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NOVEMBER 2025 ISSN 1030-2662 11 9 771030 266001 $14 00* NZ $14 90 INC GST INC GST HUMANOID ROBOTS no longer just science fiction RP2350B Computer available pre-assembled with even better features Digital Preamplifier and Crossover Contents Vol.38, No.11 November 2025 14 Humanoid Robots, Part 1 Humanoid and android robots are now a reality; while they’re not yet perfect, they are becoming more widespread. We look at what makes a humanoid robot, from the definition to the hardware and software. By Dr David Maddison, VK3DSM Robotics feature 54 Power Electronics, Part 1 In this series of articles, we explore the broad concept of power electronics. This covers circuits with the primary function of handling electrical energy. Part 1 starts off by focusing on DC-DC converters. By Andrew Levido Electronic design 62 Large OLED Panels Page 47 Power Rail Probe Power Electronics Part 1: Page 54 We often use OLED panels in our projects because of their low power draw and ability to draw graphics and text. The modules described in this article are still compact (<65mm), but larger than what we normally use. By Tim Blythman Low-cost electronic modules Part 2: Page 68 92 Telequipment D52 Oscilloscope The D52 dual-beam 6MHz oscilloscope from the 1960s was a British-made competitor to the well-known Tektronix oscilloscopes. This scope was sold with different CRT phosphors such as green, blue and yellow. By Dr Hugo Holden Vintage Electronics 28 RP2350B Computer Requiring nearly zero soldering, with many I/O pins, more memory and better audio; the RP2350B Computer is an improved version of our older Pico/2/Computer. You can buy it pre-assembled, or have it fabricated. By Geoff Graham & Peter Mather Computer project 47 Power Rail Probe This handy piece of gear measures and evaluates ripple switching noise and transients riding on DC supply rails. High-performance versions can cost thousands of dollars, but you can build this for less than $100. By Andrew Levido Test equipment project 68 Digital Preamp & Crossover, Pt2 This advanced preamplifier uses digital processing and can also act as a crossover. It has three digital inputs, two digital outputs, four analog stereo inputs, four stereo outputs, high-fidelity USB and stereo monitoring channel. By Phil Prosser Audio/hifi project 79 Over Current Protector Use this simple circuit to sound an alarm or disconnect a load when a lowvoltage DC current flow exceeds a preset value. The preset value can be set from 1A to 20A and uses a reed switch to function. By Julian Edgar Simple electronic project Digital Preamplifier and Crossover 2 Editorial Viewpoint 6 Mailbag 82 Circuit Notebook 84 Serviceman’s Log 90 Online Shop 99 Subscriptions 100 Ask Silicon Chip 103 Market Centre 104 Advertising Index 104 Notes & Errata 1. 400×168-pixel 4-colour e-paper display 2. Mini GPS speedometer PCB 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): $72.50 12 issues (1 year): $135 24 issues (2 years): $255 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 2 Editorial Viewpoint IPv6 is growing in popularity IPv4, the internet protocol introduced in the early 1980s, has been the backbone of the internet ever since. But it has a fatal flaw: its address space is only 32 bits, limiting the number of unique addresses to 4,294,967,296. That might sound like plenty, but with over eight billion people on Earth, there aren’t enough addresses to go around – especially once you factor in businesses, governments and infrastructure, who also need many addresses. There are a few reasons for this limit. Nobody thought the internet would grow to the size that it has. Also, since every internet packet contains a source and destination address, each 8 bits of address space adds two bytes to every single packet traversing the ‘net. In practice, the problem has been managed with network address translation (NAT), where many devices share a single public address. NAT has kept the internet running, but it adds complexity, can cause reliability issues and it breaks the end-to-end principle of networking. IPv6 solves these problems. Instead of 32 bits per address, it uses 128, giving 2128 or about 3.4 × 1038 unique addresses. That’s so vast that instead of receiving just one address, each user gets a block of them, often hundreds or thousands. Every device in your home or office can have its own globally routable address. Despite being standardised back in 1995, IPv6 adoption has been slow. Change is always difficult, and IPv6 is more complex to administer. Still, progress is being made; on the 2nd of August this year, Google measured IPv6 usage at 50% of all internet traffic. Large providers like Amazon Web Services are also pushing customers towards IPv6 by charging for scarce IPv4 public addresses. Ironically, some of their tools are still not fully IPv6-ready, making the transition more difficult than it should be, as we recently found out. We enabled IPv6 across our public and private networks last month, including our web and mail servers. The process wasn’t trivial, but it was much easier than expected. And the best part is that IPv6 runs alongside IPv4 in ‘dual stack’ mode. For example, our website can now be reached via either 54.79.90.108 (IPv4) or 2406:da1c:f0:271c:adb0:cae7:e127:5cf8 (IPv6). If your ISP and router support IPv6, you’re probably already using it without even realising. My home router and ISP support IPv6, so it was just a matter of enabling it in the router settings, then the inevitable fiddling with opaque configuration variables until it sprang into life, with my local machines receiving globally routable IPv6 addresses. Unsurprisingly, countries with large populations like India and China already make extensive use of IPv6. Australia and many other ‘western’ countries, which got large IPv4 allocations in the early days, lag behind in adoption. I think that may start changing soon as the tide turns and IPv4 is no longer the default. The transition won’t be quick, but it is inevitable. Over time, IPv6 will restore the simplicity, reliability and scalability the internet was meant to have. Printing and Distribution: Update to our Vintage Radio Collection: it now includes articles from 1987 to 2024, a total of nearly 500 individual articles. Like before, it is available as a download or on a USB. Previous purchasers can download the new articles at no extra cost. See siliconchip.au/Shop/3 for details. 14 Hardner Rd, Mount Waverley VIC 3149 54 Park St, Sydney NSW 2000 Cover image: the TOCABI robot by Mathew Schwartz https://unsplash.com/photos/a-person-wearing-a-helmet-td116npEPgQ Silicon Chip by Nicholas Vinen Australia's electronics magazine siliconchip.com.au AI-powered engineering AI is reshaping engineering. Learn how it’s changing the way engineers design, test and optimize. Listen to podcasts, read articles and explore various tech resources. ©2025 Mouser Electronics, Inc. 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The series is offered in 150mm, 200mm and 300mm sizes. Each model recharges in under three hours, so you will never look for a battery again! You’ll never need a 20mm Battery Again 129 (Q175) SYDNEY MELBOURNE BRISBANE PERTH ADELAIDE (02) 9890 9111 (03) 9212 4422 (07) 3715 2200 (08) 9373 9999 (08) 9373 9969 09_SIC_271025 $ 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”. RIP Jeff Monegal Jeff Monegal, former of Oatley Electronics, sadly passed away on the 20th of September this year. He wrote or was involved in 29 articles for the magazine from June 1989 (Universal Temperature Controller) to March 2013 (Capacitor Discharge Unit and Automatic Points Controller for Model Railways) plus more in Electronics Australia. Jennifer Monegal, North Maclean, Qld. A blast from the past I thought readers would be interested in this photo I saw on Facebook, with the caption “#OnThisDay 2nd of July 1948, ‘Sun’ 1938 Dodge pictured in Sydney equipped with radio during Two-way car radio trials… Developed by the staff of the Radio & Hobbies magazine who were part of Fairfax.” Dr David Maddison, Toorak, Vic. Comment: this photo was published on page four of the August 1948 issue of Radio, TV & Hobbies, part of a short article titled “First Radio News Car In Australia!” by John Moyle, who was then editor of the publication. Silicon Chip magazine for the visually impaired I was saddened to read Mick Olden’s letter in the September 2025 issue in which he announced that he would be discontinuing his subscription due to vision loss. Never fear, Mick! At Vision Australia, we’ve been producing an audio accessible version of each edition of Silicon Chip for many years now. All you need to do is become a member of our national library service – if you request to receive Silicon Chip, the latest audio recording will arrive in your library inbox every month. You’ll also have access to the thousands of other books and magazines available to you. Can’t find what you’re after? You might like to request material to be added to the collection, or just for your own use. What’s more, the service is free! Our volunteer narrators read all the articles in Silicon Chip, apart from any sections that rely heavily on diagrams. All projects, however, are briefly summarised. If you live with a print disability and would like to make use of this service you can join by phoning the Vision Australia Library on 1300 654 656. Email: librarymembership<at>visionaustralia.org Web: www.visionaustralia.org/services/library/join David Tredinnick, Audio Production Coordinator Vision Australia, Kooyong, Vic. Transmission Line Calculator giveaway The antenna article in the February 2025 issue reminded me of working many years ago on HF antennas and transmission lines at Standard Telephones and Cables (STC) in Liverpool, NSW (siliconchip.au/Series/434). I purchased the Transmission Line Calculator manufactured by W&G Melbourne for the Department of Civil Aviation. It is in perfect condition, housed in a leather pouch, and I would like to offer it to any interested reader (perhaps the author, Roderick Wall VK3YC). I live in suburban Sydney and it is available for free or cost of postage. If you’re interested, email Silicon Chip and they can forward it on to me. Colin Fisher, ex VK2CFC, via email. Australian-made drones A 1938 Dodge pictured in Sydney equipped with radio during a two-way car radio trial. 6 Silicon Chip I was prompted to write the following letter by your September 2025 article on aerial drones by Dr David Maddison (siliconchip.au/Article/18847). This Australian-designed and -built Turana naval gunnery practice drone was a project of the early 1980s at Government Aircraft Factories. This cruise missile had a rocket motor (same as the anti-submarine Ikara missile) to establish flight, and a French (Micro-Turbo) gas turbine to 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. 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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. www.blackmagicdesign.com/au Download free on the DaVinci Resolve website Learn More! NO SUBSCRIPTIONS • NO ADS • NO USER TRACKING • NO AI TRAINING maintain flight. The gas turbine gave about 160lbs-force (217Nm [712N]) of thrust. The drone flew at around 450 knots (833km/h) for about 30 minutes. Control of the flight path was from the ship’s operations room. It had a membrane-lined fuel tank to stop the fuel sloshing around and interfering with the flight dynamics! It also had a miss-distance microphone probe to calculate how close to it the naval shells exploded. The Turana was designed to be fished out of the sea and refurbished by naval staff, ready to be launched again. Well, that was the plan, anyway. It needed a few engineers, technicians, and a couple a days to get it back in the air! The little parachute symbols on the fin indicated the number of previous successful flights. These images below are from a publicity brochure to promote interest in the GAF Telemetry Unit, with a view to selling them. R. S., Emerald, Vic. Solar Diverter requires certain inverter capabilities Like N. K. from Kedron (Ask Silicon Chip, August 2025), I too was confused by the Solar Diverter project in the June 2025 issue (siliconchip.au/Series/440). The article states that it reads the solar export data directly from the inverter but my SMA three-phase inverter has no knowledge of export power, as it does not have a current transformer (CT) on the grid side of the meter (unless you buy and install a rather expensive “SMA Energy Meter”). The same goes for our previous Fronius inverters – again, unless you buy their “Fronius Smart Meter”. However, further research clarified things. “As of February 2023, all new solar installations in Queensland above 10kVA require a 8 Silicon Chip GSD (Generation Signalling Device)... to allow electrical distributors to remotely curtail your solar feed-in when required.” This is named ‘dynamic feed-in control’, ‘dynamic feed-in limitation’ or ‘flexible exports’, and is used by the distributed network service provider (DNSP) to prevent the grid from being overloaded or made unstable from excessive solar generation, particularly with the increasing number of domestic PV installations. The DNSP can also curtail your feed-in (export), to avoid having to upgrade otherwise overloaded power lines. It turns out that Victoria mandated that all new installations from the 1st of March 2024 must have dynamic feed-in control. WA will introduce this requirement for new installations sometime this year. Dynamic feed-in control is a quite recent requirement – the majority of existing installations throughout Australia do not have this capability, do not have export monitoring CTs, and therefore can’t work with this Diverter. It is interesting that WA’s approach to the problem was to limit the maximum solar size to 5kW – my inverter clips to that power during summer for a couple of hours around midday (sometimes). Your author recently upgraded to an integrated 25kW three-phase inverter – that is a huge system. It sounds like this inverter is only suitable for new, niche market installations. I am wondering, however, if it would be possible to modify the Solar Diverter to monitor my inverter using Bluetooth instead of WiFi, as I have an app that reads voltages, currents, and power on each of the three phases, and the same for each of the solar panel MPPT strings. Australia's electronics magazine siliconchip.com.au With the built-in offset, it may be possible to divert power based on generated power, as the offset would be enough to source everything in my home during the middle of the day anyway. Then, everything greater than that offset generation could be diverted. Ian Thompson, Duncraig, WA. Ray Berkelmans comments: the Solar Diverter project does rely on your solar system having an energy monitoring system (production and export power, at least) built-in, or as an add-on. That limits it to more modern systems, as energy monitoring didn’t start becoming common until the second half of the 2010s. For example, my 2016 Sungrow system had production monitoring, but not export (at least not as part of their basic installation). I believe that after 2018, full energy monitoring was standard on the Sungrow systems. I suppose we should have been clearer on this! As for modifying the Solar Diverter project to communicate over Bluetooth instead of WiFi (with a nominal ‘houseuse’ offset), that is certainly a possibility. Establishing this communication is the key; after that, it should be fairly straightforward. Another possibility is obtaining your energy stats from the web, if your inverter OEM makes it available. Most manufacturers make these data available via an API. Implementing these API calls with the Arduino is reasonably straightforward with libraries like ESP8266HTTPClient.h. Bear in mind that you won’t be able to refresh your energy data as frequently, since OEMs tend to cap the number of API calls. For example, in my first iteration of this project, SolarEdge limited API calls to 300 per day. Additional comment: one has to wonder why the inverter power-monitoring add-ons are so expensive (and don’t come as standard on an expensive inverter) when you can buy a basic single-phase power monitor rated at 10A for around $10 online, and one capable of IoT integration for $20-25. The cost for manufacturers to add the capability to an existing product must be even less. On magazines, books and automotive safety Thank you for continuing to produce Silicon Chip. I have been intending to send some comments for a while, and finally, here they are. In the August Editorial viewpoint, it was announced that the magazine price would rise. Considering the massive rises in many other products, I don’t find this price rise unreasonable at all. However, there is a condition, and that is to maintain Silicon Chip as a hobbyist-friendly magazine. For many years, I subscribed to a certain American electronics magazine that had a mix of articles suiting readers from the inexperienced to the professional. However, as the years passed, the hobbyist-friendly articles slowly disappeared and were replaced with articles requiring a depth of knowledge that only professionals could have. In all but name, it had become an industry magazine. Some time after I stopped subscribing to it, it was combined with another magazine with a hobbyist readership. Other magazines haven’t fared so well. They have failed by becoming an advertising platform only, producing poor quality projects and/or becoming too high-tech for the subscribers. 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Jaycar reserves the right to change prices if and when required. electronics, here are two that made life for me much better earlier in my career: • The Art of Electronics by Horowitz & Hill • Operational Amplifiers and Linear Integrated Circuits by Robert F. Coughlin & Frederick F. Driscoll I bought these over thirty years ago and have never regretted their purchase. They are old books, but I am sure that second-hand copies can be found. I watched a video last week in which the presenter praised the actions of Europe’s crash testing organisation, Euro NCAP. The organisation will only award the highest safety ratings to vehicles if the makers have fitted physical, easy-to-use, and tactile controls to basic functions such as wipers, indicators, and hazard lights etc. Researchers claim that the use of touchscreens have the greatest impact on driver reaction times compared to things like drugs and alcohol and, from the bar charts shown in the video, the reaction times to respond to an emergency from using a touchscreen (I assume that’s what they mean) is many times that of the reaction times for drugs and alcohol. I hope some car manufacturers take the hint and do away completely with touchscreens or any screens. They are only a gift to lazy designers and programmers. George Ramsay, Holland Park, Qld. Comment: we like making electronic circuits, and we realise that at least some of them need to be approachable for beginners (along with our feature articles). We also have no intention of repeating the downfall of Electronics Australia! An alternative to the HWS Solar Diverter I read your article on the Solar Diverter project in the June & July 2025 issues (siliconchip.au/Series/440). My method of controlling power to the water heater is different because I have a solar hot water system with roof heating panels, 27kWh of batteries and 6kW of solar photovoltaic panels (with a 5kW inverter export limit). This is what I have done to maximise the solar for the whole house: 1. Taken the hot water system from the off-peak controlled load circuit and put it on the battery whole-house backup circuit. 2. Installed a timer to make sure that the hot water electric system is on only after peak tariff time and when the sun is no longer up (23:00 hours to 06:00 hours). This maximises the efficiency by not using electricity when the solar system is heating the water. Only in June and July do I need to have active control of the Tesla Power­ Wall 2, because there is low solar energy available then. The software of the Tesla is not quite able to cover what is needed, so manual control is required to do the mode switching and backup level control during those months. This is also required for Tesla PowerWall 2 systems where there are multiple units; the import limits needs to be set so the mains breaker current limit is not exceeded. For each PowerWall 2, the limit is 5kW. For two units thus it would be 10kW plus normal house loads. So if you have a 32A breaker, it needs to be set for a 7.7kW import limit. This will limit the total input to 7.7kW, including the house loads, including charging the battery in timebased use. It will reduce the charge power but leave house power as needed. The export does not need to be limited as the inverter already has the 5kW limit and the battery is not used for export. SC Wolf-Dieter Kuenne, Bayswater, Vic. 12 Silicon Chip Australia's electronics magazine siliconchip.com.au siliconchip.com.au Australia's electronics magazine November 2025  13 HUMANOID & AN Agility Digit www.agilityrobotics.com Boston Dynamics Atlas https://bostondynamics.com/atlas Unitree H1 www.unitree.com/h1 Tesla Optimus www.tesla.com/en_eu/AI Like many ideas that started as science fiction, humanoid and android robots are now a reality. They have not yet been perfected – but they are here. We’ll likely see them entering widespread use over the next couple of decades. V ideo phones, vertically landing rockets, artificial intelligence (AI) – not long ago, these things were purely in the realm of science fiction. But now they are everyday technologies. Humanoid robots aren’t very far behind. Traditional robots, typically found in factories, are mostly stationary and perform repetitive tasks. In contrast, humanoid robots functionally resemble people. Android robots are humanoids designed to very closely resemble humans, to the point of being almost indistinguishable from us. So far, no robot has been developed that is truly indistinguishable from a human, but some can pass superficial inspection. Examples of such androids include the 14 Silicon Chip Japanese Actroid-DER and the South Korean EveR-4, both of which we will discuss later. This series comprises two articles; this first one will discuss the general aspects of and technology behind humanoid robots, while the follow-up next month will cover a range of robots that are currently in development, being demonstrated or in use. Why humanoid robots? Humanoid robots are ideal for working in spaces designed for humans. Unlike conventional robots that are designed for a specific range of tasks and are often stationary, humanoid robots can, if sufficiently advanced, do anything a human can do. They can have many flexible joints and Australia's electronics magazine high mobility. They don’t have to be the same size as a human; they can be smaller or larger as required for their job. Some examples of jobs that humanoid robots are ideal for are: O Caring for hospital patients O Construction work O Customer service (eg, retail) O Handling inquiries in public places like airports and train stations O Hotel check-in staff O Domestic duties (eg, housework) O Factory floor work (assembly, moving objects and inspections) O Warehouse work O Risky, dangerous or unpleasant tasks The rate of advancement of humanoid robots is rapid due to the siliconchip.com.au NDROID ROBOTS Part 1: by Dr David Maddison, VK3DSM Figure 02 www.figure.ai 1X NEO Gamma www.1x.tech/neo convergence of improved mechanical design, artificial intelligence, faster computer chips and advances in computer and chip architectures. Humanoid robots can address labour shortages and our ageing population, as well as perform dirty, undesirable, repetitive tasks that humans don’t want to. They’ll do it 24/7, more precisely and for no pay. This has resulted in a greatly increased demand for such robots. The future use of humanoid robots raises ethical concerns, but that has always been the case with the introduction of more advanced automation, even since the time of the Industrial Revolution. People tend to move on to other forms of employment if displaced. Also, despite incredible advances, the robots are not taking over; not yet, anyway... What is a humanoid robot? There is no strict definition, but siliconchip.com.au Apptronik Apollo https://apptronik.com/apollo typically a humanoid robot features a human-like appearance, including two arms, two legs, a head, a torso and a size similar to humans. They are designed to mimic human behaviour. This mimicry stems from their ability to move, converse and provide information, express emotions through facial expressions and perform natural language processing (NLP) using artificial intelligence (AI), enabling conversations and instruction-­giving. Their movements are designed to enable useful tasks, such as picking up, carrying and placing objects, while AI allows them to receive instructions or engage in conversation, distinguishing socially engaging robots from those used purely for industrial purposes. Parts of a humanoid robot The main components of a humanoid robot are: 1. The body structure incorporating Australia's electronics magazine Booster Robotics T1 www.boosterobotics.com/robots/ limbs, a torso and a head, usually made from aluminium or plastic composites. 2. Motors (actuators) and joints, with the motors acting as the ‘muscles’. 3. Sensors, such as cameras (eyes), microphones (ears), gyroscopes and accelerometers (as in vestibular part of the human ear) and touch sensors. 4. A ‘brain’ comprising three key parts. a The main computer processor, which acts as the central hub. It is responsible for overall control, coordinating the robot’s actions by running AI software. b AI software serves as the ‘mind’, enabling advanced tasks like recognising objects, perception, learning from experience, making decisions and planning movements. This can include a large language model (LLM) and/or vision language model (VLM). This AI software might use the main processor or may also run on November 2025  15 specialised hardware like GPUs (graphics processing units) or TPUs (tensor processing units) for efficiency and speed, and is typically trained using machine learning rather than just programmed. c Microcontrollers are distributed throughout the robot, managing specific hardware subsystems like motors in the arms and sensors in the hands, in real time, ensuring precise control under the main processor’s guidance 5. A power source, such as a battery pack. 6. Wireless communications systems. Actuators and joints Actuators for humanoid robots may be hydraulic, pneumatic or electric. There are also small actuators for facial ‘muscles’, for robots capable of facial expression. Electric actuators are the favoured types these days due to their compactness, lightness, simplicity, quietness and good power-to-weight ratio. They usually use DC motors or servo motors, often with reduction gears to increase torque. Fig.1 shows a typical commercially available actuator from ASBIS that could be employed in a humanoid robot. It has an EtherCAT Ethernet controller, a pair of 19-bit encoders to enable precise rotation accuracy, a high-torque brushless DC motor, clutch brakes that lock the actuator in the event of power loss, a harmonic reducing gear, and a cross roller to ensure rigidity for axial and radial loads. Fig.2 shows the RH5 experimental humanoid robot and the range of movements of its joints possible with its particular types of actuators, along with the symbols used to represent them. This robot has a total of 34 degrees of freedom (DoF) – see the panel at lower right. Communication and networking Humanoid robots need to communicate for a variety of reasons, such as to receive updated instructions, updated software, teleoperation (remote control by a human), remote processing for complex tasks, progress tracking, fault monitoring or other reasons. They can connect wirelessly via common means such as 5G, Bluetooth, Zigbee, IoT, WiFi and MQTT (Message Queuing Telemetry Transport). Voice communication with humans is possible using a speaker and microphone; spoken instructions can be interpreted using natural language processing by an LLM. Power supplies Humanoid robots are mostly powered by lithium-ion batteries. Some are in the form of a removable battery pack that is quickly swappable to avoid significant downtime while the robot recharges. Some robots, such as early Boston Dynamics robots intended for military use, used on-board petrol or diesel generators, as a military robot cannot be quickly recharged in the field. However, we are not aware of any military humanoid robots under development that use internal combustion engines. Robot designers take care to ensure robots use power efficiently to maximise their use time between charges Fig.1: a commercially available actuator that can be used in a humanoid robot. Source: www.asbis.com/aros-robotic-actuators 16 Silicon Chip Australia's electronics magazine or battery swaps. Systems are being developed to allow humanoid robots to connect to a charger or change battery packs themselves. Processors Neural networks are the basis of human and animal brains, and are important for artificial intelligence and humanoid robots. They are flexible and can learn and model new and changing relationships that are non-linear and complex. They are thus highly suitable for tasks like speech and image recognition. Artificial neural networks (ANNs) can be either modelled in software or hardware (or as biological circuits in some experimental arrangements). There are several types of processors that can be used to power AI for robots (or in general) including: O CPUs (central processing units), as used in regular computers O GPUs (graphics processing units) O TPUs (tensor processing units) O Neuromorphic processors In addition to AI functions, hardware subsystems may be controlled by other processors. The CPUs used in humanoid robots are very powerful and, while not specifically designed for AI purposes, can still satisfactorily run AI software. A CPU may also be used in combination with another type of processor. GPUs, or graphics processing units, were originally developed for graphics applications but have been adapted for neural networks in artificial intelligence due to their ability to handle many calculations at once. This parallel processing is essential for training AI to perform tasks like vision in humanoid robots. Widely recognised as the world leader in AI chips, NVIDIA uses GPUs as the foundation of its AI technology. NVIDIA’s AI chips, such as the H100, A100, RTX series GPUs, Grace Hopper Superchip GH200, and Blackwell accelerator architecture, are optimised with NVIDIA’s CUDA (compute unified device architecture) software for parallel computing. A popular choice for humanoid robots is the NVIDIA Jetson series platforms. These processor modules integrate an energy-efficient ARM CPU and GPU, and can be used for AI tasks, such as image recognition and deep learning. A TPU, or Tensor Processing Unit, siliconchip.com.au Fig.2: the actuation and morphology of an RH5 humanoid robot. The red, green and yellow symbols represent the type of joints: S: Spherical, R: Revolute, P: Prismatic, U: Universal. Source: https://cmastalli.github.io/publications/ rh5robot21ichr.pdf is a specialised chip designed and developed by Google, optimised for machine learning. Unlike CPUs and GPUs, which evolved for AI from general computing and graphics roles, TPUs were built from scratch for this purpose. They excel at matrix operations, a core component of neural networks, and demonstrate superior performance in tasks like training large models, outperforming CPUs and GPUs in specific low-precision workloads. TPUs are used in applications such as natural language processing, image recognition for navigation and recommendation systems, powering Google’s AI services. They show great promise for use in humanoid robots, where their efficiency could enhance real-time vision and decision-­making. Still, only one current humanoid robot, Gary (described next month) is known to use them. Neuromorphic processors are designed to emulate the structure and function of a human brain, although they are not nearly as complex. They employ mixed analog and digital processing to generate neural signals, providing radically different computational outcomes than traditional digital computing using von Neumann architectures. siliconchip.com.au The experimental iCub humanoid robot (described next month) is a robot said to use such a processor. This biological-style approach results in a more energy efficient processor, with some architecture like that of a brain. Examples of neuromorphic chips include Intel’s Loihi, IBM’s TrueNorth and NorthPole, BrainChip’s Akida and the SENeCA (Scalable Energy-­efficient Neuromorphic Computer Architecture) research chip. Neuromorphic processors use spiking neural networks (SNNs), where information is processed as discrete spikes in a manner similar to biological neurons, rather than continuous activation, as with artificial neural networks (ANNs). Degrees of freedom (DoF) Degrees of freedom means the number of independent motions a robotic appendage such as an arm or a leg can make. The more degrees of freedom it has, the more flexible and useful it is. Consider a very simple robot arm. A single robot joint such as a wrist that can rotate about one axis (yaw) represents one DoF. Shoulder joints that can move on two axes (pitch and yaw) add two more DoF. A hinged elbow joint allowing flexion/extension is another DoF. So a simple robot arm that has a shoulder, elbow and wrist would have four DoF. The hand (or other gripping mechanism) does not count, as it is considered the ‘end-effector’, the component that is being manipulated. DoF typically only refers to joint motions, not the internal components of the endeffector. For robot arms, six DoF is the minimum required for full position and orientation control of the end-effector. A count of seven or more is considered ideal. The more DoF a robot has, the more mechanically complex it becomes and the more advanced the required control algorithms and training become. A human arm has seven DoF: three in the shoulder (flexion/extension, abduction/adduction & internal/external rotation), one from the elbow (flexion/extension), one from the forearm (pronation/supination) and two from the wrist (flexion/extension & radial/ulnar deviation). Australia's electronics magazine November 2025  17 Fig.3: a model of a proposed humanoid robot with an ‘organoid’ brain. Source: www.datacenterdynamics.com/en/news/chinese-scientists-developartificial-brain-to-control-brain-on-chip-organoid-robot/ Neuromorphic processors are not yet widely adopted currently due to a lack of hardware maturity, challenges integrating them with existing ecosystems, the need for new programming paradigms and the lack of computational power compared to other processors. Other processors To relieve the computational burden from the rest of the robot’s ‘brain’, control of some hardware such as a hand or knee joint may be performed by small integrated computer chips called microcontrollers. In some cases, field-­programmable gate arrays (FPGAs) and application-­ specific integrated circuits (ASICs) are used for very high-performance tasks, such as complex motion control algorithms. These offer specialised hardware acceleration for particular tasks, improving efficiency and real-time performance. Organic ‘brains’ Neural networks can also be built with biological neurons. One Melbourne-­based company has developed an experimental “wetware” computer, although it has no current application in humanoid robots (www.abc. net.au/news/science/104996484). Researchers are also looking at neural networks made from human cells. For example, researchers at Tianjin University and the Southern University of Science and Technology in China have interfaced human brain cells onto a neural interface chip to make a neural network ‘brain’ that can 18 Silicon Chip be trained to perform tasks. This brain has not yet been incorporated into a robot as proposed (Fig.3), but brain cells on a chip were stimulated and trained to navigate environments and grip objects when interfaced to an external robot. The collection of brain cells is called an ‘organoid’, and is not a real human brain, but possesses the neural network architecture of one and is about 3mm to 5mm in diameter. The size limit is imposed due to the inability to vascularise the cells (incorporate blood vessels). If this hurdle is overcome, much large structures can be fabricated. Of course, there are ethical implications of using human cells for such applications. Skin materials Silicone elastomers (rubbers) are commonly used for the skin of humanoid robots with realistic facial and other features. They are soft and highly deformable, like real human flesh and skin, plus they can be readily coloured and moulded and formulated for particular properties. Fig.4 shows an example of a silicone skin on a humanoid robot chassis. Many companies make silicone products. One that we came across that might have suitable products is Smooth-On (www.smooth-on.com). A team of researchers at Aalto University and the University of Bayreuth have developed hydrogel skin materials. Hydrogel is a gel material that contains a high proportion of water. It is soft, pliable and moist, much like skin and flesh. Australia's electronics magazine Fig.4: an example of silicone skin on a humanoid robot chassis, the discontinued Robo-C2 from Promobot. Source: https://promo-bot.ai/robots/ robo-c/ These researchers developed hydrogel materials suitable for the skin of realistic humanoid robots. They are even self-healing, so any cut or other minor damage will repair itself; see www.nature.com/articles/s41563025-02146-5 Another concept under development is ‘electronic skin’. This emulates human skin, with the ability to sense pressure, temperature, deformation etc using flexible electronics embedded into a silicone or similar matrix (see our article on Organic Electronics in the November 2015 issue; siliconchip. au/Article/9392). Incredibly, as a proof-of-­ concept project, scientists from the University of Tokyo, Harvard University and the International Research Center for Neurointelligence (Tokyo) have made a robot face using cultured living human skin (Fig.5), although it would no doubt soon die without associated nourishment. That is scarily reminiscent of The Terminator. Operating systems and frameworks Operating systems (OS) for humanoid robots are specialised software that extend beyond traditional computer operating systems. They integrate real-time processing and AI for the robot’s ‘brain’. These systems orchestrate critical tasks, including the real-time control of actuators, sensors and power systems, as well as balance, locomotion, environmental interaction and task planning. They rely on real-time operating systems (RTOS) like the siliconchip.com.au open-source FreeRTOS or RTEMS to ensure low-­latency, deterministic responses for precise sensor-actuator coordination. Complementing these operating systems, ‘middleware’ facilitates communication between diverse software components. For instance, the data distribution service (DDS) in opensource ROS 2 (Robot Operating System 2), a widely used robotics framework, enables modular, scalable, and interoperable data exchange. Frameworks like ROS 2 and NVIDIA Isaac (based on ROS 2) provide structured environments to integrate AI and manage robotic functions. Most humanoid robots use opensource Linux-based operating systems, such as Ubuntu with ROS 2 or RTLinux with built-in real-time capabilities, due to their flexibility and compatibility with AI frameworks. These systems support advanced AI algorithms, including LLMs like various GPT models, for natural language understanding; VLMs, like CLIP (Contrastive Language-Image Pretraining), for scene and object recognition; and reinforcement learning for optimising movement and acquiring new skills. This enables continuous learning and adaptation in dynamic environments. For example, the ROS 2 framework, running on Linux, powers robots like Boston Dynamics’ Atlas for dynamic locomotion and manipulation. NVIDIA’s Isaac platform, built on ROS 2, supports AI-driven perception and control in robots like Tesla’s Optimus and Figure’s Figure 01 for human-­robot collaboration. Together, Linux-based operating systems and frameworks like ROS 2 enable humanoid robots to perform diverse tasks, from industrial automation to assistive caregiving, with precision and adaptability. Fig.5: human skin grown for proposed use on humanoid robot. The mould is on left, the skin on the right; the eyes are not real. Source: www.cell.com/cellreports-physical-science/fulltext/S2666-3864(24)00335-7 Simulation platforms NVIDIA’s Isaac Sim (see https:// developer.nvidia.com/isaac/sim) is a robotics simulation platform built on the Omniverse framework. It can be used to create digital ‘twins’, ie, virtual replicas of physical robots, including humanoids, to train AI and test software as well as avoiding damage to people or robots if a real robot was used – see Fig.6. Digital twins help train neural networks (eg, those in foundation models like RT-2X; discussed later) on siliconchip.com.au Fig.6: a robot simulation from NVIDIA Isaac Lab, which is related to NVIDIA Isaac Sim. Source: https://developer.download.nvidia.com/images/isaac-lab1980x1080.jpg simulated sensor data. For operating systems, they test software stability (eg, real-time control loops), and validate algorithms (eg, path planning). Isaac Sim simulates sensor inputs (eg, cameras and gyroscopes) and interactions with objects, both crucial for AI development. It integrates Australia's electronics magazine with robotics frameworks like ROS 2, aligning with operating systems and software used in robots like Tesla’s Optimus or NASA’s Valkyrie. These digital twins enable robot learning and simulation by replicating real-world physics and sensor data, supporting the development November 2025  19 of operating systems and algorithms for tasks like movement and object interaction. Besides Isaac Sim, other notable alternative simulation platforms that we don’t have space to delve into include: O Gazebo (open source) https://gazebosim.org/home O Webots (open source) https://cyberbotics.com O CoppeliaSim (commercial) www.coppeliarobotics.com O MuJoCo (open source) https://mujoco.org Each excels in specific areas. Gazebo has great community support; Webots is perfect for industry, education and research; CoppeliaSim is flexible, with diverse capabilities; and MuJoCo has advanced physics simulation. Other software The Python programming language is widely used for robot control and AI implementation in humanoid robots. It simplifies managing actuators, sensors and motion planning, often alongside C++ in frameworks like ROS. Python’s extensive libraries, like TensorFlow and PyTorch, support developing and deploying AI models for tasks like vision and decision-making. Besides Python, other programming languages used for humanoid robots include C++ and C for control, MATLAB for research, Java for middleware, and the emerging Rust. Each complements Python, addressing specific needs in AI training, OS stability and software validation. Other operating systems used with humanoid robots worth mentioning include: O HarmonyOS 6, an operating system developed by Huawei, with its AI Agent Framework, is showing promise for operating and training robots. Examples of variations or adaptations of HarmonyOS in robotics include Kuavo, with possible variants like M-Robots OS or iiRobotOS, reflecting its customisable nature. Harmony­OS is used to operate and train the Walker S humanoid robot (described next month) developed by UBTECH Robotics for tasks like quality inspections at Nio’s factory. Fig.7: the SynTouch BioTac multimodal tactile sensor for use in robot fingers that can detect force, vibrations and temperature. Source: https://wiki. ros.org/BioTac Fig.8: some of the uses of foundation models. Source: https://blogs.nvidia.com/blog/whatare-foundation-models/ 20 Silicon Chip Australia's electronics magazine O HumaOS (www.humaos.org), a real-time, pre-emptive operating system designed for advanced humanoid robotics, enabling human-like cognitive processing and precise motor control. It is optimised for modern robotics hardware and neuromorphic processors, is developer-friendly and has comprehensive safety protocols and fail-safes. It runs on a real-time Linux core. Sensors and perception Humanoid robots must be able to sense and map their environment. They can use sensors and navigation systems including cameras, GPS/ GNSS, IMUs (inertial measurement units), lidar, microphones and tactiles. Tactiles (Fig.7) are sensors, such as in the fingertips of the robot, that measure pressure, temperature and vibration (possibly more). They may be composed of smaller sensing elements called tactels. A tactel (tactile element) is an individual sensing element that is part of a sensor array, analogously equivalent to an individual nerve on a human fingertip. Human fingertips have about 465 sensory nerves per square centimetre. A tactel sensor array can provide high-resolution sensing and could, for example, sense the texture of an object. Training robots The basis of training humanoid robots lies in the use of foundation models (Fig.8). These large-scale AI models are trained on vast amounts of real-world data, such as videos from sources like YouTube, to learn specific tasks or a range of activities. This enables them to perceive and understand their environment, make decisions and perform tasks. For example, a foundation model might be trained on thousands of videos of pouring coffee, extracting the essential generic steps to replicate the task, even if the exact scenario differs from its training data. Foundation models can be trained with text, images, videos, speech, or other structured data. Key advantages include reduced development time for new applications, greater flexibility and adaptability and the ability to generalise skills from one task to another. This is unlike task-specific programming, which has limited reuse possibilities. siliconchip.com.au Fig.9: the model framework of GO-1. In this case, it is learning to hang a T-shirt. LAM stands for latent action model. Source: https://agibot-world.com/blog/go1 Foundation models rely on neural networks, which mimic how human and animal brains operate. Individual neurons are relatively simple, but their collective communication enables complex behaviours. Especially in foundation models, parameters (see panel) are used to measure the model’s complexity and learning capacity, acting as ‘adjustment knobs’ that alter the weighting of connections between neurons and biases that allow independent operation for generalisation. A larger number of parameters enhances the ability to handle complex data but requires more computational resources. However, excessive parameters may cause the model to memorise training data rather than learn underlying patterns, necessitating careful design to optimise performance and adaptability to unfamiliar situations. Foundation models include large language models (LLMs), vision language models (VLMs), vision language action (VLA) systems, image models, audio models, or multimodal models. LLMs and VLMs are the most commonly used in humanoid robots due to their language and vision capabilities. Examples of LLMs include OpenAI’s GPT-3 (with 175 billion parameters), xAI’s Grok, and Google’s Gemini (with undisclosed parameters), trained on vast text datasets like books and web content. These models enable tasks such as interpreting commands like “walk to the door”, with the ‘large’ part reflecting their vast number of parameters that capture complex language patterns. Not all LLMs qualify as foundation models; for instance, a smaller siliconchip.com.au LLM trained only for a specialist task lacks the broad, general-­purpose training or adaptability required. Vision-language models, such as OpenAI’s CLIP and Google’s PaLI, combine image recognition with natural language understanding, allowing them to identify objects like a “red cup” based on descriptions. An LLM can work cooperatively with a VLM, where the VLM provides the perceptual context of a visual scene and the LLM interprets and responds to commands based on the scene’s contents. For example, RT-2X from Google DeepMind uses a VLM for image understanding and a reasoning module for task execution, enabling actions like picking up an object based on a verbal command. In a robot, the LLM and VLM could run on separate hardware modules coordinated by a central controller, or be combined into a single multimodal foundation model run on one module. The latter is seen in models like PaLM-E (https://palm-e.github. io), which blends language and vision for action. Humanoid robots said to incorporate combined LLMs and VLMs include Tesla Optimus, Figure 02 running Helix, and Walker S. Examples of foundation models include: AgiBot GO-1 is designed to be the general-purpose ‘brain’ of humanoid robots, to help them learn and adapt. GO-1 uses vision language models (Fig.9), in which massive amounts of real-world images and videos are fed to the models, training them how to perform specific tasks. The model algorithms then convert the data into a series of steps, enabling them to perform the required tasks. The system can form generalisations from the training data (videos of humans doing things), enabling it to perform tasks similar to what was Parameters in artificial intelligence Parameters in artificial intelligence models are a critical component, allowing the model to learn and represent associations between concepts. They include weights, biases, attention scores and embedding vectors. For example, a weight is adjusted during training to associate “cat” with “meow” rather than “bark”. Biases are extra adjustments to weights that set the tone of a sentence, such as promoting “great day” toward a positive tone based on its typical associations in the training data. Attention scores determine which parts of a sentence the model focuses on. For instance, in “The cat, not the dog, meowed”, the model prioritises “cat” and “meowed”, ignoring “dog” as the action’s source. Embedding vectors are numerical representations of words in higherdimensional space. During training, a word like “happy” is shifted closer to “joy” and farther from “sad” based on how often they appear together in the training data. AI is only as good as its training data and will incorporate any of the biases present in its training materials. As the saying goes, “garbage in, garbage out”. Australia's electronics magazine November 2025  21 shown, not just the exact tasks shown. The overall GO-1 framework comprises the VLM, the MoE (Mixture of Experts) and the Action Expert. The MoE contains the Latent Planner, which learns action patterns from human behaviour (as observed in videos etc) to build comprehension. The Action Expert is trained with over a million real-world robot demonstrations and refines the execution of tasks. The VLM, Latent Planner and Action Expert cooperate to perform actions. The VLM process image data to provide force signals (to understand the forces involved in various actions), the required language inputs to perform tasks, and understand the scene. Based on outputs from the VLM, the Latent Planner generates Latent Action Tokens and generates a Chain of Planning. The Action Expert then generates fine-grained sequences of action based on the outputs of the VLM and the Latent Action Tokens. GO-1 is a generic platform that can be used in a variety of robots. In https:// youtu.be/9dvygD4G93c it is possible to see some of the ‘thought’ processes the robot goes through as it performs various tasks. AutoRT (Fig.10), developed by Google DeepMind, is a research project and an experimental AI training system for scalable, autonomous robotic data collection in unstructured real-world environments. It enables robots to operate in “completely unseen scenarios with minimal human supervision”. It integrates VLMs for scene and object interpretation, and LLMs for proposing tasks (eg, “wipe down the countertop with the sponge”), plus robot control models (RT-1 or RT-2) for task execution. The robot’s tasks are self-generated and work as follows (from https://auto-rt.github.io): 1. The robot maps the environment to generate points of interest, then samples one and drives to that point. 2. Given an image from the robot Fig.10: how AutoRT works for a basic group of tasks. Source: https://auto-rt.github.io/ 22 Silicon Chip Australia's electronics magazine camera, a VLM produces text describing the scene the robot observes. The output is forwarded to an LLM to generate tasks the robot could attempt. 3. Tasks are filtered via self-­reflection to reject tasks and categorise them into those that need human assistance, and those that do not. 4. A valid task is sampled from the filtered list and the robot attempts it. 5. The attempt is scored on how diverse the task and video are compared to prior data, and the list is repeated. In trials, AutoRT has utilised multiple robots in multiple buildings, up to 20 simultaneously, with 52 tested over seven months to perform diverse tasks like object manipulation, collecting 77,000 trials across 6,650 unique tasks. A ‘robot constitution’ ensures safety by filtering tasks to avoid humans or hazards, complemented by force limits and human-operated kill switches. This enables robots to gather training data autonomously and safely, improving their adaptability to novel scenarios. NVIDIA’s GR00T (Generalist Robot 00 Technology) is a research initiative and development platform aimed at accelerating the creation of humanoid robot foundation models and data pipelines for managing and generating training data. It is not a single model but a framework that includes foundation models, simulation tools and data generation pipelines. It is designed to make humanoid robots more general-­ purpose, capable of adapting to new environments and tasks like navigating new rooms or handling objects with minimal retraining. GR00T features a complete computer-­ in-the-robot solution, the Jetson AGX Thor computing module, which runs the entire robot stack (cognition and control). This module is optimised for robotics, supporting VLA models (among others). It delivers over 2070 teraflops (2070 trillion floating point operations per second) of AI performance (with four-bit floating point precision). RT-2X from Google DeepMind is a VLA foundation model built upon the earlier RT-2 (Robotic Transformer 2) model. It’s designed to bridge the gap between language, vision and robotic action for controlling humanoid or other robots. It is trained on vast multi-modal siliconchip.com.au Fig.11: examples of an RT-2 model in operation, showing some of the tasks that can be performed. Source: https:// robotics-transformer2.github.io/ datasets (text, images, videos and robotic action data) using self-­ supervised learning, allowing it to learn patterns without explicit labels. It has 55 billion parameters and can generalise instructions like “put the blue block on the red one”, even with blocks differing from its training set. Here is an example of how RT-2X works: 1. Input: it receives inputs from a camera feed and a command like “sort these items”. 2. Processing: using a scaled transformer architecture (a type of neural network), it adjusts parameters (weights, biases, attention scores) to interpret the scene, reason through the task and plan actions, leveraging its pre-trained knowledge. 3. Output: it generates precise motor commands, executed at a high frequency, to control the robot’s movements. Some examples of the type of instructions the earlier RT-2 can siliconchip.com.au understand are shown in Fig.11. There has been no public disclosure of what exact foundation model Tesla’s Optimus humanoid robot uses, but it will be discussed in the section on Optimus next month. It is based on a similar AI architecture to that used by Tesla’s Autopilot and full-self-driving (FSD) systems in their cars. Transformer models A transformer model is a type of neural network that processes the entire input sequence of data, such as text or from a vision transformer model, all at once, rather than stepby-step. A key strength is its ability to understand context, helping robots interpret commands like “pick up the cup” by considering the full scene before them. It uses a feature called ‘attention’, which allows the model to determine the relative importance of data parts, such as prioritising “cup” over “table”, Australia's electronics magazine enhancing its decision-making for humanoid robot tasks. Image recognition Humanoid robots use image recognition to see and interpret their environment. This requires computer vision models, often integrated into the robot’s AI system. Key vision models used include convolutional neural networks (CNNs), vision transformers (ViTs), and multimodal models (eg, CLIP). Convolutional neural networks (CNNs) are deep learning models optimised for vision, detecting edges, shapes and patterns to build object recognition capabilities. They are used use by Tesla’s Optimus, Figure AI robots and Unitree platforms. Popular architectures like ResNet and YOLO (You Only Look Once) are trained on datasets like ImageNet, a benchmark visual database with over 14 million pictures. November 2025  23 Vision Transformers (ViTs) are another type of neural network that breaks an image into smaller components called ‘patches’ and establishes relationships between them using ‘self-attention’, similar to how language models link words in a sentence. Unlike CNNs, ViTs can understand the context of a scene and the relationships between parts. However, they are computationally intensive, a drawback compared to CNNs. Multi-modal models like CLIP by OpenAI recognise objects based on textual descriptions, such as “pick up the blue cup”. Another example is Gemini-based robotics systems from Google DeepMind, built on the Gemini 2.0 framework, which powers advanced AI models. These models are integral to VLA systems, enhancing a robot’s ability to act on visual and language inputs by enabling perception, reasoning and action. Foundation models like GPT-3, Grok and RT-2X are trained on diverse datasets, including images and text. Image recognition models can be part of these foundation models; for example, CLIP and RT-2X incorporate vision components within their multi-modal frameworks. However, some CNNs trained only on limited datasets, like items in a certain factory, aren’t considered foundation models due to their lack of broad adaptability. Learning to walk Teaching a robot to walk is one A mid-level layer facilitates communication between them, relieving the main processor of the burden of 0 | A robot may not injure real-time walking tasks. This mirrors humanity or, through inaction, human walking, where the spinal allow humanity to come to harm. cord’s central pattern generators han1 | A robot may not injure a dle rhythmic motion, while the brain human being or, through inaction, directs overall activity and posture. allow a human being to come to Training a humanoid robot to walk is harm. a key development focus. One method 2 | A robot must obey the orders involves kinematic models, which are given it by human beings except mathematical representations of the where such orders would conflict robot’s structure, joint configurations with the First Law. and motion constraints. Alone, these 3 | A robot must protect its models produce a basic, often stiff own existence as long as such gait by focusing on geometry without protection does not conflict with accounting for forces, addressed by the First or Second Law. dynamic models. You could make the argument Challenges like walking on uneven that modern-day autonomous terrain or adapting to disturbances military vehicles already require advanced strategies, effeccontravene these “laws”. tively tackled by integrating kinematic models with dynamic simulations and of many aspects of robot training. AI-driven optimisation. It involves training it to coordiAI techniques, such as genetic algonate movements to achieve a stable, rithms and reinforcement learning, human-like gait. This relies on kine- enhance kinematic models to achieve matic models, dynamic models and more human-like motion. Genetic AI techniques such as reinforcement algorithms optimise gait parameters learning, genetic algorithms or imita- (eg, joint angles and torque) by emution learning. lating an evolutionary approach, The control algorithms for commer- rewarding closer-to-natural patterns, cial humanoid robots are typically while reinforcement learning lets proprietary, but the experimental RH5 robots ‘learn through experience’, humanoid robot (Fig.12) offers insight adjusting actions based on rewards into a hybrid approach. This system or penalties. uses local control loops for lower-­ Alternatively, transformer-based level functions, such as managing foundation models, pre-trained on joint torque and balance, and central human motion data and fine-tuned for controllers for high-level tasks like gait synthesis, offer advanced motion determining gait direction and speed. prediction. Stability is ensured with Asimov’s Laws of Robotics Fig.12: the electronic control units in an RH5 robot. Source: https://cmastalli.github.io/publications/rh5robot21ichr.pdf Fig.13: a Simscape Multibody model shown at a high level. Source: www.mathworks.com/help/sm/ug/humanoid_ walker.html 24 Silicon Chip Australia's electronics magazine siliconchip.com.au ‘zero-moment point’ (ZMP) control, maintaining the centre of pressure within the support polygon of the robot and imitation learning mimics human walking from demonstration data. Commercial tools like MathWorks’ Simscape Multibody (Fig.13, www. mathworks.com) handle kinematics (motion) and dynamics (forces), modelling 3D structures with torque-­ activated hip, knee, and ankle joints, and passive shoulder joints for arm swing to aid balance by counteracting torso motion. The contact forces between feet and the ground are simulated to ensure stability, with Simulink feedback controllers adjusting joint stiffness and damping. Training with MathWorks’ Global Optimization Toolbox for genetic algorithms or MathWorks’ Deep Learning Toolboxes and Reinforcement Learning Toolboxes refines walking, creating a feedback loop where optimised gaits inform the central controller, executed by local loops for natural, robust movement. In recent years, these combined approaches have transformed humanoid robot walking from stiff, mechanical motions to fluid, human-like gaits, paving the way for practical applications in diverse environments. World Robot Competition Mecha Fighting Series China Media Group held the World Robot Competition Mecha Fighting Series to showcase humanoid robotics technology. The robots were teleoperated by humans, but the robots autonomously provided balance and other basic functions. For details, see Fig.14 and https:// youtu.be/N7UxGVV_Fwo Artificial general intelligence We hear about artificial intelligence all the time but there is another concept beyond that, called artificial general intelligence (AGI). This is where a machine can emulate human intelligence in terms of self-learning (far beyond the ‘training’ of AI), reasoning, understanding and problem solving; even understanding and emulating human emotions. Humanoid robots endowed with AGI would be capable of great mischief in the wrong hands; this is the subject of many dystopian science fiction movies, such as The Terminator and I, Robot. To protect against such dystopian scenarios, in 1942, Isaac Asimov devised the Three Laws of Robotics and later added another one, although these have been criticised as not being a comprehensive ethical framework to govern the behaviour of intelligent robots. Still, they are a good starting point (see the panel). Experts agree that AGI has not been achieved yet, but at the current rate of progress, who knows when it could arrive. In 1949, Alan Turing proposed a test of intelligence behaviour known as the Turing test. This involves a human engaging in a text-based conversation Glossary of Terms AI – Artificial Intelligence; machines simulating human intelligence, such as learning, reasoning and problem-solving ANN – Artificial Neural Network; computational models inspired by human brains, used in machine learning ASIC – Application-Specific Integrated Circuit; a custom-designed chip optimised for a specific function or task CNN – Convolutional Neural Network; deep learning models optimised for vision, detecting edges, shapes and patterns CPU – Central Processing Unit; a general- purpose processor that executes instructions & manages computing tasks DoF – Degrees of Freedom; independent movements a robot joint or mechanism can perform End Effector – a tool/device at a robotic arm’s end that interacts with objects FPGA – Field-Programmable Gate Array; a chip programmable for specific hardware tasks post-manufacturing GPU – Graphics Proccessing Unit; a processor specialised for highly parallel tasks like machine learning LLM – Large Language Model; an AI model trained on massive text datasets to generate or understand language Multimodal – An AI that processes and integrates multiple data types (text, images, audio, video etc) Neuromorphic Processor – a chip that uses artificial neurons to mimic the human brain NLP – Natural Language Processing; an AI’s ability to understand, interpret and generate human language Organoid – a simplified version of an organ designed to imitate it RTOS – Real-Time Operating System; an operating system that guarantees timely processing for critical tasks Tactel – Tactile Element; a sensor element that detects touch, pressure or texture information Teleoperation – operating a machine remotely TPU – Tensor Processing Unit; a Google- designed chip optimised for accelerating machine learning workloads. Transformer – a neural network architecture that uses attention to process sequential data efficiently VLA – Vision-Language Action; an AI that combines visual input and language to perform actions or tasks VLM – Vision-Language Model; an AI that Fig.14: two Unitree G1 robots fighting in the Mecha Fighting Series. Source: China Media Group. siliconchip.com.au Australia's electronics magazine combines image understanding with text comprehension and generation November 2025  25 with either a machine or another human, and determining if they can distinguish between the two. If the human cannot distinguish between the two, the computer is deemed to display true intelligence. In 2022, ChatGPT-4 passed a rigorous implementation of the Turing test, the first time a computer did so, leading some to speculate that the Turing test was not a strict enough test for machine intelligence. Since then, uncanny valley moving still humanoid robot healthy person bunraku puppet affinity stuffed animal 50% corpse Ethics Clearly, AI and robotics are improving by the day, and it won’t always be for the good of humankind. Consider a mass-produced army of military robots produced by a hostile power, or robots used for crime and violence. As John Connor said of The Terminator, “It can’t be bargained with. It can’t be reasoned with. It doesn’t feel pity or remorse or fear and it absolutely will not stop”. We are not at that stage yet, but it may happen within the lifetimes of many readers, maybe even within ten years. Humanoid robots and artificial limbs industrial robot human likeness other systems like LLaMa-3.1 and GPT4.5 have also passed Turing tests. 100% prosthetic hand zombie Fig.15: the ‘uncanny valley’ describing the possible emotional response to various humanoid robots compared to their likeness to humans. One curve is for a moving robot, the other for a still one. They both become significantly negative before reaching the positive response to a human. Source: https://w. wiki/EoPq The development of humanoid robots also has benefits for artificial limbs for humans, as the basic design of a human-like limb for a robot will also be suitable for use with humans. Our article about Artificial/Prosthetic Limbs in March 2025 (siliconchip.au/ Article/17782) discussed this. The limbs of Tesla’s Optimus have been proposed for this purpose. The uncanny valley The “uncanny valley” is a psychological response to humanoid robots at various levels of realism, developed by Japanese roboticist Masahiro Mori. It speculates that a robot which is ‘almost human’ in appearance will elicit an eerie response that a more human or less human looking robot would not – see Fig.15. Another example could be the Ameca robot by Engineered Arts, due to its very realistic facial motions (see Fig.16; https://engineeredarts.com/ robot/ameca). Or the Sophia robot by Hanson Robotics (see Fig.17; www. hansonrobotics.com/sophia). There is some experimental evidence that this phenomenon is real. It suggests that certain design elements should be incorporated into humanoid robots to avoid revulsion (for example, making them look clearly different from people). Next month Fig.16: Ameca is a robot with a realistic-looking head developed by Engineered Arts. Source: https:// engineeredarts.com/robot/ameca/ 26 Silicon Chip Fig.17: another robot with a realisticlooking head is Sophia by Hanson Robotics. Source: https://www. hansonrobotics.com/sophia/ Australia's electronics magazine The second half of this series will be published next month. It will describe notable historical and current humanoid robots, like those shown on the SC lead page. siliconchip.com.au EXPLORE THE ELEGOO® RANGE (AU) TL4976 TL4984 TL4830 EXPLORE THE ELEGOO® RANGE (NZ) TL4842 NEW DIMENSIONS. NEW POSSIBILITIES. 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Jaycar reserves the right to change prices if and when required. RP2350B Computer Words & MMBasic by Geoff Graham | Design & Firmware by Peter Mather This board is an improved version of the Pico 2 Computer that requires almost no soldering, has more I/O pins available, a much improved stereo audio output and a few other nice tweaks. › RP2350B Computer Assembled Module (SC7531, $90) includes a fully-assembled PCB, except for the optional components › RP2350B Computer Front & Rear Panels (SC7532, $7.50) pre-cut panels with white silkscreen printing on a black solder mask W e introduced the Pico/2/Computer, in the April 2025 issue, a lowcost computer that can run BASIC and is excellent for creating programs, games, controlling external circuits and generally messing around with an easy-to-use but capable computer. It was based on the Raspberry Pi Pico 2 module, which was one of the few components you had to solder to PWM PWM0B Serial COM1 RX PWM1B PWM2B COM2 RX PWM9B PWM10B PWM11B PWM8B PWM9B PWM10B I²C SCL ANALOG PINS 28 Silicon Chip SPI TX I²C SCL I²C2 SCL COM1 RX SPI TX I²C SCL I²C2 SCL COM2 RX SPI TX I²C SCL I²C2 SCL COM2 RX SPI TX I²C SCL I²C2 SCL COM1 RX SPI I²C SCL I²C2 SCL PWM3B PWM8B I²C SPI2 TX the mostly preassembled circuit board. Since then, the RP2350 processor chip, which is at the core of the Pico 2 module, has become available for individual purchase. Using an expanded version of this chip has allowed us to update the design with more features. The new features of this design are: ∎ It uses an RP2350B processor soldered directly to the PCB with supporting components that make Function I/O Pin Function GND 1 2 GND 3.3V 3 4 3.3V overclocking of the processor (to support HDMI video) easier. That also means you no longer need to obtain and solder a Pico 2 module to the board; it’s now fully pre-assembled. ∎ It includes a proper audio output with a built-in digital-to-analog converter (DAC) to deliver high-fidelity, noise-free stereo audio. ∎ It provides more general purpose I/O (GPIO) pins for connecting to SPI I²C Serial PWM COM1 TX PWM0A GP01 5 6 GP00 SPI RX I²C SDA GP03 7 8 GP02 SPI CLK I²C2 SDA GP05 9 10 GP04 SPI RX I²C SDA GP07 11 12 GP06 SPI CLK I²C2 SDA PWM3A GP33 13 14 GP34 SPI CLK I²C2 SDA PWM9A GP35 15 16 GP36 SPI RX I²C SDA GP37 17 18 GP38 SPI CLK I²C2 SDA GP39 19 20 GP40 SPI2 RX I²C SDA GP41 21 22 GP42 SPI2 CLK I²C2 SDA GP43 23 24 GP44 SPI2 RX I²C SDA GP45 25 26 GP46 SPI2 CLK I²C2 SDA 5V 27 28 5V GND 29 30 GND Table 1 – GPIO Pin Capabilities Australia's electronics magazine PWM1A COM2 TX COM2 TX PWM2A PWM10A PWM11A COM2 TX PWM8A PWM9A COM1 TX PWM10A PWM11A note that pin 1 is at the bottom right of the PCB siliconchip.com.au external circuits. This includes seven that are analog-capable (they can measure voltages). ∎ It has support for a PSRAM chip that can add 6MiB of additional RAM for MMBasic. ∎ It uses a larger flash memory chip that provides a 14MiB internal “A:” drive. This version does not make the original design obsolete; rather, it adds some polish and a few bonus features to the original design. For readers who missed the original Pico/2/Computer article, the basic features of both designs are: ∎ A low-cost boot-to-BASIC computer with keyboard support and video output. ∎ DVI/HDMI video output with resolutions up to 1280 × 720 pixels. ∎ Support for up to four USB devices, including keyboards, mice and game controllers. ∎ A microSD card socket supports cards formatted in FAT16 or FAT32 with capacities up to 32GB. ∎ An accurate internal clock that is battery backed. ∎ A built-in full-featured BASIC interpreter that includes its own fullscreen editor, support for programs up to 184kiB and general purpose RAM of 220kiB. Both versions are self-contained, low-cost computers that can be programmed in BASIC. You can have fun creating your own programs, learning or teaching programming, or simply have fun exploring an easy-to-use computer with a lot of potential. They also make capable embedded controllers. Video output The video output is DVI/HDMI in six resolutions: 640 × 480, 720 × 400, 800 × 600, 848 × 480, 1280 × 720 and 1024 × 768 pixels. The firmware generates a DVI signal, but HDMI monitors automatically support DVI, so this is transparent. It means we can use an HDMI connector, which is the standard for modern monitors. However, you cannot use other HDMI features, such as audio, over the HDMI cable. Using the MODE command, you can select a variety of colours and resolutions, with lower resolutions supporting more colours. The built-in BASIC program editor uses the full resolution and, by using the TILE functionality, colours characters for you. Keywords are cyan, comments are green etc. This siliconchip.com.au makes for a colourful and intuitive program editing experience. Four Type-A USB sockets are provided, supporting USB keyboards, mice and game controllers. The keyboard input includes support for the function keys, arrow keys, etc and can handle wireless keyboards with a USB dongle, so you do not need to be restricted by a cable. A USB mouse is very useful with the built in MMBasic program editor, where it gives you the ability to position the insert point and copy and paste using the mouse. Within a BASIC program, you can query the mouse position and the state of the buttons and, as with the keyboard, you can also use a wireless mouse. One or two USB game controllers can also be used. Within the BASIC program, you can get the current position of the joystick and discover what buttons are pressed. This is most useful if you are creating games for the computer. Digital audio A new feature in this Computer is the I2S interface to a DAC (digital-­toanalog converter) for the audio output. I2S was developed by Philips Semiconductor (now NXP Semiconductors) as an interface for transferring digital audio between a microcontroller and a DAC in an appliance. The Pico/2/Computer used a pulsewidth modulation (PWM) scheme for generating its audio output, which required a low-pass filter to remove the carrier frequency. This is a simple method for generating the audio but, despite an advanced filter design, some of the carrier frequency was still in the output, and the filter reduced the high frequency range of the audio signal. In this design, the I2S signal is processed by a dedicated 32-bit audio DAC chip. The I2S protocol transfers data as numbers, so the audio frequency response is perfectly flat from 20Hz to 20kHz. Purists with good audio systems will appreciate this feature as MMBasic can play files in high-quality stereo WAV, FLAC, MP3 or MOD formats. External storage is provided by a microSD card slot, which can accept cards up to 32GiB formatted in FAT16 or FAT32. The files created can be read/written on personal computers running Windows, Linux or macOS. The PicoMite firmware uses the SPI Australia's electronics magazine Processor: Raspberry Pi RP2350B (dual-core ARM Cortex-M33 & dual Hazard3 RISC-V) Clock Speed: 252-375MHz (depending on the video resolution) Firmware: PicoMite/MMBasic V6.00.03 or greater Non-volatile program memory: 184kiB General usage RAM: 220kiB (expandable to over 6MiB) Internal File Storage: 14MiB Removable file storage: microSD Card, FAT16/FAT32, up to 32GiB Video output: DVI via an HDMI connector <at> 640 × 480, 720 × 400, 800 × 600, 848 × 480, 1280 × 720 or 1024 × 768 pixels Audio output: 5.5V peak-to-peak (2V RMS), response flat from 20Hz to 20kHz Audio formats supported: singlefrequency tones, stereo WAV, FLAC, MP3 & MOD USB ports: four Type-A for peripherals, one Type-C for power/ console and one micro Type-B for firmware loading Keyboard support: standard or wireless USB keyboard (without a built-in mouse) Mouse input: standard or wireless USB mouse Gamepads: up to two SNES controllers with USB Type-A connectors Clock: battery-backed real-time clock & calendar (typical accuracy ±3sec/month) External console: serial over USB <at> 115200 baud via the USB Type-C socket External I/O connector: 30 pins with 22 GPIOs, including 7 with analog input ability, plus ground, 3.3V and 5V outputs Power supply: 5V <at> 220mA via the rear USB Type-C socket PCB size: 100 × 90mm Optional case size: 130 × 100 × 30mm November 2025  29 30 Silicon Chip Australia's electronics magazine siliconchip.com.au protocol to communicate with the card, with all types (Class 4, 10, UHS-1 etc) being supported. A battery-backed real-time clock and calendar (RTCC) keeps track of the correct time, which can be accessed from within a BASIC program. It is also used to stamp files with the correct creation time. This clock is very accurate (within a few seconds per month), and is supported by a battery when the power is removed, so you will rarely need to set the time. For controlling external devices and circuits, 22 GPIO pins are brought out to a 30-pin connector on the rear panel. All of these can be set as a digital input, digital output or a mixture of serial I/O, I2C, SPI, PWM and analog inputs. Also provided on this connector are the ground pins, +5V and +3.3V power supply outputs. Table 1 lists the pins on this connector and their functions. Circuit details Fig.1: this is the full circuit for the RP2350B Computer. At the centre is the RP2350B processor in a QFN-80 package. It has 48 general purpose I/O (GPIO) pins, many of which are used for internal functions, with the rest routed to the I/O connector on the rear panel (CON8). Other major components are the four-port USB hub (IC20), the stereo audio DAC (IC27) and the power supplies (including REG1 & REG34). siliconchip.com.au Australia's electronics magazine Fig.1 shows the full circuit for the RP2350B Computer, which is based around the RP2350B processor (IC28) in an 80-pin QFN package. This chip has 48 GPIO pins, many of which are used for internal functions (HDMI/ DVI video, SD card interface etc). As noted above, 22 are routed to the I/O connector (CON8) on the rear panel. The default clock rate for the RP2350B processor is 150MHz, but to generate HDMI video, we need to overclock it up to 375MHz. To support this, we use an integrated crystal oscillator to generate the base clock of 12MHz, which is multiplied in the RP2350B to give the core CPU clock. Using a dedicated oscillator results in a more stable clock with much less jitter than using a simple crystal as used in the Raspberry Pi Pico 2 module, which helps with overclocking. The RP2350B has eight analog inputs (pins 49 to 58), with seven of these available on CON8. To support accurate analog measurements, we have included a noise filter for the AVDD pin on the chip. AVDD is used as the reference for analog measurements and this filter, along with the PCB layout and a noise-free 3.3V supply, ensure that accurate and noise-free analog measurements can be made. Flash & PSRAM memory The PicoMite firmware, the BASIC program and other data is held in IC6, November 2025  31 The RP2350B Computer uses a small 100 × 90mm PCB with the RP2350B processor soldered directly to the board. This is difficult to hand-solder, so we recommend either buying the board fully assembled from the Silicon Chip shop, or having it assembled by a company with a pick & place machine. a Winbond W25Q128JVSIQ 128Mbit (16MiB) flash memory chip. This uses a quad SPI interface, and is designed to allow the RP2350B to execute its program directly from this chip. It can also operate with high clock speeds on the quad SPI interface (133MHz), which means that it can keep up when the RP2350B is overclocked. Even though the SPI interface transfers data four bits at a time, and has a high clock speed, it is still quite slow compared to the RP2350B’s on-chip memory. To reduce this effect, the RP2350B uses a built-in SRAM cache, and the firmware is configured to move critical sections of its code to the on-chip RAM for execution. As a result, there is very little impact on the performance from using off-chip flash memory. On startup, the RP2350B checks if the flash memory is present and that it contains a valid program. If either are not found, it will automatically enter its firmware load mode. This involves creating a pseudo flash memory drive on the USB interface that looks like a USB drive to a Windows, Linux or macOS computer. You can use this interface to copy new firmware to the flash memory. In our design, the BOOT switch is 32 Silicon Chip used to pull the chip select line low on the flash memory chip, which essentially disables it. When used on powerup, this causes the RP2350B to enter its firmware loading mode. IC33 is an optional external PSRAM chip (APS6404L-3SQR-SN) that sits on the same quad SPI bus as the flash memory chip. This has a capacity of 64Mbits (8MiB) and is used to expand the internal RAM of the RP2350B. The PicoMite firmware will automatically add this to the general purpose RAM seen by the BASIC interpreter, allowing the BASIC program to define very large arrays. The internal RAM of the RP2350B is more than enough for the vast majority of applications, so we have left this footprint vacant on assembled boards. Still, if you want to create truly enormous arrays in MMBasic, you can easily add the specified chip yourself. It comes in an easy-to-solder package and MMBasic will automatically recognise it once it is installed. Be warned that PSRAM is a lot slower than the internal RAM, so there will be a performance penalty when using the extra RAM it provides. USB interfaces The RP2350B processor includes a Australia's electronics magazine USB interface and this, along with an onboard USB hub, provides four USB ports for a keyboard, mouse and gamepads. The hub function is provided by IC20, a CH334F integrated USB 2.0 four-port hub. This chip includes the USB 2.0 driver circuits (called the USB PHY) that directly drive the four USB Type-A sockets on the front panel. The CH334F also uses an ingenious system to drive the indicator LEDs showing which USB ports are active. Some CH334F chips on the market have a fault that causes the power protection feature of the CH334F to interfere with its operation so, in our design, we disable this feature. Resettable fuse PTC1 provides the necessary protection anyway. To load MMBasic onto IC28, you need to disconnect the hub and directly access the USB interface on the RP2350B. This is done with two switches (S16), which isolate the hub, and an additional Type-B micro-USB connector mounted on the PCBs front edge (CON5). This is only used to load the MMBasic firmware; the procedure will be described in detail later. Because the USB interface on the RP2350B is used for communicating with the USB hub, it cannot be used for a serial-over-USB console to siliconchip.com.au communicate with a desktop or laptop computer. Having the serial console is handy for connecting to such a computer, so we use a CH340C serial-toUSB bridge chip (IC7) to provide such a console interface. The CH340C is in a 16-pin package that includes the oscillator required to maintain the accurate timing needed for USB. It converts a TTL asynchronous serial signal from the RP2350B to a USB 2.0 signal using the CDC (communication device class) protocol over USB. IC19 is a DS3231 real-time clock & calendar (RTCC) that provides the time and date to MMBasic. This is an extremely accurate timekeeper with an integrated temperature compensated oscillator (TCXO) and it will typically keep the time within a few seconds per month. This uses a 210mAh 3V lithium coin cell (CR2032) as the backup; the DS3231 will automatically switch to this when the 3.3V power is removed. The current drawn from this cell is very low, so the battery should last for many years. The HDMI interface is one of the simpler parts of the circuit. The eight signal lines from the RP2350B are directly connected via 220W resistors to the HDMI connector (CON1), with no other components needed. The RP2350B produces a DVI signal, but HDMI transparently supports DVI so this works as the user would expect. The SD card interface is also quite simple, with the SD card plugged into CON6 being directly driven by four sequential signal lines from the RP2350B (GPIO29 to GPIO32). The stereo audio output is generated by the firmware running on the RP2350B as an I2S data stream, which is fed to IC27, a Texas Instruments PCM5102APWR 16/24/32-bit audio DAC. Three signal lines from the RP2350B (GPIO10, GPIO11 and GPIO22) form the I2S channel. The DAC generates two analog audio outputs of about 2V RMS, which are coupled to the audio output jack, CON7. Power supply The input power for the board is +5V supplied via the rear panel USB-C socket for power and the external console (CON2). The 5V rail powers the front-panel USB ports, but the rest of the Computer runs from 3.3V. A simple AMS1117-3.3 linear regulator, REG1, produces the 3.3V rail. Using siliconchip.com.au Parts List – RP2350B Computer (also see BOM XLS file) 1 double-sided PCB coded 07204251, 90 × 100mm 1 Multicomp MCRM2015S or Hammond RM2015S instrument case (optional) AND 1 pair of black front & rear panel PCBs (07204252-3, 124 × 27mm each) OR 4 M3-tapped Nylon spacers and M3 × 6mm panhead machine screws (for feet) 1 CR2032 3V lithium coin cell (BAT1) 2 10μH 500mA 0.32W M2012/0805 SMD inductors (L13, L14) [Microgate MGFL2012F100MT-LF] 1 10μH 15mA 1.15W M2012/0805 SMD inductors (L29) [Sunlord SDFL2012S100KTF] 1 30V 750mA resettable polyfuse, M3216 size (PTC1) [BHFuse BSMD1206-075-30V] 1 latching right-angle PCB-mount pushbutton (S13) [XKB Connectivity XKB5858-Z-E] 1 right-angle tactile pushbutton switch, 6mm actuator (S15) [HCTL TC-6615-7.5-260G] 1 dual DIP switch (S16) [YE DSWB02LHGET] 1 momentary SMD tactile pushbutton switch (S17) [XKB Connectivity TS-1187A-B-A-B] Connectors 1 CR2032 cell holder (BAT1) [Myoung BS-04-A1BJ005] 1 HDMI socket (CON1) [HCTL HDMI-01] 1 USB-C Socket (CON2) [Kinghelm KH-TYPE-C-16P] 2 right-angle horizontal stacked USB Type-A sockets (CON3, CON4) [Shou Han AF SS-JB17.6] 1 USB micro Type-B socket (CON5) [Shou Han MicroXNJ] 1 microSD card socket (CON6) [Shou Han TF PUSH] 1 SMD stereo audio jack socket (CON7) [Shou Han PJ-313 5JCJ] 1 2×15-pin right-angle 2.54mm-pitch header (CON8) [HCTL PZ254-2-15-W-8.5] 1 3-pin header, 2.54mm pitch (CON9) (optional; for serial wire debugging) 1 50kW 3.8 × 3.6mm SMD trimpot (VR1) [Bourns TC33X-2-503E] Semiconductors 1 Raspberry Pi RP2350B microcontroller, QFN-80 (IC28) 1 128Mbit QSPI flash memory, SOIC-8 (IC6) [Winbond W25Q128JVSIQ] 1 CH340C serial/USB bridge, SOIC-16 (IC7) 1 DS3231MZ real-time clock & calendar, SOIC-8 (IC19) 1 CH334F quad USB hub, QFN-24 (IC20) 1 MAX809R reset supervisor IC, SOT-23-3 (IC24) 1 PCM5102APWR stereo DAC, TSSOP-20 (IC27) 1 APS6404L-3SQR-SN 64Mbit QSPI PSRAM, SOIC-8 (IC33) (optional) 1 12MHz crystal resonator, 3.2 × 2mm SMD-4 (X1) [YXC X322512MSB4SI] 1 12MHz oscillator module, 3.2 × 2mm SMD-4 (XO4) [TOGNJING XOS32012000LT00351005] 1 AMS1117-3.3 low-dropout 3.3V linear regulator, SOT-223-3 (REG21) 1 TPS7A7002DDAR adjustable low-dropout voltage regulator, SOIC-8 (REG34) 1 AP2317A P-channel Mosfet, SOT-23-3 (Q2) 1 red SMD LED, M2012/0805 size (LED1) [Foshan NationStar NCD0805R1] 1 red SMD LED, M1608/0603 size (LED2) [Hubei KENTO Elec KT-0603R] 5 green SMD LEDs, M1608/0603 size (LED3-LED7) [Hubei KENTO Elec KT-0603R] 2 SS14 40V 1A schottky diodes, SMA package (D1, D2) Capacitors 3 100μF 6.3V B-case tantalum electrolytic [AVX TAJB107K006RNJ] 1 22μF 25V X7R M3216/1206 ceramic [Samsung CL31A226KAHNNNE] 7 10μF 50V X5R M3216/1206 ceramic [Samsung CL31A106KBHNNNE] 1 10μF 25V X5R M2012/0805 ceramic [Samsung CL21A106KAYNNNE] 2 2.2μF 16V M1608/0603 X5R ceramic [Samsung CL10A225KO8NNNC] 1 2.2μF 6.3V M1206/0402 X5R ceramic [Samsung CL05A225MQ5NSNC] 2 100nF 100V M2012/0805 X7R ceramic [Samsung CL21B104KCFNNNE] 2 100nF 50V M2012/0805 X7R ceramic [Yageo CC0805KRX7R9BB104] 1 100nF 50V M1206/0402 X7R ceramic [Samsung CL05B104KB54PNC] 23 100nF 16V M1206/0402 X7R ceramic [Samsung CL05B104KO5NNNC] 1 10nF 50V M2012/0805 X7R ceramic [Samsung CL21B103KBANNNC] 2 2.2nF 50V M2012/0805 NP0/C0G ceramic [Samsung CL21C222JBFNNNE] 1 1nF 50V M2012/0805 X7R ceramic [Samsung CL21B102KBCNNNC] Resistors (all SMD 1%) 1 1MW (M1206/0402 size) 2 1kW (M1608/0603 size) 2 20kW (M1206/0402 size) 3 470W (M1608/0603 size) 2 10kW (M2012/0805 size) 2 220W (M2012/0805 size) 4 10kW (M1206/0402 size) 9 220W (M1608/0603 size) 2 5.1kW (M1206/0402 size) 2 10W (M2012/0805 size) 1 4.7kW (M2012/0805 size) 1 2.2W (M2012/0805 size) a linear regulator avoids the electrical noise created by a switching regulator, which can interfere with sensitive circuits such as analog inputs. A system supervisor device (IC24, MAX809R) is used to monitor the 3.3V power rail and provide a reset signal to the RP2350B processor, to ensure it shuts down cleanly when the power is removed. It drives the reset pin of the RP2350B low immediately when the voltage falls below a certain threshold, and will maintain it low for a short time after it has risen above the threshold. In addition to the main 3.3V power supply, the RP2350B needs a second power supply called the Digital Core Supply (DVDD), which powers the CPU cores. Normally this is 1.1V, but for the clock speeds needed to generate HDMI video, it needs to be set higher (typically 1.3V). In the Raspberry Pi Pico 2 module, this voltage is provided by a switching regulator that is integrated in the RP2350 chip but that causes some problems, including the need for an expensive and hard-to-source inductor. To avoid this, we use an external linear regulator, a TPS7A7002DDAR (REG34), which must be correctly adjusted before power is applied to the computer. The procedure for this is described later. Building it Fig.2 shows where all the parts go on the PCB. Like the Pico/2/Computer, this design makes extensive use of surface-mounting parts. While these can all be hand-soldered, it is not easy, and can be quite time-consuming. So, while it is possible to assemble this computer by hand, we recommend either buying it assembled from siliconchip.com.au/ Shop/20/7531 or having it assembled by a PCB fabricator. For the latter, we recommend JLCPCB in China. The process of ordering the assembled boards from them is simple. First, download three files from the siliconchip.au/Shop/10/3259. These are “RP2350B Computer Gerbers.zip”, which contains the design files for the PCB, “RP2350B Computer BOM.xlsx”, which is the Bill of Materials (parts list), and “RP2350B Computer CPL.xlsx”, which contains the component positions on the PCB. On the JLCPCB website (https:// jlcpcb.com), click on the “Instant Quote” button and drag the “RP2350B 34 Silicon Chip Fig.2: the overlay diagram for the RP2350B Computer. We recommend having the board preassembled due to the QFN-80 package RP2350B microcontroller. Note: if you’re not using the Computer with an enclosure, make sure not to leave it where children have access to it alone. Due to the risk of them swallowing the cell. Computer Gerbers.zip” file onto the blue button labelled “Add Gerber File”. JLCPCB will then read the files, display an image of the PCB and fill in the defaults for manufacturing options such as thickness, colour etc. You might want to select a different colour for the solder mask, but you can leave these options at the suggested defaults. Scroll to the bottom of the page and select “PCB Assembly”. This will display more options, which you can also leave at their defaults – other than selecting how many boards you want them to assemble (their minimum is two). Then click on the “Next” buttons until you reach the page requesting the BOM and CPL files. Add these files, then click on the “Process BOM and CPL” button. The website will display a list of the parts, the quantity and their prices. All the components should be in stock but, if not, you can search for a substitute or even omit it and source it separately (which implies that you will solder it yourself). Clicking “NEXT” again will take you to the final quote detailing the total price and by clicking on “SAVE TO CART”, you are done. You then need to go through the usual payment process. to mount it in a case. All you need is four rubber feet stuck to the bottom of the PCB to avoid scratching your desk (or tapped spacers in the corners, for the same reason). However, the PCB is designed to fit in a Multicomp MCRM2015S enclosure available from element14/Farnell. The same enclosure is also available as the Hammond RM2015S from Mouser, DigiKey etc. For the front and rear panels, we have designed black PCBs with the lettering in white text. These can be ordered from the Silicon Chip shop or from a PCB fabricator (for this, download the Gerber files from the Silicon Chip website). One nice thing about these panels is they have all the required holes, round or rectangular, neatly cut out for you! If you are ordering the panels from JLCPCB, you should tick the option “Order Number (Specify Position)”, as that instructs JLCPCB to place their tracking number on the rear of the panel. In the “PC Remark” section, you should add a note informing them that this design does not have any tracks and will be used as a front or rear panel on a box. Otherwise, they may reject the design as being incomplete. Boxing it up When you receive the assembled boards, there are three steps that you need to take: The RP2350B Computer’s PCB is quite small, so you do not really need Australia's electronics magazine Setting it up siliconchip.com.au On the rear panel (from left to right) are the 30-pin external I/O connector with 22 GPIOs, the HDMI video connector, the power switch, a USB Type-C connector for power and the external console, a reset button, and the stereo jack for the audio output. 1. Adjust potentiometer VR1 to set the DVDD voltage. It is important that this is done before power is applied. Leaving the potentiometer in some random position could destroy the RP2350B processor. 2. Load the PicoMite firmware. 3. Configure the firmware. By increasing the Digital Core Supply (DVDD) above the nominal 1.1V, we can overclock the RP2350B to reach the clock speeds (up to 375MHz) required to generate HDMI video. It is important that this is set before applying power to the board, as too high a voltage will certainly damage the RP2350B. Set your multimeter to its resistance mode and, with the board unpowered, place the probes across the test points marked DVDD and TP1. Adjust potentiometer VR1 to give a reading of 18kW. This will set the DVDD voltage to 1.3V when the board is powered, and that should allow the RP2350B to correctly boot and generate a clear and stable DVI/HDMI video signal. To load the firmware, start with no power applied and flip both switches on the PCB marked USB HUB to the DISABLE position. Then place the RP2350B into bootloading mode by holding the BOOT button down while plugging a USB cable from the front micro-USB socket into your desktop or laptop computer. siliconchip.com.au This will power up the Computer, causing the RP2350B to act like a USB memory stick and create a “disk drive” on your computer via the USB cable. The RP2350B Computer requires MMBasic version 6.00.03 or later, as this has support for I2S audio. You can download this from siliconchip. au/Shop/6/833 or the author’s website at https://geoffg.net/picomitevga. html (scroll to the bottom of the page). Extract the file PicoMiteHDMI­ USBV6.00.03.uf2 (or a later version) from the ZIP. You can then copy this file to the “disk drive” created by the RP2350B, and it will write the contents of the file to the flash memory chip. When it finishes, unplug the USB cable from the front USB socket and flip both switches on the PCB marked USB HUB to the ENABLE position. This will enable the USB hub and the front panel USB sockets. While the virtual drive created by the RP2350B looks like a USB memory stick, it is not; the firmware file will vanish once copied, and if you try copying any other type of file, it will be ignored. If you later upgrade the firmware, note that loading the PicoMite firmware may erase all the flash memory, including the current BASIC program, any files in drive A: and all saved variables. So make sure that you backup this data first. Australia's electronics magazine For the final configuration step, you need a desktop or laptop computer (or another USB serial console capable device) and use that to connect to the external console on the RP2350B Computer. This process is described in the panel overleaf. At the command prompt on the external console, enter the following command: OPTION RESET HDMIUSBI2S This will set up the firmware for your hardware configuration, including enabling the DVI/HDMI video output, and will save you from having to enter multiple OPTION commands for each hardware feature. After that, you can connect an HDMI monitor and keyboard/mouse, press the reset button and you should see the MMBasic startup banner on the monitor, as shown in Screen 1. This is also a good time to set the date and time for the real-time clock. The command to do this is: RTC SETTIME year, month, day, hour, minute, second Here, “year” is two or four digits, and “hour” is in 24 hour notation. Don’t forget to insert a CR2032 cell in the holder so the time will be remembered. As a final test, use the command: OPTION RESOLUTION 1024 November 2025  35 Screen 1: when you have loaded the PicoMite firmware, configured it and rebooted the computer, this is the startup screen that you should see. At this stage, you are ready to start running programs or creating your own. This will set the HDMI output to its maximum resolution of 1024 × 768 pixels, and set the CPU clock speed to its maximum of 375MHz. The result should be a stable image on your monitor. Adjusting DVDD As described earlier, we need to increase the DVDD voltage, which powers the CPU cores, to facilitate overclocking. This is done by adjusting the onboard potentiometer as per Table 2. By default, the RP2350B requires a DVDD of 1.1V, which is generally good for clock frequencies of up to about 220MHz. However, the firmware with HDMI capability will automatically set the clock frequency in the range of 252MHz to 375MHz, depending on the selected video resolution, so a higher voltage is needed. We have tested many prototypes and found that a DVDD of 1.3V generally works well, which is why we recommend setting this voltage when configuring the board. However, if your Computer will not boot or shows strange behaviour, you can try DVDD voltages of 1.35V or 1.4V to see if that corrects the problem. The absolute maximum that you should select is 1.45V. If your Computer still does not work, it is likely Resistance (TP1-DVDD) DVDD 6.0kΩ 1.10V 9.0kΩ 1.15V 12.0kΩ 1.20V 15.0kΩ 1.25V 18.0kΩ 1.30V 21.0kΩ 1.35V 24.0kΩ 1.40V 27.0kΩ 1.45V 30.0kΩ 1.50V * 33.0kΩ 1.55V * 36.0kΩ 1.60V * * not recommended due to instability 36 Silicon Chip that overclocking is not the cause of your problem. Instead, you probably have some other fault on the board, which you should find and fix, rather than pushing the DVDD voltage even higher. You can set DVDD to voltages even higher than 1.4V if you wish to run the risk of damaging the RP2350B – but all processors should work correctly with 1.3V or 1.35V. You can also try DVDD voltages lower than 1.3V, and the RP2350B will run slightly cooler. However, this benefit will be limited, as raising the DVDD voltage and overclocking the processor only causes its temperature to increase by a few degrees Celsius. Fault finding While testing the settings for the DVDD voltage, it is possible to get the RP2350B and the firmware into a state where MMBasic will not boot or display a stable image on the monitor. If that happens, adjust the DVDD potentiometer to 6kW (giving a DVDD of 1.1V) and load the firmware file at: https://geoffg.net/Downloads/ picomite/­Clear_Flash_RP2350.uf2 This will reset the RP2350B to its factory state, allowing you to retry the setup procedure from the start. A good test of a correctly functioning RP2350B is to load the stock PicoMite firmware without USB and HDMI support. This will run the RP2350B at its default frequency of 150MHz, and does not require any support circuitry except the 3.3V power and a DVDD of 1.1V. To run this test, remove the power, then adjust the DVDD potentiometer to 6kW and set the onboard DIP switches to DISABLE. Then plug your desktop or laptop computer into the front panel USB socket while holding down the BOOT button on the PCB. You can then load the firmware file Pico­MiteV6.00.03.uf2 (or later) from the firmware download ZIP file. When this has completed, the firmware will create a serial-over-USB Australia's electronics magazine connection with your computer using the USB cable plugged into the front panel (leave the DIP switches in the DISABLE position). The PicoMite firmware user manual goes into detail on how to use this console connection, but with this you can load programs and test the processor as much as you like. If this simple test does not work, check the main power to the RP2350B (3.3V) and the DVDD voltage (1.1V). If these are correct, that leaves a faulty RP2350B chip or its soldering as the main suspects. Using MMBasic The BASIC interpreter in the Pico­ Mite firmware is called MMBasic. It is a modern implementation of the BASIC language that can handle large and complex programs. MMBasic includes features like long variable names, 64-bit integers, double-­ precision floating-point numbers and string variables. It does not need line numbers, and includes modern features such as subroutines/functions, CASE and multiline IF-THEN-ELSE statements. On startup, MMBasic will display the command prompt (the greater-than symbol, “>”) and wait for a command to be entered. It will also return to the command prompt if your program ends or generated an error message. When the command prompt is displayed, you can run a wide range of commands. For example, you can list the program held in memory (LIST) or run it (RUN). Almost any command can be entered at the command prompt, and this can be used to test a command to see how it works. A simple example is the PRINT command, which you can test by entering PRINT “Hello World” at the command prompt. To enter a program, you can use the EDIT command, which starts the integrated full-screen editor. This is described in detail in the PicoMite User Manual. However, if you want to give it a test, all you need to know is that anything that you type will be inserted at the cursor, the arrow keys will move the cursor and backspace will delete the character before the cursor. Finally, the F1 key will save the program and exit. The firmware will automatically create a pseudo 14MiB ‘disk drive’ in the flash memory. This is called siliconchip.com.au drive “A:”, and can be used to store programs, images, music, configuration data, log files and much more. In addition, SD cards formatted as FAT16 or FAT32 up to 32GiB can be used for removable storage, and are referred to within MMBasic as drive “B:”. Files created in this file system can be read on Windows, Linux and macOS computers. Both file systems support long filenames, subdirectories, long file paths, random access and more. The PicoMite User Manual is an invaluable resource that contains a detailed description of the capabilities of the firmware and the MMBasic interpreter. Particularly useful is a tutorial on programming in BASIC at the rear of the manual. It is written in an easyto-read format, with plenty of examples, and is recommended for anyone who is new to programming in BASIC. This manual is included in the firmware download from the Silicon Chip website or the author’s website at https://geoffg.net/picomite.html (scroll to the bottom of the page). MMBasic graphics features MMBasic has an extensive range of features that complement this computer’s colourful, high-resolution video. Most are associated with the type of graphics that you would need for games, but they are also useful for business graphics and general programs. These commands and functions are described in detail in the Pico­Mite User manual, and in a tutorial that is included with the firmware distribution files. Each DVI/HDMI resolution is selected with the OPTION RESOLUTION command and, for each resolution, there are a number of colour modes that can be selected with the MODE command. These modes will increase the visual size of each graphic pixel and use the memory saved to support more colours. For example, with the resolution set to 640 × 480 pixels, you can select MODE 1 which will result in a monochrome 640 × 480 pixel display, or MODE 4, which will quadruple the size of each graphic pixel and provide more colours so that the user will see an image of 320 × 240 pixels in 32,768 colours. In both modes, the physical monitor will continue to see a video signal with a resolution of 640 × 480 pixels. siliconchip.com.au Connecting to the External Console You communicate with MMBasic via the console, which is where you see the command prompt and type in your commands. In the RP2350B Computer, the main console is the keyboard and HDMI monitor, but you can also open an external console on your desktop or laptop computer. This is provided via the rear-panel USB connector, which is normally used to power the computer. However, it can also provide a serial-over-USB interface for the external console. This function is provided by the CH340C USB/serial bridge. This chip (and the similar CH341) is used in many Arduino Nano clones, and the driver for it is included by default in Windows 10/11 and Linux. Many macOS builds also include the driver. This means that you can simply plug your RP2350B Computer into your desktop computer and a connection will be automatically made. However, if you do need a driver, help is available at https://sparks.gogo. co.nz/ch340.html When you connect the RP2350B Computer, it will create a virtual serial port on your computer; you need to determine the number of this port. In Windows, this can be found in Control Panel → Device Manager → Ports (COM & LPT). The PicoMite User Manual included in the firmware download goes into more detail. On your desktop computer, you then need to run a terminal emulator. For Windows, we recommend Tera Term, which can be downloaded from http://tera-term.en.lo4d.com. Within the terminal emulator, you need to set the serial port number discovered above and set the baud rate to 115,200 baud (the default speed used by the RP2350B Computer). You should then be able to hit the Enter key in the terminal emulator and see the MMBasic command prompt (“>”). When you are connected to the remote console, you can treat it the same as a keyboard/monitor combination directly connected to the RP2350B Computer. You can issue commands, edit programs and run them. You can also use the XModem protocol to transfer files to and from both computers. The PCB is designed to fit in a Multicomp MCRM2015S or Hammond RM2015S enclosure. At lower left are the four USB Type-A ports that can accept USB keyboards, mice and game controllers. To the right of those is a micro Type-B USB connector for loading the firmware, and finally, a microSD Card connector that will accept cards formatted in FAT16 or FAT32 with capacities up to 32GiB. Australia's electronics magazine November 2025  37 Screens 2 & 3: the software package for the RP2350B Computer includes clones of two classic games, Tetris and Pacman. They are provided so that when you get your computer running, you can immediately start having fun! Colour is specified as a true colour 24 bit number, like on a PC. The top eight bits represent the intensity of the red colour, the middle eight bits the green intensity, and the bottom eight bits the blue. You also have at your disposal functions that give you shortcuts for selecting commonly used colours and defaults, such as the RGB() function. There are ten basic drawing commands that you can use within MMBasic programs to draw graphics. These include drawing lines, boxes, circles and even complex polygons. The TEXT command is one of these, and is particularly powerful, allowing text to be positioned anywhere on the screen in a variety of fonts and orientations. The RP2350B Computer includes eight built-in fonts. These range from tiny to large and most cover the full ASCII range, with some including extended graphics characters. You can also define your own fonts using the DEFINEFONT command; additional fonts are included in the PicoMite firmware download. These fonts cover a wide range of character sets, including a symbol font (Dingbats) that is handy for creating on-screen icons etc. Framebuffers, layers & sprites To create moving graphics like those used for games, MMBasic includes support for framebuffers and layers. These are areas of memory with the same width and height as the DVI/ HDMI image, and the same colour depth. Framebuffers can be used to construct an image that can then be rapidly copied to the physical display. Layer buffers are slightly different, and are used to create partial images that can sit on top of a background image, which can be moved over the static background. Sprites are very useful as they allow the programmer to display elements over a background and then move them over the background without corrupting the background image. In addition, the programmer can use the sprite functions to detect collisions between sprites and between a sprite and the edges of the display. The LOAD IMAGE and LOAD JPG commands can be used to load an image from a file and display it on the HDMI monitor. These can be used to draw a logo or add an ornate background to the graphics drawn on the screen. The 3D Engine provided by MM-­ Basic includes ten commands for manipulating 3D images, including setting the camera, creating, hiding, rotating etc. These are documented in a separate manual in the PicoMite firmware download, which provides a description of the 3D Engine and how to use it. Also included in the firmware download are clones of two classic games: Tetris and Pacman (see the screenshots). So, when you get your RP2350B Computer running, you can immediately start wasting time. SC Have fun! Most of the complexity is in the software loaded into the Raspberry Pi RP2350B processor. This has the same features as the RP2350A version used in the Raspberry Pi Pico 2, but comes in a larger package with more (48) I/O pins. The Raspberry Pi foundation has recently made this chip available for individual sale, so now we can use it in our own designs. We have designed black front & rear panel boards with the lettering in white. These can be ordered from the Silicon Chip Shop or a PCB fabricator. 38 Silicon Chip Australia's electronics magazine siliconchip.com.au TECH Spree! END OF YEAR altronics.com.au 360° adjustable stand with hanging hook. BONUS! 129 $ T 1345 X 0217 HOT SELLER! Ultra High Speed Mini Jet Blower Vac NEW! 29.95 $ This high power rechargeable fan/ vacuum is great for servicing computer equipment, cleaning keyboards - even inflating air mattresses for camping. T1346 FREE vacuum accessory valued at $14.95 High speed jet fan with up to 1.5 hours use per charge. USB C rechargeable. All metal design. If you use a few cans of air duster a year, it pays for itself in no time! Cool Air, Anywhere! This lightweight and easy to carry 3-in-1 portable fan provides a cool breeze anywhere you need it. 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A 0328 Multi Channel Wireless Doorbell Sale Ends November 30th 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 0011 H igh-performance commercial power rails probes are available, but they cost many thousands of dollars, putting them out of reach for most hobbyists. This project proves it does not have to be that way. The probe described here offers good performance for less than $100 in parts. Passive oscilloscope probes are not really suited to looking at the ripple, switching noise and transients that can occur on power rails, especially those produced by switching converters. These are usually millivolt-level signals that are riding on top of a comparatively high DC voltage. Also, there is usually a lot of radiated noise that can be picked up by a standard passive probe with its 150mm-long ground clip wire. You will have to switch your oscilloscope to AC coupling to eliminate the DC offset to get the vertical resolution necessary to see the ripple and noise. This is fine if you are only interested in high-frequency artefacts, but no good for transients with time constants in the milliseconds range, like those you might encounter with a step change in load. AC-coupling introduces a highpass filter with a cutoff frequency in the 1-10Hz range into the signal path, which means the low-frequency and DC components will not be displayed accurately. You may be able to use DC coupling if your scope’s offset control has sufficient range. However, on the millivolt ranges, the offset is typically limited to a volt or two, so you likely won’t be able to get the trace on the screen at all. A power rail probe sits between the power rail being measured and the oscilloscope. It typically has an input impedance of 50kW, so it does not load the power rail too much, and an output designed to connect to a scope input in 50W impedance mode. The probe allows the DC offset to be removed but preserves the bandwidth from DC all the way to the upper bandwidth of the scope. P wer Rail Probe This is one of those pieces of test equipment that you don’t really need, until you do. It allows the measurement and evaluation of ripple, switching noise and transients riding on DC supply rails. Project by Andrew Levido If your scope does not have a 50Ω termination option, you could use a separate terminator (for example, the Amphenol 112667). Commercial models typically offer bandwidth up to the GHz range, can offset ±25V DC and can handle active signals in the range of ±1V. They usually attenuate the signal slightly, but this attenuation is known – and importantly – is constant across from DC to the upper bandwidth limit. The Power Rail Probe described here meets most of those specifications. It has a DC input impedance of around 50kW and can offset power rails up to ±25V. It can handle a signal amplitude of at least ±1V and has a nominal attenuation of -1.7dB ±0.3dB from DC to at least 100MHz. The actual limit is almost certainly a fair bit higher, but that is how high I can measure with my test equipment. The whole thing is built into a small plastic case using the same look and feel as the Current Probe and Differential Probe described in the January (siliconchip.au/Article/17605) and February 2025 issues (siliconchip.au/ Article/17721). Like them, it is powered by a lithium polymer cell that can be recharged via a USB-C power source. Design The block diagram of the Probe is shown in Fig.1(a). There are two signal paths in parallel: a low-frequency path, where the DC offset is applied, and a high-frequency path that keeps the shape of the waveform intact. This architecture is necessary because the offset circuitry uses op amps and is therefore limited in bandwidth. We will come back to the design of the offset circuitry later, but first we will focus on the two signal paths. If we assumed the offset is zero and the buffer is perfect, the circuit reduces to the LC parallel topology shown in Fig.1(b). I have added the 50W load presented by the oscilloscope and shown a voltage source for clarity. You will probably identify this circuit as a classic LC notch filter. At the Figs.1(a) - (c): the Power Rail Probe has a low-frequency signal path for the offset and a parallel high-frequency path, so it has very high bandwidth. The two paths would form an LC notch filter unless we introduce some resistance to lower the Q. siliconchip.com.au Australia's electronics magazine November 2025  47 (or DC), the capacitor will present an infinite impedance, and the inductor will present a zero impedance, so the attenuation will be given by the voltage divider formed by Rs and Rl. At very high frequencies, the inductor will appear to have infinite impedance and the capacitor zero impedance, so the attenuation will again be Rl ÷ (Rs + Rl). Series-parallel equivalent circuit The PCB is sparsely populated & none of the devices are overly difficult to solder. resonant frequency of 1 ÷ (2π√LC), the LC network will appear to have infinite impedance, so the response will have a distinct notch as shown in Fig.1(c). The steepness and depth of the notch is dictated by the Q of the filter. We obviously don’t want such a dip in our frequency response, so we need to introduce some resistance into the circuit to lower the Q. We can do this by inserting resistors Rs in series with the inductor and capacitor, as shown in Fig.2(a). I have added the ‘S’ subscript to the inductor and capacitor values for reasons that will soon become apparent. These resistors should be equal in value to keep the attenuation constant at the extremes. For example, at very low frequencies It is hard to visualise what happens at the resonant frequency, since the capacitor and inductor are no longer in parallel. However, we can take advantage of a special property of complex impedances, called series-parallel equivalency. This just states that at any given frequency, there is a parallel and series combination of elements that behave identically when viewed from the terminals. Fig.2(b) shows us what the network would look like after transformation. This means that there is a parallel Rp/ Cp circuit that behaves exactly the same as the series Rs/Cs circuit in the high-pass branch, and a parallel Rp/Lp circuit that behaves exactly the same as the series Rs/Ls circuit in the low frequency branch at the resonant frequency. The component values in the parallel circuits will differ from those in the series circuits, but the behaviour will be the same. The formula in that figure shows how the parallel and series impedances are related. With this transformation, the inductor and capacitor are now in parallel, so will have an infinite impedance at the resonant frequency. The impedance of the two paths at this frequency will therefore be determined by the two resistors in parallel (Rp). To keep the attenuation at the resonant frequency the same as at high Figs.2(a) & (b): the resistors in series with the inductor and capacitor form voltage dividers with the load resistance at very high and very low frequencies. This parallel equivalent circuit (b) behaves identically to (a) at any given frequency if the values are chosen appropriately. This allows us to calculate component values for a flat frequency response. 48 Silicon Chip Australia's electronics magazine and low frequency cases, we need each Rp to be twice the value of Rs. Substituting this relationship into the equation for Rp in Fig.2, we can see that Rs must be equal to Xc or Xl (which will be identical to each other at the resonant frequency). Using either one of these, plus the expression above for the resonant frequency, gives us the result that, for a flat response, Rs should be equal to √L ÷ C. I chose Rs to be 10W to give an attenuation of 1.2 (around -1.7dB), in line with the commercial units. This means the inductance should be 100 times the capacitance (in terms of henries and farads), so I chose 10µH and 100nF – both readily available values. These values give a crossover frequency of around 159kHz. The low-frequency path Fig.3 shows the full circuit of the Power Rail Probe. The ‘ground’ of the main signal path circuit (the horizontal line across the middle) is produced by op amp IC1c and the divider at its input. It settles at half the battery (cell) voltage, around 1.85V. The power supply for the op amps is therefore between ±2.1V and ±1.8V depending on the cell’s state of charge. Op amp IC1a forms an inverting, summing amplifier which adds the input voltage (via a 51kW resistor) with an offset voltage derived from potentiometer VR1. The input voltage is amplified by a factor of -1 (ie, inverted) due to the op amp’s feedback resistor also being 51kW. The ±1.8V present at the wiper of VR1 is amplified by -15.5, offsetting the input voltage by up to ±27V (or more if the battery voltage is higher). The second op amp, IC1d, is configured as an inverting buffer to flip the signal back to the right sense. I have used a potentiometer with a mechanical detent and centre tap that is connected to the virtual ground. This makes the zero-offset point very easy to find. This is helpful because it is very easy to lose the trace on the millivolt range if the pot can shift the voltage by ±25V. An easy-to-find zero point makes it much easier to get the trace back on screen. That said, a standard three-terminal pot would work just fine. The choice of op amps is quite important for the proper operation of the circuit. For once, we don’t care siliconchip.com.au Fig.3: the circuitry is fairly straightforward, using op amps to generate an adjustable offset voltage that’s applied to the low-frequency signal path. Potentiometer VR1 is a little unusual in that it has a centre tap and detent, to ensure that its wiper is at signal ground when centred. too much about input offset voltages, since the whole circuit is designed to add an offset. As long as it is no more than a few millivolts, the trace should be on the screen with the pot centred. We also don’t have to worry too much about the op amp’s input common-­mode range because we are using inverting amplifiers, which have their input voltages fixed at zero, and we have split supplies. We do need to use op amps that can operate at low supply voltages, and we need a reasonable output capability, since IC1d is driving a 60W load, and we’d like to swing as close to the ±1.8V rails as possible. We need the same drive capability for IC1c, as it is driving the other end of the same load. The most important op amp selection criteria is bandwidth, or more specifically, phase shift; a requirement not necessarily obvious given that the crossover frequency is only 159kHz. You could be forgiven for assuming that an op amp with a bandwidth of a few MHz would be fine in this application. Fig.4 shows the open loop gain and phase of one candidate, the TLV2460 family. These look promising at first, with a rail-to-rail output swing, ±80mA output drive, ±2mV offset voltage and a bandwidth of 6.4MHz. siliconchip.com.au However, close examination of the phase plot reveals a problem. Most op amps have internal dominant pole compensation that rolls off the open-loop gain response at -20dB/decade, as shown here. It also means the phase shift through the op amp is around -90° over much of its bandwidth. This roll-off is necessary for the stability of the op amp. If the phase shift were to reach -180° before the gain dropped below unity (0dB), the op amp would oscillate. You can see from the plot that the phase shift through the op amp starts to drop from -90° at around 300kHz, and is down to -100° around 1MHz. This will be a problem for us, since any deviation from -90° will cause a phase shift in our closed-loop response. If there is an appreciable phase shift through the low-frequency path relative to the high-frequency path, the two signals will add destructively, and we will see a dip in the overall frequency response near the Fig.4: the open-loop gain and phase plot for the TLV2460, from its data sheet, shows that the phase begins to deviate from -90° at around 300kHz, well below its gain bandwidth (GBW) figure of 6MHz. Australia's electronics magazine November 2025  49 Fig.5: a -90° open-loop phase shift (red trace to blue trace) results in a near-zero closed loop phase shift for a non-inverting amplifier. The phase shifts are exaggerated for clarity in this diagram. Fig.6: the open loop gain and phase plot for the TPH2504 shows that the phase remains very close to -90° all the way to 10MHz or thereabouts. The horizontal scale of this graph is strange, though. crossover frequency when both signals are contributing to the total. Op amp phase shift can be a bit hard to wrap your head around. How can an op amp with an open-loop -90° phase shift produce an amplifier with zero closed-loop phase shift (or 180° with an inverting amplifier)? Hopefully Fig.5 helps explain this. The upper chart shows the input and output voltage waveforms of an op amp configured as a non-inverting buffer. The red trace is the input voltage applied to the non-inverting input, and the blue trace is the output voltage, which is also applied to the inverting input via the feedback. I have shown an exaggerated phase shift between them to make the point. The green trace shows the difference between these waveforms. This is the voltage between the op amp’s two input pins that is amplified to produce the output. In reality, this voltage will be tiny, due to the high open loop gain of the op amp, but it will not be zero. You can clearly see that the phase shift between this open loop input voltage and the output voltage is close to -90° because of the dominant pole. If this phase shift were to increase (in the negative direction) to -100° like the TLV2461’s data suggests, the phase shift between the input voltage and the output voltage would increase to -10°. The TLV2460 is therefore going to introduce a significant phase error near to the crossover frequency, and we have two of these op amps in series, doubling the problem. The solution is to choose an op amp with a much higher bandwidth and/or a much more stable open-loop phase response, up to 10MHz at least. A bit of searching turned up the 50 Silicon Chip TPH2504 family. This is an op amp from 3-Peak – a company I had never heard of until this year. They seem to make some op amps with very impressive price/performance ratios. This one has ±2mV input offset, ±100mA drive capability and 120MHz gain-bandwidth (GBW). A quad pack IC of these costs less than $3.00 in small quantities. Fig.6 shows the open loop gain and phase plot from its data sheet. I have to say that this is one of the dumbest graphs I have seen in a while, because the horizontal scale increase by a factor of 100 every major division instead of by a decade like every other log-frequency graph you have ever seen. Why? Nevertheless, you can see that the phase shift remains near -90° all the way to 10MHz. extraneous switching noise into a device that only exists to allow us to measure the switching noise of the circuit under test! Fortunately, as the required signal amplitude is limited to ±1V, it is feasible to use the battery voltage directly, with the signal common derived from the mid-point as described above. This decision has two design implications. The previous designs used an unprotected LiPo cell and relied on the under-voltage lockout built into the DC-DC converter IC to prevent over-discharge. Not having this feature means choosing a cell with a built-in protection circuit (or adding a separate protection circuit, which would make the overall circuit more complex). I also chose to use a standard connector to provide a bit more flexibility regarding cell choice. Any cell with Capacitor and inductor the requisite protection board and a There is not much else to say about JST PH style connector that fits in the the signal paths. I used a 100V C0G/ case should work. NP0 ceramic capacitor in the high-­ The second design implication is frequency path because we want the that we now have separate ‘grounds’ capacitance to remain constant with for the signal circuit (half the cell volttemperature and DC bias. Don’t substi- age) and the charging circuit (cell negtute another dielectric like X7R here. ative). In most cases, the signal comIn the low-frequency path, I chose mon will be connected to mains Earth an inductor with a reasonably tight via the oscilloscope’s BNC terminal. ±5% tolerance and a fairly high It’s also possible (likely?) that the USB (40MHz) self-resonance. A typical charging port, and hence the charging inductor has a tolerance of ±20%, common, will be grounded. so ±5% is pretty good without being Unless we fully isolate the two cirunnecessarily expensive cuits, there is the potential for a short circuit. The solution is to use a twoPower supply pole power switch to ensure the two Unlike the Differential Probe and circuits can never be connected to the Current Probe, the Power Rail each other. Probe cannot use a DC-DC converter The charging circuit is identical to to create the power rails. The last thing my previous designs. The input is a we want to do is to inject a bunch of power-only USB-C connector followed Australia's electronics magazine siliconchip.com.au Parts List – Power Rail Probe Fig.7: assembly should be quite easy and fast as there are only a few parts. Take care with the orientation of the LEDs, TVS diode and the quad op amp. by a resettable fuse and a 5V TVS protection diode. These are included to protect against a rogue USB-C source applying a voltage higher than 5V to the connector. The two 5.1kW resistors signal the USB C power source to supply 5V at up to 3A. Yellow LED1 illuminates when the LiPo cell is charging and goes out when full charge is reached. The green LED (LED2) indicates that the unit is switched on. The charger, IC2, is configured to provide a 280mA charging current, so it should recharge a 400mAh cell in under two hours. The overall operating current consumption is 25-50mA depending on the signal level, so the battery life should be 8-16 hours. Construction All components mount on a single 56 × 82mm PCB coded P9058-1-C. For once, there are no tiny leadless parts, so assembly requires nothing but a soldering iron and a steady hand. You can commence by fitting the surface-­ mount parts according to the overlay diagram, Fig.7. Watch the polarity of the LEDs, the TVS diode and the TSSOP quad op amp. The rest don’t matter, or are hard to get wrong. siliconchip.com.au 1 double-sided PCB coded P9058-1-C, 56 × 82mm 1 front panel label, 41 × 60mm 1 Hammond 1593LBK plastic enclosure, 92 × 66mm 2 PCB-mounting right-angle female BNC connectors (CON1, CON2) [Molex 73100-0105] 1 USB-C power only socket (CON3) [Molex 217175-0001] 1 JST 2.0mm pitch 2-pin right-angle header (CON4) [JST S2B-PH-K-S] 1 10μH ±5% 480mA 240mW 40MHz SMD inductor, M4532/1812 size (L1) [Murata LQH43NH100J03L] 1 0.75A 24V M3226/1210 PTC polyfuse (PTC1) [Littelfuse 1210L075/24PR] 1 PCB-mount right-angle DPDT toggle switch with short actuator (S1) [E-Switch 200MDP1T2B2M6RE] 1 top-adjust, centre-tapped, centre-detent 50kW linear potentiometer (VR1) [Bourns PTT111-3220A-B503] 1 400mAh 38 × 25 × 6mm LiPo cell with JST PH connector (BAT1) [Core Electronics CE04375] 2 3mm diameter, 0.6in/15.24mm rigid convex light pipes [Dialight 515-1302-0600F] 1 knob (to suit VR1) 4 #4 × 6mm panhead self-tapping screws 1 small tube of cyanoacrylate glue (superglue) 1 38 × 25mm foam-cored double-sided tape pad 4 small self-adhesive rubber feet (optional) Semiconductors 1 TPH2504 quad 250MHz RRIO op amp, TSSOP-14 (IC1) 1 MAX1555EZK-T Li-ion battery charger, TSOT-23-5 (IC2) 1 yellow SMD LED, M2012/0805 size (LED1) 1 red SMD LED, M2012/0805 size (LED2) 1 SMBJ5.0CA unidirectional transient voltage suppressor, DO-214AA (TVS1) Capacitors (all 50V SMD X7R ceramic, M2012/0805 size, unless noted) 2 10μF 16V 1 100nF 100V NP0/C0G, M3216/1206 size 5 100nF Resistors (all SMD ±1%, M2012/0805 size, unless noted) 4 51kW 2 1kW 2 5.1kW 2 510W 1 3.3kW 2 10W The USB connector has surface-­ mount pads for the terminals, as well as through-hole mounting pads. The best way to mount this is to first solder it in place via the through-hole pads from the bottom, then turn the board over and solder SMT pads. Finish the PCB assembly with the battery connector, the BNC terminals, the switch and the pot. That’s all there is to it. Testing Check your work carefully, then connect the battery or an external supply set to 4.0V. Switch it on and you should see the green LED light. Use a multimeter to measure the power supply voltages with reference to one of the BNC connector shields. The bottom ends of the two 100nF Australia's electronics magazine capacitors just to the left of VR1 are convenient places to probe. You should read around +2V on the leftmost capacitor and -2V on the one to its right. Anything between ±1.8V and ±2.2V is fine. You can check the DC offset with the pot centred by measuring the voltage between the centre pin and shield of the output BNC connector. The voltage should be within ±5mV of zero. You can check the output voltage swing with the same set-up. Simply turn the pot either way until the output saturates. The voltages should be well above ±1.0V, even at the lowest battery voltage. With a fully charged battery, they will be closer to ±1.3V. You can check the battery charger is working by switching the unit off November 2025  51 Fig.8: a rendering of the finished assembly, with the battery plugged in and taped to the PCB, ready to install in the case. The test set-up used a conventional scope probe and a home-made RG316 probe to measure the output of this AC-DC converter module. and connecting a USB-C power source. Unless the battery is fully charged, the yellow LED should light, and the battery voltage should climb slowly. The LED extinguishes when the battery reaches full charge, at around 4.2V. Final assembly You can now fix the battery in place with a small piece of double-sided tape, as per Fig.8, then turn your attention to the case. Mark out and drill the two end plates and the top according to Fig.9. The aperture for the USB connector is best opened up after drilling by using a sharp craft knife or scalpel to remove the material between holes drilled at each end. I used a few small files to neaten things up. You can then apply the label to the top surface of the lid. The artwork is available to download (siliconchip.au/ Shop/11/2771). I printed mine full-size on glossy adhesive paper, then laminated that with some transparent self-adhesive vinyl. Cut it to size and fix into the recess in the lid, starting at one end to avoid capturing bubbles. I opened up the two light-pipe holes by pushing a sharp probe through the label into the holes in the case. The pot shaft opening is large enough to use a blade to remove the label over the aperture. Install the light pipes from the top of the case, and secure them on the underside with a drop of superglue. Thread the end panels onto the PCB assembly and lower it into the bottom of the case, making sure the end panels go into the slots provided for them. The board is held down by four 6mm-long #4 self-tapping screws. Pop the top case on and secure with the screws provided. I added four small self-adhesive rubber feet on to the bottom of the case. Fit the knob and you are finished. Using it The Power Rail Probe is dead easy to use. Connect the output to your oscilloscope with a 50W BNC cable and set the input to 50W termination. Set the vertical scale to a few hundred millivolts initially. Connect the Power Rail Probe’s input to your circuit and switch it on. With your circuit under test powered up, you should be able to adjust the offset pot to get the scope trace very close to zero. Fig.9: drill the top and the flat end-plates of the enclosure according to this diagram. The contoured end-plates supplied with the case are not used. 52 Silicon Chip Australia's electronics magazine siliconchip.com.au The finished Power Rail Probe, mounted in its 99 × 66mm plastic enclosure. The front panel label for the Power Rail Probe. Note the very small dots below the POWER and CHARGE labels. These are for the SMD LEDs, which shine through the panel via 3mm diameter light pipes. Punch 3mm holes centred on those dots after the label is affixed to the case. You can now zoom down the vertical scale appropriately, tweaking the offset pot slightly if necessary to keep the trace centred on the screen. Just remember the output on screen is attenuated by about 1.2 times (the attenuation will be within the range of 1.1-1.3 times). The connection you make between the power rail probe and your device under test will be the single most important factor in the measurement’s usefulness. Probing any high-frequency signal can be difficult, especially when you are working with switching power supplies. They tend to be environments rich in radiated and conducted interference that can easily upset your measurements. I set up a small experiment to demonstrate this, using a Zettler modular AC-to-DC converter rated at 15V and 5W. This is the one used in the Variable Speed Drive for Induction Motors project (November & December 2024; siliconchip.au/Series/430). I measured the unloaded output voltage of this switch-mode module with a conventional passive oscilloscope probe, with a 150mm ground clip and with a custom ‘probe’ made up of a short length of RG316 coax with a BNC connector fitted to one end. The photo at left shows the test setup. The scope capture (Screen 1) tells the story. The scope probe’s ground loop acts as a very effective antenna to pick up all sorts of switching hash radiating from the converter module. As a result, the underlying ripple is more-or-less invisible below the noise in the yellow trace from the probe. The home-made probe (green trace) has a INPUT OUTPUT 50 kΩ 50 Ω LOAD Maximum ±50 V Power Rail Probe POWER OFFSET CHARGE ±25 V Charge OFF - ON P9058 Charge much smaller loop area and picks up proportionately less noise. The faint vertical spikes you can see on the green trace are real signal artefacts caused by the very high voltage rates-of-change in the primary switch being capacitively coupled to the output. Their irregular spacing shows that the converter is operating in burst mode due to the very light load. Using coax probes like this is not something I invented. Commercial power rail probes come with similar unterminated cables for this purpose. However, there is a much cheaper alternative. I buy 1m RG316 BNC-toBNC cables from AliExpress and cut them in half to yield two test probes. You can reuse them many times, but they eventually get too short and have to be discarded. At the time of writing, three such cables cost less than $25.00 delivered. That’s way less than the cost of buying the cable and connectors to making them myself. Conclusion Scope 1: the results from the test shown at upper left. The waveform measured by the standard probe (yellow trace) is completely buried in switching noise, while the green waveform from the Power Rail Probe is much more informative. siliconchip.com.au Australia's electronics magazine A Power Rail Probe is far from the most essential piece of test equipment you will ever own. However, if you are looking at the dynamic response of converters that take place over tens of milliseconds, at voltage levels where you may run out of DC offset in your oscilloscope, there may be no alternative. Building this Probe is likely to be the most cost effective way to get that capability. SC November 2025  53 By Andrew Levido Power Electronics Part 1: DC-DC Converters Power electronics is a very broad term that describes circuits with the primary function of handling electrical energy. In this series of articles, we will explore this area, with practical examples. I will share some useful tools and techniques. P Fig.1: power electronics is a broad field, encompassing a knowledge of the load and the control loop as well as switching, drivers and filters. switching like electromagnetic interference (EMI) and poor power factor. • Switch drivers: this might not seem very interesting, but power electronics switches can have demanding drive requirements. The control terminals of the switches are often floating at high voltages, or switching rapidly between different voltages. The driver circuits therefore often have to include bootstrap power supplies, level shifting and high-voltage isolation. • Control loops: most power electronics circuits require some form of closed-loop control. This can be a simple voltage regulator in a DC-to-DC converter, or may involve multiple electrical or electromechanical sensors spread across a complex industrial machine. • Loads: the power electronics designer has to have a good understanding of the load, its characteristics in operation and any feedback transducers that may be involved. As well as covering this breadth, power electronics requires an ability to look at the system through different lenses at different times; from a wide-angle perspective, right down to a detailed microscope-level viewpoint. For example, take capacitors. In this article, we will introduce a highlevel analysis technique that assumes the average current through a capacitor is always zero. Later, we will have to zoom right in and look at the nonideal behaviour of the same capacitor, including its equivalent series resistance (ESR) and the effects of voltage and frequency on its dielectric. In the following article next month, we will consider capacitors from a complex impedance perspective. It is really important to use the right analysis lens at the right time. If you go too detailed too soon, you can become hopelessly mired in unnecessary Australia's electronics magazine siliconchip.com.au ower electronics is all around us – the rapid growth of renewable energy, electric vehicles and the near-ubiquity of switching power supplies means that a huge percentage of our electrical energy is generated, transmitted or consumed by power electronics. Fundamentally, power electronics systems convert electrical energy from one form (a source) to another (a load). Consider a smartphone; there is power electronics in the charger, converting the mains to an isolated low voltage. There is more in the battery charging circuit within the phone, and yet more to provide the many low-voltage power rails necessary for its operation from the battery. That battery is most likely a single LiPo cell, a type of lithium-ion cell, which will vary from around 4.2V when fully charged to around 3.3V when discharged. So the internal power supply electronics needs to be designed to convert that varying voltage to several fixed, regulated voltages for consistent performance of the various subsystems in the phone (processor, display, RF etc). At the other end of the spectrum, there are the kilowatt and megawatt-­ scale power electronics systems controlling industrial processes including variable-speed motor drives, robotics and a whole range of other applications. Electric and hybrid vehicles 54 Silicon Chip also rely on power electronics for their battery charging and management systems, and of course, in the drivetrain. This series will be more academic than a lot of articles in Silicon Chip magazine, with formulae and fairly detailed analysis. However, we aim to make this comprehensible to just about anyone interested in the subject, so we will try to avoid any mathematics beyond what is (or at least should be) taught in high school. We will also make sure to provide examples and down-to-earth explanations. We want to make this discussion accessible, despite the complexity of the topic! Breadth and depth What makes power electronics especially interesting (and maybe a little bit daunting) is the enormous breadth and depth of the field. You can get an idea of its breadth by looking at Fig.1. This shows the scope of a typical power electronics system. It consists of the following subsystems: • Power switching: this is the heart of any power electronics system. Power is switched by semiconductor switches such as Mosfets, IGBTs, diodes, thyristors and the like. • Input and output filters: filters form an integral part of most power electronics systems, as we shall see. They can also help ameliorate some of the negative consequences of complexity. Conversely, if you stay at too high a level for too long, you may over-simplify things and miss something important. I think this constant zooming in and out is one of the reasons why some people find power electronics difficult to grasp. I am going to try to be very explicit about which lens we are using and when, to help dispel some of the complexity. To that end, we are going to zoom right out and start our analysis of DC-DC converter topologies with an annoyingly simple example. Fig.2: the simplest possible DC-DC switching converter. This is not very practical, but does reduce the average voltage efficiently. It’s basically just pulse-width modulation (PWM). A simple start Let’s start by assuming I want to build a switching DC-to-DC converter to reduce a source voltage, Vsrc, by 50% to power some load (Vload = ½Vsrc). The simplest possible approach is shown in Fig.2. If we operate switch S1 with a 50% on/off duty cycle (ie, on and off for equal periods), I think you would agree that the average voltage in the load (green dotted line) will be half that of the source voltage. The efficiency of the circuit will be 100%, since there are no lossy elements (much better than a linear regulator, which would be 50% efficient), so that is a win. Of course, I am ignoring the obvious fact that the output voltage (green solid curve) will be far from a smooth DC voltage. Before we move on to address this shortcoming, I want to take a minute to establish some conventions around the variables I will be using throughout this series. • I will use lower-case variables to represent time-varying or AC quantities; for example, v2 or q. • I will use upper-case variables for fixed or DC quantities, like Rload or Vsrc. • I will use angle brackets to indicate an average value, like ‹v2›. Obviously, it only makes sense to average time-varying values. I am using q(t) to describe a time-­ dependent control function that dictates the state of the switch. In the example of Fig.2, the control function (red trace) is a digital signal with a value of either 0 or 1. The label adjacent to S1 indicates that it is closed when q(t) = 1, and, by implication, is open when q(t) = 0. The period of the control function is T, and it is on for a time DT, where D siliconchip.com.au Fig.3: adding filters to the input and output of a simple switch produces a buck converter. The use of average value analysis allows us to work out the transfer function very easily. is the duty cycle, which can have any value between zero and one. The cycle period T is the inverse of the switching frequency, f sw. The next step is to add a filter to the circuit of Fig.2 to smooth the output. In Fig.3, we have added an LC low-pass filter (L1/C2) to the output, and a capacitor, C1, to the input. The input capacitor is unnecessary if the voltage source is perfect, but I have put it in because it is almost always required in real life, and it will come in handy later. We will assume for now that the inductor and capacitor values are very large compared to the switching frequency so that the filtering is almost perfect. In this case, any capacitor voltage ripple or inductor current ripple are negligible. The switch has now been expanded to two complimentary switches: S1, which is closed when q(t) = 1 as before, and S2, which is closed when q(t) = 0. The latter is necessary to provide a path for the inductor current (which can’t change instantaneously) when S1 is opened. Average value analysis We are going to use a tool known as average value analysis to understand the transfer function (the relationship between the output and the input Australia's electronics magazine quantities) of this circuit. This kind of analysis is very useful for understanding the operation of a circuit at the highest level. We don’t need to know any component values, or even the switching frequency, to complete this analysis. Average value analysis requires our circuit to be in a condition known as ‘periodic steady state’ (PSS), which just means that the circuit is in a steady (unchanging) state at the macroscopic level. PSS therefore ignores transients like those that occur at start-up or where the load suddenly changes. In this state, each switching period looks exactly the same, even though voltages and currents change during the cycle. If each period is identical, it follows that all voltage and current waveforms must start and end each period at the same value. Something interesting happens to capacitors and inductors in PSS. Since the voltage across a capacitor starts and finishes each period at the same level, the average voltage across it must be constant. This implies that the average current through the capacitor must be zero. A similar thing happens for inductors. In PSS, the average current through an inductor must be fixed. This means the average voltage across it must be zero. We can therefore write November 2025  55 two equations that help us with average value analysis: ‹ic› = 0 and ‹vl› = 0. Be careful with this – it applies only to the average voltage and current during PSS. Now we can perform an average value analysis on the circuit of Fig.3. If the average voltage across the inductor is zero, it should be apparent that ‹vx› = ‹v2›. We can also calculate ‹vx› from the green chart in Fig.3 and see that ‹vx› = DVsrc. We can further see that, due to the perfect LC filter, ‹v2› is equal to Vload. Putting these together, we find the circuit transfer function is Vload = DVsrc. Since D must be between zero and one, Vload must be equal to or lower than the input voltage. This circuit is a classic buck converter (‘buck’ meaning step-down in this context). Setting D to 0.5 gives us an output voltage of half the input voltage, as we wanted. This time, the output voltage is DC, ie, smooth. If the average capacitor currents and inductor voltages are zero in PSS, there can be no average energy change, and therefore no power dissipation in the inductor or capacitors. This means that the converter input power and the output power must be equal (Isrc • Vsrc = Iload • Vload). Substituting the voltage transfer function derived above gives the current transfer function Iload = Isrc ÷ D. Let’s just pause for a second here and recap what we have done. Using nothing but the average value analysis rules (in PSS, ‹ic› = 0 and ‹vl› = 0), and a diagram of vx, we have derived the voltage and current transfer functions for the classic buck converter. No fancy maths is required. We have not had to worry about component values or the switching frequency – just the assumption that the LC filter time constant is much larger than the switching period T. Average value analysis is a powerful tool for understanding the basic function of switching converters. While we are on a roll, let’s look at what happens if we swap the source and load in our circuit. This is worthwhile to illustrate just how important the filters are in determining the operation of a power electronic converter. have also switched the designations of the capacitors, voltages and currents so the subscript 1 is still associated with the source and subscript 2 with the load. I have also swapped the control sense of the two switches. S1 is now on when q(t) = 0, while S2 is on when q(t) = 1. This aligns with the conventional way this type of converter is described, but does not change its operation. Again, using average value analysis, we can see that if the average inductor voltage is zero, ‹vx› must equal ‹v1›, which is in turn equal to Vsrc. We can see from the graph of vx (green curve) that its average ‹vx› = (1 – D)Vload, so the transfer function of the converter must be Vload = Vsrc ÷ (1 – D). We can use conservation of power as above to find that Iload = Isrc(1 – D). Since D ranges between zero and one, the load voltage varies between Vsrc when D = 0 and approaches infinity as D approaches 1, so the output must be equal to or higher than the input. Therefore, this is a classic boost converter. Additional topologies We usually draw the boost converter with the source on the left, but I have done things this way to bring out the fact that the filter and switch arrangement is the same for both converters. Fig.5 summarises what we have just covered and adds several more topologies. I have used Mosfets and diodes in place of the switches to show how these circuits are usually implemented. If you think about it, a diode can be considered a sort of passive switch, as it goes into and out of conduction depending on the voltage across it. While diodes are typically less efficient than Mosfets (due to their minimum forward voltage), they have the benefit of requiring no active control circuitry. The first new converter is the buckboost which, as its name suggests, should be able to produce a voltage above and below the input. This time, it should be obvious the average value of vx must be zero, because the average value analysis rules dictate that the average inductor voltage must be zero. However, we can see that when Q1 is on, vx must equal Vsrc, and when it is off and the diode is conducting, vx must equal Vload. Vload must thus be negative to make the average of ‹vx› zero, as required by the average value analysis rules. You can probably see from the plot of vx that for the average to be zero, the area DVsrc when Q is on must equal the area −(1 – D)Vload, which is shown in the second equation. Rearranging gives the voltage transfer function shown in blue. As we expected, the output voltage is in the range of zero (when D = 0) and negative infinity (D = 1). Of course, there will be a practical upper limit on the output voltage of these converters (usually on the order of a few times the input voltage), but for the purposes of this high-level analysis, it can be infinite. The next converter we will look at is the Ćuk converter (pronounced “chook”). This was first presented by the American academic Slobodan Ćuk in 1976 (he was born in Belgrade, Yugoslavia, which is now part of Serbia). It is a departure from the previous converters, which use the inductor as the primary energy storage element. The Ćuk converter uses a capacitor (C3 in Fig.5) as the main energy storage device, with the now-familiar LC filters on the input and output. Fortunately, we can use average value analysis to work out the transfer function in just the same way as we have before. The upper waveform is the voltage at vx and the lower waveform is the voltage vy. When the Mosfet is on, vx is zero and the left-hand end of C3 is A ‘reverse’ buck converter Fig.4 shows our new converter. It is exactly the same as the buck converter, but I swapped the source and load. I Fig.4: the classic boost converter is just the buck converter from Fig.3 with the source and load switched. 56 Australia's electronics magazine Silicon Chip siliconchip.com.au grounded. This means that vy must be equal to −‹vc›. When the Mosfet is off, vy must be zero, so the right-hand end of C3 is grounded, meaning vx must be equal to +‹vc›. This leads to the first two equations that describe the average values of vx and vy, respectively. The input and output filters mean that ‹vx› is equal to Vsrc, and ‹vy› is equal to Vload, as shown in the next line of equations. Finally, we can combine these to produce a transfer function that is identical to that of the buck-boost converter, complete with voltage inversion. Why would one use a Ćuk converter when it has the same transfer function as the simpler buck-boost converter? Firstly, the Mosfet is ground-­ referenced, making the drive circuit simpler. Secondly, it is possible to wind the two Ćuk inductors on the one core is such a way that the output ripple is dramatically reduced. Finally, having LC filters on both input and output, the Ćuk converter can have lower EMI than other converter topologies. The final type of converter I want to cover is the ‘single ended primary inductor converter’, generally abbreviated to SEPIC. This one also uses a capacitor as the energy transfer element. We’ll analyse this in the same way as all the others. When the Mosfet is on, vx is zero and when it is off, vx is the average capacitor voltage ‹vc› plus the output voltage Vload, as shown in the waveform. The average value of vx is given by the first equation. In this converter, ‹vy› must be zero due to inductor L2; therefore, ‹vx› must equal ‹vc›. We also know that, due to the input filter, Vsrc = ‹vx›, so we can re-write the first equation in terms of Vsrc, as shown in the third equation. Finally, we can rearrange this to get the voltage transfer function, which turns out to be similar to the buckboost and Ćuk converters, except not inverted. The SEPIC converter can therefore produce a positive voltage between zero and (in theory) infinity. As you might imagine, there are many other variations on this theme, and their characteristics are not always obvious from just looking at the circuit. I hope that you have seen that average value analysis is a simple way to get to grips with switching converters. Getting practical Enough theory for now. I want to build the buck converter we have been discussing, to see what’s involved and how closely reality matches the theory. I am also going to simulate it using a free circuit simulator called QSpice. To complete this design, we will have to zoom down into some of the detail, especially when it comes to capacitors. Fig.5: five common DC-DC converter topologies. Average value analysis allows us to understand their steady-state behaviour – and that of any converter you come across. siliconchip.com.au Australia's electronics magazine November 2025  57 We will start with some specifications. The input voltage is nominally 12V, but let’s allow for a range of 10V to 14V. We want an output voltage of 6.0V and a maximum output current of 600mA, so a 10W load. We can use the transfer function derived above to calculate the required duty cycle range: 0.43 ≤ D ≤ 0.6. I will use a TPS5410 DC-DC converter chip in this example. This is a pretty old chip, and not necessarily one I would recommend for new designs, but it has a couple of advantages for us. It has a fixed switching frequency of 500kHz and uses an external flyback diode. These make it a good match to the theoretical circuit, and allow us to measure the inductor current ripple fairly easily. The circuit is shown in Fig.6. I have shown the connection of the internal Mosfet so you can see how it matches up with S1 in Fig.3. We will more-orless follow the design procedure set out in the chip’s data sheet, but I will take a bit of time to explain the formulas it provides so you can see how they are arrived at. The capacitor Cboot is used by a bootstrap circuit within REG1 to create a drive voltage for the internal Mosfet that is a few volts higher than Vsrc. We will just use the manufacturer’s recommended value of 10nF here. The output voltage feedback comes via the voltage divider R1/R2. The Vsens voltage on pin 4 should be 1.22V when the output voltage is at the desired level (6V in our case). If we let R2 = 10kW we can calculate that we need a value of 39.2kW for R2. This is very close to the standard value of 39kW, so we will use that. I will use an MBRA130LT3 schottky diode for S2 (D1) since I have one on hand. This is a 1A, 30V fast diode, so should be fine for this application, since the peak current should be just a little over the load current of 600mA. That’s it for the easy parts. Input capacitor selection The design process in the data sheet suggests that we start by selecting C1 to give the desired worst-case voltage ripple at the input. Fig.7 shows the data sheet equation (at the bottom) and the circuit fragment that will help us understand it. The capacitor is shown together with its equivalent series resistance (ESR), since this will be significant in calculating the ripple. The capacitor ripple voltage ∆vc is given by the top equation – the first part is the basic equation for the change in capacitor voltage as the current ic is extracted, and the second part is the voltage across Resr from Ohm’s law. Fig.7 shows us that when S1 is closed, the capacitor discharge current ic will be the net of the load current Iload, less the charging current, Isrc. The worst-case current occurs when D = 0.5 and Isrc = ½Iload. The capacitor current for the worst-case ripple must therefore be ½Iload. The worst-case ripple voltage is therefore given by the second equation, which substitutes ½Iload for ic and 0.5T for ∆t. This is almost identical to the data sheet formula. I have highlighted each term in a different colour so you can see how they are related. The mysterious ¼ term in the data sheet formula is simply the ½Iload factor and 0.5 worst-case duty cycle combined. f sw is the switching period T shifted from the numerator to the denominator. The only real difference between the two equations is the missing ½Iload factor in the ESR term. This will just make the ripple estimate a little bit higher, which is of little consequence. Now we have to choose a capacitor with the appropriate value and ESR. This is not simple exercise when dealing with high-frequency circuits such as this. I want to use a multi-layer ceramic capacitor (MLCC) for its low ESR, in parallel with an aluminium electrolytic for bulk storage. For the MLCC, I chose a 4.7µF 25V X7R model (Samsung CL21B475KAFNNNE), while for the electrolytic, I will use a 100µF 35V unit (Panasonic EEE-FP1V101AP), both of which I have in my parts bins. It’s complicated! Now it is time to get out the microscope, because in high-frequency power electronics circuits (and indeed in many circuits), you can’t necessarily take capacitors at face value. The chart at the top left of Fig.8 shows that, although our 4.7µF MLCC capacitor is rated for 25V, its nominal capacitance will fall by 70% (to 1.4µF) when biased with 12V. This is a ‘feature’ of many MLCC dielectrics like X7R and X5R that you should be aware of. The capacitance also goes down with temperature and ageing, but not significantly in this application. This is a good reason to choose MLCCs with a higher voltage rating than might seem necessary at first (or, in applications requiring lower capacitance, selecting a more stable dielectric like C0G/NP0). The lower graph shows that, at 500kHz, the capacitor’s ESR is about 4.5mW, which is very low, and one of the main reasons you see these capacitors in switch-mode circuits. Fortunately, the capacitance of the electrolytic is relatively fixed with applied voltage and, according to its data sheet, it has an ESR of around 80mW at 100kHz. There is no data for higher frequencies, so we will assume this ESR holds at 500kHz. Figs.6 & 7: we built this example of a buck converter (see left diagram) as a practical exercise to see if the actual results matched the theory. The worst case input voltage ripple occurs when the duty cycle is 50% (see right diagram). The lower-most equation is copied from the data sheet, while those above it show how it was derived. 58 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.8: the plots on the left show that the capacitance and ESR of an MLCC can be very different from the nominal values under DC bias and at high frequency. The circuit and formulae above shows how we combine parallel impedances; for example, when paralleling capacitors with significant ESR. Editor’s note – be careful with such assumptions because wet electrolytic capacitors have physical limitations in response time. Our two capacitors will be in parallel, but the diagram on the right of Fig.8 shows us why we can’t assume the total capacitance will be the sum of the two capacitances, or that the total ESR will be the parallel combination of the two resistances. Instead, we have to calculate the complex impedance of each capacitor/ESR combination (left equation), then calculate their parallel impedance (right equation) and decompose that to obtain the equivalent capacitor and resistance value. I use a spreadsheet to do these (literally) complex calculations, and the results can be surprising and sometimes counter-intuitive. For example, my spreadsheet shows that the parallel combination we will be using will have an equivalent capacitance of 11.8µF and an ESR of 69mW at 500kHz. Plugging these values into the input ripple formula suggests we can expect a peak-peak ripple voltage of about 46mV (67mV if you use the data sheet siliconchip.com.au calculation, with its extra current in the ESR term). Inductor selection The next item we need to select is the inductor. The lower blue formula in Fig.9 is from the data sheet, and the circuit fragment shows us the simplified circuit when S2 is closed. It should be apparent that the voltage across the inductor is equal to the output voltage, Vload. During this period, the inductor current will ramp down by some amount, ∆il, that represents the peakto-peak current ripple. The first formula in the figure describes the general relationship between the rate-of-change of current in inductor and the voltage across it, arranged to make the inductance the subject. The second equation therefore shows the minimum inductance required to limit the current ripple to some value ∆il. In this equation, vl has been replaced by Vload and ∆t by (1 – D)T. The data sheet formula is almost identical to this; the expression (Vin(max) – Vout) ÷ Vin(max) evaluates to 1 – D, and T moves to the denominator as f sw. The current Australia's electronics magazine ripple is expressed as a factor (Kind) of the load current. The random-­looking 0.8 is there as a safety factor, to allow for inductor tolerance in the case you use an inductor with a value of exactly Lmin. If we choose to have maximum ripple current of 100mA, we can calculate that we need an inductor with a value greater than 85µH. The nearest larger practical value is 100µH, so that is what we will use. If we back-­ calculate the ripple using this value, we get an expected peak-to-peak ripple current of 68mA. The peak inductor (and diode) current will be the average load current plus half of the ripple current, or 634mA. I chose a VLS6045EX-101M inductor from TDK. This has a peak current rating of 1.1A and a DC resistance of 470mW (we want to keep that resistance low for good efficiency, as all the current flows through it). Output capacitor selection The capacitance of the output capacitor is not all that critical as far as output ripple is concerned – the output cap’s ESR is usually the important parameter. In theory, you could keep adding output capacitance to make the ripple as low as you want, but this would cause problems with the performance of the voltage regulating control loop. We will cover (some) control theory in the next article, but for now it is enough to know that the internal compensation in this particular controller requires the closed-loop crossover frequency to be in the range 3kHz < fc < 30kHz. Fig.9: the data sheet equation for peak to peak current ripple at the bottom of the figure is derived from the basic relationship between current and voltage in an inductor. November 2025  59 Fig.10: simulation of the circuit (left) yields results (above) that are very consistent with the calculated values. The closed-loop crossover frequency must also be lower than the frequency of the ‘pole’ formed by the output capacitor and its ESR. The closed-loop crossover frequency is the frequency at which the closed-loop gain falls to zero. The manufacturer helpfully provides an expression that relates fc to the output filter corner frequency, f lc. Given we know the inductance, we can determine that C2 must be between 165.6µF and 31.4µF (at the loop crossover frequency, not necessarily at 500kHz). We can therefore use the same 4.7µF/100µF pair as we did for the input, since with 6V DC bias and the 4.5kHz crossover frequency the, parallel capacitance is about 102.5µF and the ESR is 76mW. This will have an ESR pole at 22kHz, much higher than the crossover frequency, so we should have a stable control loop. Notice that we have used the loop frequency to calculate the capacitance and ESR for loop stability, and that we will use the switching frequency to calculate them for ripple below. This is a great example of why power electronics can seem confusing – the same capacitor has different apparent values depending on the type of analysis we are performing. 60 Silicon Chip The output ripple is then more-orless trivial to calculate, as it is just the output cap’s ESR multiplied by the peak-to-peak ripple current. At 500kHz with 6V bias, the tables and the spreadsheet tell us that total capacitance will be 9µF and the ESR 56mW. With a current ripple of 68mA, we should see about 3.8mV of peak-topeak voltage ripple at the output. That much ripple is not likely to be a problem for whatever it is driving. With additional filtering, it could be reduced well below 1mV. Simulation Simulation is a powerful tool we can use to analyse the behaviour of power electronics circuits. There are a few very capable free simulators available. I have been using QSpice recently, as its user interface (UI) seems to be better than some of its competitors. Like everything in power electronics, the trick to good simulation is to work out what is important and what can be simplified or ignored. Fig.10 shows where I landed. A subcircuit (not shown) produces a control signal for the switch with a period of 2µs and a duty cycle of 0.5. I have given the input voltage a source impedance of 1W, which is Australia's electronics magazine reasonable, as perfect voltage sources don’t exist in reality. The input and output capacitances are represented by capacitors with series ESR resistances using the values that we just calculated. I have added the inductor’s series resistance for completeness. S2 is represented by a generic schottky diode, and S1 by a switch with an on-resistance of 110mW, like the Mosfet in the TPS5410. The “.tran” directive tells QSpice to perform a transient analysis over one second, but to display only the last millisecond. This is necessary because, when the converter starts from zero, it takes a little while to reach a steady state. The simulation output at the top of Fig.10 shows the inductor current at the top, the input voltage ripple in the centre and the output voltage ripple at the bottom. QSpice offers some handy utilities, including one to measure the peak-to-peak values of the displayed waveforms. You can see that the current ripple is 62mA, the input ripple is 55mV and the output ripple is 4.3mV. This accords pretty well with the calculated values (68mA for current ripple, 46mV or 67mV for input ripple and 3.8mV for output ripple). This is not surprising, since the simulation is using the same inputs as the calculations. The proof of the pudding would be to build the circuit and see how it performs. Test results I did just that, and the measured results are shown in Fig.11. The first oscilloscope trace is the current through the diode (measured across a 0.5W series resistor). This is a lot easier than measuring the inductor current directly. The ripple is derived from the slope on the top of the waveform. The measured ripple current is around 64mA, in line with the calculated value of 68mA. The input ripple (centre) current looks a lot like that in the simulation, but you can see some ringing on the waveform. This is caused by stray inductance in the circuit (for example, in the leads to the power supply) resonating with the input capacitance. The scale is 20mV/division, so the peak-to-peak ripple is in the region of 45mV, again very close to the calculated value of 46mV. siliconchip.com.au Finally, the output ripple is roughly the same shape as the simulation with the exception of switching spikes. These are due to the fast transitions of vx making their way through the inductor’s stray parallel capacitance. Nevertheless, the amplitude of the underlying ripple is about 4mV peakto-peak, bang on the calculated 3.8mV value. If you want to eliminate the switching spikes, you can add a secondary LC filter; sometimes a ferrite bead is all it takes. But keep in mind that it may (likely will) affect transient regulation. I should point out that making these measurements is not trivial. If you were to use a normal ‘scope probe with its 150mm-long ground clip, you would see a whole lot of noise superimposed on these signals. Instead, I used a piece of thin 50W coax (RG316) with a BNC connector on one end. The screen on the other end is stripped back about 10mm, with the core and screen connected directly across the capacitor or resistor whose voltage is being measured. For signals that never exceed a volt or so, like the voltage across the 0.5W resistor used to measure the diode current, you can connect the coax directly to a scope with the 50W terminator enabled. You can’t do this for higher voltage signals, such as when measuring the input or output ripple, since the 50W terminator is usually not rated for more than a few volts. You may be able to use the normal high-impedance input and AC coupling, but I use a home-made power rail probe to eliminate the DC offset, allowing me to safely use the 50W input with its better noise performance. That device is described in a separate project in this issue, starting on page 47. Conclusion This introduction has demonstrated that power electronics is a field that requires the designer to shift back and forth between high-level circuit analysis and the minutiae of component behaviour. This is what makes it endlessly fascinating to me. Next month, we will look in detail at what is involved in designing the control loop of DC-to-DC converters like this one. Not understanding such control loops is probably the #1 problem that people have implementing SC such DC/DC converters! siliconchip.com.au Fig.11: I built the circuit and measured the diode current (top), input voltage ripple (centre) and output voltage ripple (bottom). The results are very close to the calculated and simulated values. Australia's electronics magazine November 2025  61 Using Electronic Modules with Tim Blythman Large OLED Panels The displays that we describe in this article are similar to other OLED screens we have reviewed and used previously, although they are larger. Since bigger is usually better, we thought we ought to try them out. O ften we have used this style of OLED panel in projects because they are compact, use little power and allow both text and graphics to be displayed. They also have very high contrast. The 0.49in OLED module that graced the Audio DDS Oscillator exemplifies this (September 2020; siliconchip.au/Article/14563). The Oscillator generates an audio signal and shows its frequency on the OLED screen, while running from a pair of AAA cells, all in a unit less than 75mm long. Since then, we have produced numerous projects using OLED displays, including several Tweezers-style test instruments. Jim Rowe previously looked at different OLED variants in the October 2023 (siliconchip.au/Article/15980) and November 2024 (siliconchip.au/ Article/17027) issues. These modules often integrate a Solomon Systech SSD1306 or Sino Wealth SH1106 controller IC. They take control inputs over an I2C bus and drive the display matrix accordingly. Some readers would like to use larger versions of these display modules in our projects to provide a larger and more legible display. However, we know that the larger displays use a different controller IC, so they are unfortunately not a direct replacement. So, this article will investigate these displays and their differences from similar, smaller displays. We’ll also look at how easy it is to substitute them for the smaller displays, and what software changes are needed. The SSD1309 IC The larger units we tested all use the Solomon Systech SSD1309 controller IC. We have seen comments to the effect that the registers in the SSD1309 match those of the SSD1306, so it sounded quite possible that using these modules would be straightforward. Some of these large displays using the SSD1309 have a seven-pin header and are configured to use an SPI interface. With these modules being bigger, there is more space for the longer header. However, we’ve stuck to those that include an I2C interface, similar to the smaller units, and those we purchased specify a display size between 1.54in and 2.42in, equivalent to 39mm and 61mm. The previous, smaller displays vary from 0.91in to 1.3in (23-33mm). Table 1 summarises the modules we purchased and tested. Like TVs and mobile phones, the display size is measured diagonally, from lower left to top right. We’ve included sources Module name Display size OLED_M154_4P (Photos 1 & 2) 1.54in (36mm) (some local), but in most cases, searching for the controller name “SSD1309” is the easiest way to find similar products on websites like eBay and AliExpress. We have previously used a version of the 2.42in display in the Hot Water System Solar Diverter project from the June & July 2025 issues (siliconchip. au/Series/440). We found a comparison of some Solomon Systech OLED driver ICs (siliconchip.au/link/ac7s) and noted a handful of differences between the SSD1306 and SSD1309. They both offer control of a monochrome 128×64 pixel panel with 256 steps of contrast control. For a monochrome OLED panel, contrast is effectively the same as brightness. The SSD1309 can sink more common (ie, row) drive current from the display (40mA maximum vs 15mA for the SSD1306). The SSD1309 can also operate with a higher voltage, but does not incorporate an internal charge pump like the SSD1306. OLEDs typically require a higher voltage to work than conventional LEDs, hence the need for such circuitry. Circuit details Let’s look at the circuit of one of the modules, the Waveshare 2.42inch Module size Source Current draw all pixels off/on (full brightness) 43 × 38mm eBay 156327080574 2mA/285mA Core Electronics CE09964 2mA/237mA 2.42OLED-IIC (Photos 3 & 4) 2.42in (61.5mm) 70 × 48mm Waveshare 2.42inch OLED 2.42in (61.5mm) 62 × 40mm module (Photos 5 & 6) Core Electronics WS-25742 8mA/290mA Table 1 – Modules tested (names are as printed on the modules) 62 Silicon Chip Australia's electronics magazine siliconchip.com.au OLED Display Module, shown in Fig.1. The other modules differ in their exact circuitry, but this example is representative of the features that are present in all. This is the module that was used in the Hot Water System Solar Diverter project. The driver IC is present in a so-called COG (chip on glass) package that is bonded to a thin sheet of glass along with the actual OLED matrix. The connections between the driver IC and the OLED matrix are made on the glass using traces of ITO (indium tin oxide), a conductive material that is also transparent. The connections between the module PCB and driver IC are via a 26-way flat flexible cable, which is also attached to the glass. The 26-way connector is labelled OLED1 in the circuit diagram. U1 is an RT9193 3.3V low dropout (LDO) regulator that provides the 3.3V rail needed by the controller. This part can work with up to 5.5V on its input, so this circuitry allows the module to work with 5V microcontrollers. U2 is an AP3012 1.5MHz switching boost regulator with an external diode for asynchronous rectification. Its output divider sets its output to 12.5V, based on a 1.25V reference voltage at the FB pin. This circuitry replaces the integrated charge pump circuit used by modules based on the SSD1306. The data sheet for the SSD1306 indicates that the charge pump circuit can only generate up to 7.5V, so an external circuit is needed to generate the higher voltage needed for the larger panel. U3 is a TXB0108 automatic bi-­ directional level converter IC that interfaces between different logic levels. It too can work at up to 5.5V on its ‘B’ side, so it is also suitable for 5V microcontrollers. The other modules do not include a level-converter IC, but are permanently configured to use I2C communications. Since I2C is an open-drain bus, a 5V microcontroller will usually have no problem communicating with a 3.3V driver IC, as long as a 3.3V supply is present. Thus, the level converter is primarily needed to allow the module to use the SPI bus. The two 4.7kW resistors provide the pullups needed for an I2C bus. They are also connected in SPI mode, but will simply be overridden by the external microcontroller actively driving siliconchip.com.au Fig.1: the regulator and boost circuitry (U1 and U2) in this circuit diagram for the Waveshare 2.42in module is common to the units we tested, although the others lack the level conversion (U3) chip, so are set up for I2C comms by default. those pins. The 910kW resistor shown connected to the Iref pin sets the display drive current. The driver IC has pins BS0, BS1 and BS2 to set its communication mode. BS0 is pulled low by a connection internal to the COG assembly, while BS2 is pulled low on the module PCB. By default, BS1 is also pulled low and thus the module is configured for operation with a 4-wire SPI bus. J1 and J2 are 0W resistor links that can be moved to change how they are set. Both the SSD1306 and SSD1309 controllers can be set for I2C, 3-wire SPI and 4-wire SPI, as well as two parallel bus types, although not all module types will make the necessary pins available. Most of the monochrome OLED modules we have seen are fixed to I2C mode, with the exception of this Waveshare unit. JP1 is changed to set BS1 high and enable I2C mode, while J2 bridges two pins together in I2C mode; these need to be separate in SPI mode but connected in I2C mode. A copy of the SSD1309 data sheet can be downloaded from www.hpinfotech.ro/ SSD1309.pdf Variants Here is a brief overview of the different modules. For consistency, we Photos 1 & 2: the fivepin header seen here seems to be common to 1.54in variants of this module. It’s not much bigger than the 1.3in modules, but it can draw more current and is bright. Source: www.ebay.com.au/ itm/156327080574 Australia's electronics magazine November 2025  63 Photos 3 & 4: the generic 2.42in version of this module has a four-pin header that matches the smaller modules, while the blackened bezel improves the appearance and robustness of the unit. The locations marked D1 and D2 are fitted with 0W resistors, as required for correct I2C operation. Source: https://core-electronics. com.au/large-oled-i2c-display-ssd1309.html tested those mainly with a white light output, although we did try some other colours. Some have options for blue, green and yellow. The first is the 1.54in variant, as seen in Photos 1 & 2. It is the most similar to the 0.96in and 1.3in modules, and comes closest to being a ‘drop-in’ replacement. It has a five-pin header instead of a four-pin type, but the four GND, Vcc, SCL and SDA pins are centred at the top of the module in the same fashion as the smaller modules. The fifth pin is marked as RES (reset), and was not fitted with a pin in the samples we received. There is a jumper resistor on the rear of the PCB that can be used to set the I2C slave address. The default is 0x78, with the other option marked as 0x7A. These are 8-bit addresses that correspond to 7-bit addresses of 0x3C or 0x3D, respectively. All units we tried were set to the 0x78 address that we typically use. The units that we purchased were supplied with plug-socket jumper wires, which would be well-suited to experimenting with an Arduino board fitted with header sockets, such as an Arduino Uno or similar full-sized board. 2.42in module The generic 2.42in module (Photos 3 & 4) also has the familiar four-pin header at the top of the display, as well as on the left hand-side, which gives some flexibility for wiring. Using the top headers, it too can be simply plugged into the place of one of the smaller modules and has a jumper resistor that can be used to set the I2C slave address. There is a broad border with plated mounting holes. This unit also has a metal bezel covering the OLED glass assembly. As well as giving the unit a more finished appearance, it has the benefit of protecting the fragile glass. With any of these OLED modules, including the smaller types previously reviewed, when we have seen the glass cracked or damaged, it has usually resulted in the display failing, with pixels not illuminating, so this is a handy addition. We also tested a few variants of this display, since we found some available in different colours (see Photo 7). These behaved much the same as Photo 7: the green version of the generic 2.42in module is a striking colour that brings back memories of monochrome computer terminals from many years ago. It is a comfortable fit for the existing GPS Speedometer PCB. the display listed in Table 1, although they did need to have their D1 and D2 diodes replaced by 0W resistors, as seen in Photo 4. It appears that these diodes are provided to protect the display controller from incorrect voltages on the SDA and SCL lines. This should not be a concern if the correct (as required for I2C) open-drain outputs are used, even if the connected microcontroller operates at a different logic level. Without replacing at least diode D2 (on SDA), the display may not work, since the diode blocks the display controller’s acknowledgement of the microcontroller’s commands. Waveshare module The Waveshare module (Photos 5 & 6) has the same display dimensions as the generic part, but is more compact. The underlying PCB is barely larger than the glass assembly, and the unit is fitted with M2.5 standoffs soldered to the rear of the PCB instead of having plated holes. As noted earlier, this module can be set to work with either I2C or SPI. As well as a 0.1in (2.54mm) pitch header, there is a JST header on the board, and the module is supplied with a seven-way JST-to-socket jumper wire (‘DuPont connector’) breakout cable. The 0.1in header is mounted parallel to the PCB, unlike the other modules. Thus, this module is not really a drop-in replacement for the smaller OLED modules. There is no jumper resistor to set the I2C slave address, but it can be set with one of the other pins. The SSD1309 data sheet indicates that the DC pin is used to set the optional bit of the slave address, so it is simply necessary to tie this to either Vcc or ground. For our tests, we configured the module to use I2C mode and connected DC to ground, resulting in this module responding to address 0x78 as expected. Testing We started testing the generic 2.42in module, since we are accustomed to using these modules with an I2C bus. To test the claim that the registers in the SSD1309 match those of the Photos 5 & 6: the Waveshare 2.42in module has an SPI interface by default, but can be configured for I2C by moving two resistors. It is compact, but does not have a header that matches those commonly found on the smaller displays. Source: https://coreelectronics.com.au/242inch-oled-display-module-128x64px.html 64 Silicon Chip Australia's electronics magazine siliconchip.com.au SSD1306, we plugged one of the larger modules into the four-way header on one of our Coin Cell Emulator prototypes. Fortunately, all these modules use the same GND, Vcc, SCL, SDA pin order, although we have seen a handful that swap GND and Vcc! In a pleasant surprise, the display powered up and showed the expected display for the Coin Cell Emulator. This also means that the default I2C address is the same as for the smaller modules. A thorough inspection of the respective data sheets revealed a few registers that do behave differently, but it appears that the registers that we have used for much of our software are in fact identical, with the exception of the charge pump register, which is not present on the SSD1309. The data sheet notes that registers that are not present should not be written to, so the software does not strictly follow the constraints of the data sheet. However, the same code seems to work fine. It would not be difficult to make the necessary changes to fully comply with the data sheet. In all of our tests, we did not note any problems using software written for the SSD1306 with the SSD1309 controller. We also had an enquiry about fitting a larger display to the GPS FineSaver project from June 2019 (siliconchip. au/Article/11673). We had produced a simplified version of this in the July 2025 Circuit Notebook column as the GPS Speedometer (siliconchip.au/Article/18523). This version used a larger font to slightly increase the size of the displayed figures. So we also tried plugging these modules into the simplified PCB for the GPS Speedometer and found that both the 1.54in and 2.42in versions worked without changes to the software. Although we haven’t performed any long-term testing with this arrangement, we think this might be worth trying if you need a larger display for your GPS Speedometer. Photo 7 shows it with a 2.42in display fitted. Comments Versatile One thing that we noticed with the generic 2.42in module was that the switch-mode circuitry gave off an audible squeal, which became louder as more pixels were lit up and the load increased. It was clearly audible when all pixels were at full brightness, but was not as noticeable during more typical displays such as text, where a lesser fraction of the pixels were lit. This display also showed some artefacts, which appeared to be related to matrix scanning. For example, if a row of pixels was lit up, they appeared dimmer than adjacent pixels in rows that were not fully lit. In other words, the drive current seemed to be inconsistent; perhaps another shortcoming of the switchmode circuitry. We didn’t notice those sorts of effects with the other two displays. The current draw values shown in Table 1 tend to back this up and, not surprisingly, the 1.54in module looks more intense, since it draws similar current but has a smaller display area. The lower current draw of the generic 2.42in module suggests its output is sagging under load, and Battery Checker This tool lets you check the condition of most common batteries, such as Li-ion, LiPo, SLA, 9V batteries, AA, AAA, C & D cells; the list goes on. It’s simple to use – just connect the battery to the terminals and its details will be displayed on the OLED readout. Versatile Battery Checker Complete Kit (SC7465, $65+post) Includes all parts and the case required to build the Versatile Battery Checker, except the optional programming header, batteries and glue See the article in the May 2025 issue for more details: siliconchip.au/Article/18121 siliconchip.com.au Australia's electronics magazine November 2025  65 it does look distinctly dimmer when all pixels are lit. Photo 7 shows a green variant fitted to the GPS Speedometer PCB. The pixel dimming effect is most pronounced in views like this, where there are distinct horizontal elements. It is barely noticeable when the usual numeric display is showing. You might recall that some of our other projects using smaller OLED modules have a current draw of around 5-10mA, which is low enough to run from a coin cell. While the values given in Table 1 are with all pixels lit, we don’t think these large displays will be suitable for use with coin cells. The displays are at a size where the pixels are quite noticeable, around 0.3mm to 0.4mm across. Indeed, even the black borders between the pixels are apparent from a normal reading distance. It’s perhaps reminiscent of a vacuum fluorescent display (VFD), so might be handy if you are looking to create a retro appearance. Code examples We took the opportunity to write some code to test the modules. The latest versions of the Picomite BASIC software natively support I2C OLED panels, so it was easy to use a Pico for our tests. The Pico can also be programmed using the Arduino IDE. All of our examples (both Picomite BASIC and Arduino) use the same wiring diagram shown in Fig.2. We used the PicoMiteRP2040V6.00.03.UF2 variant of the firmware, although it should work with any version that supports an external display panel (ie, all but the HDMI or VGA capable versions). These two OPTIONs set up the display panel: OPTION SYSTEM I2C GP0,GP1 OPTION LCDPANEL SSD1306I2C,LANDSCAPE The OLED_DEMO.BAS file runs through a few demonstrations, including text in a variety of fonts and some shapes. It also shows a spinning cube, making use of the 3D engine that is included with Picomite BASIC. You can also try loading the OLED_ DEMO.uf2 directly onto a Pico. We were able to test the current draw by using the CLS 0 and CLS 1 commands to turn all pixels off or on once the display was configured. Arduino For the Arduino IDE, we used version 2.35.30 of the u8g2 library (https:// Fig.2: this wiring diagram can be used for either a Pico or Pico 2 microcontroller, although we only tested a Pico with our code examples. Other boards based on RP2xxx processors should also work when GP0 is connected to SDA and GP1 to SCL. 66 Silicon Chip Australia's electronics magazine github.com/olikraus/u8g2). It can also be installed by searching for “u8g2” in the Library Manager. The sketch we have written is based on the GraphicsTest.ino demo example from the u8g2 library. It shows a different set of animations. We have included the requisite constructor for an SSD1309 controller connected to I2C0 on pins 0 and 1, using the same wiring as the Pico­ mite example. The demo code shows several different drawing, text and animation examples. The sketch, library and a compiled UF2 file can be found in the Arduino folder of the software downloads (siliconchip.com.au/Shop/6/3563). Summary While there is a lot of similarity with smaller OLED modules, these larger parts have a few subtle differences from the smaller OLED modules that mean that they may not be a drop-in replacement. Their larger size means a higher current draw, so they will not be suitable for many battery-powered applications. In cases where power is not an issue, they could work well. The GPS FineSaver is a good example, where the car’s accessory socket can provide ample power and the larger display will be useful, although the higher current draw might be troublesome for the linear regulator on that project. Thus, we suggest using the 5V USB power input. Their larger size may make them more delicate and susceptible to damage. It is a pity that the generic 2.42in module seems to have inferior power circuitry, since the metal bezel protecting the glass looks to be a useful and elegant addition. Some models may need minor modifications to work correctly. The 2.42in versions of the OLED are almost as large as some LCD touch panel modules; we have used 2.8in versions of these LCD panels in numerous projects. The LCD panels typically have a touch sensor and 16-bit colour, so are quite a bit more versatile. Searching for the controller name (SSD1309) at online sellers seems to be the best way to find these and similar modules; the sources of the modules we tested can also be found in Table 1. Note that there are also some SPI versions of SSD1309-based display SC modules available. siliconchip.com.au FROM EVERYDAY PRINTS TO SHOW-STOPPERS. Feed your printer what it deserves. Explore the extensive range of NEW TO FROM JUST $ Filament JAYCAR THE RELIABLE PRINT CLASSIC /RL ADD SPARKLE TO YOUR PRINTS TL6414 TL6440 TL6457 PLA+ ONLY $22.95/1kg Roll 16 Colours TL6457 - TL6472 TL6432 Rapid PLA+ ONLY $24.95/1kg Roll 10 Colours TL6435 - TL6445 HIDE THE LINES, KEEP THE STYLE Galaxy PLA ONLY $34.95/1kg Roll 3 Colours TL6431 - TL6433 DURABLE PRINTS, DONE FAST SILKY TEXTURE, GLOSSY FINISH EASY LIKE PLA, TOUGH LIKE ABS TL6485 TL6513 TL6418 Silk PLA ONLY $24.95/1kg Roll 13 Colours TL6418 - TL6430 MATTE PLA ONLY $24.95/1kg Roll 12 Colours TL6483 - TL6494 . 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Jaycar reserves the right to change prices if and when required. PART 2: PHIL PROSSER Digital Preamplifier and Crossover This advanced preamplifier uses digital processing to provide unprecedented flexibility. It has three digital inputs, including high-fidelity USB, four analog stereo inputs, four stereo outputs, two digital outputs (including USB) and a stereo monitor channel. Having described how it works, let’s get into the assembly process, starting with the circuit boards. T he Digital Preamp is housed in a slimline 1U (44.5mm-tall) rack-mounting case, although it can just as easily sit on a shelf. Specifically, we used the Altronics H5031 vented black aluminium case. Since rack cases have a standard height and width, the only real variable is the depth. In this case, it is 255mm, which is on the low end for rack cases. So most 1U vented rack cases should be suitable for this build, but we think the H5031 is an excellent choice unless you have a particular reason for wanting to use another. The result is very neat, and the required metalwork is not hard – although there is a fair bit of drilling to do on the rear panel. It houses the IEC C14 mains input connector, mains fuse holder, holes for the USB input, S/PDIF input/output and 10 dual RCA connectors for analog inputs and outputs. Before we get to preparing the case, though, let’s assemble the PCBs. It is not an overly difficult process, but there are a lot of parts to fit onto three boards, so it will take a while. Power Supply PCB assembly Build the Power Supply board as shown in its overlay diagram, Fig.14. Assembling this board is straightforward, and a quick job compared to the main board. Features & Specifications Four stereo analog inputs (1V RMS maximum) Frequency response: 7Hz to 43kHz <at> -3dB (with PCM1798 DACs) One analog input can be configured to handle 2V RMS+ S/PDIF coaxial and TOSLINK digital audio inputs Monitor output for analog inputs Four independent stereo output channels, 2V RMS full scale High sampling rate/bit depth USB audio stereo input and output Programmable equalisation, crossovers, relative attenuation & delay for each output Memory for four different configurations Attenuation at 20Hz: 0.3dB; Attenuation at 20kHz: 0.0dB Volume control: +12dB gain to -128dB attenuation in 0.5dB steps Total harmonic distortion plus noise (THD+N): 0.003% across the audio band (largely unchanged to >40dB attenuation) 68 Silicon Chip Australia's electronics magazine siliconchip.com.au siliconchip.com.au The completed Power Supply PCB. We have used a small amount of silicone sealant on the heatsinks and inductor to keep them stable. D6 100nF 470mF 47mH L3 100mF 12V AC ~ 2200mF 100mF + + 2200mF D4 LM337 4004 L2 2200mF D5 4004 + 2200mF BR1 KBL404 10 m F 10mF 100nF 100nF D1 100nF + + + 2200mF 2025-02-16 v2.1 Digital Crossover Power Supply 47mH L1 ~ REG1 LM317 220W 1.5kW 4004 F2 1A F1 1A 10mF D2 4004 + CON4 10mF CON2 100mF L4 330µH GN D CON1 +10V GND -10V REG3 5819 + 100nF CON3 12V AC LM2575T-5 + +5V GND + Start by fitting the resistors. There are only two different values; the 220W resistors will have two red stripes at one end, while the 1.5kW resistors will start with brown and green stripes. Follow with the diodes; these all have the cathode stripes either to the right or upward. Make sure the schottky diode (D6) goes in the correct position, near REG3. With these parts in, you can fit the 100nF MKT and higher-value electrolytic capacitors. We have arranged these so that, in each case, their longer “+” lead goes towards the top of the board when the silkscreen is the right way up. Next, mount the inductors. There are three bobbin-style inductors and one toroidal type. The three bobbin inductors are all the same value; they must have current ratings of at least 500mA. Put a dab of neutral-cure silicone sealant under the toroidal inductor to keep it stable and avoid stress on the solder joints. Follow with the connectors (with the terminal block wire entries going towards the nearest edge of the board), fuse holders (retaining clips outwards), fuse and bridge rectifier. Make sure the bridge’s positive terminal goes nearest to the terminal blocks as shown in Fig.14. Next, install the LM2575-5 switchmode regulator. Make sure this is the 5V version, and that you install it with its heatsink tab facing the edge of the PCB. The PCB footprint is right for the bent lead version of this device; if you get the version with leads all in a row, gently bend the first, third and fifth leads out to suit the PCB pad arrangement. Next, mount the LM317 and LM337 linear regulators to their heatsinks (a folded piece of aluminium similar to the dimensions of the Altronics H0625 will do) using insulating washers and bushes. The heatsinks must be no more than 26mm tall, so that the power supply board will fit inside the case later. If using the specified heatsinks, mount them flush to the PCB; this is required for it to fit in the case. Add a dab of neutral-cure silicone sealant to the base of each heatsink to ensure it is stable and does not move around in use. When soldering the devices to the board, make sure you don’t get REG1 (LM317) and REG2 (LM337) mixed up. 47mH 220W 1.5kW REG2 10nF 2200mF 10 m F GND 10mF 100nF Fig.14: the power supply board assembly is straightforward. The main thing to watch is the orientation of all the electrolytic capacitors and bridge rectifier. Make sure the terminal block wire entries are accessible and the fuse holder retaining clips are on the outside. Finally, don’t forget the heatsinks for REG1 & REG2 – they are required! Testing the power supply With everything mounted, connect a DC power supply set to anything between 15-25V, with its negative output to ground, and positive output to either of the AC inputs. Check the +5V output. This should measure 4.9-5.1V. If there is no output, verify you have the fuses in and that the 1N5819 diode is the right way around. Also check that you have the LM2575 (REG3) the right way around. On one prototype, we bent the leads the wrong way, and can attest to the fact that the device doesn’t work when it is back-to-front! Australia's electronics magazine Check the voltage on the positive DC output connector, CON2. You should measure 9.7-10.3V on its left-most terminal. If not, check around the LM317 device (REG1), especially the 220W and 1.5kW resistors and the orientation of its protection diodes. Now connect the positive of your power supply to the ground input terminal, and the negative to either of the AC inputs. Repeat the above check on CON2, but this time look for a negative voltage with a magnitude of 9.7-10.3V on the right-hand terminal. That verifies the power supply is November 2025  69 470mF 470mF + + D1 Make no mistake, this is a big board. It measures 331 × 150mm with 553 parts – see Fig.15. Plan to assemble this in stages, and mount groups of parts in batches so you don’t lose track of where you are at. We find it very helpful to make a copy of the parts list and to install groups of components one at a time, then cross them off the list. Our strategy is to get the onboard power supply working first, then the input and output switching, then the microcontroller (so we can see the LCD working), then the rest. This strategy does need to consider mounting the SMD parts first, as that is easier with some ‘elbow room’. First, install 10mm standoffs on all CON16 CONTROLS GND 18pF 18pF 23 12 GND X2 CLATCH 8MHz CDATA CCLK COUT 1 IC17 25AA256 1 100nF Digital Preamplifier assembly Silicon Chip IC15 PIC32 100nF 100nF A working, so it’s time to move onto the main Digital Preamplifier board. 70 10mF 470W 4.7kW 10 m F 34 100nF FB16 1kW 10kW CON19 LCD JP1 1 CON21 LCD BIAS CON8 1 DVDD3.3 LCD - REVERSE MOUNT mounting holes. The four at the front of the board remain there for installation, while the two at the rear should be removed when you install the board to the rear panel of the case. A few things to consider before we get stuck in. If you are using the ADAU1467 Core Board, do not load anything inside the area marked DSP CORE or DSP ADAU1467. Also, if you are using PCM1794A DAC ICs instead of PCM1798s, you must use the alternative resistor and capacitor values, which are marked on the PCB. A trick we use for through-hole parts is to insert several, then place a sheet of paper over them, allowing us to flip the board over without them falling out. The general loading order is then: 1. Fit all the surface-mounting capacitors and resistors, which are mostly in M2012 packages, except for 100pF CLIP BAT85 BAT85 1kW 100 m F 47mF + IC6 NE5532 1kW 100nF 91W 91W IC8 NE5532 47 m F 10kW 10kW + 100 10W 47mF BA D16 10W 470pF 100nF D11 100nF 100 m F 10W 10kW 10kW 100nF 47kW COIL 100nF 22mF 100kW 100kW BC547 100nF D13 4.7kW IC7 NE5532 470pF 47 m F RLY5 4148 D18 100nF 10W 1 ADC 47mF 100nF GND FOR P 2.7nF 820W DSP CORE 10mF 100nF 100nF 100nF 100nF 1kW 10mF 10mF 100nF 100nF IC18 ADAU1467 100nF 100nF 100nF 10mF Microcontroller VR44 20kW 1k W 10kW 22 m F 470pF 100kW 4.7kW D12 D19 D23 D22 BAT85 BAT85 BAT85 BAT85 4148 D17 10kW D20 BAT85 33mF D21 BAT85 D25 BAT85 680W D24 BAT85 91W 2.7nF 10nF 2.7nF 1 CON9 ADC TEST CON17 (ICSP) 100nF Australia's electronics magazine COIL RLY4 CON7 220W 1mF 1 Q8 IC9 CS5381 220pF 100nF 100pF 100W 100W 150pF 4.3kW 100nF 5.6nF 10mF FB1 X1 100nF CON12 D3 470mF 1 LED2 LD1117V33 REG1 -10V + 100nF FB4 100nF 100nF GND Power + Supply 100nF 4004 +10V LD1117V33 REG2 FB14 100nF FB2 4.7kW PIC32MX270F256D-50I/PT + + 100nF 100nF 10nF 10nF 100nF + + 10mF 10nF 10nF FB15 100kW 100nF 100nF 100nF 10mF 100nF Q1 1 + D10 4148 47mF Q4 BC547 CON11 BC557 D7 L5 470mF 470mF +5V 47mH GND FB6 470mF 100nF 100nF 470mF FB7 10mF 100nF FB3 100nF 10mF 680W 100nF 220W 100nF + 100 m F 100 m F 33mF 220 m F 4004 REG3 D4 Q12 BC547 10kW MCLR V+ GND PGED PGEC BC547 10kW + D6 10mF AVDD_3.3 100kW 100kW Q13 47kW 220 m F BC557 100kW 100kW Q2 10kW 4.7kW 4.7kW 10kW 4148 4.7kW 4148 4148 Q9 BC547 4.7kW 1 10kW 5V_DAC LRCLK 4.7kW IC16 MAX22345SAAP+ Q10 BC547 D5 COIL RLY3 10kW 22 m F 100kW Q7 GND MCLK LRCLK BCLK SDATA 100nF CON13 10mF DIGITAL I/O 100nF 100W 1 J2 Q6 COIL FB12 100pF BC547 BC547 RLY2 4148 4148 D9 INPUT SWITCHING D14 10nF 4.7kW Q5 LM317 (100nF) 100nF J1 TOSLINK TX 4004 1 100kW 4.7kW COIL RLY1 4148 D8 22m F 100pF 100nF J3 100kW 100pF Q3 BC547 5.6W 10kW 10kW 1 (OPT2) 100kW IC13 74LVC244 miniDSP MCHStreamer 4.7kW 1 75W 75W FB10 470pF * 22m F FB13 BC547 FB8 FB11 BT 100pF 680W 91W * 22mF CON14 * 100pF Q1 NJT4030P FB9 1 2 3 CON10 OUT 100nF S/PDIF * ATTENUATION 100nF RESISTORS 22 m F * IN OPT1 TOSLINK RX CON5 680W TUNER 680W CON4 AUX1 100pF CON3 AUX2 2 2m F CON2 100nF 12.288MHz 18pF 100W 18pF 2025-03-24 the capacitors in the μF range, which will be larger. The numbers in square brackets (“[]”) are for when you are using the ADAU board. There are: T 1[0] × NJT4030P transistor in an SOT-223 package T 4 × 47μF tantalum capacitors T 2 × 33μF tantalum capacitors T 22[17] × 10μF tantalum/ceramic capacitors T 42[29] × 100nF ceramic capacitors T 5 × 10nF ceramic capacitors T 2 × 2.7nF ceramic capacitors T 5 × 220pF ceramic capacitors T 4[2] × 18pF ceramic capacitors T 10 × 10kW resistors T 1[0] × 4.3kW resistor T 2[1] × 1kW resistors T 1 × 470W resistor T 5 × 220W resistors T 2[1] × 100W resistors T 5 × 22W resistors siliconchip.com.au 100nF 100nF 12.288MHz IC4.1 100nF 100nF 1 PCM1798 SDATA 1 10 m F BCLK LRCLK 10kW MCLK GND CON1.1 10mF W 18pF 74LVC244 22W 22W 22W 22W 22W 47kW 180W 180W 200W 200W 100 m F + 100 m F 2.7nF 100nF 2.7nF 2.7nF 10mF 100nF 47mF 100nF 10kW 220W 27nF 100nF 2.7nF 10mF 10mF IC4.4 100nF 100nF PCM1798 SDATA 1 1 10mF BCLK LRCLK 10kW MCLK GND CON1.4 DAC Ch2 Mar 2025 Digital Preamp V2.3a TGM Was Here 2025 T 16{0} × 820W resistors T 0{32} × 750W resistors T 17{1} × 220W resistors T 16 × 200W{270W} resistors T 16 × 180W{0W} resistors (wire links can be used as 0W resistors) T 1 × 5.6W resistor 3. Fit the 15 [14] ferrite beads by inserting resistor/diode lead off-cuts or tinned copper wire through the beads and then soldering them to the board. If you need the AUX1 input to handle more than 1V RMS, swap FB8 & FB9 for resistors and then install the attenuator resistors to make dividers (see the red text in Fig.15). This approach can be used to make the other inputs handle high voltage if needed. 4. Fit all the MKT polyester and through-hole ceramic capacitors: T 49 × 100nF T 8{0} × 27nF Australia's electronics magazine 820W 100nF IC3.4 NE5532 220W 220W 27nF 2.7nF 100nF 47mF 100nF 10mF 10kW 10mF 100 W IC1.4 NE5532 + 820W 820W 220W 220W 200W 10W 10W 220W 220W IC1.3 NE5532 47kW 100W 4.7kW BC547 180W 180W 200W 200W + 100nF 2.7nF 820W 820W 220W 10mF 100W 47kW 47kW 100W 4.7kW BC547 180W 180W 200W 2.7nF 820W 820W IC2.2 NE5532 2.7nF 100nF 180W 27nF 2.7nF DAC Ch3 2. With those all in place, install all the diodes and through-hole resistors. We recommend doing these now as you can still flip the board and solder things flush to the PCB without too much fiddling. Keep the lead off-cuts as you will need them later for the ferrite beads. Numbers/values in braces (“{}”) are for PCM1794A DAC ICs: T 3 × 1N4004 diodes T 13 × 1N4148 (or 1N914) diodes T 12 × BAT85 diodes T 12 × 100kW resistors T 11 × 47kW resistors T 13 × 10kW resistors T 17 × 4.7kW resistors T 5 × 1kW resistors T 5 × 680W resistors T 10 × 100W resistors T 4 × 91W resistors T 2 × 75W resistors T 12 × 10W resistors siliconchip.com.au 27nF IC4.2 IC4.3 100nF 100nF 100nF 100nF PCM1798 1 PCM1798 SDATA 1 1 SDATA 1 BCLK 10mF BCLK 10mF LRCLK LRCLK 10kW MCLK 10kW MCLK GND GND CON1.3 CON1.2 DAC Ch4 100nF IC10 100mF 180W 200W 100mF 8.2nF 820W 820W 10mF 100nF 10mF 47mF 100nF 10kW 10mF 8.2nF 8.2nF 8.2nF 100nF 10mF 2.7nF 8.2nF COIL 100nF RLY6.4 8.2nF IC2.4 NE5532 100nF 2.7nF + 100nF 100nF Q14.4 4148 220W 220pF 100nF 47mF 100nF 10kW 100nF 27nF 100nF 200W 10W 10W IC2.3 NE5532 IC1.2 NE5532 2.7nF 100nF 10mF 100W 47kW 47kW 100W 4.7kW BC547 220W 2.7nF 820W 820W 220W 220W 2.7nF 100nF 200W + CON8.4 OUT1 100nF 180W 200W 100 m F 27nF 180W 220W 100W 47kW 180W 200W + 100nF 100nF 100nF IC18 ADAU1467 100nF + 8.2nF 220W 220pF 100nF 100 m F 200W 10 W 10 W 220W 220pF DSP CORE 200W 27nF 820W 820W ADC GND 220W 220pF nF 180W COIL RLY6.3 8.2nF 8.2nF 8.2nF IC3.2 NE5532 2.7nF 180W 220W 220W 2.7nF 100nF 820W 820W 100nF FOR PCM1794A 2.7nF TO 2.2nF 820W TO 750W 8.2nF Q14.3 4148 100nF 100nF 27nF COIL RLY6.2 8.2nF 8.2nF 200W 100mF + 100mF 100nF 7m F 200W 10W 10W + 100 m F FOR PCM1794A 220W TO 560W OMIT 27nF 8.2nF 200W 820W 47mF + 1kW 1kW 100 m F IC6 NE5532 1kW 100nF 10W Q14.2 4148 180W 220W + 100nF 180W 100nF + 100mF 10W mF 47kW D16 10W mF FOR PCM1794A 200W TO 270W 8.2nF TO 2.7nF 180W TO 0W 1kW 10W BAT85 8.2nF D15 100mF BAT85 IC5 NE5532 BAT85 BAT85 47kW 8 D11 100nF IC1.1 NE5532 8.2nF 100nF D13 COIL RLY6.1 180W 100kW Q14.1 BC547 4148 220W 47m F 100nF 47m F IC3.1 NE5532 10mF IC2.1 NE5532 22mF 47kW 100W 4.7kW 100pF 100W 100W CON8.3 OUT2 CON8.2 OUT3 IC3.3 NE5532 CON8.1 OUT4 CON6 MONITOR OUT DAC Ch1 Fig.15: building this board will take a while, so make sure you’re organised. It’s best to break it up into several sessions, and follow our suggested order of assembly. The most important thing is to get all the SMD ICs orientated correctly, make sure the solder flows onto all the pins and pads, and fix up any solder bridges that form. Clean off the flux residue so you can inspect all the joints properly. T 1 × 10nF T 16 × 8.2nF{2.7nF} T 16 × 2.7nF{2.2nF} T 4 × 470pF T 1 × 150pF At this point, you have fitted all the low-profile parts other than ICs. Now we can complete the onboard power supply section so we can test it. Load everything else in the section of the board marked Power Supply, at lower left. Use insulator kits and jiggle the pins of the heatsinks into the holes in the PCB to secure them. While finishing the power supply, it is ideal to fit the following across the whole board: T 14 × BC547 NPN transistors T 2 × BC557 PNP transistors T 8 × 10μF electrolytic capacitors T 5 × 47μF electrolytic capacitors T 14 × 100μF electrolytic capacitors November 2025  71 ◀ This Digital Preamplifier was built using the discrete ADAU1467 chip. We have gone to a fair bit of bother to get all the capacitors facing the same way; check yours as you go. Remember that the + indicates the side where the longer lead is inserted (the stripe on the can indicates the opposite, negative side). Power supply testing You can now apply 5V DC to the digital power input, CON11. This should draw only a nominal current as there is no load. Measure the voltage on the DVDD3.3 test point, which is next to the LCD header, CON8, and close to the bottom edge of the PCB. You should measure 3.2-3.4V. If not, verify your applied voltage, check for anything getting hot and ensure you have all the capacitors in the right way around. Next, measure the voltage on the AVDD3.3 test point, which is just to the left of diode D6, below the DIGITAL I/O section. You should again measure 3.2-3.4V. If not, find what is wrong, most likely a capacitor or regulator back-to-front. Now apply ±10V to the analog power input, CON12. You can use the previously assembled and tested power supply board for this, feeding in low-voltage AC (eg, from a 12V AC plugpack). This should also draw only nominal power. Measure the voltage at the 5V_DAC test point, which is near the AVDD_3.3 test point you checked earlier. This should be 4.85-5.15V. If those are all correct, power it down as it’s time to move onto the next section of the board. Filling the I/O sections With the power supply rails working, we can move onto the next stage and get the inputs and outputs working. This means fitting the remaining parts in both the DIGITAL I/O and INPUT SWITCHING sections, in the upper-left and upper-mid parts of the board. Fit the following: T 8 × 100pF ceramic capacitors T 8 × 22μF bipolar electrolytic capacitors (they are not polarised) T 9 × 5V telecom relays; ensure they go in the right way around T 10 × 2-way RCA sockets; make sure these are neat and align with one another The best way to test the board now is to connect it to the power supply board and use that to power everything. Connect the 5V DC, grounds 72 Silicon Chip Australia's electronics magazine siliconchip.com.au siliconchip.com.au Before we make the LCD cable, we need to discuss how it will connect to the LCD screen itself. The screen will have a space for a a 14-way (7×2) DIL header. We need to use this type of screen, rather than the more common type with a 16-pin SIL header, because those latter types are too large to fit in the limited space available in a 1U rack case. The LCD module will need a 7×2 header, and you will need to extend the wires through to the backlight. We used an 8×2 header and cut the spare pins off, then running light duty hookup wire to the backlight pads. This allowed us to plug the 8×2 IDC header in. Double-check the power supply pins on your module; the Altronics module should be a straight plug-in (with the IDC socket orientated correctly), but the other ones specified may have swapped power and GND pins! If so, you will have to swap them in your cable. With that in mind, cut a 250mm length of 16-way cable and install the IDC connector(s), making sure that it will be able to go from the LCD connector on the main board (most likely CON8) to the rear of the LCD panel once installed. Make sure the IDC connectors are fulled crimped on both cables. If they aren’t compressed adequately, some wires may be open circuit, and the TGM Was Here Mar 2024 22nF BACK S1 22nF 10kW 22nF IR RX CON2 10kW Digital Preamp Controls v1.1 1 22nF UP 22nF S2 10kW CON1 DOWN 22nF S3 10kW Fig.16: compared to the other two, the control board is a doddle. Make sure all the controls are square and fully pushed down onto the board before soldering them, though. 10kW Now we really start to bring the Digital Preamplifier to life. Load all the single-row pin headers. These can be snipped or snapped off 40-way header strips. These are: T 6 × 5-way pieces for the ADC, DAC and SPI test points. These are not essential, but can be really handy for debugging. T 1 × 2-way section for the microcontroller reset capacitor enable. Remove the jumper on this if you need to reprogram the micro. T 1 × 6-way section for the programming header, CON17. There are also some DIL headers to fit: T Solder a 5×2 section for the controls (CON16). T Only one LCD header is needed. If you plan to mount the LCD with a 90° header soldered to the rear of the LCD (ie, on the inside of the case), fit CON8. If you have an arrangement where you 10kW Microcontroller section can actually solder the header to the front of the LCD, use CON19 (although we can’t see how this can be done). Next, mount the 20kW trimpot, then solder in the 8MHz crystal, 25AA256 EEPROM IC and the PIC microcontroller. Soldering surface-mount parts has been described in many articles so I won’t go into great detail. The main thing is to ensure the parts are aligned with their pads and, critically, orientated correctly before soldering more than one pin. Use plenty of flux paste and do not be scared to add too much solder, then use wick to remove solder bridges. A bit more flux paste will make the wick extremely effective. Always inspect every pin on the devices after soldering them using a loupe or microscope. Another good trick is to use a phone with macro photograph capability; the pictures on page 77 of the ADAU chip were taken with an iPhone 15. To test this section of the circuit, we’ll need cables to connect the LCD panel and control board. You’ll also need to assemble the control board, as per Fig.16. There aren’t too many components on it, so fit them starting with the lowest profile parts, moving to the tallest. To connect the LCD panel and control board to the main board, you need lengths of 16-way and 10-way ribbon cable. Cut a 300mm length of 10-way cable and use a vise (or proper tool if you have one) to crimp 10-way IDC sockets onto both ends. Orientate the connectors so that, once installed, the cable will exit the main PCB in the direction of the front panel control board. Make sure that the pin 1 marker at each end goes to the same edge of the ribbon. 10kW and ±10V rails. You can power the whole lot from a ±15V power supply connected to the AC inputs, or a 12V AC 1A plugpack (but only short-term). On powering it up, you should find: ● The voltages at CON11 & CON12 are as expected, and the AVDD_3.3, DVDD_3.3 and 5V_DAC rails/test points are good. ● After a few seconds, the output relays should click on. If this doesn’t happen: > Check that the emitter of Q9 goes from 0V up to more than 3V a few seconds after power on. If not, there is something wrong with what is driving this. Are the BC547 and BC557s in the right spots? > Check that the anode of D10 goes high a few seconds after power-on; this is just below pin 1 on CON13 for the MiniDSP. > There are two pairs of resistors in the upper-left corner of the power supply section, 10kW/10kW and 4.7kW/4.7kW. Check that their junctions settle to about the same voltage; if they don’t, something is awry. Check the part values and orientations in this section. ● Finally, check your relay driver transistors and the back-EMF diodes, and make sure the relays are not backto-front. If the relays click on after a few seconds, everything is looking good, so we can move on. 22nF TP1 RE1 ITSOP4136 IRD1 73 following tests won’t go too well. But you don’t want to crush the connectors to the point that they fracture. Parts List – Digital Preamplifier & Crossover Now connect the LCD screen and Control PCB to the main PCB using your new cables. Make sure you have the headers the right way around, and pin 1 on the PCBs aligns with pin 1 on the cables. To verify this, use a DMM set on continuity mode to check for GND continuity between all three boards once they are connected. If you can’t find continuity, check the cables and connectors. Power the Digital Preamplifier from its Power Supply PCB, as before. Check that the current draw is less than 200mA DC or 500mA AC and nothing gets hot. You will then need to adjust the LCD bias by turning VR44, the sole trimpot on the main board. Adjust this up and down until you get either clear text or squares on the display. If you have not programmed the PIC yet, now is the time to do so. If you purchased your PIC microcontroller from the Silicon Chip Online Shop, it will come pre-programmed, so you won’t need to program it. Remove the jumper from JP1 if one is inserted, and use a PICkit or Snap programmer connected to CON17 and the Microchip MPLAB X IPE to load the 0110725A.HEX file into the PIC. We have always used the Digital Preamplifier’s power supply during programming. Once the chip is programmed, you should see a boot screen on the LCD, then the Digital Preamplifier should go into the idle volume set mode. Rotate the rotary encoder; in this mode, it acts as a volume control, so you should see the Attenuation level go up and down. Next, get a Philips RC5 compatible TV remote control (eg, a universal remote set for a Philips TV) and check this also controls the volume. You may need to try a few different Philips TV codes until you find one that works. Then press the channel up and down buttons on the remote. You should hear the relays click. If any of these don’t work, and especially if the display doesn’t work: ● Check that the 8MHz crystal has a waveform at 8MHz using an oscilloscope. ● Check that the LCD_RS, LCD_E and LCD_RW lines, as well as LCD_D4 through LCD_D7, have signals on them 1 1U black aluminium 19-inch rack-mount case [Altronics H5031] 1 16×2 wide-angle blue LED backlit alphanumeric LCD [Altronics Z7018] ♦ 1 four-layer PCB coded 01107251, 331.5 × 150.5mm 1 12V+12V 30VA toroidal mains transformer [Altronics M4912C] 15 small ferrite beads (FB1-FB4, FB6-FB16) [Altronics L4710A] 1 47μH 0.5A high-frequency inductor/choke (L5) [Altronics L6217] 1 TOSLINK fibre optic receiver (OPT1) [Altronics Z1604] 1 TOSLINK fibre optic transmitter (OPT2) [Altronics Z1603] 9 5V DC coil 2A DPDT telecom relays (RLY1-RLY5, RLY6 × 4) [Altronics S4128B] 1 3A 250V AC DPDT switch [Altronics S1050] 1 20kW top-adjust miniature trimpot (VR44) 1 12.288MHz crystal, HC-49 (X1) 1 8MHz crystal, HC-49 (X2) 2 16 × 22mm PCB-mounting heatsinks for TO-220 devices (for REG1 & REG3) [Altronics H0650] ♦ Mouser 758-162KCCBC3LP can be substituted but the power & ground pins may be swapped Hardware 2 TO-220 insulator kits [Altronics H7210] 1 225 × 46mm piece of 1-1.5mm thick aluminium, Presspahn or similar material 10 4G × 6mm self-tapping screws [Altronics H1145] 4 M3 × 10mm tapped spacers 8 M3 × 16mm panhead machine screws 12 M3 × 6mm panhead machine screws 20 M3 shakeproof metal washers 4 M3 flat metal washers 10 M3 hex nuts 5 100mm cable ties 4 large adhesive rubber feet [Altronics H0950] 1 rubber boot for the mains input socket [Altronics H1474] 5 9.5mm rubber grommets [Altronics H1456] 1 3D-printed LCD bezel (details to come) Wire & cable 3 1m length of 7.5A mains-rated blue wire 1 1m length of 7.5A mains-rated brown wire 1 1m length of 7.5A mains-rated green/yellow striped wire 1 1m length of 16-way ribbon cable 1 250mm length of 13mm diameter clear heatshrink tubing 1 1m length of 5mm diameter clear heatshrink tubing Connectors 6 5-way pin headers, 2.54mm pitch (CON1 × 4, CON9, CON21) 10 2-way vertical PCB-mounting red/white RCA sockets (CON2-CON6, CON8 × 4, CON10) [Altronics P0212] 1 2-way polarised header with matching plug and pins (CON7) 2 2×8-pin headers, 2.54mm pitch (CON8, CON19) 1 2-way miniature terminal block, 5/5.08mm pitch (CON11) 1 3-way miniature terminal block, 5/5.08mm pitch (CON12) 1 2×5-pin header, 2.54mm pitch (CON16) 1 6-way pin header, 2.54mm pitch (CON17) 1 2-way pin header, 2.54mm pitch, plus jumper (JP1) 1 chassis-mounting IEC C14 10A mains input socket [Altronics P8320B] 1 panel-mounting M205 safety fuse holder [Altronics S5992] 2 16-way IDC crimp connectors [Altronics P5316] 2 10-way IDC crimp connectors [Altronics P5310] Semiconductors 16 NE5532(A) dual low-noise op amps, DIP-8 (IC1.1-IC3.4, IC5-IC8) 4 PCM1798 or PCM1794A DAC ICs, SSOP-28 (IC4.1-IC4.4) 2 74LVC244APW,118 octal buffers/line drivers, TSSOP-20 (IC10, IC13) 1 CS5381 ADC IC, TSSOP-24 (IC9) 1 PIC32MX270F256D-50I/PT 32-bit microcontroller, TQFP-44 (IC15, 0110725A.HEX) 74 Australia's electronics magazine Testing the microcontroller Silicon Chip siliconchip.com.au Additional Parts for the Preamp 1 25AA256-I/SN 32kB serial EEPROM, SOIC-8 (IC17) 1 Analog Devices ADAU1467WBCPZ300 digital signal processor, LFCSP-88 (IC18) 2 LD1117V33 3.3V low-dropout regulators, TO-220 (REG1, REG2) 1 LM317T adjustable linear regulator, TO-220 (REG3) 1 NJT4030P 40V 3A PNP transistor, SOT-223 (Q1) 2 BC557 45V 100mA PNP transistors, TO-92 (Q2, Q11) 14 BC547 45V 100mA NPN transistors, TO-92 (Q3-Q10, Q12-Q13, Q14.1-Q14.4) 1 5mm red LED (LED2) 3 1N4004 400V 1A power diodes (D1, D3, D6) 13 1N4148/1N914 75V 200mA signal diodes (D4-D5, D7-D10, D14, D17-D18, D26.1-D26.4) 12 BAT85 30V 200mA schottky diodes (D11-D13, D15-D16, D19-D25) Through-hole capacitors 7 470μF 25V low-ESR radial electrolytic 2 220μF 25V radial electrolytic 14 100μF 25V low-ESR radial electrolytic 2 47μF 50V bipolar radial electrolytic 5 47μF 25V low-ESR radial electrolytic 8 22μF 50V bipolar radial electrolytic 8 10μF 50V 105°C radial electrolytic 1 1μF 63V radial electrolytic 49 100nF 63V/100V MKT 8 27nF 63V/100V MKT 1 10nF 63V/100V MKT 16 8.2nF 63V/100V MKT 1 5.6nF 63/100V MKT 16 2.7nF 63V/100V MKT 4 470pF 100V C0G/NP0 ceramic [Kemet C317C471J1G5TA] 1 150pF 50V C0G/NP0 or SL ceramic 8 100pF 50V C0G/NP0 or SL ceramic SMD capacitors (SMD 0805 size 50V X7R ceramic unless noted) 4 47μF 16V tantalum, SMC case [Kyocera AVX TAJC476K016RNJ] 2 33μF 16V tantalum, SMC case [Kyocera AVX TPSC336K016R0150] 22 10μF 10V tantalum, SMA [Kyocera AVX TPSA106K010R0900] 41 100nF 5 10nF 2 2.7nF ±5% C0G/NP0 5 220pF C0G/NP0 4 18pF C0G/NP0 Through-hole resistors (all ¼W ±1% metal film unless noted) 12 100kW 16 820W 10 100W 11 47kW 5 680W 4 91W 13 10kW 17 220W 2 75W 16 4.7kW 16 200W 12 10W 5 1kW 16 180W 1 5.6W SMD resistors (all M2012/0805 size ±1% unless noted) 10 10kW 2 1kW 5 220W 5 22W 1 4.3kW 1 470W 2 100W siliconchip.com.au Optional parts for MCHStreamer USB interface 1 miniDSP MCHStreamer or MCHStreamer Lite kit 1 MAX22345SAAP+ four-channel (3+1) digital isolator, SSOP-20 (IC16) 2 2×6-pin headers, 2.0mm pitch (CON13, CON14) [Mouser SAMTEC 200-SQW10601LD] 2 100nF 0805 50V X7R ceramic capacitors Alternative parts to ADAU1467 chip 1 ADAU1467 Core board 2 2×18-pin female headers Control board parts 1 double-sided PCB coded 01107252, 108.5 × 24mm 1 TSOP4136 infrared receiver (IRD1) 1 90° PCB-mounting rotary encoder with integral switch (RE1) [Altronics S3352] 3 SPDT momentary 90° PCB-mounting subminiature pushbutton switches (S1-S3) [Altronics S1498] 1 2×5-pin header, 2.54mm pitch (CON1) 1 3-pin polarised header (CON2; optional) 7 22nF radial MKT or ceramic capacitors 7 10kW axial ¼W resistors Power supply parts 1 double-sided PCB coded 01107253, 127 × 76mm 3 2-way miniature terminal blocks, 5/5.08mm pitch (CON1, CON3-CON4) 1 3-way miniature terminal block, 5/5.08mm pitch (CON2) 4 M205 PCB-mounting fuse clips (F1, F2) 2 M205 1A fast-blow fuses (F1, F2) 3 47μH 0.5A high-frequency inductors/chokes (L1-L3) [Altronics L6217] 1 330μH 3A high-frequency vertical-mounting toroidal inductor (L4) [Altronics L6527] 2 Mini-U flag heatsinks [Altronics H0625] 2 TO-220 insulator kits [Altronics H7210] 3 M3 × 16mm bare metal panhead machine screws 8 M3 × 6mm bare metal panhead machine screws 4 M3 × 10mm metal tapped spacers 12 M3 metal shakeproof washers 4 M3 flat washers 4 M3 hex nuts 1 3.2mm solder lug [Altronics H1503] Semiconductors 1 LM317T adjustable linear regulator, TO-220 (REG1) 1 LM337T adjustable linear regulator, TO-220 (REG2) 1 LM2575T 5V buck regulator, TO-220-5 (REG3) 1 KBL404 400V 4A SIL bridge rectifier (BR1) [Altronics Z0076A] 4 1N4004 400V 1A power diodes (D1-D2, D4-D5) 1 1N5819 40V 1A schottky diode (D6) Capacitors 6 2200μF 25V low-ESR electrolytic 1 470μF 25V low-ESR electrolytic 3 100μF 50V low-ESR electrolytic 6 10μF 50V 105°C electrolytic 6 100nF 63V/100V MKT 1 10nF X2 Resistors (all axial ¼W ±1% metal film unless noted) 2 1.5kW 2 220W Australia's electronics magazine November 2025  75 when booting and when you rotate the encoder after booting. If not, are the plugs the right way around? Have you used the right 16-way header? Is the LCD contrast on pin 3 of CON19 adjustable from 3.3V down to about -1.8V or so? ● Check the soldering of the PIC; are there any dry joints, or bridges or pins where solder has not adhered to the pad? The microcontroller soldering is by far the most likely problem in this part of the circuit. With the microcontroller up and running, check the LCD backlight; modules are wildly inconsistent in how these are wired and set up. We found that some modules needed the 100W series resistor reduced or linked out to get decent backlighting brightness. Next, familiarise yourself with the user interface: ● The buttons to the left of the Control knob simply control the channels. ● The button to the right of the Control knob is an exit/back button. ● The Control knob can be pushed as an Enter button. Go through the following steps: 1. Push the exit button. You can now rotate through “Save”, “Load”, “Channel Setup”, “EQ Setup” and “Exit to Idle”. 2. Select “Channel Setup” and push in the Control knob. 3. You can set the following: Low Crossover (XO) frequency, Low XO slope, High XO frequency, High XO slope, channel attenuation, channel invert, channel delay in millimetres (1mm ≈ 2.9us) and mono output for channel 1. 4. Make sure these are set to sensible value, and for testing, set Low XO Slope and High XO slope to “none”. This disables the crossover for that band for now, which is useful during testing, as every channel will simply reproduce the input signal. 5. Exit to the Idle screen & click the Control knob. This will save the configuration data to EEPROM. If the system hangs on this, you have a connection problem to the EEPROM (IC17); check the soldering of the EEPROM & associated PIC microcontroller pins. 6. Go into the EQ setup menu. 7. Go through all 15 EQ settings and select “none” for the EQ type. ◀ This photo shows the PCBs & LCD connected so that they could be tested before wiring it up in the enclosure. 76 Silicon Chip siliconchip.com.au An example of a dodgy solder joint on the DSP chip. This is visible as an absence of the clean solder fillet on the third pin in from the left, and possibly the pin next to it. We apply a generous dollop of flux gel (from an Altronics syringe); don’t be stingy and definitely don’t bother trying to reflow the pins without adding flux. Look how much better the joint looked after reflowing! This is the same photo that was shown in the panel last month. 8. Go back to the main menu & click the Control knob to save this state. 9. Double-check the volume control works on the remote. 10. Click up and down channels; the input relays should click to change the input selected. on this and you will have a lot of dry joints on your pins. A thin layer of solder on this is sufficient. 3. Now tin the pads on the chip itself – both the outer pins and its ground tab. Again, ensure all are well tinned but that the central tab has only a thin layer of solder. 4. If you have too much solder on either the PCB or DSP heat spreader tab, use solder wick to remove some. 5. Put flux gel all over the PCB footprint. Be generous; this is essential. 6. Align the chip’s pin 1 with the marking on the PCB. Don’t worry too much about exact alignment, as the chip will be floating around soon. 7. Set your hot air gun/wand to 350°C or so, with a medium airflow rate. 8. Holding your hot air gun in one hand, and your tweezers in your other hand, start heating the board in the DSP area. Keep those tweezers handy to allow you to poke the hot chip around in the air stream. 9. Starting slowly, and from 10cm or so, work your way in as it heats up. Watch the capacitors around the DSP as they are smaller and will show signs of the solder flowing before the DSP does. 10. Bring the hot air gun in closer, to 5cm or so. You might see the DSP chip move around. Try not to make this occur too much. Use your tweezers to poke it back to about where it belongs. 11. You will see some capacitors reflow when you are close to the right temperature. Then the DSP chip solder will melt. There will be a visible change from the DSP chip sitting in the flux, to the solder melting and wetting between the chip and PCB. This will create surface tension, which will pull the chip onto the ground pad. If close to the correct alignment, the pins will pull it into place. 12. Keep the heat on for a little while, and if the chip has pulled itself onto the wrong pads (and of course it will), use your tweezers to poke it into alignment. Once in about the right place, it will snap into place with the surface tension of the solder. 13. We found that gentle and small pushes of the chip got it properly aligned in a few seconds. Work gently and stay calm; the surface tension will help you. Your job is to get the DSP square and in about the right spot. 14. Gently remove your hot air gun and admire your work. 15. While the board is still warm, inspect the solder joints. If any are not pristine, you need to address those now (refer to the photos above). Make sure all the connections are cleanly soldered and show that visible fillet of solder. 16. If there are a lot of dodgy joints, don’t despair; resolder them as described above. One of our chips required quite a lot of touching up, but it worked perfectly in the end. The above procedure might sound scary, but we went through it quite a few times, including removing chips and resoldering them to other boards, with success. We are not in any way expert, so it can’t be that hard. Using the ADAU1467 DSP If you are using the ADAU1467 Core Board, there should be no parts inside the area labelled DSP CORE or DSP ADAU1467. If there are, remove them. Next, load the 36-way DIL sockets. We cut ours from 40-way sockets from Altronics. The best way to mount the sockets is to mate them to your core board, then install the sockets to the PCB. This way, when you solder them to your Digital Preamplifier PCB, they will be perfectly aligned to your module. The EEPROM boot switch on our Core Board was set to ON. It seemed to work fine when set there. You can now plug in the core board. Make sure you get it the right way around; the 10-way header goes at the top. If you are loading the ADAU1467 chip by hand, you will need a hot air gun/wand, a soldering iron with a fine tip, flux gel/paste, fine-point tweezers, a magnifying glass or microscope and, ideally, a camera or phone with a good macro mode. There are many good videos on the internet for this, but essentially, the steps are: 1. If you have no experience in soldering SMD parts, buy the core board. 2. Tin the pads on the PCB. Don’t put so much solder that there are bridges, but make sure all the small pads are well tinned. Do not overdo the central heat spreader tab, or the chip will float siliconchip.com.au Australia's electronics magazine Testing the ADAU1467 DSP 1. Apply power and check that no smoke comes out. The DSP draws a fair current when running all the inputs and outputs, but in this configuration, it drew less than 300mA from our ±15V DC supply. So a 12V AC 1A plugpack should be OK (for now). November 2025  77 2. Use a DVM to measure the voltage on the collector (tab) of the NJT4090P; you should see 1.1-1.3V DC. If you don’t, it is very likely that you have a dry joint on the DSP chip. Check this, especially around pin 3 and its power pins until you get that 1.2V rail up. 3. Wait until the microcontroller is booted. Then, using an oscilloscope, look for a 12.288MHz sinewave on the 100W resistor just below the 12.288MHz crystal. If you don’t see this, it is likely that there is no communication between the DSP chip and the PIC. To debug this: a. Monitor the signals on CON21. This is the SPI interface from the PIC to the DSP chip. Look for activity on CLATCH, CDATA and CCLK on boot and when you change volume. b. If there is no data on any one of these three lines, you have a soldering problem at the PIC microcontroller. Check these pins on the PIC and fix the problem. c. If there is data on all of these lines (noting that COUT is data from the DSP and normally not active), you have a soldering problem on your DSP chip. These lines are on the side of the chip next to the crystal; find the dodgy connection and reflow it. 4. With this interface working, look at the LRCLK lines of channels 1-4. You should see a 192kHz waveform. Similarly, you should see a BCLK signal at 12.288MHz and MCLK at 24.56MHz. If any are absent, hunt down the dodgy solder joint and fix it. Now you have the DSP talking to the PIC and running. Fitting the ADCs & DACs We are almost there; it’s time to mount the ADC and DAC chips. You don’t need to install all channels. As mentioned previously, you have a choice of two different ADC chips and two DAC chips. Make sure you have the right resistors and capacitors installed for the DAC you selected, or else the gain and filter will be wrong. 1. Fit the CS5361/81 ADC chip and associated 1μF and 220μF throughhole capacitors. 2. Install the clipping LED header (CON7). We have not run this to any LED on the front panel on our prototypes, but you can if you wish. 3. Mount the four PCM1794/98 DACs ICs. These are a little fiddly, but not too bad. Be sure to check your soldering on each with a magnifier. 78 Silicon Chip 4. Fit all 16 NE5532(A) dual operational amplifiers. You can use sockets, if you wish; it will make swapping them easier, but they can oxidise over time and eventually lead to problems. 5. Load the last two 47μF bipolar capacitors (either way around). At this point, you should have everything on the board except the TOSLINK transceivers, MiniDSP headers and digital isolator. We have also seen a short circuit between the Iref pin and the adjacent ground, which changed the output amplitude. Ensure that all channels generate the same output levels. If any channel is missing or lower in amplitude (most likely half), check the soldering of the DAC output lines. The output is balanced, and if one pin has a dry joint, you will see a half-­ amplitude output. Further testing MiniDSP & TOSLINK interfaces 1. Apply power. You should see a lot more current draw; ours drew about 0.4A on the positive rail with a ±15V supply. This is all those NE5532s and the DSP having data to work on. At this point, powering it from a plugpack is becoming difficult (unless you have a particularly beefy one, eg, >1.5A). So you're best off using a dual bench supply, or two floating bench supplies connected in series. 2. The power supply heatsinks should get quite warm to touch, but not ‘burning hot’. 3. Use a ‘scope to look for data on the ADC Test Header (CON9). You should see data on the SDATA line, and if you trigger your ‘scope using the LRCLK line, you will see the data aligned with the LRCLK. This is currently noise being measured by the ADC. If you don’t see this data, check that the LRCLK, BCLK and MCLK signals are present. If they are, look for soldering problems on the ADC. Otherwise, examine the DSP chip and fix any bad solder joints you find. Now look at the same SDATA lines for each of the output DAC channels. Turn the volume right up to +12dB. There should be data on all output channel data lines. Again, if not, check the MCLK, BCLK and LRCLK lines, and make sure they are present. If not, fix the DSP chip soldering. You should now be able to feed audio into an input, select that input using the controls and see it on all the outputs, given we disabled all crossovers and equalisers right at the start of testing. Present a 1V 1kHz sinewave to the Bluetooth input, select it using the controls on the front panel, and look at each of the channel outputs. With all channel filters disabled and the gains set to zero, the output signals should all have the same amplitudes. If they are not all the same, check for solder bridges on the outputs of the DAC chips. Australia's electronics magazine Now fit all the remaining parts, which should be: T The MAX22345 isolator (IC16) T The TOSLINK receiver (OPT1); the transmitter (OPT2) is not used and is experimental only. T The two 12-way pigtail headers that come with the MiniDSP MCHStreamer. These are wired pin-to-pin with pin 1 aligned and the pigtails standing straight up. These plug onto J1 and J3 of the MCHStreamer (not J2). With those in place, we can do more testing: 1. Plug the MiniDSP into your PC, Mac or Linux box. 2. Install the ASIO drivers for the MiniDSP onto your PC, or on Mac/ Linux, simply select the MiniDSP as the current audio device. 3. Play some audio on the computer. Use an oscilloscope to look for a signal on the LRCLK test point that we have added on the production PCB, just to the right of the MAX22345, labelled LRCLK. This needs to be present for the Digital Preamplifier to receive the audio. 4. Select the MiniDSP interface using the controls. This should allow you to stream data from your PC to your Digital Preamp. Check that the output signals are as expected. 5. In the Monitor menu, you can also select which channel is sent back to your computer; the Digital Preamp can route this audio to the MiniDSP while doing everything else. At this point, you should have a set of fully loaded PCBs that are operational and ready to install in the case! Next month We still have a fair bit left to do, but we’ll pick this up in the next issue. That final article will have the case drilling and cutting details, final assembly instructions, wiring, final SC testing and usage guide. siliconchip.com.au Over-Current Protection Simple Electronic Projects with Julian Edgar This very simple project can sound an alarm or disconnect the load when a low-voltage DC current flow exceeds a preset value. T here are many applications where a device needs to be shut off, or a warning given, if a load draws excessive current. This little project can be configured to activate at any current level from about 1A to 20A, costs almost nothing and is suitable for a wide range of low-voltage DC circuits. Example uses include: • an over-current warning or cutout for battery-operated power tools • switching off a motorised door, gate or similar if an obstruction is met while it is moving • protecting simple power supplies • protecting analog model railway controllers if a derailment occurs that short circuits the supply The approach Conventional over-current monitoring is usually done by sensing the voltage drop across a resistor in series with the load. As the current flow increases, so does the voltage across the resistor. However, to minimise the voltage drop (and power dissipation in the resistor), the resistor’s value is usually very low. This small voltage needs to be amplified by additional circuity before being compared to a fixed voltage that corresponds to the maximum allowable current. However, in this project, the current flow is sensed completely differently. Instead of the resistor/amplifier/ comparator approach, a simple reed switch is used. A reed switch closes when subjected to a magnetic field. The magnetic field is normally provided by a magnet being brought close to the switch. Instead, we place a coil of wire around the reed switch. The coil is placed in series with the load, so the full load current passes through this coil. The strength of the magnetic field generated by this coil depends on the The Jaycar SM1002 reed switch closes when a magnetic field is present. This can be provided by either a magnet or coil of wire. siliconchip.com.au current flowing through the winding and its number of turns. When the current reaches a level that develops a sufficiently strong magnetic field, the switch closes. That can sound an alarm, or via a latching relay, disconnect the load. If we want to alter the current at which the reed switch closes, we simply change the number of windings around the switch. Reed switches vary in their specifications, so (say) six turns around one switch may cause the switch to close at 2A, but with another switch, the same six turns may cause the switch to close at 3A. The trick is to test the switch until you get the behaviour you want. We are using the fairly typical Jaycar SM1002 reed switch. It has a glass envelope, is 16mm long and 2mm in diameter, and is rated to handle 0.5A (500mA). If substituting another, make sure it’s a normally-open type. Calibrating the reed switch The lower the number of turns around the reed switch, the higher the current at which the switch trips. The minimum number of turns is one (used in the power tool application covered shortly), and the maximum is mostly dictated by how many you can fit around the reed switch. Using 0.5mm diameter enamelled wire, it’s fairly easy to fit 16 turns on the switch. This gives a trigger point of about 1A. Using a single turn results in a trigger point of about 20A. Because the load current all passes through the coil, using overly thin wire will increase the voltage drop and power dissipation in the coil. However, this works out well because higher current values require fewer turns, allowing the use of thicker wire. For example, 16 turns of 0.5mm wire gives a measured voltage drop of only 1.4mV at 1A. Use the thickest wire that still allows a sufficient number of turns to be wound around the reed switch. It is very important to note that reed switches are fragile – the glass envelope breaks easily. Do not wind the coil directly on the reed switch! Instead, wind it around a former like the shaft of a small screwdriver or a drill bit. If you are using the Jaycar reed switch, a former diameter of just under 2mm works well, and the resulting coil will be a friction fit over the reed switch. Calibrating the device So, how do we calibrate the reed switch to trigger at our desired current? The easiest approach is to use a variable bench power supply with a current readout. Connect your multimeter across the reed switch with the multimeter in continuity mode (ie, it sounds a buzzer when the reed switch closes), which is best done using alligator clip leads. Place the wound coil around the reed switch. Connect the coil switch in series with the power supply & load; the load can be one or more wire-wound resistors (you may not need a load if your bench supply has current limiting). Starting at zero current and voltage, increase the voltage while watching the current display. When the multimeter sounds its buzzer, Rugged reed switches Reed switches are also available in fully encapsulated plastic packages, with the glass reed switch concealed inside. Usually, such switches are sold with a matching magnet for security system applications. We tested some reed switches like these, and got good results, so if you’re concerned about the fragility of the glass switches, you could try one of these. But they’re more expensive. 16 turns of 0.5mm diameter enamelled copper wire on the reed switch. This gives a switching current of about 1A with the Jaycar SM1002 reed switch. Australia's electronics magazine November 2025  79 indicating that the reed switch has closed, take note of the current reading. If you need a higher current trip point, reduce the number of turns on the coil. If you would like a lower current trip point, add more turns. If you don’t have a variable power supply, you could use a resistor bank that gives the calculated correct current flow and then alter the number of turns until the reed switch closes. For example, if you want the switch to close at 2A and you are using a 12V supply, use wire-wound resistors that provide a 6W load (12V ÷ 2A). In this case, the resistors will need to dissipate 24W, so you could use six 1W 5W resistors in series. They’ll still get hot, though, so only keep the circuit powered briefly on each test. Technically, the relationship between the trip point and number of turns around the reed switch should be linear, but I did find some variation during my testing. Perhaps this was because the coils were not always identical except in the number of turns. The reed switch ‘naturally’ has hysteresis – the switch-off current is considerably lower than the switch-on current. For example, the switch may close at 1A and open at 600mA. Alarms and disconnects Sounding an alarm when current flow exceeds the set point is very easy – as shown in Fig.1, you just need to wire a buzzer in series with the reed switch and connect both across a voltage source. Choose the buzzer voltage to match the supply or, if using a buzzer with a lower operating voltage, use a series resistor to drop the voltage to suit. Disconnecting the load when the setpoint is reached is a little more complex. Fig.2 shows my approach. A relay disconnects the load if the setpoint is exceeded. However, if that were the entire circuit, the relay would operate, the load would disconnect, the current would drop to zero, the reed switch would open, and then the process would repeat! To avoid this, we use a relay with an additional set of contacts that causes the relay to latch (ie, to stay engaged) once it has been pulled in. This is achieved by wiring the relay’s second common (C) and normally open (NO) set of contacts in parallel with the reed switch. A momentary reset button opens this circuit, causing the relay to drop out, or you could power-­cycle the device to reset it. Note that a diode is placed across the relay coil, protecting the reed switch’s contacts against the inductive spike from the relay’s coil. 80 Silicon Chip This Makita 18V battery-operated drill comes apart easily, with normal Philips head screws holding the two halves of the body together. Fig.1: the over-current buzzer circuit. When sufficient current flow occurs through the coil, the reed switch closes, activating the warning buzzer. This will work with a device powered by a DC mains supply in place of the battery. Fig.2: the over-current disconnect circuit. When sufficient current flows through the reed switch, it closes, pulling in the relay and disconnecting the load. The relay latches in that state, with the system able to be reset by pressing the pushbutton or by cycling power (eg, removing the battery). Australia's electronics magazine siliconchip.com.au An optional buzzer can be wired in parallel with the relay’s coil so the user knows why the power was cut. The red and black wires going to the motor are the only ones we need to access. Either the negative or positive connection to the motor can be cut (I cut the negative as it was easier). I used normal multi-stranded cable tinned... Adding an over-current alarm to a battery drill ... with solder to rejoin the wires and ensured the coil turns could not short together. The reed switch has been slipped into place to show how it will fit. The motor and buzzer power/ground connections, insulated with tape. The tape will later be wrapped around the reed switch as well, leaving only its connections exposed. I used a 12V buzzer with a 100W dropping resistor to suit the measured 19.5V supply. It was easily loud enough to be heard through the case with the drill running (otherwise, make a small hole in the case). After being tested, the bare connections can be covered with silicone sealant. siliconchip.com.au Australia's electronics magazine If you have been using power tools for a long time, it’s likely you’ve developed a good feel for their use. For example, when you are drilling a large hole, you start with a smaller drill bit and you’ll also know to go gently when you move onto the big drill bit. However, people who are new to power tools literally have no idea about these things! Instead, they’ll work a power tool until it goes up in a puff of smoke. I’ve seen it happen... To prevent that, you can add this over-current alarm to a battery-­operated drill, which causes a piezo buzzer to sound long before the drill stalls. It can even sound a more subdued, pulsating warning as the drill load gets close to being excessive, with brief current spikes being just enough to momentarily close the reed switch. Simply use the circuit shown in Fig.1, with the buzzer powered by the drill’s motor power feed. Here, a single turn of wire around the reed switch worked well in giving an alarm prior to the drill stalling, and the alarm does not sound under normal loads. However, that was pure luck; in some cases, adjustments may be required to get a suitable result. One approach is to open up the drill, cut a wire to the motor and extend the cut ends outside the case. Close the drill up again, and you have an easy way of trialling different numbers of turns around the reed switch. To load the drill, lock a straight shaft in the drill chuck and then clamp this shaft between two pieces of wood in a bench vice. By tightening the vice, you can vary the load. If the drill has a two-position gearbox, always test on the faster speed (lower torque). Never try to load the drill when it is disassembled – the motor could leap from the casing and cause injury. Many battery drills develop a lot of torque, so you will need a firm hand as you increase the load on the drill by clamping the blocks more tightly around the spinning shaft. Test in short bursts, for your sake, as well as the motor’s. Conclusion This is a simple and inexpensive modification that can protect tools or other devices from being overloaded and damaged. There also isn’t a lot to go wrong – the parts should last essentially forever, SC especially if rarely triggered! November 2025  81 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. Driving a 400×168-pixel four-colour e-paper display As described in the June 2019 article on e-paper displays (siliconchip. au/Article/11668), they contain millions of tiny microcapsules or microcups filled with charged particles in different colours, like black, white, red, or yellow. When an electric field is applied, the particles move within the capsules, changing their position or orientation to reveal or hide specific colours on the surface. With e-paper, the image is created by reflecting external light, whereas most other displays work by emitting light. This lack of backlighting is a key reason for their ultra-low power consumption and also helps to make them easily readable in bright environments, and less strain on the eyes. E-paper displays retain their image even after power is cut off. That’s because the microcapsules don’t reset – they remain in their last state. It’s similar to drawing on paper: once drawn, the image stays. It only becomes invisible when there’s no light to reflect off it, or when the display is reset to hide the colours. This four-colour e-paper display is available from AliExpress for around $20 (AliExpress 1005008563587380). There are many other similar colour e-paper displays available in different sizes, which may work with my software. I found some sample code to test the display, but it only worked with a dew point. It uses a real-time clock module for timekeeping and an AHT10 temperature/humidity sensor. As a playful touch, I also added a small raspberry image that randomly appears in different positions on the WiFi.mode(WIFI_OFF); // We are not using WiFi btStop(); // Disables Bluetooth // Reduce CPU frequency for low power consumption setCpuFrequencyMhz(40); // Lower I2C clock speed for low power Wire.setClock(100000); // Turn off ADC & other RTC peripherals to reduce power consumption esp_sleep_pd_config(ESP_PD_DOMAIN_RTC_PERIPH, ESP_PD_OPTION_OFF); fixed image. Despite several attempts, I couldn’t change the image or get anything else to work. There seemed to be no proper library available to control this display. Recently, I discovered two updated libraries, and by combining them, it’s now possible to control this display & many other types of e-paper displays. For graphical output, you’ll need to convert your image into a bitmap format before rendering it. I wrote code to create an analog-­ digital hybrid clock that also displays temperature, relative humidity, and screen, filled with random colours. This adds a bit of charm and life to the display. For running it on battery, I have switched off all the unnecessary peripherals of the ESP32 (see the code block above). To further save power, between screen updates, the ESP32 is placed in deep sleep mode. That means the loop() function will not continue running. However, before using deep sleep in your final code, you should check how your code works inside loop(); if you bypass the deep sleep The finished e-paper display should just fit into a UB3-sized case, but it might be a very tight fit with the wiring. Larger and smaller colour e-paper displays are also available; this code could be adapted to drive some of them, depending on their controllers. 82 Silicon Chip Australia's electronics magazine siliconchip.com.au entry, your loop cycle will play out normally. I’m using a 3.7V 600mAh Li-ion battery to power the clock. The device wakes up once every minute, updates the display, and then returns to deep sleep mode. During the active phase (about 3-4 seconds), the device draws around 6-7mA, while in sleep mode, the current drops to 30μA. Based on this duty cycle, the battery can easily last up to two months on a single charge! Correct GPIO pin connections are critical for the display to work properly. While the I2C pins can be reassigned from the available GPIOs, the code must be updated accordingly. I’ve used only one side of the ESP32, so my pin selections reflect that constraint. To help with GPIO configuration across different boards, the file GxEPD2_wiring_examples.h is included in the main code to provide reference pin mappings for a variety of supported boards. The libraries used are available from https://github.com/ZinggJM/GxEPD2 and https://github.com/olikraus/ U8g2_for_Adafruit_GFX Download these two ZIP files and then add them into your Arduino IDE (Sketch → Add Library → Add .zip Library… ). The other essential libraries, RTClib.h and Adafruit_AHTX0.h, may be installed using Sketch → Add Library → Manage Libraries... The sketch consists of 4 files: 1. GxEPD_wiring_examples.h: board-specific wiring details 2. GxEPD_selection_check.h: epaper specific variables 3. GxEPD2_display_selection_new_ style.h: e-paper specific include files 4. GxEPD2_U8G2_epaper.ino: the main sketch file All these files are available in a ZIP you can download from siliconchip. au/Shop/6/3339 While e-paper’s refresh rate and colour range currently lags behind that of LCDs or OLEDs, advancements are steadily closing this gap. The arrival of seven-colour e-paper marks a significant leap forward. With improving controller support and better libraries, DIY and commercial adoption is bound to grow. This project is just a small glimpse into that promising future. Bera Somnath, Kolkata, India. ($120) siliconchip.com.au Miniaturised GPS Speedometer PCB I decided to build the simplified GPS Speedometer design described by Tim Blythman in Circuit Notebook, July 2025. However, I thought the mostly unpopulated PCB was a bit large for my needs, so I designed a smaller version. I made it to fit into a section of 2-inch (50.8mm) diameter PVC plastic pipe, with the intention of mounting it like an additional instrument in my hobby car. You can see how it works in the photo, although it still needs paint and a bracket to mount it. The pipe has an inner diameter of 47mm. You can download the Gerber files to make your own version of this board from siliconchip.au/ Shop/10/3349 or order a PCB from siliconchip.au/Shop/8/7562 To allow everything to fit onto Australia's electronics magazine the 47mm diameter round PCB, some components mount under the OLED screen, with others on the back of the board. Apart from the microcontroller and OLED screen, most of the remaining parts are SMDs to keep the design compact. In my build, I used long spacers in the two 3mm mounting holes to sandwich the PCB inside the pipe. The front and rear panels were made from a 3mm Perspex/acrylic sheet. Be careful when sourcing the OLED screen as there are two slightly different types available. I used what seems to be the slightly smaller version of the screen, which has the mounting holes a bit closer together. Glenn Percy, Narre Warren South, Vic. ($80) November 2025  83 SERVICEMAN’S LOG Remotely Interesting Dave Thompson The internet is a blessing and a curse. It lets us do lots of things from just about anywhere, but it can also give access to people we don’t want accessing our files and bank accounts! This has made some people nervous about remote access, and that makes my job more difficult. This modern age is something else; I’ve said and thought it, as have many others. However, engineers and philosophers have been saying so since the dawn of time. At one point, a sundial was the pinnacle of technology. They still exist, albeit mostly as garden ornaments, but I have seen some very old, used and working examples in Rome and other historic places. Modernisation is always a double-edged sword. What makes better microwave ovens also makes more effective weapons. Since we first had the technology, remotely controlling something has been a prized goal. Early radio-controlled model aeroplanes were basic and usually only had just one channel controlling a rudder via an escapement-type arrangement. The transmitters were large, valve-based, battery-­ powered, and usually just a switch to change between left, right and oh-it’s-crashing modes. The range was not great back then. These days, the transmitters and receivers are much more advanced and reliable, with multiple channels, continuous controls and such. Some even provide remote point-of-view (POV) video from the aircraft! When I was a kid, back in the chalkboard days, my parents had a remote control for their TV. It was my siblings and me. Fortunately, we only had two channels, so a trained chimp could have done it. It wasn’t long before Dad modified our TV to use a wired remote: a metal box with a 84 Silicon Chip pushbutton that had a wire running around the skirting board into the back of the TV. I, for one, was very relieved by this innovation. Pretty soon, those old clunky ultrasonic controllers came along. I still see them occasionally on old American TV shows, making an exaggerated click sound and hand movement when operated. Even when the newfangled infrared (IR) LED types replaced them, the remotes on those shows still made the click sound! In the 1980s, suddenly everything was remote controlled. Stereos, radios, heaters, ovens; anything that would help sell appliances. It got so bad that people had special pockets in their chairs for all the remotes. Then the universal remote came along, and that changed everything (pun intended!). Of course, most of us still have multiple remotes these days for all our devices, but the whole remote philosophy really expanded and came into its own during the recent pandemic. Many companies found that their employees could work from home and the job would still be done (something some of us have been doing for so long that we’ve forgotten what the others look like!). In fact, many found that the better work/life balance actually improved productivity and boosted output, even though fewer actual hours were being worked. Spending time working that would otherwise be wasted commuting helps a lot, too! This caused a lot of wringing of hands and gnashing of teeth amongst bosses and ‘human resources’ departments, who considered that despite the increased productivity, they were somehow being cheated out of chargeable labour by allowing people to work from home. Some companies have embraced the new ethos, and why not? Some have a policy that workers can choose to come to the office or work from home, or use a ‘hybrid’ model that involves doing both on different days. Some ask that workers come in at least a few times per week/month to stay in touch with their teams. The reality is that with technology the way it is now, people can use the likes of Zoom, Teams or even a basic remote desktop app to do their jobs effectively. In some cases, the company can even close or downsize expensive and capital-draining offices in Australia's electronics magazine siliconchip.com.au Items Covered This Month • The perils of remote access • Repairing a car’s ignition unit • A dim clock backlight • Sony ICF7600D receiver repair Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz Cartoonist – Louis Decrevel Website: loueee.com favour of working from home, with appropriate expenses and compensation. Of course, we computer nerds have been able to operate computer systems remotely since the 1990s. One could argue that hackers have also been able to, because if you open the door to someone, a sneak thief may take the opportunity. A huge industry was then built around network and server security. As is becoming all too clear, this is far from foolproof; we are always hearing about breaches in defences, especially now we have state-sponsored players in the mix. Software like Norton’s PC Anywhere and eventually Microsoft’s Remote Desktop (which is built into all versions of the operating system for client use, but only Pro versions for controlling use) became the gold standard of remote access software. Now, anyone with an internet connection and the correct access permissions could ‘remote in’ and control the host computer as if they were sitting in front of it. As soon as these apps were released, the bad guys started looking for ways through them. Local firewalls became extremely important, and everyone had to learn a new set of new words if they were going to use these utilities. Windows started shipping with a built-in firewall; routers and modems had their own hardware firewalls, and techs suddenly had migraines from all the hoops they had to jump through to allow authorised remote connections to happen. Nowadays, it is relatively straightforward with utilities like TeamViewer and virtual private networks (VPNs), which offer a certain amount of built-in security, depending on how they are set up. The problem is that most ‘hackers’ and scammers now realise that trying to get through is very difficult compared to the old days, so they play to the obvious weak links in all these systems: the user. And they are very good at it. The way to gain access to siliconchip.com.au someone’s system is to get the user to install a remote viewing app and give the scammers access. Of course, the ways they do that are as varied as the scammers. I have known several people who have lost considerable sums of money to these con artists. In one, a 70-year-old widow was played for over a year to the tune of $85,000 in a so-called ‘lonely hearts’ con by some very glib, professional shyster. I warned her it was a scam (she called and asked me about it and I told her to bail). Her bank put a hold on payments going overseas, but she overrode them or went to a money transfer place and sent it that way. While technology is robust enough nowadays that I haven’t seen an actual virus infecting a computer in over 10 years, users are unfortunately falling for these scams more and more. During the pandemic, I was still getting a few support calls, and I would ask them to download and install the run-and-stand-alone version of TeamViewer to be able to see what was going on with their machines. TeamViewer is a popular remote control program for Windows machines. I used that because it doesn’t require any fiddling with network settings, nor even installation. You just run the downloaded file and choose ‘run once’. When it fires up, they then send me the randomised computer ID number and password displayed in the app, and I can then connect Australia's electronics magazine November 2025  85 and log in right away from my machine. Once there, I can do whatever I need as if I’m sitting in front of it. I repair any problems; transfer any files I might need to run locally there; and do whatever. But many users are so paranoid now (and rightly so!) that as soon as I suggest I can do that, they get nervous and hem and haw. Many would ask if I could come out to their place and do it, but under the lockdowns, that just wasn’t possible. Not to mention that I didn’t want to put myself at risk anyway – I haven’t contracted COVID-19 yet, and I have no plans to change that at this stage! For those that did agree, I did the job and often fixed their problems, but then when it came to payment, they would stall and say, well, you never really did anything, so I’m not paying. That was extremely disappointing coming from long-term clients, and of course once I log out, I can’t log back in and return it to how I found it. Without the machine physically in the workshop, I have no leverage regarding payment, and instead rely on the goodwill of people to actually pay for the job I’d done. Of course, I altered my prices where required, but overall, it left a sour taste. That was pandemic times. Lately I’ve had a few overseas clients from Australia, the USA and England, and the same model still stands. I can use remote control to gain access to the computer and help the customer. But of course, this Servicing Stories Wanted Do you have any good servicing stories that you would like to share in The Serviceman column in SILICON CHIP? If so, why not send those stories in to us? It doesn’t matter what the story is about as long as it’s in some way related to the electronics or electrical industries, to computers or even to cars and similar. We pay for all contributions published but please note that your material must be original. Send your contribution by email to: editor<at>siliconchip.com.au Please be sure to include your full name and address details. 86 Silicon Chip is only for software-related problems where Windows is still running. If it isn’t, then we have a problem. So how to resolve problems like Windows won’t start, the network adaptor is not found, or it is faulting and I can’t access the computer remotely? I had to change strategies and see if I could inspire the owners to do the job for me. Now, obviously, some are not going to be up to that, but for those who might be able to help, I’d give them the option and use a well-known phone video call app to see what we could do together. This method is far more difficult. While most people have a smartphone these days, not everyone has this app installed. So that’s the first hurdle. Once they download and install it, we then do a test call. It works pretty well, even on slower connections. The video quality is good enough; with communications sorted, we can get down to basics. It could be as simple as rebooting the machine – many people don’t know that holding the power button down resets it. If that doesn’t work, we can look at the BIOS, Windows startup menus and trapping stop codes/blue screens that often flash so quickly on modern machines nobody is even aware they are there. That can tell me a lot. How this process goes tells me a lot about the person at the other end, and whether I have to suggest getting someone else in physically. Recently, I was chatting with a client who had relocated to northern Spain and was having trouble with their laptop. It was too hot to touch and had slowed right down, so of course my immediate question was: are they using it on their lap or a duvet or similar that could be blocking the air intakes on the bottom? I was told that it was sitting on a timber table and running from the mains power supply. There are only two reasons it could be that hot: the CPU fan isn’t running, or the airways are blocked inside. Either way, it was going to have to come apart. This was not going to be a problem, as I knew this person was handy with a screwdriver and could pull it apart. The problem was that they hadn’t attempted a challenge like this on a new, aluminium-­bodied, slimline device. Half of my task here was going to be giving them the confidence to do the job. I found a strip-down video on YouTube for this model and sent them step-by-step instructions on where the screws were, including a couple hidden under bumper feet. The biggest challenge was for them to crack the clips holding it together. As is typical of me, I have a dozen different spudgers to do this with. He used his fingernails at my suggestion and eventually cracked the back off. He’ll need a manicure, but otherwise, all was well. As I thought, the fan was choked, as I could see as he played the phone camera over the innards. He had no compressor, so it was a vacuum cleaner to the rescue. It sucks (har!), but needs must. I advised him to keep holding onto the nozzle at the end to ground it as much as possible, and avoid getting near the motherboard itself, a challenge given the tight confines of a laptop. Still, he managed to get rid of most of the dust and lint that always builds up in those ducts and heatsink vents. Once done, he just reassembled it and fired it up, and all was well. No fan thrashing, no heat buildup. So, a good fix. But how does one charge? I didn’t. They did all the work. I just stood by, advising via the internet. It is not easily Australia's electronics magazine siliconchip.com.au chargeable anyway, even without the logistics of the international payment systems. Another interesting fix happened recently with a friend of my wife. This friend lives in the USA and is currently enduring a bathroom renovation and all that entails. If you’ve ever done any renovation work, you know it takes three times as long and costs twice as much as we budget for, not to mention the mess. I heard they had allowed one week for the reno; I thought that was a very optimistic timeframe. From personal experience, just clearing the old stuff off the wall, the tub, loo and shower out was going to take longer than that, even if all you used was a sledgehammer! Anyway, while the subbies were moving around, they somehow damaged an electric ‘Roman’ style blind. Usually, these come with a cord of some kind with which to raise and lower it. Like an old blind that people of a certain age will remember, you pull it down by the bottom and is held in place until you give it a little more, then it rolls up again. These blinds have no springs to wear out; the cord winds them up and down. Anyway, this was a custom-made blind that spanned a set of doors, so it was quite large, and it was controlled by a motor at one end. This was powered by batteries and a controller that replaced the cord. Somehow, someone had cut through it, leaving the controller/ battery holder on the floor. Tradies! So, another WhatsApp call then. I could see the problem; it was obvious, really. But this should be a simple fix. The difficulty was that this woman didn’t even know how to hold a screwdriver. The male of the house was no help either, so it was down to me to guide her in fixing the problem. I told her she would need an inline connector and found and sent a link to one that should do the job. I also included a link to a small pack of heatshrink tubing. It could all be delivered within 24 hours (which is still amazing to us here), so we prepped the rest in the meantime. Luckily, the wires were coded as to positive and negative, as many cables are, with a black stripe down one side. I got her to strip the wires; without a stripper, or even a Stanley knife, we had to improvise. A sharp paring knife was used, and she was very careful (almost too careful) not to hit the wiring inside the insulation. But she got the plastic clear and twisted the ends. The other bits arrived the next day, and she cut the heatshrink tubing to size and slipped a big piece over the whole lot, then she used the twin inline connector to reconnect that battery pack. She’d found a small jeweller’s-type screwdriver and managed to connect everything up. She tested the control, and the blind operated as expected. I got her to put the heatshrink over the whole connector, and she used a BBQ lighter to carefully shrink it down. She was chuffed, and it was a good fix. Job remotely done! Transistor-assisted ignition unit repair In the last years of high school, an adult friend bought me a copy of Electronics Australia. This got me interested in electronics, and I continued to buy EA magazines while at school and after leaving. I built several of the projects, sometimes buying kits and sometimes sourcing the parts myself. A few years after finishing school in 1970, I got my first siliconchip.com.au Australia's electronics magazine November 2025  87 car, a 1962 EK Holden station wagon. I had to rebuild it as it was missing many parts, including the engine and the entire front end. Through the late 1970s, 1980s and early 1990s, I had several 1960s Holdens. In the December 1979 issue of EA, there was a transistor-­ assisted ignition unit featured. After reading the article, I decided to build one for my car, which had the standard Kettering ignition system with points, condenser and coil. The article promised better performance and better fuel economy. I don’t remember if I sourced the parts or bought a kit from one of the multitude of kit suppliers back in the day; possibly the latter. After installing the unit, I notice an improvement in performance, with the engine running smoothly and increased torque at lower engine RPM. The car went well for quite some time, but then suddenly stopped for no apparent reason. I did some troubleshooting and determined that the transistor-assisted ignition unit had failed, which was a big disappointment, as it had been going well up until then. A quick rewire back to the standard Kettering ignition and I was on my way again. I had installed the transistor assisted unit in such a way that in case of a failure, I could easily swap back to the original ignition system. Later, at home, I took the unit out of the car and inspected it. I could see straight away that the three 2.7W 1W resistors had overheated and burnt part of the circuit board, destroying the tracks and causing an open circuit. I decided that the three parallel 2.7W 1W resistors were under-rated for the application, so I replaced them with two 1.8W 5W resistors that I had on hand, spacing the resistors off the board. Because the PCB tracks no longer existed, I used the leads from the resistors to make new “tracks”. I reinstalled the unit and I had no more problems with it after that. I still have it, but our current cars have either fuel injection or electronic ignition with a carburettor, which has made this unit, which was excellent for its time, redundant. Bruce Pierson, Dundathu, Qld. Sony ICF7600D receiver repair I had a Sony ICF7600D radio receiver for many years, which I purchased on Norfolk Island when travelling with the RAAF in the 1970s. It was a beautiful radio, made in Japan, with synthesised tuning, an LCD readout and a separately powered clock. The bands it covered were LW, MW, SW to 30MHz, plus the extended VHF FM band, and it had SSB demodulation support. It had two dedicated AA cells for the clock and four for the radio, which could also be powered from a mains power supply. I relied on this radio as a secondary alarm clock during my time as a regional airline pilot, as I could never be late; therefore, I relied on the separate cells. After leaving the industry, I used the radio less, and it languished in a drawer. I forgot to remove the cells, and they inevitably leaked, so I cleaned the compartments and contacts and all was well. Many years later, I decided to get rid of things that I had 88 Silicon Chip Australia's electronics magazine siliconchip.com.au ← The circuit for a transistor ignition unit from the December 1979 issue of Electronics Australia, which Bruce built to put into a 1962 Holden station wagon. A simple self-oscillating white LED driver to replace a fluorescent lamp. When Q1 switches on, it shorts out the bottom end of L2. When it switches off, the voltage at that point flies up above the 1.5V supply to power the two white LEDs. not used in a while, including the radio. I plugged it in to test it, but nothing happened; it was completely dead. Trying fresh cells instead of the AC adaptor did nothing. On opening the case, evidence of the previous leaking cells was visible near the compartment and the connecting wires appeared corroded, so I cleaned everything and replaced the wires. The radio still refused to work. I was able to download a schematic diagram, but my board looked slightly different. I started tracing the 6V from the cells and it was apparent on one side of a wire with a ferrite bead, but not on the other. Assuming a dry joint, I resoldered the wire. As I did, I noticed that the wire moved within the bead. Using tweezers, I pulled half of the wire out and, on close inspection, it was corroded inside the bead, likely due to the aforementioned cell leakage. A new piece of copper wire simply brought the radio to life. Rowan Wigmore, Hadspen, Tas. I soldered the toroid winding and a 2N5551 NPN transistor with a 1kW base resistor onto a small piece of matrix board, and connected two white LEDs in series between the collector and emitter of the transistor. The clock has two small perimeter slots on its face at the 11 o’clock and five o’clock positions that are relatively transparent. I hot glued LEDs at these positions with the lens pointing inwards. When the backlight switch was operated, the LEDs lit up, and the hands could be easily seen. While the backlight is no longer spread evenly over the whole of the clock face, the LEDs provide sufficient illumination to easily check the time during darkness. SC Phillip Webb, Hope Valley, SA. Seiko Bedside Clock backlight repair In the early 1990s, I received a Seiko bedside alarm clock in recognition of 20 years’ service with my then employer. This clock has performed perfectly in timekeeping, but its fluorescent backlight gradually dimmed over time, then stopped functioning altogether. I finally got around to opening the case, and discovered that at some point in time, the 1.5V dry cell battery had leaked all over the small circuit board that drives the fluorescent backlight. I cleaned up the board as best I could, but could not coax the backlight into life. I immediately thought of replacing the backlight with white LEDs, but realised they needed about 3V to get them to light. Years ago, I had played around with the “Joule Thief” circuit that was easily able to light LEDs from a 1.5V cell. Looking through my boxes of parts, I found a compact fluorescent lamp (CFL) driver board with a small toroid that would be perfect for making a Joule Thief transformer. I stripped the old winding out and wound 12 turns bifilar. siliconchip.com.au Australia's electronics magazine November 2025  89 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. 11/25 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 PIC12F617-I/P 110dB RF Attenuator (Jul22), Basic RF Signal Generator (Jun23) 2m VHF CW/FM Test Generator (Oct23) Active Mains Soft Starter (Feb23), Model Railway Uncoupler (Jul23) Battery-Powered Model Railway Transmitter (Jan25) PIC12F675-I/SN Tiny LED Xmas Tree (Nov19) PIC16F1455-I/P Railway Points Controller Transmitter / Receiver (2 versions; Feb24) Battery-Powered Model Railway TH Receiver (Jan25) Dual Train Controller (Transmitter / TH Receiver, Oct25) PIC16F1455-I/SL Battery Multi Logger (Feb21), USB-C Serial Adaptor (Jun24) Battery-Powered Model Railway SMD Receiver (Jan25) USB Programmable Frequency Divider (Feb25) Dual Train Controller (SMD Receiver, Oct25) PIC16LF1455-I/P New GPS-Synchronised Analog Clock (Sep22) PIC16F1459-I/P K-Type Thermostat (Nov23), Secure Remote Switch (RX, Dec23) Mains Power-Up Sequencer (Feb24 | repurposed firmware Jul24) 8CH Learning IR Remote (Oct24), Heat Transfer Controller (Aug25) Vacuum Controller (Oct25) PIC16F1459-I/SO Multimeter Calibrator (Jul22), Buck/Boost Charger Adaptor (Oct22) PIC16F15214-I/SN Silicon Chirp Cricket (Apr23), Mic The Mouse (Aug25) PIC16F15214-I/P Filament Dryer (Oct24), Tool Safety Timer (May25) PIC16F15224-I/SL Multi-Channel Volume Control (OLED Module; Dec23) NFC IR Keyfob Transmitter (Feb25), Rotating Light (Apr25) PIC16F18146-I/SO Compact OLED Clock & Timer (Sep24), Flexidice (Nov24) Versatile Battery Checker (May25), RGB LED ‘Analog’ Clock (May25) USB-C Power Monitor (Aug25) PIC16LF15323-I/SL Remote Mains Switch (TX, Jul22), Secure Remote Switch (TX, Dec23) STM32G030K6T6 Variable Speed Drive Mk2 (Nov24) PIC16F1847-I/P PIC16F18877-I/PT Digital Capacitance Meter (Jan25) Dual-Channel Breadboard PSU Display Adaptor (Dec22) Wideband Fuel Mixture Display (WFMD; Apr23) PIC16F88-I/P Battery Charge Controller (Jun22), Railway Semaphore (Apr22) PIC24FJ256GA702-I/SS Ohmmeter (Aug22), Advanced SMD Test Tweezers (Feb23) ESR Test Tweezers (Jun24) PIC32MX170F256D-501P/T 44-pin Micromite Mk2 (Aug14), 4DoF Simulation Seat (Sep19) PIC32MX170F256B-50I/SP Micromite LCD BackPack V1-V3 (Feb16 / May17 / Aug19) Advanced GPS Computer (Jun21), Touchscreen Digital Preamp (Sep21) PIC32MX170F256B-I/SO Battery Multi Logger (Feb21), Battery Manager BackPack (Aug21) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) STM32L031F6P6 SmartProbe (Jul25) $20 MICROS ATmega32U4 ATmega644PA-AU PIC32MK0128MCA048 PIC32MX270F256D-50I/PT Wii Nunchuk RGB Light Driver (Mar24) AM-FM DDS Signal Generator (May22) Power LCR Meter (Mar25) Digital Preamplifier (Oct25) $25 MICROS PIC32MX170F256B-50I/SO + PIC16F1455-I/SL Micromite Explore-40 (SC5157, Oct24) PIC32MX470F512H-120/PT Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) PIC32MX470F512L-120/PT Micromite Explore 100 (Sep16) $30 MICROS PIC32MX695F512H-80I/PT Touchscreen Audio Recorder (Jun14) PIC32MZ2048EFH064-I/PT DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) DIY Reflow Oven Controller (Apr20), Dual Hybrid Supply (Feb22) KITS, SPECIALISED COMPONENTS ETC RP2350B COMPUTER (NOV 25) Assembled Board: a fully-assembled PCB with all non-optional components, front and rear panels are sold separately below (SC7531; see p28, Nov25) - front & rear panels (SC7532) - 8MiB APS6404L-3SQR-SN PSRAM SOIC-8 IC (SC7530) DUAL TRAIN CONTROLLER MICROCONTROLLERS (OCT 25) PICKIT BASIC POWER BREAKOUT KIT (SC7512) (SEP 25) - PIC16F1455-I/P programmed with 0911024D.HEX (Transmitter) - PIC16F1455-I/P programmed with 0911024S(or T).HEX (Receiver, TH) - PIC16F1455-I/SL programmed with 0911024S(or T).HEX (Receiver, SMD) firmware ending with “S.HEX” is for train 1, while “T.HEX” is for train 2 Includes all parts except the jumper wire and glue (see p39, Sep25) MIC THE MOUSE KIT (SC7508) Includes all parts except a CR2032 cell (see p64, Aug25) RP2350B DEVELOPMENT BOARD (AUG 25) $90.00 $7.50 $5.00 $10.00 $10.00 $10.00 siliconchip.com.au/Shop/ PICO/2/COMPUTER (SC7468) (APR 25) 433MHz TRANSMITTER KIT (SC7430) (APR 25) ROTATING LIGHT FOR MODELS KIT (APR 25) PICO 2 AUDIO ANALYSER SHORT-FORM KIT (SC6772) (MAR 25) USB PROGRAMMABLE FREQUENCY DIVIDER (SC6959) (FEB 25) NFC PROGRAMMABLE IR KEYFOB (SC7421) (FEB 25) COMPACT HIFI HEADPHONE AMP (SC6885) (DEC 24) PICO COMPUTER (DEC 24) Includes an assembled PCB, separate Raspberry Pi Pico 2 and front/rear panels $120.00 Includes the PCB and all onboard parts (see p75, Apr25) Complete kit which includes the PCB and all onboard components (see p60, Apr25): - SMD LEDs (SC7462) $20.00 - Through-hole LEDs (SC7463) $20.00 The Pico Audio Analyser kit from Nov23, but with an unprogrammed Pico 2 $20.00 Complete kit: includes all components (see p85, Feb25) $37.50 Complete kit: includes all required items, except the cell (see p67, Feb25) (AUG 25) Assembled Board: a pre-assembled PCB with all mandatory parts fitted, optional components are sold separately below (SC7514; see p49, Aug25) - 40-pin header (two are required, SC3189) - 8MiB APS6404L-3SQR-SN PSRAM SOIC-8 IC (SC7530) $20.00 $50.00 $60.00 $25.00 $30.00 Complete kit: includes everything except the power supply (see p47, Dec24) $70.00 $1.00ea CAPACITOR DISCHARGER KIT (SC7404) (DEC 24) $5.00 Includes the PCB and all components that mount on it, the mounting hardware USB-C POWER MONITOR KIT (SC7489) (AUG 25) (without heatsink) and banana sockets (see p36, Dec24) $30.00 Includes all non-optional parts except the case, cell & glue (see p39, Aug25) $60.00 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 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 VARIOUS MODULES & PARTS - two 1nF ±1% capacitors (ESR Meter, Aug23; SC4273) - 0.96in 128x64 white OLED without PCB (SmartProbe, Jul25; SC7397) - Talema AC-1010 10A Current Transformer (SC3315) *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. $2.50 $7.50 $20.00 PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT MODEL RAILWAY TURNTABLE CONTROL PCB ↳ CONTACT PCB (GOLD-PLATED) 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 PICO DIGITAL VIDEO TERMINAL ↳ FRONT PANEL FOR ALTRONICS H0190 (BLACK) ↳ FRONT PANEL FOR ALTRONICS H0191 (BLACK) ARDUINO FOR ARDUINIANS (PACK OF SIX PCBS) ↳ PROJECT 27 PCB WII NUNCHUK RGB LIGHT DRIVER (BLACK) 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) DATE MAR23 MAR23 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 MAR24 MAR24 MAR24 MAR24 MAR24 MAR24 APR24 APR24 APR24 MAY24 MAY24 MAY24 JUN24 JUN24 PCB CODE 09103231 09103232 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 07112231 07112232 07112233 SC6903 SC6904 16103241 08101241 08104241 07102241 04104241 04112231 10104241 SC6963 08106241 Price $5.00 $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 $5.00 $2.50 $2.50 $20.00 $7.50 $20.00 $15.00 $10.00 $5.00 $10.00 $2.50 $5.00 $10.00 $2.50 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT ↳ ADJUSTABLE THROUGH-HOLE ↳ FIXED THROUGH-HOLE USB-C SERIAL ADAPTOR (BLACK) AUTOMATIC LQ METER MAIN AUTOMATIC LQ METER FRONT PANEL (BLACK) 180-230V DC MOTOR SPEED CONTROLLER STYLOCLONE (CASE VERSION) ↳ STANDALONE VERSION DUAL MINI LED DICE (THROUGH-HOLE LEDs) ↳ SMD LEDs GUITAR PICKGUARD (FENDER JAZZ BASS) ↳ J&D T-STYLE BASS ↳ MUSIC MAN STINGRAY BASS ↳ FENDER TELECASTER COMPACT OLED CLOCK & TIMER USB MIXED-SIGNAL LOGIC ANALYSER (PicoMSA) DISCRETE IDEAL BRIDGE RECTIFIER (TH) ↳ SMD VERSION MICROMITE EXPLORE-40 (BLUE) PICO BACKPACK AUDIO BREAKOUT (with conns.) 8-CHANNEL LEARNING IR REMOTE (BLUE) 3D PRINTER FILAMENT DRYER DUAL-RAIL LOAD PROTECTOR VARIABLE SPEED DRIVE Mk2 (BLACK) FLEXIDICE (RED, PAIR OF PCBs) SURF SOUND SIMULATOR (BLUE) COMPACT HIFI HEADPHONE AMP (BLUE) CAPACITOR DISCHARGER PICO COMPUTER ↳ FRONT PANEL (BLACK) ↳ PWM AUDIO MODULE DIGITAL CAPACITANCE METER 5MHZ 40A CURRENT PROBE (BLACK) BATTERY MODEL RAILWAY TRANSMITTER ↳ THROUGH-HOLE (TH) RECEIVER ↳ SMD RECEIVER ↳ CHARGER USB PROGRAMMABLE FREQUENCY DIVIDER HIGH-BANDWIDTH DIFFERENTIAL PROBE NFC IR KEYFOB TRANSMITTER POWER LCR METER WAVEFORM GENERATOR PICO 2 AUDIO ANALYSER (BLACK) PICO/2/COMPUTER ↳ FRONT & REAR PANELS (BLACK) ROTATING LIGHT (BLACK) 433MHZ TRANSMITTER VERSATILE BATTERY CHECKER ↳ FRONT PANEL (BLACK, 0.8mm) TOOL SAFETY TIMER RGB LED ANALOG CLOCK (BLACK) USB POWER ADAPTOR (BLACK, 1mm) HWS SOLAR DIVERTER PCB & INSULATING PANELS SSB SHORTWAVE RECEIVER PCB SET ↳ FRONT PANEL (BLACK) 433MHz RECEIVER SMARTPROBE ↳ SWD PROGRAMMING ADAPTOR DUCTED HEAT TRANSFER CONTROLLER ↳ TEMPERATURE SENSOR ADAPTOR ↳ CONTROL PANEL MIC THE MOUSE (PCB SET, WHITE) USB-C POWER MONITOR (PCB SET, INCLUDES FFC) HOME AUTOMATION SATELLITE PICKIT BASIC POWER BREAKOUT DUAL TRAIN CONTROLLER TRANSMITTER DIGITAL PREAMPLIFIER MAIN PCB (4 LAYERS) ↳ FRONT PANEL CONTROL ↳ POWER SUPPLY VACUUM CONTROLLER MAIN PCB ↳ BLAST GATE ADAPTOR DATE 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 JUL25 JUL25 AUG25 AUG25 AUG25 AUG25 AUG25 SEP25 SEP25 OCT25 OCT25 OCT25 OCT25 OCT25 OCT25 PCB CODE Price 08106242 $2.50 08106243 $2.50 24106241 $2.50 CSE240203A $5.00 CSE240204A $5.00 11104241 $15.00 23106241 $10.00 23106242 $12.50 08103241 $2.50 08103242 $2.50 23109241 $10.00 23109242 $10.00 23109243 $10.00 23109244 $5.00 19101231 $5.00 04109241 $7.50 18108241 $5.00 18108242 $2.50 07106241 $2.50 07101222 $2.50 15108241 $7.50 28110241 $7.50 18109241 $5.00 11111241 $15.00 08107241/2 $5.00 01111241 $10.00 01103241 $7.50 9047-01 $5.00 07112234 $5.00 07112235 $2.50 07112238 $2.50 04111241 $5.00 9049-01 $5.00 09110241 $2.50 09110242 $2.50 09110243 $2.50 09110244 $2.50 04108241 $5.00 9015-D $5.00 15109231 $2.50 04103251 $10.00 04104251 $5.00 04107231 $5.00 07104251 $5.00 07104252/3 $10.00 09101251 $2.50 15103251 $2.50 11104251 $5.00 11104252 $7.50 10104251 $5.00 19101251 $15.00 18101251 $2.50 18110241 $20.00 CSE250202-3 $15.00 CSE250204 $7.50 15103252 $2.50 P9054-04 $5.00 P9045-A $2.50 17101251 $10.00 17101252 $2.50 17101253 $2.50 SC7528 $7.50 SC7527 $7.50 15104251 $3.50 18106251 $2.00 09110245 $3.00 01107251 $30.00 01107252 $2.50 01107253 $7.50 10109251 $10.00 10109252 $2.50 POWER RAIL PROBE NOV25 P9058-1-C NEW PCBs $5.00 We also sell the Silicon Chip PDFs on USB, RTV&H USB, Vintage Radio USB and more at siliconchip.com.au/Shop/3 Vintage Electronics The Telequipment D52 Dual-Beam Oscilloscope The D52 dual-beam 6MHz oscilloscope was quite the creation in the late 1960s. It was British made and a definite competitor with the American-made Tektronix scopes. Within Australia, both Tektronix and Telequipment Scopes were marketed and sold by Tektronix Australia Pty Ltd in NSW. By Dr Hugo Holden T he Telequipment scopes had very characteristic front panels and knobs. Some Telequipment apparatus with these knobs got used as props on the panels of the flying craft in Gerry and Sylvia Anderson’s brilliant puppet TV series, The Thunderbirds. As soon as I saw a Telequipment scope, I recognised the appearance as being what I had seen on some control panels in that TV show as a boy. Perhaps that was one thing that made me more interested in them. The original arrangement on these units used UHF sockets for the scope’s probes, as can be seen from the advertising photos. I changed them to BNC connectors on my scope to make them compatible with many more modern probes. BNC panel connectors that are made to be an insulated panel mount fit perfectly into the hole for the UHF sockets. My scope has the orange filter. This was an option that Telequipment offered when it was fitted with a dual-phosphor CRT. The CRT has a short blue and long yellow persistence phosphor. This is designated as P7 (or a GM suffix). If you were interested in short timeframe events, you would fit a blue plastic filter in front of the CRT (this blocks yellow). Alternatively, if you were interested in slower events, such as a cardiac ECG, you fit the orange filter which lets the yellow through, tinting it orange, while blocking the blue. Many D52 scopes simply had the usual green medium-persistence phosphor designated P31 (GH) with a green filter. A blue (P11 phosphor) CRT option was also available, but only in Photo 1: using the orange filter shows just the slower of the two phosphors, so very fast transients are removed. Photo 2: without the filter, the traces look white; the result of the yellow and blue light mixing. Photo 3: the phosphor looks blue when viewed through the side wall of the cathode ray tube. Australia's electronics magazine siliconchip.com.au 92 Silicon Chip the 12-pin version. There were two CRT variants for this scope, with either 12- or 14-pin bases. Therefore, for the D52, there were five possible CRTs it could use, according to the manual. Photo 1 shows the typical result with the orange filter. With the filter removed, the trace looks white (Photo 2), which is the blue and yellow mixing. The yellow phosphor was applied to the CRT glass first, then the blue after that. Looking at the inside of the CRT (which can be seen through the side wall of the tube), the internal appearance of the phosphor is vivid blue (Photo 3). The D52 is a valve-based scope; nearly all the circuitry in the timebase and vertical amplifier circuits uses valves, mainly the ECC88 dual triode, ECF80 triode-pentode and 6AL5/EB91 dual diode. However, this design has an interesting arrangement to support the ×10 gain function. 2N3702 silicon transistors, two per vertical amplifier channel, are creatively switched into the circuit to achieve it. Also, the power supply uses solid-state rectifiers and a single ACY22 germanium transistor to support a -12V supply. There are also numerous 1N914 silicon signal diodes in the circuit. The CRT’s EHT rectifiers were long stick multi-disc element selenium types; these parts gave trouble and required replacement. The dual-beam oscilloscope Most cathode ray tube (CRT) based dual-beam oscilloscopes actually use a single-beam CRT; the two (or more) beams are created electronically. They have a channel switching circuit that effectively creates a duplicate channel. The switching is either done on alternate horizontal traces or it is chopped between traces at a high frequency. The latter switches between two vertical amplifiers and two beam positioning controls to create the two traces. The typical scope, in two channel mode, has an ALT or a CHOP switch to select the method. In other words, all the heavy lifting to make the scope two or more channels is done by the scope’s electronics, not the CRT. The D52 is different. It has a real twin-beam CRT, but with one electron gun – see Fig.1. The gun is arranged with a beam splitter element, which splits one beam into two after it is emitted from the CRT’s cathode. There is siliconchip.com.au electronic circuitry. Normally, there would be a blanking amplifier for the task. The timebase It has speeds of 500, 200, 100, 50, 20, 10, 5, 2 & 1ms/cm and those numbers again at μs/cm. The horizontal amplifier’s user X gain control expands the trace to 10 screen diameters, and the shift control has enough range to allow any part of that expanded traced to be centred on the screen. This timebase was known for easy triggering. I have had no difficulty with it. Vertical amplifiers Fig.1: the Telequipment D52 uses a special cathode ray tube that splits the electron beam into two streams that are steered together horizontally (X1/X2) but differently in vertical directions (Y1’/Y2’ & Y1”/Y2”). also an adjustable magnet on the rear of the CRT socket that makes sure the split beams have equal intensities. The two separate beams go on to pass via different sets of Y deflection plates in the same tube. Only one set of X deflection plates is required to create the horizontal trace for both beams. The CRT is quite the masterpiece of electron optics; it also sported post-deflection acceleration. This allowed the tube to have relatively high sensitivity of the deflection plates, but also a high EHT, which favours high beam brightness. The CRT also has an inter-plate shield (IPS) electrode to reduce the interactions of the two Y sets of plates. The service manual omitted advice on how to set the IPS voltage. It is usually set to the average deflection plate voltage, which is 207V in the D52. One other interesting feature of the CRT is that, to achieve retrace blanking, they incorporated an additional control element into the CRT, called a modulation plate. This is nothing to do with X modulation, which is introduced into the CRT’s grid in the usual way. It is to fully cut off the beam cleanly for horizontal retrace. It appears amazingly effective. This is another feature of the particular CRT that eliminated more Australia's electronics magazine The vertical amplifier circuit, Fig.2, shows the arrangement with the original 2N3702 PNP transistors that are used for the ×10 gain boost circuit. When I first got the scope, the transistors in both channels were damaged. At the time, I didn’t have the exact parts. Ultimately, I replaced them with 2N3906s, which are better for the task (as explained below). The cathode currents of the ECC88 cathode follower V2A & V2B drive the transistor’s emitters. Since it is a differential amplifier, the transistor’s inter-base resistance (RV36) controls the gain. The output voltage is developed across the 8.2kW collector load resistors. When ×10 gain is not wanted, the transistor’s collector and emitter terminals are simply shorted out by the switch, and the cathode follower behaves as a standard voltage buffer. The circuit is the same for both channels, although some components are shared. Frequency-compensation networks are generally required in oscilloscope amplifier circuitry, either at the emitters or bases, to keep the response flat. This is because a combination of resistance and capacitance rolls off the high-frequency response. The arrangements to solve the problem (typically used in Tektronix scopes) are shown in Fig.3. However, the Telequipment D52 scope did not have any frequency compensation networks associated with the transistors in the ×10 gain function. Thus, the scope’s bandwidth was significantly limited in the ×10 gain mode. The D52’s vertical amplifier performance is very good in ×1 gain mode. The vertical input sensitivity November 2025  93 Fig.2: the vertical amplifier circuitry of the scope uses four ECC88 dual triodes (V1-V4) and two 2N3702 PNP silicon transistors (TR1 & TR2) per channel. The two silicon diodes (MR21/MR22) are shared between the channels. The transistors are responsible for the extra gain required in ×10 mode. is 0.1V/cm or 10mV/cm in ×10 gain mode, which is good for a scope of this age. More modern CRT scopes of the 1970s and 1980s went to 5mV/ cm and eventually to 2mV/cm (eg, the Tektronix 2465B). The trigger circuits also sported filters to help the scope lock on to TV frame or line sync pulses. There is a general assumption that the bandwidth specification is for the -3dB point. In at least three cases I know of, that is not even close. The D52 was rated for DC to 6MHz on the 0.1V/cm setting and DC to 1MHz in the ×10 gain or 10mV/cm mode. However, they underestimated it. I tested it using a Tektronix SG503 levelled sinewave generator terminated into 50W at the scope’s input on the 0.1V/cm setting. The vertical amplifier’s frequency 94 Silicon Chip response was flat to over 6MHz, and only 3dB down at 7.9MHz. In ×10 mode, it was flat to 1MHz and 3dB down at around 1.6MHz with the original 2N3702 transistors. In ×1 mode, with the transistors shorted out, the output impedances of the cathode followers of V2A and V2B a few hundred ohms. However, with the transistors switched in, in ×10 mode, the collector load resistance becomes 8.2kW. This, in conjunction with the transistor’s output capacitance (about 12pF) and the additional capacitance of the wiring and V3’s input capacitance, rolls of the HF response to 1-2MHz. The best PNP silicon transistor replacement I could find was the 2N3906, which has an output capacitance of only 4.5pF. With these transistors installed, the frequency response Australia's electronics magazine in ×10 mode substantially improves to be 3dB down at 3.17MHz. It probably would be possible to improve this further by adding a frequency compensation network, but I decided that I would leave the scope original, aside perhaps from the better transistors I had installed. I also checked the attenuators in the D52; they are excellent and properly frequency compensated, so they do not alter the vertical amplifier bandwidth on any setting. Self-cracking resistors Valves V2 and V4 both have 100W resistors in series with their control grids. These are known as ‘stopper resistors’. They form a low-pass filter in conjunction with the valves’ input capacitance, which prevents (stops) very high frequency instability, siliconchip.com.au Photo 4: with the leads being within the bodies of these resistors, when the leads corroded and expanded, the bodies cracked. Photo 5: these VMI 1N6519 rectifiers are rated at 10kV & 500mA. They are quite rare. Fig.3: these two compensation networks can be applied to differential amplifiers to extend their high-frequency response. They compensate for the inherent roll-off due to Miller capacitances and non-zero source impedances. especially in the VHF and UHF region. Similar resistors are used in the timebase section. These particular 100W resistors were all made by the same factory to the same design, and it was a disaster waiting to happen. One would imagine the failure rate of a resistor in this application to be extremely low because the current and power dissipation are negligible. I pulled the D52 scope out from a period in storage and, on powering it, there were multiple failures in both the timebase and vertical amplifier stages. Initially, I thought it would have to be a power supply problem, but it was not. After several tests, I noticed that some of the valves had very low plate and cathode currents. The readings appeared to make no sense. Then I started to discover that several of the siliconchip.com.au 100W stopper resistors in series with the control grids had gone completely open circuit. The control grids were floating, accumulating a negative charge and cutting off the valves. I removed six of these resistors to study them. The construction of the resistor was a cylindrical ceramic rod coated in a carbon film. There was a hole in each end in the ceramic rod with a metallised coating where the wire leads were soldered in. This is in contrast to the method where metal end caps are used. Corrosion in the holes had caused the leads to expand, cracking the resistor bodies. One resistor was cracked totally in half and only barely holding together (Photo 4). Metals oxides tend to occupy more volume than the metals they’re based on, so if they are encased in a rigid structure, the pressure slowly builds up over time. For example, rust (iron oxide) crystals expand under the paint on painted steel surfaces, causing the paint to bubble. It is a superior idea for a ceramic bodied resistor to have pressed-on end caps, but I suppose the creators of these Australia's electronics magazine resistors did not consider what could happen to them over the next 50 years. EHT failures The 2.6kV EHT for the CRT’s final anode is derived from a 1060V tap on the main power transformer. It feeds two capacitors and two diodes in a typical twice-peak voltage doubler. The two rectifiers in the EHT circuit were a type of long selenium stick rectifier in a cardboard tube. These are made up of multiple small discs stacked in series to create a rectifier with a high reverse breakdown voltage. The method does result in a relatively high forward resistance and a high forward voltage drop, but the CRT’s final anode current is very low. For example, the tube’s beam current is limited to 500μA. However, these stick selenium rectifiers failed and developed significant reverse leakage, overloading the 1060V transformer output. I replaced them with some excellent EHT rectifiers made by VMI (Voltage Multipliers Inc). VMI makes high-quality high-voltage rectifiers for many industrial and military applications. Occasionally, some November 2025  95 Photo 6: I wrapped fibreglass tape around the new capacitors to make them the same size as the originals. Photos 7 & 8: the new rectifiers and capacitors in place; and the recapped power supply board (below). turn up on eBay, presumably parts left over from an assembly contract. I managed to land a pair of 1N6519 rectifiers and had them in my parts box for a rainy day (Photo 5). The original stick rectifiers were rated at 3.4kV and 5mA, while the 1N6519 rectifiers are rated at 10kV and 500mA. They have a relatively fast recovery, suited to high-frequency supplies. In this case, that feature is not required. The new EHT rectifiers resulted in an increase in the EHT output from 2.6kV to 2.9kV, ie, about +11%. The total CRT EHT voltage is higher too, because the CRT’s cathode circuit is configured to run at -960V. While the CRT’s maximum beam current is limited to 500μA by the circuitry, the individual electrons, being accelerated by a higher voltage gradient between the cathode and final anode, acquire more energy before they hit the screen phosphor. Thus, the beam brightness increased even without a significant increase in cathode current. Some people fit a series resistor when replacing selenium rectifiers with silicon types, to lower the resulting voltage to near what the selenium rectifier gave before. In this case, I decided it was not required, and the improved performance was helpful. I also discovered that both the capacitors in the EHT voltage doubler section were electrically leaky. This had possibly provoked the failures of the selenium rectifiers. The main 96 Silicon Chip output filter capacitor appeared to be a large oil-filled type, rated at 0.05μF (50nF) & 3.5kV. The other coupling capacitor to the first rectifier is a lot smaller, rated at 0.05μF (50nF) & 2kV. The replacement capacitor I used was created from two 0.1μF 3kV capacitors in series to halve their capacitance and double their voltage rating. Balancing resistors are not required for film caps of the same value to share Australia's electronics magazine charge, as they have practically zero leakage. Due to the fact that the new capacitors have a smaller diameter than the originals, I wrapped them in 0.2mm-thick fibreglass sheet and finished them off with Scotch 27 fibreglass tape. The capacitor in the righthand side of Photo 6 is the original 50nF 3.5kV part, which was 36mm in diameter and 80mm long. siliconchip.com.au An advert from page 48 of Electronics Australia magazine, April 1969, showing multiple different Telequipment oscilloscopes for sale. These scopes were sold by Tektronix distributors in Australia. siliconchip.com.au Australia's electronics magazine November 2025  97 Photo 7 shows the two VMI rectifiers fitted and the two new capacitors in the voltage doubler. The electrolytic capacitors Most of the other capacitors in the scope were in good order, although some of the electrolytics in the power supply had started to draw excessive current and heat up. I replaced the defective ones, shown in blue in Fig.4. I went to a considerable amount of trouble to decide if C412, a three-­ section 32μF 450V capacitor (highlighted in green) should be replaced. After removing it, extensive testing of its capacity, leakage at its full rated voltage and its ESR were all perfectly normal, so I re-fitted it. I also could not find anything wrong with the main 120μF voltage doubler capacitors (highlighted in red). Summary The Telequipment D52 is a very nice vintage oscilloscope. It does have limitations compared to more modern CRT scopes; its bandwidth is not particularly wide, although better than the 6MHz advertised. The D52’s power supply system is non-regulated (that probably would have given the engineers at Tektronix bad dreams), so line voltage variations can affect the trace. The internal physical construction is good. One plus is that its unique twin-beam CRT does not have any problems associated with CHOP and ALT modes that can sometimes affect traditional twin-beam scopes. If you find one of these scopes and want to restore it, I would replace the selenium EHT stick rectifiers and EHT filter capacitors off the bat (if it still has the original parts), because when they fail, it stresses the main power transformer. Likely at least one or two of the electrolytic capacitors will require replacing. Also, it pays to check all the 100W grid stopper resistors in case they suffer from the self-cracking disease. When the cracks start, the resistor initially goes high in value, then after a while, it suddenly goes completely open circuit. It is probably worth replacing the original 2N3702 transistors with 2N3906s to improve the high-­frequency performance in ×10 gain mode. The scope is a great workshop asset, especially when fitted with a dual-phosphor tube, making it particularly good at examining long-­duration events. One application I put it to was to record the output of Sputnik-1’s Manipulator circuit, which switches at 2.5Hz, with characteristic steps in the waveform that correspond to the time when neither relay in the manipulator is closed. You can see a video of the scope displaying this waveform at https://youtu.be/k15GSKK_UY0 SC Fig.4: the scope’s power supply circuitry with parts of interest highlighted in different colours: the EHT voltage doubler in orange, main voltage doubler capacitors in red, a special three-section 32μF 450V capacitor in green and the faulty electrolytic capacitors that needed to be replaced in blue. 98 Silicon Chip Australia's electronics magazine siliconchip.com.au Subscribe to OCTOBER 2025 ISSN 1030-2662 10 The VERY BEST DIY Projects ! 9 771030 266001 $14 00* NZ $14 90 Digital er ifi Preampl over ss and Cro eaker , Part 2 Autonomous Australia’s top electronics magazine m nt S p Du Co a l T r nt r a i oll n er u cu Va op ler sh ol rk ntr Wo Co Pend a INC GST INC GST Vehicles and Driver Assistance Sys 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. tems 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 $72.50 $82.50 $52.50 1 year $135 $155 $100 2 years $255 $290 $190 6 months $85 $95 1 year $160 $180 2 years $300 $335 6 months $105 $115 1 year $200 $220 All prices are in Australian dollars (AUD). Combined subscriptions include both the printed magazine and online access. 2 years $390 $425 Prices are valid for the month of issue. Try our Online Subscription – now with PDF downloads! Autonomous Vehicles; October 2025 Vacuum Controller; October 2025 Pendant Speaker; October 2025 USB-C Power Monitor; Aug-Sep 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 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 Calibrating the SSB Shortwave Receiver I built this project from June & July 2025 (siliconchip.au/Series/441) and it is now operational. I’m up to the calibration steps. I can’t find test point TP5 referenced in the article on the circuit diagrams or PCB silkscreens. Also, a signal generator is required for the final calibration step. Is that an RF signal generator or a function generator? I’m hoping the latter. Thanks so much for an amazing project. This has been a fabulous build. (T. R., North Manly, NSW) ● It looks like TP5 was omitted; it should be on pin 6 of IC2. Still, the important thing is to get maximum voltage on TP6 by adjusting the trimmer capacitors. The tuning is fairly broad. An RF signal generator is required, preferably with an output that can be reduced down to 10μV. Many signal generators have a minimum output level that’s too high. To get around this, connect a wire to the antenna terminal (about 1m should be enough) and similarly, a wire to the output of the signal generator. There should be enough RF coupling between the wires to be able to tune the trimmers. Can the HWS Solar Diverter be upgraded? I have an 8kW hot water system. The Solar Diverter you published in the June & July 2025 issues is rated at 3.6kW (siliconchip.au/Series/440). Would it be impractical to substitute the Triac with a higher-rated device like a BTA100-800 mounted on a separate heatsink? I realise the wiring, heatsinking and fan cooling would need a considerable upgrade. Thanks for a great magazine. (S. B., Hawker, ACT) ● We don’t think our design can safely be modified to handle more than double the design’s maximum specified power/current. We suspect you would need a 50A external contactor to control it, and the software would need to be modified to switch it on or off at a much lower rate (eg, every 60 seconds). Most realistically, it would have to just be on/off control (ie, deciding whether to heat at any given time or not). Dr Berkelman comments additionally: I think one of the first planning tasks would be an assessment of the USB to PS/2 Keyboard Adaptors Make it easy to use a USB keyboard on most devices that support a PS/2 interface. Both kits include everything except the Jiffy box and 6-pin mini-DIN to mini-DIN cable(s) – see SC6869, $10. The mounting hardware and optional headers and sockets are supplied. The Pico is supplied blank and requires programming. This version is standalone and includes a mouse adaptor. Perfect for older PCs with PS/2 sockets. ps2x2pico Kit SC6864 : $32.50 + postage This version fits into our VGA PicoMite project (July 2022, siliconchip.au/Article/15382), replacing its PS/2 socket. Can also be used standalone. For the VGA PicoMite Kit SC6861 : $30.00 + postage For more details, see the January 2024 issue: siliconchip.au/Article/16090 100 Silicon Chip Australia's electronics magazine siliconchip.com.au available solar export power to drive such a large element and what volume of water needs heating, to see if the exercise would be worthwhile. This would involve looking at his solar export history and doing a backof-the envelope calculation on how much water S. B. can realistically heat in a day. If it is a three-phase element, he will need phase-level detail in his export. The Modbus Poll test program that we mention in our article will help. Versatile Battery Checker ‘scan failed’ I have built the Versatile Battery Checker (May 2025; siliconchip.au/ Article/18121) from your kit but am having a problem that I hope you can help me with. Using a 9V battery and a 1.5V cell, the checker switches on OK. It will go into calibration mode, but when I select “Run auto”, it says, “Scan failed check battery”. So I went out and bought two new batteries. Unfortunately, the same thing happens again. If I run a test, it says, “I too HIGH”. Can you please help diagnose this problem? (S. D., Bundaberg, Qld) ● It’s possible that a hardware fault (dry solder joint, wrong component etc) could cause this error, so first we suggest you double-check that everything is correct and soldered properly. If there is a short circuit of some sort on the BUT (battery under test) circuit, that could cause a problem, especially if a bigger battery is connected. We’ve had a few readers reporting similar error messages, and in most cases, it seems like the batteries aren’t capable of providing enough current to do the calibration, even though we used a fairly generic 1.5V AA cell in our tests. It would help if you could tell us the brand and model of batteries/cells you are using. Also, please verify that the main screen is correctly showing the voltage of the BUT and that it is being detected properly. A current-limited power supply should also work well for calibration purposes. Try setting it to 2V/2A and see if you can complete the calibration with the power supply in place of the BUT. If you are confident in your construction, a small (eg, 14500 or 18650 size) lithium-ion cell should also be siliconchip.com.au Frankensteining a Battery Charge Controller I have questions about John Clarke’s Battery Charge Controllers from the April 2008 and December 2019 issues. I have some IRF1405 Mosfets. Is it possible to use the Mosfet driving circuit after IC1’s pin 9 from the 2008 design with the software and remainder of the circuit from the 2019 design? Can I use an electronic transformer with a 17-18V DC output as the power supply? (Slava, Kyiv, Ukraine) ● It is not possible to use the Mosfet driver circuitry from the April 2008 12V Battery Charger with the December 2019 Battery Charge Controller unless the software is also changed. That’s because the 2008 design requires an AC waveform to switch on the Mosfet via the isolating transformer, while the 2019 design uses DC (high = on, low = off). Due to the way the Mosfet is driven, this may be difficult to do. Since both circuits provide a similar function, you could just build the April 2008 circuit instead of using sections of circuitry from each circuit. Yes, you can use an electronic (switch-mode) DC supply for the charger. suitable for initial calibration, and should be able to provide a fair bit more current than an alkaline AA cell. Versatile Battery Checker error message I have assembled the Versatile Battery Tester (May 2025; siliconchip.au/ Article/18121). However, when starting the calibration process, I get the message that the current is too high. I have used two different 1.5V pen cells, one being a brand new “Energiser Max Plus”. Do you know what is causing this fault? (P. C., Wantirna South, Vic) ● There shouldn’t be any reason for that message during the calibration unless there is a hardware fault. We take it that the cell voltage is being displayed correctly. We suspect that there is a hardware fault causing the current to be misread or misapplied. Check the component values and soldering, especially in the top half of the PCB. If you can email some high-resolution photos, we’ll check that everything looks correct. You could also try reloading the defaults as per Screen 14 on p32 of the article, in case the calibration parameters are off. Identifying parts in the Rotating Light kit I recently received my order of two SC7463 kits from you, but I am having trouble identifying D1 and REG1. There are some numbers and letters on each component, but I have difficulty in determining which is the diode and which is the regulator. They are about the same size physically, but one is slightly wider. Australia's electronics magazine I would be grateful if you could provide me with the expected codes so I can identify which is the diode and which is the regulator. (G. H., Camden, NSW) ● The RB491D diode marking is D2E (data sheet, page 1, right-hand side). The MCP1703AT-5002E/CB regulator marking is JLxx (data sheet, page 17, first table). For the specific batch likely used in our kits, it will be JLDW. You can double-check that you have D1 right with a multimeter set on diode test mode. Probing pins 2 (anode) and 3 (cathode) should give you a reading of about 0.3V. Pin 3 is the one by itself, and with pin 3 at the top, pin 2 is at lower left. The regulator is unlikely to give such a reading. Options for improving GPS signal I recently built the RGB LED Analog Clock kit (May 2025; siliconchip.au/ Article/18126) intending to have it on my desk at work. However, my office is inside a building, and I am concerned about the reinforced concrete, metal doors etc blocking the GPS signal. It’s fine at home, but at the office, it never gets past the starting phase. Is there any way of adding an antenna or something else that could boost the ability to get the signal from the satellites? (B. D., Perth, WA) ● We think you have two main options: 1. Swap the GPS receiver for one that uses an external antenna, like the Neo-7M (siliconchip.au/Shop/7/6737) or Neo-8M. We can supply an external antenna for the 7M (siliconchip. au/Shop/7/6738), although we don’t know if the attached 3m cable will be long enough for you. November 2025  101 2. Switch to getting the time over WiFi (NTP). To do that, replace the GPS module with a Raspberry Pi Pico W. See our article in the June 2023 issue on how this is done (siliconchip. au/Article/15823). I just finished assembling the Secure Remote Switch (December 2023; siliconchip.au/Series/408) transmitter (discrete version) and the matching Receiver kits. The boards seem to work fine up to a point. I can place the receiver in learn mode and synchronise the transmitter as per the instructions. The learn light goes off, and the receiver responds to the transmitter with two flashes on the ACK light, but without operating the relay. I have tried to re-synchronise the transmitter a few times. Occasionally, the remote will activate the relay (on with S2 and off with S3), but only the first time after synchronising. The relay operates as expected using the local switch, so as far as I can see, all aspects of the hardware are functioning. The different treatment of local and remote commands is within the software. Have you had any reports of similar behaviour, or are you able to make any suggestions? I thought I would just ask before wading into the software for clues, especially as it is written in assembly language. (C. C., West Beach, SA) ● We think the problem could be that the UHF receiver is overloaded by the signal when the transmitter is too close to it. Try setting up in learn mode with the transmitter at least one metre (preferably several metres) away. Similarly, operate the transmitter for testing or in normal use some meters away from the receiver. If that doesn’t solve it, let us know and we’ll consider other possible problems. respect to the PIC16F1455 IC’s specifications. Firstly, parameter D323 (Vddfminusb) states, “Required VDD for USB operation on PIC16F1454/5/9” is 3.6-5.5V but you have regulated the Vdd supply to 3.3V. Also, parameter D325 (Cusb3v3 Required Capacitance on Vusb3v3) is 0.22-2.2μF but you only have a 100nF capacitor on the Vusb3v3 pin. The third problem I have is the input protection resistors on ports RC3, RC4 and RC5. If the serial input is at 5V and USB is not connected, this would exceed the maximum input current, ie, 22.7mA (5V ÷ 220W). (S. G., Boise, Idaho, USA) ● These are relevant concerns. The circuit appears to work fine even though Vdd is 3.3V, we suspect because the internal regulator transistor is switched fully on (in dropout). In this condition, the capacitance on the Vusb3v3 pin isn’t so critical for stability, since the regulator’s feedback loop isn’t doing anything. However, the Vusb3v3 voltage will be lower than the desired 3.3V due to the regulator being in dropout. We should have connected the Vusb3v3 pin directly to Vdd, as is recommended for the PIC16LF145x chips when using the USB peripheral. This can be achieved with the existing board by running a thin wire between pins 1 and 11 of IC1. As for the pin current limits being exceeded if the serial input is driven to +5V with USB disconnected, there won’t actually be 5V across the 220W protection resistor. The pin’s internal clamp diode won’t conduct until the pin has risen to around 0.7V, meaning the initial current flow will be 19.5mA ([5.0V – 0.7V] ÷ 220W), just within the absolute maximum limit of ±20mA. Also consider that as soon as the clamp diodes start conducting, this current will flow into the Vdd rail, charging up the bypass capacitors and reducing the voltage across the protection resistors further, to around 2V. Thus, the steady-state current will be closer to 13.6mA (3V ÷ 220W). USB-C Serial Adaptor circuit queries Strange readings from RF Power Meter I decided to build your USB-C Serial Adaptor from the June 2024 issue (siliconchip.au/Article/16291). Upon receiving your kit, I started to look closely at the circuit. I have found a couple of potential problems with I built the 1MHz to 6GHz RF Power Meter (August 2020; siliconchip.au/ Article/14542) but have encountered a problem. The display is showing “RF Pwr = -28.6dBm = 8.3mV At = 00” without any connection to the input. Secure Remote Switch may have RF overload 102 Silicon Chip Australia's electronics magazine All decoupling capacitors are fitted as per the circuit. The detector output is supplying noise with a DC component; if an RF signal is applied, the noise decreases and the DC voltage increases. Jim bypassed the 78Lxx on the RF module because it needs at least 7V and a filtered 5V supply is provided. The RF module I am using is not exactly the same as Jim used, but I wired it up the same way as described. As a test, I wired a 1kW pot across the pins used by the RF module, providing a variable DC for the ADC, and was able to measure down to 4.7μV (-93.5dBm). Do you have any suggestions of where to look? (A. E., Colyton, NSW) ● It sounds like the log detector module is incompatible or faulty as it should not be delivering a significant DC voltage with no input signal. We think you need to swap it for the same one that Jim used, and it will probably then work. The reader responded that replacing the log detector caused the noise level to drop to within specifications. Odd behaviour from DCC Programmer I have found that my DCC Programmer shield (October 2018; siliconchip. au/Article/11261) is producing a positive digital AC waveform. With my multimeter on AC and the probes connected one way, it reads approximately 14-15V (with a 12V DC input). With the probes the other way, the reading varies from 0 to 5V, so I can’t read a decoder if the loco is facing the wrong way. As the components are inexpensive, I’ve changed them all with no effect, and have gone through all the connections without finding a problem. The EN pin shows 10V when I was expecting 5V. The POL pin shows 5V, as expected. Do you have any suggestions as the where the problem may be? (G. B., Wurtulla, Qld) ● From your initial description of a positive AC waveform, it sounds like one of the out-of-phase signals is not being generated correctly. Measuring 10V DC on the EN pin suggests that there is a wiring problem or other fault. As you wrote, 5V is expected there. If you have changed all the parts, we wonder if perhaps the Uno itself 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 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 August-September 2025 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. Lazer.Security PCB PRODUCTION USB-C Power Monitor Short-Form Kit SC7489: $60 siliconchip.au/Series/445 This kit includes all non-optional parts, except the case, lithium-ion cell and glue. It does include the FFC (flat flexible cable) PCB. WE HAVE QUALITY LED’S on sale, Driver sub-assemblies, new kits and all sorts of electronic components, both through hole and SMD at very competitive prices. check out the latest deals at www.lazer.com.au ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, address & credit card details, or phone (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 November 2025  103 Advertising Index Altronics.................................39-46 Blackmagic Design....................... 7 Dave Thompson........................ 103 Emona Instruments.................. IBC Hare & Forbes............................ 4-5 Jaycar..................IFC, 10-11, 27, 67 Keith Rippon Kit Assembly....... 103 Lazer Security........................... 103 LD Electronics........................... 103 LEDsales................................... 103 Microchip Technology.............OBC Mouser Electronics....................... 3 OurPCB Australia.......................... 9 PCBWay....................................... 13 PMD Way................................... 103 SC Battery Checker..................... 65 SC USB-C Power Monitor......... 103 SC Keyboard Adaptors............. 100 Silicon Chip Shop.................90-91 Silicon Chip Subscriptions........ 99 The Loudspeaker Kit.com.......... 87 Wagner Electronics..................... 12 Errata and on-sale date High power H-bridge uses discrete Mosfets, Circuit Notebook, November 2017: the PCB design is missing a connection between pin 3 of IC1 and the pad of the 3.6kW resistor immediately next to pin 5 of IC1. This can be fixed by adding a short length of insulated wire. Next Issue: the December 2025 issue is due on sale in newsagents by Thursday, November 27th. Expect postal delivery of subscription copies in Australia between November 25th and December 12th. 104 Silicon Chip is damaged. Have you tried our DCC_ Programmer_Shield_V2.ino sketch? It is a much simpler way of testing the hardware. We would be interested to see waveforms (or AC/DC voltages) on IC1’s pins 5 and 9; they might indicate which of the out-of-phase signals has the problem. If you have any photos of your construction/arrangement, please send them to us so we can look for any obvious problems. Options for making a Driveway Monitor The driveway to our house is about 50m long. I would like to detect a car coming when it’s within about 20m from the house; there is a convenient garden to install a sensor there. A signal would go to the house to switch a light on for a prescribed time. A standard IR sensor mounted at the house does not have this range. Can I use John Clarke’s Driveway Monitor project from the July & August 2015 issues (siliconchip.au/ Series/288) to do this? Are the parts still available 10 years later? If not, perhaps I could run a solar-powered IR motion sensor in the garden and communicate to the house via WiFi to switch the light on. That’s all I really need. (R. W., King Creek, NSW) ● For a while, it was difficult to find the main detector IC used in the 2015 Driveway Monitor (the HMC1021S) at a reasonable price. However, DigiKey has recently obtained a very large number (over 10,000) and they are selling them for $11.58 each (siliconchip.au/ link/ac85). So for now, at least, it is still possible to build our 2015 design. Still, Jaycar sells a wireless driveway sentry that flashes LEDs and plays a ‘ding dong’ tone when a vehicle is detected. Its output could be adapted to switch on a light. See www.jaycar. com.au/p/LA5178 Synchronising older clocks to GPS time Some time ago I built a couple of your Big Digit 12/24 Hour LED clocks, as described in the March 2001 issue (siliconchip.au/Article/4235). The clocks work well and have been put into service in a couple of our local churches. However, they still need to be manually adjusted from time to time to keep the clocks accurate, and also Australia's electronics magazine when daylight saving begins and ends. I notice that you have presented many clocks in Silicon Chip over the ensuing years and have more recently also presented enhancements to many of them, enabling them to be GPS synchronised. That seems a very worthwhile exercise, and I wonder whether John Clarke’s design I mentioned above could be modified simply to improve its accuracy. If so, how could I interface a GPS module, and where would it connect in the circuit? I know I could probably build one of your more recent designs, but seeing as I have already built otherwise good clocks, I wonder whether they could be improved with the addition of a GPS module. (N. A., Canberra, ACT) ● The Big Digit 12/24 Hour LED Clock uses a 4MHz crystal for timekeeping (and also to run the microcontroller), so you would need a way of producing a GPS-locked 4MHz signal to do what you suggest. We have published several circuits that can provide a 10MHz reference locked to satellite signals, such as the May 2023 GPS-Disciplined Oscillator (siliconchip.au/Article/15781). So it could be done if we can find a way to convert a 10MHz signal to 4MHz. While you can certainly do that with a phase-locked loop (PLL), there is a simpler method that may work. Build the GPSDO and feed its 10MHz output to a decade counter like the 74HC4017. That chip can run from 5V, operates to over 70MHz and has 10 outputs that go high in sequence, numbered Q0 through Q9. If you then connect the Q0, Q2, Q5 and Q7 outputs to the four inputs of half of a 74HC4002 dual 4-input NOR gate, you should get a 4MHz square wave at the corresponding output. It will have significant jitter, but we don’t see why that will matter in this application, since the PIC16F84 is rated to run up to 10MHz, and the shortest pulses in this scheme are only equivalent to a 5MHz clock. Note that you could pick any four non-consecutive outputs from the 74HC4017, where Q0 and Q9 are considered consecutive. 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