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OCTOBER 2025 ISSN 1030-2662 10 9 771030 266001 The VERY BEST DIY Projects! $14 00* NZ $14 90 INC GST l Digitaifier pl m a e r er P v o s s o r an d C Du a Co l Tra nt r ol l i n er u cu Va r op lle sh ro rk nt Wo Co t S pe a ker, Pa m Penda n INC GST rt 2 Autonomous Vehicles and Driver Assistance Systems ALL NEW CATALOGUE! It’s Back & PRINTED Exciting news! The Jaycar Engineering & Scientific Catalogue has returned, and it’s our biggest issue yet, with 604 pages packed full of the latest products, components, and tools. ONLY 9 $ 95 ^ The catalogue will be available for purchase from our stores or online. Prefer digital? A convenient flipbook version will also be available online. www.jaycar.com.au | www.jaycar.co.nz Australia New Zealand BJ5000 $9.95 BJ5002: $11.90 Scan the QR Code or visit: AU: jaycar.com.au/p/BJ5000 NZ: jaycar.co.nz/p/BJ5002 Limited print run. Be quick before they sell out! ^Price Shown in $AUD - NZ price is $11.90 Contents Vol.38, No.10 October 2025 12 Autonomous Vehicles Part 1: Page 29 Fully autonomous vehicles and advanced driver assistance systems make a driver’s job easier (or redundant!). We explain how they work, what different systems have been developed and the different levels of autonomy. By Dr David Maddison, VK3DSM Automotive technology 46 HomeAssistant, Part 2 Here’s how to set up your own fully featured home automation system using a Raspberry Pi. In this final part of the series, we cover the advanced features like cameras, dashboards, remote access and more. By Richard Palmer Home automation Digital Preamplifier and Crossover 68 Finding Bargain Speakers This article will help you know what to look for when searching for goodquality second-hand speakers on a budget. By Julian Edgar Audio & hifi 94 Vintage Reinartz 2 TRF Receiver John Reinartz was a skilled radio designer, and in the 1920s he published a circuit for a two-valve tuned radio frequency (TRF) receiver. A redesign was later published by David Whitby in Electronics Australia, with a kit manufactured by Technicraft in Katoomba, NSW. By Philip Fitzherbert & Ian Batty Vintage Radio 29 Digital Preamp & Crossover This advanced preamplifier uses digital processing and can also act as a crossover. It has three digital inputs, two digital outputs, four analog stereo inputs, four stereo outputs, high-fidelity USB & a stereo monitoring channel. By Phil Prosser Audio/hifi project 54 Vacuum Controller Automatically switch on a vacuum when a tool like a circular saw is started. It has an adjustable run time after the appliance is turned off, optional blast gate control and is rated for up to 10A <at> 230V AC for each appliance. By John Clarke Workshop project 72 Dual Train Controller Wirelessly control two different model locomotives from a single box (and possibly up to 10 trains and onboard sounds!). This is an add-on to the Battery-Powered Model Train project from January 2025. By Les Kerr Model railway project 80 Pendant Speaker, Part 2 We show you how to build, test and tune your new Pendant Speaker. It’s easy to assemble using a pre-made enclosure and can be configured differently depending on how you will be mounting and using it. By Julian Edgar Audio/hifi project Vacuum Controller For workshops, starting on p54 2 Editorial Viewpoint 4 Mailbag 24 Circuit Notebook 52 Subscriptions 86 Serviceman’s Log 92 98 Online Shop – Parts Online Shop – Kits 99 Ask Silicon Chip 103 Market Centre 104 Advertising Index 104 Notes & Errata 1. Driving a numerical VFD with a PIC SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke – B.E.(Elec.) Technical Staff Bao Smith – B.Sc. Tim Blythman – B.E., B.Sc. Advertising Enquiries (02) 9939 3295 adverts<at>siliconchip.com.au Regular Contributors Allan Linton-Smith Dave Thompson David Maddison – B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Geoff Graham Associate Professor Graham Parslow Dr Hugo Holden – B.H.B, MB.ChB., FRANZCO Ian Batty – M.Ed. Phil Prosser – B.Sc., B.E.(Elec.) Cartoonist Louis Decrevel loueee.com Founding Editor (retired) Leo Simpson – B.Bus., FAICD Silicon Chip is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 626 922 870. ABN 20 880 526 923. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Subscription rates (Australia only) 6 issues (6 months): $72.50 12 issues (1 year): $135 24 issues (2 years): $255 Online subscription (Worldwide) 6 issues (6 months): $52.50 12 issues (1 year): $100 24 issues (2 years): $190 For overseas rates, see our website or email silicon<at>siliconchip.com.au * recommended & maximum price only Postal address: PO Box 194, Matraville, NSW 2036. Phone: (02) 9939 3295. ISSN: 1030-2662 Printing and Distribution: 14 Hardner Rd, Mount Waverley VIC 3149 54 Park St, Sydney NSW 2000 2 Silicon Chip Editorial Viewpoint We need Intel My editorial in the September 2024 issue was titled “Intel is in trouble”, and it turned out to be uncomfortably accurate. Intel once seemed like a juggernaut, but a mix of strategic missteps and what I would call complacency has left the company struggling for relevance. Once enormously profitable, it is now fighting to survive. Intel still doesn’t have many true rivals. A decade ago, it was practically a monopoly; now AMD, Apple, NVIDIA and even Qualcomm are pressing hard. Yet Intel remains hugely important. The computer industry needs it – not just as a supplier, but to keep competition alive. Intel’s history proves it can innovate. From its groundbreaking DRAM, EPROM and flash memory in the early 1970s, to the x86 architecture in the late ’70s, and later technologies like USB, Thunderbolt, Ethernet and integrated WiFi, the company helped shape modern computing. I believe Intel will endure, possibly with government support, since it is ‘too big to fail’. But I hope it can claw its way back into competitiveness on its own. It has rebounded before, and it can again. Ironically, the seeds of today’s situation were sown in Intel’s glory days. Its main rival in the early 2000s, AMD, surged with the Athlon 64 in 2003 and the dual-core Opterons and Athlon 64 X2s in 2005. But from 2007 to 2009, a mix of design bugs and poor yields drove AMD to the brink of bankruptcy. To survive, it spun off its fabrication plants into a new business, GlobalFoundries, and became a fabless chip designer. For most of the 2010s, AMD floundered with the underwhelming Bulldozer architecture. With AMD weak, Intel grew complacent. For much of the decade, its ‘new’ CPUs were minor refreshes of the same four-core design. Worse, Intel’s long dominance in semiconductor manufacturing collapsed when it failed to make the transition from 14nm to 10nm processes in a timely manner. Intel moved to 14nm in 2014 with their Broadwell architecture. They planned to move to 10nm in 2016, but they ended up being mostly stuck on 14nm until Alder Lake in 2021. Five years is a long time to be standing still in the world of technology! This broke Intel’s streak of being at the forefront of semiconductor process nodes since the late 1980s. Meanwhile, AMD tapped the rapidly advancing process technology of Taiwan Semiconductor Manufacturing Company (TSMC). They moved from 10nm to 7nm, then 5nm and 4nm, all while Intel stalled. TSMC is now widely considered the world leader in cutting-edge semiconductor fabrication; even Intel uses them for their latest desktop processors. While TSMC was improving its semiconductor manufacturing technology, AMD was preparing its comeback. In 2017, it launched the Zen architecture, offering up to eight cores versus Intel’s typical four. Then in 2019 came Zen 2, a bombshell: up to 16 cores by joining two 8-core ‘chiplets’ together with a separate I/O die. AMD has refined that formula ever since, now producing CPUs with an incredible 192 cores, while Intel resorted to ever-higher powers and voltages to stay competitive in the desktop space. This culminated in the chip degradation problems I covered last year. Intel has also now adopted the chiplet concept they once derided. So get well, Intel; we need you to keep the industry competitive and innovative. If this saga proves anything, it’s that in semiconductors, complacency is fatal. AMD learned that lesson the hard way in the 2010s. Intel is learning it now – the question is whether it can turn that lesson into innovation before it’s too late. Note: a couple of days after writing this, the US Government bought a 10% stake in Intel. by Nicholas Vinen Australia's electronics magazine siliconchip.com.au MAILBAG your feedback Letters and emails should contain complete name, address and daytime phone number. Letters to the Editor are submitted on the condition that Silicon Chip Publications Pty Ltd has the right to edit, reproduce in electronic form, and communicate these letters. This also applies to submissions to “Ask Silicon Chip”, “Circuit Notebook” and “Serviceman’s Log”. Schematics or documentation wanted for stroboscope I would like to know if any reader can assist me with a circuit schematic and any available servicing information for the Strobotron (Neon flash tube stroboscope) shown in the photos, and made by Weston Electronics P/L Sydney. This unit dates from the 1960s and has a dial reading in CPS (Hz) and RPM and a range of 200 RPM to 3600 RPM. It contains a 6AQ8 double triode and a Ferranti NSP1 neon flash tube. I am happy to pay copying and/or postage expenses. You can contact me by emailing Silicon Chip. Gary Hovey, Braidwood, NSW. Another magazine giveaway Like so many of your readers, I have been an avid reader of your magazine for many years, but now need to downsize. I have a full set of Silicon Chip magazines, in excellent condition, from 1989 to 2025. They are free to a good home. Interested readers can email Silicon Chip to pass a message on to me. Alex Danilov, Naremburn, NSW. One pair of Ultra-LD Mk.3 amplifiers is blowing fuses I am writing regarding a pair of Ultra-LD Mk.3 amplifiers (July-September 2011; siliconchip.au/Series/286) that I built from Altronics kits (K5154). I have experience building several Mk.2, upgraded Mk.2 and Mk.3 amplifiers already, without any problems so far, but these particular Mk.3s had me stumped. They are powered via the recommended toroidal transformer and power supply board. All commissioning steps per the construction article went great – devices were isolated from the heatsink, quiescent current was set successfully, DC offset on the speaker 4 Silicon Chip output was negligible as expected, and audio through my test speaker sounded fantastic. However, at some time after fitting the fuses to both amplifier modules, the 2.5A mains fuse blew at power-on. I replaced the fuse, removed all four fuses from the two amplifier modules and re-inserted the test resistors in place of the fuses in one amplifier module at a time. The quiescent current was still as set. Through testing, I have found that when the amplifier is powered off for a very short time, or a long time, it powers up just fine. But if the mains supply is switched off for around 30 seconds, then switched back on, the amplifier appears to latch up, with the test resistors dropping nearly the full rail voltages. If I discharge both rails’ capacitors with a resistor first, the amplifier will always power up correctly, and still appears to operate properly when it does, producing great sound. The only way I have stopped this phenomenon happening is to back the quiescent current off nearly completely, ie, 1V or less across the test resistors, which is not as intended. Both modules exhibit the same behaviour, whether powered from their own power supply or from another Ultra-LD Mk.2’s power supply (that amp works fine). The positive rail appears to discharge twice as quickly as the negative rail, judging by the LEDs on the power supply board. I think the bias circuit is not remaining stable when the amplifier is powering up with residual voltage on the rails, and presumably uneven residual voltage at that. Still, I was at a loss for what to do about it, especially considering the Mk.3 amplifier I built before this, with the same power supply setup, exhibited no such problem. Australia's electronics magazine siliconchip.com.au I chipped away at this over the past couple of weeks; my understanding of the circuit has increased, but I am no master at amplifier design! Since they were dropping almost the full rail voltage across the safety resistors, I can only deduce that the output transistors were switched on hard. All transistors were making good contact with the heatsink, and were electrically isolated (both sets were removed and refitted to the heatsink to confirm). With my limited knowledge, I experimented with increasing the value of the 68W resistor at the emitter of Q7, since my understanding is that it limits overall bias current. I then reset the quiescent current via VR1 to the published figures. On one module I settled on 168W, on the other 136W (two 68W resistors in series). This allowed me to achieve the correct quiescent current with absolutely no ill symptoms at switch-on. Since then, I have had successful listening tests, the quiescent current has remained stable, and there have been no problems with the amplifiers. I would love to better understand if that move is unexpected, or if it’s detrimental to performance, but for now I am happy to have stable, lovely sounding amplifiers. Callum Martin, via email. Comment: while Q7’s emitter sets the VAS current that flows through the bias generator, the bias is mainly controlled by the resistances between the pins of Q16. Changing the VAS current will have a small effect on the biasing of the output transistors and the quiescent current, but it will have a larger effect on the VAS gain and the amplifier’s maximum slew rate. We think the reason this change worked for you is that it has reduced the open-loop gain, which will improve stability. So it probably was oscillating. Blowing fuses (especially the DC fuses on the module) is a common sign of instability and oscillation, since the amplifier can draw a lot of current during sustained oscillation (the brief oscillation that sometimes can happen on recovery from clipping in marginally stable amplifiers may or may not blow them). It’s hard to say why this particular module is prone to oscillation when the others you’ve built were not. Perhaps the compensation capacitors were slightly lower in value than expected, or some of the transistors had a higher gain or transition frequency than normal. Our guess is that the effect on performance will be pretty small. If you ever wanted to return the VAS current and bias to their normal levels, you could try adding a small (eg, 10-22pF) C0G/NP0 ceramic capacitor between the base of Q8 and the collector of Q9. Such a capacitor is easily tacked onto the underside of the PCB, and it would improve the amplifier stability by rolling off the open-loop gain without affecting much else. Details of SpaceX’s early challenges Thought I’d mention this for the benefit of readers following David Maddison’s ‘deep-dive’ on SpaceX in the July & August 2025 issues (siliconchip.au/Series/442). There is a book I highly recommend; it gives a blow-by-blow account of the tortured beginnings of SpaceX and the almost insurmountable obstacles they had to overcome along the way. Written with the co-operation and approval of Elon Musk, it is called “Lift-Off!”, by Eric Berger. A short preview is available online at siliconchip.au/link/ac89 6 Silicon Chip Also, I’m sure this will be of interest to audiophiles: a development from the cutting-edge of speaker design, the VECO ultra-low distortion dynamic speaker. See the video at https://youtu.be/-pXeETlY4uU Andre Rousseau, Auckland South, New Zealand. Overcoming challenges in assembling several modules I received the 433MHz Receiver Module kit (SC7447) and started assembling it today. The two inductors appear identical – both are 0603 size, both have a green body all around, and each has an identical black stripe on half of one side. I checked the inductor’s resistance specifications, which are 0.54W and 0.60W for the 33nH and 39nH parts, respectively. My Fluke 79III DMM has a 40W scale that can be calibrated to take out the lead resistance. Unfortunately, the Fluke measured both inductors as 0.3W. So I pulled out my MICRON Q 1135, which claims “19999 counts”. With this DMM on its ohms range, I didn’t get the figures shown, but at least somewhere near them. Importantly, I could measure about 0.03-0.05W difference between the two devices, so I have some confidence that I have discriminated between the inductors. I also had difficulty distinguishing between the two 1.5pF and two 10pF capacitors, which are also the same size, and my Advanced Test Tweezers were not able to measure them accurately enough for me to figure out which was which. Thankfully, when I queried this, Silicon Chip responded that the 1.5pF capacitors were in clear plastic tape and the 10pF capacitors were in paper tape, allowing me to tell them apart. Unfortunately, I lost one of the 10pF capacitors, but I was able to get another one from my local Altronics store. Building the 433MHz Transmitter kit went a bit more smoothly. There were 5pF and 12pF capacitors supplied, but the Advanced Test Tweezers reading differences allowed me to discriminate between these. The two inductors are identifiable by size differences (0603 vs 0805) - but I was surprised to see only one face holding the pads on one of these – you have to get the correct face down! Finally, I had to Google the package markings on the SOT23 parts – the BAT54C was marked KL3, and the MCP17003302 was marked CSxx. I think this kit stretched the limits of my 75+ year old eyesight and hand coordination skills! Nevertheless, I was able to reflow solder both boards, fit the connectors, and fire them up. I connected the RX data line to a CRO to monitor signal transitions and powered the transmitter separately with a 4.5V battery on a separate breadboard (with a 173mm whip antenna). I tied the TX data line high and switched the power to the transmitter on and off. I could see clear changes on the CRO between on and off with the transmitter about 12m or so away using the receiver’s onboard antenna – the signal became noisier beyond that. I added a 173mm whip to the receiver, then could see clear and sudden changes about 30m away (maybe further, but I ran out of sight lines). With the transmitter off, the CRO showed a band of black (noise) using the sweep setting I had, but this would change to a clear trigger point and very few other transitions in the same band. So it looks like everything is working – I will have to try it using a modulated data signal. Australia's electronics magazine siliconchip.com.au FREE Download Now! Mac, Windows and Linux Edit and color correct using the same software used by Hollywood, for free! Creative Color Correction 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. 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Download free on the DaVinci Resolve website NO SUBSCRIPTIONS • NO ADS • NO USER TRACKING • NO AI TRAINING I also reflowed and completed one of the NFC programmable IR Remote Keyfobs, programmed it, and it is now in service with our TV. While I was at it, I reflowed the bottom of a Micromite Plus Explore-64 board, supporting the board by the edges, then did a second reflow pass for the microcontroller and all other parts on the top of the board (including the USB connector). I just had to use solder wick to clear up a few solder bridges on the microcontroller. This board fired straight up, so I loaded and saved the UNIO library, then loaded my 500+ lines of processing code – it all worked fine. Ian Thompson, Duncraig, WA. Faulty microcontroller affected serial comms Firstly, thanks for the magazine and your continued support of electronics in Australia. I recently purchased the kit for the RGB LED Clock (May 2025; siliconchip.au/ Article/18126), and assembly went really well with no problems with solder bridges. The LED test completes correctly. However, I don’t get any GPS sync; the red LED chaser continues with no change. I had GPS data at pin 3 of the PIC when probed with a CRO, and a full 0V to 5V swing. I connected a USB to serial dongle to the GPS TX/RX pins in-circuit and found valid GPS sentences at 115,200 baud. I purchased another PIC and replaced it in the clock, and it is now working properly. So either the supplied PIC was faulty, or I damaged it on installation. Paul Philbrook, Walkley Heights, SA. Valve type confusion Initially, US manufacturers simply issued their own coding systems for valves. By the mid-1930s, by common agreement, a simple two-digit numerical sequence was settled on. The “10” is a high power triode, but the “11” and “12” are low-power types, with the “15” a pentode IF/ RF amplifier. It’s impossible to know what a valve is by its type number without looking it up. Two common base types existed: the UX base was inserted into a sleeve socket with leaf-spring contacts at the bottom. A side ‘bayonet’ lug, sliding down a slot in the socket’s interior, would lock the valve against the contacts when the valve was twisted slightly. The UY base is the more familiar type, where the socket carries individual contact sleeves into which the base pins slide, making contact and retaining the valve. The generic ’80 full-wave rectifier could thus be coded as a UV80, UX80, UY80, or UX280/UX380, or the CX380 from Cunningham. The UV/UX prefixes were dropped, leading to the ’80 coding form. After the brief and inexplicable Radio Manufacturer’s Association (RMA) 1942-1944 alphanumeric system, where a 2G21 was a subminiature battery pentagrid, and a 2J30 was a 235 kilowatt magnetron (!), the new Radio Electronic and Television Manufacturer’s Association (RETMA) system commenced in 1944. This RMA/RETMA system applied a heater/filament voltage-­sequence, letters-number-of-elements code. Again, it’s not obvious that a 6BA6 is a pentode, a 6BE6 a pentagrid, a 6AL5 a duo-diode and a 6AQ5 an output valve. By number-of-elements, the 6BE6 should be a 6BE8! 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ADELAIDE 08_SIC_300925 $ Cast Iron Multi Purpose Bench Vice - Rotating Head & Swivel Base with Lock - MPV-12 English/European manufacturers applied their own systems. The Mazda 6F22 is a 6.3V amplifier pentode, while the 6P15 an output valve. GEC, Osram and Marconi’s L63 is an indirectly heated triode, the KT88 is an output tetrode, and the X61 is a triode-hexode converter. Maybe the previous codings of AC/PEN (an indirectly heated pentode), the AC/TH1 triode-hexode, or the PENDD4020 duo-diode output pentode are more explicit. The first European Philips/Mullard system does not distinguish valve types: the E415 is a 4V triode with an amplification factor of 15, the E442 is a 4V audio/RF/IF pentode. The second issue of the Pro Electron standard introduced a coding system that included the heater/filament voltage, valve type, and base type. The valve descriptions in this system are sufficiently detailed that, in most cases, data sheets aren’t necessary unless you’re doing a detailed design or sourcing a replacement. We know that the EF89 is a 6.3V pentode on a 9-pin miniature all-glass base, while the EF91 is similar, but on a 7-pin miniature all-glass base. Outside of these well-known coding systems, US and UK military authorities established the VT (US), VT/VR (UK) and CV (UK) systems. So, a VT50 could either be a US issue or a UK type. Many US types were originally RMA civilian types, with a hyphenated Vacuum Tube (VT-) prefix, so a VT-50 should be a US type. The VT-50 is simply the military version of an RMA type 50. This is a power triode on a four-pin UX base, and its civilian version appeared in catalogues by 1935. Be aware that only a minority of US VT- coded valves carry over the original civilian type numbers. The UK-issue VT50 (with no hyphen) should be a VT (Valve, Transmitting) version of a civilian type, but usually with no corresponding numbering. It’s hard to see such a low-power valve classed as a ‘transmitting’ type, and the original HL2 is very definitely described as a receiving type. The VT50 appeared in a military amplifier unit in 1927. For a condensed VT-RETMA conversion chart, see the rear cover of Radio Waves, January, 2025. For conversions from the British CV series to RETMA, see the rear cover of the April 2024 issue of Radio Waves. Maybe you need a 5U4, and have a VT52, which looks like a full-wave rectifier. You check the list and Bingo! VT52=5U4. Readers may know of many helpful websites that they rely on for obscure and hard-to-get information. One of my top favourites is Frank Philipse’s outstanding valve data bank at https://frank.pocnet.net or for the full, searchable index with data sheets, go to https://frank.pocnet.net/other/ ServiceTypes/VTnumbers.html For just $50 a year, joining the Historical Radio Society of Australia (HRSA), you get our quarterly Radio Waves magazine, membership of Australia’s premier Radio Society, and access to experts in all phases of restoration, monthly meetings and quarterly Auctions. You can also visit our invaluable valve and transistor banks for tested replacement valves and transistors at very reasonable prices. See https://hrsa.org.au SC Ian Batty, Rosebud, Vic. 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 10 Silicon Chip Australia's electronics magazine 0417 264 974 siliconchip.com.au SERIOUS POWER, SERIOUSLY GOOD VALUE! $ INTEGRATED BLUETOOTH® FOR SMARTPHONE CONNECTIVITY ONLY 999 INTEGRATED CARRY HANDLES MB4102 IP21 RATED 12V CIGARETTE SOCKET & 2 X 12VDC OUTLETS USB-A WITH QUICK CHARGE 3.0 & USB-C WITH POWER DELIVERY PURE SINE WAVE OUTPUT FOR SENSITIVE ELECTRONICS CHARGE VIA 12V, MAINS POWER OR VIA SOLAR PANEL BUILT-IN HIGH CAPACITY LIFEP04 BATTERY WITH ADVANCED BATTERY MANAGEMENT SYSTEM INTEGRATED MPPT SOLAR CHARGER UPS FUNCTION TO KEEP DEVICES RUNNING DURING POWER BLACKOUTS MB4102 HIGH POWER MODELS INCLUDE 12V 30A HIGH CURRENT OUTPUT 5 YEAR WARRANTY WHEELS & LUGGAGE STYLE HANDLE SCAN QR CODE TO LEARN MORE MB4102 (S1) MB4104 (S2) MB4106 (S3) MB4108 (S5) Output Power (Total) 2000W Continuous 4500W Peak 2500W Continuous 5400W Peak 3600W Continuous 7000W Peak 5000W Continuous 7000W Peak Capacity 1024Wh (12.8V 40Ah) 2048Wh (51.2V 40Ah) 3072Wh (51.2V 60Ah) 5040Wh (48V 105Ah) 6 Mains Outputs 4 5 6 Pure Sine Wave Output • • • • USB-C Output 2 (100W max.) 2 (100W max.) 2 (100W max.) 2 (60W max.) 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Dimensions (W x D x H) 384 x 232 x 295mm 460 x 270 x 305mm 641.5 x 304.5 x 437.5mm 641.5 x 304.5 x 437.5mm Warranty 5 Years 5 Years 5 Years 5 Years Availability In-store and online In-store and online Order online or in-store Order online or in-store RRP RRP $999 RRP $1999 RRP $2999 RRP $4999 Explore our great range of 3D Printing gear, in stock on our website, or at over 140 stores or 130 resellers across Australia and New Zealand. jaycar.com.au 1800 022 888 | jaycar.co.nz 0800 452 922 Prices shown in $AUD and correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. Autonomous Vehicles ADVANCED DRIVER ASSISTANCE SYSTEMS Driving automation includes fully autonomous vehicles (that can drive entirely by themselves) as well as advanced driver assistance systems (ADASs), which make a human driver’s job easier. Both technologies have made significant strides in recent years. By Dr David Maddison, VK3DSM The ‘future of driverless cars’ from an advertisement in the Philadelphia Saturday Evening Post, 1956. Source: www.saturdayeveningpost.com/2018/05/driverless-cars-flat-tvs-predictions-automated-future-1956/ 12 Silicon Chip Australia's electronics magazine siliconchip.com.au T his article will be about automation in ground vehicles only; we have previously discussed aerial automation in several articles, including the recent one on Drones (also known as UAVs) in the September issue. We also discussed autonomous underwater vehicles in the September 2015 issue, and autonomous agricultural vehicles in June 2018. Classifications Whether or not a vehicle is autonomous is not a simple yes/no answer; there are different levels of autonomy. Thus, there are several schemes to categorise levels of vehicle automation. One of the most commonly used is from the Society of Automotive Engineers (SAE), embodied in their J3016 standard. It defines six levels of vehicle automation. For SAE levels 0-2, the driver is fully driving the vehicle and remains in complete control. Level 0: No driving automation. The vehicle may provide warnings and momentary assistance only, such as automatic emergency braking, blind spot warning and lane departure warning. Most entry-level cars on the market today are at this level. Level 1: Partial automation with a single feature for the vehicle to control, like steering, braking or acceleration. May include lane centring or adaptive cruise control. Many cars on the road today have one of these features. Level 2: Partial driving automation. The vehicle can control (when necessary) steering, braking and acceleration, such as lane centring and adaptive cruise control. A reasonable proportion of cars on the road today have both of these features, and they come on most new higher-end vehicles. Level 3: Conditional driving automation. This includes environment detection, with capabilities like automated overtaking or negotiating traffic jams. The driver must be prepared to take control of the vehicle when required. Examples include Audi A8L Traffic Jam Pilot, Mercedes Benz Drive Pilot, Honda Legend Traffic Jam Assist and BMW Personal Pilot L3. Note that these systems may not be approved in certain locations. For SAE levels 4-5, the driver is not usually required to take control of the vehicle (and may not be able to, as it might not have controls). siliconchip.com.au Level 4: High level of driving automation. The vehicle drives itself under nearly all circumstances. An example is a driverless taxi for use on local roads (eg, Waymo’s One; https:// waymo.com/waymo-one/), shuttle buses in controlled urban environments, delivery services with trucks (Gatik is partnering with Isuzu) and public transportation. Mercedes Benz is trialling level 4 driving on various roads in Beijing. Pedals and steering wheel may not be fitted to a Level 4 vehicle. Such a vehicle likely cannot go off road. Level 5: This is similar to level 4, but more advanced. Whereas level 4 is fully automated, it is restricted to certain structured environments, like road networks. Level 5 has full driving automation under all possible circumstances, including off road. There is currently no example of a widely available car that meets the level 5 criteria. How do autonomous vehicles work? An autonomous vehicle requires many integrated systems to function. That includes multiple sensors to sense and map the environment; actuators to operate systems like steering or brakes; algorithms to guide tasks like parking, lane keeping, or collision avoidance; machine learning to handle a range of scenarios; powerful computers to orchestrate this all; and complex software running on reliable operating systems. A multitude of data from the sensors must be brought together in a process called sensor fusion. Sensor fusion involves merging data from numerous sensors to create a more comprehensive and accurate view of the environment than can be supplied by individual sensors. It is equivalent to how a human combines information from multiple senses (sight, hearing, balance etc). The controlling computer receives instructions from a person about where to go, then plots a route and sends appropriate instructions to the actuators to move the vehicle in the required direction. At the same time, the vehicle is constantly monitoring its environment for collision avoidance, lane keeping, observing speed limits, stopping at signals and stop signs, and observing other traffic rules. Australia's electronics magazine Important Developments Some significant developments toward advanced driver assistance systems and autonomous vehicles are: 1939 the GM Futurama display at New York World’s Fair prophesied a future in which there were semi-automated vehicles equipped with lane centring, lane change & blind spot assist systems, as described in the book Magic Motorways by Norman Bel Geddes. 1952 GM introduced the Autronic Eye, an automatic headlight dimming system, on some Oldsmobile and Cadillac models. 1958 Chrysler offered cruise control, invented by a blind engineer, Ralph Teetor. 1964 Twilight Sentinel was introduced on some Cadillac models, controlled by a photocell to sense ambient light levels and turn the headlights on or off. It was introduced in other models throughout the 1970s and later. Some versions switched on the lights whenever the wipers were activated, to improve safety in low-visibility conditions. 1977 Japan’s Tsukuba Mechanical Engineering Laboratory developed an experimental car that could drive itself on specially marked streets. 1978 Rain sensing wipers were invented by Australian Raymond J. Noack (siliconchip.au/ link/ac6o). 1989 the Volkswagen Futura concept car had four-wheel steering to autonomously manoeuvre into parking spots. 1992 the Mitsubishi Debonair used lidar to warn the driver if they were too close to the vehicle ahead, but couldn’t control the vehicle. 1995 the Mitsubishi Diamante had an adaptive cruise control using lidar but could not apply the brakes. 2003 Honda introduced the Collision Mitigation Brake System to automatically apply the brakes if it detected a collision was imminent. 2004 DARPA held their inaugural Grand Challenge, a series of competitions to encourage the development of “autonomous ground vehicles capable of completing a substantial off-road course within a limited time”. 2006 the Lexus LS460 was sold with a Lane Keep Assist feature that steers vehicle back into lane if it deviates. 2015 Tesla offers the “Autopilot” feature on their Model S. 2019 Mercedes Benz and Bosch test automated valet parking at Stuttgart Airport in Germany, to guide a car autonomously to a pre-booked parking place. 2023 Mercedes Benz’s DRIVE PILOT system is approved in Nevada, USA, to drive on certain freeways during daylight below 40 miles per hour (64km/h). 2024 BMW obtained approval for Personal Pilot L3 in Germany, similar to Mercedes DRIVE PILOT. October 2025  13 Figs.1 & 2: the architecture of a typical autonomous vehicle. ML = machine learning, AI = artificial intelligence, DL = deep learning, UI/UX = user interface/user experience, AUTOSAR = Automotive Open System Architecture, ROS = robot operating system, RTOS = real time operating system, V2X = vehicle to everything. It will also monitor itself, to ensure sufficient fuel or battery charge, while looking for places along the way to refill. Figs.1 & 2 show the generic hardware and software architecture of a typical autonomous vehicle, along with information flows and actions. Environment sensing Autonomous vehicles, or vehicles with ADAS (Advanced Driver Assistance System), need ‘eyes’ to see the environment around them, as well as other sensors. The main sensors are lidar for 3D mapping; radar; sonar; cameras; and GPS/GNSS for locating the vehicle. Other sensors such as gyroscopes and accelerometers can provide ‘dead reckoning’ navigation when there is no GNSS signal available, such as in tunnels. Those sensors are usually also used to detect if the vehicle is veering off course (eg, due to skidding on a slippery road), allowing the vehicle to take corrective action, and also to detect collisions (eg, to trigger airbags). The vehicle will probably also have sensors to detect the temperature, ambient light level (to control lights) and so on. It may even have a microphone to listen for the siren of an emergency vehicle, so it can pull over to let it pass. Lidar stands for Light Detection and Ranging. It is like radar, emitting laser pulses (rather than RF pulses, as in radar) from a rotating assembly to make a three-dimensional map (point cloud) of the environment based on the time for the reflected signal to return. An example of a commercial lidar device for ADAS or autonomous vehicles is the HESAI Automotive-Grade 120° Ultra-High Resolution LongRange lidar (siliconchip.au/link/ac6p) – see Figs.3 & 4. That model is said to acquire 34 million data points per second to a range of 300m. ADAS and autonomous vehicles usually have multiple cameras. The Figs.3 & 4: a HESAI lidar (Light Detection and Ranging) unit shown inset. Under it is an example of lidar imagery (a point cloud) with 128 channels (bottom) and the superior HESAI unit with 1440 channels (top). Source: www.hesaitech.com/product/at1440-360 14 Silicon Chip Australia's electronics magazine imagery from these has to be turned into meaningful data that can be used by the controller. This is done by software to create a three-dimensional map (point cloud), while extracting other useful data. An example of software used for this is Nodar Hammerhead (siliconchip.au/link/ac6s), shown in Fig.6. Sonar sensors use ultrasonic sound waves to measure distance, providing short-range information about objects in the immediate vicinity of the vehicle. Radar sensors use microwave radio beams to measure the range, velocity and direction of objects within their field of view. The sensors need to work regardless of conditions such as heavy snow, rain, ice, fog, road line markings being obscured or absent, changes in road surfaces, debris on the road, dirt roads etc. No single sensor is good at everything under all conditions, so a variety of sensors are needed. For Fig.5: environmental sensing by an autonomous vehicle with multiple cameras, radars, ultrasonic systems and a lidar unit. Original source: www.mdpi.com/1424-8220/23/6/3335 siliconchip.com.au example, the sensors shown in Fig.5 are fused to produce the capability shown in Fig.7. Software Hazard assessment Relevant software standards include ISO 26262, which is a process for managing and reducing risks for electrical and electronic systems in road vehicles. It covers planning, analysis, design, implementation, verification, validation, production, operation and decommissioning. It includes guidance on model-based development, software safety analysis, dependent failure analysis, fault tolerance and more. ASIL refers to Automotive Safety Integrity Level, a risk classification system specified by ISO 26262. It defines functional safety as “the absence of unreasonable risk due to hazards caused by malfunctioning behavior of electrical or electronic systems”. There are four levels of risk associated with system failure: A, B, C & D, with A being the lowest level and D the highest level of hazard if a system fails – see Fig.9. The higher the risk level, the greater the required reliability and robustness of the particular system. AEC-Q100 is a standard that ensures the safety of electronic parts used in cars, focusing on reliability stress-­ testing of integrated circuits. Fig.6: an actual image from the Nodar Hammerhead at upper left and the processed image outputs from their stereovision software at upper right and bottom. Source: www.nodarsensor.com/products/hammerhead Fig.7: the capabilities of the sensors from Fig.5 fused to show the overall detection capability for cameras, radar & lidar at lower right. Original source: www.mdpi.com/14248220/23/6/3335 Fig.8: the architecture of NVIDIA’s DriveOS software. ◀ According to Synopsys, today’s autonomous cars use 100 million lines of code, and in the near future, they will have 300 million lines. Operating systems for autonomous vehicles include QNX Neutrino (used by Acura, Audi, BMW and Ford among others; Unix-like); WindRiver VxWorks (also used by BMW, Ford and the Mars Perserverance rover); NVIDIA’s DriveOS (see Fig.8, used by Audi, Mercedes-Benz, Tesla and Veoneer); along with Integrity. Apple, Google and Microsoft also have their own versions of autonomous vehicle operating systems in use or under development. AUTOSAR AUTOSAR (AUTomotive Open System Architecture; www.autosar.org) is a global automotive and software industry partnership to develop and implement an open and standardised siliconchip.com.au Australia's electronics magazine October 2025  15 software, electrical and electronic framework for “intelligent mobility”. It defines things such as common interfaces, communications protocols, data formats etc. The layered architecture of AUTOSAR includes an application layer (vehicle specific), a runtime environment (that manages communications between software components), a basic software layer (communications and memory management, etc) and a control unit abstraction layer, to allow software to be developed regardless of specific hardware – see Fig.10. Fig.9: the ASIL hazard assessment levels for the failure of various systems on an autonomous vehicle. A indicates the least concern of failure, while D is of most concern. Source: www.synopsys.com/glossary/what-is-asil.html Advanced Driver Assistance Systems Fig.11: the Cruise self-driving car. Source: https://unsplash.com/photos/a-carthat-is-sitting-in-the-street-PkKsHQ5u4g8 These systems can help a human to operate a vehicle at SAE automation levels 0 through 5, or be integrated under the control of a master system to drive a vehicle autonomously. Unfortunately, the names of these features and their dashboard symbols are not always standardised between manufacturers. Adaptive Cruise Control is a system that automatically adjusts vehicle speed to maintain an appropriate separation from the vehicle in front. It uses sensors such as radar (typically at 24GHz or 77GHz), lidar or binocular cameras (eg, Subaru’s “EyeSight” system) to determine the distance to the car ahead. Adaptive Headlamps use a system to automatically adjust the headlight beam to avoid dazzling oncoming drivers (in theory, at least). The distance to oncoming drivers, if any, is estimated and the beam reach is adjusted appropriately. There is no binary high- or low-beam in some systems; just a continuously variable range. In one system by Mercedes, for example, the beam reach is adjusted between 65m and 300m, and adjustments are made every 40ms according to information from a vehicle camera that determines the distance to other vehicles. Anti-lock Braking Systems (ABSs) are designed to prevent a vehicle from skidding under hard braking, which can both result in longer stopping distances and make steering ineffective. It was originally introduced for rail vehicles in 1908 (although for a different purpose; to improve brake effectiveness), and 1920 for aircraft, but it was not universally adopted. The widespread adoption of ABS Australia's electronics magazine siliconchip.com.au Fig.10: the AUTOSAR software architecture, the acronyms stand for VFB: Virtual Functional Bus; RTE: Runtime Environment; BSW: Basic Software. Original source: Fürst, Simon “AUTOSAR – A Worldwide Standard is on the Road” – siliconchip.au/link/ac6t 16 Silicon Chip for aircraft happened in the 1950s. These were hydraulic systems, but an electronic system was developed for the Concorde in the 1960s. The modern ABS system for cars was invented in 1971 by Fiat and has been used on many models since then. It has been required on almost all cars sold for decades now. Modern systems monitor the rotational speed of each wheel and compare that with the speed of the vehicle. If one wheel is rotating slower than the rest of the vehicle, the brake pressure for that wheel is reduced, unless the car is turning. Brake pressure can be reduced or reapplied up to 15 times per second, and each wheel can be controlled individually. In more modern vehicles, the ABS system is also part of the electronic stability control system. Automatic Emergency Braking uses forward-looking vehicle sensors, such as radar and lidar, to sense the distance and time to impact of a vehicle or other obstacle. If the driver does not brake in time, the brakes are automatically applied. This might also be used in conjunction with automatic emergency steering (if fitted) if the braking distance is insufficient. Automatic Emergency Steering tries to steer a vehicle away from an imminent collision. Hazards that can be avoided include cars, cyclists, pedestrians, animals or road debris. Automatic emergency braking may also be implemented. Decisions are made based on inputs from radar, lidar, cameras, ultrasonic sensors etc. The process for action is: 1. Detection; continuous monitoring from sensors 2. Assessment; the control module uses data from the sensors to determine the vehicle velocity, trajectory, distance to the obstacle etc 3. Decision; if a collision is determined to be imminent and cannot be avoided by emergency braking alone, the calculations are made for a steering manoeuvre 4. Action; the steering actuator is activated by the control module to steer the vehicle on a path calculated to avoid the obstacle and any other obstacles 5. Notification; the driver is notified of the action There are various levels of Automated Parking, from basic to fully automatic. For automated parking to siliconchip.com.au ◀ Fig.12: the process of automatic parallel parking. Original source: “A novel control strategy of automatic parallel parking system based on Q-learning” – siliconchip.au/link/ac6u Fig.13 (below): possible parking scenarios for Volkswagen’s Parking Assist. Original source: Green Car Congress – siliconchip.au/link/ac6w work, the parking space needs to be ‘parameterised’ so that the appropriate vehicle direction, steering angle and speed can be computed – Fig.12 shows a reverse parking scenario. Other parking scenarios are possible, for example, right-angle parking. Volkswagen is one of many manufacturers who have developed automated parking, which they call “Parking Assist”, through three generations, plus fully automatic parking. Their first generation only allowed for reverse parking into parallel spaces, with a maximum of two moves, and the target space had to be 1.4m longer than the vehicle. Vacant parking spaces could be detected at up to 30km/h. It used ultrasonic sensors. Their second generation could perform multiple manoeuvres to park, as shown in Fig.13. It used cameras in the side mirrors, at the front and the rear, as well as ultrasonic sensors. The third generation could park the vehicle into a much smaller space and detect vacant spaces at speeds up to 40km/h. Australia's electronics magazine These Parking Assist modes correspond to SAE Level 1, and require driver supervision. Beyond that, Parking Assist at SAE Level 4 provides for fully automated parking with no human intervention required. Automated Valet Parking is a system developed by some manufacturers for a car to park and retrieve itself in certain parking garages. Infrastructure is required at the car park, as well as communication between the vehicle and the car park via V2X technology (see below) to receive instructions and location information within the car park. For more on this, see the video at https://youtu.be/30eB8Jj7xh0 Tesla also have an “Actually Smart Summon” feature, where the car will unpark itself and come to the driver with the use of a smartphone app as long as the car is within 65m of the driver, with a clear line of sight, and is not on a public road. Automatic Wipers: rain-sensing wipers were invented by an Australian Raymond J. Noack. Moisture is October 2025  17 windshield LED photodiode raindrop Fig.15: the output of the Tesla Driver Drowsiness Warning, which is not visible to the driver. Source: www.vehiclesuggest. com/tesla-hackerfigured-out-a-wayto-fool-tesla-camerabased-drivermonitoring-system Fig.14: the operation of an automotive rain sensor. In the presence of raindrops, there is some loss in the strength of the infrared beam reflected. Source: https://w.wiki/ERxC detected on the windscreen, and the wipers are activated at an appropriate speed and interval. The rain sensor is typically located in front of the rear-view mirror, and monitors infrared light reflected back from the outside surface of the glass, as per Fig.14. Blind Spot Monitors use radar or cameras to monitor a driver’s so-called ‘blind spot’ and provide a warning before they attempt to move into it if something is detected there (eg, a motorbike). Subaru’s EyeSight Camera system uses a pair of stereo cameras and was first launched in 1989. It is used for Adaptive Cruise Control, but can also provide sensory input for pre-collision braking that detects cars, motorcycles, bicycles and pedestrians. In the USA, the system was found to reduce rear-end crashes and injuries up to 85%. Subaru is working to integrate an AI judgement capability into its EyeSight system. Climate Control is a feature in most vehicles now, providing both heating and cooling. It is important for both safety and comfort, for example, to ensure that the windows remain clear while driving. Some cars have automatic defogging features, including some Kia and Hyundai models. Collision Avoidance System is a system that monitors a vehicle’s speed, the distance to the vehicle in front and its speed, to provide a warning or take corrective action if a collision is imminent. Sensors, such as radar and lidar, are used to determine vehicle parameters, like speed and distance. Automatic Emergency Braking and Automatic Emergency Steering are two possible systems that are used to implement collision avoidance. Crosswind Stability Control was first used by Mercedes Benz from 2009 in some cars, then later, vans and trucks. A deviation caused by crosswinds can be automatically corrected with the vehicle’s ESC system by several methods, such as steering, torque vectoring to provide more Fig.16: an algorithm flowchart for implementing electronic stability control (ESC). Original source: https:// autoelectricalsystems. wordpress.com/2015/12/20/ electronic-stabilityprogramme-esp 18 Silicon Chip Australia's electronics magazine drive force on the left or right side of the vehicle, or differential braking. Driver Drowsiness Detection uses cameras and sensors such as eye-­ tracking sensors to monitor driver behaviour and sound an alarm to alert the driver if drowsiness is detected. Drowsiness is detected by sensing behaviours such as yawning, eye blinking rate, eye gaze, head movements, facial expressions and driving behaviour, such as lane deviations and speed variations. Machine learning analyses behaviour patterns and learns to identify behaviours corresponding to drowsiness. The idea is to alert the driver to rest before they fall asleep. Tesla Driver Drowsiness Warning uses a camera to monitor the driver and sounds an alert if drowsiness is detected. Volkswagen monitors lane deviations and steering movements to detect drowsiness. Other companies offering this feature include BMW (Attention Assistant), Citroën (AFIL/LDWS), Jeep (Drowsy Driver Detection), Subaru (Driver Monitoring System), Toyota (Safety Sense) and Volvo (Driver Alert System). Others also include Ford, GM, Hyundai, Kia. Some fleet operators, such as trucking companies, install centrally monitored driver drowsiness detection systems in their vehicles, which are monitored using AI systems and/or humans. Fig.15 shows the output of a Tesla Driver Drowsiness Warning obtained by <at>greentheonly as he tests the camera with different scenarios such as “driver’s eyes nominal”, “driver’s eyes down/closed/up”, “view of head truncated”, “driver looking left/right”, “camera dark/blinded”, “driver head down”. You can see his video at https:// youtu.be/pZWR4MQBI4M siliconchip.com.au Driving Modes such as for snow, ice, sand, hill ascent and descent control etc are available on some vehicles. The vehicle’s performance is optimised via control algorithms with the throttle response, traction control, stability control, transmission behaviour etc, adjusted as required. Electronic Stability Control (ESC) expands on ABS by adding a steering angle sensor and a gyroscopic sensor. If the intended direction of the vehicle doesn’t correspond to the actual direction it is travelling (ie, it is losing traction), the ABS system can individually brake between one and three wheels to bring the vehicle back into alignment with its intended direction. The steering wheel sensor also provides information for Cornering Brake Control (CBC) to take into account the differential rotational speed of the wheels on the inside and outside of the curve. A typical control algorithm is shown in Fig.16. Heads-up displays (HUDs) convey information to the driver, such as speed, the current speed limit, the distance to the vehicle ahead, turns for navigation etc. This information is projected onto the windscreen; see Fig.17. Ice Warning is important in colder climates as ice is often not visible on the road (‘black ice’) and this is a serious safety hazard. A variety of detection systems are used, such as multispectral imaging systems, to examine the road surface; thermal imaging systems; air temperature and humidity measurement; weather data from external sources; or information from vehicleto-­infrastructure (V2I) or vehicle-to-­ vehicle (V2V) systems. Intelligent Speed Adaption (ISA) is a system that reads road signs or uses other data to ensure that the driver stays within the speed limit for that section of road. There may be a warning if the driver exceeds the limit, or the driver may be able to request the car travels at or below the limit. Intersection Assistance is when a vehicle is equipped with side-looking radar to detect if drivers are coming at right angles to the car; brakes can be automatically activated to avoid a collision. Lane Deviation (or Departure) Warning uses cameras to monitor lane markings, to warn a driver if they start to depart from the lane they are in, or to siliconchip.com.au Fig.17: a head-up display rendering showing various ADAS parameters. Source: www.eetimes.com/add-ar-displays-for-adas-safety Fig.18: the Night Vision Assistant on an Audi A8. Source: https://w.wiki/ERxE Fig.19: the live 360° camera view on a Mazda CX-9. keep them in the centre of the lane even if they are not actively steering the vehicle. Lane Change Assistance uses sensors to detect if vehicles are in the driver’s blind spots, and will alert the driver if they are. Navigation in an ADAS vehicle may involve route recommendations or alternatives, choice of toll or no toll roads, advice on traffic congestion Australia's electronics magazine etc. The vehicle may receive real-time updates as conditions change, such as traffic congestion forming. Position information is obtained with GPS or another GNSS system. Night Vision is a system using infrared cameras to improve driver awareness at night or in poor conditions – see Fig.18. The first car to be offered with this technology was the 2000 Cadillac de Ville. October 2025  19 Do autonomous cars get confused? This short video shows Waymo cars honking at each other: https://youtube. com/shorts/PkVSoTZBh8U This video shows a Waymo vehicle not taking the passenger where they wanted to go on a simple trip: https://youtu.be/-Rxvl3INKSg A police officer pulls over a Waymo: https://youtu.be/7W-VneUv8Gk Omniview is a type of camera system that gives a 360° and/or bird’seye view of a vehicle. It is known by many other names, such as Surround View. It was first introduced as on the 2007 Nissan Elgrand and Infinit EX, as “Around View Monitor”. Video feeds from four to eight cameras are synthesised into a bird’s-eye view to assist drivers with park, or to remotely view their vehicle and its surrounds – see Fig.19. There is quite a bit of processing required to convert the images from the cameras into a (mostly) seamless 360° image. The steps include: 1. resizing the images 2. removing lens distortion 3. perspective transformation 4. stitching the images together 5. displaying the results Such systems can also be retrofitted. One example we found is the Taffio 360° Surround View Set (siliconchip. au/link/ac6q). Parking Sensors are usually ultrasonic rangefinders that give the driver an audible (and visual) indication of how close they are to objects. Typically, the closer the vehicle is to an object, the faster it beeps. These systems are often accompanied by a rear-facing camera, which may have lines marked on the image to assist the driver with determining the path of the vehicle in relation to obstacles. Reversing Cameras are a common feature now (required in new cars) and a relatively simple one to implement. The first known vehicle reversing camera was on the 1956 Buick Centurion concept car. The first commercially produced car to have one was the 1987 Toyota Crown in the Japanese market. Temperature Sensors are used to measure inside and outside temperatures, and may contribute to ice warning data or the operation of the climate control system. Traction Control is a system to ensure that wheels don’t lose traction with the road during heavy acceleration. Each wheel has a speed sensor, and the speed data is sent to the ECU, which compares it with the speed of 20 Silicon Chip the vehicle. If there is a mismatch, taking into account if the car is cornering or not, the engine torque is reduced or a brake is applied on the wheel. Traffic Jam Assist is a feature that uses Adaptive Cruise Control and Lane Departure Warning to take over driving in traffic jams. A safe distance is maintained with the vehicle in front. Traffic Sign Recognition uses a camera to recognise traffic signs, such as stop and speed limit signs, giving appropriate warnings to drivers. Traffic sign recognition is facilitated by the Vienna Convention on Road Signs and Signals, which has attempted to standardise road signs across various countries, although Australia is not a signatory. Traffic sign recognition systems use a variety of different algorithms, such as recognising the board shape and using character recognition to read the writing. A further level of complexity uses convolutional neural networks (CNN), which are trained with real signage and use deep learning to recognise various signs. The output of the Freeman Chain Code and shape determination of the algorithm can also be used as an input to CNNs. A typical sign recognition algorithm includes the following steps: 1. capture an image of the sign(s) with a colour camera 2. convert the image from RGB to HSL (hue, saturation, lightness) 3. apply a Gaussian smoothing filter 4. detect edges using a Canny edge detector algorithm 5. use a Freeman chain code algorithm to detect letters and numbers 6. use a polygonal approximation of digital curves to detect the sign shape 7. display the result Tyre Pressure Monitors use either inferences from other data or direct pressure measurements. For indirect systems, parameters such as wheel speeds, accelerometer outputs and other vehicle data are used to make inferences about tyre pressure, and a warning is issued to the driver to check pressures. Australia's electronics magazine That is not as accurate as direct measurement systems, which use a sensor in each wheel to determine the pressure. The sensor may either be battery-­ operated, which requires maintenance to replace the battery, or may be wirelessly supplied with power like RFID systems. Wrong Way Driving Warning is a system on some vehicles to alert the driver if they are driving in a direction which they are not meant to, as determined by GPS data. It doesn’t seem to be widely implemented. V2X stands for vehicle-to-everything and describes wireless communication between the vehicle and any other vehicle or entity with which the vehicle may interact. Vehicle to infrastructure (V2I) and vehicle to vehicle (V2V) are related systems. Operational Design Domain The Operational Design Domain (ODD) defines the set of conditions such as environmental, geographic, time of day etc under which the vehicle is certified to operate safely. In other words, it is a recognition of the limitations of the autonomous system. If the situation in which the vehicle finds itself is outside of the ODD; for example, certain traffic or road conditions, it might warn the driver or passenger and deactivate itself to allow the driver to assume control. Alternatively, the vehicle may park itself. Various standards and regulators have defined the exact meaning of ODD. An example is Mercedes Benz stating the following for its Drive Pilot Level 3 system for supervised autonomous driving, which is certified for use in California and Nevada: ...requires speeds below 40 miles per hour, clear lane markings, not too much road curvature, clear weather and lighting conditions, and a high-definition map to be available in the system’s memory... Warning sounds Electric autonomous vehicles can be so quiet that pedestrians may not hear them, so they are required to make a sound at lower speeds. In Australia, as of November 2025, all new electric, hybrid and hydrogen-powered cars, buses and trucks will be required to be fitted with noise-making systems which make a noise of 50dB below 20km/h. Similar laws apply in the EU, Japan, the UK and the USA. siliconchip.com.au Legal liability for accidents For SAE levels 0-3, the driver must be able to take control of the vehicle at any time, and they will be liable for any accidents, as they should be constantly monitoring the vehicle, ready to take control at any time. For levels 4 & 5 vehicles, there is no “driver”; they might not even have any access to vehicle controls. It is unclear who would be responsible for an accident that may occur. Fully autonomous vehicles We will now look at examples of autonomous vehicles, starting with one from Australia. Australian road trains Australian company Mineral Resources (www.mineralresources. com.au; MinRes) developed worldfirst autonomous road trains that can haul 330 tonnes of iron ore along 150km of private road in Western Australia, from the Ken’s Bore mine site to the Port of Ashburton. The trucks are converted Kenworth models. There are 150 trucks in the fleet, and they drive at 80km/h. There is an interval of 2-3 minutes between each truck as they constantly run along the road delivering iron ore. Hexagon (https://hexagon.com) performed the conversions – see Fig.20. According to their description, this includes: a sensory system for awareness (truck performance, surroundings and location); an autonomy layer, the brains for decision making; and a by-wire system for controlling the vehicle. Table 1 – Tesla autopilot features (source: https://w.wiki/3wkp) Feature Autopilot Enhanced Autopilot Full Self Driving Traffic-aware cruise control Autosteer Navigate on autopilot Auto lane change Autopark Summon Smart summon Traffic & stop sign control Autosteer on city streets ✔ ✔ ✖ ✖ ✖ ✖ ✖ ✖ ✖ ✔ ✔ ✔ ✔ ✔ ✔ ✔ ✖ ✖ ✔ ✔ ✔ ✔ ✔ ✔ ✔ ✔ ✔ Fig.20: the world’s first autonomous road train, in Australia. Source: www. mineralresources.com.au/our-business/onslow-iron-project/autonomous-roadtrains Buses and shuttles The Apalong is a Level 4 driverless bus from China that has been in production since 2017 – see Fig.21. It travels at between 20km/h and 40km/h and can accommodate 14 people. It uses Baidu’s Apollo 3 Open Driving Platform (https://github.com/ ApolloAuto/­apollo). Cars Tesla is constantly updating the software in its vehicles. It has a feature called “Autopilot” or “Enhanced Autopilot” available in all its cars produced since 2019, as well as some vehicles offering “Full Self-Driving” (FSD; supervised). The capabilities of different versions of the software depends on the siliconchip.com.au Fig.21: the Apalong autonomous bus from China. Source: https://w.wiki/ERxF Autonomous vehicle software Few manufacturers have released the code for the autonomous cars, but the Stanford Racing Team, the progenitor of Waymo One, released the code for the vehicle that won the 2005 DARPA Grand Challenge event at: https://sourceforge.net/projects/stanforddriving/ The vehicle ran this code, written in C and C++/ on a Linux operating system running on Pentium M CPUs. Australia's electronics magazine October 2025  21 Fig.22: a Tesla Hardware 3 (HW3) Full Self Driving (FSD) board. A lot of the circuitry at the top and bottom is the power supply for the two large UBQ01B0 multi-core processors. Source: https://w.wiki/ERxG Fig.23: an autonomous mining truck for transporting minerals. Source: Fortescue Metals Group Ltd – www.mining-technology.com/features/australialeads-the-way-in-autonomous-truck-use market and local laws. Tesla classifies these systems as SAE Level 2, possibly for legal reasons, as FSD is arguably a Level 4 technology (see Fig.26). The FSD v12 software is available for later vehicles with Hardware 4 (HW4; in Model S and Model Y after January 2023). It uses a neural network and artificial intelligence that has been trained on millions of video clips. Older versions of the code were reliant upon rule-based algorithms written in C++, but later versions now use an ‘end-toend’ neural network that constantly learns and adapts. End-to-end means that the entire FSD system is a neural network, not just parts of it. The high-level Python programming language is used for machine learning, with C++ for embedded systems. The software all runs under the Linux operating system. Samsung makes the processor for HW4, a custom ‘system on a chip’ (SoC) device that has 16GB of RAM and 256GB of storage. The internals of the HW4 computer can be seen at: siliconchip.au/link/ac6l siliconchip.au/link/ac6m The second link states that HW4 is running Linux kernel 5.4.161-rt67 Fig.22 shows a Tesla FSD board. We can see that the main chips are labelled UBQ0180. Wikichip (see siliconchip. au/link/ac6n) states these are FSD chips that incorporate “3 quad-core Cortex-A72 clusters for a total of 12 CPUs operating at 2.2 GHz, a Mali G71 MP12 GPU operating 1 GHz, 2 neural processing units operating at 2 GHz, and various other hardware accelerators. The FSD supports up to 128-bit LPDDR4-4266 memory”. Each chip contains 6 billion transistors. As it was first shipped in Teslas in 2019, we believe this unidentified board is a Hardware 3 or HW3 board. Table 1 illustrates the capabilities of Tesla’s Autopilot, Enhanced Autopilot and Full Self Driving. Fig.24: the Liebherr T 264 battery-electric autonomous mining truck, jointly developed with Fortescue. Source: Liebherr – siliconchip.au/link/ac6v Mining vehicles Australia is the world leader in the use of autonomous mining trucks – see Fig.23. As of May 2021, we had 575 such vehicles, compared to 143 in Canada, 18 in Chile, 14 in Brazil, 12 in China, 7 in Russia, 6 in Norway, 5 in the USA and 3 in Ukraine. Fortescue and Liebherr jointly developed an autonomous battery-­electric Australia's electronics magazine siliconchip.com.au 22 Silicon Chip T 264 truck, resulting in an order for 475 Liebherr machines. The T 264 is 8.6m wide, 14.2m long, 7.2m high with the dump body on and can carry a payload of 240 tonnes. The truck itself weighs 176 tonnes. The prototype truck (Fig.24) has a 1.4MWh battery weighing 15 tonnes that’s 3.6m long, 1.6m wide and 2.4m high. It’s made up of eight sub-packs, each consisting of 36 modules. It can regeneratively charge as it goes downhill. Taxis Waymo One (https://waymo.com/ waymo-one) is an autonomous taxi service currently available in the US cities of Austin, Los Angeles, Phoenix, San Francisco and soon Atlanta and Miami. Waymo One is a subsidiary of Alphabet Inc, Google’s parent company. Waymo vehicles have been under development since 2015, and in 2020 offered the self-driving service without safety drivers present in the car. The company traces its origins to the 2005 and 2007 US Defense Advanced Project Agency’s (DARPA) Grand Challenge competitions and the Stanford Racing Team. They won first place in 2005 and second in 2007. Waymo have applied their self-­ driving technology to several vehicle platforms; currently they use Jaguar I-Pace EVs (Fig.25), with whom they have a partnership, at an estimated additional cost of US$100,000 ($156,000) per vehicle. As of May 2025, approximately 1500 autonomous Waymo One vehicles were in service, mostly the I-Pace. Waymo vehicles are twice as safe as human drivers according to accident statistics, but have nevertheless been involved in incidents, mostly minor. A Waymo One taxi can be summoned via an App. Amazon’s Zoox (https://zoox.com) could be considered a ‘competitor’ to Waymo. They are also an autonomous taxi service operating in California and Las Vegas, Nevada. Their vehicles are fully electric and have no steering wheel (see Fig.27). Fig.25: Waymo’s modified Jaguar I-Pace EV. I-Paces have been discontinued, but Waymo acquired a large number and continues to deploy them. Source: https:// waymo.com/blog/2018/03/meet-our-newest-self-driving-vehicle Fig.26: a screenshot taken from an example video of Tesla’s FSD (Full-Self Driving). Source: www.tesla.com/fsd Further reading More details on some of these ADAS systems can be seen in our features on Automotive Electronics, December 2020 and January 2021 (siliconchip. SC au/Series/353). siliconchip.com.au Fig.27: an Amazon Zoox robotaxi, which is design as a fully-autonomous taxi (see https://zoox.com). Source: https://w.wiki/ESSv Australia's electronics magazine October 2025  23 CIRCUIT NOTEBOOK Interesting circuit ideas which we have checked but not built and tested. Contributions will be paid for at standard rates. All submissions should include full name, address & phone number. Driving a numerical VFD with a PIC Vacuum fluorescent displays (VFDs) have been around since the 1950s. They were widely used in consumer electronics, especially in calculators and point-of-sale terminals. They have since been replaced by LED displays and LCDs. However, VFDs have not disappeared (nor have the closely related vacuum tubes), they are still used in specific applications due to their unique advantages. Comparing 7-segment VFDs to LEDs and LCDs, VFDs consume less power than LEDs and are brighter than LCDs. VFDs also perform better than LCDs at low temperatures, down to around -40°C. There are a variety of driver ICs available but this circuit shows that it’s relatively easy to drive a numeric VFD even from a PIC with very few pins. A multiplexed 9-digit, 7-segment VFD, salvaged from an old pocket calculator (a Casio fx-21 from 1977!), is driven by a PIC10F222, using just two standard logic ICs: a 4017 decade counter and a 4033 7-segment decoder. The VFD power supply is 9V (the ICs 24 Silicon Chip can handle up to 20V). A separate regulator (not shown) is used to provide 5V to power the PIC. Bipolar NPN transistors Q1 & Q2, plus Mosfet Q3, along with some pull-up resistors, act as voltage level shifters to interface the 5V PIC to the 9V+ ICs. Despite being an input-only pin, the GP3 pin of IC3 is used here as a pseudo-output. That is possible because there is a weak pull-up current that can be enabled or disabled on inputs GP0, GP1 & GP3 simultaneously. Since GP0 and GP1 are driven from low source impedances, we can effectively enable or disable the weak pull-up on just GP3. When the pull-up is enabled, current flows into the base of Q1, switching it on. Otherwise, the 15kW pulldown resistor holds it off. Another trick is that GP3 controls two separate inputs on IC1 and GP2 controls two inputs on IC2. This is done using two 10kW/10nF low-pass filters that act as pulse stretchers, as described at siliconchip.au/link/ac6y Australia's electronics magazine This means that, after enough pulses have been sent to the relevant IC to cycle through all the VFD digits or segments, it will reset after a brief delay, ready for cycling through them again. The PIC firmware (siliconchip.au/ Shop/6/2797) was programmed in assembly language. It is fully commented and can be easily ported to other similar chips. The test firmware makes periodic voltage measurements through analog inputs GP0 and GP1, then refreshes two 4-digit displayed values (the digit in the middle of the VFD is not used). The current consumption is about 20mA at 5V, primarily due to the filament current of the VFD. The current drawn by other parts of the circuit, including the +9-20V supply, is minimal. 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SAVE $10 29 $ D 2331 Sale Ends October 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 0010 PART 1: PHIL PROSSER Digital Preamplifier and Crossover This advanced preamplifier uses digital processing to provide unprecedented flexibility. It has three digital inputs, including high-fidelity USB, four analog stereo inputs, four stereo outputs, two digital outputs (including USB) and a stereo monitor channel. Individual filters and equalisation can be applied to each pair of outputs, allowing it to act as a digital crossover! Four stereo analog inputs (1V RMS maximum) Frequency response: 7Hz to 43kHz <at> -3dB (with PCM1798 DACs) One analog input can be configured to handle 2V RMS+ S/PDIF coaxial and TOSLINK digital audio inputs Monitor output for analog inputs Four independent stereo output channels, 2V RMS full scale High sampling rate/bit depth USB audio stereo input and output Programmable equalisation, crossovers, relative attenuation & delay for each output Memory for four different configurations Attenuation at 20Hz: 0.3dB; Attenuation at 20kHz: 0.0dB Volume control: +12dB gain to -128dB attenuation in 0.5dB steps Total harmonic distortion plus noise (THD+N): 0.003% across the audio band (largely unchanged to >40dB attenuation) O ur interest in hifi at Silicon Chip runs from simple and ‘purist’ designs such as our Class-A and Class-AB amplifiers, and simple chip-based designs, through to much more complex approaches including high power and even the (very) occasional valve design. We love them all. This author is no exception, owning more audio equipment than most people would consider reasonable, much of it home-built. The larger and more serious hifi setups all incorporate active crossovers, either analog or digital. siliconchip.com.au Our wish-list for an ideal preamplifier includes not only an active crossover but also a USB interface that supports high fidelity playback and recording of music, and of course, switching for four or more analog inputs. This can become cumbersome where the crossover is housed in one box, the USB interface in another, and switching and gain control in another. The aim of this project is to roll all the above into a single ‘Digital Preamplifier’ that fits in a 1U chassis. This allows you to connect your analog audio sources, plug in your USB Australia's electronics magazine connected laptop or phone, TOSLINK source, and provide the functions of a normal preamplifier along with those of an active crossover, equaliser and delay controls for your loudspeakers. For those whose preference is more at the ‘simple is beautiful’ end of the audio spectrum, you may not want to build this device. However, we think you will still find the circuit and other details of this design interesting. That said, if you are into open-baffle speakers, the significant equalisation required for those might make you take a second look at this project. October 2025  29 ADC dynamic range Digital audio provides about 6dB of dynamic range per bit. So the old CD standard of 16 bits gives about 96dB of dynamic range. At the time CDs were released, this was awesome, and even now it is more than sufficient for excellent audio. However, a 24-bit system has more like 134dB between full-scale and the least significant bit (LSB). Consider a real world application like a preamplifier, where the sources can have real impedances, and the ADC sees an input signal-to-noise ratio of, say, 100dB over the 20Hz to 20kHz bandwidth. This is a touch over 16 bits’ worth of digital data above the noise floor. All our remaining bits in the 24bit ADC will be noise plus any signal which may be below the noise floor. If we have the same noise level, but 100kHz of bandwidth presented to the ADC, we will see a noise level about 14dB higher, or 86dB full-scale, in the region of 14 bits’ worth. This is what you see if you look at the ADC I2S data with an oscilloscope. This might sound terrible, but it is not. Remember that the ADC is simply representing the voltage it sees at its input, and these are the peak levels you will see on the SPI data. Most of this is outside the audio band and completely inaudible. The ADC is, in fact, faithfully digitising signals way down in to the -130dB region; way down below the full bandwidth noise floor. There is no question that superb sound quality can be achieved with a decent signal source, a simple preamplifier, basic power amplifier and speaker using a passive crossover. However, the step in capability we achieve in this project through the inclusion of a digital signal processor (DSP) is profound. So come along for the journey of designing and building a no-­ compromise Digital Preamplifier. We will not just present the design, its features, specifications and performance but will also go over some of the challenges faced in pulling together a complex design into something that is reasonably easy to build. The heart of this project is the Analog Devices ADAU1467 IC. This is a 32-bit processor that runs at 294MHz and is optimised for audio DSP tasks. This device has a very rich set of features, including: ● four dedicated stereo inputs and four stereo outputs ● the ability to process data at up to 192 kilosamples per second (192kSa/s) ● the ability to store 400ms of audio data at 192kSa/s ● four stereo asynchronous sampling rate converters (ASRCs) ● an S/PDIF interface ● fully programmable using some very high-level tools We have paired this with: ● a high-quality analog-to-­ digital converter (ADC), the CS5361 or CS5381; the latter provides a better signal-to-noise ratio (SNR) ● up to four high-quality digital-­ to-analog converters (DACs), Analog Devices PCM1798 or PCM1794A chips (the latter provides higher performance) ● a miniDSP MCHStreamer, which provides audio input/output for a computer over USB, making this The Digital Preamp is very capable and compact; its predecessor, which spanned two cases, is shown below. 30 Silicon Chip Australia's electronics magazine preamplifier a very fancy sound card ● switching for four analog inputs ● a PIC microcontroller-based user interface, which allows the whole preamplifier and DSP to be controlled and set up using three buttons and a rotary dial or remote control Everything fits in a single 1U (44mm-high) case, making this a compact and powerful all-in-one preamplifier, switch, crossover and DSP. Simply plug it into your amplifiers and, once set up, all this digital complexity is completely transparent to the user. In my system, this one compact unit replaces the bottom two devices shown in the photo at lower left, saving quite a bit of space! Digital vs analog So, how does this Digital Preamp compare to an analog design? We can hear the wailing and gnashing of teeth from purists at all this digital processing in their signal path. Concern about a DSP like this is ultimately little different to concern about using an op amp in the signal chain. Music & sound has passed through hundreds of op amps by the time it gets to your stereo. In this age, the recording and mixing process includes many DSPs too. No doubt, we need to get the design of a device like this right. But if done properly, the fact that the signal is digitised is transparent. The beauty of it is that, once we have the signal in the digital domain, we can easily apply complex filtering, delay individual channels and implement parametric equalisation with little-to-no reduction in quality. The fact the data is processed as 32-bit numbers means we do not face the old-school challenge of dealing with accumulated errors as we would if we were processing 16-bit data. As an example of the low impact that our Digital Preamplifier has on the audio path, it can take a digital input from the USB port, process it and generate analog output. We can then feed that signal back to an analog input, digitise it and send it back to the PC, all with a distortion result in the region of 0.002%. That’s basically CD quality (which is still considered pretty good these days). This is an interesting test, as it shows that a digital preamplifier can have less impact on the signal chain siliconchip.com.au The Digital Preamp comes with as many inputs/outputs as you would expect from a higher-end system. Each stereo digital output can have different filtering and delay configured, allowing it to also act as an active crossover. than some analog preamplifier circuits. distortion performance. The noise floor is at about -125dB. Performance Overall configuration The performance of the Digital Preamp is essentially defined by the DAC chips used. We measured the performance of the ADC (CS5361/81) using a Stanford Research Labs DS360 signal generator to drive the input to the preamplifier, with the miniDSP monitor output used to analyse the digitised audio. The measured THD was less than 0.0003%, which is consistent with the ‘typical’ specified performance of the ADC chip. Spectral analysis of the ADC data from this test shows no meaningful noise spurs from the switch-mode power supply; 50Hz hum is more than 105dB down. Routing the ADC output to the miniDSP for analysis on a computer, it is clear that the ADC we have chosen is very good indeed, with the distortion products being barely measurable. Turning to the DACs (PCM1794A or PCM1798), their specified THD+N at 44.1kHz is 0.0004%, so slightly higher than the ADC. But we are running them at 192kHz, to allow the preamplifier to operate right across the audible spectrum, and to set aside any concern with bandwidth limitations out to 40kHz. The PCM1794A THD+N operating at this sampling rate is 0.0015%. Our THD measurements are flat at 0.002% across the entire audio band, which is consistent with that. Reducing the volume level with the same input signal by 10dB, 20dB and 40dB shows that the distortion products fall along with the level, so operating the preamplifier with 40dB attenuation has little impact on the The block diagram, Fig.1, shows the signal flows through the Digital Preamplifier. Starting with the inputs, all analog inputs go through a switching section, allowing the chosen one to be digitised using the CS5361/81 ADC chip. The resulting audio data goes into serial port zero of the ADAU1467. Note that the selected buffered analog input is made available on the Monitor output. The ADAU1467 sets the ADC to operate at 192kSa/s. The miniDSP MCHStreamer receives digital data from your PC siliconchip.com.au and delivers data to serial port one of the ADAU1467. The digital audio input can be coaxial (S/PDIF) or optical (TOSLINK). These go to an input switch, which routes the selected signal to an S/PDIF receiver in the ADAU1467. The ADAU1467 chip performs all audio processing, under the control of the PIC microcontroller over an SPI serial interface. Both the miniDSP MCHStreamer and S/PDIF inputs go via their own ASRCs, which synchronise their input sampling rate to the DSP’s sampling rate. Any of the digital, USB or analog inputs can be selected inside the ADAU1467 and routed to the miniDSP Fig.1: the block diagram for the Digital Preamplifier. The digital, USB and analog audio is all routed through the ADAU1467 DSP engine, under the supervision of a microcontroller. Australia's electronics magazine October 2025  31 Soldering the LFCSP-88 ADAU1467 chip We will discuss this more in the construction section (in a later issue of the magazine), but it is worth noting that soldering these ICs is not as hard as we thought. Probably the trickiest part is not putting too much solder on the ground pad. We found we were using far too much, and the IC was floating on it, resulting in poor connections at the edge pads. To address this, after reflowing the IC using a hot air gun, we used a soldering iron to draw a bead of solder along each side, to ensure all the pads were properly soldered. If you use a lot of flux, you can draw a big blob of solder along, and as the pads are small, they don’t have enough surface tension on the solder to form bridges. This quickly solders all the remaining edge pads. You can see the result here. Despite the DSP chip not having any leads, thanks to extended pads on the PCB, it isn’t too difficult to hand-solder. Still, if you are not confident, you’re better off ordering the carrier board with chip already on it. MCHStreamer output. This output goes via another ASRC, which synchronises this output stream to the MCHStreamer sampling rate. The digital audio stream then runs through three parametric equalisers, which operate on the full input data stream, so these affect all output channels. The data is then split into four channels, each being processed similarly. Each has a further three parametric equalisers, followed by crossover filters and delay modules. The four streams are finally routed to the four DACs that provide the analog outputs of the Digital Preamplifier. All DSP processing is done by the ADAU1467 at a 192kSa/s sampling rate, which is just over 5μs per sample. This defines the channel delay resolution and the Nyquist bandwidth limit – though the output DAC analog reconstruction filter has a narrower bandwidth than this. So that filter defines the system’s upper frequency cutoff. Volume control is applied across all channels after all signal processing is complete, and is also implemented digitally. We have measured the performance of volume controls implemented using the PGA2310, a fine volume control chip, and found there to be no real difference compared to using a good 24-bit DAC like the PCM1794/8 and adjusting the volume in the digital domain. While you might worry at reducing the volume resulting in loss of resolution, any spurs and harmonics are so far into the noise floor (below -120dB) that this concern is unfounded. Circuit details Due to the complexity of the overall circuit, and the repetition of certain blocks (specifically the four DACs), we will be presenting the circuit in 10 bitesized chunks. These are spread across two PCBs; eight are on the main PCB, while the other two are the separate main power supply PCB and the front panel controls. The eight circuits that comprise the main PCB are: 1. Analog input switching 2. The ADC 3. Digital audio I/O 4. The DSP core 5. The DACs (four almost identical blocks) 6. The miniDSP interface, which connects to the commercially made MCHStreamer USB interface board 7. The microcontroller section, which includes the LCD interface 8. The onboard power supply, which filters and further regulates the output of the separate PSU board There are a further two circuit sections on separate PCBs: 9. The user controls (rotary encoder, buttons etc) 10. An external AC-to-DC power supply board that feeds the main board We’ll look at each of these in turn. Analog input switching The analog input switching in the digital preamplifier, shown in Fig.2, is pretty conventional. Developing this Digital Preamp required a lot of time and effort; shown in the photo is a prototype that had served its purpose. Yes, I did salvage all the expensive bits... 32 Silicon Chip Australia's electronics magazine siliconchip.com.au All analog inputs have RF suppression beads and 100pF capacitors to reject RF that may be picked up by the input leads or signal source. These have no effect on audio-­ frequency signals. This is followed by 22μF DC-blocking capacitors, biased to ground by a 100kW resistors. These ensure that all inputs have no DC offset, and as you switch between them, there will be no clicks or pops. You will note that on the second auxiliary input (at the top) we have included two optional resistors. If you have a signal source that delivers over 1V RMS, like a CD, DVD or Blu-ray player, you can swap the ferrite beads for (say) 2kW resistors and solder 1kW resistors into these spots. Such a configuration allows for up to 3V RMS without clipping on the ADC. We don’t envisage you will have many really high level inputs, but if you do, you can add similar resistors to other inputs. The -3dB corner frequency of this input stage is defined by the 22μF capacitor and the 100kW bias resistor paralleled with the 47kW resistor at the input to the buffer op amp, which itself has an input impedance of more than 30kW. This frequency is 0.5Hz (1 ÷ [2π {100kW || 47kW || 30kW} × 22μF]), which is way outside the audio band, and will have no impact on audio performance. IC5, an NE5532(A), buffers the input signal and provides a sample of this to the monitor output. It also drives the ADC inputs. You can use a standard NE5532; the A version has slightly better noise limits, although both types have extremely low noise and distortion. We have included 100W series resistors on the monitor output, but remember that this should not be used to drive heavy loads or long lines, as Fig.2: the four stereo analog inputs are routed to the ADC using this circuitry. Switching is via signal relays, followed by an op amp based buffer. siliconchip.com.au Australia's electronics magazine October 2025  33 Fig.3: the left & right channel signals from Fig.2 are digitised here. IC6a/IC6b are inverters that generate complementary signals, which are filtered by IC7/IC8 and clamped by schottky diodes before reaching the ADC chip, IC9. this is a really important signal in your preamp. You will note there are 10W/100μF low-pass filters on the ±10V supply rails. These are included to isolate this section from the other sub-rails that operate from these supplies. The ADC The ADC chip we have selected is the CS5361 or CS5381. The circuit with this is shown in Fig.3. It is pretty much straight from the manufacturer’s datasheet; we have used this configuration in the past with great success. The initial version of the preamplifier used a lower-cost ADC, but we were not happy with the noise floor, so we moved to the tried and true, but more expensive, CS5361/81. 34 Silicon Chip We feel the lower-cost CS5361 is fine for the job, but for a slight premium, you can splash out on the CS5381, which has a 5dB-odd margin in THD+N. Both provide superlative performance. Things to note in this section are the use of the NE5532 dual op amp IC6 configured as a pair of signal inverters. This is required to generate the balanced inputs the ADC requires. We have selected 1kW as the feedback/ input resistance, which finds a good balance between low resistance and thus noise, and ensuring the NE5532 is not loaded too much. Following this are the manufacturer-­ recommended drive circuits, which are unity gain buffers with 91W resistors included to ensure the operational Australia's electronics magazine amplifier is not upset by the notoriously difficult load that the input to the ADC presents. We have spent a lot of time testing alternative ADCs and drive circuits over the years, in the pursuit of low noise and distortion. While the manufacturer’s recommended circuit is fine, we have learned the importance of the 2.7nF NP0/C0G ceramic capacitors across the ADC input pairs. In one test, we tried several different capacitors, ranging from greencaps through silver mica and everything in between. Using a reputable NP0/C0G ceramic capacitor is essential, as distortion increases of over 10dB will be seen if you use something incorrect, such as an MKT capacitor. This is a result of the input presenting siliconchip.com.au a complex load, which will expose even minor non-linearities in these capacitors. Appropriate capacitors are available from the likes of Mouser, DigiKey and element14. You will note that we have another set of local ±10V filtered rails (±10Vfilt2), as we have in all areas of the circuit. This may be over the top, but is a small cost to ensure we have clean rails and minimal risk of noise being coupled between sections of the circuit. CON9 is an I2S test header for the ADC. It is really useful to probe this with an oscilloscope; the LRCLK and MCLK signals in particular. If you are wondering if the ADC is working, trigger your scope off LRCLK and probe SDATA. Note, though, that the ADAU1467 DSP drives MCLK and LRCLK, so do not expect to see anything on these lines until it is up and running. We have included BAT85 clamp diodes on the input to the ADC to protect it from signals that go above the +5V rail or below 0V. This will occur if the input is over-driven, or if an input is connected with a large DC offset. These protect the ADC chip from such excursions. The ADC inputs are internally protected, but we want these as ‘belts and braces’ protection so that your expensive Digital Preamp is safe from abuse. We have tested the distortion performance with and without these protection devices, and there is no measurable difference. The first version of the digital preamplifier used a much cheaper ADC, which we ultimately concluded was a false economy. If you’re going to spend several $100s to build the Digital Preamp, you might as well spend a few more dollars to get the best ADC. of the ADAU1467’s internal ASRCs. These have around 139dB of dynamic range and can up-sample or down-sample with ratios of up to 1:8 and 7.75:1. So we can accept input signals with sampling rates from about 24kSa/s up. When up-sampling, the ASRC generates interpolated data to maintain a 192kHz data stream sampling rate. IC13 is a buffer to drive an S/PDIF output from the digital output signal from the ADAU1467 chip. However, this is not routed to the rear panel, as we don’t have any use for it in our system. It is there if you need it, and it should work (in theory...). DSP core The circuit for the DSP part of the device is shown in Fig.5. The ADAU1467 is an application-specific IC (ASIC) made for audio processing and provides much of the functionality of the Digital Preamplifier. A major reason for selecting this part is that it provides multiple ‘clock domains’, allowing us to integrate the S/PDIF and miniDSP (USB) devices. It also provides sufficient signal processing power and memory for all the volume control, equalisation, filtering and delay functions we require on each stereo band. Once we determined that the ADAU1467 was the right part, we stopped to have a think. This chip only comes in an 88-lead, 12 × 12mm LFCSP package with a 5.3mm square exposed pad underneath. We put in a lot of effort to stick to through-hole parts where we can, and Digital audio I/O We have included S/PDIF (coaxial) and TOSLINK (optical) digital audio receivers, and included the ability to decide which goes to the ADAU1467 DSP. It includes a receiver that can handle the raw (low-level) signals from a coaxial link. The switching circuitry is shown in Fig.4. The clock for the digital audio stream is generated by the signal source. This means that we need to synchronise the input clock source to the Digital Preamplifier clock source; otherwise, we will end up with more samples than we need, or not enough. For this we use another siliconchip.com.au Fig.4: the digital I/O is quite simple as there are just two digital inputs (one TOSLINK [OPT1], one S/PDIF [CON10]) that are selected by a single relay. The outgoing digital signal is fed directly to OPT2, and to the S/PDIF output RCA connector via buffer IC13 and a 75W impedance-matching resistor. Australia's electronics magazine October 2025  35 when forced to use SMD parts, endeavour to use manageable packages, selecting the largest lead pitch we can. This part not only has a ‘fine lead pitch’, it doesn’t even have leads! The project kind of sat on the shelf for a while, and in the end Phil decided to build the Digital Preamplifier for himself, as a lot of the design and software was ready to go from previous designs. He toyed with the idea of going back to one of the older ADAU devices that he has used in the past, but this would have demanded compromise on performance, and we really wanted to use a recent device. 36 Silicon Chip As it turns out, soldering the chip was not as hard as he initially thought (see the accompanying panel on page 32). We also found a way to avoid soldering it entirely if you are dead set on that! The layout and peripheral components around the ADAU1467 (IC18) are straight from the data sheet. Besides the support components, mostly this part of the circuit is just routing signals to and from all the other parts. All the components around IC18 are surface-­mounting types, because the chip runs at a high clock rate (nearly 300MHz) and needs excellent Australia's electronics magazine local filtering of the supply rails. We have stuck to M2012/0805 devices where we can; they are massive (2.0 × 1.2mm) compared to the lead pitch on the chip, anyway. We have included a clock buffer for the system master clock (IC10), which runs at 24.576MHz. This distributes this clock signal to the ADC and DACs. We have also included a header for probing the SPI interface between the PIC microcontroller and the ADAU1467. This is mainly for debugging, but you might find other uses for it. When we were building the first prototype of the Digital Preamplifier, we siliconchip.com.au The Core boards cost about $80 at the time of writing, which is a bit of a premium on the $30 cost of parts from Mouser/DigiKey. Still, if you do not feel confident in soldering the chip, we recommend you shell out for one of these. We tested two, and both worked fine. DACs Fig.5: the DSP core is where all the digital signal processing occurs. It’s little more than IC18 and its support components. If you don’t fancy soldering IC18, you can buy it on a carrier board and plug it into the two headers shown at upper-right. In that case, none of the other parts shown here but IC10 are installed. became aware of the “ADAU1467 Core Board” and development boards on eBay and AliExpress. This board is pretty much exactly the same as our ADAU1467 core circuit, which we replicated from the OEM design notes. So much so that we were able to buy one, and ‘graft’ it onto our board, simply leaving off IC18 and its support components. So we rolled this into our design, and now you are able to choose whether you solder that 88-pin leadless chip, or leave the whole section off and plug in a purchased ADAU1467 Core Board to the two DIL headers shown at upper-right in Fig.5 (and in this photo). siliconchip.com.au There are up to four onboard DACs, all based on PCM1794A or PCM1798 chips. The circuit for one of these is shown in Fig.6. These chips are pin-compatible, with the PCM1794A being more ‘premium’, offering 127dB dynamic range vs 123dB and a THD+N of 0.0004% vs 0.0005% at 44.1kSa/s. We are running the whole digital signal processing part of this design at 192kSa/s for a couple of reasons. Firstly, if we want to implement time alignment with simple buffer delays applied to individual channels, the delay resolution is defined by the DSP clock rate. 192kSa/s is 5.2μs per sample. It would be possible to implement a filter to generate this phase shift at a lower sampling rate, but that would substantially complicate the programming and affect phase linearity across the band. A second reason for using a 192kSa/s sampling rate is to ensure that the frequency response is flat for the entirety of the audio band and well beyond. We want the Digital Preamplifier to be as transparent as practical. We have used the CS4398 in several other designs with great success. However, while developing this Preamp, stocks were low and lead times long. So we went to the PCM1794A/98. If you look at the datasheet for this DAC, you see excellent specs, a dynamic range and signal-to-noise ratio of 123dB (129dB for the PCM1794A), and a THD+N of 0.0015% for both. Hold on, didn’t we just say that the THD+N was 0.0004%? Looking more closely at the datasheet shows that this is true at 44.1kHz but at 88kHz, the THD+N doubles to 0.0008%, and at 192kHz, it nearly doubles again, to 0.0015%. None of these are even remotely a problem, and the dynamic range of these chips is even better than our usual CS4398. With their superlative SNR, they are very well suited to our application, where we will be performing volume control digitally. We spent some time measuring this sampling rate dependency of the THD figure. Especially given that super low noise floor. With a 1kHz, 1.8V RMS output (0.9V RMS input), the second harmonic is at 0.0015%, which is entirely consistent with the specified performance. The noise floor is about 130dB below full scale. The Digital Preamplifier design keeps wiring and cabling in a high-end hifi system to a minimum. This version uses the plug-in ADAU1467 Core Board rather than a discrete chip. Australia's electronics magazine October 2025  37 We found some low-frequency spurs that were mains-related and might be because the Digital Preamp sat on top of the signal generator during testing. As with the ADC, we have included an I2S header (CON1) on each channel. These provide test points for the MCLK, LRCLK, BCLK and SDATA signals. Once the DSP chip is running, you should see a 192kHz square wave on the LRCLK line, with the data and other clock signals synchronised to it. The circuit is pretty much what’s recommended by the manufacturer, and as it does what it says on the box, we see no need to change it. A relay is included for each channel that disconnects the output at power-up and power-down. This prevents unwanted noises being sent to the speakers. USB interface This is a somewhat expensive, but we think really important, component of the Digital Preamplifier. It allows high-quality audio to be received from and sent to a computer via a USB port. It does this by interfacing to an external board. The interface is electrically isolated, as shown in Fig.7. The MCHStreamer Lite (which excludes the unnecessary optical input) costs ~$150. We have seen several other USB-to-I2S data converters, but no alternatives at a good price that can also perform the I2S-to-USB task. If you do not need to record audio from your Digital Preamplifier on your Fig.6: one DAC channel; the op amps and associated resistors and capacitors form the reconstruction filter. This circuit is replicated four times on the board, with only the DAC_SCLK_CHx, DAC_DATA_CHx and physical output connector varying between them. 38 Silicon Chip Australia's electronics magazine siliconchip.com.au computer, you could substitute the miniDSP MCHStreamer with an ‘output only’ alternative and wire it into the miniDSP headers. The MCHStreamer interface has been kept as simple as possible. The headers allow the MCHStreamer to be connected to the Digital Preamplifier board using flying leads. Only a handful of wires are actually needed, but to keep things tidy, we used the plugs and flying leads miniDSP provided and soldered all the pigtails to the PCB. We have placed the connectors on the board so that if you solder the pigtails with the connector standing straight up from the PCB, the pigtails simply go straight down into corresponding PCB pads without any wires crossing over etc. You then bend the wires to plug into the miniDSP as shown in the photos. The MCHStreamer deals with the USB to I2S conversion. On a Windows computer, you need to install ASIO drivers; once you have made the purchase from miniDSP, they are available for you to download and use on all Fig.7: this circuit snippet interfaces the MCHStreamer USB audio I/O interface with the rest of the circuitry. It’s isolated to avoid hum loops and such. your devices. On Linux and Mac computers, the device will simply work. The MAX22345SAAP+ isolates the computer’s USB port from the Digital Preamplifier. This avoids annoying hum loops, which are a notoriously common with laptops and PCs. This isolation is for noise reduction only; it is not galvanic isolation to provide mains or high-voltage protection. Microcontroller The microcontroller circuit shown in Fig.8 does a few things: Fig.8: the microcontroller circuit, which configures the DSP and handles the user interface. The buttons and rotary encoder connect via CON16, while the alphanumeric LCD is wired up via either CON8 or CON19. siliconchip.com.au Australia's electronics magazine October 2025  39 Replacing the PCM1798 with a PCM1794A While the Preamp can be built with either PCM1794A or PCM1798 DAC chips, and they are pin-compatible, some components need to be changed; the circuit is shown with values to suit the PCM1798. The reason for this is that the full-scale output current is different, being 7.8mA for the PCM1794A ($25 per chip) and 4mA for the PCM1798 ($10 per chip). To change from the PCM1798 to PCM1974A, there are a handful of resistors and capacitors that need to be different values, and a couple of parts that are omitted. These are listed in the notes in Fig.6 and on the PCB silkscreen. ● It loads the required software into the ADAU1467 on power-up ● It displays information on a 16×2 character alphanumeric LCD ● It handles sensing for the pushbuttons and rotary encoder ● It initialises and communicates with all the other chips, like DACs and ADCs ● It handles input selection, volume control, equalisation etc ● It decodes and handles infrared remote control signals The chip (IC15) comes in a 44-pin QFP package that is not difficult to solder. We thought about implementing a fancy graphical display, but there’s pretty limited space on the front of a 1U case, which is just 44.5mm tall. While the Digital Preamp is a fairly advanced piece of gear, the alphanumeric LCD provides enough space to do what we need, ie, adjust volumes, switch between inputs and set up digital filters. The user interface to the Digital Preamplifier needs to: ● Let you set up the channels in terms of crossover parameters, slopes, relative attenuation and frequencies ● Let you set up the equalisation ● Let you set the subwoofer channels for mono or stereo output ● Select the channel to monitor ● Select the input to listen to ● Change the volume Once the unit is set up, it is only the last two things you will ever really do. We generate a negative bias voltage for the LCD from the -10V rail using a simple LED voltage drop (LED2). We need this as we are running the 16×2 LCD from just 3.3V, and the panel needs close to 5V on the bias to operate properly. Every 16×2 LCD we have seen works well this way, and this makes the LCD data interface compatible with the 3.3V PIC microcontroller. 40 Silicon Chip A typical 16×2 LCD screen has a 16-pin SIL interface, which we have adapted for convenience to an 8×2pin header (CON19). This way, we can crimp an IDC plug onto a ribbon cable and simply plug it into the PCB. The wires at the other end can then be soldered to the LCD’s SIL header, or via another IDC plug and a small adaptor board that we’ve used before. Controls The controls (buttons, rotary encoder etc) are mounted on a small, separate PCB; its circuit is shown in Fig.9. The board houses three push button switches, a rotary encoder with an integrated pushbutton switch, and a TSOP4136 infrared (IR) receiver. This mounts to the front panel using the rotary encoder boss and nut. The rotary encoder on the front panel is a volume control most of the time. There are two buttons to the left that let you switch through the available inputs. The GUI defaults to showing the volume and input selected. If you push the volume control in, it will save the current parameters. If you push the button to the right of the control, which is like a ‘back’ button, you can rotate through the other menus, which allow you to change: ● Crossover parameters ● Equalisation ● Load a setup ● Save a setup to one of three spots On power-up, the system reads the configuration from its EEPROM. There will not be valid data on the first power-­­up, so the software will use default values. Remember to save your setup once you enter it; after that, the system boot to your main configuration on power-up. Power supply All that remains of the circuit is the power supply. This is split into two parts, because the main rectification, filtering and pre-regulators are on a standalone power supply board. We have done this to ensure that all the rectification and switching ‘stuff’ happens away from the mixed signal analog and DSP board. It also means that if we want to change the packaging or power supply, we can do this simply. The circuit of this separate power supply board is shown in Fig.10. This is pretty conventional; it generates a 5V digital supply and ± 10V DC rails for the analog parts of the Digital Preamplifier. The main challenge here is the need for well over 250mA from the analog rails and in excess of half an amp on the 5V rail. This makes it difficult to design it to run from a DC supply, with a voltage inverter generating the negative rail. It makes using a single AC input (such as from a plugpack) less than a great idea. We were using a 16V AC 1.38A plug pack in this way during tests, and when the DSP was loaded, the plugpack fuse blew! The plugpack Fig.9: the small control board circuit; CON1 connects directly to CON16 shown in Fig.8. Australia's electronics magazine siliconchip.com.au also produced high (±22V) unfiltered analog rails, resulting in high dissipation in the regulators. Instead, we are using a dual 12V AC secondary 30VA mains transformer to drive the power supply board, mounted in the same case, near the supply board. REG1 & REG2 need heatsinks; they will get toasty warm, but they do pass our ‘can you hold your finger on them’ test. The digital rail uses a switch-mode buck (step-down) converter. This is required to efficiently drop the unregulated 16V rail down to a regulated 5V. The LM2575-5 (REG3) does not get hot and can operate without a heatsink. We have used generous main filter capacitor banks, with three 2200μF capacitors per side. You could probably get away with half that; the main reason for using this many was the ripple current. Two 1000μF capacitors were within specification in this circuit based on their ripple current rating, but they got warm during operation, which does not bode well for a long service life. So we switched from two to three devices and (more than) doubled their capacitances to be safe. The regulators are fed through 47μH/100μF LC low-pass filters. These, along with cuts in the ground plane, seek to isolate digital current paths to the main filters from the analog regulators. Onboard regulation The +5V, +10V & -10V supplies from CON2 & CON3 on the power supply board are fed to CON12 & CON11, respectively, on the Digital Preamplifier board – see Fig.11. The main digital supply is +3.3Vdig. This is generated from the incoming 5V rail using a low-drop out regulator (REG1, LD1117V33). This is distributed on a power plane on the fourlayer PCB (more on that later). The ADAU1467 DSP also has an analog 3.3V input, which we don’t really rely on, but we have included a separate regulator to provide clean power to it (REG2). We figured if we left this off, we would regret it at some point! It just depends on how the software in the ADAU1467 is written. The ±10Vfilt1 rails are simply filtered versions of the ±10V supplies from the power supply board. As we’ve seen in the other circuits we’ve looked at, many of them have additional filtering to feed the individual ICs. The 5V analog rail for the DACs (+5Vdac) is derived from the +10Vfilt1 rail, as we want this to be as clean as possible, and definitely do not want digital or switching noise from the other 5V rail creeping in. The power supply also includes circuitry to control the output-enable relays (the bottom third of Fig.11). This holds the output relays off during power-up and disconnects the outputs as soon as power is removed. This is extremely important when driving a power amplifier directly, as we need to suppress any start-up and shutdown ‘thumps’. There are two main sources of these; the first is the operational amplifiers and DC decoupling capacitors settling. The second is the ADC and DAC, which use a single-rail analog stage with the input and outputs offset by 2.5V. This offset is removed by Fig.10: this separate power supply board converts the 2 × 12V AC inputs from a toroidal transformer to the +5V and ±10V rails that power the whole Digital Preamplifier. Note that the case is Earthed and the PCB Earth connection is via one of the PCB’s mounting holes. siliconchip.com.au Australia's electronics magazine October 2025  41 AC-coupling the signals, but charging and discharging these capacitors takes a little time. The start-up circuit monitors the ‘half rail’ voltage between the positive and negative rails, via two 4.7kW resistors near the centre of the circuit. This is compared to the same half-rail voltage but filtered by a 220μF capacitor. Q2 and Q11 together sense a difference in excess of ±0.6V, and if this is detected, they switch on Q13, which disables the output. This capacitor is discharged at powerup, so it ensures the system is muted then. Also, as the rail voltages drop at power-off, this holds charge and forces the output to be muted as soon as one of the rails has dropped by 0.6V. PCB design As briefly mentioned earlier, the rather large main PCB is a four-layer design (the power supply needs only two layers). The main advantage of doing it this way is that we can have two signal layers (on the top and bottom of the PCB) and power/ground planes on the internal layers. This greatly simplifies the job of routing the PCB, as we need to do very little to correctly connect the power and ground pins of most components. It also keeps voltage drops nice and low. Fig.12 shows the power plane with multiple rails. These allow distribution of the digital and various analog rails to each section of the circuit. As we’ve seen in the circuit diagrams, each main analog section has its own sub-rails derived from the ±10V rails using 10W/100μF low-pass filters. The blue areas in Fig.12 show the internal layer that distributes the various power rails. The pink area is the ground plane; it extends throughout the whole of the blue area, too. The top plane of the PCB is primarily digital traces (orange/brown), while the bottom plane of the PCB primarily carries the analog signals (mauve). Once we get power and ground traces onto their own planes, routing becomes a lot easier, and we are able to choose optimal routing of signals without the need to accommodate those power and ground traces at the same time. Fig.13 shows the copper traces with the power plains hidden. Here, you can see how we have separated the digital and analog sections of the circuit. You will also note the differential output lines near the DAC chips (towards the upper right) running close together in pairs. This has been done throughout the layout to minimise hum and noise pickup. This extends to the output. Similar attention has been paid to the input stage and ADC. Packaging We have used an Altronics H5031 one-rack-unit (1U) case to hold all Fig.11: the Digital Preamp’s onboard power supply circuitry. This includes a filter for the ±10V rails, a +5Vdac analog supply that’s derived from them, two +5V and two +3.3V digital rails derived from the incoming 5V supply, plus the power on/off output disconnection control circuitry shown at the bottom. 42 Silicon Chip Australia's electronics magazine siliconchip.com.au this. It is very neat and not hard to do the metalwork for – although there is a fair bit of drilling on the rear panel. The rear panel houses the IEC mains connector, mains fuse, holes for the USB & S/PDIF inputs, plus 10 dual RCA connectors for the analog inputs and outputs. Next month That’s all we have space for in this issue – that was a lot to take in at once! Next month, we will present the parts list, PCB assembly and initial testing instructions. After that, the third and final part will cover case drilling & cutting, final assembly, wiring and usage SC of the Digital Preamplifier. Figs.12 & 13: by making the PCB a four-layer design, we have the luxury of an internal power and ground plane, along with the top/bottom layers, which are used mainly for signal routing. The blue areas are the internal copper pours for power distribution, while the pink area is the internal ground plane (left diagram). The diagram on the right shows the board without the power planes, so you can see the top & bottom layers more clearly. You can see how clean the signal routing is, since power and ground tracks are not needed on these layers. We keep the digital and analog tracks separate by routing them on opposite sides of the PCB. Both diagrams are shown at 59% of actual size. siliconchip.com.au Australia's electronics magazine October 2025  43 LOOKING TO REFRESH YOUR WORKBENCH? 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Shop at Jaycar for even more service aids & essentials: • Adhesives & Insulation Tapes • Solder & Soldering Aids • Wire & Heatshrink Tubing • Fasteners & Cable Ties • Ultrasonic Cleaners • Tools & Workbench Accessories Explore our great range of 3D Printing gear, in stock on our website, or at over 140 stores or 130 resellers across Australia and New Zealand. jaycar.com.au 1800 022 888 | jaycar.co.nz 0800 452 922 Prices shown in $AUD and correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. Part 2 by Richard palmer HOME ASSISTANT R P with a aspberry i Having set up a custom Home Automation (HA) system, we now look at advanced features like cameras, custom dashboards, IR remote control, notifications and remote access on a mobile phone, tablet or PC. L ast month, our article on Home Automation explained how to set up a Raspberry Pi to act as a Home Automation hub. We also presented a project article to build a Satellite, allowing the connection of all sorts of low-cost sensors, relays, displays and more. We mentioned some cameras that can be connected to this HA system but didn’t give instructions on doing so. We will now explain how to connect a few different types of camera. After that, we will create a custom dashboard, a temperature history chart and an adjustable thermostat. We will then look at switching devices on and off with infrared remote control, set up remote access from a smartphone or tablet using a VPN and create an intruder alert with a passive infrared (PIR) sensor detects motion. Finally, we will explain how to back up your HA system in case something goes wrong. configure. Daylight image quality was limited, but good enough for many purposes. The ONVIF IP camera was the most complex to set up, requiring a smartphone app to connect it to the network. Two of the four IP cameras we obtained were not ONVIF-compliant, despite their specifications saying they were. Once connected to the network using the mobile phone app, the two ONVIF-compliant cameras were automatically set up by HA. These cameras produced the best pictures overall, particularly in poor light or darkness. Both had pan and tilt capabilities that could be accessed from HA. USB camera setup Plug the USB (UVC) camera into a spare port on the Raspberry Pi. There is no need to switch the hub off to do this. Click on your name at the bottom of the left menu bar. Enable the “Advanced mode” slider in the first block of options. Go to Settings, then System, then Hardware and click on the ALL HARDWARE link. Type “video” into the search box. Click on the down arrow next to the first entry that resembles “video0”. Copy the “Device path:” value. It will be something like “/dev/video0”. Exit the menu and go to Settings, then Add-ons. Install the “File editor” add-on by going to the ADD-ON STORE and searching for “file”. Once it has finished installing, enable the “Watchdog” and “Show in sidebar” options and start the add-on. Once it has started, click on the File editor link in the sidebar menu. The file “/homeassistant/configuration. yaml” should open automatically. If not, click on the folder icon at the top left corner of the panel and select Setting up cameras Three of the options for adding a camera to HomeAssistant are explored below: a USB camera connected directly to the HA hub; a $10 ESP-CAM converted into an ESPHome webcam, and an ONVIF compliant IP camera with pan and tilt functions. Each has advantages and disadvantages. The UVC-compliant USB camera was the easiest to configure, but must be plugged directly into the HA hub. It provided good images in daylight. The ESP-CAM has WiFi and was the least expensive and straightforward to 46 Silicon Chip Screen 8: the USB camera’s card in the Overview dashboard. Screen 9: the ESP-CAM card with the LED toggle visible. Australia's electronics magazine siliconchip.com.au “configuration.yaml”. Click the red edit icon at the bottom right-hand corner of the screen. Add the code shown in Block #1 at the end of the file (you need to type the indentation spaces exactly like this, not just the text - indents are two spaces), and save it with the red disk icon at the top right. Restart Home Assistant using the cog icon at the top right of the screen. Once HA has restarted, the camera card should appear in the Overview dashboard – see Screen 8. Setting up the ESP-CAM ESP-CAMs have an ESP32 microcontroller attached to a small camera module. If the USB daughterboard was not supplied with your camera, you will need a USB-to-TTL serial adaptor to complete the process. You can find instructions for doing that from siliconchip.au/link/ac5x Now connect the ESP-CAM to a USB port on the HA hub. In ESPHome Builder, click on +NEW DEVICE and name your device ESP-CAM or similar. Select ESP32 as the device type. Click INSTALL, then select “Plug into the computer running ESPHome Device Builder”. A USB Serial device should be identified. Select it, and the firmware should automatically compile and upload. It might take some time for the ESP32 platform files and libraries to download before compilation begins. Once the compilation and ESP32 programming are complete, the ESP-CAM should be visible in the ESPHome Builder tab. Add the code from Block #2 to the device’s YAML configuration file in ESPHome Builder and re-install the firmware wirelessly (again, you must include any spaces at the start of the lines exactly like this). Once the device has rebooted, go to Settings then Devices & services and accept the discovered device, naming it ESPCAM or similar. Re-load the Overview dashboard and a new entry for ESP-CAM, and its associated LED switch should appear within a minute or so – see Screen 9. The ESPCAM LED slider enables the onboard LED. If the camera image does not appear, it is likely that your camera doesn’t follow the original AI-Thinker pinouts. Opening the logs may help you figure out what’s going on. Several other pin-out options are available in siliconchip.com.au CODE BLOCK #1 ## USB_camera.yaml camera: - platform: ffmpeg name: USBcam input: /dev/video0 CODE BLOCK #2 ## ESPCAM.yaml esp32_camera: external_clock: pin: GPIO0 frequency: 20MHz i2c_pins: sda: GPIO26 scl: GPIO27 data_pins: [GPIO5, GPIO18, GPIO19, GPIO21, GPIO36, GPIO39, GPIO34, GPIO35] vsync_pin: GPIO25 href_pin: GPIO23 pixel_clock_pin: GPIO22 power_down_pin: GPIO32 ## Image settings name: ESPcam id: ESPCAM switch: - platform: gpio id: espcam_led name: “ESPCAM LED” pin: 4 CODE BLOCK #3 ## SamsungTV_IR.yaml ## IR funtions for Pico external_components: - source: github://pr#5974 components: [remote_transmitter] refresh: always ## IR infra red remote_transmitter: pin: 0 carrier_duty_percent: 50% ## toggle power on/off button: - platform: template name: “TV on/off” id: TV_toggle on_press: - remote_transmitter.transmit_pronto: data: “paste hex string here” CODE BLOCK #4 {{now() - state_attr(‘’automation.Intrusion’’, ‘’last_triggered’’) > timedelta(minutes = 1) }} CODE BLOCK #5 ## intruder_alert_enable.yaml - platform: template name: “Intruder active” id: Intruder_active optimistic: True the documentation at siliconchip.au/ link/ac5y IP camera setup While integrating an IP camera into HA is straightforward, finding a camera compliant with the ONVIF standard for pan, tilt and zoom (PTZ) can be tricky. Marketplaces like eBay or AliExpress will return hundreds of matches to a search for “ONVIF Australia's electronics magazine These code blocks will be available as a download from siliconchip.com.au/ Shop/6/2482 webcam” or “ONVIF IP camera”. Check in the item’s specifications for a mention of ONVIF compliance. I had the most success with V380 cameras that also indicate ONVIF compliance. Install the camera on your local network using the app that applies to your camera, eg, V380 or V380 Pro. I found the V380 mobile phone app straightforward to use; the cameras behave like October 2025  47 Screens 10 & 11: the IP camera’s dashboard card (left), and the dashboard card with pan and tilt controls added. a WiFi hotspot when first switched on. This time, we’ll launch the installation via a link on the HomeAssistant website. Navigate to the ONVIF page on the HomeAssistant webpage (www.home-assistant.io/integrations/ onvif) and click on the blue ADD INTEGRATION TO MY button. Accept the invitation to open another HA settings page as well as the “Do you want to set up ONVIF” prompt. Allow the device setup to search automatically for your camera. Your camera should appear in the “Select ONVIF device” pop-up options. Select it and click SUBMIT. Name your camera “IP camera” and finish the setup. Refresh the Overview dashboard and the camera should appear, as shown in Screen 10. The pan and tilt functions can’t be enabled in the automatically configured Overview dashboard, as additional code needs to be added to the display card. These functions will be enabled later, when creating a custom dashboard. sign icon inside the dashed box to create the section, then click the “+” sign within the section to create a new card. Type “picture” into the search box and select “Picture glance” from the results. Select your IP camera from the Camera entity drop-down menu. In the “Entities (required)” section, delete the existing entries. Click on SHOW CODE EDITOR immediately below. In the “entities:” section of the existing configuration, below the existing “- entity” line, paste the contents of the IP_camera.yaml file from the download pack (siliconchip.au/ Shop/6/2482) and save the configuration. The “camera_image” line should be after the pasted text. Click DONE to exit editing mode. The pan and tilt controls on the camera card should look like those shown in Screen 11; you can test them now. If the arrows don’t appear on the camera card, it’s likely that you have pasted the file into the wrong spot or your camera’s stream name is different from the one in the file. In the latter case, make all references to the camera the same as the one in the “entity” line. A temperature history chart This section relies on you having built the Satellite described last month, which incorporates a temperature sensor, relay and LED indicating when the relay is on. To create another card for the temperature graph in a new section on the dashboard, enter editing mode and click on the “+” sign. Type “history” into the search box and select “History graph”. Change “Hours to show” to 1. Under the “Entities” heading, delete any existing entity and add “myHome Temperature” from the drop-down list, then save the result. A graph of the temperature over the last hour should appear, as shown in Screen 12. A custom dashboard So far, we’ve relied on the Overview dashboard, which is maintained automatically by HA. While it displays all the enabled devices, more advanced features are not available. The system supports multiple dashboards, so we will create one to enable the pan and tilt functions of the IP camera and to graph temperature over time. Go to Settings, then Dashboards and select + ADD DASHBOARD. Select the “New dashboard from scratch” option and make the Title “myDash”. “Show in sidebar” should be enabled. Select your new dashboard from the main left menu and click on the edit pencil at the top right corner of the screen. To create a card for the IP camera in a new section on the dashboard, click on the four squares and a “+” 48 Silicon Chip Screen 12: the custom temperature-over-time chart shown at the bottom and the relay LED history shown at the very top. Australia's electronics magazine siliconchip.com.au To complete the dashboard, we can add a timeline to show when the thermostat was switched on. Re-open the card by clicking on the pencil that appears when you hover over the control. Add a second entity, “myHome Relay LED” to the card. Click Save and a timeline should appear above the graph. Click DONE to exit editing mode. Place your finger on the temperature sensor. When the LED lights due to the AC On automation triggering, the end of the grey bar should turn yellow as the temperature graph spikes – see the top of Screen 12. A better thermostat The thermostat created in last month’s article lacks a key feature: the ability to easily change the temperature setpoint. HomeAssistant has a generic thermostat integration that can control the relay. First, disable the two existing AC automations in the Automations settings menu by moving their Enable sliders to the left. Go to Devices settings and add an integration called “Generic thermostat (helper)”. Name it “AC Thermostat”; select “Cooling mode”, use the “myHome Temperature” sensor and “myHome Relay LED” as the Actuator switch, then set the Cold tolerance to 1. The minimum and maximum target temperatures can be set to 10 and 30, respectively. Scroll down and click NEXT. Add temperature values into the Comfort and Eco presets, then click SUBMIT and FINISH. The card will appear in the Overview dashboard – see Screen 13. The setpoint is displayed in the centre of the card and is controlled by moving the larger open circle on the gauge. Enable the thermostat by clicking the snowflake icon. The relay LED should switch on when the setpoint is 0.5°C lower than the room temperature, and off when the setpoint is 0.5°C higher. The activity bar above the temperature graph that we created earlier should show the Relay LED’s activity as the thermostat is exercised. To use one of the temperature presets, click on the three dots at the topright of the card. A drop-down menu at the bottom right of the pop-up allows selection of any available presets (Screen 14). Selecting None will revert to the last manual setting. A home air conditioner (especially a siliconchip.com.au split system) is likely to have an infrared remote control. The TV remote control below could readily be adapted for this purpose. IR remote control Adding remote functions for devices with infrared remotes involves adding a button to your dashboard and connecting it to an appropriate code for the IR LED to transmit (like the one on our Satellite). Finding the correct codes for your device may take some hunting around. The most comprehensive source I have found is IRDB (siliconchip.au/ link/ac5z). The free sign-up allows five codes per day to be downloaded. The code begins with a patch to enable the IR function on a Pico. By the time this is in print, the “external_components:” section may no longer be required. If the code compiles properly, then leave it in; otherwise, try without it. A Button input is then defined, which will appear on the dashboard. Finally, get the PRONTO IR code from IRDB and paste it into the “data:” line. A separate section of code starting with “– platform: template” will need to be created for each additional function button (see Block #3). The SamsungTV_IR.yaml code in the download pack includes the code to toggle a Samsung TV’s power. Once the Satellite has been updated, a “TV on/off” button labelled PRESS should appear in the myHome card on the Overview dashboard – see Screen 15. If you have a Samsung TV, point the IR LED toward the TV and press the button. The TV should switch on or off with each button press. The appropriate codes for many other TV brands should be available from the IRDB database. Screens 13 & 14: the thermostat card (above) and accessing the thermostat presets (below). Access from a phone or tablet To provide access to a smartphone or tablet dashboard while connected to your local WiFi network, install the HomeAssistant app for iOS or Android. Start the app & follow the prompts. If you don’t enable location permissions, the device tracking function and the sensors on the mobile device won’t register properly with HA. The Notifications permission will be used in a later example, so enable it now. Enter the username and password you created earlier in HomeAssistant into the app. All HA functions should Australia's electronics magazine Screen 15: myDash on a mobile phone, with the TV on/off button visible near the bottom. October 2025  49 Screen 16: the TailScale website console page. The HomeAssistant entry needs to be made an Exit Node, and the detected subnet approved in the “Edit route settings” dialog. Screen 17: the TailScale control panel after a PC and phone have been added. be available. As mentioned before, creating and using a profile on HA without the ability to administer the system is a good idea for everyday and particularly mobile use. Virtual private network Remote access to HA from outside your local network requires several elements: a URL that is recognisable externally, a way to convert that to an IP address and secure access to the HA hub through your internet router. There are several different approaches to providing remote access to HomeAssistant, which are discussed at siliconchip.au/link/ac60 WunderTech provides a complete examination of the pros & cons of each method at siliconchip.au/link/ac61 Virtual Private Network (VPN) connections are relatively easy to set up and offer a high level of security. Tail­ Scale has a free offering that is a recommended HA option for remote access. TailScale needs to be installed on every device that has remote access. Each connects to TailScale’s cloud service to discover the other members. In most cases, no router settings need to be changed when using TailScale. 50 Silicon Chip The VPN requires setting up a Tail­ Scale account plus configuration of HA and your mobile device. If you find the instructions below difficult to follow, there are several good YouTube tutorials on connecting HA to TailScale. I found the one by Joyce Lin to be helpful (https://youtu.be/EJ3cjoJAaQA). Go to TailScale’s website (https:// tailscale.com) and set up a free account. It requires you to use an existing identity provider rather than setting up a new username and password. If your preferred identity source is not in the list, the OpenID Connect (OIDC) option can provide linkage to a wide range of additional providers. To add the integration in HA, go to the Settings then Add-ons menu and click the + ADD-ON STORE button. Search for “TailScale” and follow the installation prompts. Enable all four options in the configuration panel, then start the add-on and then click the OPEN WEB UI button. Log HomeAssistant into TailScale with the same credentials you used to create the account, re-authenticating if required. Next, connect your Home­ Assistant to your TailNet. The final step of the installation Australia's electronics magazine process on HomeAssistant opens a browser window that logs you into TailScale’s control panel. Under the “homeassistant” entry, there will be several blue indicator boxes – see Screen 16. If they have exclamation marks in circles, click on the ellipsis (…) at the end of the homeassistant line and select “Edit route settings”. Select both check boxes and then Save. The “Exit node” option allows HA to act as a server on your personal TailNet. You can now log into HomeAssistant from any device that is connected to your TailNet. The Subnet router option authorises the HA hub to route traffic from satellite devices through the TailNet. Install the TailScale app on your mobile device from the app store and log in to it. The HA app should now be able to access your hub when outside your wireless network’s range. Similarly, TailScale can be added on a PC – see the “linus” entry on Screen 17. Switching off WiFi on your phone, if it is enabled, will allow this feature to be tested. The HomeAssistant app on your phone will ask for a new IP address. http://homeassistant:8123 should do the trick, as TailScale provides address translation and routing services. After a few seconds, your connection to HA should be restored. An alternative, configured with just a few mouse clicks, is Home Assistant’s Cloud service, which has a 31-day free trial followed by subscriptions at around $11 per month or $110 per year, including GST. Your default HomeAssistant login has full administrator privileges on the remote device. For better security, creating a second, less-privileged account. Go to the Settings then People menu on the main HA screen then click + ADD PERSON and it will lead you through the process. Do not enable the Administrator option for this new account. Thermostat notification Notifications are implemented by creating an action in an automation. To create a new automation, add a Trigger, selecting Entity and then State as the type. In the When panel, select “AC Thermostat” as the entity, “Current action” as the Attribute. Set “From” to Idle and “To” to Cooling, then click on + ADD ACTION at the bottom of the screen, select siliconchip.com.au “Notifications” and “send a persistent notification” Fill in an appropriate message and click the SAVE button – see Screen 18. Each time the virtual AC switches on, a timestamped notification message will appear in the Notifications panel on all connected devices. To disable the automation, go to the Automations menu & move the slider attached to the automation to the left. A PIR intruder alert Now let’s create an automation that produces a notification each time the PIR sensor on the Satellite is triggered. The trigger will be the myHome.PIR entity. Set “From” to Clear and “To” to Detected, then click on “+ ADD ACTION” at the bottom of the screen and select Notifications. If you have set up remote access on a phone, select “send a notification via mobile_app_xxxx”. Put “Intruder alert!” in the message and in the title and click SAVE; name your automation “Intrusion”. If you have not enabled remote access at this point, use the “Persistent notification” option instead. Every time something moves in front of the PIR sensor, a notification message will be sent. If a human intrusion occurs or the cat decides to play in front of the sensor at midnight, you’ll be flooded by messages. A time delay on the automation being re-triggered will limit the number of messages. To delay re-triggering, a condition is added to the automation that detects the last time it was triggered and calculates whether it was longer than one minute ago. The automation is not re-triggered if the time was less than this. Edit the Intrusion automation, using the “And if” clause, and select Template from the “Other conditions” option. Enter the code in Block #4 (all on one line), which is also in the intruder_alert_enable.yaml file, into the “Value template *” box. Save the automation and test it. You should be able to trigger the PIR sensor multiple times, but only receive a notification on your mobile device if the PIR is triggered more than a minute after the last notification. To create a switch to turn off these notifications entirely, place the code from Block #5 directly under the Relay LED switch code and update the Satellite. siliconchip.com.au Edit the Intrusion automation, adding another condition. Select Entity and “myHome.Intruder active”. Set the State field to On, then save the automation. The new switch should appear on the myHome card in the Overview dashboard – see Screen 19. If the switch is off, no notifications should be sent. Two useful tools in debugging automations are the Logbook in the main menu and TRACES when editing the automation. In TRACES, clicking on an icon in the sequence will display what happened at that point in the automation’s flow. Backups Backups are important in maintaining the integrity of your setup over time. HA’s update function triggers a local backup of specific components each time the configuration is changed, or the system is updated. Backup information is stored in several folders on the SD card. To enable regular backups, go to Settings then System then Backups. In the “Backup settings” panel, enable “Use automatic backups” and adjust the Schedule and Retention parameters as desired. In the “Backup data” panel, disable History and Media, as these can generate large video files that may fill the SD card and crash the system. Scroll down to the “Encryption key” panel and download the emergency kit. The encryption key and instructions in the kit will be required to restore from the backup. If you want to save backups externally, HA can access external and cloud storage. I found that the most straightforward path was to make HA’s files accessible via an SMB (CIFS) file share (see siliconchip.au/link/ac62). To do this, install the “Samba share” add-on. Using the Configuration tab at the top of the installation page and add a password for remote access. The Username and Workgroup fields can be left as they are or changed to meet your needs. Start the add-on with “Start on boot” and Watchdog both enabled. After a minute or so, you should be able to see a HOMEASSISTANT host in your computer’s file browser under Network (if using Windows) or the appropriate heading on Mac or Linux (you may need to install the samba package to access it in Linux). If it doesn’t appear, try refreshing or re-opening your file browser window. Map network drives for the “backup” and “config” folders, using the credentials you saved in the Samba configuration tab. Use your PC’s backup tool to regularly save the files. Conclusion In this series, we have touched on some key elements of home automation using the HomeAssistant and ESPHome platforms. We hope it has whetted your appetite to explore more of the many features these platforms SC offer. Screens 18 & 19: setting up the “When” parameters for the AC Thermostat notification (left). The myHome Overview dashboard card with all features enabled (below). Australia's electronics magazine October 2025  51 Subscribe to SEPTEMBER 2025 ISSN 1030-2662 09 The VERY BEST DIY Projects ! 9 771030 266001 $14 00* NZ $14 90 INC GST INC GST AERIAL DRONES the latest hobby, commerc ial, military and passenger PICkit Basic Programm er Microchip’s new low-cos t programmer & how to add a 3.3/5V power breakout board Australia’s top electronics magazine Pendant Speaker A high-performance hanging speaker with a 170mm woofer and 90W power rating 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. drones HomeAssistant Run your own fully featured home automation system using a Raspberry Pi USB- C Power Monitor Measure voltage, current , power and energy for nearly all USB-C devices Published in Silicon Chip If you have an active subscription you receive 10% OFF orders from our Online Shop (siliconchip.com.au/Shop/)* Rest of World New Zealand Australia * does not include the cost of postage Length Print Combined Online 6 months $72.50 $82.50 $52.50 1 year $135 $155 $100 2 years $255 $290 $190 6 months $85 $95 1 year $160 $180 2 years $300 $335 6 months $105 $115 1 year $200 $220 All prices are in Australian dollars (AUD). Combined subscriptions include both the printed magazine and online access. 2 years $390 $425 Prices are valid for the month of issue. Try our Online Subscription – now with PDF downloads! Aerial Drones; September 2025 USB-C Power Monitor; Aug-Sep 2025 Mic the Mouse; August 2025 RP2350B Development Board; August 2025 An online issue is perfect for those who don’t want too much clutter around the house and is the same price worldwide. Issues can be viewed online, or downloaded as a PDF. To start your subscription go to siliconchip.com.au/Shop/Subscribe GOT A BIG IDEA? WE'VE GOT THE BOARD FOR IT. From simple builds to ambitious creations, Jaycar has Arduino® -Compatible boards to match. XC4410 BREADBOARD FRIENDLY FOR EASY PROTOTYPING BEST SELLER BEST COMPATIBILITY WITH SHIELDS, SENSORS AND MODULES ARDUINO® COMPATIBLE NANO $ COMPACT DESIGN WITH SIMILAR FEATURES TO THE UNO ONLY 4595 ARDUINO® COMPATIBLE UNO $ OUR MOST POPULAR DEVELOPMENT BOARD. . XC4414 FROM 3895 . XC4410/11 XC4420 EMULATE A USB KEYBOARD, MOUSE, JOYSTICK, ETC. 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SHOP AT JAYCAR FOR: • Great Value Starter Kits • Arduino® Compatible Development Boards • Wide range of Shields, Modules & Sensors • Great range of Breadboards & Prototyping Accessories Explore our great range of soldering gear, in stock on our website, or at over 140 stores or 130 resellers across Australia and New Zealand. jaycar.com.au - 1800 022 888 jaycar.co.nz - 0800 452 922 All prices shown in $AUD and correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. This Vacuum Controller switches on a vacuum when an appliance such as a circular saw is started. It runs the vacuum for a preset period after the appliance is switched off to draw up remaining dust. It includes optional blast gate control, and interlinking between units, for use with more than one tool. John Clarke’s Vacuum Cont V acuuming up dust produced by woodworking machinery is a necessity for cleanliness, safety and health reasons. Manufactured and natural timber dust can be toxic or become an irritant to the lungs if breathed in, ultimately causing health problems. Dust from timbers such as western red cedar can increase the risk of developing throat cancer. Wearing a face mask limits the amount of dust entering the lungs. However, fine dust in the air can also become an explosion hazard. Ideally, this dust should be vacuumed up as it is produced, to minimise airborne wood particle dust. Besides, who wants to clean up a workshop full of sawdust after doing some work? Incidentally, vacuuming air through ducting tubes made from metal or plastic can cause an electrostatic charge to build. If not Earthed, the charge buildup can produce sparks, resulting in dust explosions. It is important to provide Earthing for metal ducting and include Earthed bare wires within any plastic pipes to prevent this (see siliconchip.au/ link/ac71). Major dust producers include circular saws, thicknessers and routers. Where there is more than one appliance, you would typically have a single vacuum unit, with ducting between 54 Silicon Chip them. A valve in the ducting at each appliance, called a ‘blast gate’, can be opened or closed for the vacuum to draw dust only from the appliance concerned (otherwise, the suction would be too weak). With our Vacuum Controller, the operation of the vacuum and blast gates is fully automatic. Switch on your appliance, and the vacuum will automatically start and run for as long as the appliance is running. Then, once the appliance is switched off, the vacuum will continue to run for a preset period. Blast gate control can be automated provided the blast gates are electrically operated by actuators or solenoids. Solenoids use an electromagnet that pulls in a plunger whenever the solenoid is powered. A spring is used to return the plunger to its resting position when power is off. An actuator is essentially a DC electric motor that drives a rod out or in using a worm gear. If you are not familiar with actuators, you can see an example of one at siliconchip.au/link/ac72 When used with the Vacuum Controller, the blast gate associated with the powered on appliance is opened. The appliance or appliances that are not operating will have their blast gates closed. Australia's electronics magazine A woodworking workshop setup for removing dust is not a topic that we will investigate in detail here. There is much detailed information on it at siliconchip.au/link/ac73 and other reputable websites on the topic. Presentation Our Vacuum Controller can be built to suit your workshop. Its most basic form is a single Vacuum Controller unit that switches a vacuum for a single appliance. The Vacuum Controller detects when its appliance is running and powers the vacuum. We call this Vacuum Controller the master unit. It is the only unit that contains the switching components for the vacuum. The optional blast gate control can be connected to this unit. This provides relay contacts to enable control of a solenoid or actuator to open or close the blast gate. It is connected via an 8P8C RJ-45 connector that allows standard Cat 5/Cat 6 leads to be used. You can use a different connector should more current be required (more on that later). For each appliance after the first, you will need another partially populated Vacuum Controller board. These extra units don’t include the switching components for the vacuum, as they are connected back to the main unit. This interlinking allows any of the siliconchip.com.au Appliance & vacuum ratings: up to 10A at 230V AC Appliance on-detection threshold: 166mA (~40W) Vacuum run time after appliance is off: adjustable from half a second to 30s Blast gate opening and closing time compensation: 0-7.5s Vacuum wind-down period compensation: 0-7.5s Can be used with a single appliance or multiple appliances via interlink connections Optional blast gate control option for each appliance; it opens for the appliance being used Cat 5/6 or telephone cables for interlinking & blast gate control Fully automatic operation plus manual operation for vacuum and blast gate Power, vacuum and blast gate indicators troller interconnected Vacuum Controllers to control the action of the vacuum via the master unit. When a Vacuum Controller unit detects that its connected appliance is on, the master unit is signalled to switch on the vacuum. If using blast gates, there are two possible control methods that can be selected. The default is to only open the blast gate for the currently operating appliance. The other option will keep the blast gate open for the last used appliance. This gate will close when a different appliance starts. Fig.1 shows, as an example, the arrangement of three interlinked units. Interconnection is via RJ-10 4P4C sockets and 4-wire telephone style cabling with RJ-10 plugs for an easy interconnection system. For Home workshops The master unit includes two mains inputs and two mains outlets (General Purpose Outlets [GPO]). These are to supply the appliance and the vacuum independently. Each mains input must plug into a separate mains outlet to allow for up to 10A <at> 230V AC (2300VA) to be drawn from each. Circular saws can be rated at 1800VA or more and vacuums at around 1200VA, so it is not feasible to run both from the one 10A mains outlet. The mains supply for the appliance is directly connected between the input and output via a current transformer inside the Vacuum Controller unit. This current transformer is used to monitor the appliance current. When current is detected, it indicates to the Vacuum Controller that the appliance is running and so switches on the vacuum via the second mains output. Power for the vacuum is switched using a heavy duty relay. If more than one Vacuum Controller is built, subsequent units only require one mains power input and one mains outlet for that unit’s connected appliance. The vacuum is only switched on and off via the master unit, which is signalled to switch via the interlinking connection between units. If blast gate control is installed, interlinking sets the blast gate open for the appliance that is running and closes the blast gates for those units that do not have their associated appliance running. There is the option to have the blast gate for the last running appliance kept open after the appliance is switched off. This speeds up switching on the Left: the Blast Gate Control Adaptor is a simple PCB that can be built to convert RJ-45 8P8C (eight position/eight conductor) connections to screw terminals. Right: the Vacuum Pump Controller has two 230V 10A power outlets for supplying the appliance and vacuum. siliconchip.com.au Australia's electronics magazine October 2025  55 vacuum if you use the same tool again. When the blast gate is closed, it needs to wait for the blast gate to open before the vacuum is started. If the blast gate is already open, the vacuum can start immediately. LED indicators are included on each for power, vacuum running and blast gate open. Two momentary pushbutton switches provide manual control of the vacuum and the blast gate. The blast gate LED, associated switch and other blast gate related components can be left off if you don’t need this feature. Also, the interlinking components are not necessary if you only intend to build one master unit. One or two additional units can be connected to the master unit and be powered from it. The master unit has a mains transformer to power itself, and the resulting 12V is supplied to other units via the interlink connections. If more than three units are required, then the fourth unit will need to include another power transformer. This allows for up to six to be connected in total. Because the Vacuum Controller can be built with several options, the circuit and PCB overlay diagrams show the separate sections of the circuit, some of which may not be required in each unit. Similarly, the parts list separates out the parts for each section. Timers and operation Three timers are used in the operating logic: the vacuum timer, blast gate operating period timer and the vacuum wind-down timer. The vacuum timer sets the period for which the vacuum runs after the appliance is switched off. This can 56 Silicon Chip be adjusted from 0-30s. The blast gate timer should be set to the time taken for the blast gate to open or close, allowing the blast gate to be fully open before the vacuum is started. It prevents damage to the vacuum pipe work and blast gates if all blast gates are closed when the vacuum starts. The blast gate timeout can be set up to 7.5s. If blast gate control is not used, it can be set to zero, for no delay in starting. The vacuum wind-down timer is included so that the blast gate does not close until the vacuum motor has stopped after being switched off. It can be set for up to 7.5s, preventing excessive vacuum pressure by keeping the blast gate open while the vacuum is spinning down due to inertia. The Vacuum Controller is initially in a waiting state until either its connected appliance is switched on, or the interlink signal indicates that the appliance connected to another unit is switched on. As long as neither are on, it continues to wait. When the connected appliance switches on, the blast gate is powered on if it isn’t already open. The blast gate LED flashes during the opening period (this is skipped if it was already open). The interlink signal then becomes active. At the same time, the vacuum motor and its indicator LED are switched on. After the appliance is switched off, the vacuum timer starts. When it ends, the vacuum is switched off, along with the interlink signal. If JP1 is in, the vacuum LED flashes during the pump wind-down period. In this case, after the wind down period, the blast gate closes and its Australia's electronics magazine LED goes off. If JP1 is out, the blast gate and LED stay on, and the vacuum wind-down period is bypassed. Either way, it then goes back to the initial state, checking for the appliance or interlink signal to become active. If, rather than the connected appliance switching on, the interlink signal becomes active, all units other than the one with the connected appliance on will have their blast gate closed, if not closed already. The blast gate LED flashes during the closing period. Then the blast gate LED switches off. The vacuum and LED then switch on, and stay on as long as the interlink signal remains active. When the interlink signal goes off, the vacuum motor is switched off. It then returns to the initial waiting state. Note that the state of the blast gate is stored in non-volatile memory, so the on/off setting for each blast gate is restored on power-up. This does not apply to when the blast gate was set open manually via button S2. Switching the vacuum on manually using switch S1 will cause the master unit to switch on the vacuum. The vacuum LED on the unit where S1 was pressed will light but flash off momentarily once per second to indicate manual mode. Automatic running by interlink signal or appliance detection is disabled until the vacuum is switched off via S1 on the unit that initiated manual operation. Manually opening the blast gate on any unit does not affect automatic operation. When an appliance switch-on is detected by one of the units, the blast gates will be closed for all units that did not detect an appliance-on, and remain open or be siliconchip.com.au Fig.1: one control unit is required for each tool that’s connected to the vacuum system. Two, three or even more units can be linked together, as shown here. Only the first unit connects to the vacuum, and just the first (and the fourth, if there are four to six) requires the second mains input. In use, apply power to the fourth unit (ie. the second mains input unit) before the first unit. The blast gate connections are only required if you’re using a blast gate system. opened at the unit that detected the appliance-on event. Note that the timer periods are determined by the Controller that has detected the appliance that’s switched on. If it is not the master unit, the vacuum run period is controlled via the interlink signal from another unit. This allows you to set different periods for each tool. Circuit details The circuit is shown in Fig.2. It is in several sections; if you don’t want blast gate control, that part of the circuit can be left off the PCB. Similarly, if you just have a single tool to connect, the interlinking section can be left out. When a second or third unit is built, they do not require the mains power section to be populated. They can instead receive 12V power from the master unit. More than three units can be joined, but one mains power supply is required for every three. Power is interconnected using CON7 and CON8 via jumpers at JP2 and JP3. If more than three units are connected, the supply must be broken between the third and fourth unit by leaving JP2 or JP3 out. The master Vacuum Controller is the only unit that requires the vacuum control section, comprising relay RLY1, driving transistor Q1, diode D1, the 1kW base resistor for Q1, the mains power input and output connectors (CON13/CON14) and fuse F2. The Vacuum Controller is based around microcontroller IC1. This monitors the appliance current flow, trimpot settings (VR1, VR2 & VR3), switches S1 and S2, jumper selection JP1 and the interlinking signal. It also drives relays RLY1 & RLY2 for vacuum and blast gate control, LED2 and LED3, and the interlinking signal. RLY1 and RLY2 are switched on by the RC4 and RB7 outputs of IC1, respectively. Both use 1kW current-­ limiting series base resistors to drive transistors Q1 and Q2. When a transistor is switched on, its collector goes low, connecting one side of the relay coil to ground. The 12V supply at the other end of the coil powers the relay. Diode D1 across RLY1’s coil, and diode D2 for RLY2, quench the backEMF voltage from the coil when these are switched off. RLY1 is a single-pole, single-throw (SPST) relay with 30A, 250V AC contacts to drive the vacuum. Mains active from the vacuum IEC C14 mains input power connector (CON13) is controlled via the relay contact to switch mains outlet (CON14) power on or off. RLY2, for blast gate control, is a 5A double-pole, double-throw (DPDT) relay. All its relay contacts are connected to screw terminals (CON5) and to CON6, an RJ-45 connector. This allows for an easy connection using Cat 5 or Cat 6 cabling. A small adaptor PCB can be used to convert the RJ-45 connections to 6-way screw terminals at the other end, for wiring to the solenoid or actuator. Current detection Appliance current flow detection is via the Active mains wiring between the appliance input (CON11) and output (CON12); the Active wire passes through current transformer T2. This forms the primary winding for the current transformer. T2 produces an output current from its secondary winding that’s related to the current flow through the mains Active wire. The lid (shown left) requires holes for the three LED indicators and the manual control switches. We have used fibre optic cable to transmit the light, as the LEDs are mounted to the PCB. siliconchip.com.au Australia's electronics magazine October 2025  57 The 10kW loading resistor gives about 4V AC output with a tool current flow of 1A and the single pass of the Active mains wire through the current transformer core. While the input current to output voltage for T2 is not very linear using a 10kW loading resistance, we use this high value to increase the sensitivity. A 100W loading resistor would be used for measuring current more accurately. That would provide a more linear relationship, but sensitivity would be reduced to only give 1V for a 10A primary current with a single turn through the transformer. Since we are not interested in current reading accuracy, we use the higher-­sensitivity connection to detect the appliance running current. The startup current for the appliance can be well over 20A, so the output voltage from the current transformer could be quite high (possibly around 80V). We limit this voltage using a transient voltage suppressor (TVS1) that clamps the voltage to about 13.8V AC. This limits the current into the following op amp inputs to a safe level. Voltage rectification The output from T2 needs to be rectified to give a DC voltage suitable for monitoring by microcontroller IC1. A standard bridge rectifier requires a signal greater than ±1.2V peak to begin producing a rectified voltage. Fig.3: the Blast Gate Adaptor circuit (top) and wiring to use for a blast gate with an actuator (bottom). With power applied with the polarity shown, the blast gate should close. You can test this by switching on the 12V supply with the controller off; if the blast gate opens, reverse the connections. 58 Silicon Chip A precision full-wave rectifier allows the detection of voltage well below this (down to a millivolt or less). The rectification is done purely by op amps (IC2a and IC2b), without the aid of diodes. We have set the gain of this precision rectifier to 1.5 times. Rectifying the incoming AC voltage without diodes is possible, provided that the op amp has specific characteristics. These include being able to operate correctly (without output phase reversal) when a voltage is applied that’s below its ground supply rail. In addition, the op amp must be able to pull its output close to ground. If you are interested in how this works in detail, this is described in the section entitled “Precision full-wave rectification”. A 2.2kW resistor and 10μF capacitor filter the rectified waveform at the output of IC2a to produce a smoothed DC voltage suitable for IC1 to monitor via its AN6 analog input and internal analog-to-digital converter (ADC). Trimpots VR1 to VR3 are used to set time periods. VR1 sets the period over which the vacuum runs after an appliance is switched off. The voltage at VR1’s wiper determines the time period, and can be set between 0V and 5V. This voltage is converted to a digital value within IC1 using the AN7 analog input that connects VR1’s wiper to the ADC. The VR1 setting gives a time period ranging from about 0.5s when rotated fully anti-clockwise through to 30s when rotated fully clockwise. Similarly, VR2 and VR3 can be adjusted in voltage, but these settings provide time period settings of 0-7.5 seconds. VR2 is the blast gate operation period (the time it takes the blast gate to open or close fully). This determines when the vacuum starts after detecting the appliance associated with the blast gate starts up. VR3 is for setting the vacuum wind down period, the time the vacuum takes to stop after being switched off. We keep the blast gate open until the vacuum has stopped running, whereupon the gate closes. There is an option to keep this gate open when the appliance and vacuum stops and, in this case, the wind down period can be set to 0 (VR3 fully anti-clockwise). The blast gate will close automatically when a different appliance runs if there are more appliances and Vacuum Controllers all interlinked. Australia's electronics magazine Switches S1 and S2 are momentary pushbutton switches connected to the RA5 and RA4 digital inputs of IC1. With the switches open, these inputs on IC1 are pulled high via internal pull-up currents. When a switch is pressed, it pulls the input pin low, close to 0V. Blast gate wiring The connection for a solenoid is easy enough, with the common and normally (NO) contacts used to switch power to the solenoid when the relay is energised. Fig.3 shows how wiring is made for an actuator. An actuator is essentially a DC electric motor that drives a rod in or out using a worm gear. The actuator requires current flow in one direction to open the actuator, by driving the motor in one direction, and current flow in the opposite direction, reversing the motor, to close the actuator. Operating the actuator is achieved using the DPDT relay contacts. The actuator includes end-stop switches that prevent the actuator from running once it has reached its open or closed limits. It is important when used with our Vacuum Controller to wire the actuator so that it opens the blast gate when the relay is on, and closes the blast gate when the relay is off. Power supply Power for the circuit is derived by a mains transformer. This is connected to the appliance power input IEC C14 connector (CON11) and fuse F1 via terminals CON1 & CON2. Transformer T1 has two 9V AC outputs that are connected in parallel. The output is rectified by bridge rectifier BR1 and filtered with two 470μF capacitors to produce around 12V, which powers the two relays. The 12V is also applied to REG1, a 5V regulator, to supply IC1 and IC2. The transformer can deliver enough current to run three of these circuits. Only the master unit has the vacuum control section, hence RLY1, so only one such relay needs to be powered. RLY2 (if used) for blast gate control is only switched on in one of the Vacuum Controller units at a time. Since the relays are the major current draw, there isn’t much of an extra burden when more units are attached. The 12V power for the following units is coupled via the interlinking cable and JP2 (for CON7) or JP3 (for siliconchip.com.au Fig.2: the circuit mainly comprises microcontroller IC1, a currentsensing system comprising current transformer T2 and op amp IC2 (cyan dashed box), a basic mains power supply (red dashed box), vacuum switching (mauve dashed box), blast gate switching (dark blue dashed box) and interlinking components (green dashed box). CON8). For the connection between the third and fourth unit, where the fourth unit has another mains power supply, at least one of the power jumpers between these two units must be left off to isolate the two separate 12V supplies. Interlinking Transistor Q3 provides the interlinking feature. This transistor is driven at its base via a 10kW resistor by IC1’s RB5 output. When RB5 is taken high, the transistor switches on, pulling siliconchip.com.au its collector low. With the transistor off, the collector is held high via the 10kW pullup resistor. The collector voltage is the interlinking voltage. Any transistor in any of the interconnected Vacuum Controller units can pull this line low to indicate that their appliance is running. When no transistors are on, then the interlink signal is held high (5V) via the 10kW resistor and any other 10kW resistors in other interconnected units. Australia's electronics magazine In the unlikely event that more than 10 separate Vacuum Controller units are interconnected, these resistors should be increased in value, or some left off, to keep the total parallel resistance at 1kW or higher. When a unit detects its connected appliance is on, it opens the connected October 2025  59 blast gate. The low interlinking signal causes the remaining blast gates associated with the remaining appliances to be closed. This low interlink signal will also indicate to the master unit that the vacuum should run. The units are interlinked using the RJ-10 4P4C socket (or sockets) at CON7 and CON8. The first (master) and last unit require one of these, while the others all require both. Construction options Fig.4 shows the parts layout on the main board. It is divided into the same sections as the circuit diagrams, with dashed boxes in corresponding colours, since not all components are necessarily required. The ‘core’ components outside these boxes are required for all builds. For the master unit, the mains power (red) and vacuum control (mauve) sections are also required. To use the blast gate option, the components in the dark blue box are also required. Typically, CON6 is used so that connection to the blast gate can be made using a Cat 5 or Cat 6 cable, suitable for handling up to 1A. If you require more current, up to 5A, use the CON5 screw terminals instead, along with suitably rated wiring, passing through a cable gland in the case. For secondary units, the mains power section (red) isn’t required unless you’re building more than three units. Essentially, you’ll need to build this section on every fourth unit. Interlinking between units requires only one RJ-10 socket (CON7 or CON8) on the master or final unit. All others (assuming there are more than two) require both sockets. JP2 and JP3 are used to connect the +12V power as required. Construction The Vacuum Controller unit is built on a double-sided, plated-through PCB coded 10109251 that measures 151 × 109mm. Most of the components are installed on this PCB, and it is housed within an IP65 enclosure measuring 171 × 121 × 55mm. We’ll describe construction assuming everything is installed, so ignore any components that are mentioned if they don’t apply to your build. Start by fitting the resistors. These have colourcoded bands, shown in the parts list, but you should also use a digital multimeter to check each resistor before mounting it. Diodes D1 and D2 are next on the list. Make sure these are orientated correctly before soldering their leads. BR1 can be installed, again with the correct polarity, lining up the + printed on it with the one on the PCB. We used a socket for IC1, although it could be soldered directly, assuming it has already been programmed. Similarly, IC2 can be mounted on a socket or directly onto the PCB. Install the headers for JP1, JP2 and JP3 next. Follow with the capacitors. There are two types used: electrolytic and MKT polyester. The electrolytic capacitors need to be orientated correctly since they are polarised, with their longer leads through the holes marked with + symbols. The MKT polyester capacitors can be installed either way around. REG1 mounts horizontally. Bend its leads to suit the PCB holes and secure its tab with an M3 screw and nut before soldering the leads. Q1-Q3 can then be fitted; they are all the same type; orientate them as shown in Fig.4. CON1 to CON4 can now be installed. Note that the wire entry for CON3 is toward REG1; for CON4, the entry is toward the lower edge of the PCB. Then fit CON5-CON8. CON5 isn’t needed if you intend to use CON6 instead. CON5 allows for heavier-duty wiring to the blast gate. The cable will need to be secured to the side of the enclosure with a cable gland, or via circular (8-way) audio connectors or similar. Fig.4: follow this overlay diagram to assemble each control board, but note that some boards may not require the parts inside each outlined section (for example, the second and third control boards in a system don’t require the mains power supply). The colour coding of the dashed sections corresponds to the same sections in the circuit diagram, Fig.2. 60 Silicon Chip Australia's electronics magazine siliconchip.com.au Precision Full-Wave Rectification We use a dual op amp to rectify the AC signal from the current transformer, either an LMC6482AIN or MCP6272 (IC2). One stage (IC2b) is connected as a unity gain-buffer, while the other (IC2a) provides the 1.5 times gain. The points labelled A to E in Fig.2 correspond to the example waveforms shown here in Fig.a. We’ll describe the operation using a 2V peak-to-peak sinewave at point ‘A’. This makes the description easier since the sinewave peaks at +1V and −1V. The rectification for the negative and positive waveforms are described separately. For the negative half of the cycle, the signal applied to the non-inverting pin 5 input of IC2b via the 15kW resistor will cause the voltage at that pin (point B) to be clamped at around -0.3V due to IC2b’s internal input protection diode. The output of IC2b (point C) therefore sits at 0V during negative portions of the cycle, since its output can’t go below the negative supply rail (0V). IC2a adjusts its output (point E) so that the voltage at its inverting input pin 2 (point D) matches the voltage at non-inverting input pin 3 (point C). Since pin 3 is at 0V, pin 2 will also be at 0V. Therefore, the 10kW resistor from point D to ground has no voltage across it, and it plays no part in the circuit during the negative portions of the cycle. With the 10kW resistor essentially out of the circuit, IC2a operates as a standard inverting amplifier with both inputs (points C and D) at 0V. Its gain is therefore −30kW divided by 20kW, which equals −1.5 times. So the −1V peak waveform is amplified and inverted to produce +1.5V peak at point E. With a positive voltage at the input (point A), the situation is more complicated. Firstly, the voltage at pin 5 (point B) is reduced below 1V peak due to the divider formed by the 15kW and 18kW resistors. So the peak voltage becomes 0.5454V, ie, 1V × 18kW ÷ (15kW + 18kW). Point C will also peak at 0.5454V, since IC2b is working as a unity-­ gain buffer producing the same voltage at its output as its non-­ inverting input. Once again, op amp IC2a adjusts the output voltage (point E) so that the voltage at the inverting input at pin 2 (point D) matches the voltage at the non-inverting input, pin 3 (point C). To determine the resulting voltage, we calculate the currents through the three resistors connected to point D. The current through the 10kW resistor is waveform D voltage divided by 10kW, which peaks at 54.54μA (0.5454V ÷ 10kW). The current through the 20kW resistor, with 1V peak at the input (point A), will be 22.73μA, ie, (1V[A] − 0.5454V[D]) ÷ 20kW. So we have 22.73μA flowing into the node at point D via the 20kW resistor and 54.54μA flowing away from that node via the 10kW resistor. The extra current of 31.81μA (54.54μA − 22.73μA) to balance currents at node D needs to come via the 30kW resistor. Remembering that voltage at point D peaks at 0.5454V, the required voltage at point E is 1.5V, ie, 31.81μA × 30kW + 0.5454V. So the circuit operates as a full-wave rectifier with a gain of 1.5. The degree of precision depends on the op amp parameters and resistor tolerances. The lower the offset voltage of the op amp and the lower the op amp input bias current, the more accurate the full-wave rectification will be, particularly at low signal levels. We are not overly concerned with accuracy here. We just need full-wave rectification of the incoming AC signal from the current transformer that works down into the tens of millivolts range. A standard diode-based rectifier would not give any output in this case, due to the relatively large voltage drops across the diodes. The scope output shows the operation of the full-wave rectifier for a 1V peak (2V peak-to-peak) current waveform resulting from an approximate 40W load through the appliance and current transformer. The waveform applied to the input of the full-wave rectifier (point A) is on channel 1 of the oscilloscope, shown in yellow. Channel 2’s cyan waveform is the full-wave rectified waveform (measured at point E). This is a 1.48V peak output waveform at 100Hz compared to 1V peak at 50Hz for the input sinewave. The discrepancy of 20mV is due to tolerances in the resistors that are only ±1% types, the op amp offset voltages, and the accuracy of the oscilloscope readings. The yellow trace is a 1V peak sinewave applied to point A in the circuit (the input of the precision rectifier), while the cyan trace is the output of the rectifier at point E. As expected, the negative parts of the sinewave are flipped to be positive, allowing us to easily measure the average current. Fig.a: the expected waveforms at points A-E on the circuit (Fig.2) for a 1V peak sinewave from current transformer T2. The output (E) is a rectified version of the input (A) but 50% higher in amplitude. siliconchip.com.au Australia's electronics magazine October 2025  61 The next step is to install the relay, RLY1, with the coil terminals toward CON3. The relay is secured using M4 machine screws and nuts, with each screw inserted from the underside of the PCB. RLY2 mounts directly on the PCB. Transformer T1 is a PCB-mounting type; install it now. We use a cable tie that wraps around the transformer and through slots in the PCB to secure the transformer. The cable tie is necessary to prevent the solder joints or pins fracturing if the unit is dropped. Current transformer T2 also needs extra support for its mounting for similar reasons. Apply glue to the transformer base before inserting its pins into the PCB and soldering it in place. We used JB Weld epoxy resin, since this adheres well to most types of plastics. The light pipes are held together over the LEDs when you lose the lid. Blast gate PCB assembly If using blast gate(s) with the RJ-45 socket option, you will probably want Fig.6: the locations of cut-outs on three sides of the case, plus the dimensions of the IEC socket packing piece and the light transporter assembly jig. All the possible holes for chassis-mounting connectors etc are included, although some are optional. 62 Silicon Chip Australia's electronics magazine siliconchip.com.au to build one of the Blast Gate Adaptor PCBs for each gate. This converts the RJ-45 8P8C connections to screw terminals. It is coded 10109252 and measures 44 × 33mm – see Fig.5. This can be mounted near the blast gate actuator or relay. Assembly is simple – just solder the RJ-45 socket and screw terminals to the board and it’s ready. Final assembly The Vacuum Controller units are secured to the base of their enclosures using M3 screws that go into the integral brass inserts. Before attaching the PCB, cutouts are required for the IEC C14 connectors at one end of the enclosure and the RJ-45 and RJ-10 socket(s) at the other end. The only hole that’s required in every case is the IEC C14 connector for the tool or appliance and its corresponding GPO cut-out; the other holes are required only for those boards where matching parts are fitted. Start by drilling and shaping holes using the template shown in Figs.6 & 7. The two IEC C14 connectors used on the master unit have a shared mounting hole at the middle of the enclosure end, where one connector is stacked over the other. The large cutouts for the mains GPO and IEC C14 connectors can be made by drilling a series of small holes around the inside perimeter, then knocking out the centre piece and filing the job to a smooth finish. Alternatively, use a speed bore drill to remove the bulk of the central cut-out area before filing it to shape. For the master unit, a packing piece needs to be fashioned so that the IEC C14 connector that’s stacked over the other can be spaced by the same amount. We made ours from a piece of 3mm-thick plastic cut from a discarded black UB1 Jiffy box. Once the drilling and filing is complete, the PCB can then be placed inside the case and secured with the M3 screws into the integral brass inserts. The IEC C14 connector(s) must be secured using 15mm-long M3 nylon screws, although metal nuts can be used. For the securing screws closest to the edge of the enclosure, TO-220 insulating bushes can be used to space the nut further out to avoid the nut from angling inward against the enclosure’s moulded curvature as it is tightened. siliconchip.com.au Fig.7: just five holes are required in the lid, as shown in this actual-size diagram. You won’t need all five if you aren’t using the blast gate control option. Using nylon screws prevents the possibility of the screws becoming live (at mains voltage) should a mains wire inside the enclosure come adrift and contact a screw that’s securing the IEC connector. The lid requires holes for the switches and LED bezels of the light transporters. Light transporters use fibre-optic cable and plug-in connectors from the LED to the front panel bezels. The fibre optic cables are cut to length so that they connect without bending too much when the lid is closed. This procedure can be done at the end of construction. Australia's electronics magazine Fig.5: the Blast Gate Adaptor PCB is dead simple; it just connects six of the Cat 5/6 cable’s eight conductors to screw terminals so they can be more easily wired up to the blast gate. This is suitable for gates that draw up to 1A. October 2025  63 Fig.8: the two versions of the lid panel artwork cater for units built with and without the blast gate option. There are also some side labels for connectors that you might like to use. siliconchip.com.au Fig.9: make sure to follow this wiring diagram carefully and only use mains-rated wire. Don’t leave out the cable ties; they are not just to keep it neat; they perform an important safety function (preventing loose wires from contacting low-voltage circuitry). It will be easier to install the lid and attach the light transporters if a plastic spacer is made to spread the LED connector clips 12.5mm apart. We made ours from a 3mm-thick piece cut from a discarded UB1 Jiffy box lid. When installing the lid (later on), it will be easier to make sure the light transporters correctly line up and clip over the LEDs when these are switched on (via S1 and S2 if used) so you can peep in through between the box and lid as you close it. There are two versions of the front panel label artwork, depending on whether the blast gate feature is used or not. Labels for the mains inputs and outputs and the interlinking and blast gate connectors can be independently affixed to the side of the enclosure, or on the side edge of the siliconchip.com.au lid as appropriate. The front panel label shown in Fig.8 is available from siliconchip.au/Shop/11/3002 Details on making a front panel from this artwork can be found online at siliconchip.au/Help/FrontPanels Wiring it up All wiring must be run as shown in Fig.9, using mains-rated cable. Be sure to use 10A cable where indicated (for everything except RLY1’s coil and switches S1 & S2). Brown wire is used for Active, and blue wire for the Neutral leads. The green/yellow-striped wire must be used for the Earth wiring only, and the Earth lead from each IEC connector must go straight to the corresponding GPO. Insulate all the exposed connections with heatshrink tubing for safety, and Australia's electronics magazine cable tie the wires to prevent any wire breakages coming adrift. The Active and Neutral leads are secured to the GPO using a cable tie passing through the hole in its moulding. Use neutral-cure silicone sealant (eg, Roof & Gutter Silicone) to cover the Active bus piece at the rear of the IEC connectors that joins the active pin to the fuse. Take great care when making the connections to the mains socket (GPO), ensuring you run the leads to their correct terminals; each GPO will be marked A (or L) for Active or Live, N for Neutral and E for Earth. Do the screws up tightly so that the leads are held securely. Similarly, make sure that the leads to the CON1 and CON2 screw terminals are firmly secured. CON1 and CON2 are only required October 2025  65 when the transformer (T1) is installed. These screw terminals are there to connect the incoming mains to the transformer primary windings on the PCB. Only one terminal of CON1 is used to connect the Neutral. Similarly, one terminal of CON2 is used for the Active connection. Remove the spare terminal screw on each terminal and use a mica washer (normally used to insulate TO-220 transistors) as a cover for the used terminal. Secure it using an M3 × 12mm nylon or polycarbonate screw with a 6.3mm nylon tapped standoff under the washer through the hole where you removed the metal screw. Setting it up If IC1 is already programmed, it can be inserted into its socket now, taking care to do so with the correct orientation. If IC1 is not yet programmed, do that first. Programmed processors can be ordered from our Online Shop. If you have programming facilities, like a PICkit and adaptor socket, the HEX file is at siliconchip.au/Shop/6/3013 Set VR1 to the required vacuum run time for after the appliance has been switched off. The maximum is 30 seconds in the fully clockwise position. It’s linear, so a halfway setting will give you 15 seconds. Set VR2 to the period that the blast gate takes to open or close, or fully anti-clockwise if you aren’t using that feature. If the blast gate opening and closing periods are different, set it to whichever is longer. The setting is 7.5 seconds when VR2 is fully clockwise. Adjust VR3 for the wind-down period that the vacuum takes to stop after being switched off. As with VR2, it will give 7.5 seconds when VR3 is fully clockwise, or 3.75s at halfway. When you have more than one unit, the VR1, VR2 and VR3 settings are used from whichever control unit that detects the appliance switching on, so you will need to set them all. Indicator LEDs The indicator LEDs will be either flash, be fully on or off. The Power LED is on when power is supplied to the circuit. During the blast gate opening/closing period, the blast gate LED flashes and it remains lit while the blast gate is open, switching off when it closes. The vacuum LED is continuously lit while the vacuum is running on 66 Silicon Chip Parts List – Vacuum Controller Controller unit (common parts) 1 double-sided, plated-through 151 × 109mm PCB coded 10109251 1 171 × 121 × 55mm sealed ABS or PC enclosure [Altronics H0478, Jaycar HB6218] 1 AC1010 or AX1000 10A current transformer (T2) [RS Components 7754928, 1243903] 1 3-way, 5.08mm-pitch screw terminal block (CON4) 1 M205 10A fast blow fuse (F1) 1 2-way, 2.54mm-pitch pin header and jumper shunt (JP1) 1 SPST momentary pushbutton switch (S1) [Altronics S1084A, Jaycar SP0700] 1 IEC C14 mains input socket with fuse holder (CON11) [Altronics P8324, Jaycar PP4004] 1 side-entry 10A mains GPO socket (CON12) [Altronics P8241, Jaycar PS4094] 3 3mm LED light transporters [Jaycar HP1193; pack of 3] 1 LED fibre optic spreader made from 3mm plastic (see Fig.6 and text) 3 10kW miniature top-adjust trimpots (VR1-VR3) 1 20-pin DIL IC socket for IC1 (optional) 1 8-pin DIL IC socket for IC2 (optional) Hardware and cable 1 150mm length of 7.5A mains-rated wire for S1 1 200mm length of blue 10A mains-rated wire 1 250mm length of brown 10A mains-rated wire 1 150mm length of green/yellow striped 10A mains-rated wire 1 40mm length of 5mm diameter blue or black heatshrink tubing 1 40mm length of 5mm diameter red or black heatshrink tubing 1 40mm length of 5mm diameter green heatshrink tubing 1 40mm length of 3mm diameter blue or black heatshrink tubing 1 40mm length of 3mm diameter red or black heatshrink tubing 2 M3 × 15mm nylon countersunk head screws 4 M3 × 6mm panhead screws 2 M3 hex nuts 1 TO-220 insulating bush 4 100mm-long cable ties Semiconductors 1 PIC16F1459-I/P 8-bit microcontroller programmed with 1010925A.HEX, DIP-20 (IC1) 1 LMC6482AIN or MCP6272E/P dual CMOS op amp, DIP-8 (IC2) [Jaycar ZL3482] 1 7805 5V 1A linear regulator, TO-220 (REG1) 2 3mm red LEDs (LED1, LED2) 1 (P)4KE15CA 15V bidirectional TVS (TVS1) [Jaycar ZR1160] Capacitors 1 470μF 16V PC electrolytic 2 10μF 16V PC electrolytic 1 100μF 16V PC electrolytic 2 100nF 63V or 100V MKT polyester Resistors (all ¼W, 1% axial) 1 30kW 1 18kW 4 10kW 2 470W 1 20kW 1 15kW 1 2.2kW Mains power supply parts 1 9 + 9V AC 3VA PCB-mounting mains transformer (T1) [Altronics M7018A] 2 PCB-mounting 8.25mm-pitch 300V 15A barrier screw terminals (CON1, CON2) [Altronics P2101] 1 W04 bridge rectifier (BR1) 1 470μF 16V PC electrolytic capacitor 2 M3 × 12mm nylon or polycarbonate panhead machine screws 2 M3 × 6.3mm nylon tapped spacers 2 TO-220 mica insulating washers 1 150mm-long cable tie Extra parts for master unit (besides mains power supply) 1 SPST 250V/30A 12V DC coil FRA4 relay (RLY1) [Jaycar SY4040] 1 2-way, 5.08mm-pitch screw terminal block (CON3) 1 IEC C14 mains socket with integral fuse holder (CON13) [Altronics P8324, Jaycar PP4004] 1 side-entry 10A mains GPO socket (CON14) [Altronics P8241, Jaycar PS4094] 1 M205 10A fast blow fuse (F2) 1 BC337 45V 0.8A NPN transistor (Q1) Australia's electronics magazine siliconchip.com.au 1 1N4004 1A diode (D1) 1 1kW ¼W 1% axial resistor 1 200mm length of 7.5A mains-rated wire for the relay coil 1 200mm length of blue 10A mains-rated wire 1 250mm length of brown 10A mains-rated wire 1 150mm length of green/yellow 10A mains-rated wire 1 M3 × 15mm nylon panhead machine screw 1 M3 hex nut 1 TO-220 insulating bush 1 IEC mounting spacer made from 3mm-thick plastic (see Fig.6 and text) 11 100mm-long cable ties Silicon Chip Binders REAL VALUE AT $21.50* PLUS P&P Extra parts for blast gate control (per unit) 1 DPDT 5A PCB-mounting relay (RLY2) [Altronics S4190D, Jaycar SY4052] 1 SPST momentary pushbutton switch (S2) [Altronics S1084A, Jaycar SP0700] 1 RJ-45 8P8C side-entry PCB-mounting socket (CON6) [Altronics P1448A] • 1 BC337 45V 0.8A NPN transistor (Q2) 1 3mm red LED (LED3) 1 1N4004 400V 1A diode (D2) 1 1kW ¼W 1% axial resistor 1 470W ¼W 1% axial resistor 1 Cat 5 or Cat 6 cable (not crossover), length to suit installation • 1 Blast Gate Adaptor (see below) • 1 150mm length of 7.5A mains-rated wire for S2 2 100mm-long cable ties • or replace these parts with 2 3-way, 5.08mm-pitch terminal blocks (CON5) and a cable gland or chassis connector plus wiring to the blast gate for >1A Interlinking two or more controller units (per pair of units) 1-2 RJ-10 4P4C side-entry PCB-mounting sockets (CON7, CON8) [Altronics P1442] 1-2 2-way, 2.54mm-pitch headers and jumper shunts (JP2, JP3) 1 4P4C handset (telephone) cord with RJ-10 connectors at each end; length to suit 1 BC337 45V 0.8A NPN transistor (Q3) 1 10kW ¼W 1% axial resistor Blast Gate Adaptor (per adaptor) 1 double-sided, plated-through PCB coded 10109252, 44 × 33mm 2 3-way, 5.08mm-pitch screw terminal block (CON9) 1 RJ-45 8P8C side-entry PCB-mounting socket (CON10) [Altronics P1448A] Keep your copies safe, secure and always available with these handy binders These binders will protect your copies of Silicon Chip. They feature heavy-board covers, hold 12 issues & will look great on your bookshelf. H 80mm internal width H Silicon Chip logo printed in goldcoloured lettering on spine & cover Order online from www. siliconchip.com.au/Shop/4 or call (02) 9939 3295 and quote your credit card number. *see website for delivery prices. all units when powered, but flashes on and off with an even duty cycle once per second during the winddown period. This LED also flashes momentarily off at the unit where the vacuum is set to run manually using S1. This indicates that manual mode was used, and the vacuum needs to be switched off using S1 to exit this mode before it resumes automatic operation. Don’t forget to set JP1 in each unit as required. Leaving the jumper link out will have the blast gate stay open after opening. It will only close if another Vacuum Controller unit detects its appliance is on instead. With the jumper link in, the blast gate will close after the vacuum has SC stopped running. siliconchip.com.au Australia's electronics magazine October 2025  67 Buying Second-Hand SPEAKERS Bargains can be had, but you need to know what to look for! ~ Feature by Julian Edgar ~ I t’s great fun building your own speakers, and excellent results can be gained from doing so. However, it is not a cheap process if you want good results. By the time you pay for new drivers, crossovers, wiring and connectors, then build the cabinets, the cost can really add up. So what do you do if you’re on a tight budget? The answer is to buy second-­ hand speakers. But how do you select speakers that are good, especially when you often cannot listen before buying? Size It’s a fundamental fact of life that small loudspeakers will usually sound worse than large speakers. Yes, small enclosures can sound good – but it’s technically much more difficult to achieve good outcomes, especially in the production of bass. Chances are then, the smaller the speaker, the worse it will sound. Another reason for selecting larger speakers is efficiency – larger speakers are generally much more efficient than small speakers. What this means in practical terms is that a given sound volume will be achievable with less amplifier power. While the cost per watt of amplifier power has come down a lot in recent years, lower-power amplifiers still cost less than high-power amplifiers! When browsing second-hand speakers, you’ll find many home theatre systems that use five small speakers. Often, each about as big as a closed fist. Irrespective of their brand, don’t buy these! The same applies to the tall, thin and shallow speakers often used as the front and rear speakers in home theatre systems. Again, avoid them. About the smallest enclosure you can be confident will sound OK is what used to be called a large bookshelf speaker, say 20 litres in volume, using a 5-inch (12cm) or 6-inch (15cm) diameter woofer. To roughly calculate the enclosure volume, multiply the height by width by depth in centimetres, divide by 1000 and subtract 20%. For example, if a cabinet is 40cm tall, 25cm wide and 30cm deep, the product of those is 30,000 (40 × 25 × 30). Dividing by 1000 gives you 30, then subtracting 25% (to account for the material thickness etc) gives you an estimated volume of 22.5 litres. However, for main speakers, larger enclosures of around 40-60L will likely sound better. Speakers are widely available secondhand – but how do you tell if they’re any good, especially when often you cannot listen first? Tiny speakers invariably sound terrible, no matter the brand. With speakers, bigger usually equals better. 68 Silicon Chip Australia's electronics magazine siliconchip.com.au Note that the shape of the enclosure doesn’t matter nearly as much as the internal volume. If you need narrowbut-tall tower speakers to achieve your desired aesthetics, that’s fine – as is an older, more squat enclosure. Rule #1: bigger = better. Weight The next step in selection is to feel how heavy the speaker is for its size. Almost invariably, heavy speakers will sound better than lightweight designs. There are several reasons for this. Woofers with larger magnets are much heavier than those with small magnets; crossovers that use inductors and not just capacitors are heavier; and cabinets with thicker walls and internal bracings are heavier than those without. So just by picking up the speakers, you will get a quick but usually quite reliable indicator of sound quality. Rule #2: heavier = better Passive radiators There is an enclosure design that, in effect, combines both sealed and ported approaches. This design uses a passive radiator, which is like a second woofer, but it does not have a magnet or coil. The passive radiator moves back and forth like the air in a port but without ever fully unloading the woofer. Some passive radiators are obvious (eg, they have a flat panel), while others look just like a second woofer. Passive radiator designs have the theoretical ability to develop excellent bass from small enclosures, but unfortunately no second-­hand passive radiator speakers I’ve ever bought have sounded very good! Excluding rarer designs like folded horns and similar, enclosure design falls into two basic categories: sealed and ported. A sealed design, as the name suggests, has no openings in the box – the air behind the drivers is trapped within the enclosure. The old name for this design approach – acoustic suspension – gives an indication of how the enclosure works. The springiness of the air within the enclosure provides the restoring force for the woofer’s suspension. When gently moved by your fingers, true acoustic suspension woofers tend to have a viscous, slow return movement. On the other hand, many cheaper sealed speakers use a conventional woofer that springs quickly back into position. In general, unless it is a true acoustic suspension design, a sealed enclosure is likely to deliver worse bass than a ported enclosure. The exception to this is if the sealed enclosure is large compared to the size of the woofer – and the woofer is large as well! A ported design has openings – ports – in the enclosure. These are usually on the front of the enclosure, but some speakers have them on the back. Always check both the front and the back panels for ports. Generally, a ported enclosure can achieve deeper bass from a given size of enclosure. Importantly for buyers of second-­ hand speakers, the port also allows you to see inside the enclosure without pulling out a driver. When assessing a ported speaker, use a torch and peer into the enclosure through the port. Normally, you’ll be able to see either the inside of the back or front panels. In both cases, if you can see bare chipboard, mark down the speaker. Instead, what you want to see is some type of acoustic absorbing material (foam or a fluffy material) covering the panel. This material stops internal sound reflections that tend to colour the midrange. Another thing to look at when examining the port is its design and finish. A well-designed port has flares at both ends. This reduces port noise as the air moves back and forth in the port. The rear of a lightweight speaker with a plastic enclosure – horrible! A pair of these speakers was priced quite high – many second-hand sellers have no idea of the value (or lack thereof) of the speakers they’re selling. Ports should be flared at both ends (not with square edges, as shown here) and have no internal steps. Ports also allow you to inspect the interior of the enclosure without removing a driver. The woofer cone should be able to be gently pushed inwards without any binding or scratchy sounds. Enclosure design siliconchip.com.au Australia's electronics magazine October 2025  69 Also, the inside of the port should be smooth – many ports on cheaper speakers have an external piece that connects to an internal cardboard tube, with a distinct step at the join. Finally, be wary of speakers that have either very large, very small or very short ports – yes, all of these can be correctly used, but more often than not, they’re giveaways of a poor design. Rule #3: Prefer ported enclosures Drivers The next step is to examine the drivers carefully. Let’s start with the woofer. The woofer should have a longtravel suspension. Using the spread fingers of one hand, carefully push the cone inwards. The cone should move with no binding (a voice coil that catches often gives a scratchy feel and sound) and the edge suspension should not distort or collapse. Furthermore, the cone should not change in shape, ie, obviously flex. The larger the woofer, the less distance it needs to be able to move. So if you’re looking at an older speaker with a 12-inch (30cm) woofer, don’t be concerned if it can be moved only 5mm – there will still be plenty of bass. On the other hand, a 6-inch (15cm) woofer needs to have a lot of travel to be effective. The more woofers the enclosure has, the less travel each one needs. Sharply tapping the ends of your Speaker specifications Many speakers have specifications written on the back of the enclosure. For brand name designs, you can do a quick Google search and find the same information. However, more often than not, this information is of little help – to put not a fine point on it, it’s often garbage. Really, only one specification is likely to be semi-accurate – and that’s nominal impedance. If the plaque says “4 ohms”, the AC impedance is likely to be near 4W. Stated frequency response? It’s often the complete stuff of fantasy – or the response was measured at ±12dB, making it equally useless! Power handling? Is it RMS or peak power? Or power on normal music material? Or power at great distortion just before the voice coil melts? Who knows? Without the speaker efficiency being stated, the power figure gives you no idea of how loud the speaker can play anyway. Instead, when using it, you would simply turn it down when it starts to distort (or it’s too loud for comfort). Where they are available, look at the specifications, but don’t expect to gain a lot from them. Personally, when buying second-hand speakers, I mainly just check the impedance, to ensure the designated amp can safely run them. fingers on the woofer cone will excite its resonant frequency – the resulting sound should be as deep as possible. This is an excellent test that evaluates both the woofer and its enclosure. If the speaker is fitted with a large midrange speaker, again, very gently move its cone with your fingers. It will be able to be moved only a short distance, but again, there should be no binding. The tweeter should preferably be a dome design – and don’t try to move it! Some cone tweeters can sound fine, but on any speaker of the last 20 years, a cone tweeter usually indicates it is a cheaper, lower-quality design. If you can, apply a 1.5V cell across the speaker terminals. The woofer should leap forwards or backwards (forwards, if you’ve observed the correct polarity). If you put your ear to the tweeter and midrange, you should also be able to hear sounds as the cell is connected and disconnected – especially if you draw the wire across the battery terminal to produce a scratchy noise. This test shows that all the drivers are working. Many second-hand speakers, especially at thrift shops and similar, have been damaged while on display. For example, the centre caps on woofers and dome tweeters can be pushed in. Woofer centre caps can usually be pulled out by using a fine needle or by careful use of a vacuum cleaner nozzle, but dome tweeters damaged in this way are usually ruined. Don’t buy speakers with non-­ removable grilles. The risk is simply too great; for example, the woofer’s foam suspension may have completely perished. Rule #4: carefully check the drivers Clues to quality The centre dust cap in the left photo is damaged, although it could probably be pulled back into shape with the careful use of a vacuum cleaner nozzle. However, note how badly the outer suspension is distorting when the cone is pushed inwards. This is one to leave behind! Speakers like the one on the right with dome tweeters are preferable to those with cone designs. 70 Silicon Chip Australia's electronics magazine In addition to weight, there are other clues to quality. The first is the brand name. This is a tricky area. Some wellknown consumer electronics brands have speakers that range in quality from awful to very good, while some specialist speaker brands have reputations that are vastly overblown. Definitely don’t buy on brand alone – always ensure that the above four rules are met by the speakers you’re considering. siliconchip.com.au Another clue to quality is the terminal block – if there is one! Cheap and nasty speakers typically don’t have a terminal block; instead, the cable just comes through a hole in the rear panel. Small spring clip terminals indicate the manufacturer has been cost-­cutting – not very reassuring about what’s inside the enclosure! Better speakers use gold-plated binding posts and often can be bi-wired – that is, there are separate connections for the upper and lower frequencies, invariably bridged with plates. Any speaker with adjustable tweeter and/or midrange level controls is likely to be of better quality. Editor’s note: usually only relatively modern hifi speakers offer bi-wiring – plenty of excellent older speakers have a simple pair of binding posts. Bi-wiring is mostly just a fad anyway. On some enclosures, you can see how the box was made. If that’s the case, look for the thickness of the board and whether the tweeter has been recessed to give better phasing with the woofer – in fact, anything that shows that care was taken in the design and construction. Be very wary of any speaker that looks home designed and built. It may be a brilliant design – but more often, it’s been built by someone using rules of thumb... or no acoustic design at all (if they used quality drivers, such speakers can make good donors for a new design). Do not buy speakers where some or all the drivers have obviously been replaced. Many people buy replacement drivers based only on size, not the acoustic match for the enclosure and/or crossovers. Speakers that use only one fullrange driver are typically quite inferior. Many are at the cheap and nasty end of the range, and those from higher-­quality brands usually require dedicated amplifier equalisation to sound even half reasonable. Rule #5: look for quality clues Conclusion I am a bit of a nut when it comes to speakers – I have bought literally dozens of pairs over the last 50 years. What I have found is that if the speaker is large, heavy and ported, the drivers are in good condition, and the enclosure design and construction look fine, the chances are very much that you have SC a quality pair of speakers. siliconchip.com.au Silicon Chip PDFs on USB The USB also comes with its own case ¯ 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). THE FIRST SIX BLOCKS COST $100 OR PAY $650 FOR ALL SEVEN (+ POST) NOVEMBER 1987 – DECEMBER 1994 JANUARY 2005 – DECEMBER 2009 JANUARY 1995 – DECEMBER 1999 JANUARY 2010 – DECEMBER 2014 JANUARY 2000 – DECEMBER 2004 JANUARY 2015 – DECEMBER 2019 OUR NEWEST BLOCK COSTS $150 → JANUARY 2020 – DECEMBER 2024 WWW.SILICONCHIP.COM.AU/SHOP/DIGITAL_PDFS Australia's electronics magazine October 2025  71 Project by Les Kerr Dual Train Remote Control This add-on to the Battery-Powered Model Train allows two different model locomotives to be controlled wirelessly from a single box. I n the January 2025 issue, we described how to control the speed and direction of a single model train using a 433MHz radio link (siliconchip.au/ Article/17607). Since then, I have been asked by several people if it could be modified to simultaneously control the speed and direction of two trains. That would allow two trains to run together on the same track or track layout without the expense of installing DCC. Children love the concept, as they can have one train chasing the other. The system presented here controls two trains, but it could be enhanced to control up to ten trains and operate onboard sounds like whistles and brakes. However, those extra features are for a future article. To control the speed and direction of two trains at once, I have used the same Receiver hardware but have made two new versions of Receiver firmware, one for each train. The Battery Charger presented previously also remains valid. If you have already built the single 72 Silicon Chip train controller, you will need to build a second Receiver and the new dual transmitter. I have made another refinement while adding the multi-locomotive capability. The previously described train controller Receiver was switched off by inserting a 2.5mm jack plug. This was fine if you only had one carriage, but when you added a second carriage, there wasn’t enough space between the carriages to insert the jack plug. To solve this, I made a much smaller on/off plug out of plastic that fits between the two carriages. Inserting this into the train’s jack socket switches the power to the train off, and removing it switches the train on. Fig.1 shows the dimensions of the plug. You will need two of these, one for each train. The adjacent photo shows the Dual Train Controller, which is built into a standard UB3 Jiffy box. It has a speed potentiometer and a direction toggle switch for each train, together with a power off/on toggle switch. The LED illuminates when it is switched on. Circuit details Fig.1: this plastic plug can be made with hand tools or a lathe from a small plastic cylinder using a file. It fits next to the carriage more easily than a jack plug to switch the train off. Fig.2 shows the dual transmitter circuit. It is similar to the single transmitter circuit published in the January issue but it uses a 14-pin microcontroller. Two new inputs are added for the speed and direction controls of the second train. The two train direction toggle switch positions are monitored by the microprocessor (IC1) using its RC2 and RC3 digital inputs, with +5V (switch Australia's electronics magazine siliconchip.com.au Fig.2: the Dual Transmitter circuit is an expanded version of the original, with a 14-pin PIC16F1455 instead of an 8-pin PIC12F617, plus duplicated speed and direction controls. open, held at +5V via the 10kW pull-up resistor) giving one direction and 0V (switch closed to ground) the opposite. The 100nF ceramic capacitors on these pins reduce switch bouncing and stop electrical noise from affecting the taken readings. Each train has its own potentiometer that is used to vary its speed. IC1 uses its analog-to-digital converter (ADC) channels AN4 for train 1 and AN5 for train 2. It converts the voltage on the potentiometer wipers (which are directly proportional to their rotation) to 8-bit numbers between 0 (train stopped) and 255 (full speed). 100nF capacitors to ground prevent electrical noise from affecting these readings. These measurements are continually taken; if subsequent readings are identical, indicating the positions of the speed potentiometers and switches haven’t changed, no transmission takes place. If subsequent readings are different, the new speed is transmitted along with the direction. The same happens for both trains separately. When a transmission needs to be made, IC1 produces digital data from its RC4 output at 900 baud, which goes to the 433MHz ASK (amplitude shift keying) transmitter module. Each train has its own qualifier added to the transmitted data so that only that specific train is addressed. I chose 900 baud because I found that this is highest baud rate for reliable transmission with these modules. The whole transmitter is powered from a 9V battery, which is connected siliconchip.com.au to the circuit via an on/off toggle switch (S1) and a 1N5819 schottky diode. The diode prevents accidental battery polarity reversals from destroying the circuit but has a lower forward voltage drop than a standard diode, so the battery lasts longer. A small 78L05 regulator provides +5V for the microprocessor. 100μF capacitors at its input and output reduce any ripple to a negligible level and ensure stability; the 100nF capacitors help with stability too. Receiver The Receiver circuit (Fig.3) is identical to the one published in the January issue. Signals from the Transmitter are received by the 433MHz receiver module, and the demodulated serial data is applied to the RC2 digital input (pin 8) of the PIC16F1455 microcontroller (IC2). The 8-bit train speed data and the direction data are extracted and stored in memory, then used to generate the pulse-width modulated speed signal and the direction signal. Two logic inputs, IN1 and IN2, control the H-bridge driver (IC3). To turn the motor in one direction, we apply a pulse-width modulated (PWM) signal to vary the speed to IN1 while holding IN2 high. If the train is to run in reverse, the PWM signal is applied to instead IN2 while IN1 is held high. To stop the train, both inputs are kept at the same level (both low or both high). The battery supply voltage is halved by the two 10kW resistors and the resultant ~2.4V is monitored by analog input RA4 (pin 3) of IC2 using its internal ADC. If the voltage at that pin falls below 2V (ie, the battery is below 4V), digital output RC4 (pin 6) is taken low, switching on red LED2 The Dual Train Controller conveniently fits into a UB3 Jiffy box. The drilling diagram is shown in Fig.6. Australia's electronics magazine October 2025  73 Fig.3: the same Receiver is used as before except with updated firmware so that the two trains respond to different signals. The PIC sends signals to a DRV8871 module to control the motor. to alert you that the battery needs charging. The micro also provides signals to drive the DRV8871 H-bridge IC. To turn the motor in one direction, the PWM signal is applied to digital output RC3 (pin 7), while RC5 is taken high (+5V). To reverse the motor direction, the PWM signal is applied to RC5 and RC3 is taken high. The higher the speed value, the faster the motor turns. When the speed control is near its minimum position, both RC5 and RC3 are taken low (to 0V), causing the PWM module to go into sleep mode, reducing the current drawn from the battery. The +5V supply for the 433MHz receiver and micro is provided by the S7V7F5 high-frequency voltage up/ down converter (MOD4) that takes the 4-6V battery voltage and provides a regulated +5V output. If the battery has been recently charged (it could be as high as about 6V), MOD4 steps down the voltage to +5V; if it is discharged below 5V, it steps it up. The 100μF electrolytic capacitor and 100nF ceramic capacitor reduce any noise or ripple on the supply. Similarly, the U3V16F15 (MOD3) provides the +15V DC supply for the motor. We use 15V instead of 12V to overcome any voltage drop in the tiny cables connecting the carriage to the train motor. Pololu recommends in their data sheet that you add a 47μF capacitor across the battery input when using these inverters, which I have done. Both these modules are available locally for around $9 each. There is a 2.5mm switched jack socket (CON1) so the battery can be charged. It also allows the battery power to the Receiver to be switched off simply by inserting a jack plug. With the jack plug in the socket, the battery is connected to the Charger and disconnected from the Receiver as its positive side is disconnected. Charger circuit This is how we wired up the Dual Train Controller. See Fig.7 overleaf for a simplified view of the connections. 74 Silicon Chip Australia's electronics magazine The Charger (Fig.4) is also the same as before. The battery is trickle charged at C/10 (90mA) for 16 hours unless the charger output voltage exceeds 6V, indicating the battery is fully charged. In that case, the charge current is switched off. When the power pack is switched on, 9V is applied to the 78L05 voltage regulator (REG2), which reduces the voltage to siliconchip.com.au ◀ Fig.4: the Charger circuit is also the same, using REF1 and Q2 to provide a current-limited voltage source to charge the battery. IC4 and Mosfet Q1 switch the charger off after a set time to avoid damaging the battery. The 1N4148 diode (D3) prevents the ADC input from rising above 5.6V, although that is unlikely because the battery would have to be charged to over 11V. Still, it’s possible CON2 could accidentally be connected to a voltage source, so it’s better to be safe. Dual transmitter construction +5V to power the PIC12F617 microcontroller, IC4. The two 100μF capacitors smooth out any residual ripple, while the two 100nF capacitors provide high-­ frequency bypassing. On powering up, digital output GP4 (pin 3) of IC4 pulses the green LED at 200ms intervals, indicating it is in standby mode. Pressing the Start button (S3) pulls the GP2 digital input low (pin 5), causing an interrupt routine to be triggered that takes the Charger out of standby mode and puts it into charge mode. The 100nF capacitor reduces any contact bounce from the pushbutton. This results in the green LED switching off and the red Charge LED flashing at 500ms intervals. Mosfet Q1 (IRL540N) is switched on by digital output GP5 going high, and the 16-hour countdown timer starts. When on, the drain of the Mosfet goes low, connecting the 90mA constant current source to the battery. The current source comprises the BD136 transistor (Q2), an LM285 2.5V reference diode and a 220W resistor in parallel with a 22W resistor. It works by holding the PNP base 2.5V below the +9V supply. This sets the emitter at 1.8V (2.5V – 0.7V), which matches the voltage across the siliconchip.com.au parallel resistors. They have a resistance of 20W (220W || 22W). With 1.8V across 20W, Ohm’s law (I = V ÷ R) tells us the current must be 90mA (1.8V ÷ 20W). The battery voltage is halved by the two 10kW resistors and applied to analog input GP0 (pin 7) of IC4. Once per second, it measures the voltage; if it is above 3V (battery fully charged), charging stops and the Charger goes back into standby mode, shown by the green LED flashing. If the battery voltage doesn’t exceed 6V, the charging stops after 16 hours. The 1N4004 diode (D2) prevents the battery from discharging if it is left connected when the Charger is not powered. The new dual transmitter PCB is coded 09110245 and measures 57 × 40mm – refer to the overlay diagram, Fig.5. The boards we supply are double-­sided and include two topside links. If you make it yourself as a single-sided board, you will need to replace those tracks with wire links. Start by fitting the resistors and D1, ensuring its cathode band faces as shown, then the socket for IC1, with the notched end at the top. You could solder the IC directly to the board, but if you wish to remove it later for reprogramming, you will need to use the socket. There are various ways to connect the wires to the board, but the easiest is probably to solder standard headers to the board and use pre-made wires with DuPont connectors to plug into them. Now is a good time to solder the twoway and three-way headers in place. After that, you can fit the MKT capacitors (all 100nF, not polarised), then the two electrolytic capacitors. The latter are polarised and must have their longer (+) leads inserted into the pads marked with + symbols in Fig.5 and on the PCB. Then solder REG1 in place, with its flat side facing as shown. You may need to bend its leads to fit the PCB pads. The 433MHz transmitter module has a three-pin header that goes into three pads on the board. Make sure it’s orientated with the antenna terminal towards the edge of the main PCB, then solder it in place. Fig.5: fit the components on the new Dual Transmitter PCB as shown here. IC1, D1, the electrolytic capacitors and the 433MHz transmitter module must be orientated correctly. The transmitter module is fitted vertically; it’s shown laid over here for clarity. The antenna runs above the left-hand edge of the PCB. Australia's electronics magazine October 2025  75 Don’t plug in the PIC16F1455 microcontroller yet. If you have purchased it from the Silicon Chip Online shop, it will already have the firmware loaded. If you wish to do this yourself, the files can be downloaded from siliconchip.au/Shop/6/508 – you will need a suitable programmer and adaptor socket. Make the transmitter antenna by winding 0.4mm diameter enamelled copper wire around a 2.5mm diameter former, like the shaft of a drill bit. Wind 16 close turns and ensure there is sufficient length at either end to trim it as shown in Fig.5. Then strip the insulation from the shorter end (using a sharp hobby knife or emery paper), tin it and solder it to the antenna terminal on the 433MHz module. The antenna runs above the edge of the board (not as shown in Fig.5; it was drawn that way for clarity). Finally, check for any dry solder joints or solder bridges. Case preparation Fig.6 shows the holes to make in the lid of the UB3 Jiffy box. The four 2.5mm countersunk holes are for the PCB mounting screws (they should be countersunk on the outside of the lid). The 7mm holes are for the pots, 5mm holes for the switches and a 3mm hole for the LED. The PCB mounts to the inside of the lid on M2.5 tapped spacers. Ideally, they should be around 18mm long but that size is not readily available – I custom-made mine on a lathe. 17mm spacers are commercially available and should be OK. Deburr the holes, then fit the LED, potentiometers, their knobs and the toggle switches as shown in the Fig.7: the wiring is most easily made by cutting female/female jumper leads in half, soldering the bare ends to the chassis-mounting components and then plugging the other end into standard pin headers on the PCB. photos. Attach the spacers using four 6mm-long M2.5 countersunk head screws, then hold the PCB to those spacers using four M2.5 sized machine nuts. Solder the 220W resistors between one end of potentiometers and their case as shown. To make the connection to the potentiometer cases, you will need to abrade a small section of the pot body with emery paper, a file or similar (don’t breathe the resulting dust!). Next, cut female/female jumper leads in half, strip the cut ends, solder them to the lid-mounted components and then plug the DuPont plugs onto the appropriate headers using the wiring diagram, Fig.7, as a guide. Tape the free end of the antenna to the case. The battery is attached by double-sided tape to the inside of the case, on the opposite side to the antenna. Testing Make sure that the microcontroller is out of its socket, then check the wiring of the battery connector and the orientations of the 78L05 voltage regulator and the 433MHz transmitter module. Connect the 9V battery and switch the unit on; the red LED on the front panel should glow. Use a multimeter to probe pins 1 (red) and 14 (black) of the IC socket and verify that you get a reading very close to +5V DC. If not, check that the Fig.6: prepare the Jiffy box lid with the holes shown here. The four 2.5mm holes are countersunk on the outside. 76 Silicon Chip Australia's electronics magazine siliconchip.com.au 5V regulator is the correct way around and there aren’t any solder bridges shorting the tracks. Switch off the transmitter and plug in the microcontroller; you may need to straighten its pins first. Push it in evenly, making sure that none of the leads fold up under the body when doing so, and ensure its notch is aligned with the socket’s. If you have an oscilloscope, connect it to pin 6 of the PIC16F1455 and the Earth connector to 0V. Switch on and you should capture a serial data waveform at 900 baud, similar to that in Screen 1. Attach the back of the case using the supplied screws. For the construction details of the Receiver and Charger, refer to the January 2025 issue. The PCBs are not difficult to assemble, so we have reproduced the PCB overlays in Figs.8, 9 & 11, which will be enough for an experienced constructor to build them. Also refer to the Receiver battery wiring diagram (Fig.10) and Charger case drilling details (Fig.12). Fig.8: this is the smaller Receiver, which uses mostly SMD parts. Programming the Receiver IC If you purchased the microcontrollers from the Silicon Chip Online Shop, they will already be programmed, so you won’t need to do anything further. However, if you build the Receivers using blank chips, you will need to program them before you can use them. To do this, solder wires to the +5V and 0V rails as well as pin 4 (MCLR) of the microcontroller, and the pads on pin 10 (ICSPDAT) and pin 9 (ICSPCLK). With those wires in place and the PIC16F1455 IC attached to the board, connect the wires to your programmer (check its pinout in the documentation). The Receiver firmware is available from the same link as before (from siliconchip.au/Shop/6/508). Use your PIC programmer to upload it to the chip (eg, using Microchip’s free MPLAB IPE programming software). Use the testing procedure from the January 2025 article (siliconchip.au/Article/17607) to test the Receiver but adapt it to use the Dual Transmitter that you just built. Final testing Fig.9: the slightly larger Receiver board uses mostly through-hole parts. Fig.10: the Receiver battery wiring. Fig.11: the battery Charger uses all through-hole parts and is straightforward to build. Switch on the Transmitter and set the speed controls to their Fig.12: the Charger also fits into a UB3 Jiffy box, with the required holes shown here. For full assembly instructions, refer to the January 2025 issue. siliconchip.com.au Australia's electronics magazine October 2025  77 minimum position. With engine 1 on its back and connected to its carriage, switch on its Receiver by removing the on/off plug from the jack socket. Rotate the speed control for train 1 on the transmitter; the engine wheels should start to turn, spinning faster as the control is rotated towards maximum speed. Turn the control back down and the speed should decrease to zero just before minimum rotation. Repeat this test with the forward/ reverse switch in the other position. If you change the position of the forward/reverse switch, nothing will happen until the corresponding speed control changes. To avoid damage to the train’s motors, always reduce the speed control to its minimum before operating the forward/reverse switch. Switch off the transmitter and insert the on/off plug to switch off the train, then repeat the above procedure for train 2. Testing the trains on the track Place train 1 on the track and remove its on/off plug. On the transmitter, rotate the speed controls for trains 1 & 2 fully anti-clockwise. Switch on the transmitter and slowly rotate train 1’s speed control clockwise. Train 1 should start to move in a direction depending on the position of its forward/reverse switch. Continue rotating the speed to maximum and the train should accelerate to maximum speed. Switch off the transmitter and the train should continue running at maximum speed. Switch on the transmitter again and rotate train 1’s speed control to minimum. The train should slow down and then stop. With train 1’s potentiometer in the minimum position, rotate train’s 2 potentiometer; you shouldn’t see any response from train 1. Repeat the above test after moving the reverse switch to the other position. Remove train 1 from the track and insert its on/off plug, then repeat the above test for train 2. If the red LED on the train lights, it is time to charge the batteries in the train. To do that, insert the Charger’s jack plug into the train’s socket and SC switch on the Charger. Parts List – Dual Train Remote Control 1 500mm length of 1.5mm diameter black or clear heatshrink tubing various lengths & colours of light-duty hookup wire (wire for the power to the engine can be from old USB and mouse cables) Dual Train Controller (Transmitter) 1 double-sided PCB coded 09110245, 57 × 40mm 1 black UB3 Jiffy box 1 3-pin 433MHz transmitter module, WRF43301R or XLC-RF5 (MOD1) [Little Bird, AliExpress, eBay] 1 9V battery snap with flying leads 1 9V battery (BAT1) 2 10kW linear (B-curve) 24mm potentiometers with nuts (VR1, VR2) 2 large knobs to suit VR1 & VR2 3 SPDT subminiature toggle switches (S1-S3) [Jaycar ST0300] 1 14-pin DIL IC socket (optional; for IC1) 1 40-way female header strip (cut into five 2-way and two 3-way strips using side cutters) 4 M2.5 × 6mm countersunk head machine screws 4 M2.5 nuts 4 M2.5 × 17mm tapped spacers [element14 1466854] 1 20 × 40mm (approximate) piece of foam-cored double-sided tape 1 200mm length of 0.4mm diameter enamelled copper wire 8 200mm female-female DuPont jumper leads (two red∎, two black∎, one blue∎ & three green∎) 1 PIC16F1455-I/P 8-bit micro programmed with 0911024D.HEX, DIP-14 (IC1) 1 78L05 5V 100mA linear regulator, TO-92 (REG1) 1 3mm high-brightness red LED (LED1) 1 1N5819 40V 1A schottky diode (D1) 2 100μF 16V low-ESR electrolytic capacitor 6 100nF 50V ceramic, MLC or MKT capacitors 4 10kW ¼W 1% axial resistors 2 220W ¼W 1% axial resistors Charger 1 single- or double-sided PCB coded 09110244, 63 × 32mm 1 UB3 Jiffy box 1 9V DC 150mA+ plugpack Screen 1: the waveform between pin 6 of the PIC16F1455 IC and ground is a 900 baud serial stream. 78 Silicon Chip Australia's electronics magazine siliconchip.com.au That time of year is nearly here... 1 2.5mm mono jack plug (CON2) [Jaycar PP0100] 1 chassis-mount DC socket to suit plugpack (CON3) 1 chassis-mount SPST miniature momentary pushbutton (S3) 1 8-pin DIL IC socket 5 2-way pin headers, 2.54mm pitch 6 female-female DuPont jumper wires, ideally joined in a ribbon 4 M3 × 8mm countersunk head machine screws 8 M3 hex nuts 1 500mm length of single-core screened microphone cable 1 PIC12F617-I/P 8-bit micro programmed with 0911024C.HEX, DIP-8 (IC4) 1 LM285-2.5 voltage reference diode, TO-92 (REF1) 1 78L05 5V 100mA linear regulator, TO-92 (REG2) 1 IRL540N 100V 36A Mosfet, TO-220 (Q1) 1 BD136/138/140 45/60/80V 1.5A PNP transistor, TO-126 (Q2) 1 5mm green LED (LED3) 1 5mm red LED (LED4) 1 1N4004 400V 1A diode (D2) 1 1N4148 75V 200mA diode (D3) 2 100μF 16V low-ESR radial electrolytic capacitors 3 100nF 50V ceramic, multi-layer ceramic or MKT capacitors 4 10kW ¼W 1% axial resistors 3 2.2kW ¼W 1% axial resistors 2 220W ¼W 1% axial resistors 1 39W 1W 1% axial resistor (for testing) 1 22W ¼W 1% axial resistor CHRISTMAS Spice up your festive season with eight LED decorations! Tiny LED Xmas Tree 54 x 41mm PCB SC5181 – $2.50 Tiny LED Cap 55 x 57mm PCB SC5687 – $3.00 Tiny LED Stocking 41 x 83mm PCB SC5688 – $3.00 Receiver – two are required per Transmitter 1 4-pin 433MHz receiver module, WRF43301R or XLC-RF5 (MOD2) [Little Bird, AliExpress, eBay] 1 Polulu U3V16F15 15V output step-up DC/DC converter (MOD3) 1 Polulu S7V7F5 5V output step-up/down DC/DC converter (MOD4) 1 Adafruit DRV8871 motor driver module (MOD5) 4 1.2V 900mAh NiMH AAA cells [Jaycar SB1739] 1 2×2 AAA battery holder with flying leads 1 2.5mm mono switched chassis-mounting jack socket (CON1) [Jaycar PS0105] 2 4-way right-angle pin header, 2.54mm pitch (for MOD2 & MOD5) 2 female-female DuPont jumper wires, ideally joined together 1 red 3mm LED (LED2) available from Core Electronics 🔹 🔹 🔹 🔹 Receiver (TH version specific parts) 1 single- or double-sided PCB coded 09110242, 74 × 23mm 1 PIC16F1455-I/P 8-bit microcontroller programmed with 0911024S.HEX or 0911024T.HEX, DIP-14 (IC2) 1 14-pin DIL IC socket 3 100μF 16V low-ESR radial electrolytic capacitors 2 100nF 50V ceramic, multi-layer ceramic or MKT capacitors 3 10kW ¼W 1% axial resistors 1 1kW ¼W 1% axial resistor Receiver (SMD version specific parts) 1 single- or double-sided PCB coded 09110243, 23 × 30mm 1 PIC16F1455-I/SL 8-bit microcontroller programmed with 0911024S.HEX or 0911024T.HEX, SOIC-14 (IC2) 1 100μF 16V low-ESR radial electrolytic capacitor 1 100μF 6.3V radial electrolytic capacitor 1 47μF 16V X5R M3216/1206 SMD ceramic capacitor 2 100nF 50V X7R M2012/0805 SMD ceramic capacitors 3 10kW ⅛W 1% M2012/0805 SMD resistors 1 1kW ¼W 1% M2012/0805 SMD resistor siliconchip.com.au Australia's electronics magazine Tiny LED Reindeer 91 x 98mm PCB SC5689 – $3.00 Tiny LED Bauble 52.5 x 45.5mm SC5690 – $3.00 Tiny LED Sleigh 80 x 92mm PCB SC5691 – $3.00 Tiny LED Star 57 x 54mm PCB SC5692 – $3.00 Tiny LED Cane 84 x 60mm PCB SC5693 – $3.00 We also sell a kit containing all required components for just $15 per board ➟ SC5579 October 2025  79 We introduced this new pendant speaker design last month, including some information on how we arrived at the final configuration. Now we will show you how to build, test and (optionally) tune it. Easy to assemble, with a largely pre-built enclosure Multiple configurations for different applications Uses a 6.5-inch (170mm) woofer and a dome tweeter Low-cost drivers and crossover Impedance: 4W (minimum, 20Hz-20kHz) 44cm wide, 40cm high and 7kg in weight High-Performance Pendant Speaker Part 2 by Julian Edgar T he starting point for the enclosure is a Bunnings pot that is made from recycled plastic. It is called the “Eden 40cm Black Faux Planter” (I/N 0118235); you want the 44cm size (it’s available in three different sizes). The shape is best described as a truncated, slightly curved cone. It is 44cm in diameter at the top, 22cm in diameter at the bottom and 40cm high. Bunnings states on their website that it has a volume of 26L; however, the enclosure actually has a total volume of about 37 litres. Taking into account the position of the baffle, we use an enclosed volume of about 27L. The construction steps are: 1. Cut out a strengthening panel, which fits in the bottom of the enclosure (the top when it is hanging). Glue and screw it in place inside the pot. 2. Cut a baffle, make holes in it and test fit the baffle, woofer, tweeter and port in the enclosure. 3. Disassemble the baffle, removing all the parts. 4. Glue the quilt wadding inside the enclosure. 5. Cut out and screw the grille spacing blocks to the baffle and glue the port into place (if you wish to test different port lengths, don’t glue the port yet). 80 Silicon Chip 6. Paint the baffle and port. 7. Cut the metal grille mesh and paint it. 8. Assemble all the components on the front and back of the baffle and wire it up, including the cable that goes to the amplifier. 9. Glue & screw the baffle, complete with all its components, into place. 10. Fit the grille. 11. Test it. The following steps are for the version that uses the ported enclosure and protection lamp. If you are building the non-ported enclosure, ignore anything that mentions a port. If you are building the speaker without the protection lamp, you may wish to place the baffle nearer the end of the enclosure. Doing this gives slightly better sound dispersion, and the change in internal volume is small enough not to matter a great deal. If you choose to do this, you will need to use shorter spacer blocks for the grille. However, before making the enclosure, we will make the crossover. Crossover construction The crossover comprises just three components: a 4.7μF non-polarised crossover capacitor and two 5W ceramic-bodied resistors, one that is 1W and the other 10W. Fig.2 (from last month) shows the circuit. As you can see, the capacitor and 1W resistor are in series with the tweeter, and the 10W resistor is in parallel with the tweeter. You can build the crossover on punched laminate board, as we did, or simply glue the components to a piece of hardboard or similar and then wire them point-to-point. The terminal blocks are optional – you can instead make the connections directly to the components and tie these leads into place with cable ties. None of the components are polarised. Enclosure construction #1 Making and fitting the Fig.2: the simple crossover circuit uses a non-polarised 4.7μF capacitor and two 5W resistors. Australia's electronics magazine strengthening panel The first step is to use a jigsaw to cut out the round bottom plate from particleboard. This plate needs to be siliconchip.com.au 230mm in diameter and should be the same thickness as the material that will be used in the baffle (18-22mm thick). This plate has two purposes. Firstly, it strengthens the area from which the Pendant Speaker will hang. This is needed because the bottom of the pot is thinner than the walls. Secondly, it stiffens the bottom of the pot – this is required for acoustic reasons. Glue and screw the bottom plate into place. Use plenty of Liquid Nails water clean-up adhesive; there’s quite a void to fill under and around the panel, so you will probably use a full cartridge. Then insert into the panel particleboard four screws from the bottom of the pot and four from around the periphery. Drill small diameter pilot holes before inserting these eight screws. Clean up the edge of the glue using a wet cloth that you repeatedly rinse in running water. While this part is not visible when the speaker is complete, cleaning the edge of glue is good practice for when you glue the baffle – that edge will be visible. Drill a hole in the base for the speaker cable to exit and attach the fastening from which the enclosure will hang. We used a 40mm saddle clamp with two M6 bolts; you could also use an M8 eye-bolt. In either case, use washers and Nyloc nuts or apply Loctite to the nut threads – you don’t want these nuts coming loose through vibration! Don’t attach the hanger with just particleboard screws. Photo 1: the High-Performance Pendant Speaker is straightforward to make and requires only normal handheld power tools. Photo 2: first, cut out the base reinforcement disc with a jigsaw. Doing the work on a milk crate can help to protect the blade when cutting. Photo 3: next, apply plenty of water clean-up Liquid Nails to the base of the pot before... Photo 4: ...putting the disc in place and smoothing the glue around it. Surplus glue should be cleaned up with a rag repeatedly rinsed in water. Photo 5: screws are then inserted from the sides to hold the particle board reinforcement firmly in place. Countersink these holes with a larger diameter drill bit rotated by hand before inserting the screws. Photo 6: insert particleboard screws into the reinforcement plate from the bottom. Note the glue visible through the two pot drainage holes – they must be sealed. #2 Making the baffle The next step is to make the baffle. To do this, cut a disc of particleboard 415mm in diameter. We used 22mm-thick, moisture-resistant particleboard but slightly thinner MDF should be fine. Don’t use material less than about 18mm thick. Any thinner than this and the peripheral glue won’t have enough ‘meat’ to adhere to. Also, because screws are inserted through the wall of the enclosure to further hold the baffle in place, there needs to be enough material for the screws to go into and be secure. The diameter of the baffle is less than the internal diameter of the pot because we want the baffle to slide down a little within the pot – that is, to be recessed from the outer lip by about 60mm. This gives us the needed clearance for the grille and optional protection lamp. siliconchip.com.au Australia's electronics magazine October 2025  81 Cut holes in the baffle for the: • woofer (the hole will need to be 150mm) • port (if using thin-walled 90mm PVC stormwater pipe, the hole will be 90mm) • tweeter (50mm hole) The woofer needs to be mounted in the middle of the baffle; if you mount it off-centre, the Pendant Speaker will not hang straight. The port and tweeter holes can be mounted wherever you like in the baffle – just position them to leave sufficient material around the openings for strength and ensure the 100mm-long port tube cannot foul an internal wall. Cutting the thick particleboard can be a bit difficult, especially the smaller diameter holes. The hole for the port can be cut with a jigsaw – it may be easiest to just cut it roughly undersize, then file it to the final size. Any minor mismatches in size or shape will be filled with the glue anyway, but practice cutting a small hole in a scrap piece of particleboard first. The tweeter hole is best cut with a hole saw. When using a hole saw on particle board, lift the saw often, stop the power drill (or drill press), and clean the saw’s teeth with a wire brush. Cut at a slow speed. Next, cut 90mm PVC thin-walled pipe to a length of 100mm – this will be our port. If you are cutting this by hand, first wrap a piece of tape around the pipe to give you a square line to cut against. Now temporarily mount the woofer, tweeter and port in the baffle and slide Photo 7: cutting out the baffle. To mark the required large circle, use a pencil, a scrap piece of timber and a screw to make a temporary compass. 82 Silicon Chip the baffle into the enclosure, checking that everything fits without problems. #3 Disassemble the baffle This should be self-explanatory. #4 Add the quilt wadding Cover the complete inside surface of the enclosure with one layer of 150gsm quilt wadding. Glue the wadding into place, ensuring it’s below the level where the baffle will sit (see the photos overleaf). In addition, insert a piece of bundled wadding about 500mm square on one side of the enclosure – when the baffle is placed in position, the port needs to be located on the other side. This is so that the wadding doesn’t block the port. No wadding is used on the underside of the baffle. If you are building the sealed enclosure version, attach a second 500mm square piece of loose quilt wadding to the inside of the enclosure. #5 Fitting the port and making the spacer blocks Unless you want to later experiment with different port lengths, glue the port into place now, flush with the outer surface of the baffle. Curved spacer blocks need to be made next. These support the grille while providing clearance for, especially, the protection lamp. We made the spacer blocks from two layers of the same 22mm particle board used for the baffle and strengthening plate, each about 60mm long and 40mm wide. The two layers are held together Photo 8: after cutting the hole for the woofer, make the smaller hole for the port. The jigsaw cuts a tighter radius if you move it back & forth in small steps, rather than a continuous sweep. Australia's electronics magazine with a pair of particleboard screws in each block. If you don’t want to go to the trouble of making curved spacers, 44mm tall square blocks of timber will achieve the same outcome. Use particleboard screws to attach the three spacer blocks at even intervals around the inside edge of the baffle. It’s neatest to insert these screws from the rear of the baffle. #6 Cut out the grille For the grille, we used steel welded mesh with 12.7mm square openings, available from Bunnings. This grille gives an ‘industrial’ look that is great for a shed or workshop. If you don’t want to be able to see the speaker’s components, use steel mesh with smaller holes (Bunnings sells that as well). To cut out the grille, place the enclosure upside-down on the mesh and mark around the edge. Then cut the grille about 10mm inside that line. Lay the cut-out grill over the mouth of the enclosure and keep trimming the grille until it slides into the mouth of the enclosure, leaving a small gap all around. It is better that the grille be slightly too small than too large. Patience and a pair of good side-­ cutters are needed when cutting out the mesh grille! If you are fitting the protection lamp, remember you cannot use grille cloth. Also, be careful not to select woven metal mesh, as it tends to unravel when cut into a circle. #7 Paint the baffle, port and grille Next, use spray paint to paint the baffle, port and (separately) the grille. Photo 9: cutting the hole for the tweeter. It is 50mm in diameter and is best made with a hole saw. siliconchip.com.au When painting the grille, most of the paint will pass straight through the mesh, so place it first on a surface that you don’t mind having a lot of overspray on. Only one side of the mesh needs to be painted, but move the can back and forth at a variety of angles so that the steel wire is coated from all views. Note that the mesh is galvanised, and some paints (eg, the otherwise excellent Rust-Oleum 2X) will not adhere long-term to galvanised steel. #8 Assemble all the components on the baffle and do the wiring Now we will assemble the complete baffle. First, glue the tweeter into its 50mm hole, using the panel-mount adaptor supplied with the tweeter. Some Liquid Nails applied to the back of the tweeter housing will hold it nicely in place. This hole must be fully sealed – we don’t want air leaks past the tweeter. Now mount the speaker protection lamp, if using one. To do this, enlarge the existing hole in the bulb’s bottom tang to 3mm. Nip off one of the nipple protrusions on the baseplate and also enlarge this hole to 3mm. Be very careful when drilling these holes – it is easy to damage the lamp (eg, by dropping it). A Z-shaped bracket needs to be made from scrap aluminium or something similar; this holds the lamp about 25mm off the baffle. We used a combination of a Z-bracket made from a bent right-angled bracket plus a spacer to achieve the stand-off. The Photo 10: the baffle with all the holes finished, for the port, woofer and tweeter. Once you’ve reached this stage, the rest is easy. siliconchip.com.au #8 Glue the baffle, complete with lamp is mounted via its bottom tab so that it is parallel with the baffle. Don’t mount the lamp close to the baffle. Wiring connections to the lamp are by two solder lugs that are attached with the 3mm screws; these wires pass through holes drilled in the baffle. Make the wires a tight fit through the holes and/or seal the back of the baffle where the wires pass through. The lamp is wired in series with one of the main (external-going) speaker wires. Next, cut a suitable speaker gasket from a thin foam rubber sheet before screwing the woofer into place. You can use silicone to seal around the woofer if you don’t want to make a gasket. Drill small diameter pilot holes for the screws first. If you use a gasket, you may find you need some washers under the speaker flange ears to stop them being pulled downwards as you tighten the screws. The crossover can be mounted next, on the back of the baffle. It mounts via spacers and four particleboard screws. If you want permanent access to the crossover, it can be mounted on the front face of the baffle – there is clearance from the grille to allow this. Now complete all the wiring connections, including the main cable to the speaker that passes through the hole in the strengthening plate. Seal this hole with glue or silicone. Before gluing and screwing the baffle into place, test the drivers and crossover by playing some quiet music through the system. There should be output from both the tweeter and woofer! all its components, into place Double-check that everything on the baffle is correctly assembled, wired and fully screwed into place. After the next step, there is no going back! If you want to have access to the crossover during tuning, do not glue the baffle in place at this stage and see the “Tuning alternatives” section. Apply a generous amount of water clean-up Liquid Nails glue around the inside of the enclosure at – and a little above – the height at which the baffle will sit. Slide the baffle down, remembering to orientate it so that the port is on the opposite side of the enclosure to the extra internal wadding. Ensure the baffle is evenly lower than the edge of the enclosure by 60mm. As you slide the baffle into place, glue will probably squeeze up between the baffle and the enclosure wall. With the baffle now positioned at the correct height, use a wet finger to wipe this glue smooth all around the periphery. If there are any gaps, add more glue and wipe it along the gap with your finger. Before the glue can dry (immediately), use a wet cloth to remove all surplus glue. Keep rinsing the cloth and repeating the process until there is a neat line of glue around all the exposed joins, including around the grille spacer blocks. Do not get glue on the woofer or tweeter. Don’t panic if it looks like glue is going everywhere; just keep wiping and rinsing the cloth. Remember, you must use water clean-up Liquid Nails (or equivalent) Photo 11: when making the grille spacer blocks, use the compass to mark the outer line; the inner line that the jigsaw is cutting along is estimated using the outer shoe of the saw. Photo 12: the painted baffle and enclosure, complete with lifting clamp. The port and grille spacer blocks have already been installed on the baffle. Australia's electronics magazine October 2025  83 Photo 13: the wire grille, cut to size so that it fits within the mouth of the enclosure. This can be done while waiting the for glue to harden. Photo 14: the interior of the enclosure lined with quilt wadding. The bottom piece has been inserted, and the glue applied for the long peripheral piece. Speaker lying on its side on the floor. Use a frequency generator (or a phone app like Signal Gen from Media Punk Studios) and an amplifier to quietly do a slow sweep from 20,000Hz down to 30Hz. There should be no buzzes, whistles, or rattles. If you hear problems, isolate where the sound is coming from (eg, a loose port, a leak around the frame of the woofer, or a leak between the edge of the baffle and the enclosure) and then fix that. If the grille rattles, cut it a little smaller so its edges don’t touch the inner walls of the enclosure. If you hear a buzz, ensure it’s not something in the room becoming excited, rather than the speaker itself. If all is fine, redo the frequency sweep a little louder; however, never use sinewaves at high volumes, as the speaker drivers can be damaged. Depending on the quality of your hearing, you should be able to hear speaker output from about 45Hz to 15,000Hz – even higher if you have young ears! Hanging the speaker Photo 15: the outer piece has now been put in position. Note the extra inserted piece of wadding on the left; this goes on the opposite side to the port. The speaker cable can also be fed through a hole drilled in the baseplate. Photo 16: the protection lamp is held in place by a bolt through the enlarged hole in its bottom terminal. The Z-shaped bracket is attached to the front of the baffle via a spacer and particleboard screw. glue. Don’t use the normal building adhesive! The next step is to hold the baffle in place with particleboard screws. Drill small pilot holes, countersink them by turning a large drill bit by hand, then insert four particleboard screws through the wall of the enclosure into the baffle’s edge. Space these screws evenly around the enclosure. These screws are for added structural integrity – we don’t want the baffle falling out! Now seal the speaker cable exit with glue or silicone sealant. Let the glue harden for at least 12 hours in warm conditions; longer if it is below 20°C. There is a lot of glue in the enclosure, and it takes plenty of time to harden – don’t get impatient and start testing the speaker too early! When the glue is hard, paint the edge of the baffle where the glue is showing. You can use a brush to do this, or if you mask of the drivers and lamp, you can use the spray can again. Any black overspray is barely visible on the black enclosure, but you can wipe off any you see with a rag moistened in paint thinner or turpentine. The heads of the countersunk screws through the enclosure walls can be left as they are, or painted black with a small brush. 84 Silicon Chip #9 Fit the grille The grille is attached to the spacer blocks using small particleboard screws and washers, or particleboard screws and small metal or plastic cable clamps. Paint these black after you have attached the grille. The grille is susceptible to resonant vibration, so it must be firmly attached. #10 Testing When you have assembled the speaker, test it by connecting it to an amplifier. Unlike later testing, this testing can be done with the Pendant Australia's electronics magazine The Pendant Speaker will likely be suspended from a high ceiling or roof. Before building the speaker, carefully consider how you are going to mount it – especially how you’re going to safely get up to the required height. Since you’ll probably be using a ladder, be aware that about one person a week dies in falls from ladders in Australia, and a staggering 120 people a week are hospitalised due to ladder accidents. The speaker must be suspended using a chain or steel cable of adequate load rating (eg, 20kg). Use chain that has welded (rather than just bent) links. Do not use plastic chain. Note that if you use a chain and it has any loose links (eg, a ‘tail’ has been left), the chain may resonate at certain frequencies. The chain or cable must be screwed or bolted to a joist or rafter of appropriate strength. The anchor must not be just plasterboard. Don’t be tempted to leave out the speaker strengthening plate – this helps reinforce the base of the pot (which becomes the top of the enclosure) and also better joins the sides to the base. In really rugged conditions (eg, a very windy outdoor area), we suggest that the woofer be bolted into place siliconchip.com.au rather than being held with only particleboard screws. Also, in this application, we suggest an internal chain be used to connect the hanger (the saddle clamp or eye bolt) and one of the woofer mounting bolts. Tuning alternatives The sound from this speaker, as with all speakers, will be greatly affected by its environment. For example, if the speaker is positioned close to a ceiling, the 100mm-long suggested port may make the speaker too boomy. Also, if the location in which you are playing music is jam-packed with ‘stuff’ (eg, a very busy home workshop), the treble will be absorbed to a much greater degree than if the speaker is playing in a bare shed. That’s not to mention that my smooth response may be perceived as your lack of bass, and your strong bottom end may sound to me like one-note bass! So if you wish, you can test some enclosure tuning alternatives to suit your space and taste. If you want maximum tuning flexibility, test without the baffle glued into place. Instead, use just screws to hold the baffle in position. That way, you can easily remove the baffle and make tuning changes to the crossover. Use tape or the equivalent to temporarily seal any leaks around the baffle’s edge. The grille will need to be removed for this testing. This time, don’t test the speaker with it sitting on the floor; instead, you must hang it in similar conditions to how it will be used. I will assume that you have built the ported version and have not yet glued the port’s plastic tube into place. Cut some alternative port tubes of varying lengths. In addition to the suggested 100mm, also try 125mm, 75mm and 50mm. Listening to a song that you know well, test the different vent lengths, including having no plastic tube in place at all (ie, the vent length is just the thickness of the baffle). You should be able to hear distinct changes in the bass response, especially when you swap straight from the longest to the shortest vent. With the shortest vent (the bare hole), the bass will be much peakier and muddier. As you increase the length of the port tube, it will become smoother but also quieter. Using a frequency generator app on your phone will make the results of these port changes clearer. Next, block the vent (eg, by stuffing a strip of rolled up foam rubber – or even just a rag – into the port). As you will hear, the resulting sealed enclosure gives the smoothest result, but also the least bass. If you are intending to use the speaker primarily on voice, now try the speaker with (1) the port sealed, and (2) with the open port length that gave your chosen best response with music. ABC News radio, either streamed or on FM, is a good source of voice. When testing on voice, you should be able to clearly hear that the speaker works better with a sealed vent. The L-pad resistors we have used for the tweeter reduce its output by about 3dB. If you want more treble, you can leave these resistors out (but don’t leave out the crossover capacitor!). Alternatively, if you want less treble, you can instead use a 2W 5W resistor in series and a 4W 5W resistor in parallel with the tweeter; this will give about a 6dB reduction in output. Of course, you don’t need to do any of this testing – you can just take our word for what works best! Conclusion This project is the first pendant speaker in Silicon Chip. We think it is an excellent fit for many scenarios, especially given its ease of construction and ability to have its response tailored to different uses & tastes. This is a design that should have many applications. No longer do you need to have silence in those spaces with high ceilSC ings, or even no ceiling at all! Photos 17 & 18: the photo at left shows the rear view of the completed baffle with the woofer, tweeter and cables that go through the baffle to the protection light and the crossover. The port, woofer, tweeter, protection lamp and two of the grille spacing blocks can be seen in the photo at right. Note the line of lighter coloured glue that runs around the join. After the glue has hardened, paint it black to match the baffle, then fit the grille and you’re finished! siliconchip.com.au Australia's electronics magazine October 2025  85 SERVICEMAN’S LOG Large animals, laptops & Laphroaig Dave Thompson’s column will be back next month. In the meantime, here are some repair stories from our readers! The elephant test Back in the 1980s, the traffic management authorities encountered a new problem with the equipment used to detect vehicles at intersections with signals. Until then, a vehicle crossing a detection loop in the road caused a small decrease in inductance due to the sheet metal body acting like a shorted turn. Out of nowhere, vehicle detectors were experiencing problems ranging from locking up to failing to detect vehicles. Eventually, someone observed that the problem seemed worse when heavy freight vehicles crossed the detection loops. The theory was put forward that the weight of the vehicle caused the detection loop to act like a strain gauge, dropping the Q factor of the resonant circuit. Such tiny changes in resistance seemed an unlikely cause to some of us. My employer was in the early stages of manufacturing a new 8-channel vehicle detector that scanned loops many times faster than competing products, and was extremely anxious to have a product that was immune to these ‘negative actuations’. We believed that weight was not the problem, but how to prove it? Firstly, I sent a technician to the local freight depot to ask drivers if they would mind doing a lap of our test track to help us identify which brand of tyres “caused the traffic lights to spend more time red” (an invented story). That did the trick; half an hour later, there was a queue of semi-trailers lined up at our works gate! We sent each semi for a slow lap around our test track, and as each rig cleared the test station, the anxious driver would ask if his tyres were OK. We told them all that they were OK but, in fact, a large proportion of them were causing the problem and we were carefully noting all the markings on each tyre. One driver called back as he drove off, “I hope youse catch them barstards with the shonky tyres”! Items Covered This Month • Testing, traffic & troubleshooting • Refurbishing a Toshiba P750 laptop • The intoxicated wheelchair 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 86 Silicon Chip Our observations proved nothing, as the rigs all varied in weight. A brain storming session was held to find a way to prove or disprove the strain gauge theory so strongly held by some. We needed a very heavy weight to pass over the detection loops, but that weight had to be non-metallic if it was to prove anything. Large plastic water tanks, piles of timber railway sleepers, a load of dry sand were all suggested and ruled out, as the weight had to be reasonably concentrated, applied suddenly and removed promptly to realistically simulate a vehicle driving across the detection loop. A massive slab of concrete was considered and rejected because the ‘blue metal’ aggregate in concrete has mild magnetic properties. After over an hour of fruitless discussions, I suggested, almost in jest, “what we really need is a large full-grown elephant to walk over the loops”. To my surprise, the product manager thought it was a great idea, and gave me the go ahead to contact any circuses in the area and, failing that, try to arrange with the zoo to hire an elephant for a few hours! Before my first call, I had to deal with an urgent call from VicRoads claiming that one of our traffic signals controllers was playing up whenever one of their new thyristor-­ controlled trams passed by. They wanted us to send someone down immediately to fix the problem. The following morning, I found myself in the Melbourne CBD with a bunch of VicRoads engineers anxious to demonstrate the problem. It indeed turned out to be a vehicle detector problem that corresponded to the passing of a tram. Connecting my loop analyser, I could see that it was an extreme case of ‘negative actuation’, and seemed to support the strain gauge theory that we didn’t want to be true. Inspecting the detection loop revealed that the feeder cable had been newly installed in a trench that actually went under the tram tracks and, more importantly, the rails dropped by about 6mm whenever a tram passed over them! The fact that the problem started when the new Z trams entered service was just a coincidence. The actual problem was caused by a newly installed feeder cable getting Australia's electronics magazine siliconchip.com.au crushed every time a tram of any sort passed over it. After the transport people repaired the concrete rail bases, the problem disappeared. The strain gauge supporters backed down and the elephant hire was put on hold for the time being. After checking out the tyre markings from the previous week’s semitrailer test runs, it was found that the problem corresponded 100% with steel-belted radial tyres on high-bed vehicles. The sheet steel in car bodies acts like a shorted turn above about 25kHz. Vehicle detectors typically operate between 40kHz and 100kHz. They see a small frequency increase when a vehicle passes over, but the very fine steel wire in steel belted radials acts more like a low-loss magnetic core and causes a small frequency decrease. On small passenger vehicles, the steel of the vehicle body is very close to the detection loops and so generally swamps the effect of the steel-belted tyres, but with high-bed vehicles, the body of the vehicle is raised almost to the limits of detection, and cannot cancel out the effect of the tyres. The software detection algorithm was modified to recognise and compensate for the phenomenon, and the problem went away without the use of a single elephant. The Chinese trade delegation Shortly after word got around that we had a new, faster, more sensitive self-tuning vehicle detector on the market, a delegation from the People’s Republic of China turned up looking for traffic control products. We had just installed a vehicle detector demonstration site right outside the main lab windows, and I hastily sent a couple of staff members home to get their bicycles to demonstrate how sensitive our detectors were. The most important fellow in the delegation didn’t seem to understand any English, relying upon a young lady in his group to translate everything. After witnessing the flawless detection of a series of cars and bicycles, the translator approached me and said that the chairman wants to know if our vehicle detectors would detect bamboo bicycles! Apparently, back in the mid-1980s, China made bicycles out of bamboo. I was stunned for a second, but then replied that this was possible if the wheels had a loop of copper wire installed under the tyre. He seemed satisfied with the reply, and the delegation moved on to inspect traffic signals controllers. Bell and Oriel Again in the 1980s, VicRoads had installed many of our traffic signals controllers, including one at the busy intersection of Bell St and Oriel Rd. It was Thursday, and I had just settled plans for the long weekend when an urgent call came in siliconchip.com.au from Melbourne saying that our traffic controller at the intersection was going berserk every few minutes, and we had to send an engineer immediately. I was told that I was it, so I was unhappily booked in for a flight in a couple of hours! I phoned VicRoads and asked to speak to someone on-site. This was before the days of mobile phones, but they patched me through to their mobile radio network so I could speak to a signal technician there. What he described made no sense, so I asked him to take various voltage measurements around the site, including the most remote pedestrian pushbutton. This should have returned a reading of 32V, but he told me it was jumping around by a few volts constantly, and every minute or so it dropped briefly down to 15V or so. After the delay of him having going back to the van to report it to me, I asked him what buildings or industries were nearby – all medium high-rise, was the reply. When is the problem worst, I asked? Mostly at peak hour, he replied. I then asked him to check the Neutral-Earth link on the switchboard. It was present, so I asked him to put one meter lead on the Neutral block and press the other into the Earth as far from the controller as the leads would allow. A minute later, he returned to the van to report that the Neutral-to-Earth voltage was jumping all over the place, and briefly approaching 100V! Obviously, there was no Neutral-Earth link at the substation! The power authority was called, and was most embarrassed to find that the ‘missing link’ was indeed at the nearby substation. The nearby buildings all had lifts, and the starting current drawn by these was possibly the cause of the frequent-­ but-random variations due to phase imbalances. I would have expected the lifts to have three-phase motors, but perhaps not. The local Earth peg at the controller simply could not cope with the out-of-balance currents involved. The problem ceased as soon as the Neutral-Earth link was restored at the substation, and I was saved a trip to Melbourne for the long weekend. Melbourne Fire Brigade Around 1983, the Melbourne Fire Brigade replaced all their old ‘smash glass and press button’ remote building alarms. The new devices were all-electronic, and the overall system provided the firemen with a printout of the fire location and the nature of the business. The old system had required a young lady in the office to look up the address manually and write it on a slip of paper for the departing crew. Unfortunately, the new system proved troublesome for two reasons. Firstly, the fire crews did not like it, and secondly, an increasing number of remote alarms were failing. I was sent to investigate the problem, and watched the system until a real call-out occurred. I was dismayed to see the firemen poke their walky-talky antennas into the printer and ‘give it a squirt’! The system crashed immediately, so the fire address had to be determined the old way, in panic mode. While the fire crew was away, I had Australia's electronics magazine October 2025  87 the system console top removed and lined with heavy aluminium foil, Earthed at one point. Ferrite beads were also installed on the emitter leads of all power transistors in the various switch-mode power supplies. At the next call out, senior managers watched anxiously as the firemen slid down the pole and approached the console. The printer churned out their instructions perfectly and completely ignored their repeated attempts to disrupt operations. Next came the failing stations. Looking at a map of Melbourne, it became apparent that all new outstations outside a certain radius of headquarters were responsible for the failures. Measurements of voltages and currents around the network did not make sense until I discovered that all new installations were wired with indoor telephone cable instead of the much heavier gauge outdoor cable! The problem turned out to be simply voltage drop. Some non-technical person had discovered that the thinner cable was very much cheaper, and so had ordered it instead of the heavier cable normally used. The network was rewired with considerable haste, and it worked perfectly from then on. Penalty payments ceased, and I had one very happy boss. Graham Lill, Lindisfarne, Tas. Toshiba P750 laptop refurbishment Our son gave us a Toshiba Satellite P750 laptop that someone else had given to him. It was in very good condition, so I thought it might be in working order. I plugged in a charger and it booted up to the login screen of Windows 7, but the account was password protected, so I couldn’t log in. It didn’t really matter as I would wipe the hard drive and install Windows 10 instead. The first hardware problem was that the battery was dead flat and wouldn’t charge. I didn’t want to have to buy a new battery for it, so I grabbed the highest amperage charger I could find and left it charging overnight in the shed. I didn’t want to leave it charging in the house due to the small risk of starting a fire. Sometimes dead flat batteries will charge up again by using this method. Other times, they won’t, but there’s nothing to lose by trying. The next day, the battery was fully charged, so I could go ahead with wiping the hard drive and installing Windows 10. One problem with Windows 10 version 21H2 is that it won’t fit on a single-layer DVD, so I had to use an 8GB flash drive. It took a couple of hours to complete the process, as we cannot get NBN here, other than satellite. With the USB ready, I tried to boot the laptop with it, but it would not boot from the USB. So I had to use my DVD with Windows 10 20H1 and use the USB to update later. I booted from the DVD and started the Windows 10 setup. The first thing I did was to delete the existing partition on the 500GB hard drive. I like to make two partitions on hard drives when I install Windows. In the case that the C:\ drive gets corrupted, the data on D:\ drive should not be affected and Windows can be reinstalled or repaired on the C:\ drive. I made a 60GB partition for Windows and then the rest of the space on the hard drive for D:\ drive for data. Then I got a message saying that Windows could not be installed on this partition, because the hard drive was about 88 Silicon Chip to fail. Presumably, Windows had checked the SMART data and found that the drive was on its way out. That was good to know before I proceeded. I checked my stock of laptop hard drives; I only had one 500GB hard drive left, which had come from one of my previous laptops that had died when it hadn’t been used for a few years. I set up the new hard drive with two partitions, installed Windows 10 20H1 and set up an account. All went well, so I plugged in the USB drive and upgraded to Windows 10 21H2. After the laptop rebooted, I went to log in and all hell broke loose. Every time I pressed a different key on the keyboard, random windows, apps and messages popped up. I didn’t know what was going on as I’ve never had anything like this happen in all the time I’ve been working on computers and laptops. I suspected a keyboard fault, so I plugged in a USB keyboard, but the same thing happened. This didn’t really prove anything anyway, as the onboard keyboard was still connected and any fault with it would still affect the USB keyboard. I wanted to test the onboard keyboard, so I decided to wipe the Windows partition and revert to the earlier version of Windows 10. After reverting to the earlier version of Windows 10, I logged in and opened Notepad to test the keyboard. I was correct that there was a fault with the onboard keyboard. The W and the 5 keys did not work, but the 5 did work on the numeric keypad. Then I found that lower case B worked, but if I pressed the shift key to get an uppercase B, I got nothing. But if I pressed the Caps Lock key, I could get an uppercase B. Now I wanted to make sure that there were no other problems with the laptop, and that the problem with it going crazy was caused by the faulty keyboard. I checked on eBay and I could get a replacement aftermarket keyboard for $35, including postage, so I would consider that later. It looked like removing the keyboard would be tricky, as there was no obvious way to remove it. Other laptops may have a removable panel or obvious signs of clips to depress, but this laptop had neither. I searched for a YouTube video on how to remove the keyboard, but there was none for the P750, only other Toshiba models. I remembered that some time ago I had to replace a keyboard on a laptop and in that case, removing the optical drive allowed the keyboard to be pushed up and unclipped. So I removed Australia's electronics magazine siliconchip.com.au the optical drive, but there was no access to the keyboard. However, a closer look showed a small clip that was accessible. I used a small screwdriver to lift the clip, and the corner of the keyboard popped up, enabling me to carefully lift it, popping another clip. I could see that there was something else holding the keyboard in besides the clips, and I found two screws on the back that needed to be removed. Now the keyboard lifted up and I could disconnect the connector to remove it. I plugged in the USB keyboard, booted into Windows and I upgraded to version 21H2 with no problems; I could now log on without everything going haywire. So the fault was indeed with the original keyboard. Before ordering a replacement keyboard, though, I wanted to check the RAM. I removed the cover over the RAM and I found that the two 4GB modules were not a matched pair. One was 1333MHz, and the other was 10600S. I checked my stock of RAM and found two matching 4GB modules that were rated 12800S, so I fitted them. I tried to boot from the MemTest86 CD, but the laptop just kept booting into Windows. I wondered if the USB keyboard had anything to do with it, so I reconnected the onboard keyboard to see if that made any difference, but it didn’t. After several attempts, I decided to try logging in to Windows again and, to my astonishment, I was able to log in successfully. What happened? It seemed that the keyboard was now working properly. I opened Notepad and checked the keyboard again and it worked perfectly. The only thing I could think of is that the keyboard connector had not been sitting correctly previously, although it looked OK when I’d removed the keyboard. I would need to remove the hard drive to test the RAM because apparently Windows 10 had installed some sort of boot loader to prevent the laptop from booting from any non-Windows 10 media. This is probably a ‘security siliconchip.com.au feature’, but it’s very inconvenient. I removed the hard drive and was able to boot the MemTest86+ CD to check the RAM, which tested good. The next day, I switched on the laptop and when I went to log into Windows, the problem with random apps opening recurred. So the keyboard had ‘unfixed’ itself and it would need to be replaced. I ordered a new keyboard on eBay and waited for it to arrive. Seeing that I had removed the old keyboard, I had good access to the CPU fan, so I could clean it and the heatsink. I took the laptop out to my workshop and I used a small screwdriver to stop the fan from spinning while I blew the dust out of the heatsink through the side exhaust slot. Then I cleaned the fan with a damp cotton bud, ready to install the new keyboard when it arrived. It took 10 days for the keyboard to arrive and it worked fine when fitted, so I could continue setting the computer up. I don’t like the Windows 10 start menu, as it’s much harder to use than the old Windows XP start menu, so we use Classic Shell to set the start menu to the Windows XP style, which is far more practical. We use a lot of portable software, like browsers and other applications, so I would now copy it onto the new laptop. We do not use the default Windows folders for downloads, documents, photos and other data, which is all stored on D:\drive for convenient access and backup. This makes finding files easy, instead of having to fish through Windows folders to find things. With everything now set up, the laptop was ready to use. For a bit of work, $35 for a new keyboard and a replacement hard drive I already had, I now had a good working Core i7 laptop with Windows 10 that was ready to use. This refurbishment was fairly straightforward compared to some of the laptops I’ve worked on previously. Bruce Pierson, Dundathu, Qld. Australia's electronics magazine October 2025  89 Bruel & Kjaer sound level calibrator model 4230 repair The B&K calibrator is an expensive item even second-­ hand, but I was able to buy it online for a song, hoping that it was OK. If not, I felt I had enough instrumentation to check and repair it, so I took the risk. It is described by the manufacturer as “a simple to use, pocket size acoustic calibrator which gives an accurate sound pressure level of 94dB at 1,000Hz”, so how difficult would it be to check this instrument out if there were any problems? It arrived in the mail missing its leather case (hence the low price); it had been placed inside a small foil-lined plastic bag. The description on eBay said it was in “working order”. I opened the battery compartment only to find the 9V battery clip broken and badly corroded. I managed to extract the circuit board (which was retained by a tiny screw) and soldered a new battery clip to it. I then fitted what I thought to be a fresh battery. I pressed the button to activate the device and, sure enough, out came a 1kHz tone. A half-inch (12.7mm) pre-calibrated microphone showed a sound pressure level of exactly 94dB, and I was happy that it all looked good! The B&K manual states that the signal will last up to one minute with a new battery, but this calibrator signal continued for longer... much longer! It continued even when I left it to go to lunch. I replaced the battery because I had no idea what would happen with a flat battery as opposed to a healthy one; would it go on for longer than a minute or shorter than a minute? The manual didn’t say. The same problem occurred. I unclipped the battery to stop the thing from oscillating and flattening the battery, then turned to the manual for clues. Fortunately, the seller kindly included the complete manual plus a loose-leaf page from a service manual. It had an assembly diagram, a PCB layout with all components, a parts list and also a circuit diagram (shown below). It also described the checking procedure and how the calibrator could be adjusted. The circuit indicates that a press of button N1 temporarily short circuits C4, a 100μF capacitor, and when it starts to re-charge via R11 and R12, it activates the calibrator and sets up oscillations via V2 and the L1/C2 network, activated by V4 and V6. Once C4 is fully charged, V5 switches the oscillator off; this takes approximately 10 seconds. My reasoning was that C4 was probably faulty, so I replaced it and that restored everything to normal. Now I could understand why the 9V clip was broken; the operator had to pull the battery out every time the calibrator was finished for the day! It was corroded because the battery was probably left in for extended periods in a discharged condition when the operator forgot to pull it out. Now I have a really accurate microphone calibrator and am looking for an original leather case. I guess the plastic bag is a small compromise for a bargain price! Allan Linton-Smith, Turramurra, NSW. Don’t drink and drive (a wheelchair) I worked in the IT department of a corporate enterprise, but was trained as an electronic engineer with a known aptitude for repairing gear. In the department were two smart colleagues, who could only move one hand and relied on an electric wheelchair for mobility. I assisted them in various chair adjustments to improve comfort over the years and was always willing to help them out. One day I was called over and told, “My chair had an accident and won’t drive properly now and needs some adjustments.” So I packed a bag of tools and headed off on the 30-minute drive. When I arrived, my colleague was in a manually operated chair, with the electric chair in the corner. I asked what had happened to try to determine how we had arrived at the current situation. Well... it turns out they engaged in friendly games of poker on Friday nights, including various quantities of beer and whisky. In the course of game play, while throwing chips in etc, The Bruel & Kjaer 4230 sound level calibrator circuit is pleasingly simple. 90 Silicon Chip Australia's electronics magazine siliconchip.com.au a rather full glass of whisky got knocked over, and the contents flowed across the tray table on the chair and into the major control box via the joystick. As a result, the chair had taken off and veered into a table leg, and twisted the foot mounts before it was switched off. I had never worked on a microprocessor-controlled wheelchair before, but knew they were somewhat regulated and had multiple user profiles for speed, acceleration and sensitivity. This particular user had a high-­sensitivity controller. I said I would take a look, but couldn’t guarantee anything. Rather than switch it on full of whisky, I proceeded to remove the controller and joystick assemblies from the chair. While these are normally sealed, the corrugated rubber around the joystick had seen better days, and had several tears in it that enabled the outside to get in. I removed the rubber overlay and the joystick from the controller, inverted the control box, and extracted at least two shots of dark-brown liquid! Quite a drinking session, I thought, while also wondering if I could rescue it. Thinking about the best way to clean it, I decided that even more alcohol may be the best ‘solution’. I carried a container of IPA (isopropyl alcohol) for cleaning PCBs, but had not planned a full assembly wash-out. I proceeded to pour several more shots of IPA (not beer!) into the joystick and controller, swished it around and lightly brushed it in, around and under the electronic boards and joystick mechanics. The joystick was a Hall-effect type, so thankfully there were no potentiometers to gum up. I felt further joy when I examined the control board and discovered there were no adjustment pots on it either. The good thing about software adjustments is that whisky cannot make its way into non-volatile memory. When I poured the IPA out, there was still some colour to it (it’s clear when pure), so I repeated the procedure until it came out clear. The joystick X-Y mechanism had a very light sliding spring on the shaft to help the return it to the centre. As the user needed the lightest control possible, meaning it had to return to the centre null reliably, I ensured the X-Y bushings were clean, and the sprung bush sliding on the control shaft was returning to the centre reliably. I further cleaned the few plugs and connectors, and applied a spray of DeOXIT on the connections, then plugged it back together. Not having any operational experience in wheelchair control, I nervously powered it up. A bargraph lit up to indicate the battery voltage was OK (24V DC) and the chair just sat there. That was good, I was told. Moving the stick forward, I was rewarded with a click and forward motion. My these things are sensitive! Further testing showed that left, right and back all responded as expected. After resetting the mechanical footrests, reattaching the control box and adjusting it to the user’s needs, he was mobile again. I suggested he may want to go to his chair dealer and get it checked out, but he said he had confidence in me and left it. I know it kept working OK for many more years until he upgraded it. So it seems that whisky is not too bad for electronics, but IPA is better. For people, it’s better to put the whisky in their mouth and not the electronics! SC Dave Williams, California, USA. siliconchip.com.au Australia's electronics magazine October 2025  91 SILICON CHIP .com.au/shop ONLINESHOP HOW TO ORDER INTERNET (24/7) PAYPAL (24/7) eMAIL (24/7) MAIL (24/7) PHONE – (9-5:00 AET, Mon-Fri) siliconchip.com.au/Shop silicon<at>siliconchip.com.au silicon<at>siliconchip.com.au PO Box 194, MATRAVILLE, NSW 2036 (02) 9939 3295, +612 for international You can also pay by cheque/money order (Orders by mail only) or bank transfer. Make cheques payable to Silicon Chip. 10/25 YES! You can also order or renew your Silicon Chip subscription via any of these methods as well! The best benefit, apart from the magazine? Subscribers get a 10% discount on all orders for parts. PRE-PROGRAMMED MICROS For a complete list, go to siliconchip.com.au/Shop/9 $10 MICROS $15 MICROS ATmega328P ATtiny45-20PU PIC12F617-I/P 110dB RF Attenuator (Jul22), Basic RF Signal Generator (Jun23) 2m VHF CW/FM Test Generator (Oct23) Active Mains Soft Starter (Feb23), Model Railway Uncoupler (Jul23) Battery-Powered Model Railway Transmitter (Jan25) PIC12F675-I/SN Tiny LED Xmas Tree (Nov19) PIC16F1455-I/P Railway Points Controller Transmitter / Receiver (2 versions; Feb24) Battery-Powered Model Railway TH Receiver (Jan25) Dual Train Controller (Transmitter / TH Receiver, Oct25) PIC16F1455-I/SL Battery Multi Logger (Feb21), USB-C Serial Adaptor (Jun24) Battery-Powered Model Railway SMD Receiver (Jan25) USB Programmable Frequency Divider (Feb25) Dual Train Controller (SMD Receiver, Oct25) PIC16LF1455-I/P New GPS-Synchronised Analog Clock (Sep22) PIC16F1459-I/P K-Type Thermostat (Nov23), Secure Remote Switch (RX, Dec23) Mains Power-Up Sequencer (Feb24 | repurposed firmware Jul24) 8CH Learning IR Remote (Oct24), Heat Transfer Controller (Aug25) Vacuum Controller (Oct25) PIC16F1459-I/SO Multimeter Calibrator (Jul22), Buck/Boost Charger Adaptor (Oct22) PIC16F15214-I/SN Silicon Chirp Cricket (Apr23), Mic The Mouse (Aug25) PIC16F15214-I/P Filament Dryer (Oct24), Tool Safety Timer (May25) PIC16F15224-I/SL Multi-Channel Volume Control (OLED Module; Dec23) NFC IR Keyfob Transmitter (Feb25), Rotating Light (Apr25) PIC16F18146-I/SO Compact OLED Clock & Timer (Sep24), Flexidice (Nov24) Versatile Battery Checker (May25), RGB LED ‘Analog’ Clock (May25) USB-C Power Monitor (Aug25) PIC16LF15323-I/SL Remote Mains Switch (TX, Jul22), Secure Remote Switch (TX, Dec23) STM32G030K6T6 Variable Speed Drive Mk2 (Nov24) PIC16F1847-I/P PIC16F18877-I/PT Digital Capacitance Meter (Jan25) Dual-Channel Breadboard PSU Display Adaptor (Dec22) Wideband Fuel Mixture Display (WFMD; Apr23) PIC16F88-I/P Battery Charge Controller (Jun22), Railway Semaphore (Apr22) PIC24FJ256GA702-I/SS Ohmmeter (Aug22), Advanced SMD Test Tweezers (Feb23) ESR Test Tweezers (Jun24) PIC32MX170F256D-501P/T 44-pin Micromite Mk2 (Aug14), 4DoF Simulation Seat (Sep19) PIC32MX170F256B-50I/SP Micromite LCD BackPack V1-V3 (Feb16 / May17 / Aug19) Advanced GPS Computer (Jun21), Touchscreen Digital Preamp (Sep21) PIC32MX170F256B-I/SO Battery Multi Logger (Feb21), Battery Manager BackPack (Aug21) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) STM32L031F6P6 SmartProbe (Jul25) $20 MICROS ATmega32U4 ATmega644PA-AU PIC32MK0128MCA048 PIC32MX270F256D-50I/PT Wii Nunchuk RGB Light Driver (Mar24) AM-FM DDS Signal Generator (May22) Power LCR Meter (Mar25) Digital Preamplifier (Oct25) $25 MICROS PIC32MX170F256B-50I/SO + PIC16F1455-I/SL Micromite Explore-40 (SC5157, Oct24) PIC32MX470F512H-120/PT Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) PIC32MX470F512L-120/PT Micromite Explore 100 (Sep16) $30 MICROS PIC32MX695F512H-80I/PT Touchscreen Audio Recorder (Jun14) PIC32MZ2048EFH064-I/PT DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) DIY Reflow Oven Controller (Apr20), Dual Hybrid Supply (Feb22) KITS, SPECIALISED COMPONENTS ETC DUAL TRAIN CONTROLLER MICROCONTROLLERS (OCT 25) PICKIT BASIC POWER BREAKOUT KIT (SC7512) (SEP 25) - PIC16F1455-I/P programmed with 0911024D.HEX (Transmitter) - PIC16F1455-I/P programmed with 0911024S(or T).HEX (Receiver, TH) - PIC16F1455-I/SL programmed with 0911024S(or T).HEX (Receiver, SMD) firmware ending with “S.HEX” is for train 1, while “T.HEX” is for train 2 Includes all parts except the jumper wire and glue (see p39, Sep25) MIC THE MOUSE KIT (SC7508) Includes all parts except a CR2032 cell (see p64, Aug25) RP2350B DEVELOPMENT BOARD (AUG 25) $10.00 $10.00 $10.00 $20.00 $37.50 siliconchip.com.au/Shop/ ROTATING LIGHT FOR MODELS KIT (APR 25) PICO 2 AUDIO ANALYSER SHORT-FORM KIT (SC6772) (MAR 25) USB PROGRAMMABLE FREQUENCY DIVIDER (SC6959) (FEB 25) NFC PROGRAMMABLE IR KEYFOB (SC7421) (FEB 25) COMPACT HIFI HEADPHONE AMP (SC6885) (DEC 24) PICO COMPUTER (DEC 24) FLEXIDICE COMPLETE KIT (SC7361) (NOV 24) Complete kit which includes the PCB and all onboard components (see p60, Apr25): - SMD LEDs (SC7462) $20.00 - Through-hole LEDs (SC7463) $20.00 The Pico Audio Analyser kit from Nov23, but with an unprogrammed Pico 2 Complete kit: includes all components (see p85, Feb25) Complete kit: includes all required items, except the cell (see p67, Feb25) (AUG 25) Assembled Board: a pre-assembled PCB with all mandatory parts fitted, optional components are sold separately below (SC7514; see p49, Aug25) - 40-pin header (two are required, SC3189) - 8MiB APS6404L-3SQR-SN PSRAM SOIC-8 IC (SC7530) $50.00 $60.00 $25.00 $30.00 $70.00 $1.00ea Complete kit: includes everything except the power supply (see p47, Dec24) $5.00 CAPACITOR DISCHARGER KIT (SC7404) (DEC 24) Includes the PCB and all components that mount on it, the mounting hardware USB-C POWER MONITOR KIT (SC7489) (AUG 25) $30.00 Includes all non-optional parts except the case, cell & glue (see p39, Aug25) $60.00 (without heatsink) and banana sockets (see p36, Dec24) 433MHz RECEIVER KIT (SC7447) (JUN 25) VERSATILE BATTERY CHECKER KIT (SC7465) (MAY 25) RGB LED ‘ANALOG’ CLOCK KIT (SC7416) (MAY 25) USB POWER ADAPTOR COMPLETE KIT (SC7433) (MAY 25) Includes the PCB and all onboard parts (see p66, Jun25) Includes everything in the parts list (including the case), except the optional components, batteries and glue (see p30, May25) $20.00 $65.00 Includes all the parts except the power supply. When buying the kit select either a BZ-121 GPS module or Pico W (unprogrammed) for the time source (see p66, May25) $65.00 Includes everything in the parts list and a choice of one USB socket: USB-C power only; USB-C power+data; Type-B mini; or Type-B micro (see p80, May25) $10.00 PICO/2/COMPUTER (SC7468) (APR 25) 433MHz TRANSMITTER KIT (SC7430) (APR 25) Includes an assembled PCB, separate Raspberry Pi Pico 2 and front/rear panels $120.00 Includes the PCB and all onboard parts (see p75, Apr25) $20.00 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) VARIOUS MODULES & PARTS $30.00 - two 1nF ±1% capacitors (ESR Meter, Aug23; SC4273) $2.50 - 5V 3-pin boost regulator module (2m CW/FM Test Generator, Oct23; SC6780) $3.00 - 5V 3-pin buck regulator module (2m CW/FM Test Generator, Oct23; SC6781) $4.00 - 0.96in 128x64 white OLED without PCB (SmartProbe, Jul25; SC7397) $7.50 - Talema AC-1010 10A Current Transformer (SC3315) $20.00 *Prices valid for month of magazine issue only. All prices in Australian dollars and include GST where applicable. # Overseas? Place an order on our website for a quote. PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT MODEL RAILWAY TURNTABLE CONTROL PCB ↳ CONTACT PCB (GOLD-PLATED) 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 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) DATE MAR23 MAR23 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 MAR24 APR24 APR24 APR24 MAY24 MAY24 MAY24 JUN24 PCB CODE 09103231 09103232 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 16103241 08101241 08104241 07102241 04104241 04112231 10104241 SC6963 Price $5.00 $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 $20.00 $15.00 $10.00 $5.00 $10.00 $2.50 $5.00 $10.00 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT DC SUPPLY PROTECTOR (ADJUSTABLE SMD) ↳ ADJUSTABLE THROUGH-HOLE ↳ FIXED THROUGH-HOLE USB-C SERIAL ADAPTOR (BLACK) AUTOMATIC LQ METER MAIN AUTOMATIC LQ METER FRONT PANEL (BLACK) 180-230V DC MOTOR SPEED CONTROLLER STYLOCLONE (CASE VERSION) ↳ STANDALONE VERSION DUAL MINI LED DICE (THROUGH-HOLE LEDs) ↳ SMD LEDs GUITAR PICKGUARD (FENDER JAZZ BASS) ↳ J&D T-STYLE BASS ↳ MUSIC MAN STINGRAY BASS ↳ FENDER TELECASTER COMPACT OLED CLOCK & TIMER USB MIXED-SIGNAL LOGIC ANALYSER (PicoMSA) DISCRETE IDEAL BRIDGE RECTIFIER (TH) ↳ SMD VERSION MICROMITE EXPLORE-40 (BLUE) PICO BACKPACK AUDIO BREAKOUT (with conns.) 8-CHANNEL LEARNING IR REMOTE (BLUE) 3D PRINTER FILAMENT DRYER DUAL-RAIL LOAD PROTECTOR VARIABLE SPEED DRIVE Mk2 (BLACK) FLEXIDICE (RED, PAIR OF PCBs) SURF SOUND SIMULATOR (BLUE) COMPACT HIFI HEADPHONE AMP (BLUE) CAPACITOR DISCHARGER PICO COMPUTER ↳ FRONT PANEL (BLACK) ↳ PWM AUDIO MODULE DIGITAL CAPACITANCE METER 5MHZ 40A CURRENT PROBE (BLACK) USB PROGRAMMABLE FREQUENCY DIVIDER HIGH-BANDWIDTH DIFFERENTIAL PROBE NFC IR KEYFOB TRANSMITTER POWER LCR METER WAVEFORM GENERATOR PICO 2 AUDIO ANALYSER (BLACK) PICO/2/COMPUTER ↳ FRONT & REAR PANELS (BLACK) ROTATING LIGHT (BLACK) 433MHZ TRANSMITTER VERSATILE BATTERY CHECKER ↳ FRONT PANEL (BLACK, 0.8mm) TOOL SAFETY TIMER RGB LED ANALOG CLOCK (BLACK) USB POWER ADAPTOR (BLACK, 1mm) HWS SOLAR DIVERTER PCB & INSULATING PANELS SSB SHORTWAVE RECEIVER PCB SET ↳ FRONT PANEL (BLACK) 433MHz RECEIVER SMARTPROBE ↳ SWD PROGRAMMING ADAPTOR DUCTED HEAT TRANSFER CONTROLLER ↳ TEMPERATURE SENSOR ADAPTOR ↳ CONTROL PANEL MIC THE MOUSE (PCB SET, WHITE) USB-C POWER MONITOR (PCB SET, INCLUDES FFC) HOME AUTOMATION SATELLITE PICKIT BASIC POWER BREAKOUT DATE 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 FEB25 FEB25 FEB25 MAR25 MAR25 MAR25 APR25 APR25 APR25 APR25 MAY25 MAY25 MAY25 MAY25 MAY25 JUN25 JUN25 JUN25 JUN25 JUL25 JUL25 AUG25 AUG25 AUG25 AUG25 AUG25 SEP25 SEP25 PCB CODE Price 08106241 $2.50 08106242 $2.50 08106243 $2.50 24106241 $2.50 CSE240203A $5.00 CSE240204A $5.00 11104241 $15.00 23106241 $10.00 23106242 $12.50 08103241 $2.50 08103242 $2.50 23109241 $10.00 23109242 $10.00 23109243 $10.00 23109244 $5.00 19101231 $5.00 04109241 $7.50 18108241 $5.00 18108242 $2.50 07106241 $2.50 07101222 $2.50 15108241 $7.50 28110241 $7.50 18109241 $5.00 11111241 $15.00 08107241/2 $5.00 01111241 $10.00 01103241 $7.50 9047-01 $5.00 07112234 $5.00 07112235 $2.50 07112238 $2.50 04111241 $5.00 9049-01 $5.00 04108241 $5.00 9015-D $5.00 15109231 $2.50 04103251 $10.00 04104251 $5.00 04107231 $5.00 07104251 $5.00 07104252/3 $10.00 09101251 $2.50 15103251 $2.50 11104251 $5.00 11104252 $7.50 10104251 $5.00 19101251 $15.00 18101251 $2.50 18110241 $20.00 CSE250202-3 $15.00 CSE250204 $7.50 15103252 $2.50 P9054-04 $5.00 P9045-A $2.50 17101251 $10.00 17101252 $2.50 17101253 $2.50 SC7528 $7.50 SC7527 $7.50 15104251 $3.50 18106251 $2.00 BATTERY MODEL RAILWAY TRANSMITTER ↳ THROUGH-HOLE (TH) RECEIVER ↳ SMD RECEIVER ↳ CHARGER DUAL TRAIN CONTROLLER TRANSMITTER DIGITAL PREAMPLIFIER MAIN PCB (4 LAYERS) ↳ FRONT PANEL CONTROL ↳ POWER SUPPLY VACUUM CONTROLLER MAIN PCB ↳ BLAST GATE ADAPTOR JAN25 JAN25 JAN25 JAN25 OCT25 OCT25 OCT25 OCT25 OCT25 OCT25 09110241 09110242 09110243 09110244 09110245 01107251 01107252 01107253 10109251 10109252 NEW & RELATED PCBs $2.50 $2.50 $2.50 $2.50 $3.00 $30.00 $2.50 $7.50 $10.00 $2.50 We also sell the Silicon Chip PDFs on USB, RTV&H USB, Vintage Radio USB and more at siliconchip.com.au/Shop/3 Vintage Radio The Reinartz 2 TRF receiver from Electronics Australia Just over 100 years ago, John Reinartz was the consummate radio designer. He was brilliant and his circuits put many amateur radio enthusiasts on the air. His innovation opened up shortwave as we know it to general use. By Philip Fitzherbert & Ian Batty R einartz’s publication, “The Reflection of Short Waves”, put forward theories that contradicted the academic teachings of the day. Those theories are now proven scientific fact. He was the first person to plan and take part in trans-Atlantic two-way communication at 100 metres (3MHz). He is also credited with contact from the US to England, and from the US to Australia, both for the first time, using 20 metres (15MHz). This was an incredibly short wavelength for the time. In the very early 1920s, Reinartz published a circuit for a two-valve receiver, a TRF circuit with adjustable feedback, which was published in the American Radio Relay League’s QST magazine, in the June 1921 edition. It was later updated for the March 1922 edition. Reinartz went on to head up the US Navy Radio and Radar Laboratory during World War 2. He held many patents, but never profited from any of them. Reinartz was honoured by many 94 Silicon Chip organisations in his lifetime; he was a real pioneer of early radio. Fast forward to July 1984. Interest in early radio circuits was fairly strong and Electronics Australia published an article by David Whitby on a receiver based on Reinartz’s. This used parts available in 1984, as opposed to its 1920s forebears, although some of them (like the valves) were already obsolete at the time, being available only as ‘new old stock’ (NOS). The kit was manufactured by Technicraft of Katoomba, NSW, and sold by several outlets. The unit was designed to look and feel like a set from the 1920s. It is built on a timber baseboard with a circuit board screwed to it (not a printed circuit board). It has sockets for the valves and the plug-in spiderweb coils. It carries connection points for headphones, aerial, Earth and other necessary voltages. The baseboard is pre-drilled, and instructions for assembly are Australia's electronics magazine provided. The baseboard was unfinished as supplied, but normal staining, polyurethane gloss coating and much sanding gives a very pleasant appearance on which to build the receiver. Circuit details The full circuit is shown in Fig.1; it is based on Reinartz’s design. The set uses the 200pF section of a double-­ gang tuning capacitor to tune the main winding of the plug-in coil. It uses what was called a ‘leaky grid’ regenerative detector. The antenna tuned circuit feeds to the grid of the first VT50 valve (V1). From the anode of the VT50, the second (90pF) section of the tuning capacitor forms the basis of the regeneration. This arrangement gives some regeneration circuit ‘tracking’, so you don’t have to continually fiddle with the reaction as you tune to different frequencies. The reaction control is fine-tuned by a Philips “Beehive” trimmer capacitor siliconchip.com.au Fig.1: the Reinartz-derived radio receiver circuit from Electronics Australia, July 1984, page 54. Capacitances are in microfarads (μF) unless otherwise stated, similarly resistance is in ohms (W). in series with the reaction coil, which is thus able to control the RF current through the coil. Adjustment of the capacitor provides precise control of the amount of positive feedback (regeneration). The physical layout here is interesting. The trimmer is fitted horizontally on the circuit board. Its top is connected to a threaded shaft, which exits via the front panel. This is a very clever use of modern parts, which I’m sure would have appealed to John Reinartz! This set’s circuit follows the later March 1922 outline. It added a second valve to give better matching to a set of headphones. This is described further below. L3 is an RF choke that prevents loading of the regeneration system by the following stage(s). It also operates in conjunction with bypass capacitor C5 to prevent RF currents from passing to the output stage. An RF choke in this position was always a feature of the Reinartz sets. siliconchip.com.au The VT50 medium-μ triode is an ex-RAF (UK) disposal item, designed in the 1920s. First manufactured in the USA in 1924, it is identical to the HL2K. The second valve, again a VT50, gets its drive via C6 into the grid of the valve, which is used as an audio amplifier for driving the headphones. The original circuit allows a choice of values for demodulator load R2 and output grid return R3. As built, these were 100kW and 1MW, respectively. How good is it? For any two-valve set to give 1mW of output with just 5mV of signal in is pretty impressive. While 1mW doesn’t sound like much, it’s loud for headphones. For ordinary listening, the level would be in the hundreds of microwatts range. The set tuned from the middle of the broadcast band at 1.05MHz, up past the 180m Ham band at 1.75MHz, and up to 2.7MHz. Australia's electronics magazine Tuning was affected by the antenna – no surprise, as it connects directly via C1 onto the stator of the main tuning capacitor, C2a. The best sensitivity was gained at 2.5MHz. This gave 1mW of output with full regeneration for only 5mV input with 400Hz modulation. The RF bandwidth, for a 3dB drop-off, was about ±500Hz (really!). With no regeneration, it spread out to ±177kHz, and needed around 140mV of RF input to give the 1mW audio output. This implies that regeneration increases the demodulator’s stage gain by around 30 times. It’s the equivalent of another HL2K running at full gain. Take your pick: you can have great sensitivity with a signal that sounds like it’s coming through a drainpipe, or the channel just next to your station (possibly more than one!). With moderate regeneration, the audio response was -3dB down at 2.5kHz. I should mention that the October 2025  95 Photos 1 & 2: the top view of the set with the reaction control in the centre highlighted is shown here, while the wiring hidden under the base is shown in the photo at lower right – it couldn’t be much simpler! low-­frequency cutoff is 22Hz (really, again). With only one coupling capacitor, it shouldn’t be surprising that the demodulator’s low-frequency response is so dramatic. Time to tune in to Beethoven’s Ode To Joy and experience the bass fiddles in their full glory. You will need a good set of earphones, though. At its best performance, 5mV input for 1mW output at 2.5MHz, the RF stage is delivering some 1.2V of audio to the output grid at maximum sensitivity. That implies that the RF stage gain is 240 (1.2V ÷ 0.005V). Not bad for a triode with an intrinsic gain (μ) of just 27 times. But the audio stage, for 1.2V input, Fig.2: the output voltage of an ideal triode is μ × Vg, ie, μ times the input signal voltage (Vg). However, the intrinsic resistance of a real triode (Rp) forms a voltage divider with the load resistance (Rl), reducing the magnitude of the voltage applied to the load. 96 Silicon Chip only delivered about 1.4V to the headphones, a gain of just 1.2. That’s only just more than unity. We can do better. The model for a triode is a voltage generator with an output of μ × Vin. But the generator has an internal resistance, Rp, which is in series with the load resistance, Rl – see Fig.2. The stage gain – and thus the output voltage – will depend on the relative values of Rp and Rl, using the triode voltage gain formula: The μ of the HL2K/VT50 is 27 at a specified anode current of 3mA and anode voltage of 100V. With the load as a pair of 2kW headphones, Av is theoretically about 2. The difference between the measured and calculated gain is easily explained; the HL2K’s Rp is quoted at 18kW, but that’s only for an anode current of 3mA. This circuit’s lower anode current of about 1mA increases Rp, so its increased series resistance means even less voltage across the headphones’ 2kW impedance. A quick back-of-theenvelope indicates an effective Rp of around 40kW. So, why bother with the second valve at all? It’s a question dating back to Lee de Forest’s low-gain Audions, with a μ value less than 5. Still, the Audion’s low output impedance allowed it to drive a transformer. Using a primary-­ secondary step-up in the transformer allowed the stage to develop substantial power gain, with the Audion itself needing virtually no driving power into its grid. The first valve needs a load impedance of 50~100kW to give useful voltage gain. Shunting that with headphones would drastically cut the stage gain, so the second valve’s main function – as originally designed – is to present virtually no loading to the first valve, thereby allowing the demodulator to develop its full potential gain. But a stage gain barely more than unity? Raising the load impedance would increase the second stage’s gain, so I switched my Marconi TF8793A wattmeter up to a 20kW load impedance. With that, I got a voltage gain of around 6.6, increasing the set’s Fig.3: a redrawn version of the circuit from Fig.1. Resistors R2 & R3 can be a range of values as shown in Fig.1. Australia's electronics magazine siliconchip.com.au V intage Radio Collection now covering March 1988 – December 2024 Updated with over 35 years of content Includes every Vintage Radio article published in Silicon Chip from March 1988 to December 2024. In total it contains nearly 500 articles to read. Supplied as quality PDFs on a 32GB custom USB All articles are supplied at 300DPI, providing a more detailed image over the print magazine. Physical and digital versions available Buying the USB gives you access to the downloadable copies at no extra charge. Or if you prefer, you can just buy the download version of the Collection. $70 PDF Download SC4721 siliconchip.com.au/Shop/3/4721 $80 USB + Download SC6139 siliconchip.com.au/Shop/3/6139 sensitivity to under 1mV of RF input for 1mW out. This higher impedance could be provided by a suitable 3:1 audio transformer, making the 2kW headphones appear as a 20kW load to the valve. This would also give better fidelity at full volume. The HL2K’s low anode current had it clipping at 1mW output with the 2kW load, while the 20kW load allowed a visually perfect sinewave of around 4.5V peak-to-peak to develop the 1mW output. Considering that a 1mV RF signal, modulated at the standard 30%, contains only about 0.3mV of audio, it looks like the overall gain from antenna terminal to output is around 15,000 times (4.5V ÷ 0.0003V). Beat that! We noticed one peculiarity in the design: neither of Reinartz’s two original circuits (like the March 1922 QST circuit) include a resistor from grid to ground for the demodulator, or any other form of biasing. This omission had frustrated Lee de Forest’s application of the Audion at audio frequencies, and was remedied by Lowenstein’s 1917 “Grid Bias” patent. Considering Reinartz’s formidable engineering skills, this omission cannot be a mistake. We sense a mystery lurking in this simple design. Perhaps, dear reader, you can help us out. Postage starts at $12 within Australia for the USB. See our website for overseas & express post rates. A final note; the HL2K/VT50 uses the “British” B4 base (Fig.4). This has pin 1 offset to provide indexing, unlike the American UX4, which has two large and two small pins (the follow-on B5 adds a fifth pin in the centre). The B4’s numbering is unusual, with pin 1 opposite pin 2, then pin 3 opposite pin 4. While it’s not obvious from the circuit diagram, this method places the anode and grid connections opposite each other, with the filament connections (at RF/audio ground) between to provide some shielding. The UX4 places anode and grid adjacent to each other, with an increased possibility of undesirable output-­ SC input coupling and instability. Fig.4: the B4 valve base has pins 1 & 2 offset from the centre, so it can only be inserted one way, even though all four pins are the same size. siliconchip.com.au October 2025  97 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. USB-C Serial Adaptor Complete Kit SC6652: $20.00 June 2024 siliconchip.au/Article/16291 Includes the PCB, programmed microcontroller and all other parts required to build the Adaptor. 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. 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 RGB LED Analog Clock quirks I would like to share my experience with the RGB LED Analog Clock (May 2025; siliconchip.au/Article/18126). I built it from the Silicon Chip kit and everything was straightforward. When it came to soldering the LEDs, I put one at 12 o’clock, one at 3 o’clock, one at 6 o’clock and one at 9 o’clock to balance the board and make them easy to solder. Then I added one at each of the number locations until I had twelve fitted. The soldering went well, with only a few bridges, which I cleaned up with solder wick. When I tested it as per the instructions, I got what I thought were odd results. I could see it was trying to scan around the LEDs, but the one at the 6 o’clock location (LED31) was lit blue. I initially thought this was a fault, as the other LEDs were also dimly flashing other colours. In the end, I fitted all the LEDs and, when tested, they all chased correctly. I then realised that the blue illuminated LED was indicating the baud rate. I have the version with the GPS module, and at first, could not get it to lock the time. I placed the unit next to the largest window in my house, but it still did not lock. I left it on for an hour, and when I came back, it had acquired the time. I adjusted the settings, and all was well except the AM and PM indicators do not work. They do light in the test mode; can you suggest why they don’t light during operation? Also, now that the clock is mounted on the wall above a window in my workshop, it sometimes loses lock for up to several minutes and then locks back in. I presume it is because it has lost signal from the satellites, but I find it odd that it comes and goes. Can anything be done to improve reception? The GPS module is mounted where shown in the instructions. (P. M., Christchurch, NZ) ● The software checks to see if either AM/PM LED is present by applying a pull-up/pull-down current and seeing if it conducts to the Component substitutions in SSB Shortwave Receiver I am building the recent SSB Shortwave Receiver (June & July 2025; siliconchip.au/ Series/441) and have some questions about sourcing the parts. I am wondering if it is okay to use 0.315mm enamelled copper wire (ECW) in lieu of 0.35mm to wind the 3-10MHz toroid (T1) and 0.63mm in lieu of 0.6mm (T2). Jaycar sells these diameters of ECW, and I’d rather source it locally than order online. As for the 100μH axial inductor, that value isn’t available at Jaycar or Altronics. Would a 150μH inductor be OK instead? 100μH ferrite chokes for high-frequency applications are available, but I suspect they’re not suitable for this receiver. (T. R., Manly, NSW) ● In the frequency range that the radio operates, the skin effect will dominate the current-carrying capability of those diameters of wire. There will be a tiny change in geometry, but that should not make any noticeable difference. To summarise, the wire gauge is not critical; the thicknesses we provided were more of a guide than strict specifications. Using the 0.315mm wire will make the 42 turns fit slightly more easily compared to the specified 0.35mm wire. The change in Q would be insignificant for either substitution. It’s strange that Altronics sells 68μH and 150μH RF inductors but not the very common value of 100μH. Jaycar’s website says that the LF1534 is still available in some stores; you could probably get the staff to transfer some to your local store. These inductors are just being used to block AC on the supply to the drains of Mosfets Q8 & Q9, so the value is not critical. 150μH would also work. Of course, there are plenty of 100μH axial RF inductors available online, including from AliExpress. siliconchip.com.au Australia's electronics magazine opposite pin. We are not sure why that would fail, as it worked reliably on our prototype, but it seems it has failed in your case. One solution would be to reflash the chip with software that is hard-coded to drive them no matter what. We can supply a modified HEX file if you have the ability to reflash it (SNAP programmers are pretty cheap these days). If you’re experiencing GPS signal drop-outs, you might want to consider trying a WiFi time source (WiFi Time Source for GPS Clocks, June 2023; siliconchip.au/Article/15823). The signal must be marginal; there are reasons why it may come and go, including the satellites moving through the sky, and sources of interference coming and going. Another option would be to use a GPS module like the Neo-7M or Neo-8M (we sell the 7M, Cat SC6737) with an external antenna. But that assumes you have a better place to put the antenna and a way to route the cable there. More on ferrite bead properties I read Nicholas Vinen’s Editorial Viewpoint in the April 2025 edition on ferrite beads. I understood it all except for the statement in the third-last paragraph, that “Much of the impedance is real resistance, but not all”. My understanding is that the ferrite bead offers inductive reactance, which increases with frequency until, as shown by the accompanying curves, capacitive leakage starts to take over. Resistance would remain mostly constant. Am I misunderstanding what Nicholas meant by “real resistance”? (E. B., Bayview, NSW) ● We suggest you read this PDF from Abracon, especially pages 4 & 5, where it explains the resistance and gives a graph: siliconchip.au/link/ac8a The key point to realise is that a typical LC circuit tuned to a resonant frequency is a high-Q network, meaning it has a sharp, narrow impedance October 2025  99 peak. Its losses are minimal; it stores and exchanges energy between the inductor and capacitor, rather than dissipating it. A ferrite bead, on the other hand, is deliberately made lossy and low-Q. At its ‘resonance’, the inductive and capacitive reactances largely cancel, leaving the resistive losses of the ferrite material to dominate. This broad, flat impedance characteristic is what allows it to dampen a wide frequency band, instead of acting like a narrow filter. How is battery power fed back to the grid? As usual, Silicon Chip is full of fascinating articles. Some of them I can even understand! (B.E. Elec., U. of Qld, 1961). Brandon Speedie’s Power Grid articles share useful info about solar generation and battery storage (March & April 2025; siliconchip.au/ Series/437). His Figs.11 & 12 explain how power from the solar array is fed to the grid and stored. Still, I am puzzled about how the power from the battery storage is fed back into the load. Are the DC/DC converters bidirectional devices? A brief explanation of the workings of such a device would be appreciated. (J. A., Diamond Creek, Vic) ● Brandon’s article shows two possible ways to do this, but there are actually about five or six different methods in use for connecting battery banks to PV solar systems. His Fig.11 (AC-coupled retrofit): A battery bank is added with its own inverter/charger connected to the mains AC. The solar inverter delivers power to the grid, and the battery inverter takes some of this power to charge the batteries. When discharging, the battery inverter feeds AC back into the grid. This method is simple to retrofit but relatively inefficient (due to double conversion) and uses extra hardware, so it is less cost-effective for new builds. Examples include the Tesla Powerwall, SMA Sunny Island and Selectronic SP Pro (AC-coupled). His Fig.12 (DC-coupled with bidirectional DC/DC): Here, the DC/DC stage is bidirectional, as shown by the double-ended arrows. It charges the batteries from the PV array when Versatile there’s surplus, and can discharge them back into the inverter’s DC bus. The inverter then converts this power into AC and exports it to the grid. This avoids duplicating inverters, but still involves extra conversion steps. Examples include Huawei/LG Chem systems and SolarEdge DC-­ coupled storage. Hybrid inverters: These integrate PV and battery inputs into a single inverter stage. By handling charging/ discharging directly on the DC bus, they avoid double conversion, improving efficiency and simplifying installation. The limitation is that they usually require new installs and support only approved batteries. Example systems include Sungrow, Fronius GEN24 and Victron Multiplus with MPPT. Simple charge-controller systems: An MPPT charge controller charges batteries directly from PV. A separate inverter then draws from the batteries to supply AC. This approach is common in smaller or off-grid setups, but less efficient, doesn’t scale well, and is usually chosen because the hardware is inexpensive. DC bus/multi-port systems: A central DC bus accepts multiple sources 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 100 Silicon Chip Australia's electronics magazine siliconchip.com.au (PV, batteries, EVs, even fuel cells). A single inverter manages the blend and synchronises with the grid. These systems are highly efficient and flexible, but often proprietary and more expensive. Examples include Schneider, Delta and Huawei multi-port inverters. Distributed AC-coupled (microinverter) systems: Each panel has its own microinverter, and modular batteries have their own small inverters/ chargers. Everything is AC-coupled, which makes the system highly modular and resilient but less efficient. A good example is the Enphase IQ system with Encharge batteries. Finding a replacement for an unusual LCD I’m searching for a replacement LCD module for a pool chlorinator and have found your shop item, Cat SC4203. Could you please provide some more details or confirm whether it is a direct replacement for the Longtech LCM2004D3 seen in the photo opposite? (S. G., via email) ● It will not be a direct replacement. Our module has all the connections in a row, while yours looks like it has the backlight connections on the edge and data connections at the top. Also, yours has fewer pins, indicating it may be an SPI or I2C display, not parallel. We found a couple of options from Mouser that look similar to your module, but we can’t guarantee they are suitable replacements: siliconchip.au/link/ac87 siliconchip.au/link/ac88 While those screens are not an exact match for yours, the pinouts look very similar, if not identical. Based on the specifications on Mouser’s website, they almost certainly use SPI/I2C serial interfaces. Modifying the Mains Power-Up Sequencer I’m looking at building the Mains Power-Up Sequencer (February and March 2024; siliconchip.au/ Series/412). My intention is to use the ‘current detect’ option to power a floodlight when the submersible pump feeding the house water supply on my rural property switches on. The LED floodlight will be visible from the house so that I can monitor the pump operation; if the pump and floodlight are operating when they siliconchip.com.au shouldn’t be, I’ll know that there’s a leak in the system somewhere. The text of the article states, “It should be noted that the Sequencer is not designed for electric motors such as power tools”, but I’m not clear why. The pump is rated at 1100W and I don’t see any components in the current path of the Sequencer that could not handle the resulting current draw. I’ve measured the power consumption of the pump using a cheap Bauhn power meter at 900W with one tap turned on; I presume it would be higher with multiple taps turned on because the pump would be working harder. Possibly, the comment means that the project doesn’t provide ‘soft start’ functionality (which is not an issue for this application) or, maybe it relates only to the secondary (switched) appliances. Would this project be suitable for my application and, if not, why not, and would it be feasible to modify the circuit to suit? The equipment in question is a Divertron 1200 submersible single-­ phase pump, described as having an asynchronous motor. It has an integrated controller that activates the pump when a tap is turned on, rather than a freestanding controller. Hence, the switched mains is not available to power the LED floodlight. The Bauhn power meter reports 1W of consumption when the pump is in standby, ie, powered on but not operating because no taps are on. Hopefully, that wouldn’t cause any false triggering. The slave LED floodlight Australia's electronics magazine on OUT2 is about 10W. I’ve been reading your magazine for many years and Electronic Australia, then R, TV & H before that. I enjoy it immensely and really look forward to the magazine arriving in my letterbox each month. (T. F., Little Hartley, NSW) ● The Mains Power-Up Sequencer should be suitable for your purpose. The reason we suggested not using the sequencer with electric motors is that they can draw a very high startup current of up to 10 times the rated current, and the Triac is not rated for such a high peak current flow. However, in your application, you are only switching lighting and just need to detect when the pump is on or off. You could just bypass the OUT1 Triac by not installing it; leave off the relay and associated parts so that the mains Active input and output are directly connected by a wire that passes through the current transformer. The water pump’s current flow will be sensed to switch on output OUT2, where you would connect your light. Oversight in Mains Power-Up Sequencer I built the Mains Power-Up Sequencer (February & March 2024; siliconchip.au/Series/412) using your kit with the original firmware (A) and components as per the parts list to support Mains Detection. It has assembled quite well, despite not having the holes for the cable ties for the toroids in the PCB. Once October 2025  101 finished, I checked everything as per the assembly instructions and then performed the initial test; that seemed OK. I then went to the test for the Mains Detection using the changed status of S1. The unit powers on and, without any lead in the Mains Detect input, it cycles as though it is still doing the initial test. It cycles up after each delay to light all four outputs, then starts the switch-off cycle with delays. Once finished, it starts the cycle again. I checked the S1 switch connection to pin 12 of the PIC, and it was at 0V (indicating Mains Detect mode, as expected). I am now a bit lost as I believe that with the main power on, nothing should happen with any output until the Mains Detect input was powered. This is currently not the case. Have I missed something? (J. H., Glass House Mountains, Qld) ● There was an oversight in the instructions regarding which components to fit for the Mains Detection option. We published an erratum in the July 2025 issue explaining this. There is a 10μF electrolytic capacitor next to pin 4 of IC10 that’s shown inside the Current Detection section, suggesting it only needs to be fitted if using the Current Detection feature. This capacitor is actually required for both the Current Detection and Mains Detection features, so please add it, as it helps to reject EMI/RFI. Without it, in a high-EMI environment, the unit may falsely trigger, even if there is no voltage at the Mains Detection input. are compatible, so either transmitter can be used with either receiver. They have a different PCB and they use different enclosures. Compatibility between Secure Remote Switches I wanted to build an active direct injection (DI) box, and was wondering if the Balanced/Unbalanced Converter from the June 2008 issue (siliconchip. au/Article/1857) could be used as the basis for a DI box. If so, are any changes required? I want to build two or three into the one cabinet to use as a live recording setup. I realise that the input impedance should be high for a guitar input, and wondered if it is the input components or the op amp that determine the input impedance. As for the balanced-to-­ unbalanced side of the same project, I am thinking of using it to convert a balanced line-level signal to unbalanced headphone amp inputs. Thanks and keep up the great work. (A. S., Collector, NSW) You published a Secure Remote Mains Switch project in July & August 2022 (siliconchip.au/Series/383) and a slightly different Secure Remote Switch in December 2023 & January 2024 (siliconchip.au/Series/408), both by John Clarke. The former is designed to switch 230V AC loads, while the latter is optimised for 12/24V DC loads. Are these projects compatible? In other words, is it possible to use the transmitter from one with the receiver of the other, and vice versa? (E. Z., Turramurra, NSW) ● The two transmitters use the same software and similar circuits; the power supplies differ somewhat. They 102 Silicon Chip Dog Blaster output frequency is too high I recently built the Barking Dog Blaster from the September 2012 issue (siliconchip.au/Article/529). The Mosfet gate pulses seem to be at the correct frequency, but for some strange reason, when I measure the signal at the piezo/inductor, I get a reading of 49kHz. I cannot get it lower than that. It looks more like a sawtooth wave than a sinewave. Can you throw any light on this? (S. V., Noosa Heads, Qld) ● That the Mosfets are driven with the correct frequency suggests everything is working correctly up to the Mosfets. Please check that the transformer is wound correctly. With regards to the sawtooth waveform, it would help to know if that is measured with an open-circuit output or with the transducers connected. Also, is it before or after the filtering? If you are still not getting anywhere with this, please send us an oscilloscope photo of the Mosfet drain waveforms. Still, we really think this is a problem with the transformer winding or connections. The reader later replied that after rewinding the transformer the frequency was correct. Advice on building an active DI box Australia's electronics magazine ● The balanced-to-unbalanced and unbalanced-to-balanced converter is not ideally suited for use as a DI box unless changes are made. A DI box provides an unbalanced high-impedance input and a low-impedance balanced output for driving a balanced cable. The unbalanced input is not a high-impedance design, although it could be altered to increase its input impedance by using 1MW resistors (or 10MW if very high impedance is required) to replace the input 100kW and 10kW resistances. Note that guitars that include their own preamplifier don’t necessarily require a high input impedance at the DI Box input. The op amp does determine the input impedance to some extent, assuming the resistor values at the input are sufficiently high. A JFET input op amp like the TL072 has a higher input impedance than the LM833, although the LM833 has lower distortion. You could use an OPA2156 or OPA2134, which is a bit more expensive but has the high input impedance of a TL072 with better performance. The 100pF input capacitor can be altered to match the guitar loading requirements. For more information regarding an active DI box, see our article on the DI Box (August 2001; siliconchip.au/ Article/4158). Typically, a DI box also includes a ground lift switch that lets the user decide whether to ground the signal to prevent hum. This could be added to the unbalanced-to-balanced converter. Changing Magnetic Preamplifier gain I have built up the Magnetic Preamp you described in the August 2006 issue (siliconchip.au/Article/2740). While it works well and I am very happy with it generally, I am finding its output level to be somewhat lower than the AM radio signal of the radiogram that I am integrating it with. I had to replace the old unrepairable Collaro record with a Garrard record deck using a magnetic cartridge due to perished idler wheels on the Collaro. I experimentally modified the feedback volume control pot resistance by fitting an extra 68kW in series with the pot, and this lifts the gain to almost enough. Of course, the volume control now has very little effect. continued on page 104 siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip KIT ASSEMBLY & REPAIR FOR SALE DAVE THOMPSON (the Serviceman from Silicon Chip) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, New Zealand, but service available Australia/NZ wide. Email dave<at>davethompson.co.nz LEDsales KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com PCB MANUFACTURE: single to multilayer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www.ldelectronics.com.au August-September 2025 LEDS, BRAND NAME AND GENERIC LEDs, filament LEDs, LED drivers, heatsinks, power supplies, kits and modules, components, breadboards, hardware, magnets. Please visit www. ledsales.com.au PMD WAY offers (almost) everything for the electronics enthusiast – with full warranty, technical support and free delivery worldwide. Visit pmdway.com to get started. Lazer.Security PCB PRODUCTION USB-C Power Monitor Short-Form Kit SC7489: $60 siliconchip.au/Series/445 This kit includes all non-optional parts, except the case, lithium-ion cell and glue. It does include the FFC (flat flexible cable) PCB. WE HAVE QUALITY LED’S on sale, Driver sub-assemblies, new kits and all sorts of electronic components, both through hole and SMD at very competitive prices. check out the latest deals at www.lazer.com.au ADVERTISING IN MARKET CENTRE Classified Ad Rates: $32.00 for up to 20 words (punctuation not charged) plus $1.20 for each additional word. Display ads in Market Centre (minimum 2cm deep, maximum 10cm deep): $82.50 per column centimetre per insertion. All prices include GST. Closing date: 5 weeks prior to month of sale. To book, email the text to silicon<at>siliconchip.com.au and include your name, address & credit card details, or phone (02) 9939 3295. WARNING! Silicon Chip magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of Silicon Chip magazine. Devices or circuits described in Silicon Chip may be covered by patents. Silicon Chip disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. Silicon Chip also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Competition & Consumer Act 2010 or as subsequently amended and to any governmental regulations which are applicable. siliconchip.com.au Australia's electronics magazine October 2025  103 I would prefer to leave the existing control in place. Looking at the circuit, it seems as though I could equally reduce the value of the 1kW resistor in series with the 47μF non-polarised capacitor. Can I reduce the value of that 1kW resistor to 470W (or even less) without affecting the audio quality too much? (P. W., Pukekohe, New Zealand) ● Yes, that 1kW resistor can be reduced in value to increase the overall gain. The 47μF capacitor in series with it would need to increase in Advertising Index Altronics.................................25-28 Blackmagic Design....................... 7 Dave Thompson........................ 103 Emona Instruments.................. IBC Hare & Forbes............................... 9 Jaycar..................IFC, 11, 44-45, 53 Keith Rippon Kit Assembly....... 103 Lazer Security........................... 103 LD Electronics........................... 103 LEDsales................................... 103 Microchip Technology.............OBC Mouser Electronics....................... 3 OurPCB Australia........................ 10 PCBWay......................................... 5 PMD Way................................... 103 SC Battery Checker................... 100 SC Christmas Decorations......... 79 SC USB-C Power Monitor......... 103 SC Vintage Radio on USB........... 97 Silicon Chip Binders.................. 67 Silicon Chip PDFs on USB......... 71 Silicon Chip Shop...........92-93, 98 Silicon Chip Subscriptions........ 52 The Loudspeaker Kit.com............ 8 Wagner Electronics..................... 91 Errata and on-sale date 433MHz Transmitter, April 2025: Fig.3 on page 74 has the pin labels DATA and VCC transposed. The PCBs supplied are labelled correctly. Next Issue: the November 2025 issue is due on sale in newsagents by Monday, October 27th. Expect postal delivery of subscription copies in Australia between October 24th and November 12th. 104 Silicon Chip value proportionally to maintain low frequency (bass) response. So if you reduce the 1kW resistor to 470W, you would change the 47μF non-polarised capacitor be 100μF. Note that increasing the gain will increase the noise from the preamplifier. Transistor-controlled Ignition system wanted I am wondering if there is a Silicon Chip magazine project or circuit of a TCI (transistor controlled ignition) module that goes on an ignition coil for a basic lawnmower type magneto circuit (without a 12V battery – not a CDI system). This would be for a twostroke Victa Powertorque mower. I can see CDI projects in 2008 and 2012, but my understanding is the TCI module that triggers firing the spark plug is quite different. It has no capacitors inside, using just transistors and resistors. Some Googling revealed a patented ignition coil TCI module from some company called Atom Industries in 1979 to replace a breaker points system. There is a magnet on the flywheel and it obviously passes the iron core on the ignition coil and induces a voltage in the primary circuit. Then I believe the voltage goes from the primary coil to the silver TCI box that has a transistor circuit that triggers the circuit, feeding voltage to the secondary windings and on to spark plug for firing. Basically, that TCI box replaces the old points breaker system. (E. M., Kew, Vic) ● As far as we can tell, these ignitions originally used points. They charged the coil via the flywheel magnets and closed the points, then fired the ignition when the points opened. They were thus a mixture of Kettering and magneto ignition systems. Instead of the points, they now use a trigger coil and flywheel magnets with either a CDI circuit or a transistor trigger, like the reverse-engineered Atom circuit at siliconchip.au/link/ac76 Our article on Replacement CDI Module for Petrol Motors (May 2008; siliconchip.au/Article/1820) described how it works for CDI versions, but it required a separate trigger coil. The Atom transistor unit appears to use the primary winding of the ignition coil as the trigger coil. The reverse-­ engineered circuit linked above should work for your lawnmower. Australia's electronics magazine We haven’t published such a circuit ourselves. Fixing an old-style remote control Years ago, I built the Studio Remote Control Preamp (September-November 1993; siliconchip.au/Series/168). The third-party remote control has now forgotten its programming. I bought the kit from Jaycar (Cat KC5142) but they no longer have info on the kit in their system and were not able to help. I’m writing in the hope that someone may still have an operational remote for the preamp kicking around and may be able to re-program mine for me, or if there is some other method you may know that I could use to reprogram it. Although the remote that came with the kit was third party, the instructions included a circuit design for a remote based around the MV500 Plessey semiconductor, as the kit uses the MV601 receiver. I don’t think the MV500 is still readily available, but if I am wrong, please let me know. (M. S., Melbourne, Vic) ● The remote control for the Studio Remote Control Preamplifier used the Plessey remote control set of chips: the SL486 receiver and MV601 IR decoder for the receiver, and the MV500 for the remote unit. The MV500 also requires a 500kHz crystal or ceramic resonator, such as the Murata CSB500E, and a transistor or Mosfet to drive the infrared LED. The receiver requires a photodiode as well. The problem could be with any one of these, or some other component. Typically, the universal remote controls that are now available do not support the Plessey infrared coding scheme. It is an outdated method of infrared control using high-current, brief IR pulses. It may be that the remote control is operating and the receiver is faulty. Perhaps you could test the remote using an oscilloscope on the receiver, looking at the signal across the infrared diode and the pin 8 output of the SL486. You can probably make a suitable remote control transmitter using the MV500 and the switches on the remote that are there already. 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