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AUGUST 2025 ISSN 1030-2662 08 9 771030 266001 The VERY BEST DIY Projects! Mthiec Mouse $1300* NZ $1390 INC GST INC GST Ducted Heat Transfer Controller RP2350B Pre-Assembled Development Board USB-C USBPower Monitor Measure current, voltage, power, energy & time on all modern USB-C devices NEXT-LEVEL PRINTING HAS LANDED AT JAYCAR Jaycar now stocks an extensive range of ELEGOO® FDM & Resin 3D printers and materials, from entry-level favourites to powerhouse machines trusted by enthusiasts. • 7 NEW Filament Printers • 6 NEW Resin Printers • Wide range of Filament and Resin EXPLORE THE ELEGOO® RANGE (AU) Explore our great range of ELEGOO® 3D Printing gear, in stock on our website, or at over 140 stores or 130 resellers across Australia and New Zealand. jaycar.com.au 1800 022 888 | jaycar.co.nz 0800 452 922 EXPLORE THE ELEGOO® RANGE (NZ) Contents Vol.38, No.08 August 2025 11 SpaceX, Part 2 There’s more to cover on SpaceX’s enormous Starship rocket, and after that, we’ll look at their launch and recovery facilities, some notable SpaceX missions to date and then consider their future. By Dr David Maddison, VK3DSM Space technology 23 Amplifier Cooling, Part 1 Designing the chassis for an amplifier (especially a large one) is crucial to achieving the best possible cooling performance and therefore a long life. We also look at upgrading the cooling in existing amplifiers. By Julian Edgar Electronic system design 34 A Thin-Film Pressure Sensor s p a c e X Part 2: Page 11 Thin-film pressure sensors are an affordable way to measure force and weight, albeit without high accuracy. By Tim Blythman Low-cost electronic modules 52 Rigol DHO924S Oscilloscope Rigol’s new DHO900 series has a plethora of modern features in a compact package. We describe what these new features are, and what it’s like to use. Review by Tim Blythman Test equipment 67 The Boeing 737 MAX story We explain how the failure of a single electronic part led to two fatal air crashes. By Brandon Speedie Aerospace technology 38 USB-C Power Monitor, Part 1 Our Power Monitor measures current, voltage, power, energy and time on all modern USB-C devices, and even legacy USB devices with an adaptor. It’s a self-contained unit, and is powered by a 400mAh rechargeable battery. By Tim Blythman Test & measurement project RIGOL DHO924S Oscilloscope 2 Editorial Viewpoint 4 Mailbag 73 Subscriptions 82 Circuit Notebook 84 Serviceman’s Log 91 Vintage Radio 98 Online Shop 100 Ask Silicon Chip 103 Market Centre 104 Advertising Index 104 Notes & Errata 46 RP2350B Development Board Like a Raspberry Pi Pico 2 on steroids, this breadboard-friendly module has 47 available I/O pins, including eight that can measure analog voltages. It’s also optimised for overclocking! By Geoff Graham & Peter Mather Single-board computer project 60 Mic the Mouse Mic the Mouse doesn’t eat much, just the occasional 3V lithium cell, and it makes a good project for playing pranks on family and friends. By John Clarke Toy project 74 Ducted Heat Transfer Controller Improve the energy efficiency of your home by transferring warm or cool air between rooms automatically using this smart controller. Part 1 by Julian Edgar & John Clarke Home automation project Page 52 1. High speed transmission opto-couplers 2. A wireless battery charger 3. 3-way latch using SCRs Silvertone Model 18 AM/FM radio by Associate Professor Graham Parslow SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke – B.E.(Elec.) Technical Staff Bao Smith – B.Sc. Tim Blythman – B.E., B.Sc. Advertising Enquiries (02) 9939 3295 adverts<at>siliconchip.com.au Regular Contributors Allan Linton-Smith Dave Thompson David Maddison – B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Geoff Graham Associate Professor Graham Parslow Dr Hugo Holden – B.H.B, MB.ChB., FRANZCO Ian Batty – M.Ed. Phil Prosser – B.Sc., B.E.(Elec.) Cartoonist Louis Decrevel loueee.com Founding Editor (retired) Leo Simpson – B.Bus., FAICD Silicon Chip is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 626 922 870. ABN 20 880 526 923. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Subscription rates (Australia only) 6 issues (6 months): $70 12 issues (1 year): $130 24 issues (2 years): $245 Online subscription (Worldwide) 6 issues (6 months): $52.50 12 issues (1 year): $100 24 issues (2 years): $190 For overseas rates, see our website or email silicon<at>siliconchip.com.au * recommended & maximum price only Postal address: PO Box 194, Matraville, NSW 2036. Phone: (02) 9939 3295. ISSN: 1030-2662 Editorial Viewpoint Supplier price increases I had hoped we could avoid raising the magazine’s cover price or subscription rates this year. Unfortunately, several factors beyond our control mean we must do so to continue producing a magazine with the same level of quality and content. The new prices (listed below) will take effect from the next issue, or for subscribers, on renewals from the 1st of September. If you’d like to lock in the current, lower rates, you can extend your subscription now and save a few dollars. While I dislike price increases as much as anyone else, if you compare the price-to-content ratio of Silicon Chip to other magazines, I think it’s still a good deal. Over the past couple of years, we’ve worked hard to reduce our business operating costs to avoid price rises. However, those savings have been more than wiped out by increased supplier costs. That left us with a decision: reduce the amount of content in each issue, or raise prices to maintain it. I believe most readers would prefer the latter, so that’s the path we’ve chosen. The costs of both printing and postage have increased substantially this year. I negotiated a favourable printing deal at the end of last year that I hoped would last for at least 12 months. However, I have recently been told it is no longer available. As a result, our printing costs increased by 27% virtually overnight. It looks like there may soon be less competition in the magazine printing industry in Australia. Of course, less competition and less choice means higher prices. Australia Post is also increasing prices again. In January 2020, you could mail a regular letter for $1.00. By the time you’re reading this, they will be charging $1.70. You don’t need to be a mathematical wizard to calculate that’s a 70% increase in around five years – way above the rate of inflation. As a comparison, the change in the Silicon Chip cover price since 2013 (from $9.95 to $14.00) fairly well matches the rate of inflation over those years. Also, companies are reducing the amount they are spending on sponsorships and advertising. One advertiser pulled out after being hit by the ridiculous US tariff situation. Others are simply tightening their marketing budgets for various reasons. When advertising revenue drops, the only practical way to make up the shortfall is by charging more for the magazine. I’m hopeful that our recent cost-cutting measures, such as relocating from the large Brookvale office to more affordable premises, will help limit further price increases in future. But, in the end, we’re still at the mercy of our suppliers. I want to keep this magazine going for many years to come, and that means it has to remain financially viable – without reducing quality. So, from the September 2025 issue onwards, the cover price of the print edition will be AU$14.00 or NZ$14.90; the online issues will not increase (see prices in the masthead). The subscription prices will change as shown in the table below. by Nicholas Vinen Subscription Prices, effective 01/09/2025 New Prices Print (AU) Printing and Distribution: 24-26 Lilian Fowler Pl, Marrickville 2204 2 Silicon Chip Combined (AU) Print (NZ) Combined (NZ) RoW 6-month $72.50 $82.50 $85 $95 $105 12-month $135 $155 $160 $180 $200 24-month $255 $280 $300 $335 $390 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”. Low tempco voltage references with zener diodes I was interested to read in the latest Silicon Chip magazine about stable voltage references (Precision Electronics pt8, June 2025; siliconchip.au/Article/18312). There is a very interesting aspect that most don’t know about. That is because it was deployed in alternator voltage regulators, as a temperature-stable comparator, in the days before op amps were in widespread use (from the mid1960s to the 1970s). The designers had figured out the negative tempco (temperature coefficient) of a transistor base-emitter (B-E) junction was around -2mV/°C. They also knew that zener diodes that broke down below around 5V tended to have a negative tempco too. But those with a breakdown of around 7-10V or more had a positive tempco. Often in alternator regulators, the ‘comparator’ that monitored the alternator’s output operated at around 14.2V. They monitored the voltage with a resistor divider and a series zener diode, plus a transistor’s base-emitter junction. When the voltage rose above 14.2V, this switched on the input transistor, switching off other transistors to cut off the drive to the rotor’s field coil. When the alternator output voltage fell below 14.2V, the rotor’s field was switched on again. It was a switch-mode system, with a switching frequency, due to the electromagnetic delays in the alternator itself, typically being a few hundred hertz. In any case, the ‘trick’ was to make it temperature stable, so a zener diode was chosen that had a positive tempco that exactly cancelled the negative tempco of the input transistor’s B-E junction. Many manufacturers just had the zener diode and the transistor on the same PCB in close proximity. However, Lucas electrical industries in the UK did better. They wised Un-potted alternator regulator PCBs discovered inside the defunct Lucas Electrical plant in the UK after it closed down. The zener+transistor four-legged device acted as a perfectly temperaturecompensated comparator. 4 Silicon Chip up and realised that the perfect zener diode and transistor combo should be in the same package for thermal reasons, so they created the ‘four legged device’ (photo below). Most technicians have never heard of the four-legged device because all of Lucas’ alternator voltage regulators were potted in a difficult-to-remove black resin. As far as I know, the Lucas semiconductor plant was the only one to make it. I have removed one and subjected it to tests. Say you have a transistor with a grounded (common) emitter and a collector load resistor, and provide just enough base current to bias it into Class-A, so the collector voltage is half the supply voltage. If you then heat the transistor, the collector voltage crashes to near-zero in short order because of the negative tempco of the transistor’s B-E junction. When I did this test with Lucas’ four-legged device, and put it in an oven at 130°C, the collector voltage did not change at all. They had perfectly balanced it, and I was beyond impressed, especially because of its very simple nature. When the Lucas factory in the UK closed down, an archivist managed to get in there and copy some documents and photos, including two of their alternator regulator PCBs that were not potted in resin yet. That’s how we managed to get the photo. Dr Hugo Holden, Buddina, Qld. The cost of grid-scale battery storage Matthew Prentis (Mailbag, May 2025) is making an error in evaluating the cost of grid-scale battery storage. The spot price and the asset LCOE, while both usually measured in $/MWh, are different metrics. Batteries make much of their money from relative pricing, ie, the arbitrage between high and low spot prices. The LCOE of lithium-ion storage is currently between $100 and $200 per MWh in Australia. If there is sufficient interest, I would consider covering energy sector subsidies in a future article, though this would cover all fuel types. Renewable subsidies are only a relatively small fraction. Brandon Speedie, Alexandria, NSW. An alternative to the Solar Diverter project Regarding the Hot Water Solar Diverter project in the June & July 2025 issues (siliconchip.au/Series/440), I had an electrician install a timer within the meter box that switches on the water heater for a set time from midday. In my case, 90+% of the time, the panels are producing maximum solar feed-in during this period. Also, midday is an off-peak time to buy power in Tasmania. Australia's electronics magazine siliconchip.com.au A 5kW system more than covers the 3.6kW hot water heater’s power needs. As you are probably aware, these timers are the same size as the breakers, so it’s a very quick, reliable and cheap option. We are a two-person household, so we only need ours on for approximately two hours per day. I also installed a mains LED across the element, making it easy to check how long it’s actually on. Geoff Young, New Town, Tas. The error is only small, but noticeable, and would not be detectable with a 2kW load on. I purposefully switched it off during the day because I noticed a peak charge on a circuit where I expected none. In my case, the error is about 0.6kWh in a 30-day period (equivalent to a load of approximately 10W). I wonder if some of your readers may have a similar problem. Wolf-Dieter Kuenne, Bayswater, Vic. Solar inverter registering a load when there is none Synchronous vs asynchronous motors I have discovered that there is a small error in my Landis+Gyr E360 grid-tied solar inverter when the controlled load circuit is on and I have solar energy available for export. I discovered this when the load was disconnected by turning the circuit breaker off during the day while exporting solar energy. I found that while exporting over 1.5kW, I got a recorded energy draw on my meter for the circuit that had no load connected. It occurs because the meter has 2 current transformers: one that measures the controlled load (now disconnected) and one measuring the export power or normal day circuit. What I believe is happening is that the two CTs are in close proximity, giving mutual induction into the controlled load circuit CT, and thus a positive reading for that circuit. That circuit does not register power export, only import. It requires both the controlled load switch to be on and measurements enabled for readings to be given. The controlled loads are now being switched on when solar energy is available to use solar energy for what used to be powered using off-peak loads at night. I would like to comment on a Mailbag letter by Robert Budniak published in the March 2025 issue on running induction motors at reduced voltages. In his summation, he ignored that the original Mailbag letter from Ian Thompson referred to squirrel cage AC induction motors, which are asynchronous and not synchronous types. One must take into account the rotor slip in an AC induction motor to accurately calculate the torque. There are also power factor differences. The short video at https://youtu. be/tl1N6_flY5k does an excellent job of graphically illustrating the differences. Andre Rousseau, Auckland South, New Zealand. Running Linux within Windows I have a machine set up with both Windows 10 and Ubuntu Linux. It is a 4th Generation Intel Core i7, so not a new system, but it has reasonable memory capacity and an SSD for storage. A Microsoft feature called “Windows Subsystem for Linux”, or WSL2 for short, is used to run Ubuntu Linux. After activating WSL2 and installing Ubuntu from the 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 6 Silicon Chip Australia's electronics magazine 0417 264 974 siliconchip.com.au Tilting head to 900 Digital Readout Speed Display 2 Speed Gearbox Digital Depth Display YOUR TURNING SOLUTION 3MT Spindle Work Light Dovetail Vertical Z-Axis Geared Headstock D1-4 Camlock Spindle 3MT Tailstock 3MT Tailstock Induction Hardened TU-3008G-20M OPTI-TURN LATHE & MILL DRILL COMBINATION Sawrf Drip Tray PACKAGE DEAL K149 5,049 inc GST $ SAVE $275 OFF RRP TU-3008G - Opti-Turn Bench Lathe PACKAGE DEAL This new TU-3008G model geared head lathe of very modern design has many convenient facilities ideal for the enthusiastic model engineer for small component manufacturer. A very rigid 180mm cast iron bed width, induction hardened and ground slideways gives a high level of precision turning. The lathe capacity is 700mm between the centres and 300mm swing over the bed and with a generous 38mm spindle bore allowing larger stock to be placed through the headstock. The workhorse that drives this lathe has an upgraded powerful 2hp (1.5kW) motor providing smooth running. Other very useful features included are cross and longitudinal power feeds that's not normally found of small conventional lathes, quick lock tailstock and both metric and imperial thread cutting, ranging from 8-56 tpi or 0.2-3.5mm pitch. Also included are a 4-way indexing tool post with 16mm tool shank capacity, fine adjustment on the tailstock for taper turning and the rear splash guard. A 160mm 3-jaw chuck with reverse jaws is also supplied. ORDER CODE: L691 TU-3008G - Opti-Turn Bench Lathe PACKAGE CONTENTS L691 + M647 ORDER CODE: M647 The BF-20AV mill head attachment has more throat & height capacity than the the BF-16AV and allows for larger work to be machined, it also is specifically designed to suit the TU-2506V & TU-3008G Optimum bench lathes; converting them into a universal combination lathe/ mill when mounted together. In addition this compact setup has the advantage of that it requires less valuable floor space then the two separate conventional machines. View and purchase these items online: www.machineryhouse.com.au/SIC2507 SYDNEY BRISBANE MELBOURNE (03) 9212 4422 (08) 9373 9999 PERTH ADELAIDE 1/2 Windsor Rd, Northmead 625 Boundary Rd, Coopers Plains 4 Abbotts Rd, Dandenong 11 Valentine St, 11/20 Cheltenham Pde Woodville (02) 9890 9111 (07) 3715 2200 Kewdale Specifications & prices are subject to change without notification. (08) 9373 9969 06_SC_280723 For full specifications visit www.machineryhouse.com.au/k149 Microsoft store, you end up with an icon on the desktop called “Ubuntu 20.4”. Double-clicking this icon brings up an Ubuntu window in four seconds. From then on, you can swap between Windows 10 programs, and the Ubuntu window instantly. The main reason I wanted to install Ubuntu was so I could run a small bash script that compresses Raspberry Pi SD Card images. I use several Raspberry Pis for different activities, like gathering solar generation and uploading it to www. pvoutput.­org, monitoring water levels in tanks, switching a bore pump on/off as required etc. The bash script “pishrink.sh”, which only runs on Linux, will compress the image from a RPi 16GB or 32GB SD card down to about 4GB in size. This 4GB image file can then be stored on a hard disk. Every so often, a Raspberry Pi stops with a corrupted SD card. The easy fix is to use the official RPi imager software to copy the compressed backup image from the hard disk onto a new SD card, plug the SD card in to the RPi, and all is good. While WSL2 is good, it has limitations. A recent enhancement is the addition of the “--mount” option, which allows a hard disk that has been formatted to ext4 (one of the main Linux file system types), connected to a SATA port on your computer, to be accessible from Windows. Unfortunately, Microsoft has made the “--mount” option only available for Windows 11, not Windows 10 (except for the people using the Windows 10 Insider Build Versions). The end result is that you are forced to upgrade to Windows 11 to use this option. As a test, I installed a new SSD on this PC and loaded Windows 11 onto it. I was able to connect and access an ext4-formatted hard disk, then extract the files I wanted. Since then, I have gone back to Windows 10, as all my other PCs use Windows 10, and I have limited need to access an ext4 hard disk any more. Sid Lonsdale, Cairns, Qld. A trick for finding solder bridges I am currently assembling the RGB LED ‘Analog’ Clock from May 2025 (siliconchip.au/Article/18126), and soldering the 60 RGB LEDs is indeed a fun job. I used an old trick to check for almost-invisible solder bridges between the slim pads that I thought might be a help to other readers. A sharp blade slid between the pads will easily let you feel if there is any bridge present. If there is, it can be removed with solder wick. David Coggins, Beachmere, Qld. Building a replica Philbrick K2-W valve op amp I noticed some errors in the circuit diagram of the Philbrick K2-W valve op amp in the article on the History of Op Amps (August 2021 issue; siliconchip.au/ Article/14987). The 500pF capacitor and parallel resistor are actually returned to ground (0V), not the -300V rail as shown. There’s a second 7.5pF capacitor missing, which connects between the top of the 2.2MW resistor (the control grid of the third triode) and the top of the 120kW resistor (the cathode of the fourth triode). I was already working on this circuit, so your article arrived at a fortuitous time. I’ve made a copy of the device with modern closer-tolerance and more stable resistors (the original were 10% carbon types). I started with Philbrick’s original 1953 circuit and made some minor resistor changes. It worked (first time!) surprisingly well, configured as a -2× inverting amplifier with Philbrick’s suggested offset null “Bias” control. The output is close to the expected values, within the limits of component tolerances and measurement error. Next, I was able to obtain a couple of original devices. One example worked with limited accuracy, the other was way off. I cut open the latter device; it turned out to be built in the point-to-point style, typical of the era. Do you know of anyone else who’s replicated this historic device, or is mine unique? Godfrey Manning G4GLM, Edgware, UK. Comment: the 500pF capacitor and 9.1kΩ resistor going to -300V instead of 0V was our error in redrawing the circuit, but the original circuit we have doesn’t show the 7.5pF capacitor. We wonder if it was a change made in later production versions, or perhaps on request by the customer for extra stability, depending on the device’s configuration in use. It may have been required for stability with lower gain, but would have limited the bandwidth in higher-gain applications. The left photo shows the replica K2-W valve op amp, and the adjacent photo is an internal shot of an original Philbrick K2-W after it was removed from its housing. 8 Silicon Chip Australia's electronics magazine siliconchip.com.au Modern op amps are sometimes available in a unity-­ gain-stable version and higher-bandwidth version, with the only difference being whether a dominant pole capacitor like this is present. For example, the OPA134 (8MHz, unity gain stable) is very similar to the OPA604 (20MHz, minimum gain of five times). Good experiences with JLCPCB assembly I’ve just read the editorial in the June 2025 issue. I know of the problem with the bad CH334F chips, being an active member (and administrator) on The Back Shed forums. I understand where you are coming from, and I totally agree – it could have been a disaster from your board-­ ordering point of view. Having said that, I think that you were simply unlucky with the timing. JLCPCB have been stellar in all my SMD assembly orders with them (hundreds now), and of all the boards I have ever ordered, there was never an SMD assembly problem. The CH334F problem does appear to be the exception, rather than the rule, and it was unfortunate that you happened to be caught up in it. Don’t let that put you off ordering assembled PCBs, as 99% of the time, it goes well. The other way to ensure you are not bitten by any potential problems such as this is to order smaller batches, instead of putting all your eggs in one basket, so to speak. That also helps to spread out the budget for the purchase of assembled boards, if you get them in several smaller batches, which is what I have been doing for years now. Love the magazine, keep up the good work. Graeme Rixon, Rictech Ltd, New Zealand. We’re still lagging behind in HD TV broadcasting Monochrome TV broadcasting commenced in Australia in 1956, with colour added in 1975. The conversion to digital broadcasts in 2001 required the purchase of a new TV or a set-top box. Most broadcasters had to buy new transmitters, along with studio equipment. New Zealand started converting from analog PAL TV to DVB-T with MPEG-4 compression in 2011 and finished in 2013. In Australia, Freeview 2022 made HEVC (H.265) decompression compulsory, but not DVB-T2. Satellite coverage for blackspots still uses the older DVB-S standard, which only supports standard definition (SD) video. With MPEG-4, HD video takes the same bandwidth as SD video encoded using the older MPEG-2 format. HE-AAC audio provides a similar reduction in data usage compared to the older MP2 scheme. DVB-T can transmit around 23Mbit/s, whereas DVBT2 supports up to 34.5Mbit/s in the same 7MHz bandwidth. Unfortunately for viewers, older TVs and boxes are not compatible with DVB-T2, so a new TV or set-top box is required. For broadcasters, around 2778 transmitters would need their modulators replaced; fortunately, the expensive highpower sections are unaffected. The AS 4933:2015 standard already requires support for MPEG-4 video and HE-AAC v2 audio. Yet the industry has dragged its feet for nearly a decade, with the first complete MPEG-4 conversion only occurring in Tasmania in October 2023. WIN TV and Seven Regional have now upgraded most areas except remote Australia, Sydney, Melbourne, and Brisbane. siliconchip.com.au Australia's electronics magazine August 2025  9 SBS now uses MPEG-4 nationally, except for Channel 3, which remains SD. The ABC has been broadcasting MPEG-4 HD on Channel 20 for some time, and will convert ABC News and ABC Entertains to MPEG-4 HD in June 2025. Once Seven completes the MPEG-4 conversion in the remaining cities, there will be little justification for simulcasting the same primary programs in blurry SD MPEG-2 on the ABC, SBS, and Nine Network. Network Ten is already broadcasting in HD on Channel 1. A range of updated standards now governs digital TV in Australia: • AS 4933:2024 applies to TVs and set-top boxes sold in Australia. These must support MPEG-4 video and HE-AAC audio. • AS 4599:2025 defines transmission characteristics for both DVB-T and DVB-T2. • AS 5362:2024 covers DVB-T2 receivers, which enable Ultra HD (UHD) or more HD channels over the same 7MHz bandwidth. • Other standards relate to outdoor antennas (AS 1417) and coaxial/MATV systems in buildings (AS 1367). These new standards will replace the 2015 versions, which become obsolete in November 2026. For most viewers, this means their current equipment is likely compatible. However, some older TVs or boxes may need replacement. Viewer Access Satellite Television (VAST) provides free-to-air coverage in remote areas and black spots via Optus satellites. These use DVB-S2 and HEVC, and receivers must meet government-specified standards. The system is funded by the Commonwealth Government. The latest version of the ETSI EN 302 307-2 (2024-08) standard extends DVB-S2 to support UHD broadcasts via satellite. This is a global standard used widely across Europe and elsewhere. While we are still upgrading to standards from around 2015, much of the world has moved on. DVB-T2 is already used in 84 countries, covering 3.6 billion people. Modern TVs often already support DVB-T2 and HEVC. You can now buy DVB-T2/HEVC-capable set-top boxes for around $45, and new VAST receivers with DVB-S2 and HEVC support are also available. If we upgraded 16 sites of five transmitters each per year, we could complete a national switchover in 10 years. Each broadcaster would also need to update its program feed with HEVC video and E-AC-3 (Enhanced AC-3) audio encoders. After the switchover, support for DVB-T could be phased out. HEVC is backward-compatible with MPEG-4, so this transition could be managed smoothly. Large-screen UHD (4K) TVs have been available for several years, and retailers often use high-resolution promotional videos to sell them. It’s not always clear which TVs can receive DVB-T2 broadcasts, even though most can stream UHD video-on-demand thanks to built-in HEVC decoders. Australia has now been using DVB-T for over 20 years, making an upgrade to DVB-T2 increasingly urgent. Instead of being technology leaders, broadcasters have fallen behind. It’s now up to electronics manufacturers to drive progress, and the broadcasters must catch up. SC Alan Hughes, Hamersley, WA. icomretail.com.au 10 Silicon Chip Australia's electronics magazine siliconchip.com.au Last month, we introduced SpaceX’s Falcon 9, Falcon Heavy, Super Heavy and Starship launch vehicles and described their engines and capabilities. This second and final instalment will cover their launch sites, some of the more notable missions and what they are planning for the future. Part two by Dr David Maddison VK3DSM Starship’s seventh test flight Image source: SpaceX / <at> Space_Time3 via X (Twitter). siliconchip.com.au Australia's electronics magazine August 2025  11 Fig.30: a rendering of what SpaceX’s HLS might look like on the Moon. Fig.31: a rendering of the lunar Starship version with landing legs. Fig.32: a concept from 2019 for a Starship CLPS vehicle. hen we left off in the previous issue, we had just described how Starship is launched atop the massive Super Heavy launch vehicle, powered by 33 Raptor engines. While Starship is still in the testing phase, it is intended to be able to deliver cargo and crew to the Moon and ultimately, Mars. It may even be refuelled in orbit, allowing a much heavier cargo to be sent to distant planets. After we look at some of these aspects of Starship, we’ll go through some of the more notable SpaceX missions to date, then look at two of their larger competitors and what they have done lately. Like last month, uncredited images are from SpaceX or public domain sources. The main variants of Starship envisioned are the Human Landing System (HLS), for landing on the Moon (Figs.30 & 31), the propellant tanker (see Fig.35), the propellant depot (Fig.36) and a cargo version. The version of Starship intended for Mars settlement will have heat shielding and flaps for guidance – see Figs.33 & 34. The CLPS Lander will refuel. It turns out that one reason SpaceX chose methalox as a fuel is that it can be manufactured on Mars. Methane fuel and oxygen for oxidiser can be produced on Mars from CO2 in the atmosphere and hydrogen from water, which is now known to exist on Mars beneath the surface and elsewhere. The reaction used to make methane is the Sabatier reaction, CO2 + 4H2 → CH4 + 2H2O. The fuel could be manufactured using electricity from solar energy or nuclear reactors. Hydrogen can also be extracted from water by electrolysis, which provides a supply of oxygen at the same time. Alternatively, the hydrogen could possibly be transported from Earth in a tanker spacecraft. Starship fuel depots could also be sent from Earth and placed in Martian orbit to later fully refuel Starship for a return trip. The fuel sent would be methane and oxygen. Or hydrogen could be transported for manufacturing methane on the Martian surface. The Perseverance rover, which landed on Mars in 2020, successfully W The SpaceX Commercial Lunar Payload Services (CLPS) lander is a part of a contract to NASA to provide lander services to deliver payloads to the Moon as a precursor to landing astronauts on the Moon. Payloads have already been delivered to the Moon using Falcon 9 rockets. SpaceX has also proposed a Starship variant for these missions (see Fig.32). How will Starship get to Mars, land and leave? The most likely way Starship will go to Mars is as follows. Starship will be launched into Earth orbit and then be refuelled from a Starship tanker or fuel depot. Then, an energy-efficient path known as a Hohmann transfer orbit will be used to take Starship to Mars in 7–10 months. Starship will enter the Martian atmosphere using aerodynamic drag to slow down, then flip to a vertical position for a propulsive landing using its Raptor engines. Once landed on Mars, there is a lot of speculation about how Starship Fig.33: an artist‘s impression of Starships at a Martian settlement. 12 Silicon Chip Fig.34: another artist’s concept of a Mars settlement. Source: www.spacex.com/updates/ Australia's electronics magazine siliconchip.com.au Fig.35: a proposed method of inorbit refuelling of Starship. Fig.36: refuelling in orbit from another stripped-down Starship. Fig.37: the glass-coated silica-fibre tiles that protect Starship’s exterior. performed the Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE) to produce oxygen from the Martian atmosphere, although not methane. Carbon monoxide (CO) is a byproduct of the reaction used in that experiment; it can be reacted with water or hydrogen to produce methane. Starship more tolerant of a failure of the heat shield than the Shuttle was. The heat shield on the Dragon capsules is phenolic-impregnated carbon ablator (PICA-X). The material ablates or burns away, carrying excess heat with it. SpaceX also coats most vehicles with a heat-resistant, protective white paint for thermal control, thought to be a formulation known as AZ-93 (www.aztechnology.com/ product/1/az-93). complexity of landing legs on the booster. However, landing legs will be used for landing Starship on the Moon and Mars, at least until a Mechazilla is built in those places. Starbase has two Orbital Launch Mounts; Starships intended for re-­ entry to Earth will not need landing legs. Thermal protection systems For re-entry, Starship uses several types of thermal protection: 1. Its silica-fibre-based hexagonal tiles can withstand a temperature of 1400°C; they are similar to what the Space Shuttle used and have a similar consistency to Styrofoam. They are coated with a special heat-­resistant black glass layer (see Fig.37). There are 18,000 tiles, which is 6,000 fewer than the Space Shuttle used. 2. There is a secondary ablative layer under the primary tile heat shield for extra protection. 3. The Starship skin is made of stainless steel, which is far more resistant to heat than the aluminium of the Space Shuttle, and will make Launch pad & recovery Due to the enormous power of the Starship engines, a lot of damage was done to the launch pad and surrounding area in early tests, requiring modification of the launch support structure. Fig.38 shows the water deluge system (flame deflector) used to absorb some of the energy of the rocket exhaust. For recovery, the Super Heavy booster is caught in the “chopsticks” of the Orbital Launch Mount or “Mechazilla” launch tower, in a remarkable feat of guidance and control. This is done to avoid the extra weight and Fig.38: a full pressure test of Starship’s launchpad flame deflector on the 29th of July 2023. siliconchip.com.au Spaceports Starbase in Boca Chica, Texas (Fig.39) is the main site for launching the Starship rockets, including those that will be launched to the Moon and Mars. It is also the headquarters of SpaceX, and a production and test site for Starship. Apart from Starbase, the other launch sites used by SpaceX are: Kennedy Space Center (Launch Complex 39A or LC-39A, leased from NASA) in Florida – previously used for the Apollo and Space Shuttle programs. It is now used by SpaceX, mostly for Falcon Heavy launches, including cargo and crewed missions with Dragon, and more complex missions. Fig.39: part of Starbase, showing a Starship on display. Source: SpaceX. Australia's electronics magazine August 2025  13 Fig.40: a Falcon Heavy being prepared at Vandenberg Space Force Base. Photo by Jack Beyer via X.com. Cape Canaveral Space Force Station in Florida has multiple launch pads, including Cape Canaveral Space Launch Complex 40 (SLC-40), which has been leased and upgraded by SpaceX since 2007 for launching Falcon 9 rockets. It has made at least 230 launches. It launched its first crewed mission in September 2024. It also has landing pads for Falcon 9 and Falcon Heavy reusable boosters: Landing Zones 1 and 2 (LZ-1 and LZ-2). Vandenberg Space Force Base (Space Launch Complex 4 or SLC-4E) is in California, and is used to launch satellites into polar orbits of the Earth and Sun-­synchronous orbits using Falcon 9 and Falcon Heavy (see Fig.40). Fig.41: a Falcon 9 lands on the 52 × 91m platform of a drone ship off the coast of the Bahamas. Drone ships The drone ships used for Falcon 9 and Super Heavy booster recoveries are ocean-going barges, correctly known as autonomous spaceport drone ships (ASDSs) – see Fig.41. They have been made autonomous for the recovery of Falcon 9 boosters. The landing platform is about 52 × 91m, while the Falcon 9 v1.1 landing leg span is 18m. They are towed into position with a tug, then kept in place by autonomous station-keeping. After a landing, crews board the ASDS and secure the rocket. One of the ASDSs uses a robot called the “octagrabber” to secure it. Why not use parachutes? Port Canaveral in Florida is used as a base for the drone ships that operate in support of booster recoveries in the Atlantic Ocean from launches at Kennedy Space Center and Cape Canaveral Space Force Station. The Port of Long Beach is a base for the drone ship doing recoveries in the Pacific Ocean from Vandenberg Space Force Base. The Space Shuttle used parachute recovery for its main boosters, so why does SpaceX use propulsive recovery, which is much harder to perfect? The difference is that the Shuttle jettisoned its boosters at a relatively low altitude and speed, whereas the SpaceX boosters are not jettisoned until near orbital velocity. The speed and energy involved preclude a parachute recovery. The second stage of Falcon is not reused, as it’s too complicated to Fig.42: deploying Starlink satellites. Source: NASAspaceflight.com Fig.43: the Sora-Q mini-rover from Hakuto-R. Photo by テレストレラッソ. 14 Silicon Chip Australia's electronics magazine recover. That’s a reasonable compromise because the second stage is a relatively simple and inexpensive structure. The trunk of the Dragon capsule is not recovered either. Unlike the Space Shuttle, which was more what you might call ‘refurbishable’ than ‘reusable’ (it cost about as much to refurbish between flights as building a new one), the SpaceX boosters are economically reusable. From a cost point of view, the Shuttle was a disaster, but the genuine reusability of the SpaceX boosters helps to significantly reduce the cost of launches. Very little needs to be done to a landed booster for its reuse. It’s pretty much just checked over and refuelled, then it is ready to go! Starlink’s role in SpaceX’s operations According to the video at https:// youtu.be/lgt4zSD9UUc, SpaceX plans to use the Starlink satellite network to maintain communications with Crew Dragon capsules during the re-entry phase when the plasma layer surrounding the vehicle normally causes a communications blackout. Fig.44: the Intuitive Machines-1 Odysseus lander. siliconchip.com.au Fig.45: the Intuitive Machine-2 Athena lander carries the Micro Nova Hopper. Source: Intuitive Machines. There is no other published information that we could find about the extent to which SpaceX platforms use or do not use Starlink. Notable SpaceX missions Hakuto-R Mission 1 On the 11th of December 2022, a Falcon 9 was launched to deliver the Japanese Hakuto-R Moon lander (Fig.43), but unfortunately, an error in the lander’s radar altimeter caused it to keep hovering at an altitude of 5km until it ran out of fuel and crashed. Hakuto-R Mission 2 (Resilience) Hakuto-R Mission 2 was launched on the 15th of January 2025 to deliver a payload to the Moon, including a lunar micro rover developed by ispace as a technology demonstrator for reliable transportation and data services on the Moon. This mission shared the same Falcon 9 launch vehicle as Blue Ghost Mission 1 (see below). Intuitive Machines-1 On the 15th of February 2024, a SpaceX Falcon 9 launched the first commercial mission to successfully soft-land on the Moon. It was also the first American-made spacecraft to land Fig.46: Polaris Dawn launched in the dark, carrying Jared Isaacman, Scott Poteet, Sarah Gillis & Anna Menon. on the Moon since the 1972 Apollo mission. The Odysseus lander (Fig.44) carried a variety of instruments. It landed on its side, but the instruments functioned and it was judged a success. Intuitive Machines-2 Also known as Polar Resources Ice Mining Experiment-1 (PRIME-1), this lander, called Athena (Fig.45), was launched on the 27th of February 2025 using a Falcon 9 rocket and landed on the Moon on the 6th of March. It carried The Regolith and Ice Drill for Exploring New Terrain (TRIDENT), to drill for ice as a source of water for future habitation. The MSolo mass spectrometer was included to measure the amount of ice in the drill samples, as well as the Micro Nova Hopper. Unfortunately, the mission failed as the spacecraft landed on its side, like the Odysseus mentioned above. The Polaris program Polaris (https://polarisprogram. com/) is a private space flight program established by Jared Isaacman, now nominated to be the next NASA Administrator. The program was established under a contract with SpaceX. Isaacman’s first flight as a private astronaut on a Crew Dragon spacecraft was on the 16th of September 2021, to raise money for St. Jude Children’s Research Hospital. The first flight under the Polaris program was on the 10th of September 2024, on Crew Dragon, taking the occupants to an apogee of 1400km, higher than any human has been in orbital flight since the flight of Gemini 11 in 1966 (with an apogee of 1368km) – see Fig.46. Two other flights are planned under the Polaris program. Blue Ghost Mission 1 On the 2nd of March 2025, Firefly Aerospace’s Blue Ghost Mission 1 lander landed on the Moon, having been launched by a SpaceX Falcon 9 (see Fig.47). Among ten science investigations that spacecraft will perform will be receiving GPS signals using the Lunar GNSS Receiver Experiment (LuGRE) to investigate extending the navigational capability of GPS to the Moon and beyond. We wrote about using GPS beyond Earth orbit, including near the Moon, in our October 2020 issue (siliconchip. au/Article/14597). There are also the Next Generation Visiting Starbase What is Max Q? As of the time of writing, you can visit Starbase and the surrounding areas. We suggest you look at the following links if you want help planning a trip to go there: During a rocket launch, including those of SpaceX, one often hears the expression that the vehicle is going through Max Q (or “max q”). This is the time of maximum aerodynamic drag on the vehicle and maximum stress, when something is most likely to go wrong. The engines are frequently throttled back during Max Q to minimise the structural load on the vehicle. • https://siliconchip.au/link/ac5m • https://siliconchip.au/link/ac5n • https://everydayastronaut.com/ how-to-visit-Starbase/ • https://siliconchip.au/link/ac5o siliconchip.com.au Fig.47: a rendering of the Blue Ghost lander on the moon’s surface. Australia's electronics magazine August 2025  15 Fig.48: at 1.2m in diameter, the Dragon cupola is the largest Fig.49: four astronauts wearing Starman suits in the Dragon capsule to protect against depressurisation. window in space, made from layers of polycarbonate. Retroreflectors (NGLR), targets for Earth-based lasers to accurately measure Earth-Moon distances. The first laser retroreflectors were placed on the Moon by Apollo 11 astronauts in 1969, followed by Apollo 14 (1971) and Apollo 15 (1971). They are still in use today. This mission shared the same Falcon 9 launch vehicle as Hakuto-R Mission 2, launching on the 15th of January 2025. This was the first commercial venture to fully successfully land a spacecraft on the Moon. International Space Station rescue mission Due to technical problems with the Boeing Starliner that was docked with the ISS, astronauts Butch Wilmore and Suni Williams were unable to return to Earth at their scheduled date of the 14th of June 2024 (their mission was originally meant to last for eight days). The problems with Starliner were not solvable in any reasonable amount of time, so SpaceX offered a rescue mission but that offer was not accepted by the previous US Administration. However, the new US Government accepted the offer, and they launched a rescue mission on the 14th of March 2025, docking on the 16th. The spacecraft was a Crew Dragon launched by a Falcon 9. It delivered four new astronauts and finally returned to Earth on the 18th of March 2025, carrying Wilmore, Williams and two others. The full video of the re-entry and splashdown is available at www.spacex.com/launches/ mission/?missionId=crew-9-return For a shorter version of the video, see https://x.com/SpaceX/ status/1902116771806732511 or https://youtu.be/fd-bMz4fGN4 Fram2 Fram2 was a private mission paid for by Maltese billionaire Chun Wang. He and several of his guests, including Australian Eric Philips, were launched by a Falcon 9 on the 31st of March 2025 and they splashed down in the Pacific Ocean on the 4th of April. After stage separation, the booster landed on the drone ship named “A Shortfall of Gravitas” in the Atlantic Ocean. Their Dragon capsule was inserted into a polar retrograde orbit, the first time astronauts have ever been put into polar orbit. The capsule communicated with Starlink via a laser beam, Fig.50: a Crew Dragon with its Trunk attached prepares to dock with the ISS. The white part is the IDA. 16 Silicon Chip the same way Starlink satellites communicate with each other. A cupola for viewing was placed beneath the nose cone (Fig.48), in the area normally used for docking with the ISS and exiting Dragon. There was an amateur radio station onboard transmitting SSTV (slow scan TV on 437.550MHz) images as part of a high school and university competition. Among a variety of 22 experiments, the crew took the first x-ray of a human ever in space. The mission websites are https://f2.com/ and https://fram2ham.com/ plus there is a video at www.spacex.com/launches/ mission/?missionId=fram2 Dragon to the Moon As an alternative to the hugely expensive, delayed and problematic Boeing Space Launch System (SLS) and Lockheed Martin Orion spacecraft for landing people on the moon, Dr Robert Zubrin of the Mars Society and Homer Hickam have suggested sending a modified Crew Dragon, incorporating features from Red Dragon, to the Moon. This mission would involve both the Falcon 9 and Falcon Heavy, but there would be no landing. That mission Fig.51: the Dragon capsule as it was about to dock with the ISS on the Crew-5 mission. Australia's electronics magazine siliconchip.com.au would resemble Apollo 8 (1968), orbiting the moon but not landing. An alternative mission that would involve landing would be to launch Crew Dragon into low Earth orbit, with astronauts then transferring to Starship HLS (which never lands on Earth), fuelled in Earth orbit, to land on the Moon. The return to Earth would be a reverse of that. Space suits The Starman suit, also known as the intravehiclar activity (IVA) suit, is custom made for the astronaut who will wear it; the helmets are 3D-printed to the required shape. This suit protects against depressurisation only; it has no radiation protection, so it cannot be used outside the spacecraft. Astronauts regard these suits as very comfortable. Astronauts can be seen wearing these suits in Fig.49. SpaceX also has a space suit for extravehicular activities (EVA). This suit is also suitable for use inside the spacecraft, and among its many features is a heads up display within the helmet to display parameters such as pressure, temperature and humidity etc – see Fig.52. Docking adaptors With increasing space activity, it is important to have standard docking interfaces between spacecraft. One standard is the International Docking System Standard (IDSS). The NASA Docking System (NDS) is NASA’s implementation of this system; it is used on the ISS, the Boeing Starliner, the Orion spacecraft and Crew Dragon 2. The ISS used to use the Russian-­ developed docking standard of APAS95 (as did the Soyuz, former Space Shuttle and former Mir space station), but the International Docking Adapter (IDA) was brought to the ISS by SpaceX Dragon and used to convert those adaptors to the NASA Docking System, which complies with the International Docking System Standard. An IDA is shown in Fig.50. Fig.51 depicts a Dragon capsule as it is about to dock with the ISS. Note the Draco thruster firing and the open docking hatch (nose cone) of the Dragon with the docking interface inside. If you want to try your hand at docking with the ISS with a simulator, visit https://iss-sim.spacex.com/ Starlink Starlink is a subsidiary of SpaceX, with SpaceX launching thousands of Starlink satellites to provide satellite-delivered internet services almost worldwide (and now telephony). Starlink can provide download speeds of up to 200Mbps, with uploads of 10–40Mbps and latencies of 25–80ms. As of the 27th of February 2025, there were 7052 working Starlink satellites in orbit at about 550km altitude (see Fig.53). They can be seen at night with the naked eye, making them a concern to astronomers. SpaceX has permission to launch a total of 12,000 satellites (Fig.54), and is seeking permission to increasing that number to as high as 30,000. On the 5th of December 2024, Elon Fig.53: the Starlink constellation at the time of writing. Source: https://satellitemap.space/?constellation=starlink siliconchip.com.au Fig.52: the SpaceX EVA suit can be worn outside a spacecraft. Musk wrote, “The first Starlink satellite direct to cell phone constellation is now complete. This will enable unmodified cellphones to have internet connectivity in remote areas.” (https://x.com/elonmusk/ status/1864571206004838425). For more about Starlink, see our article on it in the June 2023 issue (https:// siliconchip.au/Article/15815). SpaceX’s software SpaceX’s software (and hardware) obviously must be reliable, especially those used for flight operations. They use Linux-based systems for flight computers; flight software and other systems are written in C++. A stripped-down version of Linux is Fig.54: a depiction of Starship delivering the next generation of Starlink satellites. Australia's electronics magazine August 2025  17 used; it is tailored to the demands of spaceflight. SpaceX maintains its own Linux kernel with the PREEMPT_RT patch installed to enable real-time processing for applications like engine control and navigation (standard Linux is not real-time capable). They also use custom drivers. The flight software runs on triply redundant dual-core x86 processors, all performing calculations in parallel. If the result of one core disagrees with the others, it is ignored. This provides fault-tolerance without having to use expensive radiation-hardened computers. LabVIEW by National Instruments is used for data logging and monitoring of various parameters. A variety of different software is used for web applications. For Enterprise Resource Planning (ERP), they use a proprietary system called WARPDRIVE for all sorts of day-to-day management functions. Siemens NX is used for computer-­ aided design (CAD), engineering analysis and manufacturing processes. It creates 3D models and can perform simulations to predict performance, including structural analysis and aerodynamics. Teamcenter is used for managing product data such as CAD files, documentation, CNC code etc. It maintains revisions and allows collaboration between different departments. NX and Teamcenter operate together and help reduce SpaceX’s costs and improve reliability of products. • Is developing the New Glenn heavylift orbital launch vehicle. • Is involved in the Blue Moon human-capable lunar lander for the NASA Artemis program, which can land people and 3600–6500kg of cargo to the lunar surface (depending on version). • Is working on the Blue Ring spacecraft for refuelling, transporting and hosting satellites. • Is working on the Orbital Reef low Earth orbit space station to support ten people; it is expected to be operational in 2027. It will support both commercial space activities and tourism. Like Blue Origin, Virgin Galactic (founded by Richard Branson) also offers space tourism services. It is believed to charge US$450,000 (~$750,000) for a sub-orbital trip into space, with around 700 people on the waiting list. They have made seven commercial passenger-carrying flights, the last being on the 8th of June 2024. It reached an altitude of 87.5km. They’re working on a new space plane, the Delta-­class (Fig.56). Other private space ventures Videos to watch While this article has been primarily about SpaceX, there is news on two other private space ventures involving crewed vehicles. Blue Origin (www.blueorigin.com) is owned by Jeff Bezos. It is providing commercial sub-orbital passenger flights into space on the New Shepard sub-orbital rocket system (Fig.55). Its last flight at the time of writing was on the 25th of February 2025, when it took six paying passengers to an altitude of around 100.5km. You can watch a replay of the flight at https:// youtu.be/zXRzcSw_bdc The cost per passenger is unknown. So far, they have made ten passenger flights. In addition to space tourism, Blue Origin: • Produces engines for other spacecraft. • How SpaceX Reinvented The Rocket Engine: https://youtu.be/nP9OaYUjvdE • The Real Reason SpaceX Developed The Falcon 9: https://youtu.be/LmK18kPfMjA • How SpaceX Reinvented The Rocket: https://youtu.be/7vE95eBX6M0 • Why The Raptor Engine Is Ahead of Its Time: https://youtu.be/6cwue7jMkww • What Really Happened to Starship: https://youtu.be/tlAo_6CG9o8 • SpaceX Upgrades Everything Inside Crew Dragon: https://youtu.be/dThdld_f0Rk • Does the SpaceX Crew Dragon have a toilet: https://youtu.be/GT5Sm6v4oqo • Lunar Lander Missions on SpaceX 18 Silicon Chip Fig.55: Blue Origin’s New Shepard suborbital rocket system. Source: Blue Origin SpaceX’s future SpaceX has dramatically decreased the cost of delivering cargo to space, and will likely continue to do so. Elon Musk’s vision is to have a fleet of rockets with a turnaround time the same as passenger aircraft. He also wants a fleet of 1000 Starships continuously running 100–150 tonnes of cargo and/ or passengers into Earth orbit, the Moon or Mars. Australia's electronics magazine Fig.56: Virgin Galactic’s latest Deltaclass spaceplane. Source: Virgin Galactic Rocket: www.youtube.com/live/ XOLnPRCpdYU • China Tested Mechazilla Chopstick Clone: https://youtu.be/ohREX1PDYY0 • This Is the End of Boeing: https://youtu.be/7f56Qldi_Fo SC siliconchip.com.au August Tech BUYS SAVE $34 A0323 65W 15000mAH 125 $ altronics.com.au SAVE $420! 649 $ ONLY WHILE STOCKS LAST! SL4576W 100Ah 100Ah LiFePO4 Slimline Lithium Battery Ultra slim 75mm profile with full current discharge capability and a 5 year warranty. Space at a premium in your camper, caravan or 4WD? This compact battery is perfect for remote power solutions without taking up precious cargo space for your gear. Pre-fitted with Anderson input and output connections and battery capacity gauge. 600 x 275 x 75mm. Watch TV on the go with a 12V telly. 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SAVE 27% 36 $ D 0510A Sale Ends August 31st 2025 Shop in-store at one of our 11 locations around Australia: WA » PERTH » JOONDALUP » CANNINGTON » MIDLAND » MYAREE » BALCATTA VIC » SPRINGVALE » AIRPORT WEST QLD » VIRGINIA NSW » AUBURN SA » PROSPECT Or find a local reseller at: altronics.com.au/storelocations/dealers/ Shop online 24/7 <at> altronics.com.au © Altronics 2025. E&OE. Prices stated herein are only valid until date shown or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. B 0008 Keeping a high-power amplifier cool is vital to its longevity. Designing the chassis properly is important for achieving the best possible cooling performance. It’s even possible to improve the cooling of existing amplifiers if necessary. This photo shows the Silicon Chip 500W Power Amplifier from AprilJune 2022. Part 1 by Julian Edgar Cooling Audio Amplifiers L ow-power amplifiers are easy to cool; a reasonably modest heatsink is sufficient for cooling to occur through natural convection in the air. That’s satisfactory in many domestic situations. But if it’s a powerful amplifier that you push really hard, or it’s mounted in a hot location, things aren’t so easy! I recently ran into major problems with amplifier cooling. First, the two amplifiers were working at higher power levels than I’d ever previously used them. Second, rather than being located inside a cool house, they were stacked in a much hotter roof space. The outcome was fried amplifiers... So it’s important to design an amplifier for proper cooling – and if it’s already built, you might need to make some adjustments to fix a less-thanideal design. This series will cover both aspects. Requirements Amplifiers generate heat in three key siliconchip.com.au areas. The most important heat generators are the output devices, whether they are transistors or ICs. Perhaps 3/4 of the heat generated by a typical amplifier is created by these components. However, significant heat is also generated by the power supply, mainly in the bridge rectifier, the transformer and assorted other devices like voltage regulators (if present). Cooling an amplifier falls into two categories: specific cooling, typically by thermally connecting certain high-temperature components to a large heatsink, and general cooling, typically by allowing ventilation or forced air through the enclosure. Where possible, these two requirements should be kept separate. For example, if the main heatsink is buried deep within the case (which is not at all uncommon), the heatsink will warm nearby components. Conversely, if the heatsink is mounted on the outside of the case, this heat can move straight to the wider Australia's electronics magazine environment, so it won’t impact interior case temperatures so much. Another option is to mount the output devices on a tunnel heatsink with a fan sucking air in through a vent on one side of the case and blowing the warm air out a vent on the other side. Unless that warm air is being sucked back in somewhere else, it will have minimal effect on other components in the amplifier. Heatsinks Heatsinks work in two quite different ways. As it names suggests, a heatsink absorbs heat. As it does, its temperature rises. Say we are using a huge 1kg block of aluminium as a heatsink. The specific heat value of aluminium is 0.9J/°C/g, so to raise the temperature of our block of aluminium by 1°C requires 900J (0.9J × 1°C × 1000g). That’s equivalent to 900W of power for one second, 450W for two seconds or 225W for four seconds. So after 60 August 2025  23 seconds at 225W, the heatsink temperature will have risen by 15°C. If the ambient temperature is 25°C, our 1kg heatsink will already be at 40°C after just a minute! If we ran our very powerful amplifier (that we are assuming dissipates 225W) in only 10-minute bursts, we’d be fine. But running it for an hour, the transistors will get hot enough to burn out. So our heatsink will be quite inadequate. You can see that the name ‘heatsink’ is a bit of a misnomer; what we call heatsinks primarily work as heat exchangers. Heat exchangers are devices that transfer heat, often to the air (or sometimes to water, or even oil). Heat exchangers While we have referred to amplifiers throughout this article, any piece of equipment that needs to dissipate a lot of heat will benefit from these techniques. This includes inverters, speed controllers and electronic loads. Heat exchangers shed their heat in three different ways. The first is conduction. If you run an amplifier at full power, switch it off, then pick it up and moved it, you might find that the shelf it was sitting on is warm. The amplifier has heated the shelf primarily through conduction – although that’s more likely if the prototype amplifier is yet to gain feet, and there was a big contact area between the amplifier and the shelf. Conduction is important to amplifier cooling in two ways. First, the heat source (output transistor, output IC, bridge rectifier etc) needs to conduct heat to the heat exchanger (heatsink). You could have the best heatsink in the world, but if the device can’t transfer heat into it fast enough, the device could still fail. The heat transfer depends on numerous factors such as the device’s packaging, which will act as an insulator to some extent, but must be present to transfer the heat onto a large, flat surface suitable for clamping to the heatsink. It also depends on how flat the surfaces are and how firmly they are pressed together. Because perfectly flat surfaces are unlikely, thermal paste is usually applied between them, to help fill in the gaps. But it isn’t a perfect heat conductor either. Thermal paste should not be used to bridge large gaps – the mounting surfaces of both the electronic device and heatsink need to be as flat as possible. Ensure the compound is still runny; if it has started going hard, discard it. Second, in many amplifier designs, the case itself can act as a heat Australia's electronics magazine siliconchip.com.au A car amplifier I built with the cover removed (shown at the bottom). The smallest possible enclosure dimensions were required, preventing the use of conventional finned heatsinks. The front, rear and bottom aluminium panels of the case all act as the heatsink. They are bolted together with generous flanges coated with heatsink grease. The car amplifier fan is controlled by an off-the-shelf module (lower right) that can be easily set to different temperatures using DIP switches. The bottom sheet metal panel of this car sound amplifier was replaced with clear acrylic. A fan has been added under the sheet (a thin fan was required) and it draws air out of the case. Air is admitted to the case through the chamfered holes shown inset, positioned above added finned heatsinks. Cooling other equipment 24 Silicon Chip An amplifier I built that uses thermostatically controlled fan cooling. The temperature controller and display are on the front panel. A fan in the centre of the top panel draws air out of the amplifier, aiding natural convectional flow. There is a similarly sized vent on the bottom panel. At the rear of the amplifier, the main heatsink is positioned horizontally, with a fan blowing air along the fins. The fans switch on at 40°C. Despite working hard during some hot days, in 10 years, the 250W amplifier’s heatsink has never exceeded 45°C. exchanger. That’s especially so if the enclosure is made from aluminium, which is a decent conductor of heat (good electrical conductors are also usually good heat conductors). To do this effectively, the various enclosure panels need to be in intimate contact so the heat is readily conducted to all parts of the enclosure. When a heat exchanger conducts its heat to the adjacent air, it takes very little time for that thin layer of air against the heat exchanger fins to warm up. Once the temperature difference between the air and the heat exchanger drops to nothing, the heat transfer stops. The trick is to move that air away, replacing it with cooler air. This can occur due to natural convection; the warmed air is less dense and so it rises, being replaced with cooler air that is drawn in from below. Convectional flow is largely vertical, so for a heatsink to work effectively by convection, it requires vertical fins along which the air can slide, and no obstructions above or below those fins. The amount of heat that will be exchanged with the air in a given period is heavily dependent on the exposed surface area of the heat exchanger – more is better. Increased surface area is provided by using fins and having a textured (rough) surface to each fin. Fins in most large amplifier heat exchangers are often relatively thick and few. Having numerous very thin An amplifier during construction. The two finned heatsinks have been mounted face-to-face to form a tunnel. One fan is used at each end of the tunnel – one blowing & one sucking. An efficient fan-forced heatsink design – note the fins on the fins, giving a massive surface area. This main heatsink is external to the case, preventing heat being shed from this heatsink and warming internal components. siliconchip.com.au Australia's electronics magazine August 2025  25 This 250W amplifier was originally cooled just by convection. However, this proved insufficient, so two fans were added (see below). Note how the fan shrouds (upturned baking dishes) cover the top of the heatsink fins, drawing air past them. With a setup like this, nothing can be placed on top of the amplifier! Note the heavy gauge aluminium angle used to thermally link the output devices to the exterior finned heatsinks, and how the rear and bottom panels are aluminium and are thermally connected to also act as heatsinks. Heavy aluminium angle is also used to cool the two bridge rectifiers. fins is more effective, but thinner fins are more easily damaged. A good example of this is an air conditioner, which will usually have lots of very thin fins, but if you bump it, they will be squashed. Convectional airflow can also be used to cool the interior of the amplifier – the ‘general’ cooling we mentioned earlier. To achieve this, we need to take a similar approach to heat exchanger cooling – placing vents on the top and bottom of the amplifier enclosure and then ensuring there are no restrictions to that gentle natural air movement. Vents in amplifier enclosure side panels do very little unless there is forced airflow (ie, fans). One major downside to vertical convectional flow is that it is easily impeded by stacking equipment on top of each other, using mounting feet that are too short, and decorations (like flower pots) that may be placed on the top of exposed amplifiers to make them look better. We’ve also seen cats lying on top of amplifiers to keep warm – it may be great for the cat, but not the amplifier! The final heat exchange mechanism is radiation; however, this is the least important. Black heatsinks will radiate heat more effectively than silver or light-coloured heatsinks, but the 26 Silicon Chip difference is relatively small unless the heatsinks are getting very hot. Black anodised heatsinks are around 6-8% more effective than silver ones under normal circumstances. So it’s clear that while amplifier heatsinks are heatsinks, more importantly, they are heat exchangers with the air. Conduction and convection are critically important in cooling heat exchangers. Convectional flow requires careful design and construction, especially in giving free vertical movement to cooling air. Heat exchangers should have the maximum possible exposed surface area. Fans As we suggested above, convectional flow can be thought of as being quite fragile – easy to disrupt and requiring specific heat exchanger fin orientation. Rather than relying on convection, we can use a fan or fans – either to aid the natural convectional flow, or to replace it. Let’s look first at aiding convectional flow. Say we have a commercial amplifier that is running very warm. Its heatsink is located in the middle of the enclosure, with its fins orientated vertically. There are grilles in the top and bottom enclosure covers, and convectional flow is supposed to provide the cooling. To increase this convectional flow, Australia's electronics magazine we can add a fan to either the top or bottom of the case. If it’s on the top, it should draw air out of the enclosure and blow it up. If it’s on the bottom, it should draw cool air from below the amp and blow it into the enclosure. Either way, because it is aiding natural convectional flow, the result will be much more effective than, say, attaching a fan to the side of the heatsink itself. In some cases, the new top or bottom fan can be fitted within the enclosure – even a quite small fan will, in my experience, massively improve flow over purely convectional air movement. If the amplifier is too tight inside to do this, and the amplifier is not normally able to be seen, cutting a hole in its lid and adding an external fan sitting on top will work well. Rather than aiding convectional flow, you can instead decide to organise the heat exchanger purely to suit the fan. For example, the heat exchanger fins can be horizontal. The key criterion is that the air movement provided by the fan must pass along as much of the exposed area of the heatsink fins as possible. For example, two long finned heatsinks can be mounted facing one another, forming a heatsink tunnel. A fan at one end blows into the tunnel, while one at the other end extracts siliconchip.com.au heat from the tunnel (one fan may be enough to do both jobs). The electronic devices bolt to the outside of the heatsinks. For its size, this approach is one of the most efficient ways of cooling an amplifier. This is the approach used in our Variable Speed Drive Mk2 (November & December 2024; siliconchip.au/ Series/430) and it proved very effective. Fans should always move air along heat exchanger fins – we want air to slide along the fins, pick up heat, then depart. We don’t want air to just be turbulently whizzing around! It’s also important to consider what happens to the warm air after it has picked up the heat from the fins. We don’t want it to end up pushed against a solid panel where it will splash back and heat up other components. We also don’t want it to circulate around back to the input side of the fan, or the air will just end up getting hotter and hotter. Ideally, it should go straight out of the case once it’s warm. Conventional PC-type axial fans are the most common and cheapest fans available, and they are also easily salvaged at no cost from many discarded consumer items. There’s also the significant advantage (for use in amplifiers) that many silent or almost-silent types are available that still move a reasonable amount of air. However, squirrel cage (cross-flow) fans can move a huge amount of air, can be very quiet (or very loud, depending on their design) and their long, thin shape lends itself to low-­ profile amplifiers. In the past, this type of fan has been quite expensive, but they’re now cheaply available from Chinese suppliers, including low-­ voltage designs. However, if you decide to use one of these fans, be prepared do so some sheet metal work – they typically don’t just bolt into place, but instead need some baffles made. The flow of air through an enclosure needs to adequately cool the various hot components. This will not occur if the airflow can take a ‘short-cut’ route, for example, passing straight from an inlet grill to the adjacent outlet fan. However, it can be difficult to picture where the airflow will go just by looking at the amplifier. Two airflow visualisation techniques can be used, though. The first is to stick short (eg, 10mm) siliconchip.com.au An older hifi amplifier heatsink, pictured with normal and thermal cameras. The thin fins give an excellent surface area, while the thick metal base conducts heat along the heatsink from the widely separated output devices. The temperature is only about 10°C over ambient, even after testing at high loads with the top cover in place. Sometimes individual components can run very hot. Typically, they have been fitted with small heatsinks, but they seem quite ineffective. This component is running at nearly 49°C with a 20°C ambient temperature. Australia's electronics magazine August 2025  27 Sizing inlets and outlets Any fan that draws air out of an amplifier must have an equivalent inlet vent area. For example, if a 90mm diameter fan is fitted (a cross-sectional area of about 6000mm2), the inlet vent area must also be about 6000mm2. This inlet can comprise a single 90mm diameter opening, or multiple openings that add up to the same cross-sectional area. However, note that as the diameter of the inlets decreases, their restriction to airflow increases – so if the inlet area comprises mesh with small openings, the total of the openings will need to be greater. There is no immediate disadvantage in oversizing the ventilation inlet area, although having too many vents may make it difficult to control the airflow patterns. If the inlet vent area is too small compared to the outlet fan area, the result will be a reduction in air pressure inside the case. This can make the fan(s) less effective, increase noise and dust collection and sometimes result in uneven cooling. In general, it’s preferable to have neutral or a slightly positive pressure inside the case. pieces of cotton thread inside the amplifier and then temporarily replace the lid with a sheet of clear glass or plastic (don’t leave the lid off – the airflow direction will be quite different with the lid removed). With the fan switched on, the direction that the cotton pieces point will show the directions of airflow. Ensure that the power supply capacitors have fully discharged before opening the amplifier. The same applies after you have finished your flow testing and need to remove the threads. The other approach, which works very well, is to again temporarily replace the top cover with a clear sheet, but this time use a source of smoke, like an incense stick, to make the airflow visible. Light the incense stick, allow it to flame for a few moments, then blow it out. A thin stream of smoke will be released from the end of the stick. Allow the smoke to be drawn in by the fan and watch where the airflow goes by looking at the smoke pattern. If the amplifier has multiple inlet openings, place the incense stick in front of each in turn. It’s almost certain that the internal airflow will show unexpected patterns. We will use this technique next month when modifying an amplifier’s cooling. If the cooling airflow is bypassing key components, the easiest solution is to place one of more baffles or guides to redirect the airflow. Cardboard can be temporarily used during flow testing. Then, when effective baffle designs have been developed, it can be replaced with aluminium sheet or, if there is insufficient clearance to live areas, with Presspahn, acrylic or a similar insulating material. Fan control Because of the noise, people often object to the use of fans in hifi amplifiers. After all, who wants a quiet passage ruined by the whirr of a fan? Two approaches can be used to overcome this objection. The first is to use a thermal switch to switch on the fan only when the heat exchanger temperature is too high. A normally open mechanical temperature switch, closing at say 40°C, is the simplest way of achieving this. However, such switches are not as widely available as they once were, and so it may be easier to use an electronic temperature switch. These prebuilt boards are available with relays, remote sensors and adjustable temperature setpoints. They are very cheap, and some have panel temperature displays – which can be reassuring to watch when your fan-cooled amplifier is belting out the tunes! One disadvantage of this approach is that, unless your fan(s) are totally silent at full speed, you may notice them switching on and off. Also, given that the ambient temperature may vary, and amplifiers dissipate power even when idle, it’s almost certain that the fans will be on (and running at full pelt) some of the time when the amplifier is in use. Another approach, which works very effectively, is to have the fan(s) operate at a slow speed whenever the amplifier is switched on. Experiment with suitable series resistor values until you find one that slows the fan to the point of inaudibility, but still allows the fan to flow a reasonable amount of air. You can then use the temperature switch to short out the resistor, changing the fan to full speed when an elevated temperature occurs. Because the heat exchanger is always fan cooled, When selecting amplifier and power supply modules, look carefully at the heatsinking. This bridge rectifier heatsink has vertical fins (good), but the bottom of the heatsink is completely blocked to convectional airflow (bad). While designed to be mounted horizontally, mounting this amplifier module with the heatsinks fins vertical and the board slightly raised to give bottom clearance will dramatically improve cooling. The two bridge rectifiers on the right need to be raised on extension wires to give clearance for fitting heatsinks, with their fins aligned with those on the main heatsink. 28 Silicon Chip Australia's electronics magazine siliconchip.com.au albeit at a low speed, it will take a lot longer for the heat exchanger to reach the ‘fan full speed’ temperature. Note that some fans use bearings that require a certain minimum speed before the bearing operates properly. If the bearing squeaks or makes any other noise at low speed, increase the minimum fan speed. Another great option is to use our Fan Controller & Loudspeaker Protector (February 2022; siliconchip. au/Article/15195), which controls the speed of up to three PWM-­ capable fans. You can set it so that the fans are off at low temperatures, switch on at low speed as the temperature rises, then increase in speed until the temperature stabilises. This gives you the best of all worlds: complete silence (passive cooling) when possible, effectively silent fan-forced cooling under most conditions, and highly effective cooling when the ambient temperature is high and/or the amplifier is producing a lot of heat. While it’s a little on the expensive side, Jaycar’s YX2584 is a good example of a fan that runs basically silently at full speed. It’s a 120mm, 12V DC type with maglev bearings (that run virtually forever; the rated life is 100,000 hours) and it flows 1795L/min with a noise level of 25dBA. Even in a quiet environment, you’d be unlikely to notice that noise. You could also consider a fan from a manufacturer like Noctua or BeQuiet!, both known for fans with a good balance between airflow and noise. That’s all we have space for this month. Next month, we’ll show you how to test an amplifier at high loads SC and improve its fan cooling. Measuring heatsink temperature under full load using an infrared thermometer. A good amplifier cooling system should keep the heatsink temperature less than 25°C above ambient – in this warm room, this reading is just on that limit. Both Thermalright and Noctua make excellent fans. Although Noctua’s are very reliable, they are much more expensive compared to other manufacturers. Squirrel cage fans, sometimes call cross-flow fans, work well for amplifier cooling, especially where the enclosure is not very tall. Air can be drawn-in through one or more vents, then discharged through a rear slot against which the fan is positioned. These fans can be quiet and flow a lot of air. Both mains-powered and low-voltage DC designs are available. Modules like the one shown to the right can easily have the overly small heatsink unbolted and a very much larger heatsink substituted. I use four of these modules in an amplifier with a fan-cooled heatsink about ten times as big as the one provided! siliconchip.com.au Australia's electronics magazine August 2025  29 EXPLORE THE ELEGOO® RANGE (AU) TL4976 TL4984 TL4830 EXPLORE THE ELEGOO® RANGE (NZ) TL4842 NEW DIMENSIONS. NEW POSSIBILITIES. 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Jaycar reserves the right to change prices if and when required. EXPLORE THE ELEGOO® RANGE (AU) EXPLORE THE ELEGOO® RANGE (NZ) Using Electronic Modules with Tim Blythman Thin-Film Pressure Sensor Being able to sense force and pressure is handy as it allows properties like weight to be measured. While industrial-grade pressure sensors are available at higher prices, thin-film pressure sensors use a simpler technology and are much cheaper. F orce and pressure sensors are used in industrial applications. In addition to directly measuring pressure (such as in a gas reaction vessel), they can measure liquid volumes and weight. Pressure can be related to liquid volume since the height of a liquid column and its density dictate the amount of pressure it exerts. If you can apply the pressure over a known area, the applied force can also be known and thus the weight-derived force due to gravity can be determined. Just about any product you can buy by weight or volume has been precisely measured out using a sensor such as a strain gauge. These are among the more common types used for this purpose since they have the necessary accuracy. Of course, accuracy comes at a cost, and many projects don’t need the kind of accuracy these devices provide. That said, strain gauge sensors and their interface electronics are readily available to the hobbyist if that level of accuracy is needed. Thin-film sensors So-called thin-film pressure sensors are also known as force-sensitive resistors; simply put, they are devices that change their resistance when force is applied to them. This makes them quite easy to use since a simple resistive voltage divider is sufficient to get a reading using an ADC (analog-to-­ digital converter). The force-sensitive resistor consists of a polymer containing conductive particles. The polymer is applied as a thin film (hence the name) to an array of conductive electrodes. As pressure is applied, the conductive particles touch the electrodes and each other, reducing the resistance. Fig.1 shows the construction of a typical device. We’ve seen similar sensors created by sandwiching a layer of conductive foam (such as used for packaging DIP ICs) between two blank PCBs or similar conductive plates. As the foam is compressed, its resistance decreases. Thin-film pressure sensors have hysteresis and thus poor accuracy; error figures of around 10% or higher are typical. Not only does the reading vary quite a bit, but it will also depend on the sensor’s recent history. So they are not suitable for precise measurements. However, they are often used as touch sensors since touch sensing does not require a high degree of accuracy. As long as the touch force can be coupled to them, they can work behind a protective surface in harsh conditions. Some force-sensitive resistors are constructed as long, thin devices with three terminals, like a potentiometer. A touch moving along the length of the resistor is analogous to moving the pot’s wiper, so the touch position can be estimated. Sensor modules Fig.1: pressure applied to the sensor brings together conducting particles within the substrate and closes the gap between the active area and substrate, reducing the sensor’s resistance. The black region of the sensor is a high-resistance polymer that’s embedded with carbon. The silver areas are conductive electrodes that expand the sensor’s active area. The sensor electrodes are connected to terminals that are soldered to a module PCB featuring a resistor, mounting holes and a 3-way pin header. It is possible to purchase bare force-sensitive resistors, but they are also available attached to a module with a pin header, making them easy to interface to a microcontroller board such as an Arduino main board. We tried the Duinotech XC3738 Arduino Compatible Thin-Film Pressure Sensor from Jaycar Electronics. It consists of a sensor attached to a module PCB. The PCB has a three-way header and a single 510kW resistor, marked as R1. There is an unpopulated Australia's electronics magazine siliconchip.com.au 34 Silicon Chip Fig.2: The circuit on the Duinotech Thin-Film Pressure Sensor module is a simple voltage divider. As the sensor is in the upper half, the output voltage increases as pressure is applied. There is an empty footprint for a capacitor, which we recommend fitting. Fig.3: the module provides an analog voltage related to its supply voltage, so its connections are simple enough. The V (or +) pin should be fed from a voltage that matches the ADC reference used to measure the voltage from the S pin. Our sample code uses analog input pin A0. Screen 1: Test Sketch 930.00 933.00 930.00 929.00 798.00 901.00 907.00 917.00 920.00 916.00 923.00 918.00 924.00 926.00 925.00 927.00 925.00 928.00 926.00 51000.00 49196.14 51000.00 51603.88 143796.99 69056.60 65226.02 58953.11 57097.83 59574.24 55254.60 58333.33 54642.86 53423.33 54032.43 52815.53 54032.43 52209.05 53423.33 The output from the test sketch shows the raw 10-bit ADC reading and a calculated sensor resistance based on the module’s nominal 510kW resistor value. Even with a steady weight, there is some drift. footprint for a capacitor on the module; this is marked C1. Fig.2 shows its simple circuit. A 5V or 3.3V supply is applied between the V and G (alternatively labelled + and −) pins. Since the sensor’s resistance decreases as pressure is applied, the voltage at the S pin will increase with more pressure. Circuit and software Fig.3 shows the simple circuit we used to test the module with an Uno R4. Since the Uno R4 has socket headers and the module has plug headers, we made the connections using plugsocket jumper wires. We expect that almost any Arduino board with an analog input can be substituted. The “XC3738_test.ino” sketch uses the ADC to read the voltage at its A0 pin and displays the raw 10-bit ADC reading (from 0 to 1023) and the calculated force-sensitive resistor resistance (siliconchip.com.au/Shop/6/502). This was a simple way to get a feel for how the module responds to being squashed and squeezed. When no pressure was applied, we got a reading of 25, indicating a sensor resistance of around 20MW. We could get a reading over 1000 with firm pressure between our fingertips, indicating a resistance near 10kW. siliconchip.com.au As you can appreciate from Fig.1, the sensor is quite thin, and it’s not immediately clear how it could be used to weigh an object or vessel. We measured the sensor tip with callipers to be around 0.3mm thick. The Jaycar website offers a basic data sheet, and we found some more detailed data sheets for similar devices from Interlink Electronics (www. interlinkelectronics.com). That firm appears to be one of the pioneers of this technology. The sensor on the XC3738 looks quite like Interlink’s FSR 400 sensor. We also found an Integration Guide on the SparkFun Electronics website with numerous tips for this type of sensor (siliconchip.au/link/abx5). This guide doesn’t exactly correspond to the Duinotech sensor, but we found it very helpful. They state that the sensors should not be exposed to sharp surfaces. They are not waterproof and have an air vent that runs parallel to the external leads, allowing their internal pressure to equalise. The guide seems to focus on measuring weights and notes that a pressure measurement would require the vent to be in contact with air at atmospheric pressure. So we will concentrate on applications that measure weight rather than pressure. Testing The guide notes that the sensors are tested by applying force via a silicone rubber ball. We recommend adding small rubber feet (see Fig.1) to help spread the load on the sensor and protect it from impacts. We also added a 100nF capacitor to the vacant C1 footprint on the module. August 2025  35 Rubber is recommended in designs where some degree of movement is expected. It also protects the sensor from sharp edges and impacts while spreading the force uniformly across the active area. With that in mind, we found some self-adhesive rubber feet about 5mm in diameter, similar in size to the sensor’s active area. We attached one to each side of the sensor’s tip. Screen 1 shows the output of the XC3738_test sketch with a half-full (half-empty?) glass resting on the modified sensor. The ADC reading is moving around a bit; the sensor measures around 50kW. We then rigged up a container to balance on the sensor to see if it could be used to measure weight. The blue trace in Fig.4 shows the results of our first experiment. The curve indicates quite a narrow working range, with a notable offset from zero grams before a meaningful reading is registered. The values near the centre of the graph tended to drift around a bit, even with a steady weight, sometimes by up to 100 ADC steps. To test the hysteresis, we noted the values as we filled and then emptied the container, but due to the large amount of drift, we couldn’t draw any firm conclusions about hysteresis. Many microcontroller ADC peripherals recommend a source impedance of no more than 10kW. The data sheet for the RA4M1 microcontroller on the Uno R4 suggests 6.7kW at most. The divider on the Thin-Film Pressure Sensor module is typically dominated by the 510kW resistor, so it would usually have a much higher impedance than the recommended value. That could lead to ADC readings being affected by noise and even the ADC sampling process. The typical solution is to fit a capacitor here to provide a low-impedance voltage source; we generally use a 100nF part for this role. Such a value results in a time constant of around 50ms, which we figure should not affect any weight-­ measuring applications. It might be a bit high if you are using the module as a touch sensor to detect brief touches, though. So we fitted a 100nF M3216 (1206 imperial) SMD capacitor to the C1 footprint on the module, visible in our photo. We then repeated the weight experiment and recorded the red curve in Fig.4. We still noted quite a bit of drift around the middle of the graph. Overall, the response is similar, although the values span a wider range; the capacitor clearly makes a positive difference. The useful working range in either case is approximately 150-300g. There is some response to changing weights above this range, but it is not as distinct. We wonder if replacing the resistor with a lower value might provide better resolution at higher weights at the cost of losing resolution at lower weights. In use The narrow working range sounds quite limiting, but it could be expanded with the appropriate arrangement of levers and pivot points. With the sensors being relatively cheap, a second Fig.4: the blue curve shows the raw 10-bit ADC readings from the sensor with different weights applied. The red curve shows the effect of fitting a 100nF capacitor to the module on the readings. As you can see, the module has a useful response between about 150g and 300g when fitted with rubber feet. 36 Silicon Chip Australia's electronics magazine or third sensor could be added to share the load and thus the measured weight. Many electronic scales use an array of four strain gauges to ensure the weights are measured consistently, even if they are unevenly distributed. The thin film pressure sensors do not produce a change in reading near zero, which is not ideal. Adding an extra weight could help offset the reading, allowing it to measure lower weights. That said, the accuracy is not great, and we suspect that the sensors will be more useful in indicating a full or empty state (with perhaps a handful of steps in between) than a precise weight. The integration guide noted earlier also suggests that calibration is necessary if precision is needed. This section of the guide also states that temperature compensation may also be included in the calibration, with an expected resistance change of up to 10% with temperature. The guide mentions that humid conditions (95% RH) can change the sensor’s resistance, so this should also be considered if the sensor is used in a moist or humid environment. Conclusion Thin-film pressure sensor modules such as the Duinotech XC3738 are handy for detecting changes in weight or pressure, but they are not wellsuited to precision applications. They are more realistically useful when you want to detect the presence or absence of weight. We recommend adding a capacitor and rubber feet to the sensor to help in weight-measuring applications. Without the rubber feet, we’re not sure how it would be possible to apply a meaningful force to the sensor. The capacitor helps ensure it has the correct source impedance to suit a typical ADC. The module’s response is expected to vary under different conditions and between different units. Individual calibration is probably the best way to counteract any of those sorts of variations. So, these devices are better suited to one-off projects than production devices. The XC3738 Arduino Compatible Thin-Film Pressure Sensor is available from Jaycar Electronics; see: www.jaycar.com.au/p/XC3738 SC siliconchip.com.au FREE Download Now! Mac, Windows and Linux Edit and color correct using the same software used by Hollywood, for free! DaVinci Resolve is Hollywood’s most popular software! Now it’s easy to create feature film quality videos by using professional color correction, editing, audio and visual effects. Because DaVinci Resolve is free, you’re not locked into a cloud license so you won’t lose your work if you stop paying a monthly fee. There’s no monthly fee, no embedded ads and no user tracking. Creative Color Correction Editing, Color, Audio and Effects! 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Learn more at www.blackmagicdesign.com/au Download free on the DaVinci Resolve website NO SUBSCRIPTIONS • NO ADS • NO USER TRACKING • NO AI TRAINING USB--C USB Part 1 by Tim Blythman Power Monitor It is always handy to know what voltage and current a USB device is using. Now that USB-C is prevalent, it’s time for a USB-C Power Monitor. It can be used for all modern USB-C devices, as well as legacy USB devices, with the right adaptor. T here are many situations where it’s helpful to see how much power or current a USB device is drawing, or what voltage is being applied to it. This design makes that very easy, and it works with virtually all modern USB-C devices. Say you have a fast charger and a smartphone or tablet that’s capable of fast charging. While the situation is getting better, there are cases where they are incompatible and will not actually fast charge, or will, but only at a modest rate. With this device, you can see exactly how much power is being transferred. Another situation is if you are developing a USB device and you want to see how much power it draws when performing certain functions, or whether it’s correctly signalling the power supply to give it a certain voltage or amount of power. Ideally, you want a compact device that can just be plugged between two devices, with a screen to show the voltage, current, power, energy and more. That’s exactly what this device is. It doesn’t even matter which way around you connect it – it can monitor current and thus power flow in either direction! It doesn’t need an external power supply, either. Its controls are simple yet intuitive; it uses just three pushbuttons and an OLED screen. A bit of history This project is, in a sense, an update of the USB Power Monitor from the December 2012 issue (siliconchip.au/ Article/460). It was a small PCB with a USB-A plug at one end and a USB-A socket at the other. This allowed it to be fitted inline at any place you might connect a USB-A plug, including a computer or USB power supply. That USB Power Monitor displayed information on an LCD screen, such as the USB bus voltage and current drawn at the socket, as well as calculating power. It took its power from the USB supply upstream of the current measuring shunt, and could measure down to 1μA. An update published in the Circuit Notebook section of the October 2013 issue (siliconchip.au/Article/4999) added the ability to measure energy consumption by accumulating the power usage over time. This update did not require any changes to the hardware; it was a simple firmware upgrade. While the earlier Monitor can still be useful, its legacy Type-A connectors rule out the option of working with newer USB 3.x features, such as Power Delivery (PD) or SuperSpeed USB data transfer. USB-C is now very widespread. We have recently switched to using USB-C sockets on practically all projects that need a USB connection. Last year, USB-C was legislated in the European Union as the standard charging port for mobile phones and similar gadgets. The demand for higher currents, higher voltages and the consequent higher power levels means that a USB-C Power Monitor is necessary for some scenarios. USB-PD (power delivery) is currently rated to provide up to 48V at 5A, well beyond what the older USB Power Monitor can tolerate or measure. Of course, legacy USB 2.0 devices with the older USB-A and USB-B connectors can work with the newer Monitor with simple adaptors. However, there is a lot more to the USB-C Power Monitor than just adding USB-C connectors to the older design! We’ll describe some of the technical features that apply to USB-C and how they have affected our design. If you Short-form Kit (SC7489, $60): this kit includes all the non-optional parts listed except the case, lithium-ion cell and glue. It will also include the FFC (flat flexible cable PCB) for joining the two PCBs. 38 Silicon Chip Australia's electronics magazine siliconchip.com.au Features & Specifications ● Main screen reports current, voltage, power, energy (in J or Wh) & time ● Configuration channel (CC) status screen ● All 24 USB data lines pass through ● Self-contained with 400mAh rechargeable lithium battery ● Internal battery means no extra load on the USB circuit under test ● Compact case is only 80 × 40mm ● Automatic offset trimming ● Voltage measurements: up to 60V with 10mV resolution ● Current measurements: up to ±5A with 1mA resolution; 10μA resolution below ~25mA ● Power: up to 300W with 1mW resolution (limited by V and I) ● Energy: up to 999999J (1mJ resolution) or up to 999Wh (10μWh resolution) ● Battery consumption: <20mA, giving 20 hours of usage per charge ● Sleep mode: <10μA drawn from battery, less than typical self-discharge want more background on USB technology, we have a panel listing several Silicon Chip features and projects that involve USB on a more technical level. Early USB was simple The original USB 1.0 specification dates back to 1996, and uses much the same hardware and electrical arrangement as the later USB 1.1 and USB 2.0 standards. Two conductors (Vbus and GND) are provided for a nominal 5V power supply. Another two conductors (D+ and D−) providing a bi-­ directional differential signalling pair. A separate shield connection is also present. These connections are carried through the original USB Power Monitor, with only the Vbus line interrupted by a current measuring shunt. All these earlier specifications have been carried forward into the newer versions of the USB specifications, although many aspects are now considered ‘legacy’. The design of the plugs and sockets enforced upstream and downstream ends. Assuming the standards have been followed, this means that current can only flow one way, and thus the USB Power Monitor’s simple design only needed to handle current flowing in one direction. The supply voltage was fixed at a nominal 5V, meaning that it could directly power a 5V microcontroller without even needing a regulator. In fact, all the ICs on the original USB Power Monitor run directly from the USB 5V supply. Given USB’s broad usage as a power supply and for charging, it was also useful when no USB communication takes place. For example, you could siliconchip.com.au use it to check how much current a mobile phone used while charging. The USB-C standard USB-C is a 2014 design that allows all USB protocols, so far up to USB4, to be transmitted. Importantly, USB-C only specifies things like the connectors and cables; it permits many other protocols aside from USB. Some other communication technologies that can be carried over USB-C include Thunderbolt, PCIe, HDMI and DisplayPort (including digital video & audio). The USB-C connector is symmetrical and can be inserted in two ways (no more fumbling to figure out the right way!). It can also be used at both ends of a cable, so the cable itself does not enforce an upstream or downstream end; current and data can flow either way in a USB-C cable. In fact, USB-C allows the power source or sink role to be separate from the USB host or device function. USB-PD (USB power delivery) provides a means to negotiate voltages up to 48V and currents up to 5A. So clearly, there are many factors that need to be considered in designing a USB-C capable power monitor. Because of all these features, a USB-C receptacle can have up to 24 conductors, plus a shield. Some of these are symmetrically arranged duplicates. For example, there are four ground pins and four Vbus pins to share the current load, as shown in Fig.1. The plug is mirrored relative to the socket. In the receptacle, there are two each of the D+ and D− legacy USB data pins. There are four more differential pairs, two in each direction. These are the same pairs that were introduced with USB 3.0, and the blue-coloured connectors that marked the new SuperSpeed transfer rate. The four remaining conductors are for signalling related to USB-C’s features. The two CC (configuration channel) lines are the channel over which USB-PD communication takes place. Our article “How USB Power Delivery works” (July 2021; siliconchip.au/ Article/14919) gets into the details of the power delivery protocol. There are now chips specifically designed to handle USB-PD communications, and these are often found in the so-called ‘trigger’ or ‘decoy’ modules that can request a specific voltage using USB-PD’s digital signalling. The photo overleaf shows an example of such a module. Early versions of USB-PD supported up to six power profiles at various currents and voltages of 5V, 12V or 20V. Subsequent revisions added support for 9V, 15V, 28V, 36V and 48V. A more recent protocol, known as PPS (Programmable Power Supply), allows voltages to be requested up to 21V in 20mV steps and current limits in 50mA steps. Fig.1: USB-C’s design incorporates rotational symmetry, removing the need to flip the connector like earlier USB plugs/sockets. This requires extra conductors, with many being duplicated. The configuration channel lines provide cable rotation detection for correct operation. Australia's electronics magazine August 2025  39 The main PCB of the Power Monitor connects to the USB Breakout board using a flexible PCB (FFC). A typical USB-PD trigger board has a USB-C socket, a USBPD interface IC and an output connector. This example sets the requested PD voltage by solder jumpers; some can be controlled digitally, with an I2C serial interface or similar. The simplest signalling is done via pullups and pulldowns on the CC lines with specific resistor values; this can be used to offer or request the legacy 5V supply voltage. We have used this arrangement in our projects using USB-C sockets for 5V power. Fig.2 shows the basic arrangement using the resistor-based signalling, which is quite simple and elegant. Only one CC line is typically connected through in a cable; this allows both devices to determine the orientation of the conductors if the cable has been flipped. The source will only apply Vbus if it sees that a sink has connected with the correct pulldown resistance. The pulldown can be applied by a simple resistor to ground, so the signalling will work even on a device that has no power to begin with. Cleverly, Vbus switching can be achieved by not much more than a logic-­ level P-channel Mosfet. The Mosfet’s gate is pulled up until a sink is connected, switching the Mosfet off. The sink’s Rd resistor pulls the gate low and turns the Mosfet on, allowing the source to provide current to the sink. The current that the source applies to the CC line also encodes a Vbus current capacity, and the sink can detect this by the voltage across the Rd resistor on the CC line. This allows sink devices to limit their current draw to what the source can provide. The second CC conductor can 40 Silicon Chip also supply power to the electronics embedded in an ‘e-marked’ cable. In this role, it is known as Vconn, indicated by the resistors labelled Ra in Fig.2. E-marking involves embedding a chip inside the cable. One use of such a chip is to indicate to the source that the cable can handle 5A. Any cable that is not identified as such is limited to 3A. The CC lines are also used to communicate other USB-C features, such as support for alternative modes. Finally, there are the two SBU (sideband use) lines, which are used by an audio adaptor accessory mode and the USB4 protocol. It’s also possible to use them for a specific custom purpose through USB-PD negotiation. In summary, USB-C offers a lot more variety in voltages, currents and protocols than the legacy standards and connectors. So the USB-C Power Monitor has more to do than just measure the current and voltage. We need to be able to measure voltages up to 48V and monitor currents up to 5A in either direction. There are signals, such as those on the CC lines, that we can monitor for connectivity and possibly take control of. We considered including a USB-PD chip to allow monitoring of the power delivery communications, but ultimately decided against doing so. Most of these chips are in leadless packages (eg, QFN) that are difficult to solder. We also thought it would be best to avoid a situation where multiple chips are trying to communicate over the same configuration channel bus, lest that lead to improper voltages being requested, potentially causing damage to equipment connected to the Monitor. USB-C specifications It is an unfortunate fact that the USB-C Power Monitor (or any design like it) cannot meet the USB-C specifications. As you can see from the photos, it has a USB-C socket at one end and a USB-C plug at the other. As such, it is effectively a USB-C extension cable. Such cables are simply forbidden by the specification. Consider what would happen if a 5A e-marked cable were connected to a 3A extension cable. The signalling for the 5A cable would be passed through the 3A cable, and the source would behave as though both cables are capable of 5A when they might not be. Extension cables also diminish the signal integrity due to the extra junctions between the plugs and sockets and the cable length. This means that the higher speed communications are more likely to be compromised. Fig.2: the basic signalling used on the CC lines requires sources and sinks to use specific resistor values (or current sources/sinks) to determine rotation and the current required. Before a source can apply power on Vbus, it must detect that a sink is correctly connected. Australia's electronics magazine siliconchip.com.au Providing two USB-C sockets on the Monitor (effectively turning it into a cable joiner) would be possible, but would result in much the same concerns. The specification also allows cables to omit some internal conductors, since the cable orientation sensing can deal with that scenario. Connecting two such cables with a joiner could result in some signals not being passed through at all. We performed several speed tests with different devices through our Power Monitor, comparing the performance between having the Monitor inline or not. We did not find a device for which it made a difference. It takes some powerful gear to run the high-speed (many GHz) tests needed to validate USB 3.2 communication, and we do not have access to such test equipment. However, by making the USB-C Power Monitor as short as practically possible, we minimise the possibility of introducing signal integrity problems. Still, we cannot guarantee they can’t happen. So, while the USB-C Power Monitor can’t comply with the USB-C specifications, we have worked hard and performed some thorough testing to ensure that it works with as many devices as possible. Circuit details The circuit shown in Fig.3 is split over two PCBs joined by a 7-pin header (CON4) at each end. The smaller PCB (inside the dashed box) has a USB-C plug (CON1) and a USB-C socket (CON2). All the Vbus and GND connections are joined at each end to simplify routing; this is actually required in the USB-C specification. Apart from a few, all the other lines are connected straight through, forming the forbidden USB-C extension lead. The Vbus, CC1 and CC2 lines each have a resistor between CON1 and CON2. The 15mW shunt resistor in series with Vbus is for measuring the current flow. The resistors inline with CC1 and CC2 allow us to determine the source and sink nature of whatever is connected to CON1 and CON2. The extra resistance is about the smallest we could use to reliably detect that difference, while being low enough to not affect the CC detection thresholds according to the specifications. siliconchip.com.au Parts List – USB-C Power Monitor 1 double-sided green PCB coded 04102251, 78 × 11 × 0.8mm 1 double-sided black PCB coded 04102252, 80 × 40 × 0.8mm 1 flat flexible PCB (FFC) coded 04102253, 18 × 40mm OR 5cm of 7-way ribbon cable OR 30cm of light-duty flexible cable 1 80 × 40 × 20mm enclosure [Hammond 1551KBK, Altronics H9004] 1 small lithium-ion rechargeable pouch cell with protection circuitry [Altronics S4723] 1 Amphenol 12401981E412A straddle-mount 24-pin USB-C plug (CON1) [DigiKey, Mouser] 1 Würth 632723100011 24-pin SMT+through-hole USB-C socket (CON2) [DigiKey, Mouser] 1 5-pin header, 2.54mm pitch (CON3; optional, for ICSP) 1 USB-C SMD power-only socket (CON5) [GCT USB4135 or equivalent] 1 M2016/0806 size 4.7μH 1A inductor (L1) [Murata LQM2MPN4R7NG0L] 1 128×32 pixel 0.91-inch I2C OLED module (MOD1) 3 Adafruit 5410 reverse-mount SMD tactile switches (S1-S3) [DigiKey, Mouser] 1 tube of neutral-cure silicone sealant or similar flexible adhesive 1 piece of foam-cored double-sided tape (to secure BAT1) Würth 632723300011 is an alternative but it might be harder to solder 🔸 🔸 Semiconductors 1 PIC16F18146-I/SO 8-bit micro programmed with 0410225A.HEX, SOIC-20 (IC1) 1 INA296A3 or INA282 current monitor, SOIC-8 (IC2) 1 AD8541A or NCS325 rail-to-rail CMOS op amp, SOT-23-5 or SC-70-5 (IC3) 1 MCP73831T-2ACI/OT Li-ion charge regulator, SOT23-5 (IC4) 1 MCP16252T-I/CH boost regulator, SOT-23-6 (REG1) 1 3mm bi-colour red/green LED (LED1) 1 BAT54C common-cathode schottky diode, SOT-23 (D1) Capacitors (all SMD M2012/0805 size X7R ceramic) 5 10μF 16V 5 100nF 50V Resistors (all SMD M2012/0805 size ⅛W, 1% unless noted) 2 1MW 1 22kW 2 220W 1 390kW 3 10kW 1 100W 1 150kW 6 5.1kW 1 10W 1 120kW 2 1kW 1 15mW M6331/2512 size 3W Articles on USB technology If you wish to delve into the technical details of USB, the following Silicon Chip articles may be of interest: ● USB: Hassle-Free Connections To Your PC by Peter Smith (November 1999): siliconchip.au/Article/4436 ● The History of USB by Jim Rowe (June 2021): siliconchip.au/Article/14883 ● How USB Power Delivery (USB-PD) works by Andrew Levido (July 2021): siliconchip.au/Article/14919 ● El Cheapo Modules: USB-PD chargers by Jim Rowe (July 2021): siliconchip.au/Article/14920 ● El Cheapo Modules: USB-PD Triggers by Jim Rowe (August 2021): siliconchip.au/Article/14996 The following projects may also be of interest: ● USB Power Monitor by Nicholas Vinen (December 2012): siliconchip.au/Article/460 ● USB Cable Tester by Tim Blythman (November & December 2021): siliconchip.com.au/Series/374 ● USB-C Serial Adaptor by Tim Blythman (June 2024): siliconchip.au/Article/16291 Australia's electronics magazine August 2025  41 Typical currents in the CC lines are in the hundreds of microamps (from source current Ip to sink resistor Rd), so the drop across the 220W resistors is in the tens of millivolts. This is the precision of the voltage thresholds in the specifications. When a CC line is allocated to a Vconn role, it can supply 5V power at up to 200mA to electronics in an e-marked cable. Clearly, 220W is too high to allow 200mA to be passed successfully, although our testing didn’t find any cables that had problems with this. A typical e-marked cable will try to source Vconn from both ends of the cable using diodes or similar to prevent Vconn being carried through the cable. So if you run into problems, try reversing the Monitor; that should allow Vconn to be sourced from the other end. CON4 breaks out the important signals back to the main PCB for monitoring. There is a ground connection, and two wires for Vbus, CC1 and CC2, fed from each side of their respective resistors. CON4’s connections are arranged symmetrically so that the entire PCB can be rotated 180°. This means that if you prefer the USB-C plug on the left and the USB-C socket on the right, you can wire the boards in this fashion during the construction phase. Main circuit A microcontroller is required to make measurements and drive the display to report them. We’re using an 8-bit PIC16F18146 (IC1), since it has some useful internal peripherals, including a 4.096V reference, an 8-bit buffered digital-to-analog converter (DAC) and a 12-bit analog-to-digital converter (ADC). IC1 has the usual 100nF bypass capacitor on its power and ground pins (1 and 20 respectively). A 10kW resistor pulls up the MCLR pin (pin 4) to allow normal operation, unless a programmer is connected at ICSP header CON3. Pins 1, 4, 18, 19 and 20 are taken to CON3 for programming and debugging. Pins 11, 12 and 13 connect to tactile switches S1, S2 and S3. They are configured with internal pullups, and the micro detects the pin level changing to low when the switch is pressed, closing the circuit to ground. A pinchange interrupt allows the micro to be 42 Silicon Chip woken up from deep sleep by pressing any of the switches. These 8-bit PICs have a good output pin drive strength and so can directly power other circuit elements, allowing them to be switched off when the Monitor needs to be in low-power sleep mode. Pin 16 powers OLED module MOD1, a 128×32 pixel monochrome display, so it can show a few lines of text or similar. IC1’s pins 14 and 15 provide a bit-banged I2C serial interface to control the OLED. IC1’s pin 2 is used to provide power to IC2 and IC3, as well as to control the ENABLE pin on REG1. With both pin 2 and pin 16 low and the microcontroller in low-power sleep, only IC1 and REG1 draw power from BAT1. The nominal 5V rail falls slightly below the cell voltage (because of the diode and resistor). The greatest current draw is the 6μA flowing through REG1’s feedback divider, with IC1 and REG1 drawing less than 1μA each, for a total under 8μA. Analog circuitry IC2 is a current shunt monitor that amplifies the voltage across the 15mW current measuring shunt connected via CON4. It has a gain of 50, so its output voltage is 0.75V for every amp through the shunt. IC2 is equipped with two reference inputs (REF1 and REF2); the output voltage is offset against the average of the voltage at these two pins. The twopin reference feature makes it easy to set up a mid-rail reference for bidirectional current sensing, although we don’t use that here. Instead, we feed both reference pins with a voltage supplied from pin 17 of IC1. This is derived from an 8-bit DAC connected to a 4.096V internal reference. By setting the DAC, we can change the IC2 reference to be anywhere between 0V and 4.096V. This allows us to nearly double the span available for readings. For currents in one direction, we set the reference to near (but not quite) 0V and we have almost 4V of range, allowing up to 5A to be measured. If the current reverses direction, the reference is taken near 4V, allowing similar magnitudes to be measured in the opposite direction. IC3 is a single op amp configured to amplify the output from IC2 (relative to the same reference) by a factor of 100. The 100nF capacitor across the Australia's electronics magazine Fig.3: the circuit is split into two sections connected by CON4s; one section has a USB-C plug (CON1) and a USB receptacle (CON2), wired straight through apart from some resistors. The other section has microcontroller IC1, which measure voltages, currents and so forth and displays them on the OLED module. feedback resistor provides low-pass filtering of the amplified signal. IC1’s pin 9 is used for ADC readings of the low range (amplified) voltages from IC3, while pin 3 samples the higher range voltages directly from IC2. The ADC peripheral can perform differential readings, so the reference is simply used as the second channel for these readings. This scheme gives us more dynamic range to accurately read currents in both directions over the two ranges. The 150kW/10kW divider connected to one of the Vcc pins of CON4 is used for measuring the Vbus voltage. The 100nF capacitor on its lower leg provides a lower source impedance to charge up pin 10’s ADC sampling capacitor. With a 4.096V reference, the divider allows up to 65V to be measured, comfortably above the 48V siliconchip.com.au currently allowed by the USB-C specification. CC sensing The remaining resistors are used to drive and sample the two CC lines. Normally, pins 5, 6, 7 and 8 are set as analog inputs to monitor the state of the CC lines. The series 5.1kW resistors do not noticeably affect the sensed voltage when these pins are inputs. The state of the pins can determine what current the source can provide. By monitoring for the slight voltage difference across the 220W resistors, it can also determine which end is the source and which end is the sink. The 5.1kW resistors also allow the USB-C Power Monitor to behave as a power sink by driving one or more of these pins to a low logic level (0V). This allows you to check the siliconchip.com.au capabilities of a source, even if a sink is not connected. It is only a very limited use of the CC signalling. But USB-C now allows scenarios which seem improbable; for example, a mobile phone attempting to charge a laptop computer. So we think the ability to identify such situations could be helpful. Power supply One interesting problem is that we realised a USB-C cable does not always provide power, even if it is connected to a suitable source such as a computer or power supply. Thus, we needed a way to power the USB-C Power Monitor independently. We chose to use a lithium-ion rechargeable battery (BAT1). This has the advantage that the power supply is decoupled from the USB-C circuitry, Australia's electronics magazine and the USB-C Power Monitor does not load the circuit under test, apart from a voltage divider totalling 160kW, which draws about 31μA at 5V. We used similar circuitry to our other recent projects that include a Li-ion cell. The most recent was the Compact OLED Clock and Timer (September 2024 issue; siliconchip.au/ Article/16570). In this case, 5V power for charging comes in via CON5, a power-only USB-C socket with the 5.1kW resistors necessary to identify it as a power sink. The MCP73831 charger, IC4, has a 10μF smoothing capacitor on its input pin and another on its output to the battery. The MCP73831 monitors the charging current and voltage of BAT1 and provides a multi-stage charging regime. It has a status output and the August 2025  43 The Breakout PCB is used to provide the USB connections and will be described in more detail in next month’s issue. charging current can be programmed. All in a tiny 5-pin SOT-23 package! The charge current is set to 45mA by the 22kW resistor connected to IC4’s pin 5 (PROG). The STAT pin drives one side of bicolour LED1; it is low during charging and is high when it is complete. The arrangement of 1kW resistors allows the LED to light up red during charging and green when charging is complete. Dual diode D1 is a common-­cathode schottky type. Power from the battery and CON5 are connected to its anodes, so there is no load on the battery when power is available at CON5. The remainder of the circuitry is powered from D1’s cathode, and because there is no draw on the battery while charging, IC4 can charge it fully. This arrangement also means that the USB-C Power Monitor can be powered directly from CON5 even if a battery is not fitted. The cathode of D1 is connected to MCP16252 boost regulator REG1, which also has 10μF bypass capacitors at its input (pin 6) and output (pin 5). This part has an ENABLE input at its pin 3. When this pin is low, the REG1’s input is connected directly to its output, providing a low-quiescent-­ current mode with no voltage boost. When ENABLE is taken high, the boost regulator operates. It has internal N-channel and P-channel Mosfets. The SW pin (pin 1) is pulled low by the N-channel Mosfet, drawing current through inductor L1. When this Mosfet switches off, the P-channel Mosfet switches on, dumping current from the inductor into the output and boosting the voltage. Using a Mosfet as an active switch is more efficient than using a diode, since there is negligible voltage drop across the switch when it is on. The 390kW/120kW divider at the output provides feedback for the regulator and sets the output to a nominal 5.2V. After the 10μF capacitor on REG1’s output is a 10W resistor and a further 10μF capacitor to provide a degree of filtering for the rest of the circuit. At the circuit’s nominal 20mA draw, the 10W resistor drops about 0.2V, leaving close to 5V. Software As we noted, the PIC16F18146 has a handy set of peripherals, so we’ll describe those next, along with some aspects of the software operation. The capabilities of the ADC are critical to this project. The PIC provides an internal reference that can be set to a nominal 1.024V, 2.048V or 4.096V, and can be used to set the ADC scale. The 4.096V reference is used for most of the analog readings and its measured value (in millivolts) is stored in non-volatile memory at the time of manufacture. Being able to use the 4.096V range is the main reason for the boost converter (REG1). The 4.096V reference will not be functional if the supply is only 3.7V, as might be the case for a Li-ion cell that is nearly flat without this boosting. The analog peripheral is actually described as an ‘Analog-to-Digital Converter with Computation’ (ADCC) module. It can produce a 12-bit result and can also accumulate multiple results. The accumulator has 18 bits, so the software configures it to accumulate 64 12-bit results, giving a notional 18-bit result. Since the total ADCC error is around two bits, the lower two bits are discarded, and the software works with convenient 16-bit numbers. It takes about two milliseconds to perform the 64 samples, so the processor sets it running and uses an interrupt routine to store the readings, then commence the next sample while it continues with other tasks. A set of 13 samples is taken in round-robin fashion; the two current readings are taken in differential mode using the pin 17 VREF voltage as the second channel. The voltages across the 220W resistors in the CC lines are also measured in differential mode; this allows us to note the sign and determine the direction that the current is flowing in those lines. All these differential readings are also validated by taking corresponding single-ended (absolute) readings. For example, this allows us to detect when the low-range current reading approaches the rails, an indication that we should shift the reference (by setting the DAC) to allow more headroom or use the high-current range instead. A second 8-bit DAC is internally connected to IC1’s supply. The DAC is set to code 32, or 1/8 of the supply. The ADCC sample of this channel uses the 1.024V reference, meaning that we can accurately check that the supply voltage is high enough for the 4.096V reference to work and that the other readings are correct. A timer peripheral is also used to provide an internal clock. This is set to The “>” button cycles through various screens, while the up/down buttons are used to adjust values and modes. 44 Silicon Chip Australia's electronics magazine siliconchip.com.au Screen 1: the main screen reports the Vbus voltage and current (including direction). Power and accumulated energy are also calculated; a timer is available too. Another screen can be used to monitor and test the condition of the configuration channel lines. count at an integer fraction of a second and make the calculations easy (for an 8-bit processor) without using computationally complex floating-point values. The time each sample set takes to complete is also recorded. This is necessary because the most accurate ADCC results can be achieved when the ADCC is run from its own internal oscillator and completely decoupled from the micro’s other internal clocks. The appropriate scaling factors are applied to provide the numerical values that are needed. Derived values like power (current multiplied by voltage) and energy (power multiplied by time) are also calculated. This part of the software also sets flags indicating which of the low or high current ranges is valid and should be used. These measurements continue to run any time the micro is active and not sleeping; the results are displayed according to the screen that the user has selected. The main screen, for example, reports the same basic statistics as the older Monitor: voltage, current (now including direction), power and total energy. The energy totaliser is paired with a timer; both can be started, paused and reset together. The totaliser also runs in the background if other screens are selected, providing seamless operation. Another screen allows monitoring and control of the CC lines, while a third can be used to put the Monitor into low-power sleep mode or check the battery voltage. You can also access the configuration screens by a long press of S3. Most of the configuration is involved with trimming the calibration factors to suit the components used in a specific build, although there are also the options to adjust the screen brightness and choose between watt-hours (Wh) or Joules (J) for the units displayed for energy. We’ll look more at the user interface later. Hardware The two PCBs fit into a compact 80 × 40 × 20mm enclosure; we used a siliconchip.com.au Hammond 1551KBK, which is available from Altronics (Cat H9004). One PCB replaces the lid, so the final unit is only 18mm high, but is slightly longer than 80mm because of the plug protruding at one end. Both PCBs require reasonably good soldering skills to build. Fully featured USB-C plugs and sockets are only available with very tight pin spacings of around 0.5mm. When the Breakout PCB is completed, it can be tested in isolation by using it as an extension for a USB-C cable. Thus, it is possible to detect problems early in the process. The PCB hosting CON1 and CON2 must be 0.8mm thick because the plug (CON1) is a so-called ‘straddle-mount’ that clips over the edge of the PCB. It sounds fussy, but the mounting style allows the part to be precisely placed before soldering begins, and we actually found it easier to work with than the socket (CON2). The upper PCB is populated with M2012 (imperial 0805) sized passives, which are 2mm long. This is about the minimum size we consider easy to handle. There are a couple of SOIC chips and a few SOT-23 variants with three, five and six pins. Since the top PCB is also the lid, there are a couple of unusual constructions steps. If you have built the likes of the Compact Clock and Timer (or read its article), these will be familiar. The two PCBs must be joined with wires. Our early prototypes used pluggable headers, but we found that these had enough variation in resistance to interfere with the performance of the current-measuring shunt. We designed a flat flexible cable (FFC) that can be soldered to the PCBs to give a simple and elegant connection. You can also use hookup wire for this, or a section of 7-way ribbon cable, if you find the FFC is too expensive or difficult to source (we’ll supply the FFC with our kits – see the panel). We had originally planned to use a 10440-sized lithium-ion cell as the battery. These are the same physical size as a AAA cell, and there is just enough room to fit a AAA cell holder to allow simple and safe connection of the cell. However, we think that our final design, using a small, rectangular pouch cell like Altronics’ Cat S4723, works better. The slim shape is a better fit for the available space, and the nominal 400mAh capacity is higher than we have seen in 10440 lithium cells. This cell measures 38 × 25 × 6mm and includes protection circuitry. Many small pouch cells are available from various online sellers. So you might find an alternative with slightly different dimensions that still fits. Until next month This is a very detailed project, and we have run out of room to describe it in this issue. The second part next month will include the construction, setup, calibration and use of the USB-C SC Power Monitor. Silicon Chip kcaBBack Issues $10.00 + post $11.50 + post $12.50 + post $13.00 + post January 1997 to October 2021 November 2021 to September 2023 October 2023 to September 2024 October 2024 onwards All back issues after February 2015 are in stock, while most from January 1997 to December 2014 are available. For a full list of all available issues, visit: siliconchip.com. au/Shop/2 PDF versions are available for all issues at siliconchip.com.au/Shop/12 We also sell photocopies of individual articles for those who don’t have a computer Australia's electronics magazine August 2025  45 RP2350B development board Think of this as the Pico 2’s bigger sibling – more pins, more I/O, more speed, more storage and more memory. It’s perfect for breadboarding, too. Also, like the Picos, it can be purchased pre-assembled! T he Raspberry Pi Pico is well known to our readers, and has been designed into many of our projects as a drop-in, self-contained compute module. It has been a runaway success for the Raspberry Pi Foundation, with over 4 million of this handy module sold since its launch in 2021. In August 2024, they improved on it with the Pico 2, based on the new RP2350A processor, which has also been very popular. The RP2350A processor also has a lesser-known sibling called the RP2350B, which is often overlooked. This has the same features as the A variant, but comes in a larger 80-pin QFN package with 48 I/O pins vs the 30 I/O pins of the RP2350A. The Raspberry Pi foundation does not offer a module based on this chip, but recently they have made it available for individual sale – so now we can design our own RP2350B based module. Thus, we present the RP2350B Development Board. This is similar to the Raspberry Pi Pico 2, but it uses the RP2350B, with nearly all of its 48 I/O pins available for experimenters – a vast improvement over the Pico 2. This board can be used as a general-purpose compute module when you need a lot of I/O pins, or as a development board while designing a circuit around the RP2350B chip. Features The RP2350B Development Board is designed to suit solderless breadboards with two rows of 32 pins on a 2.54mm/0.1-inch pitch. This is similar to the standard Raspberry Pi Pico, and this layout can also be used as a plug-in module in your own PCB designs. In our module, 47 of the RP2350B’s 48 I/O pins are routed to the edge connectors. This is useful when you need a lot of I/O; for example, when driving a high-performance LCD panel with a parallel interface, or constructing your own multi-key keyboard. The one I/O pin not available, GPIO00, is used as the PSRAM IC chip select (CS) signal. On the edge pins of the module, we have also included numerous grounds, plus +3.3V and +5V outputs. One extra benefit of the RP2350B is that eight of the I/O pins are capable of analog measurements (vs four on the RP2350A), and these are also available for use in your programs. The diagram opposite lists the full capabilities of each I/O pin. The module is self-contained, including a 3.3V regulator. The input power supply is nominally 5V, but ∎ Processor: Raspberry Pi RP2350B ∎ Cores: two ARM Cortex-M33 and two Hazard3 RISC-V ∎ Clock Speed: default 150MHz; overclockable up to around 400MHz ∎ Flash memory: 16Mbytes ∎ RAM: 520kiB, expandable to over 8MiB ∎ I/O pins: 47 (eight with analog capability) ∎ I/O connectors: two rows of 32 pins, 2.54mm/0.1-inch pitch, 25.4mm/1-inch separation ∎ Power supply: 5V nominal (4.5-12V) <at> 95mA (150MHz clock) ∎ Size: 82 × 28mm Words by Geoff Graham | Design by Peter Mather RP2350B Assembled Board (SC7514, $30): includes a fully-assembled PCB with nearly everything from the parts list, except for the optional components a range of 4.5-12V is acceptable. A USB-C socket is provided for power and loading the firmware. The firmware loading process works exactly the same as with the Raspberry Pi Pico, ie, you hold down the BOOT switch while plugging the USB into your desktop or laptop computer. The flash memory used for storing programs and data in this design has a capacity of 16Mbytes (the Pico 2 has 4Mbytes). The PicoMite BASIC interpreter occupies just 2Mbytes, which leaves plenty of flash free to create an internal “disk drive” with a capacity of about 14Mbytes. Our design also supports an 8Mbyte PSRAM chip. This sits on the same quad SPI bus as the flash memory, and can be used to add to the internal RAM of the RP2350B. Overclocking The RP2350B Development Board is designed for overclocking, which means running the processor cores at a higher clock speed than specified in the data sheet. This enables the module to be used in high-performance applications, such as generating DVI/ HDMI video. The default speed for the RP2350B is 150MHz, but some people have claimed to have overclocked it to over 600MHz. A more reasonable goal is the 372MHz needed to generate DVI/ HDMI video. To support the faster speeds, our design uses an adjustable linear regulator to generate the digital core supply voltage (DVDD). This powers the chip’s core digital logic, and in our design, can be accurately adjusted from 1.1V to over 1.4V. Higher voltages allowing the CPU to run faster. In the Pico 2, this voltage is provided by an on-chip switching regulator, which is not suited to high siliconchip.com.au PWM PWM0B SERIAL I2C SPI COM1 RX I²C SDC SPI I2C GPIO47 SPI2 RX I²C2 SDL Pin Pin 5V 5V 3.3V 3.3V GND SERIAL PWM PWM11B GPIO01 GPIO46 SPI2 CLK I²C2 SDA PWM1A I²C2 SDA SPI CLK GPIO02 GPIO45 I²C SDL COM1 RX PWM10B PWM1B I²C2 SDC SPI TX GPIO03 GPIO44 SPI2 RX I²C SDA COM1 TX PWM10A GND GND GPIO04 GPIO43 SPI2 TX I²C2 SDL GPIO05 GPIO42 SPI2 CLK I²C2 SDA I²C SDL COM2 RX PWM8B SPI2 RX I²C SDA COM2 TX PWM8A PWM2A COM2 TX I²C SDA PWM2B COM2 RX I²C SDC SPI RX PWM3A I²C2 SDA SPI CLK GPIO06 GPIO41 PWM3B I²C2 SDC SPI TX GPIO07 GPIO40 GND GND GPIO08 GPIO39 SPI TX I²C2 SDL GPIO09 GPIO38 SPI CLK I²C2 SDA PWM4A COM2 TX I²C SDA PWM4B COM2 RX I²C SCL SPI2 RX PWM5A I²C2 SDA SPI2 CLK GPIO10 GPIO37 PWM5B I²C2 SCL SPI2 TX GPIO11 GPIO36 GND GND PWM6A COM1 TX I²C SDA SPI2 RX GPIO12 PWM6B COM1 RX I²C SCL GPIO13 PWM10B COM2 TX PWM10A GPIO35 SPI TX I²C2 SDL GPIO34 SPI CLK I²C2 SDA PWM7B I²C2 SCL GPIO15 GPIO32 GND GND GPIO16 GPIO17 COM1 RX I²C SCL SPI RX PWM9A COM1 RX PWM8B SPI RX I²C SDA COM1 TX PWM8A GPIO31 SPI2 TX I²C2 SDL PWM7B GPIO30 SPI2 CLK I²C2 SDA PWM7A I²C2 SDA SPI CLK GPIO18 GPIO29 PWM1B I²C2 SCL GPIO19 GPIO28 GND GND GPIO20 SPI RX PWM9B I²C SDL PWM1A SPI TX PWM11A I²C SDA GPIO33 COM1 TX I²C SDA PWM11B SPI RX GPIO14 PWM0B PWM9A COM2 RX I²C2 SDA SPI2 CLK PWM0A PWM9B I²C SDL PWM7A SPI2 TX PWM11A I²C SDL COM1 RX PWM6B SPI2 RX I²C SDA COM1 TX PWM6A GPIO27 SPI2 TX I²C2 SDL PWM2A COM2 TX I²C SDA PWM2B COM2 RX I²C SCL GPIO21 GPIO26 SPI2 CLK I²C2 SDA PWM3A I²C2 SDA GPIO22 GPIO25 I²C SDL COM2 RX PWM4B PWM3A I²C2 SCL GPIO23 GPIO24 I²C SDA COM2 TX PWM4A 3.3V 3.3V SPI TX clock speeds because of the electrical noise it generates. Additionally, it is difficult to implement, as it requires a specialised inductor, which is hard to find. In our design, the DVDD voltage is provided by a TPS7A7002DDAR linear regulator (REG34) that is both inexpensive and does not generate any electrical noise. The onboard trimming resistor (VR1) is used to set the DVDD voltage. Note that it is important that this is set before power is applied to the board. If DVDD is accidentally set too high, it can damage the RP2350B chip. We have also used an integrated crystal oscillator to generate the base clock of 12MHz for the RP2350B. This is different from Raspberry Pi Pico 2, which uses a simple crystal for this purpose. The integrated crystal oscillator provides a more stable clock with much less jitter. Jitter can be a problem siliconchip.com.au when the base clock frequency is multiplied many times in the RP2350B to give the core CPU clock. Development environments All the familiar development environments used with the Raspberry Pi Pico 2 can be used with this board. This includes: ∎ The official Raspberry Pi C SDK for C/C++ development, which can be used from the command line on a desktop or laptop computer, or within popular integrated development environments like Visual Studio Code (VS Code), Eclipse and Clion. ∎ MicroPython, which is a full implementation of the Python 3 programming language running directly on the Development Board. This includes an interactive prompt to execute commands immediately via a USB serial port. ∎ Our own PicoMite firmware, Australia's electronics magazine SPI2 RX PWM5B PWM5A ANALOG PIN which implements a feature-rich BASIC interpreter (MMBasic) with support for audio, LCD panels, SD cards, game controllers, HDMI/VGA video and PS2/USB keyboards. This firmware includes its own full-screen editor so programs can be developed, tested and run on the development board in a highly productive environment. Circuit details Fig.1 shows the full circuit for the RP2350B Development Module. At the centre is the RP2350B processor. All its general-­purpose I/O pins are routed to the two connectors at the edges of the The RP2350B has the same features as the RP2350A in the Pico 2 but has more pins, including 48 GPIOs. August 2025  47 Fig.1: the circuit diagram for the RP2350B Development Board/Module. USB-C socket CON2 is used both for supplying power (5V DC) and communicating with the RP2350B. The USB 5V supply is regulated to 3.3V by REG21 to power oscillator XO4, PSRAM IC33 and flash chip IC6. The RP2350B's nominally 1.1V core supply is generated by adjustable regulator REG34, so it can be increased for overclocking. 48 Silicon Chip Australia's electronics magazine siliconchip.com.au PCB (CON35/36), except for GPIO00, which is used as the chip select signal for the PSRAM (IC33). One other pin (GPIO25) is special as it drives the onboard LED, LED2. If you do not need this indicating function, the I/O pin can be used as a general purpose I/O with the extra load presented by the LED and its 1kW current-­ limiting resistor. The input power for the board is a nominal 5V DC; the RP2350B and the other chips on the board run from 3.3V, which is supplied by a simple AMS1117-3.3 low-dropout linear regulator. The official Raspberry Pi Pico modules have a much more complex design for the power supply, using a switching regulator, but this can cause significant electrical noise that interferes with analog measurements and sensitive circuits such as audio input/ output. Most designs do not need the wide voltage range of the switching regulator, so our design avoids the noise problems and still provides a useful input supply voltage range of 4.5-12V. The RP2350B needs another voltage supply called the digital core supply (DVDD), which we mentioned earlier as essential for overclocking. This powers the chip’s core digital logic. In our design, it is provided by REG34, an adjustable linear regulator controlled by trimpot VR1. IC6 is a W25Q128JVSIQ 128Mbit (16Mbyte) flash memory chip made by Winbond Electronics. It uses a quad SPI interface and is designed for true XIP (execute in place) operation, which allows the RP2350B to execute its program directly from this chip. The W25Q128JVSIQ can operate with high clock speeds on the SPI interface (133MHz); this is important when overclocking the RP2350B. The RP2350B also has a built-in SRAM cache, which operates to mitigate the effect of the relatively slow quad SPI bus interface. The BOOT pushbutton switch (S16) pulls the chip select line (CS) low on the flash memory chip, which essentially disables the flash memory. When power is applied, the RP2350B will interpret the disabled memory as a signal to enter its bootloader mode, which is used to load a new firmware image. IC33 is an optional external PSRAM chip (APS6404L-3SQR-SN), which sits on the same quad SPI bus as the siliconchip.com.au Parts List – RP2350B Development Board 1 double-sided PCB coded 07107251, 82 × 28mm 2 momentary SMD tactile pushbutton switches (S15, S16) [XKB Connectivity TS-1187A-B-A-B] 1 USB-C USB 2.0 data + power socket (CON2) [Kinghelm KH-TYPE-C-16P] 1 50kW 3.8 × 3.6mm SMD trimpot (VR1) [Bourns TC33X-2-503E] 2 32-pin male headers, 2.54mm pitch (optional) Semiconductors 1 128Mbit QSPI flash memory, SOIC-8 (IC6) [Winbond W25Q128JVSIQ] 1 Raspberry Pi RP2350B microcontroller, QFN-80 (IC28) 1 APS6404L-3SQR-SN 8MiB PSRAM, SOIC-8 (IC33; optional) 1 12MHz oscillator module, 3.2 × 2mm SMD-4 (XO4) [TOGNJING XOS32012000LT00351005] 1 AMS1117-3.3 low-dropout 3.3V linear regulator, SOT-223-3 (REG21) 1 TPS7A7002DDAR adjustable low-dropout voltage regulator, SOIC-8 (REG34) 1 white SMD LED, M1608/0603 size [KT-0603W] Capacitors (all SMD multilayer ceramic capacitors) 3 10μF 50V X5R, M3216/1206 package [Samsung CL31A106KBHNNNE] 18 100nF 16V X7R, M1206/0402 package [Samsung CL05B104KO5NNNC] 1 10μF 10V X5R, M1608/0603 package [Samsung CL10A106KP8NNNC] Resistors (all SMD M1206/0402 ±1% unless noted) 1 1MW 2 1kW 2 20kW 1 33W 5 10kW 2 33W (0603 size) 2 5.1kW 2 150W (0603 size) The finished RP2350B Development Board shown at 75% of actual size. The 32-pin headers are not included with the assembled board flash memory chip. This has a capacity of 64Mbits (8Mbytes) and it can be used to augment the internal RAM of the RP2350B. How it is actually used depends on the running program. For example, PicoMite BASIC will automatically add it to the general-­ purpose RAM seen by the BASIC interpreter, allowing for very large arrays to be defined. Because the PSRAM must communicate over a serial interface, it is a lot slower than the internal RAM of the RP2350B. It also can limit the amount of overclocking that the board is capable of; however, it should still reach the speeds needed for generating DVI/ HDMI video. The internal RAM is normally more than enough for most applications, so for this and performance reasons, the PSRAM location is not populated in our design. However, it can be easily added to the BOM (Bill of Materials) for automated assembly or, as it is in an easy-to-solder 8-pin SOIC package, you can add it yourself. Australia's electronics magazine This chip is available from Mouser for around $3 in small quantities: https://au.mouser.com/ProductDetail/­ 878-APS6404L-3SQR-SN Building it The RP2350B chip comes in an 80-pin QFP package, which is designed for automated surface-mount soldering. It can be hand soldered, but this is a challenge, even for someone skilled in SMD soldering. So, practically speaking, you have two options for obtaining this module. You can purchase it fully assembled from the Silicon Chip Online Shop, or you can use an SMD assembly service such as JLCPCB’s to build the board. We recommend JLCPCB (https:// jlcpcb.com) for the automated assembly, as they have proved reliable and reasonably priced in the past. JLCPCB also source the components at a good price and they do everything, including making the board, making the solder stencil, applying the solder paste, August 2025  49 Resistance (TP1-DVDD) DVDD 6.0kΩ 1.10V 9.0kΩ 1.15V 12.0kΩ 1.20V 15.0kΩ 1.25V 18.0kΩ 1.30V 21.0kΩ 1.35V 24.0kΩ 1.40V 27.0kΩ 1.45V 30.0kΩ 1.50V 33.0kΩ 1.55V 36.0kΩ 1.60V Fig.2 (above): the overlay diagram for the RP2350B Development Board. The table at the top of the page can be used as a reference for overclocking the RP2350B IC. placing the components and reflow soldering them. Their minimum quantity for assembly is two boards. However, if you do want a number of boards, it is hard to see why you would want to undertake the hand assembly of this board when the automated assembly option is relatively cheap. To order boards from JLCPCB, you will need to download three files from siliconchip.au/Shop/10/2832 (they all come in one download package). The package includes a ZIP file with the Gerber files that contain the PCB design, a Bill of Materials spreadsheet listing all the parts required, and a CPL spreadsheet that contains the placement information for the pickand-place robots. Ordering assembled boards from the JLCPCB website is reasonably simple. Go to https://jlcpcb.com and create an account with them. Then, drag and drop the “RP2350B Development Board Gerbers.zip” file onto the “Add gerber file” box to the left of the Instant Quote button on their front page. The website will process the file and display an image of the PCB. Click on the switch marked “PCB Assembly”, then click “NEXT” until you reach a screen that prompts you to drag and drop the “RP2350B Development Board BOM.xlsx” and “RP2350B Development Board CPL.xlsx” files. After supplying those files, you can continue and then accept all the defaults. However, you may wish to change the quantity of PCBs made (minimum of 5), and the number that you want assembled (minimum of 2). Note that boards purchased from the Silicon Chip shop or assembled by JLCPCB will not include the two 32-pin headers required for use with a solderless breadboard. You will have to add these yourself (if required). Adjusting the DVDD voltage When you receive the boards, there is one adjustment that you need to make: using VR1 to set the digital core supply voltage (DVDD). The RP2350B Development Board has all its components mounted on the top, with the pin designations listed on the reverse. It is available fully-assembled, apart from the two pin header strips. The module is quite small at 82×28mm (shown here enlarged for clarity). It is designed to suit solderless breadboards, with two rows of 32 pins on a 2.54mm/0.1in pitch, or it can be used as a plug-in module in your own PCB designs. 50 Australia's electronics magazine Important: the potentiometer must be adjusted before applying power to the board. Leaving it in a random position may damage the RP2350B chip. Set your multimeter to the resistance mode and, with the board unpowered, place the leads across the test points marked DVDD and TP1. Adjust potentiometer VR1 to give a reading of 6kW. This will set DVDD to 1.1V, which is the standard voltage for a clock speed of 150MHz (the default for the RP2350B). This should also work for clock speeds up to 250MHz. If you wish to overclock the RP2350B, you need to do two things: increase DVDD and set the desired clock speed in the program by setting CPU registers. Typically, a DVDD of 1.3V will allow the RP2350B to run up to 400MHz, with intermediate values suitable for clock speeds between 250MHz and 500MHz. The table at left lists some resistance values and the resultant DVDD voltages. A maximum of 1.4V for DVDD should be safe. However, if you wish, you can try higher voltages with a risk of damaging the RP2350B processor. When the board is powered, this setting can be checked by measuring the voltage between the DVDD test point and any GND point. Note that overclocking the RP2350B Development Board is not guaranteed, although all the samples we tested have reached a speed close to 400MHz. Also note that when a PSRAM chip is fitted, the maximum overclock speed will typically be slightly reduced. Using the module Power for the board is supplied via the USB-C connector. This is the normal mode when you are developing a program, as the board will be connected to a desktop or laptop computer that is used to load or edit the program. When the board is used as an embedded controller (ie, not connected to a computer), power can be supplied via a 5V pin on the edge connector. This supply can be 4.5-12V. In this case, you cannot use the USB connector at the same time, as that would cause a conflict between the two power supplies and possibly damage your computer. To prevent this possibility, you can use a switch or jumper to isolate your power supply whenever the USB connector is used. siliconchip.com.au ◀ The RP2350B Development Board is ideal when you need many I/O pins. One example is driving a high quality LCD panel with a parallel interface; this can require 15-23 I/Os, difficult for a Pico 2 to accommodate but easy with our module. Some development environments, such as MicroPython and the PicoMite BASIC interpreter, use the USB connector with a terminal emulator on a computer to edit and manage the programming environment. Other, hosted development environments, such as the C/C++ compiler, will build the program on the desktop or laptop computer, which then needs to be transferred to the module. To load this firmware, you simply hold down the BOOT button while restarting the module (the RESET button is good for that) and then copy the firmware to the pseudo USB drive that is created on your computer by the RP2350B chip. How you use the RP2350B Development Board will depend on the firmware that you have running on it. The PicoMite BASIC interpreter can be downloaded from siliconchip.au/ Shop/6/833 This is a complete OS with a Microsoft BASIC compatible interpreter and extensive hardware support, including HDMI/VGA video, PS/2 and USB keyboards, touch-sensitive LCD panels, SD cards and much more. For a full description of the PicoMite firmware, read the article on the Pico­ Mite 2 (February 2025; siliconchip.au/Article/17729) or visit the author’s website at https:// SC geoffg.net Songbird An easy-to-build project that is perfect as a gift. SC6633 ($30 plus postage): Songbird Kit Choose from one of four colours for the PCB (purple, green, yellow or red). The kit includes nearly all parts, plus the piezo buzzer, 3D-printed piezo mount and switched battery box (base/stand not included). See the May 2023 issue for details: siliconchip.au/Article/15785 siliconchip.com.au Australia's electronics magazine August 2025  51 RIGOL DHO924S Digital Oscilloscope Review by Tim Blythman It’s been a while since we have reviewed an oscilloscope, and Rigol’s new DHO900 series has a slew of modern features with a compact footprint. This review covers these new features and looks at what it’s like to use out-of-thebox. We’ll also have a brief look at their DM858 digital multimeter. 4 channels 125MHz or 250MHz bandwidth Parallel, UA - RT, I2C, SPI, LIN, CA - N protocol analyser Sampling rate of 1.25Gsps (shared between active channels) Optional 25MHz, 10V peak-to-peak waveform generator 12 bits analog resolution 7in touchscreen LCD (1024 × 600 pixels) Sine, square, ramp, noise, arbitrary waveforms (from CSV file) Sample memory of 50 million points Period, frequency, rise time, fall time, duty, count, delay, phase and more measurements Maths functions, FFT, Bode plot (using the A - FG as a source), pass/fail 52 USB device, HDMI, LA flash drive) interfaces - N, USB host (mouse, Silicon Chip Australia's electronics magazine 15V DC, 3A - (65W USB-C PD) PSU siliconchip.com.au A fter seeing this oscilloscope at Electronex and being impressed, Emona loaned us a unit to review. The first thing we noticed about the DHO924S is its compact size. For comparison, the Rigol MSO5354 that we reviewed in February 2019 (siliconchip.au/Article/11404) measures 37 × 20 × 13cm (9.62L), while the DHO924S is only 26 × 16 × 8cm (3.33L). The enclosure is also a striking black colour. The DM858 digital multimeter appears to use the same case as the DHO924S, so it is a similar size, shape and layout. We also borrowed one of those; our review of it is in a panel later in the article. The DHO900 series The DHO900 series comprises four models: DHO914, DHO914S, DHO924 and DHO924S. S-suffixed parts include an arbitrary function (waveform) generator output, while the DHO914 variants offer 125MHz bandwidth against the DHO924’s 250MHz bandwidth. The DHO924S has the highest specifications in the series. Rigol’s DHO naming refers to a high-resolution digital oscilloscope; it has a 12-bit ADC (analog-to-digital converter), while many ‘scopes we have seen only offer 8-bit resolution. There are four analog inputs, so that’s the ‘4’ in the naming scheme. The DHO924S also has a 16-input logic analyser, but an optional active logic probe is required to use this feature, so we did not test it. We find that four channels are ample for most scenarios, and the analog channels can also be used as inputs to digital features, such as the serial protocol decoder. There is also a DHO800 series, which offers 12-bit resolution in a mix of two- and four-channel options but lacking the logic analyser option. They have a lower bandwidth and lack some of the other features of the DHO900 ‘scopes, but are similar in that they have the same compact form factor. The legs pivot out during use or fold flat for storage. When the legs are extended, the unit leans back about 20°. The legs and base of the unit have chunky rubber feet and the ‘scope does not feel like it will tip or slide away while the controls are being operated. There is an Earth socket for a banana plug, and the brass insets are threaded for M4 VESA mounts with a 100mm spacing. With the DHO924S being so thin, it becomes practical to mount it to an adjustable monitor arm, so it no longer takes up any desk space. Apparently, users are also 3D-printing a variety of adaptors to suit the VESA mounts to adapt to their ‘scopes. The four input BNC connectors are along the bottom of the ‘scope next to the ground and test signal clips. The connector for the optional active logic probe is under the display, along with a USB-A socket and the power button. Compared to the likes of the Rigol MSO5354, there is only one pair of vertical scale knobs, despite there being four channels. The active channel is selected by the same numbered, colour-coded pushbuttons that are used to switch channels off and on. We found this to be intuitive enough and, as it offers more room for the main display, it seems like a reasonable compromise. The oscilloscope package includes four switchable probes (more on them later), a USB-A to USB-B cable, an Earth lead terminated with banana plugs and a USB-C PD (power delivery) power supply, which indicates that it can deliver 5V, 9V, 12V, 15V or 20V. The oscilloscope uses 15V, according to our USB-C Power Monitor. The USB-C plug has a pin and latch arrangement that secures it. That means that the power supply cannot be easily used to power other devices, but does not stop another suitable power supply from being used to power the oscilloscope instead. Being an isolated power supply necessitates the inclusion of the Earth lead, since USB-C does not provide a means for Earthing. In other words, the oscilloscope is floating unless the separate Earth lead is connected. This is an interesting pitfall that may not be immediately apparent to those accustomed to ‘scopes that are normally Earthed via their mains lead. Also, since it isn’t directly mains-­ powered, it is not possible to trigger off the mains waveform without a separate connection. After powering on the ‘scope, it took almost a minute to start up and display the expected screen. Along the way, the message “Android starting” appeared, hinting at the underlying software. The DHO924S we tested ran Android 7.1.2, which dates from 2019. The LCD has a touch panel, which works as you might expect for an Android device. You can tap on virtual buttons, drag the cursors around and even perform a pinch-to-zoom. There is a “Touch Lock” button to disable the touch panel. Out of the box experience The photos show the front and back of the DHO924S. The back panel has two BNC connectors; one of these is for the arbitrary function generator, the other an auxiliary output. By default, the latter emits a pulse when a trigger event occurs. There are also Ethernet, USB-B, HDMI and USB-C connections. siliconchip.com.au There are several ways to connect to a PC or external monitor. The VESA mounts allow the unit to be mounted on a monitor arm, freeing up bench space. While this is a DHO800 series ‘scope, the back of the DHO900 series is identical except for having a black case. Australia's electronics magazine August 2025  53 Four PVP2350 350MHz switchable passive probes are included, along with the accessories shown here. The ‘scope also includes a power supply & USB cable. The ‘R’ icon at the bottom-left corner of the display opens a menu that includes features beyond what you might expect from a traditional ‘scope, such as settings, operating system utilities and the like. Screen 1 shows the contents of this menu. The front panel looks much like any other ‘scope, with the familiar adjustment knobs for vertical and horizontal scale, trigger and RUN/STOP controls, along with other controls to operate the custom features that are seen in modern oscilloscopes. The “Quick” button can be programmed to perform one of several different actions; by default, it saves a screenshot. The two ‘Flex Knobs’ near the top do not have a fixed use; their function changes depending on the items selected in various menus. The functions are marked on-screen by small ‘1’ and ‘2’ icons. The Flex Knobs allow all manner of values to be adjusted instead of being manually entered into a keyboard on the touch panel. This will be handy when values just need to be tweaked by a small amount. These knobs can also adjust the cursors when they are turned on. Probes Screen 1: despite the numerous features, it’s easy to find most menu options. A good place to explore is the R menu at the lower left corner of the screen. This also gives a good overview of the advanced features. The DHO924S comes standard with four Rigol PVP2350 350MHz passive probes, which are switchable between 10:1 and 1:1 attenuation (as usual, the full bandwidth is only available at 10:1). Each probe includes an assortment of colour-coding rings and a ground spring, as well as the requisite compensation adjustment tool. The leads are 1.2m long, and their slim cords are light enough to not take up too much space. There is no probe detection (for automatic probe attenuation setting), so these must all be set manually. Using it Screen 2: once we had the ‘scope’s IP address from this screen, it was easy to connect to the Web Control interface. The Utility menu also includes the setup and self-calibration options. Since we were keen to try out the more modern features of the DHO924S, we hooked up an Ethernet cable. We found the IP address of the ‘scope from the Utility menu, as seen in Screen 2. Typing that into a browser’s address bar gave us a Web Control Page, allowing us to open a Web Control window that shows the oscilloscope’s screen. Screen 2 was captured on our PC using the Web Control window; it’s identical to what appears on the Australia's electronics magazine siliconchip.com.au 54 Silicon Chip ◀ Screen 3: hooking the ‘scope’s function generator back to one of its inputs shows off its sensitivity. The 2mV peak-to-peak square wave is the lowest amplitude that it can deliver. Screen 4: tapping on each channel’s vertical settings shows the full signal path and its associated parameters. You can still see the waveform under the transparent window, allowing the trace to be adjusted with ease. ‘scope’s screen and even gives access to the controls that would otherwise require the touch panel. Any device with a browser and WiFi connection should work. We had no trouble controlling and viewing the ‘scope on an Android mobile phone’s browser. This makes it much easier to explore the features of the ‘scope, although we think it’s a bit of an omission that there aren’t controls for the various hardware buttons and knobs. Still, most settings can be set via menu panels. The HDMI interface just works. We plugged in a HDMI cable, connected it to a monitor and the ‘scope’s display appeared on the screen without having to change any settings. The output appears to be identical to that on the LCD, scaled up to use the entire viewable area of the monitor. We’ll delve further into the various interfaces a bit later, including some software that Rigol offers. The relevant downloads can be found at www. rigolna.com/download/ There is a self-calibration mode that is recommended to be performed after the ‘scope has warmed up to operating temperature (after about 30 minutes). The self-calibration process took about 24 minutes to run on the unit we were testing. The sampling rate is shared between the four channels, since there is only one analog-to-digital converter IC. Using two channels halves the available sampling rate, while using three or four channels will reduce it to a quarter. So the maximum sampling rate can only be achieved if only one channel is in use. Similarly, the sample memory is also shared between the channels in use. Noise performance Using the inbuilt arbitrary function generator, we looped a 2mV peak-topeak 1kHz square wave signal back into the ‘scope with no attenuation and with the bandwidth limited to 20MHz. The result is seen in Screen 3. Some of this noise will be from the function generator, but clearly, the DHO924S has no trouble resolving signals below 1mV, which is pretty impressive. Inputs The front of the DHO924S is compact, thanks to the channel vertical controls being shared. The channel to adjust is selected by one of the numbered buttons. Above these are the Flex Knobs, which adjust values depending on the current sub-menu. siliconchip.com.au Australia's electronics magazine Opening the menu options for the inputs reveals the signal flow diagram seen in Screen 4. Some of the options can be adjusted by tapping on the diagram itself. You can use the Flex Knobs, as indicated by the yellow hexagons. August 2025  55 Screen 5: measurements are added to the Result panel at right. This panel can scroll up and down, so more than five results can be added. The options relating to the horizontal (time) axis are shown here. Screen 6: this display has both reference waveform (orange) and pass/fail mask (blue) active. The auxiliary output at the rear of the ‘scope can be set to produce a pass/fail signal. Screen 7: a Bode plot expands to take up most of the available screen space. Most of the windows are movable and adjustable, so you can customise the viewport to suit your preferences. Screen 8: the ‘scope’s help system includes a PDF copy of the manual that can be viewed on the 7-inch display. 56 Silicon Chip Australia's electronics magazine siliconchip.com.au For numerical values, a pop-up keyboard can also be used to enter values. The main parameters are also displayed on the channel widget near the bottom of the screen, and you can see the appropriate parameters for the arbitrary function generator displayed on the G channel too. Maths and measurements Handy features on most modern ‘scopes include various mathematical functions and trace measurements; the DHO924S is no exception. The measurement menu can be accessed from a fixed button on the right-hand side or via the ‘Measure’ button at the topright of the screen, on the touch panel or even via the main ‘R’ menu button. The area at top-right actually hides several different buttons that can be accessed by swiping left or right. Fortunately, most menu items can be accessed in different ways, so you can choose whatever option is most intuitive. There are 41 different measurements available; Screen 5 shows some of these active, as well as the horizontal (time-based) measurements that are available. The vertical options include voltage-based (peak-to-peak, RMS etc) measurements, while the remainder are time and phase delay measurements between two input channels. The Setting option allows thresholds to be set. These default to 10%, 50% and 90% levels of the waveform, which worked quite well for us during our tests. You can also view various statistics, such as average, minimum or maximum of the measured parameters, or view a histogram of the measurements as they are gathered. Four ‘Math’ channels are available, including operations such as summing or differencing two channels. Single-­channel operations such as logarithm, exponent, derivative, integral and square root are available. FFT (fast Fourier transform) or spectrum analysis is also possible. Functions The menu shown in Screen 1 gives an idea of the DHO924S’s built-in functions. When measurement or maths windows are open, they can be dragged around and reorganised (something we’re not used to on a ‘scope). A Reference waveform can be captured (“Ref”) from an active channel to be visually compared with the siliconchip.com.au changing input. A more rigorous signal check can be performed using the Pass/Fail function. This requires a mask against which the active channel is compared; the results of the Pass/Fail can optionally be fed to the auxiliary BNC connector on the rear of the scope. The mask can be loaded from a file or can be easily created by applying margins (in time and voltage) against a sampled input channel. A typical example of such a mask is the so-called eye diagram used to verify high-speed signals, such as USB or HDMI. Screen 6 shows the Reference and Pass/Fail functions. The protocol decoding feature supports Parallel, UART, I2C, SPI, LIN and CAN signals, although you would probably need the optional active logic probe to do much with a parallel bus. There are many parameters available to adjust, including polarity, parity and bit order, although the defaults look to be sensible for commonly used configurations. There is a button to swap SDA and SCL in I2C mode, so it’s reasonable to just hook the ‘scope up without worrying too much about which wire is which. It can decode up to four separate buses at once, which is more than sufficient for most applications. The Bode plot function is only available on models with an arbitrary function generator, since the generator is used to provide the input waveform. The Bode plot window expands to take up most of the display, as seen in Screen 7. The Auto function is the same automatic configuration utility that is found on other ‘scopes to quickly set up the timebase, voltage scale and trigger selection based on the active signal. It can also be accessed from the hardware button in the top right corner of the ‘scope. The Display settings can select trace persistence and change other parameters as trace and grid intensity, as well as window transparency. On the bottom row are functions related to the operating system functions of the unit. The Help feature is actually an on-screen viewable PDF version of the manual, which can be seen in Screen 8. Silicon Chip PDFs on USB ¯ A treasure trove of Silicon Chip magazines on a 32GB custom-made USB. ¯ Each USB is filled with a set of issues as PDFs – fully searchable and with a separate index – you just need a PDF viewer. ¯ Ordering the USB also provides you with download access for the relevant PDFs, once your order has been processed ¯ 10% off your order (not including postage cost) if you are currently subscribed to the magazine. ¯ Receive an extra discount If you already own digital copies of the magazine (in the block you are ordering). EACH BLOCK OF ISSUES COSTS $100 NOVEMBER 1987 – DECEMBER 1994 JANUARY 1995 – DECEMBER 1999 JANUARY 2000 – DECEMBER 2004 JANUARY 2005 – DECEMBER 2009 JANUARY 2010 – DECEMBER 2014 JANUARY 2015 – DECEMBER 2019 OUR NEWEST BLOCK COSTS $150 JANUARY 2020 – DECEMBER 2024 Other connections OR PAY $650 FOR THEM ALL (+ POST) The front USB-A socket can be used for either a mouse or flash drive (a USB hub allows both to be connected WWW.SILICONCHIP.COM. AU/SHOP/DIGITAL_PDFS Australia's electronics magazine August 2025  57 simultaneously). The mouse is used as you might expect, to interact with items on the screen. We think that support for a keyboard or numeric keypad might be handy for parameter entry, since this can sometimes be awkward to do with an on-screen keyboard. A USB flash drive can be used to transfer screen captures or waveforms for the arbitrary function generator. It can also be used to upgrade the firmware. The ‘scope has internal storage and can connect to an SMB (network) file server via Ethernet. We often use screen captures or ‘scope grabs for articles in the magazine, so we thought we would use a USB flash drive to transfer the necessary files for this article. But it turns out that the web control and network interface mean that is unnecessary, since we can download captures directly to a PC. The Web Control’s Print Screen tab has buttons to take a screenshot or record a video; the image or video is displayed in the browser window and can be simply downloaded onto the PC from there. We noted in our review of the MSO5354 that its web control response was a bit slow; in comparison, the DHO924S feels much snappier. The USB-B socket on the rear of the ‘scope can be used to control the DHO924S, but we found that the Ethernet connection was more useful, since the PC does not need to be near the ‘scope as is required for a USB connection. Other notes There is a sleep mode which can be used instead of a full shut-down. This has the advantage that the ‘scope only takes about 20s to be ready from sleep, and also retains its last operating state. The main downside is that the power supply must remain active to retain this state. Using our USB-C Power Monitor, we recorded a peak of 2.6A at 15V, consistent with the 3A maximum recommended in the user guide. During sleep, we recorded a draw of around 230mA at 15V, while a full shutdown reduces this to about 1mA. The web control view would occasionally reset, changing the window size and stealing the focus from another window if it did not already have focus. If the network connection is lost, a message is displayed in Chinese. The same message is shown if a second browser window attempts to connect to the web control. Software SCPI (Standard Commands for Programmable Instruments) is a standard for the control of test equipment and instruments. The DHO924S presents an SCPI interface on Ethernet port 5555, and it can also be accessed via USB. In the April 2023 issue, we wrote about the free TestController software (siliconchip.au/Article/15740), which can interface with SCPI-capable devices. Rigol provides a Programming Guide which outlines the SCPI commands specific to the DHO900 series if you wish to control the DHO924S this way. Rigol also provides software that can connect to its ‘scopes and other hardware. The Ultra Sigma software can connect to the DHO924S via Ethernet or USB, and has an SCPI Panel Control, which can send commands and read data using the SCPI interface. Screen 9 shows the main window for Ultra Sigma with both the DHO924S and DM858 connected. Ultra Sigma appears to be only available for Windows, although the web control should work on a browser under most operating systems. We have heard, but it has not been confirmed, that Rigol will release updated PC software later this year. Overall impressions With the numerous menu options, it was easy enough to find a specific function and everything feels intuitive. The ‘scope feels like it has all the features we might need and probably a few we don’t realise we need yet. All the controls of the DHO924S feel quite snappy and responsive, whether using the knobs and buttons, the touch panel or the web control interface, although the waveforms will freeze while dragging. We didn’t often touch the wrong item on the touch panel, since most objects are quite large, but it happened at times, and felt slightly fiddly. Using a mouse was much more precise, so that is a good option. We mostly used the web controls for much the same reason. The noise level, bandwidth and number of channels makes this oscilloscope suitable for a wide range of jobs, for which an expensive high-end ‘scope would have been required in the not-too-distant past. Conclusion If we were looking for a ‘scope right now, the DHO924S would definitely be on the shortlist. The web control and Ethernet interfaces make it very easy to capture screen grabs and other waveforms and analyses. It also makes it easy to control the many functions of the ‘scope. The unit is compact and light. It’s responsive and intuitive to use, and most of the specifications easily exceed the ‘scopes that we currently use. Screen 9: the Ultra Sigma program can interface with many Rigol instruments. Here, both the DHO924S ‘scope and DM858 benchtop multimeter are connected. Ultra Sigma includes an SCPI control panel. 58 Silicon Chip Australia's electronics magazine The DHO924S is available from Emona Instruments for $1448 + GST: https://emona. com.au/products/electronic-testSC measure/dho-924s.html siliconchip.com.au DM858 Digital Multimeter Review We haven’t had much need for a benchtop multimeter, with the handheld variants being sufficient for most purposes. A benchtop multimeter falls between a handheld multimeter and an oscilloscope, including a 5.5 digit display capability and features like those you might normally see on an oscilloscope. The DM858 comes with a power supply and a pair of CAT II multimeter leads, as well as a pair of alligator clip adaptors that screw onto the ends of the probes. Like the DHO924S, the power supply is a 65W USB-C PD (power delivery) PSU. The DM858 only requires 12V at up to 10W, with our USB-C Power Monitor indicating a typical draw of just 7W. The back panel connectors are almost the same as the DHO900 series ‘scopes, with only the HDMI Using the DM858 is easy for anyone who has used a multimeter. The extra socket missing. It has a USB-B socket for connection banana sockets allow four-wire (Kelvin) resistance measurements. to a computer, and an RJ45 jack for Ethernet. One BNC socket is for an external trigger input, while the other can output a pulse after each measurement. Since it is much the same case, the same 100mm VESA mounts are present. Apart from the HDMI output, most of the user interfaces are the same as the DHO924S; the Ethernet and USB connections on the back of the unit can be used for remote access. Web Control for the DM858 works similarly, as does access to the SCPI interface over Ethernet. The front USB-A socket supports a USB flash drive or a mouse, and it has five banana sockets on the front panel, along with the fuse for high-current measurements. Three of these sockets are used as you might expect, with one common input used in conjunction with another input for high-range current measurements. The third input is used for all other measurements, such as voltage, resistance, capacitance and so forth. The other two connections can be used for Kelvin (four-wire) resistance measurements. The Kelvin technique is often used to measure low resistance values, since it eliminates contact and lead resistance that might interfere with the measured resistance. In use The DM858 takes about a minute to boot up and it then shows a DC voltage reading. The default, slow update rate is easy to follow. There are two faster update rates available. There are buttons for typical multimeter measurements, such as voltage, current (DC and AC), resistance, continuity, diode, capacitance and frequency; standard operations are fairly obvious. Some features, including four-wire resistance measurement and diode mode, are accessed by pressing the Shift key. The overall interface is very similar in feel to the DHO924S, with a 7-inch touch panel offering menu items above and below the main display. An ‘R’ menu in the bottom-left corner offers a range of functions that duplicate some of the controls, besides allowing access to the system controls and settings. Other features Despite being labelled a multimeter, the DM858 can display a slow-moving trace, but it’s more like a chart recorder than an oscilloscope. The fastest update rate is around 10Hz. There are simple ‘Math’ functions, such as applying an offset to a reading, as well as statistical results such as minimum, maximum, average and standard deviation. Voltages can be converted to dB values. The DM858 can also interface to sensors such as thermocouples and thermistors, with several inbuilt probe types and presets being provided. An adjustment for cold junction temperature can be added. Other custom sensors can be monitored by supplying a list of measured value (resistance, voltage, current etc) and display value (such as temperature) pairs. This makes it possible to set the meter up as a custom display to suit just about any type of sensor. Summary We found the DM858 easy to use. It offers numerous handy features above those of most multimeters. We would make good use of the Web Control interface to allow remote viewing and operation. The DM858 digital multimeter can be purchased from Emona Instruments at: https://emona.com.au/dm858/dm-858.html The DM858 is small enough that it can be mounted using a VESA mount. It also has an Ethernet connection on the rear, as shown in the photo above. siliconchip.com.au Australia's electronics magazine August 2025  59 Stops ises if ‘scar ed’ e ey Fl mo c i Mthe e s u Mo es at ul g in h as g no Em J ’s oh n Cla rke kin ma use s sound t o en H e r d ar fi nd if hidd Draw s little p ow Mice make good pets but you still have to take care of them. This little critter doesn’t eat much (just the occasional lithium cell) and won’t make a mess or escape from its cage! B uilt on a mouse-shaped printed circuit board (PCB) and using relatively few parts, Mic the Mouse is ideal for fun and can be used to play pranks on family and friends. Mic the Mouse only produces squeaking sounds when everything is quiet. Make a noise, and he goes quiet. This makes him difficult to locate. He will start squeaking again, but only after a period of silence. Mic the Mouse (Mic for short) is best described as mousy coloured and mousy shaped. To further add to the realism, there is provision for whiskers. He sits vertically, with a slight lean backwards, and is supported at the rear using a stand that attaches to the back. Elephants and mice have been known in folklore and animations to have a unique relationship (see siliconchip.au/link/ac63), which is why the rear stand is reminiscent of an elephant’s rear end. Or perhaps it’s just because that’s a suitable shape to hold the mouse up. Nobody knows what happened to the front half of the elephant – except maybe Mic! It is also well-known that mice have a unique relationship with humans. The poem by Robert Burns, entitled “To a mouse”, begins: “The best laid plans of mice and men, often go awry and leave us nought but grief and pain for promised joy”. This couldn’t be more true with Mic the Mouse. Hunt him down you try, but Mic is elusive. He won’t reveal his 60 Silicon Chip whereabouts if you make any noise. But wait quietly and he will begin his merry squeaks again. Hide Mic in a cupboard, on a shelf, or simply in plain sight, and have others become horrifically aware that there is a mouse in the house. But where? You may be confronted by Mic’s eye flashing in a terrifying manner. Previous designs Way back in August 1990, we published an electronic cricket called Horace (siliconchip.au/Article/6925). Horace was similar to Mic the Mouse, except it chirped cricket sounds rather than producing mouse sounds. It only chirped when there was quiet, and was quiet himself when there was ambient noise. It utilised an electret microphone, quad op amp IC and a piezo transducer. This was powered by a 9V battery and its current draw was 3mA. With a 600mAh capacity, Horace could run for about 200 hours or about 8 days continuously. The reason for the “Horace” name has been lost in time. We published various updated cricket designs in December 1994, July 2011, June 2012 and October 2017, culminating in Silicon Chirp (April 2023). The reason for Mic’s name is a bit more straightforward. Firstly, it keeps up the tradition of alliterative names for animal characters like Dorothy the Dinosaur, Peppa Pig and so on. The other reason is that Mic uses a microphone to listen for sounds. Australia's electronics magazine To make Mic the Mouse a similar size to a real mouse, we need to use a few tricks. A 3V lithium cell is much smaller than a massive (by comparison) 9V battery. However, a 3V cell does not have as much capacity (200mAh, 600mWh) compared to a 9V battery (600mAh, 5.4Wh), so the current consumption needs to be kept as low as possible. To get a reasonable cell life, we need to reduce the current consumption from the 3mA of Horace the cricket down to at least 1mA to get the same cell life. However, we can do a lot better than that; we reduced the current draw to an overall average of 105μA. That’s a reduction of around 28 times compared to Horace! This was achieved by using a lowpower microphone and a microcontroller to mini mice (sorry, minimise) the current draw by only powering the microphone when required. Also, we only flash the LED eye momentarily to mini mice the power used. Like a real mouse, it sleeps to reduce its current consumption to an absolute minimum; it is woken up periodically by a timer. It’s a bit like hibernation, a trick Mic has stolen from bears. The low current microphone we use is a MEMS (micro-­electromechanical systems) type, as used in phones. It is supplied in a tiny package that measures just 2.75 × 1.85 × 0.95mm and requires reflow soldering as the contacts are underneath the package. That makes it difficult to hand-solder. siliconchip.com.au Coin cell warning! This project contains a small lithium ‘coin’ cell that represents a serious health risk should the cell be swallowed by a child. Young children are most at risk. Read the information sheet at www.schn.health.nsw.gov.au/factsheets on the dangers of small cells. Ensure that the cell is kept secured using the cell capture screw and nylon spacer and that it is tightened fully to prevent undoing by hand. Keep this project away from small children. Also, keep unused cells in a secure place away from children, such as in a locked medicine cupboard. New cells should be kept within the original secure packaging that requires scissors to open until required for use. If you have any older button/coin-cell powered devices that provide easy access to the cells, store them in a safe place when not in use. Alternatively, devise a method to make the cell access more difficult, such as gluing the cell compartment shut so that a child can’t open it. Fortunately, the MEMS microphone is available pre-soldered on an inexpensive module, which also includes an amplifier and 3V regulator. Circuit details Mic’s complete circuit is shown in Fig.1. It’s based around microcontroller IC1, a PIC16F15214-I/SN, powered by a 3V lithium cell (BAT1). Power is applied via a slider switch. Mic does not draw much current, typically only about 0.36μA while asleep. This rises to around 1mA when monitoring for ambient sounds and 1.6mA while making noise. Diode D1 is included as a safety measure to prevent damage to IC1 should the cell be inserted incorrectly. The cell holder doesn’t stop you from inserting the cell with the incorrect orientation (it should be positive side up). With the positive side down, the cell will be shorted out by contact with the sides and top spring contacts. However, during insertion, there could be a brief period when there is no contact with the cell holder sides, so the circuit could be supplied with a reversed polarity voltage that could damage IC1. In that case, D1 clamps this voltage to a low level. The cell will lose some of its capacity if left connected in reverse for more than a few seconds, but that’s better than damaging the chip. IC1 is clocked by an internal 4MHz oscillator. Its power supply pin is bypassed with a 1μF capacitor. IC1’s job is to supply power to and monitor the MEMS microphone module (MIC1) output, drive the piezo transducer to make mouse sounds, flash the LED used for Mic’s eye and also check if S2 is pressed. The MEMS microphone module (MIC1) is powered via IC1’s RA4 digital output, which goes high (near to the cell voltage) when required. When powered, the A output on the module (pin 3) provides an amplified signal from the MEMS microphone. The circuit of the microphone module that includes the MEMS microphone is shown within the dashed box in Fig.1. Its onboard regulator, U1, supplies 3V to the MEMS microphone itself (U3) and provides a bias voltage to pin 1 of the op amp, U2. U1 is a low-dropout regulator, so with a 3V input, its output won’t be much below that. The output from the MEMS microphone (U3) is amplified by op amp U2, which is configured with a gain of 50. The non-inverting input is held at half supply using the two 10kW divider resistors across the 3V supply. So, with a 3V supply to the MEMS module, the DC output from U2 is typically at 1.5V. A MEMS module output signal when subject to noise is shown in Scope 1. For data on the MEMS microphone and module, see siliconchip.au/link/ ac64 and siliconchip.au/link/ac65 The current consumption of the MEMS module is typically 287μA at 3V. That’s the total of U1 (7μA typical, 15μA maximum), U2 (80μA typical, 185μA maximum) and U3 (50μA typical, 150μA maximum). The voltage divider comprising the two 10kW resistors in series across the 3V supply also contributes 150μA. We measured our module’s draw as 330μA. The PIC16F15214 (IC1) monitors the microphone signal using its AN5 analog input. We have AC-coupled MIC1’s output to that pin using a 100nF capacitor and biased the voltage to 0V via a 10kW resistor. This has the signal at the AN5 input (pin 2) normally sitting Fig.1: the components inside the dashed cyan box are on the MEMS microphone module. IC1 monitors its output and determines when to flash the eye LED and create squeaking noises using the piezo sounder. siliconchip.com.au Australia's electronics magazine August 2025  61 Scope 1: this oscilloscope trace shows the output from the MEMS microphone module after AC coupling to the AN5 input (pin 2) of IC1. The signal level goes above 100mV peak. close to 0V and swinging above and below that. A diode clamp internal to pin 2 of IC1 will limit negative excursion to -0.3V, while the 1kW series resistor limits the current in the clamping diode. We do this so that pin 2 sits near 0V with no signal (ie, silence). Also, while the 10kW/10kW resistive divider in the module theoretically causes the signal to sit at exactly half the supply voltage, the supply voltage can vary because it’s coming from a microcontroller output which has a fairly significant output impedance of around 116W. That means that supply to the MEMS module can be anywhere between about 33-58mV less than the IC1 supply due to the voltage drop at the RA4 output. The MEMS module current draw also varies, so it is difficult to predict the MEMS module’s idle output voltage with sufficient accuracy to allow for threshold detection of any small signal that is superimposed on it. Re-biasing the signal to 0V solves this difficulty. Noise detection To detect ambient noise, we convert the voltage at the AN5 input into a 9-bit digital value every 1ms (1000 times per second). The digital value ranges from 0 to 511. If this exceeds a specific threshold value, it is detected as noise. This threshold can be adjusted between 1 and 10 in ten steps, corresponding to an analog range of about 12-65mV (assuming a 3V supply). 62 Silicon Chip Scope 2: the RA0 (yellow) and RA1 (cyan) output waveforms when producing mouse sounds. The signal bursts vary randomly in length, with variable periods of silence in between. It isn’t obvious from this that the signal frequencies and duty cycles also vary. Lower threshold settings give Mic a greater sensitivity to noise. More on this later. Mouse sounds IC1’s RA0 and RA1 output pins drive the piezo transducer to produce the mouse noises. The piezo is driven in bridge mode by the two outputs, increasing the AC voltage across it to produce a louder sound. When the RA0 output is high, RA1 is low and vice versa. In one condition, there is +3V across the piezo transducer, and in the other, -3V. This results in a 6V peak-to-peak square wave. A 100W resistor limits the peak current into the transducer’s capacitive load as the outputs switch. The mouse sounds comprise various frequency bursts with variable length gaps in-between. The signal frequency varies between bursts and also within each burst. Scope 2 shows three such bursts. While not visible in Scope 2, there is considerable detail within each signal burst. At the beginning of each burst, the duty cycle starts off quite low. This means the piezo transducer is driven only with brief pulses, resulting in a low volume. As the duty cycle increases, the output from the piezo transducer also increases. The duty cycle is increased a little each cycle until it reaches a 50%. A similar change in the duty cycle occurs at the end of each burst. The duty cycle is reduced on each cycle until it reaches zero, so that the volume Australia's electronics magazine falls back to zero. This gives the signal bursts soft starts and soft finishes, preventing loud clicking sounds from being produced by the piezo transducer at the beginning and end of each burst. We also use lower duty cycles to reduce the volume level within each burst instead of having a constant level. A varying volume level sounds more natural. The greatest volume available from the piezo transducer is when it is driven at 50% duty, as shown in Scope 3. The push-pull drive from the RA0 and RA1 outputs is visible too. This is necessary to provide a sufficient sound level from a supply voltage of just 3V or less. The drive frequency also varies over the burst period. If we were to just have the same frequency throughout, it would sound just like bursts of a single tone, like Morse Code. By having a frequency mix, the bursts sound considerably less electronic in nature. Mic’s eye LED1 is driven via the RA2 output via a 1kW current-limiting resistor. This LED is made to flicker when Mic is producing sound. The LED is also used to indicate the threshold level used to detect ambient noise during the setup process. It flashes between one and ten times to indicate the chosen threshold value. The LED also flashes briefly when Mic is powered up to acknowledge this. Pushbutton S2 is used to set this siliconchip.com.au Scope 3: an expanded view of the drive to the piezo transducer, showing how the ~3V peak square wave signals from RA0 & RA1 (yellow and cyan) combine to form a 6V peak-to-peak square wave across the transducer (red trace). The duty cycle here is near 50%. threshold. IC1 detects that S2 is closed by monitoring its pin 4 digital input (RA3). When S2 is pressed (closed), the voltage is close to 0V. When the switch is open, an internal pullup current in IC1 keeps the RA3 input high. The S2 switch closure is only checked during power-up; if it’s low (closed) then, the threshold setup process starts. Power control Much of the design work went into minimising the current draw from the small 3V cell. Shutting down the circuit is the major way to do this. When IC1 is in sleep mode, its oscillator is off and the power supplies to the MEMS module and LED are also switched off. A separate ‘watchdog’ timer starts running in sleep mode, to wake IC1 periodically. This varies between 4, 8, 16, 32, 64, 128 and 256 seconds in a randomised order. To extend the sleep periods and save more power, IC1 is sent back to sleep immediately upon waking 30 times. This provides an off-time between two minutes (when there is a 4s watchdog timeout) and about two hours for the 256s timeout. During this period, the current consumption is very low; we measured this at 0.36μA with a 3V supply. IC1 itself draws just 0.9μA in sleep mode, including the watchdog timer and oscillator current draws. After these 30 sleep periods, IC1 powers up the MEMS microphone module and checks for ambient sound. During this period, its current siliconchip.com.au Scope 4: this is similar to what’s shown in Scope 3, except the duty cycle is lower, at around 20%. This reduces the output sound level. consumption is about 1mA. This is mainly due to the MEMS module consumption at about 330μA, and IC1 drawing around 660μA while running. There needs to be a 2-16 minute quiet period (again a randomised value; it’s either 2m, 4m, 8m or 16m) before it is deemed to be quiet enough for the mouse to make noises. Should noises be detected during the listening period, IC1 will go back to sleep for another randomly chosen sleep period. If no sound was detected, Mic the Mouse will begin to make mouse sounds. During this time, his current consumption is around 1.6mA. These sounds run over a variable-length period between 100ms and two minutes; a typical duration is around 30 seconds. If noise is detected in between making the mouse noises, Mic will go back to sleep and stop making noises. All the components are located on for mounting the stand. Australia's electronics magazine There is a brief 5ms delay between each mouse sound ceasing and the beginning of monitoring ambient noises at the AN5 input. This wait is to prevent the MEMS microphone from picking up sounds from the piezo transducer. Adding up the total current draw taking into account the typical sleep, checking for ambient sound and the mouse sounds operation periods, we estimate the overall current draw is an average of 105μA. It is checking for ambient noise (drawing 1mA) around 9% of the time, making mouse sounds (1.6mA) around 1% of the time and in sleep mode (0.36μA) 90% of the time. Considering a typical 3V cell has a capacity of 200mAh, we expect Mic the Mouse to operate on the one cell for around 1905 hours. That’s 79 the rear of the PCB along with the slots August 2025  63 Mic the Mouse with his stand shown separately. Note the use of a spacer to secure the coin cell. days if Mic is left on continuously. If power is switched off, the current draw from the cell becomes close to zero, with the only draw being cell leakage and diode D1’s reverse leakage. These are very low and in the nanoamps (nA) region. If you handle the cell with your fingers across the insulating ring between the positive and negative contact areas, the leakage current can be higher due to skin oils bridging the terminals. Cleaning the cell with methylated spirits or similar will prevent this extra leakage from occurring. 1 double-sided plated-through white PCB coded 08105251, 96 × 53mm 1 double-sided-plated through white stand PCB coded 08105252, 48 × 31mm 1 Fermion MEMS microphone module (MIC1) [Core Electronics SEN0487] 1 30 × 5.5mm passive piezo transducer (PB1) [HYR-3006/AT3040] 1 SIL SPDT mini vertical slider switch (S1) [SS12D00G3] 1 4-pin 6.2×6.5mm tactile switch (S2) [SKHMQME010 or similar] 1 CR2032 surface-mount folded phosphor bronze PCB mount cell holder (BAT1) [BAT-HLD-001 or similar] 1 CR2032 3V lithium cell 1 3-pin header, 2.54mm pitch (usually supplied with the MEMS microphone) 1 260mm length of white 0.8mm diam. bamboo cord [Spotlight 80325284] 5 M3 × 10mm nylon or polycarbonate screws (cheese or countersunk head) 4 M3 nylon or polycarbonate hex nuts 2 M3 nylon, polycarbonate or metal hex nuts 1 M3 × 6.3mm tapped nylon standoff/spacer Semiconductors 1 PIC16F15214-I/SN 8-bit micro programmed with 1810525A.HEX (IC1) 1 SMD 75V 500mA fast signal diode, such as 1N4148WS or LL4148 (D1) 1 3mm standard brightness red LED (LED1) Capacitors (all SMD M2012/0805 or M3216/1206) 1 1μF 50V X7R 1 100nF 50V X7R Resistors (all SMD M2012/0805 ⅛W or M3216/1206 ¼W) 1 10kW 1% 2 1kW 1% 1 100W 1% component overlay diagram is shown in Fig.2. Check that the tabs on the stand fit into the Mouse slots before assembly. If it is difficult to fit the two together, a small amount of filing may be necessary. The stand should be removed while installing parts on the Mouse PCB. If you are going to use countersunk screws, the front of the PCB will need its holes countersunk so that the screw heads fit neatly, almost flush with the PCB face. Begin by installing the microcontroller (IC1), which comes in an 8-pin SOIC SMD package. You will need a soldering iron with a fine tip, a magnifier and good lighting. First, place the chip with its pin 1 locating dot to the lower right and with the IC leads aligned with the pads. Then solder a corner lead and check that it is still aligned correctly. If it needs to be realigned, remelt the soldered connection and move the IC to align it again. When correct, solder all the remaining pins. Any solder that runs between the IC pins can be removed with solder-wicking braid (ideally with the aid of a little flux paste). Continue by installing the resistors. These will have value codes printed on them, with the last number indicating how many zeroes follow. For the resistors used, the codes will be 101, 100R or 1000 for 100W, 102 or 1001 for 1kW and 103 or 1002 for 10kW. Two resistors and one capacitor are located beneath the MEMS microphone module, so these need to be Complete Kit (SC7508, $37.50): includes everything except the CR2032 cell siliconchip.com.au Construction The parts for Mic the Mouse fit on a double-sided plated-through PCB coded 08105251, measuring 96 × 53mm, with a white solder mask and black labelling. The rear stand plugs into the component side of the Mouse PCB to support it; it is also a PCB, coded 08105252, that measures 48 × 31mm. The main Parts List – Mic the Mouse installed before the MEMS module is in place. The 100nF and 1μF capacitors can be soldered in next; their orientations do not matter. These will not be marked with values, but the 1μF capacitor is likely to be thicker than the other. Diode D1 can now be installed, taking care to orientate correctly. There is sufficient tinned copper area to allow MiniMELF/SOD-80 or SOD-323 package devices to be soldered in. S1 is a through-hole slide switch but you should insert its pins into the allocated holes high off the PCB so the leads don’t protrude through to the other side of the PCB. You can then solder the switch pins to the top side of the pads, not the underside, keeping the visible side of Mic unmarred by solder joints. The on-­ position for this switch is marked on the silkscreen. Switch S2 is surface-mounting tactile pushbutton switch, so solder its four corner pins to the pads. The two mounting holes on the MEMS module need to be drilled out to 3mm to allow the module to be raised off the PCB using nuts as spacers, and secured with M3 machine screws and nuts. The MEMS microphone module is connected electrically using a standard 3-pin 0.1-inch/2.54mm pitch header. Solder this header initially on the component side of the mouse PCB, with the lead ends flush with the non component side, like with the slide switch. After that, slide the black plastic spacer off the pins. Before soldering the MEMS microphone module, attach it to the mouse PCB using M3 nylon or polycarbonate screws and nuts, with the screw heads on the non-component side and one nut securing the screw to the PCB on the component side. The MEMS module is then placed on the screws and two more nuts added to hold the module in place. Do not use metal nuts as they could cause short circuits. With the module attached with the screws, you can then solder the three pins to the pads on the MEMS microphone module. The cell holder is mounted with the cell entry side towards the mouse's ears. That allows the cell capture screw to keep the cell in place, preventing small children from removing it. This complies with Australian Standard AS/NZS ISO 8124.1:2002. While Mic the Mouse is not really a project for very young children, it could be used in a household where young children live or visit, who could potentially swallow button cells if they find one and manage to remove it. For our project, the cell is held within a compartment, with the exit blocked by a 10mm M3 screw that is inserted from the non-component side of the PCB and secured on the cell holder side with a 6.3mm-long nylon tapped standoff. When tightened with a screwdriver, the standoff cannot easily be removed by hand. An alternative to the standoff is two M3 nuts, with the top one used as a lock nut. The cell holder is a half-shell type; its metal contacts the positive side of the cell. A tinned copper area on the PCB completes the cell holder, providing the negative connection to the cell. LED1 is a leaded component, with its leads bent so that they are U-shaped, returning past the LED body. The LED’s lens is positioned over the mouse’s eye hole; it does not protrude through the hole fully. Solder the leads from the component side and make sure the (longer) anode lead is soldered to the pad on the PCB marked “A”. The wires for the piezo can be soldered to the PCB (the positions are marked ‘piezo’). The wires will need to be cut shorter than supplied. The wires will probably be red and black, but it does not matter which colour wire goes to which PCB pad. Typically, including in this case, the transducer is not used as a polarised component. You will need to drill the mounting holes on the piezo unit out to 3mm to suit the M3 screws. The piezo transducer is then secured with two 10mm-long M3 screws and two nylon, polycarbonate or metal nuts. Now insert the CR2032 cell into its holder, secure it with the screw and M3 tapped standoff and switch on the power with switch S1. If all is well, the eye LED will momentarily flash to acknowledge power has been connected. The eye also very briefly flashes at the end of each sleep cycle. Programming IC1 That test assumes IC1 has already been programmed, which it will be if you buy it from us, either by itself or as part of a kit. If you intend to program the PIC yourself, the firmware (1810525A.HEX) can be downloaded from siliconchip.au/Shop/6/2698 If the chip has already been soldered to the board, but is unprogrammed, you will need to wire up a programming adaptor to the PCB, such as a PICkit. Since there is no in-circuit serial programming (ICSP) header, you will need to make the Fig.2: there are about 14 different components mounted on the PCB; don’t miss the three that are under the MEMS microphone module. The five pads numbered 1-5 in red are the points you can solder wires to for in-circuit programming of IC1. They correspond to pins 1-5 of a PICkit programmer or similar. siliconchip.com.au Australia's electronics magazine August 2025  65 five connections separately. They go to pads marked 1-5 on the PCB and in Fig.2; these correspond to the pins on the PICkit programming header (1 = MCLR etc). Sensitivity to sound As mentioned previously, sensitivity to ambient sound can be adjusted so that you can select the sound level that Mic reacts to, over a range of 1-10. Lower values provide higher sensitivity to sound, ie, Mic will detect lower noise levels. Higher values mean less sensitivity, so more noise is required to silence Mic. To adjust sensitivity, switch it on using S1 while holding down S2. This initiates the adjustment mode, where Mic’s eye blinks out the sensitivity setting. There is one blink for each sensitivity level. You can test each sensitivity level after the flashes have finished; you have up to 16 seconds to test each level. The eye will flash in response to your making noises. If the eye continuously flashes due to the detection of background noises, the setting is too sensitive, and a higher value should be selected. To change to the next sensitivity level, press S2 before the 16 seconds are up. This will cause the eye to flash out the next sensitivity level. You can then test this sensitivity level for up to 16 seconds. Once the sensitivity value has reached 10, the next value will be 1 again. The selected sensitivity is stored in flash memory, and will be remembered if the power is switched off. If you wait out the 16 seconds after releasing S2, Mic will begin to make squeaking sounds. This is a quick way to have Mic make some sounds for testing. While making these sounds, Mic also checks whether there is ambient sound. If detected, any mouse sounds will cease, causing him to go to sleep. On a normal power-up without S2 pressed, mouse sounds will begin after about four minutes from switch-on. This period will also depend on whether there is ambient noise present that would prevent Mic from sounding. Further mouse sounds could occur up to two hours later. Adding some whiskers Versatile The whiskers are made using white 0.8mm bamboo cord. The whiskers can be up to about 30mm in length, so cut each length of cord to about 65mm, allowing two whiskers to be formed by folding the length in half. Then insert each end into two adjacent holes in the whisker region, from the component side of the mouse. Coat the cords with a thin smear of PVA glue so that they will become stiff when dry. You will need to orientate the whiskers by having the mouse body supported on a stand so that the PCB sits horizontally, with the whiskers hanging downward until the glue is dry. Finally, the rear stand can be attached at the component side with its two protrusions placed into the slots on mouse PCB. The piezo wire leads will add some holding force to keep the stand in place. Modifications If you want to reduce the volume of the mouse squeaks, increase the resistance of the resistor in series with the piezo transducer. Increasing it from 100W to 1kW will reduce the apparent volume by about 50%. Higher values will provide an even lower volSC ume level. Battery Checker This tool lets you check the condition of most common batteries, such as Li-ion, LiPo, SLA, 9V batteries, AA, AAA, C & D cells; the list goes on. It’s simple to use – just connect the battery to the terminals and its details will be displayed on the OLED readout. Versatile Battery Checker Complete Kit (SC7465, $65+post) Includes all parts and the case required to build the Versatile Battery Checker, except the optional programming header, batteries and glue See the article in the May 2025 issue for more details: siliconchip.au/Article/18121 66 Silicon Chip Australia's electronics magazine siliconchip.com.au The Boeing 737 MAX & MCAS A predictable disaster by Brandon Speedie Image source: Aka the Beav, www.flickr.com/photos/87117889<at>N04/23514088802 (CC-BY-2.0) Boeing’s MAX version of their venerable 737 aircraft has had its share of problems, from two deadly crashes in 2018 and 2019 to the latest drama with the door plug falling off in flight. This article explains how the failure of a single electronic part led to two fatal crashes. A merican aircraft manufacturer Boeing launched the 737 MAX in 2017 to much fanfare. It is the first narrow-body aircraft to be made predominantly of composite materials, which are lighter than the magnesium and aluminium alloys of its predecessor: the 737 NG (Next Generation). The MAX also features new high-­ bypass turbofan engines from CFM International, as well as reprofiled winglets to reduce drag. All of these improvements aim to increase fuel efficiency, one of the main operating expenses of a passenger flight. Unfortunately, the high bypass turbofan engines are also bulky; bulk that wasn’t compensated for with the rest of the aircraft design. Under load, the aircraft was inherently unstable and ultimately unsafe. Lion Air Flight 610 On 29th October 2018, a recently built 737 MAX took off from Jakarta. Shortly after taking to the air, its pilots were bombarded with warnings on the flight deck, and the aircraft began siliconchip.com.au to pitch downward into a dive. The pilots wrestled with the controls to try to maintain altitude, which would briefly arrest their descent, only for the nose of the aircraft to pitch down again moments later. This wrestle between the pilots and the aircraft continued for 13 minutes after take-off, before the plane crashed into the water off the coast of Jakarta, killing all 189 passengers and crew. Upon recovering the ‘black box’ flight recorder, investigators found an automated system was overriding pilot input, despite the autopilot being disengaged. Ethiopian Airlines Flight 302 On the 10th of March 2019, another recently-­ b uilt 737 MAX departed Addis Ababa in on route to Nairobi. Similarly to the Lion Air crash, the pilots were immediately bombarded with warnings after takeoff. The nose of the aircraft again pitched down, despite the pilots straining to pull back the control yoke. The aircraft crashed into a field six minutes after take-off, Australia's electronics magazine killing all 157 passengers and crew. The black box showed an almost identical scenario to the Lion Air flight: repeated nose up commands from the pilots, which would then be overruled by an automated system that placed the aircraft into a dive. The Airbus A320neo To understand how this automated system was permitted to overrule human input, we need to look across the Atlantic to Boeing’s main competitor, the European Union’s Airbus. Eight years prior, Airbus announced a new aircraft that would be in direct competition with Boeing’s 737. This new variant is called the neo (New Engine Option) which was groundbreaking for its ability to accept two different engines: the CFM LEAP 1-A or the Pratt and Whitney GTF. Airlines loved the choice, as it gave them the flexibility to select the highest fuel efficiency engine for a given configuration. The A320neo sold faster than any aircraft ever before. Boeing knew their August 2025  67 Fig.1: typical drive (red) and receive (cyan & green) waveforms for a resolver. Original Source: AD2S1210 data sheet Fig.2: the configuration of a resolver. A sinusoidal excitation applied between R1 and R2 inductively couples a current into the rotor. The resulting magnetic field induces voltages in orthogonal receive coils S1-S3 & S2-S4, which will vary in response to the rotor position. Original Source: Analog Devices – siliconchip.au/link/abwg existing 737 NG could only be fitted with the older CFM56, which was much hungrier on fuel. They didn’t have a product that could compete. Enter the 737 MAX Boeing executives scrambled to come up with a solution. Many engineers considered the 737 to be in need of a replacement; its original design was over 40 years old. There were existing plans to replace the 737 with a brand new plane. However, Boeing couldn’t afford the lengthy time to market for a new design, so they instead decided to update the 737 NG so that it could accept a new high efficiency engine from CFM International. The CFM LEAP 1-B is a high-bypass turbofan, meaning that most of the air that flows through the engine bypasses the turbine and is ejected without being used in combustion. This configuration is highly efficient, but requires a significantly larger diameter than the CFM56 that was used by the 737 NG. To fit the larger engine to the 737, Boeing engineered a compromise. Ideally, the engines should be mounted centrally to give the most stable flight characteristics. But even with longer landing gear, the new LEAP was too large to fit under the wings. Boeing had to mount the new engine higher and further forward than was optimal. This caused the aircraft to tend to nose-up under thrust, giving the 737 MAX significantly differing flight characteristics to its predecessor. This was enough of a departure from the previous design that 737 pilots would need training in the new handling characteristics. Boeing knew that airlines would prefer to avoid additional flight training. Removing pilots from the air to spend days in a simulator is costly and disruptive. To avoid this requirement, they instead decide to write some software to compensate. Unfortunately, this code was reliant on a single point of failure: the AoA sensor. Angle of attack (AoA) sensor Protruding externally from the side of the aircraft’s nose is a small fin (see Photos 1 & 2). This winglet rotates with the direction of airflow during Photo 2: an angle of attack sensor on the 737 MAX (below the antennas near the nose). Like most other jets, the 737 MAX has a second sensor on the other side of the nose for redundancy. Source: Business Insider – siliconchip.au/ link/abwh Photo 1: An angle of attack sensor showing a winglet that aligns with the airflow direction. Source: https:// bluemarble.ch/wordpress/tag/aoavane/ 68 Silicon Chip flight, thereby giving an indication of the relative angle of the wing with respect to oncoming air. This is known as the wing’s angle of attack (AoA), an important indication for the pilot to ensure they don’t exceed the aircraft’s performance envelope. When flying level at cruise altitude, the plane should have a shallow angle of attack, meaning low lift and low drag from the wings. At take-off, the wings will have a higher angle of attack as the aircraft pitches into a climb, providing more lift but with greater drag. Should the pilot attempt to climb too aggressively, the angle of attack could exceed a critical threshold, at which point the wing will begin to experience flow separation. The resulting turbulence results in a sudden loss of lift, a dangerous situation known as a stall. Given the angle of attack sensor is located in a vulnerable position on the side of the aircraft’s nose, it is commonly damaged by bird strikes or debris. It is also vulnerable to freezing up in icy conditions (there is a heater to prevent that but it can fail or be Australia's electronics magazine siliconchip.com.au overwhelmed). Therefore, many passenger planes have an AoA sensor on each side of the nose to provide redundancy in case of damage or a fault in one of them. The resolver The AoA winglet is attached to an angular position sensor known as a resolver. This sensor is similar to a rotary encoder, except it is analog, in contrast to the digital quadrature output of the encoder. Resolvers are favoured in high-reliability applications due to their rugged build quality. Its theory of operation compares to an induction motor – see Fig.2. An excitation signal is applied to the signal coil, typically in the order of 10kHz and 10V. This excitation induces a current in the rotor, which in turn induces a signal in the two receive coils. These receive coils are perpendicular, so they are 90° out of phase of each other, as shown in Fig.1. Given a sinusoidal excitation, the received signals will be complimentary sine and cosine pairs. If the rotor’s angular position changes, the coupling between the excitation signal and the two received signals will change, ie, their mutual inductance varies. This property can be used to sense the angular position of the rotor, using the scheme shown in Fig.3. Effectively, this is a phased-locked loop (PLL) that includes the resolver itself, facilitating an angular accuracy better than 0.01°. The Boeing 737 MAX that was involved in the Lion Air flight 610 crash. Source: PK-REN – www.flickr.com/photos/pkaren/45953419622/ (CC-BY-SA-2.0) An Airbus A320neo aircraft. Source: BriYYZ – www.flickr.com/photos/ bribri/28915135713/ (CC-BY-SA-2.0) Circuit Analysis Fig.4 shows an example resolver sense circuit based on the Analog Devices AD2S1210 “resolver to digital converter”. An advantage of this circuit is it combines both the excitation and sensing circuitry into a single IC. This allows the sensed signals to be used as feedback to adjust the phase of the excitation signal and therefore null out any angular position errors. The excitation signal is derived from the nominal 8.192MHz crystal clock, which is internally divided down to a range between 2kHz and 20kHz, as set by an internal configuration register. The synthesised waveform is sent to the digital-to-analog converter (DAC), which drives complementary outputs EXC and EXC at around 3.6V peak-topeak, giving a total voltage swing of 7.2V peak-to-peak. Fig.3: a block diagram of a resolver sense circuit. A DAC synthesises a sinusoidal waveform from the reference oscillator, which excites the drive coil, ultimately inducing a flux in the rotor. A “type II tracking loop” is used to cancel errors in the sensed angular position, which allows the AD2S1210 IC to achieve excellent accuracy. Original Source: Analog Devices – siliconchip.au/link/abwg siliconchip.com.au Australia's electronics magazine August 2025  69 Fig.4: a simplified circuit diagram of the AD2S1210-based resolver sense circuit. The reference oscillator is derived from the 8.192MHz crystal. The EXC outputs have weak drive strength and need to be amplified by op amps and complementary emitterfollower transistors pairs to match the low input impedance of the resolver sense circuit. Original Source: AD2S1210 data sheet The output DAC has weak drive strength (100μA), which is a poor match for the low input impedance of the resolver excitation coil, typically around 100W. Two external pushpull current amplifiers are needed. These amplify the complimentary EXC outputs to drive most resolvers with ease. The EXC voltage is applied to the inverting input of the op amp via a 10kW input resistor. The non-inverting input is supplied with +3.75V, derived from a 22kW || 10kW voltage divider tapping off the 12V rail. This provides a DC offset to avoid the need for a separate negative supply rail. The output of the opamp drives a push-pull output made up of complementary BC846B and BC856B pairs. Biasing for this pair is provided by the 2.2kW and 3.3W resistors, in combination with diodes D1 and D2. The voltage gain is set by the ratio of the 10kW input resistor and 15.4kW feedback resistor. A 120pF parallel capacitor provides some high-frequency filtering to improve stability. Additional filtering is provided by the supply bypassing capacitors, parallel 4.7μF and 10nF types. The 5V supply and ground are separated for the digital, analog and reference supplies, further improving noise immunity. The two sense coils are connected to the SIN, SINLO, COS, and COSLO inputs on the AD2S1210 via input protection circuitry. Series resistance and zener diodes provide circuit protection, while the anti-aliasing capacitors low-pass filter the sensed voltage to make it suitable for driving the downstream receive circuit. Optional voltage dividers formed using added resistors Ra and/or Rb can be used to attenuate the voltage if its amplitude is too great to suit the differential ADC on the AD2S1210. As the resolver output is analog, its angular resolution is only limited by the resolution of this ADC. In the AD2S1210, up to 16 bits are provided, which gives an impressive 0.005° resolution. Once digitised, the sine and cosine inputs are compared to the excitation signal using a so-called Type II tracking loop. This feedback loop constantly adjusts the excitation phase to minimise the angular position error. The calculated position is made available Australia's electronics magazine siliconchip.com.au 70 Silicon Chip to the flight computer over a digital interface, which can be a 4-wire serial or 16-bit parallel interface. For more on how this circuit works, see siliconchip.au/link/abwf On the 737 MAX, the flight computer erroneously received the wrong angle of attack from the resolver, ultimately causing two plane crashes (another was narrowly avoided by an alert copilot). Air Crash Investigation In the aftermath of the Lion Air crash, investigators discovered an irregularity with the resolver attached to the left side AoA sensor. In the weeks prior, the angular position readings had shown intermittent errors. Detailed analysis revealed a crack in the resolver, which presented as an open circuit when the aircraft was out of service and the resolver cooled below 60°C. This wasn’t detected by maintenance staff while the aircraft was in service due to the action of the AoA heater, which caused the resolver to expand and close the circuit, restoring normal operation. The Ethiopian airlines investigation revealed a similar problem with the left side AoA sensor, likely caused by a bird strike 44 seconds after lift-off. Wind tunnel tests revealed an impact with a bird weighing 226 grams at 170 knots was enough to snap off the AoA winglet, and leave the resolver misoriented. In both crashes, bad readings from the left side AoA resolver caused some automated software to activate: the Manoeuvring Characteristics Augmentation System. The MCAS (Manoeuvring Characteristics Augmentation System) Modern passenger airliners are ‘flyby-wire’ systems, meaning that the pilot’s control yoke is not directly connected to the control surfaces on the jet by wires or hydraulics like in older aircraft. Pilot inputs (like pressure on or movement of a control stick or yoke) are read by sensors and fed to the flight computer. Software ingests these readings, along with other sensors on the aircraft such as airspeed, air density, temperature, and so on. It then commands the appropriate movements of the control surfaces to affect the aircraft’s attitude, matching the pilot’s commands. siliconchip.com.au Fig.5: a vertical airspeed comparison of Lion Air flight 610 and Ethiopian Airlines Flight 302. You can see how the pilots were fighting with MCAS to try to gain altitude. Original Source: https://w.wiki/AGgf MCAS is an addition to the normal flight software on the 737 MAX to compensate for the suboptimal positioning of the engines. As mentioned earlier, the compromises to the design forced by reusing the existing airframe created a nose-up tendency under thrust. This could allow pilots to inadvertently approach a stall condition. As that did not happen with previous 737 models, pilots migrating to the MAX from an earlier model would not be expecting it. Boeing reasoned that they could write software to compensate for the resulting tendency to lift the nose under thrust, by programming in opposing control movements. That would make the plane feel similar to operate to its predecessor, avoiding the need to retrain pilots. Australia's electronics magazine This software (MCAS) uses the angle-of-attack sensor to determine if the aircraft is pitching nose up. If the plane is reaching the critical AoA, the flight computer operates the motorised ‘speed trim’, actuating the rear aileron to pitch the nose back down again. The speed trim is an existing system on the 737 that allows pilots to ‘trim’ the aircraft to a neutral attitude, by providing an adjustable offset to the rear aileron to compensate for uneven weight distribution. This avoids the need for them to constantly press on the control stick to stop the aircraft from pitching up or down. Boeing deliberately decided not to mention MCAS in their flight manuals. Pilots were not briefed or trained in its operation, as they wanted to be able to sell the aircraft to airlines as not August 2025  71 needing any pilot retraining. In combination with two other fatal flaws, that turned out to be a big mistake. Grounding Following the Ethiopian Airline crash, many countries around the world moved to ground the 737 MAX. The USA eventually followed, taking the unprecedented step of banning all 737 MAXes from flying until Boeing could confirm their airworthiness with the FAA. The grounding lasted 20 months, during which time Boeing was forced to wind back the influence of the MCAS software and train pilots on its use. New simulator sessions were also conducted to provide pilots familiarity with the differing flight characteristics of the plane. Boeing was ultimately penalised US$20 billion in fines and compensation, and lost an estimated US$67 billion in cancelled orders. Conclusion It is now mandatory for the MCAS system to use two AoA sensors. This brings MCAS in line with other critical flight systems, which must not have a single point of failure. We still can’t quite figure out why MCAS only Undelivered Boeing 737 MAX aircrafts at Boeing Field in Seattle. Source: SounderBruce – https://w.wiki/AGhr (CC-BY-SA-4.0) used the data from one sensor when two were already fitted to the aircraft! It seems like a baffling oversight. Apparently, Boeing believed that MCAS was not ‘safety critical’. Early iterations of the MCAS system could not move the aileron enough to cause a loss of control, but that was changed before the first aircraft were delivered, without revisiting the decision not to use the data from the second AoA sensor. If its existence had initially been disclosed to the pilots, simply having an off switch for the MCAS system while leaving the trim motors under manual control might also have saved SC hundreds of lives. PIC Programming Adaptor Our kit includes everything required to build the Programming Adaptor, including the Raspberry Pi Pico. The parts for the optional USB power supply are not included. Use the Adaptor with an in-circuit programmer such as the Microchip PICkit or Snap to directly program DIP microcontrollers. Supports most newer 8-bit PICs and most 16-bit & 32-bit PICs with 8-40 pins. Tested PICs include: 16F15213/4, 16F15323, 16F18146, 16F18857, 16F18877, 16(L)F1455, 16F1459, 16F1709, dsPIC33FJ256GP802, PIC24FJ256GA702, PIC32MX170F256B and PIC32MX270F256B Learn how to build it from the article in the September 2023 issue of Silicon Chip (siliconchip.au/Article/15943). And see our article in the October 2023 issue about different TFQP adaptors that can be used with the Programmer (siliconchip.au/Article/15977). Complete kit available from $55 + postage siliconchip.com.au/Shop/20/6774 – Catalog SC6774 72 Silicon Chip Australia's electronics magazine siliconchip.com.au Subscribe to JULY 2025 ISSN 1030-2662 07 The VERY BEST DIY Projects ! 9 771030 266001 $13 00* NZ $13 90 INC GST INC GST The SmartProbe The perfect device for troubles hooting circuits. Probe voltages and test continuity with one hand, then put it in your pocket Solar USB Charging Charge your USB devices without paying a cent for electricity Hot Water Solar System Diverter Get the most out of your solar panels – this issue has the assemb ly and testing instructions ...and much more in this Australia’s top electronics magazine issue! SpaceX THE IR LATEST DEVELO 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. PMENTS, INCLUDING STA RSHIP 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 SmartProbe; July 2025 Length Print Combined Online 6 months $70 $80 $52.50 1 year $130 $150 $100 2 years $245 $280 $190 6 months $82.50 $92.50 1 year $155 $175 2 years $290 $325 6 months $100 $110 1 year $195 $215 All prices are in Australian dollars (AUD). Combined subscriptions include both the printed magazine and online access. 2 years $380 $415 Prices are valid for the month of issue. Hot Water System Solar Diverter; June-July 2025 SSB Shortwave Receiver; June-July 2025 Renew or extend your subscription before September 1st to get in before the prices go up (see page 2). To start your subscription go to siliconchip.com.au/Shop/Subscribe Part 1 by Julian Edgar & John Clarke This smart controller can improve the energy efficiency of your home. It can transfer warm or cool air between rooms automatically when needed. Ducted Heat Transfer Controller T his device controls a mains-­ powered fan that is used to transfer heat between rooms via ducts. The controller can be used manually, automatically, or based on a timer. The wall-mounted LED gives an indication of the temperature difference between rooms. » Powered by the 230V AC mains » Operates during all seasons without changes » Three different operating modes » Adjustable temperature difference and hysteresis » Optional adjustable timer » Optional fire alarm feature » Wall plate button with sound and LED indicators » Sensor disconnection indication » Temperature difference options: 1, 1.5, 2, 3, 4, 5, 6, 8, 10 or 11°C » Hysteresis options: 0.5, 1, 1.5, 2, 3, 4, 5, 6, 8 or 10°C » Timer options: 15m, 30m, 1h, 2h, 3h, 4h, 5h, 6h, 8h, 12h or multiples thereof » Modes: manual, timed, or automatic » Fire alarm function: switches on RLY2 and rapidly pulses the piezo buzzer and LED when the temperature rise of either sensor is >8°C per minute or 70°C is exceeded (this does not replace a smoke alarm!) » Maximum total fan current: 10A reasons reason for this. The first is that the heater has been shut down – the damper closed to reduce the airflow. The second reason for smoke emissions is burning green wood that has high moisture levels. With current heaters that must meet emissions standards, a wood heater burning dry wood at full power produces no visible emissions. But the key point is ‘at full power’ – throttling the heater output reduces its efficiency and increases emissions. That’s where a fan-forced heat transfer duct comes in. It is much better to keep the wood heater burning furiously and transfer some of that heat to other rooms in the house than it is to shut the heater down. Since most homes using wood heating have only one heater, using a transfer duct also works to warm more than just the room where the heater is located (see Fig.1). The second reason for using a ducted heat transfer system is in houses that use passive solar heating. In southern Australia, windows facing north can be used to warm the house in winter. The sun shines in through these windows, heating the wall and floor surfaces of the room, and subsequently the air within. Because the sun is higher in the sky in summer, projecting eaves can shade these windows in summer, so Australia's electronics magazine siliconchip.com.au Advantages The most common reason for using a ducted heat transfer system is when the source of heat for the house is confined largely to one room. There are two likely situations where that would occur: a wood heating stove is located in one room, or passive solar heating occurs largely at one end of the house. While in some jurisdictions, wood heating is frowned upon (for example, the Australian Capital Territory is phasing out wood heaters), wood heaters can be environmentally acceptable and, in some areas, cost little to run. Wood heaters are effectively carbon neutral; the carbon dioxide absorbed by the trees during their growth is released when the wood is burnt. Wood heaters have a bad reputation for emissions – we’ve all seen wood heater flues emitting a stream of smoke for many hours. There are two Features & Specifications 74 Silicon Chip WARNING: Mains Voltage Air return paths are required A heat transfer duct works by moving air – that is, pushing air from one room to another. But unless the air has a return path, the duct will not be very effective. Without a return path, air pressure will rise in the destination room, slowing the transfer of air. It’s therefore best to leave some internal doors open so that good circulation can be achieved. the northern windows don’t heat the house when you don’t want them to. In the northern hemisphere, this is reversed – you want southerly windows. However, the number of rooms in a house that can face north is quite limited, so this type of heating can usually work in only one or two rooms. That’s especially the case if the house was never designed with passive solar heating in mind. In this case, a ducted heat transfer system can be added to move solar heat to other rooms. The problem with commercial options Fan-forced heat transfer ducts are commercially available for installation in new or existing builds (see the photo overleaf). Typically, they comprise flexible ducting and one or two mains-powered fans. Common duct and fan diameters are 150mm, 200mm, 250mm and 300mm. The fan and duct are usually mounted in the roof space with the inlet and outlet grilles located in the ceiling. Generally, these require you to switch them on manually when desired. You can certainly do that, but it’s a little trickier than it first appears. One thing that makes it tricky is that the temperature differences can be very small. For example, in a house that uses passive solar heating, the temperature difference from the ‘warm’ northern room to the southern ‘cool’ part of the house may initially be only 2°C. That difference may increase quite slowly – over hours. Without either walking back and forth to feel the temperatures, or consulting room thermometers, the best time to turn on the fan isn’t at all obvious. That’s if you’re even home at the time! Luckily, this Transfer Controller can do the work for you. Also, you may want the fan to operate for some time after you go to bed – you’re no longer in the heated lounge room, and you want that residual heat distributed through the house. Or you want to be manually in charge of when the fan operates, but with a monitoring LED showing when the heated room is warmer by, say, 3°C than the room at the other end of the duct. Our Controller can perform all these functions. In long ducts, more than one fan may be needed. The controller can run fans up to a total power consumption of 2300W (10A at 230V). Since most This Direct Heat Transfer Controller operates directly from the 230V AC mains supply; contact with any live component is potentially lethal. Do not build it unless you are experienced working with mains voltages. duct fans are quite low in power, it can likely drive however many fans you need. If running multiple fans in the duct, ensure they both blow in the same direction! Operating modes The main function of the Ducted Heat Transfer Controller is to switch on the fan in the duct – the output is simply on or off. However, when it activates that fan depends on the mode. Each mode is selected by switch BCD4 on the printed circuit board (PCB) – as with the other set-up features, it is expected that this will be set and then not frequently changed. In all modes, the user interface is a neat wall-mounted, spring-return rocker-type pushbutton with a white monitoring LED visible around the periphery of the button, and a beeper mounted behind. The other two inputs are temperature sensors – one in the room at each end of the duct. Mode 0 is manual mode. In this case, the pushbutton is used to switch the fan on and off. Mode 1 provides manually triggered timed operation. Pressing the pushbutton switches the fan on for a specified period. Each quick press of the button adds (for example) one hour of operation, so one press gives one Fig.1: a Ducted Heat Transfer System takes the heat from one room and distributes it to one or more other rooms. A fan in the duct is used to move the air, and our controller determines when the fan switches on. Source: Vent-Axia. siliconchip.com.au Australia's electronics magazine August 2025  75 This 150mm Ducted Heat Transfer System uses a single fan to distribute the air to two other rooms. Note that this duct is uninsulated – not a good idea. Source: JPM Brands Switch BCD1 (temp. difference) BCD2 (hysteresis) BCD3 (timer period) BCD4 (mode) 0 1°C 0.5°C 15 minutes Manual 1 1.5°C 1.0°C 30 minutes Timed 2 2°C 1.5°C 1 hour Automatic 3 3°C 2°C 2 hours Automatic 4 4°C 3°C 3 hours Automatic 5 5°C 4°C 4 hours Automatic 6 6°C 5°C 5 hours Automatic 7 8°C 6°C 6 hours Automatic 8 10°C 8°C 8 hours Automatic hour, two presses gives two hours etc, up to a maximum of five presses. A BCD switch preset determines the base period, from 15 minutes to 12 hours. Mode 2 is fully automatic. In this mode, the fan operates when the temperature difference between the two ends of the duct exceeds a preset threshold. In addition to mode selector switch BCD4, the PCB has three more adjustments. BCD1 is used to set the temperature difference that needs to occur before the fully automatic mode (Mode 2) switches on the fan. This can be set to 1, 1.5, 2, 3, 4, 5, 6, 8, 10 or 11°C. BCD2 is used to set the hysteresis. This is the difference between the switch-on and switch-off temperatures. This can be set to 0.5, 1, 1.5, 2, 3, 4, 5, 6, 8 or 10°C. It must be set lower than the temperature difference. Let’s imagine the temperature difference is set to 4°C and the hysteresis is set to 1°C. If the heated room is at 20°C and the unheated room is at 16°C (a difference of exactly 4°C), the fan will switch on. It will stay on until the difference in temperature decreases to 3°C; eg, the unheated room warms to 17°C. In use, if the fan switches on and off too frequently, increase the hysteresis setting. On the other hand, if the temperature of the room at the other end of the duct varies up and down too much, decrease the hysteresis. BCD3 sets the timed period that occurs in Mode 1 with each button press. In the example above, I suggested that each press gives a onehour extension of the on-time. However, each button press can actually be set to be 15m, 30m, 1h, 2h, 3h, 4h, 5h, 6h, 8h or 12h. Refer to Table 1 for all the BCD switch settings. 9 11°C 10°C 12 hours Automatic Monitoring LED and beeper Table 1 – BCD switch settings While we have described the function of the controller as operating a fan-forced duct that transfers warm air to a cooler room, the system can also transfer cool air to a warmer room. In fact, no changes are needed to do this because the system operates based on the temperature difference between the two rooms, rather than how much cooler the room is at the far end of the duct. For example, say you have the difference in room temperature set to 3°C and the Mode set to 2 (Automatic). When the room at the end of the duct is 3°C warmer than the room at the beginning of the duct, the fan will switch on, transferring cooler air to the hotter room. Of course, the source room needs to be the same room in both winter and summer. In addition to the pushbutton switch, the wall-mounted indicator is equipped with one LED and a beeper. The beeper operates in the same way in all modes: a single beep indicates switch on (a short press of the button) and a triple beep indicates switch off (achieved by a longer press of the button). The triple beep comprises a single beep followed by a quick double beep. The LED can show different information in each mode. In manual mode, if the fan is off, the Australia's electronics magazine siliconchip.com.au What about transferring cool air? 76 Silicon Chip LED is off, possibly flashing on briefly. If the fan is on, the LED is on, possibly flashing off briefly. If it’s flashing briefly every two seconds when the fan is off, that indicates the measured temperature difference is greater than or equal to the set temperature difference, so you might want to switch it on. Similarly, if it’s briefly flickering off while the fan is on, that means the temperature difference has fallen below the set difference (including hysteresis), indicating you may want to switch it off. Manual Timed operation (BCD4 position 1) has LED behaviour that is the same as the manual mode. Automatic mode (BCD4 position 2) has different LED behaviour. If the system has been disabled, the LED flashes. If the fan is on, so is the LED. If the fan is off, again, so is the LED. A summary of these modes is shown in Table 2. Other potential uses This device can also control a powered ventilator or fan; for example, one that ventilates a hot roof cavity in summer. In this use, one temperature sensor is placed in the roof cavity (or other hot area needing ventilation) and the other outside in an area protected from the weather (eg, under the eaves). In this application, the best settings will probably be Mode 2 (automatic), with the temperature difference set higher than you would use for internal house use (eg, 10°C with 5°C of hysteresis). Another use is for solar air heaters. While uncommon in Australia, these have been widely used in solar homes in the United States. In this approach, air is heated by a flat plate collector – a little like a traditional solar water heater but with air rather than water heated through contact with the plate. When the air in the heater rises sufficiently in temperature, a fan can be used to move that heated air into the house through conventional air-­ conditioning ducts. In this application, one sensor would be placed so that it is exposed to the air in the heater (but shielded from direct sunlight), while the other would be placed inside the house. The temperature difference would be set quite low (eg, 3-4°C, with perhaps 2°C of hysteresis). Parts List – Ducted Heat Transfer Controller 1 polycarbonate IP65 enclosure, 171 × 121 × 55mm [Altronics H0478, Jaycar HB6218] 1 double-sided, plated-through PCB coded 17101251, 151 × 112mm 1 lid panel label (84 × 65mm) and side panel label (64 × 10.5mm) 1 3VA 9+9V PCB-mounting mains transformer (T1) [Altronics M7018A] 1 FRA4 250V 30A AC SPST relay with 12V DC coil (RLY1) [Jaycar SY4040] 1 PCB-mounting 250V 10A AC SPDT relay with 12V DC coil (RLY2) [Altronics S4160C, Jaycar SY4066] 4 PCB-mounting 10-position BCD switches (BCD1-BCD4) [Altronics S3001] OR 4 2×4-pin headers and 12 jumper shunts 1 2-way header, 2.54mm pitch (JP1) 1 jumper shunt (JP1) 2 15A 300V 2-way screw terminals, 8.25mm pitch (CON1, CON2) [Altronics P2101] 1 2-way screw terminal, 5/5.08mm pitch (CON3) 1 3-way screw terminal, 5/5.08mm pitch (CON4) 3 8P8C RJ45 PCB-mounting horizontal sockets (CON5-CON7) [Altronics P1448A] 1 IEC mains input socket with integral fuse [Altronics P8324, Jaycar PP4004] 1 mains lead with IEC plug 1 surface-mounting mains socket (GPO) [Altronics P8241, Jaycar PS4094] 1 20-pin DIL IC socket (optional, for IC1) 1 fast-blow 10A M205 fuse (F1) Hardware 2 M4 × 10mm panhead machine screws with matching hex nuts 2 M3 × 15mm panhead nylon machine screws 5 M3 × 6mm panhead machine screws 3 M3 brass hex nuts 1 200mm cable tie and 8 100mm cable ties 1 3-6.5mm diameter wire entry cable gland Wire & cable 1 200mm length of black 7.5A hookup wire 1 50mm length of light-duty red hookup wire and light-duty black hookup wire assorted lengths of 10A mains-rated green/yellow striped wire (150mm length); brown wire (200mm length); and blue wire (100mm length) 3 Cat 5, Cat 5E or Cat 6 patch leads, lengths to suit installation assorted lengths of clear heatshrink tubing (70mm length, 5mm diameter; 30mm length, 4mm diameter; and 50mm length, 1mm diameter) Semiconductors 1 PIC16F1459-I/P microcontroller programmed with 1710125A.HEX, DIP-20 (IC1) 1 7805 1A 5V linear regulator, TO-220 (REG1) 3 BC337 NPN transistors, TO-92 (Q1-Q3) 1 W02(M) or W04(M) 1.5A 200V/400V bridge rectifier (BR1) 16 1N4148 200mA 75V diodes (D1-D16) 3 1N4004 1A 400V diodes (D17-D19) Capacitors (16V PC radial electrolytic, unless specified) 2 470μF 1 100μF 2 100nF 63V/100V MKT polyester Resistors (all ¼W, 1%) 5 10kW 2 2.2kW 4 1kW 1 470W Control panel parts (per panel) 1 double-sided, plated-through PCB coded 17101253, 51 × 67mm 1 Clipsal Iconic 3041G single Gang Switch Grid Plate ● 1 Clipsal Iconic 3041C-VW single Gang Switch Plate Cover (Skin Only) ● 1 Clipsal Iconic 40FR-VW Fan Dolly Rocker Vivid White ● 1 Clipsal Iconic 40MBPRL-VW 10A Momentary Bell Press Switch Mechanism with LED ● 1 panel label, 45 × 30.5mm 1 top-entry 8P8C vertical RJ45 socket (CON10) [Altronics P1468] 1 3-16V self-oscillating piezo buzzer [Altronics S6104] 1 2-way vertical polarised header, 2.54mm pitch, with matching plug and pins (CON11) 1 2-way terminal block, 5/5.08mm pitch (CON12) 1 8P8C double adaptor (only required if using two control panels) [Altronics P7052A] ● available from electrical wholesalers, including www.sparkydirect.com.au The complete circuit for the Ducted Heat Transfer Controller is shown in Temperature sensor parts 2 60 × 60 × 20mm vented enclosures or similar [Jaycar HB6116] 2 double-sided, plated-through PCBs coded 17101252, 20 × 37.5mm 2 8P8C RJ45 PCB sockets (CON8, CON9) [Altronics P1448A] 2 DS18B20 temperature sensors (TS1, TS2) [Altronics Z7280 or Z6386] siliconchip.com.au Australia's electronics magazine Circuit details August 2025  77 Fig.2. Microcontroller IC1 monitors the temperatures via sensors TS1 & TS2, which connect to the main board via 8-way Cat 5 (or similar) cables and RJ45 plugs/sockets. In each case, pin 4 carries the digital signal, pin 8 the 5V supply for the sensor and pins 5 & 7 are grounds. TS1 & TS2 are Maxim DS18B20 1-wire digital thermometers. Just one data line (DQ) is required for serial communications. A minimum of one extra connection for the common ground connection is also required. Power for the sensor can be derived from the data line, but we include a Enabling the fire alarm feature The Ducted Heat Transfer Controller can also be configured as a fire alarm. Because the system has temperature sensors that would normally be placed at divergent ends of the house, monitoring of these sensors provides a widespread back-up system to the legally required smoke detectors. When this function is enabled by shorting the pins of JP1, each temperature sensor is monitored for both the temperature and the rate of temperature change. If the temperature exceeds 70°C and/or the rate of temperature change exceeds 8°C per minute, the beeper and LED rapidly pulse. Relay RLY2 is also energised, which can power a low-voltage warning siren, switch on low-voltage lights etc. If the fire alarm goes off, a short press of the wall-mounted button will switch off the buzzer, but the LED will continue to flash. A long press will switch off the buzzer, LED and RLY2, and the system will be re-armed to monitor again for fire. Note that this is a mains-powered system with no battery back-up. It should always be used in conjunction with traditional battery-powered or battery-­ backed smoke detectors. We suggest that this function be activated in all installations since it’s unlikely to ever be triggered unless there is a fire. 78 Silicon Chip Australia's electronics magazine direct 5V supply connection (Vdd/V+) since we have enough wires and this makes signalling easier. Two-way communication between the microcontroller and temperature sensor is possible since the DQ pin is an open drain with a pull-up resistance of 2.2kW. Open drain means that the drain of a Mosfet connects to this pin, so when the Mosfet is on, the pin is pulled to 0V, while if it is off, it is pulled up by the resistor. A Mosfet at either end of the wire can be used to pull it down to 0V, so a signal can be sent by the device at either end of the wire. The microcontroller uses its RC2 and RB4 I/O pins to request temperature readings and get them from the sensors. The DS18B20 has a temperature reading accuracy of ±0.5°C from -10°C to +85°C. Temperature readings are available in 0.125°C steps, but for this project, we measure the temperature in 0.5°C increments. BCD switches The four BCD switches that select the various mode, temperature and timer features have internal contacts siliconchip.com.au Fig.2: microcontroller IC1 reads the positions of BCD switches 1-4 (or the alternative jumper sets) to determine is jobs. It then reads the temperatures from sensors TS1 & TS2 connected via Cat 5/5E/6 cables and determines when to energise relay RLY1 to connect mains power to the fan(s). that connect the “1”, “2”, “4” and “8” terminals to ground in a combination that totals to the switch setting. For example, if the switch is set to the 9 position, the “1” and “8” terminals will be connected to ground but the other two won’t. This allows IC1 to sense 16 possible positions for each switch using four wires (although these switches only have 10 positions). Rather than the common (C) terminal of each switch being connected to ground, they are connected to a separate pin on microcontroller IC1. This way, the micro can pull them high one at a time, and use the same four lines (RA1, RC5, RA0 & RC4) to read the position of the selected switch. Isolation diodes D1-D16 are required because, while the other switches can be set to have their common terminals floating while one switch is sensed, those switches could still end up effectively shorting two or more of the sense lines together, depending on their positions. We need the diodes to ensure the switches don’t affect each other during the sensing procedure. siliconchip.com.au During switch sensing, any open BCD switch will be pulled low to 0V via one of the 10kW pull-down resistors. BCD switches can be expensive, so we have provided an alternative system using a 2×4-pin header with up to four jumpers placed on it to replace each BCD switch. Fig.3 shows how the jumper settings equate to BCD settings. Since these settings are rarely (if ever) changed, there’s little disadvantage in using jumpers on headers instead. Control Panel The wall-mounted control panel for the Ducted Heat Transfer Controller comprises switch S1, LED1 and a piezo buzzer. This is all incorporated in a Clipsal sprung-return rocker switch plate that includes an indicating LED. The piezo buzzer is an addition to the switch Fig.3: this shows the simple binary codes you need if using jumpers instead of the BCD switches. IC1 also monitors switch S1 and the four selection switches, BCD1 to BCD4. In response to these settings and temperature readings, the microcontroller can sound the piezo buzzer, light LED1 and switch on RLY1 to drive the duct fan. IC1 can also switch on RLY2 if the fire alarm feature is selected with JP1 and is then activated. Australia's electronics magazine August 2025  79 The Ducted Heat Transfer Controller is housed in a polycarbonate IP65 enclosure (upper right photo). An IEC mains cord supplies power and the duct’s fan plugs into the power outlet on top. The temperature sensor and control panel connections are made using RJ45 sockets and Cat 5/5E/6 cables. The Controller is easy to build, with only through-hole components used. Care must be taken with the mains voltage wiring, though. The faceplate (upper left photo) incorporates a momentary rocker switch, piezo buzzer and a white LED that lights the periphery of the switch. The wall plate can be mounted vertically or horizontally – this one is configured for vertical mounting. The ‘floppy ears’ can be easily removed (they’re not needed for normal mounting). The room temperature sensors are each located in small, ventilated wall enclosures (photo shown at right). 80 Silicon Chip Australia's electronics magazine plate to complete the control panel. The control panel connects to the main board via another Cat 5/5E/6 cable and RJ45 plugs/sockets. LED1 is driven from the RB6 output of IC1 through a 470W resistor to ground. The LED current is around 4.25mA, assuming a voltage drop of 3V across the white LED. Switch S1 is connected between GND and the RB5 input of IC1, with this input pulled to 5V via a 1kW resistor when the switch is open. If the switch is closed, RB5 will be pulled to GND and IC1 can detect that. The piezo buzzer is powered from 12V using transistor Q3 to switch the negative side to ground. When the buzzer is required to sound, the RC7 output of IC1 is driven high to switch on Q3 by delivering current to its base through a 1kW resistor. Relays RLY1 & RLY2 are switched on via the RC3 and RC6 outputs of IC1, respectively. Both use a 1kW base resistor to drive a transistor to power the relay coil. Transistor Q1 is used for RLY1 and Q2 for RLY2. Diode D17, across RLY1’s coil, and D18, across RLY2’s coil, quench the back-EMF voltage from the coil when these are switched off. RLY2 is uncommitted and is intended to drive a low-voltage siren for the optional fire alarm function. RLY1 connects the incoming mains Active to the fan socket when the fan should be powered. The output socket’s Neutral and Earth pins are permanently wired to the input socket. Power for the circuit is derived via a mains transformer that produces a 9V AC output. This is rectified by bridge rectifier BR1 and filtered by two 470μF capacitors, giving close to 12V DC. This is used to power the two relays and the piezo buzzer. REG1 is a 5V regulator that drops its 12V input to 5V to supply IC1 and the DS18B20 temperature sensors. Next month That’s all we have space for this issue. Next issue, we’ll cover building the unit and setting SC it up. siliconchip.com.au Table 2 – smart remote push button/LED/buzzer Mode Push button/buzzer Fan status Faceplate LED ‘0’ Manual fan on/off Short press – beep – on Runs when fan manually switched on Fan off Temp difference < set point LED off Longer press – double beep – off Fan off Temp difference > set point LED flashes momentarily on once every 2s Fan on Temp difference < set point LED flashes momentarily off once every 2s Fan on Temp difference > set point LED fully on ‘1’ Manual fan timed operation Quick press or presses = on for set Runs for period of operation, e.g. when timer timer period is set for 30m, 1 quick press runs when set fan for 30m, 5 quick presses sets ‘on’ period at 150m (2.5h) Longer press – double beep – off Fan off Temp difference < set point LED off Fan off Temp difference > set point LED flashes momentarily on once every 2s Fan on Temp difference < set point LED flashes momentarily off once every 2s Fan on Temp difference > set point LED fully on ‘2’ or more Automatic Short press – beep – system on Runs when System disabled temperature LED flashing difference exceeds Fan off preset level LED off when system activated Fan on LED on Longer press – double beep – system switched off Fire alarm activated (JP1 shorted and fire detected) Buzzer sounds rapidly and LED flashes rapidly at 5Hz Fan off N/A Short press, buzzer sound is off, LED flashes rapidly Long Press, LED and buzzer off and retests for fire siliconchip.com.au Australia's electronics magazine August 2025  81 CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions will be paid for at standard rates. All submissions should include full name, address & phone number. High speed transmission using regular opto-couplers This circuit shows how you can achieve high speeds with low power consumption using standard, inexpensive opto-couplers. It can be difficult to get high speed out of readily available and inexpensive opto-couplers. For example, the 4N35’s data sheet says you can achieve rise and fall times below 10μs if you drive the opto-coupler in a not-very-practical way. The example given in the 4N35 data sheet is the same as shown in circuit (a) but using a 100W pull-up resistor to a 10V supply, and choosing the LED drive resistor such that the phototransistor’s output current is 2mA. This means the output signal will vary from 9.8V to 10.0V as the LED switches on and off, so you’ll need more circuitry to turn this into a useful signal. Also, 10V may be difficult to achieve if you’re using a battery to supply the output circuit, 2mA will run your battery flat more quickly than 82 Silicon Chip you’d like, and the LED resistor will vary from one circuit to the next due to opto-coupler variability. Circuit (b) here overcomes these problems. It works with any supply voltage, and with as little as 10μA of pull-up current. As shown, it will couple a 19,200bps RS-232 signal with a pull-up current of 14 microamps. You can see the results in the Scope 1, which shows a lowercase “u” transmitted via RS-232. From top to bottom, the four traces shown are: 1. The output of circuit (a) using a 220kW pull-up resistor in place of the 1kW resistor shown 2. The output of circuit (b) using the 220kW pull-up resistor 3. The output of circuit (b) with the optional high-current output stage 4. The RS-232 input signal The main reason opto-couplers are slow is because they have a phototransistor output and the phototransistor switches into saturation. Like ordinary Australia's electronics magazine transistors, phototransistors are slow to come out of saturation. In the top oscilloscope trace, the phototransistor switches on fast enough, but off very slowly. One way to help the phototransistor switch off faster is by connecting a resistor between the base and emitter. This improves the switch-off time significantly, but the Miller Effect then comes into play, slowing the rise time and preventing the rise time from being as fast as the fall time. A better way to achieve high speed is to short the phototransistor’s base and emitter together, effectively turning the phototransistor into a photodiode. This gives much better speed, and the photodiode behaves like a microscopic solar cell. When the LED is on, the photodiode generates about 450mV at about 10μA. By stacking two opto-couplers together, we get 900mV, enough to drive a small-signal transistor. This is the BC546 shown in circuit (b), although any small-signal NPN transistor will probably work. The 1nF capacitor is known as a ‘speed-up capacitor’. When connected this way, it helps the BC546 to switch off quickly. The pull-up resistor can supply anywhere from 10μA to 1mA. The optional extra stage allows loads up to 100mA. Note the LED connected in anti-­ parallel across the opto-coupler’s LED pins. This is added because the opto-coupler’s LED will be damaged if more than 5V is applied across the LED in reverse. It limits the reverse voltage to no more than 2V. An ordinary diode could be used. Circuit (c) uses a similar principle, but a micropower comparator turns the 450mV output of the photodiode directly into a logic-compatible output. Note that you can’t use a dual opto-coupler in place of the two opto-couplers, as there is no base connection available in dual opto-­ couplers, preventing you from shorting the base and emitter of each siliconchip.com.au Wireless battery charger Three-way latch This circuit shows a simple way to wirelessly charge a small battery. It is built around NPN transistor Q1 (2N3866), diode D1 (1N4148), LED1 and a few other components. Transistor Q1 forms a 100MHz RF medium power oscillator. Inductors L1 and L2 are made with four close turns of 0.9mm diameter enamelled copper with a diameter of 6mm. Coil L2 is kept near L1 (2mm apart). There is no electrical connection between L1 and L2, but RF signals from L1 get induced to L2. The voltage and current obtained from L2 are sufficient to drive LED1 or charge a 1.2V NiCd rechargeable cell after being rectified and filtered. After assembling the circuit on a PCB, enclose it in a suitable plastic box. Place L1 and L2 next to each other such that LED1 glows when switch S1 is in the TEST position. When S1 is in the CHARGE position, the cell will be charged. The alternative section shown in the cyan box can replace the right-hand section to make it work even if the polarity of one coil is reversed. Raj. K. Gorkhali, Hetauda, Nepal. ($60) phototransistor together. There are also some single opto-couplers that don’t have a base connection either. In case you’re wondering if you could stack ten or more opto-couplers together, and use the resulting voltage as a supply for an electrically isolated circuit, yes, you can. But as this arrangement can only supply microamps, you’ll need good design skills to make a circuit that can run from so little power. Also, special opto-coupler chips are available that do this internally; for example, the PVI5050 and the PVI1050 (among others). Such chips are commonly used in solid-state relays, with the output driving a Mosfet. Russell Gurrin, Highgate Hill, Qld. ($120) Scope 1: a lowercase letter “u” transmitted via RS-232 using the different circuits shown above. siliconchip.com.au Australia's electronics magazine In the configuration shown, it drives three LEDs individually. When one SCR is switched on via the momentary switch through the 10kW resistor, the anode voltage of that SCR drops suddenly. The 100nF capacitors send a negative pulse to the anode of the adjoining SCRs, causing them to switch off. This circuit can be extended to a higher number of SCRs, although you may need to increase the value of the capacitors as they are effectively in series (eg, for coupling a pulse from SCR1 to SCR3 or vice versa). The circuit is reset by disconnecting power. The LEDs can be replaced by opto-couplers to control external equipment, eg, to drive relays to make a ganged latching switch. Joe Curulli, Perth, WA. ($60) August 2025  83 SERVICEMAN’S LOG Mirror, mirror on the door Dave Thompson Our five-year-old car was coming to the end of its warranty. Typically, everything goes wrong about a week after that, with the previously perfect car suddenly becoming one of those jalopies from the old silent movies, where everything literally falls off, leaving the hapless driver sitting on the road with a steering wheel in their hands. This meant we were faced with a relatively major firstworld decision. Having only purchased used cars all my life, and having to deal with the headaches those cars inevitably brought, being able to own a brand-spanking-new car was a real luxury. Anyway, we ended up with a new car, which of course means learning all the new tech onboard and what all the buttons and switches do. Modern cars are apparently more advanced than the 1970s moon lander, and that’s a fact (which I read on the internet, so I am sure it is true). I can almost believe it with the radar, the cameras and all the electronic doodads and gizmos (you can tell I’ve spent a lifetime in electronics). But it is a learning curve, and the manuals that come with these cars are like those olde world phone books we used to get. It took me half an hour to find out how to change the clock for daylight saving time! Of course, once I discovered the appropriate section in the book, it took mere seconds to figure out how to do what I wanted. But my point is that modern cars are hugely complex machines. Saying that, they are apparently not clever enough to switch clocks over automatically, like computers and phones have done for decades when daylight saving clicks in. Or at least, our one isn’t. Maybe it’s because they are all built down to a price these days. I also note that the car’s clock, built into the instrument display, is not tied to the multimedia/GPS display system, so often there are two slightly dissimilar times being shown. That’s not a big deal, of course, but it seems silly that an integrated GPS/computer system and the car’s basic display functionality don’t talk to each other. Or maybe I’m just an older guy pushing the wrong buttons... I have to say this thing is a nice place to be, and a real step up from the original Mini I used to 84 Silicon Chip drive, which almost broke my spine every time I went out in it due to the still quake-damaged roads here. It had all the onboard technology of a particularly low-spec wheelbarrow. Then my 1997 MG-F was great, until it kept breaking down and I was getting far too old to be seen in it, especially with the top down. I won’t even mention the inelegance of me getting in and out of such a low car in public! A computer on wheels So this car is a lot larger than our previous cars, and although it is bristling with the sort of technology and cameras you would expect to see on the latest Apache helicopter gunship, I still try to rely mainly on my old-fashioned (yet increasingly fading) eyesight to make sure nothing is nearby, or that I am not running over or hitting anything that could cause any legal problems. This is the way I’ve always done it, but I can feel the ever-increasing pull of using the onboard tech to compensate for my flagging senses. I’ve also noticed that many younger drivers just rely on the cameras and radar rather than actually looking out the windows, which is very disconcerting. Backing down a driveway by a school and relying solely on the camera display in the centre console is frankly frightening. This was reinforced recently by me driving for an appointment in town with a very challenging car park. It isn’t that the spaces are overly tight, like so many are now (especially when driving a bigger car than a Mini!), but because the building has all these huge square concrete pillars holding it up. It’s like it is on stilts, and there is car parking below. I always avoid parking under structures like this after experiencing some Australia's electronics magazine siliconchip.com.au pretty terrifying quakes here, watching similar pillars flex like they were made of rubber and start cracking while we were trapped in stand-still traffic trying to get out of a mall carpark. Once you see a road waving and breaking apart, things are never the same. So, I try to park outside places like this, and fortunately, there were half-a-dozen spaces on the outside edge of the building. The only free space in the line was beside a pillar, so that’s the one I took. It was tight, but using the cameras and my vision, I got in OK, despite the proximity warnings going off madly and filling the car with beeping noises. I went off happily to my appointment, knowing I had a close parking spot, and all was well in the world. I was out in good time and back to the car. In the meantime, someone had replaced the car that was originally to my right. I’m not suggesting they snuck in and swapped it, but obviously the original parker had left and someone else came in. Boxed in This ‘new’ car was a large Range Rover (probably owned by some medical staff if the personalised plate was anything to go by), and they had parked it quite close to my door. It was a struggle to squeeze my no-longer-so-nimble frame into the car, but I did it without marking his car with my door and vice versa. I fired up the steed, and of course, the usual cacophony of beeps and sirens went off. Radar to the front shows I am nosed into a decorative hedge, and to the sides, there were other cars. It is so distracting, especially as I’m the sort who has to switch off the radio to see better! There were also people driving behind me to watch out for, so a lot was going on. I was most concerned about this huge square pillar beside me, on the left. I didn’t want to hit it, and hitting the Range Rover was not an option I wanted to explore. I very gingerly backed out, trying to take in everything in around me. Then it happened; I touched the very outside of my wing mirror on that $%#%<at>! post. Ironically, there was a rubber buffer on each corner, but that was just out of my sight line. The mirror has a transparent side-light indicator plastic piece that protrudes from it, which I can’t see from the cabin. I just touched it on the pillar, blowing the plastic parts of the mirror off. As you could imagine, the air was blue. siliconchip.com.au I stopped, as there were bits on the ground (I saw them fly off) and I didn’t want to run over anything. It seemed that I had popped the coloured plastic back off the mirror, and two clear plastic lenses that were inside the assembly onto the car park floor. Great. I looked at the bits in my hands and decided that this was too hard while blocking a car park accessway. I did pop the body-coloured plastic cover back on, and it simply clipped into place, but I could see that one of the clips was missing and one of the clear lenses had broken in two. Those extra bits just went in the back seat. Of course, I felt really good about myself at this point. Nice new car, broken bits. Excellent. So that was an interesting trip home, and of course, there’s the inevitable explanation to the longhaired general about how and why something got broken. That went as you would expect. But, I pulled my sleeves up, as I am a serviceman, and something must be able to be done about this! As I mentioned, I’d already popped the coloured plastic housing of the mirror back onto the body. What was missing from that were the clear plastic bits that made up the rest of it. I retrieved them from the back seat to see what damage I’d done. There are two clear pieces; one is thinner and was broken in half. The other was complete, but the concrete pole damaged its end. If I had a 3D printer, I might have been able to make something that would work, but it was apparent that my skills ran out the moment I broke it. On top of all that, the paint on the edge of the mirror had been scraped, and the white undercoat showed through, so at the very least that would have to be sanded and touched up. All in all, this was looking like a ‘too hard basket’ job for me. It’s a shame because the rest of the mirror was fine; the bit under the cover was undamaged, and the guts of it were pristine. There is so much tech in these things. The glass itself has LEDs built into it; cameras, radar sensors, and even the positioning motors and cabling are all packed into the housing somehow. My old Mini’s wing mirror required me to get out in all weathers to adjust it, then get back in the car, then get out again to adjust it further. Half the time I couldn’t see anything in it anyway due to fogging, rain and the wrath of God. Essentially, it was hopeless, but these new ones on modern Australia's electronics magazine August 2025  85 Items Covered This Month • Objects in mirror are closer than they appear • Repairing the cable on a National fan • Fixing a young laser printer • The decorative fix • A voltmeter that only looked perfect 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 cars are something to behold. Except mine, of course, now that it’s broken. Right to replace That’s the thing, though; it isn’t really broken. Sure, a few cosmetic bits are broken, but it could be repaired and repainted. Still, I expect any repairer is just going to take it off and throw it in the skip. It has a few blemishes, but it still works; the radar and cameras in it still operate properly, and I can still see stuff behind me. The problem is that repair guys don’t seem interested in replacing small parts (if they’re even available!) or repainting the housing. They just charge it up to insurance and put on a new one. Everyone in the system is making a killing, except for the poor chump paying their insurance and knocking wing mirrors on concrete poles. A friend of mine has another new Japanese brand car and had a similar incident in his driveway. He went through the same process, and was told it would be at least a month to replace the mirror and would cost the $1500 excess as well. That seemed ridiculous to him, and so he went and took his car to a local body shop, or collision repair centre (whatever they are called these days) and for 50 bucks and a dozen beers, the guys there plastic welded it, resprayed it and refitted it within a day. I couldn’t even tell it had been repaired. So where is all this juicy insurance money going? It seems like a huge rort. But then again, I suppose it always has been. The system is set up to rip money from somewhere. Rants aside, I thought I might go down the same road and went to a local place. I do like to support local businesses, as many locals have supported me over the years. I pulled up into their car park and asked them about the mirror. The guy looked at it and the parts I presented, then hummed and hawed and said it would be cheaper to replace the whole thing. I asked for a breakdown of what it would cost to touch up and cover and replace the plastic lens parts, and he basically said those parts are not available. They’d have to organise a whole new mirror, but not to worry; insurance would cover it. This seems incredibly wasteful, just to throw this monthsold part into the bin (if that’s really what they do with it). So it seems I will be going down the mainstream route and playing into the system. I don’t approve, but in this case there is nothing I can do. I can’t get the parts, I can’t repair what I have due to bits missing and even if I could do it, it would likely look shoddy and vex me for as long as we owned the car. 86 Silicon Chip A wasteful system This reeks of this whole ‘right to repair’ debacle. In the old days, they would simply repair something like this with all their skills and return it to the car, all without creating a mountain of waste. If that ‘old’ mirror doesn’t end up under the bench for spares, where does it go? In a skip and then a landfill? What a waste of resources, with all that tech in it, all for the sake of a few dollars’ worth of plastic parts. I understand these companies don’t want to invest capital into parts only to have them sitting on a shelf somewhere gathering dust, and then when the model involved isn’t about anymore, those components are wasted anyway, selling very rarely. But I am sure there was a law here that any cars sold in this country had to have a 20-year supply of spare parts. That could be just folklore, and any spare parts laws might be legally bent to mean just tyres or complete wing mirrors or even bulbs for the headlights. I recall going to local parts places with dad and asking for a flange valve regulator for a 1959 Standard 10, and the guy would just go to the shelf and get one. Then say, oh, sorry, you want a right-hand one, then go back and get it. I think those days are gone. And that’s a shame. This is exactly the same as computer manufacturers now. The only real parts you can source now are from used models bought by companies who disassemble the machines for parts and sell them on. Unfortunately, in my experience at least, what I get from them is often not what was shown on the website. Long story short, I had to take it in and got a loaner car for a few days while they swapped out the mirror. Of course, it looks exactly the same; we haven’t had it long enough for any sun-faded colour mismatching. Still, the whole experience, from the shame of doing it in the first place and the having to resort to the repair system, gave me some pause for thought. National fan cable repair My wife recently found an old National fan at the local tip shop recently and asked if I wanted to get it. These old fans are very reliable, and I thought it had a very good chance of working, so we did. The only visible problem was that someone had cut the plug off the end of the figure-­ eight power cable. Australia's electronics magazine siliconchip.com.au I knew I had a plug at home that was designed for this type of cable, so we got the fan and headed home. We have several old fans at home that are not in very good cosmetic condition, but they are reliable. Some must be over 50 years old now. The fans available in department stores these days are incredibly unreliable. They have a non-resetting thermal fuse buried deep within the motor windings, so if the fan motor gets too warm, the fuse blows and that’s the end of it. There is no way to repair them, short of replacing the motor, which is not available. They are cheap junk. I couldn’t find the figure-eight plug I knew I had, and decided not to fit a regular plug to the cable, as it would not be secure due to the smaller size of the cable. Instead, I would just replace the cable with one I pulled from another defunct appliance. I found a nice cable with a two-pin plug that matched the fan well. It would look original and better than the old figure-eight cable that the fan came with. The fan’s bottom panel was held on with five screws, one in each of the four rubber feet near the corners and one in the middle of the base. With the screws removed, I set the panel aside. The old cable was secured with a cable clamp and wired into a terminal block. After unscrewing the four screws, I had the old cable free, and I prepared the new cable ready to install. A short time later, I had the new cable installed, replaced the bottom panel, and the fan was ready to use. It worked straight away, so the cut-off plug was the only thing wrong with it. This fan only has two speeds, unlike most, which have three speeds. It’s amazing what shows up at the tip shop from time to time. However, I have found that in more recent times, that there seem to be fewer people throwing things out and more people shopping at the tip shops. This means fewer goodies are available for purchase, although it’s still possible to find a variety of useful items. It’s just a matter of being there at the tight time to nab a bargain. Bruce Pierson, Dundathu, Qld. Servicing Stories Wanted Do you have any good servicing stories that you would like to share in The Serviceman column in SILICON CHIP? If so, why not send those stories in to us? It doesn’t matter what the story is about as long as it’s in some way related to the electronics or electrical industries, to computers or even to cars and similar. We pay for all contributions published but please note that your material must be original. Send your contribution by email to: editor<at>siliconchip.com.au Please be sure to include your full name and address details. purchase. There was a CD-ROM used to install it, which I had forgotten about, so I immediately inserted it to reinstall the drivers. It also checked for updated firmware, but the updates made no difference; the Brother printer continued refusing to print. I checked the print queue after trying to print documents and also several test prints, but there was nothing in the print queue. So it would appear that the data flowing from the computer was not being processed because of some fault at the receiving end. The disc supplied had an easy setup for wireless printing so I figured that if I could re-route the data via wireless, I could bypass the input from the USB cable and establish that the printer was functioning and maybe able print pages wirelessly. After going through the time-consuming setup and having to restart everything, including the household server, a page was finally printed successfully, but it was not the end of the problem! When I tested a photo or graph, I got nothing, or sometimes a fraction of a printed page and it took forever to print just a letter. Brother HL-L3230CDW laser printer repair Normally, this is a very reliable printer. In fact, it is the best colour laser printer I have owned. After only about two years of use, I was shocked to get a weird message and a failure to print. Every time I pressed “print”, the printer lit up the green “data” LED, but after about 10 seconds, the yellow “error” light began to flash. Then it just stopped and showed “ready” on the LCD panel. Checking all the connections and restarting both the printer and computer changed nothing. The troubleshooting option on Windows 10 printers and scanners proved worthless. I checked on the Brother website and downloaded the updates, but still no cigar! So I brought in the previous colour laser printer, an HP CP1025nw, which I had stored in the large Brother cardboard box to keep it in good condition to use as a backup. It was retired in good condition and with plenty of ink, but it was a bit slower than the Brother and sometimes had problems grabbing paper when I was doing big runs for my labels. When I lifted the box down, apart from a huge friendly Huntsman spider that jumped out, I noticed that the Brother box had a picture of the items included with the siliconchip.com.au Australia's electronics magazine August 2025  87 Silicon Chip kcaBBack Issues $10.00 + post $11.50 + post $12.50 + post $13.00 + post January 1997 to October 2021 November 2021 to September 2023 October 2023 to September 2024 October 2024 onwards All back issues after February 2015 are in stock, while most from January 1997 to December 2014 are available. For a full list of all available issues, visit: siliconchip.com.au/Shop/2 PDF versions are available for all issues at siliconchip.com.au/Shop/12 We also sell photocopies of individual articles for those who don’t have a computer As luck would have it, I accidentally pressed “print” via the USB connection and bingo! It printed OK. I was just about to pack up the backup printer back into its snug box when I noticed that a document failed to print and I got the same error message as I received on day one. Why? Checking the cable connections again, I noticed that the particular cable I was using looked a bit old and had square and faded plugs at both ends, so I thought it was a good idea to replace it. Everything then worked perfectly! Replacing the old cable, the fault returned. How could I have not done this before? I think it is a lesson that we think that USB cables are bulletproof, even though we jerk them in and out and stretch them when we move computers and printers around. My daughter has wrecked so many chargers by pulling USB connectors out at funny angles, and so it seems my printer cable that had been used for years on five or six different printers ultimately suffered the same fate. My initial analysis of the situation removed any thoughts about a simple cable, because my previous experience was that computers have computer problems and printers have printer problems and the humble USB cable was too humble to worry about! These days, when you buy a new printer, the USB cable is rarely included. I think in future I will buy brand new ones instead of cheap old ones from op shops! Allan Linton-Smith, Turramurra, NSW. Decorative village repair A friend asked me if I could look at a family heirloom that stopped working. It is a ‘village’ house with many decorative lights. A light source shines through a colour wheel driven by a 12V AC motor. The light is diffused onto many fibre light pipes scattered throughout the display. It’s simple and effective. Someone in the past had ‘fixed’ it by shoehorning a 20W halogen lamp into the house; the original lamp was an 8W MR8 halogen lamp, with it and the motor powered by a 12V AC 1.25A plugpack. The overloaded plug pack eventually failed. AC plugpacks are not very common, and halogen lamps were phased out years ago! After many phone calls, then 45km of suburban traffic, I sourced both original rated items from two widely spaced dealers who had old supplies. The lamp was the MR11 size and would fit OK. Later, I sourced an MR11 LED replacement lamp from Bunnings and fitted a diode in series with it (hidden inside a red sleeve) to convert the AC to DC. The diode also reduces the power to the lamp for a longer life with little effect on the light output for the display. A good deed by the non-technical resulted in hours of time and parts to repair! Victor Duffey, Rosanna, Vic. HP410C voltmeter repair I am an avid collector of old HP and Tektronix test equipment, so when a friend offered me their HP410C in exchange for some Marconi RF coil standards, I jumped at the deal. It was in fantastic physical condition, but had some problems that deserved my ministrations... Firstly, it was inaccurate; the meter reading was either too low or too high depending on what range I set it to. I tried a quick calibration, which highlighted the many problems that I was about to find. One of the main PSU capacitors was bad. It was a rather large 2400μF 20V part. I replaced it with a 4700μF Kemet electrolytic capacitor, which mounted on one of my oval capacitor adaptor PCBs for retro work, as the original ‘big can’ type is not cheaply available anymore. This capacitor filters the 6V rail that supplies the heater to the probe valve diode, among other things. At this stage, I discovered the big T03 germanium series pass transistor was worn out to the point that it measured as two leaky diodes! Luckily, Rockby had 2N1544s on sale a while ago, which turned out to be the exact equivalent of the original Motorola 1850-0098 PNP germanium transistor. Shown at left is the decorative village, and the original MR8 lamp is visible in the adjacent photo. 88 Silicon Chip Australia's electronics magazine siliconchip.com.au The last part I replaced in the PSU was a 38V zener diode which decided to avalanche at 32V these days (I guess 50 years is a bit much to ask). At this point, I thought I was really getting somewhere. However, there were three other problems. The first was simple: a 100W resistor at the AC probe telephone-style plug that sits across the heater rail was burnt out and making intermittent contact, causing the needle to behave erratically when measuring AC voltages. When this was replaced, the 410C settled down nicely. Next, FSD (full-scale deflection) on the lowest of the three ranges was impossible to get right. I found a 6MW resistor with a tolerance of 0.5% on the attenuator switch that was reading 6.3MW. Luckily, I had a junk 410C with one that was OK, as I don’t think a 6MW resistor was in my parts box. Now I was getting really close, but the most interesting repair was to come! The final hurdle was the moving meter itself. As some people know, HP eventually made their own meters, and they were individually calibrated by having someone print the label on each and every face when testing the meter movement. This incredible feat of engineering, combined with the taut-band movement, made HP simply the best money could buy; even AVO meters didn’t come close, as they just selected from several differently scaled faces to ‘best suit’ the chosen movement. This meter had lost magnetism in the ‘permanent’ magnet. When I should have gotten an FSD reading at 1mA, I only received about 85% of full scale. Due to this, and possible slackening of the taut band, the other readings were well off. So there was no way to make it work by calibrating the 410C to this particular meter movement. I decided to have a go at re-magnetising the meter. I carefully disassembled the inner workings of the moving coil meter and removed the magnetic core. I wound this with several turns of thick multi-strand wire and then shorted this across a large 12V AGM battery. However, that was not enough to make an improvement. I went for broke and got a second 12V AGM battery and put them in series for 24V DC at considerable current; I estimate that the surges were over 100A! This had the desired effect, and the permanent magnet was now strong enough to make the needle read FSD <at> 1mA. There was still the small detail of the meter now being different enough to not line up with the previous graduation markings. I decided to calibrate this in a similar way to the HP of old by connecting my current calibrator to the meter and running it at 0.1mA, 0.2mA, 0.3mA all the way to 1mA. At each point, I marked the meter face to show where the graduations should be. I handed this to a friend who knows far more about vector diagrams than myself; he created a new meter scale to accurately reflect the current calibration of the meter. This was printed on a quality vinyl sticker and placed over the original face. After that, the calibration went smoothly, with all attenuation scales are bang-on, and the unit cleaned up like new. Yes, it was a lot of work, but very interesting at the same time. It’s quite satisfying to have repaired a classic and still very usable meter. SC Deon Vandenberg, Torquay, Qld. siliconchip.com.au Australia's electronics magazine August 2025  89 SOnline ilicon Chip Shop Kits, parts and much more www.siliconchip.com.au/Shop/ Rotating Lights April 2025 Dual Mini LED Dice August 2024 USB Power Adaptors May 2025 SMD LED Complete Kit SC7462: $20 TH LED Complete Kit SC7463: $20 SMD LED Complete Kit SC6961: $17.50 TH LED Complete Kit SC6849: $17.50 siliconchip.au/Article/16418 siliconchip.au/Article/18112 This kit includes everything needed to build the Rotating Light for Models, except for a power supply and wire. Includes either 3mm through-hole or 1206sized SMD LEDs. Choice of either white or black PCB. CR2032 coin cell not included. You can choose from one of four USB sockets (USB-C power only, USB-C power+data, mini-B or micro-B). The kit includes all other parts. siliconchip.au/Article/17930 Compact HiFi Headphone Amplifier Complete Kit SC6885: $70 Complete Kit with choice of USB socket SC7433: $10 Capacitor Discharger December 2024 December 2024 & January 2025 siliconchip.au/Series/432 This kit includes everything required to build the Compact HiFi Headphone Amplifier. The case is included, but you will need your own power supply. Programmable Frequency Divider Complete Kit SC6959: $60 Feb25: siliconchip.au/Article/17733 Includes all onboard components, except for a power supply and the optional programming header. Short-Form Kit SC7404: $30 siliconchip.au/Article/17310 Includes the PCB, resistors, semis, mounting hardware and banana sockets. Case, heatsink, thermal switch and wiring are not supplied. → Subscribers receive a 10% discount on all purchases, except for subscriptions (postage is not discounted). → Prices listed do not include postage. Postage rates within Australia start at $12, rates are calculated at the checkout. Vintage Radio Silvertone Model 18 AM/FM mantel radio from 1952 The Silvertone model 18 is an excellent example of a 1952 US radio. The plastic case shows some heritage from the Bakelite era. From left-toright, the knob controls are for volume, AM-FM selection and tuning. By Associate Professor Graham Parslow M any Bakelite radios of similar appearance were made in the 1940s. However, thermo-mouldable plastics, which were new in the early 1950s, were significantly cheaper and faster to produce. The old celluloid dial covers that degraded to become brittle and opaque were replaced by clear polystyrene that is naturally transparent. One downside to polystyrene is that organic solvents, including acetone, can degrade the surface, leaving permanent splotches. The dial cover on this radio is in excellent condition after seven decades. Brass and gold-tone features were common on US radios at this time, as embodied by the dial cursor, the stylistic “S” and the knobs. US dials were calibrated by frequency, not call signs, due to the sheer number of stations that would clutter the dial. Transmissions at the same frequency should not be offered as the reason. There is no problem with putting multiple stations at the same frequency on the dial because they would be at considerable geographical separation. Silvertone is a house brand This label attached to the interior of the Silvertone 18 case has company information, the serial number and some basic servicing guidelines for the set. siliconchip.com.au Australia's electronics magazine The label glued to the bottom identifies the radio as Silvertone catalog number 18, October 1952. The list price was US$37.95. Sears, Roebuck and Co is an American chain of department stores founded in 1892 by Richard Sears and Alvah Roebuck. The company began as a mail-order catalogue company, progressing to retail locations from 1925, beginning in Chicago. The 110-storey Sears Tower in Chicago (now known as the Willis Tower) was the tallest in the world in 1974. Sears filed for Chapter 11 bankruptcy in October 2018, but a restructure allowed them to continue trading at a reduced scale. August 2025  91 Fig.1: the FM tuner is across the top of the circuit diagram, with the AM section below it and the power supply at lower middle. A 3PDT switch selects between FM and AM modes; it also switches valve V4 so that it operates as an FM IF amplifier in FM mode and an AM IF amplifier in AM mode. Capacitor C38 allows the mains cord to operate as an FM antenna for strong stations. Sears and Roebuck had used the Silvertone brand going back to the 1930s. Howard W. Sams & Co were the radio manufacturers in this case. Likewise, in Australia, Myer stores contracted manufacturers of convenience to produce the in-house Aristone branded radios. Commendably, this radio has the circuit pasted onto the side of the 92 Silicon Chip case. The service notes provided by the manufacturer can be downloaded from siliconchip.au/link/ac1x From the ten pages of impressively detailed service notes, one page is shown here that itemises components on the top of the chassis. The photo of the top of the chassis also shown overleaf shows the tuning capacitor shield in place. Australia's electronics magazine Another page of the documentation shows the itemisation of components beneath the chassis. I have not seen documentation from any Australian radio manufacturer of the period as comprehensive as this. The history of FM radio in the United States Edwin Armstrong (born December siliconchip.com.au 18, 1890) served with the US army in France during WW1. During this period, he developed the superheterodyne receiver system. The superheterodyne radio shifts the high-­ frequency radio signal of interest to a lower ‘intermediate’ frequency. The original aim was to get the frequency down to a range better suited to amplification by early triode valves. siliconchip.com.au It had the serendipitous effect of achieving precise tuning at the broadcast frequency, that otherwise needed a cascade of tuned circuits (called TRF circuits, TRF standing for tuned radio frequency). In this radio’s circuit (Fig.1), that mixing is performed by ‘converter’ valve V3 (a 6BE6 heptode). It has two control grids, one connected to pin 1 Australia's electronics magazine and one at pin 7. The incoming signal, tuned by variable capacitor A6 and the secondary of transformer L8, is applied to pin 7. At the same time, a transformer-­ coupled oscillator circuit, developed by Armstrong and named after him, acts as the local oscillator, which tracks at a higher frequency than the tuned signal (a fixed interval above). August 2025  93 The oscillator is formed by transformer L9 and tuning capacitor A5, and its output is applied to the control grid at pin 1. Feedback to maintain oscillation comes from the valve’s cathode, at pin 2. The alternative Hartley oscillator is cheaper, using a coil with only one tapped winding, but the Armstrong oscillator has proved highly reliable and is more commonly chosen. The output at the anode (pin 5) contains the amplified RF signal, oscillator signal, plus their sum and difference products. It is the difference product, at the intermediate frequency, that passes through the following tuned stages to ultimately be demodulated to produce audio. Introducing FM radio Armstrong began developing FM (frequency modulation) based radio in 1928, and argued strenuously for its adoption to replace AM. The time was not ripe, and early attempts to commercialise FM in 1941 in the USA faltered, in part due to allocating only 40 channels spanning 42–50MHz. In 1945, the FM band was reassigned to 88–106MHz. By 1952, limited FM stations were transmitting, so most buyers would pick a cheaper AM-only radio. Stereo FM broadcasting in the US took off in the 1960s, and by the 1970s became the dominant music source, relegating many AM stations to talk-only programs. FM has the virtue of rejecting the majority of the electromagnetic interference (EMI) that plays havoc with AM transmissions. As a result, the signal-­to-noise ratios are far superior to AM. Another virtue is high fidelity, transmitting the full range of human hearing, due in part to greater frequency separation between stations. Unfortunately, the 5-inch (127mm) speaker in this radio does little justice to the potential for high fidelity. Power supply The top view of the Silvertone 18 chassis and a matching diagram which has every component (on this side) labelled. Note the large tuning capacitor shield, which was removed in the diagram. 94 Silicon Chip Australia's electronics magazine US radios of the period were commonly transformerless, using serieswired valve heaters with the high-­ tension rectified directly from the mains. Mains-direct radios are hazardous to work with, particular if an auto-transformer (variac) is used. Happily, this radio uses a transformer to interface with the US mains that is nominally 117V. This radio was restored using a step-down transformer. Fortunately, the transformer on this radio was substantial enough to not heat up excessively with a 50Hz source rather than 60Hz. The mains supply in the USA is nominally 110120V at 60Hz. 220-240V is also available for larger appliances, due to there being two out-ofphase 110-120V conductors in the grid. Because of the lower frequency of our mains, even if the voltage is adapted using a step-down transformer, some US equipment will not be happy running at 50Hz. There is typically less iron in their transformer cores, as less is required given the higher operating frequency. siliconchip.com.au They can therefore saturate at lower than expected currents and overheat when running from 50Hz mains. Thankfully, the transformer in this set seems to have a generous core and that did not appear to be a problem during my testing, with the transformer remaining cool. The rear of the radio shows the AM loop antenna with a threescrew connection strip below. The connections are for an external AM antenna, external FM antenna and Earth. In my location, the loop antenna was all that was needed for AM. The AM receiver The tuning capacitor, designated A6, tunes from 540kHz to 1600kHz, while tuning capacitor A5 tunes the oscillator from 995kHz to 2055kHz to generate a 455KHz intermediate frequency (IF). As mentioned earlier, the IF signal emanates from the anode of the 6BE6 mixer valve (V3). The first IF transformer is A3/A4 (L12), delivering the IF signal to V4, a 6BA6 IF amplifier. The second IF transformer, A1/A2 (L14), passes its output to detector valve V6, a 6T8. When the switch is set to AM, detected audio passes via L14 to the volume control potentiometer, R1. The dial for this radio is printed onto a metal sheet, and is in excellent condition given its age. The FM receiver The FM section can work on high signal stations without an external aerial due to coupling the RF input to the mains lead via 100pF capacitor C38 (ie, the mains lead acts as an antenna if the station is strong enough). The untuned RF signal is amplified by V1, a 6BA6. The desired signal in the 88-108MHz band is tuned by variable capacitor A13 and heterodyned with the output from the oscillator, tuned by A12 and L6. The intermediate frequency is 10.7MHz, so the oscillator tracks 10.7MHz above the tuned RF signal. The first half of the 12AT7 (V2) is the converter, with the RF signal fed to the grid (pin 1). The same grid receives local oscillator input generated by the A12 cluster on the circuit diagram. The second half of the 12AT7 is an IF amplifier. V4 is an additional IF amplifier that does double service as an AM IF amplifier, depending on the band that is selected. The 6BA6 designated V5 is another IF amplifier. V6, the 6T8 ratio siliconchip.com.au The back view of the chassis shows the loop antenna and the external antenna terminal (the yellow wire). The second terminal is for an optional FM antenna and the third is Earth. detector, generates detected audio at R21 that passes via the FM selector switch to the volume control pot, R1. A ratio detector has two diodes conducting in opposite directions connected to a centre-tapped transformer secondary. In this case, both diodes are within a single envelope (V6). Ratio detectors have the significant advantage for FM demodulation that they do not respond to AM signals, making them more resistant to interference. Australia's electronics magazine If this was a full-wave rectifier, the output would be one polarity, but a ratio detector passes positive signals at one diode and negative at the other. The output is the sum of the diode voltages and the centre tap voltage. The output signal from across the diodes is filtered by a high-value capacitor, C3 (4µF) in this radio. It is bled to Earth by R20 (1.5kW). The combination of the capacitor’s opposition to voltage changes August 2025  95 The other two 6BA6s also measured as open circuits on their heaters. Previously swapping 6BA6s within the radio had done nothing; it now became clear why. It was shades of the movie True Lies – they were all bad! Inserting two replacement 6BA6 valves into the FM section instantly produced FM reception. Why would three identical valves all fail? My best guess is that some transient surge blew the most vulnerable heater filaments in the 6.3V AC line. Perhaps someone connected the radio to 230-240V. There was a crack in the case that was repaired using two-part epoxy car filler. This photo was taken before the epoxy was refined using an angle grinder. and the resistive loading produces a nearly constant amplitude for the output. This action gives FM its superior immunity to electrical interference. The set applies AGC for AM operation as usual, but it also applies AGC in FM operation. FM usually relies on the last IF stage being driven into overdrive and acting as a limiter to deliver a constant-amplitude signal to the ratio detector. The use of AGC implies that the last stage does not provide limiting for all FM signal levels, so it needs the AGC to provide the same volume for all stations. For FM, the audio output is converted to a DC level by 220kW resistor R23 and 5mF capacitor C17 and is used to bias the input signal and the signal applied to the first IF amplifier, V4. That path is disabled when V4 is used as an AM IF amp. (the final working power was 49W). So something was not drawing (enough) power. Valve V4 (6BA6) is common to both the AM and FM functions. With AM selected, injecting a 400Hz-modulated signal at the IF frequency of 455kHz to the grid produced nothing. However, a signal to the anode passed through as 400Hz audio. So it was a matter of working backwards to find the fault. Fortunately, it soon became evident what the problem was. V4’s 10kW screen resistor had 0V across it, as did its 68W cathode resistor. Everything indicated a non-­ conductive valve V4. This is classic for a non-functional cathode heater. Sure enough, its heater pins 3 and 4 were open-circuit. Replacing V4 from my stock got the AM function working, but not FM. Case restoration Examination of the crack at the bottom of the right-hand side revealed that a substantial chunk was missing. I fixed this gap using two-part epoxy car filler. To achieve this, I covered a section of aluminium sheet with a 90° flange in masking tape to make removal of the former easy after the epoxy had set. I laid the radio on its side and filled the gap coarsely with epoxy. The external surface of the radio had the epoxy set flat by conforming to the former. Once it had hardened, I used an angle grinder to profile the inside to size. I then painted over the pink epoxy with satin black paint, and it effectively disappeared. Conclusion The Silvertone 18 is a high-quality set with good performance. Its style is of its time, but offering FM was defiSC nitely ahead of its time. All three 6BA6s in the set had opencircuit heaters. Replacing them was all I had to do to get the set working. The audio section After the volume control, a 6T8 triode acts as a preamplifier for the 6V6 beam tetrode, V7. This 6T8 triode is actually part of V6; the 6T8 encapsulates one triode and three diodes. The 5-inch (127mm) speaker has an impedance of 3.5W. There is no negative feedback from the speaker transformer secondary, so the distortion due to the transformer is not reduced. Electrical restoration When I got it, the radio was dead. I ruled out the usual causes of complete failure in my preliminary assessment. The AM/FM switch checked out OK and the audio circuitry worked from the slider on the volume pot. The valves were all well-seated and HT was good at 201V/182V across the π filter. The initial power draw was 39W 96 Silicon Chip Australia's electronics magazine siliconchip.com.au R&S®ZNB3000 Vector Network Analyzer FAST FORWARD TO RESULTS The R&S®ZNB3000 is the instrument you need for RF component production. This latest addition to the Rohde & Schwarz network analyzer portfolio offers best-in-class RF performance, combining high measurement accuracy with exceptional speed. With its high throughput rate, it is especially suitable for high-volume production and short ramp-up time environments. For more information visit: www.rohde-schwarz.com/solution/ZNB3000 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. 08/25 YES! You can also order or renew your Silicon Chip subscription via any of these methods as well! The best benefit, apart from the magazine? Subscribers get a 10% discount on all orders for parts. PRE-PROGRAMMED MICROS For a complete list, go to siliconchip.com.au/Shop/9 $10 MICROS $15 MICROS ATmega328P ATtiny45-20PU PIC10LF322-I/OT PIC12F617-I/P 110dB RF Attenuator (Jul22), Basic RF Signal Generator (Jun23) 2m VHF CW/FM Test Generator (Oct23) Range Extender IR-to-UHF (Jan22) Active Mains Soft Starter (Feb23), Model Railway Uncoupler (Jul23) Battery-Powered Model Railway Transmitter (Jan25) PIC12F675-I/P Train Chuff Sound Generator (Oct22) 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) PIC16F1455-I/SL Battery Multi Logger (Feb21), USB-C Serial Adaptor (Jun24) Battery-Powered Model Railway SMD Receiver (Jan25) USB Programmable Frequency Divider (Feb25) 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) PIC16F1459-I/SO Multimeter Calibrator (Jul22), Buck/Boost Charger Adaptor (Oct22) PIC16F15214-I/SN Silicon Chirp Cricket (Apr23), Mic The Mouse (Aug25) PIC16F15214-I/P Filament Dryer (Oct24), Tool Safety Timer (May25) PIC16F15224-I/SL Multi-Channel Volume Control (OLED Module; Dec23) NFC IR Keyfob Transmitter (Feb25), Rotating Light (Apr25) PIC16F18146-I/SO Compact OLED Clock & Timer (Sep24), Flexidice (Nov24) Versatile Battery Checker (May25), RGB LED ‘Analog’ Clock (May25) USB-C Power Monitor (Aug25) PIC16LF15323-I/SL Remote Mains Switch (TX, Jul22), Secure Remote Switch (TX, Dec23) STM32G030K6T6 Variable Speed Drive Mk2 (Nov24) W27C020 Noughts & Crosses Computer (Jan23) ATSAML10E16A-AUT PIC16F1847-I/P PIC16F18877-I/PT High-Current Battery Balancer (Mar21) 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 Wii Nunchuk RGB Light Driver (Mar24) AM-FM DDS Signal Generator (May22) Power LCR Meter (Mar25) $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 MIC THE MOUSE KIT (SC7508) (AUG 25) RP2350B DEVELOPMENT BOARD (AUG 25) USB-C POWER MONITOR KIT (SC7489) (AUG 25) 433MHz RECEIVER KIT (SC7447) (JUN 25) VERSATILE BATTERY CHECKER KIT (SC7465) (MAY 25) RGB LED ‘ANALOG’ CLOCK KIT (SC7416) (MAY 25) USB POWER ADAPTOR COMPLETE KIT (SC7433) (MAY 25) Includes all parts except a CR2032 cell (see p64, Aug25) 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) Includes all non-optional parts except the case, cell & glue (see p39, Aug25) 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) $37.50 $60.00 $20.00 $65.00 Includes everything in the parts list and a choice of one USB socket: USB-C power only; USB-C power+data; Type-B mini; or Type-B micro (see p80, May25) $10.00 (APR 25) Includes an assembled PCB, separate Raspberry Pi Pico 2 and front/rear panels $120.00 ROTATING LIGHT FOR MODELS KIT (APR 25) Complete kit which includes the PCB and all onboard components (see p60, Apr25): - SMD LEDs (SC7462) $20.00 - Through-hole LEDs (SC7463) $20.00 433MHz TRANSMITTER KIT (SC7430) Includes the PCB and all onboard parts (see p75, Apr25) PICO 2 AUDIO ANALYSER SHORT-FORM KIT (SC6772) (APR 25) (MAR 25) The Pico Audio Analyser kit from Nov23, but with an unprogrammed Pico 2 USB PROGRAMMABLE FREQUENCY DIVIDER (SC6959) (FEB 25) NFC PROGRAMMABLE IR KEYFOB (SC7421) (FEB 25) CAPACITOR DISCHARGER KIT (SC7404) (DEC 24) PICO COMPUTER (DEC 24) FLEXIDICE COMPLETE KIT (SC7361) (NOV 24) MICROMITE EXPLORE-40 KIT (SC6991) (OCT 24) DUAL-RAIL LOAD PROTECTOR (SC7366) (OCT 24) PicoMSA PARTS (SC7323) (SEP 24) COMPACT OLED CLOCK & TIMER KIT (SC6979) (SEP 24) Complete kit: includes all components (see p85, Feb25) $60.00 Complete kit: includes all required items, except the cell (see p67, Feb25) $25.00 $30.00 (DEC 24) $1.00ea COMPACT HIFI HEADPHONE AMP (SC6885) Complete kit: includes everything except the power supply (see p47, Dec24) $70.00 $5.00 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 PICO/2/COMPUTER (SC7468) siliconchip.com.au/Shop/ $20.00 $50.00 Includes the PCB and all components that mount on it, the mounting hardware (without heatsink) and banana sockets (see p36, Dec24) $30.00 For full functionality both the Pico Computer Board and Digital Video Terminal kits are required. Items shown unbolded are optional (see p71, Dec24) - Pico Computer Board kit (SC7374) $40.00 - Pico Digital Video Terminal kit (SC6917) $65.00 - PWM Audio Module kit (SC7376) $10.00 - ESP-PSRAM64H 64Mb SPI PSRAM chip (SC7377) $5.00 - DS3231 real-time clock SOIC-16 IC (SC5103) $7.50 - DS3231MZ real-time clock SOIC-8 IC (SC5779) $10.00 Includes all required parts except the coin cell (see p71, Nov24) Includes all required parts (see p83, Oct24) Hard-to-get parts: includes the PCB and all semiconductors except the optional/variable diodes (see p73, Oct24) Hard-to-get parts: includes the PCB, Raspberry Pi Pico (unprogrammed), plus all semiconductors, capacitors and resistors (see p63, Sep24) Includes everything except the case & Li-ion cell (see p34, Sep24) *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. $30.00 $35.00 $35.00 $50.00 $45.00 PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT Q METER MAIN PCB ↳ FRONT PANEL (BLACK) NOUGHTS & CROSSES COMPUTER GAME BOARD ↳ COMPUTE BOARD ADVANCED SMD TEST TWEEZERS SET DIGITAL VOLUME CONTROL POT (SMD VERSION) ↳ THROUGH-HOLE VERSION MODEL RAILWAY TURNTABLE CONTROL PCB ↳ CONTACT PCB (GOLD-PLATED) WIDEBAND FUEL MIXTURE DISPLAY (BLUE) TEST BENCH SWISS ARMY KNIFE (BLUE) SILICON CHIRP CRICKET GPS DISCIPLINED OSCILLATOR SONGBIRD (RED, GREEN, PURPLE or YELLOW) DUAL RF AMPLIFIER (GREEN or BLUE) LOUDSPEAKER TESTING JIG BASIC RF SIGNAL GENERATOR (AD9834) ↳ FRONT PANEL V6295 VIBRATOR REPLACEMENT PCB SET DYNAMIC RFID / NFC TAG (SMALL, PURPLE) ↳ NFC TAG (LARGE, BLACK) RECIPROCAL FREQUENCY COUNTER MAIN PCB ↳ FRONT PANEL (BLACK) PI PICO-BASED THERMAL CAMERA MODEL RAILWAY UNCOUPLER MOSFET VIBRATOR REPLACEMENT ARDUINO ESR METER (STANDALONE VERSION) ↳ COMBINED VERSION WITH LC METER WATERING SYSTEM CONTROLLER CALIBRATED MEASUREMENT MICROPHONE (SMD) ↳ THROUGH-HOLE VERSION SALAD BOWL SPEAKER CROSSOVER PIC PROGRAMMING ADAPTOR REVISED 30V 2A BENCH SUPPLY MAIN PCB ↳ FRONT PANEL CONTROL PCB ↳ VOLTAGE INVERTER / DOUBLER 2M VHF CW/FM TEST GENERATOR TQFP-32 PROGRAMMING ADAPTOR ↳ TQFP-44 ↳ TQFP-48 ↳ TQFP-64 K-TYPE THERMOMETER / THERMOSTAT (SET; RED) MODEM / ROUTER WATCHDOG (BLUE) DISCRETE MICROAMP LED FLASHER MAGNETIC LEVITATION DEMONSTRATION MULTI-CHANNEL VOLUME CONTROL: VOLUME PCB ↳ CONTROL PCB ↳ OLED PCB SECURE REMOTE SWITCH RECEIVER ↳ TRANSMITTER (MODULE VERSION) ↳ TRANSMITTER (DISCRETE VERSION COIN CELL EMULATOR (BLACK) IDEAL BRIDGE RECTIFIER, 28mm SQUARE SPADE ↳ 21mm SQUARE PIN ↳ 5mm PITCH SIL ↳ MINI SOT-23 ↳ STANDALONE D2PAK SMD ↳ STANDALONE TO-220 (70μm COPPER) RASPBERRY PI CLOCK RADIO MAIN PCB ↳ DISPLAY PCB KEYBOARD ADAPTOR (VGA PICOMITE) ↳ PS2X2PICO VERSION MICROPHONE PREAMPLIFIER ↳ EMBEDDED VERSION RAILWAY POINTS CONTROLLER TRANSMITTER ↳ RECEIVER LASER COMMUNICATOR TRANSMITTER ↳ RECEIVER 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 DATE JAN23 JAN23 JAN23 JAN23 FEB23 MAR23 MAR23 MAR23 MAR23 APR23 APR23 APR23 MAY23 MAY23 MAY23 JUN23 JUN23 JUN23 JUN23 JUL23 JUL23 JUL23 JUL23 JUL23 JUL23 JUL23 AUG23 AUG23 AUG23 AUG23 AUG23 SEP23 SEP23 SEP23 OCT22 SEP23 OCT23 OCT23 OCT23 OCT23 OCT23 NOV23 NOV23 NOV23 NOV23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 JAN24 JAN24 JAN24 JAN24 FEB24 FEB24 FEB24 FEB24 MAR24 MAR24 MAR24 MAR24 MAR24 MAR24 MAR24 PCB CODE CSE220701 CSE220704 08111221 08111222 SC6658 01101231 01101232 09103231 09103232 05104231 04110221 08101231 04103231 08103231 CSE220602A 04106231 CSE221001 CSE220902B 18105231/2 06101231 06101232 CSE230101C CSE230102 04105231 09105231 18106231 04106181 04106182 15110231 01108231 01108232 01109231 24105231 04105223 04105222 04107222 06107231 24108231 24108232 24108233 24108234 04108231/2 10111231 SC6868 SC6866 01111221 01111222 01111223 10109231 10109232 10109233 18101231 18101241 18101242 18101243 18101244 18101245 18101246 19101241 19101242 07111231 07111232 01110231 01110232 09101241 09101242 16102241 16102242 07112231 07112232 07112233 SC6903 SC6904 Price $5.00 $5.00 $12.50 $12.50 $10.00 $2.50 $5.00 $5.00 $10.00 $10.00 $10.00 $5.00 $5.00 $4.00 $2.50 $12.50 $5.00 $5.00 $5.00 $1.50 $4.00 $5.00 $5.00 $5.00 $2.50 $2.50 $5.00 $7.50 $12.50 $2.50 $2.50 $10.00 $5.00 $10.00 $2.50 $2.50 $5.00 $5.00 $5.00 $5.00 $5.00 $10.00 $2.50 $2.50 $5.00 $5.00 $5.00 $3.00 $5.00 $2.50 $2.50 $5.00 $2.00 $2.00 $2.00 $1.00 $3.00 $5.00 $12.50 $7.50 $2.50 $2.50 $7.50 $7.50 $5.00 $2.50 $5.00 $2.50 $5.00 $2.50 $2.50 $20.00 $7.50 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT 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) ↳ STANDALONE VERSION DUAL MINI LED DICE (THROUGH-HOLE LEDs) ↳ SMD LEDs GUITAR PICKGUARD (FENDER JAZZ BASS) ↳ J&D T-STYLE BASS ↳ MUSIC MAN STINGRAY BASS ↳ FENDER TELECASTER COMPACT OLED CLOCK & TIMER USB MIXED-SIGNAL LOGIC ANALYSER (PicoMSA) DISCRETE IDEAL BRIDGE RECTIFIER (TH) ↳ SMD VERSION MICROMITE EXPLORE-40 (BLUE) PICO BACKPACK AUDIO BREAKOUT (with conns.) 8-CHANNEL LEARNING IR REMOTE (BLUE) 3D PRINTER FILAMENT DRYER DUAL-RAIL LOAD PROTECTOR VARIABLE SPEED DRIVE Mk2 (BLACK) FLEXIDICE (RED, PAIR OF PCBs) SURF SOUND SIMULATOR (BLUE) COMPACT HIFI HEADPHONE AMP (BLUE) CAPACITOR DISCHARGER PICO COMPUTER ↳ FRONT PANEL (BLACK) ↳ PWM AUDIO MODULE DIGITAL CAPACITANCE METER BATTERY MODEL RAILWAY TRANSMITTER ↳ THROUGH-HOLE (TH) RECEIVER ↳ SMD RECEIVER ↳ CHARGER 5MHZ 40A CURRENT PROBE (BLACK) USB PROGRAMMABLE FREQUENCY DIVIDER HIGH-BANDWIDTH DIFFERENTIAL PROBE NFC IR KEYFOB TRANSMITTER POWER LCR METER WAVEFORM GENERATOR PICO 2 AUDIO ANALYSER (BLACK) PICO/2/COMPUTER ↳ FRONT & REAR PANELS (BLACK) ROTATING LIGHT (BLACK) 433MHZ TRANSMITTER VERSATILE BATTERY CHECKER ↳ FRONT PANEL (BLACK, 0.8mm) TOOL SAFETY TIMER RGB LED ANALOG CLOCK (BLACK) USB POWER ADAPTOR (BLACK, 1mm) HWS SOLAR DIVERTER PCB & INSULATING PANELS SSB SHORTWAVE RECEIVER PCB SET ↳ FRONT PANEL (BLACK) 433MHz RECEIVER SMARTPROBE ↳ SWD PROGRAMMING ADAPTOR DATE MAR24 APR24 APR24 APR24 MAY24 MAY24 MAY24 JUN24 JUN24 JUN24 JUN24 JUN24 JUL24 JUL24 JUL24 AUG24 AUG24 AUG24 AUG24 SEP24 SEP24 SEP24 SEP24 SEP24 SEP24 SEP24 SEP24 OCT24 OCT24 OCT24 OCT24 OCT24 NOV24 NOV24 NOV24 DEC24 DEC24 DEC24 DEC24 DEC24 JAN25 JAN25 JAN25 JAN25 JAN25 JAN25 FEB25 FEB25 FEB25 MAR25 MAR25 MAR25 APR25 APR25 APR25 APR25 MAY25 MAY25 MAY25 MAY25 MAY25 JUN25 JUN25 JUN25 JUN25 JUL25 JUL25 PCB CODE Price 16103241 $20.00 08101241 $15.00 08104241 $10.00 07102241 $5.00 04104241 $10.00 04112231 $2.50 10104241 $5.00 SC6963 $10.00 08106241 $2.50 08106242 $2.50 08106243 $2.50 24106241 $2.50 CSE240203A $5.00 CSE240204A $5.00 11104241 $15.00 23106241 $10.00 23106242 $12.50 08103241 $2.50 08103242 $2.50 23109241 $10.00 23109242 $10.00 23109243 $10.00 23109244 $5.00 19101231 $5.00 04109241 $7.50 18108241 $5.00 18108242 $2.50 07106241 $2.50 07101222 $2.50 15108241 $7.50 28110241 $7.50 18109241 $5.00 11111241 $15.00 08107241/2 $5.00 01111241 $10.00 01103241 $7.50 9047-01 $5.00 07112234 $5.00 07112235 $2.50 07112238 $2.50 04111241 $5.00 09110241 $2.50 09110242 $2.50 09110243 $2.50 09110244 $2.50 9049-01 $5.00 04108241 $5.00 9015-D $5.00 15109231 $2.50 04103251 $10.00 04104251 $5.00 04107231 $5.00 07104251 $5.00 07104252/3 $10.00 09101251 $2.50 15103251 $2.50 11104251 $5.00 11104252 $7.50 10104251 $5.00 19101251 $15.00 18101251 $2.50 18110241 $20.00 CSE250202-3 $15.00 CSE250204 $7.50 15103252 $2.50 P9054-04 $5.00 P9045-A $2.50 DUCTED HEAT TRANSFER CONTROLLER ↳ TEMPERATURE SENSOR ADAPTOR ↳ CONTROL PANEL MIC THE MOUSE (PCB SET, WHITE) USB-C POWER MONITOR (PCB SET, INCLUDES FFC) AUG25 AUG25 AUG25 AUG25 AUG25 17101251 17101252 17101253 SC7528 SC7527 NEW PCBs $10.00 $2.50 $2.50 $7.50 $7.50 We also sell the Silicon Chip PDFs on USB, RTV&H USB, Vintage Radio USB and more at siliconchip.com.au/Shop/3 ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Send your email to silicon<at>siliconchip.com.au Hot Water System Solar Diverter questions I enjoy all your articles and projects, with their explanations. I was very interested in the Hot Water System Solar Diverter project in the June 2025 edition (siliconchip.au/Series/440). However, this project has left me with questions that other readers may also be wondering about. 1. The diverter is supposed to obtain power export data from the inverter. How does an inverter ‘know’ how much of its power output is being self-consumed and how much is being exported? I understand that the inverter measures the energy it produces. However, is it able to differentiate between its energy that is self-­ consumed and that which is exported to the grid? 2. The graph in Fig.1 on page 37 shows consumption/self-­consumption rising and falling sharply during daytime. Consumption loads during the day are typically lower than in the evenings. Unless the household is frequently switching big loads on and off, consumption would not swing as the graph suggests. The consumption seems to follow the pattern of the clouds that affect solar production. Is there more explanation for this graph? 3. The ‘diverter’ is just a switch that turns the hot water heater on and off, even with the smarts in the software. I had imagined the diverter would have a changeover capability, so the heater can be fed from the mains or solar (or neither in the case of batteries). 4. If the diverter simply supplies power to the hot water heater only when there is excess solar output, Why is the RGB LED ‘Analog’ Clock PCB round? I built the Mesmeriser LED clock from one of your kits in 2005/2006. I had much joy building the clock (my background is in electronics), and it ran faithfully on my office wall for nearly twenty years. It failed about a year ago. I don’t remember exactly what happened to it, but I decided it was ‘time’ to retire it. So, I am excited to see Nicholas Vinen’s ‘timely’ new version in Silicon Chip’s May 2025 issue, and I’ll have to buy that kit and start all over. But it occurred to me that as well as a typical round clock face, why not a square clock face, or tilt the square 45° for a diamond shape? Why stop there? Pick almost any shape you can think of: oval or rectangle (horizontal or vertical), triangle etc. A square or vertical rectangular shape could be built into a proportionately sized grandfather clock case to sit on a hall table. I have no idea of the cost to make a different shaped PCB, that may make the options prohibitive. But if it can be done cheaply, LEDs chasing around a non-round shape could appeal to some, myself for one. Hell, I might have to buy a different shape for every room in the house! Alternatively, I could make my own odd-shaped clock face and extend the relevant LED connections from the supplied round PCB. Some of the more urgent jobs around the house might just have to wait! Keep up the great work. (G. M., Pukekohe, New Zealand) ● The cost is generally based on the area of the rectangle that the PCB fits inside, so a square clock PCB that’s 200 × 200mm would cost the same as the 200mm diameter circular one we decided on. Essentially any PCB shape is possible, but the design would have to be redone in the new shape, with the LEDs painstakingly arranged and wired up. Still, a skilled PCB designer could probably redo it in a few hours. Ordering large PCBs is expensive, so we have to pick the shape that most people would want for a clock. We figured, given the option, most people would choose the circle, so that’s what we stuck with. Ordering two or three different batches of boards in different shapes would have increased the amount of work and cost substantially. 100 Silicon Chip Australia's electronics magazine wouldn’t there be cold water on low-solar days? Am I missing something here? (N. K., Kedron, Qld) ● Our replies below: #1. A typical grid-feed inverter has a current transformer in its grid interface. It measures the energy flowing into or out of the grid from the premises the same way an electricity meter would. Inverters that lack such a transformer will calculate local consumption as production minus export. #2. The consumption follows the production in this case because that is the purpose of the HWS Solar Diverter. It determines how much excess solar generation is available and adjusts the average HWS element power to use as much of it as possible without drawing from the grid. So the plot shows it doing its job, despite the constantly varying generation levels during that day. #3. The heater can be fed by mains or solar, since the two are merged at the grid-tied inverter. If the heater is switched on when there is excess solar production, it’s powered by solar. If it’s switched on when there’s little to no solar production, it’s powered by the grid. That’s the same as any appliance in a home with a grid-tied inverter. #4. The unit has a HWS temperature sensor and can command the unit to draw power from the grid if necessary. This is the feature described on the first page of the article as “Automatic override if the HWS temperature is still cold by the end of the solar day”. RGB LED Clock time zone is set manually I have almost completed the RGB LED ‘Analog’ Clock project (May 2025; siliconchip.au/Article/18126); I just need to get the Raspberry Pi Pico W time source working properly. I previously set up one of these for my Compact OLED Clock and Timer project without any difficulty. This time, the unit sets the time at GMT, 10 hours behind the correct time. I set the latitude/longitude to my siliconchip.com.au location, and although the info from the NTP insists that I am at a location 100km away, it is still within the correct time zone. I also set the IPAPI parameters. I can’t understand this. Have I set something wrong? Can you please assist? (D. C., Beachmere, Qld) ● The RGB LED Analog Clock doesn’t use the latitude/longitude data to set the time zone, so the location data should not matter. In fact, the same applies to the Compact OLED Clock; it defaults to GMT+10 (since that applies to the majority of our Australian readers). Having the correct time zone in this case is little more than the coincidence of the defaults matching your time zone. With that said, the RGB LED Analog Clock should default to the same GMT+10 time zone, and we are unsure why that is not the case. The time zone can be manually set and the full details are on page 75 of the project article. Briefly, a long press on the A button enters the time zone setting mode. Short presses on A or B will adjust the time zone earlier or later in 15-minute increments. A long press on B will toggle daylight savings (assuming it is a one-hour offset), while a second long press on A will exit this mode. How to retain a car CD player’s memory Discovering that our household had no working CD players, I decided to use an old car audio head unit that I had taken out of one of our many vehicles. I sourced a suitable 12V power supply, and have made a timber enclosure for it. Like all car audio units, its settings are retained by the continual presence of 12V DC. I’d prefer not to have my unit on all the time, so I decided to include some sort of battery backup to feed the ‘settings supply’. I thought at first that supercapacitors or the like might be a suitable store. The spec sheet doesn’t mention it, but testing shows the current draw when ‘off’ to be as much as 20mA. Given that, I assume that supercapacitors are out, as I was hoping for at least a few days of off-time without the settings getting lost. I looked around online, but did not find any products or circuit designs that I consider being definitively siliconchip.com.au Differential Probe capacitor confusion I’ve run into a problem with the PCB for this project (February 2025 issue; siliconchip. au/Article/17721). The pads for C16 are a short circuit. Could you please check your stock of boards for a short circuit between the pads of C16? It could be that I bridged these pads with solder. However, unlike C15’s pads which I’ve been able to clean up, I cannot remove the short between the pads of C16. I check all SMD components as I go for continuity and shorts; that’s how I found this problem. I’ve removed C16 and cleaned the pads, but still had a short. I then removed C15 as a sanity check, and it’s fine. (B. P., Jeir, NSW) ● Given this board’s relatively small clearances between tracks, or tracks and ground pours (6 thou/0.15mm), a fault isn’t completely out of the question, although it would be very unusual. This is a standard clearance required by many finepitch SMD ICs. Modern PCB manufacturing is pretty reliable, and most boards are electrically tested by the manufacturer. We wonder if you may have accidentally soldered the two capacitors horizontally rather than vertically, as shown by the red outlines in the accompanying diagram. That would be easy to do as the nearest components are also horizontal and there are no outlines marked on the PCB (since there isn’t much space). If you did that, the upper capacitor would be between two ground pads and thus would appear shorted. If that’s the case, it should be possible to carefully desolder the components, rotate them, and resolder them to the board correctly. suitable. This is probably indicative of the fact that I’m misguided in my approach! What do you recommend I use to feed the 20mA supply? (A. J., Mindarie, WA) ● A 12V sealed lead acid (SLA) battery or a compatible LiFePO4 12V battery that’s charged using a 12V battery charger would do the job. Something like a 4.5Ah rating would provide a few days of ‘settings’ storage, although a 1Ah battery should be suitable if only a couple of days without power is normal. The batteries and battery chargers are available from Jaycar and Altronics. Head units will happily run from up to 14.4V (as they would see when the car’s engine is running), so you could use a single power supply to run the player and charge the battery, although this does rely on enough active usage over time to keep the battery charged. You could use a 15V DC regulated Australia's electronics magazine supply with a single series diode to obtain ~14.3V to run the player, then another series diode to drop it to ~13.6V to float charge the battery. A low-value resistor in series with the battery can limit the initial charging current to avoid overloading the supply (eg, a 2.2W 5W resistor should keep the maximum charging current under 1A). Will the VGA PicoMite work with a Pico 2? I recently read about the VGA PicoMite and saw that you are selling a kit for it. I am wondering if the kit is compatible with Raspberry Pi Pico 2. If I use a Pico 2 instead of the included Pico, and install the latest PicoMite V6 firmware, will everything will work as expected? Also, I want to upgrade the default Pico with the latest version of the August 2025  101 PicoMite firmware. Will the kit still work? (J. C., via email) ● Geoff Graham responds: I have just updated my web page to clarify this. Yes, the VGA PicoMite hardware will work with either a Pico or Pico 2, as long as the appropriate firmware is installed (see the PicoMite 2 article from February 2025 at siliconchip.au/ Article/17729). There’s nothing stopping you from upgrading the firmware in the supplied Pico. How were EPROMs programmed in 1997? Dr Hugo Holden’s article in the January 2025 issue about retrieving data from old microcontrollers piqued my interest. I built the colour TV pattern generator from your June and July 1997 issues. It is still working well, but it would be a shame if the EPROM failed. I am curious to know what programming setup was used at the time. I have looked on eBay etc and noticed that there are some EPROM programmers available, but they don’t appear to support the device used in the colour pattern generator. I realise that the technology is dated now, but it would be interesting to build a project that runs on modern PC software that can talk to these old chips. As mentioned in Hugo’s article, it can save some specialised gear from the scrap heap. (G. C., Toormina, NSW) ● We used a basic EPROM programmer driven by a computer programmed in BASIC. Unfortunately, the details of that setup are lost in the mists of time. The Windows-based EPROM programmer by Jim Rowe that was published in late 2002/early 2003 (see siliconchip.au/Series/110) would be able to program these devices. However, the software would need to run within a DOSBox emulator on a modern Windows computer. You would also need a USB to Centronics interface converter. An easier solution would be to purchase the XGECU T48 Universal Programmer that we reviewed in April 2023 (siliconchip.au/Article/15735). Its software runs natively on Windows 10/11. GPS Time Source not getting valid data I’m having problems with the Clayton’s GPS Time Source project (April 102 Silicon Chip 2018; siliconchip.au/Article/11039). I’m using the ESP8266 D1 Mini module, as you used in the article on page 58 of that issue. I compiled the code using Arduino IDE V2.3.5, set for an ESP8266 “LOLIN(WEMOS)D1 R1”. The code is “NTP_client_for_ ESP8266_GPS_V13skt.zip”, downloaded yesterday from the Silicon Chip site. It compiles OK and programs the ESP8266, although there are many warnings in the compile window. After programming, I managed to set it up for my home router SSID and password OK. However, the time it sends to the IDE serial port seems to be incorrect. The time was approximately 04:01 UTC according to my PC, but I got the following serial data: $GPRMC,001632.009,V,3746.000,S,14 453.000,E,0.00,000.00,010118,,,*22 $GPGGA, 001632.009,3746.000,S,1445 3.000,E,0,04,1.0,0.0,M,0.0,M,,*7B $GPGSA,A,1,,,,,,,,,,,,,,1.0,1.0,1.0,*2D $ESP82,connected,SSID Telstra****** chan 6,10.0,0.52,0,0,0*03 Do you have an idea what’s causing this? (G. P., Narre Warren South, Vic) ● The output that you’ve included looks normal, but suggests that the Time Source has not been able to acquire the time successfully through NTP. The V in the $GPRMC sentence means that the data is ‘void’ and is not yet valid. The time it is reporting is 00:16:32 on 1/1/2018, which is 16 minutes after the default time programmed into the sketch when it starts. The 010118 in the output (near the end of the $GPRMC line) is the date field. So the time is wrong because it is using a default. We suggest you start by rebooting the D1 Mini module to force it to retry. If you have another WiFi network, that might be worth trying, too. We’ve heard reports of ESP8266 modules not working in cases where there are 2.4GHz and 5GHz networks with the same name. What appears to happen is that the router kicks the modules off the 2.4GHz network to see if it will join the 5GHz network instead. Of course, the ESP8266 only has a 2.4GHz radio, so this does not work. Some readers have successfully renamed their 5GHz networks as a work-around. For example, I’ve added a ‘_5G’ suffix to the 5GHz SSID of my home network. Australia's electronics magazine We don’t think that the warnings are a concern since the project compiles successfully. We are sure that these warnings are due to changes to the board profile since the last update from a few years ago. We suggest using these versions of the board profiles: V11 should be used with ESP8266 Boards Manager Profile version 2.7.4 and earlier. V12 should be used with ESP8266 Boards Manager Profile version 3.0.0 and later (tested with V3.0.2). The newest ESP8266 board profile is version 3.1.2, which we haven’t tested, so it would be worth trying with a 3.0.x version. You can select a specific version and downgrade to it in the Boards Manager. Troubleshooting Turntable Driver I have just built the Precision Turntable Driver (May 2016; siliconchip. au/Article/9930). I tested it today and got the following very strange results. Initially, it produced 230V AC after adjusting trimpot VR1. Pins 5 and 14 of IC1 read 4.95V DC. I was able to power my turntable (with its AC synchronous motor) for a few minutes. Since my turntable runs about 5% fast (about 35.4 RPM, for some reason), I tried repeated presses of the ‘slower’ button. It did not reduce the speed back towards 33.3 RPM. However, the ‘faster’ button did increase the speed incrementally, up to nearly 40 RPM. Shortly after this, I noticed the power LED was flashing slowly, in a sort of slow pulsing fashion with the LED never completely going dark. This was accompanied by a faint tapping sound that was synchronised with the LED flashing. I plugged the turntable back in, but it appeared to get no power and didn’t spin, unlike the initial trial described above. I examined the PCB very carefully under bright light to make sure I had no solder bridges or short circuits, but of course I don’t know if all the semiconductors, capacitors etc are OK. (P. L., Kaleen, ACT) ● Based on the photo supplied, there are some long component pigtails extending from the PCB. You should check that they don’t short to the enclosure (or, even better, trim them). Otherwise, the construction looks good. 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 WE HAVE QUALITY LEDs 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 Micromite Explore-40 October 2024 Complete Kit SC6991: $35 siliconchip.au/Article/16677 Includes the PCB and all onboard parts. Audio Breakout board and Pico BackPack are sold separately. FOR FREE: To give away, one decommissioned and partly disassembled YUKI KP-480 pick and place machine. Contact: Graham – 0458 071 074 Location: Hobart, Tasmania ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, address & credit card details, or phone (02) 9939 3295. WARNING! Silicon Chip magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of Silicon Chip magazine. Devices or circuits described in Silicon Chip may be covered by patents. Silicon Chip disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. Silicon Chip also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. siliconchip.com.au Australia's electronics magazine August 2025  103 Advertising Index Altronics.................................19-22 Blackmagic Design..................... 37 Dave Thompson........................ 103 Emona Instruments.................. IBC Hare & Forbes............................... 7 Icom Australia............................. 10 Jaycar............................. IFC, 30-33 Keith Rippon Kit Assembly....... 103 Lazer Security........................... 103 LD Electronics........................... 103 LEDsales................................... 103 Microchip Technology.............OBC Mouser Electronics....................... 3 OurPCB Australia.......................... 6 PCBWay......................................... 5 PMD Way................................... 103 Rohde & Schwarz........................ 97 SC Micromite Explore-40......... 103 SC PIC Programming Adaptor... 72 Silicon Chip Back Issues..... 45, 88 Silicon Chip Battery Checker.... 66 Silicon Chip PDFs on USB......... 57 Silicon Chip Shop...........90, 98-99 Silicon Chip Songbird................ 51 Silicon Chip Subscriptions........ 73 The Loudspeaker Kit.com.......... 89 Wagner Electronics....................... 9 Errata and on-sale date Vintage Radio – Emerson 888, May 2025: Ian Batty quoted his favourite “weak signal” station as 3WV at Warrnambool. Fellow HRSA member Bob Forbes informed him that the station at Warrnambool is actually 3WL (1602kHz), ABC South Western Victoria. His reference is actually 3WV (594kHz), ABC Radio Wimmera at Horsham, around 300km from Rosebud. Next Issue: the September 2025 issue is due on sale in newsagents by Thursday, August 28th. Expect postal delivery of subscription copies in Australia between August 27th and September 12th. 104 Silicon Chip It seems like the plugpack power supply is not delivering power or there is a short circuit or something drawing a lot of current in the circuit. Start by checking the plugpack output. Is it capable of delivering 2A? If it seems OK, perhaps there is a component drawing extra current. It would get hotter than expected. The fact that the power LED flashes suggests that the plugpack is switching on and off, and is possibly overloaded. We recommend using an Altronics M8945A (15V DC, 2.4A) or M8945B (15V DC, 3.5A) plugpack to power the Precision Turntable Driver. Jaycar’s MP3492 could also be used, although its 2A rating is only just high enough. As for the inability to reduce the speed, we think it is likely a fault with the button or its wiring. Editor’s note: the reader later replied that the plugpack was at fault. RIAA Preamplifier wanted I have been asked to restore a 1950s chest-type valve radiogram that has great sentimental significance to its owner. Unfortunately, the existing Collaro record changer looks to be beyond help, with perished rubber parts. The only solution is to retrofit a newer turntable/record changer. I envisage using something like a later model Garrard fitted with a magnetic cartridge. The radiogram won’t have sufficient audio gain to be driven directly from a magnetic cartridge, but I can easily add a solid state preamplifier, hidden inside the cabinet of the radiogram. Have you published a design for a mono (or stereo) RIAA magnetic phono preamp that can provide up to 300-400mV output? If so, do you have PCBs available for it? The equalisation curves are different between LPs and 78s. I don’t know what the record playing expectations of the radiogram’s owner are as yet. I am assuming that 78 magnetic cartridges are still available, should the owner plan on playing 78 records. I am aware that the output level of the preamp depends on the output level of the cartridge. Assuming there is a suitable design, can I tweak the preamp’s output level by changing the amount of feedback on the preamp’s IC, or is the feedback loop entirely dedicated to the equalisation Australia's electronics magazine components? Also, what are its power supply requirements? (P. W., Auckland, New Zealand) ● We published a Magnetic Cartridge Preamplifier in August 2006 (“Build A Magnetic Cartridge Preamplifier”; siliconchip.au/Article/2740). This is a stereo preamplifier and its gain should be suitable for your required output level. This level depends upon the cartridge signal output with record groove modulation. The PCB is available from our Online Shop (siliconchip.com.au/ Shop/8/860). You can adjust the gain by changing the components. We also have a SPICE simulation file that can be used to check the response if changes are made. Changes to the gain shouldn’t be necessary normally unless a low output cartridge is used, such as a moving coil type. It can run from a 12V AC 250mA plugpack. The circuitry has onboard 12V regulators to provide the required ±12V rails. How to make a whistle filter I am trying to build one of your old projects, but it uses parts that are no longer available. Can you tell me how to make a 9kHz whistle filter coil and a 15.625kHz whistle filter coil? (W. O., Miller, NSW) ● The 9kHz notch filter would be for an AM receiver, while the 15.625kHz filter would be to remove the horizontal scan frequency from an analog CRT TV. The components used can include an inductance, a capacitance and a resistance, or simply resistors and capacitors, with or without op amps. For passive filters, go to siliconchip. au/link/ac79 and scroll down to RLC notch filter. That will give you the details and equation to relate the notch frequency to the component values. You can work out the details for winding an air-cored inductor, if required, using the online calculator at siliconchip.au/link/ac77 Or, for a ferrite-cored inductor, use the online calculator at siliconchip.au/ link/ac78 (you will need to know the AL value of the ferrite core). Active filters can be easier to build than passive filters using an inductor, since these can just use resistors and capacitors, as described on Rod Elliott’s website at https://sound-au. 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