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JANUARY 2026 ISSN 1030-2662 01 The VERY BEST DIY Projects! 9 771030 266001 $ 00* NZ $14 90 14 INC GST INC GST Digital Command Control DCC Base Station to provide power and data to model railway tracks Acoustic Imaging using a camera and microphone array to ‘see with sound’ Power Electronics, Part 3 the properties of transformers and inductors, and their use in power converters Weatherproof Touch Switch a simple switch with no moving parts that can be used outdoors Earth Radio, Part 2 hear solar and atmospheric disturbances with this receiver Remote Speaker Switch switch up to six pairs of speakers connected to a single amplifier www.jaycar.com.au Contents Vol.39, No.01 January 2026 12 Acoustic Imaging Acoustic imaging is a technology that can be used to determine the source of sounds and provide visual feedback. This can be useful in applications like trying to find a gas leak or the testing the acoustics of a concert hall. By Dr David Maddison, VK3DSM Scientific feature PAGE 12 10 26 Power Electronics, Part 3 In this series of articles, we explore the principles of power electronics. In this part, we cover the fundamentals of transformers & inductors, followed by how to use them, within the context of isolated DC-DC converters. By Andrew Levido Electronic design 49 How to use DCC ACOUSTIC IMAGING This in-depth guide to using our DCC Decoder and Base Station covers the trackwork, using and programming configuration variables (CVs) and more. It also serves as a helpful introduction to DCC. Part 3 by Tim Blythman Model train feature 66 How to Design PCBs, Part 2 Setting up PCB design rules to suit fabricators is important. We also provide some tips and tricks to help you during schematic capture and PCB layout. After that, we describe how to get your PCB design made into reality. By Tim Blythman Making your own PCBs 35 DCC Base Station The next main component needed for a complete DCC system is a base station, to provide power and data to the tracks. Our Base Station uses a Pico 2 microcontroller module and suits HO/OO and N-scale operations. Part 2 by Tim Blythman Model train project 56 Remote Speaker Switch Remotely switch up to six pairs of speakers connected to a single amplifier. Or combine many Remote Speaker Switches to switch up to 18 pairs of speakers. Suitable for amplifiers up to 400W or 800W per channel. By Julian Edgar & John Clarke Audio project 78 Weatherproof Touch Switch This sealed touch switch has no moving parts and can be operated even if you’re wearing gloves. All you need is a piezo touch switch, a flip-flop module and a 6V DC coil relay. By Julian Edgar Simple electronic project 80 Earth Radio, Part 2 Solar and atmospheric disturbances, like storms or auroras, can be heard using this ‘natural’ radio receiver. It is battery-powered and utilises a portable loop antenna, so you can use it nearly anywhere. By John Clarke Scientific / radio receiver project Page 35 DCC Base Station 2 Editorial Viewpoint 4 Mailbag 61 Subscriptions 75 Silicon Chip Kits 76 Circuit Notebook 86 Online Shop 88 Serviceman’s Log 94 Vintage Radio 101 Ask Silicon Chip 103 Market Centre 104 Advertising Index 104 Notes & Errata 1. Scale speed checker for model railway 2. HTTP to HTTPS bridge Rebuilding the Kriesler 11-99 by Fred Lever 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 Printing and Distribution: 14 Hardner Rd, Mount Waverley VIC 3149 54 Park St, Sydney NSW 2000 2 Silicon Chip Editorial Viewpoint Myths about SMD soldering I often see people recommending that a soldering iron with a fine tip should be used for soldering surface-­ mount devices (SMDs). While a fine tip sometimes comes in handy, most of the time it is not what an experienced technician will use to solder SMDs. The problem is that small tips have poor heat transfer; you need good heat transfer to solder SMDs properly. I think there are a few reasons that this advice persists. To start, it seems to make sense if you have little experience soldering. To solder small parts, you need a small tip, don’t you? Another is that I suspect many people are not using enough flux, or the right flux, when soldering. Using the right flux is like magic. With it, solder seems to ‘know’ where it should go! I generally use a medium conical tip (the kind that often comes with the soldering iron) for most SMD work, as well as most through-hole components. Perhaps that is out of laziness. But it works pretty well, even for finepitch ICs. The only time it doesn’t work is for parts like QFNs where you have to get in really close to the device, and the larger ball end of the tip has trouble making contact. I’ve seen experienced soldering technicians recommend using large chisel tips because they overcome that problem; you can angle them to get into tight spaces, but they still have a large tip with a high thermal mass so that they don’t lose temperature as soon as they touch cold solder. They also have a large surface area to transfer heat when you need it. Regardless, you may be doing yourself a disservice if using a fine tip for general SMD soldering. I’ve tried it and it’s so frustrating trying to get heat into the joints. Sometimes such a tip isn’t even capable of transferring enough heat into joints on larger parts to form proper fillets! The thing is that when you add a proper flux paste or gel (not liquid – that’s for different applications), enough to coat the pads and pins, all you need to do is touch molten solder to the pin/pad interface and it’ll be pulled into place. Do it quickly, with the right technique, and you can perfectly solder a whole side of an IC, with perhaps 14 pins, in a few seconds. The excess solder will simply stay on the iron tip; only the amount needed flows onto the part or pad. I must warn against a technique I’ve seen some people use where they apply solder paste to a device pin and then touch it with the iron to melt it and reflow the joint. It sounds like a good option, but the hot iron hitting the cold solder paste can cause the tiny, invisible solder balls to fly off at high speed, landing who knows where. They could cause problems later. Solder paste is best used with a hot air wand or reflow oven, where it can be melted slowly and in a controlled manner. If you don’t want to deal with hand-soldering SMDs, those are good options, but I primarily use a hot air device for removing parts, not soldering them. I’m always worried I will blow parts away during soldering! Still, obviously it is possible with the right technique. Writing this reminds me of a YouTube video where Louis Rossmann (a major figure in the Right to Repair movement) demonstrates replacing an SMD display connector on a MacBook that has dozens of small pins. He uses a large chisel-tip soldering iron with a lot of flux gel, and you can clearly see what he is doing under the microscope: https://youtu.be/z1EOTP51fz0?t=1116 by Nicholas Vinen Cover background image: https://unsplash.com/photos/shooting-star-in-night-sky-5LOhydOtTKU Australia's electronics magazine siliconchip.com.au MAILBAG your feedback Letters and emails should contain complete name, address and daytime phone number. Letters to the Editor are submitted on the condition that Silicon Chip Publications Pty Ltd has the right to edit, reproduce in electronic form, and communicate these letters. This also applies to submissions to “Ask Silicon Chip”, “Circuit Notebook” and “Serviceman’s Log”. Getting a 4MHz clock from a 10MHz reference On page 104 of the November 2025 issue (Ask Silicon Chip), there was a discussion about deriving a 4MHz clock signal from a 10MHz GPS-locked reference. Back in the day, I used to design logic circuitry, and my immediate thought on reading this was: does the 10MHz reference have a 1:1 mark:space ratio? If so, it consists of a train of positive and negative edges with regular 50ns intervals. Generating a ~25ns pulse on each edge and ORing these would produce a 20MHz clock locked to the reference. I’m not sure if a 74HCT123 dual retriggerable monostable chip would be fast enough to do that, but it might. To divide this by five to get a 4MHz clock, a 4017 decade counter and NOR gate could be used as described in that magazine using, say, the Q0 and Q5 outputs. Colin Ramsay, Indooroopilly, Qld. Comment: Dr Hugo Holden had the same thought. He breadboarded the circuit using a 74HC132 and 74HC86 as the frequency doubler and a 74HC390 to divide by five (see the circuit below). It works as expected. He provided the accompanying scope grab showing it working. Weather station integration with Home Assistant Regarding Duncan Wilkie’s letter to the editor on integrating a weather station with Home Assistant (Mailbag, p4, December 2025), I have a Fine Offset WH2950 weather station. I’ve had a few over the years. I’m using the Ecowitt integration with Home Assistant and it brings in the weather data just fine. I use some of the values inside HA, and also to display some values on a ‘clock’ running on a tablet in my bedroom. I have a convoluted arrangement where the WH2950 sends its data to my (hosted) website for use there, and I POST it on to my HA instance at home. I have HA running on an old Dell XPS laptop. On one side of my kitchen sink, I have the weather station console, and on the other side, I have an Android tablet running HA using Fully Kiosk Browser. It works well. Being a ‘maker’, I add stuff to HA that I have cobbled together from ESP8266 and ESP32 devices. My latest effort is an ESP32 plugged in to the laptop receiving (and one day sending) ESP-NOW messages, which have a greater range and much quicker cycle time on battery-­powered devices like temperature senders. My laptop also runs MQTT for use with my Tasmota devices and boards, with relay boards controlling sprinklers, pond pumps etc. I suggest that Duncan buys a weather station to use with the benefits a complete unit brings, and spends his ‘making’ time on devices that you can’t buy or are too expensive for what they do. Ken Wagnitz, Craigburn Farm, SA. More on Home Assistant weather stations In the December edition, Duncan Wilkie asked about adding a rain sensor to Home Assistant. Since the tipping bucket sensor (SEN0575) just produces pulses, all you need to do is count them and scale appropriately. I believe that for this type of gauge, it is five pulses per millimetre of rain (ie, each pulse represents 0.2mm). Dave Walmsley, Wallsend, NSW. How valve guitar amplifiers produce a unique sound I wanted to explain briefly the essential reasons why a valve-based guitar amplifier sounds so different from a transistor-­based amplifier. With an acoustic guitar, the player and the guitar alone control the sound of the music. This small circuit generates a 4MHz clock signal from a 10MHz input; the scope grab shows it working. 4 Silicon Chip Australia's electronics magazine siliconchip.com.au W LI H VE IL S E Y R E NC CO M RDED IN IA G ! Get high end digital film camera features on phone or iPad! Blackmagic Camera unlocks the power of your phone or iPad by adding digital film camera controls and image processing! You can adjust settings such as frame rate, shutter angle, white balance and ISO all in a single tap. Recording to Blackmagic Cloud lets you collaborate on DaVinci Resolve projects with editors anywhere in the world, all at the same time! Live Sync to Blackmagic Cloud Cinematic Quality Images Remote Camera Control and Multiview Blackmagic Camera puts the professional features you need for feature film, If you’re positioning an iPhone in an area that’s hard to reach, or shooting with television and documentaries in your pocket. Imagine having a run and gun multiple phones using Blackmagic Camera, you can get full control using camera on hand to capture breaking news whenever it happens! Or use remote camera control! Simply set your iPhone or iPad to be the controller, Blackmagic Camera as a B Cam to capture angles that are difficult to reach with and you can change settings for all iPhones using the same Wi-Fi network. Plus traditional cameras, while still retaining control of important settings. you can view each camera’s shots in a multiview! Interactive Controls for Fast Setup Blackmagic Camera has all the controls you need to quickly setup and start shooting! The heads up display, or HUD, shows status and record parameters, histogram, focus peaking, levels, frame guides and more. You can shoot in 16:9 or vertical aspect ratios, plus you can shoot 16:9 while holding the phone vertically if you want to shoot unobtrusively. www.blackmagicdesign.com/au Blackmagic Camera records an HD proxy that uploads to Blackmagic Cloud in seconds, so your media is available back at the studio in real time. The ability to transfer media directly into the DaVinci Resolve media bin as editors are working is revolutionary and has never before been possible! Any editor working anywhere in the world will get the shots! Blackmagic Camera Free Download Learn More! With an electric guitar, a coil picks the signal up, and the amplifier and speaker also form part of the sound path. Let’s assume the coil pickup and speaker faithfully reproduce the signal and consider the effect of the amplifier only. Examples of the waveforms coming from the pickup coil with a plucked guitar string are shown in Photos 1-8. While basically sinusoidal, the presence of ‘partials’ or harmonics puts a lot more bumps into the fundamental string sinewave shape. It is those extra bumps that make the ‘voice’ or sound of the instrument. If you fed those signals through a transistor-based amplifier without any modeling or wave-shaping, that is exactly what the speaker would reproduce and you would hear. Second, let us look at the wave shapes from some of my valve guitar amplifiers when fed with a sinewave and adjusted for harmonics. The output valves and the output transformer can add a significant amount of harmonic content into the waveform. Low-order harmonics (Photos 9-11) generally add agreeable overtones to the sound. The changes are not too intrusive and rather ‘woodwind’ in quality. Once the wave is overdriven into amplitude limiting, as in Photos 12 & 13, the harmonics are of a higher order and the sound becomes more strident. Photos 14 & 15 are well and truly into the ‘fuzz’ area. Photo 15 shows a bass line with a pair of output valves driven well into saturation and cutoff, plus an output transformer and power supply unable to follow the fundamental. The blue trace is the speaker signal and the yellow trace a sinewave to compare. Overlaying the harmonics visible in Photos 9-14 onto the already harmonic-strong waveforms seen in Photos 1-8 provides the ‘voice’ of the guitar. What the resultant wave-shape to the speaker depends on so many variables. In playing simple notes, Photos 11 (wood-windy) & 15 (fuzzy) are not far off what you see at the speaker. The introduction of transistors also coincided with the ability to provide large amounts of negative feedback in amplifier designs. This tends to reduce the harmonic distortion levels to a minuscule amount. A valve amplifier driven hard used to produce 15% THD, while the newer transistor amplifiers reduced that to 0.15% or lower. Thus, the worst that a transistor amplifier may do is simply go into clipping, as shown in Photo 16. The harder you drive it, the more square the wave becomes. That usually just sounds horrible. Of course, the whole argument between valve and transistor amplifiers is irrelevant if you’re using an effects box. They can simulate any sound you like at the click of a button. Some guitar players these days like to use modelling amplifiers, which use transistor-based amplifiers but with built-in effects to emulate many other kinds of amplifiers, including valve amplifiers. The above explanation contains a lot of generalisations. The basic premise of harmonic strings being overlayed with another set of adjustable harmonics, or outright limiting, is the key to understanding what a musician means when talking about ‘valve sound’. Fred Lever, Toongabbie, NSW. 1 3 5 7 9 11 13 15 The dangers of cheap Li-ion cells Photos 1-16: shown left-to-right, top-to-bottom. 6 Silicon Chip After what happened tonight, I think I need to offer a warning about Li-ion cells. There I was, with my battery-powered Australia's electronics magazine siliconchip.com.au SSB receiver running, and one of the 14500 cells exploded; and I mean exploded! It flew out of the battery holder and onto the floor, smoking. Fortunately, I was not in the line of fire; it could have caused a nasty injury! It must have suffered an internal short circuit. I am thankful that it was not a larger 18650 cell! You can see the remains in this photo. What is the moral of this story? This was not a particularly cheap cell, but it was from China. The quality control may be insufficient. So where do we buy Li-ion cells that are likely to be good quality? Charles Kosina (still rather shaken), Mooroolbark, Vic. Comment: Jaycar and Altronics might be a good place to start; while we can’t necessarily vouch for the quality of their cells, we think you have less chance of cells bought there exploding than something bought from eBay, Ali­ Express etc. Real saga building the Dual Hybrid Power Supply I am nearing completion of the Dual Hybrid Power Supply project (February & March 2022; siliconchip.au/Series/377). After some initial testing, I needed to fix a few incorrectly orientated diodes on the regulator boards. Those boards are now functioning as per the testing instructions. I then got stuck on the control board. The LD1117 regulator got very hot after a few seconds, and the LCD screen had no output (other than just the blue backlighting). I checked the orientation of the SMD diodes on the board, and they were OK. I also checked for solder bridges etc and that my ribbon cables have the correct orientation. I removed the LD1117 and measured 16mW between pins 1 & 2 and 2.6mW between pins 2 & 3. After conferring with Phil Prosser, I finally found a very hard-to-see short circuit on the microcontroller. Unfortunately, I destroyed the board while finding it. So I rebuilt the control board, and this time, there were no shorts! The LCD lit up, but all I got on the screen were solid blocks with no information. Adjusting the contrast up and down had an effect, but there was still no text. I reflowed the microcontroller pins with flux and carefully went over the chip using a macro lens and couldn’t find any problems. I then looked at the 5V rail. I found 5V DC coming in on Pin 10 of the IDC cable. However, it dropped to 1.92.1V by the time it reached pin 16 of IC7 and pin 1 of IC6. I replaced Q7 thinking it might be shorted, but that didn’t make any difference. I also removed the two 100nF caps, and that didn’t make any difference either. So, I again contacted Phil Prosser, and he gave me further guidance. I unplugged the two regulator modules and the display came alive. I then tested with the regulator modules plugged in one at a time. With one regulator module plugged in, everything worked, regardless of which socket I plugged its cable into, and I could control its output voltage. With the other regulator module plugged in, the fault symptoms returned, regardless of where I plugged it in. So the fault lay on that regulator module. ourPCB LOCAL SERVICE <at> OVERSEAS PRICES AUSTRALIA PCB Manufacturing Full Turnkey Assembly Wiring Harnesses Solder Paste Stencils small or large volume orders premium-grade wiring low cost PCB assembly laser-cut and electropolished Instant Online Buying of Prototype PCBs www.ourpcb.com.au 8 Silicon Chip Australia's electronics magazine 0417 264 974 siliconchip.com.au Phil helped me diagnose it further. We came to the conclusion that the fault must be in one of the MAX14930 digital isolator ICs on that regulator module, because that’s really all that the 10-way header, CON3, connects to. So Phil sent me a spare chip. I replaced the most likely culprit (I lifted one track, but I repaired it) and it’s now working! Finally, I can finish off the calibration and assemble everything into the case. It was great getting so much assistance from Phil Prosser, and I also learned a lot through the process of his helping me. Brett van der Leest, Maidstone, Vic. An open-source humanoid robot design After reading your article on “Humanoid & Android Robots” (siliconchip.au/Series/451), I thought this information about an open-source robot build might be relevant. If anyone is interested in getting started in the field of robotics, the open-source InMoov project is an excellent place to begin. The project was started in 2012 as the first opensource prosthetic hand by French sculptor and designer Gaël Langevin, and it has since developed into a full-size robot. InMoov is controlled by the open-source MyRobotLab software, which recently received a major update to the Nixie version, featuring an improved graphical user interface (GUI). The MyRobotLab InMoov2 software includes a virtual InMoov that can run all the functions and AI of a physical robot without the need for any hardware. A full InMoov is not required to use MyRobotLab InMoov2; individual components, such as a hand or arm, can be controlled independently. A popular option within the community is to print just the head and neck. More information is available from https://inmoov.fr or Gael Langevin’s YouTube channel (www.youtube.com/ user/hairygael). Mathew Prentis, Port Augusta, SA. Fed up with Windows Like me, I’m sure a lot of home users of Windows have been seeing the message “Your PC doesn’t currently meet the minimum system requirements to run Windows 11”. Sure, I’ll just go out and spend $2000-$3000 purchasing a new PC that may, or may not, work with future Microsoft products. I performed an audit of all the software packages I currently use with Windows and discovered to my delight that all I need to do is switch to Linux! I settled on Ubuntu, as it has a very large support base, a built-in suite of MS office compatible products, an enormous library of other applications and a really cool name that loosely translates to “humanity to others”. The three PCs that I have converted now have a newfound ‘spring in their step’ and are not bogged down with all the background processes that slowed them down under Windows. I had no previous Linux experience, but still found the process of change stress-free. For those of us of a certain age, I found it empowering to occasionally go back to a command-line interface (CLI). Just make sure you have backed up all your files! R. C., Clayton, Vic. Comment: Ubuntu is a solid choice, although perhaps SC not the most beginner-friendly. siliconchip.com.au Australia's electronics magazine January 2026  9 MORE THAN JUST RAIN OR SHINE Multi-function Weather Stations that forecast the weather 6 MODELS FROM $ • Indoor & outdoor temperature • Temperature alert alarm • 12 Hour weather forecast XC0366 ONLY $99.95 • Indoor & outdoor temp • Hygrometer • Dew point & heat index • 12 Hour weather forecast XC0412 ONLY $139 9995 GREAT VALUE • Indoor & outdoor temp • Wind speed with direction • Dew point & heat index • Rain gauge with rate • 12 Hour weather forecast XC0432 ONLY $249 Limited stock, check stores for stock Our stylish weather stations are feature rich with useful atmospheric measurements such as temperature, humidity, barometic pressure, moon phase, rainfall plus data logging, alarms, time, calendar and more. From simple forecast displays to detailed modelling we have a model to suit any budget. 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Jaycar reserves the right to change prices if and when required. ACOUSTIC IMAGING Image source: https://unsplash.com/photos/empty-chairs-in-a-room-3rW1HAakg8g By Dr David Maddison, VK3DSM Those of us lucky enough to still have good hearing in both ears can instinctively tell where sound is coming from. However, some sounds can be difficult to locate; sometimes, doing so is a matter of life and death! That is where technology comes to the rescue, with Acoustic Imaging Systems. W ouldn’t it be nice to locate the source of a sound that we can hear but can’t see or locate precisely? Depending on their level, frequency and spectra, sounds are not as easy to locate as certain other phenomena, such as light leaking into a darkened room. Seeing sounds as an image is not altogether unusual. Animals such as bats and dolphins use sound to ‘see’ (see Fig.1). The same can be said for medical ultrasounds and submarine sonar. With active sonar, a sound wave is emitted and its reflection from the target is analysed to form an image. Alternatively, for passive sonar, no sound is emitted by the sonar; instead, it listens to sound waves emitted or reflected by objects being surveilled. Directional or stereo microphones, or our ears, can give some cues as to the location of a sound based on differential timing, frequency shaping (due to the shape of the ear and head) and so on. However, it can be difficult to 12 Silicon Chip locate a sound precisely; sometimes we only know the general area. At times, sounds can appear to come from one place but are really coming from another, perhaps due to reflections, refraction, standing waves or other phenomena. However, there is a way to visualise the source of sounds precisely, making them visible to us in the same way as we can see the source of light leaking into a darkened room. The source of the sound can be rendered visible by a device called an acoustic imaging camera. In contrast with the active sonar mentioned above, where acoustic signals are reflected back to form an image, in acoustic imaging, signals are only received from an external source. Like passive sonar, acoustic imaging relies on detecting sounds directly from the source, but it visualises sound fields for applications like industrial monitoring, setting it apart from passive sonar’s underwater tracking role. With an acoustic imaging camera, Australia's electronics magazine sound waves are detected and pinpointed using a microphone array for precise location. The sounds are overlaid in real time (or sometimes later) onto a digital camera image of the scene of interest. Acoustic imaging can also detect sounds inaudible to the human ear (eg, infrasound or ultrasound). It should be noted that, confusingly, there are other devices also called acoustic cameras that emit acoustic signals for tracking like active sonar. In this article, unless stated, we are only describing the passive devices. The core of acoustic imaging lies in beamforming, a technique that electronically shapes received sound (or radio) signals into focused beams by adjusting their timing (phase) and strength (amplitude) to enhance sounds from specific directions while reducing others. We previously mentioned beamforming in our September 2020 article about 5G Networks (siliconchip. au/Article/14572). siliconchip.com.au Visualising sounds as acoustic imaging is just one application of this technology. Others include acoustic microscopy, ultrasound imaging, photoacoustic imaging and thermoacoustic imaging, as well as sonar, which will not be discussed in this article. Sonar was already described in some detail in our June 2019 article on that topic (siliconchip.au/Article/11664). How it is used Examples of the use of acoustic cameras include locating the source of an unwanted sound to rectify it, such as reducing noise in prototype motor vehicles, aircraft, trains or other vehicles. It can also be used to locate a gas leak in a chemical plant, which often can be hard to detect otherwise (eg, if it’s a clear gas escaping). Alternatively, we might want to analyse the frequency spectrum of sounds emanating from certain locations for various diagnostic or suppression purposes. We can also map traffic noises or locate the origins of noises from wildlife. It could also be used to analyse the source of noise entering a building from outside, so that soundproofing can be installed. In fact, just about anywhere there is a sound that needs to be eliminated, located or analysed, there is an application for the acoustic camera. We previously published a review of the CAE SoundCam (October 2020; siliconchip.au/Article/14610). It was one of the first commercial devices on the market and took ~15 years to develop. In this article, we will go into more detail about the theory of operation of such devices and the latest developments. 17th century CE Sir Isaac Newton attempted to measure the speed of sound and understood sound to be a wave like a water wave. 1626 Sir Francis Bacon emphasised the importance of investigating “the nature of sounds in general” which he called “acoustica”. His observations and experiments on sounds were published posthumously in 1627, in Sylva Sylvarum (siliconchip.au/link/ac95). He observed “frisk and sprinkle” when he rubbed the rim of a glass of water. 1671 Robert Hooke saw patterns on a flour-covered plate along which a violin bow was drawn. 1680 Ernst Chladni repeated and enhanced Hooke’s work and developed a method to show the various modes of vibration of rigid plates. 1877-1878 Lord Rayleigh laid the foundations for the theory of the behaviour of sound waves in his treatise, “The Theory of Sound”. 19th century Hermann von Helmholtz made substantial contributions to acoustics. 20th century Microphones and oscilloscopes greatly facilitated the study of acoustics. 1910s to 1920s Sonar was developed for imaging underwater. 1917 Nobel Prize winner Jean-­ Baptiste Perrin invented the télé- sitemètre for the French military, for the acoustic detection of enemy aircraft. In 1917, it was said to be able to detect aircraft 7-8km away with an angular error of 2-3°. It used two sets of a number of sub-arrays of listening horns grouped together and combined via an acoustic waveguide to a listening point at each of the observer’s ears. It was a type of acoustic beamforming before its modern implementation with computers and signal processing. A version appeared on the cover of 1930 Popular Mechanics (Fig.2). According to the magazine, that version “automatically registers their flying speed, altitude and distance from the finder”. 1930s to 1940s Directional microphone arrays emerged for sound ranging during World War II, advancing multi-microphone techniques. Phased array antennas were used similarly for radar. 1940s to 1950s Phased arrays of hydrophones were used for sonar. Sonar principles were applied in the development of medical ultrasound. 1960s to 1970s acoustic methods were developed for non-destructively testing materials, eg, looking for cracks in aircraft parts or other critical components. Beamforming techniques were used in medical ultrasound. History of acoustic imaging Developments leading up to acoustic imaging included the following discoveries regarding the behaviour of sound and developments in beam-forming: 6th century BCE Pythagoras studied musical sounds from vibrating strings. 4th century BCE Aristotle suggested that sound propagates as motion through air. 1st century BCE Vitruvius contributed to the acoustic design of theatres and determined the correct mechanism of sound wave transmission. 6th century CE Boethius documented a link between pitch and frequency. siliconchip.com.au Fig.1: an image of a man as seen by a dolphin’s natural sonar. Source: www.speakdolphin. com/pressRelease/ Press_Release_what_the_ dolphin_saw.pdf Fig.2: the cover of Popular Mechanics from 1930 shows a version of Jean Baptiste Perrin’s télésitemètre. Australia's electronics magazine January 2026  13 Fourier Transforms for Dummies Fourier transforms let us view signals in terms of their frequencies rather than time; a bit like turning a recording of a song into its individual notes. Fourier theory says that any waveform can be represented as the sum of sinewaves of different frequencies, phases and amplitudes. If you are not familiar with a Fourier transform, it may seem like a complex and exotic mathematical concept that you are unlikely to ever fully understand. However, it actually turns out to be relatively simple when you think about it the right way. One way to approach it is to consider the inverse Fourier transform first. If a Fourier transform turns regularly sampled time-domain amplitude data into frequency/phase data (as a complex number, but don’t worry about that now), the inverse Fourier transform turns frequency/phase data back into a set of points sampled at fixed intervals in time. Its output is exactly the input of the original Fourier transform. The frequencies that we’re breaking the signal down into are at fixed intervals (eg, DC, 100Hz, 200Hz, 300Hz etc), so the output of the Fourier transform is simply a series of amplitudes and phases, with each frequency ‘bin’ allocated a scaling factor and phase offset. We can easily visualise how to reverse the Fourier transform. You take a sinewave at each frequency, scale it by the corresponding amplitude value, shift it by the phase shift, and add the lot together. Voilà, you have your original waveform back. Mathematically, this is just a linear operation – a kind of matrix multiplication – where each row represents one sinewave at a different frequency. After all, a sinewave of a specific frequency sampled at specific intervals is simply a set of numbers between -1 and +1 calculated using the sin(ωt) function. If we expand that function to Asin(ωt + φ), where A is the amplitude scaling factor and φ is the phase shift, we get our original sinewave back. Then we just need to add them up, giving us the final formula: In this formula: xn is the nth input sample; N is the total number of samples in the transform; k is the frequency bin index; and Xk is the result for a given k. If you haven’t studied high-level maths, that may look like gobbledegook, but it’s essentially just performing the sum-of-scaled-and-phase-shifted-sinewaves mentioned above, with some normalisation applied so the magnitude of our result matches the original scale. Now, through the lovely properties of linear algebra, it turns out that the forward Fourier transform has almost exactly the same formula, with just a sign change and the removal of the scaling factor (as per convention). It is: How can our sum-of-sinewaves algorithm break down a time-domain signal into its constituent sinewaves? It makes sense if you think of it this way: what a Fourier transform is essentially doing is calculating the correlation between the input signal and each sinewave at a different frequency. A correlation is a statistical calculation that tells you how similar two sets of data are, with a larger result meaning they are more similar. Its formula is quite simple: In other words, the correlation between two sets of discrete data is simply the sum of the products of corresponding data points. If you think about it, if your data rises and falls at a similar rate to the sinewave you’re correlating it with, you’re going to get a large resulting sum. If they are not synchronised, the products are going to essentially be random and cancel out when you sum them. So, the scary-looking Fourier transform formula above is basically just doing this correlation with a set of sinewaves at different frequencies, and out pop the correlated sinewave amplitudes. By using complex numbers, the transform simultaneously captures both amplitude and phase; the magnitude of the complex number gives the amplitude, while its angle gives the phase. Finally, to resolve any confusion over the use of complex numbers giving us the phase shift; there is a simpler, geometric way to think of what we’re doing. Effectively, we are correlating the input signal with each sinewave along with its corresponding cosine wave, ie, the same sinewave phase shifted by 90°. The cosine component (the real part) measures how much the input aligns with a zero-phase reference wave. The sine component (the imaginary part) measures how much it aligns with a 90°-shifted version of the same frequency. Together, these two numbers form a 2D vector: one axis for cosine, one for sine. That vector’s angle gives you the phase of that frequency in the signal, ie, how far along the cycle your signal’s version of that frequency is compared to the reference cosine. The length (magnitude) of that vector gives you the amplitude, or how strongly that frequency appears in your signal. In summary, the Fourier transform is a set of two orthogonal correlations, with sine and cosine waves, at various frequencies, producing vectors where the angle represents phase shift and the length, amplitude. So while it’s advanced mathematics, it’s also incredibly elegant once you understand what’s going on. 14 Silicon Chip Australia's electronics magazine Fig.3: the concept of beamforming. The beam is electronically scanned to capture the signal from various parts of a soundscape, producing a sound map. 1970s the first experimental acoustic imaging systems emerged, using arrays to map sound sources, influenced by sonar and ultrasound. In 1974, John Billingsley invented the first “acoustic telescope”, a precursor to the acoustic camera. 1976 Billingsley and Roger Kinns develop a full-scale acoustic microscope system to analyse sounds from the Rolls Royce Olympus engine used in the Concorde. It used 14 condenser microphones, with signals digitised with 8-bit resolution at a sampling rate of 20kHz. The computer used had a memory of 48kiB and data was stored on floppy disks with a capacity of 300kiB. The processed data was displayed on a colour TV. This was the basis of modern systems, and in the following decades, improvements were made in the sampling rate, number of microphones, digitisation resolution, software and size and portability of the equipment. This was also the first time a real engineering problem, the determination of noise sources from the engine, had been analysed with acoustic imaging techniques. 1980s to present digital signal processing methods were developed, and high-speed computers enabled realtime beam-forming. 1997 a reporter coined the term “acoustic camera”. 2001 the first commercial acoustic camera was introduced by GFaI tech GmbH (www.gfaitech.com). The introduction of commercial devices marked the transition from research to practical tools, integrating digital signal processing (DSP) and array technology. siliconchip.com.au Fig.4: beamforming in the time domain using the delay-and-sum technique. Original source: www.gfaitech.com/knowledge/faq/delayand-sum-beamforming-in-the-time-domain Fig.5: how a Fourier transform converts data between the time and frequency domains. Original source: https://visualizingmathsandphysics. blogspot.com/2015/06/fouriertransforms-intuitively.html 2000s to present advances in array design and software have refined acoustic imaging for industrial and environmental use. How they work An acoustic imaging camera uses an array of multiple microphones to detect the source of a sound. One microphone cannot locate the source of a sound; two microphones can to a certain extent, like our ears, but even that does not give precise locations. For example, the shape of our ears combined with our brain is how we determine where sound is coming from. If you were to change the shape of your ears, it would take some time before your brain could readjust, and therefore you wouldn’t be able to precisely pinpoint where sound was coming from. An array of microphones, often 64 or more, is necessary so that triangulation and advanced mathematical techniques can be used to locate the source of the sound very precisely, while also filtering them by frequency. The microphones may be sensitive to frequencies from around 2kHz to 100kHz (well above what we can hear, ie, ultrasound). The precise method used to locate sounds is called beamforming, a signal processing technique also used for radio waves. It is how a mobile phone tower focuses its radio lobe directly at your phone to maximise the signal it receives while using minimal power and not interfering with other devices. In acoustic imaging, beamforming works differently. The camera, acting siliconchip.com.au as a receiver, focuses on acoustic energy naturally emitted by a sound source, enhancing sounds from specific directions while ignoring others. Essentially, it is the reverse process used for transmitting signals. Acoustic beam-forming The microphone array of an acoustic imaging camera is in the form of a geometric array. Sound waves reaching individual microphones are processed in such a way that some sounds from particular directions are selectively reinforced while others from different directions are attenuated by adjusting their relative amplitudes and phases. The ‘sound field’ is scanned either sequentially or digitally all at once, similar to how a spectrum analyser can be swept or a ‘snapshot’ processed using a Fourier transform. This amplifies and reinforces sounds from particular directions while attenuating others, thus building up an image showing intensity and frequency of sounds from particular areas – see Fig.3. Methods of acoustic beamforming using microphone arrays to produce directional images include: Delay-and-sum technique This is one of the simplest and most common methods of acoustic beamforming. Consider a microphone array that is picking up sound waves from multiple directions. Because sound waves travel at a more-or-less constant, finite speed (about 343m/s in air at sea level with average pressure, temperature and humidity), the sound waves from a Australia's electronics magazine specific direction will arrive at each microphone at a slightly different time. That time difference is determined by the distance between the microphone and the sound source. Delayand-sum adjusts for these time differences in software by delaying the signal from each microphone so that waves from the desired direction align exactly when it adds them together. If a desired sound wave comes from straight ahead, the closest microphone will receive it first; others will be slightly delayed. The software of the signal processor will delay the signal of the first (closest) microphone the most, and the others less so. When the signals are summed, the desired signal from straight ahead is reinforced, while others from undesired directions are attenuated or cancelled. Since this technique focuses on one direction at a time, it is repeated across the entire sound field, thus building an image. It is computationally straightforward, making it suitable for realtime imaging. This is less effective than other techniques in noisy environments or in complex sound fields, though. It generates a sound intensity map only, and does not separate individual sound frequencies. The beamforming and acoustic map generation process seems complicated, but it is simple in principle (although more complex in practice). Fig.4 shows an example with two sound sources, Source 1 (red) and Source 2 (blue), and four microphones (yellow circles). The steps are: 1. Signal acquisition: microphones record the sounds from a sound field January 2026  15 Fig.6: delay-and-sum beamforming in the frequency domain. of interest; four waveforms recorded are shown at the bottom. The plots show sound pressure (vertical axis) vs time (horizontal axis). The relative positions (in time) of the red and blue waveforms vary for each microphone based on its relative proximity to the sound source. 2. A time delay is added: each waveform has a distance along the time axis (horizontal) relative to its position from the source. The actual distances can be worked out by knowing the distance between the microphones and sound sources, and the speed of sound. We are interested in mapping Source 1 (Source 2 can be mapped at another time on another part of the sound field scan). A variable time delay indicated by ∆tx is added to each microphone waveform so the signals from Source 1 (red) for each microphone are aligned. 3. Signal summing: the signals with the time delays ∆t1, ∆t2, ∆t3 and ∆t4 are summed, resulting in a combined waveform where the signals from Source 1 are strengthened and those from Source 2 are not. 4. Signal normalisation: the signals are then normalised based on the number of microphones. The time delay to the largest peak is a measure of the position of the sound source in the sound field. 5. Mapping: the process is repeated over the entire sound field to create an acoustic map, showing the sound 16 Silicon Chip intensity at different locations. Frequency-domain beamforming This technique processes sound in the frequency domain rather than the time domain. Thus, the frequency spectrum of each sound source can be analysed. It allows the determination of which frequencies come from which directions so that acoustic maps of both sound intensity and frequency can be created. It uses beamforming techniques on each frequency band. It is computationally intensive and is often performed by post-processing data rather than in real time. Frequency domain beamforming is shown in Fig.6. In the approach described here, it is based on delayand-sum beamforming. The steps are as follows: 1. Signal acquisition: identical to the delay-and-sum technique. 2. Fourier transformation: the ‘Fourier transform’ is a powerful mathematical tool that converts a signal such as sound pressure over time, known as the time domain, into its underlying frequency components and their amplitudes, represented in the frequency domain (see panel). It decomposes a signal into a combination of sinewaves that represent both the amplitude and phase angle for each frequency component in the signal. Plots of amplitude vs frequency and phase angle vs frequency can be made from this information. This offers two views of the same data, revealing, for example, which frequencies dominate (see Fig.5). For instance, just as a piano chord can be separated into individual notes, the transform can break down the hum of machinery into its distinct frequency parts, aiding acoustic imaging analysis. 3. Phase vs frequency determination (Fig.6): Fourier analysis is applied to the amplitude vs time signal from each microphone to give a spectrum showing phase vs frequency representing the signals received at each of the four microphones. Each of the four signals from each microphone can be seen to have a different phase angle as a function of the frequency. 4. Phase adjustment: a time delay correction aligns the phases for Source 1, making its red signals in phase, Fig.8: adaptive beam-forming; the reception pattern of the lobes of the microphone array is shown. Undesired signals coming from directions other than the main beam are nulled in the signal processing. Original source: www.researchgate.net/publication/283639759 Australia's electronics magazine siliconchip.com.au Fig.7: phased-array beam-forming. The signals from each microphone (p1, p2 & p3) are phaseshifted into alignment and summed for each look direction to maximise signal strength. Source: https://dspace.mit.edu/ handle/1721.1/154270 while Source 2’s blue signals remain out of phase. This is evident in the lower middle graphs of Fig.6, where red signals align at the same phase angle, and blue ones diverge. 5. Summing: the adjusted signals are summed and normalised by the number of microphones. The in-phase red signals of Source 1 strengthen (overlapping as a single peak), while the out-of-phase blue signals interfere destructively, reducing their strength. 6. Mapping: the summed values for each frequency can be plotted on an acoustic map, with the positions of the sources of each frequency being determined from the time delay and phase angle information, resulting in a “heat map” of sound intensity and frequency. Phased-array technique The phased-array technique is a beam-forming method that uses precise control of the phase, the position of each acoustic signal’s sinewave cycle received by microphones, to electronically steer the listening beam across the sound field (see Fig.7). Unlike delay-and-sum, it adjusts the phase of each microphone’s signal, causing acoustic wavefronts to interfere constructively and reinforce sounds from the target direction while destructively cancelling others. This offers excellent directional precision, ideal for imaging dynamic sources, but demands computationally intensive processing and careful equipment calibration. Adaptive beam-forming Adaptive beamforming (Fig.8) adjusts to challenging sound environments by modifying delays and microphone weightings (amplification) in real time to suppress noise or interference, such as from a specific direction. This dynamic approach requires significant processing power, although it is ideal for complex acoustic imaging tasks. Acoustic imaging system configurations Acoustic imaging cameras come either as fully integrated all-in-one units (handheld) or as separate micro- phone and camera arrays, data acquisition units and a laptop computer (see Fig.9). The sound map being recorded and processed here is shown in Fig.10. Handheld acoustic imaging cameras For industrial inspection purposes, it is often more convenient to use an all-in-one handheld acoustic camera rather than separate system components. The SoundCam Ultra is a handheld unit that images audible sound and ultrasound (see siliconchip.au/link/ ac97). It is used for compressed air/gas leak localisation, vacuum leak localisation, partial discharge localisation, condition-based monitoring, animal studies and non-­destructive testing. Another example is the GFaI tech Mikado. It uses an array of 96 digital MEMS microphones and a Microsoft Surface Pro tablet as its data processing and display unit – see Fig.11. Acoustic microphone arrays Separate microphone arrays are also available for use with the separate Fig.9: a GFaI tech acoustic imaging camera system with separate components (microphone array, data recorder and computer) recording sounds from a sewing machine. Source: www.gfai. de/fileadmin/user_upload/GFaI_product_ sheet_acoustic_camera_en.pdf Fig.10: a sound map from the sewing machine being recorded in Fig.9. Source: www.gfai.de/fileadmin/ user_upload/GFaI_product_sheet_ acoustic_camera_en.pdf siliconchip.com.au Australia's electronics magazine January 2026  17 cameras, data recording units and a computer with the appropriate software. The spacing and relative location of microphones in an acoustic imaging array are crucial, carefully designed to optimise goals like resolution (clarity of sound sources), side-lobe suppression (reducing unwanted beams) and spatial aliasing reduction (avoiding imaging artefacts). These microphone arrays can be 2D linear (square or rectangular), circular, random, or even follow a Fibonacci pattern, similar to a sunflower. Various 3D arrangements are also possible. A key design rule is that the microphone spacing should be less than half the wavelength of the highest frequency to prevent aliasing (derived from the Nyquist-Shannon sampling theorem). The relevant equation is d = v ÷ 2fmax, where d is the spacing in metres, v is the speed of sound in air (343m/s), and fmax is the maximum frequency to be imaged. For example, to image up to 5kHz (a wavelength of 68.6mm), the spacing should be about 34mm; for up to 20kHz (a wavelength of 17.15mm), it should be around 8.6mm. One example of a 2D microphone array is the SoundCam Octagon (Fig.12), which has 192 MEMS microphones along with an integrated camera, data recorder and notebook computer running suitable software. The large number of microphones allows very high resolution imaging and acoustic holography (more on that later). Another example of a 3D microphone array is GFaI tech’s Sphere48 AC Pro48 channel system for acoustic measurements in 2D and 3D with 48 electret condenser microphones (see siliconchip.au/link/ac96). It has a frequency response from 20Hz to 20kHz. It is designed for sound localisation in confined spaces such as a motor vehicle. It is used with NoiseImage software that allows sound sources to be isolated, localised and analysed with respect to both frequency and time response. It also allows a 3D acoustic map to be produced, and imagery is provided by an integrated Intel RealSense Depth Camera to record depth information. Suggested uses include noise, vibration and harshness (NVH) analysis in cars, trains and aeroplanes; location of squeaks and rattles in vehicles; leakage detection; and sound design and analysis of building acoustics. An additional example of a 2D array is the Fibonacci120 AC Pro (Fig.13), a 120-element microphone array in the form of a Fibonacci pattern. It allows near-field and far-field measurements and, according to the manufacturer, the spiral pattern gives the “highest possible spatial resolution and the best possible map dynamics”. A further example of a microphone array is the GFaI tech Star48 AC Pro (siliconchip.au/link/ac9c). It is optimised for mid-range frequency measurements of outdoor objects like aircraft flyovers or the observation of large wildlife, like elephants. Applications In this section, we will discuss various applications of acoustic imaging. Acoustic detection of drones Hostile drones pose risks to military and civilian people and infrastructure; therefore, their detection is extremely important. Drones can be flown autonomously, without RF communications (or via fibre-optic cables), making their detection even more difficult. Their small size can also make radar detection difficult. Airspeed Electronics Ltd (www. airspeed-electronics.com) has developed passive acoustic imaging arrays to detect drones (Fig.14), which can each detect small quadcopters at a range of 200-300m. Each sensor can be integrated into a network to make a fully scalable array connected by wireless mesh radio. Multiple sensors enable accurate target location via triangulation. A drone’s acoustic signature also provides valuable information such as the number of rotors, pitch imbalances and rapid pitch variations, which allow the drone class to be detected, an estimate of its payload mass (weight can affect the rotor pitch) and whether the drone is manually or autonomously controlled. Airspeed’s microphone arrays use phased-array signal processing to help separate drone sounds from other background noises. Electret condenser microphones are used in Airspeed’s microphone arrays as they have superior performance to MEMS Fig.12: the SoundCam Octagon has an integrated camera and data recorder. Source: www.gfaitech.com/products/ acoustic-camera/all-in-one-soundcam-octagon Fig.13: the GFaI tech Fibonacci120 AC Pro. Source: www.gfaitech.com/fileadmin/gfaitech/documents/ datasheets/acoustic-camera-fibonacci-array-120datasheet-20.pdf Fig.11: the GFaI tech Mikado. The object behind the device is the microphone array (the video camera is not visible). Source: www. gfaitech.com/products/ acoustic-camera/handheldsoundcam-mikado 18 Silicon Chip siliconchip.com.au microphones, according to the company. Airspeed performs its own in-house modelling and performance evaluation of microphones; a simulation of a microphone array is shown inset in Fig.14. Fig.15 shows the dashboard from a sensor array tracking a small drone. Aircraft An example of the acoustic analysis of a business jet is shown in Fig.16, The image shown represents a spectral analysis for the third octave band of 315Hz at 53dBA (“A-weighted decibel”, a sound measurement weighted to reflect human hearing). The hardware setup is the same as described below for the car measurements. The software used was Photo 3D and Spectral Analysis 3D for precalculated narrowband analysis to create acoustic photos from a spectrum. Building acoustics Acoustic imaging can be used in concert halls and other large interior spaces to optimise acoustics. It can diagnose and correct acoustic problems such as undesirable echoes (reflections), absorption of sounds, or differential absorption or reflections of sounds of different frequencies. Acoustic imaging can be used to optimise ‘acoustic comfort’ in buildings by detecting the source of sound leaks or the effectiveness of various acoustic treatments. For example this video (https://youtu.be/ykchSQX-sfg) shows a Sorama CAM iV64 being used to detect sound leaks around a window frame. Fig.14: a network of Airspeed’s TS-16 acoustic remote sensors at the British Army’s AWE-24 exercise, Salisbury Plain, UK. Inset: a simulated beam pattern from a microphone array at 1.2kHz. Source: www.airspeed-electronics.com/ technology Fig.15: drone tracking by Airspeed using an acoustic image array. The image at upper left shows the target drone location by azimuth and elevation. At upper right is a polar plot, while the lower left shows a view from the target drone; at lower middle is a spectrogram of the target, and the lower right shows the predicted target type based on spectral information. Source: www.airspeedelectronics.com/technology Cars Automotive and other engineers strive to minimise NVH (noise, vibration & harshness) in vehicles (or other machines). For cars, NVH can be perceived as unwanted and unpleasant for passengers and drivers. These sounds may originate from the engine, drivetrain, suspension, tyres, road, air conditioning, wind noise etc. One way to locate the source of these noises is through the use of acoustic imaging cameras. Some examples of locating such noises are shown in Figs.17 & 18. The experimental setup to obtain those images comprised the GFaI tech Sphere48 AC Pro microphone array mapping frequencies from 291Hz to 20kHz. Fig.16: acoustic measurement and location-finding in a Bombardier BD-700 - 1A10 business jet. Source: www.gfaitech.com/ applications/aircraft-interior siliconchip.com.au Australia's electronics magazine January 2026  19 Figs.17 & 18: analysing and locating noise sources in VW interiors with a microphone array. Source: www.gfaitech. com/applications/ vehicle-interior Also used were an mcdRec data recorder with a sampling rate of 192kHz and a depth of 32 bits, and Noise­Image software with the Acoustic Photo 2D and Acoustic Photo 3D modules for mapping the sound sources onto a common interior or exterior CAD model. Other software modules used include the Record Module, Spectral Analysis, Advanced Algorithms and Project Manager. Cooling fans Acoustic imaging technology can be used to develop quieter cooling fans in electronic equipment. For example, PC fan manufacturer Cooler Master uses this technology, as shown in Fig.19. Notua also use similar technology to develop their fans, this includes acoustic imaging to map noise (siliconchip. au/link/ac99). Drone-based acoustic imaging Acoustic imaging cameras can be mounted on drones (see Fig.21) for various purposes such as industrial inspection, natural disaster response or security. The obvious problem of self-induced drone noise can be reduced by spectral (Fig.20) and other methods, such as making sure the beam-forming direction ignores any part of the drone’s airframe. Fig.19: Cooler Master computer fans are developed with a Sorama acoustic camera. Source: https://youtu.be/0UFli2BUCL4 Fig.20: a block diagram of a spectral ‘denoising’ scheme to remove selfgenerated noise from a drone-mounted acoustic camera. Original source: https://doi.org/10.3390/drones5030075 Fig.21: the Crysound (www.crysound.com) CRY2626G is the first dronemounted acoustic camera designed for detecting pressurised system leaks and electrical partial discharge. Source: https://sdtultrasound.com/ products/crysound/cry2626g/ 20 Silicon Chip Australia's electronics magazine Echoes in rooms The sampling rates for acoustic imaging can be as high as 200kHz. Thus, it is possible to watch echoes bounce around a room, as shown in Fig.22. The picture shows all the bounces, but in reality they happen sequentially. Electrical discharge inspection Detecting high-voltage partial discharges from insulation and corona discharges is a necessary task to prevent dangerous or expensive problems in high-voltage installations. Techniques such as infrared thermography are not always reliable for detecting them because certain types of discharges might not cause a significant temperature rise, or not pinpoint the exact location of the problem. In addition, in a high-voltage installation, heat may be generated for other reasons. It is also often difficult to detect the sounds that these discharges make using the ear or microphones. Thus, acoustic imaging can be a good tool to detect such problems. siliconchip.com.au Fig.22: echoes bouncing around a room. Sources: https:// petapixel.com/2023/03/23/how-acoustic-cameras-can-seesound/ & https://youtu.be/QtMTvsi-4Hw Acoustic imaging is also potentially safer in the hazardous environment of high-voltage installations, as it can be used from further away than some other techniques. An example of discharge detection is shown in Fig.23. The instrument used is the Fluke ii915. Research has shown that the frequency of sound emissions from electrical discharges is mostly in the range of 20-110kHz, with 95% of the acoustic energy in the range of 48kHz to 100kHz, with a peak frequency of 68.3kHz. Thus, this instrument is optimised for detection at those frequencies. Fixed or mobile applications The Sorama L642 (https://sorama. eu/products/l642-acoustic-monitor) can be permanently mounted on a pole or placed on a mobile robot for continuous monitoring or inspections. It can be used indoors or outdoors, in a Fig.24: detecting a noisy vehicle exhaust with a Sorama L642. Source: https://sorama.eu/solutions/vehicledetection-system siliconchip.com.au Fig.23: detecting high-voltage electrical discharges using the Fluke ii915. Source: www.seesound.com.au/partialdischarge factory environment or even an urban environment to monitor noises and their sources. One application is to detect noisy vehicles, as shown in Fig.24 and https://youtu.be/fQEkkFGPbU8 Gas leak detection Acoustic imaging can be used for gas leak detection and is able to detect leaks that people cannot even hear. This method of gas leak detection is considered superior to, or at least supplemental to, gas detectors, because acoustic imaging can detect a small leak before there is a substantial buildup of gas (see Fig.25). fireworks, noisy vehicles or alarms going off. Hydrogen leak inspection Finding hydrogen leaks is difficult, as hydrogen can escape from the smallest openings. Acoustic cameras such as those from Sorama have been designed specifically to be able to detect hydrogen leaks from tanks, pipes and valves – see Fig.26. Mechanical inspection Acoustic imaging can discover defective parts of machinery, such as a defective robot joint that has developed a squeak. General environmental monitoring The Sorama L642 series can be used for noise measurements and anomaly detection in urban environmental monitoring, such as identifying the location of inappropriately lit Mining equipment Sounds from mining equipment can be identified and appropriate action taken. These sounds can indicate a possible occupational safety concern. One example is abnormal noise from Fig.25: gas leak detection using a Sorama acoustic imager. Source: https://sorama.eu/solutions/gas-leakinspection Fig.26: detecting a hydrogen leak from a valve using a Sorama camera. Source: https://sorama.eu/solutions/ hydrogen-leak-inspection Australia's electronics magazine January 2026  21 the conveyor bridge of an excavator (see siliconchip.au/link/ac99). Road noise management We already mentioned the Sorama L642, but other companies make devices for monitoring noisy vehicles. Noisy vehicle detection technologies are already on trial in Australia: siliconchip.au/link/ac91 siliconchip.au/link/ac92 Editor’s note – there are several large boxes in the middle of Foreshore Road near Port Botany in Sydney, powered by solar panels, that appear to be used to monitor noise from the many trucks on that road. Apart from Sorama, companies that make noisy vehicle detection systems include SoundVue (https://soundvue. com – used in Australia), General Noise (www.generalnoise.co.uk) and acoem (www.acoem.com/en). Fig.27: an overhead view of Philips Stadion with acoustic camera data overlaid. Source: https://sorama.eu/fan-behavior-analytics-with-acoustic-data-engaginginsights-for-sports Fig.28: an acoustic image of a high-speed train. Source: www.gfaitech.com/ knowledge/faq/passby-2d-integration-time Fig.29: studying elephant vocalisations in Nepal. Source: https://youtu.be/ Xl7LnAob2T8 22 Silicon Chip Australia's electronics magazine In stadiums Acoustic imaging is used to analyse, map and localise cheers from fans in stadiums. Competitions can be organised to enhance fan engagement so that the loudest and proudest fans win. The winner for the noisiest fans or real-time noise production by fans can be determined with a “SoundSurface map” display on the large screen being shared in real time at the stadium and on social media – see Fig.27. The noise level changes second by second and corresponds to events happening within the game being observed, such as scoring a goal. There are two different Sorama acoustic camera systems installed at the Philips Stadion in the Netherlands. One is the Sorama L642XL, which is equipped with 64 microphones arranged in a sunflower pattern to provide seat-level accuracy, right down to individual fan reactions. The other system uses 30 Sorama L642 cameras, covering all seats, to observe crowd behaviour at a higher level. The system can also detect unwanted chanting, shouting, slurs or breaking glass. Trains Investigating noises emanating from trains was one of the first commercial usages of acoustic imaging. An acoustic image of a high-speed train is shown in Fig.28. Not surprisingly, the wheels seem to be the main source of noise, but there was also noise from siliconchip.com.au Figs.30 & 31: examples of vibration analysis using the GFaI tech WaveCam software on large structures such as a wind turbine and tower, and smaller structures such as a car engine. Source: www.gfaitech.com/products/structural-dynamics/ vibration-analysis-with-wavecam the pantograph. This discovery led to design efforts to minimise noise from that source. Vibration analysis Vibration analysis can be used as a supplementary technique to acoustic imaging. It is performed optically, using a camera and software to detect small variations in an image due to vibrations. GFaI tech offers the WaveCam software for this purpose. Figs.30 & 31 show some examples of such vibration analysis. A combination of both vibration analysis and acoustic imaging can be used to give a deeper understanding of a vibration and noise problem, as shown in the video at https://youtu. be/0Z7E5Ql7Xiw Vacuum cleaner development Perhaps one of the noisiest domestic appliances is the vacuum cleaner, so it is not surprising that considerable efforts are made to quieten these machines. Figs.32 & 33 show frame grabs from Steve Mould’s video at https://youtu.be/QtMTvsi-4Hw showing sources of sound from a vacuum cleaner; one at 400Hz, the other at 7000Hz. Wildlife Acoustic imaging cameras have been used to study wildlife vocalisations, such as elephant sounds, including infrasound – see Fig.29. A better understanding can thus be made of how animals communicate and the parts of the body involved in generating various sounds. Acoustic holography Acoustic holography is a specialised technique that reconstructs the entire sound field (a 3D representation of the distribution of sound waves), including amplitude and phase over a surface or volume, based on measurements taken at a limited set of points. It uses wave propagation principles to create a ‘holographic’ representation, akin to optical holography, but with sound waves. It uses some of the same techniques as acoustic imaging, such as acoustic wave analysis, microphone arrays and signal processing, and can be seen as an extension of acoustic imaging. It has niche applications in research, requiring extremely advanced mathematical models. Acoustic imaging maps sound sources using beamforming, while acoustic holography extends this by reconstructing the full sound field, including phase, for a detailed analysis. Acoustic imaging can be seen as a ‘snapshot’, while acoustic holography is a complete 3D model of sound. The future of acoustic imaging Over the last few years, the cost of acoustic imaging has gone down, and the capabilities have gone up. Possible or likely developments in the future include higher-resolution microphone arrays, integration with AI for automated source detection, plus cheaper and more portable designs. Challenges include improving low-­ frequency detection, reducing setup complexity (although existing handheld units are virtually ‘plug & play’), and handling reverberation, where the sound reflects off multiple surfaces even after the source has stopped. Research trends include advanced signal processing, wearable sound cameras (possibly with military applications) and multi-modal imaging (say, measuring vibration and sound at the same time by the same device). Future applications include the use in robotic imaging, smart cities and SC consumer applications. Figs.32 & 33: frame grabs from https://youtu.be/QtMTvsi-4Hw showing noise from a vacuum cleaner. On the left, it shows the 400Hz noise from the tube, while on the right, the 7kHz noise is coming exclusively from the motor. siliconchip.com.au Australia's electronics magazine January 2026  23 NEED TOOLS THAT MEASURE UP? We have a GREAT RANGE of multimeters at everyday GREAT JAYCAR VALUE, to suit hobbyists and professionals alike. 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To design an isolated converter, first we need to understand how transformers work, plus their potential roles in DC/DC and AC/DC converters. This article will start with transformer/inductor fundamentals, then move on to using them. T Fig.1: this shows the relationships between the key magnetic quantities: field intensity, flux and flux linkage. Together, these allow us to determine the inductance of the coil. The left side of Fig.1 shows a winding of several turns of wire around a magnetically permeable core (we’ll consider what that means soon). The N-turn winding carries a current i, which induces some kind of magnetic flux (or field in some textbooks) denoted by the Greek capital phi (Ø), shown in red. The core itself has a cross sectional area A and an average length l. By convention, the direction of the flux follows the ‘right-hand rule’ illustrated at the bottom left of the figure. If you curl the fingers of your right hand in the direction of current flow, the resulting flux points in the direction of your thumb. Gauss’ law for magnetism tells us that the net flux entering and leaving any closed region is zero, which means that flux lines have no beginning or end – they must always be closed loops. For us, this just means that all of the flux leaving the coil at the top enters it again at the bottom. For now, we will assume that all of the flux is confined to the core. You can think of this arrangement in two ways at the same time; as loops of current enclosing a flux, or as loops of flux enclosing a current. Flux is driven around the core by a ‘driving force’ known as the magnetomotive force (mmf) that describes the amount of current linking with the flux. This mmf is N times the current i, since the current passes through the flux loop once for each turn of the winding. We can also describe this magnetising force as a magnetic field intensity, which we denote with the letter H. This is defined by Ampère’s law to be equal to Ni ÷ l, or the mmf per unit length of core. The right-hand side of the figure shows a section of the core with the Australia's electronics magazine siliconchip.com.au he DC-DC converters we have looked at so far have been non-isolated types. That means there is a direct electrical connection between the input and output. In many cases, we want the output to be isolated from the input; for safety reasons, if the input is connected to the mains, or because we need the output to be referenced to a different potential than the input. Isolation is usually achieved using a transformer. Adding a transformer to a switching converter can provide a host of other benefits – for example, it can reduce the range of duty cycle (and consequent component stress) required to achieve high step-up or step-down ratios. It can also allow us to get multiple outputs from a single converter. As we have seen in this series so far, we cannot get very far in the field of power electronics before coming up against magnetic components such as inductors and transformers. Like everything else, it is the second-order non-ideal behaviour of these components that will catch us out if we are not careful. Transformers, in particular, are highly specific to the application, so 26 Silicon Chip sooner or later we will have to roll our own. This means that a solid understanding of magnetics theory is necessary before we get to isolated DC-DC converters, so let’s dive in. Back to basics One of the reasons magnetics can be confusing is the number of terms that sound similar but have different meanings. This comes about because magnetics was one of the earliest areas of electrical engineering to be studied by the likes of Gauss, Ampère and Faraday, who each invented their own terms, which we live with to this day. With terms like magnetic field intensity, magnetic flux, magnetic flux density, magnetic flux linkage, magnetic permeability and magnetic permeance, it is no wonder many of us get confused. Don’t even get me started on Maxwell’s equations! (We covered those in the November 2024 issue – siliconchip.au/Article/17029). I promise that it is not as hard to wrap your head around as you might think. As usual, I will not cover this topic in a rigorous academic fashion, but from the perspective of a working engineer. We will employ just a little basic algebra. flux lines passing through it. As we have seen, the magnetic field intensity H drives a total flux Ø through the core, equal to µHA. This results in a flux density, B, which is simply the amount of flux divided by the cross-sectional area of the core. B is also related to H by the magnetic permeability, or µ, of the core according to the relationship B = µH. Permeability is a measure of how ‘easily’ a given field intensity can create a flux density in the core. Materials with a higher permeability will develop a higher flux density for a given field intensity. The permeability of a material is usually expressed as the permeability of free space, µ0 (which is equal to 4π × 10-7H/m) multiplied by a unitless relative permeability, µr. The permeability of free space is the basic measure of how much flux a given current will produce in a vacuum or in air. The relative permeability is a measure of how many times more permeable a material is than this baseline. Thus, you often see permeability expressed as µ0 × µr. Relative permeabilities for magnetic materials range from a few hundred for mild steel, to 5000-10,000 for transformer steel, up to 40,000 or more for some ferrites. In addition to the flux and the flux density, we need to introduce the concept of flux linkage, which describes how a flux links with a winding. From Fig.1, you should be able to see that the red flux lines pass through each turn of the winding, giving it a flux linkage λ = NØ (λ is the Greek letter lambda). So, to sum up, the current flowing in a winding produces a magnetic field intensity, which drives a flux around the core. This produces a flux density in the core that is related to the field intensity by the permeability, and to the total flux by the cross-sectional area of the core. The resulting flux passes through the winding, resulting in a flux linkage, λ. Fig.2: reducing magnetic geometries to equivalent circuits makes analysis much easier, since you can use all the usual circuit theory tricks. magnetic field. In our example, the magnetic flux will change proportionally to changes in the current, so it follows that a voltage is produced across the terminals of our winding as the current through the winding changes. The changing coil current effectively induces a voltage in itself. This is known formally as self-inductance, but we usually just refer to it by the shorter name “inductance”. Inductance kind of wraps up all of the N, H, B, Ø, and µ malarky into a relationship between the current and the flux linkage. In fact inductance, is defined as the flux linkage per unit of current, L = λ ÷ i. For the mathematically inclined, you can see how this works by working out an expression for the inductance of the arrangement in Fig.1. Combining the equations for field intensity (H = Ni ÷ l) and flux density (B = µ0 µr H) we get B = µ0 µr Ni ÷ l. Multiplying by the area gives us the total flux Ø = µ0 µr NiA ÷ l. We can then use the formula for flux linkage (λ = NØ) to get λ = µ0 µr N2iA ÷ l, and finally use the formula for inductance to arrive at L = N2 × µ0 µr A ÷ l. The inductance is therefore the product of the square of the number of turns multiplied by a term related to permeability of the core and its dimensions. This latter term is referred to as the permeance of the core (not to be confused with the permeability). If you know the permeance of a core, you can easily calculate the number of turns required to obtain a given inductance. Manufacturers of cores usually provide the permeance in their data sheets as an “Al” value, in units of nanohenries per turn squared or similar. Electric circuit model The inverse of permeance is reluctance, which is an extremely useful quantity we can use to build a model of magnetic systems that is analogous to electric circuits. In these circuits, reluctance (denoted R) is equivalent to resistance and the mmf (F), equal to Ni, is equivalent to voltage. The resulting flux (Ø) is analogous to current. Fig.2 shows the electrical circuit equivalent of the magnetic circuit in Fig.1. The circuit obeys the magnetic version of Ohm’s law, so F = ØR. We can use all of our usual circuit analysis techniques, so this is really helpful to calculate inductances and the like when faced with more complex core geometries such as that in Fig.3. At the top, we have a classic E-I core with a winding on the centre leg that is wider than the outer legs. Fig.3: analysis of an E-I core and a gapped core using the magnetic equivalent circuit shows how easy it can be to calculate the inductance of complex geometries. Inductors You might have noticed that this is a bit circular – the current in the winding produces a flux that links with the winding. By introducing the third member of the magnetic holy trinity, Mr Faraday, we can use this to understand how inductors work. Faraday’s law states that a voltage is induced in a winding by a changing siliconchip.com.au Australia's electronics magazine January 2026  27 The magnetic equivalent circuit is shown to the right. It is easy to calculate the reluctance of the centre leg, R1, and that of the two outer legs, R2, based on the dimensions of the core and its permeability. You can then use what you know about resistors in series and parallel to calculate an equivalent reluctance and therefore the inductance as shown in the figure. Fig.3 also shows another common configuration, where a very narrow air gap is included in the magnetic circuit. This is done to increase the stability of the inductance and the amount of energy that can be stored in the core. The reluctance of the air gap is much higher than that of the core, because the relative permeability of air is one, compared to many thousands for the core. This means the inductance is dictated by the air gap, and is largely independent of the core material. This can be a good thing for the stability of the inductance, since the relative permeability of most core materials changes with temperature and flux density, as we will see below. I won’t cover the maths, but for the same reason, for a given flux density, the amount of energy that can be stored per unit volume is much higher in the air gap than in the core. In fact, it is common to assume that all of the energy is stored in the gap, and it’s not unusual to start the design process for inductors by selecting a core with sufficient gap volume (the area of the core times the gap length) to store the required energy each switching cycle. Leakage As usual, I have made a few simplifications in the above discussion, and some other factors come into play when we get into the nitty-gritty of magnetics design. One of these is leakage flux. In the above examples, we assumed that all of the flux was constrained to the core. Fig.4 shows that this may not be the case – some flux may leak away from the core and pass through the air where there is a lower reluctance path; however, it will always return, due to Gauss’ law. The effect of this on the magnetic circuit is shown in the right-hand side of the figure. The leakage paths form a leakage (generally high) reluctance, which appears in parallel with the core reluctance. You can see from the formula that this leakage will result in a slightly increased inductance over the ideal case. It will be useful later to think of the leakage producing an extra ‘leakage inductance’ in series with the main core inductance, as shown in the lower equation. Saturation, hysteresis and residual flux We have also assumed up until now that the relationship between field intensity and flux density is linear, described by a simple proportional relationship of permeability. The reality (as always) is a little more complex. A typical magnetic material has a B-H characteristic like that in Fig.5, although it is shown a bit exaggerated for clarity. Remember that H is the magnetising ‘drive’, proportional to the winding current, and B is the resulting flux density. There are three important things to note. First, the path that B follows when H is increasing is not the same as it does when H is decreasing; there is hysteresis. Second, neither path passes through the origin. When H is zero, there will be some residual flux density Bres (either positive or negative) present in the material when it is not excited. Thirdly, the slope of the characteristic (the permeability) saturates at some flux density, Bsat – it deviates from the ideal value of µ shown in red as the field intensity increases. We normally want to avoid saturation (although there are some notable exceptions where this characteristic is used to advantage), so we take some care to ensure the maximum flux density stays well below the saturation level. Losses We have also so far assumed inductors are lossless, but of course, we know this cannot be the case. Losses in magnetic components fall into two categories: copper losses (sometimes called winding losses) and core losses. Copper losses include the familiar ohmic loss determined by the resistivity of the winding material, its cross sectional area and its length. Be aware that the resistivity of copper, the most common winding material, is temperature-dependent and increases by approximately 40% for every 100°C temperature rise. Make sure to calculate losses using the resistivity at the highest operating temperature you will see in the winding. Resistive losses are exacerbated by a phenomenon known as ‘skin effect’. As the frequency of a current passing through a conductor increases, eddy currents create magnetic fields inside the conductor that force the current outward, so it flows only in the outside ‘skin’ of the conductor. The higher the frequency, the more the current is forced to the outside of the conductor. The ‘skin depth’ is a measure of how much of the conductor is effectively useful. For copper, the skin depth is about 9.2mm at 50Hz, which explains why high-current AC busbars tend to be broad but are rarely more than 10mm thick. At 100kHz, the skin depth is about 0.2mm, and at 1MHz, it is just Fig.4: flux leakage in an inductor produces an extra leakage reluctance in parallel with the core’s reluctance, and increases the total inductance slightly. Fig.5: magnetic materials have a less-than-ideal B-H characteristic that includes hysteresis, saturation and residual flux density. 28 Silicon Chip Australia's electronics magazine siliconchip.com.au 65µm. There is no point in using a cylindrical conductor with a diameter greater than twice the skin depth, since there will be no corresponding reduction in resistance. At 100kHz, for example, any conductor with a diameter larger than 0.4mm will be a waste of copper. For this reason, the magnetics in high-power switching converters use multiple thin conductors in parallel, or are wound with copper foil (or even multiple parallel layers of copper foil). You can also use Litz wire, which is an intricate arrangement of fine insulated wires twisted together into bundles, which are themselves twisted together. It is lovely stuff, but expensive. Core losses also come from two sources: eddy currents and hysteresis. Eddy current losses are resistive losses caused by currents circulating within the core material. In conductive core materials like steel, these losses are mitigated by making the core from thin laminations that are insulated from each other by an oxide layer. You will have seen these laminations in the cores of E-I type mains transformers. Toroidal mains transformer cores are wound from a long thin strip of steel (like a roll of sticky tape) to achieve the same end. At higher frequencies, we tend to use cores made of materials that have poor electrical conductivity, such as ferrite or sintered metal oxides, to avoid eddy current losses. Hysteresis loss is caused by the shape of the B-H curve. When the material is magnetised in one direction, it takes some magnetic force in the other direction to overcome the residual flux and bring the flux density back to zero. This takes energy, which becomes heat in the core. The amount of loss is proportional to the area within the hysteresis loop, so choosing a material with a narrower Fig.7: a realistic transformer has leakage inductances due to imperfect coupling of the flux, and a magnetising inductance due to the finite permeability of the core. hysteresis curve will help minimise these losses, as will limiting the maximum flux density excursions. Manufacturers usually provide a measure of core losses for their materials in kW per cubic metre for a (usually pretty small) range of frequencies and flux densities in the data sheets. You have to multiply these by the core volume to get an estimate of core loss in your application. Transformers Adding a second winding to our inductor, as shown in Fig.6, produces a transformer. If the flux is perfectly linked by both windings, as shown here, the transformer is said to be perfectly coupled. While we are at it, let us also assume that the core is so permeable that the reluctance is zero. This is, after all, an ideal transformer. Since the flux linked by each turn on both windings is identical, so is the voltage produced across each turn. Each winding voltage is therefore proportional to the number of turns in that winding. The ratio of voltages v1 : v2 is equal to the turns ratio, N1:N2. Due to the sense of the windings in the diagram and the right-hand rule, the total mmf is the sum of the Ni values of each winding. If current flows into the dotted ends of either winding, it produces a clockwise flux as shown. I have indicated the direction of flux for a current into the dotted terminal by a red arrow on the electrical equivalent circuit on the right. Fig.6: adding a second winding to a core produces a transformer. The currents in the windings oppose each other, reducing the flux to almost zero. siliconchip.com.au Australia's electronics magazine The magnetic circuit shows that even though the two mmfs are pushing flux around the core in the same direction, when one is excited, the other will see an mmf of the opposite polarity. The mmf seen at F2 due to a positive F1 will be negative and vice versa. This means that a current entering the dotted terminal of one winding will force a current out of the dotted terminal on the other winding. If the reluctance is zero, the mmfs will be equal in magnitude as well as opposite in sign. In other words, the ratio of transformer currents i1 : i2 is equal to -N2:N1. Don’t get too worried about the negative sign here; it is just there because convention says positive current flows into the dotted terminal. In an ideal transformer, then, perfect flux linkage means the voltages are related by the turns ratio (v1 : v2 = N1:N2), and zero reluctance means the currents are related by the inverse of the turns ratio (i1 : i2 = N2:N1). The net flux in the core must be zero since the input and output mmfs cancel out as they are identical but opposite in sign. The impedance looking into one winding with the other open will be infinite (it will look like an open circuit), and when the other is short-­ circuited, it will be zero. A transformer model While ideal transformers are handy for circuit analysis, they are not realistic. We can summarise these non-­ idealities in the equivalent circuit of Fig.7. There is an ideal transformer in the centre of the diagram. The inductances in series with each side are leakage inductances caused by incomplete coupling of the flux, as we saw in Fig.4. I have shown a leakage inductance on either side of the transformer, but it is also sometimes handy to have it all ‘lumped’ onto one side or the other. For example, if we wanted to show Ll 2 on the same side as Ll 1, we would shift it over but multiply its value by (N1÷N2)2. We could equally move Ll 1 January 2026  29 to the same side as Ll 2 by multiplying its value by (N2÷N1)2. Since any real transformer core has a finite reluctance, the opposing mmfs of each winding will not completely cancel out, and there will be some level of residual flux in the core. This is represented by the parallel inductance known as the magnetising inductance. This is responsible for the small current that will flow in a transformer’s primary winding when its secondary is open circuit. There are also copper losses and core losses in transformers, driven by the same mechanisms as discussed above for inductors. The copper losses can be represented by appropriate resistances in series with the leakage inductances, and the core losses by a resistor in parallel with the magnetising inductor. I have not bothered to show them here to keep things simple. The forward converter Knowing what we do about magnetics, we can begin to understand isolated DC-DC converters. In the upperleft corner of Fig.8 is a non-isolated buck converter that we are by now very familiar with. To its right is an isolated version of the same topology, known as a single-ended forward converter. An ideal (for now) transformer with a turns ratio of N:1 has been inserted pretty much in the middle of the buck converter’s switch Q1, which now consists of a Mosfet (Q1) on the primary side and diode (D2) on the secondary side. When Q1 is on, current flows into the dotted primary terminal of the transformer. A current, scaled by a factor of N, emerges from the dotted secondary terminal and passes through D2, forming the second half of the switch feeding the filter inductor. When Q1 and D2 are off, the filter inductor current flows via diode D1, just as it does in the non-isolated converter. The transfer function of the forward converter is the same as the buck converter, but scaled by the transformer turns ratio, N. I have drawn the forward converter with the Mosfet in the positive input line to match the buck converter, but in reality, it is typically moved to the ‘ground’ side of the transformer primary to make its gate drive simpler, as shown in the circuit at lower left in Fig.8. In this circuit, I have also added the magnetising inductance to the transformer, and a clamp circuit consisting of diode D3 and zener diode ZD1. You can probably already see why these are necessary. We don’t need to worry about the leakage inductances, as they are in series with the ideal transformer, so there is always a path for their current to flow. They will affect voltage regulation a bit, but we won’t worry about that now. This is a ‘single-ended’ converter because power flows through the transformer only during the part of the cycle when Q1 is conducting. This means that when the Mosfet switches off, the magnetising current needs a path to flow or else the Mosfet’s drain terminal voltage will spike and it will be toast. The clamp circuit limits the Mosfet drain voltage to the sum of Vin plus the zener voltage. The energy stored in the magnetising inductance is dissipated in the clamp every cycle. The price we pay for the convenience of the transformer is the additional complexity and power dissipation of a clamping circuit, and the additional voltage stress on the switch. There are several other ways to implement the clamping circuit, two of which are shown at lower right in Fig.8. The first, a resistor-capacitor-diode (RCD) clamp, relies on a capacitor to absorb the energy, which is then dissipated in the parallel resistor. This is probably the cheapest option and is often seen in low-cost designs. A more efficient option is to add an extra winding to the transformer and a diode, as shown in the energy recovery clamp partial circuit. When the Mosfet switches off, the magnetising current causes the transformer terminal voltage to rise until the clamp diode conducts. If the clamp winding had the same number of turns as the primary, the Mosfet drain voltage would be Fig.8: the single-ended forward converter is essentially a buck converter with Q1 replaced by a Mosfet, transformer and diode. The transformer’s magnetising inductance requires the addition of a clamp circuit, as shown along the bottom of the figure. 30 Silicon Chip Australia's electronics magazine siliconchip.com.au clamped to twice Vin. You can choose the number of turns on the clamp winding to limit the drain voltage even further if necessary. As the name implies, the advantage here is that the magnetising energy is returned to the supply. Another similar variant of the single-­ ended forward converter, the isolated hybrid bridge converter, is shown in Fig.9. It is still a single-ended converter, because the Mosfets can only drive flux through the transformer in one direction, but it solves the magnetisation current problem by clamping both ends of the windings to the supply rails when the Mosfets are off. The Mosfets are never subject to more voltage stress than the supply rails, but the gate drive for the upper Mosfet is more complex in this configuration. Double-ended forward converters An obvious(?) next step would be to replace the diodes in the hybrid bridge converter with Mosfets to produce a full-bridge converter. This has the huge advantage of driving flux in both directions in the transformer and allowing us to use a full-bridge rectifier on the secondary side. The single-ended converter can only drive the magnetising flux around the transformer core in one direction (remember, the magnetising flux is what’s left in the core after most of the Fig.9: the isolated hybrid bridge converter solves the problem of magnetising inductance at the cost of circuit complexity. flux is cancelled out). In a double-ended converter such as this one, the magnetising current can change sign. We can therefore utilise the full range of flux density in the core material, making for a more efficient and smaller transformer. Being able to use a full-bridge rectifier means we can use a smaller filter inductor, since the frequency at the output of the rectifier is twice the switching frequency. This type of converter does require that we take care to limit the duty cycle of each phase to less than 50%, or we run the risk of switching on the upper and lower Mosfets at the same time, with catastrophic results. The price to pay for such advantages is complexity. There are now two highside and two low-side Mosfets to drive, and four output diodes. Moreover, the arrangement means that two of these Mosfets and two diodes are in series each cycle, so the efficiency is less than ideal. If only we could get the advantages of the double-ended converter without these disadvantages! Well, you can, by using a more complex transformer, as shown at the bottom of Fig.10. This is the transformer-coupled half-bridge or push-pull topology, and it has all the advantages of the full bridge, but is considerably simpler. There are only two switches, and both are ground-referenced. Only two diodes are required, and the output current only ever passes through one of them. Nice. The flyback converter Next, I want to cover the flyback topology, which is an isolated topology derived from the boost converter (Fig.11). This time, we split the circuit in the middle of the inductor, creating two coupled sections. It looks a lot like a transformer, but strictly speaking, does not behave that way. Fig.10: double-ended converters can drive flux through the transformer core in both directions, increasing the efficiency of the magnetics. siliconchip.com.au Australia's electronics magazine January 2026  31 Fig.11: the flyback converter is derived from the boost topology. The ‘transformer’ is actually two coupled inductors – the windings never conduct at the same time. When Q1 is on, current flows into the dotted primary terminal of the ‘transformer’. True transformer action would require it to emerge from the secondary’s dotted terminal, but it cannot, because it is blocked by the diode (D1). The secondary winding is effectively open circuit, so the ‘transformer’ acts like an inductor, building up flux and storing up energy in the core. When the Mosfet switches off, the primary winding is open-circuited and the magnetic field begins to collapse, reversing the voltage on both windings and allowing D1 to conduct. Now that the primary winding is open-circuit, the flyback transformer secondary acts like an inductor and the current ramps down, just as it does in the boost converter. The only difference is that the turns ratio means the secondary current is scaled by a factor N. The voltage transfer function for the flyback converter is therefore the same as for the boost converter, but scaled by the turns ratio. While the flyback circuit looks a lot 32 Silicon Chip like the forward converter, the crucial difference is in the operation of the transformer. A forward converter has a true transformer in that the net flux largely cancels (except for the magnetising flux), and no appreciable energy is stored. The output filter inductor remains the primary energy storage element. In flyback converters, the ‘transformer’ is also the energy storage element. Since the two windings never conduct simultaneously, the flux increases significantly. Flyback transformers are really two-winding inductors and usually have gapped cores. If you are ever unsure about what topology you have, take a look at the dots on the transformer, and work out if both windings can conduct at the same time or not. The fact that flyback converters combine the energy storage element and the isolation element into one piece of magnetics (and because they use The Mornsun LM25-23B12 25W 12V isolated power supply. one less diode) is one of the reasons why they are the most common topology for small mains converters. That includes many phone chargers, plugpacks and other low-power DC-DC converter modules below about 50W. Flyback converter transformers do not have the magnetising inductance concern that single-ended forward converters do (because they are not really a transformer), but they do have a problem with leakage inductance, as shown at the bottom of Fig.11. When the Mosfet switches off, the energy stored in the core is delivered to the secondary, but any that is stored in the primary side leakage inductance has no place to go since it is, by definition, not linked by the secondary winding. So weirdly, it turns out that a practical flyback converter needs a similar type of clamp as a single-ended forward converter, but for a different reason altogether. A professional design To add a practical twist, I want to take a close look at the design of a commercial flyback converter, because you can learn a lot by looking at designs by experts. The converter I chose is a Mornsun LM25-23B12, an offline isolated 25W switcher with a 12V DC output. It can accept input voltages in the range of 100V to 277V AC and can deliver 2.1A at 50°C. You might think this is an AC-DC converter and not a DC-DC converter, and by some definitions, you would be right. Still, I will argue that, like many mains-powered supplies, it is an AC-DC converter followed by a DC-DC converter. The AC-DC side of this converter is a simple bridge rectifier, so all the interesting stuff is happening in the DC-DC part. These converters are built to a price, but they do claim to meet a bunch of international specifications for safety & EMC (electromagnetic emissions compliance). Looking at the construction & component choice, I don’t siliconchip.com.au Fig.12: the reverse-engineered circuit of a commercial 25W switching converter (the Mornsun LM2523B12). The text describes some of the interesting design features. doubt that this is a well-designed unit. The accompanying photos show the power supply and both sides of the PCB. It is a single-sided board with through-hole components on the top side and SMT parts on the bottom. The slots milled into the board are to provide creepage isolation between primary and secondary and between high voltages. The circuit, as best as I could reverse engineer it, is shown in Fig.12. Starting on the left is the mains input, with a fuse and an inrush-limiting NTC resistor. An X2 capacitor and common-­ mode inductor provide some filtering to minimise the amount of EMI (electromagnetic interference) conducted back onto the mains. This filter is followed by a full-wave bridge rectifier and three 15µF 400V DC capacitors in parallel, to smooth the input to the flyback converter. The negative side of the high-voltage DC supply is tied to mains Earth via a 2.2nF X1 capacitor, and to the output negative rail by two 1nF X1 capacitors in series. These capacitors provide a path to shunt high-frequency noise to Earth without compromising the safety or isolation. The power circuit looks like any flyback circuit, with one side of the transformer primary connected to the positive supply and the other to the drain of the Mosfet switch, which is incorporated into the SDH8666Q control IC. The Mosfet’s source is connected siliconchip.com.au to the current sense (CS) pin, which is connected to the negative supply via a 0.5W shunt resistor (three parallel 1.5W resistors). This chip uses current-mode control, and this is the current-­sense resistor. An RCD clamp with a 120kW resistor (two parallel 240kW resistors) and an unmarked capacitor protects the Mosfet from spikes caused by the transformer leakage inductance I described above. On the secondary side, the rectifier consists of two SK3150AS schottky diodes connected in parallel. These are 150V 3A diodes, and I guess two are used in parallel since the peak current could easily be twice the maximum output current of 2.1A. The diodes are followed by two parallel 470µF electrolytic filter caps. I am a bit surprised not to see a ceramic cap in parallel with these, given the switching frequency is in the 65kHz range. These caps must be working hard from a ripple current perspective (but presumably within their specifications). A secondary filter comprising a small inductor and a 47µF capacitor helps eliminate a lot of the switching noise on the output. Isolated voltage feedback and control loop compensation is provided via the circuit at lower right. This uses a TL431 shunt reference and opto-­coupler in a clever (but common) arrangement. I think this circuit is worth a bit of Australia's electronics magazine a closer look, so I have redrawn it in Fig.13. The converter’s output voltage is divided down and compared to the 2.5V reference internal to the TL431. The resulting error voltage at the TL431’s anode is converted to a current by Rb to drive the opto-­ coupler’s LED. A current proportional to this will flow into the coupler phototransistor’s collector and be converted back to an error voltage by the pullup resistor internal to the control chip. Fig.13: the Mornsun voltage feedback, error amplifier, isolation and loop compensation circuit uses a TL431, and opto-coupler and a handful of passives. The compensator is a Type II circuit, suitable for current-mode controllers, as described last month. January 2026  33 I calculated the circuit’s small-­signal transfer function using the complex impedance method we covered last month. As we would expect with a current-mode controller, the result is characteristic of a Type II compensator. I will spare you the maths. The constant terms at the front of the transfer function relate to the opto-coupler’s current transfer ratio (CTR), and the resistors on each side that convert voltage to current to voltage. The interesting part is inside the brackets. There is a pole at the origin and another formed by the capacitor Cb and the pullup resistor Rpu inside the controller. There is also a zero formed by Ra and Ca. This zero cancels the output capacitance/load resistance zero, and the Cb/Rpu pole cancels the zero formed by the output capacitor and its ESR. The purpose of the capacitor directly under the opto-coupler in Fig.12 is a bit of a mystery, but as it measures about 22pF and is connected at the output of the TL431’s internal op amp, I suspect it is there for stability and plays no meaningful part in the control loop. The next interesting part of the flyback converter is the power supply for the control chip. This is derived from an auxiliary winding on the flyback transformer via a diode and a couple of capacitors to supply the Vcc pin of the controller. You may ask yourself how this circuit can possibly start, given that the chip is powered by its own output. The chip has a clever trick up its sleeve in that there is an internal high-voltage depletion-mode (normally on) Mosfet connected to the DRAIN pin (pin 6) that initially provides a small trickle current to charge the 22µF capacitor on the Vcc pin. To keep the power dissipation in the depletion Mosfet to a minimum, this current is very small – nowhere near enough to power the chip – so the chip is not enabled until the Vcc voltage reaches some fairly high predetermined level. At this point, the chip switches on and uses the charge stored in the 22µF cap to run for long enough for the external supply to take over. Once everything is up and running, the depletion-mode Mosfet is switched off to save energy. This leaves only the DEM pin, which is fed from the auxiliary secondary winding prior to the rectifier diode. This pin is used to (roughly) sense the output voltage to provide output overvoltage protection, and something called “valley lockout”, which appears to be a mechanism to prevent the chip restarting too quickly due to small dips in the input voltage. The DEM pin can indirectly sense the converter’s output voltage because the voltage on the auxiliary winding is proportional to the output voltage (less one diode drop) according to the turns ratio. I suspect that the valley lockout works by ignoring short dips in the input voltage (sensed at the DRAIN pin) if the output voltage (sensed at the DEM pin) does not also drop. This would prevent the start-up sequence described above from happening unnecessarily for very short mains interruptions that don’t impact the output. That’s it for this month. Next month, we will have a look at AC-to-DC converters, and we will go through the design process for a simple DC power source in detail. We will build and test the circuit to see how well the theory SC and practice align. Silicon Chip as PDFs on USB ¯ A treasure trove of Silicon Chip magazines on a 32GB custommade USB. ¯ Each USB is filled with a set of issues as PDFs – fully searchable and with a separate index – you just need a PDF viewer. ¯ 10% off your order (not including postage cost) if you are currently subscribed to the magazine. ¯ Receive an extra discount If you already own digital copies of the magazine (in the block you are ordering). The USB also comes with its own case THE FIRST SIX BLOCKS COST $100 OR PAY $650 FOR ALL SEVEN (+POSTAGE) NOVEMBER 1987 – DECEMBER 1994 JANUARY 1995 – DECEMBER 1999 JANUARY 2000 – DECEMBER 2004 JANUARY 2005 – DECEMBER 2009 JANUARY 2010 – DECEMBER 2014 JANUARY 2015 – DECEMBER 2019 OUR NEWEST BLOCK OF ISSUES COSTS $150 → JANUARY 2020 – DECEMBER 2024 WWW.SILICONCHIP.COM.AU/SHOP/DIGITAL_PDFS Ordering the USB also provides you with download access for the relevant PDFs, once your order has been processed 34 Silicon Chip Australia's electronics magazine siliconchip.com.au By Tim Blythman Decoder Base Station Using DCC Remote Controller DCC Booster DCC Base Station Image source: https://unsplash.com/photos/ a-toy-train-traveling-through-a-lush-green-forest-rxBE5UF-Dsk Following on from the DCC Decoder last month, the other main component needed to add DCC to a model railway is a DCC Base Station. It provides power and data to the tracks. It’s based on a Pico 2 microcontroller module connected to an LCD touchscreen, so it’s easy to customise. D igital Command Control (DCC) is a system to operate model railways in a more realistic fashion than previous techniques such as DC/analog voltage control. The latter involves using a controller to apply a voltage to the tracks, connected straight to the locomotive motor via wheel pickups, to allow control of speed and direction. To turn a conventional analog model railway into one using DCC requires specific equipment in the locomotives and for the controller. The DCC Decoder from last month can be installed in a model locomotive to enable DCC operation. That article also covered some of the background of DCC. The DCC Decoder receives power and commands from a DCC base station. It then controls the motor and lights in the locomotive according to those commands. The DCC base station thus takes the place of a controller in a DCC system. The DCC standards are maintained by the NMRA (US National Model Railroad Association) and our designs have been tested to work with commercial gear from brands such as DigiTrax, NCE, TCS and DCC Concepts. siliconchip.com.au On page 49, we have a detailed guide on working with DCC. It will focus on using our Decoder and Base Station, but much of it will also be applicable to commercially available devices. The Base Station There is quite a bit of variety in what might be expected from a DCC base station. Some, like the Complete Arduino DCC Controller (January 2020; siliconchip.au/Article/12220) rely on a computer running the JMRI (Java Model Railway Interface) software. JMRI can show layout maps, mimic panels, rolling stock rosters and can even automate operations. At the other end of the spectrum are simple base stations that are designed to allow simultaneous operation of a few locomotives and allow some amount of decoder programming; enough for someone converting to DCC for the first time. Features & Specifications 🛤 Designed for small HO/OO and N scale operations 🛤 Pluggable screw terminals for easy connection to tracks 🛤 PCB front panel to suit UB3 Jiffy box or on a custom control panel 🛤 DC jack for plugpack, or screw terminal power inputs 🛤 Controls for five locomotives including speed, direction and four functions each 🛤 Automatic current sensing with adjustable trip limit 🛤 128 speed steps 🛤 Uses a Raspberry Pi Pico 2 and 3.5in 480×320-pixel LCD touchscreen 🛤 Main track output: up to 10A 🛤 Supply/track voltage: 8V-22V (don’t exceed 17V with our DCC Decoder) 🛤 Programming track output: limited to 250mA Australia's electronics magazine January 2026  35 At a minimum, the base station needs to have a processor of some sort to process user input and encode the DCC data for output. The user input might include selecting a decoder address or a request to send programming data to the track, as well as the operation of locomotive controls. Some sort of driver is needed to generate the DCC signal for power and control. There are systems that even provide a means to connect extra user panels. Since DCC is intended to allow more than one train to operate, it makes sense to allow multiple users to have control over the data that is transmitted, more on this shortly. On a hardware level, a base station must be able to drive the DCC track voltage, which is an AC square wave about 12V-15V in amplitude (24V-30V peak-to-peak) with a frequency varying around 6kHz. There should also be some current sensing and circuit protection, since the output could easily be a few amps or more, and it isn’t too hard to accidentally short the tracks. Our Base Station is intended as a simple and economical way to try out the world of DCC, but it still offers many features. All the controls are based on a 3.5in LCD touchscreen showing one of five different ‘pages’, each of which can be allocated to a decoder address. There are also pages for performing DCC programming and configuring the Base Station itself. We have also designed a DCC Remote Controller unit that can connect to an expansion port on the Base Station. Each Remote Control can control three locomotives; multiple Remote Controls can be connected in daisy-­chain fashion to a Base Station. We will present the DCC Remote Controller add-on project next month. Hardware The hardware for the DCC Base Station is fairly simple, so let’s start by looking at the circuit in Fig.6. Modulation of the main DCC signal is handled by two BTN8962 half-bridge drivers, IC2 and IC3. These are the same drivers used in the Arduino DCC Controller, and can handle up to 30A, so should be robust in a circuit limited to 10A. Each chip drives one of the rails to either 15V or ground under the control of signals DCC1EN, DCC1A and DCC1B from the Pico 2 module. If DCC1EN is low, both INH pins are low and the drivers are disabled 36 Silicon Chip (high-impedance). When DCC1EN is high, the outputs of IC2 and IC3 follow the inputs DCC1A and DCC1B, respectively. We’ve provided 1kW series resistors to afford some protection to the Pico 2 in the event of a critical failure of the driver ICs. When their high-side drivers are active, IC2 and IC3 source current from their IS pins in proportion to the current flowing to the output; the ratio is approximately 1:10,000. Since only one driver is active at a time, we combine the currents through dual diode D2. This current develops a proportional voltage across the 1kW resistor at its cathode. The 10kW resistor and 100nF capacitor smooth out peaks due to the varying DCC signal, and the voltage is sampled by one of the ADC (analog-to-digital converter) pins of the Pico 2 via GP27 so it can monitor the track load current. The outputs of IC2 and IC3 are connected to CON1, a pluggable screw terminal. Bicolour LED1 and its dropping resistor provide a visual indication of the voltage output at CON1. There is also a 100kW resistor that pulls the INH pins of IC2 and IC3 low if they are not otherwise driven. The driver for the programming output does not need to be as powerful, so we have used the same DRV8231 motor driver (IC1) as in the Decoder. The standards indicate that a programming output should be limited to supplying 250mA; the 3.7A-rated DRV8231 will handle that with ease. IC1’s control signals connect on lines DCC2A and DCC2B via 1kW series resistors. Its Vref pin is fed from 3.3V and with a 0.1W resistor on the ISEN pin, the current limit is set to 3.3A. The voltage across the 0.1W resistor is monitored by an ADC pin on the Pico 2 to allow the programming current to be measured. We apply the 250mA limit through a pair of 2W 33W resistors on the driver outputs, which can handle short-­ circuit conditions continuously with up to 16V at the input. The programming output is intermittent and only active for seconds at a time under direct supervision of a user, so we think this will be adequate. The resistors provide this soft limiting to prevent the DRV8231 from shutting down its outputs, since that would corrupt the DCC data stream. The outputs from IC1 are available Australia's electronics magazine at CON2 and are shown by bicolour LED2. The presence of a short circuit will be obvious, since LED2 will not light up when expected. Other circuitry The MOD2 LCD panel needs seven data lines to interface an SPI-mode controller to its LCD driver and touch controller; these are taken from appropriate pins on MOD1. MOD2’s LED backlight is driven by P-channel Mosfet Q1 from the 5V Vsys rail. Q1 is in turn switched by Q2, which is controlled by a pin on the Pico 2, GP3. The 10kW/1kW divider combined with a 1μF capacitor across the incoming supply from CON3/CON4 is connected to the last free analog/ADC input on the Pico 2. This allows the supply voltage to be monitored and displayed. Two of the remaining free pins are connected to CON5 (a four-way header) and CON6 (an RJ45 socket) for connection to external control boxes, along with the 3.3V and ground rails. We have chosen the GP0 & GP1 pins since they are capable of both I2C and UART (serial) operation. They have 2.2kW pullups to the 3.3V rail. S1 connects to the 3VEN pin on MOD1; when this line is pulled low, by S1 being pressed, the 3.3V supply on the Pico 2 is shut down. This can be siliconchip.com.au Fig.6: The Base Station circuit is based on the Pico 2 microcontroller module, MOD1, and an LCD touchscreen, MOD2. The incoming supply powers these through buck regulator REG1 and also feeds IC1, IC2 and IC3. Those three chips provide the DCC outputs under the control of MOD1. used to reset both the Pico 2 and any connected control boxes, since they are also powered from 3.3V. An external momentary pushbutton connected in parallel with S1 could be used to provide an emergency stop feature. Power supply A DC supply of 8-22V is provided to either CON3, a DC jack, or CON4, a pair of screw terminals. These are connected in parallel with the intent that one or the other is used. The DC jack should be good for up to 5A, while the screw terminals can handle up to 10A. We’ve specified an 8V to 22V supply voltage range because those are the siliconchip.com.au limits set by the DCC standards. The components on this rail are all rated up to 30V. You’ll also need a suitable DC power supply wired with a positive tip. A basic 12V supply capable of at least an amp will be sufficient to run some tests and operate the Base Station and a few small locomotives. Fuse F1 provides circuit protection, with reverse-connected diode D1 forcing the fuse to blow in the event of a reverse-polarity voltage being applied. This arrangement is preferred at higher currents, since the polarity protection diode must carry the full current at all times if arranged for reverse blocking. The 1000μF capacitor provides the Australia's electronics magazine bulk bypassing for the supply. REG1 is used to provide the low-voltage rail for the microcontroller and display modules. It is a switch-mode device, since we will be driving a backlight (typically 300mA) at 5V, dropping around 10V from the supply. A linear regulator would dissipate 3W or more if used here. REG1 is an MCP16311, the same device we used in the Homemade 78xx Switchmode Regulator from August 2020 (siliconchip.au/Article/14533). The circuit here is much the same as the 5V version of the Switchmode Regulator, although we have used common E12 resistor values of 56kW/10kW January 2026  37 to give a nominal output of 5.3V with a 0.8V reference voltage. This is a classic buck regulator circuit, with inductor L1 storing energy between switching cycles under the control of REG1. The 5.3V rail has a 100μF electrolytic capacitor for filtering, and the circuit includes the four ceramic capacitors needed by the regulator. Since the 5.3V rail passes through schottky diode D1 to the remainder of the circuit, we have near enough to 5V at the point of use. Connected to D1’s cathode is pin 39 (Vsys) of the MOD1 Pico 2 microcontroller module, along with the MOD2 LCD touch panel module supply. The Pico 2 has its own diode from the USB supply feeding into the Vsys pin. These diodes prevent back-­ feeding from the regulator to USB or vice versa. A connection to MOD1’s micro-B USB socket can also be used to provide power to the low-voltage (5V and 3.3V) circuits for testing. Software From the hardware, we can see that we have a high-power (up to 10A) driver output that will be used for the main DCC track signal. The second driver output will be used for the programming output. We can monitor the drive currents via two of the ADC inputs, with the incoming supply being measured by the third. The Pico 2’s second processor core spends most of its time monitoring the CON1 current so that it can react promptly if there is a fault. If the current limit is reached, the output is switched off for one second, then back on. It might switch off again immediately if the fault has not been cleared. This core also measures the other analog channels when needed. Both DCC signals are provided by a callback function from a timer interrupt; the interrupt triggers every 58μs. DCC uses pulse lengths of 58μs (nominal) to signal a binary ‘1’ and a pulse length of 100μs or longer to signal a ‘0’. Two 58μs periods are used to generate a 116μs pulse length for transmission of a ‘0’. The callback function provides digital signals to control IC1, IC2 and IC3. It processes each packet’s bits in turn, and flags when it is ready to receive the next packet. A packet takes around 6ms to deliver, so our main software loop simply needs to supply fresh packets as needed. If there is no data available, so-called ‘idle’ packets can be sent to keep valid DCC traffic on the rails. This can occur if the processor is otherwise busy doing other processing, such as updating the display. All display pages in the user interface have buttons for switching the DCC output off and on, so power can be shut off to the track immediately if there is a problem. A stop button also sets the speed of all locomotives to zero. The voltage and main track current are also shown at all times. The main control page provides five tabs, each of which can be allocated a DCC locomotive address. There are controls for speed, direction and function (eg, lighting) outputs. Two packets are needed to send all this data for each locomotive, so a queue of 10 packets is kept updated and sent in round-robin fashion. The interior layout is similar to many of our LCD BackPack projects, with the LCD screen connected to a main PCB assembly via a 14-way header & tapped spacers. 38 Silicon Chip Australia's electronics magazine When a control is changed, such as a speed control being adjusted, a priority system allows the relevant packet to be output as soon as it is changed. This makes the system more responsive to user input. There are two other pages. One provides settings pertaining to the Base Station and includes things such as calibration values for the current and voltage readings and user-settable parameters, like a software-controlled current limit. Programming output The remaining page controls the DCC signal on the programming track output at CON2. In general, at most one decoder (and thus locomotive) should be connected to the programming track. This is because ‘service mode’ programming does not distinguish locomotive addresses. CON2 supports direct, paged, physical and address-only programming modes. Of these, direct mode is the newest and fastest, although it has been around for at least 20 years already, so most modern decoders should support it. We recommend using this mode unless it does not work with a specific decoder. Programming involves writing values to certain CVs (configuration variables) to change the behaviour of the decoder. Physical mode only supports a very limited number of CVs, while paged mode supports more through the use of a page register. Service-mode programming relies on specific patterns of packets, including repeated packets and so-called ‘reset’ packets to ensure that programming does not occur unless intended. These patterns are noted in the standard, but we have also validated them against the output of a commercially available DigiTrax base station. DCC also implements an acknowledgement feature, which can be used to read back data programmed into decoders. The acknowledgement involves the decoder loading the output with a 60mA or higher load; typically, by briefly driving its motor outputs. Thus, the Base Station can also perform a read-back of CVs to check their values or confirm them after writing. Our circuit allows the acknowledgement to be seen as LED2 dimming due to the load on the 33W resistors. The Programming page can also siliconchip.com.au send operations-mode programming packets. They are not sent via the CON2 programming track; instead, they go to the main track via CON1 instead. These packets are addressed, so they use the currently selected decoder address from the main pages. There is no read-back, since operations mode does not use the acknowledgement scheme described above. We’ll look more closely at the software operation after the Base Station has been completed. Our separate article will also provide more detail about programming decoder CVs with the Base Station. Control panel If you are planning to fit the Base Station into a larger panel, such as the control panel for an existing layout, then we recommend that you use the panel PCB as a template to trace the outline of the shape. Tracing around the main PCB (before it’s assembled) will give you an idea of the amount of material you need to cut out of your panel to fit the Base Station assembly into it. The LCD panel mounting holes can be used to align the two PCB outlines. You will probably have your own ideas about what connectors you will use, so you may not want to fit the standard connectors until you have worked out how it will connect to your layout. If you don’t think you’ll use the CON6 remote control connector, the tab that protrudes from the PCB can be carefully snapped off. This means that a hole does not need to be cut in the case for CON6. It can still be fitted later, since the traces do not cross onto the tab, but it will lack mechanical support. Construction Start by assembling the main PCB, which is coded 09111244 and measures 130 × 68mm. Most components are on the top, including the majority of surface-mounting parts. The smallest parts are M3216 size (imperial 1206), so construction is not too difficult. Gather your SMD equipment and consumables, including flux paste, solder wicking braid, tweezers and a magnifier. Begin with the SMD parts on the top of the PCB, followed by the two SMD parts on the reverse. After cleaning off any flux residue, the handful of siliconchip.com.au Parts List – DCC Base Station 1 Base Station PCB assembly (see below) 1 black panel PCB coded 09111244, 130 × 68mm 1 3.5in LCD touchscreen module (MOD2) [Silicon Chip SC5062] 4 M3 × 8-10mm black panhead machine screws 4 M3 × 6mm panhead machine screws 4 M3 × 12mm tapped spacers 4 M3 nylon hex nuts 1 UB3 Jiffy box [Altronics, Jaycar, Bud Industries CU-1943] 1 DC power supply to suit layout (see text) Base Station PCB assembly 1 double-sided PCB coded 09111243, 55 × 131mm 1 Raspberry Pi Pico 2 microcontroller module programmed with 0911124B.UF2 (MOD1) 1 14-way 0.1in socket header strip (for MOD2) 2 2-way 5mm/5.08mm pluggable screw terminal blocks (CON1, CON2) [Altronics P2592 + P2512, Jaycar HM3102 + HM3122, or Dinkle 2EHDRC-02P + 2ESDV-02P] 1 PCB-mounting DC barrel jack (CON3) 1 2-way 5mm/5.08mm screw terminal (CON4; optional) 1 4-way 0.1in R/A locking header (CON5; optional, for remote control) 1 RJ45 PCB-mount socket (CON6; optional, for remote control) [Altronics P1448 or P1448A] 1 22μH 1.3A SMD inductor, 6×6mm (L1) 1 6 × 6mm through-hole tactile switch with short (~1mm) actuator (S1) 2 M205 fuse clips (F1) 1 M205 fuse to suit PSU (F1) 1 small tube of neutral cure silicone or similar to secure the capacitors Semiconductors 1 DRV8231DDAR motor driver IC, SOIC-8 (IC1) 2 BTN8962TA half-bridge drivers, TO-263-7 (IC2, IC3) 1 MCP16311(T)-E/MS buck regulator, MSOP-8 (REG1) 1 SSM3J372R or AO3401(A) P-channel Mosfet, SOT-23 (Q1) 1 2N7002 N-channel Mosfet, SOT-23 (Q2) 1 SS14 40V 1A SMD schottky diode, DO-214AC (D1) 1 BAT54C dual common-cathode SMD schottky diode, SOT-23 (D2) 1 1N5404 or 1N5408 3A silicon axial diode, DO-27 (D3) 2 3mm bicolour red/green LEDs (LED1, LED2) Capacitors (all SMD MLCC, M3216/1206 size, except as noted) 1 1000μF 25V radial electrolytic 1 100μF 25V radial electrolytic 5 1μF 50V X7R 4 100nF 50V X7R Resistors (all SMD M3216/1206 size, ±1%, ⅛W except as noted) 1 100kW 9 1kW 1 56kW 2 33W M6332/2512 size, 2W 4 10kW 1 0.1W 4 2.2kW The DCC Base Station is a simple but complete system for starting out with DCC. The Base Station has controls for five locomotives. We have also designed a DCC Remote Control that can provide extra controls. Figs.7 & 8: the board uses a mix of surface-mounting and through-hole components and modules. Most components are on the top side of the PCB, but we have placed F1 on the back to allow easy access if needed. through-hole parts and modules can be fitted. Figs.7 and 8 are the overlay diagrams for the top and bottom, respectively. You can find photos of the PCB assembly on earlier pages. Regulator REG1 comes in an MSOP package with the closest pin pitch on the board, so start with it. Spread flux paste over the pads on the PCB and rest the chip in place. If you can’t see the pin 1 marking on the silkscreen, it is near the 56kW resistor. Tack one lead, check the positioning and then solder the remaining pins when it is correctly placed and flat against the PCB. Follow with the SMD diodes and transistors, being sure not to mix up the three different SOT-23 parts. Single diode D1 must have its cathode stripe facing correctly, towards the ‘K’ on the PCB. Follow by soldering IC1, then IC2 and IC3. Since IC1 will be operating at a small fraction of its limit, we have opted not to solder the exposed thermal pad on its underside. Tack one lead, adjust and solder the remaining leads when you are happy with its position. 40 Silicon Chip For IC2 and IC3, be sure to add a generous amount of flux to the pads before placing the part, and turn up your iron if it is adjustable. Tack one of the smaller leads in place, then add a good amount of solder while applying your iron to the large tab and pad near CON1. If your iron cannot provide enough heat, you can try preheating the board or supplementing the iron with a hotair tool. When the solder flows freely and the flux is smoking, you will know that the joint is solid. Finish by carefully soldering the remaining leads. The remaining SMD parts are all passives. Inductor L1 is larger than the others, so solder that now while the iron is hot, then turn it back down for the remaining passive components. All the values are marked on the silkscreen, so take your time and make sure that they are all placed correctly. Finish with the two 100nF capacitors on the back of the PCB. Clean off any flux residue using your choice of solvent and allow the PCB to dry. Inspect it closely for bridges, dry Australia's electronics magazine joints and pads that do not have solder adhering correctly. Fix any problems before proceeding. At this stage, the circuitry around REG1 is complete, so you can test it by applying a current-­ limited power supply (such as a 9V battery) to the pads of the (not-yet fitted) 1000μF capacitor. You should see 5.2V-5.4V on D1’s anode relative to ground (the negative lead of either electrolytic capacitor). Programming the Pico 2 We suggest programming the Pico 2 now, since it will be more difficult to access its BOOTSEL button when the LCD is affixed above it. We also recommend using the flash_nuke.UF2 firmware image to ensure that the Pico 2’s flash memory is blank first, although this should not be strictly necessary if the Pico 2 is brand new. Hold the BOOTSEL button on the Pico 2 and connect it to the computer, then copy the flash_nuke.UF2 file to the RP2350 virtual drive that will appear. Wait for the drive to disappear and then reappear, then copy the 0911124B.UF2 firmware. The LED on MOD1 should light up, indicating that the firmware has been loaded correctly and is running. The remaining through-hole components For simplicity, we recommend soldering the Pico 2 directly onto the siliconchip.com.au PCB, surface-mount style. You can use headers, but since full-height headers would be too tall, you will need to use low-profile headers and no sockets. That will work, but the clearance is very tight. The 14-way header socket for the LCD can also be fitted now. Make sure all headers are mounted squarely; you can use MOD1 and MOD2 to align them. Solder CON1 and CON2, the pluggable screw terminals, and follow with your choice of CON3 or CON4, since only one of these is needed. You should also fit either CON5 or CON6 if you plan to use the Remote Controller. We preferred to use the RJ45 socket (CON6), since we can use standard Cat 5/6 cables to connect Remote Control units. Next, mount the fuse clips for F1 (with the retention tabs on the outside), large diode D3 and the 100μF capacitor on the rear of the PCB. You can slot a fuse into the clips to keep them aligned. Switch S1 and the 1000μF capacitor are the last parts on the top of the PCB. Make sure to bend the capacitor leads the right way before soldering and add some glue or silicone to secure the capacitor bodies to the PCB. Leave off LED1 and LED2 for now. To fit the LCD panel and align the LEDs, start by attaching the M3 × 10mm machine screws to the front panel PCB using the nylon nuts. The nuts will act as spacers for the LCD panel below. Slot the LCD panel over the screws, making sure that the 14-way header is at the end opposite the LED holes in the panel. Secure the LCD panel with the tapped spacers. Now guide the LEDs into their holes on the main PCB, but do not solder them. Their polarity does not matter, since a DCC signal is effectively alternating current. Attach the LCD panel assembly to the main PCB, making sure that their 14-way headers connect. Secure the main PCB using the M3 × 6mm machine screws. Bring the LEDs up so that they are just poking out through the front of the panel and solder them in place, then trim the LED leads and check that you have a fuse fitted. The rating of the fuse should match that of your chosen power supply. Initial checks The 5V-powered parts of the Base Station can be supplied from the Pico 2’s USB socket, so USB power is sufficient to check that the processor and LCD touchscreen are working. Connect USB power to the Pico 2 and see that the LCD backlight switches on and Screen 1 is visible on the panel. Verify the touch panel calibration by trying some of the buttons. The default touch calibration should work for all 3.5in panels, but there are parameters that can be edited if it does not. Check the “Arduino library and software” panel overleaf, as this has more details on adjusting the calibration and customising the software. If all is well, disconnect the USB cable. Testing and setup A 9V battery is a good choice for a current-limited power supply, but just about any plugpack that can deliver a few hundred milliamperes at 8V-22V Screen 1: the SET and PR buttons can be used to access Screens 2 and 3, respectively. One of the five tabs can be selected using the L1-L5 buttons, while the address can be changed by using the button at upper left. siliconchip.com.au should be sufficient. Check that the Base Station powers on and that the voltage display at lower right matches the power supply voltage. The displayed current should be 0.0A. The SET page (Screen 2) holds the calibration parameters (I1x, I2x, Vx and IO/S). The software current limit for the main track is ILIM. Most of the calibration parameter defaults should be usable, but the current offset (IO/S) can vary wildly. This parameter is due to IC2 and IC3 producing a non-zero current signal at zero current, so the offset setting is necessary to cancel this out. If you use a different supply voltage, this may change. If you wish to redo this calibration, reset the IO/S parameter to zero before doing so. Make sure nothing is connected to the MAIN (CON1) output and change the ILIM parameter to 9A by pressing the ILIM button and typing 9 ENTER on the on-screen keypad. Press the yellow ON button, which should cause the MAIN LED to light. You should be able to see that both the red and green elements are on in the LED; if not, then there is likely a fault in one of the drivers. The current display should also show a non-zero value around 4A to 5A, although anywhere between 1A and 9A can be expected according to the BTN8962 data sheet. Take that reading and enter it in the IO/S field. The current reading should now drop to 0A with the offset applied. Now adjust the ILIM value to suit your power supply. All values are immediately saved to flash memory, Screen 2: apart from the calibration parameters, the button at lower right saves the currently selected locomotive selections (L1-L5). Pressing this button should show SAVED, after which L1-L5 will be automatically loaded when the Base Station is next powered on. Australia's electronics magazine January 2026  41 so you don’t need to perform an extra step to save them. The other parameters should be within a few percent without adjustment, so should not be changed unless you have an accurate way of measuring the voltage and currents. Enclosure preparation The panel PCB has been designed to fit a UB3 Jiffy box; Figs.9 & 10 show the cut-outs needed to fit the assembly into this box. We have not included holes for CON4 or CON5, since we have not used them in our prototype. The 6mm hole for the CON3 DC jack suits our power supply, but you may need to enlarge it if your plug has a short shaft. If you’re planning to use CON4 instead, you can make a hole in front of that for wires to pass through. Similarly, if you plan to use CON5 instead of CON6, you could omit the rectangular cut-out for the RJ45 socket and drill a hole for wires to pass through instead. The three rectangular holes can be made with vertical cuts from the top of the case. Score the horizontal cut with a sharp knife and snap off the tab with pliers. The round hole is simply drilled with a twist or step drill. The PCB assembly takes the place of the Jiffy box lid, and can be secured using the screws that are provided with the box. We prefer to surface-mount the Pico 2 module. If you find that the holes are slightly misaligned, you can trim the sides of the holes using a sharp hobby knife. Using it We’ll now take a look at the basic operation of the Base Station. Those who have experience with a DCC system should be able to take what they need from these brief instructions. Note that only 128-step speed instructions are issued. For more details about getting started with DCC for the first time, refer to our separate article in this issue, starting on page 49. When the Base Station is powered on, it starts on the main page, seen in Screen 1. Buttons L1-L5 select the active locomotive, which is highlighted. The controls above this operate on the active locomotive. The top left button can be used to change the selected address controlled by L1-L5. DCC uses two types of addresses; a short address is seven bits, and is valid between 1 and 127, although values above 99 are generally avoided since they conflict with some programming packets. Long addresses are 14 bits and are valid from 1 to 10239, enough to hold all four-digit numbers. In both cases, zero is not valid, so it is used to indicate that the tab is inactive. This is shown as three dashes in the address box. Any address entered with three or more digits is treated as a long address. To use a long address in the range of DCC Base Station Short-form Kit (SC7539, $90): includes everything in the parts list, except for the case, power supply, glue, CON4 & CON5 headers 42 Silicon Chip Australia's electronics magazine siliconchip.com.au Screen 3: the default of DIR (direct) mode programming is the newest and should work with all modern decoders (including our own design from last month). You can use this to read or write the decoder’s CVs (configuration variables). 1 to 99, add leading zeros to pad the value to three or more digits. Long addresses are displayed with five digits using leading zeroes. There are a few safety interlocks in the code. You cannot set two tabs to use the same decoder address, and you cannot change an address without reducing the speed to zero first. That helps to prevent conflicting control commands and runaway trains! The REV, FOR, STOP and F0-F3 buttons control the commands that are sent to the addressed locomotive. F0 has a toggle action, since it is usually used for controlling a light such as a headlight. You might see it referred to as FL for this reason. F1 and F2 are momentary-action and are typically used to control a horn or whistle. The four indicators above the buttons show the state. F3 is provided with a toggle action, so there is another latching control available. Switch on the DCC track power (ON) if it is not already. To operate a locomotive, enter its address at upper left, then select the direction (FOR or REV) and switch on the headlight (F0) if needed. Drag the slider to change the speed, which is displayed with the direction on the top line. Pressing the yellow STOP button will set the speed of all locomotives to zero, while OFF can be used to shut off power in an emergency. The current display will be green if it is below the limit, or red if it has tripped. You will also see the MAIN LED go out when a trip occurs. Screen 3 shows the page used for CV programming. This is accessed through the PR button on the main page. DIR, PAG, PHY and OPS refer to direct, paged, physical and operations mode programming, respectively. DIR, PAG and PHY modes occur on the CON2 programming track, while OPS packets are sent to the CON1 main track to the currently active locomotive, as selected by L1-L5. Power is only applied to the PROG output when a read or write is occurring on the programming track, so you will see the PROG LED light up during these times. Pressing BACK during programming will cancel the operation. The CV to be programmed is entered with the CV# button. It can be read with the READ button, with the value shown below it if the read was successful. A value to be written is entered in the box below WRITE and pressing the WRITE button performs that action. The status of the last or current action is shown at the top of the page. The LONG address is actually a pair of CVs (17 and 18). They can be edited separately, but the LONG button manages the value of both of these together when reading or writing a long address. Press LONG instead of entering a CV# to access this mode. Note that you will need to set the long addressing bit (CV29, bit 5) to activate the long address once set. Other information The Software panel overleaf has more information on the libraries used in writing the software for this project, so you should have a look at that if you wish to compile the sketch yourself. Our separate feature article has more depth on using our Decoder and Base Station as a complete system. We recommend reading it if you are new to DCC. The Decoder article from last month also has information about the most common CVs, including all that are implemented by that Decoder. That article also includes a glossary of DCC terms. Figs.9 & 10: with rectangular holes abutting the top edge of the case, it is not difficult to make the cuts needed. Once the PCB assembly is complete, you can use it to judge whether any of the holes need trimming. siliconchip.com.au Australia's electronics magazine Conclusion The DCC Base Station is a simple but complete control unit for DCC Decoders. Once you have built it, adding Decoders to the locomotives on your layout will provide most of what is needed to convert a layout to DCC operation. January 2026  43 Arduino library, software & screen calibration This panel provides a bit more background on the libraries and other code that are used for anyone interested in compiling the Arduino code, either to make some tweaks or perhaps create your own version. We’ll also discuss how to calibrate the touch panel. The following assumes that you have an assembled Base Station PCB connected to a 3.5in LCD touchscreen or, at least, the same wiring between a Pico 2 and the LCD panel. A solid background using the Arduino IDE would help. Many of the functions used by the main sketch are in the util.h file. Near the top of this file are some defined colours, so you can adjust the colour scheme easily. The dcc.cpp and dcc.h files contain the DCC-specific drivers. LCD driver The LCD driver library is the main external library we have used, and this is the TFT_eSPI library. It can be found at https://github.com/Bodmer/TFT_eSPI or installed by searching for TFT_eSPI in the Arduino Library Manager. We also use the TFT_eWidget library (https://github.com/ Bodmer/TFT_eWidget) to draw the GUI elements. These libraries are quite powerful and offer anti-aliasing on the fonts and GUI elements, so the display looks very nice. You will need to install these libraries and any dependencies they require. Rather than using a configuration within the sketch, this library uses a global (library-level) configuration for the display pinout and driver selection. You will need to set this up before doing anything else with the library. The code for this configuration is noted in the util.h file. It requires creating a profile in the “libraries\TFT_eSPI\ User_Setups” folder to suit the display type and wiring; this is the PICO_ILI9488_DCC.h file that you will find in the software bundle. Then edit the User_Setup_Select.h file to include the PICO_ILI9488_DCC.h file as the active configuration. This configuration will now be used for all sketches compiled with this library, so you can try any of the example sketches using the Base Station display hardware. You can subsequently change configurations by editing the User_Setup_ Select.h file. The Examples → Generic → Touch_calibrate sketch can be used for touch panel calibration. Upload this sketch and open the serial monitor. Run the calibration, and the results are displayed on the serial monitor. The updated values can be used to set the calData array in the main sketch file before compiling. That’s all there is to changing the calibration. tool at https://vlw-font-creator.m5stack.com, we converted this into a VLW file using a size of 36pt. We then used the HxD hex editor program to convert the file data into a byte array that could be embedded in the sketch; this is the asimov_36.h file. DCC code The DCC code has been written with the Pico/Pico 2 architecture in mind, so you will need the arduino-pico board profile installed. The DCC code depends on this profile and the Ticker library that calls the DCCcallback() function every 58μs. The code provides functions to create all manner of DCC packet types with both long and short addresses. The main track DCC output implements a short queue that can be filled with the queuePacket() function. If the queue is empty, the code will produce idle packets to keep valid data on the track. As the DCCcallback() function consumes the packets, new packets can be added. For the most part, the software updates an array of the 10 packets that are needed to control the state of the five locomotive outputs. As the queue empties, the software cycles through the array and delivers each of the 10 packets in turn. There is a loco_t data type that can be used to hold the information (speed, direction, address etc) about a decoder. Most packets can be created directly from the loco_t object using straightforward function calls. For the simplest implementation of a mainline track output, create a loco_t object and set its various elements (address, speed, direction etc). Create two dccPacket_t objects and call the speedPacket128() and F04Packet() functions to load these packets with speed and function data, respectively. Use the packetQueueSpace() function to see if there is space in the queue and, if so, queue the packets with the queuePacket() function. Keep updating the loco and packets, and continue queuing fresh packets as needed. The DCC output can be switched on and off with the dccSwitchOn variable. The programming track output works slightly differently; it doesn’t have a queue. It is expected that the packets for the programming track are managed from a tight loop that produces the specific packets as needed at the correct times. SC Fonts The anti-aliased fonts used in this project require a different data format than we have previously used. The asimov_36.h file contains the font data we created to suit this display. There are online tools to create custom font data from computer font files. We started with the open-source Asimov font in the OTF font file format. Using the The RJ45 socket on the right-hand side of the Base Station can be used to connect extra controllers. 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See latest catalogue for freight rates. *Devices for illustration pursposes only. By Tim Blythman Decoder Base Station Using DCC Remote Controller DCC Booster Getting Started with DCC Digital Command Control (DCC) is a versatile standard for model railways that continues to evolve. Our recent DCC project articles have included some basic background information; this article provides an in-depth guide to using the Decoder and Base Station, plus more details on DCC. W e have covered the background and workings of DCC in a few different articles over the years. We have also produced several related projects, including the recent DCC Decoder and DCC Base Station. The Decoder article included a glossary, which you might find useful if you are new to DCC. Even if you aren’t using our hardware, you might find it to be a handy guide. There is a vast range of model railway gear available that is DCC-­ compatible, or can be modified to work in a DCC system. We can’t provide enough detail to address every scenario or manufacturer, so we’ll assume you have some basic knowledge of the operation of model railways under DC or analog control, and the related electrical principles. The DCC Decoder project showed a simple example of fitting our Decoder to a small N-scale mechanism, with some general advice. If you aren’t sure about your locomotives and rolling stock, a web search for the manufacturer and model appended with “convert to DCC” can be a good start. You should verify that your locomotives will run well on DC before undertaking the conversion. While DCC has many talents, it won’t help if a locomotive is not in good mechanical shape. This includes making sure that the motor and gearbox are lubricated and running smoothly. You should also check that the wheels and the track pickups are clean. Power supply We used a regulated 12V 2.5A power supply for most of our testing, and found it to be perfectly adequate. The driver ICs have a low on-resistance, so the track voltage will be very close to the supply. 12V is the rated voltage for the motors in many locomotives around N & HO scales. So a 12V supply should be suitable if you are starting out with our Decoder and Base Station. siliconchip.com.au The over-current sensing of the Base Station is intended to be fast, since short circuits are very possible. A metallic item dropped on the track, or a derailed vehicle, can create a direct connection between the rails. Our tests showed reaction times of around 200μs to shut off power in such a condition. A discharged capacitor can appear like a short circuit, which is why the keep-alive capacitor on the Decoder is charged through a resistor. It’s not advisable to connect large capacitors directly to the Decoder supply rails. Sound-equipped decoders can be troublesome in this regard, since they usually include large capacitors to ensure that sounds are played without interruption. Our DCC Decoder We noted in the Decoder article that our Decoder design offers a few handy connections that are not seen in many commercial decoders. We wouldn’t be surprised if our readers use DCC to add ‘bells and whistles’ to their rolling stock, but there are a few things to check before doing so. Normally, the 12V BLUE connection works as the supply for the function outputs, which are switched on by having their negative terminals pulled to circuit ground by the Mosfet drains. It’s also possible to power a fixed output by connecting it between the BLUE pad and the ground pad, both shown in Fig.1 overleaf. A high-value capacitor directly connected here would appear like a short circuit to the Base Station at switch-on. Incandescent globes, which have a low resistance when cold, might behave similarly. So these things should be approached with care or avoided entirely. A continuous load can also interfere with programming, since it will draw current in a similar fashion to Australia's electronics magazine an acknowledgement signal. Our Base Station measures the quiescent current during programming to help differentiate the acknowledgement, but it’s possible that a heavy load will cause excessive drop across the 33W resistors and not leave enough voltage to power the Decoder. One way to avoid this is to provide a switch of some sort to disable such a load when needed. Since space is often tight in a scale locomotive, a pair of header pins closed by a jumper shunt could be an option. A couple of small LEDs (with their ballast resistors) should be fine and will help give an indication of when power is present at the Decoder. Drawing power from the 3.3V and ground connections (also shown in Fig.1) will present much the same concerns. Be aware that the 3.3V regulator must be able to handle any extra dissipation caused by an external load current. Thus, we suggest that no more than 10mA load be applied to the 3.3V connection. A separate regulator could be fed from the 12V BLUE connection if you need a lower-voltage and/or higher-current regulated supply. The track Trackwork is the other aspect that may need attention. For example, you should already know about running feeder wires and how power is routed through things like points and crossings. Some points (or turnouts/ switches, as they might be known) can make or break certain connections depending on how they are set. Many sets of points are designed to isolate unused tracks, making it easier to operate multiple locomotives on a DC power supply, since the isolated tracks can be used to change which trains respond to an analog controller. Peco’s InsulTrack system is an example of this. A good rule of thumb with DCC is to January 2026  49 Fig.1: These are the connections to the Decoder as presented last month. The 12V and 3.3V connections can be handy, but there are a couple of provisos that must be observed. Fig.2: the problem caused by a so-called balloon loop is the potential for a short circuit at the place where the loop closes on itself. It is not limited to DCC operation, although it might not be apparent on some DC layouts where the points are used to switch track power. If you can run your finger along one rail and end up at a point on the other track opposite to where you started (such as following the outer track in this diagram), you might have such a loop. 50 Silicon Chip Australia's electronics magazine power all tracks at all times, since we can rely on DCC to ensure that each locomotive operates independently. One option is to divide the layout into electrically isolated sections with separate feeds, often called blocks. Many manufacturers provide insulated rail joiners for this purpose. This can allow a block to be isolated if there is a fault, such as a derailed train causing a short circuit. A separate switch, breaker or fuse can be used to control power to each block. Separate blocks also allow the locations of trains to be sensed electronically, by monitoring the current draw of the rolling stock within each of those blocks. We presented a design in Circuit Notebook of June 2023 to do just that (siliconchip.au/Article/15828). Being able to sense trains can allow for some clever operations, such as automatic operation of signals or level crossing lights. Some keen modellers have even used this as part of an automatic train control system. Another proviso is that some track arrangements that loop back on themselves (such as triangles and balloon loops) can cause problems, as you can see in Fig.2. These concerns are much the same for layouts that operate with DC. Some strategically placed insulated track joiners can also help with this. The DCC Reverse Loop Controller from October 2012 (siliconchip.au/ Article/494) explains the concern in more detail and provides a circuit that can be used to solve it from a different angle. The Loop Controller uses a DPDT relay to reverse the polarity of the DCC signal to avoid a short circuit; a manually operated DPDT switch can be used to test if this approach would work. If you are starting out with model railways for the first time, you don’t need much track to test the DCC Decoder and DCC Base Station. You might prefer to set up a length of standalone track to see what is possible, and to get an idea of how DCC behaves. Photo 1 shows the short test track we used during development and testing of the Decoder and Base Station. It will be a good idea to have a safe place at each end of the track in case you get a runaway. A circular track loop can help to lessen the damage that might occur if something goes wrong. One option is to put some tape on one rail to break siliconchip.com.au Fig.3: using a DPDT switch like this can make it easier to use the programming track. The locomotive can be driven onto the track while the switch is in the MAIN position (to the left). The switch is changed to the right (PROG) position so that the locomotive’s decoder can be programmed. Then the switch is returned to MAIN so that the locomotive can be driven away. Photo 1: we used 1m of ‘flexi-track’ as our initial test track. The track can be easily connected to the main or programming outputs on the Base Station using the pluggable terminal blocks. the circuit to the wheels if the locomotive gets too close to the end of the track. This can at least ensure that it isn’t able to launch itself off the workbench! You’ll need to move the locomotive between the main and programming tracks. We have seen some modellers use a DPDT switch to effect this, as shown in Fig.3. This allows locomotives to be driven onto the programming track, programmed, then driven away, instead of needing to be lifted from one to the other. Make sure that the switch is never in the programming position while a locomotive is sitting over the gap between the rails, since this may cause a short circuit between the programming track and mainline track circuits. For the arrangement in Photo 1, we can simply unplug the track and move the plug over to the other socket to connect our locomotive to the programming output. There is a negligible chance of a short circuit occurring with this technique. Programming CVs Configuration variables (CVs) are an aspect of DCC that does not have a parallel in DC or analog operation. CVs can be incredibly powerful, and at the same time, can be confusing and may cause unpredictable side effects if they are not understood. siliconchip.com.au If you have just fitted your first locomotive with a Decoder and want to simply test it out, you don’t need to worry about CV programming at all. The Decoder should respond to address 3 without any changes, and this will be sufficient to see that the Decoder installation has worked. If you have a handful of locomotives, we recommend sticking to using short (two-digit) addresses, since it is one less factor to worry about if things aren’t working. Even if your locomotive carries a three- or four-digit fleet number, the last two digits are usually unique enough to identify it, so they can be used as the short address. How CV programming works The details of CV programming are laid out in full in Section 9.2.3 of the DCC standards. Still, we’d like to offer a brief, practical overview for those who are interested in simply having something that works and how to fix it if it doesn’t. As we mentioned in the Base Station article, the Base Station sends out specific packets to the programming track to perform programming. Apart from the actual programming packets, there are ‘reset’ packets that form part of the sequence to ensure that programming only occurs when intended. When the Base Station sends out a packet, the Decoder may choose to Australia's electronics magazine acknowledge the packet by placing a 60mA (or higher) load on the programming track. This is the only means of the Decoder communicating back to the Base Station. The acknowledge is typically achieved by the Decoder briefly driving the locomotive motor for around 5ms; this can be seen by the locomotive appearing to twitch sporadically during programming. A handy side-effect of the 33W resistors on our Base Station is that this load will cause LED2 to briefly dim during an acknowledgement. Some modern motors we tested are so efficient that they would not even sink 60mA, which can hamper programming. On our Base Station, this condition is shown with the message “Low acks”. If you are sure that acknowledgements are occurring, the I2x multiplier can be increased to trick the Base Station into thinking that the correct amount of current is being sunk. Table 1 lists some of the messages that might be seen on the Base Station during programming. These appear in the top-right corner of the LCD. The table includes possible reasons for errors and potential solutions. We’ll concentrate on direct-mode programming, since this is generally the best mode to use; it is supported by both our Decoder and Base Station. January 2026  51 Table 1: DCC Base Station programming error messages Message Notes OK, done A successful read has occurred and the value shown for the CV contents is correct. Read OK A successful read of a long address has occurred and the value shown is correct. OK, verified A successful write has occurred and the data has been verified. Sent Since there is no acknowledgement possible in operations mode, this indicates that the programming packets were sent correctly. Out of range The CV number or value is out of the valid range. CV values are only eight bits (values between 0-255). Check the value before entering it again. Select mode No programming mode is selected. Cancelled The operation was cancelled by the user. Not supported Physical programming modes only support a limited range of CVs (1, 2, 3, 4, 7, 8 & 29). Check the CV or choose a different programming mode. Read error The Base Station did not receive the expected acknowledgement and the read did complete successfully. This is typically caused by poor track contact corrupting communication, but it may occur if the Decoder does not support the requested CV. Read error #1, Read error #2, Read error #3 These only occur in paged mode, since multiple packets must be sent to configure the Decoder’s page register before programming. Higher numbers indicate that the failure occurs at a later stage. Write error #1, Write error #2, Write error #3 Writing (in all modes) involves performing a write followed by a verify, so higher numbers suggest that the verify might have failed. In this case, the CV might contain the correct value, but it could not be confirmed. Not allowed In operations mode programming, writes to CV1, CV17, CV18 or CV29 are not permitted. Power off Operations mode programming cannot occur if the track power is off, so try switching it on, if safe to do so. No address There isn’t an address selected for the current L1-L5 tab, so there is no address to use for operations mode programming. Timeout Operations mode programming has not completed within the expected time. It may be that a fault has shut off the track power so that packets cannot be sent. Low acks Direct mode programming has not seen any acknowledgement activity. Check track contact and if you are sure that the Decoder is sending acknowledgements, or try adjusting I2x to increase sensitivity. Data error The two high bits of CV17 are not set as required for a valid long address. The decoder may or may not respond correctly. Value error The value of CV17 and CV18 is not in the range for a valid long address. The decoder may or may not respond correctly. Some of the CVs are also supported by operations mode programming, meaning that they can be edited on the main track. Unfortunately, there is no acknowledgement or read-back on the main track. The direct-mode programming packets fall into four categories: byte write, byte verify, bit write and bit verify; the Base Station uses all but the bit write method. Each CV is effectively an 8-bit value in an EEPROM location on the Decoder, so CV programming is little more than reading and writing these memory locations. A byte write updates an entire 8-bit 52 Silicon Chip value. The byte-write packet includes a 10-bit CV address and the new 8-bit value. If the Decoder receives the packets (two consecutive, identical packets must be received for security), and successfully performs the write to EEPROM, it responds with an acknowledgement. We can then send a byte verify command containing the 10-bit CV address and the 8-bit value, effectively asking, “Does the 10-bit address contain the 8-bit value?” An acknowledgement means “yes”. So performing and confirming a write to a CV is straightforward. Australia's electronics magazine Reading a CV is a bit more complex. We use the bit verify command instead; this includes a 10-bit CV address, a three-bit value (allowing one of eight bits to be selected) and one data bit. The question becomes, “Does the 10-bit address contain this data bit at the selected bit position?” Thus, 16 bit-verify commands are sent, both of two values (0 and 1) for each of the eight bit positions. If all is well, the Decoder will reply with eight acknowledgements out of 16. If we receive a different number of acknowledgements (or none), we know the data is incorrect. This is the advantage of direct mode, since the physical and paged modes can only perform a byte verify command. Without knowing what the value might be beforehand, the Base Station must cycle through all 256 byte values and receive exactly one acknowledgement to be sure of correctly reading the CV. You’ll come to recognise whether a CV read is occurring correctly. Since you can typically see or hear the locomotive twitching, you can count the eight acknowledgements as they happen. An unfortunate side-effect of the twitching is that the locomotive can move to a dead spot on the track, which can cause programming to fail. We find that simply holding the locomotive gently in place and applying gentle downward pressure (to enhance track contact) can help with programming. Patience is often the key. An important question is which CVs to program; we’ll cover these roughly in order of importance. CV29 CV29 is unique in that it contains several important but unrelated option bits. Our Decoder implements only three bits in CV29. If used with our Base Station (which only produces 128-step speed packets), bit 1 should be set (a value of 2) for compatibility. Bit 0 can be used to reverse the direction of the motor, while bit 5 selects between short and long addressing, which we will cover shortly. In case you aren’t familiar with binary arithmetic, the following offers specific CV values for our Decoder working with our Base Station. For our Decoder, CV29 can only have a value of 0-3 or 32-35. If the value is 0-3, the short address is used; otherwise, the long address is used. If CV29 siliconchip.com.au is odd, then the motor will operate in reverse compared to if it is even. If the value is outside this range, something may not be right. In summary, set CV29 to 2 if you want to use the short address or 34 if you want to use the long address. If the locomotive operates in the opposite direction to that expected, add 1, giving a value of either 3 or 35. One handy feature is that, once fitted with a decoder, the direction becomes intrinsic to the locomotive. A DC or analog locomotive will move in the same direction (along the track) after being picked up and rotated 180°, since both the track and motor direction have been reversed. DCC does not care about track polarity, so its ‘front’ is always the same end. Addressing The Decoder address is paramount. For this, you might find the glossary in the Decoder article to be a handy reference because there are three addresses that can be associated with a Decoder. The short address (CV1) is the first, and is set to 3 by default. You might hear this called the twodigit address, since all values from 1 to 99 are valid. Address 0 is never valid for any address type. For the very first DCC decoders, the short address was the only CV. The most significant bit (uppermost) of CV1 is always ignored. Values from 100 to 127 may work, but might be ignored by some systems, since packets to some of these addresses have the same format as service mode programming packets. It is best to avoid them. There is a long address that can be used instead; this can be from 1 to 10239 (40 × 256 – 1), so two CVs are needed to store the necessary 14 bits. CV17 holds the top six bits (in its six lower bits); it must also have its upper two bits set. Therefore, values of 192 to 231 are valid for CV17. CV18 simply holds the lower eight bits, and all values are possible. The long address might sometimes be called a four-digit address. Note that long addresses and short addresses can both take on values from 1 to 99, but they are not the same. For example, short address 42 and long address 0042 (written as four digits to show it is a long address) can both be used without conflict at the same time by separate decoders. Finally, there is a consist address siliconchip.com.au (CV19), which can be considered more dynamic. While the short and long addresses would probably be set once when the decoder is installed, the consist address allows a Decoder to be allocated an address on a more short-term basis. In DCC, a consist typically refers to two or more locomotives that are coupled together and thus should be operated in synchrony. Temporarily assigning the same consist address to all the locomotives in a consist allows this to happen transparently. The consist address, like a short address, is seven bits in length and responds to the same packet addressing scheme as other short addresses. The most significant bit is used to operate the locomotive in reverse to its normal direction, which is useful if it is coupled back-to-back with another locomotive. Briefly, if the consist address is set (ie, the lower seven bits are non-zero), the Decoder will respond to speed and function packets to this address. Otherwise, bit 5 of CV29 will decide whether long addressing (bit 5 set) or short addressing (bit 5 clear) is active. So there are five CVs that affect what address a Decoder responds to. It’s a good idea to check all these CVs if there is an apparent failure of the Decoder to respond to the selected address. Table 2 shows some example combinations and the resulting behaviour. We also found a handy online tool to calculate values for CV17, CV18 and CV29 at siliconchip.au/link/ac7x Speed and acceleration CV2, CV3, CV4, CV5 and CV6 control the speed and acceleration behaviour. It’s not necessary to change these, but we find that setting at least CV2 (start voltage) makes for more intuitive operation. Fig.4 shows in graphical fashion how CV2, CV5 and CV6 work. Their setting can vary depending on the motor and the condition of the Table 2: configuration variables related to addresses CV1 CV17 CV18 CV19 CV29 Behaviour 3 0 N/A N/A Bit 5 clear, eg, 2 Typical factory default; the Decoder will respond to short address of 3. 0 0 0 0 Bit 5 clear, eg, 2 Not valid for DCC; the Decoder will not respond to any packets. 3 0 0 21 N/A Since the consist address is set, the Decoder will respond to short address 21. 3 0 0 149 N/A 149 − 128 = 21. Since the consist address is set, the Decoder will respond to short address 21; the locomotive will operate with forwards and reverse swapped. N/A 209 120 0 Bit 5 set, eg, 34 (209 − 192) × 256 + 120 = 4472, and bit 5 in CV29 is set. The Decoder will respond to long address 4472. Photo 2: guides like this YouTube video can be helpful in finding tips and tricks for installing a DCC decoder. The 8-pin socket (above the right-hand brass flywheel) is common on locomotives labelled as ‘DCC-ready’, and conforms to the NEM652 standard. Matching plugs can also be found by searching online stores for NEM652. Source: https://youtu.be/h8YT16ZAKKY Australia's electronics magazine January 2026  53 locomotive. The general idea behind these CVs is to adjust the locomotive operation so its performance is similar to others on the layout. CV2 sets the voltage that is applied at the lowest speed step, so a good principle is that CV2 is set at a level that just causes the locomotive to start moving, eliminating the dead spot that would otherwise occur at the lower speed steps. The easiest way to do this is to simply run the locomotive a bit and determine the lowest speed step (as shown in the top line of the Base Station display) at which the locomotive moves. Note that it might require a higher step to get started than to continue moving. For example, our test subject chassis from the Decoder project starts moving at around step 17, but will continue if the speed is dropped to 12. This is due to the extra voltage needed to overcome static friction while stopped. We double this value to 24, since there are 127 speed steps, but CV2, CV5 & CV6 work on a scale up to 255. If you find that the top speed is too high, CV5 can be lowered to reduce this; the default value of 0 for CV5 means the same as 255 (ie, full voltage). Set this in a similar fashion, by finding a comfortable ‘fastest’ speed step value; double it, and program it into CV5. CV3 and CV4 control acceleration and deceleration. These should be treated with care, since high values (which mean slow acceleration) can make it appear that the locomotive is not responding to controls. Experiment with CV3 first, since keeping CV4 at 0 will allow prompt deceleration in an emergency. Values around 5 should allow you to get a feel for what is a useful value for CV3; you can then try a similar value in CV4. Keep in mind that all these CVs will interact to a degree. For example, changing the speed CVs (CV2, CV5, CV6) will change the apparent acceleration, since the voltage applied at each of the steps has changed. Function outputs Photo 3: the Flying Scotsman carries the fleet number 4472. Using the last two digits (72) will typically be enough to uniquely identify a scale model of it on small layouts. The default function output mapping of our Decoder is typical. The F0 control has two aspects, one that is active when forward is selected, and one in reverse. By default, these are mapped to the white (CV33=1) and yellow (CV34=2) decoder wires, respectively, and would be used to drive something like a directional headlight. Our Base Station has controls for F1, F2 and F3, so CV33-CV37 are meaningful. Each of these CVs corresponds to a bit in the commands sent in the function packets. The values in the CVs dictate which outputs respond when the packet has a specific bit set. The behaviour is a logical ‘OR’, so that if any bit AND function combination gives a non-zero result, the corresponding output switches on. With four outputs, each CV has four bits that can be set, so the valid values for CV33-CV37 are 0-15. A value of 0 means that a command will have no effect, while a value of 15 means that the command will activate all outputs. A simple example that you might find useful can be applied if you find that the headlights are operating in reverse. Changing CV33 to 2 and CV34 to 1 will swap this, so that the yellow wire operates in forward and the white wire in reverse. One alternate configuration we have seen is to set CV33 to 5 and CV34 to 6, meaning that the F1 output (green decoder wire) is active any time that the F0 control is on, and it does not matter which direction the locomotive is operating. This could be used to control the interior lighting in a railcar at any time that the headlight control (F0 on the Base Australia's electronics magazine siliconchip.com.au Fig.4: the red line on this graph shows how the values of CV2, CV5 and CV6 can be used to change the speed mapping of a decoder. The blue line shows the mapping that occurs if CV6 is left at its default value of 0, while the green line shows the mapping if both CV5 and CV6 are left at 0. 54 Silicon Chip Station) is active. Table 3 shows this configuration. Table 3: function & output mapping CV33 F0F CV34 F0R CV35 F1 CV36 F2 CV37 F3 Notes 2: Yellow wire CV47-CV64 are set aside as CVs that manufacturers can use for custom purposes. CV49-CV52 are often used to control special effects on the function outputs, such as flashing. The Decoder project article describes how the values in these CVs work for our Decoder. We have used CV47 to control the voltage compensation feature, which is also explained in the Decoder article. Remember that fixed address CV programming (specifically CV1, CV17, CV18 and CV29 for our Decoder) can only occur on the programming track. This still gives the option of programming other CVs on the main track with operations mode, although without the luxury of read-back and verification. This means that the speed, acceleration and function mapping outputs can all be changed on the main track. This might also be handy for remapping the CV49-CV52 function effects and seeing the results immediately. CV19 (the consist address) is permitted to be set in operations mode. Operations mode programming packets are received without regard for the consist address. In other words, operations mode programming packets should be sent to the fixed short or long address for the Decoder. This means the consist address can be reset by writing ‘0’ to CV19 at the fixed address. This means that the locomotives in a consist can and must be configured separately. In a so-called triple-header, it would make sense to disable the headlight of the middle locomotive, which can be done by programming the function mapping or special effects CVs off for just that locomotive. If you find that the Decoder configuration has been corrupted, our Decoder has a factory reset option that sets all the CVs back to their original values. It simply requires programming CV8 with a value of 8. This is listed in the standards, so other manufacturers should offer this feature. Once you do get your Decoder configured to your liking, it is a good idea to check the CVs by reading them back and noting down the values. This can form the basis of programming other Decoders, or can be a reference if you need to perform a factory reset. Other manufacturers will offer other CVs with different features, but the siliconchip.com.au 1: White wire 4: Green wire 1 2 4 4 5 6 8: Purple wire Total CV value 8 0 8 0 This configuration has the white and yellow wires operating as their defaults, with the white wire driving a headlight in the forward direction and the yellow for reverse, as long as the Base Station’s F0 control is on. The bits for the green wire being set (using values of 4) mean that it is also active when the F0 control is on, regardless of the direction of travel. Photo 4: this layout design from Les Kerr (see page 85 of the February 2024 issue) has two loop tracks, plus some sidings, and would be perfect for having a handful of trains running at the same time using the DCC Base Station. majority listed here are standardised. Operations With all that out of the way, you are probably looking forward to operating trains! With our Base Station, the touchscreen only gives access to one set of controls at a time, but you can set one locomotive moving, then switch to a different control with L1-L5 buttons. The previously activated locomotive will continue operating as set. If you have a continuous loop, it’s easy to set one train running around that loop and switch over to a different locomotive and use it to shunt in the sidings. Even if only one train is moving at a time, DCC makes it much Australia's electronics magazine easier to switch between controlling different trains. Expansion Next month, we plan to present our DCC Remote Controller. This add-on connects to the Base Station and provides an extra set of independent locomotive controls. The Remote Controller has a daisy-chain feature, so multiple can be added. The protocol it uses is quite simple. Any device that can generate asynchronous serial data at 9600 baud and 3.3V can send data to the Base Station and command DCC packets to be sent to the track. We’ll explain this further SC in the project article. January 2026  55 Words by Julian Edgar Circuit & PCBs by John Clarke Remotely switch up to six pairs of speakers connected to a single amplifier – or up to 18 pairs connected to three amplifiers! Remote Speaker Switch S peaker switches have been around for many years. Typically, they comprise a box with interlocked switches and connections to an amplifier and multiple pairs of speakers. To select one pair of speakers, you press the appropriate switch. However, these speaker switches have some major disadvantages. The first disadvantage of a conventional speaker switch is that nearly all use terminals that accept only lightgauge wiring. If you want to maintain thick wiring connections all the way from the amplifier to the speakers, for maximum sound quality or high power use, you can’t. The second disadvantage is that all the speaker and amplifier wiring connections need to be routed to where the switch is located – and that can be awkward. For example, if you want a wall-mounted switch that selects between three pairs of speakers, you need to find space inside the wall cavity for eight dual-conductor cables – six for the speakers and two for the amplifier. Especially if you are using heavyduty cable, that can be nearly impossible! Such a wiring approach also often requires overly long cable runs, reducing sound quality and limiting the power handling. The third disadvantage of a conventional speaker switch is that it works with only one amplifier. This is a significant problem if, for example, you 56 Silicon Chip are using one amplifier to power the main speakers and a second amplifier to power subwoofers in the same system. Operating the speaker switch will swap the main speaker output (eg, to a different room) but the subwoofers in the first room will continue operating, and those in the new room won’t start working! To do this changeover with a conventional speaker switch, you would need two switch boxes – one for each amplifier – and press two switches each time. Our new Remote Speaker Switch overcomes all those shortcomings – and gives more benefits besides. Firstly, in our system, the wallmounted speaker selection switch is remote from the main switching box. This means that the main box can be placed right next to the amplifier(s) – it doesn’t have to be anywhere near the selector switch. This approach greatly simplifies the speaker wiring. The connection between the speaker selector switch and the main box is via a plug-in Cat 5/6 cable. You can easily fit this single cable inside any wall cavity. In fact, thin white Cat 6 cables are available that can even be run down the inside corner of a room, while being nearly invisible. Secondly, while the Remote Speaker Switch PCB has the facility to switch two pairs of speakers, by using multiple daisy-chained PCBs, it allows you to select between up to six pairs of Australia's electronics magazine speakers. For example, you can have a pair of speakers in: • two outside areas • the lounge room • the games room • a home office • a bedroom Then, at the turn of the knob, you can select any one of these speaker pairs. Or, more simply, you can use one PCB to switch off an interior pair of speakers and switch on an exterior pair! Thirdly, the Remote Speaker Switch PCBs can be linked to allow the single wall selector to control multiple amplifiers, each working with their own speakers. For example, this will allow bi-amped speakers to be switched, or, as touched on earlier, systems with a second amplifier driving subwoofers. It is possible to switch up to three amplifiers and their associated speakers, so up to 18 speakers can be controlled! In our system, the wall selection switch uses LEDs to show the system status. One LED shows that the power is switched on, while another shows which pair of speakers is selected. The faceplate can be configured to match the number of speaker pairs you are switching. For example, while the switch has positions for six pairs of speakers, if you are switching only three pairs, you can configure the switch for three speaker positions siliconchip.com.au How the Switch is organised Let’s look now at how the Remote Speaker Switch can be organised. The building blocks of the system comprise the Relay Switching PCB and a Control Panel PCB, joined by Cat 5/6 cable. The simplest use of the Remote Speaker Switch is to switch between two pairs of speakers. To do this, you will need one Relay Switching PCB and one Control Panel PCB, as shown in Fig.1. To switch a single amplifier to more than two pairs of speakers requires more Relay Switching PCBs, with one more PCB for every two pairs of additional speakers. In all versions, only one Control Panel PCB is used. These additional Relay Switching PCBs are each configured slightly differently to suit their role. The selection of which speakers they will handle is made by positioning two siliconchip.com.au SILICON CHIMP LEFT SPEAKERS 2 RIGHT Ultra-LD Mk.3 Stereo Amplifier 2 x 135W RMS POWER INPUT 1 INPUT 2 INPUT 3 R + – VOLUME MUTE ACK L + – ON + LEFT AMP+ AMP– – 1, 3 O R 5 SPK+ SPK– + + – + – – 2 , 4 OR 6 SPK+ SPK– CON1 _ A NO NC NC NO CO M D2 4004 CO M COIL COIL 4004 2.2kW RLY2, RLY4 OR RLY6 2.2kW RLY1, RLY3 OR RLY5 D1 + _ A CON2 LED8 R1 100nF Q1 SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 1.5kW R3 FUSE TO SUIT PLUGPACK BC337 R5 D3 4004 CON3 AMP+ AMP– RIGHT A POWER LED1 S1 2 A 3 1 4 LED2 12 5 11 6 10 9 REV.A © 2025 7 8 CON5 SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 SPK+ SPK– 2 , 4 OR 6 R2 1.5kW Q2 100nF R4 R6 BC337 CON6 © 2025 (RJ-45 SOCKET) A LED7 SPK+ SPK– 1, 3 OR 5 REMOTE SPEAKER SWITCH 2.2kW GND +12V LED9 CON4 2.2kW and have only three speaker selection LEDs visible. The system can easily be expanded in the future. Extra relay boards can be plugged in, and the faceplate is easily removed and extra LEDs added for more speaker switch positions. Finally, because we are using heavyduty relays to do the switching, there is no audio degradation. We believe the Remote Speaker Switch has sufficient versatility to work in even complex home and commercial systems. LEFT SPEAKERS 1 RIGHT + > Versatile speaker selector with a wall-mounted rotary switch > Modular design is expandable to up to three amplifiers and 18 pairs of speakers > Simultaneously switches main and subwoofer amplifiers/speakers > Wall switch is configurable for the number of speaker pairs that can be selected > Uses standard household wall plate > LED indicators on Control Panel for power and selected speakers > Quick and easy plug-in Cat 5/6 cable connections > Terminal strips allow for heavy-duty speaker cables > Suitable for amplifiers up to 400W (4Ω) or 800W (8Ω) per channel > Can also switch 70/100V public address speakers > No signal degradation 01106252 REMOTE SPEAKER SWITCH resistors appropriately on the PCB – you can think of them as moveable links. Let’s call the two pairs of speakers that the relays switch Speaker Pair 1 and 2. To achieve this switching, the two 1.5kW resistors are positioned at the ‘Speaker 1 and 2’ positions on PCB 1. PCB 2, that will switch the next pair, needs to be configured to switch what we will call Speaker Pair 3 and 4. This is achieved by instead installing the two 1.5kW resistors at the ‘Speakers 3 and 4’ positions. These two PCBs will then work together, the first PCB switching speaker pairs 1 and 2, and the second PCB switching speaker pairs 3 and 4. As you’d then expect, to switch Speaker Pair 5 and 6 requires a third PCB, with this one configured with Australia's electronics magazine (RJ-45 SOCKET) (RJ-45 SOCKET) 01106251 REV.A FITS IN UB1 BOX The lead photos show the wall-mount rotary switch and Relay Switching board. The LEDs on the rotary switch show its position and power status. Also, the RJ-45 connectors on the Relay Switching board make connecting it to the Control Panel easy, and can be used to daisy-chain multiple boards to handle more speakers or amplifiers. ◀ Fig.1: the simplest use of the Remote Speaker Switch is to select between two pairs of speakers driven by a single amplifier. The Control Panel PCB is mounted on standoffs with the LEDs positioned through the drilled holes in the grid and face plates. The vertical RJ-45 socket is different from those used on the Relay Switching board. January 2026  57 L SPEAKERS 1 R L SPEAKERS 2 R L SPEAKERS 3 R L SPEAKERS 4 R L SPEAKERS 5 R L SPEAKERS 6 R AMPLIFIER 1 SILICON CHIMP Ultra-LD Mk.3 Stereo Amplifier 2 x 135W RMS POWER INPUT 3 MUTE ACK L + – ON + RIGHT CHANNEL CONNECTIONS NOT SHOWN FOR CLARITY. LEFT AMP+ AMP– 1, 3 OR 5 SPK+ SPK– + – + – 2, 4 OR 6 SPK+ SPK– LEFT AMP+ AMP– 4004 CON3 GND +12V SPK+ SPK– 1, 3 OR 5 SPK+ SPK– 2, 4 OR 6 CON5 CON6 (RJ-45 SOCKET) (RJ-45 SOCKET) (RJ-45 SOCKET) 1.5kW CON3 SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 REMOTE SPEAKER SWITCH © 2025 01106251 REV.A GND +12V FITS IN UB1 BOX L SPEAKERS 1 R A LED9 AMP+ AMP– RIGHT SPK+ SPK– 1, 3 OR 5 SPK+ SPK– 2, 4 OR 6 SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 R2 Q2 100nF 4004 A CON5 CON6 (RJ-45 SOCKET) (RJ-45 SOCKET) (RJ-45 SOCKET) NO BC337 R5 1.5kW CON3 SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 REMOTE SPEAKER SWITCH © 2025 L SPEAKERS 2 R 01106251 REV.A GND +12V FITS IN UB1 BOX L SPEAKERS 3 R NO COM D2 + R3 R6 BC337 NC NC A CON2 R1 D3 CON4 COM LED8 100nF Q1 R4 1.5kW _ COIL 2.2kW 4004 COIL 2.2kW 4004 R3 BC337 R5 D3 CON4 + R1 R4 R6 BC337 COM CON2 LED8 100nF Q1 4004 FUSE TO SUIT PLUGPACK D3 AMP+ AMP– RIGHT A NO RLY2, RLY4 OR RLY6 FUSE TO SUIT PLUGPACK _ R3 BC337 R5 Q2 100nF NC NC D1 D2 4004 A LED9 SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 NO FUSE TO SUIT PLUGPACK + SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 COM 2, 4 OR 6 SPK+ SPK– RLY1, RLY3 OR RLY5 _ COIL R2 CON2 LED8 100nF Q1 2.2kW COIL 1.5kW 4004 COM 2.2kW 4004 COIL 2.2kW 1.5kW NO RLY2, RLY4 OR RLY6 _ + R1 NC NC D1 D2 1, 3 OR 5 SPK+ SPK– – CON1 RLY1, RLY3 OR RLY5 + A NO LEFT AMP+ AMP– + – _ RLY2, RLY4 OR RLY6 _ COM 2, 4 OR 6 SPK+ SPK– CON1 RLY1, RLY3 OR RLY5 D1 1, 3 OR 5 SPK+ SPK– + – + CON1 + – 4004 R + – COIL INPUT 2 2.2kW INPUT 1 VOLUME L SPEAKERS 4 R LED9 AMP+ AMP– RIGHT SPK+ SPK– 1, 3 OR 5 SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 SPK+ SPK– 2, 4 OR 6 CON4 CON5 CON6 (RJ-45 SOCKET) (RJ-45 SOCKET) (RJ-45 SOCKET) R2 Q2 100nF R4 R6 BC337 1.5kW REMOTE SPEAKER SWITCH © 2025 L SPEAKERS 5 R 01106251 REV.A FITS IN UB1 BOX L SPEAKERS 6 R AMPLIFIER 2 SILICON CHIMP Ultra-LD Mk.3 Stereo Amplifier 2 x 135W RMS POWER INPUT 3 MUTE ACK L + – ON + RIGHT CHANNEL CONNECTIONS NOT SHOWN FOR CLARITY. LEFT AMP+ AMP– 1, 3 OR 5 SPK+ SPK– + – + – 2, 4 OR 6 SPK+ SPK– LEFT AMP+ AMP– GND +12V Q2 100nF CON5 CON6 (RJ-45 SOCKET) (RJ-45 SOCKET) (RJ-45 SOCKET) R4 R3 R6 BC337 1.5kW BC337 R5 CON3 SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 REMOTE SPEAKER SWITCH © 2025 01106251 A REV.A GND +12V FITS IN UB1 BOX L SPEAKERS 1 R LED9 AMP+ AMP– RIGHT SPK+ SPK– 1, 3 OR 5 SPK+ SPK– 2, 4 OR 6 SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 R2 Q2 100nF 4004 A CON5 CON6 (RJ-45 SOCKET) (RJ-45 SOCKET) (RJ-45 SOCKET) NO BC337 R5 1.5kW CON3 SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 REMOTE SPEAKER SWITCH © 2025 L SPEAKERS 2 R 01106251 REV.A GND +12V FITS IN UB1 BOX L SPEAKERS 3 R NO COM D2 + R3 R6 BC337 NC NC A CON2 R1 R4 1.5kW COM LED8 100nF Q1 D3 CON4 _ COIL 2.2kW 4004 COIL + CON2 R1 D3 CON4 COM 2.2kW 4004 A LED8 100nF Q1 4004 FUSE TO SUIT PLUGPACK 4004 CON3 SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 SPK+ SPK– 2, 4 OR 6 NO RLY2, RLY4 OR RLY6 FUSE TO SUIT PLUGPACK _ R3 BC337 R5 D3 SPK+ SPK– 1, 3 OR 5 NC NC D1 D2 4004 A LED9 AMP+ AMP– RIGHT NO FUSE TO SUIT PLUGPACK + SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 COM 2, 4 OR 6 SPK+ SPK– RLY1, RLY3 OR RLY5 _ COIL R2 CON2 LED8 100nF Q1 2.2kW COIL 1.5kW 4004 COM 2.2kW 4004 COIL 2.2kW 1.5kW NO RLY2, RLY4 OR RLY6 _ + R1 NC NC D1 D2 1, 3 OR 5 SPK+ SPK– – CON1 RLY1, RLY3 OR RLY5 + A NO LEFT AMP+ AMP– + – _ RLY2, RLY4 OR RLY6 _ COM 2, 4 OR 6 SPK+ SPK– CON1 RLY1, RLY3 OR RLY5 D1 1, 3 OR 5 SPK+ SPK– + – + CON1 + – 4004 R + – COIL INPUT 2 2.2kW INPUT 1 VOLUME L SPEAKERS 4 R LED9 AMP+ AMP– RIGHT SPK+ SPK– 1, 3 OR 5 SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 SPK+ SPK– 2, 4 OR 6 CON4 CON5 CON6 (RJ-45 SOCKET) (RJ-45 SOCKET) (RJ-45 SOCKET) R2 Q2 100nF R4 R6 BC337 1.5kW REMOTE SPEAKER SWITCH © 2025 L SPEAKERS 5 R 01106251 REV.A FITS IN UB1 BOX L SPEAKERS 6 R AMPLIFIER 3 SILICON CHIMP Ultra-LD Mk.3 Stereo Amplifier 2 x 135W RMS POWER INPUT 3 MUTE ACK L + – RIGHT CHANNEL CONNECTIONS NOT SHOWN FOR CLARITY. LEFT AMP+ AMP– 1, 3 OR 5 SPK+ SPK– ON + + – + – 2, 4 OR 6 SPK+ SPK– LEFT AMP+ AMP– 4004 CON3 CON5 CON6 (RJ-45 SOCKET) (RJ-45 SOCKET) (RJ-45 SOCKET) 2.2kW LED1 S1 A 2 A 3 1 4 LED6 LED2 12 5 A 11 6 A 10 LED5 REV.A © 2025 9 A LED4 7 8 1.5kW BC337 R5 CON3 LED3 01106252 REMOTE SPEAKER SWITCH Silicon Chip 01106251 REV.A FITS IN UB1 BOX GND +12V SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 A LED9 AMP+ AMP– RIGHT SPK+ SPK– 1, 3 OR 5 SPK+ SPK– 2, 4 OR 6 SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 R2 Q2 100nF CON5 CON6 (RJ-45 SOCKET) (RJ-45 SOCKET) (RJ-45 SOCKET) BC337 R5 1.5kW CON3 © 2025 REV.A FITS IN UB1 BOX NC NC NO COM D2 + REMOTE SPEAKER SWITCH 01106251 NO A CON2 R1 R3 R6 BC337 D3 CON4 COM LED8 100nF Q1 R4 1.5kW 4004 A RLY2, RLY4 OR RLY6 _ COIL 2.2kW 4004 COIL 2.2kW 4004 COIL R3 R6 BC337 © 2025 A POWER R4 D3 CON4 A LED7 SPK+ SPK– 2, 4 OR 6 COM + R1 REMOTE SPEAKER SWITCH 2.2kW GND +12V SPK+ SPK– 1, 3 OR 5 NO CON2 LED8 100nF Q1 4004 FUSE TO SUIT PLUGPACK D3 AMP+ AMP– RIGHT A NC NC GND +12V SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 FUSE TO SUIT PLUGPACK _ R3 BC337 R5 Q2 100nF NO D1 D2 4004 A LED9 SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 COM 2, 4 OR 6 SPK+ SPK– RLY1, RLY3 OR RLY5 _ FUSE TO SUIT PLUGPACK + SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 2.2kW R2 4004 COIL 1.5kW CON2 LED8 100nF Q1 58 COM 2.2kW 4004 COIL 2.2kW 1.5kW NO RLY2, RLY4 OR RLY6 _ + R1 NC NC D1 D2 1, 3 OR 5 SPK+ SPK– – CON1 RLY1, RLY3 OR RLY5 + A NO LEFT AMP+ AMP– + – _ RLY2, RLY4 OR RLY6 _ COM 2, 4 OR 6 SPK+ SPK– CON1 RLY1, RLY3 OR RLY5 D1 1, 3 OR 5 SPK+ SPK– + – + CON1 + – 4004 R + – COIL INPUT 2 2.2kW INPUT 1 VOLUME LED9 AMP+ AMP– RIGHT SPK+ SPK– 1, 3 OR 5 SPK+ SPK– 2, 4 OR 6 CON4 CON5 CON6 (RJ-45 SOCKET) (RJ-45 SOCKET) (RJ-45 SOCKET) SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 R2 Q2 100nF R4 R6 BC337 1.5kW REMOTE SPEAKER SWITCH © 2025 01106251 REV.A FITS IN UB1 BOX Fig.2: up to six pairs of speakers can be driven, one pair at a time, by a single amplifier; as shown in the dashed box. This approach is ideal for switching between speakers in different rooms. If fewer than six sets of speakers are used, some relays and/or boards can be omitted, and the number of LEDs fitted to the Control Panel would be reduced. This whole diagram shows the outputs of three amplifiers, with each able to be switched between up to six speaker pairs. This is ideal for speaker bi-amping (or tri-amping!) and can also be used with systems using separate amplifiers for the main speakers and subwoofers. The input signals to the amplifiers can be different. Australia's electronics magazine siliconchip.com.au the two 1.5kW resistors at the ‘Speakers 5 and 6’ position. Refer to dashed box in Fig.2 for these configurations. Note how in Fig.2, all the Relay Switching PCBs and the Control Panel are connected by Cat 5/6 cables. The amplifier is connected to each Switching PCB. The interconnecting cables supply power to the extra PCBs, so separate power connections don’t need to be made. As you can also see in this figure, in this configuration, not all the RJ-45 connectors need to be installed on the PCBs. Furthermore, on the PCBs powered by the Cat 5/6 cables, you do not need to install the input power terminal strip or the fuse holder. You only need to have those on one of the boards. What about driving multiple pairs of speakers from multiple amplifiers? If running more than two pairs of speakers from each amplifier, the resistor positions on the PCBs are configured just as was described above. That is, the PCB for Speaker Pair 1 and 2 use resistors placed at the ‘Speaker 1 and 2’ positions, the PCB for Speaker Pair 3 and 4 use resistors at the ‘Speakers 3 and 4’ positions, and PCB for Speaker Pair 5 and 6 use resistors positioned at ‘Speakers 5 and 6’ positions. As before, the PCBs are linked by Cat 5/6 cables, with one of PCBs connected to the switch. However, in this configuration, each set of PCBs is fed by a separate amplifier, as shown in Fig.2. As you can also see in Fig.2, not all the RJ-45 connectors need to be installed on the PCBs – the exception is the PCB that also connects to the switch. It uses all three connectors. If you are switching two amplifiers that each drive two pairs of speakers, you need just two Relay Switching PCBs. This would be the case if you were switching a system that, for example, used two amplifiers to drive inside and outside main speakers and subwoofers. In this case, on each PCB, the ‘Speaker 1 and 2’ resistor positions would be used, as shown in Fig.3. Incidentally, while we have been talking about switching from one pair of speakers to another, there are also switch positions where no speakers are connected. You will need one Relay Switching PCB to handle 1-2 speakers, two PCBs to handle 3-4, or three PCBs for 5-6 speakers. This applies regardless of whether you are using one or more amplifiers. siliconchip.com.au Parts List – Remote Speaker Switch 1 12V DC plugpack (100mA+ for each Relay Switching board) 1+ Relay Switching boards (see below) 1 Control Panel board (see below) various Cat 5, Cat 5E or Cat 6 patch leads with lengths to suit the installation Relay Switching board (per board) 1 double-sided, plated-through PCB coded 01106251, 132 × 80mm 2 DPDT 12V 10A cradle relays (RLY1, RLY2) [Altronics S4311, Jaycar SY4008] 2 6-way barrier terminals with 8.25mm pin spacings (CON1, CON2) [Altronics P2106] 1 2-way PCB screw terminal, 5/5.08mm Pitch (CON3) ♦ [Altronics P2038, Jaycar HM3172] 3 8P8C RJ-45 Ethernet PCB sockets (CON4-CON6) [Altronics P1448A] • 2 M205 PCB fuse clips (F1) ♦ 1 M205 fuse, current rating to suit plugpack (F1) ♦ 2 BC337 45V 0.8A NPN transistors (Q1, Q2) 3 1N4004 400V 1A diodes (D1-D3) 2 3mm or 5mm red LEDs (LED8, LED9) 2 100nF 63/100V MKT polyester capacitors 2 2.2kW ¼W axial resistors 2 1.5kW ¼W axial resistors 1 UB1 Jiffy box (optional) 4 6.3mm M3-tapped spacers and short M3 machine screws (optional) • can be reduced to 1 for a single Relay Switching board or 2 for the first and last boards in a string ♦ only required on one board Control Panel board (one required) 1 double-sided, plated-through PCB coded 01106252, 43 × 61mm 1 standard electrical wall plate 1 Clipsal Classic blank grid and plate [C2031VX-WE] 1 single-pole, 12-way PCB-mounting rotary switch (S1) [Altronics S3021, Jaycar SR1210] 1 knob to suit S1 (6.35mm/¼in shaft) 1 8P8C RJ-45 vertical top entry socket (CON7) [Altronics P1468] 7 3mm or 5mm standard brightness LEDs (LED1-LED7) • 2 2.2kW 1/4W axial resistors 4 20mm nylon M3-tapped spacers 4 M3 × 10mm countersunk head machine screws 4 M3 × 10mm panhead machine screws • reduce quantity if switching fewer than six pairs of speakers The Clipsal grid plate with the Control Panel PCB mounted on the rear (left). Note the use of countersunk screws to hold the board in place. These are needed so that the cover plate (right) will correctly slip into place. The drilled grid plate is used as a template to drill the cover plate. Australia's electronics magazine January 2026  59 In the above example, we used two amplifiers, each driving main speakers and subwoofers, and we used the Switch to change from inside to outside speakers. But what if you don’t have outside subwoofers? In that case, you’d simply connect nothing to the ‘outside’ output of the Switch connected to the subwoofer amplifier, so that when you switch from inside to outside, all the inside speakers switch off, but only the main outside speakers switch on. It’s also easy to switch off all the speakers from the remote panel. In fact, there is an ‘off’ switch position between the detent for every pair of speakers. This approach has been taken for two reasons. First, the ‘off’ position is only ever one click away – you don’t need to rotate the switch all the way back to the starting point to switch the speakers off. Second, providing an ‘off’ position between every speaker selection setting ensures that two pairs of speakers can never be momentarily operating. It gives time for the relay to switch off before the next one switches on. Finally, the Remote Speaker Switch LEFT SPEAKERS 1 RIGHT SILICON CHIMP can also switch 70/100V public address (PA) speakers. In this application, the Switch’s wiring connections are just as they are for 4/8W speaker systems; with 70/100V systems, many more speakers can be on the one circuit. Circuit details The circuit is shown in Fig.4. It is divided into two sections: the Control Panel that has the rotary switch, and the Relay Switching section, where the relays are powered on or off for the speaker switching. Both the Control LEFT SPEAKERS 2 RIGHT Using the Switch with a remote amplifier Ultra-LD Mk.3 Stereo Amplifier 2 x 135W RMS One reason we included a power-on LED on the Control Panel (LED7) is for use with remote amplifiers, ie, where the amplifier is inaccessible (eg, mounted in an equipment cabinet or roof space). In this case, you likely have the ability to remotely switch the amplifier’s power on and off. By powering the Remote Speaker Switch from the same source, the power indicator LED on the Control Panel will also tell you when the amplifier is (or amplifiers are) on. POWER INPUT 1 INPUT 2 INPUT 3 R + – VOLUME MUTE ACK L + – ON + LEFT AMP+ AMP– + – 1, 3 OR 5 SPK+ SPK– + – + – – 2, 4 OR 6 SPK+ SPK– CON1 _ NO NC NC NO COM D2 4004 COIL 4004 A COM COIL + 2.2kW RLY2, RLY4 OR RLY6 2.2kW RLY1, RLY3 OR RLY5 D1 + A _ CON2 LED8 R1 100nF Q1 SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 1.5kW R3 D3 FUSE TO SUIT PLUGPACK BC337 R5 4004 CON3 GND +12V LED9 AMP+ AMP– RIGHT CON4 SPK+ SPK– 1, 3 OR 5 SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 SPK+ SPK– 2 , 4 OR 6 CON5 R2 1.5kW Q2 100nF R4 R6 BC337 CON6 REMOTE SPEAKER SWITCH © 2025 (RJ-45 SOCKET) SILICON CHIMP 01106251 (RJ-45 SOCKET) (RJ-45 SOCKET) REV.A FITS IN UB1 BOX LEFT SUBWOOFERS 1 RIGHT LEFT SUBWOOFERS 2 RIGHT + + Ultra-LD Mk.3 Stereo Amplifier 2 x 135W RMS POWER INPUT 1 INPUT 2 MUTE ACK L + – A + – + – – 2, 4 OR 6 SPK+ SPK– RLY2, RLY4 OR RLY6 11 _ COM NO NC NC NO COM D2 4004 5 2.2kW LED2 12 COIL D1 4 2.2kW RLY1, RLY3 OR RLY5 A 3 COIL 2 4004 S1 1, 3 OR 5 SPK+ SPK– CON1 LED1 1 6 A 01106252 REMOTE SPEAKER SWITCH Fig.3: a common use for the Remote Speaker Switch is to switch the output of two amplifiers, one powering the main speakers and the other powering one or two subwoofers. For example, the same amplifiers can be used to drive inside or outside speakers. + LED8 100nF Q1 R1 1.5kW R3 BC337 R5 D3 A CON2 CON3 GND +12V SPEAKER 1 OR SPEAKER 3 OR SPEAKER 5 F1 FUSE TO SUIT PLUGPACK REV.A © 2025 7 8 4004 9 _ 10 Silicon Chip – + LED7 LEFT AMP+ AMP– A POWER 60 ON 2.2kW 2.2kW INPUT 3 R + – VOLUME LED9 AMP+ AMP– RIGHT CON4 SPK+ SPK– 1, 3 OR 5 CON5 SPK+ SPK– 2, 4 OR 6 SPEAKER 2 OR SPEAKER 4 OR SPEAKER 6 R2 1.5kW Q2 100nF R4 R6 BC337 CON6 REMOTE SPEAKER SWITCH © 2025 (RJ-45 SOCKET) (RJ-45 SOCKET) (RJ-45 SOCKET) 01106251 REV.A FITS IN UB1 BOX siliconchip.com.au Subscribe to DECEMBER 2025 ISSN 1030-2662 12 The VERY BEST DIY Projects ! 9 771030 266001 $14 00* NZ $14 90 RGB INC GST INC GST LED Star Pre-assembled and ready to decorate in time for Christm as HOW TO DESIGN YOUR OWN PC All the steps needed to make and order your own printed circuit boards BS DCC Decoder for model locomotives Australia’s top electronics magazine 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. HUMANOID ROBOTS 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! RGB LED Star; December 2025 Humanoid Robots; November-December 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 Are Cat 5/6 cables necessary? We chose to use 8P8C connectors and RJ-45 cables to link the boards because they are inexpensive, easy to use, available in a wide range of lengths, and make the system modular. However, if you want to do the extra work, there is nothing stopping you from soldering any multi-core cable with eight conductors (or more) directly between the boards. This allows the use of suitably terminated old multi-core telephone cable etc. However, we don’t think the small cost saving is worth the extra work. If you decide to do this, make sure they are all soldered pin 1 to 1 through to pin 8 to 8. Note that, with the Cat 5/6 network cables, you must use straight-through cables rather than crossover cables. Panel and the Relay Switching sections include indicator LEDs. This split matches the separation of components between the two PCBs. The Control Panel uses a single-pole 12-way (SP12T) rotary switch (S1) to select the speakers you require. Relays in the Relay Switching section handle the actual switching between the amplifier and speaker. On the Control Panel, one LED indicates each switch position. None are lit in the off positions, but one (from LED1 to LED6) will light when a set of speakers is selected. The rotary switch can be limited to positions 1 to 4, allowing the selection of either Speaker 1 at position 2 or Speaker 2 at position 4. Positions 1 and 3 are off positions. For more speaker selections, the switch can be set to operate up to position 6 for an extra speaker selection (Speaker 3), or to position 8 for another selection (Speaker 4). Similarly, position 10 selects Speaker 5 and position 12, Speaker 6. The wiper of switch S1 is connected to a 12V supply, and when the switch is in one of positions 2, 4, 6, 8, 10 or 12, the LED connected to these terminals (LED1 to LED6) will light due to the current flowing through the 2.2kW resistor to ground. At the same time, the switched 12V is connected to a terminal on CON7, an RJ-45 socket. Power is also supplied to this socket at pins 1 and 2. This socket is connected to the Relay Switching board(s) via a Cat 5/6 cable. LED7 lights via a current limiting 2.2kW resistor that’s connected to the 12V supply. This indicates that there is 12V supplied from the Relay Switching board through CON7. The relay switching circuitry mainly comprises two relays, RLY1 & RLY2, for switching two sets of stereo 62 Silicon Chip speakers. To switch extra speakers, another board with identical circuitry can be built. The first circuit is for Speaker 1 (RLY1) and Speaker 2 (RLY2), the second for Speaker 3 and Speaker 4, and the third circuit for Speaker 5 and Speaker 6. These boards are interconnected using daisy-chaining 8-wire Cat 5 or Cat 6 leads between CON6 on one board and CON4 on the next. The relay coils are not directly driven from the switch contacts because the switch contacts are only rated for 150mA, and each relay draws 75mA when powered. Since more than one relay could be driven at the one time, the contact current will reach or exceed the switch rating, reducing the switch’s life. Therefore, an NPN transistor is used to drive each relay coil (Q1 or Q2) and only the base current (just under 3mA) used to drive that transistor is passed through the switch contact. Transistor Q1 is used to drive RLY1, while transistor Q2 drives RLY2. In the first circuit for Speaker 1 and Speaker 2, the bases of Q1 and Q2 will be driven via resistors R1 and R2, respectively. When building the second circuit for Speaker 3 and Speaker 4, the transistor bases are driven via resistors R3 and R4 instead. The third circuit, for Speaker 5 and Speaker 6, has the bases of Q1 and Q2 driven via R5 and R6. Each relay coil has a normally reverse-biased diode (D1 for Q1 and D2 for Q2) across it. This shunts the back-EMF from the coil when the transistor switches off. The 100nF capacitor across the 12V supply provides a reservoir for this charge, so the 12V rail’s voltage doesn’t increase much each time the relay switches off. There is also one LED across each Australia's electronics magazine Fig.4: the Control Panel (left) uses a 12-position rotary switch with indicator LEDs. The Relay Switching board (right) uses two transistors to drive the relays that switch the speaker connections. The RJ-45 sockets allow easy connection to the Control Panel and other relay boards used to expand the system. relay coil that lights when the relay is on. The Altronics relays include an internal indication relay, but other, compatible relays may not. In addition, the internal LEDs require the coil to be connected with a specific polarity, while the external LED orientation is designed to suit the drive arrangement, regardless of the coil orientation. Power for the circuit is via a nominally 12V DC plugpack. Fuse F1 adds protection if a short circuit occurs, while diode D3 is connected in reverse across the supply so that if the supply is connected with the wrong polarity, the diode will conduct and the fuse will blow. The current requirement is up to 100mA for each set of two relays. So if you use three relay circuits, a 300mA plugpack is required. You can use a higher-rated plugpack. Each relay is used to drive a stereo pair (left and right) speakers from an amplifier, switching the positive (+) amplifier terminals. The negative terminals (−) of each stereo amplifier are permanently connected to the outputs, but the channel negatives are not joined. This allows siliconchip.com.au the use of bridge-mode amplifiers, which are increasingly common. In that case, the negative output terminals are not at ground, but actively driven to swing in the opposite voltage polarity to the positive terminals. Construction Both boards are straightforward to assemble. The Relay Switching board is built on a double-­sided PCB coded 01106251 that measures 132 × 80mm – see Fig.5. Fit the low-profile components first – the resistors, capacitors, diodes, LEDs and transistors. The position of the two 1.5kW resistors depends on whether this board will switch the first, second or third pair of speakers. The diodes, LEDs and transistors must be inserted the right way around – follow the markings on the PCB and in Fig.5. The longer lead of the LED is the anode (marked with an “A” on the PCB). Insert the terminal blocks for the power supply and speaker connections next. The speaker terminal blocks can go either way around, but the power supply terminal block’s openings must face the bottom of the PCB. Next, solder in the fuse clips, ensuring the tags that hold the fuse in place are on the outside at each end. The RJ-45 sockets can be soldered into place next. The solder pads are fairly close together, so check after soldering that you have not made any bridges – use a magnifying glass to do that if necessary. Finally, solder the two relays into Fig.5: the Relay Switching PCB is easy to build. The diodes, LEDs and transistors must be inserted the right way around. After soldering, check for bridges between the RJ-45 socket pins – these are quite close together. siliconchip.com.au Australia's electronics magazine January 2026  63 place. You will have to push down firmly to get the relay terminals to project sufficiently through the PCB. The number of RJ-45 sockets each board requires depends on the amplifier and speaker configurations you are switching – see Figs.1-3. Also, only one board requires the fuse holder and input power terminal strip – the remaining linked boards get their power feeds via the Cat 5/6 cable connections. Having said that, we chose to insert all these components on every board – it gives more versatility, should the system requirements change in the future. Building the Control Panel Making the Control Panel and mounting it takes several steps. We will assume that you are using the specified Clipsal Classic blank grid and cover plates. Copy or print out the drilling template (Fig.6) at actual size (100% scale) and position it on the grid plate. Ensure the position you have chosen on the grid plate will allow the PCB to fit within the wall opening. Use clear adhesive tape to hold the drilling template in place and then drill the four 3mm holes for the PCB standoff mounts. Countersink these holes by hand with a larger drill bit – the screws that mount the standoffs must be flush with the outer surface of the grid plate. Next, drill the holes for the power LED and switch position LEDs. Remember that you need to drill holes to match the number of speaker pairs you are switching; they can be either 3mm or 5mm holes, depending on what size of LEDs you have chosen to use. Now drill the 10mm hole for the Fig.6: the drilling template for the Control Panel. All dimensions are in millimetres, and this diagram is shown at 100% scale. shaft of the rotary switch. It is not held in place with its shaft mounting nut; instead, it is held by the PCB. If you are switching fewer than six pairs of speakers, the nut & washer will need to be removed, and the switch rotated fully anti-clockwise, before you can access the tab washer that sets the number of positions the switch can move through. You will also likely have to shorten the shaft of the switch to suit the knob you are using. This is easiest done by placing the shaft in a bench vice and using a fine-tooth hacksaw to cut the plastic shaft to length. Clip the faceplate over the grid plate and, using the drilled grid plate as the template, drill the faceplate holes from the rear – that is, the holes for the shaft and all LEDs. Do not drill the four holes for the PCB mounts through the faceplate! Deburr all the drilled holes in both plates with a larger diameter drill bit by hand. Now it’s time to assemble the Control Panel PCB, which is coded 01106252 and measures 43 × 61mm – refer to Fig.7. Solder the two 2.2kW resistors to the PCB, then mount the rotary switch. Attach the nylon standoffs to the PCB. Insert the leads of one of the LEDs into the holes in the board, then offer the PCB up to the rear of the grid plate. You can then easily push the LED through the appropriate grid plate hole before soldering the LED leads into place, making sure the longer lead goes into the hole for the anode (“A”). Repeat the process for each of the LEDs. Doing it this way means the LED leads are all precisely the correct length (LEDs with short leads may need tinned copper wire extensions). The switch rotates clockwise, as viewed from the front. Insert the first LED in the upper-most PCB position – this is, for the first pair of speakers. Install the LED for the next pair of speakers in the next clockwise PCB position – and so on, for the number of speaker pairs you are switching. Note that the power LED is optional – if you don’t want it, you can leave it out. Now solder the RJ-45 socket into place, noting that it is placed on the underside of the PCB and is a vertical (top-entry) socket, unlike those on the Relay Switching board. Mount the PCB to the grid plate using the previously attached nylon standoffs and countersunk head 3mm screws. Remember to feed the LEDs through their appropriate holes as you mount the PCB. Check that the drilled cover plate neatly fits over the grid plate and clips into place. Testing When you have finished building the switch and relay boards, check the soldering carefully with a magnifying glass. You are looking for cold joints (dull finish), incomplete soldering or solder bridges. Connect the Control Panel and Relay Switch boards with a Cat 5/6 cables. You can connect one at a time for testing if you’ve fitted the power supply Fig.7: there are just a few components on the Control Panel board so it shouldn’t take long to assemble, but prepare the switch plates first, as described in the text. You only need to install the LEDs that you want or need, ie, one per set of speakers switched (LED1-LED6), plus the power indicator (LED7), if desired. 64 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.8: the cutting details for the optional Jiffy box enclosure for a Relay Switching board. The hole positions shown suit a PCB attached to the base using 6.3mmtall standoffs. components to all of them; it doesn’t matter which connector the cable goes into on the Relay Switch board. Otherwise, connect the Control Panel to the Relay Switch board that has the power supply input. Apply 12V power and rotate the speaker selection knob. One relay (and its associated LED) should activate with the switch knob at the uppermost (12 o’clock) position, then switch off at the next clockwise switch click. Another relay and LED should activate at the next clockwise click. If all is well and you are using multiple Relay Switching boards, switch off power and use another Cat 5/6 cable to daisy-chain the next Relay Switch board. Switch the power back on and check that this works as required – depending on your switching arrangement, either the second board will mimic the behaviour of the first, or its relays will activate at further switch positions. Continue the testing until you’ve verified that all the boards are working. Mounting it The rotary switch is designed to mount behind a standard wall plate. However, if you wish, the Control Panel could be mounted in a box. The relay board fits in a UB1-sized Jiffy box using 6.35mm standoffs. If you are using multiple Relay Switch boards, multiple Jiffy boxes can be used, side-by-side or on top of each other. Fig.8 shows the template for cutting holes in the box sides to allow access to the RJ-45 sockets. However, as the boxes are likely to be hidden from view, round holes could instead be drilled at each of these positions – this will be quicker and easier. To allow the speaker and amplifier connections to the terminal strips, cut a rectangular hole in the appropriate wall of the box or drill a hole. Installation We’ll initially assume that you are Driving speakers in parallel switching one amplifier between two pairs of speakers. Connect one pair of speakers to the Relay Switching board. Using the “Spkr 1,3 or 5” terminals, make both the left and right speaker connections. Then connect the amplifier’s outputs to the board, again to the left and right inputs. Power up the switching system and amplifier. The speakers should work when the switch is set to position 1, and be muted with the switch in other positions. When that is working, power it off and connect the second pair of speakers, using the “2,4 or 6” terminals. You should then be able to switch between the two pairs of speakers. For more complex switching, start with the simplest switching and then build the system from there, checking each step by playing audio and confirming that the speakers are working properly. With complex systems, there are a lot of wires to connect, so always test the system step-by-step rather than SC connecting everything at once. Only the ‘master’ board needs the input power terminal strip and the fuse – the other boards will receive power via the interconnecting Cat 5/6 cables. The Remote Speaker Switch does not allow the operation of multiple pairs of speakers at once. That is, it can connect Pair 1 or Pair 2 to an amplifier, but not Pair 1 and Pair 2 at the same time. This means that, assuming all the speakers have the same impedance, the impedance seen by the amplifier does not change, irrespective of the selected speakers. However, if the amplifier is wired to drive two pairs of speakers, the Remote Speaker Switch can switch between multiple sets. For example, let’s say the speakers are all 8W and the amplifier is happy with a 4W load. You can wire two pairs of speakers in parallel, so that each channel has two speakers (four in total), and each channel gives a 4W load to the amplifier. Then, you can use the Switch to alternatively select another four speakers, wired in the same way. So, while we have shown only one pair of speakers connected to each Remote Switch output, if the impedance doesn’t become too low, you can use two pairs of paralleled speakers on each amplifier output. siliconchip.com.au Australia's electronics magazine January 2026  65 HOW TO DESIGN Printed Circuit Boards Part 2 by Tim Blythman Professionally made PCBs have become easy to source and quite cheap over the last decade. That means just about anyone who wants to design a custom circuit can make one. So how do you go about turning an idea into a printed circuit board? I n the first part of this series last month, we looked at some of the background surrounding PCB design and manufacture. There was a panel describing the manufacturing process and how the various parts of a Gerber file set are turned into the finished product. We also described the importance of library files and some of the other aspects of Altium Designer (or similar ECAD software) that can streamline the process. For example, Manufacturer Part Search can be used to download the libraries for many parts, so that you don’t have to worry about the process of creating component symbols and footprints. In this article, we will discuss the importance of PCB design rules and show you some of the tips and tricks that we have gathered that will help you during schematic capture and PCB layout. We’ll also explain how you can export your completed design from 66 Silicon Chip Altium Designer and then have it made into actual PCBs. Starting a project We won’t delve into too much detail about actually using Altium Designer, since there are numerous guides online, and we realise that other software packages are available. The Altium Academy YouTube channel has videos on many topics, including a series dedicated to getting started. We’ll focus more on some of the processes and habits that we think will be helpful. At the same time, we don’t want you to get bogged down in minute details. The default settings will be more than adequate for most cases, and you’ll learn more by simply practising the art of schematic capture and PCB design. We mostly use local projects and manage our own version control, so we generally start a project by creating a new project file (File → New → Project) Australia's electronics magazine using our PCB code as a name, possibly appended with a brief description. This will create a new folder with that name; the folder will contain a PrjPcb (project) file with the same name. We typically keep a set of SchDoc and PcbDoc files to use as templates, which helps us to maintain the same style and saves us from having to set up PCB design rules from scratch every time. You might need to start with blank files (File → New → Schematic or File → New → PCB) and develop these as you go. These should be in the same folder as the PrjPcb file. Open the Projects panel and add the files to the project by right-­clicking on the PrjPcb file in the panel and selecting “Add Existing to Project”. This ensures that the files are all associated with each other. Also ensure that your library files are available. Open the Libraries Preferences window from the Components panel. The Install button can be used to add your library files to the list of libraries that are referenced. Make sure that your schematic library is selected in the drop-down menu of the Components panel. If you’re starting from scratch, the most important things to check in your PCB file are that the settings for minimum track-to-track clearance and minimum track width are sensible. For example, around 8 thou (8 mils or 0.2mm) is a sensible initial setting for both. You may also need to adjust the minimum hole size (check your manufacturer’s capability). The minimum via diameter should be roughly twice the minimum hole size. Schematic capture Fig.9 shows a snippet of one of our schematics; note the modular nature. It’s also possible to add notes and frames to label the various parts of the circuit. All these things, as well as components and wires, can be found in the Place menu. Component data sheets will often dictate components like bypass capacitors that need to be included nearby. They might even suggest a PCB layout, which will be helpful in the later stages. Keeping these components as a group will remind you of their purpose. Keeping everything in small groups like this can make it easier to manage the different parts of the circuit. It siliconchip.com.au makes it easier to move things around if that is needed, since there isn’t a mess of connecting wires that need to be adjusted. Instead, the various wires are connected through ‘ports’, which have the names shown. Ports with the same name connect to each other. The names are also carried over to the nets in the netlist (the computer’s internal representation of the wiring connections) and thus the PCB design. Nets that only travel short distances within a group do not need to be named, but it can help to do so. This approach makes it easier to manually copy these small snippets around between projects. Altium Designer also makes it possible to save the corresponding PCB layouts with its Reuse Blocks feature. This is one area where there are two (or more) schools of thought. The approach I will describe here is probably the easiest for the designer, but it can make it more difficult for others to understand your circuit. At the extreme other end are people who insist on connecting everything in the circuit diagram with wires and barely use ports. The result can look messy, but at least you can follow the wires to see what connects where. Perhaps you can find a happy middle ground! the PPS module, so it is easy enough to change the pin allocations by shuffling the ports around if you find that helpful during PCB layout. Sometimes it’s necessary to assign functions to micro pins randomly, then rearrange them as you work on the layout. If you see a red squiggly line near a component pin, that indicates a possible conflict, such as having two outputs connected together. This usually indicates a problem, since the outputs could conflict if set to different logic levels. Sometimes this is a valid arrangement, such as when two slave devices are connected to an SPI bus. In this case, MISO pins are necessarily connected together. While there are settings to disable this warning, we find it is better to know and understand the problem and appreciate that it will, in the SPI case, need to be handled in software. Another common place you will see the red error marker is when two components have the same designator (eg, R1 & C5). Altium Designer’s default is to create each with a “?” suffix (eg, R?), which is simply an indication that these need to be updated before proceeding. Common circuit blocks Many of our designs use microcontrollers, and the in-circuit serial programming (ICSP) header and MCLR pull-up resistors are usually required. Thus, you can copy them from a previous project to save time. It’s easy enough to change the resistor between a through-hole and SMD footprint as required, and rename the 3V3 rail to suit a different supply voltage. Most of our designs use the same standard 0.1in (2.54mm) pitch header for the ICSP connector as this allows a programmer to plug straight in. The 3V3 and GND named ports can be copied and pasted and then wired to the microcontroller chip as needed. Similarly, the VSENSE line will be wired to an ADC pin on the microcontroller, so its port can be copied over, too. Copying the port ensures that you don’t make a mistake while typing its name. Newer 8-bit PICs like the PIC­ 16F18146 allow digital peripherals to be mapped to just about any pin using siliconchip.com.au The process of setting the designators is called annotation; there are several automated options under the Tools → Annotation menu. We often use “Annotate Schematics Quietly”, since that is the quickest. The designators can also be changed manually in the Properties panel of each object. It is a good idea to annotate each section of the circuit as it is laid out, so that related components are numbered consecutively. If there are many components, they are annotated from left-to-right and top-to-bottom. Thus, you can annotate multiple sections in order by temporarily laying them out in the desired order, annotating and then moving them into their final position. As you lay out the schematic file, be sure to pick the correct footprint for each component, so that you don’t miss that step. We often copy and paste resistors and capacitors after the first of these has been picked. Since most of these passives will use the same package, they will probably use the same footprint, and that is an easy way to ensure it. Don’t be tempted to pick a random package and ‘fix it later’ as you may forget and end up with a board that doesn’t fit your components! While you’re at it, add test points as needed. Since they are part of the PCB, they won’t cost anything (they can also act as vias). We’ll move on to PCB layout next, but this is hardly ever a strictly linear process. You might find you need to come back and change the circuit (maybe multiple times!) because something has been missed or needs to be changed. PCB layout Fig.9: using named ports will allow your circuit to be laid out in neat modular groups, and will also give the nets useful names when it comes to the PCB layout stage. Australia's electronics magazine To commence PCB layout, the netlist needs to be translated into footprints and their associated connections. The Tools → Update PCB Document menu item initiates this process. This commences a process that is given the impressive name of an Engineering Change Order (ECO). The ECO summarises the changes that will occur to the associated PcbDoc file and mostly reflects the connections between components more than the physical layout. Sometimes, you might see something in the ECO that doesn’t make sense, telling you that there is a problem with the schematic file. January 2026  67 Errors at the ECO change will also flag inconsistencies between the pins in a schematic library and the pads in a footprint library, or perhaps that a specific footprint can’t be found. These sorts of errors need to be corrected within the libraries or in the schematic before proceeding. Don’t be surprised if you need to go back and forth between the schematic and PCB layout at least a few times before you’re ready to start placing the components and routing the board. Fig.10 shows an ECO that might be seen before PCB layout commences. You might go back later and make a minor change to the circuit that only results in a handful of items listed in the ECO. The red text refers to errors detected in the schematic document. Fig.11 is the PCB document immediately after the first ECO has been executed and all the components and nets have been added. The lines connecting the components are the so-called ‘rat’s nest’ – each line is a net indicating that a pair of pads need to somehow be joined with copper. Design rules Before commencing PCB layout, it’s a good idea to check that your design rules are appropriate. In Altium Designer, they can be accessed (when in the PCB Editor) from the Design → Rules menu. Fig.12 shows the Design Rules window. We mentioned in our recent Altium Designer 25 Review (siliconchip.au/ Article/18307) that the new Constraint Manager can be used to perform much the same task. Since PCB manufacturer capabilities have not changed much, we haven’t felt the need to transition to the Constraint Manager; our existing Design Rules are working well. Many PCB manufacturers also supply a downloadable set of design rules that can be imported directly into various EDA tools. PCBWay has its downloads at siliconchip.au/link/ac8o Altium Designer’s Design Rules also include various preferred values, so you might like to check these, too. Keep in mind that there are some scenarios that might satisfy the design rules but still not be possible to manufacture; the converse may also be true in some cases. For example, routed slots with perfectly square corners cannot be manufactured with a traditional CNC routing or milling process, since the round bit cannot achieve this shape. They may be possible with a laser CNC process at extra cost. A contrasting example is a so-called net antenna, which is typically a copper trace that does not connect two pads and simply ends. In most cases, this is unwanted, since the free end may pick up or radiate RF noise. Of course, if you actually want to create an antenna, you can ignore the ‘error’ flagging the net as an antenna. Another case is the maximum drill diameter being exceeded. In most cases, such holes can be manufactured by CNC routing instead of being drilled. With all that said, most designs for manual assembly are unlikely to fall foul of these traps. The manufacturers that we have dealt with are keen to help out and will often double-check a design if there is any ambiguity. For example, we have designed panel PCBs that lack drilled holes (intentionally) and the manufacturer has asked us to confirm that we have not accidentally omitted the drill file. Component placement There are two critical steps in PCB layout: component placement and trace routing. You will probably go back and forth between the two. Since the components need to be placed before they are connected, a good initial component placement makes the routing stage much easier. To say that PCB design is an art definitely has some truth; it is also true that there is no one correct way to place components or route traces. There will be designs that are poor and some that are good or even excellent, but even those judgements can be subjective. For example, some people like to use ground pours extensively, while others find they can cause noise problems and prefer to route ground connections manually (perhaps with pours in some areas but not others). With that said, it’s always good practice to keep bypass capacitors as close as possible to their corresponding IC pins (one trick is to put an SMD component directly under the IC!). Similarly, power traces should be laid out Fig.10: the engineering change order (ECO) lists all the internal changes that are happening to a PCB design when modifications are made to the circuit schematic (or vice versa). It is a convenient point to check for errors that might have occurred during schematic capture. Fig.11: the chaotic appearance of a freshly generated PCB can be intimidating, but if you group the components as you did during schematic capture, it can be tackled in small steps. 68 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.12: design rules can also be quite intimidating, but most PCBs intended for manual assembly will have fairly relaxed requirements. Items like the track width, track spacing and hole size are worth checking. to minimise their enclosed loop area; this is often as simple as routing them alongside each other. There have been a handful of times when we have had a design mostly laid out and have needed to restart from scratch, although that is rare. It may be that the design has required one extra component that just cannot be accommodated in the existing layout. ‘Ripping up’ and re-laying a set of tracks is not all that uncommon, though. Other times we have reached the realisation that routing all the required connections is just not possible with the existing component placement; perhaps swapping a handful of microcontroller pins will solve the mess, but at the expense of having to redo a lot of the routing. This can come down to trial and error, although practice will help speed up the process. You’ll note that during the schematic capture phase, we suggested grouping the components into functional groups. A good first step is to move the footprints around so that they are similarly grouped in the PCB document. The process is to route the siliconchip.com.au connections within each group, then connect the groups together. For example, if you have an op amp IC in the circuit, you can place the IC with its bypass capacitor(s), feedback components (mainly resistors & capacitors) and so on. Then you can move that ‘block’ around to see the best place to locate it on the PCB, with the aid of the rat’s nest. At times, it is surprising how much space traces can take up on a PCB, so leave space between components if possible. Extra space will also make assembly easier. The small groups can be arranged quite tightly, but remember to leave room for designators and component values if you want to include them. That room often ends up being a good amount of space to add traces. We usually don’t start routing with the smallest possible track widths or smallest possible vias because larger tracks and vias have better properties (lower resistance, lower inductance, less likely to lift during soldering etc). This means that if we get desperate, we can reduce the widths and sizes Australia's electronics magazine in some areas to give ourselves some extra breathing room. Of course, if you start with everything at minimum size, your routing job will be easier, but then you will likely have to go back later and redo areas to thicken traces where you can (at least if you want to get an optimal result). There might be a couple of components that you decide need to be fixed at a certain location. External connections, such as plugs, sockets and DC jacks need to be near the edge of the PCB. A display should be front and centre, with controls located below it, so that the display is not covered while the controls are being operated. In fact, it’s often a good idea for the first steps of PCB layout to define the size and shape of the PCB based on the case it’s going in, then place all the mounting holes, then all the connectors, LEDs, switches and such that have to go at certain locations around the edge. It then becomes much clearer where certain other components have to go. If you have components that need to stay in place, their location can January 2026  69 Fig.13: laying out your components into groups and then aligning pads with matching nets is a simple strategy but works quite well. Remember that part data sheets will sometimes offer PCB layout suggestions (especially switch-mode regulators). be locked from the Properties panel, which stops them from being accidentally moved. Fig.13 gives an example of a simple strategy that we commonly use. These components are the same as the VSENSE divider seen in Fig.9, dropped in the PCB document as they might be after an ECO. On the left, we have simply grouped them; note that the net names are visible, which helps us to recall their purpose in relation to the rest of the circuit. The right side of Fig.13 shows how these might be wired together. Within the group of components, we find matching nets and align these side by side, rotating the part as needed. The logical flow used is from left-to-right, to match the schematic and the PCB’s external connections. Fig.14 shows a section of the Versatile Battery Checker from the May 2025 issue (siliconchip.au/Article/18121) that has been given a similar treatment. The three components on the right have a similar arrangement to that shown in Fig.13. This gives a very neat result when there are multiple components with the same package size (M3216/1206 in this case) lined up in a row. The SOT23 transistor also fits in quite well. This system also works for arrangements like biasing and coupling networks, such as in audio and other analog circuits. Here, we can use the Properties panel to quickly align multiple components. All components in the group are selected and can be aligned horizontally by setting their Y coordinates to the same value. Each then has its X value set at equal intervals. A 3mm spacing is used for most of the parts in Fig.14. You can also take advantage of the document grid and snap-to-grid 70 Silicon Chip to align components like this. If the circuit uses mostly throughhole parts, a grid spacing of 100mil (0.1in or 2.54mm), or a fraction of this, like 25mil, will allow the parts to naturally snap into the locations dictated by their pin spacings. We generally use a metric grid (1mm or perhaps 0.5mm) for laying out surface-mounting parts. Remember that the snap settings may overrule the grid spacings. Note how in Fig.13, we haven’t laid out a trace for the GND pads. Instead, we plan to connect this to a copper area that will probably cover most of the PCB. This is known as a polygon pour, and you can see these connections in Fig.14. As the name suggests, they can be just about any shape or size. A polygon pour is a copper layer region that can be defined and allocated to a net. When it is ‘poured’, it is shaped so that it avoids anything else within its limits, but will connect to that specific net, kind of like pouring concrete around obstacles on the ground. It effectively fills the area with copper. On many layouts, a polygon pour can remove the need to connect the pads for at least one net (usually GND) and typically more. We often use a polygon pour for ground nets because it is effectively ‘free’ and has the most pads to connect. Multiple polygons can be used in different parts of the board and on both sides of the PCB. Many four-layer boards will have entire layers made of polygon pours allocated to just a single net or a few nets, such as ground or power rails. Thus, polygon pours can help route multiple nets, either partially or fully. Depending on your settings, you may need to manually repour the polygons after making edits near them Australia's electronics magazine or components that are within their extents. Tools → Polygon Pours → Shelve can be used to hide polygons if they are making the screen difficult to navigate. One of the tricks we use is to route ground normally (to ensure that the polygon will actually be able to connect everything), then use the “Select connected copper” command to ‘rip out’ all the copper tracks and replace them with a polygon pour. We can then tweak it by adding via stitching etc. You can see that the connections between the pads and the polygon pour are through narrow copper necks. This is called thermal relief; if the pads were directly connected to the copper area, soldering would be difficult, since the large copper area would draw too much heat away from the pad. Thermal relief settings are adjustable, but we have never had any problems using the defaults. Since the ground net is likely to have the most pads connected, a ground polygon pour can do a lot of work. It is also a very large copper area, so it will have a low resistance; a ground or power circuit is also a good place to have this property. Layers If you use through-hole components on a two-layer PCB, all component pins already have a connection to both sides of the PCB due to the plated through-holes. A handy trick is to run the traces on one layer horizontally and vertically on the other. This works especially well if you have buses with multiple traces running in parallel. Essentially, every throughhole pad is a free via. If you need to join traces on both sides of a PCB, remember that vias are also available (and also free). A via is much like a plated through-hole pad that doesn’t connect to anything else, although they can be much smaller. Since they don’t need to have an external connection, they are often covered in solder mask; this is called a ‘tented via’. We recommend that you set your design rules to enable tented vias. These days, manufacturers even provide the option to plug vias (fill them with glue) and cap them (cover with glue) so they can’t corrode. You can use vias to switch between layers if you need to change between running traces horizontally and vertically. While vias do have a small siliconchip.com.au resistance and impedance (capacitance and inductance), it can be largely disregarded for most things apart from high-speed and RF design. You can also use vias to connect polygon pours on opposite layers. Indeed, most low-voltage (24V) and low-current (1A) designs that are not related to high-speed or RF will work with just about any routing that completes the necessary connections and has traces at least 0.5mm wide. If you’re placing through-hole components on both sides of a PCB, be sure to check that you can solder parts on one side after parts are fitted on the other! While it can be tempting to put components on both sides, because tracks and vias take up board area, it’s often easier to stick to putting components on one side and using the other for track routing. This makes assembly easier. If you have to sprinkle the odd component on the back, like a few bypass capacitors or a shunt resistor, that won’t make assembly much more difficult. It is possible to run a via directly into a surface-mounting pad from a polygon pour or track on the other side of the PCB. This usually works fine for hand-assembled boards, but be aware that the hole will pull solder away from the part and for these reasons, they are not recommended for boards to be soldered by a reflow process. For boards designed to be reflowed, there are ways to safely put vias in pads; they usually involve the plugging/capping option mentioned earlier (which may incur extra cost), or at least tenting the via on the opposite side of the board. Still, that’s an advanced topic we won’t get into any further here. The simplest strategy is to run a short trace and move the via so that it is just outside the pad and will remain covered by solder mask. Checking As you go along, it can help to occasionally run a DRC (design rule check; Tools → Design Rule Check; then Run Design Rule Check). At the start of your layout, this will probably be dominated by “unrouted net” errors. As the name suggests, these are connections that have not yet been made. Any errors apart from unrouted nets are probably worth investigating at this stage. Some errors you get can be safely disabled or ignored (eg, silkscreento-­silkscreen clearances). Others, like short circuits or clearance violations, should be fixed. We often start routing the circuit subsections and then run a DRC to see if any other errors occur; these might mean that the current component layout needs to be changed. You can also see which nets have the most unrouted net errors and might benefit from being connected by a polygon pour. As you work your way through the design, the number of errors reported by DRC should shrink, and how many are left gives you a good idea of how much work is left to be completed. If you’re starting to run into routing difficulties and you’re still seeing 50 unrouted nets, it may be time to rethink your strategy! Double-clicking on an error in the DRC report should zoom in on the location where the error has occurred. If you find that the screen gets too busy with error markers, they can be removed by selecting Tools → Reset Error Markers. Fig.15 shows an example of a DRC report and one of the detected errors. Autorouting Altium Designer has an autorouter (Route → Autoroute) that can do most of the work of routing. It can work quite well for simple designs, but we don’t often use it because we feel that manual routing gives a more neat, elegant and optimal result. We find it can be handy on layouts that are simple but tedious, especially if there are a lot of short traces to be run. Another way we have used it is to find inspiration in finding ways to route traces where we can’t see an obvious solution (routing a complex PCB can sometimes feel a bit like trying to solve a Rubix Cube blindfolded...) There are also tools to help with making your layout neater, particularly regarding traces. Glossing is a tool that works to help lay the traces. It has many settings and is automatically applied during routing, but you can also manually gloss a selected track with the Route → Gloss Selected menu option. Tidying up Once you can run the DRC and get no reported errors, your PCB design is almost complete; what’s left is mostly ‘tweaking’. Component layout and routing the traces in a PCB Fig.14: you can also use the Properties panel to exactly align the X- and Y-coordinates of components. Note the numerous vias connecting the polygon pours to their counterparts on the other side of the PCB. Fig.15: a design rule check will provide a detailed report of what still needs to be done to lay out the PCB. The line shown here is the obvious connection, but more complex cases might require a different solution if many pads are to be connected. siliconchip.com.au Australia's electronics magazine January 2026  71 are necessary facets, but they aren’t the only ones in a well-designed PCB. You’ll note that our PCBs have detailed information on the silkscreen layer, which often requires some attention, too. Even if you are happy to use the component designators, they will probably need to be rotated and aligned to look neat. Having space between rows of components can help here. Fig.16 shows the appearance of the silkscreen markings before (left) and after (right) we reworked the designators and added component values to passives. You can see that even before beginning, the designators are scattered around, having been rotated with their components. We need to rotate them, align them, add values and then organise them in such a way that it is clear which value belongs to which component. This only shows one side of the PCB. For this project; the other side has more components, as well as our logo, the PCB code (including a version letter code) and project name. It helps to use whatever space is available to add useful information. If there is room, you can even add notes, instructions, polarity markings and I/O pin maps as appropriate. Check that the board outline and any cutouts correspond to the lines marked out in GM15 (or whichever layer you have chosen). If you aren’t sure, the Tools menu has various options for turning entities in Altium Designer (board outlines and cutouts) into lines and arcs. Look under the Convert submenu. Remember that for all of Altium Designer’s abilities, the final Gerber export step simply takes the shapes on the various PCB layers and renders them into a very simple output. Many high-level entities, especially board outlines and cutouts, will have no effect unless they are part of an exported layer. It’s also a good idea to view your design in 3D and confirm that everything looks as it should. You can toggle the 3D bodies using Shift-Z to check that the silkscreen markings look correct under the components. You can even export a 3D model (File → Export → STEP 3D) and 3D-print it to see that it aligns with your chosen enclosure. Another handy check is to export as a PDF (File → Smart PDF). Since the PDF format preserves dimensions, you should be able to print the PDF on paper and check that the footprints and layout match your components. We recommend doing this if you have not previously completed a PCB design. Even after this stage, there will be some chances to view the Gerber file output and see that it corresponds to what you intended in your design. There will always be room to make changes until you check out at the PCB manufacturer’s online store. The engineers will check the designs and may ask you to review and re-upload the files if they find a problem. Gerber file export If you are happy with all the checks provided so far, you can export the PCB file to a set of Gerber files. There are a few steps required. The seven layer files are exported, followed by the drill file. These eight files are then bundled together into a ZIP file for upload to the PCB manufacturer’s portal. All the file export options are found under File → Fabrication Outputs. “Gerber Files” is of course the choice for the seven layer files. Fig.17 shows this window in the most recent versions of Altium Designer. The options shown are those that we used for our projects. Note that most PCB manufacturers still seem to use imperial units (inches). You should have two copper layers, two silkscreen layers and two solder mask layers. There will also a file for the board outline; we use GM15 but you could use GM1 or something else depending on what’s convenient. The board outline and any cut-outs inside it are simply defined by line and arc segments that join end-to-end to make a set of closed shapes. You’ll see that there is also the option of exporting a paste mask layer; these files would be used to create a solder paste stencil to apply solder paste to the PCB as part of a reflow soldering process. They are not needed in a manually soldered design. Next, the drill file can be exported using the “NC Drill Files” option. Fig.16: adding component values and cleaning up the silkscreen layer is another skill that requires an artful touch. We like to use the BoM as a checklist to make sure we do not miss any of the components. 72 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.17: recent versions of Altium Designer use this simplified Gerber export window. We suggest you select inches as the units, since that is the unit that most PCB manufacturers still use. Fig.18: naturally, the drill file settings also need to operate in units of inches to match the other files in the Gerber set. We also like to tick “Use drilled slot commands (G85)” so that pads with slotted holes are exported correctly in the drill file. Fig.18 shows the settings we use. Both these commands will open a view in the Camtastic viewer, but we typically ignore this and it can be closed without saving. The exported files should be in the Project Outputs sub-folder of your project. These files are then collated into a ZIP file, which bundles everything together. We like to add the board dimensions and other non-default manufacturing options to the file name, since these are not recorded anywhere. Otherwise, it’s easy to forget to specify things like the desired solder mask colour or board thickness when ordering PCBs, unless they are the defaults of green & 1.6mm. Fig.19 shows the eight selected files and the ZIP file with its annotations. There are a few other files exported to the outputs folder that are not needed for PCB manufacturing. The CSV file is the BoM (bill of materials) that we mentioned in the previous article. It can be exported from the schematic editor with the Reports → Bill of Materials option. Ordering boards There are many options for ordering PCBs these days, as you have probably siliconchip.com.au seen in advertisements in this magazine. Fig.20 shows the ordering page for PCBWay. Here, we have uploaded a ZIP file Gerber set, and it has been rendered in this view. There is also a separate Gerber viewer that can be accessed at www.pcbway.com/project/ OnlineGerberViewer.html It’s worth having a quick glance at the renders to see if they show any obvious problems. For example, if the drill files are exported with different units to the layer files, the holes may not line up correctly. You can also check that all layers are present and correct, and the PCB appears as you expect. The upload page has automatically detected the dimensions of this twolayer board. You can check that the dimensions are as expected. Factors like hole size and track spacing might also be detected, so you should check these are what you have intended. Generally, boards up to 100 × 100mm are quite cheap, as seen here. The defaults (as shown) are likely to be quickest and cheapest, so are the best choices for prototypes. Options like different solder mask colours are still fairly cheap and fast, as are PCB thicknesses down to around 0.8mm. Australia's electronics magazine Fig.19: the eight selected files here have been collated into the ZIP file near the bottom of this list. We have also added the dimensions and thickness of the PCB to the filename so we don’t forget to specify them when ordering the board. January 2026  73 On the other hand, changing to a different substrate or surface finish can dramatically increase the cost of the boards and may also add to the lead time. It’s easy enough to click through the different board options to see what is possible. Note that some options can require other choices. You might have seen features like edge connectors or castellated pads along the edge of a PCB; these look simple, but can also end up being expensive additions to a design, since they may require extra processing steps to achieve. There are also slower, cheaper shipping options available. We generally like to order several designs at the same time and spread the cost of faster delivery amongst them, since the total shipping cost does not increase much for extra boards. Each board is finalised by pressing Save to Cart, after which you can upload a different design and configure it as needed. After this, the process is much like any other online store. You’ll need to supply a shipping address and make payment before manufacturing begins. Then, you just need to wait until your creation arrives. Summary The ability to have PCBs manufactured has become much more accessible over the last decade, as well as becoming faster and cheaper. PCB design software such as Altium Designer continues to improve and add new features. There really isn’t a better time to start designing PCBs. There are many tools, features and tips in Altium Designer. While Altium provides many learning guides, there are also online communities that can be helpful in finding out how to achieve a specific end. Of course, this series has only just skimmed over the very simplified basics of the topic; there are many other aspects we haven’t mentioned or only briefly touched on. As we stated, designs involving RF, high voltage, high current or high speeds will need settings, design rules and knowledge that we have not covered. Next month’s issue will include an article on advanced PCB design techniques. We’ll also describe the process for ordering PCB assemblies, like the RGB LED Star from the December issue SC (siliconchip.au/Article/19372). 74 Silicon Chip Fig.20: there are many options available for PCB ordering and manufacture, but the defaults are often the cheapest and fastest. The PCBWay website offers these renders of the Gerber files, providing another simple way to check that the design is as you intended before they start making boards. Note also the link to a separate Online Gerber Viewer feature, which will give you a better view. Australia's electronics magazine siliconchip.com.au SOnline ilicon Chip Shop Kits, parts and much more www.siliconchip.com.au/Shop/ Rotating Lights April 2025 SMD LED Complete Kit SC7462: $20 TH LED Complete Kit SC7463: $20 USB-C Power Monitor August-September 2025 Short-Form Kit SC7489: $60 USB Power Adaptors May 2025 Complete Kit with choice of USB socket SC7433: $10 siliconchip.au/Article/17930 siliconchip.au/Series/445 siliconchip.au/Article/18112 This kit includes everything needed to build the Rotating Light for Models, except for a power supply and wire. This kit includes all non-optional parts, except the case, lithium-ion cell and glue. It does include the FFC (flat flexible cable) PCB. You can choose from one of four USB sockets (USB-C power only, USB-C power+data, mini-B or micro-B). The kit includes all other parts. Compact HiFi Headphone Amplifier Complete Kit SC6885: $70 PICKit Basic Power Breakout Board September 2025 December 2024 & January 2025 siliconchip.au/Series/432 This kit includes everything required to build the Compact HiFi Headphone Amplifier. The case is included, but you will need your own power supply. Mic the Mouse Complete Kit SC7508: $37.50 August 2025 siliconchip.au/Article/18637 It includes everything needed to build one Mic the Mouse, except for solder, glue and a CR2032 cell. Complete Kit SC7512: $20 siliconchip.au/Article/18850 Includes the PCB, all onboard parts and a length of clear heatshrink tubing. Jumper wire and glue is not supplied. → Subscribers receive a 10% discount on all purchases, except for subscriptions (postage is not discounted). → Prices listed do not include postage. Postage rates within Australia start at $12, rates are calculated at the checkout. 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. Scale Speed Checker for model railway This model railway speed checker measures the time a train takes to travel between two infrared (IR) sensors and uses the distance between them, the model scale factor and the required speed units factor to show its scale speed on a 128 × 64 pixel OLED screen. “Initialising”, “Timing” and “Resetting” status messages are displayed to indicate the progress of the measurement process. An RP2040 Zero microcontroller board is used to control the process, programmed using the Arduino IDE. An IR LED, IR phototransistor and a comparator form the start and stop sensors. The comparator threshold (sensitivity) is adjustable with its associated trimmer potentiometer. This is a common arrangement found in many inexpensive IR detector modules. Jumper blocks (JP3, JP4) have been added to transpose the input 76 Silicon Chip connections to the comparators so the sensors can operate in reflective mode or beam breaker mode as required. The opto-couplers at the RP2040’s inputs were found to be effective in isolating noise pickup in long sensor connecting cabling. This is a real problem with DC-operated models with commutator and brush motors. Rather than having to specify a fixed sensor separation distance or asking the constructor to modify the Arduino sketch to customise it for every unique situation, setting the sensor separation distance (in mm) is done by placement of shunts on JP1 representing it as a binary number. The values are summed, so 10 shunt positions allow the separation distance to be set in 1mm increments up to 1023mm (just over one metre). Jumpers on jumper block JP2 allow the user to set the scale, speed units, whether or not a configuration summary is displayed at initial power-up Australia's electronics magazine Circuit Ideas Wanted We pay for your interesting original circuits. We can pay you by electronic funds transfer, credit or direct to your PayPal account. Email your circuit and descriptive text to editor<at>siliconchip.com.au and whether operation is speed checking mode or a simple counting demonstration mode. Other model scales, speed units and separation distance units can be catered for by adjusting constants within the Arduino IDE sketch and modifying the calculation formula to suit. At power-up, there’s an initialisation period during which “Initialising” is displayed. Both the sensors must remain clear for a set time before “Ready” is displayed and a speed measurement can proceed. When the first (start) sensor is triggered, a “Timing” message is displayed. It remains until the second siliconchip.com.au An HTTP to HTTPS bridge Drawing inspiration from the Hot Water System Solar Diverter article (June & July 2025; siliconchip. au/Series/440), I set about learning to use https://thingspeak.com for the first time. I create most of my embedded software in Microchip MPLAB X in C. For TCP data connections, I use (the now vintage and very cheap) ESP12S modules. These modules use AT+ commands via the microcontroller’s UART and act as the TCP engine for my low-capacity microcontrollers. Soon I was able to get a ThingSpeak interface working; it reported and started plotting graphics. You can subscribe to the site for better graphics and data reporting. However, in August 2025, the reporting stopped. The HTTP request reported “301 Permanent Redirect to https://thingspeak.mathworks.com”. ThingSpeak joined with MathWorks and now only accepts HTTPS connections. The ESP12S can handle the security certificates, but that consumes many resources of the small module and reduces the maximum number of simultaneous TCP connections to one (rather than four with HTTP). The code to handle the certificates also seriously complicates the C code. My project stalled. So I used a Raspberry Pi Zero W, using Linux, Python3 and a Python script to act as an HTTP-to-HTTPS bridge. The Pi Zero W resides headless and powered by the USB port on the back of the router. I chose to connect to the bridge via HTTP on a sundry port, 3001, for the sole reason of being different from the usual ports, 80 and 8080. The bridge resides on the private side of the router and is safely tucked away, with no port forwarding on the router. Private-side devices find it easily via the router’s DNS server. The Python script was developed in Visual Studio on Windows 10 and was transported to the Pi via SSH. You can download it from our website at: siliconchip.au/Shop/6/3568 I am now very appreciative of the amount of man-hours in the development of the hardware on the Raspberry Pi Zero W (now obsoleted by the Pi Zero 2W), Linux, Pi OS, Python3, Tera Term, Visual Studio, MPLAB X, the Pi installer and the Raspberry Pi website – all given away for free! Michael Harvey, Albury, NSW. ($70) (stop) sensor is triggered, at which point a speed is calculated and displayed. Switches S1 & S2 control the duration that the scale speed is displayed. If pin GPIO26 is low due to S1 being closed, the speed is displayed only for a time defined in the sketch. If GPIO26 is high because S1 is open, the speed is held on the display until that pin is taken low by the momentary operation of pushbutton switch S2. On clearing the display, a reset period like the initialisation period applies to ensure the sensors are both clear before preparing to take another speed measurement. A “Resetting” message is displayed. The RP2040 was programmed using the Arduino IDE with the Raspberry Pi Pico / RP2040 / RP2350 package by Earle Philhower installed and the “Waveshare RP2040Zero” board selected. Initially, a 1.3-inch OLED display with an SH1106 driver IC was used, controlled using the Adafruit SH110X Library. Later, a 2.42-inch display using an SSD1309 driver was substituted and found to operate with the same library without needing any rework of the main programming.. The only adjustment needed was to the parameters for drawing border rectangles for the opening splash-screen. For more information on the 1.3inch OLED screen, see the October 2023 issue (siliconchip.au/Article/ 15980). Also, the November 2025 article on larger OLEDs (siliconchip.au/ Article/19224) includes some information about two different 2.42-inch OLEDs. The software for this project can be downloaded from siliconchip.au/ Shop/6/3565 Bob Martindale, Mill Park, Vic. ($120) siliconchip.com.au Australia's electronics magazine Ideal Bridge Rectifiers Choose from six Ideal Diode Bridge Rectifier kits to build: siliconchip. com.au/Shop/?article=16043 28mm spade (SC6850, $30) Compatible with KBPC3504 10A continuous (20A peak), 72V Connectors: 6.3mm spade lugs, 18mm tall IC1 package: MSOP-12 (SMD) Mosfets: TK6R9P08QM,RQ (DPAK) 21mm square pin (SC6851, $30) Compatible with PB1004 10A continuous (20A peak), 72V Connectors: solder pins on a 14mm grid (can be bent to a 13mm grid) IC1 package: MSOP-12 Mosfets: TK6R9P08QM,RQ 5mm pitch SIL (SC6852, $30) Compatible with KBL604 10A continuous (20A peak), 72V Connectors: solder pins at 5mm pitch IC1 package: MSOP-12 Mosfets: TK6R9P08QM,RQ mini SOT-23 (SC6853, $25) Width of W02/W04 2A continuous, 40V Connectors: solder pins 5mm apart at either end IC1 package: MSOP-12 Mosfets: SI2318DS-GE3 (SOT-23) D2PAK standalone (SC6854, $35) 20A continuous, 72V Connectors: 5mm screw terminals at each end IC1 package: MSOP-12 Mosfets: IPB057N06NATMA1 (D2PAK) TO-220 standalone (SC6855, $45) 40A continuous, 72V Connectors: 6.3mm spade lugs, 18mm tall IC1 package: DIP-8 Mosfets: TK5R3E08QM,S1X (TO-220) See our article in the December 2023 issue for more details: siliconchip.au/Article/16043 January 2026  77 Weatherproof Touch Switch Simple Electronic Projects with Julian Edgar We’ve seen weatherproof switches, and we’ve seen touch switches. But have you ever seen a 100% sealed touch switch with no traditional moving parts that can be operated even while wearing gloves? W hile browsing the parts in an electronics surplus store, I came across a sealed metal disc, complete with an inbuilt LED. It was about 40mm in diameter and about 15mm deep. It appeared to be designed for panel mounting, and used a large retaining nut. Two pairs of wires escaped from the fully potted rear surface. The store owner said something about “piezo”, so I assumed it was a piezo buzzer with an inbuilt LED. I really wasn’t sure – but I bought a few anyway. When I got them home, I looked at them more closely. A tag on one of the wire pairs said “Everswitch” and then gave the LED’s voltage rating: 5V. There was also a separate 24V AC/DC 0.2A rating. This didn’t look like a piezo buzzer – maybe it was a switch? Pressing on the front face of the disc gave no apparent movement – so it wasn’t a microswitch. One pair of wires was colour-coded red and black, probably for driving the LED. The other two were both red, so they had no apparent polarity. Maybe it was a capacitance touch switch? But where Fig.1: the manufacturer’s (Everswitch) block diagram for the piezo touch switch. The LED part is easy to understand, but what on earth powers the control circuitry and solid-state switch? Read on to find out! 78 Silicon Chip was the power supply? This was sure getting confusing! I then searched for the part number and found that what I’d got was a pair of “touch metal piezo switches”. I even found a circuit diagram showing how to use the switch (Fig.1), but I am afraid that confused me even further. Yes, the red/black pair was to drive the LED; great. But the other part of the diagram appeared to show a piezo crystal connected to an control circuitry that in turn drove a switch (presumably a solid state one). But again, where was the power supply for the control circuitry and switching transistor? Then I discovered the answer. Piezo switches internally generate their own power from the deflection of the crystal. Amazingly, this provides enough power to operate the internal electronics. Lo and behold, when I checked the continuity across the two red wires, yes, they were connected when the face of the switch was firmly pushed. The switch stayed closed until the electrical charge dissipated – for a quarter of a second or so. So with the Everswitch, we have a completely sealed, weatherproof Photo 1: The mystery object – a 40mm diameter metal disc with... Australia's electronics magazine switch that can cope with a wide temperature range (-20°C to +75°C) and has a basically unlimited life (50 million operations, apparently)! Now that I knew what to look for, I found that metal piezo touch switches are widely available. They’re priced from about $8. I thought the best application for the piezo switch was a completely weatherproof switch to be positioned outside, possibly in the rain, snow and searing heat. It could operate a mains-switching relay through a latching circuit – one press to turn the relay on, another to turn it off. That’s when I discovered a second exciting and synergistic product. A bistable switching module Available via eBay and similar sellers, it is a very effective and tiny module. Find it by searching for “bistable flip-flop latch switch module” or similar. Ensure that the one you buy looks exactly like the one pictured. The cost is from about $5 delivered, and the main board is just 14 × 11mm. It comes with the header fitted and ready to connect. Photo 2: ... two pairs of wires coming from the rear potted surface. It turned out to be a fascinating device – an internally powered piezo touch switch. siliconchip.com.au Photo 4: The piezo touch switch, tiny flip-flop module and a mains 6V relay. With these components and a short amount of time, you can easily make a completely weatherproof switch that can even be operated when wearing gloves. This module will operate from 3-18V and it acts as a bistable switch. The momentary closing of an added normally-open pushbutton energises the output, with another push switching the output off. The switching transistor can handle 1.5A and it has an in-built protective freewheeling diode, so inductive loads like relays and solenoids can be driven directly. Various trigger times can be set by soldering links between pads on the rear of the module. For example, required pushbutton ‘on’ times before the module triggers can be set at one, two or four seconds. However, as bought, the module worked perfectly with the piezo switch as the momentary input. Completing the circuit All that is then needed to complete the circuit for a mains switch is a relay and a power supply. In my case, so that the 5V LED in the piezo switch could be operated, I selected a 5V DC plugpack power supply. I also chose a relay with a 6V coil – it works fine on the slightly lower supply voltage (the ‘pick up’ voltage of a 6V relay is typically around 4.5V). Fig.2 shows the resulting circuit. If you are using the relay to switch mains voltages, ensure that the relay is rated appropriately and insulate all mains connections. The relay should be mounted in an insulated or Earthed enclosure, with cable clamps or glands fitted to prevent the mains wiring from being inadvertently pulled out. Of course, a mains switch is only one potential use for this combination of the piezo touch switch and flip-flop module. Given that the flip-flop can handle up to 1.5A, it can directly drive low-voltage loads up to 18V. The current consumption of the piezo touch switch is zero (I still find that hard to get my head around!) and the flip-flop module draws only 2µA in its quiescent state and 2mA when its internal switch is on. These specifications lend the switch combination to battery and/or low-voltage renewable energy projects as well. Photos 5 & 6: The front and back of the tiny flip-flop module. The module will work with any supply voltage from 3-18V and can carry up to a claimed 1.5A. It can even directly drive relays. for security, or to simply give a very sleek product design. And, talking about security, if you want a hidden switch to release an electronic lock or switch off a burglar alarm, again, the piezo touch switch is ideal. Finally, metal piezo touch switches are often used in commercial applications where vandal-proof switches are needed. Another option After building this, I came across similar switches on AliExpress (1005003286484536; siliconchip.au/ link/ac4p); one is shown in Photo 3. They lack the LED but are available in three sizes and two finishes for around $6 each plus $9 for delivery. I think they are really good – epoxy sealed, with lower finger pressure required to trigger them than the one SC I bought earlier. Other uses Photo 3: this piezo switch from AliExpress is easier to operate and well-sealed but has no integral LED. siliconchip.com.au Because the required deflection of the piezo switch is imperceptibly small, it can be positioned behind other surfaces to disguise its presence. For example, it can be located behind the plastic front panel of a piece of equipment, giving a completely hidden on/off switch. The 200-400g pressure needed to activate the switch easily flexes the panel sufficiently. Such a hidden switch can be good Australia's electronics magazine Fig.2: the circuit for the mains switch. Note the orientation of the flip-flop module with the two components on the front face. The momentary touch switch triggers the flip flop – one press to switch on its output, and another press to switch it off. January 2026  79 Image source: https://unsplash.com/photos/aerial-photography-of-flowers-at-daytime-TRhGEGdw-YY Earrth Ra Ea Rad dio John Clarke’s Parrt 2 : w� Pa w�ispe isperrs of of the sk sky This ‘natural radio receiver’ lets you listen to the VLF and ELF emissions of solar and atmospheric disturbances, like storms or auroras. Having described how it works last month, let’s start building it. T he Earth Radio comprises a single-­PCB receiver that runs off a 12V DC supply or internal 9V battery, plus an external loop antenna on a timber frame measuring 690 × 690 × 98.5mm. That’s very compact for something that will pick up radio signals with wavelengths of many kilometres! Ideally, the whole thing should be kept away from sources of interference, including mains distribution wires. Because it’s battery-powered and portable, you can use it in the Fig.10: fit the components on the PCB as shown here. Take care with the orientations of the ICs, diodes, trimpots, electrolytic capacitors, transistors and LED. 80 Silicon Chip middle of a field or other open area, where it will have the best chance of picking up the very small signals that travel around the world through the Earth’s atmosphere. Construction The Earth Radio is constructed using a double-sided, plated-through PCB coded 06110251 that measures 96 × 69mm. The PCB is housed in a Ritec ABS translucent black instrument case (or equivalent) that measures 104 × 79 × 40mm (its dimensions may be rounded to 105 × 80 × 40mm). A separate loop antenna connects via screened cable and a jack plug. While assembling the board, refer to the overlay diagram, Fig.10, which shows what components go where. Begin by fitting the resistors and the three diodes. Verify the value of each resistor before installation by checking the colour code and measuring it with a multimeter. Ensure diodes D1, D2 and D3 are installed with the cathode stripes orientated as shown in Fig.10 and on the PCB screen printing. Diodes D1 and D2 are small, glass-­ encapsulated 1N4148 types while D3 is a larger, black 1N5819 schottky diode. Next, mount the sockets for the three ICs, taking care to orientate them as shown, with the notched ends towards pin 1 in each case. Then fit the 3.5mm jack sockets, CON1-CON3. Follow with trimpots VR1 to VR6 and VR8. The adjustment screws need to be orientated as shown for the resistance to change as expected. These come in several different values, so be sure to place the correct value in each position. They will be printed with a code indicating the value, although you can also check it by measuring resistance across the outer two leads. siliconchip.com.au The finished Earth Radio, with and without the 9V battery. The PCB attaches to the case using four self tapping screws. Install the capacitors next, starting with the smaller ones. The electrolytic types that come in cans need to be orientated with the correct polarity – the longer lead is positive, and this goes next to the pad marked with a + symbol. The stripe on the can is negative, so it will be opposite this. The smaller MKT and ceramic types can be installed either way around. Now you can fit the DC socket (CON4), volume pot (VR7) and the two switches, S1 & S2. Pass the 9V battery clip lead through the two holes provided near the terminals before soldering them to the pads. This is for strain relief, preventing the wires from breaking off. You can use PC stakes or just solder the wire ends into the PCB holes. The red wire is the positive and black is the negative lead. A 9V battery holder clip attaches to the PCB using a 6mm-long M3 machine screw, with a nut on the underside of the board. LED1 can be installed now after bending its leads by 90°. Position it so the top of the LED dome is 12mm in front of the PCB edge, with the centre of the LED lens located 5mm above the top face of the PCB. When bending the leads, make sure the anode (longer) and cathode (shorter) leads are orientated correctly for the PCB, as per the A (anode) and K (cathode) markings. Panel cutouts Before mounting the PCB in the case, you will need to make the cutouts siliconchip.com.au on the front panel as per Fig.11. It shows the hole positions required for the LED, switches, 3.5mm jack sockets, DC power input socket and volume potentiometer. Front panel labels are provided in Fig.12. You can print out these onto vinyl labels (or similar) ready to attach to the panels. The holes can be cut out with a sharp craft knife. For more information on making panel labels, see www.siliconchip.com.au/Help/ FrontPanels Once the labels have been applied, attach the front and rear panels to the components on the edges of the PCB and secure them with the mounting nuts for the 3.5mm jack sockets and volume potentiometer. Next, secure the main PCB to the enclosure base with the screws supplied with the enclosure. Setting it up For a 50Hz notch (eg, for use in Australia and New Zealand), connect Fig.11: all the cut-outs on the front and rear panels are round holes that can be made with a drill. There are six holes required in the front panel and two in the rear panel. While some dimensions are relative, always measure from the edges. Australia's electronics magazine January 2026  81 Fig.12: these front and rear panel labels can be downloaded as a PDF from siliconchip.com.au/Shop/11/3561 then printed and attached to the panels. a DMM set to measure resistance between TP1 & TP2 and adjust VR1 for a reading of 68.1kW. Do the same for TP2, TP3 and VR2. Then connect the DMM between TP4 and TP5 and adjust VR3 to get a reading of 34kW. For a 60Hz notch, the procedure is the same, but adjust VR1 and VR2 for 56.2kW and VR3 for 28.1kW. Set VR4 and VR8 fully anti-clockwise, then adjust VR5 and VR6 fully clockwise. Connect a 9V battery or external 12V DC supply and check that LED1 lights with the power switch on. The circuit should draw around 13mA at 9V or 15mA at 12V. If that checks out, switch it off, wait for the capacitors to discharge, then insert IC1, IC2 and IC3 into their sockets. Make sure that their pin 1 dot/notch is at the same end as the notch on the socket and ensure the pins don’t fold up as you push them into the sockets. Remember that IC1 is the OP07. To check the quiescent current of the headphone amplifier, measure the voltage across each 1W resistor with the circuit powered back up. These should be less than 0.5mV each. If more than that, adjust VR8 clockwise to reduce the voltage and hence dissipation in the output transistors. If your 47nF capacitors for the Twin-T filter are all within 1% of 47nF, no further adjustments of VR1-VR3 are necessary. VR4 can be adjusted clockwise to deepen and narrow the notch. VR4’s resistance setting can be measured between pins 1 and 5 of IC2. Typically, 220W is a suitable compromise to ensure the notch is wide enough to cater for mains frequency variations and the slight errors in the values of the 47nF capacitors. If your 47nF capacitors are all more than 1% away from 47nF (ie, below 46.5nF or above 47.5nF), VR1 to VR3 will require trimming for best the nulling of mains hum. You can use a signal generator set at 50Hz (or 60Hz) and at a level of 200mV RMS, assuming a 600W output impedance. If you don’t have a suitable AC signal generator, a mains AC plugpack can be used with the voltage reduced using a resistive divider to achieve about 200mV RMS. Add a 560-680W resistor between the junction of the divider and the Earth Radio, and apply the signal between the tip and ring of CON1 via a 3.5mm stereo jack plug. You can use an oscilloscope to monitor the signal at the CON3 output or use headphones (or earbuds) to monitor this instead. Make sure the notch filter is enabled with S1 in the down position, and connect the oscilloscope probe to the tip or ring terminal or insert the earphone or headphone plug into CON3. Adjust VR1 and VR2 by small amounts each (either way) to minimise the loudness of the 50/60Hz output tone. Similarly, adjust VR3 to minimise it. Then adjust VR4 clockwise by a few turns and adjust VR1, VR2 and VR3 again. Keep adjusting VR1, VR2 and VR3 along with the depth trim pot VR4 until you achieve the best possible nulling. As mentioned, VR4 is best set at 220W or more, with its resistance measured between pins 1 and 5 of IC2. Loop antenna details Fig.13: a side view of the timber frame on which the antenna wire is wound. We made the antenna frame as shown in Figs.13-15. You could come up with your own design, provided Australia's electronics magazine siliconchip.com.au 82 Silicon Chip that the wire is wrapped around a square frame of similar dimensions. The wire loop comprises side-byside turns. The loop antenna we made uses 20 × 12mm DAR (dressed all round) timber and 8mm dowelling. We used pine, but hardwood should be used for a more permanent outdoor installation. There are two rectangular frames made from 690mm lengths each side, and a 960mm diagonal to triangulate the frame. The two frames are separated by 26.5mm using 8mm diameter dowelling in each corner of the frame. Extra dowels are used at the centre of each square frame piece to give extra stiffness. The 26.5mm spacing provides for 40 turns of 0.63mm enamelled copper wire side-by-side, allowing for a 16μm thickness of enamel around the wire. The enamel adds up to 1.3mm over 40 turns, while the 0.63mm diameter copper wire accounts for 25.2mm of the overall 26.5mm spacing required. The wire loop is wound over the corner dowels. The overall size of the loop is a 660 × 660mm square with a slight radius at each corner as the wire curves over the outer-most quarter segment of each dowel. The 960mm diagonal braces strengthen the frame, keeping it square by preventing it from collapsing into a rhombus shape. The two diagonals are interconnected across the centre of the frame by gluing a short piece of 20 × 12mm pine to add strength. The frames, diagonals and wire loop are 690mm, 960mm and 660mm long, respectively. These convenient but similar values are due to the decision to use a 660mm square loop and have the dowel holes be 19mm in from each end of the lengths. We started the design with the goal of a 660mm square wire loop. This provides for a loop antenna that can fully use standard wire reel lengths while providing a reasonable signal capture area. For the wire loop, the 8mm dowel corner pieces need their centres to be spaced apart by 8mm less than 660mm (that’s half a dowel diameter each end). So that’s 652mm. Then these 8mm holes are located 19mm in from each end of the frame pieces. This means the overall frame side pieces need to be 652mm + 19mm + 19mm for an overall length of 690mm. siliconchip.com.au Fig.14 (left): an end-on view of the antenna frame, showing how the sideby-side wire windings are held on dowels between the two sides of the timber frame. Fig.15 (right): the various lengths of timber needed to make the antenna frame. Australia's electronics magazine January 2026  83 For the diagonal braces, the centre-­ to-centre spacing of the dowel holes need to be calculated using Pythagoras’s Theorem. With two sides at 652mm, we calculate the hypotenuse length as 922.07mm, rounded to 922mm. Adding the 19mm distances on each side of the hole positions, we get 960mm. Building the antenna Construction is straightforward and requires just a few basic hand tools such as a tape measure, square, saw, drill and sanding paper. Mark out the lengths on the timber pieces. We cut our lengths using a fine-toothed blade saw to provide neat cuts. Drill the 8mm diameter holes in each piece, then cut the dowel pieces: two 98.5mm long, four 74.5mm long and two 50.5mm long. We filed down a series of flats on the dowel along the sections at each end where they enter the 8mm holes in the frame. This provides clearance for glue within the hole around the dowel. A fully round dowel in the same-sized round hole will push the glue out of the hole. Alternatively, use fluted dowel, if available. PVA glue can be used to adhere the pieces together. Assemble the frame pieces and apply glue to the dowels to attach the frame pieces. Wipe off excess glue with a damp cloth. When the glue is dry, you can glue in the bracing spacer that goes in between the braces. Clamp it in place until glue dries. Finally, sand off the frame to a smooth finish and coat it with paint or clear varnish. Winding the coil The finished Earth Radio shown from various angles (not to scale); note that the front panel is an older revision (see Fig.12). A kit is available for $50 (SC7582) and includes all required parts, except for the case, battery, timber and wire. 84 Silicon Chip Australia's electronics magazine Three reels of 0.63mm diameter enamelled copper wire are used. As a reel finishes, we join the end to the next reel to provide the 105m total length required for the antenna loop. Start by wrapping a 100mm length of the 0.63mm diameter wire around the frame near one corner dowel, ready to wind on turns. This holds the wire start in position. Place each winding neatly side-by-side. The wire will need to be joined every 13 turns or so, since each wire reel only contains about 36m of wire. For the wire joins, strip about 10mm of the enamel from the two ends using a sharp hobby knife or emery paper, then place a 20mm length of 1mm heatshrink tubing over the wire end siliconchip.com.au on the new reel, moving it well away from the end so it won’t receive any heat as the two ends are soldered together. It is best to have joins positioned along one of the sides rather than over a corner bend; cut the wire shorter if the join would occur on a corner bend. Once the join is made, slide the heatshrink over the join and shrink it down with a hot air gun. Continue winding to complete the 40 turns. End the loop by wrapping the wire around the corner dowel. If using 0.5mm diameter wire, the procedure is the same but you only need two reels and one join. There will be a few more turns, but because the wire is slightly thinner, it should still fit in the space available. Now the two wire ends need to be soldered to twin-core shielded cable. Just connect the two shielded wires in the cable to the loop wire ends. The shield at the antenna end is left unconnected – cut it back to the end of the insulation so it can’t short to anything. The wire connections need both to be insulated with heatshrink tubing. Next, secure the cable to the frame with a clamp. We used a TO-220 transistor clamp (Jaycar HH8600) and screw, although a clamp fashioned out of a small piece of 1mm thick aluminium, a small P-clamp or cable ties would be suitable as well. The far end of the twin core shielded cable is terminated to a stereo 3.5mm jack plug. The twin cores connect to the tip and ring connections, while the shield attaches to the sleeve of the jack plug. Testing Testing can be performed by holding the antenna frame by hand and listening using headphones or earbuds and keep the volume to a minimum with VR7 to avoid hearing damage. VR5 sets the overall gain and volume of the receiver at IC3a’s output, while VR6 sets the recording level output following this amplifier. In use, while holding the antenna above your head, rotate the frame for minimum noise and hum. It is quite sensitive to detecting artificial electromagnetic-induced noise, so it is best to use it well away from any mains supply and overhead wiring. It may be that you will need to move to a large park or country area to prevent such noises encroaching on the siliconchip.com.au A clear shot of the loop antenna that we built. Figs.13-15 only show the antenna frame, but you can attach a rod to keep it upright with length and material to suit your needs. sounds you are listening for. For more permanent use, the frame can be supported about 4m above ground level. This can be done using a length of 25mm timber dowel, which can attach to the loop antenna frame with screws or cable ties. The dowel can be supported using a metal pole or star post that’s hammered into the ground. Whispers of the sky Catching the tweeks, choruses and whistlers can be elusive, especially if you intend to be listening at the time. Instead of listening all night and morning, you can record the signals and check them later. You may choose only to record when the conditions are best, such as during solar events. You can get information about space weather and solar events from the Australian Bureau of Meteorology at www. sws.bom.gov.au One thing to watch for is that if you are recording its output, the recorder can possibly create electrical noise that the Earth Radio will pick up. Typically, a recorder that operates from a battery supply will produce less noise than one operating from a mains supply. In some instances, there may be less noise when the Earth Radio’s ground is connected to an Earth stake. The recorder can be digital or analog, but a digital version makes it easier to search the recording for interesting noises later. Australia's electronics magazine You can also import an analog recording (or the signal directly from the Earth Radio) into a computer with software such as Audacity (which is free). Using Audacity is an ideal way to process the signal. It can amplify it, run filters and remove noise using the Effect → Volume and Compression or Noise Removal or EQ and Filters menu option. This can clean up the recorded signal so you just hear the desired waveforms. After processing, export it as a .mp3 or .wav file suitable for loading into Raven Lite 2. This is the spectrograph software we used. It is very intuitive to use for loading an audio waveform and showing the spectrogram. Audacity software is free, open source software for recording and editing sounds and is available from www. audacityteam.org/download Raven Lite 2 is available from www. ravensoundsoftware.com/raven-­litedownloads/ Order the Raven Lite 2 version and ‘purchase’ the licence, which is free. Both Audacity and Raven Lite are available for Windows, Mac and Linux systems. For more information on some of the atmospheric phenomena this radio can pick up, see our article titled “Atmospheric Electricity: Nature’s Spectacular Fireworks” in the May 2016 issue (siliconchip.au/Article/9922). SC Happy listening! January 2026  85 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. 01/26 YES! You can also order or renew your Silicon Chip subscription via any of these methods as well! The best benefit, apart from the magazine? Subscribers get a 10% discount on all orders for parts. PRE-PROGRAMMED MICROS For a complete list, go to siliconchip.com.au/Shop/9 $10 MICROS $15 MICROS 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) PIC16F18126-I/SL DCC Decoder (Dec25), RGB LED Star (Dec25) PIC16F18146-I/SO 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 DCC BASE STATION KIT (SC7539) (JAN 26) Includes everything but the plastic case, power supply and some optional parts. The Pico 2 is supplied but not programmed (see p39, Jan26) $90.00 RGB LED STAR KIT (SC7535) Includes the mostly-assembled board and all non-optional components except the power supply (see p43, Dec25) (DEC 25) $80.00 EARTH RADIO KIT (SC7582) (DEC 25) DCC DECODER KIT (SC7524) (DEC 25) RP2350B COMPUTER (NOV 25) Includes everything to build the radio itself except the case and battery, plus the plug for the antenna (see p65, Dec25) Includes everything in the parts list (see p73, Dec25) $55.00 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) (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) $25.00 $90.00 $7.50 $5.00 $10.00 $10.00 $10.00 siliconchip.com.au/Shop/ 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) 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) 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) 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 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) $20.00 Complete kit which includes the PCB and all onboard components (see p60, Apr25): - SMD LEDs (SC7462) $20.00 - Through-hole LEDs (SC7463) $20.00 Complete kit: includes all components (see p85, Feb25) $37.50 $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 The Pico Audio Analyser kit from Nov23, but with an unprogrammed Pico 2 $20.00 $20.00 Complete kit: includes all required items, except the cell (see p67, Feb25) $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 *Prices valid for month of magazine issue only. All prices in Australian dollars and include GST where applicable. # Overseas? Place an order on our website for a quote. PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT 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) ↳ 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) DATE 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 JUN24 JUN24 JUN24 JUL24 JUL24 JUL24 AUG24 PCB CODE 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 08106242 08106243 24106241 CSE240203A CSE240204A 11104241 23106241 Price $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 $2.50 $2.50 $2.50 $5.00 $5.00 $15.00 $10.00 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT ↳ 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 POWER RAIL PROBE RGB LED STAR EARTH RADIO DCC DECODER DATE 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 NOV25 DEC25 DEC25 DEC25 PCB CODE Price 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 P9058-1-C $5.00 16112251 $12.50 06110251 $5.00 09111241 $2.50 DCC BASE STATION MAIN PCB ↳ FRONT PANEL REMOTE SPEAKER SWITCH ↳ CONTROL PANEL JAN26 JAN26 JAN26 JAN26 09111243 09111244 01106251 01106252 NEW PCBs $5.00 $5.00 $5.00 $2.50 We also sell the Silicon Chip PDFs on USB, RTV&H USB, Vintage Radio USB and more at siliconchip.com.au/Shop/3 SERVICEMAN’S LOG A damp sort of holiday Dave Thompson I recently had to go on holiday again. I know what you’re thinking: that sounds a bit iffy. Still, please hear me out. About eight months ago, we went to Airlie Beach in Queensland, Australia (which is in the same country this fine magazine is produced). We went mainly for the Whitsundays and the Great Barrier Reef, and also to try to escape the drudgery of our day-to-day working lives by seeing and experiencing something really new, all without having to travel for 45 hours to further climes. It was certainly beautiful there, and the reef was stunning. It was everything we imagined, and more, though we of course were just like any other tourists – the locals likely hated us for being there, choking up their cafes and restaurants, while blocking their footpaths and venues as we saw the sights. We were so enamoured that we decided to book another break, this time to the northern end of the reef, basing our stay in Cairns – which lays claim to be the gateway to the Great Barrier Reef (although we never did find that famous arched sign they use in all the Cairns tourism promos). It helped that we had friends living there. Even our friends and local merchants didn’t know where that sign was; still, local knowledge is everything, and we took a lot of advice from them. Anyway, this isn’t a travel column. But stay with me, because it gets interesting – from an engineering point of view! So, I had to go on this holiday. It was booked well in advance, and well-planned by her in-laws, so my role was simply to tag along and carry the heavier bags. We sorted our house here, as in getting someone to look after it and feed the cats, and departed for the airport at some ungodly hour in the freezing cold (why do all flights anywhere from here leave so early? I must find out...). At this point, being in the tropics seemed very appealing! It’s weird to walk into an airport in winter clothes and arrive six hours later sweating like an English prince in the glare of the world’s media. We knew some people from here who had been to Cairns the week before; they had said it was perfect weather, and we’d be right. Brave words! going well. So, we thought we’d made a sensible decision. We stayed in an apartment booked through the usual systems that are in vogue now, and we were surprised to find when we arrived that there were about a gazillion apartments in this relatively new harbour-front complex. I guessed tourism is increasing there, with the number of rooms they have in the town. Many of these apartments were managed by, um, the management of the complex, but many were also individually owned and some rented out by the owners, the latter describing the one we were staying in. When we arrived and were shown around it by a lovely woman, we were impressed. It was well-built and well-­ appointed. It was clean and obviously had been well looked after. My serviceman’s ears and eyes picked up some things that didn’t quite fit the brief, but all in all, it was a place to get our heads down at the end of a gruelling day braving the weather and being the tourists we were. Arriving in Queensland A little taste of home When we arrived, it was raining. And I don’t mean rain like we get here (drizzle, really), but rain you would need gills to survive in. This introduced us to a new phrase that we would hear a lot during our ten-day stay. “You’re in the tropics now”. OK, we know that Cairns is getting up there latitude-wise, but this wasn’t supposed to be monsoon season. We didn’t go there without doing some due diligence and understood that the ‘monsoon trough’ that they all talked about there would likely hit properly a few months after we’d left, all My first interesting observation was when we arrived on the third floor and exited the lift. It was freezing in that hallway. I don’t mean a little cold; I mean like being in the chiller room of a booze shop cold. We could see our breath. OK, aircon is essential in some places, especially when it is 30°C+ outside, but this seemed excessive. The downstairs areas were nowhere near as chilled as this. When we got to our apartment/room and she opened the door, I heard a weird whistling sound as we entered and the door closed behind us. I put it down to a noisy door-closing 88 Silicon Chip Australia's electronics magazine siliconchip.com.au actuator; you know, those pneumatic or hydraulic devices that are mounted at the top of doors and close them automatically, once opened. But something was a bit off; the sound wasn’t quite right. But we’d only just arrived, so I assumed it was just a quirk of the room. Once we were settled in and unpacked, we took in the lay of the land. This place had several ‘French’ doors that opened onto separate balconies. The first thing I noticed was that there was a considerable gap in the bottom of the ‘main’ balcony door, compared to the tight fit at the top. It also didn’t open very easily, not running in its track that well. This meant the building was off-square, something I notice in Christchurch a lot now after the quakes knocked many homes out of plumb. This in itself isn’t a problem; many homes are not as square as they were when they were first built. But this factors into subsequent events. The first indication there was a problem was the low whine that came into the bedroom when we went to bed. No, this was not me complaining about the bed. It appeared to be coming from the windows that faced out to the balcony, except there wasn’t a breath of wind outside. Rain, there was lots, but wind? None. I went and opened the main door to see if I could find the source, and the noise suddenly stopped. Closing the door again started the sound, even before I could completely close it. I discovered I could open it about a centimetre at handle height and the noise disappeared. As sleeping with this sound was not an option, we had to leave the door open slightly. No problem; it was hot and humid, but we had ceiling fans and aircon happening. Indoor pool There was another problem when I got up the next morning and stepped into a pool of water in the kitchen. This is, of course, concerning. Everything in that area (by the balcony door) was soaked in water. I turned on the main light and got down to look along the floor to see what was going on; my thoughts were the fridge/freezer had defrosted or there was a leak from the apartment above. There was a puddle under the fridge. When I looked closer, the whole fridge was wet, so that if I ran my finger down it, water dripped off my hand. But the water was all over the floor, not just by the fridge, all the way to the entry door (the one that whistled). This warranted further investigation. It wasn’t the best way to start a holiday! I cleaned up with towels as best I could and contacted reception, who told me that, as they didn’t manage this apartment, I had to talk to the landlord. This I did, and he was great and said this hadn’t happened before and he’d get right onto it. In the meantime, I investigated further. The bulk of the water was coming from the entry door, which opened out into the frigid hallway. The inside of the door was dripping profusely, and all around the frame and the door closer. The walls nearby were damp, but not awash like the door was. The card lock and closer were also rusted around the edges – not much, but enough to imagine that ‘this not happening before’ might be a bit of a fudge. I also noticed that opening any of the windows or the balcony doors not only solved the low hum but also resulted in the entry door not whistling when we opened and closed it. Interesting indeed! siliconchip.com.au Items Covered This Month • A damp holiday • Repairing a YaeCCC DC power supply • Fixing a Victa slasher lawnmover • Going back to an old design 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 Someone from the building maintenance team came up and checked the flat upstairs, but said there was no one in it and no obvious leaks. He then came down and looked into our place and said it looked a lot like condensation. If this were the case, why had it never shown up before? I’d certainly never seen such a thing, and I am no stranger to being in ‘the tropics’. Of course, the obvious answer as implied that it was somehow our fault, not running the ceiling fan (which we did) or not running the aircon (which we also did). Not a big fan The interesting thing about this place was that it had two bathrooms, and each had an extractor fan that we couldn’t switch off. These were no wimpy extractors like you can buy at the local big box store – from their noise and power, I think there was a Rolls Royce jet engine somewhere on the roof running these in most apartments! Now, I understand that keeping the air moving in apartments in ‘the tropics’ was important, as the humidity outside can be horrendous to people like me who come from essentially cold, dry places. But it seemed weird to have aircon running (also built into the building with control panels in each room) and ceiling fans as well, given that the air was being extracted, anyway. So, with our apparent inexperience of these systems in the tropics, what do we run? The extractors are obviously there to keep humidity down, but we Australia's electronics magazine January 2026  89 didn’t realise that then; we just assumed they were there to keep the bathrooms from steaming up (especially since one had the clothes washer/dryer in it). The landlord and the management of the complex, who had been involved, recommended we keep the doors and windows closed and both fans and aircon running at all times, as the outside humidity had been extremely high the past few days due to the non-monsoon-type rains. The resort receptionist, who was very helpful, told us that many mornings when she came in, she had to wipe down the walls behind her and the big reception desk in front of her. The ‘lobby’, such as it was, is open to the elements (though under cover), but there are no closing doors or even glass walls to the street outside. Residents and guests can just wander in from the car/bus drop-off area up to the desk. This must have played havoc with the three computers and many phones they had lined up along the desk, but I guess that’s just part of the job! A few quirks to the room and complex, then. The problem remained though; the entry door sweated badly, and the fridge doors also poured water onto the floor. And the hallway outside was freezing. My serviceman’s brain told me they must be related. Back to normal A day later – after lots of extra towels were dispensed to help us clean up the now constant water, we went out and to our surprise, the hallway was at a normal, cool-but-notAntarctic temperature. We mentioned this to the reception people, and they said yes, the aircon on that floor turned out to have been faulty but was now fixed. At least we wouldn’t freeze coming back from the pools... We spent the day out, returned in the evening, and our room had dried almost completely, with only a few drops beneath the door. The fridge door was dry, as were the previously damp walls and entry door fittings. Interestingly, the whistle didn’t happen either when we opened and closed the door, a sound we had almost gotten used to. Nor did we hear anything when the balcony doors were shut – no low annoying hum to keep us awake and requiring that we crack the windows or doors. It likely also helped that now the weather was not so monsoonish (although locals were seemingly always at pains to tell us that the previous day’s rains were nothing like the actual monsoon season!). I think what was happening was a kind of a perfect storm of circumstances (I know, just our luck!). Firstly, it was teeming down outside, so both the temperature and humidity were very high, as was the atmospheric pressure. Next, the very cold temperature in the hallway of the apartment building. The various floors are essentially sealed and climate-controlled areas, with fire doors and interconnecting security doors. Only the ground floor/ outdoor/pool areas were open to the weather. This created a low-pressure system inside the building, which was worse on our floor, where the aircon had gone into Antarctic mode. This also generated the whistling and humming when our windows were closed, or the main door opened, despite the fact, or perhaps because of, the gaps in the room’s joinery. So the front door was freezing on one side, warmer on 90 Silicon Chip the other, and the pressure in the room created an environment for condensation to build like crazy, resulting in us having to mop the floor. I would have thought the extractor fans and aircon would have seen to it, but they simply couldn’t cope with the amount of humidity, and the pressure/temperature difference between the rooms. Sadly, by the time we had all that sorted, we were due to leave. It was a very nice place, but I’m sure all the rooms on that floor would have experienced the same perfect storm of broken aircon, high atmospheric pressure and unseasonal humidity. As an aside, I did find out how to disable the annoying extractor fans, which were quite loud. Even though they put out a white/pink noise vibe, they were still distracting when trying to get to sleep or even watch TV, on top of the noise of the air conditioning system. The day we were packing up to depart, we went down to the pool for one last dip. When we came back up after lunch and drinks, the hallway was frigid once again. We called reception and advised them, but as we were leaving, we just wanted to get our stuff and go. The whistle at the door was back, and the hum from the doors and windows, and of course, the condensation had started to build up on the door and frame already. This was despite the fact that it hadn’t rained for the past few days, and the humidity wasn’t nearly as high as it had been. The pressure difference was still obvious, though; as they say up there, it is just a fact of life in the tropics! YaeCCC DC power supply repair I bought this power supply online when I started working from home pre-COVID-19, so it’s probably six years old. It wasn’t expensive; in fact, it was probably the cheapest one I could find. I don’t know how to say the brand name; however, I’m sure one of my old colleagues would have pronounced it “Yuck”! Still, it has been good, and I can’t complain. I use it most working days, sometimes all day, although usually at way less than its 6A rating. The Yuck is a switch-mode design with no linear regulator, so it probably is a bit noisy. However, my work is Australia's electronics magazine siliconchip.com.au An excerpt from the onsemi data sheet showing a DC-DC converter using the TL494. The Yuck PSU is similar but has an extra transformer between the TL494 and chopper transistor bases. mainly with microprocessors, which aren’t fussy in this regard. It has an annoying design characteristic that the output capacitor is after the current limit circuit, so if you set the voltage a bit high, then connect it to a low-voltage load like a light-emitting diode (LED), it will dump the output capacitor into the load, potentially blowing it up. Been there, done that. Any PSU that has the current limit incorporated into the switch-mode control loop will behave like this, and I’ve just learned to live with it. Recently, I noticed noise in one of my designs, and quickly traced it to the output of the Yuck. The noise was pretty significant – a couple of volt spikes at around 60kHz superimposed on the output voltage. It looked like switching noise, so I removed the lid and had a look at the output capacitors. I was expecting one of them to be bulging or to have leaked, but they both looked OK. They measured OK with the Fluke 189 meter too. Just in case the caps had a highESR fault, I briefly tried adding a capacitor to the output, with no improvement. At this point, I was a bit stumped. Switch-mode converters generally feed energy into the output capacitor via a diode – there isn’t really any opportunity for anything to get out of whack and noise to suddenly appear. When there’s voltage at the transformer output, the diode conducts it into a capacitor, and when there’s not, it doesn’t. Some switch-mode supplies replace the diodes with a Mosfet synchronous switch – if one of these was driven at the wrong time, it could conceivably result in spikes, but this PSU is an older design and just used two diodes. The main controller was a TL494. Looking at the Texas Instruments data sheet for it, I didn’t see anything about output noise, apart from layout guidelines – the layout wouldn’t have changed recently. For good measure, I also looked at the onsemi version of the TL494 datasheet, and it didn’t give me any clues either. The TL494 is a bi-phase PWM controller – it drives two switches out of phase. Both switching transistors looked OK and showed the same values on the meter. Same for the output diodes. siliconchip.com.au The data sheet shows a possible DC/DC converter design – the Yuck was generally similar to this, but includes an isolating drive transformer between the TL494 and the switches, since the switches are chopping rectified mains. Looking at the signals with the oscilloscope, you’d expect to see similar waveforms on both phases. Since I didn’t have a mains probe, I looked at the transformer outputs (ie, the output diode anode) and found the opposite – one side looked pretty regular, but the other was far from it. I found similar results at the TL494 outputs, before the drive transformer. I wasn’t sure what this really meant, but it didn’t look right, so in the absence of any better idea, I thought about replacing the TL494. My local Jaycar didn’t have them; however, the Bankstown store had packs of 10 on clearance for $2.95 plus postage. So I ordered a pack of 10 – two packs of 10 arrived a couple of days later. I’m not sure why I received two packs – I can only think that Jaycar must have really wanted to clear them out! Australia's electronics magazine January 2026  91 Fitting a new one was fairly quick, and I managed to do it without lifting any pads. Powering on, it worked first time, with no problems at all. No noise, just like was when I bought it. I still have no idea how the controller could drive the switches in a way that makes the output noisy. However, I’m just glad my PSU is back working; I need it. If anyone needs an SMD TL494, please let me know; I have a few spare! D. T., Sylvania Southgate, NSW. Victa Slasher repair Around 30 years ago, I bought a Victa 160cc 24-inch (61cm) slasher from a friend. We have five acres here in Queensland, and I use this slasher to mow around the boundaries and a 5m-wide table drain at the side of our property that brings runoff from the street into our dams. Over the years, I’ve done a lot of mowing with this slasher, and I have reconditioned or replaced the 160cc twostroke engine several times. Being a retired small engine mechanic, this is no problem for me. I even managed to pick up a couple more of these 160cc engines at the local tip shop around 20 years ago. My most recent repair was a couple of years ago, when I put new piston rings in the engine. Spare parts for this now over 50-year-old engine are getting really hard to find, so there will come a time when I will have to replace the engine with a different type. When the time comes, I may replace it with a Honda four-stroke engine, but I want to keep the Victa two-stroke engine going as long as I can. Having a bunch of spare parts in these spare engines has proved to be very helpful in achieving this. Sometimes I use parts from one of the engines, or I may rebuild one of them to replace the existing engine. Over the last couple of years, the slasher has become increasingly difficult to start. I knew what the problem was; it was the condenser, which is a 180nF 260V AC rated capacitor. I had been looking for a replacement for some time, but I could not find one to suit the early Series 70 engine, as it is smaller than in later engines. This difficulty starting got to the point where I had to pull the zip starter rope around 30 times to even have a chance to start the engine. I resorted to taking the zip starter assembly off the engine and using my electric drill to start it. I dismantled a couple of the spare engines to locate a replacement condenser. I found one that I could use, but then I decided to replace the entire magneto assembly of the coil, points and condenser. I got the parts I needed, so I removed the zip starter and flywheel from the engine on the slasher and removed the existing magneto assembly. After installing the new (used) assembly, I got out my buzz box (a type of continuity meter) to set the ignition timing. At first, the buzz box was making unusual sounds; I suspected that the 9V battery was partly flat. The Victa Slasher lawnmower (left), and the buzz box (above) that was used to set the ignition timing. 92 Silicon Chip Australia's electronics magazine siliconchip.com.au I opened the case and removed the battery and tasted it with my calibrated tongue. It tasted like it was about 8V, which would explain the unusual behaviour of the buzz box. With some experience, it’s possible to estimate the voltage of a 9V battery pretty closely this way. I got my multimeter out and tested the battery and, sure enough, it read 8.1V. I got a new 9V battery and fitted it to the buzz box, then used the buzz box to set the ignition timing at 0.25 inches (0.635mm) before top dead centre. After reassembling the engine, it started on the third pull – a good sign! The following two times I used the slasher, it started on the first pull. Another successful repair to keep this old slasher going for some time to come. Bruce Pierson, Dundathu, Qld. PICAXE doorbell repair I submitted a circuit that appeared in the May 2004 issue’s Circuit Notebook section (siliconchip.au/Article/3525). It was my first attempt at producing a useful circuit utilising the then-new PICAXE 08M microcontroller. It simply monitored our outside staircase using a beam-break arrangement made from IR transmitters and receivers at the bottom and top of the stairs. When triggered during the day, it rang a doorbell; at night, the bell rang and it switched on outside lights via a solid-state relay (SSR). Coming down the stairs, there was a delay of 20 seconds for the bell, but the light would switch on straight away at night. Today, all this could be done with ready-made devices. After all this time, it works perfectly apart from one of the four bells/chimes having stopped working, and another having started sounding sick. We require four, as our house is large and we wish to hear someone approaching the front door, especially if we are in the backyard. I took the back cover off the mains-powered chime and, as expected, found a mains capacitive voltage dropper circuit regulated by a 5.1V zener diode. The components looked pristine, so after removing the 1.5μF 450V X2 capacitor, I was shocked to find it only read about 390nF. That value still allowed the zener voltage to be correct off-load, but it dropped significantly when commanded to operate the chime. The functioning doorbell with a 1.5μF capacitor at 50Hz will have a capacitive reactance of around 2.1kW, giving about 113mA of available current. Falling to 0.4μF, the reactance increases to about 8kW, only providing about 30mA. The second bell/chime had the same problem, but its capacitance was just below 1μF. Replacing both 1.5μF capacitors solved the problems. I have since read that this is not an unusual problem with metallised polypropylene capacitors. With transient voltage surges over time , the X2 capacitors ‘repair’ themselves, producing holes in the foil layers due to the self-healing process. This prevents short circuits, but the capacity diminishes each time. Eventually, the value is so far below the rated capacitance that the power supply no longer works. A multitude of devices are powered by simple capacitive dropper circuits like this. They include bathroom, bedroom and passageway low-wattage security lamps and standby power supplies for many home appliances. The list is large, and I wonder how many things have been thrown away because of an X2 capacitor that has lost its capacity. SC Paul Walsh, Montmorency, Vic. siliconchip.com.au Australia's electronics magazine January 2026  93 Vintage Radio Rebuilding the Kriesler 11-99 Never one to take the easy way out, when rebuilding this Kriesler 11-99, I decided to ‘upgrade’ it to 10-pin ‘decal’ TV-type valves. I then had a lot of fun resolving the stability problems that created! By Fred Lever T his Kriesler 11-99 is a smart-­ looking portable radio from 1968 with a modern-looking dial and single control knob. It has production number 3878 and ARTS&P number AA035355. The set is quite light at 3kg. The designs of the cabinet and circuit are efficient in material and component use, respectively. I purchased this example intending to refurbish it using new valves. As I had purchased a box of 10-pin decal TV-type valves and sockets for other projects, I decided to see if the original Kriesler 9-pin valve line up could be replaced with 10-pin TV types. If successful, I could use the same technique for future repairs. The original 11-99 used a series of 9-pin dual valves: a 6AN7 triode-­ hexode, a 6N8 dual-diode-pentode and a TV deflection valve, the 6GV8 triode-­pentode, for audio amplification. A 6V4 full-wave vacuum rectifier rounded out the lineup. That gave it the equivalent of a six-valve lineup – see the full circuit in Fig.1. I reckoned I could provide those functions using a 6V9 heptode-­triode to replace the 6AN7, a 6U9 pentode-­ triode in place of the 6N8, and a 6Y9 dual-pentode instead of the 6GV8. 94 Silicon Chip The 6V4 could be dispensed with and replaced with a silicon bridge rectifier. Being a next-generation series, the decal valves have similar or higher gains compared to the 9-pin types. So the performance of the set should be at least as good as the original. The 10-pin valves are designed to work at medium HT voltages of 200V, so the original HT power supply of around 150V looked adequate. Changing the valves I started by removing all the original valve sockets and small components, leaving large parts like the transformer, tuning gang and speaker in place. The 10-pin sockets bolted into the holes left by the 9-pin sockets. I then fitted a gland for the mains cord into the empty rectifier socket hole. Stage-by-stage, I rebuilt the set and fixed any problems at each stage before moving to the next. Fig.2 shows the changes that were required in red. To reduce the heat and increase efficiency, I deleted the valve rectifier and used a Jaycar ZR1320 silicon mini bridge rectifier. That gave about 150V DC at the first filter and 135V DC at the second filter with a draw of 20mA, the figure I wanted to limit the whole set to. A concern I had straight away was the exposed nature of both the mains and HT terminations and wiring. The Photos 1 & 2: the mains wiring was too exposed and a shock hazard. Australia's electronics magazine siliconchip.com.au Fig.1: the original Kriesler Circuit. Source: www.kevinchant.com/uploads/7/1/0/8/7108231/11-99.pdf safety level for servicing is very subpar in this type of set with a very shallow chassis. With the chassis out of the cabinet, making accidental finger contact with a live mains wire was way too easy – see Photos 1 & 2. I covered the whole of the power supply section and the volume control with insulated covers, seen in Photo 3. The audio section I wired up the audio section first, as shown in Photo 4. The 6Y9 is quite useful as an audio valve; there are a couple of watts possibly available, depending on the HT voltage and the suitability of the output transformer. It should reflect a load of around 10kW to the plate. The original output transformer had an open-circuit primary! That explained the blackened 6GV8 and tired 6V4. I fitted a Jaycar MM1900 line transformer to the speaker with the primary connected to the 0.5W tap. I was mindful of the high gain of the 6Y9 valve, but having used the type in two other projects, knew at least to start off with a grid stopper to combat self-oscillation. Photo 3: the mains wiring after fitting safety covers. siliconchip.com.au The valve is designed as a video amplifier, so it has a wide bandwidth. It was up to me to restrict the bandwidth using external components and limit the gain for stability. One step I took to reduce the total stage gain was to connect the preamplifier pentode section of the 6Y9 as a triode with grid bias. At first, I wired the 6Y9 output pentode with back bias. Upon turning the set on, I was greeted with screaming and popping noises laced with hum. To cut the story short, I simply had to ditch the back-bias and cathode Photo 4: I wired up the power supply and audio amplifier first. Australia's electronics magazine January 2026  95 self-bias the power section to be rid of the screaming and hum. Once cathode bias was applied, the crankiness went away, but the stage was drawing a lot of current. Sure enough, it was running as a sinewave oscillator at about 16kHz! Bridging the output control grid (pin 8) to ground did not stop the oscillation, so it was apparent the output pentode section was doing it all by itself, using the output transformer as a resonator. I stopped that by putting a 20nF 400V damping capacitor across the transformer’s primary. The two valves then amplified well, yielding a voltage gain of 2400 times from input grid to output plate. The overall gain of a 6GV8 is about 625 times, so the 6Y9 with 2400 times has plenty in hand to implement negative feedback if required. The power pentode drove about 4V into the speaker coil at clipping, indicating a couple of watts of output power. With that running well enough, I moved on to the detector and intermediate frequency (IF) stage. The IF section The 6U9 IF valve powered up in a grounded cathode configuration and immediately ran as a 470kHz sinewave oscillator, so I needed to bias it back up its gain slope to stabilise it and provide amplification. The simplest way of doing this was to self-bias the valve, get it under control, and let the automatic gain control (AGC) just do extra bias gain control in service. Even with that done, the stage was making hissing noises from the detector diode (the triode) and the 455kHz IFT coil resonance was limited. I had to manually cathode bias the valve back up its gain slope by increasing the bias to a silly value to get it stable. It became apparent that the base Scope 1: the initial IF system response looked pretty good. 96 Silicon Chip Photo 5: my original socket orientation had the wires crossing over, resulting in instability. Photo 6: rotating the socket 180° fixed the problem. wiring was involved in this, as moving the grid and plate leads around could ‘tune’ the instabilities in and out with squeals and popping noises! This was a lead dress issue, and all my own fault. I had mounted the socket without much thought to lead dress; the grid, diode load and plate leads were crossing over, making the valve unstable – see Photo 5. The yellow wire is the control grid drive to pin 3, the blue wire is the IF plate output from pin 7, and white is the diode load for pins 9 and 10. The leads were all too long, too close and crossing each other as the socket pin orientation was wrong. I fixed this by rotating the socket 180°, as seen in Photo 6. The yellow, blue and white wires are then short, direct and well away from each other, and the centre shielding ferrule can do its job. That was all it took to restore serenity. I left the IF stage with a low gain of about 40 times, with plenty of scope for reducing the cathode bias later to up the gain, and moved on to the front end. Scope 2: the initial oscillator grid (cyan) and plate (yellow) signals required some tweaking. Scope 3: the oscillator signals looked a lot better after adding a damping capacitor. Australia's electronics magazine Mixer and tuning coils I wired in the 6V9 as a classic grounded-cathode, grid-tuned biased-triode oscillator and a heptode tuned-grid mixer. Upon power-on, siliconchip.com.au Fig.2: my modified circuit. Besides swapping the values, most of the changes I had to make related to keeping the higherfrequency valves stable. there was no oscillator action. The tuned winding on the oscillator coil was open circuit! I stripped and rewound the coil, putting 100 turns on for the tuned winding and 30 turns for feedback. The oscillator then sprang into life, and the set received signals over the band with an indoor aerial, but there was obviously something not well as the IF output level was low, generating only -1V for the AGC signal. I performed a quick sweep check of the IF strip response to check the coils; that looked OK (Scope 1). Next, I checked the oscillator waveforms and amplitudes, looking for problems. The good news was that the triode tuned-grid amplitude was strong, at 30V peak-to-peak, and level from 1MHz to 2.5MHz (the cyan trace in Scope 2). The bad news was that the plate circuit was full of resonance (the yellow trace). I put a 220pF damping capacitor across the plate winding, and that got rid of a lot of the harmonics, or at least the higher ones (Scope 3). That siliconchip.com.au looked nicer, but it did not solve my IF problem. While scoping the 6V9 and 6U9 pins, I realised there was a large 100Hz component on the signal plates! That was not right. The HT ripple at the 6V9 and 6U9 supply point was about 0.4V, and this was getting into the signal streams and appearing at a level higher than the RF/IF signal! I fixed that in two ways. One, by separating the RF/IF stage’s HT from the audio HT with a low-pass filter comprising a 2.2kW series resistor and 10μF electrolytic capacitor to ground. Two, by providing a separate screen supply for each valve. Then the 6V9 and 6U9 were settled and stable, even when biased to a higher gain. Those two changes fixed all the stability problems the front end had. A rough check of the IF valve gain showed it was now around 60 times, depending on the AGC bias level, which now was regulating up to -6V depending on the received signal level. With the whole set working reasonably well, it was time to align the front end. Australia's electronics magazine The tuning range The dial tuning range is fixed by the reactance of the ferrite aerial rod winding and the gang. The only adjustment is the trimmer on the tuning gang. I checked the resonance range of the aerial coil (80 turns for tuning with a five-turn primary) and determined it varied from around 500kHz to 1700kHz. The stated tuning range of the 11-99 was 525kHz to 1635kHz. I took that as the figure and decided to tune the oscillator coil to give a range of 980kHz to 2080kHz (455kHz higher). Luckily, my 100-turn to 30-turn winding reached that by adjusting the one slug in the coil with the gang trimmer set at halfway. In theory, the specially shaped padderless gang should maintain 455kHz between the tuning coil and the oscillator coil. Even without an aerial wire attached, while tuning over the range, each local station came in at a good volume. Tuning over each station, I could scope a strong 455kHz resonance from the IF valve plate, and the detected audio January 2026  97 Scope 4: reducing the stability capacitor and some other tweaks made the audio sound much better. Scope 5: the oscillator tank signal. Scope 6: the mixer plate has the IF signal modulated by the audio waveform. pushed the volume control setting down below halfway. However, the speaker audio sounded muffled and unpleasant. There was around 30V peak-to-peak on the detector, so that was working well, clear of low-level diode knee distortion. The waveform on a sinewave-modulated test signal was clean, so the muffled sound was more likely due to a poor frequency response. With the front end working well, I moved back to the audio stage and investigated this further. I swept the audio response from the triode grid to the speaker coil over a range of 50Hz to 5kHz. The test showed the treble rolling off and too much bass for the tiny speaker. That rolled-off frequency response, or excessive bass, was the cause of the muffled sound. Applying a feedback loop from the voice coil to the 6Y9 triode’s cathode evened the response out a bit, while reducing the overall gain of the audio section. That was a good thing, as the volume control was working right near the start of its travel, especially with an aerial attached. I left the feedback loop and paid some more attention to the output transformer circuit. The 20nF value for the stability capacitor across the output transformer primary was the main culprit rolling off the response. The 6Y9 valve was always close to UHF instability, and would spill over at 16-30MHz if provoked, as well as oscillating at audio frequencies. That UHF instability was reduced by strapping a 220pF disc ceramic from the triode grid to ground at the valve socket end, and placing a 470pF mica capacitor across the grid feed point at the volume control end. The wire connecting the two points had to be shielded. The capacitors appear to be duplicates, but they do two different things. The disc is a shunt for UHF signals at the socket, while the mica capacitor acts as a roll-off for the IF filter at the other end of the shielded cable feed to the grid. This bypassing would be a bit unusual with normal superhet valves, but these decal valves are tiny internally and do not have the higher internal capacitances that would normally roll off the high-frequency response. I find you have to make circuits with decal valves the way IF strips are made in a TV. That is, bypass points with ceramic caps at the socket pins. Most of the resistors and capacitors in this Kriesler build are soldered right onto the valve sockets with short leads, to follow this practice. With the stage not bursting into oscillation above 1MHz, I then examined the effect of the plate roll-off capacitor on the frequency response. A few sweep tests indicated that the initial 20nF was overkill; reducing that to the final value of 6.8nF made the tonal balance much better. Scope 4 shows the final sweep response. All these changes perked up the mid-range and removed the muffled aspect of the sound from the speaker. The speaker is a small, 5-inch (127mm) type of average quality with not much baffling, so a sweep of its cone audio output would probably show most of the bass absent; the output would mostly contain mid-range frequencies. Scope 10: the audio signal at the AGC point is even cleaner. Scope 11: the audio preamp valve plate has picked up a bit of RF hash. Scope 12: the picked-up RF is gone by the time the signal reaches the power amplifier plate. Australia's electronics magazine siliconchip.com.au The audio response 98 Silicon Chip Final tweaking With those changes made, the set tone was more balanced and speech clear, so I then turned my attention back to the IF and mixer stages to get a bit more gain and better AGC. The most practical thing I could do was to carefully set the oscillator coil to shift the stations closer to the dial markings by using a deeper slug position. Scope 7: the grid of the IF valve has a much reduced IF signal component. Scope 8: the signal at the IF valve plate is significantly amplified. Scope 9: the detector diode output has a mostly clean audio signal. That had the effect of increasing the coupling of the primary and secondary coils, lifting the oscillator activity another 25%. I now had the set tuning local stations using the stick antenna alone, with the volume control between halfway and three-­ quarters, and around -3V on the AGC line. I think the oscillator coil could do with a rewind and closer coupling, but it is sufficient as-is. The tuning is very selective, mainly due to the IFT response being very sharp. I noted in the original 11-99 that they loaded the first IFT secondary with a damping resistor, presumably to broaden the skirts and widen the audio bandwidth. I tried that in my build, but there was no practical difference. I drove the antenna terminal with a 1000kHz signal amplitude modulated at 420Hz and scoped various points. In Scope 5, we see the tank resonance is not a pure sinewave. The harmonics in the primary are disturbing the tank resonance. I assume the triode is running into cutoff and saturation, but that is the best it can do. I could try re-winding the coil with fewer turns, but the effect is minor. In Scope 6, the mixer plate signal contains the 420Hz modulation and a mix of carrier and oscillator sinewaves. In Scope 7, at the IF valve grid, the bulk of the carrier station RF is rejected and a 455kHz ‘carrier’ bears the 420Hz audio signal. In Scope 8, at the IF plate, the 455kHz ‘carrier’ and modulation have been amplified by the IF valve to about 100V peak-to-peak and applied to the second IF transformer’s primary. That appears at the detector diode, on the secondary of IFT2, as shown in Scope 9. The positive swing of the IF signal has been shunted to ground, and a negative DC offset modulation signal exists. Most of the RF has been removed by the diode circuit’s filter capacitances. After the diode load resistor, the audio signal can be seen in Scope 10. Here, more RF is filtered out, leaving mostly audio-frequency components to the volume control. In Scope 11, the 6Y9 triode preamp plate has picked up a surprising amount of RF radiated hash, but by the time we get through the power valve, that has been lost and the voltage swing can be over 200V peakto-peak into the output transformer (Scope 12). Photo 7 shows the under-chassis component layout, while Photo 8 Photo 7: all the signal connections (via wires, resistors or capacitors) have been kept as short as possible to improve stability. Moving a wire or component by just a few millimetres can make all the difference! siliconchip.com.au Australia's electronics magazine January 2026  99 Photo 8: the top of the chassis has been left alone as much as possible, except for swapping over the valves. Shielding the valves didn’t seem to improve the stability, so I didn’t bother. shows the view from the top. The parts such as non-signal dropper resistors are mounted mainly on the centre tag strip, while signal-carrying parts are mounted directly on the valve base pins as much as possible. In Photo 7, the signal runs from the upper right-hand corner of the chassis down from the tuning coils, through the 6V9 mixer, IFT1 at lower right, then to the left across the chassis from IFT1 to the 6U9 IF valve, through IFT2, up to the volume control, back down to the 6Y9 output and out to the speaker. The tuning coils are unshielded, causing low-level whistles while tuning. I tried a shield can over the IF valve, and that helped there, but the problem is minor. Valve shield cans did not help with instability problems at any time, so I did not include any. Cosmetics The cabinet was originally all a bone colour, but it was warped and badly scuffed, with cracks and missing ventilation bars on the back. I just did a rough patch-up job with some epoxy resin to hide the worst of the damage. The front panel cleaned up nicely, so I left that and the dial in the original colours. The cabinet received a sanding and a couple of coats of “Go Go Blue” to give a ‘two-tone’ look, and it turned out fairly neat looking. Conclusion Photo 9: the chassis fits neatly into the restored cabinet. Photo 10: I used epoxy to fix the broken bars and fill in the cracks, then gave it a coat of paint. 100 Silicon Chip Australia's electronics magazine The set will play the local stations using the internal stick aerial. With an indoor wire attached, it will pick up all the available stations with good sensitivity and selectivity. The audio system is sufficient; the speaker level is loud, with good quality on speech and average quality on music. The AGC characteristic in still not perfect; a better-sorted system would hold the level constant no matter what aerial is connected. Still more work could be done on that. I have successfully demonstrated that the 6*9 decal series can be substituted for the original 9-pin type in a 1960s radio as long as a little care is taken to stabilise them. The article is a much-reduced version of a series posted in the special builds section of the “Vintage Radio” website hosted by Brad Leet: • https://vintage-radio.com.au/ docs/Kriesler-11-99-rebuild-111122. SC pdf siliconchip.com.au ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Send your email to silicon<at>siliconchip.com.au Setting DVDD on the RP2350B Computer I have a question regarding the adjustment of potentiometer VR1 on the RP2350B Computer (November 2025; siliconchip.au/Article/19220). I have a fairly basic DMM (Digitech QM1323) and I get different resistance readings depending on which probe is on which test point (DVDD/TP1). If the positive probe is on TP1 and the negative on DVDD, it reads about 17.6kW; if the negative probe is on TP1, it reads about 18.4kW. Is there a preferred method of measuring it, or am I doing something wrong? (M. B., Woodford, Qld) ● Geoff Graham responds: You can expect a difference, perhaps due to the DVDD input on the RP2350B partially conducting. So what you are seeing is perfectly normal. The output from the TPS7A7002DDAR is not particularly accurate anyway (possibly due to tolerances of its voltage reference), and I have found the RP2350B to be quite forgiving with relation to the DVDD. So the exact setting is not that critical. Unfortunately, the article implied that accuracy is important (something I realised after it was published). Improvements for the Digital Preamplifier I appreciate the effort that has been put into the Digital Preamplifier & Crossover project (October-December 2025; siliconchip.au/Series/449) by Phil Prosser and possibly others. It’s a testament to that work and to Silicon Chip’s faith that such a project will be popular. I’m looking at putting one together, but before I do, I’d like to make some comments and ask some questions. 1. The use of MKT polyester capacitors. These are recognised as being of limited use in audio gear where time constants are set or used, such as coupling and filters in audio circuits. Such use leads to increased distortion, often third harmonic. There are several references to this, RP2350B Computer pin numbering is inconsistent I am interested in the RP2350B Computer but have been confused by the relationship between Table 1, and the circuit diagram, Fig.1. It looks like most pins have been transposed. For example, GP01 is shown as being connected to I/O pin 5 in the table, but pin 6 in the circuit diagram. Similarly, GP00 shows as pin 6 in the table, but pin 5 in the diagram. This transposition carries right down the table; GP45 shows as pin 25, but the circuit diagram shows pin 26. The 3.3V, 5V, and GND pins do not matter, as they are all in pairs. I also note that COM1 RX is shown in the table as connected to I/O Pins 5, 13, and 25. Does this mean that any of these pins can be selected as COM1 RX (or transposed as pins 6, 14 & 26)? However, whilst there are two COM1 TX options, no COM1 enable pin is shown. Does this mean the RP2350P computer will not support RS-485 simplex communication (which is my interest)? (I. T., Duncraig, WA) ● Geoff Graham: You are correct; comparing the table on page 28 with the pin numbering in the circuit diagram, the numbers are swapped between the odd and even pin numbers. The pin numbering in the table is correct with respect to the silkscreening on the PCB and the back panel that we supply, so it is the circuit that is incorrect. COM1 RX can be used on any of pins 5, 13, or 25. The actual pin number (or GPIO number) to be used is selected by an option in MMBasic. The same goes for COM1 TX, etc. There is no enable pin on any of the serial I/O ports, as the RP2350B Computer does not support RS-485. siliconchip.com.au Australia's electronics magazine for example, Cyril Bateman’s series of articles on capacitor distortion in Elec­ tronics World from July 2002 to February 2003 and Douglas Self’s chapter two on components in Small Signal Audio Design, 4th edition. In these, they recommend and justify the use of polystyrene, polypropylene and possibly polycarbonate capacitors for audio use. The tolerance of such MKT caps (typically ±5% or ±10%), particularly for filters, may mean that you don’t get what you think you’re getting, especially in terms of frequency response. I appreciate that PCB real estate is limited, as are budgets, but I still think that the use of polyester capacitors in such a high-end project should be limited to supply bypassing and suchlike. Note that MKT polystyrene capacitors are still available in ±1% tolerance from such manufacturers as Vishay and LCR. 2. The use of what is, by now, the venerable NE5532. This is still an excellent op amp, even though it’s nearly 50 years old, but by today’s standards, it brings with it several problems. Given that, Douglas Self recommends it for many common uses as long as you don’t use those made by Texas Instruments. An article by Douglas Self in AudioXpress for January 2025 this year indicates that the 5532 used as a voltage follower has significantly increased distortion above 2kHz and is sensitive to source impedances above 2.2kW. I note that better units are somewhat more expensive, but LM4562s and OP2134s are fairly reasonable and both are available as DIP units. Are there alternatives that can provide better performance? 3. Can the op amp power supply rails be increased to ±17V or ±18V without ill effects? 4. I’m concerned about the Earthing system used, but that is based on what I’ve seen of the unit so far. I will have to wait until I see the third article to comment further. January 2026  101 5. Would you consider redesigning the PCB to suit SOIC op amps as many modern devices don’t come in DIP? (K. J., Brisbane, Qld) ● This is a noise-limited design, with the noise figures of the ADC and DAC determining the ultimate performance. Phil Prosser wrote that the measured THD+N is flat from 20Hz to 20kHz because any distortion is buried in the noise floor. That means that: a. No audible improvement in performance is likely possible without changing the ADC and DAC chips. Phil looked for better parts during the design phase and couldn’t find any at reasonable prices. b. If there could be any audible improvement in performance, it would be through lowering the noise somehow, not reducing distortion. Regarding your particular points: 1. We know that MKT/polyester capacitors are not perfectly linear, but they are pretty good. If the distortion they are introducing is so small that it’s unmeasurable under the noise, we can’t see the point in spending any more money or board real estate on better capacitors. ±5% MKT capacitors are readily available, and we suggest using them if possible. If you really want to, there is little stopping you from substituting MKP or NP0/C0G ceramics for all the MKT capacitors. Both MKP (polypropylene) and NP0/C0G ceramics are extremely linear and introduce vanishingly small amounts of distortion. However, we think that doing this would cost you some extra money for no real benefit, but there’s nothing stopping you from doing it. You may have to get creative when mounting the bulkier MKPs, if that’s the route you choose to take. NP0/C0G ceramics will probably fit without any difficulty. 2. Yes, there are undoubtedly better op amps than the NE5532, but it is still very good and inexpensive. We know that it works well in this circuit because Phil has measured the performance. Making substitutions is not recommended and will almost certainly result in worse performance. That includes the OP2134 (higher noise – definitely not a good idea) and LM4562 (tends to be unstable and is bad at rejecting EMI pickup and supply rail noise). Could the distortion be reduced by using more expensive op amps and likely other circuit changes (eg, to 102 Silicon Chip bypassing and so on)? Likely, yes. But that will just mean the distortion is even more buried in the noise. Would there be an audible change? Unlikely. Again, nothing is stopping you from using different op amps, but we think you will be spending more for worse performance (or the same performance). The ADC/DACs are the main limit on the performance. 3. We don’t see a lot of advantage in increasing the op amp supply rails, since the op amps are not the limiting factor on performance, but you probably could. It will increase dissipation in REG3, which has a small heatsink – you’d better check it doesn’t run too hot. Op amp dissipation will also increase (and there are quite a few of those). You would need a different transformer to get enough headroom to do this. This change is possible, but we don’t recommend it. 4. We know the performance is good when measured under realistic conditions, so we think Phil’s Earthing choices are likely fine, although it may depend on how you connect it to other equipment. 5. Since we recommend against changing the op amps, we can’t justify developing a new board to suit SOIC devices. We think that using adaptor boards should be OK; the pins soldered to those boards will draw heat away from the chip just like the PCB would if they were soldered directly to it. Also, the dissipation of each dual package won’t be that high running from ±10V (about 160mW each). If you must use SOIC op amps and are concerned about dissipation, you could glue a small heatsink to the top of each device. Using the Solar Diverter with an EV I was on the verge of building the Hot Water System Solar Diverter (JuneJuly 2025; siliconchip.au/Series/440) to run our 3.6kW resistive hot water system cheaply from our solar panels. Then we went and did a silly thing and bought an electric car. We don’t anticipate driving huge distances from home on consecutive days, so there’s no need for a powerful charger at home, and we will therefore rely on a 2kW “granny charger”. It would be nice to be able to charge the car with surplus solar power, Australia's electronics magazine preventing grid draw as much as possible, even if it is limited to 10A. My understanding of EV charging is that the thing that is commonly called a charger simply passes the mains unchanged from an ordinary power point to the Type 2 charging port on the car, with the real charger in the car. I am unsure if the HWS Solar Diverter, as designed, would be suitable for supplying power to charge an EV. Also, if I build two Diverters, one for the HWS and a second one for the EV, they will need to coordinate to split the available surplus solar power between the HWS and the EV. Maybe one could be the master and the other as a slave? (A. P., Norwood, Tas) ● Ray Berkelmans responds: Since the EV charger is not a resistive load, it will probably not respond well to the ‘skipped cycle’ modulation scheme used by the HWS Solar Diverter. You could do what I did and simply buy a subscription to ChargeHQ (https:// chargehq.net). It costs a mere $7 per month and it controls the power delivered to the EV. It has turned our Tesla dumb charger into a smart charger. Many brands of EV and solar inverter are supported. When we changed solar inverters to a brand that wasn’t supported, I was pleased to see that they have an API whereby you can provide your inverter export data to ChargeHQ and their control app still works. All I had to do was use a small ESP8266, read my inverter data every 30 seconds and send it to ChargeHQ via their API. Regarding which devices take priority in using the excess (export) power, I have two HWSs and an EV all vying for the same available watts. As it turns out, the HWSs get priority only because they poll the inverter every 5s and therefore have the most immediate demand. The data for the EV is updated every 30s, so only starts charging when the HWSs are up to temperature. Of the two HWSs, the smaller system on the granny flat gets priority, only because I set the excess power threshold a bit lower. Battery Checker battery holder problem I have just finished building the Versatile Battery Checker (May 2025; siliconchip.au/Article/18121) and it 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 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 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 Dual Mini LED Dice August 2024 SMD LED Complete Kit SC6961: $17.50 TH LED Complete Kit SC6849: $17.50 siliconchip.au/Article/16418 Includes either 3mm through-hole or 1206sized SMD LEDs. Choice of either white or black PCB. CR2032 coin cell not included. 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 January 2026  103 seems to work OK except with AA cells. When I run the calibration (Screen 6), I get a “scan failed check battery” error. It also does not show EXT on the top line. I am using a brand new Energiser Max battery; calibration works fine with a 12V battery and shows EXT. Running a test on the AA cell gives very erratic and unexpected results; sometimes I get a reading of 1.3W, but I also get occasional “I too high” or “V too low” errors. I have checked the cell, and it can deliver 7A when short-­ circuited. With an old 12V 18Ah SLA set to 20A, I get 17A and 11% drop, which seems about right. Thanks for a great magazine and great articles. I am 79, so this project was a real test of eyesight. I certainly would not want to try anything with much smaller components, but I guess I can put off a new eyesight test for a bit longer. (T. O., Ngaruawahia, NZ) ● We’re happy to have a look over Advertising Index Altronics.................................45-48 Blackmagic Design....................... 5 Dave Thompson........................ 103 Emona Instruments.................. IBC Jaycar.................. IFC, 10-11, 24-25 Keith Rippon Kit Assembly....... 103 Lazer Security........................... 103 LD Electronics........................... 103 LEDsales................................... 103 Microchip Technology.............OBC Mouser Electronics....................... 3 OurPCB Australia.......................... 8 PCBWay......................................... 7 PMD Way................................... 103 SC Dual Mini LED Dice.............. 103 SC Ideal Bridge Rectifiers........... 77 Silicon Chip Kits........................ 75 Silicon Chip PDFs on USB......... 34 Silicon Chip Subs...................... 61 Silicon Chip Shop.................86-87 The Loudspeaker Kit.com............ 9 Wagner Electronics..................... 93 104 Silicon Chip your construction if you can email a close-up, in-focus digital photo. The EXT message simply means that the Checker is powered from the battery under test (BUT). If EXT is not showing, we expect this to be showing 8-9V to indicate the health of the 9V battery that is powering the unit. The 1.3W reading seems quite high even for a AA cell. If it can deliver 7A, its internal resistance must be no more than around 200mW. So we think you have extra resistance in the circuit when you are testing AA cells and that is affecting the readings. Consider what is different between when you check the AA cell and the 12V SLA battery. The reader followed up with a find­ ing that the cell holder was presenting a high resistance that interfered with calibration. He was able to complete the calibration by holding the leads from the Battery Checker directly against the cell’s terminals while run­ ning the calibration sequence. 500W Amplifier design question Thank you for the fine publication that I look forward to reading each month! I am thinking of building the 500W Amplifier Module (April & May 2022; siliconchip.au/Series/380). Looking at the circuit diagram on page 30 of the April 2022 issue, I see that a 33kW resistor is connected to the wiper of trimpot VR1. Having built many Silicon Chip amplifiers in the past, this value looks too high to me, and I’m not sure if much/enough current is flowing through transistors Q1 & Q2, despite the fact that the power supply rails are ±80V. I can’t see any errata regarding an error. Is this value definitely correct? What is the design value of the collector current in Q1 and Q2? (J. D., Endeavour Hills, Vic) ● The current through Q1 and Q2 is set by the voltage across the 470W resistor at the emitter of Q5 to around 1.5mA, assuming a 0.7V base-to-­ emitter voltage for transistors Q5 and Q7. The 33kW resistor does not set the current; it is present merely to reduce the dissipation in Q5 by sharing some of the voltage drop that would otherwise be between the collector and emitter of Q5. If you multiply the 1.5mA current from Q5 by the 33kW resistor value, you will see that there will be around 49.5V across the 33kW resistor, giving a dissipation of 74.25mW (49.5V2 ÷ 33,000W) in that resistor. Since Q5’s emitter is at around +79V and the emitters of Q1/Q2 only swing a few volts above ground, you can see that there will be around 25V between Q5’s emitter and collector. That’s plenty of headroom, so the 33kW resistor won’t have any effect on the circuit’s operation except to let Q5 run a bit cooler. VHF aircraft radio receiver circuit wanted Do you have any articles or kits for receiving radio transmissions on aircraft frequencies? (A. L., Saratoga, CA, USA) ● The only article we have for an aircraft receiver is in the Circuit Notebook section of the December 2008 issue, titled “VHF Aircraft Receiver With Squelch” by Dayle Edwards SC (siliconchip.au/Article/2029). Errata and on-sale date for the next issue Four-colour e-paper display, Circuit Notebook, November 2025: diode D1 is shown backwards in the circuit diagram. Its cathode should be on the right. RP2350B Computer, November 2025: the pin numbering for CON8 in the circuit diagram, Fig.1, is mirrored compared to Table 1 and what’s shown on the back panel. The function of each pair of pins (1 & 2, 3 & 4 etc) on CON8 in Fig.1 should be swapped to be consistent. The pin numbering in Fig.2 also needs to change as it was based on Fig.1. Active Mains Soft Starter, February & March 2023: the 15V zener diodes should have been specified as 1N4744 types, not 1N4742 (which is the 12V equivalent). Next Issue: the February 2026 issue is due on sale in newsagents by Tuesday, January 27th. Expect postal delivery of subscription copies in Australia between January 26th and February 13th. 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