Fullscreen HTML5Med Res (??MB)HTML4

JUNE 2025 ISSN 1030-2662 06 9 771030 266001 The VERY BEST DIY Projects! $1300* NZ $1390 INC GST Hot Water System Solar Diverter easy-to-build Outdoor Single Sideband Shortwave Receiver siliconchip.com.au Subwoofer » Suitable for amplifiers up to 100W » Can be painted any colour to match décor » Frequency response: 35-200Hz Australia's electronics magazine » Impedance: 4Ω June 2025  1 INC GST www.jaycar.com.au www.jaycar.co.nz Contents Vol.38, No.06 June 2025 18 The 2025 Avalon Airshow This year’s airshow, again held near Melbourne, featured quite a bit of new technology, especially new drones and defences against hostile drones. There was also some new space and satellite technology on display. By Dr David Maddison, VK3DSM Aerospace exhibition report 42 Altium Designer 25 review Altium Designer 25 is the latest version of the EDA (electronics design automation) software that we use for our PCB designs. This new version supports chip-on-board routing, signal integrity checking plugins and more. By Tim Blythman EDA software review 58 Douk hybrid valve amp review This well-presented amplifier combines a dual triode preamplifier with a 100W per channel Class-D power amplifier. It’s intended to give the benefits of both technologies, and includes tone controls and a power meter. Review By Allan Linton-Smith Hifi review Page 35 Hot Water System Solar Diverter SSB Shortwave Receiver 70 Precision Electronics, Part 8 In this penultimate entry in the series, we look at how voltage references work, as they are critical to the precision of both ADCs and DACs. In turn, they are part of most modern measurement and control systems. By Andrew Levido Electronic design 35 Hot Water System Solar Diverter Page 46 2 Editorial Viewpoint 5 Mailbag 30 Subscriptions 82 Online Shop 86 Circuit Notebook 88 Serviceman’s Log 94 Vintage Radio 74 Easy-to-make Outdoor Subwoofer 101 Ask Silicon Chip Made using a prebuilt enclosure, this subwoofer can be used indoors or outdoors; for example, in a patio area. It’s attractive, inexpensive and can add substantial bottom end to most sound systems! By Julian Edgar Audio project 103 Market Centre 104 Advertising Index You can save a lot of money with this device! It lets you use excess solar power generation to power your electric water heater. Crucially, it’s a lot less expensive to put together than an equivalent commercial unit. By Ray Berkelmans & John Clarke Solar energy project 46 SSB Shortwave Receiver, part 1 This superhet-based shortwave receiver supports USB and LSB decoding and has digital tuning from 3MHz to 30MHz. It’s controlled by an Arduino and has AGC, decent noise performance, an antenna tuning adjustment & more. By Charles Kosina Radio receiver project 62 DIY 433MHz Receiver Module A companion to the 433MHz Transmitter Module we published in the April issue, this receiver matches or beats the performance of typical prebuilt modules. It also has a handy RSSI (signal strength) output. By Tim Blythman Radio control project siliconchip.com.au Australia's electronics magazine 1. Detecting smokers with a MaixCam 2. Non-contact EMF detector 3. Advanced SMD Test Tweezers case A 1970s Little General by Fred Lever June 2025  1 SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke – B.E.(Elec.) Technical Staff Bao Smith – B.Sc. Tim Blythman – B.E., B.Sc. Advertising Enquiries (02) 9939 3295 adverts<at>siliconchip.com.au Regular Contributors Allan Linton-Smith Dave Thompson David Maddison – B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Geoff Graham Associate Professor Graham Parslow Dr Hugo Holden – B.H.B, MB.ChB., FRANZCO Ian Batty – M.Ed. Phil Prosser – B.Sc., B.E.(Elec.) Cartoonist Louis Decrevel loueee.com Founding Editor (retired) Leo Simpson – B.Bus., FAICD Silicon Chip is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 626 922 870. ABN 20 880 526 923. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Subscription rates (Australia only) 6 issues (6 months): $70 12 issues (1 year): $130 24 issues (2 years): $245 Online subscription (Worldwide) 6 issues (6 months): $52.50 12 issues (1 year): $100 24 issues (2 years): $190 For overseas rates, see our website or email silicon<at>siliconchip.com.au * recommended & maximum price only Postal address: Silicon Chip PO Box 194 Matraville NSW 2036 Phone: (02) 9939 3295. ISSN: 1030-2662 Printing and Distribution: Editorial Viewpoint PCB assembly pitfalls Now and then we get requests to supply circuit boards with some or all parts pre-soldered to them. While it seems like an attractive idea on the surface, we generally have not done it for a few reasons. The first is the financial risk involved. We would have to pay for the PCBs to be made, plus the (potentially expensive) parts, then for the assembly, all before we know how many we are going to sell. However, my biggest concern was the things that could go wrong in the process. What if the parts or the boards we receive are faulty, or even the soldering? Regardless of whether we picked up these problems before or after they reached customers, we’d be unlikely to recover any of the money we had spent. We would either have to abandon it altogether, or start over and hope to avoid the same problems the second time. There’s also the fact that acting as a quasi-manufacturer distracts us from the task of publishing the magazine, which is considerably more important. When the Pico 2 Computer project was published in our April issue, we knew that the designers had built multiple prototypes that worked. They also provided us with all the files we’d need to get boards made, and even instructions on how to go about ordering them. So, I thought it was finally time to give it a try. After all, they had practically handed it to us on a plate! What none of us were expecting was that JLCPCB (the company we paid to assemble the Pico 2 Computer boards) had been delivered a batch of apparently defective CH334F USB hub chips. They started using those to assemble boards just before we ordered a large number from them. These are the hardest chips to solder or desolder on the whole board. And, of course, there is apparently no other source of these chips than JLCPCB and their supplier, LCSC. So we couldn’t order parts from a different batch in the hope that they would function correctly. This could have been a disaster. It was lucky that someone else had ordered some boards not long before we did, found they didn’t work, and contacted Peter Mather (the Pico 2 Computer PCB designer) for help. He swapped the CH334F chips between one of the new boards and a known good one, and found that the fault followed the chip, confirming that was the problem. It was also very fortuitous that there was an easy way to work around this problem. The defective part of the chip was involved in sensing an over-­ current condition on the USB ports and cutting power to them. This was sensed via a resistive divider. Removing the two resistors in that divider disabled the function, and the chips then worked perfectly. The board has a PTC thermistor as a second line of defence to limit the current drawn from the USB ports if there is a fault. So disabling this active current monitoring feature isn’t really a problem. We had to remove the resistors from all the assembled boards we received and added notes to the kits explaining that. This approach allowed us to salvage those boards and avoid a bad experience for our customers. Ordering these Pico 2 Computer boards was a way for us to ‘dip our toes in the water’ with regards to possibly providing assembled PCBs in future when necessary. I don’t want to do this as a matter of course, because I think it side-steps an important part of hobby electronics; it’s mainly when we can’t avoid using chips that most people would struggle with soldering. Inevitably, more and more new chips only come in packages like QFN and BGA. That’s simply the way that electronics is heading. In summary, I like the idea of having boards professionally assembled, but we must proceed with caution. There is still a lot that can go wrong, as this experience demonstrated. by Nicholas Vinen 9 Kendall Street, Granville NSW 2142 2 Silicon Chip Australia's electronics magazine siliconchip.com.au siliconchip.com.au Australia's electronics magazine June 2025  3 4 Silicon Chip 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”. Garbage & Recycling Reminder project is still relevant I have been reading Silicon Chip for many years now. I look forward each month to a copy in my letterbox. After a quick look through, I begin my reading. When travelling by train, I find your magazine becomes my first choice of what to take to read. I enjoy the Serviceman’s Log and some of the many project articles. I would like to suggest a simple project that could have commercial applications. I live in Brisbane and our local garbage service provides up with three bins, one collected every week and the other two on alternative weeks. After some time, it becomes a bit confusing which bin to put out with the main garbage bin each week. I would like a simple real-time device that flashes coloured LEDs on the day that a particular bin needs to go out. For example, a red LED for garbage day, green LED for the garden waste collection and a yellow LED for the recycling collection. There would need to be a setup section to set the date etc and to select the day of the week that the garbage is to be put out on the curb side. This might fit under the Mini Projects heading, or become a standalone project. Thank you for the wonderful magazine. Warren Rose, Joyner, Qld. Comment: thanks for the suggestion. The Garbage & Recycling Reminder project (January 2013; siliconchip. au/Article/1315) is pretty much what you are asking for. It has four differently coloured LEDs. We think it would be suitable for your needs and probably doesn’t need to be updated, despite being published over 10 years ago now. Smartphone reminder apps are also available. More on staying with Windows 10 I wholeheartedly agree with your stance regarding ‘upgrading’ to Windows 11. Your statement “... Windows 10 does everything I need, so why would I want to switch to something new?” says it all. If it ain’t broke, don’t fix it. After nearly 10 years of use on millions of computers, one should think that Windows 10 is reliable and stable. I have no intention of moving to another round of chaos just because Microsoft thinks I should. And, it seems, Microsoft will not allow me to do so as two of my systems are regarded as not suitable for Windows 11. Should one be forced into installing Windows 11, an internet search reveals there are ways to install it without a Microsoft account. A workaround is once Windows is installed, create a local account with Administrator privileges and use it instead. I was given a computer with Windows 11 installed. It is not connected to the internet and I have full control of it using the local account. siliconchip.com.au While on the subject of accounts, a good practice is to create user accounts and use them for all day-to-day work. Only use the administrative account for installing software or other administrative tasks. Often, even this is not required as Windows will ask for administrative privilege when required, even though logged on as a non-privileged user. This computer has separate accounts for myself and my wife. This allows individual settings for software such as browsers. Also, having unprivileged accounts adds a layer of security. Most viruses that try to take control of a machine rely on running as an administrator. I’m looking forward to the day when I don’t have to look at those circulating balls and an inaccurate percentage of work completed. Alan Cashin, Islington, NSW. A trap to avoid when cutting audio cables I decided to use stereo RCA audio cables for an Arduino project. Like Julian Edgar (“Audio Mixing Cables”, March 2025; siliconchip.au/Article/17787), I planned to cut purchased cables. However, in my case, the plan was to have bare wires at both ends. I bought quality cables from a local source. Provided I used the one cable for both halves of a given project, everything worked OK. However, I built multiple units, and when I mixed up the devices at the ends of the cable, I found that my project sometimes didn’t work. I tracked the problem to the cable – specifically the colour-coding of the wires versus the connectors. The shield conductor appears to be safe, but the left/right connector/ colour-code relationship wasn’t. The cables were wired correctly end-to-end (so the cable would work perfectly if not cut open), but the signal wires were sometimes wired to the wrong pin of the connector. The bottom line is: if you cut open such a factory-­produced cable, even high-quality ones, check that the colour-coding of the wires is correct relative to the connector. John Evans, Macgregor, ACT. How to store extension cords Regarding your Editorial Viewpoint in the June 2024 issue, if any flexible lead is regularly bent, especially on a tight radius, will break the individual fine strands of each, which can then penetrate the insulation. While working as a maintenance electrician on robotics, this was a common occurrence. These faults were often hard to find due to the strands being very fine. They would act as fuses, and the short would blow clear, with the robot then able to run again until the next two strands happen to touch. Australia's electronics magazine June 2025  5 EOFY SALE INSTANT $20K DESKTOP CNC WATERJET • Cuts Any Material: Metal, Stone, Glass, Ceramic, Composite, Plastic, Rubber and Foam • Cutting Area - 305 mm x 460 mm • Cut Bed Size - 330 mm x 485 mm • Kerf (width of cut) - 1.2 mm Now cut anything with digital precision using high-pressure water TAX WRITE-OFF TILES *UP TO 10 MIL TURN OVER* COPPER GLASS STEEL ALUMINIUM BUY AND INSTALL BEFORE JUNE 30 TO CLAIM ON SALE FROM MAY 14th TILL JUNE 30th DON'T MISS OUT 15,125 $ (W08720) SAVE $660 Pneumatic Stool GSP-795 Round Roller Seat DMRS-600 Mobile Work Bench MWB-975 • 675-795mm seat height • Ø360mm padded seat • 360° seat rotation • 135kg capacity • Ø350mm x 75mm Thick Padded Seat • 450mm - 600mm Seat Height • 5 x 360° Swivel Wheels • Elevated Tool Tray • Heavy duty steel fabricated frame • Powder coated finish 40mm high quality laminated medium density table top • 2mm high density laminate top surface is resistant to alkali and oil $ 85 (A359) $ $ SAVE $14 150 (A361) SAVE $15 SAVE $55 Rubber Mat - Anti-Fatigue RFM-1500 • 1505 x 905mm (8mm thick) • Workshop or ute • Tapered edge 297 (A400) Metric HSS Hole Saw Set Nut & Blind Riveter Set - 130 Piece - RNB40 • 11 piece set • M42 Bi-Metal high speed steel • 19, 22, 25, 32, 35, 38, 44, 51, 57, 64, 76mm • Aluminium rivet nut inserts: • M5, M6, M8, M10 (10 of each size) • Aluminium blind rivets: • Ø3.2, Ø4.0, Ø4.8, Ø6.4mm (20 of each size) LSTEEL OPTIONANUTS RIVET E AVAILABL 35 (M800) $ 8KG WEIGHS 109 (D102) 95 (N001) $ $ SAVE $23 SAVE $15 SAVE $9 CNC PLASMA ROBOT IF YOU CAN DRAW IT, DOWNLOAD IT, TRACE IT OR IMAGINE IT, YOU CAN CUT IT With Simple Trace™ technology, No external software or cad skills are required KGS ONLY 16 • If you can draw it, you can cut it • Light and Compact design • Switch between trace and cut mode in seconds with the quick change tool holder 4,125 (P8990) $ SAVE $264 * Shown with optional plasma torch View and purchase these items online: www.machineryhouse.com.au/SIC2505 CONTACT YOUR ACCOUNTANT OR BUSINESS ADVISER TO DISCUSS YOUR PARTICULAR CIRCUMSTANCE. Digital Calipers Coolant Proof • IP54 Water Resistance rating • 3 Modes of measurement – Metric, Imperial & fractional (1/128” Increments) 150mm / 6" 35 (M740) • IP67 coolant proof • Large clear screen display • Metric/Imperial conversions 200mm / 8" Digital Indicator - 34-2205 Digital Angle Rule • 12.5mm/0.5” range • Zero setting at any position • Metric/Imperial system • 55mm dial face • Data output interface • 180mm blade length • 360° range • Stainless steel • Quick lock system 110 (Q2205) 150mm / 6” 49 (M742) 198 (Q1851) 29 (M970) $ $ $ $ $ SAVE $9 SAVE $10.40 SAVE $44 SAVE $22 SAVE $9.50 Vernier Calipers - 32-1945 Combination Set - 35-200 • 0-130mm/5" • Fine Adjuster • 4 piece • 300mm/12” • Metric & Imperial rule • Cast iron ground finished 65 (Q1945) $ SAVE $12 SAVE $22 $ 110 (Q200) Nut & Bolt Identification Set - 70-608 Universal Bevel Protractor - 35-201 • 0-360° range • 5’ index value • ±5’ accuracy • Stainless steel rule • Magnified lens • 0-1” Range • Accuracy 0.0001” • Measuring face 6.5mm, Flatness 0.0008mm • Resolution 0.0001” - Vernier scale $ 125 (Q201) $ SAVE $29 SAVE $10 45 (Q101) Metric Outside Micrometers 20-111 Contour Gauge - CTG254 • Metric - (ISO) Course and fine pitch • Imperial 60 Degree UNC & UNF • Withworth (BSW) imperial 55 degree Imperial Outside Micrometer - 10-101 • 254mm length • 45mm depth • Magnetic side • Impact resistant plastic • 3 piece set 0-75mm range • 1 x 0-25mm • 1 x 25-50mm • 1 x 50-75mm • Carbide tipped anvils • 0.01mm accuracy $ 40 (Q608) $ $ SAVE $9.50 29 (M967) SAVE $6.20 SAVE $25 7W LED Work Light - HL-35LT 14W LED Work Light - HL-14LT Industrial Bench Grinder - HG-150 • 240V /10amp • 3 LED’s <at> 750 lux • Built in transformer • Flexible gooseneck arm 119 (L2814) 140 (Q111) • 300mm lamp head • Dimmer control • 500mm flexible Arm • Magnetic base • Powerful 1/2hp motor • Cast iron body & base for superior rigidity • Anti-vibration pads on the base for smooth running • Motor c/w capacitor start/stop for maximum performance • 50mm wide wheel guards to allow for fitment of wire wheels $ $ $ SAVE $24 SAVE $27 SAVE $10 149 (L2816) 1/2HP 0.37KW - WER PO MOTOR 89 (G140) INDUSTRIAL LOUVRE WALL BACKING PANELS - LP-900P Parts Storage Bin System BK-308 • Plastic ABS bins - oil & impact resistant • 303mm x 87mm x 203mm • Removable bins for easy access and refilling • Keyholes on the back for hanging • Bins open smoothly to a 40° angle & securely clip when closed • Clear front window to easily identify parts • 900 x 912 x 20mm • Includes 43 plastic buckets • Mounts to vertical walls eal D Package 429 (K043) $ $ SAVE $2.20 SAVE $138.60 OFF RRP 22 (S0360) COMPETITIVE FREIGHT RATES DELIVERED TO YOUR DOOR MORE THAN 4000 PRODUCTS ON SALE ONLINE, INSTORE OR CALL SYDNEY MELBOURNE BRISBANE PERTH ADELAIDE (02) 9890 9111 (03) 9212 4422 (07) 3715 2200 (08) 9373 9999 (08) 9373 9969 01_SIC_270225 Specifications & prices are subject to change without notification. All prices include GST and valid until 30-06-25 There are cables that are less prone to this, but they can be expensive. With extension leads, the best way to prevent this is to have them on a drum or roll them neatly and flat and, when unwinding them, do not hold each end of the cord and pull it out. This will regularly put tight bends in the cord, making it prone to fracture. Peter Zarebski, Knoxfield, Vic. More on fluidic computers I noticed you have been discussing fluidic computers lately. At an open day in 1970, at the PMG Research Laboratories displayed a simple fluidic computer, as shown in the newspaper clipping below. Digital ICs rapidly killed this technology! Bob Backway, Belgrave Heights, Vic. Serial driver trick for Windows 7 I have successfully assembled the Programmable Frequency Divider kit that I purchased from Silicon Chip a week or so ago (SC6959). I plugged it into my Windows 7 PC and the driver was successfully installed, but I couldn’t get Tera Term Pro to connect to its serial port. The Frequency Divider comes up as “Win USB generic device” in the Control Panel devices list. I plugged an Arduino into the PC and it comes up under “PORTS (COM & LPT)” and shows the Arduino connected to COM4. I then did what I should have done at the start; I tried it on my Windows 10 PC. The driver instantly installed and Tera Term could communicate with the Frequency Divider project. I then copied the drivers folder from the Windows 10 PC onto a USB drive and transferred it to the Windows 7 PC drivers folder. I went through the device manager and updated the driver. I then selected the driver manually from a list of drivers. Scrolling through the list of manufacturers, I selected Microchip and got the warning about it not being recommended. I hit next and the driver successfully installed on the Windows 7 machine. Then it was all good. Thanks for a clever bit of test gear. Geoff Coppa, Toormina, NSW. Just because it’s AI doesn’t mean it’s right I find these days that Google searches usually offer an AI answer at the top of the results. I frequently find that this answer has errors in it, even on technical or scientific matters. Just because it comes from AI doesn’t mean it’s true. In fact, AI is less trustworthy than most legitimate sources of information. It is concerning that many professionals in science, engineering, law, medicine, journalism and business now rely on AI to do their thinking for them. It is also used to write summaries of meetings and even medical consultations. A lot could go wrong there! It’s only a matter of time before there is a major engineering or medical disaster that will be attributable to what the AI said or told someone to do. If you don’t have knowledge on a subject, don’t rely on an AI to inform you. It will just make you more stupid. Dr David Maddison, Toorak, Vic. Using op amps for industrial control Thank you for the very interesting article on the History of Operational Amplifiers (August 2021; siliconchip.au/Article/14987). When I finished studying electronics in 1967, absolutely nothing was mentioned about op amps! We only experimented with valves (mostly) and some transistors at school. When I started working in 1968, I only worked with transistors and relays in safety systems for steam turbines. However, suddenly the guy working with steam turbine control moved to another office, and I had to very quickly try to get some knowledge about op amps. I bought some amplifiers and started experimenting at home. 8 Silicon Chip Australia's electronics magazine siliconchip.com.au FREE Download Now! Mac, Windows and Linux Edit and color correct using the same software used by Hollywood, for free! DaVinci Resolve is Hollywood’s most popular software! Now it’s easy to create feature film quality videos by using professional color correction, editing, audio and visual effects. Because DaVinci Resolve is free, you’re not locked into a cloud license so you won’t lose your work if you stop paying a monthly fee. There’s no monthly fee, no embedded ads and no user tracking. Creative Color Correction Editing, Color, Audio and Effects! Designed to Grow With You DaVinci Resolve is the world’s only solution that combines editing, color DaVinci Resolve is designed for collaboration so as you work on larger jobs correction, visual effects, motion graphics and audio post production all in you can add users and all work on the same projects, at the same time. You can one software tool! You can work faster because you don’t have to learn multiple also expand DaVinci Resolve by adding a range of color control panels that apps or switch software for different tasks. For example, just click the color let you create unique looks that are impossible with a mouse and keyboard. page for color, or the edit page for editing! It’s so incredibly fast! There’s also edit keyboards and Fairlight audio consoles for sound studios! Professional Editing DaVinci Resolve 19 ............................................................... Free DaVinci Resolve Micro Color Panel .............Only $809 DaVinci Resolve is perfect for editing sales or training videos! The familiar track layout makes it easy to learn, while being powerful enough for professional editors. You also get a library full of hundreds of titles, transitions and effects that you can add and animate! Plus, DaVinci Resolve is used on high end work, DaVinci Resolve’s color page is Hollywood’s most advanced color corrector and has been used on more feature films and television shows than any other system! It has exciting new features to make it easier to get amazing results, even while learning the more advanced color correction tools. There’s PowerWindows™, qualifiers, tracking, advanced HDR grading tools and more! Learn the basics for free then get more creative control with our accessories! so you are learning advanced skills used in TV and film. www.blackmagicdesign.com/au Learn More! NO SUBSCRIPTIONS • NO ADS • NO USER TRACKING • NO AI TRAINING I then worked a lot with them from the beginning of 1970 until about 1980. We used them for control of steam turbines with 2-500MW of output power. The first op amp I came in contact with was the LM709. However, it had a drawback that if fed with a little bit too high an input voltage, it sometimes ‘locked’ either at maximum output or minimum output, and it was then only possible to get it working again by removing the supply voltage for a while. When we changed to the LM301, this problem was solved. I fully agree with your conclusion that the op amp is a very flexible device. Once again, thanks for very interesting reading! Urban Ekholm, Sweden. Success building numerous DIY test instruments As an avid reader of Silicon Chip since your very first issue in 1987, I wanted to share feedback on my recent experiences with building a number of your projects over the past 6 months. I am currently redeveloping the David Tilbrook ETI Series 5000 Control Preamplifier from 1981 as a nostalgia project. The idea came about after I acquired a rusty old built-kit from a friend, before deciding to strip the boards and wiring, and replace them with new. My spare time has been absorbed with many iterations of Tilbrook’s original design, and I am now drawing close to completion. In essence, the project morphed into a multiboard redesign using KiCAD (as reviewed in your Open Source feature in the February 2025 issue). What a learning curve! Some two years later, I am now bench testing the changes using several Silicon Chip test equipment projects. I recently completed the Intelligent Dual Hybrid Power Supply by Phil Prosser (February-March 2022; siliconchip. au/Series/377). I have been building kits since the late 1970s, and had the privilege of managing Jaycar’s kit department for many years in the 1990s, working closely with Silicon Chip in getting the magazine’s projects to market. During that time, I built countless audio projects as demo units in Jaycar stores and as a general check. For the larger projects, I rewrote construction articles and added step-by-step guides with the goal of providing less experienced constructors with the confidence to successfully build complex audio kits (the magazine obviously has limited space for such in-depth guides). It was hard work, but it was incredibly fun! Your Dual Hybrid PSU design was by far the most enjoyable project I have assembled in many years, forcing me to learn new techniques such as SMD soldering (including ‘drag soldering’ for the fine-pitch microcontroller), tapping M3 holes for the heatsink, sheet metal bending, precision hole cuts and so on. Unfortunately for me, this was one project that didn’t fire up the first time. I had inadvertently swapped the specified LM2575-5.0V regulator with the adjustable version and hadn’t noticed its ADJ suffix! I believed that the LM2575 was faulty because it was providing just 1.5V output (which is actually correct for the adjustable version). After replacing these devices with the correct 5V versions, the two switch-mode modules sprang to life. However, I still had work to do. The microprocessor control board was not working as expected and, after borrowing a 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 GOT A BIG IDEA? WE'VE GOT THE BOARD FOR IT. From simple builds to ambitious creations, Jaycar has Arduino® -Compatible boards to match. BEST SELLER BREADBOARD FRIENDLY FOR EASY PROTOTYPING 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 EMULATE A USB KEYBOARD, MOUSE, JOYSTICK, ETC. ARDUINO® COMPATIBLE LEONARDO BUILT-IN USB EMULATOR $ FOR MORE ADVANCED PROJECTS THAT REQUIRE MORE I/O & PWM PINS ONLY 3495 $ ARDUINO® COMPATIBLE MEGA . FROM 5495 . XC4430 • 54 DIGITAL PINS (15 PWM CAPABLE) • 16 ANALOGUE PINS & 4 SERIAL PORTS XC4420/21 NANO UNO LEONARDO MEGA Special Feature Compact Breadboard Friendly Best Shield Compatibility USB Emulator Extra Resources, Inputs & Outputs 54 No. of Digital I/O 14 14 20 No. of Analog Inputs 6 6 12 (6 shared with Digital) 16 PWM Capable Pins 6 6 7 15 Serial Ports 1 1 2 4 Processor / Speed ATmega328 / 16MHz ATmega328P / 16MHz ATmega32u4 / 16MHz ATmega 2560 / 16MHz Program Memory^ 32kB 32kB 32kB 256kB EEPROM / SRAM 512 bytes / 2kB 512 bytes / 2kB 1kB / 2.5kB 4kB / 8kB ^Up to 4kB used by bootloader. SHOP AT JAYCAR FOR: 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. • Great Value Starter Kits • Arduino® Compatible Development Boards jaycar.com.au - 1800 022 888 • Wide range of Shields, Modules & Sensors une 2025  11 siliconchip.com.au Australia's electronics magazine • Great range of Breadboards & Prototyping Accessories jaycar.co.nz - 0800 J452 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. friend’s digital microscope to inspect the board at a microscopic level, I discovered that a tiny metal fragment behind the micro was shorting-out pins. I found this almost by accident, and very near me wanting to give up the whole affair. With the otherwise invisible fragment now removed, the supply sprang to life and I now have a phenomenal piece of bench equipment. While it certainly cost more than what I could buy a similar dual tracking supply for from China, I now have newfound skills and deeper knowledge of switch-mode PSU design and fault-finding. To me, that’s priceless. A key lesson was that seasoned constructors shouldn’t be cocky when approaching a build that, on the surface, appears straightforward! Thanks to your magazine, I now have a bench brimming with new test gear in support of my audio project. I also built the WiFi DDS Function Generator by Richard Palmer (May-June 2024; siliconchip.au/Series/416) and incorporated John Clarke’s DC Supply Protector within the case (June 2024; siliconchip.au/Article/16292). I also plan to build the combined LC/ESR Meter by Steve Matthysen (August 2023; siliconchip.au/Article/15901) over the coming days, as well as Jim Rowe’s Digital Audio Millivoltmeter (October 2019; siliconchip.au/Article/ 12018). These, along with a newly acquired Rigol DSO, will allow me to push ahead with confidence. Thanks to your magazine and its contributors for fuelling my passion for this incredible hobby that has afforded me a career of 40+ years within the industry. I view your magazine’s ongoing success as crucial. That’s why I recently decided to become a subscriber, and will continue to be for many years to come. Tim Rimington, North Manly, NSW. Alternatives to centrifugal switches for motors Regarding the discussion on speed controlling induction motors with centrifugal switches (eg, January 2025 issue, Mailbag, page 6), the ‘start capacitor’ is typically switched out of the circuit at 30% of the maximum motor rotational speed (RPM). The start winding has a thinner wire gauge than the run winding and must be switched out as soon as possible. If it cannot reach the threshold RPM or it falls below it during operation, the thermal switch mounted on the case of the motor will trip and disconnect all the power to the motor to save the start winding from burning out. These motors are not designed to operate at low speeds. If you want a lower speed than 30% (including a safety margin), use a three-phase motor or a gearbox. An interesting aside to this topic is that of electronic motor capacitor start switches. They range from simple timers that just give a time delay before switching out the capacitor to complicated back-EMF sensing circuits used to switch out the capacitor. These switches are externally mounted, requiring the installation of a wire from the start winding inside the motor to the electronic switch outside the motor. They can be retrofitted as a substitute for a failed internal mechanical switch. For details about this subject, go to https://www. stearnsbrakes.com/products/electronic-start-switches/ sinpac. These ‘SINPAC switches’ include multiple-­ capacitor switches, reversing switches, capacitor 12 Silicon Chip Australia's electronics magazine siliconchip.com.au siliconchip.com.au Australia's electronics magazine June 2025  13 start and run switches. All the wiring diagrams of the different motor configurations they are used in are available. Advising someone about a motor may be a complex business without at least using these diagrams to sort out which type of motor is under consideration and research into their characteristics. I hope this helps. Don’t forget that electronics is fun! Norman Boundy, Taylors Lakes, Vic. Estimating transformer’s current capacity from its core size I was interested in the question from B.P. of Dundathu, Qld, in the April Ask Silicon Chip column, on how the current rating of mains transformers relates to the size of the wire in the secondary winding(s). This reminded me of a very useful graph I have had since my brother gave it to me in the late 1960s. He was doing an electrician’s training course in Adelaide at the time. The graph shows the relation between the volt-amp (VA) rating of a 50Hz transformer and the cross-section area of the core; in particular, the area of the middle section of an E-I transformer. Most non-toroidal power transformers are of this type. The area can be easily obtained by measuring the height of the ‘stack’ of laminations and multiplying it by the width of the centre leg of the E core. This gives you the area of the core in, say, cm2. The graph from the 1960s is in square inches, but it shows that the area of the core of a 100VA transformer would be about 11.6cm2. The graph is printed on paper with a log-log scale, but it Silicon Chip - June .pdf 1 2/5/2025 12:25 pm shows that the VA rating is directly proportional to the core area. Double the core area, and the power rating is doubled. Thus, if your correspondent can measure the area of the transformer core, he/she can get a good approximation to its power rating and dividing that by the secondary voltage will result in the rated secondary current. Keith Gooley VK5OQ, One Tree Hill, SA. Pico 2 USB connection problem was a failed solder joint I built the Pico 2 Computer from your kit but the Pico2 wouldn’t go into bootloader mode. I knew it wasn’t a problem with the cables or computer because, using the same cables, a Pico 1 happily goes into bootloader mode. Of course, I held BOOTSEL down as I connected the USB cable. I asked Geoff Graham for help; he thought it was a soldering problem with one of the pads that connects the Pico 2’s USB terminals to the Pico 2 board, or the soldering of the USB socket used for programming. I used a piece of tinned copper single-core wire pushed into each hole, then cut it off to establish a bridge between the PCB and the Pico 2, in case there was a gap that was enough to discourage solder from joining them. That worked! Now I can wander down memory lane to when I first had to use BASIC in 1978 while in the RAAF, using a Hewlett-­ Packard HP9830 to manage aircraft repairable spares. BASIC was not my first computer language – when I was studying Aeronautical Engineering at RMIT in the early 1970s, we had to use ALGOL 65. Fun times! Thanks to Geoff Graham for taking the time to help me. SC Neil Biggar, Medowie, NSW. ® Since introducing D-STAR in 2001, Icom has consistently pushed the boundaries to refine and elevate the D-STAR experience. 14 Silicon Chip Australia's electronics magazine siliconchip.com.au BUILDING BEYOND THE BENCH? Big ideas don't stay put. Power your Arduino® -compatible projects with our range of modules, batteries, and accessories. Made to go wherever innovation takes you. USB OUTPUT $ LED VOLTAGE DISPLAY ONLY 495 $ . ONLY 2195 . POWER YOUR 5V PROJECT FROM BATTERIES POWER YOUR PROJECT FROM A LOWER VOLTAGE Boost Module Converts 2.5-5VDC from a single Li-Po or two Alkaline cells up to 5VDC. 500mA max. XC4512 DC-DC Boost Module with Display Converts 3-35VDC up to 4-35VDC. 2A max. XC4609 USB OR SOLDER TAB INPUTS EASILY ADJUSTABLE BY MULTI-TURN POTENTIOMETER ONLY 5 $ 95 $ . ONLY 1025 . RUN ARDUINO BOARDS OFF HIGHER VOLTAGE POWER MAKE YOUR PROJECT BATTERY POWERED DC Voltage Regulator Lithium Battery Charger Module Accepts any voltage from 4.5-35VDC, and outputs any lower voltage from 3-34V. XC4514 Charges a single Lithium cell from 5VDC. XC4502 PROJECT POWER Single 18650 Battery Holder PH9205 $4.40 SHOP AT JAYCAR FOR: Switched 4xAA Battery Enclosure with USB Port MP3083 $6.50 • Step Up and Step Down DC-DC Converters • Huge range of Batteries and Battery Holders • Great selection of USB and DC Connectors and Leads • Regulated DC Plugpacks and Lab Power Supplies siliconchip.com.au Switched 4xAA Battery Enclosure with DC Plug PH9283 $6.75 3.7V 18650 2600mAh Li-ion Battery SB2308 $16.95 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. Australia's electronics magazine jaycar.com.au - 1800 022 888 jaycar.co.nz - 0800 452 922 June 2025  15 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. $ ONLY 2295 . 25W Soldering Iron TS1465 SOLDERING SOLUTIONS FOR QUICK FIXES TO BIG BUILDS No matter if you’re fixing a frayed cable or soldering up your next invention, we’ve got a GREAT RANGE of soldering essentials at GREAT JAYCAR VALUE! ESD Safe Tweezer Set Solder Flux TH1760 $29.95 $ NS3070 $21.95 ONLY 87 95 . Precision Angled Cutters 1.5 to 3mm Desolder Braid TH1897 $27.95 240V Fume Extractor NS3001 - NS3096 FROM $4.55 $ TS1580 $ 0.71mm & 1mm Solder NS3026 - NS3028 $9.95EA ONLY 149 ONLY 2995 . $ ONLY 4195 . 160 Heatshrink Pack WH5524 SHOP AT JAYCAR FOR SOLDERING ESSENTIALS: PCB Holder with LED Magnifier TH1987 48W Soldering Station TS1564 Explore our great range of soldering gear, in stock on our website, or at over 140 stores or • Battery, gas and electric soldering irons and stations 130 resellers across Australia and New Zealand. • Wide range of solder • Desoldering braid and tools jaycar.com.au - 1800 022 888 • Soldering iron stands, cleaners and PCB holders • Heatshrink tubing jaycar.co.nz - 0800 452 922 16 Silicon Chip aids Australia's electronics magazine siliconchip.com.au • Tools and service 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. GOT A BRIGHT IDEA? LET’S BUILD IT! Your next big build starts here. Jaycar’s wide range of prototyping accessories delivers great value for every idea. PB8815 HP9572 FROM 6 FROM 6 $ 25 $ 75 . Breadboard Layout Prototyping Boards 6 models available. PB8815 - PB8832 PB8820 QUICK AND EASY PROTOTYPING . Breadboard Layout Prototyping Boards 400 Hole HP9570 | 862 Hole HP9572 PRICE DROP WC6027 Breadboard Jumper Kit 70 Pieces PB8850 $12.50 150mm Jumper Leads WC6024 - WC6028 FROM $7.95 MAKE YOUR OWN CIRCUIT BOARDS Blank Fibreglass Copper Sided PCBs • 4 sizes available HP9510 - HP9515 FROM $6.95 SHOP AT JAYCAR FOR: HP9570 NOW 3995 8 x 25m Hook-Up Wire Rolls . 26AWG WH3009 $54.95 MAKE PCBS IN 4 EASY STEPS 1. PRINT/COPY 2. IRON ON 3. PEEL OFF 4. ETCH 20 Piece Micro Drill Set • Sizes: 0.3 - 1.6mm TD2406 $15.95 • Soldering & Accessories • Components, Cables and Connectors • Magnifiers and Inspection Aids • Tools, Service Aids and Chemicals siliconchip.com.au $ MAKE YOUR BREADBOARD PROTOTYPE PERMANENT PBC Wash Defluxing Solution • 1 Litre Bottle NA1070 $15.95 $ JUST 4695 . Press 'n' Peel Film 5 sheets of 215 x 280mm transfer film with full instructions. HG9980 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 Australia's electronics magazine jaycar.co.nz June922 2025  17 - 0800 452 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. Report by Dr David Maddison, VK3DSM The Australian International Airshow is held in Avalon, Victoria (near Melbourne) each year and showcases the latest in aviation and related technology. It features more drones each year, but there was other interesting technology on show, too. I have reported on previous Avalon Airshows in the May 2013, 2015, 2019 & 2023 issues, so this is my fifth report. It won’t include aircraft or equipment I have reported on before unless there have been significant developments since then. I can’t describe everything I saw at the airshow; there was simply too much, so the following are the highlights of this year’s show. According to the organisers, over 200,000 people attended over six days of the event. 350 aircraft were displayed and there were 902 exhibitors from 28 countries. 291 delegations attended from 43 nations, including 20 chiefs of air forces or similar, 65 conferences, symposia and presentations were held. The show was enormous in scope, as usual, and it was pleasing to see a significant turnout from the Australian aerospace industry. Here are the most interesting exhibits alphabetically: 18 Silicon Chip Airspeed Irukandji target The Airspeed Irukandji (Fig.3, https:// airspeed.com.au/) is a supersonic practice target under development for the RAAF. It uses an Australian-made solid rocket motor, developed in conjunction with Thales Australia and Defence Science and Technology Group. It is said to be aerodynamically similar to the Beechcraft AQM-37 target (not used by Australia), which was in use from 1963 to 2022. That one relied on difficult-to-handle hypergolic propellant (two components that spontaneously combust when brought into contact). Airspeed is based in Mawson Lakes, SA and testing is being performed at the RAAF Woomera Range Complex. ALADDIN Drone The Aircraft Launched Aerial Delivery Drone (Fig.2) by Sovereign Propulsion Systems (www.sovps.com.au) based in Seaford, SA is a drone that can deliver payloads of 20–30kg for Australia's electronics magazine defence, search and rescue or disaster relief applications. It is designed to be launched out the back of an aircraft such as a C-130 Hercules. It has a six-minute flight time with a 30kg payload, or a 25-minute flight time with a 5kg payload, but no range is specified. Maximum take off weight is 65kg and the motors produce 39.6kW of power. The ‘drone head’ is separate from the ‘payload module’; the latter can be designed by third parties for any required applications. For rescues at sea, the ALADDIN payload can be delivered directly to the party being rescued, such as a stricken boat, rather than the present situation of dropping supplies in a “helibox” package into the water for the party to retrieve by themselves. Ascent Aerosystems Ascent Aerosystems is a US company that specialises in coaxial drones (https://ascentaerosystems.com/). siliconchip.com.au Fig.1: a cutaway view of the Aussie Invader 5R land speed record attempt car. Fig.2: the ALADDIN Air Launched Delivery Drone on top of a 4WD. Coaxial rotor drones have advantages over traditional quadcopter or 6/8-multirotor designs due to greater ruggedness for commercial, military and rescue operations. They are also easy to store with folding rotor blades and a cylindrical shaped body. Guidance is achieved by adjusting the pitch of the rotors and their differential speed. The Helius model (Fig.4) weighs 249g, has a body size of 275 × 75 × 53mm, a rotor diameter of 300mm, flies up to 72km/h, a mission duration of 30+ minutes, carries a 12.3 megapixel low-light camera and has a suggested price of US$4,499 (about $7000). The Spirit model (Fig.5) is 305mm tall; its body is 106mm in diameter, while the rotor diameter is 648mm. Its maximum payload is 3.0kg and the maximum take-off weight is 6.1kg. With two batteries installed, mission duration is 58 minutes with siliconchip.com.au Fig.3: the Australian Irukandji target drone uses a solid rocket motor. Fig.4: the Ascent Aerosystems Helius Nano UAV uses a coaxial rotor design. no payload or 32 minutes with maximum payload. Its top speed is over 100km/h. You can see a video of the Spirit model at https://youtu.be/J1tJGhiNrG0 and another about the Helius model at https://youtu.be/6X_LIZwTXUM Aussie Invader 5R This beautiful vehicle is a contender for the world land speed record, with hopes of achieving 1,600km/h (see Fig.1 & https://aussieinvader.com/). The vehicle is rocket powered; its Australia's electronics magazine Fig.5: the Ascent Aerosystems Spirit is larger but also has coaxial rotors. June 2025  19 Glossary • UAV: Unmaned Aerial Vehicle, an aircraft that flies autonomously or by remote control (including what is commonly referred to as “drones”). • UAS: Unmanned Aircraft System, a broad term that includes UAVs, plus the ground control station, communications equipment and other support systems. • VTOL: Vertical Take Off and Landing propellant is white fuming nitric acid (WFNA) as the oxidiser and turpentine as the fuel. That propellant mixture is hypergolic, meaning the two components spontaneously combust when combined. The combined weight of the propellant is 2.8 tonnes, which will be mostly consumed in 20 seconds. The liquids are pressure-fed at about 70bar (68 atmospheres) with no pumps for the sake of simplicity. The motor develops over 28 tonnes of thrust and, after 20 seconds, the vehicle will be travelling at 1600km/h or 1km every 2¼ seconds. At the expected speeds, there are a range of physics and aerodynamic behaviours that come into play; if this record attempt is successful, it is likely to stand for a very long time as technology is being pushed to the limit. Currently, the Aussie Invader team is looking for a long enough track to run the record attempt. It cannot be a salt lake due to a lack of grip; it needs to be a desert-baked mudflat surface at least 25km long; level, smooth and straight, into which the wheels can sink in by about 2.5cm to give extra traction and stability. Sites are being investigated in Australia (ideally), South Africa and the United States. Fig.6: a model of the ASA Roo-ver. Australian Space Agency (ASA) Roo-ver The Roo-ver (see Fig.6 & https:// www.space.gov.au/meet-roo-ver) is an Australian-made lunar rover that is expected to go to the moon on an Artemis mission. Artemis is a NASA program to re-establish a human presence on the moon. The Roo-ver will weigh about 20kg and be about the size of a typical suitcase (as the ASA describes it). It will be controlled from Earth to collect lunar soil and help to develop capabilities necessary for an ongoing human presence on the moon. Its mission duration is 14 days. The lunar soil, also known as regolith, will be studied as a source of oxygen to breathe and as an element of rocket fuel. The industry consortium building the rover is called ELO2 and comprises start-ups, small- to medium-­ size enterprises, major resource companies, universities and others. Roover is expected to go to the moon later this decade. You can watch a video about it at https://youtu.be/ hZ7Lb4VJbR4 Fig.7: the DroneSentry-X Mk2 for detecting and optionally defeating drones. The Babcock Language Translation System The Babcock Military Aviation Language Translation System is proposed to solve the apparent lack of language comprehension of aviators within some of Australia’s military coalition partners. However, according to the International Civil Aviation Organization (ICAO), English is the mandated language for all aviation radio communications and procedures worldwide, at least within civil aviation. Pilots are expected to be proficient in “Aviation English”. The prevalence of the language problem was not stated by Babcock. The translation system “… utilises neural machine processing and edge processing to deliver real-time translation of pilot-pilot, pilot-ATC, and pilot-ground staff communications. … This system employs aviation Fig.10: a rendering of the Quickstep Brolga with DROPS payload. Source: https://www.quickstep.com.au/qaam/ Fig.11: the Corvus Launcher V1 with an Innovaero Owl-B. 20 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.9: an artist’s concept of the Hypersonix DART. Source: https:// www.hypersonix.com/resources/ Fig.8: DroneSentry’s medium-range product. contextual understanding and deep learning architectures to reduce the cognitive burden of translation.” Quickstep Brolga Quickstep is an Australian company that received an Airshow award for their electric multi-mission UAS QU-1A Brolga (Fig.10 & https://www. quickstep.com.au/qaam/). It has a 6m wingspan, VTOL capability, can carry payloads of 20–30kg for up to 100km. Its automated payload interface can find, identify and attach to the correct payload. The payload container is a proprietary system by TB2 Aerospace (https://tb2aerospace.com/) called Drone Recharging Operational Payload System (DROPS). They also have a QU-3A Protean model with a 45kg payload capacity, 750km range at 160km/h and a hybrid powertrain using conventional fuels and with onboard batteries for a 15-minute hover or payload exchange time. For more details, see the video at https://youtu.be/5vpbRwzottQ Corvus Technology drone launcher Non-VTOL UAVs need some horizontal speed for launching, like conventional winged aircraft. Corvus Technology Solutions (https:// corvustechnologysolutions.com/) from Bayswater North, Vic, offers an Australian-made Electronic Launch System for any fixed-wing UAV. The Corvus Launcher V1 (Fig.11) siliconchip.com.au can launch up to 360 UAVs per hour, including ‘swarms’. It is silent, battery-­operated and mobile. It can launch UAVs weighing up to 31kg at around 90km/h. A custom cradle is required for each type of UAV. The Corvus Launcher V2 is under development. It will be able to launch 120kg UAVs at up to 90km/h and UAVs under about 20kg at 180km/h. DroneShield Small consumer or commercial drones are increasingly being used for hostile or unlawful acts such as smuggling, airport disruption or terrorist attacks. DroneShield (www. droneshield.com) is an Australian company that specialises in C-UxS (Counter Unmanned Systems), ie, the ability to detect and disable drones. They detect drones by a combination of radar and electro-optical sensors, using artificial intelligence to identify hostile drones and to disrupt their control, navigation and video data links. DroneSentry-X Mk2 (Fig.7) is suitable for mobile operations, such as mounting to a vehicle or on a tripod in the field. It has a detection range of up to 3km and a disruption range up to 500m. It weighs 46kg. DroneSentry (Fig.8) is a modular solution for close, medium or longrange detection (depending upon configuration) and optionally defeating drones. It uses optical, radar, and radio frequency (RF) sensors, edge Australia's electronics magazine computing systems and software to produce comprehensive detection and optional countermeasure solutions. Information from these sensors is correlated to provide maximum situational awareness for automatic identification and response to UxS intrusions or threats. DroneOptID is DroneShield’s AI-driven computer vision technology. It can also help to determine the drone’s payload, modifications and effectiveness of countermeasures being applied to it. The medium-range DroneSentry product (shown in Fig.8) features four Echodyne EchoShield radars, an HDC Ranger MR UC infrared (FLIR) sensor and a CompassOne navigation system to provide location, direction and heading data. It connects to the DroneSentry-C2 command and control software for sensor fusion and incorporates DroneSentry-X Mk2 detection and (optional) defeat capabilities. Hypersonix Launch Systems The Hypersonic Launch Systems (www.hypersonix.com) DART (Fig.9) is a test bed for hypersonic flight and testing anti-hypersonic weapons. DART is 3.7m long and can fly at Mach 7 (seven times the speed of sound) for up to 1000km while carrying a 9kg payload. It uses a SPARTAN fifth-­generation air-breathing hydrogen fuelled scramjet (supersonic combustion ramjet) engine. It has a 3D printed airframe and June 2025  21 weighs 300kg. DART is launched with unguided sounding rockets or guided rockets. It is fully manufactured at Carole Park in Queensland. Elbit Systems Elbit Systems (www.elbitsystems. com) had numerous products on display, including the following pilot low-light vision and helmet display systems (see Fig.13): • the BriteNite II night-vision sensor array (video at https://youtu.be/ y8xvk0G2R-E) • X-Sight helmet mounted display (HMD) for helicopter pilots (video at https://youtu.be/2rMK6p6r0rs) • HDTS (helmet mounted display and tracking system) – video at https:// youtu.be/uih6hA2uDR0 Honeywell Aerospace 757-200 We were invited on a demonstration flight of Honeywell’s 757-200 test bed aircraft, tail number N757HW, the fifth production 757 ever made. It started service with Eastern Airlines in 1983 and joined Honeywell (https:// aerospace.honeywell.com/) in 2005. They stripped out the cabin linings and most seats, reducing its weight by around nine tonnes, and modified it to take various equipment racks, engineering stations (Fig.12) a third engine mount (Fig.14) to test engines under development and various electronic equipment. It is used as a test and demonstration platform for the Honeywell Aerospace products. The systems they demonstrated include: • Satellite communications, such as L-band and Ka-band hardware. We were connected via onboard WiFi to the internet using the high-bandwidth Ka-band Viasat Global Xpress (GX) network via Honeywell JetWave X hardware. We then connected to Inmarsat’s global L-band LAISR network, giving 3+3Mbps data rates via Honeywell’s Aspire hardware. • Smart-X, Honeywell’s portfolio of runway safety products. These include Runway Awareness and Advisory System (RAAS) and SURF-A. RAAS gives alerts to the pilot during ground and air operations to avoid collisions, and includes optional SmartRunway and SmartLanding software. It uses GPS to determine an aircraft’s 3D position, track and ground speed 22 Silicon Chip and uses a detailed validated runway database of 3500 airports. It gives audio alerts to pilots, such as which runway they are approaching or on, which taxiway they are on, warns of short runways, distance remaining for a rejected take off, take off flap position, warning of a possible taxiway landing, distance remaining and other alerts. SmartRunway and SmartLanding use aircraft position data and a runway database to prevent runway excursions or incursions. SmartRunway prevents incidents on the ground such as crossing the wrong runway, crossing a runway without clearance, or taking off from a taxiway or short runway, or with the wrong flap setting. SmartLanding prevents incidents like running off the end or the side of a runway, an off-­ runway landing, landing on the wrong runway or landing on a taxiway. SURF-A enhances these by taking data from the ADS-B Out (Automatic Dependent Surveillance Broadcast Out) equipment, using advanced algorithms to identify any possible collision and alerting the pilots. ADS-B Out uses GPS and other sensors to give accurate position that is broadcast to other aircraft (it is more accurate for positioning than radar). • Weather radar; the aircraft was equipped with Honeywell’s next-­ generation Intuvue RDR-4000 3D weather radar that uses volumetric scanning and pulse compression technologies to provide a complete view of the weather from sea level to 18,300m altitude, with a 590km detection range. This allows for better avoidance of adverse conditions; using it, a 50% reduction in aircraft lighting strikes was reported, and less pilot fatigue. • Traffic Alert and Collision System (TCAS) is a suite of systems that operate independently from groundbased Air Traffic Control (ATC) for collision avoidance. TCAS involves two-way communication with other aircraft equipped with appropriate transponders. This enables a 3D map to be produced, allowing each aircraft’s range, altitude and bearing to be determined and establish whether a possibility of a collision exists. If a collision possibility exists, the TCAS responders negotiate an appropriate avoidance manoeuvre. The TCAS system also listens for ADS-B information transmitted from other aircraft. TCAS is mandated for aircraft over 5700kg take off weight or that carry more than 19 passengers. Honeywell offers several TCAS solutions. IAI APUS 25 long endurance quadcopter IAI (www.iai.co.il) has developed a long-endurance quadcopter called the APUS 25 (Fig.16), which has an endurance of up to eight hours with no payload. It achieves this using a single constant-RPM multi-fuel internal Fig.12: an engineering test station in Honeywell’s 757. Note the stripped interior. Australia's electronics magazine siliconchip.com.au combustion engine that drives four variable-pitch rotors. It has a maximum payload capacity of 10kg (with reduced endurance) and a maximum takeoff weight of 25kg. With a 5kg payload, its endurance is five hours; electrical power of up to 300W is available to power payloads. It can reach altitudes of 3353m and can hover for extended periods due to a liquid-cooled engine requiring no airflow, so it can be used for persistent surveillance. It has a maximum speed of 42 knots (78km/h) and can operate in high wind speeds, to 23 knots (43km/h). It is suitable for various missions, such as bushfire surveillance, and can perform disaster management, among many other tasks. Multiple sensor options are available. For more information, see the video at https://youtu. be/9lQ3ohSG9ss Fig.13: the BriteNite II night-vision sensor array, X-Sight helmet mounted display and HDTS helmet-mounted display and tracking system. Fig.14: Honeywell’s 757-200 has a third engine mount for testing engines under development. Innovaero Innovaero (https://innov.aero/) is a Perth-based company. They are now 51%-owned by BAE Systems Australia and work jointly on various projects. Among their products on display were the STRIX Uncrewed Aerial System (UAS), which we covered in the May 2023 article on the Airshow of that year (siliconchip.au/ Article/15773). Then there was the Owl A (Fig.15), a precision loitering munition that can carry a 1.5kg warhead and has a range of 45km. A loitering munition, also known as a kamikaze drone, is a drone carrying a warhead that flies to an area of interest, then waits in a holding pattern, looking for a target. If a target is acquired, it is engaged. If no target is acquired, the drone can return to base to be recharged or refuelled for use on another occasion. The Owl B loitering munition (Fig.17) is electrically powered and designed to loiter for 30 minutes at a range of up to 100km and return if no target is acquired. Alternatively, it Fig.16: the APUS 25 long endurance quadcopter. Source: https://www.iai.co.il/p/apus-25 siliconchip.com.au Fig.15: the Owl A loitering munition. Fig.17: the Owl B loitering munition on a Corvus Launcher V1. Australia's electronics magazine June 2025  23 can have a maximum range of 200km with no return capability. Jabiru cargo drone Fig.18: Jabiru’s JCQ50 cargo drone with a JMIC trunk container payload. Fig.19: a rendering of MIRAGE operating in ghost decoy deception mode to deceive an adversary’s sensors. Source: https:// jackal-industries-dyfl0js. gamma.site/ Fig.20: Kratos target drones; the MQM-178 Firejet is in the front, with the BQM-177i behind it. Bundaberg, Qld-based Jabiru (https://jabiru.aero/) are well-known in the recreational aviation and training markets for their one-to-four seat composite light aircraft. At the airshow, they displayed their new JCQ50 “Donkey” cargo drone (Fig.18). It is being developed with the support of the Australian Department of Defence. The drone can carry a 50kg payload up to 150km at a speed of 105km/h. It has an unusual arrangement of coaxial rotors for lift, powered by a petrol engine, plus four electrically powered twin rotors on booms (similar to a traditional quadcopter) for steering, with electrical power for them generated by the petrol engine. This greatly simplifies the design of the vehicle, as there are no complex mechanisms as required for a traditional helicopter rotor. The Donkey can be disassembled and two can be carried in a standard full-size JMIC trunk, a container used by the Australian Defence Force and other militaries (1016 × 609 × 406mm). Donkey drones can be flown using real-time remote control or in an autonomous mode. They are powered by a petrol engine in a twin-V four stroke configuration that produces 26.5kW. Jackal Industries MIRAGE Jackal Industries’ MIRAGE (Fig.19) is an adaptable military drone that can be reconfigured between the roles of ISR (intelligence, surveillance, reconnaissance), deception and electronic warfare/jamming. Kratos target drones Kratos had two target drones on display: the MQM-178 Firejet and the BQM-177i (see Fig.20). The Firejet simulates of a variety of threats. Its specifications are: • Length: 3.3m • Wingspan: 1.9m • Dry weight: 59kg • Engine thrust: 37kg • Maximum launch weight: 145kg • Internal payload capacity: 32kg • Wingtip payload: 18kg total • Wing station payload: 31.8kg total • Top speed: Mach 0.69 Fig.21: the Phoenix Jet target drone by Air Affairs Australia has a top speed of over 600km/h. 24 Silicon Chip Australia's electronics magazine siliconchip.com.au • Maximum altitude: 10,670m • Fuel capacity: 64.4L • Oil capacity: 1.9L (for making smoke) Neumann Space impulse bit (the smallest amount of thrust per pulse) of 236μNs and a total impulse (total thrust produced over time) of 1000N. It measures 96 × 96 × 100mm and weighs 1.4kg fully fuelled. For more details, see the video titled “Lab Sweet Lab - How the Neumann Drive Works” at https://youtu.be/ 4TVipU98g9s ACRUX-2 (www.melbournespace. com.au/projects) is a low-cost satellite rideshare program using a volunteer model to help students get satellites into space. The aim of this program is to take a photo of Melbourne from low Earth orbit (LEO). To do this, they are building a 3U CubeSat and a ground station. The Neumanm Space company (https://neumannspace.com/), based in Kent Town, SA, has developed the Neumann Drive, an innovative lowthrust electric ion drive for satellite propulsion. It can be used for satellite orbit raising, station keeping, formation flying and deorbiting. Unlike some other low-thrust propulsion systems, it uses solid metal as the propellant rather than liquid or gaseous fuel, which greatly simplifies its design and improves reliability. It is a Centre-Triggered Pulsed Cathodic Arc Thruster (CTPCAT). It uses a fuel rod of just about any metal (including scrap metal from space junk) that is solid at the temperatures likely to be encountered. It turns the metal into a plasma using electricity, which is ejected to create thrust. A capacitor bank produces a cathodic arc discharge to produce short (~200μs) pulses at high current (~3kA) and modest voltage (~200V) to turn the metal into a plasma. This plasma exhaust becomes detached from the spacecraft and moves away at velocities of tens of kilometres per second, imparting momentum to the vehicle. No accelerator grids are necessary, as with other systems, and the plasma is overall electron-rich and therefore electrically neutral, which means there are no spacecraft charging problems. The ND-50 model (see Fig.22) is designed for CubeSats and SmallSats. It interfaces with the spacecraft via CAN or RS422, has a supply voltage of 28V, has a power rating of 50W, a pulse rate of 0.42Hz, a specific impulse of 1800–2000s, an Fig.22: the ND-50 Neumann Drive for spacecraft maneuvering. Fig.23: the Point Blank loitering drone by IAI. The BQM-177i is designed to emulate an anti-ship cruise missile and can sea-skim at an altitude of 3.1m at Mach 0.95. Its specifications are: • Length: 5.2m • Wingspan: 2.1m • Dry weight: 281kg • Engine thrust: 453kg • Maximum internal payload: 45kg • Maximum wingtip payload: 78kg • Fuel capacity: 238.5L • Oil capacity: 8L (for making smoke) Macquarie University SkyLift Drone Macquarie University received an Airshow award for their SkyLift Drone, which is designed for parcel delivery in multi-story residences, directly to a recipient’s balcony. We would like to provide more information on this drone project, but there was no reference to it on their website at the time of writing (www. mqdronelab.com). Melbourne Space Program ACRUX-2 Rideshare siliconchip.com.au Australia's electronics magazine Phoenix Jet The Phoenix Jet (Fig.21) is a target drone manufactured by Air Affairs Australia (https://www.airaffairs. com.au/products/phoenix-jet-uav/) for use by the armed forces. Its specifications are: • Top speed: 330+ knots (600+km/h) • Endurance: 1 hour • Range: 100km range • Minimum altitude: 15m • Maximum altitude: 6000m • Maximum launch weight: 66kg • Payload: 3.5kg • Engine thrust: 40kg • Wingspan: 2.2m • Length 2.4m • Launched by: catapult • Recovered by: parachute Point Blank VTOL Precision Strike Missile Point Blank (Fig.23) by IAI is a hand-launched VTOL loitering drone that has the ability to hover above an area of interest and observe. The operator can decide to either engage a target or return to base. It weighs 10kg and is about a metre long. Praxis Aerospace Praxis Aerospace (https://www. praxisaerospace.com.au), based in June 2025  25 Fig.25: a Robinson CubeSat PCB assembly. Fig.24: Pyxis in flight, its nose cone assembly and internal electronics. Brisbane, won an Airshow award for its Sparrowhawk swarming UAS crop sprayer. Pyxis Pyxis received an Airshow award for a small thrust vectoring rocket (see Fig.24). Their objective is to “... develop a low cost and scalable guidance and control package for Australian Defence and space”. It has a wide variety of suggested uses. RAAF MQ-28A Ghost Bat The Ghost Bat (Fig.29) is an unmanned Collaborative Combat Aircraft (CCA) being developed by Boeing Defence Australia and the RAAF. It will perform a range of missions traditionally performed by fighter aircraft, as well as assisting with operations of crewed fighter aircraft. It is the first Australian-designed combat aircraft to be produced in 50 years. Its maximum operating range is 3700km. RAAF Transportable Land Terminal system and HCLOS The RAAF and other parts of the Australian military use several satellite ground stations for communications: the Panther (0.6m dish), Hawkeye III Lite (1.2m dish) and Hawkeye III (two 2.4m dishes) – see Fig.30. They can use the X, Ka and Ku bands. The RAAF also uses the Panther II Very Small Aperture Terminal (VSAT) portable satellite ground stations built by L3Harris (www.l3harris.com) – see Fig.31. These are used with Ka-band transceivers built by EM Solutions (www.emsolutions.com.au), based in Tennyson, Qld and now owned by UK company Cohort PLC. The Panther and Hawkeye terminals communicate with the Wideband Global SATCOM system (WGS), a high-capacity United States Space Force satellite communications system that is also accessible by the Australian military because Australia funded one of its satellites, WGS6. The militaries of Canada, Denmark, the Netherlands, Luxembourg and New Zealand also have access, as they funded WGS-9 as well. There is also the RAAF High Capacity Line of Sight (HCLOS), which can provide communications up to 80km with a bandwidth of 5MHz, 10MHz, 20MHz or 40MHz at 4.4–5.875GHz with a power between 0.5W and 5W (see the centre of Fig.30). Rafael Rafael (www.rafael.co.il) had several products on display. One of particular interest was an active ‘hard kill’ system to destroy hostile drones. Systems that disrupt radio data links and GPS to bring down a drone are ineffective against fully autonomous drones using inertial or optical terrain-­ following navigation. Fig.29: the Boeing Ghost Bat uncrewed jet fighter with one of Australia's 12 EA-18G electronic warfare aircraft behind it. 26 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.26: setting up a Robinson CubeSat. Fig.27: a Rafael Typhoon 30 remote weapons station (on the left) in a recent test to destroy hostile drones. The sensors on top of the tower help to guide it. Source: Rafael. However, Rafael’s Typhoon 30 RWS (Remote Weapon Station), shown in Fig.27, can be configured to shoot down hostile drones. Australia and several other countries use this system. For more details, see the video at https://youtu.be/IZf0HLwTym0 RedTail Australian company RedTail Technology (www.redtailtech.com.au) have developed a counter-drone technology called “The Katoomba”, based on a high-power laser beam capable of delivering sufficient damage to a hostile drone to disable it (see Fig.28). Its beam is directed with the aid of AI to ensure no invalid targets are engaged, and there is a high probability of a hit. It can be mounted on various platforms and is mainly for use against inexpensive commercial (hobby) drones, otherwise classified as Group 1 according to the US Department of Defense classification scheme. Robinson Aerospace Systems an Adelaide-based company that makes educational CubeSat kits called RASCubes for schools, universities and companies to build these tiny 10 × 10 × 10cm satellites – see Figs.25 & 26. Students from across the world are also designing and building payloads that will be part of Project Space Call and go into Robinson’s RASCube-1, which will be launched into space; see siliconchip.au/link/ac5r for more details. Shield AI V-BAT The Shield AI (https://shield.ai/) V-BAT is a combustion engine powered drone that can take off and lands vertically but the rest of the time, it Fig.28: two views of The Katoomba anti-drone laser system. Source: www.redtailtech.com.au Fig.31: an RAAF Panther satellite ground station. Robinson Aerospace Systems (www.robinson-aerospace.com) is Fig.30: the Hawkeye III Lite communications dish (left) with a Hawkeye III (right). The HCLOS mast is in the centre. siliconchip.com.au Australia's electronics magazine June 2025  27 Fig.33: a Stralis fuel cell assembly. Source: siliconchip.au/link/ac5u Fig.32: a group of V-BATs operating in a swarming (they call it a “Teams” configuration). Source: https://siliconchip.au/link/ac5t flies horizontally (see Fig.32). It has a mission duration of 13+ hours, using a ducted fan for propulsion. It can also hover by transitioning from horizontal flight. It can fly autonomously in environments where communications are subject to electronic warfare. It optionally has AI pilot software called Hivemind, which allows drone-swarming or what they call “Teams”. This is powered by an Nvidia GPU loaded into V-BAT’s modular payload bay. It is 2.7m long, with a 3.0m wingspan, has a gross weight of 57kg, a maximum speed of 90km/h, a service ceiling of 6100m and a payload capacity of 18kg. It has infrared cameras for surveillance; many other payloads are available, including for satellite communication. SiNAB SiNAB (www.sinab.com) is based in Taren Point, NSW. One of their products is the Phoenix Pod, for long range day and night surveillance and live air-to-ground comms (Fig.35). It has several applications in military, training and civil purposes such as bushfire spotting, mapping, border protection and disaster management. It can operate independently of aircraft systems, and just needs to be attached to an aircraft stores pylon. Stralis hydrogen-powered generator Stralis (www.stralis.aero) received an Airshow award for the development of their next-generation high-temperature proton exchange membrane (HTPEM) fuel cell to power electric aircraft instead of batteries (see Fig.33). By running the fuel cell at a high temperature, it is six times lighter than the current state-of-theart. They state that their hydrogenelectric aircraft will travel ten times further than battery-electric alternatives, and will be 50% cheaper to operate than fossil fuel-powered aircraft. The fuel cell can be used in new clean sheet design, to replace batteries in existing electric aircraft, or to retro­ fit an aircraft powered by an internal combustion engine with electric propulsion. Stratoship Australia Fig.34: Swinburne’s hydrogenpowered VTOL SHADE drone. 28 Silicon Chip Stratoship (https://stratoship.au/), based in Brisbane, is developing a high-altitude solar-powered aerial platform called Stratoship (see Fig.36). It is intended to be stationed at 20km altitude for various purposes such as agriculture, bushfire spotting, Australia's electronics magazine communications relay, defence, security, natural disaster management, observation of transportation and infrastructure, research and others. 20km high is above most clouds and jetstreams (9–15km), with relatively low wind speeds, and around 10km above commercial air traffic. The coverage area is huge; an aircraft at that altitude can see in a radius of about 500km. Stratoship is designed to provide persistent surveillance for periods from weeks to months. For more on this concept, see our article on “High-Altitude Aerial Platforms” in the August 2023 issue (siliconchip. au/Article/15894). Swinburne hydrogen UAS Swinburne University of Technology has introduced hydrogen fuel cell technology into two different UASs (uncrewed aerial systems), in a project known as H22S (Hydrogen to the Skies) – see Fig.34 and siliconchip. au/link/ac5s Tests showed comparable or enhanced performance compared to an electric or internal combustion engine UAS with a comparable takeoff weight and payload capacity. One vehicle had a payload capacity of 2kg, stored hydrogen in a 10L tank at 350bar of pressure, had an 8kW motor with hydrogen fuel cells producing 3kW continuous power or 5kW peak, and had supplementary lithium batteries. UNSW (Canberra) Cybersecurity The University of NSW (Canberra) received an Airshow award for a proposal to enhance Air Force communications security through lattice-based cryptographic protocols that are siliconchip.com.au resistant to decryption by quantum computers. Fig.35: the SiNAB Phoenix Pod provides long-range day/night surveillance and air-to-ground comms. VeloDX VeloDX (https://velodx.com/) has developed an integrated AI “system of systems” that supports all elements of all drone operations, both on the ground and in the air. Their drones are the HOLI (extended range loitering munition), POD (AI avionics suite for on-drone operations) and CASTLE (the human-machine interface). Vertiia long range hybrid VTOL Vertiia (www.amslaero.com) is an Australian long-range hydrogen-electric VTOL aircraft with a 1000km range, 300km/h top speed and triple redundancy (see Fig.37). It can carry a 500kg payload, refuel in ten minutes, is quiet (with a 65–70dBA noise level) and has 70% lower operating costs than a helicopter. Apart from hydrogen, it can also run on SAF (aviation biofuel), diesel or jet fuel. It can be configured for medical transport, cargo or passenger use. On the 18th of November 2024, Vertiia completed its first free flight by remote control and on battery power at Wellington, NSW. It’s said to be the most complex civil aircraft ever developed in Australia. They have received orders for 26 aircraft. Hydrogen testing begins this year. Fig.36: a Stratoship test-inflated with helium. Fig.37: Vertiia’s hybrid VTOL aircraft. Source: https://www. amslaero.com/our-product Wisk Wisk (https://wisk.aero/) now a subsidiary of Boeing, is developing what they say is the world’s first all-electric VTOL autonomous four-passenger air taxi (see Fig.38). Apart from cost savings by not having a pilot, they say most aircraft accidents are caused by pilot errors, so by removing the pilot, they expect to enhance safety. While the vehicle is autonomous, there is human oversight over operations at a flight operations centre, where a person will oversee the flight of numerous vehicles. They are currently working to obtain US FAA approval for this aircraft. Its specifications are: • Wingspan: 15m • Range (with reserves): 144km • Speed: 110–120 knots (200–220km/h) • Charging time: 15 minutes Forward thrust is produced by tilting one set of propellers. SC siliconchip.com.au Fig.38: a rendering of the Wisk air taxi. Australia's electronics magazine June 2025  29 Subscribe to MAY 2025 ISSN 1030-2662 05 9 771030 266001 $13 00* NZ $13 90 INC GST INC GST 60 RGB LEDs that light different colours for the hour, minute and second Optional ‘subsecond’ hand chaser GPS module or NTP time via the internet using WiFi RGB LED ANALOG CLOCK Vers rsatile Australia’s top electronics magazine Silicon Chip is one of the best DIY electronics magazines in the world. Each month is filled with a variety of projects that you can build yourself, along with features on a wide range of topics from in-depth electronics articles to general tech overviews. RNBD451 Bluetooth Module Battery Checker Published in Silicon Chip If you have an active subscription you receive 10% OFF orders from our Online Shop (siliconchip.com.au/Shop/)* Rest of World New Zealand Australia * does not include the cost of postage Length Print Combined Online 6 months $70 $80 $52.50 1 year $130 $150 $100 2 years $245 $280 $190 6 months $82.50 $92.50 1 year $155 $175 2 years $290 $325 6 months $100 $110 1 year $195 $215 All prices are in Australian dollars (AUD). Combined subscriptions include both the printed magazine and online access. 2 years $380 $415 RGB LED ‘Analog’ Clock; May 2025 Versatile Battery Checker; May 2025 Prices are valid for the month of issue. Try our Online Subscription – now with PDF downloads! Pico/2/Computer; April 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 30 Silicon Chip Australia's electronics magazine siliconchip.com.au Winter altronics.com.au WORKSHOP K 8600A 369 SALE. $ BONUS! 1kg roll of black filament valued at $39.95 (K8397A) Sale prices valid until June 30th. Creality® Ender 3 V3 SE 3D Printer The Ender 3 is a compact 3D printer offering excellent print quality with a build volume of 22Wx22Dx25Hcm and is compatible with ABS, PLA and TPU filaments. Supplied mostly assembled and can be up and running within an hour. BONUS! 129 $ T 1345 Folding Auto Ranging Multimeter HOT SELLER! Ultra High Speed Mini Jet Blower Vac This high power rechargeable fan/ vacuum is great for servicing computer equipment, cleaning keyboards - even inflating air mattresses for camping. T1346 FREE vacuum accessory valued at $14.95 High speed jet fan with up to 1.5 hours use per charge. USB C rechargeable. All metal design. If you use a few cans of air duster a year, it pays for itself in no time! NEW! 99 $ Offers advanced functionality for technicians. Its folding design stays firmly in place during testing, ideal for auto electrical work. With features like dwell angle, RPM engine speed, and duty cycle, it’s also perfect for automotive servicing. Packed with features! Q 1058 8 Outlet Surge Board & 4 Way USB Charger D 0507E 10000mAh SAVE 17% 29 $ SAVE 18% 49 $ Provides connection for all your appliances with 60,000A surge protection and 4 way USB charger (max total 3.1A output. 2.1 single port). 1.5m cable. D0511C 20000mAH P 8159 Stylish new battery banks. $ SAVE 20% With QC3.0 charging and 18W PD. A great way to keep devices charged on your travels. 40 Workshop essenrtial! T 2486 T 2192 SAVE 15% SAVE $10 38 39 $ $ 60 Pc Home Tool Kit Super Hot Blow Torch A combined driver bit and socket set with 47 bits and 9 metric sockets. Includes a handy magnetic case. A 1300°C blow torch with adjustable gas feed for a variety of tasks such as brazing and model making. Refill with T2451 butane gas $9.50. Your electronics supplier since 1976. 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 Sale ends June 30th 2025. Build It Yourself Electronics Centre® Save on Testing. Amazing value under $100 Water & dust proof! Q 1073A Q 1088 SAVE $50 SAVE $10 119 $ All-Weather True RMS Multimeter Top of the range - great features and price! Ideal for marine/mining techs. • True RMS • 40MHz freq. counter with bar graph • Max/min recording • Capacitance to 40mF. • Temp with thermocouple. 255 $ Q 2112 Identifies inductors, capacitors and resistors. Can also display parameters as a complex impedance, admittance or magnitude and impedance phase. 2 year warranty. Made in the UK. 70 $ Top Spec True RMS DMM SAVE $40 339 $ Peak® DCA Pro Component Analyser Q 2115 A detailed component analyser for connection to your PC. Ideal accessory for designers & technicians. 2 year warranty. Made in the UK. Extended resolution to 4 digits! Offers everything the serious enthusiast could need with auto ranging, min/max/rel modes, frequency, duty cycle and non contact voltage detection. SAVE $40 229 $ Peak® Atlas ESR+ Capacitor Analyser Q 2105 Measuring a capacitor’s ESR is a great indicator of condition. Just connect the probes and press test - no need to worry about polarity - for instant results! 2 year warranty. Made in the UK. SAVE 15% SAVE $30 149 $ Peak® DCA55 Component Analyser Q 2100 This easy to use, component analyser is like having a library of electronic info at your fingertips! Saves hours of looking up specs. 2 year warranty. Made in the UK. 50% OFF! 27 $ True RMS 19999 Count DMM Our first multimeter with wireless USB charging in-built! Includes top spec features such as illuminated sockets, LED torch, desk stand, True RMS, non contact voltage detection, frequency meter and relative mode. SAVE $30 Peak® LCR & Impedance Analyser SAVE $19 89 $ Extended resolution 19999 count Q 1135 .50 Q 1278B D 3002 SAVE 22% SAVE 24% HALF PRICE! Q 3004 30 $ 14.95 $ 10 $ 12V Car Alternator Tester Provides quick and easy way to test alternator/charging system function in 12V vehicles. Measure temps instantly! PoE Port Pocket Tester Folding waterproof spike temperature probe with bottle opener. -50°C to 300°C. Includes battery. Checks status of data and power over ethernet connection. Includes lead for testing socket points. SCAN TO FOLLOW US! Stay up to date on latest releases, exclusive specials and news on our socials. X 6015 OBDII Blueooth Interface Connect your car via Bluetooth to your phone to provide a wealth of diagnostic info. Works with a number of OBDII compatible apps. Like our service? Review your store on Google. Every review helps us serve you better. Soldering & More. SAVE $100 Top buy for students & makers! M 8200A 319 $ A handy benchtop cleaner! SAVE $30 109 SAVE $15 50 $ $ Low Noise Linear Lab Power Supply Fully adjustable with LCD meters for precision adjustments. Great for R&D and workshops. • Precision linear toroidal design • Fixed 12V & 5V output rails • Fully regulated • Short circuit & overload protection. X 0103A Blast away grime on jewellery, glasses and small parts! This 60W ultrasonic cleaner uses water and household detergent, coupled with ultrasonic waves to clean jewellery, small parts, DVDs etc, without damage - no solvents required. 180x80x60mm tank. The perfect balance of value for money and features for beginners or cash strapped students and enthusiasts. Slim, lightweight handle with tip cleaning sponge and iron safety holder. Full range of spare tips also available. 15 T 2356 Great for handheld soldering irons. SAVE 20% *Solder not included. $ $ T 1246A 18 Rotating PCB Holder SAVE 20% 23 Bargain 40W Soldering Station SAVE 20% Soldering Iron Stand $ T 2090 Work on boards up to 200 x 140mm. Metal base provides a sturdy work platform. T 1306 T 4015A 29 $ A 35x26cm heat resistant silicon mat, plus a 25x20cm magnetic mat to keep screws organised. The workbench classic! Quickly removes molten solder from joins. Heavy weight base with solder guide. All metal construction. *Solder not included. SAVE 23% 19 $ T 1528A 39 $ Wire Stripper & Kwik Crimper The ultimate work lamp for your electronics work bench. Combines a ratchet wire stripper, cutting blade & kwik crimper. Suits 10-24 AWG cable. This month T 4018 Magnetic Bowl 12 $ A handy 4” stainless steel bowl with magnetic base to keep screws from straying. Quality corrosion resistant stainless steel finish. SAVE 18% 22 $ T 2754A SAVE $20 X 4201 5 Dioptre No more eye strain! Ultra-bright long life LED for fantastic clarity. Why pay $400 or more for a Maggy-Lamp? Let “gadget” be your eyes. Identify those impossible to read miniature parts without straining your eyes. Great for collectors, model makers, jewellers etc. NO STRESS 30 DAY RETURNS! GOT A QUESTION? Not satisfied or not suitable? No worries! Return it in original condition within 30 days and get a refund. Ask us! Email us any time at: customerservice<at>altronics.com.au Conditions apply - see website. 109 $ Precision Nippers SAVE 24% T 1302A SAVE 20% SAVE 22% Never lose a tiny screw again! Anti Static Solder Sucker Dual Solder Reel Holder Audio Savers. SAVE $100 399 $ Amazing sound for less! C 0870A 2 x 100W FM Bluetooth Receiver Amp SAVE $136 Wi-Fi Internet Radio System with DAB+, FM & Bluetooth. A stylish, easy to use receiver with access to over 26,000 global internet stations, plus DAB+ digital radio, FM frequencies and bluetooth streaming from your devices. Digital S/PDIF and analogue RCA outputs. $ Internet radio, digital radio & wi-fi streaming in one. SAVE $50 A stylish, easy to use receiver with access to over 26,000 global internet stations, plus DAB+ digital radio, FM frequencies and bluetooth streaming from your devices. Digital S/PDIF and analogue RCA outputs. HALF PRICE! 199 $ 539 Magnetic ‘edge to edge’ grille. A 2691B Opus One® 2x30W Wi-Fi Ceiling Speakers These high performance speakers offer wireless music streaming by connecting to your home wi-fi for Apple Airplay/casting from any device. Plus you can install multiple pairs to create multi-zone audio system. 209mmØ ceiling cutout. 105mm depth. 339 $ Powerful & compact! A 2696A SAVE $60 339 $ SAVE 13% 69 $ C 5205 Boomin’ 200W RMS 10” Cinema Subwoofer! A 3104 A 3833 In-Desk Connection Hub A all-metal body desk / workbench connection panel for HDMI, mini USB C, DisplayPort, VGA and ethernet inputs. 157 x 54mm cutout. 4K <at> 60Hz ready. 8K 2 Way HDMI Switcher Offering 8K <at> 60Hz resolution this HDMI selector is ready for the latest high res AV sources. This stunning active home cinema subwoofer adds plenty of bass to any home theatre or hi-fi system. The 200W amp accepts speaker or a line level input. Features auto power on, level control, crossover adjustment, and phase reversal switch. Size: 442 x 246 x 410mm. Easy to set up anywhere! SAVE $40 Transmits & receives! 199 $ A 4201 A 3615 SAVE $40 149 $ SAVE 18% A 1103B 49 $ Send TV sound to headphones Thousands sold! Transmits or receives audio via Bluetooth. aptX low latency no lip sync issues! Can be used at home or in the car. Mini Wi-Fi LED Projector Bluetooth® 2x50W Amplifier A handy mini amplifier with Bluetooth for connection to your favourite speakers! 3.5mm and RCA inputs. Class D design. Internal headphone amplifier. Great for movie nights with friends and family! This compact projector offers excellent LED picture quality with 800x480p resolution for screens up to 4m (170”) wide! Very simple to set up with adjustable focus & projection distance (1-5m). HDMI input or Wi-Fi screen mirroring for playback directly from your device. Sale Ends June 30th 2025 Shop in-store at one of our 11 locations around Australia: WA » PERTH » JOONDALUP » CANNINGTON » MIDLAND » MYAREE » BALCATTA VIC » SPRINGVALE » AIRPORT WEST QLD » VIRGINIA NSW » AUBURN SA » PROSPECT Or find a local reseller at: altronics.com.au/storelocations/dealers/ Shop online 24/7 <at> altronics.com.au © Altronics 2025. E&OE. Prices stated herein are only valid until date shown or until stocks run out. Prices include GST and exclude freight and insurance. See latest catalogue for freight rates. B 0006 Hot Water System Solar Diverter Part 1 by Ray Berkelmans & John Clarke Solar-optimised hot water system (HWS) heating using power purely from excess solar generation Solar export data is obtained from the inverter and updated every five seconds Shows operational parameters on a 2.4-inch OLED screen WiFi logging of operational parameters to a ThingSpeak database every five minutes Automatic override if the HWS temperature is still cold by the end of the solar day Night-time power-down Active heatsink cooling Email alert (one per day) if communication with the inverter is lost Over-the-air program updates via WiFi Manual override switch You can save a lot of money with this device! It lets you use excess solar power generation to power your electric water heater. It’s a lot less expensive to put together than an equivalent commercial unit. siliconchip.com.au Australia's electronics magazine Background Image: unsplash.com/photos/sunset-view-5YWf-5hyZcw June 2025  35 S olar hot water diverters enable you to use surplus electricity generated by your solar photovoltaic system to heat water. Commercial versions have been around for decades, although they are pretty rare to find. The main reason is price; brand-name diverters often cost upwards of $900, with some (eg, Fronius) close to double that! At that price, it is hard to justify the up-front cost in terms of the savings. Thankfully, this Solar Diverter can be built for a fraction of that price! In this era of ever-diminishing solar feed-in tariffs, it makes sense to maximise consumption of your own solar power. The reality is that often, when you have plenty of solar energy to export, the grid does not need it! As of February 2023, all new solar installations in Queensland above 10kVA require a Generation Signalling Device (GSD) to be fitted so that electricity distributors can remotely curtail your solar feed-in when required. Even without this, residential supply voltages can often exceed 250V AC on sunny days, causing most inverters to shut down. Other states are considering similar so-called ‘backstop’ mechanisms. A simple timer to divert power to a load during peak solar times is a good start to optimising the usage of the available solar power. However, excess solar power is a highly variable thing with passing, or persistent, clouds decreasing solar output by an order of magnitude or more. If you have a conventional hot water system with an electric element, this project will help you make the most of your solar generation on those challenging solar days (see Fig.1). If you have splashed out on a fancy whole-of-home battery system, this project will be especially useful, because it will prevent your HWS from sucking your battery dry during the night and during poor solar conditions! How it works Our solar diverter consists of an ESP8266 WiFi-enabled microprocessor that connects to your solar inverter and reads the solar export data directly from it. If more than 0.5kW of power is being exported, the microprocessor produces a pulse-width-modulated (PWM) signal with the duty cycle being a percentage of the available export power to the maximum power demand of the HWS element. We have an Aquamax 250L HWS system fitted with a 3.6kW electric heating element. So, for example, if 1kW of solar export power is available, the duty cycle is set to 14% ([1kW – 0.5kW] ÷ 3.6kW). The duty cycle increments and decrements in steps of 2% from 0 to 100% with each program cycle, providing hysteresis during highly variable conditions. The PWM signal passes to a zero-crossing detection (ZCD) opto-coupler. This converts the PWM signal to a timing suitable for switching a Triac with the AC mains waveform. A Triac typically needs to be switched in synchrony with the sinusoidal(ish) mains waveform, switching it on near the zero voltage point (zero crossing), either from positive to negative or vice versa. To do otherwise would cause unacceptably high peak currents and excessive electromagnetic interference (EMI). Before zero-crossing detection opto-couplers came along, the timing of power switching is something that had to be handled in software, with voltage monitoring and interrupts or with much more involved hardware setups. With the ZCD opto-coupler, we are spared from such complexity! Obtaining solar export data The solar export data is extracted from your solar inverter by reading the relevant register over WiFi using the Modbus communication protocol. Before setting off to build this project, you will need to establish if your inverter supports Modbus and, if so, which register(s) contain(s) the solar export data needed. The finished and wired Hot Water System (HWS) Solar Diverter. Note the two visible acrylic covers (green and clear acrylic), which are placed to prevent contact with high-voltage components. 36 Silicon Chip Australia's electronics magazine siliconchip.com.au Fortunately, most modern inverter manufacturers have subscribed to the SunSpec Alliance, which sets open information standards for the Distributed Energy Resource industry. You can see if your inverter manufacturer is part of the alliance by checking the membership at https://sunspec.org/ members/ Even if you don’t see your inverter manufacturer listed, not all hope is lost. For example, my manufacturer, SolarEdge, is not listed, yet they still comply to the SunSpec Modbus standard and provide a very detailed Application Note (siliconchip.au/link/ ac4z) to guide users through the hundreds of registers. You will need to do some research to find out which register addresses are used by your inverter. Be aware that some models don’t have Modbus enabled by default. Check your inverter instructions and/or with your solar installer. To test whether your inverter is compliant, and to explore its data registers, you can download a Modbus simulation tool such as Modbus Poll (www.modbustools.com), which has a free 30-day trial. Under the “Connection” tab, you simply enter the LAN IP address for your inverter (check your network client list in your router), together with your server port. Most inverters use a default port of 502, but SolarEdge uses 1502. Under “Setup → Read/Write Definitions”, select the slave ID (the default is 1) and enter a start register address like 40001. After hitting OK, Modbus Poll will then display the content of the next ten registers. Until recently, my inverter was a three-phase Solar Edge SE-10K model. Since our house and HWS are connected to phase C, the most relevant register is 40209: “Phase C AC Real Power”. Readings are displayed in watts (int16) with solar export shown as positive values and grid import as negative values. During development of this project, we upgraded our solar system to a Sigenergy 5-in-1 battery with an integrated 25kW, 3-phase inverter. It stores its export data as 32-bit integer (int32) values, which are spread across two registers. For us, they are 30056 & 30057. Its export values are the opposite of the SolarEdge’s: negative for export and positive for import. The SigEnergy siliconchip.com.au Fig.1: this shows why having a HWS Solar Diverter may be required to make the most of your solar power during highly variable solar conditions. Modbus protocol can be found at siliconchip.au/link/ac50 WiFi It is worth ensuring you have an adequate WiFi signal at the point where you intend to mount the Solar Diverter. There are many free smartphone apps that will show your WiFi signal strength. You will need at least -70dB for a reliable WiFi connection. Otherwise, you may need to invest in a WiFi range extender. HWS element The other check you should make before launching into construction is to ensure that your HWS has a resistive heating element and is not a heatpump or another type of HWS. If it has an element, its specification will be written on the compliance plate, possibly near the base of the HWS. A rating of 3600W or less will confirm that this design is suitable for your HWS. Circuit details The full circuit is shown in Fig.2. MOD2 is the microprocessor module that communicates with the inverter and generates the PWM signal from its GPIO14 pin. That is fed to OPTO1, a MOC3083 zero-crossing opto-coupler Australia's electronics magazine Triac driver. This features a low 5mA trigger current (IFT) and high isolation, with a rated peak blocking voltage of 800V between the line and control circuitry. Current flowing through OPTO1’s internal LED generates an infrared signal that triggers the monolithic silicon detector, then its internal Triac and finally the external Triac to switch the HWS load. The 360W resistor on pin 1 of OPTO1 was chosen to supply the necessary current to trigger the LED. This is calculated as (3.3V – 1.5V) ÷ 5mA, where 3.3V is the supply voltage, 1.5V is the LED forward voltage and 5mA is the trigger current. When a sufficient LED current (IFT) is supplied and the AC line voltage approaches the zero point, the Triac driver latches on. This introduces a gate current in the main Triac, triggering it from the blocking state into full conduction. The main Triac here is a BTA41800B, capable of handling up to 40A RMS; more than ample for our ~15A RMS heating element load. We recommend fitting the 360W resistor at pin 6 of OPTO1, as it prevents the Triac driver from being damaged in applications where the load is inductive. It helps to limit the gate trigger current (Igt) if there is a transient June 2025  37 Fig.2: the HWS Solar Diverter circuit is based around MOD2, an ESP8266 microcontroller with WiFi. IC1-IC3 provide a way to monitor the current drawn by the HWS while OPTO1 and TRIAC1 provide PWM control of the HWS element, so its power draw can be modulated. in the mains waveform while the Triac driver was off. The 330W (1W) Triac gate resistor provides better noise and thermal immunity when the internal gate impedance of the Triac is high, which is the case for sensitive-gate Triacs. These resistors are 1W types mainly for their voltage rating. An externally mounted 20A 250V override switch (S2) allows you to bypass all electronic control circuitry, if required, and force the HWS element on. 38 Silicon Chip Current monitoring While current sensing isn’t an essential part of the circuit, it provides a helpful insight into how well the circuit is working. The main current-sensing element is an ACS770LCB-050B 50A bidirectional current sensor (IC1). A TLC2272 dual operational amplifier (IC2) buffers the output of the current sensor, feeding an ADS1115 16-bit analog-­todigital converter (ADC), IC3. So IC1 converts the load current into a voltage which is buffered by Australia's electronics magazine IC2, then converted to a digital value by IC3 and passed to the microcontroller. The ADS1115 is the fastest available ADC that communicates using an I2C serial bus, with a sampling rate of up to 860 samples per second. This is about the minimum acceptable for accurately sampling the AC current waveform. Since each complete AC sinewave lasts 20ms, this provides us with a bit over 16 samples per full wave. When measured over 100 cycles (two seconds), that gives us a fair estimate siliconchip.com.au Fig.3: the PCB is populated with a mixture of SMD and through-hole components. Note the three acrylic covers over OPTO1, IC1 and the mains terminals that prevent accidental contact with high-voltage parts. During assembly, be careful to fit OPTO1, IC2 and IC3 with the correct orientations; other parts are polarised, but their correct orientations should be obvious. between IC3 and MOD2. This is performed by general-­ purpose N-channel Mosfets Q2 & Q3, plus a few 10kW pull-up resistors. They reduce the voltage levels of the SCL and SDA lines from 5V at IC2 to 3.3V at MOD2 & MOD3, while still allowing bi-directional communication. Two temperature sensors (DS18B20s) connect via CON5 and CON6 for monitoring the HWS and heatsink temperatures. CON2 provides a connection for a light-dependent resistor (LDR), which allows our circuit to go into sleep mode when the sun goes down. Momentary switch S1 and associated 47kW resistors and a 100nF capacitor form the reset circuitry of the ESP8266. The CON10 header and jumper JP1 provide a means for programming the microcontroller on the ESP8266 module. Power supply of the current flow. ADCs that communicate using an SPI serial bus can sample faster, but require a few extra pins on the microprocessor, which we don’t have. Since we already have another I2C device in our circuit, the 2.4-inch, 128 × 64 pixel monochrome OLED siliconchip.com.au screen, communication with both devices required just two of MOD2’s pins (GPIO4 & GPIO5). The current sensing components operate at 5V to give sufficient resolution, while the microcontroller is strictly a 3.3V-tolerant device, so we need some digital level shifting Australia's electronics magazine DC power for the circuit is derived from a PCB-mounted 230V AC to 5V DC power supply (MOD1), which has a 250mA fuse (F1) in case of a fault. The 5V rail powers the heatsink fan (FAN1, connected via CON4) and the components involved in sensing the current drawn by the HWS element. CON3 provides a handy way of powering the circuit with a 5V DC power supply, or a 3.7V (nominal) Li-ion/ LiPo battery, so programming and testing can be done without having to connect AC mains power. June 2025  39 The 3.3V rail is derived from the 5V DC bus via low-dropout linear regulator REG1 (AP7365). Other LDO regulators in the same SOT-23-5 package would be equally suitable (eg, ME6211, MCP1802T or TPS7A2033), provided they can supply at least 250mA and have a compatible pinout. Construction The first step is to create the PCB assembly, which can then be mounted in a plastic box and wired up. The Solar Diverter is built on a double-­ sided, plated-through PCB with a red solder mask that’s coded 18110241 and measures 134 × 207.5mm. It is installed within an enclosure measuring 222 × 146 × 55mm. The locations of components on the PCB are shown in Fig.3. Many (but not all) of the components used are surface-mount types that can be soldered by hand using a fine-tipped soldering iron. Starting from the smallest component and working up to the largest, solder one end first (for capacitors and resistors) or one lead first (for the ICs and MOD2). Make sure the component is lined up with the other pad or pads; if necessary, remelt the initial solder joint and gently realign the part before soldering the remaining pins. If any solder bridges form between IC leads, they can be cleared using solder wick. Adding a small amount of flux paste from a syringe will make both soldering and clearing bridges easier. For MOD2, apply solder over the outside edges of the pads on this module to join them to the PCB pads, treating it like the large surface-mounting part that it is. For the through-hole parts, such as the 1W resistors, switch S1, OPTO1 and IC1, insert the leads through the associated PCB holes and solder them on the underside of the PCB. All polarised parts, including OPTO1, IC2 and IC3, must be orientated as shown in Fig.3 for the circuit to work. IC1 has large, high-current leads that must be soldered on both the top and bottom sides of the PCB to ensure low-resistance connections. The three 45A two-way barrier terminal connectors (CON7, CON8 & CON9) require sufficient solder and heat for the solder to flow over the full underside pad and to the connector terminals to provide low-resistance connections. 40 Silicon Chip Parts List – Hot Water System Solar Diverter 1 double-sided plated-through PCB coded 18110241, 134 × 207.5mm 1 ABS enclosure, 222 × 146 × 55mm [Jaycar HB6130 (ABS) or HB6220 (Polycarbonate)] 1 100 × 110 × 33mm heatsink cut to 100 × 70 × 33mm [Altronics H0563 with half the fins cut off (see text)] 1 40mm 5V fan (FAN1) [Altronics F1110 or DigiKey 102-4361-ND] 1 M205 fuse holder with cover (F1) [Altronics S5985] 1 M205 250mA fast-blow fuse (F1) 1 Light-dependent resistor (LDR1) [Jaycar RD3480, Altronics Z1619] 1 SPST pushbutton two-pin switch (S1) [Jaycar SP0611, Altronics S1127] 1 20A 240V AC IP66 weatherproof switch (S2) [Bunnings I/N 4430626] 1 3-6.5mm cable gland, for LDR and TS2 wiring 1 OLED display bezel (see text and Fig.5 next month) Connectors 1 4-pin JST XH header with 2.54mm spacing plus matching plug (CON1) * 3 2-pin JST PH headers with 2mm spacing plus matching plugs (CON2-CON4) * 2 3-pin JST XH headers with 2.54mm spacing plus matching plugs (CON5, CON6) * 3 45A 600V 2-pin barrier connector strips, 0.5-inch/12.7mm pitch (CON7-9) [DigiKey YK7010223000G-ND] 1 3-way polarised pin header with 2.54mm pin spacing (CON10) 1 2-way pin header with 2.54mm pin spacing (JP1) 1 jumper shunt (JP1) * all available in the Jaycar PT4457 JST Connectors Kit Hardware 1 3mm-thick sheet of clear acrylic, 340 × 307mm (for weather shield) 1 acrylic or fibreglass piece, 106 × 79.5 × 3mm (see Fig.5 next month) 1 acrylic or fibreglass piece, 32.5 × 15 × 1.5mm (see Fig.5 next month) 1 acrylic or fibreglass piece, 26 × 33 × 1.5mm (see Fig.5 next month) 1 transistor clamp to secure TS1 to the heatsink [Jaycar HH8610] 2 5.3mm inner diameter crimp eyelets suitable for 2.5mm2 wire 1 M4 × 15mm panhead machine screw 1 M4 × 10-12mm panhead machine screw 4 M3 × 12mm tapped spacers 8 M3 × 6.3mm tapped spacers 2 M3 × 20mm panhead machine screws 2 M3 × 15mm panhead machine screws 6 M3 × 12mm panhead machine screws 2 M3 × 10mm panhead machine screws 13 M3 × 5mm panhead machine screws 2 M4 star washers 6 M3 flat washers 3 M4 hex nuts 10 M3 hex nuts This is what you will typically see displayed on the OLED screen. It is mounted to the lid of the case as shown in the photo opposite. We have glued it onto the case for a flush fit, but you might prefer to use the standoffs to screw it in. Australia's electronics magazine siliconchip.com.au 2 20mm or 25mm corrugated conduit glands [Bunnings I/N 4330875 or 4330876] 1 small tube of thermal paste Cable & conduit 3 lengths of 4-core shielded cable for the DS18B20 temperature sensors and LDR, length to suit installation [Jaycar WB1510, Altronics W3040] 3 lengths of 2.5mm2 round cable or 2.5mm2 flat twin and Earth for S2, mains input and mains output wiring [Bunnings I/N 4430139 or 4430080] lengths of 20mm or 25mm conduit, to suit installation Modules 1 Meanwell IRM-03–5 5V/3W AC-to-DC converter (MOD1) [DigiKey 1866-3020-ND] 1 ESP8266 – ESP-12F programming and development board (MOD2) [AliExpress, eBay] 1 2.42-inch 128×64 I2C OLED display module (MOD3) [AliExpress 1005006267098554 or 1005006267098554] Semiconductors 1 ACS770LCB-050B-PFF-T bidirectional current sensor (IC1) [DigiKey 620-1541-5-ND] 1 TLC2272CD dual op amp (IC2) [DigiKey 296-1305-2-ND] 1 ADS1115DGSx 16-bit ADC (IC3) [DigiKey 296-24934-2-ND] 1 MOC3083M opto-isolated Triac driver (OPTO1) [DigiKey MOC3083M-ND] 2 DS18B20 temperature sensors (TS1, TS2) [DigiKey 4518-DS18B20-ND, Altronics Z7280] 1 AP7365-33WG-7 3.3V linear regulator (REG1) [DigiKey AP7365-33WG-7] 3 BSS138 N-channel Mosfets, SOT-23 (Q1-Q3) [DigiKey 4530-BSS138TR-ND] 1 BTA41-800BQ 800V 40A Triac, TO-3P (TRIAC1) [DigiKey BTA41-800BQ-ND] Capacitors (all SMD M2012/0805-size X7R ceramic) 1 22μF 6.3V 2 10μF 16V 1 1μF 50V 5 100nF 50V Resistors (all SMD M2012/0805-size ⅛W unless noted) 2 47kW 5 10kW 1 6.8kW 1 4.7kW 1 2.2kW 1 360W 1 360W axial 1W [DigiKey 738-RSMF1JT360RCT-ND] 1 330W axial 1W 1 120W MOD1 (the 230V AC to 5V DC converter) and fuse holder F1 can be installed now. With the holder soldered to the board, insert the M205 250mA fuse, then the transparent cover can be clipped over the top. Connectors There are several different types of connectors used on the PCB. These include a 4-pin XH JST plug and socket with 2.54mm spacing for CON1; 2-pin PH JST connectors with 2mm spacing for CON2, CON3 & CON4; and 3-pin XH JST connectors with 2.54mm pin spacings for CON5 & CON6. These are available in the Jaycar JST Connectors Kit (PT4457) or separately from online suppliers. The 3-way pin header with 2.54mm pin spacing for CON10 and the 2-way pin header with 2.54mm pin spacing for JP1 are standard headers available in strips. Heatsink & Triac mounting The Altronics H0563 heatsink is supplied with cooling fins on either side of a central flat area for mounting power transistors in TO-3 packages. For our design, one side of the heatsink with fins will need to be removed so the TO-3P packaged Triac can mount on the central flat area. Cut it off using a hacksaw, leaving a 30mm wide flat section next to the fins (see Fig.3). Use the PCB as a template to mark the six holes required, then remove the heatsink and drill them. Place the heatsink on the PCB and check they all line up. Bend the Triac leads at right angles so it can be mounted tabdown onto the heatsink with the leads inserted into the PCB pads. The Triac tab is electrically isolated from the A1 and A2 leads, so an insulating washer is not required. Apply a thin layer of thermal paste (heatsink compound) between the Triac tab and the heatsink to improve heat transfer. Secure the Triac with an M4 machine screw and nut, then solder the Triac leads to the mounting pads on the PCB. Next month Warning: Mains Voltage This Solar Diverter operates directly from the 230V AC mains supply; contact with any live component is potentially lethal. Do not build it unless you are experienced working with mains voltages. A licenced electrician is also required to install the project. At this stage, we are ready to prepare the case to install the PCB, wire it up and start testing. We’ll have the details on how to do that in the final article next month, with detailed testing instructions, as well as information on the final installation, setup, calibration and use. SC June 2025  41 Altium Designer 25 Review by Tim Blythman Altium Designer 25 is the latest version of the EDA (electronics design automation) software that we use for all of our PCB designs. This new version was released late in 2024, and we have spent some time putting it through its paces. Here is what we have found. W e have used related products for our PCB designs for over 30 years, starting with Protel Autotrax! So we were keen to see what has been updated since our review of Altium Designer 24 from August last year (siliconchip.au/Article/16425). Since that article was written, there is the news that Renesas Electronics has acquired Altium; the acquisition was completed in August 2024. Renesas is a Japanese semiconductor manufacturer that includes the semiconductor operations of companies like Hitachi, Mitsubishi and NEC. That marks an interesting geographical history for Altium, with Protel Systems Pty Ltd originally founded as an Australian company. For many years, it has been headquartered in San Diego, California. We’re most familiar with Renesas Electronics as the manufacturer of the RA4M1 microprocessor used in the new Arduino Uno R4 microcontroller board we reviewed in December 2023 (siliconchip.au/Article/16047). The Raspberry Pi 5 also uses a Renesas power management IC. AD25 overview Altium Designer 25 looks and feels much the same as previous versions, but like many modern applications, it is constantly evolving. This time we are looking at version 25.0.2. The webpage at www.altium.com/ documentation/altium-designer/new lists details of the various version updates and the versions (and subversions) to which they apply. So you can 42 Silicon Chip easily see which version has a particular feature. Some features that are present are disabled by default but can be turned on via the Advanced Settings window of Preferences. Others are available as Extensions, which can be installed from the Extensions and Updates window. Such features may still be at the beta testing stage. Beta testing means that the feature is essentially complete but not fully tested. It may still be changed if users find bugs. It is a good way to get early access to novel features, and there is usually the ability to toggle these features on and off. Just as with previous versions, it is possible to install multiple versions of Altium Designer alongside each other. You might like to do this to try out the features in a new version without committing to it until you are happy with the changes. Amongst other videos, the new features are also presented at the Altium Academy YouTube channel (www. youtube.com/<at>AltiumAcademy). These and other training materials are also available on the Home Page of the Altium Designer application. Performance Altium Designer 25 claims to have much improved performance, especially with large designs. Our designs are typically on the smaller and less complex side, so we’re not really able to put this aspect to the test. But we were certainly happy with its responsiveness in the time we’ve been using it. Australia's electronics magazine This applies to many aspects of Altium Designer, including the schematic and PCB editors, and Draftsman, as well as in collaborative tools like Altium 365 and PCB CoDesign. Operations like opening documents, repouring polygons, placing stitching vias and bulk copying and pasting have all been sped up. These improvements have been brought about through better memory management and caching of data where possible. On a related note, recent versions of Altium Designer (starting with 24.8) use the newer .NET 6 software framework. Previously, Altium Designer used Microsoft’s proprietary and now obsolete .NET Framework 4.8. Unsurprisingly, .NET 6 is also faster. Interestingly, .NET 6 is fully opensource. It is intended to be modular and works across multiple platforms (including Windows, Linux and macOS). Dare we wonder if this is the first step of being able to run Altium Designer on a Linux PC or Mac? The SI Analyzer by Keysight Another extension that sounds quite handy is the Signal Integrity Analyzer by Keysight, although this is another one that we probably won’t ever need to use due to our modest designs. As the name suggests, it is intended to perform signal integrity analysis on high-speed designs. Fig.1 shows the phases of such an analysis. It can calculate things such as impedance, delay, insertion loss and return loss based on the PCB layout. siliconchip.com.au Fig.1: the Signal Integrity Analyzer by Keysight can be used post-layout to validate signal integrity and provide checks on parameters such as impedance, delay, insertion loss and return loss. This will be very handy to validate high-speed designs before committing to PCB manufacture. Source: www.altium.com/documentation/altiumdesigner/new?version=24#sianalyzer-by-keysight-openbeta-24-10 Fig.2 (below): this trace is ‘necked down’ to fit through a narrow gap between other pads; we did this manually, using an older version of Altium Designer. The new auto-shrink feature allows this to be done automatically during interactive routing. This can help to validate the PCB before it is committed to manufacture. Signal Integrity Analyzer is currently a beta feature and requires the SI Analyzer by Keysight extension to be installed; there is a free 14-day trial available for this feature. Routing When routing the traces on a board, it is sometimes necessary to use a track narrower than the preferred width to fit through a congested or tight area. This is often described as ‘necking down’, where the trace is narrowed down to a thin neck just long enough and narrow enough to fit. Previously, you would have to do this manually, but there is now an option to auto-shrink the width to the minimum you’ve set. This will be handy, since manually creating a neck can be a fiddly process, especially if you want the result to be neat. In addition, a new design rule allows the neck to have a maximum specified length, to avoid having too much resistance or increased fragility. siliconchip.com.au Currently, both these features are in beta and need to be activated in Advanced Settings. The auto-shrink feature is enabled with the “PCB.Routing.EnableAutoShrinking” option, while the neck-down rule follows the “PCB.Rules.RoutingNeckdown” setting. There is also an option to centre traces when routing. Typically, the auto-router will place traces at the minimum allowed clearance from the nearest track, but spreading the traces out may be preferred. It can also make the routing neater, since the traces will be spread out more evenly. This is also a beta feature and is set with the “PCB.EnableTraceCentering” advanced setting. Fig.2 shows an example of a trace necking down through a narrow gap on our Thermal Controller PCB from March & April 2020 (siliconchip.au/Article/12584). Single-layer PCBs For simple designs, a single-layer PCB (with copper on just one side) can be an economical choice, especially for designs on flexible substrates. Large Australia's electronics magazine production runs can warrant the savings in eliminating a copper layer where that is feasible. It’s now possible to lay out single-­ layer PCBs by enabling the “PCB. SingleLayerStack.Support” option in Advanced Settings, then removing a copper layer from a two-layer PCB stack. Constraint Manager The Constraint Manager unifies design constraints from both the schematic and PCB layout. It works in place of the PCB Rule and Constraints Editor dialog (Design Rules). A project can be set up (at creation) to use the Constraint Manager or to use the older Design Rules. There is also a tool that can convert a project from using Design Rules into one that is compatible with the Constraint Manager. It provides a hierarchical system that is automatically translated into the priority in which rules are applied. Constraint Manager can be enabled by setting the “System.ConstraintManager” option in Advanced Settings. June 2025  43 Source: www.altium.com/ documentation/altium-designer/ constraint-manager Fig.3: the Constraint Manager provides a new interface for managing design constraints (design rules) across a project. Older projects can be upgraded to use the Constraint Manager. Fig.3 shows some views of the Constraint Manager. Importing Occasionally, we have to deal with contributed PCBs that have been designed using a different EDA tool, and sometimes we need to change them. This might be as simple as making a small change to the silkscreen markings or could involve a major revision of the copper routing layers. Some changes can be made by directly editing the Gerber files, but having access to fully editable PCB design files is better for many reasons. Firstly, that makes it possible to run design rule checks to validate that any changes do not cause a manufacturing issue like shorted traces. It then becomes possible to make further revisions if needed in the future. Whatever the reason, this means that we need the ability to import designs from other EDA tools into Altium Designer so that they can be turned into native Altium Designer files, such as SchDoc schematic files or PcbDoc PCB files. The latest version of the importer now works with KiCad designs from 44 Silicon Chip KiCad version 7 or 8. This is available as an extension known as the KiCad Importer Extension and can be found in Extensions and Updates. Their website at siliconchip.au/link/ ac41 has more information on importing designs from other tools. Fig.4 shows a screenshot from our installation of the Software Extensions that are on offer. We have previously mentioned the free online Altium 365 Viewer, which is at www.altium.com/viewer This now supports KiCad files, and we had no trouble using it to view some KiCad PCB files that we found online. Wire bonding Altium Designer can be used for designing much more than just traditional planar substrate PCBs. We have previously covered Altium Designer’s ability to work with flexible and hybrid (rigid-flex) PCBs, printed electronics and 3D-printed substrates using the 3D-MID (three-dimensional mechatronic integrated device) process. Another example is the recent Harness Designer. (Also see our article on 3D-MID technology in the April 2025 Australia's electronics magazine issue at siliconchip.au/Article/17936). One of the technologies supported by Altium Designer 25 is COB (chipon-board) using wire bonding. COB involves bare silicon chip dies being bonded directly to a PCB. Connections are made from pads on the die (die pads) to the bond finger pads on the PCB by means of bond wires. The bond wires used in COB applications are much the same as the bond wires used to connect a silicon chip to its leadframe in a traditionally packaged integrated circuit. These are very fine wires of a metal such as gold, copper or aluminium that are welded to their pads using heat, pressure or ultrasonic energy. The process is typically performed by an automated robotic system. You can see some images of a COB design at www.altium.com/documentation/ altium-designer/wire-bonding while the photos at upper right shows two examples of silicon dice bonded to a PCB. Creating a COB design involves adding a Die layer and a Bond wire layer to a PCB document or library. A complete footprint ‘package’ including die pads, bond finger pads, and bond wires siliconchip.com.au Fig.4: numerous Altium Designer extensions can be installed from the Extensions and Updates tab. This shows just some of the extensions available on our system. can be created, in which case the bond finger pads can be simply routed to on the copper layers. Alternatively, a die with die pads can be placed alongside separate bond finger pads. The bond wires are then placed manually. With the current version, wire bonding can be enabled with the “PCB.Wirebonding” option in the Advanced Settings dialog. For manufacture, a wire bonding table report can be generated. As you can see from Fig.5, Altium Designer’s 3D rendering allows you to see all aspects of a wire-bonded design. For example, you can visually check that crossed bond wires pass at different heights to avoid collisions. We find the 3D views invaluable for making sanity checks on our PCB layouts. There are three different subscription levels available for Altium Designer: Standard, Pro and Enterprise. They differ in the number of features that are included and more information is available at www.altium. com/altium-designer/licensing In addition to covering the important aspects of a feature (in this case, Single-­layer PCBs), it follows with a live demonstration of how to use that feature within Altium Designer. The free trial offer that we have mentioned in previous years is still available. It allows you to use a fully featured trial version of Altium Designer for 15 days; see www.altium.com/ altium-designer/free-trial Resources Conclusion Altium offers numerous resources to allow users to make the best use of Altium Designer. You can view a recent webinar (recorded in November) at siliconchip.au/link/ac42 Altium continues to make incremental updates to Altium Designer. While there are some bigger features that we would struggle to use fully, such as wire bonding, they are no doubt useful for larger organisations. It is good to see that they continue to improve usability and work on basic features such as routing. We hope that the switch to .NET 6 is the beginning of cross-platform support. We’re especially keen to be able to use Altium Designer on Linux, since so many of the other programs that we use already allow that. For more information on Altium Designer, visit www.altium.com/ altium-designer SC Licensing Fig.5: Altium Designer 25 now allows wire bonding between silicon dies and PCBs. This image shows an example of two COB (chip on board) dies bonded to the PCB below. Source: www.altium. com/documentation/ altium-designer/wirebonding#placing-wirebonds-in-a-pcb siliconchip.com.au Two examples of chips bonded directly to PCB pads. Source: www.rocket-pcb.com/rocket-pcbwholesale-wire-bonding-technologybulk-fabrication-for-electronics Australia's electronics magazine June 2025  45 SSB Shortwave Receiver Part 1 by Charles Kosina, VK3BAR While there are plenty of cheap radios these days, including software-defined types, I decided to build this analog shortwave radio for the satisfaction of making it myself. I learned a lot about shortwave, SSB and how radios work in the process, which you will not get just buying an ‘appliance’! R adio receiver architectures have changed dramatically in the last few years. Digital techniques have largely displaced the analog techniques from the past. Radio receivers are now available at ridiculously low prices from various internet sources. The simplest ones are the Software Defined Radios (SDR) that are a small module that plugs into a USB port. The typical coverage is from 100kHz to 2GHz; they rely on the processing power of the attached computer to recover the desired signal. They are not ‘communications receivers’, as their noise figure and immunity from intermodulation are quite poor. With no input tuneable filter, a strong signal can easily overload 46 Silicon Chip the front-end circuitry. But for many, the performance is quite adequate. The screen “waterfall display” showing signals is very useful. Still, it isn’t too hard to build an analog shortwave receiver with decent performance, as I shall explain shortly. Performance The performance of this unit is quite reasonable. I set my signal generator to 1µV (-107dBm) output and the signal-to-noise ratio was about 13dB for most of the range (slightly less at 30MHz). Inserting a 20dB attenuator gave me a signal of about 0.1µV (-127dBm) and it was still audible! At that level, communication via Morse Code (CW) Australia's electronics magazine would be possible, but it is too weak for SSB voice reception. Yes, there are the unavoidable birdies, but they do not interfere greatly. What about on-air tests? The only HF antenna I have at present is an endfed half-wave dipole on the 40m band (7MHz). This is fed with 50W coaxial cable and uses a 49:1 ‘unun’ (unbalanced to unbalanced) transformer. The measured SWR (standing wave ratio) is between 1.2 and 1.3. Unfortunately, the ambient noise here is rather high with all the electrical equipment in the surrounding houses, producing heaps of RF hash, so it needs a fairly strong signal to get through. Comparing this receiver with my Bando Technic 5D transceiver, the sensitivity is much the same. siliconchip.com.au Fig.1: a TRF receiver comprises several identical RF amplifiers tuned to the same frequency. Most very early radios used this configuration. Fig.2: the superhet was an early game changer. By mixing the amplified, tuned incoming signal with an oscillator frequency that tracks above it, the signal is shifted down to a lower, fixed (intermediate) frequency. Signals at that frequency are easier to filter out and demodulate. Fig.3: an SSB receiver is a bit more complex as it needs to operate without the carrier wave or half the signal spectrum. The modulated signal is recovered by mixing it with the output of the BFO in a second mixer stage. A list of the features and specifications for this receiver includes: ∎ Covers the shortwave band from 3MHz to 30MHz in two spans ∎ Sensitivity: 1μV (-107dBm) for a 13dB SNR (reception possible <at> 100nV/-127dBm). ∎ 2.7kHz speech bandwidth ∎ Runs from 12V DC <at> 500mA ∎ Digital tuning with frequency display ∎ Analog controls for tuning, volume, RF gain and squelch ∎ USB/LSB decoding ∎ Fast or slow AGC ∎ RSSI display ∎ Built-in speaker and headphone jack Radio receiver types I will start with a brief summary of radio techniques over the last 100 years or so. Back in the 1920s, a typical radio was most likely a TRF (tuned radio frequency) set. They consisted of several cascaded tuned amplifiers, each set to the same frequency, as shown in Fig.1. A detector extracted the audio signal at the end of the chain, which was siliconchip.com.au then amplified to drive headphones or a loudspeaker. The valves used were initially triodes, and with high feedback capacitances, were subject to instability, leading to oscillation. A neutralising system was developed to feed back a phase-shifted version of the signal, minimising or preventing this instability. Later, tetrode and pentode valves were used that had much lower feedback capacitance and obviated the need for neutralisation. Not only were these early radios difficult to set up and use, but they lacked the selectivity to reject unwanted strong signals on different frequencies. However, by using regeneration, where a portion of the amplified signal is fed back to the input grid of the triode and pentode, much higher gain and selectivity could be achieved. Enter the superhet The problems of the TRF receiver were largely overcome by the superheterodyne architecture. Edwin Armstrong is often credited with the invention of this technique, but others filed Australia's electronics magazine patents only months apart. Legal battles followed, and French engineer Lucien Lévy was awarded a patent that included seven of the nine claims in Armstrong’s application. Fig.2 shows the superheterodyne architecture. The incoming signal passes through a tuned filter, followed by an optional RF amplifier. Then follows the mixer, where the incoming signal is multiplied by another frequency from a local oscillator. The multiplication results in two extra signals, being the sum and difference of the frequencies. For example, if the incoming signal is 1000kHz, and the local oscillator is at 1455kHz, the output from the mixer will contain signals at 455kHz (1455kHz – 1000kHz) and 2455kHz (1455kHz + 1000kHz). It will also include the original 1000kHz signal. The following band-pass filter selects just the 455kHz portion, which is amplified by the IF (intermediate frequency) stage(s) and passed to a detector and audio amplifier as before. However, this technique is only suitable for receiving AM (amplitude modulated) signals. June 2025  47 To receive SSB (single sideband) broadcasts, discussed further below, an additional mixer stage is necessary after the IF amplifier(s). This mixes the IF signal with that from a BFO (beat frequency oscillator), and its output goes through a low-pass filter (LPF), as shown in Fig.3. This architecture remained the normal way that radios were built for many decades. Most of the selectivity (ie, rejecting unwanted station signals) came from the IF filter. However, consider a broadcast at 1910kHz with the common 455kHz IF. With the set tuned to 1000kHz, when mixed with the LO at 1455kHz, this signal also will produce a 455kHz output from the mixer. This is termed the image frequency, and it is why there is an input band-pass filter, to attenuate this image. A single tuned circuit was adequate for the broadcast band frequency range of 530kHz to 1,600kHz, but once shortwave broadcasting became commonplace, the single tuned circuit was inadequate at frequencies above 3MHz and resulted in ‘double spotting’ of the same input signal. This was often tolerated, but to get around it, double- and triple-­ conversion superhet sets were used for better performance. This resulted in a higher-frequency initial IF signal, which was then mixed again to obtain a lower-­frequency secondary IF signal. There are some limitations to the superheterodyne architecture. Spurious signals are generated as a result of the mixing process or from non-ideal components (like harmonic distortion). Spurious signals may be produced by the oscillator, mixer, or other components in the receiver. The local oscillator may generate harmonic signals that mix with the RF signal, producing unwanted spurious signals. In nonlinear systems, two or more signals can combine to produce additional unwanted frequencies, known as intermodulation distortion. Fig.4: this Hartley SSB receiver configuration is difficult to implement in hardware as a very accurate 90° phase shift is required across a range of signal frequencies. Fig.5: this alternative configuration is similar to the Hartley type except the 90° phase shift is split into two 45° phase shifts. It’s still difficult to make it work in the analog domain, though. 48 Silicon Chip Australia's electronics magazine Some of these spurious signals are characterised by a rapid tuning rate. The whistle or chirp that is produced changes in frequency much faster than the tuning of the receiver. Hence, they were called “birdies”. Hartley phasing There are alternatives to the superheterodyne receiver. A variation is to use the Hartley phasing method, as illustrated in Fig.4. The incoming signal (ωs) is fed into two mixers. The local oscillator is at the same frequency, and an RF phase shift network of 90° will mix with the incoming signal to produce two signals at baseband, but at 90° apart. These signals are called I (in-phase) and Q (quadrature). The Q signal is applied to an audio phase shift network, which in mathematical terms is a Hilbert transform. This shifts the entire audio spectrum by 90°. However, this arrangement is impractical. A better approach is using two separate phase-shift networks of +45° for the I signal and -45° for the Q signal, as shown in Fig.5. These are then summed and filtered to produce the demodulated signal. This is a simplified explanation of the phasing system; there are plenty of online references that give a detailed mathematical analysis. The phasing method is elegant in its simplicity, but there are practical problems in its realisation. It is relatively easy to have an accurate 90° phase shift, but the audio phase shift network requires an extremely high precision in components to maintain the accurate phase shift over the whole range of frequencies. This is why the analog method has been superseded by digital techniques. In current SDR receivers, the I and Q signals are sampled by analog-­ to-digital converters and the Hilbert transform is done by software. It does require a fast processor, as found in modern computers. I decided to investigate if a phasing receiver was practical using an analog phasing network. There are designs available to implement the Hilbert transform in hardware, but it requires careful matching and selection of components, preferably to within 0.1%. One such design is shown in Fig.6, and I built a test module to test its practicality. I bought about 50 of the 10nF siliconchip.com.au Fig.6: an example of a phase shift network that provides a more-or-less fixed phase shift across a range of frequencies. capacitors and, by measuring them to four-figure resolution, I selected a batch where all were within 0.1% of each other. The exact value is not quite as important as the matching. I originally thought that 8-pin SIL (single in-line) resistor networks with four 10kW resistors each would be closely matched, but found that was not accurate enough. The alternative was to select from lots of 10kW SMD resistors for a matched set. The hardest part is getting the other six resistors to an exact value. For example, a value of a 12,960W is needed, which is realised by two resistors in parallel, 13kW and 3.3MW. But this required measuring and selecting resistors that were close to the nominal Fig.7: the performance of the phase shift network shown in Fig.6. Even with hand-selected matching components, it doesn’t quite hit 90°, nor is it perfectly flat with frequency across the band of interest. siliconchip.com.au value. Some values were difficult to get exactly. Fig.7 shows the measured phase shift of my prototype which, while close to 90°, is not really close enough. The sideband rejection would be 40dB at best. Also, this is not the sort of design that can many readers would bother to build. It is possible to eliminate the Hilbert transform; one solution is the Weaver architecture. Following the baseband low-pass filters, we have another pair of mixers, as shown in Fig.8. The frequency injected into the second pair of mixers is at about half the bandwidth. Again, two signals 90° out of phase are needed, called the pilot tone. A further LPF extracts the wanted signal. There are many articles and papers describing the Weaver method, many with quite complicated mathematics. It is described in detail at siliconchip. au/link/ac51 I built a receiver with this architecture, copying some of the design ideas available on the internet. After many hours of trying to get decent performance, I eventually gave up. Getting the accuracy and balance between the I and Q channels just proved too hard. Overall, the receiver was far too noisy; I suspect because of the multiple mixers, and I could not get rid of the pilot tone in the output. I would be interested to hear from readers who Fig.8: the Weaver receiver configuration has some advantages over Hartley but many more mixers are required, so the resulting noise performance is less than ideal (in the analog domain, anyway). Australia's electronics magazine June 2025  49 may have built a Weaver receiver and find what their results were. Having tried all the different architectures (apart from TRF) over a period of about six months, I decided that the SSB superhet design was the most practical approach for home construction. But before we get to the circuit, here is an explanation of two modulation techniques. Amplitude modulation (AM) is where a ‘carrier frequency’ signal is Fig.9: the basic principle of amplitude modulation (AM). The high-frequency carrier amplitude varies with the instantaneous baseband signal amplitude. Fig.10: the spectra of AM and SSB transmissions. The transmission power of SSB is about ¼ that of AM without significantly reducing the received signal strength. The ultimate design multiplied by an audio frequency (AF) signal, as shown in Fig.9. We get a signal with components in three frequency ranges: the original carrier, plus two ‘side-bands’, being the sum and difference (see Fig.10). To demodulate the AM signal, all that is needed is a diode and a lowpass filter to remove the RF component. This filter may be just a single resistor and capacitor. While AM is easy to implement, is really quite wasteful. The carrier frequency carries no information at all, and the two side-bands at 100% modulation contain half the power of the carrier, with identical information. This is where the single side-band (SSB) method of communication is far more efficient. We essentially get rid of the carrier and one of the sidebands. Instead of a bandwidth of twice the baseband, our filter needs only the baseband bandwidth. The spectrum for SSB modulation is shown at the bottom of Fig.10. However, with SSB, the simple envelope detector will no longer work. To take an example, transmitting an SSB signal modulated at two frequencies, 1kHz and 2kHz, an envelope detector would give us a tone of 1kHz, being the difference between the two frequencies. For a more complex modulated signal, the output of the detector would be quite unintelligible. To recover the audio, we have to multiply the output of the IF amplifier with the signal from a beat frequency oscillator (BFO) with a second mixer. The BFO frequency is set to where the carrier frequency would otherwise be. This results in two signals in the output; one is the original baseband signal, plus another at twice the IF, which is easily removed by a low-pass filter. The filtered signal can then be amplified by an audio amplifier to drive a speaker or headphones. Receiver design Fig.11: the measured performance of the pre-built 9MHz crystal filter module. It combines a flat passband with very steep roll-offs on either side. The receiver presented here covers the frequency range of 3MHz to 30MHz, with an audio bandwidth limited to the frequencies used by human speech: 300Hz to 3kHz. This means that the IF filter bandwidth needs to be 2.7kHz (3kHz – 300Hz). This is best achieved by a multi-pole crystal filter at 9MHz. This is quite a critical item in the design. You can build your own by buying a batch of 9MHz crystals and carefully selecting them for series and Australia's electronics magazine siliconchip.com.au 50 Silicon Chip The front and rear sides of the control board. The five pots, three switches, rotary encoder, LCD screen and headphone socket form the user interface. On the rear of the control board are the Arduino Nano and clock generator modules, LCD adjustment trimpot, two electrolytic capacitors and some connectors. Note that these photos are shown enlarged for clarity. parallel resonant frequencies. But unless you have the equipment and patience to do this accurately, it is not worthwhile. I bought 20 9MHz crystals for about $6, and by selection, managed a reasonable filter after much experimentation. But a complete six-pole filter module is available from AliExpress siliconchip.com.au for about $25, with an excellent bandwidth, as is shown in Fig.11. Next, let’s look at how we deal with image frequencies. If the desired signal fs = 7MHz and the local oscillator fo = 16MHz, producing a 9MHz IF signal, a signal at 25MHz mixed with 16MHz will produce the same 9MHz IF. This is why we have an input tuned circuit. Australia's electronics magazine How sharp does this filter have to be? Using a high-quality toroid, a loaded Q of 100 is typical. There are calculators on the internet that save us the trouble of laboriously working it out; with the above example, the unwanted 25MHz image signal will be attenuated by about 50dB. That is why a relatively high IF is June 2025  51 What is a noise figure? Every device generates broadband noise that will reduce the circuit’s signalto-noise ratio (SNR). The NF is the ratio of actual output noise to that which would remain if the device itself did not introduce noise, which is equivalent to the ratio of input SNR to output SNR. There is another way of expressing the noise performance: the noise temperature, expressed in Kelvins as an equivalent temperature. It is not the physical temperature of a system, but a theoretical value that defines the temperature required to produce a specific amount of noise power. The equivalence between noise temperature and noise figure is shown below. The reference temperature, Tref, is generally 290K (16.85°C). The relationship between noise figure (NF) and noise temperature (in Kelvin). Note that it is not the actual temperature the part is operating at. desirable for higher-frequency signals, as the image frequency is well removed. If an IF of 455kHz were used, the standard for broadcast-band receivers, the image at 7.91MHz would only be 28dB down. Circuit details Figs.12 & 13 show the full circuit of the receiver, which is split across two PCBs, and the circuits correspond to them. One is the control board, while the other is the RF board. At the heart of the control board is the Arduino Nano module, which has the ATMega328 microcontroller. The display is the common 16×2 alphanumeric LCD module; the version with a blue backlight is the best choice. Potentiometer VR6 is the contrast adjustment for the LCD screen. The variable frequency oscillator (VFO) and the beat frequency oscillator (BFO) signals are generated by an Si5351A clock-generator module (MOD2), controlled over an I2C serial bus (SDA/SCL). This module can generate three different frequencies as square waves with amplitudes of about 3V peak-to-peak. In this design, the outputs used are CLK0 and CLK2; the CLK1 output is not used. The 8.2kW pull-up resistors for the SDA & SCL lines are shown greyed out in Fig.12 because they do not need to be fitted as the Si5351A module has onboard pull-up resistors. A rotary encoder (RE1) is used for frequency tuning; the step size for each click can be varied using the integrated pushbutton switch. Pressing the switch cycles through steps of 10Hz, 100Hz, 1kHz, 10kHz, 100kHz and 1MHz. The two poles of the encoder, plus its integral switch, have 33kW pull-up resistors to give defined high/ low levels and 100nF capacitors to ground for debouncing. The I2C serial bus is used to control the input circuit tuning by selecting six capacitors in various combinations for approximate tracking with frequency. Fine potentiometer VR1 is used to change the voltage on a varicap diode to interpolate the approximate values and peak the input circuit to resonance (more on this later). There is audio circuitry on this board as well. Op amp IC1b has a gain of about 5.5, and can drive headphones directly via a 3.5mm jack provided on the front panel. It has internal switching that disconnects the power amplifier driving the speaker when headphones are plugged in. Despite the existence of numerous more modern power amplifier chips, I have used the venerable LM386 (in an SMD package) to drive the speaker. It requires few external components, is cheap and with a 12V supply will deliver over 2W to an 8W speaker Fig.12: the control board circuit. Three main modules are used: the Arduino Nano ‘brain’, an Si5351 digital clock generator that produces the VFO and BFO oscillator signals and the 16×2 alphanumeric LCD module. The dual op amp provides the squelch function (IC1a) and audio gain for driving headphones (IC1b), while IC2 is the power amplifier that drives the speaker. 52 Silicon Chip Australia's electronics magazine siliconchip.com.au The control board and RF board are joined by a 16-wire flat cable between headers CON2. This supplies power to the RF board and carries signals to it as well, including the band change signal and the I2C bus (SDA & SCL). Signals coming into the control board on CON2 include the recovered audio and RSSI (received signal strength indicator) voltage. Potentiometer VR5 is the volume control, while VR2 is an RF gain control modifying the AGC (automatic gain control) voltage. Switch S3 is the SLOW/FAST AGC selection, adding a 10µF capacitor to the RSSI line for the SLOW AGC mode. The squelch control is useful in eliminating background noise from weak input signals. It works by comparing the RSSI voltage level at the inverting input of IC1a (which is used as a voltage comparator) with a DC voltage derived from potentiometer VR4. When the RSSI level is low, Mosfet Q1 is switched on, shorting out the audio. The 1MW feedback resistor provides hysteresis. The mute function is provided by a second transistor, Q2, in parallel with siliconchip.com.au The controls are all labelled on the front panel PCB. The rear of the set only has the BNC antenna terminal, DC power connector and holes so that sound from the the internal speaker can escape. Q1. I found that when the frequency was being changed, there was a loud annoying click in the audio. So during tuning, Q2 is switched on, also shorting out the audio. DC power is via CON1 and diode D1 protects against the wrong supply Australia's electronics magazine polarity. The supply voltage can range from 9-12V DC, with a maximum current drain of about 250mA. An ironcore transformer based plugpack is preferable as it does not generate RF noise, but you can try a switching plugpack; some do have low noise. June 2025  53 Fig.13: this RF board circuit connects to the control board circuit (Fig.12) via CON2. Q1-Q6 and VD1 tune the incoming signal while T1 (3-10MHz) or T2 (10-30MHz) are selected by RLY1 for band switching. Q8 is the RF gain stage; IC1 is the superhet mixer; Q9 is the first IF gain stage; Q10 is the second IF gain stage; IC2 is the BFO mixer; and dual op amp IC3 is the RSSI/AGC signal amplifier. Because the voltage regulation of iron-core plugpacks is poor, a 12V one may put out a voltage that is too high with a light load, so choose one rated at 9V DC and 500mA. Depending on the Arduino Nano, the voltage regulator may not tolerate an input voltage much greater than 12V, so be careful with the choice. You can easily blow up a Nano with excessive input voltage (trust me, I have!). The filtering on this type of plugpack may leave too much 100Hz ripple, which would be heard as hum in the output. That’s why there is a 2200µF electrolytic capacitor after D1. When S1 is switched on, there is a very high inrush current to charge this capacitor, hence a fairly high-­current schottky diode is used for D1. The ideal supply would be a ~12V battery; three 18650 cells in series give just over 11V fully charged. The background noise using a battery is significantly lower than either type of mains-powered supply. A suitable battery holder can be squeezed into the case, although taking out the cells to charge them requires removing a bracket. Still, you could integrate a charging socket. 54 Silicon Chip Most constructors will not need the optional serial debugging interface provided by Mosfets Q3 & Q4; they offer a bidirectional RS-232 compatible serial stream at header CON5. Those components can be left off if not needed. You can also connect a TTL USB/serial adaptor directly to the TXD & RXD pins of MOD1. RF module circuit As shown in Fig.13, the signal from the antenna goes to two tuned toroidal transformers selected by relay RLY1. A high Q is desirable in these transformers for maximal rejection of unwanted frequencies. The toroids are Micrometals T37-17 types with an unloaded Q in excess of 200 at most frequencies. With a 50W source on the primary winding, the loaded Q will be about 100. Transformer T1 covers the range of 3-10MHz and has a secondary inductance of 7.4µH (42 turns). The antenna winding is four turns at the ‘cold end’ of the toroid. This needs a capacitance range from 34pF at 10MHz to 380pF at 3MHz for tuning. Back in the days when valves were used, this capacitance would be part of a two- or three-gang variable Australia's electronics magazine capacitor. These days, such capacitors are relatively rare, expensive and too large. Instead, I used six fixed capacitors selected by the PCF8574 I2C extender (IC4) driving six NPN RF transistors. A BB910 varicap diode (VD1) adds to the tuning capacitance as a fine adjustment to interpolate between the fixed values. The capacitance range of the varicap is from 40pF at 0.5V down to 8pF at 9V (a varicap diode is used in reverse bias, with the voltage across it affecting its capacitance). For the range from 10.1MHz to 30MHz, we switch in transformer T2, with an inductance of 1.1μH (15 turns). Its antenna winding is two turns. Q8 is a low-noise amplifier based on a BF998 dual gate Mosfet. While technically obsolete, this is easily obtainable from many sources. Rather than another tuned circuit in the drain, I have just used a 100μH inductor, which has a reasonably high impedance over the entire 3-30 MHz range. The gain is about 20dB and, while the noise figure (NF) is not given below 30MHz, at 800MHz it is 1dB. The first mixer (IC1) is an NE612 (or SA612) IC. This has a gain of about siliconchip.com.au 17dB and a noise figure of 5dB. The NF of a multi-stage amplifier can be calculated as: NF = NF1 + (NF2 – 1) ÷ G1 + (NF3 – 1) ÷ (G1 × G2) + ... Here, NF is the total noise figure, while NF1, NF2... are the noise figures of subsequent stages, and G1, G2... the gains of the stages. Thus, with a reasonably high gain in the first stage, the overall noise figure is degraded only slightly by the following stages. The final noise figure of our circuit is about 1.5dB. That is more than adequate given the amount of ambient noise in the HF band. Another BF998 (Q9) follows the first mixer, providing another 20dB of gain. The 9MHz crystal filter follows, which has 50W input and output impedances. This is matched to the preceding BF998 amplifier by a pi network with a 3000:50W ratio. The filter introduces a loss of about 5dB. Another BF998 (Q10) is the second 9MHz IF amplifier after the crystal filter. A second NE612 (IC2) is used for the second mixer, with the ~9MHz BFO. There are two outputs available on the chip. One output is connected to op amp IC1b, which has a voltage gain of about 46 times. This is the AGC amplifier. Schottky diodes D2 and D3 rectify this voltage and charge a 1μF capacitor. This voltage is applied to the inverting input of IC3a. With no signal, this voltage is close to zero. The non-inverting input has a voltage from the RF gain control potentiometer on the front panel, and with the resistor values used, the output of IC3a is a maximum of about 4.5V. This is applied to the second gate of the three BF998 transistors for maximum gain. As the RSSI voltage rises, the AGC voltage drops, going down to zero for very strong signals for minimum gain. The assembled RF board - toroidal transformers T1 & T2 are on the left, while the crystal filter module is at lower right. Note that this photo is shown enlarged for clarity. siliconchip.com.au Australia's electronics magazine June 2025  55 The maximum supply voltage for the NE612 mixers is 9V, so 8V is provided by a 7808 regulator. With a 9V main supply voltage, this will drop to about 7.5V, which is quite adequate. The PCF8574 I2C I/O expander driving Q1–Q6 is the only chip that needs a 5V supply, which is provided by an SMD 78L05 regulator (REG2). Parts List – SSB Shortwave Receiver We’ve covered quite a lot in this article, so the construction details will be in a follow-up article next month. It will also cover programming the Arduino Nano, preparing the case, plus calibrating and aligning the Receiver. SC 1 180 × 130 × 110mm blue vented steel project box with feet [AliExpress 1005008418042828] 1 assembled control board (see below) 1 assembled RF board (see below) 1 front-panel PCB coded CSE250204, 165.5 × 97mm, with black solder mask 1 panel-mount DC barrel socket, diameters to match plugpack 1 12V 500mA+ plugpack 1 8W all-purpose loudspeaker (SPK1) [Jaycar AS3025, eBay 7.7cm 5W 226113532195] 5 13mm diameter universal knobs [AliExpress 1005006143033779] 1 25mm diameter universal machined aluminium knob [AliExpress 1005007577048515] 1 10cm male SMA to female BNC panel-mount connector cable [AliExpress 1005003990025513 select “BNC F WATERPROOF 2”] 2 16-way IDC connectors 2 2-way 2.54mm pitch polarised header plugs with matching pins 1 20cm length of 16-wire ribbon cable 4 M4 × 10mm panhead machine screws, nuts & washers (for mounting SPK1) 4 M3 × 15mm tapped spacers 4 M3 × 10mm tapped spacers 12 M3 × 6mm panhead machine screws 4 M3 × 6mm black panhead machine screws Control board 1 double-sided PCB coded CSE250202, 150 × 79.5mm 1 Arduino Nano programmed with CSE25020A.HEX (MOD1) 1 Si5351A clock generator module (MOD2) [AliExpress, eBay etc] 1 16×2 alphanumeric blue backlit LCD module (LCD1) 1 pulse-type PCB-mounting rotary encoder with integral switch and 20mm shaft (RE1) 4 10kW 9mm vertical PCB-mounting linear potentiometers with 20mm shafts (VR1-VR4) 1 10kW 9mm vertical PCB-mounting log potentiometer with 20mm shafts (VR5) 1 10kW multi-turn trimpot (VR6) 3 miniature SPDT toggle switches with solder tags (S1-S3) 3 2-pin polarised headers, 2.54mm pitch (CON1, CON3, CON4) 1 8×2-pin header, 2.54mm pitch (CON2) 1 PJ-341 3.5mm vertical PCB-mounting jack socket (CON6) [AliExpress] 2 15-pin female headers, 2.54mm pitch (for MOD1) 1 7-pin header, 2.54mm pitch (for MOD2) 1 16-pin header, 2.54mm pitch (for LCD1) 4 5mm-long untapped spacers, 3mm inner diameter 4 M3 × 12mm panhead machine screws and matching nuts 2 M2 or M2.5 × 11mm tapped spacers 4 M2 or M2.5 × 6mm panhead machine screws Semiconductors 1 LMC6482IM dual CMOS-input op amp, SOIC-8 (IC1) 1 LM386M audio amplifier, SOIC-8 (IC2) 2 2N7002 N-channel Mosfets, SOT-23 (Q1, Q2) 1 MBR540 40V 5A axial schottky diode (D1) Capacitors (all SMD M2012/0805 size 50V X7R unless noted) 1 2200μF 16V through-hole electrolytic 1 470μF 16V through-hole electrolytic 1 100μF 6.3V M3216/1206 size 4 10μF 25V X5R/X7R 2 1μF 4 100nF 1 47nF 1 1nF NP0/C0G 1 220pF NP0/C0G Resistors (all SMD M2012/0805 size 1% unless noted) 1 1MW 1 22kW 1 3.3kW 1 0W M3216/1206 size 3 100kW 1 10kW 1 68W M3216/1206 size 3 33kW 2 8.2kW 1 10W 56 Australia's electronics magazine Obtaining the components I have been careful in choosing components that are readily available from many suppliers. Virtually all can be purchased from AliExpress (www. aliexpress.com) at quite low prices. For example, the modules on the control board are an Arduino Nano, 16×2 alphanumeric LCD and Si5351a, which can be bought for a grand total of about $10 plus shipping (a few more dollars). Although some components are classed as ‘obsolete’, they are all still readily available. That includes the BF998 dual gate Mosfets and NE612 ICs. The LMC6482 op amp was chosen as it has a very high input impedance, an adequate GBW (gain bandwidth) of 1.5MHz but, most importantly, it is a rail-to-rail input/output type and can be used with a single supply voltage of up to 16V. While the BF998 is easily obtainable, be careful not to use the BF998R, which has a mirror image pinout (mounting it upside-down is not easy!). The most expensive component is the 9MHz crystal filter module, costing about $25. As I mentioned earlier, it’s cheaper to build your own, but it requires the right equipment and is quite a bit of effort. The other expensive item is the case. The metal case that I have specified is available for about $37. It comes with steel front and back panels. The front panel is replaced by a 1.6mm-thick black circuit board that has all the necessary holes and cutouts. Thus, you only need to drill holes in the back panel for the power, antenna connection, and loudspeaker (if fitted). Next month Silicon Chip siliconchip.com.au Ideal Bridge Rectifiers Additional parts for optional debugging interface 1 3-pin polarised header, 2.54mm pitch (CON5) 2 2N7002 N-channel Mosfets, SOT-23 (Q3, Q4) 3 8.2kW SMD M2012/0805 size 1% resistors 1 4.7kW SMD M2012/0805 size 1% resistor RF board 1 double-sided PCB coded CSE250203, 152 × 50mm 1 9MHz/600Hz crystal filter module (XF1) [AliExpress 1005007201667282] 2 100μH axial moulded inductors (L1, L4) 1 10μH axial moulded inductor (L2) 3 4.7μH axial moulded inductors (L3, L5, L6) 2 Micrometals Amidon T50-6 12.8mm toroidal cores (T1, T2) [Minikits T50-6] 1 80cm length of 0.35mm diameter enamelled copper wire (T1) 1 30cm length of 0.6mm diameter enamelled copper wire (T2) 3 red 5-30pF trimmer capacitors (VC1-VC3) 1 vertical SMA connector, female, standard polarity (CON1) 1 8×2-pin header, 2.54mm pitch (CON2) 1 HFD4/5 or G6K-2F-Y 5V DC coil DIP DPDT signal relay (RLY1) 4 5mm-long untapped spacers, 3mm inner diameter 4 M3 × 10mm tapped spacers 1 M3 × 16mm panhead machine screw and matching nut (for REG1) 8 M3 × 6mm panhead machine screws 4 M2 or M2.5 × 12mm panhead machine screws and hex nuts Semiconductors 2 NE612 oscillator/mixers, SOIC-8 (IC1, IC2) 1 LMC6482IM dual CMOS-input op amp, SOIC-8 (IC3) 1 PCF8574 I2C I/O expander, wide SOIC-16 (IC4) 1 7808 8V 1A linear regulator, TO-220 (REG1) 1 78L05 5V 100mA regulator, SOT-89 (REG2) 6 BFR92P low-noise RF NPN transistors, SOT-23 (Q1-Q6) 1 2N7002 N-channel Mosfet, SOT-23 (Q7) 3 BF998 dual-gate Mosfets, SOT-143 (Q8-Q10) 1 BB910 VHF varicap diode (VD1) 2 1N5711 axial schottky diodes (D2, D3) 1 LL4148 75V 200mA signal diode, SOD-80 (D4) Capacitors (all SMD M2012/0805 size 50V C0G/NP0 unless noted) 2 10μF 25V X5R/X7R 1 4.7μF 25V X7R 2 1μF X7R 12 100nF X7R 1 10nF X7R 12 1nF 1 390pF 1 330pF 1 120pF 4 47pF 2 27pF 1 10pF 1 4.7pF Resistors (all SMD M2012/0805 size 1% unless noted) 4 1MW 1 470kW 1 330kW 3 100kW 1 47kW 8 8.2kW 3 150W 2 100W 1 51W siliconchip.com.au Australia's electronics magazine Choose from six Ideal Diode Bridge Rectifier kits to build: siliconchip. com.au/Shop/?article=16043 28mm spade (SC6850, $30) Compatible with KBPC3504 10A continuous (20A peak), 72V Connectors: 6.3mm spade lugs, 18mm tall IC1 package: MSOP-12 (SMD) Mosfets: TK6R9P08QM,RQ (DPAK) 21mm square pin (SC6851, $30) Compatible with PB1004 10A continuous (20A peak), 72V Connectors: solder pins on a 14mm grid (can be bent to a 13mm grid) IC1 package: MSOP-12 Mosfets: TK6R9P08QM,RQ 5mm pitch SIL (SC6852, $30) Compatible with KBL604 10A continuous (20A peak), 72V Connectors: solder pins at 5mm pitch IC1 package: MSOP-12 Mosfets: TK6R9P08QM,RQ mini SOT-23 (SC6853, $25) Width of W02/W04 2A continuous, 40V Connectors: solder pins 5mm apart at either end IC1 package: MSOP-12 Mosfets: SI2318DS-GE3 (SOT-23) D2PAK standalone (SC6854, $35) 20A continuous, 72V Connectors: 5mm screw terminals at each end IC1 package: MSOP-12 Mosfets: IPB057N06NATMA1 (D2PAK) TO-220 standalone (SC6855, $45) 40A continuous, 72V Connectors: 6.3mm spade lugs, 18mm tall IC1 package: DIP-8 Mosfets: TK5R3E08QM,S1X (TO-220) See our article in the December 2023 issue for more details: siliconchip.au/Article/16043 June 2025  57 Douk ST-01 PRO Hybrid Valve Amplifier Big on the cute factor, this miniature amplifier glows warmly in the dark from its valve filaments, but has plenty of power thanks to a Class-D output stage. It costs $170, so how does its performance stack up? Review by Allan Linton-Smith W e have seen & tested myriad amplifiers, modules and kits. Many have totally fake or exaggerated claims about their performance, but this one is different. It is a well-engineered & well-presented package with decent performance. It combines modern technology like a Class-D amplifier, digital audio and Bluetooth with an old-fashioned triode preamplification stage. It only requires two speakers, cables and a signal source to be added. You can select between the RCA, optical (TOSLINK), coaxial (S/PDIF), USB and Bluetooth inputs with the press of a button. They include a remote control, instructions, valves, an optical lead and 24V, 4.5A plugpack power supply. A quick check on the internet uncovers many other products from them, which all appear to be well designed and presented. Features and design The heart of the Douk ST-01 amplifier is the Texas Instruments TPA3250 Stereo Class-D Amplifier IC, which is run in a bridge-tied load (BTL) stereo configuration. The small dimensions of this amplifier are a result of the absence of heavy, expensive power transformers and output transformers, instead using an external switch-mode power Fig.1: the signal from the various inputs is fed to the valve preamplifier via the tone controls. The pentode anode and screen grid are joined so it effectively becomes a triode, like the circuit shown here, creating ‘acceptable’ even harmonics. Pentodes have more of a tendency to create less-acceptable odd harmonics. 58 Silicon Chip Australia's electronics magazine supply and an efficient Class-D chip (see Fig.5). This chip can deliver 70W per channel into 8W loads with a 32V DC power supply (at TI’s specified 10% THD+N [total harmonic distortion plus noise]). However, the ST-01 delivers around 30W into 8W <at> 1% THD+N due to the limitation of the 24V 4.5A plugpack supplied. They state that you can upgrade it to 24V 6A if more power is required. By itself, the TPA3250 has very low distortion, quoted at 0.005% THD+N for 1W into 8W in the data sheet. However, this is a hybrid design with a pentode (wired as a triode) preamplifier to give a somewhat softer ‘valve sound’ – see Fig.1. This deliberately injects harmonics (but not much noise) into the system. As a result, we measured around 0.02-0.1% THD+N at 1W into 8W (see Fig.6), which is significantly better than most valve-only designs. The warm glow from the valves is complemented by a retro VU meter, which is a handy to monitor the signal levels to avoid objectionable clipping. Another interesting feature is the wide variety of valves that can be substituted for the ones supplied by Douk. There are 15 alternates listed! We tried a pair of 5654s in place of the 6K4s supplied and an audible difference siliconchip.com.au Manufacturer’s data (Douk Audio ST-01 PRO) » Audio inputs: Bluetooth, USB, coaxial [digital], optical [TOSLINK], RCA, U-disk [USB] » Audio output: Banana jacks / 3.5mm auxiliary socket » Maximum output power: 100W+100W (4Ω) [requires upgraded power supply] » Supported load impedance: 3-8Ω » Sampling rates supported: – USB input: 96kHz/24-bit – Bluetooth input: 48kHz/24-bit – Coax/optical inputs: 192kHz/24-bit » Supported USB formats: MP3, WAV, WMA, FLAC, APE » Maximum capacity of USB disk: 64GB » Treble/bass adjustment range: ±6dB » USB systems supported: Windows, macOS, Linux » Frequency response: 20Hz-20kHz (±1dB) » Signal-to-noise ratio (SNR): ≥98dB » Total harmonic distortion (THD): 0.07% » Working voltage: 18-30V DC » Dimensions & weight: 115 × 98 × 54mm, 634g Included in the package: ST-01 PRO Amplifier and user manual; 24V DC 4.5A mains power supply; remote control (without two AAA cells); USB cable; Bluetooth antenna was immediately obvious. Rather than leaving that as a subjective evaluation, we measured the actual spectra generated and examined the difference in the resultant harmonics, as shown in Fig.3. Most valve amplifier owners love to try different valves and/or different brands to evaluate the audible results. This is called “valve rolling”. Sometimes certain brands are considered superior and have superior prices, but our substituted 5654s only cost $7.63 each. By the way, if you look up the 6K4, you may find that it is a miniature triode, not a 7-pin pentode. Confusingly, there are two different “6K4”s! The Fig.3: this spectrum analysis at 1kHz & 1W shows the variation between different valves. The 6J1 is represented by the pink trace, and the 5654 by the blue trace. The total distortion is the same for both valves, but the harmonic differences are audible (eg, the blue trace is slightly cleaner below 5kHz). siliconchip.com.au triode is from Russia while the pentode is from China. The Chinese “6K4” is actually pretty close in performance to a 6J1 or 6J2 and comes in the same package, so you could substitute it with a 6J1 or 6J2. Performance The frequency response for the Fig.4: the amplifier’s response for various bass and treble settings: flat (cyan), maximum treble (green), minimum treble (blue), maximum bass (red) and minimum bass (magenta). Australia's electronics magazine June 2025  59 Fig.5: the TI TPA3250 IC contains four amplifiers that are bridged into two channels for stereo, similar to this example circuit from the device’s data sheet. The Class-D RF carrier is filtered out by sets of LC filters before the audio signal goes to the speakers. GPS-Synchronised Analog Clock with long battery life ➡ Convert an ordinary wall clock into a highlyaccurate time keeping device (within seconds). ➡ Nearly eight years of battery life with a pair of C cells! ➡ Automatically adjusts for daylight saving time. ➡ Track time with a VK2828U7G5LF GPS or D1 Mini WiFi module (select one as an option with the kit; D1 Mini requires programming). ➡ Learn how to build it from the article in the September 2022 issue of Silicon Chip (siliconchip. au/Article/15466). Check out the article in the November 2022 issue for how to use the D1 Mini WiFi module with the Driver (siliconchip.au/Article/15550). Complete kit available from $55 + postage (batteries & clock not included) siliconchip.com.au/Shop/20/6472 – Catalog SC6472 60 Silicon Chip Australia's electronics magazine siliconchip.com.au ST-01 was flat, within ±0.2dB from 20-20kHz when the controls were at the mid-position. The bass control added +12.5dB at 20Hz or cut it by -15dB. Bass boost can help make up for smaller speakers having less bass output. The treble control gave a boost and cut of +6dB and -6dB at 20kHz. That can be quite useful if your speakers have an overly muted or bright sound. Full bass or treble boost may not be effective at high power levels, as you could run into clipping. The frequency response plot shown in Fig.4 was made at 1W into 8W. The distortion (THD+N) shown in Fig.6 is 0.03-0.08% at 1kHz & 1W, which is acceptable for a hybrid amplifier. It is mainly due to the addition of harmonics (not noise) from the valve preamplifier, as was visible in the spectrum analysis graph (Fig.3). For these measurements, we used an Audio Precision AUX200/AES 17 ‘brick wall’ 20kHz low-pass filter system, which prevents the class-D carrier from interfering with the accuracy of the measurements. However, it also cuts out the second harmonic above 10kHz, third harmonic above 6.5kHz etc. Hence the dip above 6kHz in Fig.6. In this amplifier, we measured the carrier at 359kHz, and the filters attenuate that by more than 50dB. Clipping began at 20W with 0.1% THD+N into 8W, with the THD+N climbing to 1% at 30W. The clipping was noticeably ‘soft’ (see Fig.7). Around 33% more power can be delivered using a larger 24V/6A power supply than the one that comes with the amplifier. Conclusion The Douk ST-01 Pro amplifier is a very compact, lightweight and versatile device with quite decent power output and acceptable distortion levels. Its cute factor is bound to impress, especially for its warmth in small rooms. The ability to accept signals from various sources is very handy, and its price is quite reasonable for what you get. It is pretty unusual for a hybrid amplifier to accept 15 valve types. This is a plus for valve enthusiasts, and experimenting with it is quite SC fun too. Fig.6: the THD+N is 0.03-0.08% at 1kHz & 1W, which is acceptable for a hybrid amplifier and is mainly due to the addition of harmonics (not noise) from the valve pre-amplifier. The variation between the channels is due to differences in the valves, which are obviously not a matched pair. Fig.7: the THD+N vs power into 8W shows that soft clipping begins at around 20-30W, making it very usable in a smaller room, especially with large speakers, which are usually quite efficient. siliconchip.com.au Australia's electronics magazine The amplifier is tiny despite its reasonably high power output. The minuscule class-D IC has had its heatsink removed in this photo. June 2025  61 Tim Blythman’s 433MHz Digital Receiver Module We recently published our version of the ubiquitous 433MHz (LIPD band) transmitter module, which performs better than many prebuilt versions. Having found a suitable receiver IC, we then created our own version of a matching receiver module, and it is better too! W e wrote about our 433MHz Transmitter Module in the April issue (siliconchip.au/Article/17950). That article discussed the LIPD (Low Interference Potential Devices) RF band, which covers 433.05MHz to 434.79MHz and can be used without a paid licence. There are some simple provisions, including that the EIRP (equivalent isotropically radiated power) must not exceed 25mW. This is of concern for a transmitter, and we explained how our Transmitter Module was compliant. Of course, this should not be a problem with a receiver, so we don’t need to worry about that aspect for this project. These sorts of receivers and transmitters are typically used to send digital data at a low bit-rate (up to around 10kbit/s) to provide a wireless link over distances up to 100m, such as around a home. Typical applications include remote control of devices like garage doors and gates, or for sending data from remote sensors back to a base unit, as might be found in a wireless weather station. Fig.1 shows a block diagram of such a system. As we mentioned in the earlier article, multiple layers of encoding are often used to make the best use of the medium and to allow systems to coexist with others nearby by providing identity and data validation (checksum) features. We noted how the receivers use AGC (automatic gain control) to receive data at differing signal strengths. Simple OOK (on-off keying) means that it is quite straightforward to extract a digital signal from the ambient background RF noise. 62 Silicon Chip Effectively, the receiver keeps track of the average RF signal strength (over millisecond time scales). If the instantaneous RF signal is stronger than the average, a logical high is sent to the data output, while a low output is when the RF signal is weaker than average. (That explains why you get noise from the output when there’s no RF signal; atmospheric noise on that frequency will constantly vary above and below its average.) We’ve used these sorts of transmitters and receivers in numerous projects. The most recent was the Battery Powered Model Train from January (siliconchip.au/Article/17607). John Clarke even designed a 433MHz Wireless Data Range Extender, which was published in May 2019 (siliconchip. au/Article/11615). 433MHz receiver Our earlier 433MHz Transmitter Module is a drop-in replacement for the likes of the Jaycar Cat ZW3100 and Altronics Cat Z6900. It has the same pinout, general size and shape as those modules. The Transmitter Module article has comparative performance tests between our unit and the Jaycar ZW3100. This Receiver Module is intended to be a substitute for the corresponding receivers, Jaycar’s Cat ZW3102 and Altronics’ Cat Z6905A. If you compare the photos above and below, you can see that we have aimed for the same pinout and size, but you’ll note that our unit has an extra pin (for RSSI, a useful extra feature). The Transmitter Module uses a Microchip MICRF113 IC and the Receiver Module uses a MICRF220 IC. These are both intended for use in these sorts of applications on LIPD bands, which makes our design task easier. The MICRF220 IC One of the quirks of these receiver modules is that when there is no nearby transmission, the DATA pin will produce a stream of random data. This is analogous to an AM radio (for those that remember radios before they became digital!) playing static when tuned between stations. This can be a source of frustration for those using these modules for the first time, since the decoder (typically the right-hand microcontroller in Fig.1) must be able to separate this background noise from valid data. Fig.1: a matching transmitter and receiver pair form a one-way wireless link to transmit small quantities of digital data. A previous article covered the construction of a transmitter module. Australia's electronics magazine siliconchip.com.au Features & Specifications » Drop-in replacement for Jaycar ZW3102 and similar 433MHz receiver modules » Operates from 3.3-5V » Optional RSSI output (analog voltage, 0.5-2V) » 6mA nominal operating current » Optional squelch feature, configurable by resistors » Faster rise and fall times, less latency than some prebuilt receiver modules » Sensitivity with onboard antenna is superior to other modules with an external wire antenna » Short AGC settling time Fig.2: our circuit is based on the MICRF220 RF chip for receiving digital data on the 433MHz band. It requires a 3.3V supply, provided by REG1. As well as receiving data, it provides an RSSI signal so the controller can determine whether an RF transmission is occurring and how strong the signal is. One simple strategy is to look for signal transitions occurring more frequently than anticipated for the expected data stream; the presence of high frequency components is typical of the white noise that occurs with no signal. So, when frequent transitions are seen, the data can be ignored. The data sheet for the MICRF220 describes it as a “300MHz to 450MHz 3.3V ASK/OOK Receiver with RSSI and Squelch”. Squelch is a handy feature on radio receivers that can suppress the output unless a strong enough signal is received. To maintain compatibility with the older modules, our Receiver Module can be built with or without the squelch feature. It is enabled by simply fitting a single resistor. We made this optional, since some designs may depend on the noise to detect a valid signal. RSSI stands for ‘received signal strength indicator’, and it is exactly what it sounds like. There is an RSSI pin on the MICRF220 that produces an analog voltage related to the received signal strength. The data sheet gives figures of 0.5V for a -110dBm RF input level and 2.0V for -50dBm. This is the extra pin on our design. Note that the theoretical frequency range of the MICRF220 extends well beyond the 433/434MHz band. The components we have selected are intended to optimise the operation for this band; different values are needed for the likes of the 315MHz band, which sees similar use in the USA. The MICRF220 data sheet discusses this in more detail. Circuit details Fig.2 shows the circuit diagram of our Receiver Module. Power comes in through the various GND and Vcc pins on CON1 and CON2. These are chosen to match the pinouts of other receiver modules, so a few are duplicated. The MICRF220 is a 3.3V device, so we have provided a 3.3V regulator Our Receiver Module (shown in the lead photos) is the same size as boards like the Jaycar ZW3102 shown here, but has a couple of extra features. The extra RSSI pin produces a voltage related to the received signal strength. It also has an optional onboard PCB trace antenna. These photographs are shown at 125% scale for clarity. siliconchip.com.au Australia's electronics magazine to allow operation with a 5V supply. REG1, an MCP1700, can tolerate up to 6V on its input. The two 1μF capacitors are recommended input and output bypassing capacitors. The remainder of the circuit is centred on IC1, the MICRF220 receiver IC. Pin 8 (SHDN) is tied low with a 100kW resistor to enable the chip whenever it is powered. Capacitor C10 is an optional part noted in the data sheet. When fitted, it will assert the shutdown state momentarily while the chip is powered on. We didn’t find it was necessary to fit it. Power from the regulator comes into pins 5 (power) and 9 (ground) of IC1, with a 100nF capacitor providing further bypassing. The circuit around the two inductors at lower left is the recommended matching network for the RF signal going into pin 3 of IC1 from the external antenna (‘ANT’) connection. Adjacent pins 2 and 4 are RF ground. We were able to comfortably fit all the required parts in the necessary PCB area, with room to spare, so we added a PCB trace antenna. It can be connected by closing jumper JP1 with a solder blob or 0W resistor. The antenna is about 16cm long, suitable for use at 433/434MHz. Adding the length of the other connected traces, it is very close to the nominal 173mm needed for a quarter-wave antenna at 433MHz. Otherwise, an external antenna can be connected via the module’s ANT pin. June 2025  63 Scope 1: the current consumption of our module, measured with a low-side 100W shunt resistor, is very close to the 6mA noted on the data sheet. It rises slightly when the data output is high. Scope 2: the ZW3102 that we tested only drew 3mA during operation, although its data sheet indicates a maximum of 10mA. Scope 3: the blue trace is a signal applied to a transmitter module, while the green trace is the DATA output from our Receiver Module. The red trace is the output from a prebuilt ZW3102 module. Our module is clearly quicker to respond, with sharper edges. 64 Silicon Chip Australia's electronics magazine Pins 1 and 16 of IC1 connect to a 13.52313MHz crystal and its loading capacitors. Like the Transmitter Module, this circuit uses a ×32 PLL (phaselocked loop) to generate a reference frequency. You might notice that the crystal for the Receiver Module is a different frequency to that on the Transmitter Module (13.56MHz). That is because the MICRF220 uses an IF (intermediate frequency) demodulator. The PLL frequency is mixed with the incoming RF signal to produce a signal with a frequency about 1MHz lower. This lower-frequency signal is easier for the IC to extract the data from. Pins 7 and 11 (SEL0 and SEL1) select the demodulator bandwidth. We have chosen the 13kHz low-pass filter setting by leaving both of these pins to be pulled high by their internal current sources. Fitting a 10kW resistor for either or both of R1 and R2 will change this setting. Pin 13 of IC1 (CAGC) is connected to a 470nF capacitor; this value is also dictated by the data sheet and the bandwidth setting described above. The level on this pin sets the gain of the internal amplifier; it is part of the AGC control loop. This capacitor value ensures that the AGC responds at the correct rate to allow the data of interest to be received. The RSSI signal from pin 14 is internally derived from the CAGC signal by being inverted and buffered. It is fed to the extra pin on CON1 via a 1kW resistor. This protects the chip from potential short circuits. The capacitor on the pin 12 (CTH) provides bypassing of an internal reference voltage that is used by a comparator to generate the output on pin 10 (DO). Like RSSI, the DO output is protected by a 1kW series resistor between it and the external DATA pin. Pin 6 (SQ) enables the squelch feature. When left open, an internal pullup current disables squelch. Fitting R5 will pull the pin low and enable squelch. For any of pins 6, 7 or 11, the pullup is around 5μA, so a resistor of 10kW or lower will be more than sufficient to overcome the pullup. Operation The MICRF220 uses around 6mA when configured for 433MHz operation. At this level, the dropout voltage siliconchip.com.au of the regulator is less than 100mV, so it will not have much effect on the output voltage, even if a 3.3V supply is used. Most 5V microcontrollers we have seen will happily accept 3.3V logic levels, and the MICRF220 works down to a 3.0V supply voltage, so this Receiver Module will be suitable for 5V and 3.3V systems. If you are considering changing the SEL0 and SEL1 settings by adding resistors R1 and/or R2, you should check the MICRF220 data sheet closely as some other parts may need to change values. You shouldn’t need to do this, as the default bandwidth settings should work fine with lower data rates. Comparisons We thought it was important to describe the operation of our Receiver Module and the MICRF220 because it has quite an impact on the performance of the Module compared with other receiver modules. We compared our Receiver Module (using its onboard antenna) to the Jaycar ZW3102 fitted with a simple wire antenna. We used our previously described 433MHz Transmitter Module as the RF source for the tests. Our first test was to confirm the operating current of the modules. The MICRF220 data sheet notes a typical current of 6mA; the MCP1700 has a quiescent current of 1.6μA, so it does not contribute significantly to the Receiver Module’s consumption. We rigged up a 5V supply and a 100W resistor as a low-side current measuring shunt on a breadboard. The breadboard allowed us to change between the two modules without otherwise altering the circuit. Our Receiver came in right on 6mA, as seen in Scope 1. You can see that the current does come up slightly when the output pin is high; it reaches 6.1mA. The ZW3102 measured just under 3mA, whether its output was high or not (Scope 2). Interestingly, its data sheet notes a 10mA maximum, so there may be more variability amongst these modules. This shows us the latency, or delay, between the input and output. The output of our Receiver Module is not only faster (24μs vs 28μs on rising edges and 24μs vs 34μs on falling edges), but more symmetrical and it also has sharper edges. We monitored the output of both receivers when a 1kHz square wave was applied to the transmitter’s DATA input. Scope 3 shows the falling edge of a pulse on the DATA input, with the two receivers responses following. We also performed some tests to see how the receivers would respond to different OOK modulation frequencies. As we changed the frequency at the DATA input of the transmitter, we watched the receiver outputs to see how well they followed the input. Above 10kHz, the output is 90° or more behind the input for both receivers, as seen in Scope 4. You’ll see that our Receiver is still delivering a signal that is closer in time to the original signal than the ZW3102. Both receivers are receiving a solid signal at this frequency. Sensitivity You might recall from our article on the Transmitter Module that its output power can be set by altering a single resistor value. This allows us to easily produce weak signals to compare the sensitivity of the two receivers. We performed some tests to compare the relative sensitivity of the receivers. With the two receivers side-by-side on the same breadboard, we monitored how they responded to a transmitter on the other side of our laboratory; this was an Arduino connected to one of our Transmitters to output a typical encoded waveform. The first test was with the Transmitter at full power, and Scope 5 shows an interesting result. Here, we see how quickly the receivers ‘lock on’ to the signal. Our Receiver Module settles its AGC at the correct level a full Scope 4: at 10kHz, a higher frequency than used for Scope 3, you can see the difference in latency between the two modules. This is quite a bit higher in frequency than most 433MHz transmissions we have seen, with 1kHz being more typical. Latency and bandwidth For the next few tests, we rigged up the two receivers side-by-side on a breadboard, allowing them to be seen responding to the same transmissions. siliconchip.com.au Scope 5: the blue trace here is our Receiver’s RSSI pin, while the green trace is its DATA output; the red trace is from a ZW3102. You can see how much more quickly our Receiver locks on to the incoming signal and starts producing valid data. Australia's electronics magazine June 2025  65 Parts List – 433MHz Reciever Module 1 double-sided PCB coded 15103252, 11.5 × 43mm 1 5-way right-angle pin header (CON1) 1 4-way right-angle pin header (CON2) 1 13.52313MHz two-pin SMD crystal, 5.0 × 3.2mm (X1) [Abracon ABM3-13.52313MHZ-10-B4Y-T] 1 39nH inductor, M1608/0603 size (L1) [Murata LQG18HN39NJ00] 1 33nH inductor M1608/0603 size (L2) [Murata LQG18HN33NJ00] Semiconductors 1 MICRF220AY 300-450MHz ASK receiver IC, QSOP-16 (IC1) 1 MCP1700-3302 3.3V LDO linear voltage regulator, SOT-23 (REG1) Capacitors (all M2012/0805 size, X7R 50V ceramic unless noted) 2 1μF 1 470nF SC7447 Kit ($20 + postage): 2 100nF includes all the parts listed here 2 10pF NP0/C0G 2 1.5pF NP0/C0G Resistors (all M2012/0805 size, ⅛W 1%) 1 100kW 2 1kW Extra resistors for option selections 3 10kW M2012/0805 ⅛W 1 0W M1608/0603 OR bridge JP1 with solder Scope 6: using the same trace colours as Scope 5, we see the two modules responding to a weaker signal. The RSSI is lower, and the ZW3102 is producing glitches that are not seen in our Receiver’s output. 15ms before the ZW3102; you can still see glitches in the latter’s output for this time. The blue trace that we have used as a trigger is the RSSI output of our Receiver. Then we used a 1kW resistor to set the output power to 12dB below nominal. Scope 6 is the result of this. The RSSI trace sits at around 1.4V or -74dBm, and our Receiver has picked out clean data, while the ZW3102 is seeing some data but is delivering glitches too. At lower levels than this, we could not see any data on either receiver. This is useful information in that we now know that a level of around 1.4V indicates sufficient RSSI to receive a valid signal. Remember that these tests were done with the Receiver’s onboard antenna; an external antenna should give even better results. While running these tests, we also used a software-defined radio receiver to monitor the relative RSSI. It indicated that these active transmissions were only about 10dB above the background RF level. Squelch We also ran some tests to try out the squelch feature. For these, we simply shorted out the R5 pads on the PCB to pull IC1’s pin 6 low. The data sheet notes the chip will “monitor incoming pulse width before allowing activity on DO pin.” So it doesn’t appear that RSSI is used to control the squelch. Scope 7 shows a typical waveform with squelch active. You can see that there is still activity on the DATA line even when the RSSI is low. It appears that this is where the 13kHz filter is used, as signals at a higher frequency are cut off and do not appear on the output. So the squelch is helpful, but does not completely remove the need to filter out unwanted activity on the DATA pin. Construction Scope 7: even with Squelch enabled, our Receiver still produces the occasional spurious pulse on the DATA line when the RSSI is low. So you shouldn’t expect the Squelch to completely eliminate the need to reject noise on the DATA line, but it helps to reduce it quite a bit. 66 Silicon Chip Australia's electronics magazine The 433MHz Receiver Module uses some small SMD parts, although nothing that can’t be hand-soldered with a little patience. IC1 comes in a 16-pin QSOP (quarter-size small-­ outline package) with a 0.635mm pin pitch, and the regulator is a SOT-23 part. Most of the passives are M2012 (0805) size at 2.0 × 1.0mm, although the two inductors are M1608 (0603) size or 1.6 × 0.8mm. siliconchip.com.au We’ve used M2012-sized pads for the passives throughout to ease construction. Where possible, we have lengthened the pads on the PCB to make it easier to apply solder. This also gives a bit more room between the components. So you’ll need the standard surface-­ mounting gear; a fine-tipped soldering iron and some flux paste are the bare minimum. You should also have tweezers, a magnifier, solder-wicking braid and some good illumination. Your flux will probably also require a solvent for cleanup, although we find that isopropyl alcohol is a good generic option. The Receiver Module is built on a double-sided PCB that’s coded 15103252 and measures 11.5 × 43mm. Figs.3 & 4 are the overlay diagrams that show where the parts are placed. You can also refer to the adjacent photos during construction. All the mandatory components are on one side of the PCB, as shown in Fig.3. Apply flux paste to the pads for all the components on that side. Start by placing the IC over its pads on the PCB, noting the orientation of the pin 1 marker; our chip had a moulded divot, which was easy to find. Clean the iron’s tip and apply a little fresh solder. Tack one lead and check that the other pins are lined up on both sides. If so, carefully solder the remaining pins, cleaning the tip and adding extra solder as needed. Otherwise, use the iron to melt the solder and tweak the chip with tweezers until it is located correctly. If you end up with a solder bridge joining two or more pins, add extra flux paste and press the braid against the bridge with the iron, then gently draw both away once the excess solder is drawn up into the braid. Next, fit REG1, the SOT-23 regulator. It should only fit one way, with its leads down flat on the PCB, so place it, tack one lead and check the position. If all is well, solder the other two pins. If any joins don’t look great, add some extra flux and touch the iron to the pad and pin to refresh the solder. The two inductors at bottom left should be fitted next as they are the smallest remaining parts. We’ve seen some SMD inductors that only have pads on the underside, which makes them a little more tricky to solder. Don’t forget that most SMD parts are siliconchip.com.au Figs.3 & 4: to use the onboard PCB trace antenna, close JP1 with a blob of solder or 0W resistor. The rear of the PCB shows the functions of the external pins. If you wish to enable the squelch function, you can fit a 10kW resistor for R5. These diagrams are at 200% scale. usually designed to be soldered by a machine! You might be able to make out a black mark on one end of the inductors. We’ve fitted our prototypes with the band to the left and on the top, which you can see in the photos. We don’t think it will make any difference, but we recommend you do the same. RF can be strange and we don’t want to tempt the fates! Use the same technique of soldering one lead then the other once the location has been correctly fixed. You can check that the inductors are connected to their pads by doing a continuity test; they should read well under 10W. For the 33nH part, you can probe between the ANT and GND pads of CON2. For the 39nH inductor, probe between ground and the right-hand pad of the 1.5pF capacitor directly above the inductor. If either inductor reads high resistance, add more flux and try soldering each lead again. Solder the crystal (X1) next. It probably will have leads only on its underside, but the PCB pads are generously sized, so they will be easy to press the soldering iron against. As long as there’s flux paste on the pads when you place the crystal, solder should flow between the pads and crystal. Unfortunately, you can’t check a crystal for continuity as you can with an inductor. The remaining mandatory small parts are all M2012 (0805) passives, and they are marked on the PCB silkscreen. Check their values closely against the overlay diagram, since the markings are quite small. There are nine capacitors and three resistors that must be fitted. Be careful not to get the Australia's electronics magazine capacitors mixed up once you remove them from their packages; they will not be marked with values. If you wish to enable the onboard trace antenna, you need to close JP1. An M1608/0603 0W resistor will work, but the easiest way to do this is to generously apply solder with an iron to both of JP1’s pads. The solder mask will cause the solder to bead, but if you add enough solder, you should be able to bridge the pads (you can see we did it in our photos). You can now enable the squelch feature by adding a resistor (we suggest 10kW) to the R5 pads if you want. We have also labelled this with Squelch text. At this stage, we recommend cleaning the board thoroughly with your recommended flux cleaner or another solvent. Allow the board to dry and scrutinise it for bridges and pins not soldered to the pads below. If you see any problems, touch up the board, then clean it and allow it to dry again. Fitting the headers We recommended using right-­ angle headers since they will match the headers found on other common modules. However, you could choose straight headers if you need to mount the Receiver Module parallel to another PCB. It will depend on your planned application. If you are connecting the Receiver Module to an existing design, use two four-way headers. Older designs will not expect a connection for the RSSI pin, so you should leave that pad unconnected (you could run a flying lead from that pad if you want to monitor the RSSI output). June 2025  67 We recommend slotting the two groups of headers into a longer header socket to keep them aligned to the correct 0.1in pitch before soldering (see the photo below). Solder the pins in your preferred orientation, then remove them from the header socket. If you have jumpered the onboard antenna, the external ANT pin does not need to be connected. In this case, all the connections that are usually needed (GND, DATA and Vcc) are at one end of the board, and can be made using a single four-way header. An NPN transistor with a 1kW resistor between its base & emitter could also be used as a threshold detector, as shown in Fig.5. The RSSI signal is fed into the base and the 1kW resistor on the Receiver PCB forms a divider with the external resistor to set the threshold. We tried this out on a breadboard and it worked quite well. You could also bypass the LED and use the voltage at the collector as an active-low digital RSSI threshold signal to a microcontroller or other circuitry. Using it Our 433MHz Receiver Module has some handy features that make it a better choice for new designs. It generally responds more quickly to an incoming RF signal. At the same time, it is backward-­ compatible with older modules for use in legacy circuits that require a 433MHz receiver. The Receiver Module works with 5V and 3.3V systems, which we think will cover most cases. The squelch feature does not appear to eliminate noisy data output during the gaps between RF transmissions, but it does reduce it. We think that the RSSI output will be more useful in testing the validity of a signal on the DATA pin. Our Receiver consumes a bit more current than the ZW3102, but it is still low enough that it could, for example, be powered from a microcontroller GPIO pin, allowing it to be completely powered off if necessary. The Receiver Module is quite sensitive, even when just using the onboard PCB trace antenna, picking up all transmissions that the ZW3102 could with an external antenna. Our design still allows for an external antenna if SC that is preferred. Since it is a module, the usage will depend a lot on your intended project. In general, you should connect a supply of 3.3-5V to one or more of the Vcc pins and one or more of the GND pins. If you have not enabled the onboard antenna, an external antenna should be connected to the ANT pin. As we noted earlier, a 173mm-long wire (including the length of the headers and traces back to the matching network) works well as a quarter-wave antenna for 433MHz. It can be curled or corkscrewed to save space if necessary. We have found that the Receiver Module is capable of receiving nearby signals without an external antenna; you might try this for testing purposes. In general, you should have no trouble using it to replace a receiver anywhere we have specified the Jaycar ZW3102. Conclusion Fig.5: this simple circuit can be used to generate an indication that an RF transmission is being received based on the RSSI. The resistors set the threshold to about 1.2V, which we found to be a suitable level for distinguishing a valid signal from none. Our unit varied around 0.9V to 1.1V when no intended transmission was occurring. This level might be lower in a less urban area than the location of our lab. With an active transmitter, we saw values between 1.3V and 2.0V. This could be measured by a microcontroller’s ADC (analog-to-digital converter) peripheral to detect the presence of a signal. Another option is a comparator set to an appropriate threshold. Some micros (including the 8-bit PIC16F18146) include a comparator The RSSI voltage peripheral that could be used for this The RSSI pin delivers an analog purpose. The micro could then be provoltage between 0.5V and 2.0V, so a grammed to ignore any transitions on microcontroller with an analog-to-­ the DATA pin unless the RSSI indidigital converter will be well-suited cates that a strong enough signal is to monitoring the RSSI. present. We closed JP1 by bridging it with solder (you can also use a small 0W SMD resistor). You will need a generous amount to bridge the gap between the pads. 68 Silicon Chip Using a socket strip as a guide will ensure that the pins are soldered with the correct separation even though they are in two groups. Australia's electronics magazine siliconchip.com.au SOnline ilicon Chip Shop Kits, parts and much more www.siliconchip.com.au/Shop/ Compact OLED Clock & Timer September 2024 Short-Form Kit SC6979: $45 siliconchip.au/Article/16570 This kit includes everything needed to build the OLED clock, except the UB5 Jiffy box and Li-ion cell. Dual Mini LED Dice August 2024 Micromite-Explore 40 October 2024 Complete Kit SC6991: $35 SMD LED Complete Kit SC6961: $17.50 TH LED Complete Kit SC6849: $17.50 siliconchip.au/Article/16418 siliconchip.au/Article/16677 Includes either 3mm through-hole or 1206sized SMD LEDs. Choice of either white or black PCB. CR2032 coin cell not included. Includes the PCB and all onboard parts. Audio Breakout board and Pico BackPack are sold separately. Compact HiFi Headphone Amplifier Complete Kit SC6885: $70 Capacitor Discharger December 2024 December 2024 & January 2025 siliconchip.au/Series/432 This kit includes everything required to build the Compact HiFi Headphone Amplifier. The case is included, but you will need your own power supply. Programmable Frequency Divider Complete Kit SC6959: $60 Short-Form Kit SC7404: $30 siliconchip.au/Article/17310 Feb25: siliconchip.au/Article/17733 Includes all onboard components, except for a power supply and the optional programming header. 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. siliconchip.com.au Australia's electronics magazine June 2025  69 By Andrew Levido Precision Electronics Part 8: Voltage References Last month, we looked at sampling and aliasing in DACs (digital-to-analog converters) and ADCs (analog-to-digital converters). Now we will describe how voltage references work, as they are critical to the precision of both ADCs and DACs. W e have covered a fair bit of ground so far in this Precision Electronics series, but we have not looked at the important topic of voltage references in detail. We mentioned them in our discussion of analog-to-digital and digital-to-analog conversion, but now is the time for a deeper dive. In the very first article in this series, we discussed the difference between precision and accuracy. We learned that precision describes the repeatability or reliability of a measured quantity and is all about understanding and quantifying sources of error. On the other hand, accuracy is how closely a measured value matches the ‘true’ value (or an accepted proxy) of the quantity. Most of what we have covered so far has been concerned with precision rather than accuracy. Voltage references are one of the places where these two come together. Put simply, voltage references provide a fixed voltage source at some defined value. This sounds simple, but there is a lot to unpack in that statement. Initial accuracy – or not The “defined value” part is where accuracy comes into play. A voltage reference is expected to provide a known output with some specific level of accuracy; that is, some measure of how close its output voltage is to the ‘true’ value. This requirement implies the source has been calibrated somehow against a known standard. In many cases, this calibration is done for you at the factory, but sometimes you are expected to do it yourself. An example of the former is the MAX6225ACSA reference we used in the DAC circuit in a previous instalment of this series. This is a 2.5V reference with an initial accuracy of ±200ppm (±0.02%). This means the voltage will be between 2.4995V and 70 Silicon Chip 2.5005V at 25°C – a figure achieved by calibration at manufacture. Calibration would have been performed by trimming the chip’s output voltage against a voltage standard with even higher accuracy. This standard will have been itself calibrated against an even better standard, and so on, in a chain ultimately traceable to the international standard definition of the volt. Not all voltage references are trimmed to a standard voltage at manufacture. Some very expensive ultra-precision voltage references have woeful initial accuracy. The legendary LTZ1000, which will cost you the best part of $150, has an initial output voltage anywhere between 6.9V and 7.5V, but has extraordinary precision. The intention is that you will calibrate the device in which you use this reference against some external standard, then take advantage of its incredible stability to ensure it stays that way. Voltage reference errors Whether you use a pre-calibrated or post-calibrated voltage reference, knowing its stability is critical. As you would expect, changes in temperature influence voltage references; achieving a stable voltage over temperature has been one of the driving forces behind the development of voltage reference technologies. You will therefore see a figure for temperature drift in the voltage reference data sheet in the familiar absolute (V/°C) or relative (ppm/°C) units. In many cases, you will also see a ‘thermal hysteresis’ figure. This is the maximum voltage change seen after cycling the device over some fixed temperature range – typically (but not always) from 25°C to 50°C and back. This is important because of the focus on accuracy; if the voltage changes slightly with temperature, we at least want it to return to a consistent value Australia's electronics magazine each time it reaches a given temperature. To add to the growing list of errors, voltage references also drift with time, even if the temperature is held constant. Most precision voltage reference data sheets therefore include a figure for ‘long-term stability’ or similar. This can be expressed as an absolute or relative change in voltage per root thousand hours (ppm/√kh) or per thousand hours (ppm/kh). The odd unit of root-kilohours is used because long-term stability typically has a logarithmic decay characteristic, with more drift in the first 1000 hours than in the second and so on. Because of this early drift, some manufacturers of precision equipment using will ‘burn in’ the voltage references for a period before using them. This improves the long-term accuracy of the references (since the higher initial drift is done with), and allows the manufacturer to weed out any that show too much variation. To put some context around these errors, consider the MAX6225ACSA. The initial accuracy was ±200ppm with a tempco (temperature coefficient) of ±2ppm/°C and a thermal hysteresis of 20ppm. The worst-case longterm drift is ±20ppm/kh. These are all pretty good figures, but the LTZ1000 is in a different class. This latter chip includes an on-chip heater to keep the reference at a stable temperature, resulting in temperature drift in the ±0.05ppm/°C range. No thermal hysteresis figure is given, since the reference is always held at a constant temperature. Long-term stability is quoted as 0.28ppm/√kh. I should note that building a device using the LTZ1000 or similar ultra-­ precision references is no trivial task. To get the most out of the chip, you must employ some ridiculously expensive high-precision, low-tempco resistor dividers and worry about all siliconchip.com.au sorts of crazy details. Take this quote from the data sheet as an example: The Kovar input leads of the TO-5 package form thermocouples when connected to copper PC boards. These thermocouples generate outputs of 35µV/°C. It is mandatory to keep the ... leads at the same temperature, otherwise 1ppm to 5ppm shifts in the output voltage can easily be expected from these thermocouples. Air currents blowing across the leads can also cause small temperature variations... There is a whole online community dedicated to getting the best possible performance out of these and similar devices. Just search for “voltnuts”. Series and shunt references Voltage references fall into two major categories: three-terminal (series) or two-terminal (shunt) devices, both of which are shown in Fig.1. Series references ‘regulate’ an input voltage to produce the reference output. As you might imagine, the output is influenced by changes in the input voltage and by the load current, so for series regulators you will see figures in the data sheet for line and load regulation (ie, how stable the output is despite variations in input voltage and output current, respectively). In the case of the MAX6225ACSA, the line regulation is ±7ppm/V for a Vin above 10V and the load regulation is ±6ppm/mA. You should therefore ensure the input to a series voltage reference is well-regulated and keep the load current low and stable. Achieving the latter can be a bit of a juggling act: you can add an op amp buffer to minimise the load current, but this will itself introduce errors that might outweigh those produced by the reference’s load regulation. You have to crunch the numbers to work out what is optimal. On the other hand, shunt references maintain a constant voltage drop while current is flowing through them. The voltage drop is influenced by the device current, and you can see from Fig.1 that this current is determined by both the source and the load currents. Shunt references therefore usually include a single figure for output voltage change with current that encompasses both line and load regulation. You should therefore aim to keep the device current constant if you want to achieve the best results with shunt-type references, most likely by siliconchip.com.au employing an active current source and by keeping the load current fixed. Changes in shunt current with temperature will add to the shunt element’s inherent temperature drift, so your current source needs to be relatively stable with temperature. Zener references The zener diode, with its well-­ defined reverse breakdown voltage, is the simplest form of shunt reference. This breakdown characteristic occurs because of two different mechanisms: the zener effect at low voltages, and the avalanche effect at higher voltages. The zener effect has a negative tempco, while the avalanche effect has a positive tempco. As both these effects are present in zener diodes with breakdown voltages around 5-7V, it is possible to have these temperature effects more-or-less cancel each other out by careful selection of the diode and its operating conditions. For example, a BZX55C5V1 5.1V, 400mW zener diode has a tempco of between +0.02% and -0.02% (±1mV/°C). By contrast, a BZX55C12 (12V) zener has a tempco of +0.11% (+13mV/°C). The initial accuracy of the 5.1V zener won’t be great, but fed with a constant current, its voltage stability will be surprisingly good. In fact, the LTZ1000 and MAX6225ACSA both use internal zener diodes as the basis of their reference. You can temperature-compensate a zener diode by putting it in series with a forward-biased standard diode, as long as you choose a zener with a tempco of about +2mV/°C. That’s because the tempco of a regular diode’s forward drop is about -2.1mV/°C. Otherwise, you can buy temperature-­ compensated zener references like the LM329, or even the LM399, which includes an on-chip heater. We mentioned above that you need to maintain a constant current through a zener reference. For example, the BZX55C5V1 has a dynamic resistance of up to 35W, so a change in bias current of just 1mA will shift the output voltage by 35mV – as much as a temperature rise of 35°C. Fig.2 shows a clever circuit that uses the zener itself to provide a stable bias current and allows the output voltage to be adjusted to boot. The zener voltage is amplified by the non-inverting amplifier to produce an output voltage, Australia's electronics magazine Fig.1: voltage references are available as either three-terminal series pass devices or twoterminal shunt devices. In either case, keeping the input voltage or current (and the output current) constant is critical to getting the best accuracy. Fig.2: in this circuit, the zener bias current is derived from its own stable output. R1 and R2 allow the output voltage to be amplified if necessary. Vout = Vz (1 + R1 ÷ R2). The output voltage is then used to establish the zener bias current via R3, Iz = (Vout – Vz) ÷ R3. You must use a single supply with this circuit – with a split supply, it could settle into a second stable state with the zener forward-biased. If you are worried about start-up, you can add a 1MW or greater resistor from the zener’s cathode to the positive supply. You will often see the term ‘buried zener’ to describe precision zener references. This just means that the diode junction (where the reverse breakdown occurs) is formed below the surface of the semiconductor and covered with a layer of diffusion material, resulting in a more stable device with lower noise. Band-gap references Band-gap voltage references are June 2025  71 much more common than zener references these days, especially inside integrated circuits. Pretty much every voltage regulator, linear or switching, uses one. Developing a semiconductor voltage reference with a low tempco was no trivial task, but it came down to adding a voltage with a positive tempco to another voltage with a negative tempco just like the compensated zener. The idea was first used commercially by Bob Widlar in 1971. Bob Widlar was an erratic genius who pioneered the first commercially successful op amps, comparators and three terminal-voltage regulators, among many others. Part of his success was to recognise and work with the strengths of the IC production process. He understood that it was very hard to manufacture components of precise absolute value in silicon, but was relatively easy to make components with precisely matched values. The Ebers-Moll large-signal BJT model (a really useful model I strongly recommend you study) tells us that the base-emitter voltage (Vbe) of a transistor is related to its collector current (Ic) by the relationship Vbe = Vt loge(Ic ÷ Is). Vt is the thermal voltage (proportional to absolute temperature) and Is is the reverse saturation current (also highly temperature-dependant). With a fixed collector current, the base-emitter voltage has a negative tempco of -2.01mV/°C, since the tempco of the Is term dominates. However, the difference between the base-emitter voltages of two transistors Fig.3: the simplest band gap reference consists of just three transistors. The voltage across R3 (Vbe1 – Vbe2), and therefore that across R2, has a positive tempco, offsetting the negative tempco of Q3’s base-emitter voltage. 72 Silicon Chip with different collector current densities has a positive tempco. This can be achieved by using two identical transistors with different collector currents. If you are mathematically inclined, it is pretty easy to see why by simplifying the expression Vbe1 – Vbe2 = Vt(loge[Ic1 ÷ Is] – loge[Ic2 ÷ Is]). This becomes Vbe1 – Vbe2 = Vt × loge(Ic1 ÷ Ic2). Note that Is has disappeared, leaving Vt with its positive tempco the only temperature-­ dependent term. Fig.3 shows how this phenomenon can be used in practice. Identical transistors Q1 and Q2 have collector currents in a 10:1 ratio because of the values of R1 and R2. Both transistors have the same base voltage, so the voltage at the emitter of Q2 must be Vbe1 – Vbe2. The 10:1 Ic ratio means this voltage will be 2.3Vt (around 60mV). The voltage across R2 will therefore be 23Vt or about 600mV. The output voltage, Vout, will be this voltage plus the Vbe drop in transistor Q3 for an output of around 1.2V. Importantly, the tempco of Vout will be that of Vbe3, around -2.01mV/°C, plus 23 times that of V t (23 × +86.2µV/°C = +1.98mV/°C), resulting in an overall tempco of -27.4µV/°C, which is around 10ppm per °C. Not bad for three transistors. This type of reference is called a bandgap reference because its output voltage for zero tempco corresponds with the theoretical bandgap voltage of the semiconductor material (~1.14V for silicon). Paul Brokaw developed an improved circuit in 1974, overcoming some of the limitations of the Widlar circuit, which could only produce a 1.2V output and required a fairly constant supply current. Brokaw’s circuit is shown in Fig.4. Brokaw’s circuit uses transistors with identical collector currents (due to identical R3s), but with differing physical on-chip areas to achieve different current densities. The voltage across R1 is the difference in base-emitter voltages, Vt × loge(N) where N is the ratio of transistor areas. The voltage across R2 is therefore Vt × loge(N) × 2(R2 ÷ R1), which has a positive tempco due to Vt. The reference output voltage will be this voltage plus the base-emitter voltage of Q1 with its negative tempco. By choosing the right values for R1, R2 and N, you can cancel the temperature Australia's electronics magazine dependencies as we did before. Fig.5 shows the same circuit configured to provide output voltages higher than the nominal 1.2V bandgap voltage. You can buy off-the-shelf bandgap references for around 60¢ each. The Microchip LM404x series, for example, are packaged as shunt references and available with output voltages from 1.225V to 5.000V. The 2.5V version in C grade has an absolute accuracy of ±0.5%. The versatile and very popular TL431 is even cheaper. This is also a 2.5V reference with a ±0.5% initial accuracy (C grade) with a typical tempco of ±10ppm/°C. You frequently see these devices in the voltage regulation circuits of low-cost flyback switch-mode power supplies. Many Silicon Chip projects have used them too. For example, the DC Supply Protectors project (June 2024; siliconchip.au/Article/16292) used one to set the over-voltage threshold. The 500W Power Amplifier (AprilJune 2022; siliconchip.au/Series/380) also used two, as part of the load-line protection circuitry. Exotic references Another more exotic voltage reference technology is the ‘JFET pinchoff’ reference. These work on a similar principle to the bandgap reference in that the difference in pinch-off voltage of two JFETs has a negative tempco that offsets the positive tempco of a current source. The ADR420 reference uses this technique to achieve an initial accuracy of ±400ppm (B grade) with a tempco of ±3ppm/°C. Its long-term stability is 50ppm/kh. The big advantage of this type of reference over bandgap references is their very low noise. Another interesting reference technology is the floating gate reference. These rely on a Mosfet (actually an array of Mosfets) with a well-­insulated ‘floating’ gate. At manufacture, charge is applied to the gate which, like a capacitor, charges to a particular voltage. The Mosfet then acts as a high-­ impedance voltage follower to read out this voltage. The voltage will remain stable as long as the gate charge does not change. The only commercial examples I am aware of are in the ISL2090 series. The 2.50V B-grade version has an initial accuracy of ±0.02%, a tempco siliconchip.com.au of ±7ppm/°C and long-term stability of 20ppm/kh. By my calculations (assuming a gate capacitance of 100pF charged to 1V), the gate leakage must be something less than 12 electrons per hour! Amazing. Voltage reference noise Depending on your application, you may have to take voltage reference noise into account. Unlike op amps, there is little consistency in how manufacturers specify the noise in their voltage references, especially at very low frequencies (say, below 10Hz). This is the area we usually operate in, and it is the territory where 1∕f noise tends to dominate, meaning we can’t just extrapolate from a wideband noise voltage to a noise density figure. Because we are dealing with DC signals, we can almost always add some filtering to reduce the voltage noise. Many references come with a ‘noise reduction’ pin that you bypass to ground with a small capacitor to improve the noise performance. For example, the MAX6225ACSA has such a pin which, if bypassed with a 1µF capacitor, will reduce the noise density above 100Hz from around 40nV/√Hz to under 15nV/√Hz. If we add an external filter, we have to make sure it does not adversely influence the reference voltage. Fig.6 shows one example of how we could do this. R1 and C1 form a low-pass filter with a -3dB frequency of 0.016Hz. The bottom end of C1 is bootstrapped by R2/C2 so that the voltage across C1 is zero in the steady state. If we did not do this, the leakage current through the capacitors would cause a voltage error as it is dropped across R1. You should also use a lownoise precision op amp buffer so that you don’t add new errors. Miscellany Precision voltage references can be expensive, so it is worth treating them with respect. Below are a few considerations you may need to be aware of, depending on your application. Solder shift: the worst thermal shock a voltage reference is likely to experience is during the assembly process, particularly if it is reflowed onto the printed circuit board (PCB). Like thermal hysteresis, this can cause a permanent change in the output voltage, known as ‘solder shift’. You generally won’t find information siliconchip.com.au on this in the data sheets, but there are a few app notes out there that discuss it. It is only going to be of concern for very high precision applications but is worth knowing about. You might want to hand-solder the reference if your application falls into this category. Start-up time: many references use their own output to provide stabilised bias conditions (like the circuit in Fig.2), so they include start-up circuitry to ensure everything comes up in an orderly fashion. This means that the output voltage might not reach its final stable value for some time. It is not unusual for this time to be tens or even hundreds of milliseconds. Your application should be aware of this and not use the reference until it is stable. Board flex: flexing a PCB that contains a precision reference can produce a measurable change in the output. One manufacturer suggests this can be as much as a 60ppm peak-topeak change for a reference mounted on a standard 1.6mm FR4 board that is 100mm wide board and flexed up and down by 1.8mm. You can minimise such mechanical stress by fixing boards down firmly and/or by using slots in the board to mechanically isolate the reference. Leakage: leakage currents across the surface of a printed circuit board can cause errors in precision references. References with noise-filtering pins (eg, the MAX6225ACSA) can be especially vulnerable, since these usually expose a high-impedance summing node to the outside world. A few tens of nano amps flowing into or out of one of these nodes can shift the output voltage by hundreds of ppm. Flux contamination or skin oils are more than enough to allow this level of current leakage, so it pays to clean your precision boards thoroughly and to keep your fingers off them once you have. Fig.4: the Brokaw band gap reference uses two transistors with the same collector currents, but of differing areas to produce a voltage across R2 with a positive tempco to offset the negative tempco of Q1’s base-emitter voltage. Fig.5: the Brokaw band gap reference can easily be adapted to produce higher output voltages. Conclusion Precision voltage references are unique in that they are one component that combines both precision and accuracy, allowing the device they are used in to deal in absolute quantities. In the next and final article of this series, we will zoom out and look at the big picture – how one might go about the high-level design of a precision electronics device from a wholes­ystem perspective. SC Australia's electronics magazine Fig.6: this RC filter reduces the noise voltage produced by a voltage reference by limiting the bandwidth to 0.016Hz. R1 and C1 are the filter, while R2 and C2 bootstrap the bottom of C1 to eliminate its leakage current, which would be otherwise be dropped across R1, causing the reference voltage to drop. June 2025  73 M easy-to-build Outdoor Subwoofer By Julian Edgar any people have outside speakers in a deck or patio area, but they are often small, wall-mounted designs that lack adequate bass response. This subwoofer project can add a lot of that missing bass. Because it’s built around a fibre cement stool available from Bunnings, very little woodworking is needed, and the enclosure is weather resistant. This design includes a simple and cheap protection mechanism that makes the subwoofer very hard to blow up (that’s always a danger with small subwoofers). Depending on your interior décor, it can also be used inside. The enclosure The subwoofer enclosure is based on an elegant white cement stool available from Bunnings, called the “Marquee 350 × 350 × 450mm Stool Side Sorrento” (I/N 0596376). It costs $69 and, while completely hollow, still weighs a little under 14kg. You don’t need to modify it; you simply glue an internal panel into it and add feet. Fibre cement is a good material for speaker enclosures, as it is acoustically dead (it doesn’t ‘ring’ when tapped) and is quite stiff. This stool is even stiffer than most because it uses a ribbed wall design. The fibre cement can be painted any colour you want. If you wish to make the subwoofer using another design of stool, or even (gasp!) from MDF or similar, the key dimension is that a volume behind the drivers of about 18L is required. The drivers This passive subwoofer is designed to be used on an outside deck or patio. It is quick and easy to build, and will add substantial bottom-end to your small exterior wall speakers. It’s also largely weatherproof. » » » » » » » » » » 74 Excellent frequency response for its size Inbuilt protection against being over-driven Medium-power design suitable for amplifiers up to 100W Uses low-cost drivers Easy and quick construction Largely weatherproof, suitable for undercover outdoor use Can also be used indoors Can be painted any colour to match décor Frequency response: 35-200Hz Impedance: 4Ω Silicon Chip Australia's electronics magazine Two drivers are used, mounted in an isobaric (face-to-face) configuration. Both are 170mm (6.5-inch) WS 17 E units made by Visaton. Note that you need the 8W versions. These speakers are available worldwide – a web search will find your nearest stockist. We bought ours from RS Components (Stock No 431-8563), but they ended up coming from the UK. A major criterion in their selection is that they are cheap – about $47 each, including GST. The speakers come with full ThieleSmall specifications, allowing computer modelling of the enclosure. Still, when bench tested with the Smith and Larsen Woofer Tester hardware/software package, the tested specs of the two drivers differed somewhat from the official specifications, even after being ‘run in’. siliconchip.com.au Table 1 shows the advertised specifications, the test results and the final values used in the modelling. Note that the stated maximum cone displacement is 13mm – something we’ll come back to later. Enclosure modelling Three different designs were modelled using the freely available WinISD speaker enclosure design software. These designs were sealed, ported and a 4th-order band-pass configuration. Fig.1 shows the modelled response curves of each design approach. The aim was to achieve a response from about 150Hz down to 40Hz. Good efficiency was also important – that is, the greatest output for a given power. Given that the bare driver has a fairly low efficiency (85dB at 1W/1m), achieving maximum efficiency becomes an important part of the enclosure design. Of the three designs, the sealed approach was the worst in efficiency and had a lower -3dB point of about 43Hz. The band-pass design had a much higher efficiency, about 4.5dB louder in the critical area, so the equivalent of having 2.8 times the amplifier power! It had a modelled -3dB point of about 42Hz, but as is the characteristic of such band-pass designs, fell away quickly at the top end, being 3dB down at 110Hz. This concerned me, as many small outdoor speakers will struggle to get down to 110Hz. The ported enclosure had a -3dB point of 36Hz (substantially better than the other designs), and was nearly 3dB up at 110Hz. It peaked at about 65Hz (over 6dB up) and had a greater ‘area under the curve’ than the other two designs. It was modelled using a 100mm-long, 50mm inner diameter port. Note that I was not aiming for a flat response – since the sub can be used outside, it needs as much gain as possible without becoming crazily peaky. This modelling was just a starting point – it’s easy to look at lines on a PC screen and think that they represent reality, not just a model of reality. However, software modelling is a good way of getting into the region of what is wanted. What counts as a subwoofer? A traditional subwoofer works only at very low frequencies – for example, below 40Hz. That is, the subwoofer provides output below the frequencies of a conventional woofer. However, over time, this definition has become blurred. Computer sound systems, for example, typically use two small satellite speakers that might work down to only 200Hz, with the separate ‘subwoofer’ providing the frequencies below this. Many high-level and custom car sound systems use a subwoofer, but again, it typically provides the bass component below 100-200Hz. So rather than developing only very low frequencies, a subwoofer has come to be known as any separate speaker that provides the bass. If you’re listening to music, how low a frequency response is actually required? The response of human hearing is stated as being 20-20,000Hz. However, age reduces this range, and 20Hz can arguably be more clearly felt as vibrations than heard. A pipe organ can produce notes at just 16Hz, but few pipe organ recordings have this low frequency content. There’s not much point in including sounds that no speakers will reproduce! A bass guitar and a double bass go down to 41Hz, which is clearly audible. A bass drum can produce frequencies of 20-120Hz, usually centred around 40Hz. The lowest note on a standard piano is 27.5Hz. So, while having as low a frequency response as possible is desirable, in the real world, a speaker system that can reproduce down to 40Hz will give the vast majority of what is needed. Whether you then call that speaker a subwoofer is up to you! This subwoofer is not designed to fill large outside areas with booming bass. To do so, it would need to be about ten times as big, ten times as expensive and ten times as powerful! Instead, it’s designed to add bottom-end and body to normal background music played at quiet-to-moderate levels in outdoor areas. Fig.1: the model outputs (predicted frequency responses) for three different enclosure designs: sealed (blue), band-pass (red) and ported (green). The ported design was chosen. Table 1 – WS 17 E 8Ω specifications Specification Listed Speaker A Speaker B Used in modelling DC resistance 6.3W 6.1W 6.2W – Sensitivity <at> 1W/1m 88dB 85dB 85db – Resonant frequency 41Hz 45Hz 43Hz 44Hz Qms 2.83 3.45 3.22 3.4 Isobaric configuration Qes 0.81 1.10 1.01 1.1 The two drivers are mounted in an isobaric configuration – that is, Qts 0.63 0.83 0.77 0.8 Vas 31L 25L 27L 26L siliconchip.com.au Australia's electronics magazine June 2025  75 Photo 1: the Bunnings fibre cement stool. Making it into a subwoofer doesn’t change its appearance much – it will just have a slightly larger gap at its base. Source: Bunnings Photo 2: this halogen incandescent light bulb is used as the speaker protector. Its resistance rapidly rises as the current flow through it increases, limiting the maximum speaker power. Source: Narva face-to-face with a small, trapped air volume between them. The drivers are wired out of phase so that as one pushes, the other pulls. The advantage of an isobaric configuration is that the drivers act as if they are working in a larger enclosure volume, and most importantly from our perspective, the power handling of the drivers doubles from a nominal 60W (90W peak) to 120W (180W peak). The use of paralleled drivers explains the need for selecting 8W designs – the two drivers then form a nominally 4W amplifier load. The WinISD software can model isobaric configurations. Test and development To initially test the design, a disc of 22mm-thick weatherproof particleboard was cut so that it would sit within the upturned stool, about 130mm down from the end. This placement gives room for the drivers and the port to project from both sides of the baffle. Two holes were cut in the particleboard disc – one for the drivers and the other for the port. The hole for the port was made a tight fit so that different lengths of 50mm ID PVC plastic pipe could be trialled. The gap between the edge of the particleboard disc and the inner wall of the stool was temporarily sealed. A layer of polyester quilt wadding 76 Silicon Chip was placed inside the enclosure, with care taken that it did not block the port. The wadding prevents sound reflections off the hard interior surfaces. The subwoofer stool could then be tested upside-down. A frequency generator app (Signal Gen from Media Punk Studios) on an iPhone was used in conjunction with an audio amplifier to test the subwoofer on sine wave sweeps from 150Hz down to 25Hz. Always test at low volumes – you can easily blow up drivers with sinewave testing! Different port lengths were trialled, with a 190mm-long port giving better results to my ears than the modelled 100mm port. Yes, that’s a big difference, implying the enclosure tuning point has moved from about 47Hz down to about 35Hz. Testing of the completed enclosure showed an actual enclosure tuned frequency of 38Hz. Using shorter ports than 100mm gave a much peakier response – something the software modelling had shown would be the case. For example, using a 50mm ID port that was only 40mm long gave a modelled +10.5dB peak at about 75Hz. Therefore, if you’re not unduly concerned about one-note bass and just want it louder, use a shorter port like this. Extensive testing with music followed, and this showed something else. Because these are not expensive drivers with huge cone travel, driving the sub hard could bottom-out the drivers’ suspensions. This is important to understand, because many people Speaker resonance and one-note bass Many people confuse a good bass response with a pronounced bass resonance. I remember when I was young and trying to make my car sound system perform well. I’d fitted a new amplifier, new speakers and a new head unit (a cassette player in those days!). In one particular song, a note from the bass guitar caused the whole car to vibrate… something I thought was really cool. What was happening was that a major speaker resonance was being triggered, and that excited the car. Nowadays, I’d see that as a shortcoming! A speaker resonance is where, for a given power input, the audio output of the speaker sharply peaks. That is, at a particular frequency, the speaker is much more efficient at turning electrical input power into an audio output. The problem with a subwoofer having a pronounced resonance is that the output at that frequency will dominate the rest of the content. This is often termed ‘one-note bass’. One-note bass is the thump, thump you often hear in poor sound systems – all the bass, no matter its actual frequency, is reproduced as much the same-sounding thump. Australia's electronics magazine siliconchip.com.au Photo 3: the underside view of the baffle with the speakers, port, protection light bulb and terminal strip temporarily mounted. In the final design, some of the parts were orientated slightly differently. Photo 4: a closeup showing the 8mm flanged nuts used as spacers between the speaker mounting lugs, the protection light bulb mounted on its bracket and the terminal strip. over-drive subs without realising that they are doing so. When developing a subwoofer, always test it with a crossover and without the other speakers running. That is, listen to just the sub working at only low frequencies. This way, you can hear what is really happening, without the sound being masked by the other speakers. the speaker system, they will dominate the sound. For example, without a sub crossover, the lower midrange can be over-emphasised. Crossovers can be achieved by using a series inductor in the subwoofer speaker feed (not so good), or much better, using an electronic low-pass or band-pass filter. Subwoofer crossovers Two solutions were developed to prevent the sub from being overdriven. The first was to temporarily place a heavy lid on top of the upturned sub, raised from the stool body by 10mm spacers. This replicates how the sub will actually be used – inverted and placed on the ground on short feet. The use of this lid (or in use, the presence of the ground) better acoustically loads the drivers, reducing their displacement peaks. Technically, we’re also adding another chamber and port (the gap around the periphery), but that made little difference to the sound except that upper frequencies were better suppressed. You don’t want these coming out of a sub anyway. The other solution was electronic – or at least, electric. Many professional speakers used in commercial settings have a very simple approach to protecting (especially) the tweeters. They place a normal incandescent light bulb in series with the drive to the speaker. A subwoofer – especially a small one like this – must be ‘crossed over’. It must not be fed frequencies outside the range of those you’re trying to reproduce. The reason for this is that a small sub can easily reproduce higher frequencies, and if you have the sub producing them as well as the rest of Photo 5: two of these Visaton 170mm (6.5in) drivers are used in the subwoofer, mounted in an isobaric configuration. Source: Visaton siliconchip.com.au Speaker protection Australia's electronics magazine Low-voltage incandescent light bulbs have low resistance (eg, 0.7W) when they are cold but about 15 times as much resistance when they are hot – that is, when the filament is glowing brightly. Therefore, as the current flowing through the bulb increases, so does its resistance, limiting the power getting to the protected speaker. We decided to take a similar approach to protect the subwoofer drivers. Many different light bulbs were tested, including those with different voltages and wattages, and multiple bulbs wired in series, parallel and series/parallel configurations. The aim was to limit power to the subwoofer such that the speakers could not be overdriven on a variety of music. However, a lot depends on the amplifier you are using, the type of music you play – and how loudly you play it! While the light bulb approach has audio downsides (it is a non-linear compressor), and so is frowned on by purists, it works very effectively. Depending on the music type and power level, the bulb may not glow at all, glow just a little, or light brightly. Furthermore, it has a short-term memory in that if the power is repeatedly high (eg, you are loudly playing a song with lots of bass), the filament stays warm and so limits the power earlier. To put this another way, if the subwoofer is constantly being overdriven, the sub output drops a lot – it June 2025  77 Light bulb based speaker power limiters The question that is always asked by people wanting to use light bulbs as speaker power limiters is how to choose the correct bulb for the application. The bottom line is that it is nearly impossible to do it theoretically – testing is the only practical way. The difficulty with trying to specify the required light bulb theoretically is that the resistance posed by the bulb constantly varies with filament temperature. In turn, this is governed by the light bulb’s characteristics, amplifier power, the type of music being played and the impedance curve of the speaker being protected. If we were using a sinewave as the signal, it would all become much simpler – but we aren’t. Even the bulb’s maximum continuous power dissipation (ie, the wattage rating) isn’t as useful as it might first appear. In our application, the bulb is required to dissipate large amounts of power only on very short transients. Therefore, the power limiting that occurs depends in part on the response speed of the filament. Furthermore, the filament has a thermal memory. If it is dissipating large amounts of power in successive bursts (eg, there is a rhythmic bass beat), the filament stays hot between the bass notes. It therefore has a higher constant resistance and so the expected high pulses of amplifier power are not fully developed! Based on the voltage swings of the audio signal, it would appear obvious that a bulb with a higher voltage rating (eg, 60V) should be used – however, such a bulb has a higher cold resistance, so it will reduce amplifier output power all the time. That is not what we want. In the case of the project described here, the 24V 55W halogen bulb worked well. A similar result could also be achieved using multiple 24V 18W tail-light bulbs. However, they were more expensive to buy than the single 55W bulb. It’s a fascinating area, and we’d love to hear about any successful results readers have gained using light bulbs for speaker protection. Two light bulbs used to limit the power in a Bose Lifestyle speaker system. is actually louder when the amplifier is turned back down. By watching the filament lamp during testing, you can also get a very good idea of when the speaker is being driven too hard and so reduce the maximum power the sub will ever see. (More on setting up the amplifier later.) If, in ‘normal’ use, some crazy dude gets hold of the amplifier knob and cranks it right up (eg, when you’re away on holiday and the kids decide to host a party!), the light bulb will protect the speaker. If the worst comes to the worst, the bulb will likely blow before the drivers do, cutting off the subwoofer output. We have nominated using a single Narva 24V 55W bulb (part number 48701). This bulb costs about $10 from automotive parts shops. It is difficult to over-drive the sub on normal music with this bulb wired in series, using any amplifier up to about 100W. However, if you want to be less conservative, using two of these bulbs in parallel gives more subwoofer power but still some protection. Of course, you can choose to delete the protection bulbs entirely and use only a lowpower amplifier. However, we suggest using the single light bulb. Despite the combined drivers being rated at 180W peak, this does not mean that if the sub is used with an amplifier having less power than 180W, the sub requires no protection. Remember, the protection is primarily to protect the drivers from being over-driven rather than their voice coils being burned out. Warning: if the subwoofer is continuously overdriven, the protection lamp will become very hot. The subwoofer should always be placed on a firm, level and non-combustible surface like tiles, concrete or similar. It should not be placed on dry grass. Construction Construction is easy, and should take you only about an hour, spread over two days. The steps are: 1. Make the baffle and trial-fit the speakers, port, protection lamp and terminal strip to it. 2. Disassemble the baffle, removing all the parts. 3. Glue the baffle, port and feet in place and let the glue harden for 24 hours. 4. Fit and wire the speakers, protection lamp and terminal strip. 5. Test it. 78 Silicon Chip Australia's electronics magazine siliconchip.com.au Photos 6 & 7: the baffle and port glued into place with Liquid Nails. The port protrudes from both sides of the baffle, while the two drivers are positioned face-to-face in the opening. The towel under the stool protects this surface when working on the subwoofer. Once the glue has hardened, you can paint the inside of the enclosure, the baffle and the port tube. Photo 8: a close-up of the protection lamp and terminal strip wiring. Note the cable going through the baffle to the other speaker. The first step is to use a jigsaw to cut a disc of particleboard about 285mm in diameter. Measure the maximum diameter of the opening in the stool’s base – the disc should be just smaller than this. The stools are handmade and so vary a bit in size. We used 22mm-thick, moisture-­ resistant particleboard (a flooring offcut), but if you seal it on all sides with paint before gluing it into place, slightly thinner MDF should be fine. Don’t use material less than about 18mm thick – the peripheral glue needs plenty of ‘meat’ to adhere to. Cut a 165mm hole in the baffle for the drivers to sit in, and mark and drill small diameter pilot holes for the particleboard screws that will hold the drivers in place. Next, use a hole saw to make the opening in the baffle for the 50mm ID PVC pipe. The required hole diameter is 56mm – if you don’t have a hole saw of this diameter, make a smaller hole and then file it to size. The exact location of these holes is not critical – just ensure the speakers and port clear the inner walls of the stool. We recommend proper safety precautions when cutting MDF, such as using a respirator and cutting in a well-ventilated location. Drill a small hole for the inside speaker’s cable to come through from the other side of the baffle. Cut a suitable speaker gasket from a thin foam rubber sheet before dropping the first speaker into place. In the final assembly, you can use silicone if on the baseplate and enlarge this hole to 3mm. Be very careful when drilling these holes – it is easy to damage the lamp (eg, by dropping it). The lamp mounts on a small right-angle bracket that is attached to the baffle with a wood screw. Wiring connections to the lamp are by two solder lugs that are attached with the 3mm screws. Ensure the baffle assembly will fit inside the stool without the port fouling the inside wall. When you are happy that everything will fit correctly, remove the baffle and disassemble it. If using non-weatherproof MDF, paint the baffle on both sides and on all cut edges. Spread ‘water clean-up’ Liquid Nails (or equivalent) building adhesive at an appropriate height around the inside of the stool where the baffle will sit. Be generous with this glue – you want no leaks and for the baffle siliconchip.com.au you don’t want to make a gasket. The other speaker fits on top, so they mount face-to-face (see Fig.2). These speakers have an external gasket, so they seal to each other very well – no further gasket or sealant is needed between them. Use 6mm spacers between the two sets of speaker mounting holes so that the speakers are clamped firmly together, but the mounting tags are not overly bent. I used 8mm flanged nuts that had the required 6mm depth. The particleboard screws go through both sets of speaker mounting tags and the spacers, holding the two speakers firmly to the baffle. Push the 190mm PVC pipe through the hole in the baffle; the pipe projects about equally from each side. Next, mount the protective light bulb. To do this, enlarge the existing hole in the bulb’s bottom tang to 3mm. Nip off one of the nipple protrusions Fig.2: the two drivers are mounted face-to-face, being inserted into the baffle from the underside of the enclosure. Australia's electronics magazine June 2025  79 to be held in place very firmly. Ensure the glue is the water clean-up type or it will be difficult to remove the excess! (We suggest “Liquid Nails Fast Grab”, Bunnings I/N 1230096). Carefully drop the bare baffle into place and push it down onto the glue, ensuring the baffle stays level. Apply more glue around the gap between the baffle and the inside of the stool and smooth the glue with a wet finger, wiping up any excess with a wet cloth that you repeatedly rinse in water. Insert the vent, also sealing it into place with the glue. Let the glue harden for at least 24 hours. You may choose to paint the interior of the stool at this stage – ie, the baffle, glue and visible inside wall of the stool. I did so using black spray paint. A single layer of quilt wadding, about 500 × 500mm can now be glued in the bottom of the enclosure (the top when it is orientated normally). This step is optional – I am not sure it makes a great deal of difference, but it will possibly reduce ‘hollow sounding’ reflections. Place the gasket on the underside of the first speaker or, if not using a gasket, apply silicone around the upper edge of the hole. Solder the speaker’s connecting cable to its terminals, then feed this wire through the baffle hole, pushing it from the inside by placing your hand through the speaker hole. Ensure you know the polarity of your connections, eg, by using coloured wires or a cable with a trace on one conductor. Put the first speaker into place and then mount the second speaker on top, remembering to include the spacers. Insert the four screws and tighten in a series of steps using a diagonal tightening pattern. Wire the two speakers out of phase – the inside speaker’s positive connection goes to the outside speaker’s negative and vice versa (see Fig.3). Seal the wiring hole in the baffle. Next, install the protective light bulb. It mounts on a small bracket that is attached to the baffle with a particleboard screw (drill small diameter pilot holes for the screw). Do not place the lamp against the PVC vent. If you have touched the bulb’s glass at any point in the installation process, wipe it with a cloth moistened in methylated spirits. This removes any oils that may have been deposited on the glass from your fingers, which could potentially weaken the glass. The terminal strip mounts next, again with a particleboard screw into a pilot hole. Wire the drivers to the terminal strip with the light bulb in series (it doesn’t matter which lead it goes in). Because the outside driver pushes air outwards when the cone moves backwards (rather than the normal forwards), the negative terminal of the outer driver connects to the positive speaker connection terminal. Mark this with a (+). Should the vent be flared? The vent uses straight rather than flared ends. Flared ends reduce port noise (sometimes called ‘chuffing’). However, considering the size of the drivers and their isobaric configuration, a large diameter vent has been used, so air velocities in the port are relatively low. No port noise could be heard even without flares. Photo 9: testing the subwoofer with Niles wall-mounted speakers on a deck under construction. The ceiling is 2.7m high, and the deck area is about 10 × 5m. On a deck this large, two subwoofers spaced about 5m apart will give the best results. 80 Silicon Chip Australia's electronics magazine siliconchip.com.au Testing The next step is to test the subwoofer. Place it upright on its feet on a firm, flat surface. Feed the subwoofer through an amplifier and crossover, and ensure other speakers cannot be heard. Use a frequency generator app to perform a sweep from 200Hz down to 20Hz. The speaker should be audible down to about 35Hz, and there should be no buzzes, whistles or rattles. If there are, isolate where the sound is coming from (eg, a loose port or leak around the frames of the drivers) and then fix the problem. If you hear a buzz, ensure it’s not something in the room becoming excited, rather than the subwoofer itself. If the bass output is poor, check the speaker phasing, ensuring the speakers are wired out of phase. Now switch to the type of music you normally play. Do not run any high-power tests with the frequency generator. Ensure you can see if the light bulb is glowing brightly – eg, in dim conditions, it will cast a visible ring of light around the open base of the enclosure. Increase the amplifier gain until the filament is just glowing on bassy passages. Now, while not changing the amplifier gain, select music of the type that has as much bass as you will ever listen to. The light bulb(s) should light quite brightly on these greater bass passages, showing the protection is working, and the drivers should not bottom out. If the bulb is glowing brightly a lot of the time, the amplifier gain is too Fig.3: wire the two speakers out of phase so that as one pushes, the other pulls (and vice versa). The protection light bulb is inserted in one conductor of the main feed (either is OK). siliconchip.com.au Parts List – Outdoor Subwoofer 2 Visaton WS 17 E 8W speakers [RS Components 431-8563; there are many other suppliers] 1 Marquee Sorrento 350 × 350 × 450mm Side Stool [Bunnings I/N 0596376] 1 300 × 300mm 22mm-thick weatherproof particleboard sheet 1 190mm length of 50mm internal diameter PVC DWV pipe 4 25mm diameter, 10mm thick white rubber feet 1 cartridge of water clean-up Liquid Nails [Bunnings I/N 1230096] 1 Narva 48701 24V 55W automotive light bulb [Car parts supplier] 1 500 × 500mm section of dressmaker’s quilt wadding [Spotlight] 1 small terminal strip (eg, 2-way) 1 packet of self-tapping particleboard screws various lengths of wire & cable assorted small hardware items (screws, washers, nuts etc) 4 6mm spacers (particleboard screws must fit through) 1 thin foam rubber sheet 1 small steel right-angle bracket high. Of course, depending on the amplifier power, you may not see the bulb light at all. Results The prototype speaker had good output from 35Hz to 200Hz. Furthermore, the response was pleasingly smooth across this range. The measured impedance did not drop below 4W at any point in the frequency range. Using the specified protection lamp, amplifier powers up to 100W should be fine when playing normal program material. Setup Remember that the subwoofer needs its own amplifier, and that amplifier needs either a built-in subwoofer crossover or to be fed only low frequencies via an electronic crossover. Lowcost Class-D subwoofer amplifiers with built-in crossovers are readily available, but it can be much cheaper to use a surplus, bridgeable stereo amplifier with an adjustable subwoofer crossover on its input. The location of the subwoofer is important. Placing the subwoofer at the intersection of a wall and the floor causes greater loading of the speaker’s drivers. As a result, the energy of the speaker is better communicated to the air, so the bass output will increase. Placing the sub at the intersection of two walls and the floor increases this effect even more. Conversely, placing the sub on a pedestal in the middle of the room or outdoor area will reduce the output. Large changes in output are achievable by these various placements. Australia's electronics magazine The other aspect of placement is that when used outside, the closer the sub is to you, the more its presence will be felt. Unlike in a small room, where the loudness of the sub doesn’t vary much wherever you are in the room, outside the low frequencies are clearly louder when you are closer to the sub. Therefore, place it near where you will most often be sitting. When placed on the floor against a wall, the sub was effective over about a 25m2 area – it works fine in an open area about 5 × 5m. If your deck or patio area is larger than this, you could use two of these subs. To limit cone movement, the open end of the sub should always be placed on the ground (spaced upwards by its feet). If the sub is to be used upside-down with the opening facing upwards, a heavy panel should be placed over the opening, again spaced upwards by about 10mm. The sub is weatherproof in that the concrete stool can cope with rain or being sprayed with a hose. However, the sub is open underneath, so it should not be placed on grass or any other surface where there is moisture present all the time. If washing a deck or other outside area where the sub is placed, move it first. You may occasionally wish to spray some insecticide into the interior of the enclosure (including through the port) to prevent bugs and spiders making colonies. Finally, if you can obviously hear that the sub is working, it’s probably too loud – it should be just part of the music, not a separate, identifiable entity. SC June 2025  81 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. 06/25 YES! You can also order or renew your Silicon Chip subscription via any of these methods as well! The best benefit, apart from the magazine? Subscribers get a 10% discount on all orders for parts. PRE-PROGRAMMED MICROS For a complete list, go to siliconchip.com.au/Shop/9 $10 MICROS $15 MICROS ATmega328P ATtiny45-20PU PIC10LF322-I/OT PIC12F617-I/P 110dB RF Attenuator (Jul22), Basic RF Signal Generator (Jun23) ATSAML10E16A-AUT High-Current Battery Balancer (Mar21) 2m VHF CW/FM Test Generator (Oct23) PIC16F1847-I/P Digital Capacitance Meter (Jan25) Range Extender IR-to-UHF (Jan22) PIC16F18877-I/P USB Cable Tester (Nov21) Active Mains Soft Starter (Feb23), Model Railway Uncoupler (Jul23) PIC16F18877-I/PT Dual-Channel Breadboard PSU Display Adaptor (Dec22) Battery-Powered Model Railway Transmitter (Jan25) Wideband Fuel Mixture Display (WFMD; Apr23) PIC12F675-I/P Train Chuff Sound Generator (Oct22) PIC16F88-I/P Battery Charge Controller (Jun22), Railway Semaphore (Apr22) PIC16F1455-I/P Railway Points Controller Transmitter / Receiver (2 versions; Feb24) PIC24FJ256GA702-I/SS Ohmmeter (Aug22), Advanced SMD Test Tweezers (Feb23) Battery-Powered Model Railway TH Receiver (Jan25) ESR Test Tweezers (Jun24) PIC16F1455-I/SL Battery Multi Logger (Feb21), USB-C Serial Adaptor (Jun24) PIC32MX170F256D-501P/T 44-pin Micromite Mk2 (Aug14), 4DoF Simulation Seat (Sep19) Battery-Powered Model Railway SMD Receiver (Jan25) PIC32MX170F256B-50I/SP Micromite LCD BackPack V1-V3 (Feb16 / May17 / Aug19) USB Programmable Frequency Divider (Feb25) Advanced GPS Computer (Jun21), Touchscreen Digital Preamp (Sep21) PIC16LF1455-I/P New GPS-Synchronised Analog Clock (Sep22) PIC32MX170F256B-I/SO Battery Multi Logger (Feb21), Battery Manager BackPack (Aug21) PIC16F1459-I/P K-Type Thermostat (Nov23), Secure Remote Switch (RX, Dec23) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) Mains Power-Up Sequencer (Feb24 | repurposed firmware Jul24) $20 MICROS 8-Channel Learning IR Remote (Oct24) ATmega32U4 Wii Nunchuk RGB Light Driver (Mar24) PIC16F1459-I/SO Multimeter Calibrator (Jul22), Buck/Boost Charger Adaptor (Oct22) AM-FM DDS Signal Generator (May22) PIC16F15214-I/SN Digital Volume Control Pot (SMD; Mar23), Silicon Chirp Cricket (Apr23) ATmega644PA-AU PIC32MK0128MCA048 Power LCR Meter (Mar25) PIC16F15214-I/P Digital Volume Control Pot (TH; Mar23), Filament Dryer (Oct24) Tool Safety Timer (May25) $25 MICROS PIC16F15224-I/SL Multi-Channel Volume Control (OLED Module; Dec23) PIC32MX170F256B-50I/SO + PIC16F1455-I/SL Micromite Explore-40 (SC5157, Oct24) NFC IR Keyfob Transmitter (Feb25), Rotating Light (Apr25) PIC32MX470F512H-120/PT Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) PIC16F18146-I/SO Volume Control (Control Module, Dec23), Coin Cell Emulator (Dec23) PIC32MX470F512L-120/PT Micromite Explore 100 (Sep16) Compact OLED Clock & Timer (Sep24), Flexidice (Nov24) $30 MICROS Versatile Battery Checker (May25), RGB LED ‘Analog’ Clock (May25) PIC16LF15323-I/SL Remote Mains Switch (TX, Jul22), Secure Remote Switch (TX, Dec23) PIC32MX695F512H-80I/PT Touchscreen Audio Recorder (Jun14) PIC32MZ2048EFH064-I/PT DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) STM32G030K6T6 Variable Speed Drive Mk2 (Nov24) DIY Reflow Oven Controller (Apr20), Dual Hybrid Supply (Feb22) W27C020 Noughts & Crosses Computer (Jan23) KITS, SPECIALISED COMPONENTS ETC 433MHz RECEIVER KIT (SC7447) (JUN 25) VERSATILE BATTERY CHECKER KIT (SC7465) (MAY 25) RGB LED ‘ANALOG’ CLOCK KIT (SC7416) (MAY 25) USB POWER ADAPTOR COMPLETE KIT (SC7433) (MAY 25) Includes the PCB and all onboard parts (see p66, Jun25) Includes everything in the parts list (including the case), except the optional components, batteries and glue (see p30, May25) $20.00 $65.00 Includes all the parts except the power supply. When buying the kit select either a BZ-121 GPS module or Pico W (unprogrammed) for the time source (see p66, May25) $65.00 Includes everything in the parts list and a choice of one USB socket: USB-C power only; USB-C power+data; Type-B mini; or Type-B micro (see p80, May25) $10.00 siliconchip.com.au/Shop/ PICO COMPUTER (DEC 24) FLEXIDICE COMPLETE KIT (SC7361) (NOV 24) MICROMITE EXPLORE-40 KIT (SC6991) (OCT 24) DUAL MINI LED DICE (AUG 24) AUTOMATIC LQ METER KIT (SC6939) (JUL 24) For full functionality both the Pico Computer Board and Digital Video Terminal kits are required. Items shown unbolded are optional (see p71, Dec24) - Pico Computer Board kit (SC7374) $40.00 - Pico Digital Video Terminal kit (SC6917) $65.00 - PWM Audio Module kit (SC7376) $10.00 - ESP-PSRAM64H 64Mb SPI PSRAM chip (SC7377) $5.00 - DS3231 real-time clock SOIC-16 IC (SC5103) $7.50 - DS3231MZ real-time clock SOIC-8 IC (SC5779) $10.00 Includes all required parts except the coin cell (see p71, Nov24) $30.00 Includes all required parts (see p83, Oct24) $35.00 (APR 25) Includes an assembled PCB, separate Raspberry Pi Pico 2 and front/rear panels $120.00 DUAL-RAIL LOAD PROTECTOR (SC7366) (OCT 24) Hard-to-get parts: includes the PCB and all semiconductors except the ROTATING LIGHT FOR MODELS KIT (APR 25) optional/variable diodes (see p73, Oct24) $35.00 Complete kit which includes the PCB and all onboard components (see p60, Apr25): - SMD LEDs (SC7462) $20.00 PicoMSA PARTS (SC7323) (SEP 24) - Through-hole LEDs (SC7463) $20.00 Hard-to-get parts: includes the PCB, Raspberry Pi Pico (unprogrammed), plus all semiconductors, capacitors and resistors (see p63, Sep24) $50.00 433MHz TRANSMITTER KIT (SC7430) (APR 25) Includes the PCB and all onboard parts (see p75, Apr25) $20.00 COMPACT OLED CLOCK & TIMER KIT (SC6979) (SEP 24) Includes everything except the case & Li-ion cell (see p34, Sep24) $45.00 PICO 2 AUDIO ANALYSER SHORT-FORM KIT (SC6772) (MAR 25) The Pico Audio Analyser kit from Nov23, but with an unprogrammed Pico 2 $50.00 DISCRETE IDEAL BRIDGE RECTIFIER (SEP 24) Both kits include the PCB and everything that mounts to it (see page 83, Sep24) USB PROGRAMMABLE FREQUENCY DIVIDER (SC6959) (FEB 25) - All through-hole (TH) kit (SC6987) $30.00 Complete kit: includes all components (see p85, Feb25) $60.00 - SMD kit (SC6988) $27.50 PICO/2/COMPUTER (SC7468) NFC PROGRAMMABLE IR KEYFOB (SC7421) (FEB 25) Complete kit: includes all required items, except the cell (see p67, Feb25) COMPACT HIFI HEADPHONE AMP (SC6885) (DEC 24) CAPACITOR DISCHARGER KIT (SC7404) (DEC 24) Complete kit: includes everything except the power supply (see p47, Dec24) $25.00 $70.00 Complete kit: choice of white or black PCB solder mask (see page 50, August 2024) - Through-hole LEDs kit (SC6849) $17.50 - SMD LEDs kit (SC6961) $17.50 Includes the PCB and all components that mount on it, the mounting hardware Includes everything except the case & debugging interface (see p33, July24) $100.00 (without heatsink) andCbanana - Rotary encoder with integral pushbutton (available separately, SC5601) $3.00 82 Silicon hip sockets (see p36, Dec24) Australia's$30.00 electronics magazine siliconchip.com.au *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. R&S®ZNB3000 Vector Network Analyzer FAST FORWARD TO RESULTS The R&S®ZNB3000 is the instrument you need for RF component production. This latest addition to the Rohde & Schwarz network analyzer portfolio offers best-in-class RF performance, combining high measurement accuracy with exceptional speed. With its high throughput rate, it is especially suitable for high-volume production and short ramp-up time environments. For more information visit: www.rohde-schwarz.com/solution/ZNB3000 siliconchip.com.au Australia's electronics magazine June 2025  83 PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT TINY LED ICICLE (WHITE) DUAL-CHANNEL BREADBOARD PSU ↳ DISPLAY BOARD DIGITAL BOOST REGULATOR ACTIVE MONITOR SPEAKERS POWER SUPPLY PICO W BACKPACK Q METER MAIN PCB ↳ FRONT PANEL (BLACK) NOUGHTS & CROSSES COMPUTER GAME BOARD ↳ COMPUTE BOARD ACTIVE MAINS SOFT STARTER ADVANCED SMD TEST TWEEZERS SET DIGITAL VOLUME CONTROL POT (SMD VERSION) ↳ THROUGH-HOLE VERSION MODEL RAILWAY TURNTABLE CONTROL PCB ↳ CONTACT PCB (GOLD-PLATED) WIDEBAND FUEL MIXTURE DISPLAY (BLUE) TEST BENCH SWISS ARMY KNIFE (BLUE) SILICON CHIRP CRICKET GPS DISCIPLINED OSCILLATOR SONGBIRD (RED, GREEN, PURPLE or YELLOW) DUAL RF AMPLIFIER (GREEN or BLUE) LOUDSPEAKER TESTING JIG BASIC RF SIGNAL GENERATOR (AD9834) ↳ FRONT PANEL V6295 VIBRATOR REPLACEMENT PCB SET DYNAMIC RFID / NFC TAG (SMALL, PURPLE) ↳ NFC TAG (LARGE, BLACK) RECIPROCAL FREQUENCY COUNTER MAIN PCB ↳ FRONT PANEL (BLACK) PI PICO-BASED THERMAL CAMERA MODEL RAILWAY UNCOUPLER MOSFET VIBRATOR REPLACEMENT ARDUINO ESR METER (STANDALONE VERSION) ↳ COMBINED VERSION WITH LC METER WATERING SYSTEM CONTROLLER CALIBRATED MEASUREMENT MICROPHONE (SMD) ↳ THROUGH-HOLE VERSION SALAD BOWL SPEAKER CROSSOVER PIC PROGRAMMING ADAPTOR REVISED 30V 2A BENCH SUPPLY MAIN PCB ↳ FRONT PANEL CONTROL PCB ↳ VOLTAGE INVERTER / DOUBLER 2M VHF CW/FM TEST GENERATOR TQFP-32 PROGRAMMING ADAPTOR ↳ TQFP-44 ↳ TQFP-48 ↳ TQFP-64 K-TYPE THERMOMETER / THERMOSTAT (SET; RED) MODEM / ROUTER WATCHDOG (BLUE) DISCRETE MICROAMP LED FLASHER MAGNETIC LEVITATION DEMONSTRATION MULTI-CHANNEL VOLUME CONTROL: VOLUME PCB ↳ CONTROL PCB ↳ OLED PCB SECURE REMOTE SWITCH RECEIVER ↳ TRANSMITTER (MODULE VERSION) ↳ TRANSMITTER (DISCRETE VERSION COIN CELL EMULATOR (BLACK) IDEAL BRIDGE RECTIFIER, 28mm SQUARE SPADE ↳ 21mm SQUARE PIN ↳ 5mm PITCH SIL ↳ MINI SOT-23 ↳ STANDALONE D2PAK SMD ↳ STANDALONE TO-220 (70μm COPPER) RASPBERRY PI CLOCK RADIO MAIN PCB ↳ DISPLAY PCB KEYBOARD ADAPTOR (VGA PICOMITE) ↳ PS2X2PICO VERSION MICROPHONE PREAMPLIFIER ↳ EMBEDDED VERSION RAILWAY POINTS CONTROLLER TRANSMITTER ↳ RECEIVER 84 Silicon Chip DATE NOV22 DEC22 DEC22 DEC22 DEC22 JAN23 JAN23 JAN23 JAN23 JAN23 FEB23 FEB23 MAR23 MAR23 MAR23 MAR23 APR23 APR23 APR23 MAY23 MAY23 MAY23 JUN23 JUN23 JUN23 JUN23 JUL23 JUL23 JUL23 JUL23 JUL23 JUL23 JUL23 AUG23 AUG23 AUG23 AUG23 AUG23 SEP23 SEP23 SEP23 OCT22 SEP23 OCT23 OCT23 OCT23 OCT23 OCT23 NOV23 NOV23 NOV23 NOV23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 DEC23 JAN24 JAN24 JAN24 JAN24 FEB24 FEB24 FEB24 FEB24 PCB CODE 16111192 04112221 04112222 24110224 01112221 07101221 CSE220701 CSE220704 08111221 08111222 10110221 SC6658 01101231 01101232 09103231 09103232 05104231 04110221 08101231 04103231 08103231 CSE220602A 04106231 CSE221001 CSE220902B 18105231/2 06101231 06101232 CSE230101C CSE230102 04105231 09105231 18106231 04106181 04106182 15110231 01108231 01108232 01109231 24105231 04105223 04105222 04107222 06107231 24108231 24108232 24108233 24108234 04108231/2 10111231 SC6868 SC6866 01111221 01111222 01111223 10109231 10109232 10109233 18101231 18101241 18101242 18101243 18101244 18101245 18101246 19101241 19101242 07111231 07111232 01110231 01110232 09101241 09101242 Price $2.50 $5.00 $5.00 $5.00 $10.00 $5.00 $5.00 $5.00 $12.50 $12.50 $10.00 $10.00 $2.50 $5.00 $5.00 $10.00 $10.00 $10.00 $5.00 $5.00 $4.00 $2.50 $12.50 $5.00 $5.00 $5.00 $1.50 $4.00 $5.00 $5.00 $5.00 $2.50 $2.50 $5.00 $7.50 $12.50 $2.50 $2.50 $10.00 $5.00 $10.00 $2.50 $2.50 $5.00 $5.00 $5.00 $5.00 $5.00 $10.00 $2.50 $2.50 $5.00 $5.00 $5.00 $3.00 $5.00 $2.50 $2.50 $5.00 $2.00 $2.00 $2.00 $1.00 $3.00 $5.00 $12.50 $7.50 $2.50 $2.50 $7.50 $7.50 $5.00 $2.50 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT LASER COMMUNICATOR TRANSMITTER ↳ RECEIVER PICO DIGITAL VIDEO TERMINAL ↳ FRONT PANEL FOR ALTRONICS H0190 (BLACK) ↳ FRONT PANEL FOR ALTRONICS H0191 (BLACK) WII NUNCHUK RGB LIGHT DRIVER (BLACK) ARDUINO FOR ARDUINIANS (PACK OF SIX PCBS) ↳ PROJECT 27 PCB SKILL TESTER 9000 PICO GAMER ESP32-CAM BACKPACK WIFI DDS FUNCTION GENERATOR 10MHz to 1MHz / 1Hz FREQUENCY DIVIDER (BLUE) FAN SPEED CONTROLLER MK2 ESR TEST TWEEZERS (SET OF FOUR, WHITE) DC SUPPLY PROTECTOR (ADJUSTABLE SMD) ↳ ADJUSTABLE THROUGH-HOLE ↳ FIXED THROUGH-HOLE USB-C SERIAL ADAPTOR (BLACK) AUTOMATIC LQ METER MAIN AUTOMATIC LQ METER FRONT PANEL (BLACK) 180-230V DC MOTOR SPEED CONTROLLER STYLOCLONE (CASE VERSION) ↳ STANDALONE VERSION DUAL MINI LED DICE (THROUGH-HOLE LEDs) ↳ SMD LEDs GUITAR PICKGUARD (FENDER JAZZ BASS) ↳ J&D T-STYLE BASS ↳ MUSIC MAN STINGRAY BASS ↳ FENDER TELECASTER COMPACT OLED CLOCK & TIMER USB MIXED-SIGNAL LOGIC ANALYSER (PicoMSA) DISCRETE IDEAL BRIDGE RECTIFIER (TH) ↳ SMD VERSION MICROMITE EXPLORE-40 (BLUE) PICO BACKPACK AUDIO BREAKOUT (with conns.) 8-CHANNEL LEARNING IR REMOTE (BLUE) 3D PRINTER FILAMENT DRYER DUAL-RAIL LOAD PROTECTOR VARIABLE SPEED DRIVE Mk2 (BLACK) FLEXIDICE (RED, PAIR OF PCBs) SURF SOUND SIMULATOR (BLUE) COMPACT HIFI HEADPHONE AMP (BLUE) CAPACITOR DISCHARGER PICO COMPUTER ↳ FRONT PANEL (BLACK) ↳ PWM AUDIO MODULE DIGITAL CAPACITANCE METER BATTERY MODEL RAILWAY TRANSMITTER ↳ THROUGH-HOLE (TH) RECEIVER ↳ SMD RECEIVER ↳ CHARGER 5MHZ 40A CURRENT PROBE (BLACK) USB PROGRAMMABLE FREQUENCY DIVIDER HIGH-BANDWIDTH DIFFERENTIAL PROBE NFC IR KEYFOB TRANSMITTER POWER LCR METER WAVEFORM GENERATOR PICO 2 AUDIO ANALYSER (BLACK) PICO/2/COMPUTER ↳ FRONT & REAR PANELS (BLACK) ROTATING LIGHT (BLACK) 433MHZ TRANSMITTER VERSATILE BATTERY CHECKER ↳ FRONT PANEL (BLACK, 0.8mm) TOOL SAFETY TIMER RGB LED ANALOG CLOCK (BLACK) USB POWER ADAPTOR (BLACK, 1mm) DATE MAR24 MAR24 MAR24 MAR24 MAR24 MAR24 MAR24 MAR24 APR24 APR24 APR24 MAY24 MAY24 MAY24 JUN24 JUN24 JUN24 JUN24 JUN24 JUL24 JUL24 JUL24 AUG24 AUG24 AUG24 AUG24 SEP24 SEP24 SEP24 SEP24 SEP24 SEP24 SEP24 SEP24 OCT24 OCT24 OCT24 OCT24 OCT24 NOV24 NOV24 NOV24 DEC24 DEC24 DEC24 DEC24 DEC24 JAN25 JAN25 JAN25 JAN25 JAN25 JAN25 FEB25 FEB25 FEB25 MAR25 MAR25 MAR25 APR25 APR25 APR25 APR25 MAY25 MAY25 MAY25 MAY25 MAY25 PCB CODE 16102241 16102242 07112231 07112232 07112233 16103241 SC6903 SC6904 08101241 08104241 07102241 04104241 04112231 10104241 SC6963 08106241 08106242 08106243 24106241 CSE240203A CSE240204A 11104241 23106241 23106242 08103241 08103242 23109241 23109242 23109243 23109244 19101231 04109241 18108241 18108242 07106241 07101222 15108241 28110241 18109241 11111241 08107241/2 01111241 01103241 9047-01 07112234 07112235 07112238 04111241 09110241 09110242 09110243 09110244 9049-01 04108241 9015-D 15109231 04103251 04104251 04107231 07104251 07104252/3 09101251 15103251 11104251 11104252 10104251 19101251 18101251 HWS SOLAR DIVERTER PCB & INSULATING PANELS SSB SHORTWAVE RECEIVER PCB SET ↳ FRONT PANEL (BLACK) 433MHz RECEIVER JUN25 JUN25 JUN25 JUN25 18110241 $20.00 CSE250202-3 $15.00 CSE250204 $7.50 15103252 $2.50 NEW PCBs Australia's electronics magazine Price $5.00 $2.50 $5.00 $2.50 $2.50 $20.00 $20.00 $7.50 $15.00 $10.00 $5.00 $10.00 $2.50 $5.00 $10.00 $2.50 $2.50 $2.50 $2.50 $5.00 $5.00 $15.00 $10.00 $12.50 $2.50 $2.50 $10.00 $10.00 $10.00 $5.00 $5.00 $7.50 $5.00 $2.50 $2.50 $2.50 $7.50 $7.50 $5.00 $15.00 $5.00 $10.00 $7.50 $5.00 $5.00 $2.50 $2.50 $5.00 $2.50 $2.50 $2.50 $2.50 $5.00 $5.00 $5.00 $2.50 $10.00 $5.00 $5.00 $5.00 $10.00 $2.50 $2.50 $5.00 $7.50 $5.00 $15.00 $2.50 siliconchip.com.au We also sell the Silicon Chip PDFs on USB, RTV&H USB, Vintage Radio USB and more at siliconchip.com.au/Shop/3 Unit 13, 538 Gardeners Road ALEXANDRIA NSW 2015 02 9330 1700 sales<at>controldevices.net MINIATURE JOYSTICKS PUSH BUTTON SWITCHES ANTI-VANDAL SWITCHES TOGGLE SWITCHES LED INDICATORS PENDANT CONTROL STATIONS WATERPROOF SWITCHES TACTILE SWITCHES FOOT & PALM SWITCHES MAKE YOUR NEW FAVOURITE E-STORE Enjoy a quick and easy, one stop shop,with a variety of competitively priced stock items and fast processing time. Find your switch, switch accessories, LED indicators, joysticks to audio parts today on SNS. WWW.CONTROLDEVICES.COM.AU siliconchip.com.au WWW.SWITCHESNSTUFF.SHOP Australia's electronics magazine June 2025  85 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. Detecting smokers using a MaixCam board Smoking is prohibited in many places but that doesn’t stop some people. This project uses AI and a camera to catch people smoking where they shouldn’t. It can sound an alarm or even record a photo of the offender. The MaixCam’s camera captures a 320×240 pixel image in 24-bit RGB format. This image is processed using a Python script, which runs the YOLOv5 model to analyse the frame and look for a burning cigarette. The pre-trained model will not detect just smoke; a cigarette must be visible for a positive detection. On detection of a smoker, the GPIO15 pin is brought high, switching on an LED indicator and/or sounding a buzzer. A 120×120 pixel snapshot will be saved on as /snapshot/snapshot.jpg When no smoker is detected, GPIO16 is high, lighting a green LED. AI processing requires computing power. The Sipeed microcontroller on the MaixCam board has a dual-core CPU with two RISC-V C906/ARM A53 cores running at 1GHz & 700MHz, plus a 1TOPS<at>INT8 NPU, 256MB of RAM, a TFT touchscreen, SD card interface, microphone, 5MP camera and WiFi. It is just good enough to run the smoker-­ detection model and costs around US$50 (~$80). The MaixCam runs a lightweight Linux-based operating system that supports YOLOv5 to YOLOv8, with Python 3.11 for scripting and automation. It is a great choice for entrylevel AI projects or lightweight edge AI systems. MaixCam has a Pro version 86 Silicon Chip which has a ~3 TOPs NPU and is capable of more demanding tasks. Running the same computing load on a Raspberry Pi 5 (8GB) requires additional components like a TFT display, keyboard, and a power supply capable of delivering at least 3A <at> 5V, significantly increasing the overall cost. As evidence, the device will take a snapshot of the smoker and will save it to the SD card along with its metadata: the date & time, detection confidence level and bounding box. The date & time is printed on the image itself (the code can be modified to add the others as well). To get started, download the latest MaixCam operating system from https://github.com/sipeed/MaixPy/ releases In most cases, the board you purchased will already have an operating system installed. If so, you only need to connect it to your computer. There are three main ways to connect the board to your computer: USB direct connection, though SSH or using the Maixvision IDE (https://wiki.sipeed. com/maixvision). You can SSH directly to the MaixCam’s command prompt using a program like PuTTY. The user name is “root” and you will need to get the device’s IP address from your router. The password will also be “root”. Once you’ve confirmed you can access it, use scp (eg, PuTTY’s pscp command) to copy the required files to the board: smoking.mud, smoking. cvimodel and smoke_detection_snapshot_metadata.py. You can get them from our website at siliconchip.au/ Shop/6/1847 The files smoking.mud & smoking. cvimodel need to be copied into the /root/models/ directory on the MaixCam (that’s where the Python code expects them to be). Alternatively, you can install the MaixVision IDE onto your computer and then upload the files using that. On the right side of MaixVision IDE, you Australia's electronics magazine will find the “Device file manager”. Select the drive where you want to upload and then simply press the button. Never try to upload anything into the “/boot” directory of the device; it may brick the operating system. Running the code from MaixVision IDE is pretty simple. Just get the MaixCam connected to your WiFi. Connect the MaixCam by pressing the ‘connect’ icon on the bottom left and then press the ‘play’ button on the bottom left side. The code will then start running. To get the code to run at boot time, find the ‘Package’ button at the bottom left of the MaixVision IDE and make a package of your code. Provide all the data like ID, name, version, developer, description etc. Then submit and finally install it. This will create a link in the /maixapp/apps/app.info file with your name and a folder named “smoker_detection” inside /maixapp/apps/ which will have three files, one of them being main.py (which is your Python code). Now in the /maixapp/auto_start.txt file, just enter your program name and save the file. This file should not have any other entry. You can also do this in the MaixCam’s touchscreen interface after installing your code, via Settings → Start-menu → smoker_detection. Now restart the board and smoker_ detection will be auto start. Once you have it up and running, you might consider coming up with a way to send an email or SMS when a smoker is detected. Bera Somnath, Kolkata, India ($100). siliconchip.com.au Non-contact diagnostic tool detects electromagnetic fields (EMFs) This circuit picks up magnetic/ electric fields in the frequency range of 1Hz to 1MHz and converts them to an audible signal. I have been using this circuit (and its variations) for the last 20 years for diagnosing and repairing switchmode power supplies and basically any electronic device that graces my workbench. It usually allows one to pinpoint the fault in the device, sometimes even without opening the housing! It also is quite educational, and is a must for teaching institutions to obtain an intuitive understanding of electronics. It has certainly saved me hours of troubleshooting. Inductor L1 picks up the EMI field. It is a type that is frequently found in switch-mode power supplies, so you should be able to obtain it from a dud one. The signal is then amplified by op amp IC1, with its gain set by trimpot or potentiometer VR1. For signals in the audible range (eg, 50Hz to 10kHz), the output of IC1 is fed to a set of earphones via a 22kW resistor. Higher-frequency signals pass to the CD4518 divider chip, which reduces the frequency by factors of 10 and 100. Both of its outputs are mixed back into the signal sent to the earphones. The result is you can hear impulses from 50Hz to 10kHz (÷1), 10kHz to 100kHz (÷10) and 100kHz to 1MHz (÷100). 50Hz fields sound like a slow clicking, while 15kHz sounds like a distorted 150Hz tone. I have used it on many appliances and have shown schoolkids what electromagnetic radiation sounds like. You can even use a stereo version (eg, with an LF353 op amp) to help home in on the signals (or lack thereof). My enhanced version has 10kW volume controls and a three-way switch for ×1, ×10, and ×100 gain ranges. Knowledgeable readers could no doubt create their own variations. Other op amps could be used for IC1, like the ua741, CA3140 or TL071. Dr George A Davidson, Larnook, NSW. ($80) 3D-printed case for Advanced SMD Test Tweezers I have recently built Advanced SMD Test Tweezers (February/March 2023; siliconchip.au/Series/396) from the kit you sell and made a 3D printable enclosure for it. I’m new to 3D printing and modelling; I got my first BambuLab A1 mini and started learning Fusion 360 about a month ago. Still, it has worked out nicely. I have included photos of my printed enclosure and lid for it. I printed it with PLA Metal filament. The lid slides in/out into the top part, which makes it easy to access the battery for replacement. The enclosure top has two pins to hold the screen in place and accommodates 3D-printed buttons, making it much easier to control the device. The STL files can be downloaded from siliconchip.au/Shop/11/584 I printed the enclosure parts together but the buttons separately to have a nice concentric finish. Vitali Bobrov, Wysoka, Poland. ($70) siliconchip.com.au This 3D-printed case for the Advanced SMD Test Tweezers is made from a top, lid and three button extensions. Australia's electronics magazine June 2025  87 SERVICEMAN’S LOG Another mixed bag of bits and bobs Dave Thompson recently surprised us by visiting Australia. It was such a surprise, we didn’t know he was here! Having recharged his batteries, he’ll be back in July. So, for now, here are some stories from our readers. Mystery amplifier toroidal transformer replacement The mains light-bulb limiter is not a new idea, but not everyone is aware of it. My version is the simplest, comprising a 100W 230V incandescent lamp (these are getting scarce) mounted in a batten holder screwed to the wall above my bench. This is wired with a piece of two-core mains flex to a PDL40A Interrupted Phase Tapon Plug. This means that any appliance plugged into the Tapon has the lamp in series with its live connection. I leave the Tapon plugged into one outlet of a power board, and I can choose to plug the appliance under test either directly to the mains or via the Tapon. I use an inexpensive power meter to measure the mains voltage and the current drawn by the test load. Turning to the repair in question, a PA speaker had blown its mains fuse, so after fitting a replacement, I plugged it in via the lamp limiter. I expected to see the lamp briefly lighting brightly, then fading to a dim glow. This is because the amplifier main capacitors charge when power is first applied, drawing a large initial current, which then subsides. However, the lamp lit up at full brightness and stayed that way. If I had plugged it straight into the mains, it would have likely blown another fuse. There must have been a heavy short circuit somewhere in the amplifier. I dismantled the amplifier module from the cabinet and noted a large toroidal power transformer at one end. The secondary wires were easily identified and fitted with Faston connectors, allowing me to quickly disconnect them. When I plugged it back into the Tapon, the lamp immediately lit at full brightness again. That indicated the transformer was the likely culprit, but to be sure, I disconnected the transformer primary and tried again. This time, the lamp didn’t light at all. So a new transformer was required, but it had no markings on it to tell me what the secondary voltages should be. A label on the back panel told me the total power consumption was 160VA, so I needed a 160VA transformer with a 230V The original transformer (above) and replacement (below). 88 Silicon Chip Australia's electronics magazine siliconchip.com.au primary and a centre-tapped secondary of unknown voltage. I had a schematic of this unit, but there was no mention of the transformer voltage. However, someone had written 35V next to the DC rails. That seemed a little high to me, so I looked at the main capacitors on those rails and found they were only rated at 35V. The actual rail voltage would be less than that. The amplifier uses LM3886 power amplifier ICs, so I consulted the datasheet. This gives different rail voltages for 8W or 4W loads. The woofer was a 4W unit, and the datasheet said the rail voltages should be ±28V. That would suggest the transformer secondaries should be roughly 20V AC. A look at the selection of 160VA toroidal power transformers available from my regular suppliers showed two contenders: 18-0-18V or 22-0-22V AC. From experience, I know that a transformer rated at 18V will deliver closer to 20V with a light load because it is designed to deliver 18V at its full rated load. I selected the 18V unit and, when it arrived, I was surprised to find it was somewhat larger than the original. I fitted it to the chassis with a bit of fettling and wired it up. When I applied power again, all was well and the DC rail voltages measured a touch over 28V DC. I should mention that the light-bulb limiter can give tricky results with appliances with switch-mode power supplies. Most are OK, but some can draw a lot of current at startup, lighting the lamp and lowering the voltage to the power supply, which may subsequently not start. Not long after that repair came another, this time a wedge floor monitor made by the same manufacturer and using similar technology. Only this time, the woofer amplifier was a discrete design with a higher power output. The customer said there was a crack sound, and the HF horn stopped working. I initially powered the box through my light-bulb limiter; again, the lamp came on at almost full brightness Items Covered This Month • Mystery amplifier transformer replacement • A curious remote control problem • HP 8660D signal generator repair • Arlec NL0009 LED Night Light repair Dave Thompson runs PC Anytime in Christchurch, NZ. Website: www.pcanytime.co.nz Email: dave<at>pcanytime.co.nz Cartoonist – Louis Decrevel Website: loueee.com and stayed that way. The customer said it was still working, so I held my breath and plugged it directly into the mains. It came on and, as described, the woofer was working but not the horn. A quick resistance check of the horn driver revealed it was open-circuit. Connecting my ‘scope to the output of the horn amplifier explained why. There was a solid -30V across the horn, meaning the IC amplifier driving it had failed and had taken the horn with it. If I had just replaced the horn driver, the new one would have burnt out at switch on. After replacing the IC (LM3886), I tried again with the light-bulb limiter, and this time the bulb came on bright and then faded to a dim glow as expected. This suggests that the faulty IC was also drawing a lot of current; I think if it was powered up for any length of time, there would have been smoke. Paul Mallon, Christchurch, New Zealand. A curious remote control problem I had noticed that our air conditioner remote control was working poorly. It would control the AC, but it seemed less sensitive, and the AC unit did not display the set temperature. I have a separate control for each room, so tried another one with no better result. That evening, I also found that the LG TV was responding strangely. I changed the batteries in the remote and even tried a second one with no change. The next morning, I tried using the sound system with a new (replacement) remote control. This was also acting strangely; since the batteries were low, I replaced them. I then had the bright idea of checking the sound system remote itself and found that it was continuously transmitting. Opening it and carefully reseating all the buttons stopped that, and now everything else worked properly. So, although the controller was transmitting codes not recognised by the AC and TV, it was enough to interfere with both systems. Graham P. Jackman, Melbourne, Vic. HP 8660D signal generator repair I went out to the radio shack intending to check some VHF receivers using my Hewlett-Packard 8660D signal generator. However, my effort was short-lived – the sig gen didn’t want to produce any useful output. Of course, the HP that built this sig gen is very different from the HP we know today as an IT company. The test and measurement arm of HP that created the 8660D siliconchip.com.au Australia's electronics magazine June 2025  89 was spun off from the IT company many years ago and became Agilent, later renamed to Keysight. When it was released in 1971, the 8660 was truly ‘bleeding edge’; it was the first fully synthesised sig gen built by HP. Although HP built frequency synthesisers before the 8660, they lacked the modulation capability and a wide range of calibrated output levels. The 8660’s specifications were impressive. In its early form, it offered 0.01MHz to 110MHz in 1Hz steps, AM or FM modulation, and an output from +10dBm to below -140dBm. Its output was also clean, with all in-band unwanted (spurious) outputs at least 80dB below the level of the wanted frequency; a real achievement. Truly impressive for the time! Add two front-panel plugin bays for a modulation section (with various options available) and the output section (again, different modules available) and it was a very flexible design. It also had an internal plug-in bay for a “Frequency Extension Module”, which was required for the later 1300MHz and 2600MHz versions. The one specification that was a bit below par was phase noise; the analog HP 8640B signal generator stayed king of the phase noise heap for many years after the 8660 was released. Phase noise is the wideband noise created by all oscillators, with some designs much better than others. Still, the 8660 was still very usable for most purposes. All of this did not come cheap or small. Despite being designed in the early 1970s, the 8660D was still on sale in 1990. The list price in 1990, for the 2.6GHz version with plugins, would not leave you with much change from US$40,000. But you got a lot of hardware for your money – a 4U (about 175mm) high 19 inch rack-mount box over 500mm deep and weighing about 30 kg. So, when I switched it on and no signal appeared, what to do next? My first check was with a spectrum analyser and frequency counter, which confirmed that with the 8660 set to a nominal frequency in the VHF range, it had an unstable (frequency varying) output at a few MHz. Fortunately, HP instruments came with excellent documentation, usually including an operations and service manual with full schematics, part layouts, fault-finding guides and parts lists down to individual components. Scanned versions are often available online. One useful source of info on the higher-end HP equipment is the Hewlett Packard Journal. Although essentially a sales strategy, the HPJ often had articles written by the project development teams about the high-end new equipment they had developed. For the 8660, the March 1971 and December 1971 HPJ issues both had very useful information, one about the 8660 mainframe, the other about the plugins. There are two basic fault-finding options in a complex system such as this, where no functional block stands out as the most likely to create the problem. One is to start near the signal source and work through the instrument to locate where the correct signal disappears, or work backwards from the output and find where the fault stops. Starting at the source was not attractive. It is a 100MHz master oscillator which is phase-locked to a reference oscillator at 5MHz or 10MHz, which can be either internal or external. Many different signals are derived from the master 90 Silicon Chip oscillator by frequency division or multiplication, to provide the reference signals for the phase-lock loops – 7 PLLs in the mainframe, plus several more in the Frequency Extension Module and in the output plugin. That means a lot of signal paths to check, including several complex programmable frequency dividers. Starting at the output and working back looked a lot easier. The output plugin module receives only two signals from the Frequency Extension Module: one tuning from 2.750GHz to 3.950GHz in 100MHz steps, the other tuning from 3.950GHz to 4.050GHz in 1Hz steps. The desired output frequency is the difference between these. A fault found here on one signal would immediately provide a path to further investigation ‘upstream’. Although a service manual is available for the output plugin, there is none online for the Frequency Extension Module, and in any case, the Frequency Extension Module is basically impossible to test without special (and unavailable – of course!) ‘extender’ cables. If the fault was in one of these modules, the instrument was probably a write off. So, trace backwards from the output it was. I just needed to locate the relevant connections and check with a spectrum analyser to see if the expected signals were there. The instrument is a maze of cable looms carrying various signals; most of the cables are terminated with special-purpose plugin connectors that have both coaxial and standard connections – which are inaccessible with modules installed in the chassis. Sigh! As it happened, the two required signals were actually on SMB connectors, so it was only a few minutes to make a suitable adaptor cable and have a look with the spectrum analyser. Lo and behold – one signal was absent. So, the fault was probably not in the output plugin module – so that was one critical module cleared. The Frequency Extension Module has four RF signals feeding into it, all via a multi-way connector. After a bit of fiddling, I was able to make a cable that kind-of mated with the coax connectors in the multi-way plug, with the Frequency Extension Module unplugged (and hence inoperable). Another test with the speccy showed the reference signals to the Frequency Extension Module were not present. Australia's electronics magazine siliconchip.com.au So the Frequency Extension Module was probably OK, too. Big sigh of relief! Now I had a new place to look – the circuits that generate the reference frequency signals used by all the phase-locked loops. The 100MHz master oscillator is used to generate 500MHz, 100MHz, two 20MHz, two 10MHz, 2MHz, 400kHz, and 100kHz reference signals. These are easy to check in what’s called the A4 assembly, which has all the circuitry to generate the reference signals. Most, but not all, reference frequencies were MIA, so at least the master oscillator was operating, but the circuits to generate most of the reference frequencies weren’t. Then I spotted some greenish corrosion on a small area of the “A4A4 reference loop and dividers” circuit board. Closer inspection showed that an electrolytic capacitor used as a bypass on the -10V power rail had leaked onto the board and the electrolyte had eaten a couple of power supply tracks. Bingo! After that, it was easy. Clean up the board, replace the missing tracks with copper wire bridges, a new capacitor, and we were in business. Or so it seemed. As a final check, I hooked up the sig gen output to my frequency counter, which is locked to a GPS reference. That showed the sig gen was putting out a signal significantly low in frequency, which drifted in frequency as I watched. Bother! Was there another fault with one of the phase-lock loops? Then the penny dropped – the sig gen was using its internal reference, an ovenised crystal oscillator, very likely the venerable HP 10544A or something similar. This was drifting low in frequency as it came up to temperature during its warm-up phase before settling to something very close to the correct frequency. Previously, I had always used the sig gen with an external reference from a GPS-derived 10MHz frequency source, so I never saw this behaviour. So, with relief, I decided it was all good! John Morrissey, Traralgon South, Vic. Arlec NL0009 LED Night Light repair We have two separate car garages and, a few years ago, we decided that a motion sensing night light in each garage would be ideal to help find our way to the light switch or door when we come home at night. So we purchased plug-in Arlec NL0009 PIR motion sensing LED night lights from the local hardware store and installed one in each garage. These are low-cost plug-in devices and worked very well until a year or so ago, when the first one became Servicing Stories Wanted Do you have any good servicing stories that you would like to share in The Serviceman column in SILICON CHIP? If so, why not send those stories in to us? It doesn’t matter what the story is about as long as it’s in some way related to the electronics or electrical industries, to computers or even to cars and similar. We pay for all contributions published but please note that your material must be original. Send your contribution by email to: editor<at>siliconchip.com.au Please be sure to include your full name and address details. siliconchip.com.au Australia's electronics magazine June 2025  91 faulty. It was still functioning, but the light output had become very dim, so I accepted the challenge to see if it was easily repairable at minimal cost. These units come apart easily with the removal of four small Phillips-head self-tapping screws to reveal the PCB. My first thought was it could be a problem on the supply side from the incoming 230V AC to the electronics. I could not find a circuit diagram for these units, but inspection of the PCB showed the power supply to be fairly conventional. This consisted of a 330nF 275V AC rated X2 capacitor paralleled by a 390kW resistor and connected in series with a 47W resistor (on the underside of the PCB) between the incoming 230V AC supply and a bridge rectifier, BD1. Across the DC output side of this rectifier is SMD capacitor C14, plus C15, a 220uF 35V electrolytic (on the underside) and a SOD-80 type zener diode, ZD1. This provides a voltage-limited, filtered and regulated DC supply to power the night light electronics and the white high brightness LED lights. I first checked the 330nF X2 capacitor as I recalled one failure mode of these metallised film ‘safety’ capacitors is to lose capacitance over time due to internal partial discharges, which progressively degrade the metallised film. I measured the capacitance of the X2 capacitor with my DMM and found this to be about 230nF. This was significantly below its labelled value, and would certainly explain the diminished light output from the unit. I replaced this faulty component with a new 330nF X2 275V AC capacitor and its full light output was restored. About six months later, the second night light failed, but this time with no light output at all. I opened up the unit and firstly checked the 330nF X2 capacitor, finding its capacitance to be about 320nF, which was acceptable. I next used my current-limited DC bench supply to apply voltage on the AC (input) side of BD1, checking both polarities. Voltage measurements indicated about 1.6V across the bridge input, for either polarity, before a significant current draw started. This seemed to be indicating a short circuit somewhere on the output side of the bridge rectifier; 1.6V is approximately equivalent to the sum of two forward-biased diode voltage drops in the bridge. Zener diode ZD1 seemed to be the most likely culprit, followed by the two DC filter capacitors. I removed ZD1 from the PCB and, on testing, I found it to be pretty much a dead short circuit. Assuming the zener diode to be the only faulty component, the next challenge was determining what voltage it should be. The zener had what appeared to be one green band with no other markings. A quick online search was of little help, so with no zener in the circuit and the light sensing photodiode (photo 1) shaded with a small piece of black tape, I decided to apply a current-limited DC voltage to the output side of the bridge rectifier. I slowly increased the voltage while moving my hand over the PIR sensor, and at about 22V, the LEDs started to glow. Further increasing the voltage to about 28-30V resulted in a LED brightness level of about what I thought it should be. As a further check, I decided to test, in a similar way, the previously repaired Arlec unit from the other garage. This unit still had the original zener diode installed and showed the voltage developed across the zener to be about 30V, so that was good confirmation. As I didn’t have a SOD-80 type 30V zener diode on hand, I decided to try two series-connected DO-41 zeners of 13-15V, hoping this would be good enough. These diodes were easily installed sitting just above rectifier BD1, and the repair proved to be very successful. While I was at it, I decided to also replace the original X2 capacitor just in case it was heading the same way as the original X2 capacitor in the other unit. So, with a little effort and replacement of a few lowcost components, both night lights are continuing to provide their helping glow when we come home at night. SC Stephen Denholm, Tranmere, Tas. One of the repaired night lights. 92 Silicon Chip Australia's electronics magazine siliconchip.com.au The replacement grey 330nF X2 capacitor is much larger than the original but it still fits. TEST MANY COMPONENTS ITH OUR ADVANCED TEST T EEZERS The Advanced Test Tweezers have 10 different modes, so you can measure ☑ Resistance: 1Ω to 40MΩ, ±1% ☑ Capacitance: 10pF to 150μF, ±5% ☑ Diode forward voltage: 0-2.4V, ±2% ☑ Combined resistance/ capacitance/diode display ☑ Voltmeter: 0 to ±30V ±2% ☑ Oscilloscope: ranges ±30V at up to 25kSa/s ☑ Serial UART decoder ☑ I/V curve plotter ☑ Logic probe ☑ Audio tone/square wave generator It runs from a single CR2032 coin cell, ~five years of standby life Has an adjustable sleep timeout Adjustable display brightness The display can be rotated for leftand right-handed use Components can be measured in-circuit under some circumstances Complete kit for $45 (SC6631; siliconchip.com.au/Shop/20/6631) The kit includes everything pictured, except the lithium coin cell and optional programming header. See the series of articles in the February & March 2023 issues for more details (siliconchip.com.au/Series/396). siliconchip.com.au Australia's electronics magazine June 2025  93 Vintage Radio Building a 1970s Little General By Fred Lever The Little General is a classic superhet AM radio design published in the April 1940 issue of Radio & Hobbies magazine. Some time ago, I built one using parts that were available in 1946, but I decided to see what improvements could be made using parts from the 1970s. M y classic post-war styled (1946) Little General, shown in Photo 1, used octal valves and contemporary parts. The set was quite heavy and bulky by today’s standards at 280 × 200 × 200mm and 5kg, but for 1946, that was typical of what a radio enthusiast could achieve. By 1976, 30 years later, electronics and components had greatly advanced due to the advent of TV. So I decided to build a new Little General using valves and parts that were available in 1976. For inspiration, I went through my valve box and, out of dozens of TV types, found a 6CS6 pentagrid, a 6EH7 frame grid pentode and a 6DX8 triode/pentode output valve. All were new old stock (NOS), still in their original boxes. With a twogang mini condenser, a suitable aerial coil and an oscillator coil, the 6CS6 could be the tuner/converter and the 6EH7 could be used as an IF amplification stage. That IF signal would then be applied to a diode and filter to demodulate the 94 Silicon Chip AM and eliminate the remaining RF signal. As the 6DX8 is a triode/pentode, I could use the triode section as a diode and the pentode as the audio amplifier. To keep things compact, four of the new (in 1976) silicon diodes can work as a bridge rectifier in the power supply in place of a 6V4 valve rectifier. That eases the heater draw and allows a simpler transformer with just two secondary windings. The resulting set (see the lead photo) measures 230 × 150 × 140mm and weighs approximately 2kg, so it is much more compact than my 1946 style model, at 4.8L versus 11.2L. The more modern miniature valves draw much less power, reducing the size of the required power supply. Parts like IF transformers and valves are about ¼ of the size of the 1946 version. The performance is similar. had several types of mini intermediate-­ frequency transformers (IFTs) to choose from. However, I was short aerial and oscillator coils. Still, I had a box full of assorted unknown coils to go through at a later stage. I wanted to settle the size of the transformers first as they are the biggest parts on the chassis and affect the layout more than the small pieces. Using three valves, I needed 1.3A at Design process I will now go through the design process. Having selected the valves, a look through the junk boxes showed I Australia's electronics magazine Photo 1: this 1940s-style Little General radio I built earlier works well, but it’s hardly compact and fairly hefty at 5kg. siliconchip.com.au Photo 3: I placed the components on the chassis to get a rough layout, marked the locations, drilled and cut the holes and then painted it. Here it is ready to start having parts mounted to it. 6.3V for the heaters and about 30mA at 250V for the plates. That works out to about 16W, so a 20W transformer would be suitable. I had a discarded soldering iron transformer specified as “22 watts” on the sticker. I dismantled the transformer, leaving the mains primary winding on the bobbin. I replaced the soldering iron’s 30V secondary with a 6.3V winding for the heaters and a 240V winding for the HT. I then restacked the transformer, tested it with dummy loads and finally, varnished it. I had a Jaycar AS3025 90 × 50mm 8W general-purpose rectangular speaker on hand, so I decided to use that for the radio. The speaker transformer needed to reflect the 8W impedance of the loudspeaker to a higher value for the plate of the 6DX8. I had a Jaycar MM2006 2W 12V mains transformer Photo 2: the aerial coil (left) and oscillator coil (right) look a bit messy, but they tune over the required ranges. siliconchip.com.au Photo 4: I riveted the valve sockets and mains transformer to the chassis. Most other components were mounted less permanently later, via bolts or on tag strips. that I wired to a 6DX8 in a bench test circuit configured as a class-A audio amplifier to see how it performed. The transformer did an OK job of passing a couple of watts from the valve to the speaker. The impedance of the primary circuit, at maximum power transfer, was around 12kW. I dismantled the transformer, stripped off the original tapped secondary and wound back on a single secondary with a turns ratio that matched the 8W speaker to 12kW. I reassembled the transformer with a slight air gap in the lamination stack, tested it again, then dunked it in varnish. Tuning coils The mixer stage needed tuning and oscillator coils that would give a continuous frequency differential matching the intermediate frequency (IF) while adjusting the tuning gang. For example, if the tuning coil tuned from 500kHz to 1700kHz over the full rotation of the tuning gang, the oscillator coil would need to tune from 955kHz to 2155kHz, ie, 455kHz above the tuning coil (assuming a 455kHz IF). Both coils needed to be adjustable, with ferrite cores, and inductances to suit the broadcast tuning range. Note that the required ratio on the tuning coil is about 3:1, while it’s closer to 2:1 for the oscillator coil. The mini gang I intended to use had equal aerial and oscillator capacitance sections. That means series ‘padding’ of the oscillator gang capacitance is Australia's electronics magazine needed to compress the oscillator range from 3:1 to 2:1. I scratched about in my coil junk box and found nothing that looked like an oscillator coil, but I did locate a rough-looking complete ferrite core coil on a ½” (12.7mm) tube with a tuning winding and a small primary. I measured the inductances as 0.1mH for the big coil and 0.01mH for the other. When I hooked it to the gang and tested for resonance, I found it tuned from 600kHz to 1800kHz, and screwing the core in and out made a big difference to the range. That was good enough for the aerial coil. For the oscillator coil, I had a spare blank portion of a ¼” (6.35mm) IFT former left over from previous projects, so I wound on about 250 turns of scrap Litz wire and measured its inductance as 0.08mH. I added a 30-turn tickler coil of 0.01mH. I tested its resonance and, with 150pF in series with the coil, I had a tuning range of 950kHz to 2300kHz that also varied a fair bit by moving the slug in and out. Those two coils were good enough to start testing. I found a pair of mini IF cans marked “L128” and checked their resonance. Both coils resonated at around 440kHz with measurements of 1.43mH and 23W. The four adjusting cores worked on both, so they looked good to go. Building the set I dropped the parts gathered so far onto a sheet of paper and outlined a June 2025  95 Photos 5 & 6: these photos show the underside of the chassis (left) and top (right) partway through construction. Most of the larger parts are in place, with the smaller components and wiring to do. likely layout. That layout provided a template for the chassis. The chassis is so small that some light gauge sheet (from a computer case) sufficed. I centre-punched the holes and used drills and hole saws to make the cutouts. I made a few adjustments, like slotting the control spindle holes so I could drop those parts in and out easily. I sprayed a light undercoat on the inside and a light coat of white paint on the outside, giving the result shown in Photo 3. I then started mounting parts on the chassis, pop riveting some parts permanently into place, like the valve sockets and tag strips, as shown in Photo 4. Next, I mounted the heavy parts, followed by lighter parts like the coils and gang. I mounted the tuning gang using some spacers to lift the shaft to the centre height of the speaker. I left the actual dial drum for later and used a large knob to move the gang spindle temporarily. I also bolted a pot shaft to the chassis for a string drive. That shaft bush and nut were later secured to a strip of Bakelite on which the tuning coils were mounted. I made access holes in the chassis front panel for the slugs of the tuning coils. I fitted some tag strips underneath and squeezed another tag strip on the top of the chassis behind the speaker. On that, I mounted the filter capacitors and three 4.7kW PW5 ceramic resistors in parallel for ~1.5kW total to use in the HT filter. I pushed the resistors hard up against the transformer as a heat sink. Underneath, I mounted a small MB4 bridge rectifier on a tag strip and wired the HT through the filters to the 6DX8. I then completed the mains and the heater wiring to the sockets. It was time to power it up and road test the 6DX8 with the new power supply. The audio stage Having completed the power supply and 6DX8 wiring, I increased the AC input voltage in small steps using a variac to reform the electrolytic capacitors. Nothing smoked, and I measured 313V DC at the rectifier output and 6.6V AC on the heaters. The three 4.7kW 5W HT dropper resistors lowered the 313V DC to 284V DC. I had wired the 6DX8 with a 330W bias resistor, keeping in mind the plate rating of 18mA, and measured a 24V drop across the HT resistor and 6V bias, both indicating about 20mA being drawn. The audio stage tested OK with an input sensitivity of 0.5V for clipping and no audible hum. The IF stage I wired in the 6EH7 and 6CS6 and fluked the oscillator tickler coil phasing, allowing the oscillator to run immediately. I aimed to prove the IF part of the circuit first but encountered Photos 9 & 10: shown adjacent is the set with a temporary tuning knob, while above is the tuning knob string arrangment I came up with. 96 Silicon Chip Australia's electronics magazine siliconchip.com.au Photos 7 & 8: the photo on the left shows the initial stage of under-chassis wiring, while on the right I have added and wired up the smaller components too. problems feeding a 440kHz IF signal through the control grid of the 6CS6. Usually, I just kill the local oscillator and treat the converter as a straight RF valve to pass the IF signal into the control grid and through the IF transformer set. In this case, if I shut down the local oscillator, the 6CS6 valve would not pass a signal from its control grid to the plate! As soon as I unblocked the oscillator grid circuit, the valve would self-bias and work as an RF amplifier. However, if I blasted several volts of 440kHz into the 6CS6 grid, enough passed through the plate that I could at least peak the cores. There were many other problems with making the IF section work, but suffice it to say that after a hard struggle, it worked well. One important lesson I learned was that the 6EH7 needs a separate, stable screen supply, not one shared with the converter. Also, the 6EH7 is a very high-gain valve and needs an AGC bias feedback control on top of a pedestal of self-bias to work stably at all signal strengths. With the IF system working, I had to adjust the tuning and oscillator coils so that, with the tuning gang set anywhere in its range, the oscillator frequency was 440kHz higher than the tuned station frequency. The initial oscillator range of 1000kHz to 2700kHz was too high. I left the coil turns the same but changed the padder capacitor value, added a trimmer on the gang and varied the coil core position. By juggling those three factors, I achieved the desired range. The next job was to make the tuning coil resonate from 500kHz to 1800kHz. With the core set so that good coupling was achieved from primary to secondary, I could not get the bottom frequency under about 650kHz, and then the top was around 2300kHz, both too high, indicating insufficient turns on the coil. I pulled one lead end off the big winding, joined some Litz wire and wound on another 40 turns. I then got a range of 549kHz to 1890kHz, close enough to work. Next, I carefully measured the actual difference in frequency between the two coils at multiple points over the tuning range. My first tests concluded that the variation was about ±20kHz around 450kHz over the tuning range. With a bit more careful adjustment of the coils, I reduced that error to ±5kHz – see Fig.1. As a product of that process, the mean IF value increased to about 455kHz. I deemed that acceptable, as the IFTs have a passband broad enough to encompass the deviation without a significant loss of coupling. With those changes, the set started to act like a real receiver. The volume could be adjusted from zero to Fig.1: this plot shows the difference in the tuning and oscillator coil resonances (vertical axis) as the dial is rotated (horizontal axis). The red plot is what I found initially, with a variation of more than ±20kHz from an average of 450kHz. Some tweaking gave me the blue curve, within about ±5kHz from 455kHz over most of the range, resulting in more consistent performance. siliconchip.com.au Australia's electronics magazine June 2025  97 Fig.2 (above): this is my revised version of the Little General circuit. There are other changes besides the different valve lineup, such as the volume control method (attenuation of the audio signal rather than varying the valve bias) and the oscillator coil arrangement (tapped rather than two coupled windings). Fig.3 (below): the original Little General circuit diagram from Radio & Hobbies, April 1940. You can find all the changes I made in my circuit by comparing the two. Still, the overall configuration (number of valves and purpose) is very similar. 98 Silicon Chip Australia's electronics magazine siliconchip.com.au maximum, and the audio output was level no matter what station it was tuned into. At this stage, the circuit, shown in Fig.2, was pretty much final. You can compare it to the original Little General circuit, Fig.3. The AGC voltage was low on a weak station, around -1V with 4.2V across the IF valve bias resistor. On a strong station, the AGC signal measured -12V and the cathode measured 1.5V, indicating that the valve was throttled, trying to keep a consistent IF signal level. However, the set was full of heterodyne whistles! They led me on another merry chase, trying this and that with little effect. Having run out of ideas, I realised that the set, while very selective, was not that sensitive, needing a fair length of antenna to work. I decided to look at that problem first. Harking back to the 6CS6 not wanting to work as a plain RF amplifier, I tried another 6CS6 valve. For this test, I tuned the receiver with the original valve and settled the RF level so the AGC was –12V. I then swapped the valve for a grubby, well-used XTV chassis 6CS6 (from a different manufacturer), and as it warmed up, without moving anything else, I was amazed to see the AGC climb past -12V and settle at -24V! That was not just double the gain, as the AGC works up a slope throttling the 6EH7, but many times the gain. The AGC system was now working even better, with the 6EH7 operating over a huge bias range, drawing 4mA with no signal and throttling back to around 0.2mA on 2RPH, with a mean level of around 2mA on average stations. The net result was that the audio level was consistent, irrespective of the station signal level. Off-station, the background frying and fizzling from all the suburb rooftop inverters comes up, while on-station, the background noise disappears and stations tune in loudly. I then realised that the whistle problem was also gone! Thinking about this later, I suspect the 6CS6 might not have been the best choice. While it is a pentagrid, the valve was designed to be used as a sync pulse separator. A minor manufacture variation that had no effect on separator use may have a large impact when used for another application like this one. siliconchip.com.au Scope 1: testing the IF response with a swept sinewave fed into the radio reveals that it is pretty symmetrical about the ~450kHz intermediate frequency. Scope 2: the signal from the volume control pot’s wiper with a station tuned in. You can see the lowerfrequency audio signal is overlaid with higherfrequency noise, the remnant of the IF (and possibly RF) signals. Scope 3: the audio signal delivered to the speaker is cleaner than that shown in Scope 2, mainly due to filtering by the 1nF capacitor across the speaker coil. I also tried a second old 6CS6, which worked just as well as its stablemate. Still, no real conclusion can be drawn with a sample of just three valves. I suspect a radio type 6BE6 would be a better choice. Another possibility is that my NOS 6CS6 was simply faulty! Returning to the IF stage I went back to the IF, swept it, and Australia's electronics magazine took some shots of the response. The sweep response was quite symmetrical on either side of 450kHz, as shown in Scope 1. Note that this is an ‘active’ response curve as the AGC is working and limiting the gain. However, the general response is evident. When tuned to a station, after the volume control, I found a signal of over 120mV peak-to-peak with a fair amount of RF still present (Scope 2). June 2025  99 Photos 11 & 12: I turned five-ply timber on a lathe and routed a channel around to hold the string. Note the tension spring on the back of the dial. By the time we get through the 6DX8, and with the help of the top-cut capacitor on the plate, we wind up with a clean audio signal of around 140V peak-to-peak at the plate (Scope 3). Finishing it off The final chassis is not one of my neatest jobs and would benefit from being stripped out and rebuilt, with some parts moved. Placing an electrolytic capacitor next to a hot output valve is not the most sensible move. However, it was good enough to function, and I wanted to press on, finalise the cabinet and dial and get to the end. With a tuning knob spindle already mounted on the chassis, I needed a drum on the tuning capacitor to couple to the spindle. I had nothing in the junk box, so I grabbed a flat scrap of five-ply timber and made a drum about 80mm in diameter. I machined a string groove in the centre of the outer rim. I had a Jaycar ¼in (6.35mm) bore hub (Cat YG2784) that matched the gang shaft and fitted that to the centre of the timber wheel. Next, I drilled holes to thread the string ends through the drum from the rim groove. These short holes emerge at an angle at the back of the drum. One hole allowed one end of a string to be anchored to a wood screw. The string then goes around the drum, down to the spindle, two-and-ahalf times around the spindle and back up to the drum, then down through a second hole, terminated to a spring to maintain some tension on the string. I sketched out a cabinet design made of plywood with a circular dial opening and then looked for something to make a dial bezel. What I needed was something round and shiny. My eye fell on some tin cans in the kitchen recycling bin. I put a can in the lathe and bored the end out of it. Then I swung the tool post around and cut the end off, giving me a ‘chrome’ bezel. The idea for the cabinet was to have the front panel recessed from the front to protect the knobs. Otherwise, it’s a simple box made from five-ply timber with glue fillet joints and a back plate with slots to let air in and form a handle. The dial bezel and a bunch of ¼in (6.35mm) holes for the speaker completed the front panel. The back is then held in with four screws that go into the chassis blocks and two top blocks. One of those also limits the power transformer’s upward movement. With the basic box made, I sanded it down a bit and flowed on a coat of red stain. I repeated that a couple of times, with sanding in between, until I had a reasonably smooth finish. Ultimately, I decided that sticking one’s fingers into the live works to carry it was not a good idea, so I carefully added a flat strap to the top as a proper carry handle. Conclusion It has some flaws, such as parts not quite lined up straight, rat’s nest wiring and values that need optimising. These are properties of prototype radios that would be ironed out in a production run. Still, I am not a manufacturer, so it will do. As with any other scratch-built project, there was far more work involved in getting it to work than this article reveals. Much more detail can be found at the following links (parts 1-3): • siliconchip.au/link/abtk • siliconchip.au/link/abtl SC • siliconchip.au/link/abtm Photos 13-15: the last few steps required before assembly involved making the timber cabinet, which I then stained red. The complete Little General radio was more compact, weighing ~2kg; about half the weight of the radio shown in Photo 1. 100 Silicon Chip Australia's electronics magazine siliconchip.com.au ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Send your email to silicon<at>siliconchip.com.au Ceramic capacitor values measure low I recently ordered the short-form Automatic LQ Meter kit (SC6939). A set of three SMD capacitors was included, which I assume are the 10μF parts. However, upon measuring them with my SMD Test Tweezers (now one of my most-used tools), I got a reading of 5μF each. This made me think they were actually 4.7μF capacitors. I just used my Peak Atlas LCR, and it showed 10μF, so I guess they are the correct types. The SC Test Tweezers are normally reasonably accurate, so I didn’t double check. Why are the readings so far off? (M. H., Mordialloc, Vic) ● We were initially puzzled by the low capacitor readings you describe, but soon realised that they are mostly due to a design aspect of the Improved Test Tweezers and an often overlooked shortcoming of MLCCs (multi-layer ceramic capacitors). Most of the error is because of the capacitor’s behaviour under DC bias. The Tweezers work by applying 3V DC to the device under test (via a 10kW resistor) and probing the junction point. For capacitors, the Tweezers discharge the capacitor, but most of the time it has close to 3V across it. Like many MLCCs, the Samsung CL21A106KOQNNNE 10μF 16V capacitors we supply in the kit suffer from a loss of capacitance as the DC bias voltage rises. At 3V, their capacitance is down by 30%, according to the chart from Samsung below. Given that the capacitors have a +20 0 ΔC(%) -20 -40 -60 -80 -100 0 5 10 DC bias (V) siliconchip.com.au 15 ±10% initial tolerance, they could have as little as 6μF capacitance once charged to 3V (-40%). They will be down to about 10% of their nominal capacitance at the rated voltage, 16V! This is a good reason to use MLCCs with a higher than necessary voltage rating; they retain more of their capacitance when charged up. Of course, such capacitors may be larger or more expensive. We didn’t specify an accuracy for the Tweezers, but we’d say they have about ±10% accuracy for capacitance readings. This is heavily affected by oscillator accuracy (due to the timing needed for capacitance measurements), which is specified as ±8%. With the capacitor already possibly being down to 6μF, and another 10%+ error from the Tweezers, a reading of 5μF (or even lower) is possible. D1 Mini doesn’t work with 5GHz WiFi I constructed the GPS-Synchronised Analog Clock (September & November 2022; siliconchip.au/Series/391) with the D1 Mini WiFi module from a kit supplied by Silicon Chip. It works well, but I found it was rapidly flattening the two AA cells. The high drain was happening because the PIC continually powers the D1 Mini module until it can connect, and it was failing to connect to my home’s WiFi, either for long periods each day or at all. After experimenting and finding that it would readily connect to several other different WiFi routers, I noticed that my home’s WiFi router has both 2.4GHz and 5GHz band networks, with the same SSID and password. I disabled the 5GHz network and the D1 Mini connected easily to the 2.4GHz network. An alternative solution might be to rename the 5GHz network. Either way, the ability to have devices roaming freely between the two networks is lost. This does not matter to me, but I wonder if a firmware update to the D1 Mini is available to fix this Australia's electronics magazine problem properly. I can imagine, in a year or two, switching the 5GHz network back on and forgetting that this will cause the kitchen clock’s batteries to quickly go flat! (A. P., Norwood, Tas) ● It’s odd that this affects the D1 Mini, since it has no 5GHz capability. But in my home network, I have renamed the 5GHz network to use a different SSID because there were one or two devices that simply did not work otherwise. I am using a TP-Link router. Apparently, some dual-band routers try to kick devices off the 2.4GHz network (using WPA deauthenticate packets) to see if they reappear on the 5GHz network. If the D1 Mini does not handle this elegantly, then that could explain the problem. A note on GitHub suggests that the ESP8266 WiFi chip in the D1 Mini may have this problem (see https://github.com/esp8266/ Arduino/issues/8956). There is mention of forcing the 802.11g protocol, but no indication of how it can be done; it is not something we’ve ever seen as being configurable. Your fix is a good workaround; however, we now have a newer WiFi Time Source based on the Pico W (June 2023 issue; siliconchip.au/Article/15823). Programming Adaptor needs programmer Is your SC6774 kit all I need to program a PIC16F1459 chip? (P. C., Denistone, NSW) ● The PIC Programming Adaptor is just an adaptor. You still need a PICkit or similar programmer to use with it (see our September 2023 issue for details; siliconchip.au/Article/15943). Due to the large number of PICs available and different programming protocols, it is not practical for us to produce an all-in-one programmer. The PICkits, SNAPs and their clones are the best way to get that interface. The PICkit 5 is currently quite expensive, at around $150. The Microchip Snap (PG164100) is much more cost effective at around $25. Unfortunately, at the time of writing they are June 2025  101 out of stock at the likes of DigiKey and Mouser, but due back in stock by the time you read this. They are effectively a cut-down version of a PICkit 4 and don’t support powering the target device or high-voltage programming. The lack of high-voltage programming may mean they might not be suitable for some projects, but we have used a Snap to program the PIC16F1459. For a $125 saving, we think we can figure out a way to supply power to the target device! Dual Hybrid Supply CPU board problem I have nearly finished building the Dual Hybrid Power Supply project (February & March 2022; siliconchip.au/ Series/377). After some initial testing, I needed to fix up a few incorrectly orientated diodes on the regulator boards. However, those boards are now functioning as per the testing instructions. I am now stuck with the control board. The LD1117 regulator gets very hot after seconds and the LCD has no output (other than just the blue screen). I have checked the orientation of the SMD diodes on the board and they are OK. I have also double-­checked for solder bridges etc. I checked that my ribbon cables have the correct orientation too. Do you have any suggestions on how I can continue to trouble shoot? (B. L., Maidstone, Vic) ● Phil Prosser responds: the first step is to unplug everything but power from the CPU board and check the current draw. Perhaps an IC has been installed with the incorrect orientation or there is a solder bridge you haven’t found yet. If the power draw is reasonable in that condition, plug in the display and see what happens. A hot LM1117 is almost certainly a sign of something being soldered in the wrong way around. If one of the reverse diodes was the protection diode for the regulator, the full input voltage would have been applied to everything on the 3.3V rail, which could be scary. Note: B. L. later confirmed there was a short circuit on the microcontroller pins causing the excessive current draw. BIG LED Clock power supply The BIG LED Clock (January 2025 issue; siliconchip.au/Article/17603) 102 Silicon Chip looks great. I have cleared a spot on my workshop wall and ordered the major parts, but I can’t see what the power requirements are. I would have expected a plugpack or something similar in the materials list. I also didn’t see if the clock was 12- or 24-hour, or configurable. I presume that the first digit would need at least six segments for a 24-hour clock. Keep up the mighty work. (R. W., King Creek, NSW) ● We noted on page 58 of the article that our BIG Clock peaked at around 700mA with the default brightness setting, and we simply used the USB-C connector to power it, since USB is so common. Unlike the older USB specifications, USB-C supports a minimum of 900mA, so any compliant USB-C to USB-C cable should provide enough power, no matter what it is connected to. We simply ran our prototype from a computer. You could use a phone charger or other USB-C power adaptor. We figured that most readers would have something appropriate in their spare parts collection. 700mA should be comfortably within the limits of just about any USB mains adaptor, since most support 1A or more. If you have a supply that can only provide 500mA, then you could set the BRIGHTNESS #define to 40. And yes, the number of segments available limits the hardware to displaying a 12-hour clock. Adding a Fetron to a vintage radio I have a couple of queries regarding the Fetrons that Dr Hugo Holden used to make a communications receiver, described in March 2021 (siliconchip. au/Article/14777). I am restoring a 1935 Atwater Kent radio (it’s now my own set) and its performance is rather woeful. It was built as an economy set and performs like one. I am seriously considering modifying the set to have a proper IF stage & diode detector, and I wondered if I could ‘hide’ at least one Fetron somewhere in the set along with fitting a second IF transformer. Currently, the radio has one IF transformer with an extra winding for regeneration. The ‘2nd detector’ valve doubles as the detector (using grid leak detection) and the audio amplifier. While it works, there is significant distortion. I have recapped the entire Australia's electronics magazine radio and replaced most of its resistors. I have also considered adding a transistor IF stage to the set, but I am unsure how well it would work. Do you have any thoughts on this? In a ‘normal’ AM transistor circuit, the IF transformers are tapped to provide impedance matching as well as IF coupling. I considered having two transistors connected as a Darlington pair to provide a high input impedance, with the collectors of the transistors connected to a valve radio IF transformer to provide coupling to the detector diode. (P. W., Pukekohe, New Zealand) ● Dr Hugo Holden responds: you could eliminate the regeneration of the existing IF stage and add another IF stage to get the overall IF gain up, then use a standard detector. If I were doing that, I probably wouldn’t use a Fetron, because they are hard to get. Still, it would work and would avoid the need for a heater supply. A small, easy-to-get seven-pin Pentode tube such as the 6AG5 or similar and an extra IF transformer would also work. Suitable heater voltages should be available in the set. If they were the wrong voltage, there are some possible solutions. It could also be done with two high-voltage transistors. Ideally, it should probably not be a Darlington but a cascode design. Otherwise, there will not be enough input/output isolation and the IF stage could oscillate (Fetrons are inherently cascoded). I have used a single JFET in an IF stage, and it was stable due to the low feedback capacitance of the MPF102, but it was a low-voltage circuit. Higher-­ voltage JFETs likely would have to be in cascode, much like the Fetron, to work with equivalent input/output isolation to the screen-grid pentode. To increase the input impedance of a transistor cascode arrangement, a third transistor can be used as an emitter-follower to drive the cascode circuit. Generally, though, a small Pentode like a 6AG5 would be easier if a suitable heater voltage is available. Another option is to use a low heater voltage valve with heater ballast resistors. Question on expanding Multi-Spark CDI Greetings from New Zealand. I have been an avid reader since Electronics continued on page 104 siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip KIT ASSEMBLY & REPAIR FOR SALE DAVE THOMPSON (the Serviceman from Silicon Chip) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, New Zealand, but service available Australia/NZ wide. Email dave<at>davethompson.co.nz LEDsales KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com PCB PRODUCTION PCB MANUFACTURE: single to multilayer. Bare board tested. One-offs to any quantity. 48 hour service. Artwork design. Excellent prices. Check out our specials: www.ldelectronics.com.au 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. Dual Mini LED Dice August 2024 SMD LED Complete Kit SC6961: $17.50 TH LED Complete Kit SC6849: $17.50 siliconchip.au/Article/16418 Includes either 3mm through-hole or 1206sized SMD LEDs. Choice of either white or black PCB. CR2032 coin cell not included. Lazer.Security WE OFFER KITS, LEDs, LED assemblies and all sorts of quality electronic components, through-hole and SMD, at very competitive prices. Check out the latest deals at www.lazer.com.au 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 June 2025  103 Advertising Index Altronics.................................31-34 Blackmagic Design....................... 9 Control Devices........................... 85 Dave Thompson........................ 103 DigiKey Electronics....................... 3 Emona Instruments.................. IBC Hare & Forbes............................ 6-7 Icom Australia............................. 14 Jaycar........................IFC, 11, 15-17 Keith Rippon Kit Assembly....... 103 Lazer Security........................... 103 LD Electronics........................... 103 LEDsales................................... 103 Microchip Technology.............OBC Mouser Electronics....................... 4 OurPCB Australia........................ 10 PCBWay....................................... 13 PMD Way................................... 103 Rohde & Schwarz........................ 83 SC Ideal Bridge Rectifiers kits.... 57 SC GPS Clock kit......................... 60 SC Advanced Tweezers kit......... 93 Silicon Chip Shop.......... 69, 82, 84 Silicon Chip Subscriptions........ 30 The Loudspeaker Kit.com.......... 12 Wagner Electronics..................... 91 Silicon Chip Binders REAL VALUE AT $21.50 PLU S P&P Order online from www.siliconchip. com.au/Shop/4 or call (02) 9939 3295. Next issue of Silicon Chip Next Issue: the July 2025 issue is due on sale in newsagents by Thursday, June 26th. Expect postal delivery of subscription copies in Australia between June 23rd and July 11th. 104 Silicon Chip Australia’s demise. I have been involved in the electronics industry, servicing, building and importing components since the days of Mullard’s transistors (half of which did not function). I have built a number of circuits published in Silicon Chip and would like to congratulate you on your persistence in encouraging young minds to delve into both analog and digital electronics. The shrinking size of components will not help, especially for old guys like me. I have a question about John’s Multi-Spark CDI design (December 2014 & January 2015; siliconchip.au/ Series/279). I want to be able to trigger up to six spark plugs simultaneously while revving to high RPMs. Rather than building six complete units, would the output from the inverter be sufficient for one inverter to supply six individual trigger systems? (K. S., Dunedin, New Zealand) ● Thank you for your words of appreciation for Silicon Chip magazine. Regarding the Multi-Spark ignition, the coil driver section comprising IC2, Q3, Q4 and the 1μF capacitor and associated components would need to be duplicated six times for six separate ignition coils. The 300V DC generator comprising IC1, Q1, Q2, T1, the D2-D5 full-wave rectifier and associated components should be able to drive all six output circuits with the 300V DC. If the 300V is not maintained with the six outputs connected and running at high RPM, you may need to build another 300V DC section so that each will only drive three output circuits. RIAA preamp wanted for record player I have been asked to restore an old 1950s chest-type valve radiogram that has great sentimental significance to its owner. Unfortunately, the existing Collaro record changer looks to be beyond help, with perished rubber parts. The only solution I have is to retrofit a newer turntable/record changer unit. I envisage using something like a later model Garrard obtained second-hand, fitted with a magnetic cartridge. The radiogram won’t have sufficient audio gain to be driven directly from a magnetic cartridge, but I can easily add a solid state preamp, hidden inside the cabinet. Have you published a design for a mono (or stereo) RIAA magnetic phono Australia's electronics magazine preamp that can provide an output of up to 300-400mV? If so, do you have PCBs available for it? (P. W., Pukekohe, New Zealand) ● We have published a Magnetic Cartridge Preamplifier (August 2006; siliconchip.au/Article/2740). It is a stereo preamplifier with a gain that should be suitable for your application. Its output level depends on the cartridge signal output with record groove modulation. The PCB is still available from our Online Shop (siliconchip.au/Shop/?article=2740). Bouncing Kelvin causes the eyes to light up My son and I enjoyed building the Kelvin the Cricket project (October 2017; siliconchip.au/Article/10828) and would love to learn more about two aspects of his design and function. 1. If I bounce Kelvin, his eyes light up, even with the batteries out and the jumper removed. I’ve only tried this on dark rooms because the LED is too dim to see in well-lit rooms. I’ve tried leaving Kelvin alone for an hour in case there was a charged capacitor. I’ve tried different locations in case there was a strong magnetic field. Sometimes both LEDs glow, sometimes one does. 2. Do you have the PIC code in C# or pretty much any other language other than assembly, so I can learn how the functions were implemented? (B. B., via email) ● The interesting effect where the LEDs light when Kelvin is dropped is due to the piezo transducer producing a voltage when flexed. Since the transducer is in parallel with the LEDs and their current limiting resistors, they light up when this happens, but for extremely brief periods and very low currents. Piezo materials flex when a voltage is applied (producing a sound) but they also do the reverse, ie, if flexed they will produce a voltage. The dropping of Kelvin the Cricket causes piezo movement when it hits the ground, as it experiences inertial forces. The piezo element will probably ring (oscillate) with the initial abrupt stop when hitting the ground and drive the LEDs alternately as the AC waveform from the transducer changes polarity on each ringing cycle. Sorry, we don’t have C source for the software as it was written in assembly language. SC siliconchip.com.au “Rigol Offer Australia’s Best Value Test Instruments” New 2024 Products Oscilloscopes New 12Bit Scopes RIGOL DS-1000Z/E - FREE OPTIONS RIGOL DHO Series RIGOL MSO-5000 Series 450MHz to 200MHz, 2/4 Ch 41GS/s Real Time Sampling 424Mpts Standard Memory Depth 470MHz to 800MHz, 2/4 Ch 412Bit Vertical Resolution 4Ultra Low Noise Floor 470MHz to 350MHz, 2 Ch & 4Ch 48GS/s Real Time Sampling 4Up to 200Mpts Memory Depth FROM $ 499 FROM $ ex GST 659 FROM $ ex GST 1,489 Multimeters Function/Arbitrary Function Generators New Product New Product RIGOL DG-800/900 Pro Series RIGOL DG-1000Z Series RIGOL DM-858/E 425MHz to 200MHz, 1/2 Ch 416Bit, Up to 1.25GS/s 47” Colour Touch Screen 425MHz, 30MHz & 60MHz 42 Output Channels 4160 In-Built Waveforms 45 1/2 Digits 47” Colour Touch Screen 4USB & LAN FROM $ 713 FROM $ ex GST Power Supplies ex GST 725 FROM $ ex GST Spectrum Analysers 689 ex GST Real-Time Analysers New Product RIGOL DP-932E RIGOL DSA Series RIGOL RSA Series 4Triple Output 2 x 32V/3A & 6V/3A 43 Electrically Isolated Channels 4Internal Series/Parallel Operation 4500MHz to 7.5GHz 4RBW settable down to 10 Hz 4Optional Tracking Generator 41.5GHz to 6.5GHz 4Modes: Real Time, Swept, VSA & EMI 4Optional Tracking Generator ONLY $ 849 FROM $ ex GST 1,321 FROM $ ex GST 3,210 ex GST Buy on-line at www.emona.com.au/rigol Sydney Tel 02 9519 3933 Fax 02 9550 1378 Melbourne Tel 03 9889 0427 Fax 03 9889 0715 email testinst<at>emona.com.au siliconchip.com.au Brisbane Tel 07 3392 7170 Fax 07 3848 9046 Adelaide Tel 08 8363 5733 Fax 08 83635799 Perth Tel 08 9361 4200 Fax 08 9361 4300 EMONA web www.emona.com.au Australia's electronics magazine June 2025  105