LCD screen or by the simple illumination of an onboard LED. Finally, if you are not using a built-in USB outlet, connect the external USB converter(s). Ensure that no timers are activated on the controller output – you want the output on all the time. Conclusion Photo 6: a used car battery that is no longer strong enough to crank a car engine will often be suitable for this application. Such batteries are available free of charge from car workshops and battery replacement shops. However, it’s best to get a battery with bolt-on terminals rather than round battery posts like this one. If mounting the battery inside, ensure it is of a sealed design. 28 Silicon Chip Australia's electronics magazine What has surprised me over the four years that I have been running the system is its ease of use and convenience. I just plug in the devices, and they charge – obvious, huh? But they charge purely on solar power, and they charge irrespective of the weather. Also, they charge through blackouts, so there’s that safety advantage to conSC sider as well. siliconchip.com.au July GEAR UP! Great tech savings across the range. These deals must end July 31st - shop in store or online. T 2125 NEW! 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Easy croc clip or car accessory plug connection. Can even be permanently installed outdoors. Sale Ends July 31st 2025 Shop in-store at one of our 11 locations around Australia: WA » PERTH » JOONDALUP » CANNINGTON » MIDLAND » MYAREE » BALCATTA VIC » SPRINGVALE » AIRPORT WEST QLD » VIRGINIA NSW » AUBURN SA » PROSPECT Or find a local reseller at: altronics.com.au/storelocations/dealers/ Shop online 24/7 <at> altronics.com.au © Altronics 2025. E&OE. Prices stated herein are only valid until date shown or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. B 0007 SmartProbe Project by Andrew Levido The SmartProbe is an extremely handy little device for making voltage & continuity measurements. It won’t replace your multimeter, but it is designed to be the first piece of test equipment you reach for when debugging or repairing a circuit. I have made the SmartProbe very small, measuring just 60mm long, 30mm wide and 15mm thick. That’s about the size of a box of matches, for anyone old enough to remember one! A probe fine enough for modern surface-mount circuits (or through-hole parts) is fitted to one end of the case, while a short flying ground lead emerges from the other. It is equipped with a 128 × 64 pixel OLED display and an audio transducer to show voltage measurements and give feedback, respectively. There are no buttons or switches. The SmartProbe switches itself on when you pick it up, and off again when it senses no movement for a few seconds. You switch between voltage measurement and continuity modes by tapping it with your index finger. The display automatically flips rightway-up however you hold it. The unit is powered by a single CR2032 coin cell that should last many months with typical use. ±0.5%, and the input impedance is around 1MW on both ranges. In the continuity mode, the SmartProbe sources a low current (around 1mA) and displays the voltage drop seen across the probes, just as your multimeter does on the diode test range. The source voltage is 3.3V, enough to forward-bias typical diodes, transistor junctions and most LEDs. If the resistance between the probes is greater than about 60kW, the display shows “OPEN”. There is an audio indication of continuity if the measured drop is less than about 1V. The continuity beep responds within a few milliseconds, which is essential for a good user experience. The SmartProbe is not suitable for use with high-voltage or mains- ­ owered circuits. While it has a degree p of input protection, it does not have the insulation or overload ratings of a good multimeter. I considered adding AC voltage or frequency measurement capabilities, but elected to keep it really small & simple. Ultra-low power design The SmartProbe operates in either voltage measurement or continuity mode. In the former, it can measure voltages up to ±50V, switching automatically between two ranges. For input voltages below ±6V, it has a resolution of 5mV or better; for higher voltages, the resolution is 50mV. Its absolute accuracy is within » Compact size (60 × 30 × 15mm) and lightweight (24g) » Measures voltage or continuity » 128×64 pixel OLED screen » Internal buzzer for continuity checking » Measures up to ±50V » Can also test diodes/LEDs and measure forward voltage » Single fine-tipped probe with a ground clip » Powered by an internal CR2032 coin cell One of the main aims and challenges of this design was to keep the power consumption when the device is ‘off’ to a level that would give meaningful battery life, while still being able to sense movement and wake up. A CR2032 cell has a capacity of about 235mAh while discharging from 3V (fully charged) to an end voltage of 2V. I set myself the goal of aiming for a shelf life of one year (8760 hours), meaning less than 27µA of idle consumption. As we shall soon see, that goal was more than met. Before diving into the circuit, it is helpful to look at the block diagram of the front end (Fig.1). This shows the device in voltage measurement mode, with just one voltage range for simplicity. We want to convert a bipolar voltage up to ±50V, appearing between the probe and clip, to a unipolar voltage between 0V and 3.3V (V1) suitable for the analog-to-digital converter (ADC). We do this by fixing the bottom (ground clip) end of the Ra/Rb voltage divider to half the supply rail, ie, around 1.65V. Voltage V1 is therefore siliconchip.com.au Australia's electronics magazine July 2025  33 Specifications Features & Specifications Fig.1: one end of the input voltage divider is fixed to ½ of the supply voltage to provide an offset so that bipolar (±) input voltages can be measured with a unipolar ADC. The offset is later subtracted by the firmware. an attenuated and buffered version of the input voltage offset by ½Vcc, as described by the equation V1 = (Vin × Rb) ÷ (Ra + Rb) + Voffset. If we also buffer and convert the offset voltage, Voffset, we can subtract it from the converted version of V1 in firmware. The resulting digital code will be a signed value proportional to Vin. The full circuit (Fig.2) shows that there are actually two dividers and associated buffers in the SmartProbe, one for each input voltage range. For the high-voltage range, it uses a 2MW/51kW divider, while the 2MW/680kW divider is for the low-voltage range. The output of each is buffered by IC1d and IC1c, respectively, and fed to its own ADC input channel on microcontroller IC2. I chose the divider resistor values such that the voltage span seen by the ADC inputs is around 3V centred on around 1.65V (0.15V to 3.15V). This allowed me to stay away from the very ends of the ADC range and avoid a potential source of errors. I am using ±0.1% tolerance resistors here, as these are critical to achieving the required resolution and accuracy. The op amps are low-cost zerodrift (auto-zero) op amps. These have a worst case offset voltage of ±10µV with just 50nV/°C drift. Since they are connected as unity-gain buffers, there is no appreciable gain error. The offset voltage is also buffered (by IC1a) and fed to another ADC channel. All three of these input buffers are identical, including protection diode pairs (D1 through D3), and a small amount of low-pass filtering on the inputs (using 1nF/100nF capacitors) and outputs (1.5kW/1nF). Most of the filtering of these signals occurs in software, as discussed below. 34 Silicon Chip When the input voltage is outside the ±6V range, the output of the low-voltage sensing circuit (IC1c) saturates, and the digital code associated with this input moves outside the expected range. The firmware automatically switches to using the high-voltage input in this case. If the high-voltage input approaches saturation, a voltage over-range warning message is displayed. The bottom ends of the dividers are fed by a current-limited buffer, IC1b. The 10W resistor provides a bit of protection to the op amp, since its output would otherwise be connected directly to the ground clip and therefore exposed to the outside world. The input of the buffer is connected to a 100kW/100kW voltage divider fed from one of the microcontroller’s GPIO pins (PA06, pin 12). This pin is configured as a digital output. If it is high, the buffer input is half of the supply voltage, as in Fig.1. If the output is low, the bottom end of the divider is effectively connected to 0V – a state which comes in handy for continuity mode. Continuity measurement So far, we have ignored the network consisting of Mosfets Q1-Q3 and the associated passive components. These form an analog switch that is off in voltage mode. In continuity mode, the offset at the bottom of the voltage dividers is set to zero, as mentioned above, and the analog switch is on. This connects the 3.3V supply to the input probe via the 3kW resistor. A voltage of approximately 3.3V is therefore present across the probes when they are open circuit. This voltage drops as the impedance between the probe falls, ultimately to zero if the probe is shorted to the Australia's electronics magazine clip. If a diode junction is connected across the input, with its anode to the probe, the forward drop of the diode will appear across the input. In continuity mode, the voltage is read by the ADC in the same way as already described, except the offset voltage will be close to zero. The equation shown in Fig.1 will still hold, but we will no longer be able to read negative voltages; that doesn’t matter in continuity test mode. You will notice that the output of buffer IC1c connects directly to the PA03 pin of the microcontroller, as well as to the ADC input via the RC filter. PA03 is internally connected to a fast comparator that drives the continuity beep tone. The analog switch The analog switch deserves a closer look. We require a switch with a very high impedance when off, so that no appreciable current flows through the 3kW resistor when measuring voltages. The switch must withstand ±50V when open, but have relatively low on-resistance when closed. I could not find a suitable off-theshelf analog switch because the voltage requirements are relatively high, so I built my own using two P-channel Mosfets with an N-channel Mosfet to drive them. The switch is open when Q3 is off, and the gates of Q1 & Q2 are held at their source potential by the 100kW resistor. Since the gate-source voltage is zero, both Mosfets will be off. You can see what happens when an external voltage is applied by referring to the left and middle diagrams in Fig.3. If the drain of Q1 is at +50V, its source will also be at this potential due to the conduction of its body diode. Both Mosfet’s gates and sources will therefore be at +50V, so they will remain off. Q2 will therefore block any current flow, since its body diode is reverse-biased. If the drain of Q1 is at -50V, the body diode of Q2 is forward-biased, leaving the sources and gates of both Mosfets at 3.3V. Q1 now blocks any current flow. When Q3 is switched on, the gates of both Mosfets gates will be at 0V. The drain of Q2 is fixed at 3.3V, so the body diode initially conducts, causing the sources of both Mosfets to rise almost to this value. The resulting -3.3V gatesource potential is enough to switch both Mosfets on, effectively shorting siliconchip.com.au Fig.2: the SmartProbe circuit is fairly straightforward, except for a few tricks related to achieving ultra-low power consumption that are detailed in the text. out their respective body diodes and switching the analog switch fully on. The ZXMP6A17E6 Mosfets I chose have a maximum Vds of -60V and an Rds(on) of less than 0.5W with a Vgs of 2.5V (interestingly, they have six pins, but the three additional ones are just extra drain connections). The total on-resistance of the analog switch will therefore be around 1W. The P-channel Mosfets see a worstcase voltage of -53.3V. siliconchip.com.au The BSS138K (Q3), with a maximum Vds of 50V, places the upper limit on switch voltage. This is a bit of a soft limit, since the 100kW resistor limits the avalanche current if Q3 were to break down. Nevertheless, this switch is what limits the nominal maximum voltage for the SmartProbe. Digital circuity The microcontroller is a 32-bit STM32L031F6 low-power Arm Cortex Australia's electronics magazine M0+ from ST Microelectronics. This has 32kiB of flash, 8kiB of RAM and comes in a 20-pin TSSOP package. Importantly, it operates at any voltage between 1.8V and 3.6V, and can be put into various low-power modes where its current draw reduces to single-digit microamp levels while still retaining RAM contents. The display connects to the microcontroller via an I2C interface. This is a 128 × 64 pixel white OLED screen that July 2025  35 Both sides of the SmartProbe PCB. The flat flex cable on the back of the OLED is soldered to the PCB and the screen is then held down with double-sided tape. measures just 34 × 22 × 1.5mm. These displays are readily available for just a few dollars each from AliExpress. They have a SH1106 control chip onboard, and can be controlled via an 8-bit parallel or SPI/I2C serial bus. The display only needs four 100nF capacitors and one resistor added to create the necessary internal voltages (all shown to the right of DISP1). The OLED current is set by the resistor. I have used 510kW, which gives a current of about 10µA per pixel. This is nice and bright, but means that the display could draw as much as 82mA (128 × 64 × 10µA) if all pixels were on. In reality, the measured current stays under 20mA or so, since we never light more than about 25% of the pixels simultaneously. Nevertheless, the display is the main current consumer in the circuit and has to be completely shut down when the SmartProbe is inactive. To help ensure it comes up reliably when awakened, I have wired its hardware reset pin to a microcontroller GPIO pin (PC15). The audio transducer, MB1, is a small magnetic beeper that requires an AC signal to operate. This means it can deliver a variety of tones if driven at different frequencies. I have used one of the micro’s PWM outputs (routed to the PA05 pin) to drive it via Mosfet Q4. Using a PWM output allows me to set the tone by varying the PWM carrier frequency and manage the volume, and more critically, the current consumption, by limiting the duty cycle. Even so, it presents a significant (relatively speaking) load on the supply. For this reason, I used it only when I think it is really necessary. Accelerometer Because the accelerometer is the only component in this circuit that is always operational, I needed to choose it carefully. I selected the LIS2DW12 three-axis “digital motion sensor” for this application because it is specifically geared toward ultra-low-power applications. This chip (IC3) contains a three-axis MEMS accelerometer and a heap of signal processing hardware that can be configured to detect device orientation, free-fall events and tap or double-­tap events on any axis. It can detect activity and put itself into a lowpower state when it senses inactivity, waking itself up again autonomously. I took advantage of the orientation function to flip the display the right way up, the single tap function to change modes and the activity/inactivity function to turn the SmartProbe on and off. The device supports a range of sampling rates and draws anywhere between 500nA and 90µA when operating. Lower data rates result in lower operating currents, but some features we need won’t work at the very lowest data rates. For this reason, we run the accelerometer at 400 samples per second when active, dropping to 200 samples per second when ‘off’. This gives us an ‘off’ power consumption of somewhere around 12-20µA. The data sheet says the consumption will be 12µA in the mode and data rate we use, but that is specified at 1.8V and 25°C. The data provides no help in understanding what the consumption will be at higher temperatures or with voltages up to 3.0V, as it will experience in our circuit. No data usually means you can safely assume it will be worse. My measurements show consumption closer to 16-20µA with our battery voltage range and my (unairconditioned) room temperature. While that is higher than the published figures, I think it is still pretty amazing performance considering the chip is taking three 14-bit accelerometer samples every 5ms and pushing them through a fairly complex digital signal processing chain. Hardware-wise, the LIS2DW12 is very nice; it has just 12 pins, requires no external components and costs just $2.50 in single quantities. The downside is that it is only available in a 2 × 2mm leadless package. Fortunately, it does not have a thermal pad, so it is easier to hand-solder than some chips I have come across. Fig.3: the left and middle diagrams show the voltages on the analog switch in the off state with +50V and -50V applied to the input, respectively. The rightmost diagram shows them when the switch is on. 36 Silicon Chip Australia's electronics magazine siliconchip.com.au It is a complex device from a firmware perspective, but I took the time to write a (reasonably) comprehensive driver, since I intend to use this chip again. Power supply The power supply scheme is straightforward, as shown in Fig.4. There are two power rails: Vbat, which is derived from a lithium coin cell and is always available, plus a 3.3V (3V3) rail that is only available when the SmartProbe is on. The 3.3V rail is derived from the coin cell via a boost converter based around IC4, a TPS61033. The boost converter is enabled by the PWR_ON signal from the microcontroller, so the display, analog front end and beeper are only powered when the SmartProbe is on. The shutdown leakage current of the TPS61033 is specified at 0.1µA, so well within our meagre power budget. The Vbat supply is the diode-OR combination of the coin cell voltage and the 3.3V supply. The upshot of this is that Vbat will be approximately 3.3V while the device is on, but will fall to very near the battery voltage when asleep. Both the accelerometer and microcontroller will happily operate at any voltage between 3.6V and 1.8V, so this is not a problem for them. I used a pair of schottky diodes to combine the supplies to minimise the forward drop, keeping it to only about 0.2V at the low currents drawn in standby mode. Firmware The firmware architecture is shown in Fig.5. The software consists of a main loop, shown at the top, and four asynchronous tasks triggered by interrupts, shown at the bottom. Some of these asynchronous tasks communicate with the main loop via a few shared data registers and flags. When an interrupt occurs, the processor stops what it is doing and starts running code from the appropriate interrupt service routine (ISR). When the code starts from reset, the microcontroller core and onboard peripherals are initialised. This includes such things as setting up the microcontroller clocks, the I2C peripheral, PWM, timers and the like. This only needs to be done once, because when the microcontroller is stopped, the RAM contents and register data are retained. After this, the external peripherals are initialised via their drivers. This involves enabling the boost converter, initialising the accelerometer and the OLED display. This step is repeated each time the SmartProbe awakens because the display driver’s configuration registers are lost when the 3V3 rail is disabled. We also reconfigure the accelerometer, even though it is never shut down completely. We do, however, disable some of its functions before putting the microcontroller into sleep mode, so it is easier just to reprogram it completely when it wakes up. Once everything is initialised, we enter the main loop proper. Here, we check if the accelerometer has detected a period of inactivity and put itself into low-power mode. If it has, we proceed to put the SmartProbe into ‘off’ mode, as described below. If it is still active, we check if fresh data is available from the ADC sampling task. If not, we loop back and repeat the cycle, checking continuously for inactivity and new data. When fresh ADC data is available (approximately twice per second), the display is updated according to the operating mode and taking into account the orientation of the SmartProbe. This routine also takes care of the auto-ranging and over-voltage detection. ADC sampling The ADC sampling routine operates independently of the main loop, triggered every 500ms by a repeating timer. The analog-to-digital converter (ADC) peripheral within this microcontroller is extremely flexible. It is a Fig.4: the 3.3V power rail is derived from the coin cell voltage via a boost converter. This is disabled when the SmartProbe is ‘off’ but the microcontroller and accelerometer remain powered by the Vbat rail. siliconchip.com.au Australia's electronics magazine Fig.5: the firmware consists of a main loop and four asynchronous tasks, as described in the text. They communicate with each other via a few shared data and status registers (not shown). 12-bit successive approximation converter with an input multiplexer that can handle up to 18 input channels. Sixteen of the channels can be connected to input pins (not all of which are available on the 20-pin version of the chip), while two can be connected to internal sources. One of these is a 1.2V bandgap voltage reference. The ADC also includes a zero-calibration feature, which we use each time the SmartProbe becomes active. The ADC can be configured to July 2025  37 Table 1 – STM32L031F6P6 power saving modes Power Mode Core Peripherals RAM/Registers Wake-up Run On On Retained Not Applicable Sleep Off On Retained Any Peripheral Stop Off Off Retained External interrupts, low-power peripherals, RTC, watchdog Standby Off Off Lost RTC, watchdog, wake-up pin automatically scan and convert channels in a sequence. It also has a hardware oversampling capability. If this is enabled, the ADC will take a series of samples and average the results for each channel in the sequence. I used these features to create a sampling regime that eliminates a lot of the mains-frequency interference that would otherwise make achieving stable readings difficult. If we take many samples of a signal over an integral number of mains cycles and average them, any mains frequency component will average to zero. This is because the average of any sinusoidal signal over a full cycle is zero. So, if we make the ADC sample and average each input over one or more 20ms intervals, any 50Hz component will be eliminated. In the SmartProbe, the clock division options available to us mean that we can’t quite do this perfectly. The best we can manage is to take the 256 samples of each input over a period of 59.05ms – very close to three mains cycles. This means the mains cancellation will not be perfect, but we should still reduce it by 34dB (50 times) or thereabouts, which helps a lot. This oversampling and averaging also serves as a simple low-pass filter, helping to smooth out any small perturbations in the voltage being measured. The ADC is therefore set up to convert four inputs in sequence: the high and low range voltage measurement inputs, the offset voltage and the internal reference. Each is sampled 256 times, and the results averaged twice per second. Once configured, all this happens more-or-less automatically. An interrupt is triggered at the end of each conversion sequence, at which point we need to translate the averaged ADC readings into absolute voltages that we can display. The ADC output is ratiometric with the Vbat power rail – that means its output code is a measure of the input voltage as a fraction of Vbat. Vbat is nominally 3.3V when the 38 Silicon Chip SmartProbe is on, but this voltage is not regulated to the extent that would allow conversion to absolute voltages at the level of accuracy we want. Fortunately, there is a way around this, using the internal bandgap reference. This has a nominal output of 1.2V and pretty good stability. When the chip is manufactured, the value of this internal reference is measured by the ADC while the supply voltage is fixed at a fairly precise 3.00V, and the resulting code burned into non-­ volatile memory. The firmware uses this code, together with the real-time measurement of the internal reference, to calculate the Vbat voltage on each measurement cycle. Knowing the supply voltage allows us to determine the absolute value of the input voltages. It is then only a matter of subtracting the offset voltage from each of the input voltages to determine the voltage across the lower resistor in each divider as a signed integer in units of millivolts. These are later adjusted for the divider attenuation in the display update routine. When new values are calculated, they are stored in shared memory, and the flag set to let the main loop know that new data is available. Continuity mode & beeper The accelerometer is set up to detect single-tap events in the ‘vertical’ axis of the smart probe (ie, the top or bottom surface when looking at the display) and assert the interrupt line. The associated interrupt service routine responds by switching modes: opening or closing the analog switch and setting the offset voltage appropriately. A short tone sounds when changing modes – a higher frequency when switching to voltage mode, and a lower frequency when switching to continuity mode. The beeper driver makes use of the M0+ core’s dedicated tick timer, which is usually set to provide a system tick interrupt every millisecond. A tone is initiated by calling a driver function Australia's electronics magazine specifying the desired frequency and duration. The function starts the tone playing at the appropriate frequency, then returns. The tone is automatically terminated after the requisite number of 1ms ticks elapse. It is important (to me anyway) that the continuity beeper has a very fast response. The ADC samples are only updated every 500ms, which is fine for the display, but way too slow for the beep. Therefore, I used a comparator, as mentioned earlier. One of the two onboard comparators is configured to compare the low-range input voltage with a fixed internal voltage set to ¼ of the internal 1.2V reference. If the voltage at the input pin falls below 0.6V, a flag is set to indicate continuity. If it is above this level, the flag is cleared. The comparator output flag is sampled every system tick and the continuity beep is sounded if it is set. Low power operation We mentioned above that the accelerometer is configured to detect a period of inactivity and autonomously put itself into a low-power mode. When the microcontroller detects this has occurred, the rest of the circuit must be shut down until the accelerometer indicates activity has resumed. We have seen that the accelerometer consumes up to 20µA in its low-power mode, and we have a total design target consumption of 27µA or less. This leaves us with just a few microamps for everything else, including the microcontroller. The Cortex M0+ architecture supports a variety of low-power modes with differing levels of power consumption. The trade-off for lower power is longer wake-up times and more limited wake-up functionality. Table 1 shows a (very) simplified chart of the available modes and their key differences. Every one of the modes shown in the table has several variations, and it is entirely possible for a lower power mode to consume more than a higher power mode siliconchip.com.au depending on the exact configuration. “Run” is the normal operating mode of the microcontroller and has the maximum power consumption; the core and all peripherals are operating. The easiest way to reduce power in this mode (or any mode where the clocks are operating) is to reduce the frequency of the system clock below its maximum of 32MHz. I use a 3MHz system clock in the SmartProbe for this reason. In “Sleep” mode, the core clock is disabled, but the peripherals remain fully operational. RAM and register contents are preserved. This allows for a very fast wake-up (in the order of 0.35µs) but comes at the cost of around 1mA current consumption at 16MHz. As the peripherals continue to operate, pretty much any of them can wake the processor up. “Stop” mode, on the other hand, has the potential to reduce power consumption to the sub-microamp level. This is the mode I used for the SmartProbe when it’s ‘off’. Here, the core and most peripheral clocks are halted; only the real-time clock and watchdog timer continue to run if they are enabled (which they aren’t). Volatile memory is retained. Several possible sources can wake the microcontroller from stop mode, including interrupts triggered by the states of external pins changing, which is what we use. The final low-power mode is “Standby”. In this mode, almost everything is powered off, including the RAM and almost all the registers. Only a very limited selection of wake-up sources is available, and the wake-up time is the longest. Putting the processor into stop mode is in itself not enough to get the current consumption down to the very low levels we require. There is quite a lot to do both within the microcontroller and in the external circuit before executing the instruction that halts the processor. Externally, we shut the OLED display off via an I2C command, shut down the beeper PWM and turn off the boost converter. Internally, we stop the ADC conversion process and the timer that triggers it, disable the bandgap reference and the buffers that feed its output to the ADC and the comparator. We also limit the functionality of the accelerometer to just detecting activity or inactivity. siliconchip.com.au A close-up of the probe we used for our SmartProbe. We also put most of the I/O pins into analog input mode so they look like high-impedance inputs, minimising any leakage currents that might otherwise occur. The data sheet suggests that the digital input schmitt trigger buffers can be a source of leakage – hence using the analog input mode. In fact, leakage current is our number one enemy in ultra-low power circuits such as this, and it can come from some quite obscure sources. For example, consider the 4.7kW I2C pullup resistors. These are pulled up by one of the microcontroller’s GPIO pins instead of being directly connected to the power rail (Vbat) as one might do normally. Fig.6 shows why we have to do this. The I2C bus connects to the micro and the accelerometer, which remain powered up in stop mode, but also to the display, which does not. The display driver’s I2C inputs are internally protected by diodes connected as shown in the figure. In normal operation, these prevent the input pin rising more than about 0.6V above the 3.3V supply or falling more than 0.6V below ground. However, when the boost converter is off, the display driver’s positive power rail is at 0V, allowing a leakage current path from Vbat to ground via the I2C pullups, as shown by the red paths. If Vbat was at 2.5V and the protection diode forward drop was 0.5V, there would be more than 850µA leakage in total. This is 30 times more current than our target, so clearly not acceptable! Powering the pullups from a GPIO pin that can be put into a high-­impedance state eliminates this problem. Once all the internal and external extraneous current consumers are dealt with, we are ready to stop the microcontroller core and peripherals. We just have to set or clear a few bits in various control registers to ensure the core enters the correct low-power mode and that it wakes up due to the right stimulus with the right clock source. We have to disable all interrupt sources except the external interrupt pin associated with the accelerometer, and globally disable interrupts. Finally, we can execute a “Wait for Interrupt” (WFI) instruction that stops the core until an interrupt is received. It might seem odd that we globally disable interrupts if we want to wake up due to an interrupt, but the way it works is that the peripheral’s interrupt flag does the waking (in this case the external interrupt) regardless of the state of the global interrupt enable flag. By disabling global interrupts, we ensure that when the processor wakes up, it continues executing code where it left off and not in an ISR. On resumption, we have to undo all the work we did before entering low-power mode, restoring the I/O pin states, enabling the boost converter and the internal regulators and buffers we disabled. We then reinitialise the drivers to start the ADC, the display and all the rest of the stuff necessary to resume operation. Construction Fig.6: if the I2C bus was pulled up to Vbat, significant leakage currents would flow through the pullup resistors and display driver chip’s input protection diodes when the 3V3 rail is off. Australia's electronics magazine The SmartProbe is built on a small double-sided printed circuit board coded P9054-04 that measures 54.5 × 29.5mm. Both sides of the board are fairly tightly packed with surface-mounting parts, although most are M2012/0805-sized (2.0 × 1.2mm), so pretty easy to handle. The overlay diagrams, Figs.7 & 8, show where everything goes. Start assembly by mounting the trickiest part, the accelerometer (IC3). If you are using solder wire, you will need to apply some flux paste and a July 2025  39 thin layer of solder to the pads first. Try to get roughly the same amount of solder on each pad – if there is too little on one or two, you risk an open-circuit connection. If you elect to use solder paste, try to get a more-or-less even smear across the footprint. You can then reflow the chip using something like a hot air wand, making sure to get it the right way round. Despite its small size, I found this package fairly forgiving when it came to assembly. Next, solder in the boost converter chip (REG4) and then the optional programming connector, CON3, if you will use it (it isn’t necessary if you get a pre-programmed chip from our Online Shop). They should solder in fairly easily using a fine tip soldering iron, some good flux and a bit of solder wick to clean up any bridges. Mount the rest of the components on the top side of the board, except the coin cell holder and the probe connector (CON1), in the order you prefer. I tend to install the finer-pitch and smaller parts first, working my way up to the larger ones. Flip the board over and install the six passives on the back side, plus the audio transducer. Finally, add the coin cell holder and the probe connector (CON1) to the top side. It is a good idea to check your work and clean up the board with a bit of isopropyl alcohol or another solvent at this point, before installing the display. The display’s flat flex cable is soldered directly to the row of pads on the back of the board. Make sure the pin 1 designator on the flex is aligned with the small dot on the board. This should correspond with the display being face-up when folded back on itself. It should be face-down when the flat flex is straight, and it should extend over the side of the board nearest the row of pads. Align the flat flex so that about 1mm of the PCB pads are visible, and secure it in place temporarily with a couple of bits of adhesive tape. Double-check everything lines up and tack the display in place by soldering a couple of the pins. I suggest using two of the signal pins for this, rather than the pins connected to the ground plane, as they require a lot more heat. If everything still looks good, go ahead and solder all the pins, taking care not to create any short circuits. You can remove the tape and clean up with a little solvent if you need to, but keep it away from the display itself. If you intend to program the microcontroller in-circuit, do that now. You will need to make a suitable adaptor to connect the programmer to the flat flex connector. See the details in the accompanying panel. You will have to insert a coin cell (or otherwise power the microcontroller) while it is being programmed. If your microcontroller came preprogrammed, you should skip this step. You can now perform a quick test by inserting a coin cell into the holder. You should hear the start-up beep, and the display should come to life in voltage mode with a reading close to 0.000V. The least significant digit (millivolts) and the sign may move around a little, but the rest of the digits should be zero. If you do nothing, the probe should Figs.7 & 8: follow these diagrams to populate the PCB. Start with the accelerometer (IC3), as it is the fiddliest part to mount. 40 Silicon Chip Australia's electronics magazine siliconchip.com.au switch itself off after five or six seconds, and it should wake up again you give it a bit of a jiggle. This is enough to test the basic functionality. If everything is OK, you can remove the coin cell and fix the display in place with a small piece of double-sided foam tape. Fold it over and align the edges of the display glass with the outer rectangle on the PCB silkscreen. Debugging If there is a problem, do some troubleshooting before fixing the display in place. If the unit appears dead, first measure the 3V3 rail to make sure it is working when the unit is awake. If 3.3V is not present, check that the battery voltage is getting to it and the boost converter enable pin is high. The latter is a sign that the micro is at least trying to start the converter and means the problem is in the boost converter itself or there is a short on the 3V3 rail. If the 3V3 rail is fine and you hear the start-up beep, but the screen remains blank, the problem is probably in the I2C bus or with the display. Check the associated components and the soldering of the display connector. It is possible to get shorts under the flat flex that you can’t necessarily see. Use a multimeter to look for (unwanted) shorts between adjacent pins if you suspect this may be the case. The firmware does have a fair bit of error-detection built in. If an error occurs, the beeper emits a short, low tone (it is fairly quiet, so listen carefully) and displays a small fault icon on the screen. If this says “ACC!”, the code encountered a problem communicating with the accelerometer. If it says “DIS!”, the problem is with the display communication, and if it says “SYS!” the problem is a processor exception, so probably related to corrupt code. Mechanical assembly Once everything is working as expected, you can prepare the case. Mark out and cut the opening for the display and the sound hole according to Fig.9. The display aperture can be cut by drilling a series of holes inside the marking and finishing up to the line with files. I used a file to put a chamfer around the display hole – the exact dimensions are not critical as this is purely cosmetic. Drill the holes in each end of the siliconchip.com.au Parts List – SmartProbe 1 Hammond 1551JBK 60 × 35 × 15mm black ABS enclosure [Altronics H9003] 1 double-sided PCB coded P9054-04, 54.5 × 29.5mm 1 BC-2600 SMD CR2032 cell holder (BAT1) 1 CR2032 3V lithium coin cell (BAT1) 1 Wago 2946-2060-471/998-404 single entry SMD terminal block (CON1) 1 Molex 503480-0800 8-pin flat flex connector, 0.5mm pitch (CON3; optional, for ICSP) 1 X30654 128×64-pixel 3.3V graphic OLED screen with SH1106 controller (DISP1) [AliExpress 32890183042] 1 WLPH201610M1R0PP or equivalent 1µH 2A+ inductor, SMD M2012/0805 size (L1) 1 CMT-0525-75-SMT-TR SMD magnetic transducer buzzer (MB1) 1 6mm-long No.6 self-tapping screw 1 size 4 straw sewing needle 1 alligator clip 1 length of medium-duty hookup wire 1 short length of 2mm diameter heatshrink tubing 1 small piece of double-sided foam-cored tape Semiconductors 1 TP5534-SR quad chopper-stabilised op amp, SOIC-14 (IC1) 1 32-bit STM32L031F6P6 microcontroller programmed with 0411025A.HEX, TSSOP-20 (IC2) 1 LIS2DW12 ultra-low-power 3-axis accelerometer, LGA-12 2 × 2mm (IC3) 1 TPS61033DRLR adjustable boost regulator, SOT-583 (REG4) 2 ZXMP6A17E6TA 60V 2.7A logic-level P-channel Mosfets, SOT-23-6 (Q1, Q2) 2 BSS138K 50V 220mA N-channel logic-level Mosfets, SOT-23 (Q3, Q4) 4 BAV99 ultrafast dual series diodes, SOT-23 (D1-D4) 1 SDM40E20LC 20V 400mA dual common-cathode schottky diode, SOT-23 (D5) Capacitors (all SMD M2012/0805 size 50V X7R ceramic unless noted) 1 33μF 16V D-case tantalum 4 10μF 16V 8 100nF 1 10nF 5 1nF 1 100pF C0G/NP0 Resistors (all SMD M2012/0805 size, 1% unless noted) 2 2MW ±0.1% 1 1MW 1 680kW ±0.1% 1 510kW 1 220kW 5 100kW 1 51kW ±0.1% 2 4.7kW 1 3kW 3 1.5kW 1 1kW 1 10W Optional SWD flat flex adaptor 1 double-sided PCB coded P9045-A, 35 × 25mm 1 Molex 503480-0800 8-pin flat flex connector, 0.5mm pitch (CON1) 1 CNC Tech 3220-10-0300-00 10-pin, 1.27mm-pitch box header (CON2) 1 Molex 0150200079 8-way, 0.5mm pitch 100mm flat flex cable Australia's electronics magazine July 2025  41 SWD Programming Adaptor There was no space on the main PCB for the standard ST Micro SWD/JTAG programming header, which is a 2×5pin miniature shrouded box header (1.27mm pin pitch). Thus, a more compact 8-way FFC connector was used. This small PCB adapts that to the more standard connector so that a programmer can be connected via a ribbon cable with an IDC plug. Its circuit is shown in Fig.a. Because pins 7 & 8 are not connected to the main board, only the single-wire debug (SWD) protocol is supported, not JTAG. Importantly, note that the pinout of CON1 is reversed compared to CON3 in Fig.2. That’s because the FFC is inserted flat, such that the connections are reversed between those two connectors. The adaptor is built on a double-­ sided PCB that’s coded P9045-A and measures 35 × 25mm. The assembly should be straightforward, referring to the overlay diagram, Fig.b. The TP-X pin is provided to allow a custom debugging signal to be generated from the microcontroller. When using it, make sure that the FFC cable is inserted with the correct orientation between the two ends. The easiest way to check this is to verify continuity between the grounds of the SWD Adaptor board and target board before connecting the programmer. Fig.a: this SWD adaptor connects to the main circuit (Fig.2) via a flat flex cable (FFC) and allows a standard ST Micro programmer to connect via CON2. The FFC is connected such that it reverses the connections, making CON1’s pinout correspond to CON3 in Fig.2. A close-up of the Adaptor’s flex cable is shown above and the finished PCB below. We have used some tape on both ends to provide extra rigidity. eye off your needle if it is wider than about 1mm; otherwise, it may be too big for the connector. The connector I used for the probe has a spring operation. You press down on the small divot at the top to insert or remove the conductor. When released, the connector firmly grips the probe. That, plus the close fit of the hole in the case, is enough to hold the probe solidly in place. Finally, you need to clip out one of the two PCB mount bosses inside the case as it interferes with the display. The one to remove is diagonally opposite the sound hole. The PCB is secured to the case with a #6 × 6mm self-tapping screw – see Figs.10 & 11. You should solder the ground lead to the PCB before you finally mount the board. It solders in from the top (battery) side, then loops down and up again through the two strain relief holes to emerge on the same side. Thread the wire through the hole in the case before installing the board into the case. I used a ground lead with a connector on the far end, so I had to thread the near end through the case before soldering it. Remember to secure the lid to the case with the two screws provided. Coin cells are extremely dangerous for children, and it is mandatory that they are only accessible with the use of a tool. You should also be very careful about where you store them. Keep them in their special child-­resistant packaging until they are required and always well and truly away from inquisitive little hands. Using the SmartProbe Fig.b: the SWD adaptor PCB has just two components, the connectors, plus three test points. case to suit the diameter of the ground lead and probe you choose (the dimensions shown are what we used). Try to make the probe hole a close, but not tight, fit with the probe, including its insulating sleeve. If it is too loose, the probe may wobble around. I made my probe from a sewing needle. These are nice and sharp, so good for probing surface-mount parts, and 42 Silicon Chip fairly hard, so they last a while. I used a size 4 straw-type needle, but any needle with a diameter between 0.5mm and 1.0mm should do. I covered the needle in heatshrink tubing, leaving it about 5mm short of either end. The eye of my needle was a similar diameter to the shaft, so I could insert it through the case and into the connector as-is. You may have to cut the Australia's electronics magazine There is no need to calibrate the SmartProbe, but you can check its operation fairly easily with basic test equipment. The absolute accuracy is measured by setting a bench supply to some voltage near the middle of each range (I used 2V and 30V) and comparing the SmartProbe reading to that from a known good meter, preferably one with five or more digits. The three units I built were all well within ±25mV on the 5V scale and 250mV on the 50V scale (0.5% of full scale in each case). You can get an idea of its precision by taking a series of readings (the more the better) and looking at the variation between them. Successive readings should not differ more than about siliconchip.com.au ±5mV and ±50mV on the two ranges, respectively. Keep the multimeter connected when you do this, to make sure the measured voltage does not change. I measured the current consumption of the three units I built. The maximum current when on was between 15mA and 25mA, depending on the cell voltage. This means the average battery life when on will be around 12 hours. When off, the current consumption was always less than 25µA, corresponding to a shelf life of about 387 days. Of course, neither of these is a realistic scenario. However, if we assumed an on-time of 30 minutes per week (remember it switches off after five or six seconds of inaction, so this is 30 minutes of actual measurement time), a fresh cell should last a little over 4 months. The SmartProbe won’t replace my multimeters, but if it becomes the first piece of test equipment that I reach for, SC I will consider that a success! Fig.9: drill the holes in the ends of the case to sizes that suit your probe and ground wire. You want a close (but not tight) fit, so the probe is held firmly in place. The programming adaptor connected to the prototype SmartProbe. Figs.10 & 11: the PCB is secured in the case with a #6 × 6mm self-tapping screw. The probe is inserted through the hole in the case and into its connector after the PCB is mounted. Ensure the lid of the case is secured with the supplied screws to comply with the safety requirements for coin cells. siliconchip.com.au Australia's electronics magazine July 2025  43 SOLDERING STATIONS Soldering made easy with our BEST RANGE of soldering stations at the BEST VALUE, to suit hobbyists and professionals alike. LIGHTWEIGHT, EXCEPTIONALLY DELICATE LIGHTWEIGHT IRON WITH ADJUSTABLE TEMPERATURE • 10 WATT • ROTARY TEMPERATURE CONTROL DIAL $ ONLY 49 95 • 48 WATT • SLIMLINE DESIGN IDEAL STARTER STATION . TS1610 $ ONLY 5995 . 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Jaycar reserves the right to change prices if and when required. By Andrew Levido Precision Electronics Part 9: System Design In this last article in the Precision Electronics series, we look at the design of a precision electronics system from the big-picture perspective. We have already covered a lot of the building blocks; this will bring them together and show how to approach the design of a whole system. T o do this, we will look at a practical example of moving from a high-level specification to developing design goals for each circuit block, then dive in detail into a couple of the blocks for good measure. Before we get into it, I want to summarise some of the key tips and tricks we have learned from previous articles that might help guide our design. These are not hard-and-fast rules; they are just things I have found it helpful to keep in mind: • Precision and accuracy are different things. Precision is all about errors and repeatability, while accuracy is all about calibration and traceability. • Break circuits down into bitesized chunks to perform error analysis. Things can get overwhelming if the circuit being analysed is too complex. • When like quantities with errors add or subtract, add the absolute errors. When quantities with errors multiply or divide (like an input offset through a gain), add the relative (proportional) errors. • Completely uncorrelated random errors (like white noise) can be added as the root sum of squares – either absolute or relative, depending on the application. This also applies to calculating a DAC’s or ADC’s total unadjusted error (TUE) figure. • You can easily calibrate or trim out fixed errors like offset and gain errors. It is harder to do so for non-­ linearities or errors that change with temperature. The highest-precision devices use this technique extensively, often performing calibration before every reading. • In general, keep the span of precision signals away from the power rails or the ends of ADC and DAC ranges where they coincide with the supply rails. This is one place where non-­ linear errors love to hide. • Read data sheets carefully, including the graphs. Manufacturers don’t usually highlight the shortcomings of their parts in the headline specs. Use worst-case errors (not typical values) unless you have a good reason not to. • Use larger signals and lower gains where you have a choice. Input-side errors are magnified by gain stages. The signal-to-noise ratio can be improved by using larger signals. • Reduce noise by limiting circuit bandwidth and using lower-value resistors where possible. Oversampling and averaging is a useful form of bandwidth limitation. • Reduce cost by using components with no higher precision than you absolutely need. Use an error budget spreadsheet to understand the major contributors to error and focus on these first. The process of top-down design is kind of the opposite of what we have done so far, where we looked at individual circuits and calculated their errors. This time, we will divide the Fig.1 (left): the highlevel block diagram of our hypothetical power supply. This is all we need to start the design process. Fig.2 (below): the error amplifier in the control block will most likely include an inverting, summing amplifier like this. If so, the setpoint & feedback voltages must be of opposite polarity. 46 Silicon Chip Australia's electronics magazine siliconchip.com.au overall system error up to develop an error ‘budget’ that will guide the design of each subsystem. This sounds very straightforward, but in practice there is almost always a certain amount of iteration (even to the point sometimes of revising the top-level specifications). A simple power supply The example I want to work with is a simple power supply that can source a voltage in the range of 0-20V with a maximum current of 1A. We are not going to fully design this power supply here – we are just aiming to develop the error budget and look at the system considerations including coming up with a calibration strategy. I will go through a more detailed component selection and analysis for a small part of the circuit, just to show how I go about it. Let’s start with some target specifications. We want to be able to set the voltage in 100mV steps and the current limit in 10mA steps. This corresponds to a modest precision of ±0.5% for the voltage and ±1% for the current setpoint. However, we want to be able to measure the voltage and current to a precision of ±0.1% (±20mV and ±1mA respectively). These specs are all defined at nominal temperature (25°C). For simplicity’s sake, we will assume that they should be no worse than 150% of nominal over the operating temperature range. This is a laboratory instrument, so I am going to arbitrarily decide that a range of 5°C to 45°C (25°C ±20°C) will be adequate. Two-point calibration The figure below shows a system like the voltage setpoint and regulation circuit in our example power supply. The ideal transfer function for the system is y = kw, where k is the design gain (for example, some number of millivolts per LSB), w is the input digital code and y is the output quantity. There is gain, but no offset, in this ideal system. A real system may have both a gain error and an offset error, as shown on the bottom of the figure. Here, the gain (m) is close but not equal to the ideal gain, k, and there is a non-zero offset, b. The firmware correction block shown on the left takes in the input code w and applies correction gain n and offset c to produce a corrected code x, such that the output of the hardware system y has the ideal relationship with the input code w. If we measure the hardware system’s transfer function (ie, find the gain [m] and offset [b]), we can calculate the compensating gain n and offset c. Twopoint calibration is the simplest process that allows us to calculate these correction factors. The calibration cycle starts by setting the correction gain n to unity and the correction offset c to zero. This means DAC code x will equal the raw code w. The calibration firmware then sets the code to a value near the bottom end of the span (wL), as shown in the figure, and we measure the output quantity (yL) using an external meter. This value is provided to the firmware. Next, the calibration routine sets code w to one near the top of the span (wH). This is also measured and entered into the instrument. Now the firmware can calculate the hardware’s transfer function coefficients using the equations m = (yH – yL) ÷ (xH – xL) and b = yL – mxL. With this done, the correction factors can be calculated from the relations n = k ÷ m and c = –b ÷ m. These factors would be stored in non-volatile memory and used to correct the DAC code to compensate for the gain and offset errors in the hardware. Two-point calibration has the advantage of being very simple to implement. You can improve on it by using more points (called multi-point calibration), and deriving the hardware transfer function from a suitable line-of-best-fit algorithm. High-level circuit design Designs should start with a simplified block diagram, as shown in Fig.1. Here, a microcontroller (not shown) feeds a pair of DACs which, together with the signal conditioning blocks, create the voltage and current setpoints that are applied to the power supply control circuit. This circuit regulates the output voltage and manages the current limiting. Feedback of the output voltage and current is necessary to allow the control circuit to regulate properly. The voltage feedback for the control circuit comes from the power supply output via high-impedance buffer 1. This unity-gain buffer is required to minimise the current drawn from the output terminal, as this will affect the siliconchip.com.au current measurement. The same buffer provides the voltage measurement input to ADC2 via a voltage divider and a second unity-gain buffer. Current sensing is provided via a high-side shunt resistor and instrumentation amplifier. This feeds both the control circuit and the current measurement function via ADC1. We will need two DACs since we have to provide both setpoints simultaneously, but we can get away with one ADC with an input multiplexer, since we can sample the current and voltage alternately. Error amplifier The control circuit is most likely going to contain error amplifiers made Australia's electronics magazine using an inverting, summing amplifier like that shown in Fig.2. This topology has two implications for our design. First, it means that the senses of the setpoint and feedback signals need to be opposite, so the error amplifier sees the difference between the output and the setpoint. If the setpoint is negative, as shown, a setpoint increase (ie, a more negative voltage) will cause the error amplifier output to increase in a positive direction, driving the output voltage or current limit higher. Similarly, if the feedback level increases, the error amp output will be forced lower, reducing the output voltage or current limit. Secondly, the error amplifier summing junction (the op amp’s inverting July 2025  47 input) sits at 0V and actually sums currents determined by the input voltages and the values of the two input resistors, R1 and R2. The result is that the full-scale setpoint voltage and full-scale feedback voltages do not have to be the same, since we can adjust the values of the resistors to make their full-scale currents equal. We do have to be concerned with the precision of the ratio between the resistor values, as any deviation will cause an error in the setpoint. Fortunately, we do not have to worry about anything further into the controller circuity, as any offset and gain errors here are eliminated by the action of the feedback. The same is true for non-linearities in this part of the circuit, although if they are extreme, they can impact control loop stability. Block diagrams & error budget Fig.3 shows the circuit in Fig.1 broken down into four ‘signal chains’, one each for the voltage and current controls, and one each for voltage and current sensing. This is a great way to get a handle on just which circuit block impacts the overall device precision. Some of the blocks appear in multiple chains; for example, the output voltage buffer appears in all the chains. In other cases, like the setpoint signal conditioning block, there are separate but identical blocks. The task, then, is to take the overall precision specification for each signal chain and allocate it to the various circuit blocks. The duplication and repetition of blocks described above makes this a slightly complex process. I used an error budget spreadsheet like that of Table 1. I have listed the unique circuit blocks down the left-hand side and the four signal chains across the top. Where a particular circuit block appears in a signal chain, I entered the appropriate number in the matrix. I then made a stab at setting an error budget for each circuit block down the left side, while checking the totals in blue along the bottom compared to the targets shown in purple. It is best to start from the most difficult chain (the current sensing chain in this case) and work from there. You can see that some of the error budgets end up better than the target, which is OK at this stage. There is no point in allocating the error budget down to the nth degree in this process. You can see that the budget here shows the current-sensing signal chain to be just over the target. This is near enough for this stage in the design cycle. It does take a bit of experience to work out what are reasonable error assumptions for each particular block, but hopefully, some of the previous articles in this series have given you a feel for it. Clearly, a unity-gain buffer using a zero-drift op amp will have a much lower error than a 16-bit ADC. The next step is to work through the design, block by block, selecting components and topologies that will meet the targets for each subcircuit. I recommend starting with the subsection where you think it will be most difficult to achieve the target precision. This may not be the area with the highest precision requirement. Calibration strategy Fig.3: the power supply functions can be broken down into these four signal chains. Some of the circuit blocks appear in multiple chains, complicating the process of assigning error budgets to each one. The errors in Table 1 are trimmed errors, so we need to have some idea of our calibration strategy to translate these to untrimmed errors for the design process. To keep things simple, for this power supply, I plan to perform calibration manually when we build the supply and every now and again thereafter. This eliminates the need for in-system calibration circuitry. However, this implies that our calibration will only be able to improve fixed gain and offset errors at the nominal temperature. The minimum required to do this is two-point calibration (described in detail in the accompanying panel). This means calculating and storing an offset and a gain calibration value for each of the four signal chains. Australia's electronics magazine siliconchip.com.au 48 Silicon Chip In practice, the calibration of the setpoint and measurement chains can be done simultaneously. For example, to calibrate the two voltage signal chains, we would set the voltage at some low value (say 1.0V) and measure the actual terminal voltage with an external meter with sufficient resolution. We would do the same at some high value (say, 19.0V). Once entered into the system, these two values can be used to calculate calibration coefficients for the setpoint chain by comparing them with the nominal setpoint, and the measurement chain by comparing them with the values read by the ADC. Given this calibration strategy, I have made the assumption that we can calibrate fixed offset and gain errors down to 5% of their untrimmed values (ie, we can calibrate out 95% of the error). Non-linear errors and temperature dependent errors are not reduced at all by this method. Voltage setpoint design I will go through the process in some detail for a small part of the circuit to show you the idea, starting with the voltage setpoint circuit, although I have included the full set of error calculations in Table 2. To do this, we need to define some full-scale voltage levels. We will start by assuming that we have a 3.3V logic supply for the microcontroller and ±5V analog supplies, as well as the 24V unregulated supply used for the output. We would like to use a low-cost serial DAC, since the setpoint precision requirements are not strenuous. This will have to run from 3.3V to interface with the micro, so we will Table 1 – error targets for each circuit block (in purple) and the resulting error (in blue) Circuit Block Error <at> 25°C Additional Voltage Current Error ±20°C Setpoint Setpoint Voltage Sensing Current Sensing DAC 0.250% 0.125% 1 1 Setpoint signal conditioning 0.100% 0.050% 1 1 Summing node 0.013% 0.006% 1 1 Buffer 0.013% 0.006% 1 1 2 1 Current sensing 0.040% 0.020% Voltage divider 0.013% 0.006% 1 ADC 0.050% 0.025% 1 Voltage reference 0.003% 0.001% 1 1 1 1 1 1 1 Target error <at> 25°C 0.500% 1.000% 0.100% 0.100% Target additional error ± 20°C 0.250% 0.500% 0.050% 0.050% Total <at> 25°C 0.378% 0.418% 0.090% 0.105% Total additional ± 20°C 0.189% 0.209% 0.045% 0.053% Total error 5°C to 45°C 0.566% 0.626% 0.135% 0.158% be limited to a full-scale analog range somewhere below this level. If we select a full-scale voltage of 2.5V, we will have a wide choice of low-cost external voltage references. One of our precision design rules of thumb is that we should not trust analog values as they approach the power supply limits. We will have a DAC output that varies between 0V and 2.5V, depending on the input code. Given a resistor-string DAC with a 3.3V supply, we can be reasonably comfortable at the top of the range, since there is plenty of headroom between the highest tap voltage (very close to 2.5V) and the analog supply rail (3.3V). However, the bottom end of the DAC’s resistor string will be grounded, as will the DAC’s analog circuitry, so we cannot count on the lower end of the range. This is a problem because it suggests that we will lose accuracy near the bottom of the range and/or might not be able to set the output voltage or current limit right down to zero. You will recall that we need a negative setpoint signal, so we anticipated a signal conditioning block between the DAC and the controller. The simplest way to do this would be to use a unity-­ gain inverting amplifier, as shown at the top of Fig.4. With a 2.5V reference, this gives us an output in the range 0V to -2.5V, as shown in the graph on the right of the figure. Unfortunately, this does nothing to help with our near-zero problem. However, if we use a difference amplifier as shown at the bottom of Fig.4, we shift the DAC output down by Vref, rather than inverting it. The upshot is that we will get very nearly a true 0V output when the DAC is at full scale. As the DAC output approaches At Nominal 25°C Error Additional error over 25 ±20°C Abs. Error Rel. Error Abs. Error Rel. Error 2 DAC Offset Error: ±15mV, 10µV/°C 15mV 0.750% 200µV 0.010% 3 DAC Gain Error: ±1%, 3ppm/°C 20mV 1.000% 60µV 0.003% 4 DAC INL: ±4LSB 2mV 0.098% 0mV 0.000% 5 Trimmed Error: 5% of (Line 2 + Line 3, root sum squares) + Line 4 3.2mV 0.160% 208.8µV 0.010% 1 DAC: MCP48FVB22, 12-bit, Two Channels, SPI 6 Temperature Drift Error: Line 2 + Line 3, root sum of squares Setpoint Signal Conditioning: TPA1834 Op Amp, Quad Zero Drift 1 Op Amp Offset Error: ±7µV, ±0.04µV/°C 7µV 0.000% 800nV 0.000% 2 Op Amp Gain Resistor R1/R2: Vishay ACASA, 0.1%, 0.05% matched, 15ppm/°C 1mV 0.050% 600µV 0.030% 3 Trimmed error 5% of (Line 1 + Line 2) 50.4µV 0.003% 600.8µV 0.030% 4 Temperature Drift Error: Line 1 × Line 2 Table 2 – detailed error calculations each signal block (see overleaf for the rest of the table; LSB = least significant bit). Absolute error values are with respect to 2V out July 2025  49 Table 2 continued... At Nominal 25°C Error Abs. Error Rel. Error Additional error over 25 ±20°C) Abs. Error Rel. Error Summing Node: RN73C2A, 0.1%, 10ppm/°C 1 Summing Node Gain Error 0.200% 2 Trimmed error 5% of Line 1 0.010% 0.020% 3 Temperature Drift Error (Line 1) 0.020% Buffer: TPA1834 Op Amp, Quad Zero Drift 1 Op Amp Offset Error: ±7µV, ±0.04µV/°C 7µV 2 Trimmed error 5% of Line 1 0.000% 800nV 0.000% 0.000% 3 Temperature Drift Error (Line 1) 0.000% ADC: ADS1115, ∆∑, 16-bit, 4CH, I2C 1 ADC Offset Error: ±3LSB, 0.005LSB/°C 114.4µV 0.005% 3.1µV 0.000% 2 ADC Gain Error: ±0.15%, 40ppm°C 3.8mv 0.150% 2mV 0.080% 3 ADC INL: ±1LSB 38.1µV 0.002% 4 Trimmed error 5% of (Line 1 + Line 2, root sum squares) + Line 3 225.7µV 0.056% 2mV 0.080% 5 Temperature Drift Error (Line 1 + Line 2, root sum of squares) Current Sense 1 Shunt Error 1Ω: VMP-1R00-1.0-U, 1%, 20ppm/°C 10mΩ 1.000% 400µΩ 0.040% 2 In Amp: INA821: VOS ±35µv, 0.4V/°C 35µV 0.002% 8µV 0.002% 3 In Amp Input Voltage Error Total: Line 1 + Line 2 10mV 1.004% 408µV 0.041% 4 In Amp Gain Resistor RG: ERA-6ARB333V (0.1%, 10ppm/°C) 0.100% 0.020% 5 In Amp gain error (0.015% ±35ppm/°C) 0.015% 0.070% 6 Total In Amp gain error (Line 4 × Line 5) 0.115% 0.090% 7 Trimmed error 3% of (Line 3 × Line 6) 677.9µV 0.034% 8 Untrimmable temperature drift error (Line 2 × Line 3) 2.6mV 0.131% Voltage Sense Divider: RN73C2A, 0.1%, 10ppm/°C 1 Divider gain error 0.200% 2 Trimmed error 5% of Line 1 0.010% 0.020% 3 Temperature drift error (Line 1) 0.020% Reference: REF3425TD, 2.5V, 0.05%, 6ppm/°C 1 VREF error 0.050% 2 Trimmed error 5% of Line 1 0.003% 0.012% 3 Temperature drift error (Line 1) 0.012% ADC Iteration #2: AD7705, ∆∑, 16-bit, 4CH, SPI 1 ADC Offset Error: 0.0 (with internal cal), 0.5µV/°C 0V 0.000% 10µV 0.000% 2 ADC Gain Error: 0.0 (with internal cal), 0.5ppm/°C 0µV 0.000% 25µV 0.001% 3 ADC INL: ±0.003% FSR 75µV 0.003% 4 Trimmed error 5% of (Line 1 + Line 2, root sum squares) + Line 3 75µV 0.019% 26.9µV 0.001% 5 Temperature drift error (Line 1 + Line 2, root sum of squares) Current Sense Iteration #2 1 Shunt Error 1Ω: VMP-1R00-1.0-U, 1%, 20ppm/°C 10mΩ 1.000% 400µΩ 0.040% 2 In Amp: AD8223: VOS ±100µv, 1.0µV/°C 100µV 0.005% 20µV 0.004% 3 In Amp Input Voltage Error Total : Line 1 + Line 2 10.1mV 1.010% 420µV 0.042% 4 In Amp Gain Resistor RG: ERA-6ARB333V(0.1%, 10ppm/°C) 0.100% 0.020% 5 In Amp gain Error (0.02% ±2ppm/°C) 0.020% 0.004% 6 Total In Amp gain error (Line 4 × Line 5) 0.120% 0.024% 7 Trimmed error 3% of (Line 3 × Line 6) 684.8µV 8 Untrimmable temperature drift error (Line 2 × Line 3) 50 Silicon Chip Australia's electronics magazine 0.034% 1.3mV 0.066% siliconchip.com.au zero, the circuit output approaches -Vref, corresponding to the maximum output voltage. By setting the full-scale setpoint voltage to something less than -Vref; say, letting -2.0V correspond to a 20V output, we avoid the very bottom part of the DAC’s output voltage range and the errors that may lie there. The downside is that the full-scale DAC code now represents a setpoint of zero and a code near (but above) zero represents full-scale. This inconvenience is easy to remove in the firmware with a simple subtraction. So, for the sake of the exercise, we will set the voltage setpoint range to 0V to -2.0V representing, 0V to 20V, and the current limit setpoint voltage to 0 to -2.0V, representing 0A to 1.0A. We can now select a candidate DAC. I chose the MCP48FVB22 low-cost two-channel 12-bit serial DAC from Microchip for this exercise. Its specifications are shown in the appropriate section of the error budget table. Since 2V is our full-scale output, I have used that as the basis for converting between absolute and relative errors. The upshot is a DAC error of ±0.16% at 25°C with another ±0.01% over the operating temperature range, well inside our ±0.25% budget. The errors for the setpoint signal conditioning are calculated as we have shown in previous articles. I used a matched resistor array and a low-cost zero-drift op amp, which gives us an overall 25°C error of ±0.003%. In this case, the resistors’ ±15ppm temperature drift means we have an order of magnitude more error over the temperature range; however, this is still well inside the error budget. The summing node errors are dictated by the matching of the resistors – in this case, I used ±0.1% tolerance resistors with ±10ppm/°C drift. The resulting 25°C and temperature drift errors are ±0.01% and ±0.02%, respectively. The buffer uses the same zerodrift op amp as the signal conditioning, and this circuit yields errors that are so low as to be insignificant in our application. The results for each of these blocks (plus the rest, which I will not discuss in detail) are summarised in Table 3. This is similar in format to the error budget table. The calculated errors for each block are on the left, with the signal chain errors calculated as we did earlier. siliconchip.com.au Fig.4: using a difference amplifier as shown allows us to avoid using the very lowest part of the DAC’s output range (errors lie there). Circuit Block Error <at> 25°C Additional Voltage Current Error ±20°C Setpoint Setpoint Voltage Sensing Current Sensing 2 1 DAC 0.160% 0.010% 1 1 Setpoint signal conditioning 0.003% 0.030% 1 1 Summing node 0.010% 0.020% 1 1 Buffer 0.000% 0.000% 1 1 Current sensing 0.034% 0.131% Voltage divider 0.010% 0.020% 1 ADC 0.056% 0.080% 1 1 Voltage reference 0.003% 0.012% 1 1 1 1 1 1 Target error <at> 25°C 0.500% 1.000% 0.100% 0.100% Target additional error ± 20°C 0.250% 0.500% 0.050% 0.050% Total <at> 25°C 0.175% 0.209% 0.069% 0.093% Total additional ± 20°C 0.072% 0.203% 0.112% 0.223% Total error 5°C to 45°C 0.248% 0.412% 0.181% 0.316% Table 3 – we have met the targets for most errors but the voltage and current sensing circuits All the resulting 25°C signal chain errors are lower than or equal to the targets we set, but the temperature drift errors, and therefore the total errors, for the voltage and current sensing functions (shown in red) are not. Second iteration It is not at all unusual to find some problems such as this on the first pass. The process we have gone through – specifically, the detailed error calculation spreadsheet – makes it easy to spot the problem areas. These are the ADC’s ±0.08% temperature-dependent error, which contributes to both signal chains, and the current-sensing circuit’s temperature-dependent errors. The error calculation table shows us Australia's electronics magazine that ADC error is entirely due to the temperature dependency of the ADC’s gain, so the only real solution is to find a better one. The device I originally chose, the ADS1115, costs around $7 and has a gain drift of ±40ppm/°C, which I thought was appropriate for this design. The table shows us that we need to get the gain drift down to ±10ppm/°C, or ideally lower, if we are to make a meaningful improvement. The slightly fancier AD7705 is a good candidate. It features automatic calibration that all but eliminates fixed offset and gain errors, and an impressively low gain drift of ±0.5ppm/°C. This ADC costs about twice as much as the ADS1115, so we have to decide July 2025  51 Table 4 – by addressing critical areas, we have achieved our targets for all signal chains Circuit Block Error <at> 25°C Additional Voltage Current Error ±20°C Setpoint Setpoint Voltage Sensing Current Sensing DAC 0.160% 0.010% 1 1 Setpoint signal conditioning 0.003% 0.030% 1 1 Summing node 0.010% 0.020% 1 1 Buffer 0.000% 0.000% 1 1 2 1 Current sensing 0.034% 0.066% Voltage divider 0.010% 0.020% 1 ADC 0.019% 0.001% 1 Voltage reference 0.003% 0.012% 1 1 1 1 1 1 1 Target error <at> 25°C 0.500% 1.000% 0.100% 0.100% Target additional error ± 20°C 0.250% 0.500% 0.050% 0.050% Total <at> 25°C 0.175% 0.209% 0.031% 0.055% Total additional ± 20°C 0.072% 0.138% 0.033% 0.079% Total error 5°C to 45°C 0.248% 0.348% 0.064% 0.135% whether the improvement gained from the substitution is worthwhile or not. This is the type of judgement call you will frequently have to make, but with a detailed analysis such as this, we have the tools to decide where to spend money to get the best results. I decided to go for it – an easy decision, because this is just an exercise! The next area of temperature drift error is the current sensing circuit. The error tables show that most of the error comes from the instrumentation amplifier’s gain drift. Initially, I used an INA821 because we used it in an earlier article. However, we could replace it with the similarly priced AD8223. This has a significantly worse offset voltage (100µV vs 35µV), but much better gain drift (±2ppm/°C compared to ±35ppm/°C). Replacing the op amp reduces the current sense circuit’s temperature error from 0.22% to 0.08%. This illustrates another type of trade-off we sometimes encounter – trading off one specification against another in similarly priced chips. Building an error budget like I have done here is extremely helpful in working out which parameters really matter for your application. So, with the changes we have made in iteration 2 (Table 4), we have exceeded our target 25°C specifications by a factor of about two across the board. We have also met the total error over the temperature range across the board, even though the drift figure for the current sense circuit is still a bit higher than the target. This is another useful lesson – while we have to set targets for both fixed and variable errors, we can trade off underperformance in one with overperformance in the other. Conclusions With this, we have reached the end of the Precision Electronics series. If I have one closing message for the prospective precision circuit designer, it would be that a bit of time spent at the beginning with a pile of data sheets and a spreadsheet will be paid back many times over when it comes to building and validation of your designs. I am as keen as anyone to lay out a board, get my hands on a prototype and sit down at the bench, but I have learned from experience that if I skip the homework, I will pay for it later in frustration and avoidable rework! SC Songbird An easy-to-build project that is perfect as a gift. SC6633 ($30 plus postage): Songbird Kit Choose from one of four colours for the PCB (purple, green, yellow or red). The kit includes nearly all parts, plus the piezo buzzer, 3D-printed piezo mount and switched battery box (base/stand not included). See the May 2023 issue for details: siliconchip.au/Article/15785 52 Silicon Chip Australia's electronics magazine siliconchip.com.au Subscribe to JUNE 2025 ISSN 1030-2662 06 The VERY BEST DIY Projects ! 9 771030 266001 $13 00* NZ $13 90 Hot Water SyStem INC GST INC GST Solar Diverter easy-to-build Australia’s top electronics magazine Single Sideband Shortwave Receiver 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. Outdoor Subw oofer » Suitable for amplifiers up to 100W » Can be painted any colour to match décor » Frequency response: 35-200Hz » Impedance: 4Ω 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 $70 $80 $52.50 1 year $130 $150 $100 2 years $245 $280 $190 6 months $82.50 $92.50 1 year $155 $175 2 years $290 $325 6 months $100 $110 1 year $195 $215 All prices are in Australian dollars (AUD). Combined subscriptions include both the printed magazine and online access. 2 years $380 $415 Prices are valid for the month of issue. Try our Online Subscription – now with PDF downloads! SSB Shortwave Receiver; June-July 2025 Versatile Battery Checker; May 2025 RGB LED Analog Clock; May 2025 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 Feature by Julian Edgar There are so many useful parts just waiting to be collected in the consumer goods that people throw away. Here’s what to look for. SALVAGING PARTS T he electronic equipment I build seems to use a lot of cooling fans and heatsinks. Those heatsinks range from the small ones that cool individual transistors up to those that are 200mm or more in length, while the fans go from tiny ones to 150mm in diameter. The good news is that, over the years, I have paid nothing for any of them! It isn’t just fans and heatsinks. I also get free plugs, sockets, switches, bearings, stepper motors, mains filters and IEC sockets... the list goes on and on. The trick is to salvage parts from the electrical consumer goods that others throw away. Let’s look now at some of the most productive discarded goods to salvage. There are warnings for some items, so make sure you read them before doing any disassembly. Photocopiers Photocopiers are always worth salvaging, and the bigger they are, 54 Silicon Chip the better. I once saw a huge Kodak commercial printer advertised free of charge. I just had to take it away. I knew it was going to be big, but when I broke a sling trying to hoist it onto a trailer with my engine crane, I thought I was defeated. The company was so eager to get rid of it that they agreed that I could dismantle it in their car park. I could take what I wanted and put the rest in their skip (it was too big to fit in the skip without being pulled apart). I still marvel at the quality of components that I got out of that machine. But let’s get back to more normal size photocopiers... The quality and number of useful components that you’ll find in a photocopier depends a lot on the specific machine. Unfortunately, there’s no way of knowing until you pull it apart. Some photocopiers have as many five DC brushless fans, while others have only two. Some photocopiers have large Australia's electronics magazine stepper motors but other use synchronous AC motors, which are much less useful. Then again, finding out what you’re getting is part of the excitement of salvaging parts from discarded equipment. You’ll find lights and fans inside all photocopiers. The lights are high-­ voltage, high-power incandescent filament bulbs that are used both to illuminate the material to be copied and also as a heater to cook the toner as the photocopied sheets are on their way out of the machine. The latter light often includes an over-temperature switch mounted nearby. In addition, you’ll sometimes find rows of mains-powered neons or low-voltage LEDs. The fans consist primarily of conventional PC-type fans; they often run from 24V but they’ll work down to 12V without problems. Sometimes, if you get lucky, you’ll find a bunch of high-flow squirrel-cage fans. These are most often mains-­ powered, but a few work on 24V DC. siliconchip.com.au A typical older photocopier, partway through disassembly. Photocopiers are always worth savaging for their parts; the larger the machine, the better. You’ll find lenses, front-faced mirrors, low current and heavyduty switches and often good quality stepper motors. Three stepper motors (bottom) and an AC motor with a built-in reduction gearbox (top) salvaged from a photocopier. The AC motor had an output shaft speed of just 53 RPM, making it ideal for spinning an advertising sign or the like. Two cooling fans, LED lights and incandescent lights. The latter can also be used as high-power resistors. All photocopiers contain at least one very sharp lens. They are ideal for use as close-up magnifying glasses. There is a lot of salvageable hardware inside a typical photocopier, like springs, pulleys, machine screws and self-tapping screws. You can also be guaranteed to find an excellent quality lens (typical focal length: 180mm) and several mirrors. The lenses are razor sharp and make ideal hand magnifying glasses. They’re large and bright, and some are coated for better light transmission. The mirrors are front-faced and of a length that corresponds to the width of the photocopy area. Typically, they’re 10 to 20mm wide, so they’re long and narrow. I haven’t found a lot of use for them (except, oddly enough, winding high-powered resistors on them), but if you’re into lasers or other optical systems and need a very low-cost, high-quality mirror, there are plenty waiting for you! siliconchip.com.au Even if the photocopier’s main transport system is powered by an AC motor, there will still be a few low-voltage stepper motors inside. For example, if the copier uses a document feeder, there’ll be a stepper motor buried in that part of the machine. However, occasionally you stumble across gold – huge stepper motors with built-in reduction gearboxes. These are highly prized (and if you don’t want them, you can make a good profit selling them). They can be used to drive robots or three-axis milling machines, or be driven backwards and used as surprisingly powerful alternators. There are two completely different classes of switches that you’ll find Australia's electronics magazine in a copier. The most numerous are the tiny tactile PCB-mounted press-­ buttons mounted behind the membrane keypad. If these are extracted from the PCB by using a heat gun directed at the solder side, while at the same time a pair of pointy-nosed pliers is used to pull them out, many can be salvaged in a very short time. There will also be another pair of high-current switches: the main on/ off switch (normally on the back of the photocopier) and a pushbutton switch that goes open-circuit when the top half of the copier is pivoted up for repair or toner replacement. The latter two switches are definitely July 2025  55 Micromite-Explore 40 October 2024 Complete Kit SC6991: $35 mind. If it was recently powered or you aren’t sure, use our Capacitor Discharger (December 2024; siliconchip. au/Article/17310) to make sure they are fully discharged as soon as you can access them. This list of parts hasn’t been exhaustive – I haven’t mentioned the LED displays, the electromechanical counter, the electric clutches, bearings or shafts. There are usually plenty of good bits to salvage. Even if you don’t keep a lot of stuff, pulling apart a photocopier is a fun exercise in itself – it’s fascinating to see how the engineers have fitted a complex machine into a compact package. used it as a cooling spray on a turbo car intercooler! Washing machines siliconchip.au/Article/16677 Coffee machines Includes the PCB and all onboard parts. Audio Breakout board and Pico BackPack are sold separately. You wouldn’t normally think of looking inside a discarded espresso coffee machine for good parts – but, in fact, there’s a bunch of useful goodies inside. In addition to switches, pilot lights (sometimes neon, sometimes LED), stainless steel fasteners and normally closed temperature switches, there’s the pump – and what a pump! Coffee machines contain a mains-­ powered oscillating (sometimes rotary) water pump that is capable of very high pressures – over 15bar (218psi). These pumps are fantastic where you want highly atomised water – just use high-pressure hose and fittings to attach the pump to a good quality brass misting nozzle. You cannot run the pump continuously (it gets too hot), but if you cycle it on and off, it will be fine. When salvaging the pump, don’t forget to also get the rubber mounts on which it sits – in operation, these pumps vibrate at 50Hz. I’ve actually run one of these pumps from an inverter and Washing machines have changed a lot over the years. Whereas once a typical washing machine was a top-­loading, belt-driven design with mechanical timer controls, machines now include technology like directdrive motors, fully electronic controls and plenty of wiring. Those aspects make any washing machine built in the last 20 years worthy of salvaging for its internal parts. All washing machines have a powerful electric motor inside. Most machines are belt-driven; that is, they use an electric motor that’s easily removed and can then be used as a standalone motor to drive anything you want – from a workshop sander to a fan. If removing the motor, don’t forget to also get the start and run capacitor, if fitted. Some washing machines – notably Fisher & Paykel designs – use a very special, large diameter, direct-drive motor. These can be removed, complete with the stainless-steel shaft and bearings, and then used as a wind generator, water generator, or even brushless DC motor. We described how to convert one of those motors to a generator for a windmill in the January 2005 issue (siliconchip.au/Series/84), and how to use one as a motor in February 2012 (siliconchip.au/Article/766). Even if you decide you don’t want it, these motors are worth money second hand. The electric pump from a washing machine is usually quiet, relatively low power (30~40W), can handle hot Metric stainless-steel cap-screws salvaged from a coffee machine. You pay real money for stainless steel fasteners like these, but here they were free. A microswitch, two normally open temperature switches (107°C) and a DPDT mains relay rated at no less than 16A, all hidden in a discarded coffee machine. worth salvaging; they are heavy duty with typical ratings of 16A at 250V AC. Cautions When you’re pulling apart a photocopier, you need to be careful of a few things. Disassemble the copier outside while wearing old clothes – inevitably, toner will get everywhere. Some copiers use torsion bar springs to counterbalance the weight of the open top half; these springs are very powerful and if you undo their retaining screws while they’re under tension, they can fly out. Other copiers use small gas struts – another excellent salvage part. The high-voltage power supplies have onboard capacitors that could give a nasty bite – they’ll be fine if the copier hasn’t been powered-up recently, but keep the potential in Inside discarded coffee machines you’ll find a very special pump. An AC design that oscillates at mains frequency, the pump produces very high pressure (over 15bar) and is safe to use with water. 56 Silicon Chip Australia's electronics magazine siliconchip.com.au If you can get them for nothing, washing machines are well worth pulling apart for their components. The water-control solenoids from washing machines are worth salvaging, especially if they’re 12V designs. Like the one shown at upper right, however, most are mains-powered. These LEDs, pushbutton switches and the rotary encoder were salvaged from the control panels of just two washing machines. All washing machines contain mains-powered pumps as shown at lower right. They’re quiet, use little power, can handle hot water and have removable filters. water and has a removable lint filter. These characteristics make the pumps excellent for circulating water in a solar water heater or for low pressure water transfer. However, if using a pump in this way, always ensure the wiring is appropriately insulated and Earthed and that water cannot come in contact with it. There are two (sometimes three) solenoids in each washing machine. These are electrically operated valves that control water flow. Most washing machines use mains-powered solenoids, but some use 12V solenoids. The solenoids can be used whenever mains-pressure (or lower) water supply needs to be switched on and off. The lower-voltage solenoids can be easily and safely used to control siliconchip.com.au water flow in a variety of applications, including solar water heating systems, gardening or recreational vehicles. They will cope with high water pressures and are usually leak-proof. The mains-powered solenoids should be used only in insulated surroundings. Old washing machines use a mechanical pressure switch to detect the water level. The water level adjustment is achieved by altering the spring preload. These switches are simple to use, high current, very sensitive and are always worth salvaging. An example use is for warning of a low water level in a rainwater tank. More modern washing machines use variable output electronic water level sensors. That sounds good, but most of these sensors appear to use an iron Australia's electronics magazine core moving within encapsulated electronics and I haven’t found an effective way to interface with them. Many washing machines now incorporate heater elements to allow higher water temperatures than can be provided by the domestic water heater (and/or to allow a single cold water hose to be used). These machines use a temperature sensor to monitor the water. These sensors are excellent parts to grab, being of stainless-steel construction and with quite a quick reaction time. They use an NTC thermistor, where the resistance falls as its temperature rises. As such, they are suitable for temperature sensing in a range of applications. Most electronics in washing machines is ‘potted’ – that is, the boards are covered with a thick layer July 2025  57 of rubbery plastic, waterproofing them. It’s pretty well impossible to salvage components from these boards. However, the control panel is usually not potted. By placing the control panel board in a vice and using the heat gun approach described earlier, it’s possible to salvage parts in literally seconds. Parts likely to be available include LEDs, switches and rotary encoders. There is a surprisingly large amount of hardware in many washing machines. Much of it is of high quality: stainless-steel self-tapping screws, heavily plated machine screws, and – in front-loaders – many long self-tapping hex-headed bolts (they hold the drum halves together). Because the washing machine tub needs to cope with out-of-balance loads, most machines also incorporate springs to allow tub lateral movement (top loaders) or vertical movement (front-loaders). These springs are heavy-duty and a well worth salvaging. You’ll also find a variety of rubber hoses and spring clips. Finally, there’s usually plenty of wire of different gauges and colours – perfect whenever you need a short length of hook-up wire. Video cassette recorders VCRs were once among the most numerous of electronic consumer goods being discarded. Now, they’re becoming much rarer, but they do still sometime pop up as giveaways. Contrary to what you might expect, the best bits are mechanical rather than electronic. The pick of the bunch is the video drum assembly – I am happy to pull apart a VCR just for the video drum. Why? It contains a precision-ground, hardened steel shaft. It also uses two precision sealed ball bearings that perfectly match the shaft. You also have two light alloy housings, one of which is normally a press fit on the shaft and the other that houses the two bearings. Finally, there is a brass collar with a grub screw that fits perfectly on the shaft. In almost any application where you need small bearings and a shaft Shown in the left photo is the rotating video head from a VCR. Even the cheapest VCR has a good-quality spinning assembly, and in disassembling over 50 VCRs, I’ve yet to come across one with worn-out bearings. At right, the video drum from a VCR contains precision matched components, including a hardened steel shaft, two bearings and two alloy castings. The brass collar, complete with retaining grub screw, is a tight fit on the shaft. Top: PCB-mounting RCA sockets salvaged from a VCR. Right: a sensitive wind vane that uses the components from a video drum for its rotating bearing. 58 Silicon Chip Australia's electronics magazine siliconchip.com.au or axle (robotics, a wind vane, small wind generator, model car etc) these parts can be used. Furthermore, as they’re pretty well standard across all VHS VCRs; if you need two axles (or four bearings etc), just keep collecting! In addition to the video drum, inside a VCR you’ll also typically find small springs, switches, wire-wound resistors and RCA sockets. You will also often find a DC brush-type permanent magnet motor that uses a worm reduction drive to turn a slowly rotating output shaft. It would make a perfect winch for a model boat, or a merrygo-round for a model railway layout or kids’ toy. Cordless drills If VCRs are now getting scarce, the same can’t be said for cordless drills – they seem to be thrown away in their thousands every week. At the tip, at garage sales, even in kerbside rubbish pick-ups; there are now always plenty of defective battery-powered electric drills. You might even have one or more broken cordless drills tucked away at the back of your workbench. Cordless drills usually have a maximum speed of 1000RPM or even less. To reduce the speed of the DC electric motor, and to increase the torque, a planetary gearbox is used. In fact, most often there are two planetary gearsets back-to-back – rather like the gear systems used in traditional automotive automatic transmissions. And like automotive transmissions, some cordless drills let you select between ratios – more on that in a moment. For their size, planetary gears are very strong and, especially when two sets are used, allow high reduction ratios to be achieved in small volumes. Considering their size and torque capacity, these are really nice little gearboxes. The torque multiplication might be achieved by the gearbox, but if you want to be able to quickly drill holes – or screw screws – you need power. It’s provided by a high-current DC brushed motor. Brushless motors are now available in electric drills, but I haven’t seen many yet on the discard pile. Typical drill motors draw around 10A at 12V when stalled, and considering they are about the size of a D cell, that’s a powerful motor you’ve siliconchip.com.au A discarded battery-powered drill contains a powerful low-voltage, brushed DC electric motor and a compact but strong epicyclic gearbox. Many also contain a PWM speed controller. The epicyclic gearbox. Many drills use two geartrains mounted back-to-back, while some allow two different gear ratios to be manually selected. A brushed electric drill motor being driven by a crank placed in the chuck, making a low-voltage hand-powered generator. Over 2.5W is easily available, so a powerful LED can be driven, or via a 5V converter, a phone charged. Australia's electronics magazine July 2025  59 Top ten parts to salvage We’ve been looking at the parts you can salvage from specific pieces of equipment, but you can turn the process around and look at the best parts to get. Here are the top ten. 1. Knobs Whenever you see a piece of equipment with quality knobs on it, grab them! It takes literally seconds to pull knobs off, and it makes such a difference when you’re building a project if you can just go to your storage drawers and immediately lay your hands on a knob that’s just perfect for the application. It’s also interesting sorting through different knobs and feeling the way in which they work – some knobs (eg, amplifier volume controls) need to be large and smoothly contoured; others (like the adjustment knob on an electronic thermostat) need to be small and much better shaped to suit fine adjustment. 2. Switches A switch is one type of electronic component that doesn’t go out of date. Over the years, I’ve collected switches from: ∎ VCRs (miniature pushbuttons, microswitches and the contactless Hall Effect switches often used on the video drum chassis) ∎ photocopiers (the switch that deactivates the power when the lid is raised) ∎ old electric typewriters (typically, the main on/off switch is a quality pushfit rocker design) 60 Silicon Chip ∎ amplifier input selectors (a multipole rotary switch) ∎ old washing machines (the water level switch – a very sensitive pressure switch) ∎ miscellaneous heavy duty equipment (high-current switches) All are useful and, even better, easy to use. 3. Cable clamps, mounts and holders Whenever you run wires or cables around inside a piece of equipment, there’s a need to hold them in place. Inside commercial equipment, you’ll find the full gamut of cable and wire holders – bendy insulated metal strips, steel clamps, plastic clamps, clamps that pop into chassis holes and clamps that hold mains-power cables. It’s always worth collecting these. 4. Fuses Fuses are another example of a component that doesn’t date – a 50-year-old glass fuse and holder are just as useful today as back then. As a matter of course, I collect fuses from all sorts of equipment. If the fuse holder is inline or an easily removed chassis-mount design, I collect those too. You can also obtain very useful fusible links from car fuse and relay boxes, and much industrial equipment contains resettable circuit breakers. I also collect the two different sizes of blade fuse used in vehicles. It is not at all hard to collect enough fuses that you’ll never need to buy one again – or Australia's electronics magazine spend the time travelling to the shop to buy that required obscure value. 5. Relays Relays are extraordinarily useful – rugged (basically impossible to blow up unless you do something really stupid!), universal within voltage and current restraints, and easy to wire up. An enormous range of equipment and appliances have relays inside – you can easily collect one from every even moderately complex bit of gear you salvage. Commercial equipment often uses solid-state relays, and I remember picking up the ABS (anti-lock braking) controller from a car and realising with joy that it contained no less than six small high-current 12V relays! 6. LEDs The idea of salvaging LEDs from equipment can seem silly – why bother when LEDs are so cheap new? First, it’s easy to salvage LEDs you cannot readily buy in shops – those with odd lens shapes (eg, long rectangular types) and LEDs with unusual colours. Second, using the heat-gun-and-­ pliers approach mentioned above, it takes almost no time to salvage dozens of LEDs. I often use shop-bought LEDs in projects, but nearly as frequently, I’ll want something out of the ordinary and reach for my little drawers of salvaged LEDs. siliconchip.com.au I come across – they’re amongst my ‘most-­utilised’ salvaged parts. 7. Plugs & sockets If you’re trying to find the right plug for a socket (eg, a DC socket that requires the correct mains adaptor), a visit to an electronics supplier is often required. If, on the other hand, you’re building a piece of equipment and need a similar function low voltage DC plug-andsocket combination, it’s often much easier and cheaper to use some that you’ve salvaged. For example, I often use RCA-style plugs as low-voltage DC power connections – they’re polarised, non-shorting and can handle reasonable current. You can salvage RCA sockets from any audio or video consumer item that’s been thrown away. The plugs are almost as often discarded on audio interlink cables! 8. Heatsinks Heatsinks are available in discarded goods in a huge range of sizes – from small ‘tab’ style ones in power supplies to large heatsinks in audio amplifiers, and every size in between. When building projects, it pays to have a large variety of heatsinks on hand. That’s because there is often not only a requirement for heat handling but also physical requirements as to size and shape. For example, space might be tight in one direction, or the flat mounting surface on which the components are to be mounted might need to be a certain shape. I collect all heatsinks that siliconchip.com.au 9. Small motors Many items that people throw away contain electric motors. Bread makers use mains-powered universal brushedtype electric motors; electric typewriters, printers and fax machines use stepper motors; and VCRs contain small low-voltage brushed motors. And as we’ve seen, washing machines and other larger goods contain mains-­ powered induction motors. I tend to collect just the following motors types: small low-voltage brushed motors (good for making fans and kids’ toys), and large and small stepper motors (good for robots, model railways and hand-cranked generator projects). Motors (of any sort) that can be removed complete with reduction geartrains are always useful. 10. Fans Cooling fans inside discarded equipment come in all shapes and sizes. PC-style fans can be found in PCs (yes, really!) and photocopiers. Fans with removable blades can be salvaged from microwave ovens, but open a microwave only if you know exactly what you are doing – they can be very dangerous. Squirrel-cage fans are used in much industrial equipment, as well as some types of domestic heaters. Fans are typically either mains-powered or run from 12V or 24V DC. Considering the cost of new fans (especially large ones), real savings can be made in this area. Australia's electronics magazine got your hands on – especially since it cost nothing! Many cordless drills have an electronic variable speed function, achieved by pulse-width modulating the power feed to the motor. The switching transistor is mounted on a separate interior heatsink and the rest of the control electronics are integrated with the trigger switch. A reversing switch is often mounted directly above the speed control. Even if you grab just this bit, you have a high-current, low-voltage electric motor speed control (or light dimmer etc). Finally, most of these drills have an adjustable slipping clutch that allows the peak torque to be set before drive ceases. There are plenty of uses for these bits and pieces. One of the easiest is to simply pull the body of the drill apart (because they are low voltage devices, tamper-proof screws aren’t fitted, making it really easy) and cut the wires at the motor. Bend a piece of steel rod into a crank-shaped handle and lock one end in the chuck. Turn the handle and you have a powerful small DC electric generator. How powerful? On one unit I measured, it was quite easy to run a halfamp load at 5V – that’s 2.5W. 2.5W is plenty to run high efficiency power LEDs, or even work through a 5V regulator to charge a phone. If you pick a drill that has two user-selectable gear ratios, it works even better. In one ratio, turning the handle is easy, but the amount of power generated is lower. Or, you can slide over the gear selection lever and have around twice the power output at the same rotational speed – but, of course, it will be much harder to turn the handle. The motor/gearbox/clutch/chuck assembly can also be used wherever a high torque output, low-voltage mechanical drive is needed. For example, two of the assemblies can easily be combined to form the individual wheel traction motors for a small robot (or use four for the ultimate in manoeuvrability!). Alternatively, the assembly can be used as a small winch, eg, to hoist a model railway baseboard up near the ceiling when it isn’t being used. In these applications, the built-in slipping clutch is a real asset, as it stops the motor from being overloaded when SC the output is stalled. July 2025  61 Hot Water System Solar Diverter Part 2 by Ray Berkelmans & John Clarke Solar-optimised hot water system (HWS) heating using power purely from excess solar generation Solar export data is obtained from the inverter and updated every five seconds Shows operational parameters on a 2.4inch OLED screen WiFi logging of operational parameters to a ThingSpeak database every five minutes Automatic override if the HWS temperature is still cold by the end of the solar day Night-time power-down Active heatsink cooling Email alert (one per day) if communication with the inverter is lost Over-the-air program updates via WiFi Manual override switch This HWS Solar Diverter, introduced last month, monitors the solar power available from a PV array and controls the hot water system to maximise the use of power that can’t be exported. It’s a lot less expensive to build than commercial equivalents. We’ll finish Background Image: construction, then get into setup and testing. unsplash.com/photos/sunset-view-5YWf-5hyZcw 62 Silicon Chip Australia's electronics magazine siliconchip.com.au T he first article last month explained how the Solar Diverter works and also provided the parts list and the majority of the PCB assembly instructions. At this stage, we have a mostly complete PCB, ready to install in the enclosure. There are still a few parts to fit, and some wiring to be done, before we can get to the testing and calibration stages. Enclosure cutouts Holes are required in the enclosure for the fan exhaust, air entry, PCB standoffs, one for the cable gland plus those for the conduit glands. Fig.4 shows the shapes of the fan cutout and mounting holes, plus the series of air entry holes required on the opposite end of the heatsink to allow air to enter and pass through the enclosure with fan assistance. The fan mounts unconventionally because the lid’s internal flange is thicker than the enclosure base. As a result, two of its mounting holes are on the lid and two are in the base. Thus, the circular cutout for the fan is made with the lid attached to the base, but without the Neoprene seal fitted. The hole can be made using a series of small (3mm) holes around the inside perimeter and then filed to shape. The difference in thickness is about that of an M3 nut and so the bottom screws for the fan simply pass through the lower mounting holes of the fan with a nut on each screw tightening to the inside base of the enclosure. They do not secure the fan but locate it in position. It is the top two screws that secure the fan to the lid once it is positioned on the base. To make this practical, the nuts need to be attached to the rear of the fan inline with the two top mounting holes. This can be done by gluing them to the back of the top two fan mounting holes using silicone sealant or epoxy resin. Alternatively, the nuts can be adhered by heating the nuts with a soldering iron sufficient to just melt the nuts into the fan plastic. It is not necessary to use a fan guard to protect against cutting fingers on the rotating fan blades, as the fan isn’t sufficiently powerful to cause injury. Heatsink temperature sensor Temperature sensor TS1 is held against the fin of the heatsink using a transistor mount clamp and secured with an M3 screw. You will need to drill a hole through the fins to gain access to the head of this screw. Make it large enough to allow a No.2 Phillips screwdriver to be inserted to tighten or loosen the securing screw. It is important that the heatsink is mounted so it is not too close to the leads of IC1 or the Triac. The minimum clearance is 6mm. The PCB screen printing shows the position for the heatsink, with a 45° diagonal cut at the lower right of the heatsink mounting flange. This may be required to provide clearance Fig.4: the cut-outs and holes required in the case. The rectangular cut-out in the lid is larger than the OLED screen but a bezel covers everything except the visible area. Note how the fan hole spans the lid and base; you need to clamp them together, without the waterproof sealing strip, before marking and cutting the hole. Warning: Mains Voltage This Solar Diverter operates directly from the 230V AC mains supply; contact with any live component is potentially lethal. Do not build it unless you are experienced working with mains voltages. A licenced electrician is also required to install the project. Do not power the PCB from AC mains while the serial cable is plugged into the PCB. Doing so is unsafe and could destroy the USB port on your computer, the computer and/or the Solar Diverter. siliconchip.com.au Australia's electronics magazine July 2025  63 between the heatsink & IC1’s current-­ carrying lead. The PCB screen printing also shows the positions for the heatsink’s lefthand mounting screws, the right-hand mounting screws (used in conjunction with IC1’s shield as described below), the Triac mounting hole and the heatsink Earth screw position. The top side of the heatsink surrounding the Earth hole needs to have the anodised coating scraped away to ensure the Earth lugs make good electrical contact with the heatsink. The Earth screw inserts from the underside of the PCB through the heatsink and is secured using a star washer and M4 nut. The Earth lugs mount over this and are secured with another star washer and another M4 nut. Insulating shields Three shields are used to cover exposed mains connections on the PCB, for OPTO1, IC1 and the mains input section. They are mounted on M3 tapped spacers. They could be made from fibreglass (eg, FR4) but we decided to use clear or translucent laser-cut acrylic as you can see through it. These laser-cut pieces, shown in Fig.5, will be available from our Online Shop, along with the PCB. The shield mounting for OPTO1 is straightforward, using 6.3mm spacers that are secured with 5mm-long M3 screws from the underside and similar screws plus washers on top. IC1’s shield is also pretty simple as it only has two mounting holes, both of which are held in place by the same screws used to attach the right-hand side of the heatsink to the PCB, with washers under the 15mm-long M3 screw heads and nuts between the shield and heatsink. Those screws are secured with two more M3 hex nuts on the underside of the PCB. The mains wiring shield is the largest one and uses 3mm-thick acrylic (the other two can be thinner, eg, 1.5mm or 2mm). We use 12mm-long screws from the underside to secure 6.3mm spacers to the PCB, then 12mm spacers are added onto the exposed screw threads. The shield is then held to the top of the 18.3mm (6.3mm + 12mm) spacers using M3 × 5mm machine screws through the top. Test-fit this, then remove it until the mains wiring is complete (see below). Low-voltage wiring The two DS18B20 temperature sensors need to be wired to connectors CON5 and CON6 for sensing the heatsink and water system temperatures, respectively. Both sensors are wired to plugs that plug into these two headers. The wiring lengths need to be sufficient to reach the heatsink (for TS1) and the water heater (for TS2) via the cable gland. Use heatshrink tubing around the DS18B20 leads to prevent them from shorting to anything. The LDR wiring also passes through the cable gland so the LDR itself is outside of the enclosure and thus can sense the ambient light level. Connections also need to be made for the fan power, to CON4. Make sure the fan’s red wire goes to the pin marked + on the PCB. The OLED screen also needs to be wired to a plug that fits into CON1. Take care with the pinout or you could damage the screen and note that some screens may have SCL and SDA swapped, or even VCC and GND! So Fig.5: the OLED bezel and shields. These will be available as a set, along with the PCB, pre-cut to the required shapes. The OLED bezel should be opaque (eg, black) while the others can be transparent or translucent. The mains wiring shield is made from thicker material as it is larger and thus needs to be stronger. 64 Silicon Chip Australia's electronics magazine you will need to check carefully and adjust the wiring to get the right signals to the right pins of the connector (they are labelled on the PCB). SCL is the clock signal for the OLED screen, while SDA is the data line. Display and bezel The display is mounted within a cutout in the enclosure’s lid, as per Fig.4. But note that this is to suit the particular OLED screen we used; they can vary in dimensions slightly, so check yours before cutting the hole. A front bezel covers everything except the OLED display area. The bezel dimensions are in Fig.5. Mains wiring The Solder Diverter needs fixed mains wiring, so you will have to get a licenced electrician to wire it between your water heater and its mains supply. We suggest you test it thoroughly and make sure everything is working (as much as you can test) before taking this step. First, run a 2.5mm2 red mains-rated wire between the A1 terminal of CON7 and the IP- terminal for CON8. The input and output wires should use mains-rated 2.5mm2 flat twin and Earth cable, with similar wiring for switch S2. S2 is the bypass switch, a 20A mains-rated switch in an IP66 housing. The wiring should be run within 20mm or 25mm conduit. Secure the shield over this wiring once the connections have been made. Software setup We will log our data to an online repository and graphing service called ThingSpeak (see Screen 1). If you don’t already have an account, navigate to https://thingspeak.com and open a free account. You can then set up one of your allocated channels with up to eight fields, as detailed in our September 2017 article on the Arduino ThingSpeak.com ESP8266 data logger by Bera Somnath (siliconchip.au/ Article/10804). We only need four fields for our data, and you can set them up as follows: • Field 1: HWS temperature • Field 2: H’sink temperature • Field 3: Excess solar • Field 4: HWS heating Note the “Write API key” on the ThingSpeak.com website, as you will need to include it in your Arduino sketch. siliconchip.com.au Screen 1: an example of the data that will be available on ThingSpeak after the HWS Solar Diverter has been running for a few days. We will also send ourselves an alert email if the solar diverter fails to connect to the inverter for longer than 15 minutes. Otherwise, if the inverter cannot be reached, we may end up with a cold shower! For this, we will use a free email service called PushingBox (www. pushingbox.com). There is no need to open an account if you already have a Google account. Once you log in, you will be taken to the Dashboard screen, where you will see an email “Service” already configured for you. You can edit this if you need to. From here, you need to create a “Scenario”, which will action our email alert. You could name it “Solar diverter status”. Enter a Subject (eg, “Solar Diverter”) and an email Body (eg, “The solar diverter cannot connect to the inverter. Time to check it out!”). That is it! Note the DeviceID key, which we will use in our Arduino sketches. You need the Arduino IDE installed with the ESP8266 Boards Manager to program the ESP8266 module. For details on how to do this, refer to the Silicon Chip article mentioned above, or Tim Blythman’s article on “The ‘Clayton’s’ GPS Time Source” in the April 2018 issue. The Arduino IDE is a free Heatshrink tubing should be used around the leads of the LDR (lightdependant resistor, above) and the DS18B20 temperature sensor (below). The side shot of the case shows the cutout required for the 40mm fan. siliconchip.com.au Australia's electronics magazine download from www.arduino.cc/en/ software The main program file for the solar diverter is “Solar_diverter_HWS_1reg. ino” or “Solar_diverter_HWS_2regs. ino”, depending on whether your inverter stores its export data in one or two registers. These sketches can be downloaded from siliconchip.au/ Shop/6/1835 First testing step There are quite a few elements to this sketch, which has over 600 lines of code, so it is worth testing and validating the software and hardware in parts. This helps in fault-finding/ debugging but will also promote understanding of the code. July 2025  65 Screen 2: these are some of the messages you may see on the Arduino Serial Monitor when running the “Test_ping_alarm_ Pushingbox_NTP.ino” test sketch. The first part to test is the Modbus communication with your router, as well as reading the temperature sensors and displaying the results on the OLED screen. The test sketch is called “Test_Modbus_temp_display_1reg. ino”. You will need to first install the “Modbus-esp8266” library by Alexander Emelianov for this to work. You also need the “OneWire” library by Paul Stoffregen, the “DallasTemperature” library by Miles Burton and the “U8g2” library by Oliver for the OLED screen. All are available through the Arduino Library Manager. Edit the sketch to include your WiFi credentials, as well as the IP address of your inverter, port number and the register address for your data previously determined using the “Modbus Poll” program. There is a separate test program called “Test_Modbus_ temp_display_2regs.ino” if you have an inverter that holds its export data in two registers. To program the raw ESP8266 chip, select the board type as “Generic ESP8266 Module” and attach a USBto-serial converter to the PROG header on the PCB, with Rx of the serial converter connected to the Tx pin on the PCB, and the serial converter Tx pin to the PCB Rx pin. You also need to put a jumper on JP1 because the ESP needs the IO0 pin held LOW to put it in programming mode. Power the PCB from a 5V DC power source connected to CON3, being very careful to wire it up with the correct polarity. There is no reverse polarity protection! A 3.7V Li-ion battery will suffice for this, although a 66 Silicon Chip current-limited bench supply would be better. Don’t be tempted to power it from the mains just yet! With the board powered up, press tactile switch S1 to boot the ESP in programming mode. You will see a short blink of the blue on-board LED as it boots. Ensure both temperature sensors are plugged in and upload the code. Once the code is uploaded, open the Arduino Serial Monitor, remove the jumper from JP1 and press S1 again. This runs the sketch. You should see the display light up with “Connecting to WiFi...”, followed by “Connected to <IP Address>” once connected. You should then see the HWS and heatsink temperatures on the screen, as well as the solar power you are currently exporting or importing. If you don’t see anything on the screen, check the wiring on the display and the JST connector. If these appear OK, it is worth installing one of the I2C scanner libraries through the Arduino Library Manager to see if both the OLED and the ADS1115 ADC addresses can be found. The OLED should be found at 0x3C, and the ADC at 0x48. If either is missing, check for solder bridges and trace-test your connections. If you see the ESP log into your WiFi but then reboot immediately afterwards, check that both temperature sensors are plugged in. If so, check the wiring at the temperature sensor end and the JST connector end. If it seems to work, switch a load on in your house (eg, an electric jug/kettle) and verify that your solar export Australia's electronics magazine drops dramatically. Conversely, your import power will increase dramatically. Hold your hand on each of the temperature sensors in turn, and work out which is which. If the heatsink and HWS temperature sensors are the wrong way around, change the line of code in the getTemps function from: “DS18B20.getTempCByIndex(0)” to “DS18B20.getTempCByIndex(1)” and vice versa for the second sensor. Physically swapping the sensors between sockets won’t do it as they are distinguished by their fixed internal IDs. Second testing step For the next test, use the sketch named “Test_ping_alarm_Pushingbox_NTP.ino”. This will ping your inverter IP address and, if there is no response after three tries, it will send a message to PushingBox, which will send an email alert to you. It will also query a Network Time Protocol (NTP) server to fetch the current time. We need this in our main sketch to override the solar diverter when solar conditions are poor and when the HWS is below 50°C after 3:30pm. Full power will then be provided to the HWS for 2.5 hours. Those parameters can be adjusted to suit your needs, of course, but it has worked well for us. Aside from the standard Arduino libraries, you also need to install “NTPClient” by Fabrice Weinberg, the “Time” library by Paul Stoffregen, and the “ESP8266-ping” library by Alessio Leoncini, for pinging the inverter. Edit this sketch to include your WiFi credentials, your PushingBox Device siliconchip.com.au ID and your inverter LAN IP address, then upload it. In the Arduino Serial Monitor, you will see if the ping is successful or not. It will also show the alarm count and whether an alarm message has been sent (see Screen 2). Hopefully, the pings are all successful so far. If not, check that you have the right IP address for your inverter. Assuming the pings were all successful, try changing the inverter IP address in the sketch to something that is definitely not listed in the client device list of your router and re-upload the sketch. Now watch the unsuccessful pings in the serial monitor. The alarm count should increase to three before an alarm message is sent via PushingBox. Check that you receive the email. After that, cut power to the unit to avoid many alarm messages arriving. In the main Solar Diverter sketch, there is a flag that is set once an alarm message is sent, and this is only cleared on power up (or after waking from sleep), effectively limiting the messages to one per day. At this point, it is advisable to log into your router and change the LAN IP address of your inverter from dynamic (DHCP) to “Fixed”. We don’t want this to change each time the inverter starts up or our pings will fail incorrectly. can get it). For example, if the offset variable in software is 0.18 and the current reading with no load attached is 0.45A, add 0.45 to the offset variable, making it 0.63 (0.18 + 0.45). In the Arduino IDE under Tools → Port, you will now see a network port named something like “SolarDiverter at 192.168.50.180 (Generic ESP8266 Module)”. If you select this network port, you can perform sketch updates (upload) over the air (OTA). Try sending your updated sketch OTA. Note that you will no longer have access to the serial monitor output. Testing the mains switching Assuming the OTA upload worked, you are now ready to connect some wiring to test boiling a jug of water. First, double-­ check your existing wiring and the component orientation on the board. Place the PCB inside the enclosure and secure it with machine screws. Make sure the DC power source is removed and the serial cable is disconnected. Find an extension cord you can cut in half and use for temporary AC mains input and output connections. From the plug end (input), run the Active wire (brown) to the free terminal on CON7, Neutral (blue) to one terminal on CON9 and the Earth wire (green/yellow striped) with a crimped eyelet to the heatsink Earthing screw. Do the same for the wires on the socket end (output): Active (brown) to the ACTIVE OUT terminal on CON8, Third testing step The third part of testing involves checking the mains switching, current measurement and over-the-air (OTA) programming features. If you were powering the PCB by a battery in the preceding parts, you will need to change to a 5V DC source. With the PCB powered from a 5V DC source, measure the voltage at the current sensing ADC (IC2) at test point TP4. This voltage value is used in our sketch to calculate the HWS current. Enter this value in the variable “maxADCVolt” in the “Test_Accurrent_measurement_PWM_OTA.ino” sketch, along with your WiFi credentials. Set the PWM duty cycle to 100% and upload it. Check the amperage output on the serial monitor and the OLED screen, and adjust the “offset” variable so that the measured current with no load is close to zero. To do this, simply add or subtract the amount necessary to bring the measured current to zero (or as close as you siliconchip.com.au This photo shows the finished HWS Diverter in the case without the larger acrylic shield from Fig.5. July 2025  67 Neutral (blue) to CON9 and Earth to the same heatsink screw. Also check that the 2.5mm2 red wire is running from the A1 terminal on CON7 to the IP– terminal on CON8. Attach the enclosure lid, then plug an electric jug filled with water into the extension cord socket. Plug the AC input plug into a GPO and switch it on. You should see the display light up with “Connecting to <YourSSID>”, followed by the LAN IP address when connected, and finally, the current draw of your electric jug. If there is a switch on the jug, activate it and watch the current shoot up to 8.5A, or whatever the rating of your jug is. If you have a current clamp meter, you can calibrate the display output by carefully exposing an Active or Neutral wire (with the power off) and clamping the jaws around the wire. Adjust the “mVperAmp” variable to roughly match the current displayed on the clamp meter. The easiest way to adjust it is to multiply the existing value by the proportion necessary to make it read the same as the reference (clamp meter) current. For example, if the mVperAmp variable in software is 48.5 and a water jug being heated shows as 10.4A, but the clamp meter measures it as 8.5A, you would increase the mVperAmp variable to 59.3 (10.4 ÷ 8.5 × 48.5). Note that a larger mVperAmp value will reduce the current shown since it is used in the equation denominator. After making that change, re-upload the sketch OTA and check that the display roughly matches the clamp meter reading. Now adjust the “pc” variable in the sketch to vary the PWM duty cycle percentage to a lower value and re-upload the sketch OTA. Your jug current draw should be reduced proportionally; the jug will heat slower, and the light may dim or flicker. When the duty cycle is low (say below 20%), the OLED will occasionally display zero for the current draw. This is normal because it is actually quite tricky to display a pulsing current value. If you glance at your clamp meter, you will see that it is all over the place. With a load of 8A and duty cycle of, say, 25%, the current is delivered as 8A, 0A, 0A, 0A, 8A, 0A etc. So, even though we are measuring our current for a full two seconds (100 cycles), the chances of sampling a zero is quite high at low duty cycles. There is no way around it other than sampling for even longer, but that would make our program update slower than it already does. Since it is only for a visual indication of current flowing to the load, we think this is an acceptable compromise. Final testing With it passing all tests so far, it is time to upload the final sketch, which is named “Solar_diverter_HWS_1reg. ino” or “Solar_diverter_HWS_2regs. ino”. Do this over the air. The complete sketch integrates all the components you have tested above and adds a few more, such as sending the data to ThingSpeak every five minutes, using the LDR to check for daylight, the automatic override if the The HWS Diverter mounted on to a wall with the acrylic cover to protect it from rain etc. A licensed electrician is required to wire the Diverter up, so make sure to properly test it before calling one in. 68 Silicon Chip Australia's electronics magazine siliconchip.com.au water temperature is below 50°C at 3:30pm, and active heatsink cooling. Before you upload the sketch, copy your WiFi credentials and all the other parameters you have used in testing to it, including: • your PushingBox DeviceID; • the Modbus register and port; • your inverter LAN IP address; • your solar diverter LAN IP address; • your current measurement calibration details (mVperAmp, max­ ADCVolt and offset). You will also need to enter your ThingSpeak API key and Channel number. Run this sketch for a while and verify that all the components are working, and that figures are being uploaded to the ThingSpeak website. If there is a hiccup somewhere, go back to the relevant test sketch and isolate the issue. Make sure you disconnect the AC mains and revert to a 5V DC power supply if you need to poke around on the PCB. Installation & commissioning As mentioned earlier, you will need a licensed electrician for the final installation of the Solar Diverter. This will involve fixing the enclosure to the wall near the HWS. Since the enclosure does not have any flanges, you might like to make some using two 100mm PVC square down-pipe straps. Simply cut the middle (horizontal) section out and glue the sides to the sides of the enclosure. Alternatively, the enclosure has wall-mounting holes in the corners that are outside the weather seal, so you can remove the lid, mark out the four holes, drill them in the wall and mount it using screws. Talk to your electrician about adding a 20A isolation switch near the enclosure. This makes it handy to de-power or reboot the system. You can run the HWS temp sensor to the PRT valve on your HWS and add some extra lagging for insulation. Waterproofing Assuming your enclosure and HWS are not indoors but under the eaves of your house, you should add an acrylic cover as shown in the photo opposite. This will prevent driving rain from entering the penetrations in your enclosure. The cover is made from a 3mm-thick acrylic sheet, 340 × 307mm siliconchip.com.au Fig.6: if the Solar Diverter will be exposed to wind-driven rain (eg, under the eaves of a house), it must be covered with something like this acrylic shield to prevent water from entering the ventilation holes. Cut the acrylic sheet as shown, then heat it to make the bends on a former like a piece of straight timber. in size, cut and bent according to the template in Fig.6. You can bend the acrylic using a hot air gun on maximum setting, moving it continuously along the bend line. It helps to clamp the piece to a sharp edge to bend it over. Once the acrylic is soft and starts to droop, use a piece of timber to push the hot acrylic along the bend line into position. Use outdoor silicone sealant to fill the gaps in the joins. Final calibration Once it is all installed, you might like to perform a final calibration of the current sensor under the full load of your HWS element. With power to the HWS switched off, attach a clamp meter around the Active at the HWS. Power the system up and send a sketch update OTA with the duty cycle set to 100% and the time set to your current time in the section near the top of the Loop titled “// In case of poor solar conditions”. Assuming your HWS isn’t already up to temperature, this will supply the full ~15A rated power to the element. Read off what your clamp meter Australia's electronics magazine reads and adjust the “mVperAmp” variable in the sketch to suit. Re-­ upload the sketch OTA and check again. Once the current measurement is reading correctly, reset the override time in the sketch to 3:30pm or whatever time you’d like to have your HWS heating on a poor solar day. Conclusion This circuit is essentially quite simple and comprises a WiFi-connected microcontroller, two temperature sensors and the power control circuitry (zero-crossing opto-isolator and Triac) and not much more. The OLED screen, current sensing and the ThingSpeak data logging are nice add-ons but not strictly necessary. The secret sauce is in the software, reading the exported power from the inverter and using that to adjust the mains-controlling PWM duty cycle. There is also the email alert function in case the inverter can’t be reached. If you take your time and work through the test sketches, we are sure you will get to grips with the software very quickly. Enjoy the savings from using more of your own solar power! SC July 2025  69 Using Electronic Modules with Tim Blythman 8×16 LED Matrix These LED matrix panels are bright, compact and easy to drive, although there are a couple of tricks to them. After looking at the driver IC, we’ll provide demonstration software for Arduino and BASIC code for the Micromite and PicoMite. T his LED matrix module was the display and the base on which we mounted the components for our Digital Spirit Level project from the November 2024 issue (siliconchip.au/ Article/17021). We used Jaycar’s Cat XC3746 (www. jaycar.com.au/p/XC3746), although other modules with the same controller are available elsewhere. Our software should work with any of these modules as long as they use the same AIP1640 control chip. In the Digital Spirit Level article, we noted that the Matrix has pins labelled SDA and SCL. While you might think it would thus use an I2C interface, that is not the case. So we thought it would be helpful to delve into the AIP1640 driver chip and the communications protocol that it uses. That will allow us to create software to control the chip. There isn’t much more to the module than the chip and its LED matrix. The AIP1640 IC The Wuxi I-core Electronics AIP1640 is the main driver IC on the module. Fig.1 shows the circuit of the module, where IC1 is the AIP1640. It comes in a 28-pin SOIC (small outline IC) package and 24 of its pins connect to a matrix of 128 blue LEDs, with eight anode drivers and 16 cathode drivers. It has an internal 450kHz oscillator to control the multiplexing of the output drivers. Such an arrangement would be wellsuited to driving 16 common-cathode 70 Silicon Chip seven-segment displays too. The only other components are the standard 100nF supply bypass capacitor and two 10kW pull-up resistors on the communication lines. Unlike the Matrix module, the data sheet labels the communication pins as DIN and SCLK, hinting at the divergence from I2C. The power, ground, DIN and SCLK lines are wired to a locking four-way receptacle; a matching plug with wires comes with the module. This makes it easy to wire up to a development board like an Arduino Uno, since all the functions are controlled from the communication interface. You can download the data sheet for the AIP1640 controller IC from siliconchip.au/link/ac3e Control interface The data sheet includes sample communication waveforms. Fig.2 shows this, along with a single byte transmission in the I2C protocol. You can see that the AIP1640’s protocol resembles I2C, but it is not identical. The idle state appears to have both DIN and SCLK at a high level, like SDA and SCL in I2C. The text describes the lines being set low and high, whereas I2C would have the lines set low and allowed to rise to a high level through the action of the pull-up resistors. It seems that the start, stop and bit clocking restrictions are much the same as I2C, although the AIP1640 only expects eight, not nine bits. A START condition occurs when Australia's electronics magazine DIN (or SDA) goes low, while SCLK (or SCL) is high. During data transmission, DIN can only change state when SCLK is low, while the END (or STOP) condition is when DIN rises while SCLK is high. The AIP1640 sends the least significant bit (LSB) of the byte first, while I2C sends the most significant bit (MSB) first. The AIP1640 protocol denotes the first byte as a command, while I2C starts its transmissions with an address byte. The protocols are similar enough that an I2C transmission could possibly be used to control an AIP1640 controller, but it would probably not allow other I2C devices to coexist on the same bus, since the I2C addresses may clash with the AIP1640 commands. Indeed, the AIP1640 has no concept of addressing, so only a single unit can be connected to a bus. Note that the data sheet does not make any claims to I2C compatibility; any confusion appears to originate from sample code that has been posted online. Now that we’ve established that the protocol is not I2C, we can examine how to communicate with the chip. The data sheet explains that some commands are followed by data bytes. Each command must be preceded by a START condition, so the first byte is a command and subsequent bytes in a transmission are data. Table 1 shows the commands that the AIP1640 responds to. Each command is typically sent between a START and END condition, except the siliconchip.com.au Fig.1: 128 blue LEDs are driven in matrix fashion by 16 cathode drivers and eight anode drivers in the chip, with all timing controlled internally. Only two resistors and one capacitor are needed in addition to the AIP1640 driver IC. Fig.2: the protocol used by the AIP1640 has a lot of parallels with I2C, but since it does not implement an addressing scheme, it will not work on an I2C bus. Set Column command, which would be followed by data that is sent to the display RAM for output. Like many such devices, a small siliconchip.com.au amount of internal RAM stores the display data and the host controller can choose where in RAM it writes to. There are 16 bytes, corresponding to Australia's electronics magazine the GRID1 to GRID16 cathode drivers. Each bit corresponds with one of the SEG1-SEG8 anode drivers, with SEG1 being the LSB and SEG8 the MSB. You July 2025  71 Column 15 Bit 7 Bit 0 Column 0 Fig.3: the pixels are mapped logically, meaning it is quite intuitive to program the display. There is a column auto-increment setting, so writing text from left to right can be accomplished easily. The back of the PCB is as sparse, with just the control IC in an SMD SOIC-28 package, a few passive components and a four-way socket to suit the provided plug with leads. can see the mapping of this to LEDs on the XC3746 in Fig.3. A typical display driver might send a couple of commands to set up an initial state, after which pixels are written as needed to achieve the desired display and display updates are sent as required. A command might update part of the display, or it might make use of the auto-increment function and send entire screenfuls of data at a time. Power supply The AIP1640 data sheet specifies a 5V±10% supply voltage, with input voltage thresholds of 30% for a low input and 70% for a high input. We performed some tests with our Coin Cell Emulator from December 2023 (siliconchip.au/Article/16039) and found that our Matrix worked perfectly well down to around 2.8V for its supply and logic levels. With a 5V supply, the peak current draw with all pixels lit was around 140mA. There are eight PWM settings and thus brightness levels. We found that a setting of 1 or 2 (0b001 or 0b010) was adequate for indoor viewing. Level 1 draws around 20mA with all pixels lit, while level 2 draws around 40mA. The data sheet notes the different settings and their corresponding fractions of the maximum duty cycle. Unlike some controllers (eg, for some OLEDs and LCDs), there is no hardware register to flip or rotate the display. For the Digital Spirit Level, we had to invert the pixels and columns in software to have the connector at the bottom of the display. You can contrast that with the layout shown in Fig.3, with the connector at the top. driven by calls to the digitalWrite() function, which all Arduino boards and platforms support. We expect you could use any Arduino board, although we have not tried any others ourselves. Arduino connections PicoMite connections Wiring the XC3746 up to an Arduino Uno or similar board is easy enough since there are just four wires. We have written the software to be able to use any digital pins. Fig.4 shows the wiring with the default Arduino sketch settings; if you change the connections, you will need to change the driven pins by modifying the XC3746_ CLK and XC3746_DAT #defines in the library file. The “matrix” sketch uses the same library we created for the Digital Spirit Level, which provides simple functions to initialise and write to the display, including a simple font containing the digits 0-9. To use the library in your own project, simply copy it to the sketch folder and add the #include directive. The sketch lights up all pixels, switches them off, then shows a rising count of elapsed seconds on the display. We used an Arduino Uno in our examples, but there are no special hardware features or other libraries needed, so other Arduinos could be used, like the Leonardo. The pins are We’re using the PicoMite as our exemplar BASIC platform since it is easy to distribute a UF2 firmware file that contains the BASIC environment and code. The firmware files can be loaded onto the PicoMite without any special hardware using its USB flash drive bootloader (accessed by holding the BOOTSEL button while powering on the PicoMite). All that needs to be done is to copy the MATRIX.UF2 file to the RPI-RP2 virtual drive. The BASIC code should work on other MMBasic platforms, such as the Micromites, and we have also included it in the software download. You can load this directly using the AUTOSAVE or XMODEM commands. Fig.5 shows our wiring to the Pico­ Mite. We used the 3.3V supply to ensure there are no problems with the logic levels from the I/O pins differing from the supply voltage. The 3.3V regulator on the Pico can source up to 800mA, so it will have no trouble powering the Matrix. We did notice a lower brightness compared to using a 5V supply, with brightness level 2 drawing only 4mA with all pixels lit. That’s about a factor of 10 difference compared to a 5V supply. Still, it seemed to work OK, and there is scope to increase the brightness if needed. You can change the pins used by modifying the CONST values of XC3746_DAT_PIN and XC3746_CLK_ PIN in the code. The BASIC program works the much the same as the Arduino sketch, although it uses the Table 1 – AIP1640 commands Command Action Notes 0b0100bc00 Configuration If b=0, auto-increment column otherwise fixed If c=1, activate test mode 0b10000000 Turn off display 0b10001ddd Turn on display and set duty cycle ddd is three-bit duty cycle (brightness) setting 0b1100eeee Set column eeee is 0 (GRID1) to 15 (GRID16) 72 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.4: we used the connections here with our example Arduino sketch, although the data and clock pins can be altered in the code if necessary. The XC3746 comes with male jumper lead ends that can be plugged directly into a board like the Arduino Uno. Fig.5: to interface with a Pico (running MMBasic), we used the 3.3V supply to ensure there was no mismatch between the supply voltage and I/O pin logic levels. The 3.3V regulator on the Pico can supply 800mA, so it can easily drive the display. The XC3746 pack includes the display module and a set of flying jumper leads equipped with a plug, so it is easy to wire up. To connect the Matrix module to a Pico, you can solder socket headers to its pads or use a breadboard. The demo software can be downloaded from siliconchip. com.au/ Shop/6/2756 internal PicoMite timer, so it might not start counting from zero. Note that the UF2 file will only work with the original Pico and not the Pico 2. The BASIC code is compatible with the Pico 2, but you’ll need to load the latest version of MMBasic and then the BASIC code yourself. If you see the Pico’s LED flashing, that means BASIC has been loaded correctly. So if the Matrix is not working, but the Pico’s LED is flashing, check your wiring. Conclusion These LED Matrix displays are simple enough to control, although you might get tripped up if you try to use example code that works with I2C, since the interface is not the same. They are great for small numerical displays, as we have demonstrated. Despite what the data sheet says, our units seemed to operate happily on 3.3V (which bodes well for many modern microcontrollers). However, if you want maximum brightness, a 5V supply is the way to go; you may need a level shifter if your microcontroller has 3.3V I/Os. Perhaps the reason for the specified narrow voltage range is to provide a degree of uniformity to the brightness. With 128 pixels, these Matrix modules can display simple graphics or other patterns. Jaycar sells the XC3746 Duinotech Arduino Compatible 8×16 LED Matrix Display for AU$19.95. SC siliconchip.com.au Australia's electronics magazine July 2025  73 SSB Shortwave Receiver Part 2 by Charles Kosina, VK3BAR Introduced last month, this new Shortwave Receiver covers the entire shortwave band from 3MHz to 30MHz. It is digitally tuned and has a host of useful features like squelch, USB/LSB support, good sensitivity (a -107dBm signal gives 13dB SNR), fast or slow AGC, an RSSI display and it runs from 12V DC. This month, we describe how to build, test and align it. T his is not an overly difficult device to build, as it uses no tiny components or fine-pitch ICs. However, it has two boards that are fairly packed with SMDs plus quite a few though-hole components, so you should ideally have decent soldering skills if you’re going to attempt it. You also need some test equipment to calibrate the Radio. That includes an accurate frequency counter up to 100MHz and a signal generator that will work up to at least 30MHz that can produce a signal down to 10µV or less (or an attenuator to allow that). An oscilloscope with 100MHz or more bandwidth is also nice to have, but not absolutely necessary. Some sheet metalwork is needed. 74 Silicon Chip I recommend having a stepped drill bit or two (eg, 3-12mm & 12-24mm) on hand. A drill press would be ideal, but you can do it with a hand drill if necessary. There are many components overall, but the values are marked on the circuit boards to ease construction. It pays to be careful as you go through the assembly process and make sure each part goes where it’s supposed to. Mixing up two visually identical capacitors could be enough to prevent the radio from working. Construction Virtually all the components mount on two PCBs, the Control Board (Fig.14, 152.5 × 81.5mm) and the RF Australia's electronics magazine board (Fig.15, 152.5 × 51mm). There are some through-hole components used, but the vast majority are SMDs, mostly passives (resistors and capacitors) in M2012/0805 packages, which measure 2.0 × 1.2mm. These passives are on the small side if you are used to through-hole components, but we still consider them to be in the ‘easier to handle’ category compared to really small parts. So as long as you have the right tools, a decent amount of light and reasonable vision (or magnification), you should not find the assembly too difficult. Similarly, the ICs are not in really tiny packages; they are mostly SOIC types with 1.27mm lead pitch, ie, half that of a through-hole chip. Again, siliconchip.com.au Fig.14: the Control Board has parts on both sides; fit all the SMDs first, then the throughhole parts on the underside. The ICs, diodes, electrolytic capacitors and the Arduino Nano module must all be installed with the polarities shown here for the Radio to work. these are not what we would consider difficult-to-solder parts. Control board I recommend building the Control Board first and testing it before you move on to the RF Board. There are components on both sides of the board, but most of the parts, including all the SMDs, are on the front. Start by soldering the two ICs first, making sure their orientations are correct. In each case, find the pin 1 marker (a dot or divot on the top, or a chamfered edge on the side) and make sure it’s aligned as shown in Fig.14 and on the PCB silkscreen. It’s possible to solder the pins of these SOIC package devices individually with a fine-tip soldering siliconchip.com.au iron. Add plenty of flux paste to make soldering easier and reduce the possibility of bridging pins with solder. If that happens, use copper braid with a bit of extra flux paste to remove the excess solder. In fact, we usually don’t bother trying to avoid bridges as it’s so easy to clean them up later; we’re more focused on making sure the solder flows onto each pin and pad, to avoid high-resistance connections that can be difficult to find later. Follow with the passives using a similar technique. The resistors will be marked with codes indicating their values (eg, 10kW = 103 or 1002) while the capacitors will not have any markings. In both cases, it’s best to unpack a single value, then fit them all as shown Australia's electronics magazine on the overlay diagram so you can’t get them mixed up. None of the passives are polarised so they can be soldered either way around. Note that a few of these parts, like the 68W resistor and 100μF capacitor, are slightly larger than the others and so have larger pads to suit. Also, two of the 8.2kW resistors at centre left are not fitted (marked R10 & R20 on the PCB) as these are the I2C pull-ups and the Si5351 module has onboard pull-up resistors. Follow by soldering the four identical Mosfets, which are all in three-pin SOT-23 packages. The pins are small but widely spaced, so this should not be too difficult. Don’t fit any of the through-hole July 2025  75 components on the front side of the PCB (where the SMDs have been soldered) yet. The Arduino Nano and the Si5351 modules are on the back of the board and can be plugged into socket strips. This is important as if either failed, replacing them would be difficult. 15-pin socket strips are used for the Nano and one seven-pin strip for the Si5351. The only other parts on the back of the board are the headers, two electrolytic capacitors (which are polarised, so make sure they’re fitted the right way around) and the trimpot for LCD contrast. All of those can be mounted now. As well as the speaker connector (CON4), there is another two-pin header, CON3. This is connected in parallel with the headphone jack socket and may be wired to an RCA socket on the back panel for an external powered loudspeaker. Now go back to the front of the PCB and fit the remaining through-hole components. It’s important that the switches, potentiometers and encoder are square on to the board before soldering. The way to ensure this is to attach the black front panel with 16mm tapped spacers to position these correctly; make sure that all controls turn easily before soldering. For a better appearance, rather than zinc-plated screws, I used black 6mm machine screws (which you can buy at Bunnings) to attach the front panel. The jack socket is a unique part; ensure it is pressed firmly on to the board. Next, solder the 16-pin header to the LCD module. Don’t attach the LCD yet; clean the board with de-fluxing solvent and inspect all connections with a magnifier. Pay special attention to the solder joints on the socket strips for the Nano, as they are not accessible once the LCD is mounted. Before any modules are plugged in, use an ohmmeter to ensure that there are no shorts from the 12V or 5V supply lines to ground. Finally, attach the LCD module using 5mm spacers and 12mm machine screws and nuts. The Si5351a module is held in place by 6mm M2 or M2.5 screws with 11mm threaded spacers. RF board assembly If you want to take a break from assembly now, you could skip down to the “Programming the Nano” sub-heading, complete initial testing and calibration, then come back here when you get to the part where you need the RF board to be assembled. The RF board overlay is shown in Fig.15. Parts are only fitted to one side of this board. As before, start with the ICs (two NE612s, one LMC6482 and the PCF8754) and ensure they are all orientated correctly as you solder them. All are in SOIC packages. Then move on to transistors Q1-Q7; Q7 is a Mosfet, while the others are NPN RF transistors, but they all come in the same packages, so don’t get them mixed up. Follow with Q8-Q10, which have four pins since they are dual-gate Mosfets. In all three cases, the wider source lead goes towards lower right with the PCB orientated as shown in Fig.15. Fit diode D4 with its cathode stripe as shown, then REG2 after first applying a thin layer of flux paste to its pads. That will assist in soldering its tab properly. After that, solder the SMD resistors & capacitors, noting that the capacitors are again unpolarised, and all the SMDs are on the board. Mount the axial inductors next; they have three different values, so make sure the right ones go in each location. They are not polarised, so you can fit them in either orientation. Fit diodes D2 & D3 next; they are polarised, so ensure the cathode stripes both face to the right. After that, solder RLY1 in place with its pin 1 marking towards the top. Next, fit VC1-VC3, which are polarised in a sense, because we want the adjustment screws to be connected to the ground pins in each case. So orientate them as we have shown. For the varicap diode, VD1, you may get it in a two-lead TO-92 package like we did, or in an axial package, similar to a regular diode, which can be mounted vertically. Regardless, ensure its cathode lead goes to the pad marked K; with the axial package, this will be the end with the stripe. Bend REG1’s leads down and attach it to the board using an M3 machine screw and nut, ensuring its three leads go into their pads. Solder and then trim the leads. Don’t do this before tightening the screw or you could fracture the leads. I used a 16mm-long screw to attach the tab as it makes a convenient ground point for testing later. Next, install CON1 and CON2. That just leaves the crystal filter module, XF1. The crystal filter comes with SMA sockets attached, and at least the input one has to be removed. As it’s supplied, only the top connections are soldered; I used a hot air wand to carefully heat them and slide them off, but a soldering iron with a large tip could also be used instead. Take great care that other nearby components don’t get removed as well. Attach the filter to the PCB using four 10mm-long M2 or M2.5 screws, nuts and 5mm spacers. Solder wires to connect the input and output of the filter to the circuit board, one for signal and another for ground at each end. In theory, XF1 is not polarised, but it’s a good idea to mount it like we did, with the angled capacitor on Fig.15: all the parts are on the top side of this RF Board. Polarised components to pay attention to include the ICs, dualgate Mosfets, diodes, relay and variable capacitors. It’s best to remove the SMA connectors from the crystal filter module (XF1) before mounting it on this board. 76 Silicon Chip Australia's electronics magazine siliconchip.com.au the right-hand side, since that’s how we tested it. Toroid winding The 3-10MHz toroid (T1) needs 42 turns of 0.35mm diameter enamelled copper wire (ECW) for its secondary and four turns of the same wire for the primary. The secondary will take a little while to wind; do it first and neatly, with the turns almost touching each other. There is just enough room for that number of turns with a small gap in between the ends. Attaching the transformers to the PCB is one of the most fiddly parts of the assembly process. T1’s primary is soldered between the pads labelled A & B on the PCBs, and is wound near the ‘cold’ end of the secondary, while the secondary is soldered between pads C & D. I found it easier to attach the transformers to the PCB first, solder the secondary windings, then add the primary windings. It is a bit tricky but I think it is the best approach! Make sure you scrape off the enamel from the wire ends before soldering them to pads A-D; otherwise, you won’t get a good electrical connection and the radio won’t work. It helps to tin the ECW ends after scraping them; if the solder won’t stick evenly, that means you need to scrape off more enamel first. There’s also room for a tinned wire loop to help hold the toroidal core to the PCB at upper right. We recommend you add this to prevent solder joints from fracturing due to movement over time. This does not form a shorted turn as the pads it’s soldered to aren’t connected to anything. The second toroid (T2) has 15 turns of 0.6mm diameter ECW for the secondary, which you should distribute evenly. Make sure the direction of winding is such that the ends go into holes G & H in the PCB correctly. Then add the two-turn primary using 0.35mm diameter ECW, scrape and tin the ends and solder it to pads E & F. Again, solder the piece of tinned wire to hold it to the PCB. Once all components have been installed, give the board a thorough clean to get rid of surplus flux. Inspect all soldered joints and check for any shorts with an ohmmeter. Make up the connecting 16-wire cable with IDC sockets. Use a small vice or crimping tool to siliconchip.com.au Wiring up the boards is pretty straightforward with a ribbon cable connecting the control and RF boards. There’s room inside the enclosure to fit a three-cell battery holder which can be used to power the Receiver. evenly press the parts together; make sure the cable is exactly square on to the connector. Attach the loudspeaker to the two wire connector and plug this on the control board. Programming the Nano The Nano should be programmed before it is plugged in. You can use the free programming software called AVRDUDESS for Windows that you can download from siliconchip.au/ link/aaxh or use the command-line version, avrdude, if you’re running Linux or macOS. Australia's electronics magazine Connect the Nano via a USB cable and check what COM port it appears as. Select a baud rate of either 57,600 or 115,200 depending on the version of the bootloader in your Nano. Select the programmer Arduino for bootloader using STK500v1 protocol from the drop-down list; it may be the default. Press the Detect button and it should recognise the chip. It is important that the programming is done in exactly the following way, making sure that the settings in AVRDUDESS are correct. Otherwise, you could end up with a bricked Nano. July 2025  77 There are two files to be loaded: the program file, “SSB RX xx.HEX”, where xx is the version, and the “SSB RX xx.EEP” file, which is a binary file loaded into the chip’s EEPROM. There are five boxes below Options. Tick “Disable Flash Erase”. Under the Flash box, “Format” should be “Auto (writing only)”. Locate the HEX file to be loaded into Flash by searching for it in the square to the right of the Flash window. Locate the EEP file and place in the EEPROM window. Select Raw Binary from the drop-down list. Tick the Write circle under Flash and press the Go box. This will result in progress messages in the bottom window. Tick the Write circle under the EEPROM window and press the Go box. It will also have messages in the progress window. This completes the programming, and the Nano may be disconnected from your computer and plugged into the Control Board. Make sure its orientation is correct. Initial testing Connect power to the board via CON1. Make sure polarity is correct; if not, nothing will happen as there is a protection diode. The LCD backlight should be on, but there may not be any text visible. Adjust trimpot VR6 until you see text on the screen. With the Band potentiometer (VR3) fully anti-clockwise, the top line should have 3.600.000MHz and the bottom line USB or LSB, depending on the position of switch S2. There should be a cursor visible under one of the digits. When the shaft encoder is rotated, this number should change. Depending on the particular encoder used, it may operate backwards. In that case, bridge the two pads marked DIR above the LCD to reverse the direction. Switch the power off and on; the screen will show “SSB Receiver” on the top line and version number on bottom line for two seconds. Toggle the USB/LSB switch and see that it changes on the screen. Press the switch on the shaft encoder and check that each press moves the cursor to another position under the frequency. It should allow adjustments in 10Hz, 100Hz, 1kHz, 10kHz, 100kHz and 1MHz steps. The Band potentiometer is a convenient way to cycle through the most common amateur radio bands. It sets a frequency partway through each band starting with 3.6MHz, then 7.1MHz, 10.0MHz, 14.1MHz, 21.1MHz and 28.1MHz. 10MHz is not actually in a ham band, but it has WWV transmitting time and accurate frequency information. Using an oscilloscope and a frequency counter, check the outputs of the Si5351 module. CLK2 is the BFO and that should read 8999.6kHz or 8996.6kHz depending on the position of the USB/LSB switch. CLK0 should have a frequency that is the sum of the currently tuned frequency plus the BFO frequency. The accuracy of these depends entirely on the 25MHz crystal attached to the Si5351 module, so you may get slightly different values. At this point, it is advisable to perform calibration. Calibration To calibrate the set, you need to measure the actual frequency of the 25MHz crystal on the Si5351 module. This procedure will calibrate the short-term accuracy to within less than 5Hz. Switch off the receiver, then rotate the Band potentiometer fully clockwise. Switch it on and the top line on the LCD will show “Calibration”; the bottom line will show the nominal crystal frequency of 25,000,000Hz. In this mode, the frequency on OUT0 is set to exactly 10MHz. Fig.16: the recommended hole locations and sizes for the rear panel. A stepped drill bit makes drilling these straightforward. As this is at actual size, you could copy or download and print it and use it as a template. 78 Silicon Chip Australia's electronics magazine siliconchip.com.au Measure the frequency on OUT0 with an accurate frequency counter and rotate the tuning knob, which increments or decrements by 10Hz, until the output is as close as possible to 10MHz. It’s possible to get to within 1Hz. It may take many turns, as the crystal could be out by more than 10kHz. Turn the Band potentiometer anti-­ clockwise to leave calibration mode. The new value for the 25MHz crystal overwrites the original value in EEPROM loaded by the EEP file, and will be read every time the power is switched on. This calibration needs to be done at regular intervals as the crystal may age and can also drift with temperature. Case preparation The modifications to the case involve drilling four 3mm holes in the base to attach the RF board, plus numerous holes in the back panel for the power socket, antenna connectors and the loudspeaker. I used the Jaycar AS3025 rectangular speaker, but just about any small 8W speaker will be suitable. You will need to adjust the mounting hole positions if using a different speaking, though. Fig.16 shows the suggested hole pattern. I used a stepped drill bit, as they make clean, circular holes. If you have a drill press, that would be ideal, but you can hand-drill these holes neatly if you’re careful. A word of warning! The drill can grab the plate and spin it around, possibly injuring you, so for safety, always make sure the plate is clamped firmly while drilling the large holes. Alignment This should be done with the two circuit boards not yet assembled into the case to allow easier access to test points. The only adjustments on the RF board are the three variable capacitors, and they should be peaked at 9MHz. The way you do this depends on what equipment you have. Connect the control board to the RF board with the flat cable and carefully check that the two pin 1s are connected together, ideally with the red striped side of the cable to those pins (check for continuity between the pin 1 pads on the two PCBs). If you connect the cable backwards at one end, you could do damage! Switch on the power and set the frequency to, say, 7.1MHz or some other convenient frequency. Use an oscilloscope probe to check that you have the VFO signal at about 16MHz on TP3 and the 9MHz BFO on TP5. Connect a signal generator to CON1 with the output set to about 100µV. This is way above the lowest level, but is useful for the initial setup procedure. Tune the signal generator for a whistle from the loudspeaker, which should be very loud. Reduce the signal generator output until you get some background hiss from the speaker. Adjust the antenna tuning potentiometer (VR1) for maximum signal, measure the DC voltage on TP6 and tweak the three trimmers (VC1-VC3) for maximum output. Fig.17: the front panel PCB overlay for the SSB Receiver. It is shown here at 70% of actual size. siliconchip.com.au Australia's electronics magazine That’s all there is to it; the receiver should work across the whole range. You will find as you tune across 10MHz, the relay will click to switch between using T1 & T2. Final assembly The two boards and front panel can now be assembled into the case. The RF board uses M3 × 10mm threaded spacers to attach to the bottom of the case. The antenna input connects via a short ready-made cable between the SMA connector to a BNC connector on the back panel. Power is from a 2.1mm or 2.5mm ID (inner diameter) DC jack on the back panel to the two pin connector, CON1, on the Control Board. The front panel attaches to the case by four screws on the corners. Instead of using the zinc-plated screws that came with the case, I found some black screws that look better. All the rotary controls have 6mm diameter shafts. It is preferable that these have fluted shafts, as knobs for these are more common. Still, there are a few sellers on AliExpress that have knobs with grub screws (they are listed in the parts list last month). Those were ideal for D-shaped shafts but can also be used on fluted shafts. Conclusion Your Radio should now be operational and you can start scanning the bands for signals! You can even use it on the go, powered from a 12V battery. Note that while you could run this radio from a 12V vehicle battery, you must not do so (or connect it) while the engine is running as it doesn’t have protection from voltage spikes. Unless you add a suitable filter, it’s far safer to run it from its own interSC nal battery. When first running the Receiver you must calibrate it by following the text under the cross-heading “Calibration”. This ensures accurate timing. July 2025  79 CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions will be paid for at standard rates. All submissions should include full name, address & phone number. GPS Speedometer The GPS FineSaver project (June 2019; siliconchip.au/Article/11673) uses a GPS module to display the instantaneous speed. It would typically be used in a vehicle as an accurate speedometer. In addition, it uses the GPS system’s timekeeping to provide a clock feature. It also has hardware to change the volume of an audio signal based on vehicle speed. We delved into why this was a useful feature in that article. A reader recently wanted to build just the GPS speedometer component, with the speed display as large as possible, making it easier to read. Such a device could be built using the same PCB as the FineSaver, but with fewer components. It would thus be less expensive and quicker to assemble. The speed can be shown in a 80 Silicon Chip larger font since none of the other data relating to other features or settings would need to be displayed. We investigated whether larger OLED modules are available, since that would be a straightforward change and allow a larger speed display. There are, but the ones that we found have a different pinout or controller interface. So they would require a new PCB or driver to work. Therefore, we opted to change the firmware to work with a reduced component count. The cut-down version of the circuit is shown here. The parts needed include microcontroller IC1, its 100nF bypass capacitor, the 10kW pullup resistor on pin 4, the OLED screen (MOD1) and the GPS module connected to CON7. If you have a USB power supply, mini-USB socket CON6 is sufficient to provide 5V power. Otherwise, D1, REG1 and the 10μF and 100μF Australia's electronics magazine capacitors can be used to obtain 5V from a 9-12V input at CON1. The firmware still allows the display brightness to be adjusted. The parts around CON5 (trimpot, resistor and optional LDR) should be fitted if you want brightness control; otherwise, a jumper made from a component lead offcut can be used to permanently set the display to full brightness, as shown by the dashed line. We’ve changed the font so that it uses the full 64-pixel height of the OLED display without needing to be upscaled. That makes it much easier to read. The new font data ends up using about half of the available flash memory on the PIC16F1455 processor! There are no user settings at all. Instead, the choice of units is made at compilation time, with kilometres per hour (k), miles per hour (m) and knots (n) being the available options. We have created HEX files with the three siliconchip.com.au options: 0110419K.HEX, 0110419M. HEX and 0110419N.HEX. The photo shows the assembled PCB with the minimum parts fitted, including a typical display showing the speed in km/h. This has the fixed full brightness modification. If the GPS module is not fully operational and delivering valid speed data, the status is shown by one, two or three dashes. One dash indicates that no data is being received, while two dashes mean that data is being received but the checksum is invalid. That may mean an incorrect baud rate setting. The FineSaver expects data at 9600 baud, which is fairly standard for GPS modules. Three dashes mean that the GPS module is functional but has not locked onto its satellites. You might see this as the unit is starting up or if you drive through a tunnel and the GPS module loses its signal. ICSP header CON4 is fitted to our prototype. We used this during the development of our firmware, but you will not need it unless you plan to program your own chip. You can use a PICkit 3, PICkit 4, PICkit 5 or Snap programmer to work with the PIC16F1455 chip. The software, including source code and the three HEX file firmware variants, is available to download from siliconchip.au/Shop/6/1845 Tim Blythman, Silicon Chip. If the input falls below 1V, IC1a’s output is high but IC1b’s output goes low. In this state, segment d is driven directly, while segments e & f are again driven via D1 . This combination forms an “L” on the display. The diodes serve to isolate the outputs of the two comparators, ensuring they don't interfere with each other when sharing segment control. A segment current of 3mA has been selected to keep the total current within the LM393's maximum sink current of 16mA. When displaying an “H” (which lights five segments), the total current is about 15mA. Red LEDs are efficient and should be bright enough at this level; if using a different colour (eg, blue), you may need to adjust the resistor values accordingly. The 10MW resistor biases the input toward 2.5V when nothing is connected, keeping the input between the upper and lower thresholds so the display remains blank. A 100kW series resistor protects the comparator inputs in the event of accidental overvoltage, working in conjunction with the LM393’s internal ESD protection diodes. The circuit can also be made compatible with 3.3V logic levels by changing the upper 1kW resistor in the divider to 3.3kW. This shifts the thresholds to approximately 2.7V (upper), 1.7V (bias) and 0.7V (lower), aligning with standard 3.3V logic ranges. Circuit design by Silicon Chip, Idea by Raj K. Gorkhali, Hetadu, Nepal ($40). Logic level indicator This circuit displays an “H” on the 7-segment display when the input voltage is logic high, an “L” when it is logic low, and nothing if it is in between or left floating (high impedance). It uses an LM393 dual comparator, two diodes and a handful of passive components. A string of four resistors (1kW, 1.5kW, 1.5kW, and 1kW) between +5V and GND creates three reference voltages: 4V, 2.5V, and 1V. The 4V and 1V nodes are connected to the non-inverting and inverting inputs of comparators IC1a and IC1b, respectively, while the input signal is fed to their other inputs. If the input signal is above 4V, the output of IC1a goes low, sinking current through the b, c & g segments via 1kW series current-­limiting resistors. Since a red LED has a forward voltage of around 2V, each segment receives about (5V – 2V) ÷ 1kW = 3mA. Segments e and f also light up in this condition, as current flows into pin 1 of IC1a via diode D2. With segments b, c, e, f, & g illuminated, the display forms an “H”. The series resistors for segments e and f are chosen such that, despite the additional voltage drop across the diodes, they still receive close to 3mA for matched brightness. siliconchip.com.au Australia's electronics magazine July 2025  81 SERVICEMAN’S LOG Water woes and hydration hindrances Dave Thompson As a kid growing up in Christchurch in the 1960s, we were always told that our tap water was the best in the world. This had been scientifically proven by men in white lab coats many times over the years, so it must have been true. It certainly looked crystal clear and had no twigs or mud (or worse) floating in it, so I had no reason to believe this wasn’t the case. As it turns out, it was true. This was due to the vast aquifers under the Canterbury plains, near to the city. There was more than enough for everyone, which included our relatively big city and many satellite suburbs, along with all the nearby farmers’ requirements. Many smaller towns in the locality all had their own wells and supplies, and the world was rosy, and we all loved each other. Fast forward to 2010, and everything changed. We had a series of huge earthquakes here; many people were killed or injured in some of them. Three fault lines all went at once – or within cooee of each other. While the scientists at the university of Too Much Time on Their Hands assured us the quakes were all unrelated, I thought that just didn’t make sense. Why would three faults, two of which were unknown at the time, all go off at around the same time? It beggars belief. We have been expecting “the big one” here for as long as I can remember. New Zealand is positioned in the “ring of fire” that stretches right around the Pacific Ocean, with a series of volcanoes, above or below ground, causing almost all of our seismic problems. The Alpine Fault is where the Australian and New Zealand plates meet, close to our southern alps; it is likely why those mountains formed in the first place. Geologists have been telling us for years that this fault will go off again one day, and it will likely devastate the country. Excellent! An Earth-shattering kaboom In September 2010, when I was almost thrown out of bed by a huge ‘quake, I thought it had finally come. But no, that quake was from a previously unknown fault just out of town. It happened at 4:05am, and while it caused some property damage and a few injuries – some major – it was mainly just property. We all heaved a huge sigh of relief, and rebuilding and normal life resumed. The problem was that all our aquifers were very close to where the fault burst, and this damaged them, so the water quality suffered. Then, just a few months later, a much more devastating ‘quake hit us from a different fault. It killed a lot of people and injured many more, some very seriously. It trashed entire suburbs, which will never be rebuilt. About a third of the city was wiped out. Buildings collapsed and facades fell, crushing people in the street. This one had the highest lateral acceleration ever measured in a ‘quake, likely because it was so shallow, and even though the magnitude figure was lower than the 7.1 in September the previous year, at 6.4, it was more devastating. 82 Silicon Chip Australia's electronics magazine siliconchip.com.au This also affected the city’s water supply. Aquifers under the city and reservoirs were cracked or destroyed, and corrupted by mud & debris. Many of the supply pipes also broke. As a result, many people were without water; we all suddenly had to rely on bottled water. Even worse, waste systems were also destroyed, so we needed portable toilets. I think every portable toilet and bottle of water in the country was sent here. We had no power for a week, but we did have gas, which we used to boil water for neighbours who didn’t. It was the worst of times, but it often brought out the best in people. My usual long-story-short is that now our water was not as good as it once was. Boil notices for tap water were issued, and sales of water filters went through the roof, with the local big-box store selling out in days. Many resorted to using BBQs and whatever else they could fire up to get clean water. The supermarkets rationed milk, water & bread, and petrol stations rationed petrol and LPG, with kilometres-long queues forming. The city water guys worked around the clock to get pumping stations back online and repair the infrastructure that had been ruined. In many suburbs, they ran heavy polythene pipes along the footpaths to get water to affected people. The power companies did the same, laying overground cables to get power to suburbs that were dark. It was an interesting time to live. Well, well, well The upshot is that our water supply has never been the same. A few years ago, the council decided to chlorinate the water, to much wringing of hands and gnashing of teeth. They claimed it would only be for six months, until they could sort any contamination issues. Keep in mind this is at least 14 years after the quakes. It wasn’t long before the familiar chemical smell permeated our water. It may well have been clean, but it wasn’t the water I grew up with. The first thing we did was install an under-bench filter system so that, at least, our tap water didn’t reek of chlorine. A client of mine who worked for city water said that it was temporary only while they sorted out the aquifers. Our water is sourced from a 400m-deep well just a kilometre from us, and it seemed fine before they added the chlorine to it. I know I can’t analyse it, but it didn’t look or taste any different. It turns out they did it to all water supplies here ‘just in case’. As I said, they claimed it was meant to be for a few months. Now it’s a permanent thing, and the water is disgusting, but only because of the chlorine, which they promised we ‘wouldn’t even notice’. Hence the need for filters. I’m not that happy about drinking chemicals every day, and that’s aside from the ratepayers’ costs we have to stump up for it year on year. A faulty filter Anyway, rant over. We have several water filtering devices in our kitchen now because one just isn’t enough. Under-bench filter systems are expensive to keep going, so we have a couple of standalone filters. One is a ceramic, two-part, bench-standing thing with a stone and ceramic compound filter in the top half. We pour water in that part and, at the rate of one litre per siliconchip.com.au hour, it drips into the bottom tank, which has a tap. This means we can draw clean, filtered and non-chlorine tasting water from there. It works well, but it only deals with a few litres at a time. When we take a jug full from it, we fill that same jug with tap water and pour it in first, so we always have a good supply, albeit some time later, since it takes so long to passively filter through. We also have another benchtop water cooler/heater type thing. It uses a similar filter system in the top tank, and any water drawn off is filtered, as it comes from the bottom tank. The unit has a hot and a cold tap, so we can have chilled water and heated water (but not boiling). It’s a relatively cheap appliance, and as a cooler, it is OK. As a heater, it is passable, but you wouldn’t get a steaming hot coffee using that water. The cooling and heating are achieved by a Peltier element, a cheap and effective way of achieving heating and cooling, using the Thermoelectric Effect. They aren’t that energy-efficient, but devices like this are passable and much cheaper than the alternatives. A proper water cooler uses refrigerant in a heat exchanger system and deploys a decent heating element for hot water. But this one is not that advanced. We mostly just use it for its cool(ish) water. The important thing is that it is filtered; we can always put ice in it, or fill a jug and put it in the fridge. Items Covered This Month • Water woes • Repairing a Beyonwiz DP-P2 video recorder • Getting around a water pump • Fixing a Bose SoundDock Series 1 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 Australia's electronics magazine July 2025  83 So, it is a useful appliance regardless of the inability to get water really hot or cold. I hear it occasionally go into cooling mode, and we can usually trigger it by emptying the filtered water reservoir and letting unfiltered water drip through the filter system. As soon as the water in the tubes below the tanks gets a little warmer, a thermostat triggers the relevant element to heat or cool. Peltier problems With a single Peltier element, simply reversing the polarity of the power supply dictates whether the element heats or cools. They are used in all kinds of mini fridges and food warmers, but it gets a little trickier in a water dispenser with both hot and cold functions. They could use complicated switching in order to heat one side and cool the other, or they can just use two Peltier elements, one for hot and one for cold. The latter is what I found here. The problem arose when we noticed the water was not being chilled anymore. When I tried the warm water, that side was working. I emptied the bottom reservoir and filled it with room-temperature water, but while the cooling fan kicked in, after half an hour, the water was the same temperature. This required a closer look. I emptied all the water, or as much as I could, unplugged the cooler and removed the vented bottom of the unit. As usual, there were security screws used throughout. It is not really a problem when you have the bits, so there’s no real ‘security’. In other words, it’s all a waste of time and money. The bottom came away cleanly enough and exposed a printed circuit board (PCB), along with the heating and cooling modules. This, surprisingly to me, was a wholly integrated unit, which consisted of side-by-side piggy-backed small water tanks, with inlet and outlet tubes. A Peltier element was mounted on one face of the tanks, and a CPU-type heatsink and cooling fan was mounted on each end. I guess the fans draw air from the elements rather than blow air through the heatsinks. Either way, I’d never seen anything like this before. I mean, I’ve played with Peltier elements – I can buy them at Jaycar, for example, and found them interesting to experiment with. But I have not seen them used like this. The difficulty I was facing was that the elements are glued to the water tanks with something that, by the looks of it, is military-grade adhesive. Some gentle persuasion proved it wasn’t going to let go easily. I guess I could have literally scraped the element off, but that was going to be too messy. And what could I use to stick it back on with? Some kind of heat-resistant epoxy? 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. 84 Silicon Chip This was starting to look like it wasn’t worth investing more time in. I deduced this could be a standard type of part for these big box cooler/heaters and so hit the Chinese sites for a similar part. True to form, there were literally hundreds of all different types and styles for sale there. I filtered (har!) out the ones that might work, just based on looks alone, and found a few that handily had measurements listed with them – most don’t. As there were no part numbers anywhere on this one, that made it a little more difficult. The old switcheroo I jumped to the conclusion that the voltage and current supplied to the elements would be pretty much the same as all the others, so it was simply a matter of finding an assembly that was around the same size and fitted inside the space. It would also be a bonus if the mounting holes lined up, but I could work around that. With no specific mounting measurements listed, it was a gamble, but since the overall sizes and shapes were reasonably consistent between the ones I was looking at, I felt confident one would fit OK. I doubted whether this appliance manufacturer – a cheaper brand – would use something other than what was inexpensive and readily available. I took the plunge and ordered a replacement that looked pretty much identical to mine and waited the usual months for it to make its way here. It eventually did arrive. At least the filter side of the thing still worked, even if it didn’t cool the water. The new assembly was very close to the old one. The biggest hassle was taking off the single-use clips from the soft rubberised water hoses. These must have been put on with a machine of some type, so I had to carefully cut them off without damaging the hoses beneath. I didn’t want to have to replace them, too. The module had been hard soldered in – I guess they couldn’t stretch the manufacturing budget to some PCB connectors. It was simply a matter of mounting the new one and soldering the wires to it. Two of the holes lined Australia's electronics magazine siliconchip.com.au up, but the others didn’t. Although I could only use two of the four, the module was solidly mounted. The acid test was plugging it in, filling it with water and firing it up. The fans came on as the switch was toggled, and all the usual lights came up to show it was heating and cooling. I left it for 20 minutes, checking occasionally for the usual burning smells and any indication that things were not happy. It seemed OK, and the water was cooling. After a while, the fans stopped, so I assumed things were up (or down!) to temperature. I replaced the bottom cover and put the unit back into its usual position and it has been running now and cooling the water for months, so I consider it repaired. At the end of the day, though, it would have likely been cheaper and less hassle to just go and replace the whole unit. But, that means the rest of this one would end up in a landfill somewhere, so it is a mixed blessing that we can at least buy a part that will work in it. Again, it wasn’t essential that this thing cooled the water; we really just use it for filtering, but it irks me that something would fail after a relatively short time, no matter how inexpensive it may have been to buy. The Serviceman’s Curse required I at least tried to repair it and get it back in working order! Beyonwiz DP-P2 PSU repair I found a listing on eBay for a brand new Beyonwiz DP-P2 personal video recorder (PVR) for $20 plus $20 postage. I thought that was odd, as this model is now more than 10 years old. Also, a working DP-P2 is worth more than $100; even one in non-working condition is worth more than $20. I wondered if it was a scam, so I sent my mate the link with the subject “Too good to be true”. Imagine my surprise when he emailed me back and said he’d bought it! He said because it was so cheap, he took the chance on it and even if it was a scam, he could get his money back with PayPal anyway. A few days later, he emailed me to say that the unit arrived, but it was not brand new and it had no remote or anything else with it, just the PVR. When he connected it and turned it on, it came up with ERROR 0000. I told him to take the lid off and look at the power supply board to see if there were any bad capacitors. He emailed me back that they all looked fine. A high percentage of failures in these units are caused by bad capacitors; I’ve fixed many. He suggested sending the unit up for me to have a look at, but I said the postage cost is too high; I said to just take the PSU out, send that and I will have a look at it. I would see if I could fix it, but there were no guarantees. A few days later, the power supply board arrived. I could see that six large electrolytic capacitors had been replaced, three of which were a larger physical size than the originals. The soldering was good and there were no dry joints on the board, so it would be a tricky one to fix. When I had some time, I got out one of my working DP-P2 PVRs and fitted my mate’s PSU into it. Sure enough, it came up with ERROR 0000, so the PSU was definitely faulty. I got the board back out and started checking it over. I first tested all the diodes with my in-circuit transistor and diode tester, and they all tested good. On one of my other PSU boards, I’d found that D12 and D13 (UF5402 200V siliconchip.com.au Australia's electronics magazine July 2025  85 ultrafast diodes) were faulty, but on this PSU board, they were still good. The next things to check were all the electrolytic capacitors. I grabbed my ESR meter and started testing them. I’d recently repaired a DP-S1 PSU that had six faulty small capacitors. Checking over this DP-P2 PSU board, I found that most of the capacitors were good, but C7 and C11 (both 50V 33µF types) read very high at around 5W when they should be less than 1W. I checked my salvaged capacitors, but I did not have any of this value. Then I remembered that I may have purchased this value some time ago and, on checking my new parts, I found them. I replaced the two capacitors and put the PSU board back in the PVR and switched it on. This time, it came up showing Channel 7 Melbourne on the front display. I connected the HDMI cable to my HDMI switch and turned on the TV. I checked the hard drive, and there were several recordings, so I skimmed through a couple of garden shows and everything worked fine. Then I connected up the aerial and tuned in the local channels. So, my mate’s PSU was now working and I could send it back to him. While I had this PVR out, I had a look at the three DP-P2 PSUs that I had not yet fixed. I’d noted on them which voltages were missing and I’d taken the 12V regulator out of one of them in the course of troubleshooting it. This just happened to be the PSU that I’d replaced D12 and D13 on. I looked at the other two non-working boards as to which voltages were missing and I determined that the 12V regulator on one of the boards should be good, so I removed it and fitted it to the PSU that I’d replaced D12 and D13 on. I fitted the PSU to the PVR and turned it on. It now worked, indicating that my previous troubleshooting (which I hadn’t got back to) had found the last faulty component on this PSU. Looking at the other two units, I ordered some parts on eBay that I suspected of being faulty on these boards. I will get back to them when the parts arrive. Time came to post the PSU back. He received it a few days later and fitted it to the Beyonwiz DP-P2 PVR, and he reported that it is now working correctly. This was another win for both of us. Bruce Pierson, Dundathu, Qld. Water pump workaround About a year ago, we had a lightning strike in our backyard at about 1am. The EMP tripped the main circuit breaker. We discovered the extent of damage the next day, which included a damaged workshop air conditioner, the NBN box, oven, printer and the water tank pump. Lightning had actually struck a tap that was connected to the pump. It was covered by insurance, but we never got around to fixing the water pump. The tank is on the high side of the block, so gravity feed is adequate for the low side. It has been on the back-burner for a year, but I finally got around to looking at it. As it turns out, the motor survived, but the control electronics were completely blown apart. As with most devices these days, getting a spare was impossible; you can only buy the whole assembly. The photo of the control board shows how much damage several thousand volts will do. Some years ago, I bought a couple of remote control modules. These run from a 12V plugpack and the relay switches up to 10A, more than enough for the motor. I forgot why I bought them and they were never used. I put the module inside a plastic box attached to the wall next to the water tank; it is under cover so there was no need for waterproofing. The remote range is not great, about 20m, but that’s adequate. So now I can switch the pump on manually if it’s needed. I then added a mains timer for the plugpack to limit the time the pump is on. Instead of spending about $300 on a new pump assembly, the repair cost was effectively zero, as I already had all the bits. Charles Kosina, Mooroolbark, Vic. Bose SoundDock rejuvenation My daughter was cleaning out her garage and found an old Bose SoundDock Series 1. She suggested that it would be nice to get going again as the sound from it was very good. So I ended up with another job. The SoundDock looked in good condition, but there was no power supply or remote control. The SoundDock was designed to have an original iPod with a 30-pin connector plugged into it as the music source, but that was long gone. I found a Bluetooth receiver on the internet that was designed to replace the iPod, so I ordered it. I remembered repairing the power supply some years ago; it was a ±18V unit. I figured I could find two suitable power packs in my box of spares and get it going. I found the correct pin information on the net and connected the power packs. I plugged the Bluetooth module in and applied power. The LED on the module The power supply from the Beyonwiz DP-P2 personal video recorder. 86 Silicon Chip Australia's electronics magazine siliconchip.com.au The photo at upper left shows the water pump assembly, while the photo above is of the very obviously damaged control board. The adjacent photo shows one of the remote control modules that I had lying around. The relay in these modules are rated up to 10A, making them perfect for this motor. did not even light up, so it was not getting power. I decided to test the Bluetooth module separately, so I found an old iPod charging cable and connected the Bluetooth module to it. The LED lit up, and I was able to connect my phone to it. So it looked like there was no power getting to it when it was plugged into the SoundDock. I removed the covers from the SoundDock and found some components that had obviously overheated. With no circuit diagrams, it would be a nightmare to repair. I had a 30W + 30W stereo amplifier board left over from another project, and it looked like I could fit it in place of the original amplifier. I connected the new amplifier to the speakers and wired the output of the Bluetooth module to it. Once connected to my phone, the audio output was quite acceptable, so it was just a matter of fitting the new amplifier in the existing case. I made a sheet metal plate to fit and screwed the new stereo amplifier in place. I wanted to keep the original input board with the 30-pin connector, so I found some information about it on the internet and wired the audio out to the new amplifier. I decided to use a 12V 2A power pack, so I had to add a 7805 regulator to drop the 12V to 5V for the Bluetooth module. I put it all together and discovered that the Bluetooth module produced an audio announcement saying it was powered up and connected, but the audio level was way too high, so I attenuated both channels using a resistor divider network to give only 25% of the original signal level. The actual music level could be controlled by the audio player on the phone. Finally, I designed and 3D-printed a plate to fit around the Bluetooth module socket and fitted a power connector to the back so the plugpack could be easily disconnected. Now we had a great sounding music system for my daughter’s study. SC John Western, Hillarys, WA. The internals of the Bose SoundDock is shown above with a close-up shown at right. siliconchip.com.au Australia's electronics magazine July 2025  87 Vintage Radio The Eddystone EC10 Mk2 All Transistor Shortwave Radio This all band set was UK-based Eddystone’s first release of an alltransistor receiver in 1973. It’s a good performer if noisy at full gain. It has a switchable AGC, a BFO, a bandpass filter and a fine-tuning knob. Its biggest weakness is non-linear tuning. By Ian Batty Y ou may recall that Sony began with a rice cooker and National/ Matsushita with a bicycle lamp. However, Stratton and Company (who would become Eddystone) began in 1860 making much more modest goods: steel pins and hairpins. Stratton expanded into gentlemen’s jewellery, ladies’ compacts, a variety of small metal products – including knitting needles, thimbles, hat pins and crochet hooks – and a whole range of do-it-yourself kits for making model ships and aeroplanes, pearl flowers, seagrass stools and timber bead mats. Changes in fashion saw the demand for hairpins slump in the early 1920s. Needing new products to survive, manager George Laughton’s son (a radio enthusiast) asked a simple question: “Why not make wireless components?” 88 Silicon Chip It was 1923 and the die was cast. Needing a trade name, what could be better to project an aura of reliability and prominence than that of the world’s first open ocean lighthouse, the Eddystone Light? First operational in 1699, it had given over 200 years of faithful, life-saving service by 1923. Listeners in 1927 must have been fascinated by Eddystone’s first shortwave receiver. They could see the parts moving and the valves light up through a glass panel. Eddystone expanded, becoming a world-famous leader in communications equipment. You’ll find their products, especially receivers, in collections around the world. I reckon that any collection lacking an Eddystone is ‘yet to be completed’. The year 1973 was Eddystone’s Australia's electronics magazine 50th anniversary, and valve-equipped receivers were being phased out. It was not due to a lack of demand but because obtaining many of the components was no longer possible. The EC10, Eddystone’s first all-­ transistor receiver, looks the goods. It has a large, easy-to-read dial, the famous flywheel-equipped tuning mechanism and a compact size. But don’t be fooled by that size – it competes well with its valve-equipped predecessors, but with the convenience of hundreds of hours of operation using internal batteries. Description The EC10 is a general-coverage, single-conversion superhet that operates from batteries or a plug-in mains supply that replaces the battery siliconchip.com.au The rear of the EC10 has the antenna socket on the left (three to allow for a wire antenna or telescopic rod) and both high and low impedance audio outputs on the right. compartment. It uses ten transistors: five alloy-diffused high-frequency types in the tuner/IF section and five alloyed-junction types in the audio section, all PNP. Its coverage is 550kHz to 30MHz and intermediate frequency (IF) is 465kHz: • Band 1 is 18MHz to 30MHz. • Band 2 is 8.5MHz to 18MHz. • Band 3 is 3.5MHz to 8.5MHz • Band 4 is 1.5MHz to 3.5MHz. • Band 5 is 550kHz to 1.5MHz. The Mark I uses three diodes, while the Mark II adds three, for a total of six. It features a signal strength meter, which is helpful when tuning. The Fine Tuning control, which operates a variable-capacitance diode (varicap) in the local oscillator (LO) section, is essential when tuning signals in the highest band. All models feature an RF gain control and a beat frequency oscillator (BFO) for use with CW or SSB signals. There is also a switchable audio filter centred on 1kHz to improve the clarity of CW signals. The audio output is quoted as 800mW into the internal speaker. An external speaker can be used, and there is a high-impedance audio output for connection to an external audio amplifier. The set can operate with various antennas: unbalanced, balanced or a short telescopic rod. Its input impedance is 75W on Bands 1 through 4 and 400W on Band 5. Sensitivity is quoted siliconchip.com.au as better than 5μV on Bands 2-5 and better than 15μV on Band 1. The EC10’s only limitation is the failure to use a straight-line frequency tuning capacitor, so the frequency divisions are compressed towards the top end of each band. Construction The set is well-built, with the traditional ‘flywheel’ on the tuning knob. This allows the highly-geared tuning system to spin rapidly from end to end across the selected band. The chassis and front panel withdraw easily from the case and the internal construction is sound. Most electronic components are mounted on two printed circuit boards: one for the tuner (RF) and the other for IF/ audio. The IF/audio board is mounted copper-side on top, so measurements are easily made. Unfortunately, two of the IF transformers use double slugs, and the service notes describe the relocation of the IF/audio board to allow access to the inside slugs for a complete alignment and other work. Circuit description I could not find a completely legible circuit diagram online, so I have redrawn Eddystone’s original for clarity and ease of description, including the power supply circuit from my EC10 MKII. I have moved some Australia's electronics magazine components from their original locations but retained Eddystone’s numbering – see Fig.1 overleaf. I have added DC circuit voltages to the diagram, with signal voltages in two tables at the right of the drawing. Note that the band change switch sections (S1a to S1j) are all shown with Band 2 selected and viewed from the rear. Band 1 is, thus, fully anti-­clockwise, while Band 5 is fully clockwise. Eddystone showed each section from its contact side. I found this confusing, as some sections have their contact sets on towards the front of the set and others to the rear. This demanded that one visualise some sections rotating clockwise and others anti-clockwise. The EC10 uses a grounded-base RF amplifier. We’re probably familiar with common-base’s low input impedance, typically in the low tens of ohms, and its current gain of just under unity. For these reasons, voltage amplifier designs adopted the common-emitter configuration, with its much higher input impedance and current gain. However, the common-base configuration has a very high output impedance, in the hundreds of kilohms at audio frequencies. As noted in the article on General Electric’s P-807 5-­ t ransistor set (November 2015 issue; siliconchip.au/Article/9405), common-­base’s power gain – due to its July 2025  89 high output impedance – can approach that of common-emitter. Common-base’s low feedback capacitance also makes it more suited to operation at higher frequencies than common emitter, even in wideband amplifiers such as video output stages in CRT-based televisions. Common-­ base’s low input impedance is easily matched in RF circuits by tapping the 90 Silicon Chip driving tuned circuit or matching coil. Common-base’s high output impedance minimises loading of the EC10’s selected RF transformer (L7~L11) primary, thus realising the maximum Q for each primary tuned circuit. Local oscillator TR3 also operates in grounded-base configuration. While the OC171 can, in theory, work easily to the top end of the HF band in Australia's electronics magazine common-­emitter, using common-base ensures more constant output as the set is tuned to 30MHz. Tuner section All trimmers are 6-25pF types, while all transistors in the tuner and IF sections are alloy-diffused OC171s in four-lead metal TO7 cases. Antenna selector S1a selects siliconchip.com.au Fig.1: my redrawn EC10 Mk2 circuit diagram. transformers L2 (Band 1) to L6 (Band 5). Bandstop filter L1/C2 is added in series on Band 5 to improve IF rejection. The input can be unbalanced (A1 to ground, input to A2), balanced (to A1 and A2), or a factory-supplied telescopic rod to A3. The RF stage is protected against damaging overload by D4/D5, back-toback silicon diodes that limit the signal siliconchip.com.au at the selected antenna coil primary to about 600mV peak-to-peak. The antenna transformer secondaries are tuned by the tuning gang’s antenna section, C15. Bands 5 and 4 use the full capacitance sweep of C15, while Bands 3, 2, and 1 are restricted by band spread capacitors (C8/C9/ C10). Band 1’s range (around 1:1.7) is further limited by 390pF padder C11. Australia's electronics magazine All transformers in the front end are slug-tuned for low-end alignment and trimmer-tuned for high-end alignment. S1b connects the selected antenna transformer secondary to the tuning gang’s antenna section, C15. A selector ring on S1b shorts the unused antenna transformers’ secondaries, eliminating the possibility of absorption and dead spots in tuning. July 2025  91 Shock hazards I have found English-manufactured equipment to generally have dangerous mains wiring. The EC10 has a plug-in power supply, with four-pole plug PL1 connecting the supply to the main chassis. Two wires carry the 9V DC supply, and the other two carry mains to the on/off switch in the RF gain control. The wiring is lightweight gauge, and its connections to the plug are not insulated. I can vouch for this, having found out by almost throwing the set off the bench in reaction to a nasty mains shock! Similarly, the connections to the back of the switch in the RF Gain control are not insulated. Two yellow paper dots should remind the user how to connect the plug if they have not fallen off. Although the plug is mechanically polarised, it may be possible to insert it backwards, reversing the -9V DC polarity and potentially destroying the set. Additionally, the power supply’s mains lead simply passed through a grommet with no cord anchor/clamp. I rectified the first hazard by disconnecting the leads to PL1, sliding heatshrink tubing over each lead, then reconnecting and shrinking the tubing to prevent any possibility of contact with the live terminals. I also fitted a cord anchor to securely retain the power supply’s mains lead. I strongly recommend that you examine any equipment – of any origin, but especially English – for safety and proper insulation of mains connections. Left: two of the tabs on PL1 carry mains and are not insulated from the factory. Below: the rest of the power supply section. The selected transformer secondary connects, via S1c, to the emitter of RF amplifier transistor TR1. This has AGC applied to its base, which is bypassed to RF ground. TR1’s collector connects to the primary of the selected RF transformer (L7~L11) via S1d. As with S1c, this includes a shorting ring. L7/L8 are also band spread via C20/C26. The selected transformer connects to the RF section of the tuning gang (C27) via S1e. Like Band 1 antenna transformer L2, Band 1’s RF transformer, L7, has a 390pF padding capacitor, C19. The selected RF transformer’s secondary is connected to the base of converter transistor TR2 via S1f. The local oscillator signal is supplied to TR2’s emitter from the selected LO transformer (L12~L16) via S1h. Capacitor C19 reduces the LO signal’s injection level on Band 1. The LO must track at 465kHz above the incoming signal, so it uses 92 Silicon Chip a combination of the usual padding and band spreading. Bands 5, 4 and 3 use the usual padding capacitors in series with the gang. Band 5’s padder capacitor C38 (500pF) seems about right for the broadcast band, but capacitor C37 for Band 4 is a non-standard value of 1.4nF. Band 3 uses another non-­ standard value of 7nf (C46). The increasing values of these padder capacitors means that they force progressively less padding effect as the LO’s frequency span rises from Band 5 (most effect) to Band 3 (least). For Band 2 (8.5~18MHz), a 465kHz offset between the LO and signal frequencies is negligible, so C45 (47nF) is not for padding. It’s simply there to block the LO’s DC collector voltage, which would otherwise be shorted to ground via the unselected LO primary/ tuned coils in the L12 to L16 coil set. Band 1 is spread by 400pF capacitor C44 to hold the LO to a restricted span Australia's electronics magazine (around 1:1.7), so it tracks with Band 1’s antenna and RF transformers. The LO frequency span is restricted by C44 (400pF), but without the IF offset we’re accustomed to in broadcast superhets. The MKII’s fine tuning is provided via varicap diode D6. This is most effective on the higher bands. The tuner section is fed from a stabilised -4.5V supply, derived from the main supply via zener diode D3 on the IF/ AF board. This reduces tuning drift due to mains variations or battery ageing. Drift figures are quoted at better than one part in 104 (<0.01%) per °C. Converter transistor TR2 feeds the IF signal via a shielded cable to the primary of first IF transformer IFT1 on the IF-AF board. IF section Both IF amplifier transistors (TR4/ TR5) are OC171s. These alloy-diffused types exhibit low feedback capacitances of around 2pF, so they operate without neutralisation. TR4 has AGC applied, while TR5 works with fixed bias. TR4’s supply is decoupled by 1.5kW resistor R24. The voltage drop across this resistor reverse-biases AGC extension diode D1. Its anode, connected to a tap on first IF transformer IFT1, is held close to the supply voltage via the converter’s 100W decoupling resistor R18. As the AGC begins to control TR4, its collector current falls, reducing the voltage drop across R24. Strong signals will bring D1 into conduction and dampen the signal at IFT1’s primary. This means the EC10 has three gain-controlled elements: the converter, the first IF amplifier and the extension diode, giving a near-­ constant output over a wide range of signal levels. IF transformers IFT1 and IFT2 both have tuned, tapped primaries and secondaries. Final transformer IFT3 uses a tuned, tapped primary, but an untuned secondary to feed the low impedance of demodulator diode D2. The demodulator feeds audio to the low-level audio output and, via the volume control, to the audio section. The DC voltage across the volume control also drives the 100µA Carrier Level meter via multiplier resistor R48a. The demodulator’s output supplies the AGC line via R28, with the audio signal filtered out by C63. AGC is useful when receiving amplitude-­ modulated signals but is siliconchip.com.au not effective when receiving CW/ MCW (‘Morse’) or single-sideband (SSB) signals. So the AGC can be deactivated by S2. This switch cuts off the AGC voltage and biases the AGC line to a fixed value via R22, while also reducing the sensitivity of the Carrier Level meter via R49a. The AGC line is also affected by RF Gain control RV1. This is in series with the bias divider for TR4 (R20/R21), allowing the lower part of the divider to increase in resistance. This means that the ‘top’ end of R21, which connects directly to the AGC line, will become more negative as the gain control takes effect. The maximum gain reduction is about 30dB. RV1’s effect is augmented by the action of AGC extension diode D1. With no carrier, SSB signals cannot be resolved unless one is reinserted at demodulation. TR6, the beat frequency oscillator (BFO), generates a 465kHz signal that is fed back, via 1pF capacitor C67, to the collector of first IF transistor TR4. The BFO frequency is variable, via BFO Tune capacitor C70, to allow the exact adjustment needed to produce speech from an SSB transmission, rather than ‘duck talk’. Adjusting the BFO to produce a 1kHz tone is helpful when receiving weak CW signals and takes advantage of the 1kHz audio filter’s narrow passband when activated. The set can be muted using the Standby switch, which removes bias from the RF amp and the first IF amp by shorting the AGC line to ground. It’s a two-pole switch, with its second section available for custom wiring to control external equipment. allowing headphone-only operation. The output stage works with fixed bias, lacking the temperature compensation that was common in domestic receivers of the day. Power supply Power is supplied either from a plug-in battery pack containing six D cells, which were available virtually Audio section everywhere at the time, via 12V or In regular operation, the first audio 24V adaptors, or (for my set) a plug-in stage transistor TR7 (an OC81) acts as 110/240V mains supply. a simple preamplifier with load resisThe set connects to the power suptor R40. When the Audio Filter is acti- ply via a four-core cable carrying the vated, audio bandpass filter L18/C76 supply voltage and connections to the is put in series with R40. The filter, Operations switch S6, part of the RF tuned to 1kHz, gives a very narrow gain control, which selects between audio passband, greatly increasing a mains or battery power. 1kHz tone above the background noise. Be aware that the plug on the set side As noted earlier, setting the BFO is not insulated, leaving two exposed for a 1kHz tone allows the resolution metal connections at mains potential. of weak CW signals in the presence See the panel on shock hazards! of atmospheric noise or other interThe mains power supply uses a ference. transformer, selenium bridge rectifier TR7’s output goes to audio driver and pi filtering. The output voltage is transistor TR8. This feeds phase-­ held to -9V by shunt rectifier diode splitter transformer T1, which in turn D101. I found that this failed to regufeeds the two output transistors, TR9 late with low mains voltages, around and TR10, both OC83s. They form the 220V, as shown by the dial lights flickpush-pull Class-B output stage, deliv- ering on strong audio output. ering audio to the speaker via output The internal dial lights are switched transformer T2. by the momentary Dial Lights pushbutThe EC10 has a Phones socket that ton S5, allowing power conservation disconnects the internal speaker, during battery operation. The top view of the Eddystone EC10 radio with its cover removed. The resistor and capacitor added on this side of the board wire likely added at the factory as running changes. History and repairs I bought my EC10 at auction in Hawthorn back in the 1990s and it sat on the shelf for some years. In the early 2000s, I moved to Harcourt, near Castlemaine and finally popped it onto the test bench. On examination, it was pretty well dead in the RF section, although there was noise from the speaker. Examination showed that the antenna coil switch had suffered a broken wafer. I desoldered all the connections, applied superglue to each side, replaced it and rewired it. I was able to get signals, but the sensitivity was still very poor. I aligned and calibrated the RF stages, but the gain was still low. Loosening jammed slugs The IF showed a ‘double hump’, indicating severe misalignment. On correctly aligning the IF, the gain came up to the specified sensitivity of better than 5μV on Bands 5 to 2 and better than 15μV on Band 1. There are two sizes of coil slugs in the EC10: those in the RF section with hexagonal centre holes, and those in the IF transformers with continuous/ “through-hole” screwdriver slots. Be aware that these need a special long flat-bladed tool. Both types were either loose or jammed. I carefully freed all the jammed ones, but I wondered what to do so I could adjust them to position and not have them move. I long ago gave up on wax, liquid paper and nail polish, as I hope we all 1. Does the slug need alignment? You can save effort and time by using a ‘magic wand’, a piece of heatshrink tubing maybe 10cm long with a slim ferrite slug in one end and a brass slug in the other to find out before going any further. Slide the ferrite end into the coil can. If the signal improves, the coil needs more inductance for correct alignment. If that makes things worse, try sliding the brass end into the coil can. If the signal improves, the coil needs less inductance to align correctly. If both slugs make things worse, the coil is correctly aligned. 2. Do not use spray lubricants. Most of these include organic oils that can actually jam a slug in its thread. 3. If the slug has a screwdriver slot and the slot is damaged, trying to screw the slug out of the coil towards you is the worst of all worlds. You are trying to drive the slug back against the force of the screwdriver, and there may be slug debris in the threads! If the coil has two slugs, try screwing the opposite slug right out of the coil. Now that you have a (hopefully) untouched slot available on the inside of the jammed slug, use that good slot to carefully screw the jammed slug into the centre and out the end you are driving from. You can improve your chances by cleaning the coil former’s available screw threads as thoroughly as you can before trying this. Some threads in coil formers conform to Whitworth/SAE standards. 4. If you cannot get to the good end of the slug, try the ‘fridge move’. Put the set in the fridge and leave it for a few hours. Differential contraction between the slug and the former may loosen it once it all warms up. I have also successfully used a variable-temperature hot air gun to cause differential expansion. Set it to around 70ºC. Warm the coil, occasionally withdrawing the gun to feel how hot the coil or its can is. If you can leave a finger on the can for a second or two, that’s good. Anything hotter risks melting or distorting plastic parts. This method will likely soften any wax, grease or vanish, easing the job. I used this method to recover an Emerson hybrid’s IF trannie that I had unwisely used WD-40 on. 5. If the slug has a hexagonal hole (TV IF strips, Eddystone EC10 type) or a slim slot (‘Neosid’ type) going all the way through, it may be cracked into two or more parts along its length. This is the worst of all possibilities, and you may need to replace the entire coil. Destroying the slug and shaking the bits out may be possible, but you can do a lot of damage to the coil l former. In the worst case, where you cannot get an exact replacement for the windings, you may be able to find a similar, good coil l former and can, warm the coils, draw them off from the jammed former, and replace them onto the good spare. 6. If you get the slug out, thoroughly clean out the former’s threads with a tiny bottle brush or compressed air (gently!). Do not use solvents, especially acetone, as they will dissolve many plastics. Test with a good slug or a suitable thread tap. Once the thread is clear, you’ll find that slugs/taps are often a little loose in a clean former. 7. When you replace the slug(s), use thin ‘plumber’s tape’ to stop the slugs from moving – it will hold them in place but will not gum up or jam. have. My ‘magic ingredient’ is Teflon plumber’s tape, which I also use in my plumbing and irrigation work. With the RF coils’ large threads, I found I needed to fold a length of tape over itself a few times to make the slugs fit snugly. I used a single wrap of tape for the finer-thread IF coils. I used the set for a while, and two subsequent faults appeared. First, the BFO (needed for CW & SSB reception) stopped working. The oscillator used an OC171. This transistor had presumably succumbed to the dreaded ‘whiskers’, where minute dendrites grow between the transistor element and the grounded metal case within the device and eventually stop it from working. Since the BFO operated at around 465kHz, the OC171 was considerably under-rated. I had no spares, but an OC400 (with a lower cutoff frequency) worked just fine. I did need to adjust the circuit capacitance to bring the BFO back to the correct frequency, but it calibrated up correctly. The second fault appeared with massive amounts of breakthrough of the local FM band stations into the broadcast band. I lived less than 10km from Mount Alexander, which hosts most of the FM radio and TV transmitters for the Central Highlands and Goldfields. On examination, a wire connecting to the broadcast (Band 5) antenna coil had come adrift, open-circuiting the tuning for this stage. Given the amount of signal flooding in on the FM band, it appears that the front end was rectifying the FM signals and allowing them to cross-modulate into the IF. The audio filter worked, but was centred on about 800Hz and would not adjust sufficiently. I replaced the 100nF tuning capacitor C76 with a 56nF type, and got the filter to its 1kHz design frequency. A curious thing The alignment guide states that injecting a signal at the input to the IF strip needs only about 4μV to give 50mW audio output if the alignment is correct. That implies the entire RF section has near-unity gain. This mirrors the advice for an Eddystone VHF/ UHF set, the 770U, which I’d previously worked on. It appears that Eddystone regards the RF section as a ‘preselector’, siliconchip.com.au An underside view of the set. The EC10 uses 10 transistors and 18 inductors which you can see tightly packed into the central section of the board. Note the speaker, which has a relatively rare rated impedance of 3W. siliconchip.com.au Australia's electronics magazine July 2025  95 relying on the IF/AF sections to provide the majority of the gain. Performance For a first outing, it’s pretty good. I was surprised that Eddystone did not use a gang with straight-line frequency plates. The result is that frequency calibration is compressed towards the top end of each band, as happened with pocket transistor radios of the day. Roger Lapthorne (G3XBM) noted that the entire 10m band (28MHz to 29.7MHz) is only about 10mm wide on the scale. Pye Australia’s contemporary PHA 520, developed for the Colombo Plan, did use a straight-line frequency cut, making tuning much easier, especially towards the top end of its 14.5~30MHz band. The Fine Tuning control’s authority varies, giving a range of some ±30kHz at 29MHz, but only around ±2.5kHz at 1400kHz. The EC10 specification requires 50mW output, with a signal-plus-noise to noise (S+N:N) ratio of 15dB from a signal under 6µV on all bands. Table 1 shows my actual measurements. Superhet receivers are prone to image response interference, where a signal that is twice the IF frequency above (or below) the desired signal will also be received. This is rarely a problem with broadcast radios, where the antenna tuned circuit can attenuate the image by 60dB or more. A tuned RF amplifier – by virtue of its tuned interstage circuit – will improve this figure. At higher frequencies, image rejection is compromised as the bandwidth of front-end tuned circuits widens. The EC10 displayed such behaviour – see Table 2. At 600kHz, the -3dB bandwidth is ±2.2kHz, while at -60dB, it’s ±12.7kHz. The audio bandwidth from the volume control to the speaker is 80Hz to 11kHz (-3dB). While that is impressive, the response from the antenna to the speaker is only 60~1750Hz due to the IF strip’s narrow bandwidth. The audio filter, useful with CW/ MCW reception, has a -3dB bandwidth of around ±50Hz at 1kHz. Audio output was around 400mW at clipping, with 10% total harmonic distortion (THD). At 50mW, THD was a low 1.8%, rising to 3% at 10mW, evidence of crossover distortion at low levels. Figs.2 & 3: the signal strength meter indication vs input signal level with AGC on (left) and off (right). Frequency Input signal level Using three control stages, the AGC gave a 12dB rise for a signal range of 90dB. Wow. In use For the first-generation unit that it is, the EC10 works well. It is noisy at full gain, with S+N:N ratios as low as 3dB. This implies that the equivalent front-end noise is equal to the actual signal level. As noted with the Sony TR-712, it’s possible to get a lot of gain with a good amplifier design. Still, such an approach is compromised by device noise, for which germanium transistors are especially bad. Additionally, the background noise across the broadcast/HF bands, even in areas well away from the ‘fog’ created by switchmode power supplies, is commonly “some tens” of microvolts per metre. Such a noise floor means that the EC10’s useful performance will, in practice, rival that of valveequipped competitors of the day. At my location, on Victoria’s Mornington Peninsula, the broadcast band’s residual noise level well exceeds 50μV/m! This set, a Mark II, has a signal strength meter, which measures the demodulator’s DC output. With the AGC on, it effectively measures the AGC voltage, giving an essentially logarithmic response. Due to the AGC action, it provides a compressed indication on signals of any strength, showing a very broad tuning peak. With the AGC off, the meter’s indication loosely tracks the input signal’s strength, reaching the ‘8’ mark at about 35μV. Above that, the set overloads and the signal becomes distorted, so either the RF gain must be reduced or the AGC switched in. For SSB reception, you would commonly have the AGC off and use the RF gain control to adjust the set’s gain. Fig.2 shows that the signal strength meter response is logarithmic with AGC on, while Fig.3 demonstrates it’s linear, with AGC off, up to the point SC of overload. S+N:N 15dB input signal level 600kHz 2.0μV 6dB 6μV 1400kHz 0.3μV ♦ 3dB 2.5μV 1.6MHz 1.2μV 3dB 4.5μV 3.5MHz 1.5μV ♦ 3dB 5μV 3.8MHz 1.0μV 3dB 4μV Frequency Image rejection 8.0MHz 1.0μV 3dB 5μV 600kHz 64dB 9.0MHz 1.2μV 5dB 3.5μV 1.6MHz 53dB 17.5MHz 1.0μV 7dB 3μV 3.8MHz 58dB 18.5MHz 2.0μV 7dB 4μV 9.0MHz 36dB 29MHz 1.0μV 3dB 5μV 18.5MHz 16dB Table 1 – sensitivity vs frequency ♦ gain was reduced to get a useful reading Table 2 – freq vs image rejection SOnline ilicon Chip Shop Kits, parts and much more www.siliconchip.com.au/Shop/ Rotating Lights April 2025 Dual Mini LED Dice August 2024 USB Power Adaptors May 2025 SMD LED Complete Kit SC7462: $20 TH LED Complete Kit SC7463: $20 SMD LED Complete Kit SC6961: $17.50 TH LED Complete Kit SC6849: $17.50 siliconchip.au/Article/16418 siliconchip.au/Article/18112 This kit includes everything needed to build the Rotating Light for Models, except for a power supply and wire. 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. siliconchip.au/Article/17930 Compact HiFi Headphone Amplifier Complete Kit SC6885: $70 Complete Kit with choice of USB socket SC7433: $10 Capacitor Discharger December 2024 December 2024 & January 2025 siliconchip.au/Series/432 This kit includes everything required to build the Compact HiFi Headphone Amplifier. The case is included, but you will need your own power supply. Programmable Frequency Divider Complete Kit SC6959: $60 Feb25: siliconchip.au/Article/17733 Includes all onboard components, except for a power supply and the optional programming header. Short-Form Kit SC7404: $30 siliconchip.au/Article/17310 Includes the PCB, resistors, semis, mounting hardware and banana sockets. Case, heatsink, thermal switch and wiring are not supplied. → 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. 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. 07/25 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 ATmega328P ATtiny45-20PU PIC10LF322-I/OT PIC12F617-I/P 110dB RF Attenuator (Jul22), Basic RF Signal Generator (Jun23) ATSAML10E16A-AUT High-Current Battery Balancer (Mar21) 2m VHF CW/FM Test Generator (Oct23) PIC16F1847-I/P Digital Capacitance Meter (Jan25) Range Extender IR-to-UHF (Jan22) PIC16F18877-I/PT Dual-Channel Breadboard PSU Display Adaptor (Dec22) Wideband Fuel Mixture Display (WFMD; Apr23) Active Mains Soft Starter (Feb23), Model Railway Uncoupler (Jul23) Battery-Powered Model Railway Transmitter (Jan25) PIC16F88-I/P Battery Charge Controller (Jun22), Railway Semaphore (Apr22) PIC12F675-I/P Train Chuff Sound Generator (Oct22) PIC24FJ256GA702-I/SS Ohmmeter (Aug22), Advanced SMD Test Tweezers (Feb23) ESR Test Tweezers (Jun24) PIC16F1455-I/P Railway Points Controller Transmitter / Receiver (2 versions; Feb24) Battery-Powered Model Railway TH Receiver (Jan25) PIC32MX170F256D-501P/T 44-pin Micromite Mk2 (Aug14), 4DoF Simulation Seat (Sep19) PIC16F1455-I/SL Battery Multi Logger (Feb21), USB-C Serial Adaptor (Jun24) PIC32MX170F256B-50I/SP Micromite LCD BackPack V1-V3 (Feb16 / May17 / Aug19) Battery-Powered Model Railway SMD Receiver (Jan25) Advanced GPS Computer (Jun21), Touchscreen Digital Preamp (Sep21) USB Programmable Frequency Divider (Feb25) PIC32MX170F256B-I/SO Battery Multi Logger (Feb21), Battery Manager BackPack (Aug21) PIC16LF1455-I/P New GPS-Synchronised Analog Clock (Sep22) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) PIC16F1459-I/P K-Type Thermostat (Nov23), Secure Remote Switch (RX, Dec23) STM32L031F6P6 SmartProbe (Jul25) Mains Power-Up Sequencer (Feb24 | repurposed firmware Jul24) $20 MICROS 8-Channel Learning IR Remote (Oct24) ATmega32U4 Wii Nunchuk RGB Light Driver (Mar24) PIC16F1459-I/SO Multimeter Calibrator (Jul22), Buck/Boost Charger Adaptor (Oct22) AM-FM DDS Signal Generator (May22) PIC16F15214-I/SN Digital Volume Control Pot (SMD; Mar23), Silicon Chirp Cricket (Apr23) ATmega644PA-AU PIC32MK0128MCA048 Power LCR Meter (Mar25) PIC16F15214-I/P Digital Volume Control Pot (TH; Mar23), Filament Dryer (Oct24) Tool Safety Timer (May25) $25 MICROS PIC16F15224-I/SL Multi-Channel Volume Control (OLED Module; Dec23) PIC32MX170F256B-50I/SO + PIC16F1455-I/SL Micromite Explore-40 (SC5157, Oct24) NFC IR Keyfob Transmitter (Feb25), Rotating Light (Apr25) PIC32MX470F512H-120/PT Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) PIC16F18146-I/SO Volume Control (Control Module, Dec23), Coin Cell Emulator (Dec23) PIC32MX470F512L-120/PT Micromite Explore 100 (Sep16) Compact OLED Clock & Timer (Sep24), Flexidice (Nov24) $30 MICROS Versatile Battery Checker (May25), RGB LED ‘Analog’ Clock (May25) PIC16LF15323-I/SL Remote Mains Switch (TX, Jul22), Secure Remote Switch (TX, Dec23) PIC32MX695F512H-80I/PT Touchscreen Audio Recorder (Jun14) PIC32MZ2048EFH064-I/PT DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) STM32G030K6T6 Variable Speed Drive Mk2 (Nov24) DIY Reflow Oven Controller (Apr20), Dual Hybrid Supply (Feb22) W27C020 Noughts & Crosses Computer (Jan23) KITS, SPECIALISED COMPONENTS ETC 433MHz RECEIVER KIT (SC7447) (JUN 25) VERSATILE BATTERY CHECKER KIT (SC7465) (MAY 25) RGB LED ‘ANALOG’ CLOCK KIT (SC7416) (MAY 25) USB POWER ADAPTOR COMPLETE KIT (SC7433) (MAY 25) Includes the PCB and all onboard parts (see p66, Jun25) Includes everything in the parts list (including the case), except the optional components, batteries and glue (see p30, May25) $20.00 $65.00 Includes all the parts except the power supply. When buying the kit select either a BZ-121 GPS module or Pico W (unprogrammed) for the time source (see p66, May25) $65.00 Includes everything in the parts list and a choice of one USB socket: USB-C power only; USB-C power+data; Type-B mini; or Type-B micro (see p80, May25) $10.00 siliconchip.com.au/Shop/ PICO COMPUTER (DEC 24) FLEXIDICE COMPLETE KIT (SC7361) (NOV 24) MICROMITE EXPLORE-40 KIT (SC6991) (OCT 24) For full functionality both the Pico Computer Board and Digital Video Terminal kits are required. Items shown unbolded are optional (see p71, Dec24) - Pico Computer Board kit (SC7374) $40.00 - Pico Digital Video Terminal kit (SC6917) $65.00 - PWM Audio Module kit (SC7376) $10.00 - ESP-PSRAM64H 64Mb SPI PSRAM chip (SC7377) $5.00 - DS3231 real-time clock SOIC-16 IC (SC5103) $7.50 - DS3231MZ real-time clock SOIC-8 IC (SC5779) $10.00 Includes all required parts except the coin cell (see p71, Nov24) $30.00 Includes all required parts (see p83, Oct24) $35.00 (APR 25) Includes an assembled PCB, separate Raspberry Pi Pico 2 and front/rear panels $120.00 DUAL-RAIL LOAD PROTECTOR (SC7366) (OCT 24) Hard-to-get parts: includes the PCB and all semiconductors except the ROTATING LIGHT FOR MODELS KIT (APR 25) optional/variable diodes (see p73, Oct24) $35.00 Complete kit which includes the PCB and all onboard components (see p60, Apr25): - SMD LEDs (SC7462) $20.00 PicoMSA PARTS (SC7323) (SEP 24) - Through-hole LEDs (SC7463) $20.00 Hard-to-get parts: includes the PCB, Raspberry Pi Pico (unprogrammed), plus all semiconductors, capacitors and resistors (see p63, Sep24) $50.00 433MHz TRANSMITTER KIT (SC7430) (APR 25) Includes the PCB and all onboard parts (see p75, Apr25) $20.00 COMPACT OLED CLOCK & TIMER KIT (SC6979) (SEP 24) Includes everything except the case & Li-ion cell (see p34, Sep24) $45.00 PICO 2 AUDIO ANALYSER SHORT-FORM KIT (SC6772) (MAR 25) The Pico Audio Analyser kit from Nov23, but with an unprogrammed Pico 2 $50.00 DISCRETE IDEAL BRIDGE RECTIFIER (SEP 24) Both kits include the PCB and everything that mounts to it (see page 83, Sep24) USB PROGRAMMABLE FREQUENCY DIVIDER (SC6959) (FEB 25) - All through-hole (TH) kit (SC6987) $30.00 Complete kit: includes all components (see p85, Feb25) $60.00 - SMD kit (SC6988) $27.50 PICO/2/COMPUTER (SC7468) NFC PROGRAMMABLE IR KEYFOB (SC7421) (FEB 25) COMPACT HIFI HEADPHONE AMP (SC6885) (DEC 24) CAPACITOR DISCHARGER KIT (SC7404) (DEC 24) Complete kit: includes all required items, except the cell (see p67, Feb25) Complete kit: includes everything except the power supply (see p47, Dec24) Includes the PCB and all components that mount on it, the mounting hardware (without heatsink) and banana sockets (see p36, Dec24) $25.00 $70.00 $30.00 VARIOUS MODULES & PARTS - 0.96in SSD1306-based yellow/blue OLED (RF Signal Gen, Jun23; SC6421) $10.00 - 20x4 blue backlit LCD with I2C interface (ESR Meter, Aug23; SC4203) $15.00 - red & black PCB-mount banana sockets (ESR Meter, Aug23; SC4983) $6.00pr - two 1nF ±1% capacitors (ESR Meter, Aug23; SC4273) $2.50 - 5V 3-pin boost regulator module (2m CW/FM Test Generator, Oct23; SC6780) $3.00 - 5V 3-pin buck regulator module (2m CW/FM Test Generator, Oct23; SC6781) $4.00 - 0.96in 128x64 white OLED without PCB (SmartProbe, Jul25; SC7397) $7.50 *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. PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT TINY LED ICICLE (WHITE) DIGITAL BOOST REGULATOR ACTIVE MONITOR SPEAKERS POWER SUPPLY PICO W BACKPACK Q METER MAIN PCB ↳ FRONT PANEL (BLACK) NOUGHTS & CROSSES COMPUTER GAME BOARD ↳ COMPUTE BOARD ACTIVE MAINS SOFT STARTER ADVANCED SMD TEST TWEEZERS SET DIGITAL VOLUME CONTROL POT (SMD VERSION) ↳ THROUGH-HOLE VERSION MODEL RAILWAY TURNTABLE CONTROL PCB ↳ CONTACT PCB (GOLD-PLATED) WIDEBAND FUEL MIXTURE DISPLAY (BLUE) TEST BENCH SWISS ARMY KNIFE (BLUE) SILICON CHIRP CRICKET GPS DISCIPLINED OSCILLATOR SONGBIRD (RED, GREEN, PURPLE or YELLOW) DUAL RF AMPLIFIER (GREEN or BLUE) LOUDSPEAKER TESTING JIG BASIC RF SIGNAL GENERATOR (AD9834) ↳ FRONT PANEL V6295 VIBRATOR REPLACEMENT PCB SET DYNAMIC RFID / NFC TAG (SMALL, PURPLE) ↳ NFC TAG (LARGE, BLACK) RECIPROCAL FREQUENCY COUNTER MAIN PCB ↳ FRONT PANEL (BLACK) PI PICO-BASED THERMAL CAMERA MODEL RAILWAY UNCOUPLER MOSFET VIBRATOR REPLACEMENT ARDUINO ESR METER (STANDALONE VERSION) ↳ COMBINED VERSION WITH LC METER WATERING SYSTEM CONTROLLER CALIBRATED MEASUREMENT MICROPHONE (SMD) ↳ THROUGH-HOLE VERSION SALAD BOWL SPEAKER CROSSOVER PIC PROGRAMMING ADAPTOR REVISED 30V 2A BENCH SUPPLY MAIN PCB ↳ FRONT PANEL CONTROL PCB ↳ VOLTAGE INVERTER / DOUBLER 2M VHF CW/FM TEST GENERATOR TQFP-32 PROGRAMMING ADAPTOR ↳ TQFP-44 ↳ TQFP-48 ↳ TQFP-64 K-TYPE THERMOMETER / THERMOSTAT (SET; RED) MODEM / ROUTER WATCHDOG (BLUE) DISCRETE MICROAMP LED FLASHER MAGNETIC LEVITATION DEMONSTRATION MULTI-CHANNEL VOLUME CONTROL: VOLUME PCB ↳ CONTROL PCB ↳ OLED PCB SECURE REMOTE SWITCH RECEIVER ↳ TRANSMITTER (MODULE VERSION) ↳ TRANSMITTER (DISCRETE VERSION COIN CELL EMULATOR (BLACK) IDEAL BRIDGE RECTIFIER, 28mm SQUARE SPADE ↳ 21mm SQUARE PIN ↳ 5mm PITCH SIL ↳ MINI SOT-23 ↳ STANDALONE D2PAK SMD ↳ STANDALONE TO-220 (70μm COPPER) RASPBERRY PI CLOCK RADIO MAIN PCB ↳ DISPLAY PCB KEYBOARD ADAPTOR (VGA PICOMITE) ↳ PS2X2PICO VERSION MICROPHONE PREAMPLIFIER ↳ EMBEDDED VERSION RAILWAY POINTS CONTROLLER TRANSMITTER ↳ RECEIVER LASER COMMUNICATOR TRANSMITTER ↳ RECEIVER DATE NOV22 DEC22 DEC22 JAN23 JAN23 JAN23 JAN23 JAN23 FEB23 FEB23 MAR23 MAR23 MAR23 MAR23 APR23 APR23 APR23 MAY23 MAY23 MAY23 JUN23 JUN23 JUN23 JUN23 JUL23 JUL23 JUL23 JUL23 JUL23 JUL23 JUL23 AUG23 AUG23 AUG23 AUG23 AUG23 SEP23 SEP23 SEP23 OCT22 SEP23 OCT23 OCT23 OCT23 OCT23 OCT23 NOV23 NOV23 NOV23 NOV23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 JAN24 JAN24 JAN24 JAN24 FEB24 FEB24 FEB24 FEB24 MAR24 MAR24 PCB CODE 16111192 24110224 01112221 07101221 CSE220701 CSE220704 08111221 08111222 10110221 SC6658 01101231 01101232 09103231 09103232 05104231 04110221 08101231 04103231 08103231 CSE220602A 04106231 CSE221001 CSE220902B 18105231/2 06101231 06101232 CSE230101C CSE230102 04105231 09105231 18106231 04106181 04106182 15110231 01108231 01108232 01109231 24105231 04105223 04105222 04107222 06107231 24108231 24108232 24108233 24108234 04108231/2 10111231 SC6868 SC6866 01111221 01111222 01111223 10109231 10109232 10109233 18101231 18101241 18101242 18101243 18101244 18101245 18101246 19101241 19101242 07111231 07111232 01110231 01110232 09101241 09101242 16102241 16102242 Price $2.50 $5.00 $10.00 $5.00 $5.00 $5.00 $12.50 $12.50 $10.00 $10.00 $2.50 $5.00 $5.00 $10.00 $10.00 $10.00 $5.00 $5.00 $4.00 $2.50 $12.50 $5.00 $5.00 $5.00 $1.50 $4.00 $5.00 $5.00 $5.00 $2.50 $2.50 $5.00 $7.50 $12.50 $2.50 $2.50 $10.00 $5.00 $10.00 $2.50 $2.50 $5.00 $5.00 $5.00 $5.00 $5.00 $10.00 $2.50 $2.50 $5.00 $5.00 $5.00 $3.00 $5.00 $2.50 $2.50 $5.00 $2.00 $2.00 $2.00 $1.00 $3.00 $5.00 $12.50 $7.50 $2.50 $2.50 $7.50 $7.50 $5.00 $2.50 $5.00 $2.50 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT PICO DIGITAL VIDEO TERMINAL ↳ FRONT PANEL FOR ALTRONICS H0190 (BLACK) ↳ FRONT PANEL FOR ALTRONICS H0191 (BLACK) WII NUNCHUK RGB LIGHT DRIVER (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 BATTERY MODEL RAILWAY TRANSMITTER ↳ THROUGH-HOLE (TH) RECEIVER ↳ SMD RECEIVER ↳ CHARGER 5MHZ 40A CURRENT PROBE (BLACK) 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 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 PCB CODE Price 07112231 $5.00 07112232 $2.50 07112233 $2.50 16103241 $20.00 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 09110241 $2.50 09110242 $2.50 09110243 $2.50 09110244 $2.50 9049-01 $5.00 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 SMARTPROBE ↳ SWD PROGRAMMING ADAPTOR JUL25 JUL25 P9054-04 P9045-A NEW PCBs $5.00 $2.50 We also sell the Silicon Chip PDFs on USB, RTV&H USB, Vintage Radio USB and more at siliconchip.com.au/Shop/3 ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Send your email to silicon<at>siliconchip.com.au Querying the Versatile Battery Checker Regarding the Versatile Battery Checker project in the May 2025 issue (siliconchip.au/Article/18121), should the last line of the article (Nulling the wiring resistance) read “... then trim the value to 5mW”? A known-good high-CCA car starter battery should be around 4.5-5mW. Also, will the Versatile Battery Checker be made as a kit by any of the usual Australian electronics suppliers? Great magazine, as always. Keep up the good work. (L. P., Ascot Vale, Vic) ● We can expand and clarify on that section of article. Let’s say that the raw, unadjusted reading from a known-good high-CCA car starter battery is 15mW. If we know that the battery is responsible for about 5mW of that, the wiring can be assumed to measure 10mW. Thus, the correction value should be entered as 10mW. A subsequent raw reading from the same battery will be 15mW. The 10mW correction factor will then be subtracted, correctly displaying the actual battery impedance of 5mW. We are offering a complete kit (see siliconchip.au/Shop/20/7465) and it has been very popular. So much so that we have struggled to keep up with the demand. Can Pico 2 W be used for Pico 2 Computer? The April 2025 Pico 2 Computer project (siliconchip.au/Article/17939) looks interesting, but it includes no mention of whether the Pico 2 W (the wireless version) would be a drop-in upgrade for only a few dollars more. It seems like a shame where a simple swap can make such a difference, especially where WiFi or Bluetooth connectivity can make or break a project. It would appear (on superficial research) that backward compatibility would be maintained for software between the different versions. Will 100 Silicon Chip the Silicon Chip shop offer both boards as options, or just offer the 2 W version as the preferred option? As an avid reader since the first issue, there is something each month to keep me interested and it expands my knowledge. The use of a powerful microcomputer as a drop-in module reminds me of the cries of heresy that the introduction of ICs brought to the electronics world. (B. B., Darley, Vic) ● Geoff Graham responds: you cannot use the Pico 2 W in the Pico 2 Computer, primarily because the HDMI and WiFi/Internet features both push the Pico 2 to the limit in different ways. For example, HDMI requires a high clock speed, while WiFi/internet requires a complex protocol stack with reliable hardware interrupts. It is just not practical (at this time) to try to squeeze all of these into the one package. Also, they are designed for different uses; the HDMI version is intended as a ‘boot to BASIC computer’, while the Pico 2W version is mainly for use as an embedded controller. Diagnosing solder joints on Pico 2 Computer I just bought a kit for the Pico 2 Computer from your shop and I seem to have a problem. The Pico 2 won’t go into bootloader mode. It’s not the cables or my computer because, using the same cable, a Pico 1 happily goes into bootloader mode and shows up as a memory device. Yes, I’m holding BOOTSEL down as I connect the USB cable. I’m annoyed at myself for not loading the firmware before I soldered it onto the main board so I could have at least determined that the Pico 2 was OK, but it is too late for that. I have checked my soldering and there don’t seem to be any solder bridges or dry joints. I know you can’t easily diagnose it from what I’ve told you, but if others have the same or similar problem, Australia's electronics magazine there might be some hope of a resolution. (N. B., Medowie, NSW) ● In our experience, the Pico modules are very reliable. We’ve only seen one soldering fault on a USB socket once, and that would not affect you even if it were the case since you’re not using the onboard socket. We asked Geoff Graham what he thought about this and he wrote: I have never seen a Pico that cannot be bootloaded. I would be very surprised if the Pico 2 is faulty. More likely, it is a soldering fault in one of three possible areas: 1. The test pads on the Pico 2 have not been successfully soldered to the holes on the PCB. This is the most likely fault. 2. There is a soldering fault in the USB socket used for programming. 3. One or more pads on the Pico 2 are not soldered correctly – this is also a common fault. I suggest removing the programming jumpers and trying to squeeze a USB plug into the USB socket of the Pico 2. This is difficult, but if it can be done, the reader should then be able to program the Pico 2 in the usual way (hold down BOOT during power on). If that works, it will prove that the Pico 2 is OK, and it’s likely a soldering problem. N. B. later confirmed that resoldering the pads on the underside of the Pico 2 board while inserting short lengths of wire fixed it. Pico 2 Computer has faulty USB hub chip I got some Pico 2 Computer boards made by JLCPCB using the BOM and PCB files downloaded from Geoff Graham’s website. On powering it up, the red USBHUB LED lights up. The green LED that switches 5V power to the USB ports is not on, so the other four LEDs will not light either. There is +5V at the source and gate terminals of Mosfet Q1 (MDD2301). The drain is at 0V. Both boards do exactly the same thing. Everything siliconchip.com.au else seems to be working correctly: video, the real-time clock etc. (B. P., Rostrevor, SA) ● Geoff Graham responds: this sounds like a problem that we have been dealing with recently. It appears that there is a bad batch of CH334F chips out there. If the chips on your board are batch number 1163FD43, they will work. If they are 13122E20, they won’t. The fix is to remove resistors R54 and R55. This disables the over-­current protection feature in the CH334F (which is the cause of the problem). The USB ports are still protected by the resettable fuse, so this change will not cause a problem. Speaker wire with aluminium conductors I have a technical question about tinned copper cables that you may be able to answer. I bought some loudspeaker cables recently from Bunnings – one of the multicore wires in the insulated cable pair was a bright shiny copper colour, and it soldered easily. The other wire looked like a shiny tinned copper wire, but it would not solder. I tried 60/40 solder, lead-free solder and even silver solder, but none worked. I wonder if you have any experience in these matters. I have been soldering electronics for decades; I wonder what is wrong. (E. U., Castle Hill, NSW) ● It sounds like aluminium wire, which is very hard to solder. We took a guess, searched the Bunnings website and came up with Antsig 18GA Speaker Cable – 30m, which seems very cheap at $17.65. If you look under Specifications, it states, Material: PVC, Copper, Aluminium. So it seems that one conductor is copper, and the other is aluminium, presumably because it’s cheaper (and lighter) than copper. It will probably work OK if you make a mechanical connection to it (eg, using a screw connector). Current Probe doesn’t have a CAT III rating I have built several Silicon Chip projects that interact with the mains. One thing I usually do is change any banana posts and sockets to those with a CAT III safety rating. The 40A Current Probe (January siliconchip.com.au How was the TV Pattern Generator EEPROM programmed? Dr Hugo Holden’s article in the January 2025 issue, about retrieving data from old microcontrollers (siliconchip.au/Article/17609), piqued my interest. I built the Colour TV Pattern Generator from your June & July 1997 issues (siliconchip.au/Series/215). It is still working well; it would be a shame if the EPROM failed. I am curious to know what programming setup was used at the time. I have looked on eBay etc and noticed that there are some EPROM programmers available, but they don’t appear to support the device used in the colour pattern generator (TMS27C512). I realise that the technology is dated now, but it would be interesting to build a project that runs on modern PC software that can talk to these old chips. As mentioned in Dr Holden’s article, it can save some specialised gear from the scrap heap. (G. C., Toormina, NSW) ● Our memories are a bit hazy after nearly 30 years, but we think we made a basic EPROM programmer controlled by a computer running a BASIC program. The device support list for the popular TL866II programmer includes the TMS27C512 and we think the newer versions like the XGecu T48 programmer we reviewed in the April 2023 issue (siliconchip.au/Article/15735) can program them too. Alternatively, you could use the EPROM programmer by Jim Rowe published in the November 2002 to February 2003 issues and updated in June 2004 (siliconchip. au/Series/110). The software could be run within DOSBox, with Windows installed within that. You would need a Centronics interface to USB converter for the EPROM programmer to computer interface. Having said that, using the TL866II/T48 will probably be easier and more future-proof. 2025; siliconchip.au/Article/17605) is an excellent project but was let down by any lack of a CAT III interface. Some minor tweaks would lift the project into the professional category. (R. M., Currumbin Valley, Qld) ● Thanks for the feedback; it is always good to get reader comments and constructive suggestions. The Current Probe was not designed to be used in CAT III environments, which are described as: • Equipment in fixed installations, such as switchgear and polyphase motors • Bus & feeder in industrial plants • Feeders and short branch circuits, distribution panel devices • Lighting systems in larger buildings • Appliance outlets with short connections to service entrance Most Silicon Chip readers will use the device in a domestic setting with appropriate current-limiting devices, like circuit breakers and fuses. To design a device for CAT III requires much more than CAT III rated connectors – it encompasses the entire design, including the case, which would need to withstand very high energy transients. Specifying CAT III connectors alone could be misleading (in that readers may think the overall device meets the CAT III standard when it doesn’t) and Australia's electronics magazine would make it unnecessarily expensive. Just changing the binding posts to CAT III rated types would almost double the cost of construction! That said, there should be no problem using such connectors provided they are mechanically compatible. The ones you suggested have a slightly lower current rating than those we specified (32A vs 35A), which you will need to keep this in mind. Either way, we don’t advise using the Current Probe in an industrial or commercial setting. Controlling Digital Pot with IR Remote Keyfob It has been great fun building and subsequently enjoying some of Silicon Chip’s audio designs, in particular, two different powered loudspeaker projects. Adding IR remote control using Phil Prosser’s Digital Volume Control (March 2023; siliconchip.au/ Article/15693) to all three of my builds added some most welcome functionality. The only (admittedly small but pesky) negative to the completed setups has been the bulk of the recommended universal remotes, since only three buttons are needed. When I spotted the miniature IR Keyfob Remote project in the February 2025 issue, I of course ordered the kit to play with. July 2025  101 As one that is far more comfortable with hardware than software, configuring the handy little device to work with the Digital Pots has been beyond me. I followed the instructions in the article and managed to install the NDEF text record for NEC, but am at a loss to know how to find the codes that the Digital Pots respond to. I would be very grateful for instructions on how to install the two Philips RC5 codes that are programmed into the Digital Pot’s PIC16F15214. I need both because two of my speaker systems are close by. Each digital volume control has been reset to respond uniquely, as described on page 38 of the March 2023 issue. (R. M., Ivanhoe, Vic) ● We had a look through the Digital Volume Control source code to find the IR codes it used and confirmed they were reasonable using the web page at https://w.wiki/DWYG The code accepts RC5 decimal addresses 0 (TV) and 16 (preamp/ receiver), with RC5 commands 13 (mute), 16 (volume up) and 17 (volume down). The defaults correspond to the following NDEF entries for the IR Remote Keyfob: 5,0,16 5,0,17 5,0,13 The alternative codes are: 5,16,16 5,16,17 5,16,13 R. M. later confirmed that these codes work as expected. Finding instructions for Short Circuits project I built the Jiminy Cricket project quite some years ago when the instructions appeared in Silicon Chip magazine. I have bought a new kit but was surprised to find no instructions with it. Could you please tell me what past issue of Silicon Chip had the instructions in it, as I have kept all my old magazines but don’t have an overarching index for them. (R. K., Pukekohe, New Zealand) ● We have published several articles on electronic crickets but none of them were called “Jiminy Cricket”. Our only cricket kit is for Silicon Chirp, which was from the April 2023 issue (siliconchip.au/Article/15738). “Jiminy Cricket” is from Jaycar’s 102 Silicon Chip “Short Circuits Volume 2” book, and they make and sell a kit for it (Cat KJ8224). As far as we know, the only place you can find the instructions for that kit are in the Short Circuits Volume 2 book, which is listed as still available from Jaycar (Cat BJ8504). While Silicon Chip did some of the production work on that book, Jaycar remains the exclusive source for Short Circuits kits and books. Testing USB-C cables with Cable Tester Regarding the USB Cable Tester from the November & December 2021 issues (siliconchip.au/Series/374), thank you for a fantastic and useful project. I enjoyed building it, although I found it challenging to solder extremely small components. It seems to be functioning as intended, identifying the quality and resistance of each USB cable sample. However, all my USB-A to USB-C cables report (on the 2nd row of the display) either POWER ONLY or USB 2.0, depending on the orientation of the USB-C connector. I see the same result on my USB-C to USB-C cables, in one direction only; otherwise, they always display POWER ONLY. I would expect a reading like USB 3.2 etc, since most of my cables are of higher quality (eg, Comsol high speed). Maybe it’s OK, because in your article, you describe how USB-C leads only have one D+/D- pair (the wires required for a legacy USB 2.0 connection) but they can be plugged in one of two ways. So some orientations do not detect this pair. Therefore, that is the best result I can expect from a USB-A to a USB-C connection? That still doesn’t explain why my USB-C to USB-C behaves the same way, though. Could there be a problem with my tester’s soldering? Thanks again for a great publication. (J. C., Mount Waverley, Vic) ● Your observations appear to be consistent with a working USB Cable Tester. We delved into testing USB-C cables on the last page (p93) of the USB Cable Tester Project article, part two (December 2021). As you’ve found, the USB-C plug needs to be tried both ways to get a meaningful result. USB-C to USB-C cables need to have both ends tried both ways, ie, four combinations. The USB-C specification says that only one USB-2.0 pair is provided in Australia's electronics magazine USB-C cables, and you can see that in the circuit diagram (Fig.1, p30, November 2021). Only one of the USB2.0 pairs are connected in CON4 and CON6; thus, only one combination will work. With the limited number of pins (only 40!) available on the PIC microcontroller, we chose this arrangement over shorting the pins together, since it would allow the cable condition to be better understood by trying different rotations. With regards to the USB-C to USB-C cable, we think this is due to USB’s confusing terminology. USB low-speed and USB full-speed are both USB-1.1 designations, referring to 1.5Mb/s and 12Mb/s signalling rates, respectively. USB high-speed was introduced with USB-2.0 and refers to 480Mb/s. The various USB 3.0 (and subsequent 3.1 and 3.2) signalling rates are referred to as SuperSpeed and SuperSpeed+ (5Gb/s and higher). In other words, a high-speed cable, like you describe, is almost certainly only USB-2.0 compliant. If you test a SuperSpeed USB-C to USB-C cable, you should get a different result. Snooping on I2C data with a micro is difficult Some time ago, I built the USB Digital & SPI Interface Board from the November 2018 issue (siliconchip.au/ Article/11299). I would like to use it to monitor an I2C conversation between an Arduino Nano and an Si5351 clock generator board, but it appears to take control of the bus and hold the clock line low. Is there a way to configure it into a slave listening-only mode? I have also found that it sends out characters as they are typed into Tera Term without waiting for a line feed. Is this normal, or is Tera Term not the best interface for the board? (M. H., Mordialloc, Vic) ● The software, as written, does not allow the Interface Board to act like a slave, only a master. So the short answer to the first question is: no. The software could be rewritten, but the problem with a slave I2C monitor is that it has to run at the speed dictated by the master and catch all clock edges, while a master decides what should happen. The PIC16F1455 is a fairly modest 8-bit chip with a 12MHz maximum clock frequency, so 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 Mains Power-Up Sequencer February-March 2024 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. Hard-To-Get Parts SC6871: $95 siliconchip.au/Series/412 The critical components required to build the Sequencer such as the PCB, micro etc. Other components need to be sourced separately. Lazer.Security FOR FREE: WE OFFER KITS, LEDs, LED assemblies and all sorts of quality electronic components, through-hole and SMD, at very competitive prices. Check out the latest deals at www.lazer.com.au To give away, one decommissioned and partly disassembled YUKI KP-480 pick and place machine. Contact: Graham – 0458 071 074 Location: Hobart, Tasmania 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 July 2025  103 Advertising Index Altronics.................................29-32 Blackmagic Design....................... 7 Dave Thompson........................ 103 DigiKey Electronics....................... 3 Emona Instruments.................. IBC Hare & Forbes............................. 11 Jaycar.................. IFC, 12-13, 44-45 Keith Rippon Kit Assembly....... 103 Lazer Security........................... 103 LD Electronics........................... 103 LEDsales................................... 103 Microchip Technology.............OBC Mouser Electronics....................... 4 OurPCB Australia.......................... 5 PCBWay......................................... 9 PMD Way................................... 103 SC Micromite Explore 40............ 56 SC Mains Sequencer................ 103 Silicon Chip Shop.................97-99 Silicon Chip Songbird................ 52 Silicon Chip Subscriptions........ 53 The Loudspeaker Kit.com.......... 10 Wagner Electronics..................... 85 YUKI KP-480 machine.............. 103 we don’t think that is possible unless the clock provided by the master is quite slow. For example, we used a Raspberry Pi Pico running at 133MHz+ to create an I2C monitor device to capture the output of an I2C OLED, to emulate its display. Even then, the I2C master needed to be slowed substantially to capture the data successfully. The immediate output behaviour is normal since the Interface Board delivers the data as soon as it is received. Something like the Arduino IDE’s serial monitor will only send data when the line ending is entered, so that is an option if you want such behaviour. Protection diodes on amplifier outputs Regarding Electronic Australia’s Playmaster and Silicon Chip’s audio amplifiers, I am curious why there are no back-EMF protective diodes connected between the emitters and collectors on the output transistors. They are used with many commercial amplifiers, including Naim, Denon etc. I have assembled many EA and Silicon Chip amplifiers over many years for friends and myself. (D. B., via email) ● We have included such diodes in most of our amplifiers since November 2012, when they were used in the Classic-D amplifier (siliconchip. au/Series/17). Since then, they can be seen in the Ultra-LD Mk.4 amplifier from August 2015 (siliconchip. au/Series/289), the SC200 in January Errata and on-sale data for the next issue 2017 (siliconchip.au/Series/308) and the 500W Amplifier from April 2022 (siliconchip.au/Series/380). These diodes are necessary when the amplifier is used to drive a transformer, as used for 70V and 100V line connected loudspeakers. The diodes are not strictly required while the amplifier is operating within its linear range, where the negative feedback has control of the amplifier output. Only when the amplifier is in clipping, where the output operation is beyond the limits of feedback control, will the protection diodes come into effect and clamp any back-EMF. This only occurs when the amplifier is used with a significantly inductive load. Our earlier amplifiers without the protection diodes were long-lasting and reliable. Including these diodes in later designs is part of the evolution of semiconductor power amplifiers, beginning in the Electronics Australia days in the 1960s. With continued improvements over the decades, our amplifiers have become some of the best performers ever published, rivalling the best commercial amplifiers. Generally, including these diodes doesn’t seem to hurt and they may be beneficial in some circumstances. Earlier amplifiers would have omitted them due to their cost, but these days suitable diodes will not break the bank, so we might as well specify them. DIY inverters are no longer worthwhile Next Issue: the August 2025 issue is due on sale in newsagents by Monday, July 28th. Expect postal delivery of subscription copies in Australia between July 25th and August 15th. I saw advertisements in two old issues of Silicon Chip for 24V DC to 240V AC inverter kits from Altronics. I also found an old Rod Irving kit for a 2kW 24V DC to 240V AC inverter from 1992-1993. Are there more recent projects for inverter kits? (R. S., Chifley, NSW) ● While it may have been worthwhile to build your own inverter back in the early 1990s, today it definitely isn’t. Basic commercial inverters can be found under $30. A 150W inverter will cost you around $50, while $99 will get you a 400-500W inverter. You can get a 2kW inverter for under $200 from many sources. Anything we design would cost more than that in just parts, and you SC would still have to build it. Australia's electronics magazine siliconchip.com.au Vintage Radio – Emerson 888, May 2025: there are two mistakes in the redrawn circuit diagram (Fig.1). R6 is shown connected to the wrong end of T2’s secondary; it should connect to the lower side that goes to the base of TR2. Separately, the junction of C10 & R10 should connect to the base of TR3 (the bottom end of T3’s secondary), rather than the top of T3’s secondary. Power LCR Meter, March & April 2025: in Fig.8 on p36 of the March issue, the SI and SCK pins of IC5 are numbered incorrectly. SI is pin 6 and SCK is pin 5. Mains Power-Up Sequencer, February, March & July 2024: if using the Mains Detect Input feature, the 10μF electrolytic capacitor next to pin 4 of IC10 should be installed, even though it is in the Current Detection section. This prevents false triggering due to EMI pickup. Reciprocal Frequency Counter, July 2023: the lowest frequency the Counter can measure is 2Hz, not 10mHz. 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