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MARCH 2023 ISSN 1030-2662 03 The VERY BEST DIY Projects! 9 771030 266001 $ 50* NZ $1290 11 INC GST INC GST [ 3 1 ] Digital Volume Control Potentiometer A drop-in replacement for a volume control potentiometer [ 42 ] Model Railway Turntable An excellent addition to nearly any model railway layout [ 56 ] Altium Designer 23 Covering the software’s newest features [ 62 ] 30V 10A DC Load Module A programmable constant-current DC Load ...plus much more inside how we communicate underwater ADD MOTION DETECTION TO YOUR PROJECT PIR MOTION DETECTION MODULE ADD OBSTACLE DETECTION OR AVOIDANCE DUAL ULTRASONIC SENSOR MODULE • Adjustable delay times XC4444 $6.95 • 2 - 45cm 15° range XC4442 $8.95 Expand your projects with our extensive range of Arduino® compatible Modules, Shields & Accessories. OVER 100 TYPES TO CHOOSE FROM AT GREAT PRICES. ADDRESSABLE RGB LEDS DETECT WHEN PLANTS NEED WATERING SOIL MOISTURE SENSOR MODULE • Analogue output XC4604 $4.95 VIEW OVER 70 ARDUINO® PROJECTS YOU CAN BUILD AT: jaycar.com.au/projects Shop at Jaycar for: • Arduino® Compatible Development Boards • Display Modules • Servos, Solenoids & Motors • Wheels & Chassis 1.3" MONOCHROME OLED DISPLAY • 128x64 Pixel XC3728 $19.95 ADD AMAZING COLOUR TO YOUR NEXT PROJECT 5V LED STRIP WITH 120 ADDRESSABLE RGB LEDS HALL EFFECT SENSOR MODULE • 2m long, flexible, waterproof XC4390 $34.95 • Sense magnetic presence XC4434 $4.95 • Prototyping Hardware and Accessories • Project Enclosures • Servos & Motors • Switches & relays Explore our wide range of Arduino® compatible modules, shields and accessories, in stock on our website, or at over 110 stores or 130 resellers nationwide. Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. jaycar.com.au/shieldsmodules 1800 022 888 Contents Vol.36, No.03 March 2023 14 Underwater Communication There are many challenges when trying to communicate underwater using current technology. We take a look at how voice & data is transmitted through the sea to and from submarines, drones and other vessels. By Dr David Maddison Technology feature Digital Volume Control Potentiometers 56 Altium Designer 23 Page 31 We were keen to see what the latest version of Altium’s electronics design automation software had to offer. New features include multiple IC pin functions, Design Reuse Blocks and better MCAD integration. By Tim Blythman Software review 62 ZPB30A1 30V 10A DC Load This programmable constant-current DC load can be used to test power supplies and check the capacity of batteries. It’s a self-contained device that delivers good value for money. By Jim Rowe Using electronic modules 31 The Digital Potentiometer This drop-in replacement for a volume control potentiometer uses a digital IC, providing it with excellent tracking and reliable long-term performance. You can choose to build it in a compact SMD or easier through-hole version. By Phil Prosser Volume control project 42 Model Railway Turntable An excellent addition to just about any model railway layout. This project lets you turn a locomotive around at the end of a track and automatically reverses power to the track, stopping it from shorting out. By Les Kerr Model railway project 68 Active Mains Soft Starter, Part 2 We finish off the new Active Mains Soft Starter by covering how to assemble, test and calibrate it. The Soft Starter is ideal for eliminating the ‘kick’ from power tools rated up to 750W. By John Clarke Mains control project 74 Advanced Test Tweezers, Part 2 These Test Tweezers are not just for testing passive components, they can also act as a digital voltmeter, logic probe, oscilloscope, square wave generator and serial protocol analyser. In the last part of the series, we cover the construction details and how best to use the Tweezers. By Tim Blythman Test equipment project Page 42 Model Railway Turntable ADVANCED Page 74 TEST SMD T EEZERS 2 Editorial Viewpoint 5 Mailbag 13 Subscriptions 55 Product Showcase 83 Serviceman’s Log 90 Vintage Radio 95 Circuit Notebook 98 Online Shop Three STC radios by Graham Parslow 1. Regenerative BFO metal detector 2. 3D-printed robotic arm 100 Ask Silicon Chip 103 Market Centre 104 Advertising Index 104 Notes & Errata SILICON SILIC CHIP www.siliconchip.com.au Publisher/Editor Nicholas Vinen Technical Editor John Clarke – B.E.(Elec.) Technical Staff Jim Rowe – B.A., B.Sc. 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): $65 12 issues (1 year): $120 24 issues (2 years): $230 Online subscription (Worldwide) 6 issues (6 months): $50 12 issues (1 year): $95 24 issues (2 years): $185 For overseas rates, see our website or email silicon<at>siliconchip.com.au Recommended & maximum price only. Editorial office: Unit 1 (up ramp), 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 194, Matraville, NSW 2036. Phone: (02) 9939 3295. ISSN: 1030-2662 Printing and Distribution: Editorial Viewpoint An AI wrote the editorial for me What would be a good topic for an editorial in Silicon Chip magazine? A good topic could be the latest developments in microcontroller technology and their applications in various fields, the current trends in electronics design and the challenges faced by designers and engineers, the impact of emerging technologies such as the Internet of Things (IoT) and artificial intelligence (AI) on the electronics industry, or a review of new and innovative electronic products that are available on the market. The editorial could also cover topics such as electronics hobby projects and DIY (Do It Yourself). Write 400-450 words about the impact of AI on the electronics industry: Artificial Intelligence (AI) has been making its presence felt in the electronics industry for quite some time now. The technology has been rapidly advancing and its applications in various fields have increased significantly. The impact of AI on the electronics industry has been far-reaching and profound. One of the primary ways AI has impacted the electronics industry is through the development of smart and autonomous devices. These devices are capable of collecting, processing and analyzing data in real-time, making them more efficient and effective in performing their designated tasks. For example, AI-powered smart home devices can automatically adjust the temperature, lights and other environmental factors based on the habits and preferences of their owners. In the automotive sector, AI is being used to develop self-driving cars that can navigate roads and make decisions without human intervention. Another significant impact of AI on the electronics industry is the increased speed and accuracy of electronic design and testing. AI algorithms can analyze vast amounts of data and identify trends, patterns and anomalies that would be impossible for a human to detect. This has allowed for the development of more complex and sophisticated electronic systems, and has also reduced the time and resources required for testing and validation. AI has also opened up new opportunities for the electronics industry by creating new and innovative products. For example, AI-powered wearable devices and smart speakers are becoming increasingly popular and have created a new market for electronics manufacturers. Similarly, AI has been used to develop voice-controlled virtual assistants that can perform a range of tasks, from playing music to managing schedules and making reservations. However, the impact of AI on the electronics industry is not just limited to product development. It has also had a significant impact on the workforce in the industry. AI and automation have replaced many manual and repetitive tasks, freeing up workers to focus on higher-level tasks such as design, research and innovation. However, the increased use of AI has also raised concerns about job displacement, particularly among workers in low-skilled roles. In conclusion, AI has had a profound impact on the electronics industry and is changing the way we live and work. Its applications are far-reaching and its impact is only set to increase in the future. As the technology continues to evolve, it will be interesting to see how the electronics industry continues to incorporate AI and how it will shape the future of electronics and beyond. – ChatGPT by OpenAI (https://openai.com/) with prompt from Silicon Chip Extremely impressive, but I don’t think my job is in danger just yet… by Nicholas Vinen 24-26 Lilian Fowler Pl, Marrickville 2204 2 Silicon Chip Australia's electronics magazine siliconchip.com.au Ordering made easy Tools to search, check stock and purchase au.mouser.com/servicesandtools australia<at>mouser.com 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”. An easier way to upload WiFi DC Load software Several constructors of the WiFi DC Load project (September & October 2022; siliconchip.au/Series/388) have noted that the new Arduino 2.0 IDE does not have a facility to upload files to the ESP32 file system. I have written a utility to accomplish these tasks. It is located at https://github.com/palmerr23/ESP32-OTAand-File-Manager Richard Palmer, Murrumbeena, Vic. Suggestion on improving ESP32 WiFi range The WiFi DC Load project uses an ESP32 board with a PCB WiFi antenna. After assembly of the control board, I experienced problems with poor WiFi signal and the device refused to connect to my network. The WAP (WiFi access point) is some distance from my workshop, and the WiFi signal is attenuated by the building, hence the weak signal. To overcome this, I replaced the ESP32 board with the WROOM version which has a UMCC connector for an external WiFi antenna. I mounted the external antenna on the front panel to the left of the screen. The external WiFi antenna, which has a higher gain than the PCB antenna and is mounted outside the metal enclosure, solved the poor signal problems. Erwin Bejsta, Wodonga, Vic. Partially defunct multimeter giveaway I have a Agilent U1253A meter that does not power on properly with a fresh 9V battery, but when turned on, it plays a brief melody, and all buttons produce a beep when pressed. Do any readers want it for spare parts, for the cost of postage? It includes a charger, CD and calibration certificate (2010) but no leads and comes in the original box. Ric Mabury, Melville, WA. Receiving signals from Sputnik Thank you for printing the Sputnik transmitter circuit (January 2023, page 29; siliconchip.au/Article/15612). I recall hearing the beep beep on my shortwave radio, on which I first found the precise US WWV frequency standard transmitter on 20MHz, then tuned slightly HF to 20007kHz with BFO engaged. There were no digital radios in those days! I wonder if the maximum usable frequency (MUF) during those days was significantly below 20MHz; otherwise, presumably, signals would not have penetrated the ionosphere, whereas the WWV signals were reflected. It could have something to do with wave incident angles as well. siliconchip.com.au Apparently, Sputnik had two transmitters. One was at 20.005MHz, not 20.007MHz as I had indicated, plus a second at 40.002MHz. I would not have known it was 2kHz off with a pre-digital receiver. I guess they deliberately plonked it next to WWV so people could find it. They assumed a worldwide response from amateurs that would enhance their research base. However, I don’t know how they expected the feedback as there was no email etc. Sputnik was launched into a highly elliptical orbit, and part of that was evidently to explore communications back through the ionosphere’s different layers. I read that the MUF (they called it something else) was estimated at 15MHz at the time. I was amused to see they had wired the three valve filaments in series; perhaps this was ‘communism in the design’ that ensured all got the same or nothing! Dave Kitson, Claremont, WA. Errors in the Sputnik circuit The Sputnik circuit published on page 29 of the January 2023 issue has some errors, many of which are either errors in the original documentation or in the copies which are circulating. It was not a 2W transmitter; Sputnik had two 1W transmitters, but they were not operating simultaneously; the Manipulator relay alternately switched them on and off. The schematic Allan Linton-Smith found was likely taken from a Dutch amateur radio magazine published in 2016, or a copy of that. The Dutch author discovered a missing dot at the junction of the 91W and 240W resistors, which was explained in their text but not corrected on the diagram you copied. The odd thing was that the dot was missing from the 40MHz unit in the original design schematic, not the 20MHz one. So I think there was some mix-up between the two circuits in the past. Also, inductors L1 & L2 are a common-mode choke in a 20mm square, rectangular canister with a glued slug, although not drawn that way on the diagram. Also, in the unit, the common negative of all of the + supplies (called A- in the unit’s original documentation) connects to the -7.5V supply, not the +7.5V supply. The +7.5V passes via a resistor in the main transmitter housing, not in the module, to supply the heater chain. There is also a missing capacitor that was in the physical 20MHz unit itself but not on the schematic. Regardless of these small details, I am a really big fan of this circuit, especially the 20MHz module. I think it would be great to write up the circuit in a lot Australia's electronics magazine March 2023  5 of detail for the Vintage Radio section, as I have all the original design information, and it is from such a famous spacecraft. However, it will be several months before I can finish making a replica and write it up. Dr Hugo Holden, Minyama, Qld. Can AI be used for checking designs? I read with interest your January editorial regarding PCB errors and how to avoid them. I hadn’t appreciated how complicated that task is. It got me thinking that this might be an ideal job for artificial intelligence (AI). You obviously have a very well-educated and professional staff and many very capable contributors. How about developing an AI system for this purpose? You could report on the progress along the way. I am sure your readers would be very interested in it. Such a system would be of great financial value. Mauri Lampi, Glenroy, Vic. Response: AI would not be all that helpful for DRC (Design Rule Check) since the rules are pretty basic and easy to enforce. You just have to input them correctly (manufacturers often supply files you can import that do that for you) and actually click the button to check them. However, you do raise two interesting points. Firstly, could AI be used to detect less obvious errors in circuits and PCB designs? It certainly would be worth a try. We’re impressed with what AI can achieve already (see this month’s editorial). Even if the possible problems it raised were often irrelevant, it could catch some non-obvious design faults before the prototype stage, similarly to how grammar checkers can helpfully flag some errors in text. The thing is that AI research is a very specialised field. Secondly, could AI be created to design a circuit and/or PCB from scratch? Apparently, Altium Designer already incorporates such features; something we should investigate. Two different OLEDs are compatible I wrote in a while back regarding a problem I had with the screen on my Improved SMD Test Tweezers (April 2022; siliconchip.au/Article/15276). When operated in the left-hand mode, the display lost a column, causing the OLED screen characters to be not quite right. I went to use the tweezers the other day and found the OLED display to have failed. As I had a couple of the larger 0.96in cyan displays and nothing to lose, I decided to fit one. Curiously and to my surprise, the LH mode now displays correctly! Switching back to the 0.49”in OLED, the missing column fault returns. While I am running the updated PIC in the tweezers, the fault was also present with the original version of the software. You could mention this upgrade or hack to your readers, as the bigger display is a lot easier to read with my older eyes. Stu Cornall, Pialba, Qld. T12 soldering irons recommended I am an occasional reader of your magazine and would like to suggest that you alert readers to the “T12” soldering irons as they have significant advantages in cost and flexibility. If you have not tried these, I suggest the KSGER 6 Silicon Chip Australia's electronics magazine siliconchip.com.au Discover New Technologies in Electronics and High-Tech Manufacturing See, test and compare the latest technology, products and turnkey solutions for your business SMCBA CONFERENCE The Electronics Design and Manufacturing Conference delivers the latest critical information for design and assembly. Industry experts will present technical workshops with the latest innovations and solutions. Details at www.smcba.asn.au In Association with Supporting Publication Organised by Co-located with branded irons for reasonable quality, with a four-­second heat up, many sleep modes and cheap and easy-to-change change tips, similar to Hakko’s. Lindsay Mannix, Yakamia, WA. Alternative way of generating a negative bias voltage Part of the 30V 2A Bench Supply circuit (October 2022; siliconchip.au/Series/389) reminded me of a brilliant design feature in the lab supply I have been using since 1970. That supply was a project designed by a Tektronix engineer for the Boy Scout Explorer Post 876 (sponsored by Tektronix). It generated a negative bias voltage using a simple voltage doubler. Two diodes and two capacitors are connected to the same transformer winding that delivers the output power. Applied to your design, just add a capacitor between diode D3’s cathode and an AC pin of BR1. Diode D4’s anode needs to move to D3’s cathode and you can eliminate the 30V winding of your transformer. Select the capacitor value to produce the desired negative bias voltage. 50 years later, I am still learning new subtleties in the design of my Explorer Post power supply. It used 14 transistors (no ICs) and a transformer with a single untapped secondary winding to supply 0-10V at 0-1A controlled by two 10-turn potentiometers with resolution and accuracy better than an analog meter. Two light bulbs indicated when it was regulating voltage or current limiting. When I built mine, I made many extensions to the design, adding to the learning experience. Most extensions have been beneficial, but some have caused device failures over the years. I wish I could give credit to the original circuit designer, but I lost my copy of the original schematic more than 30 years ago. I only have the transcribed diagram I drew when I was in college. Sigurd Peterson, Aloha, Oregon, USA. Warning about dodgy WeMos D1 Mini modules I purchased three WeMos D1 Mini V4.0.0 modules from the UK. Of them, two exhibited voltage regulator problems as follows. I have advised the eBay seller of these findings. After programming them for the GPS Clock project, the blue LED turns on immediately after the module is powered on. My first test used a 5V 3A supply connected to the module’s VBUS(5V)/GND connections. I connected, disconnected, reconnected etc, the 5V supply 30 times at two-second intervals. The blue LED failed to illuminate a total of 23 times. The LED operated on seven occasions. The next test used a variable 2A DC supply set to 3.3V, connected to the 3V3/GND connections, repeating the connection/disconnection sequence above. The blue LED operated 30 out of the 30 times. This confirms that the ESP8266 chips are fine, and the problem is that the 5V-to-3.3V regulator is problematic regarding, I’m assuming, supplying the peak startup current of the ESP8266. I then connected the module to the computer’s USB port. When I repeated the connect/disconnect sequence at its USB socket, the blue LED failed to operate on 20 of the 30 occasions and lit on 10 occasions. This is the fundamental pass/fail indicator and the easiest to check! This confirms that the computer’s USB connection is 8 Silicon Chip operating similarly to the external 5V supply, and the computer’s USB socket can provide the necessary peak current in the same manner as the external 5V supply. Whenever the blue LED fails to illuminate while the module is being powered by the external 5V supply or the USB connection, the voltage at the 3V3 connection (the output of the regulator) reads about 1.9V. Whenever the blue LED lights, the module can be re-programmed without error. The stored program also runs fine, and the NTP timestamp is acquired (after the configuration setup has been done). However, when the LED does not illuminate, the module cannot be reprogrammed, and the programmer reports that the ESP8266 cannot be found. I received three V3.0.0 modules from Altronics this morning, Cat Z6441, listed as a “NEW” product. All three work perfectly! Graeme Dennes, Bunyip, Vic. Comments: that’s interesting, but based on your previous experiences, sadly, not surprising. It’s good to hear that the Altronics product works. We wonder if it is time to refresh the Clayton’s GPS project with the Pico W board in place of the D1 Mini. That should work quite well as it has a switchmode regulator for its 3.3V supply. More on RFI and EMI RF interference from LED lamps of all types has been a problem ever since they were introduced. Marcus Chick describes his experience with this in Mailbag, January 2023. He suggested a resistor/capacitor network could be used instead of the switch-mode driver to eliminate the interference problem. However, I agree with your response that this may result in power factor problems. The LED Party Strobe project in the January 2014 issue (siliconchip.au/Article/5673) showed that LED lights can be energised directly from a DC power source. I have successfully used this with MR16-style lamps and floodlights after removing the switch-mode driver and using a suitable series resistor to limit the current. Switch-mode power supplies have high efficiency and low cost when compared to transformer-equipped linear supplies. However, as Marcus discovered, sourcing LED lights with low emissions can be difficult. My use of a transformer linear supply is less efficient than a switchmode unit, but it does have the advantage of no detectable interference. Stan Woithe, Fulham Gardens, SA. And even more on EMI & RFI I would like to comment on the letter on AM reception difficulties in the February issue (page 7). I have been repairing valve radios since the late 1960s. In that time, RFI has gradually increased, with little, if any, policing (it must be all about revenue). Being rural, RF riding on the kilometres of aerial power lines has always been evident, and we need mains filters to get rid of as much as possible as it gets into the radios. The thing that we cannot get rid of is the ability of the valve radio to pick up lighting [sic] over vast distances. The real fun starts when you want to calibrate a radio. To get anything approaching radio silence, there are many items to shut off: Australia's electronics magazine siliconchip.com.au Keep your electronics clean, lubricated and protected. Service Aids & Essentials. GREAT RANGE. GREAT VALUE. In-stock at your conveniently located stores nationwide. 4 2 1 5 3 BUY IN BULK & SAVE!!! 1 Isopropyl Alcohol 99.8% 250ml Spray NA1066 BUY 1+ $7.95 EA. BUY 4+ $7.15 EA. BUY 10+ $6.35 EA. 99.8% 300g Aerosol NA1067 BUY 1+ $11.95 EA. BUY 4+ $10.45 EA. BUY 10+ $9.45 EA. 70% 1 Litre Bottle NA1071 BUY 1+ $19.95 EA. BUY 4+ $17.95 EA. 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Shop at Jaycar for even more service aids & essentials: • Adhesives & Insulation Tapes • Solder & Soldering Aids • Wire & Heatshrink Tubing Explore our full range of service aids, in stock at over 110 stores, or 130 resellers or on our website. • Fasteners & Cable Ties • Ultrasonic Cleaners • Tools & Workbench Accessories jaycar.com.au/serviceaids 1800 022 888 Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. • Wireless NBN: symphony orchestra (and carrier pigeon would be quicker). • UPS: noise. • Computer, circa 2000: noise. • Switch-mode supplies: almost everything. • LED lighting: another wide-range transmitter. • Electronic ballasts: especially the ones in 4ft fluorescent tube fittings; I’m lucky if they run for more than four years before failing or becoming noisy. I have even had a fax use the telephone line as a radiator, getting into the 175kHz IF via the 37m external radio antenna. My mobile also needs an antenna to avoid dropouts, connecting to a 3G tower 40km away. Marcus Chick, Wangaratta, Vic. Earth Leakage Detector will work with three-phase I want to challenge your response to B.T.’s query on “Testing three-phase gear for Earth leakage” in the Ask Silicon Chip section of July 2022 (p110). The toroid cannot tell whether two wires (for a single-­ phase circuit) or three or four wires (for a three-phase circuit) are threaded through it. All it detects is a magnetic field, and its magnitude depends on the sum of the currents passing through its centre. This sum must, of course, consider the direction of current flow in the wires. Say, positive towards the load; negative away from it. If there is no Earth leakage current, the sum of the currents in a three-phase, three- or four-wire circuit at any given instant is always zero. The 120° phase shifts between the phases do not affect this. Also, there is no need to divide the leakage current by √3 since it is the sum of the currents (which must be the current flowing to Earth) that is being measured in both the single-phase and three-phase cases. The Silicon Chip Earth Leakage Tester (May 2015 issue; siliconchip.au/Article/8553) should work without modification for both single-phase and three-phase circuits. In either case, B.T. should confirm that all wires go through the toroid in the same direction, ie, from source to load, and that the measuring instrument, like the Silicon Chip design, is measuring true RMS. Chris Armstrong, Peakhurst, NSW. Comment: You are correct. Passing all three-phase wires through a single core produces what is known as a Zero Sequence Current Transformer (ZSCT), also known as Core Balanced Current Transformer (CBCT). If there is no Earth leakage, the current output from the current transformer will be zero. Any current leakage will provide an imbalance, and the current transformer will give a reading other than zero. Variable feed-in tariff is desirable George Ramsay (Mailbag, December 2022, p9) need not be so pessimistic about rooftop solar power generation. The distribution network was never designed for distributed generation, but that doesn’t mean it can’t be adapted. The big difference between rooftop solar and other generation types is that it is largely uncontrolled and so is often on when it isn’t needed. Having too much generation in a grid can be as problematic as not having enough. The solution is both technical and commercial. Most rooftop PV owners are paid a fixed rate for feed-in, regardless of whether the grid needs them. This price has been 10 Silicon Chip in steady decline, and one reason is that it is essentially a hedge that accounts for when they are providing useful generation, but also when they aren’t. A better approach is to offer a price representative of the grid. This is known as the wholesale price and fluctuates every five minutes to match supply and demand. When the wholesale price goes negative, grid participants are signalling that there is excess generation, and they are happy to pay you to consume it. In this situation, rooftop PV owners will have a better financial outcome if they turn it off. They will also get much better feed-in rates at other times when the grid needs them. There also needs to be the technical means to turn off your inverter. The latest version of AS4777.2 (Inverter Technical Standards) mandates all inverters be compatible with DRED (Demand Response Enabling Device), a standardised interface for control (see the April 2017 issue; siliconchip.au/Article/10606). Most modern inverters can also be controlled over an API and via standard industrial automation protocols like Modbus. Rooftop PV is one of the cheapest ways to generate electricity. With these simple solutions, rooftop PV owners can earn more coin and help our grid transition to a new generation mix. Many retailers are already offering products like this, known as “time-of-use” tariffs. Brandon, Alexandria, NSW. Comment: while it makes a certain amount of sense to pay more for power when it’s needed the most, it’s hard to see how that will help in this case. Homeowners can’t decide when their solar systems can generate power; that’s mainly a function of the sun. Also, while it is an imperfect system, demand is already signalled in a sense by grid voltage fluctuations. AC mains electricity protection filters Reading your article on the DC Supply Filter for Vehicles (November 2022; siliconchip.au/Article/15544) got me thinking about AC mains electricity protection filters. How does EMP shielding work? Is this a hoax or snake oil? How does a good AC mains electricity surge protector work against downed power lines, lightning strikes, EMP, solar storms and the like? There was a three-day May 1921 solar geomagnetic storm, also known as the “New York Railroad Storm”, see www.solarstorms.org/SS1921.html Could this be a future project? Most of us do not need expensive uninterruptible power supplies. Still, we need reliable over-voltage surge protection and brownout protection, particularly if you live in a rural area, flood zone or coastal area with frequent large storms. And especially if we also own lots of expensive electrical goods and consumer electronics. Bob Crowhurst, Mitchell Park, SA. Comments: there do not seem to be suitable surge protectors commercially available for protection against lightning except for switchboard-installed devices. The PDF file you can download from siliconchip.au/ link/abi4 shows just how much needs to be done for complete lightning protection. We may consider a lightning protector for mains electrical appliances as a project. The most significant difficulty Australia's electronics magazine siliconchip.com.au Established 1930 Digital Caliper 70-605 - Measuring Box set M012 - Measuring Kit 4 Piece • CNC Machined for high accuracy • Ground Measuring Face • Black Anodized Coating for a Protective Anti Rust Coating • Precision Laser Engraved Markings 79 (Q605) • • • • SAVE $20 0 - 25mm micrometer 150mm / 6" rule 150mm / 6" vernier 100 x 70mm square 70-634 - Spring Divider • • • • 60 (M012) $ NEW RELEASE • 3 Modes of measurement IP54 • Absolute & incremental functionality • 4-way measuring $ 150mm overall length Hardened spring and legs Knurled thumb screw Polished finish 14 (Q634) $ • 200mm / 8" • 150mm / 6" 49 (M742) 35 (M740) $ $ SAVE $10.40 SAVE $9 70-636 Spring Caliper Outside 70-635 Spring Caliper Inside • 150mm overall length • 150mm overall length 14 (Q636) 14 (Q635) $ $ MEASURING EQUIPMENTS SAVE $11.50 70-630 - Double Ended Scriber 70-601 - Degree Protractor SSR-150 - STEEL RULE SSR-300 - STEEL RULE • • • • • 0-180º range • 0-100mm rule graduations • 150mm rule length • • • • • • • • 190mm in length Straight & 90º hardened steel tips Precision manufactured Knurled body for grip 12 (Q630) 27.50 (Q601) DRO5 - 3-Axis Optimum Digital Readout Counter - 1µm • • • • • • 3 (M755) $ Suits mills X, Y, Z Axis Suits lathes X, Y, Z Axis + (Z0) RPM speed 4 x LCD screen colour options Metric / inches conversion 98 x 65 x 134mm (LxWxH) 240V with 6 metre lead 349 (D695) $ SAVE 47 $ BF-20AV - Opti-Mill Head Attachment - Geared & Tilting Head WORK LIGHT $ HL-72L - 14W LED Work Light with 2.25X Magnifier • • • • • 14W - 5700K LED Dimmer control Swivel & pivoting arm Includes magnified lens 240V / 10amp 199 (L2821) $ ST-2506V - Lathe Stand • Suits TU-2506V & TU-3008G Optimum Lathes 1,045 (M647) SAVE $110 $ LED Slim Rechargeable Handheld Work Light LED Rechargeable Handheld Work Light • • • • • • • • • • • • Max output:360 lumens 3.7V 1800mAh Li-ion battery Rechargeable via USB 3 hours operating time Modes: 100% - 50%-strobe-Off Dimmable light Magnet both ends 18 (T950) TU-2506V - Opti-Turn Bench Lathe • Ø250 x 550mm turning capacity • 26mm bore, 125mm 3 jaw chuck • 1.2kW, 240V motor Max output: 400 lumens 3.7V 2600mAh Li-ion battery Rechargeable via USB 3 hours operating time 4 Modes: White COB, Red COB, Top Light On-Off, Spotlight On-Off 33 (T9501) $ SAVE $43 300mm with 0.5 & 1mm graduations 12" with 32nds, 64ths, 16ths graduations Overall size 300 X 25.4 X 0.8mm Metric and imperial measurements 5 (M756) $ • Electronic variable speed • 3MT spindle taper • Dovetail vertical Z-Axis • Head tilts ±90° • 0.85kW 240V motor $ 150mm with 0.5 & 1mm graduations 6" with 32nds, 64ths, 16ths graduations Overall size 150 X 19 X 0.8mm Metric and imperial measurements $ TU-1503V - Opti-Turn Bench Lathe - Mini • • • • Ø150 x 300mm turning capacity 11mm spindle bore 80mm 3 jaw chuck 0.45kW, 240V motor ONIC ELECTR PEEDS LE S B IA R A V 00RPM 160 ~ 30 429 (L690) 2,299(L689) $ $ SAVE $66 SAVE $220 www.machineryhouse.com.au SYDNEY BRISBANE MELBOURNE PERTH (02) 9890 9111 (07) 3715 2200 (03) 9212 4422 (08) 9373 9999 Specifications & Prices are subject to change without notification. All prices include GST and valid until 27-03-23 899 (L685) $ SAVE $80 UNIQUE PROMO CODE SIC2302 $70 FREE DISCOUNT VOUCHERS ONLINE OR INSTORE! www.machineryhouse.com.au/signup is how to test it. We have published brownout protectors previously, although incorporating brownout and lightning protection in one project is a good idea. Consider looking at the July 2016 Brownout Protector For Induction Motors (siliconchip.au/Article/10000). Regarding solar storms, there does not appear to be any good way to protect against these, except for the magnetic field around the earth that reduces the effect. The best thing about it is that it’s free! In the November 2021 issue, you published an image I sent of a magazine cover featuring an unusual portable radio. This cover of Radio-Craft magazine from June 1942 (below) shows another radio headset to detect aircraft. If you arrived at the airport wearing this today, I think they would bring out the white jackets to take you away! Graham Street, Auckland, New Zealand. with service information (eg, service manuals and schematics, help lines via telephone) and spare parts. I do not know how Consumer Protection allows them to get away with such practices. Over the last 20 years, I have visited politicians (specifically Louise Asher), but to no avail. For years afterwards, they tell you, “yes, looking into it”, but nothing ever happens. The best you can do as a tech is not to recommend those products. Try approaching Apple for a spare part (eg, an IC or a service manual). With their non-availability, honestly, as an engineer, could you recommend their product with such (nil) support? No wonder 90% of service organisations have shut down: there is little work to do and no parts available. Just ask Dave Thompson why he has had to diversify servicing anything from electric brooms to TVs. Rod Humphris, Ferntree Gully, Vic. Ethics in servicing Being locked into closed software Probably no longer a good idea Regarding your February editorial, there are probably quite a few reasons why companies refuse to do component-­level repair, such as: • Excess stock of motherboards • No skilled workers to replace an SMD IC • No equipment to replace SMD parts • Captive service (they want it all to themselves) • They would rather sell new products than spare parts or service I see the biggest problem as manufacturers or their agents failing to supply repair firms (their competition) I am writing about your response to my email, “Forced upgrades due to incompatibility”, published in the February 2023 issue on page 12. I commenced my interest in using VBA macros while subscribing to “Australian PC User” and then “Australian Personal Computer” (APC), following Helen Bradley from one publication to the other when she moved. She may have retired several years ago, as she ceased producing these columns around that time. She used to have a single-page article in each issue of PC User, followed by APC, containing a VBA macro, or a set of related and connected VBA macros, for one of the Microsoft programs (Excel, Word or PowerPoint) showing how to use the newly included function(s) provided for VBA macro routines; primarily for Excel, but with the occasional one for Word and PowerPoint. I am now a captive of the proprietary content of Microsoft Office due to its support for VBA macros, functions and keywords, making my files incompatible with, and hence unable to be transferred to, either LibreOffice or, if it is still around, OpenOffice. Their macro functions and keywords are different, and it would be a time-­consuming and difficult process to rewrite my existing macros. So, it would seem that, at least with Microsoft Office, I am locked in. Paul Myers, Karabar, NSW. Comment: we prefer to use open, cross-platform languages for this reason (and there are many available), although it’s hard to find a direct competitor to VBA macros in Excel. Note that LibreOffice has limited support for executing VBA macros, but we suspect it might not be good enough for you. December issue enjoyed Thanks for a fine ongoing publication. Publishing the James Webb article (December 2022 issue; siliconchip.au/ Article/15575) was the correct decision as it was a great read, as was the Vintage TV article in the same issue (RCA 621TS by Dr Hugo Holden), with the excellence & effort shown in its upgrade. I remember using 5BP1 display tubes from radar disposals with Radio, TV & Hobbies projects. Bruce Wilson, Warriewood, NSW. SC 12 Silicon Chip Australia's electronics magazine siliconchip.com.au Subscribe to FEBRUARY 2023 ISSN 1030-2662 02 9 771030 266001 $1150* NZ $1290 INC GST INC GST THE HISTORY OF COMPUTER MEMORY Soft Starter Active Mains ADVANCED Australia’s top electronics magazine TEST T 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. EEZERS 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 $65 $75 $50 1 year $120 $140 $95 2 years $230 $265 $185 6 months $80 $90 1 year $145 $165 2 years $275 $310 6 months $100 $110 1 year $195 $215 2 years $380 $415 All prices are in Australian dollars (AUD). Combined subscriptions include both the printed magazine and online access. Try our Online Subscription – now with PDF downloads! The History of Computer Memory; Jan & Feb 2023 Advanced SMD Test Tweezers; February & March 2023 Active Mains Soft Starter; February & March 2023 Dual-Channel Breadboard PSU; December 2022 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 Communicating when Underwater By Dr David Maddison Today, we take communication in most places for granted, and for the most part, it is possible. But underwater (and underground), things get a lot more difficult. Still, there are ways to get a message across. This article will concentrate on the challenges underwater; we will cover underground communications in a follow-up article next month. A round cities and even in rural areas, we can connect to phone towers with our mobile phones, or we can communicate via radio directly to other radios or via repeaters (eg, CB radio). We can use satellite phones or shortwave radios in remote areas, including at sea. All these methods rely on transmitting radio waves through the atmosphere, either line-of-sight to a tower, bouncing off the ground or atmospheric layers, line-of-sight to a satellite overhead, or directly from transmitter to receiver. Transmitting through water or underground is much more difficult for the reasons explained below. Communicating through liquid or solid matter Why would you want to communicate underwater or underground? Think of vehicles like submarines or underwater drones, or when people are in a cave or mine, or buried in snow. 14 Silicon Chip Common radio frequencies used for general above-ground communications are in the medium frequency (MF), high frequency (HF), very high frequency (VHF), ultra high frequency (UHF) and super high frequency (SHF) bands, from about 300kHz to 30GHz – see Table 1. These frequencies generally don’t penetrate very far into the ground or saltwater. Useful radio penetration into the ground or saltwater is generally only possible with wavelengths in the extremely low frequency (ELF) to very low frequencies (VLF) bands, from 3Hz to 30kHz. An unfortunate characteristic of these frequencies is that they have enormously long wavelengths, and consequently, vast antennas are required. However, some tricks can be used to lengthen antennas electrically. Also, receiving antennas don’t have to be as long as transmitting antennas; loop antennas can also be used for Australia's electronics magazine reception. Apart from the large antennas needed, the bandwidth and hence data transmission rate at those low frequencies is so low that voice cannot be transmitted, only simple codes. See Figs.1-3 to get an idea of the vast inductors and coils used for VLF transmissions. Why do longer radio wavelengths have greater penetrating power? Conductive materials usually block electromagnetic waves; hence, the use of metals to shield electronics from interference or shielding braids in coaxial cables. Conductors mostly block radio waves because they contain free electrons, which are caused to oscillate by the radio wave and reflect or absorb energy in doing so. The lower the frequency, the less energy is absorbed because there is less coupling of the wave with the electrons. Note also that extremely thin layers of metal do allow the transmission of some electromagnetic waves. siliconchip.com.au Figs.1-3: examples of 1960s RF variometers (variable inductors) and RF coils in a “helix house” as part of the final drive for a US Navy VLF antenna for submarine communications. These are at the US Naval Communications Station in Balboa, Panama and were made by Continental Electronics. Source: www.navy-radio.com/xmtr-vlf.htm Also, alternating currents mostly travel in the outside surface of conductors, to the ‘skin depth’, which becomes lesser as the frequency increases. The skin depth is greater in more poorly conducting materials. Seawater is also electrically conducting, although not nearly as conductive as metals. Seawater is an electrolyte that conducts mainly because of dissolved free mobile ions from common salt, primarily sodium (Na+) and chlorine (Cl−), but also others like magnesium (Mg2+), calcium (Ca2+) etc. These mobile ions absorb and reflect most radio waves at frequencies except the lowest. Freshwater is much less conductive than seawater, making radio penetration into freshwater much greater than seawater. Still, submarines rarely travel in freshwater. The electrical conductivity of seawater is typically in the range of 3-6S/m (Siemens/m), compared to the conductivity of copper at 5.8×107S/m and aluminium at 3.8×107S/m. So these metals are about 10 million times more conductive than seawater. Nevertheless, the electrical conductivity of seawater is still a problem for radio communications. However, for above-ground communications, this can be a benefit; it is possible to use seawater as the ground plane or counterpoise of an antenna. Some rocks have a high metal content, making them also somewhat conductive; this is an important consideration for antenna siting. Submarines Submerged submarines cannot communicate at regular radio frequencies, and can only receive radio signals at ELF, SLF, UHF and VLF frequencies (3Hz-30kHz; see Table 1). Because of these low frequencies, information transfer is extremely slow, far too low for voice frequencies, and only simple codes or Morse code can be transmitted. Only nine countries are known to operate VLF transmitters to communicate with submarines: Australia, Germany, India, Norway, Pakistan, Russia, Turkey, the UK and the USA. Table 1 – radio frequency bands per the ITU (International Telecommunication Union) Frequency name Abbr. Freq. range Wavelength Some common uses <3Hz >100,000km None known 3Hz-30Hz 100,000km10,000km Submarine communications Super low frequency SLF 30Hz300Hz 10,000km1,000km Submarine communications Ultra low frequency ULF 300Hz3kHz 1,000km100km Submarine communications, mine and cave communications Very low frequency VLF 3kHz-30kHz 100km-10km Submarine communications, radio navigation systems, time signals, geophysics Low frequency LF 30kHz300kHz Radio navigation, time signals, longwave AM commercial broadcasting in Europe and Asia, RFID, amateur radio (certain countries) ...continued overleaf No ITU designation Extremely low frequency siliconchip.com.au ELF 10km-1km Australia's electronics magazine March 2023  15 Table 1 (continued) – radio frequency bands per the ITU (International Telecommunication Union) Medium frequency MF 300kHz3MHz 1,000m-100m AM commercial broadcasting, amateur radio, avalanche beacons High frequency HF 3MHz30MHz 100m-10m Shortwave & amateur radio, 27MHz CB, long-range aviation & marine communications, radio fax, over-the-horizon radio Very high frequency VHF 30MHz300MHz 10m-1m Aircraft communications, amateur radio, emergency services, commercial FM broadcasts Ultra high frequency UHF 300MHz3GHz 1m-10cm TV broadcasts, microwave ovens, radars, mobile phones, GPS, wireless LAN, Bluetooth, ZigBee, satellites, Australian UHF CB Super high frequency SHF 3GHz30GHz 10cm-1cm Wireless LAN, radar, satellites, amateur radio Extremely high frequency EHF 30GHz300GHz 1cm-1mm Satellites, microwave links, remote sensing 300GHz3THz 1mm-0.1mm Remote sensing, experimental uses No ITU designation Table 2 – radio wave penetration in water for 50dB attenuation Frequency 10Hz (ELF) Source: https://jcis.sbrt.org.br/jcis/article/view/362 100Hz (SLF) 1kHz (ULF) 10kHz (VLF) 1MHz (MF) 10MHz (HF) 1GHz (UHF) Seawater 440m 140m 44m 14m 1.4m 0.44m 0.044m Freshwater 29000m 9200m 2900m 920m 92m 29m 2.9m Submerged submarines cannot transmit messages because the antenna required would be infeasibly long and the power requirements too high. Nevertheless, very long antennas are trailed behind submarines when they have to receive these signals; certain types of loop antennas can also be used. Submarines can transmit and receive at all typical frequencies if they surface, partially surface, float an antenna buoy to the surface or connect to a seabed “docking station”. However, a submarine that has surfaced or partly surfaced runs the risk of being found, either via its radio transmissions, or radar or optical reflections from its antenna masts or buoy. Its wake could also be detected by an aircraft or satellite. For a table of submarine radio communications options and the associated risks, see Fig.4. To minimise radar reflections from submarine periscopes and antenna masts, radar-absorbing materials (RAM) are applied – see our article on Stealth Technology in the May 2020 issue (siliconchip.au/Article/14422). Besides radio, submarines can communicate via acoustic and optical means, which we will also cover. descend to 600m. Escape from submarines is possible to a depth of about 200m and rescue with another submersible to about 600m. Submarines don’t always operate at their maximum depth, though; they choose the depth corresponding to the thermal layer that is most likely to prevent sonar detection for the particular sea conditions they find themselves in. The ABC news article at www.abc. net.au/news/11570886 states that the typical operational depth of an Australian Collins-class submarine is 180m. Radio signal penetration Table 2 shows the depth at which radio signals can be received through water for an attenuation of 50dB, which is a power reduction of 10000:1. That doesn’t necessarily mean that signals can’t be received deeper than that; it depends on the original signal strength and the sensitivity of the receiving equipment. Sources differ on the exact penetration of these frequencies into seawater, but they broadly agree with what’s shown in the table. Attenuation changes with salinity and temperature. Depending on the radio frequency, it is likely that a submarine will have to alter its depth to be able to receive radio signals. Fig.5 shows radio wave attenuation for Submarine operating depths The operating depth of submarines is said to be from the surface to 300m-450m below for modern Western nuclear submarines. Some sources claim that Russian Yasen-M boats can 16 Silicon Chip Fig.4: submarine RF communications options and associated risks. LDR = low data rate, MDR = medium data rate, P/D = periscope depth, ESM electronic support measures (intelligence gathering through passive listening). Based on: https://man.fas.org/dod-101/navy/docs/scmp/part06.htm Australia's electronics magazine siliconchip.com.au To receive VLF signals, submarines are typically equipped with both. The Ambrose Channel pilot cable (ULF) Fig.5: radio attenuation for a range of water conductivities and frequencies. Seawater (the most conductive) corresponds to the top two curves. Original: from a 2012 paper by Emma O’Shaughnessy quoted at www.quora.com/Whycant-radio-waves-transmit-through-water The Ambrose Channel is the only entrance to the Port of New York and New Jersey. Delays due to bad weather were once a huge and expensive problem, so in 1919-1920, they laid a cable on the bottom of the channel, which carried a 500Hz, 400V AC signal that could be detected about 1km away. Ships carried two induction coils and an amplifier to receive the signal. By switching between coils, they could determine which side was closer. The signal was mechanically keyed with Morse code that spelled NAVY. Arguably, this was the first use of what could be interpreted as a ULF signal for underwater communications. different frequencies and water conductivities. has been tested, as we will investigate shortly. The Grimeton Radio station (VLF) Optimal frequency in the ELF to VLF range Receiving electric versus magnetic fields As per Table 2, VLF is the highest useful frequency range for communication with submerged submarines. The lower the frequency, the better the penetration into seawater. Still, as the frequency reduces, so does the rate at which data can be transmitted. The complexity and cost of the transmitter also increase dramatically as the frequency drops. For this reason, VLF has been chosen as a happy medium for submarine radio communications, although ELF Radio signals have an electric field component and a magnetic field component. An example in everyday use is a long-wire antenna on an AM radio vs a ferrite rod or loop antenna. The long wire is sensitive to the electric field, and the ferrite rod or loop to the magnetic field. It is much easier to build an antenna to receive the electric field component, but it is also much larger. Long-wire antennas are possibly more sensitive but also more prone to electrical noise. Fig.6: an Alexanderson Alternator at the Grimeton Radio Station. Source: https://w.wiki/6DPN The Grimeton Radio station is a World Heritage listed Swedish radio station that operates at 17.2kHz and 200kW. It uses no electronics but generates a carrier wave for Morse Code with a high-frequency alternator called an Alexanderson alternator (see Fig.6). It is an obsolete technology that was even obsolete when the transmitter was built. It was used for transatlantic wireless telegraphy from the 1920s to 1940s. Later, it was used by the Swedish Navy for submarine communication. It was in service until 1995 but now operates twice yearly – see siliconchip.au/link/ abik for the transmission schedule. There is an Australian reception report at siliconchip.au/link/abil, meaning the signal travelled 14,000km – almost to the other side of the planet. For further information, see http://dl1dbc.net/SAQ/ and https://w. wiki/67Wd Goliath (VLF) The first use of VLF radio waves to communicate with submerged submarines was by Nazi Germany in WW2. Their Goliath transmitter could communicate with submarines anywhere in the world to a depth of between 8m and 26m, depending on water salinity, temperature and the distance from the transmitter. It used a 1MW vacuum tube transmitter tuneable between 15kHz and siliconchip.com.au Australia's electronics magazine March 2023  17 Fig.7: the Belconnen transmitter towers in 1951. Source: https://bpadula.tripod. com/australiashortwave/id45.html Fig.8: the Naval Communication Station Harold E. Holt, call sign NWC. Source: https://w.wiki/6DPP 60kHz (20km to 5km wavelength) at 12 specific crystal-controlled frequencies, plus other frequencies with reduced power below 19kHz. The operation modes of Goliath were: a) Morse code, mainly at 16.55kHz, using on-off keying b) Hellschreiber at 30-50kHz with AM tone pulses (see our articles on Digital Radio Modes in April & May 2021; siliconchip.au/Series/360) c) Low-quality voice at 45-60kHz with very low bandwidth (see Table 3) Modes a) and b) could use Enigma encryption. After the war, the transmitter system including the antennas was disassembled and taken to the then Soviet Union in 3000 rail cars, and reassembled about 150km from Moscow. It is still used today, operated by the Russian Navy, to transmit messages to Russian submarines along with time signals! Its call sign is RJH90 and it operates between 20.5kHz and 25.5kHz according to a specific schedule; see https://w.wiki/6DP5 Belconnen Naval Transmitter Station, Australia (VLF) The Royal Australian Navy transmitter facility at Belconnen, ACT, consisted of three 183m-tall VLF transmitting masts 400m apart. They were orientated east-west for maximum transmission directivity into the Pacific and Indian Oceans – see Fig.7. The complex was completed in 1939 and operated until 2005. At the time of its completion, it was the most powerful naval transmitting station in what was then the British Empire. It operated at 44kHz and was used to communicate with surface ships and submarines. For submarine communications, we can estimate that a 44kHz signal would penetrate seawater to a depth of 10m for about 50dB attenuation. The original power was 200kW but was upgraded to 250kW after an overhaul in 1959-1961. In conjunction with a similar facility in Rugby in England, communications could be made anywhere in the world. One report from an ex-technician states that the antenna system was “an ‘inverted L’ type with a huge capacitive top hat” supported by three towers. He also said that “the final ‘tank circuit’ was housed in its own building, and fluorescent lights did not need to be connected to power”. The facility also contained HF transmitters that served both military and civilian purposes. At the peak of its operations, it had 38 HF transmitters ranging from 10kW to 40kW and 50 antenna systems. In 1956, it broadcasted radio to the world about the Olympic Games in Melbourne. Naval VLF transmitter operations were transferred to Harold E. Holt Communications Station at North West Cape, Western Australia, in 1995. We don’t know how far away submarines could receive transmissions from Belconnen when submerged. Still, for the alternative site in Rugby in England, the page at siliconchip.au/ link/abim indicates that submarines could receive 16kHz signals with an antenna depth of about 7m and a range of about 3200km with loop antennas. The reception range increased dramatically when not using loop antennas; presumably, long wires were used instead. Also see the video titled “Track 6 Belconnen Transmitting Station” at https://youtu.be/lX39drhaI7g Naval Communication Station Harold E. Holt (VLF) The Naval Communication Station Harold E. Holt (Fig.8) is based in northwest Western Australia, was built in 1968 and is a joint Australia/ Fig.10: a side elevation view of the VLF antenna system at Cutler, Maine shown in Fig.11. 18 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.9: the Naval Communication Station Harold E. Holt antenna system. US facility for communicating with submarines. It operates at 19.8kHz and 1MW, so we can surmise a penetration depth into seawater of approximately 10m. However, due to its high power, the actual depth may be greater. The antenna consists of a central 387m-tall tower surround by six 364m-tall towers and a further six 304m-tall towers; see Fig.9. It is described as a ‘trideco’ antenna. The wires from the central mast to the 12 surrounding towers create a capacitor ‘plate’, with six ‘panels’ parallel to the ground and driven at the centre (see Figs.10 & 11 of a similar antenna). Rather than the central mast being the radiating element, there are six vertical wire “downleads” that radiate the VLF waves. There is a “counterpoise” system at ground level or Table 3 – Goliath system voice Frequency -3dB bandwidth 15kHz 30Hz 20kHz 63Hz 30kHz 250Hz 60kHz 1230Hz Source: siliconchip.au/link/abjd siliconchip.com.au Fig.11: the US Navy VLF antenna system at Cutler, Maine, which is very similar to the one at Harold E. Holt. Note the vast dimensions. Australia's electronics magazine March 2023  19 buried within the ground (it is not clear which). The antenna design is extremely efficient at 70-80% compared to other VLF antennas with efficiencies of 15-30%. There is not a lot of information available on this antenna and transmitter system but a very similar US Navy system is installed at Cutler in Maine, USA. See siliconchip.au/link/abj7 Fig.12 shows a submarine VLF receiver from 1972, the same era as this transmitter. US Navy ELF program Fig.12: the configuration of submarine VLF receiving equipment with the AN/BRR-3 set circa 1972. It operates at 14-30kHz with a loop antenna, longwire buoy antenna or whip. Source: www.navy-radio.com/manuals/01011xx/0101_113-03.pdf Fig.13: part of a 23km arm of the ELF antenna in the forest at Clam Lake, Wisconsin. Source: www.navy-radio.com/commsta-elf.htm 20 Silicon Chip Australia's electronics magazine As described earlier, transmitting at VLF frequencies allows a submarine to receive signals up to a submerged depth of around 14m. The submarine can be deeper than this, but it must trail a buoyant antenna at the reception depth. ELF frequencies from 3Hz to 30Hz and SLF from 30Hz to 300Hz offer much deeper radio penetration, allowing submarines and their antennas to remain at normal operating depths. Losses with SLF are very low – see Table 4. Experiments with ELF and SLF started in 1962 using a leased 70km length of HV power line in Wyoming that was disconnected at night. In 1963, a 176km antenna was built from Lookout Shoals, North Carolina to Algoma, Virginia. This was driven with 60A at frequencies between 4Hz and 500Hz with a radiated power of 1W. Signals were detected by the submarine USS Seawolf 3200km away, at an unspecified depth. In 1968, there was a proposal to build a transmitter that operated at 40-80Hz. The SLF system was called Project Sanguine and would have had 9700km of cable covering 58,000km2 or ~40% of the US state of Wisconsin. One hundred underground power stations were to produce 800MW of electrical power for transmitters. A small-scale test was performed at Clam Lake, Wisconsin, with two 23km crossed antennas (see Fig.13). The antenna was made of 15mm diameter aluminium cable mounted on 12m timber utility poles. That project was abandoned in 1973 for various reasons, but small-scale research continued. The system was designed with extensive redundancy to withstand a nuclear attack. In 1981, the then President Ronald Reagan revived the project at a much siliconchip.com.au smaller scale, and construction started in 1982. The existing 46km Clam Lake antenna was kept, while a new 91km antenna was built in Republic, Michigan, in the shape of the letter F with two 23km segments and one 45km segment, 238km away from Clam Lake (see Fig.14). There is no significance to the F-shape; it was due to land availability. An important siting consideration for the antennas was the very low conductivity bedrock in those areas. This enabled more rock to form part of a much larger antenna, as the current must flow much deeper to complete the electrical circuit. The signal generated travels in the natural waveguide between the Earth and the bottom of the ionosphere – see Fig.15. The antennas were ground dipoles, as shown in Fig.16. The antenna is fed from the halfway point by a power plant transmitter (P) at 300A and 76Hz or 45Hz. The ends of the antenna are grounded in 91m-deep boreholes. An alternating current passes between the grounded ends of the antenna (I) through the bedrock and along the above-ground wires. The arrows point in just one direction for clarity, but the direction of the current flow alternates. This current creates an alternating magnetic field (H) that radiates ELF waves, shown in yellow. The radiation pattern is directional, with the strongest signal coming from the ends of the wires. Hence, antennas must be built in at least two or more orthogonal directions for omnidirectional use. When combined, the effective radiated power of the two systems was 8W, from an input power of 2.6MW – an efficiency of just 0.0003%! Due to the low bandwidth of the system, it took about 15 minutes to transmit a three-letter coded message. Usually, the message contained instructions on where and when to surface, come close to the surface or release an antenna buoy to receive a more comprehensive message. The system would constantly transmit an ‘idle’ message, indicating to a submarine that they were still within the receiving range. The system became operational in 1989 and covered about half the world’s surface. It was decommissioned in 2004, with the US Navy stating that VLF systems had evolved to siliconchip.com.au Table 4 – losses & antenna efficiency for the SLF band Frequency 45Hz Propagation loss per 1000km 0.75dB Loss per 1m seawater penetration 0.23dB Relative transmitting antenna efficiency -4.4dB 76Hz 140Hz 1.2dB 2.0dB 0.27dB 0.36dB 0.0dB 2.5dB Source: www.navy-radio.com/commsta/elf/elf-1402-81A.pdf Fig.14: a map showing the location of the Clam Lake and Republic transmitter antennas in red. P G G H I 14 mi (23 km) Australia's electronics magazine Fig.15 (above): electric field lines radiated from an ELF/SLF transmitter travel in the natural waveguide between the Earth and ionosphere. A similar radiation pattern applies to VLF. The deepest sub receives ELF, another receives VLF with a buoyant antenna, while another floats a buoy. Fig.16 (left): a ground dipole of the type used in Project ELF (one of the 23km segments). Source: https://w. wiki/6DPK March 2023  21 the point that this system was unnecessary. In the video at https://youtu.be/ eC1cqwGkOwY, a technician who worked on submarines comments that the ELF/SLF receivers were synchronised with the transmitter using caesium beam clocks. If a noisy signal were received from one direction, the receiver delay would be adjusted so the same signal could be picked up, coming from the other side of the world. TACAMO Fig.17: schematic view of two trailing VLF antennas behind a Boeing E-6A, part of the TACAMO communications system. Source: https://nuke.fas.org/ guide/usa/c3i/e-6.htm TACAMO (“Take Charge and Move Out”) is a US system of communications links designed to survive a nuclear attack, keeping in contact with its submarine fleet if land-based transmitters are destroyed. To establish VLF communications, long antennas are trailed behind a Boeing E-6B Mercury aircraft (based on the Boeing 707; see Fig.17). The E-6B has two trailing antennas, one 8km long and the other 1.5km long. Once deployed, the aircraft goes into a tight banking turn. The longer wire hangs as vertically as possible, while the other wire trails behind the plane, forming an L-shape. The transmitter used is the 200kW AN/ART-54 High-Power Transmitting Set (HPTS) consisting of a Solid State Power Amplifier/Coupler (SSPA/C) OG-187/ART-54 and Dual Trailing Wire Antenna System (DTWA) OE-456/ART-54. For more details, see the TACAMO comms flight manual for the E-6A at siliconchip.au/link/abj8 (the earlier version of this aircraft). April 22nd, 2015, even though they could have repurposed it for several other uses, including by SBS, who wanted to use it for a radio tower. See my video of the tower titled “Woodside Omega Navigation System Tower VLF Transmitter, Victoria, Australia” at https://youtu.be/S_T7hd0oXUE From Table 2, we can see that a 10kHz signal would penetrate seawater to a depth of around 14m with 50dB of attenuation. Australian Omega transmitter (VLF) Oberon submarine VLF communications equipment We covered the Omega navigation system in detail in the September 2014 issue (siliconchip.au/Article/8002). The Omega system was shut down on September 30th, 1997. After that, the Omega transmitter at Woodside, Victoria, was modified for reuse by the Royal Australian Navy for submarine communication until December 31st, 2008 (see Fig.18). It was converted for use at 10-14kHz to support a 100-baud, two-channel MSK (minimum-shift keying) transmission with a 100kW antenna input power and a radiated power of 36.5kW. Its designation was VL3DEF. Sadly, the tower was demolished on Oberon-class submarines are now obsolete; they were designed in Britain, built between 1957 and 1978 and served five countries, including Australia. The last Oberons in use were decommissioned in 2000. While it’s hard to find information about VLF and other communications for submarines presently in use, there are details on the obsolete Oberon communication schemes. Fig.19 shows their various antenna options: ALK a VLF aerial in a recoverable buoy ALM an omnidirectional VLF aerial comprising a series of loops in the fin 22 Silicon Chip Russian Zeus ELF/SLF transmitter The Russian Navy has an ELF/SLF transmitter called ZEVS (Zeus) on the Kola Peninsula, east of Finland. It was first noticed in the West in the 1990s and usually operates at 82Hz with MSK modulation, although it is thought to be capable of transmitting from 20Hz to 250Hz. It is believed to have two ground dipole antennas of 60km, driven at 200A to 300A. Apart from military purposes, it is also used for geophysical research. Australia's electronics magazine Fig.18: the former 432m-tall Omega Tower Woodside, a frame grab from the video at https://youtu.be/S_ T7hd0oXUE Note the concrete helix building to the right. ALN a telescopic HF/UHF mast ALW a buoyant, disposable VLF wire aerial AMK a UHF/IFF (IFF = identification, friend or foe) combined antenna associated with the ECM (electronic countermeasures) mast AWJ an emergency whip aerial for use on the surface only Fig.20 shows the VLF receiver used on these boats. They operated at 14-22.5kHz with 150Hz bandwidth and were only suitable for telegraphy reception, not voice or transmission. VLF data rate There is not much published information on data rates for VLF comms. Still, Continental Electronics Corporation (https://contelec.com/case-­ history-lfvlf), a major manufacturer of naval VLF equipment, states on its website that: Very Low Frequency (VLF) communications transmitters use digital signals to communicate with submerged submarines on at frequencies of 3-30 kHz. The Navy shore VLF/LF siliconchip.com.au Fig.19: antenna options for the Oberon class submarine, once used by Australia. The original is from a manual published by San Francisco Maritime National Park Association (https://maritime.org/doc/oberon/operations/index.php). transmitter facilities transmit a 50 baud submarine command and control broadcast which is the backbone of the submarine broadcast system. We assume this is with optimal frequency and conditions. One baud is about one bit per second, so this is 6.25 bytes per second; the actual rate will be less due to parity bits etc. That works out to about 300 characters per minute. The average word length is about five characters, so about 60 words per minute can be transmitted under optimal conditions (this paragraph would take ~30s). That rate could be doubled or even tripled with data compression. Continental Electronics also made equipment for the Harold E. Holt VLF transmitter mentioned above. receive VLF comms while the submarine stays more deeply submerged. A submarine can still remain fully submerged for higher frequencies but deploy a buoy with the appropriate antennas. Alternatively, the boat can surface and risk being detected, as shown in Fig.4. Figs.21 & 22 show a buoy from GABLER Maschinenbau GmbH that can be deployed from a submarine via a reel mechanism, using 8mm-thick buoyant wire that is up to 6km long. The buoy has various sensors, antennas and a camera. Its buoyancy can be controlled so the antenna can remain Fig.20: a CFA receiver, type 5820AP 164474, as used on Oberon-class submarines. Source: http://jproc.ca/ rrp/rrp2/oberon_cfa.pdf just submerged for VLF reception. A 30m antenna rod for HF reception is at the end of the cable, just before the buoy. The system allows for the reception of VLF signals (7-30kHz), the reception and transmission of satellite communications when the buoy is on the surface, and the reception of HF signals at the surface. Regarding satellite communications, it can receive and transmit to Iridium, NEXT and other systems, and it can receive GPS, Galileo, GLONASS and BeiDou navigation signals. Unmanned aerial vehicles (UAVs) can also be controlled from the buoy. Buoyant antenna systems Ideally, a submarine should not have to surface to receive or send signals. As already discussed, a submarine can deploy a wire antenna to receive VLF. This antenna floats to a shallow enough depth that it can Fig.21: the GABLER reel mechanism and buoy for trailing submarine antenna system. Source: www. gabler-naval.com/wp-content/ uploads/2021/05/GABLER-Naval_ BWA_2021-05_EN.pdf Fig.22: components of the GABLER digital buoyant wire antenna system: 1) Submersible winch. 2) Antenna tow cable with VLF antenna 3) Towed Digital Antenna and Satcom Controller (TDASC), incorporating HF antenna. 4) Inboard control and interface unit. Source: same as Fig.21. siliconchip.com.au Australia's electronics magazine March 2023  23 Underwater acoustic communications Underwater communications can also be acoustic. The earliest example of this was with bells, but today, ultrasonic transducers are used. There are many difficulties with underwater acoustic comms, such as multipath propagation, strong signal attenuation, environmental noise and variation in acoustic properties of water due to temperature and salinity layers. Many modulation modes have been developed for underwater acoustic comms, such as frequency-shift keying (FSK), phase-shift keying (PSK), frequency-hopping spread spectrum (FHSS), direct-sequence spread spectrum (DSSS), frequency and pulse-­ position modulation (FPPM and PPM), multiple frequency-shift keying (MFSK) and orthogonal frequency-­ division multiplexing (OFDM). Acoustic signals are only transmitted from a submarine when stealth is not a concern, as submarine or shipbased sonar systems can determine the origin of such signals. “Gertrude” underwater acoustic telephone During WW2, the USA developed an underwater telephone called the AN/BQC-1 (see Fig.23) and variants, nicknamed Gertrude. It used SSB (single side-band) acoustic communications at 8.3-11.1kHz or a CW signal at 24.26kHz. Voice communications were possible to about 450m, but calls could be heard at about 1.8-4.5km distance. It was used to communicate with other Fig.23: the “Gertrude” underwater telephone from WW2. 24 Silicon Chip submarines and surface vessels. Some versions of this device are still used today, but for stealth reasons, modern submarines try to avoid using them. JANUS (acoustic) JANUS is an open-access NATO standard for underwater acoustic communications for military and civilian use (see www.januswiki.com/tiki-­ index.php). It is a standard that serves a similar purpose as IEEE 802.11 for WiFi but for underwater acoustic use, allowing devices from different manufacturers to interoperate. Devices announce themselves at a shared frequency of 11.5kHz and then can negotiate a different frequency or transmission protocol. The system has been tested at distances up to 28km. The present JANUS standard frequency is defined by STANAG 4748 and uses 9.44-13.6kHz. The present frequency band for military underwater telephony (UWT) is 8087-11087Hz (STANAG 1074/1475), which overlaps somewhat with JANUS. There is a proposal to reserve 4375-7625Hz for military use and 24.75-31.25kHz for civilian purposes. UT3000 (acoustic) The ELAC UT3000 2G (see Fig.24) combines analog and digital underwater communications into one device and is compatible with STANAG, JANUS and other standards. It can deliver up to 1400W of acoustic transmission power. It performs functions such as telephony, telegraphy, digital data transmission and reception, noise measurement and distance measurement. It also has an emergency beacon mode and operates from 1kHz to 60kHz. CUUUWi (radio/acoustic) CUUUWi (‘cooee’) is a communications gateway between underwater and above-water mobile phone and satellite phone users for voice and text – sees Fig.25-27. It was developed under an Australian government grant by L3Harris Technologies. The system is designed to find (from distress signals) and then communicate with stricken submarines, or provide encrypted communications with submarines (or other underwater platforms) at speed and depth. A gateway surface vehicle (or fleet), such as an unmanned surface vessel (USV), is required to receive radio communications from surface vessels or satellites and convert them to acoustic communications for underwater reception. A range of up to 10km (20km in good conditions) is possible. The system can also be used for subsea platforms, including autonomous underwater vehicles (AUVs), seabed sensors, submarines, ships and divers. The system is compatible with various NATO standards, including JANUS. It can detect standard 8.8kHz underwater beacons and 37kHz emergency locator pulses, as commonly fitted to submarines, and will soon be on aircraft ‘black boxes’ and maritime voyage recorders. Surface modes include satellite communications, 4G/3G/GSM and VHF. Underwater modes include underwater telephone (UT3000), HAIL (Hydro Acoustic Information Link) Fig.24: the ELAC Sonar UT3000 2G acoustic underwater communications device. Source: www.researchgate.net/figure/UT3000digital-underwater-communication-system_ fig2_281904054 Australia's electronics magazine siliconchip.com.au IridiumSATCOM Voice/SMS + CUUUWi Command & Control IridiumSATCOM Surface Vessel Voice/SMS + CUUUWi Command & Control Shore Operations Wi-Fi (<50M) CUUUWi Gateway 500Kb/s (<100M) Rich Data Fig.26: the GPM300 MASQ acoustic modem, part of the CUUUWi system. CUUUWi Gateway Voice/SMS (<10km) AUV APFA ultrasonic modem supporting rapid data channel CCSM ● HAIL ● UT3000 & MASQ Fig.25: the CUUUWi system with communications between satellites, surface vessels, a submarine and an AUV (autonomous underwater vehicle). Source: www.l3harris.com/sites/default/files/2020-09/ims-maritime-datasheetCUUUWi_0.pdf and MASQ (Multichannel Acoustic Signalling Quality of service). Deep Siren (radio/acoustic) Raytheon, Ultra Electronics Maritime Systems and RRK Technologies Ltd developed Deep Siren Tactical Paging (See siliconchip.au/link/abjc) for the US Navy. It uses disposable buoys deployed from a submarine to transfer messages from Iridium satellites to the submarine via an acoustic data link. The range of the system is 50 nautical miles (92.5km) or more from the buoy to the submarine, and the submarine can operate at normal speed. In contrast, a sub has to run at reduced speed when towing antennas, such as those on a floating buoy or VLF cable. The buoy can be deployed from a surface ship, aircraft or from a submarine’s garbage chute(!). System testing started in 2008 and it was demonstrated in 2011. Its current operational status is unknown. TARF (acoustic/radar) Translational Acoustic-RF Communication is an experimental system developed by the Massachusetts Institute of Technology (MIT). Sound waves from an underwater source cause vibrations on the surface that can be picked up via a sensitive radar operating in the 300GHz range. See the video titled “Getting submarines talking to airplanes, finally” at https:// youtu.be/csYtAzDBk00 siliconchip.com.au Range limits of underwater acoustic communications Nature may have the answer to this. It is said that humpback whales communicate acoustically and can be heard by another up to 6400km away. Underwater Optical Communications (UWOC) There were hopes in the 1980s that airborne or spaceborne lasers could be used to communicate with submarines. With the SLCSAT (Submarine Laser Communication Satellite) and similar proposals, the idea was that a laser beam would be directed toward the ocean in the approximate submarine area and a communications channel would be established. Blue lasers for such a system were developed by Northrop Corp, and a highly sensitive laser detector by Fig.27: an 8.8kHz emergency location pinger with a battery lasting 300 days. These can be picked up by the CUUUWi system and would help locate aircraft black boxes, submarines in peril etc. Lockheed Corp. As far as we know, this system was never put into service. From UWOC in use today and reported below, it appears that underwater optical links in seawater can only work over a few tens of metres. The attenuation and scattering of light in seawater are just too great. However, an optical link could presumably be established between a buoy on the ocean surface and an aircraft. Blue-green lasers have been developed for naval use that can transmit data at 90Mb/s over water for up to 10km, but when used underwater, the data rate drops to 7-10Mb/s over 10-20m (as described at siliconchip. au/link/abin). Aqua-Fi (optical) Basem Shihada et al. from the King Abdullah University of Science and Relevant videos and links ● VLF signals that individuals have received: www.sigidwiki.com/wiki/ Category:VLF ● 1972 US Navy manuals for VLF communications: www.navy-radio.com/ manuals/shore-vlf.htm ● An experimental, compact piezoelectric VLF antenna: siliconchip.au/link/ abit and www.nature.com/articles/s41598-020-73973-6 ● The companion site for the Australian VLF transmitter at Belconnen, “16 kHz VLF, Rugby, England”: https://youtu.be/Unlg2gY2Zrs ● On the Goliath transmitter, “The Radio Network that Communicated with Nazi Subs”: https://youtu.be/OSNCvJN5Xoo ● “Project E.L.F. – The history of communicating with submarines underwater - #HamRadioQA”: https://youtu.be/eC1cqwGkOwY ● “Reception of signals from submarines on VLF”: https://youtu.be/ UYaK3tWXbn0 Australia's electronics magazine March 2023  25 Technology in Saudi Arabia developed an underwater Internet access architecture that used a Raspberry Pi computer and off-the-shelf green LEDs or 520nm lasers to transmit data. They obtained a maximum data transfer rate of 2.11MB/s. They did not specify the communications distance, but diagrams in the PDF at siliconchip.au/link/abio suggest up to 10m for LEDs or 20m for lasers. However, the picture of the lab demonstration shows a distance closer to two metres. Using online SDR radios to listen to VLF signals You can use a computer sound card or audio input to receive VLF signals with a PC, antenna and software only. There are many articles and videos on how to do this. For example, see: www.prinz.nl/SAQ.html | siliconchip.au/link/abj9 | www.vlf.it siliconchip.au/link/abja | siliconchip.au/link/abjb There is an experimental online VLF-HF SDR receiver (EA3HRU) at http:// sdrbcn.duckdns.org:8073/ in Pallejà, Barcelona, Spain. Select VLF mode in the menu. Blue laser diodes Reported in Nature Portfolio (www. nature.com/articles/srep40480), a 450nm blue GaN laser diode modulated by quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) can transmit data through seawater at a rate of 7.2GB/s over 6.8m or 4.0GB/s over 10.2m. Underwater data nodes (optical or acoustic) Underwater data nodes could be established for submarines or AUVs so that they can establish a high-­ bandwidth connection with their command centre without surfacing (see Fig.28). This would allow them to receive information much faster than VLF or ELF radio, and transmit it too, without having to release a floating antenna or buoy. A faster data channel could be established than with satellites, so there would be less exposure time for the antenna buoy or periscope. This would also provide an alternative means of communication if satellites and landbased transmitters are destroyed. Fig.28: an underwater communication range of 1020m is within the capability of a blue-green laser. Source: www. mobilityengineeringtech.com/ component/content/24599 26 Silicon Chip A screen grab from the online SDR radio EA3HRU in VLF mode. The idea is that an underwater vehicle would manoeuvre close to the communication node on the seabed and establish a comms channel by optical or acoustic means. China’s laser sub-hunting system (optical) It is not hard to imagine that the following laser system built to hunt for submarines could also be used to communicate with them if the laser system was modulated with data. According to ABC News (www.abc. net.au/news/11570886), China has developed a blue-green laser system for shining light from aircraft into the ocean and looking for a reflection indicating the presence of a submarine. The laser is beamed from an aircraft at an altitude of 1.6-3.2km and will find a submarine as deep as 160m. The article notes that a Collins-class submarine has a typical operational depth of 180m. The objective is to build a satellite that can find subs as deep as 500m. This system is similar in principle to the Australian-developed LADS (Laser Airborne Depth Sounder) for seafloor mapping, which could be adapted for submarine communication. However, as noted above, optical communications underwater are of limited range. See our previous article on sonar in Australia's electronics magazine the June 2019 issue (siliconchip.au/ Article/11664). LUMA LUMA X is an underwater optical modem (www.hydromea.com) that can transfer data at up to 10Mbit/s over 50m, enough for HD video – see Fig.29. It is suitable for use with autonomous underwater vehicles (AUVs) and remotely operated vehicles (ROVs). Next month Underground communications pose some similar challenges to underwater communications. There are quite a few different aspects to communication underground, so we’ll cover them in a separate article in next SC month’s issue. Fig.29: the Luma underwater optical modem. Source: https://files. hydromea.com/luma/Hydromea_ LUMA_X_datasheet.pdf siliconchip.com.au aarkcerh M M Build It Yourself Electronics Centres® SAVE $370 999 $ r space. Upgrade your make st. K 8604 arch 31 Sale prices must end M Everything a maker space needs in one compact unit! SAVE $26 99 $ T 2040 y for Top bu nts & de the stu ers! a m k Amazing value under $100 Micron® 68W Compact Soldering Station This latest design benchtop soldering iron offers convenience and plenty of power for the enthusiast. Offers precise dial temperature control with temperature lock. In-built sleeper stand shuts down the unit when not in use saving on power costs. Includes a fine 1.2mm chisel tip, solder reel holder and tip sponge. 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Not included with product. B 0003 Find a local reseller at: altronics.com.au/storelocations/dealers/ Digital Volume Control POTENTIOMETER By Phil Prosser We got tired of volume control potentiometers going scratchy after just a few years and the very poor balance at low volumes. This drop-in replacement uses a digital IC, so it tracks exceptionally well and will give top performance for decades. The SMD version fits in the space occupied by most regular pots, while the through-hole version does a similar job but is a bit easier to build. W e have had to replace volume controls in our prized equipment too often due to them going ‘noisy’. In the September 2022 issue, a reader wrote in with that exact same problem; we know it affects many people. In one spectacular failure, a ground tab on the volume pot for my work stereo failed, resulting in that channel running flat-out all night, to greet co-workers at full blast the next morning! The gauntlet was thrown down recently when building a remote volume control. The motorised pot literally failed out of the box, the crimped-on tabs being loose (we know others have experienced this too). There must be a better solution! Why aren’t there pot-sized volume digital controls that use some of the excellent electronic volume control ICs with a digital rotary encoder? Well, now there are! The original concept for this project was a straight-out replacement for a volume pot. Our illustrious Editor asked the innocent question: “If you have a PIC in there to control the volume IC, why not have IR remote control as well?”. As it turned out, that was not too difficult to provide. The resulting SMD design is a very modest size at just 25mm wide by 36mm deep. It’s just a little larger than a typical dual-gang log pot, as shown in the photos. While this small size is clearly a boon in many situations, we knew that some readers would baulk at building it. While the board is quite packed, none of the parts are that small. Still, it wasn’t too much work to come up siliconchip.com.au Features ☑ Based on the PGA2311UA stereo digital volume control IC ☑ Two independent channels (expandable up to four, six or more) ☑ Automatically remembers the last volume setting ☑ Volume adjusted by a rotary ☑ ☑ ☑ ☑ ☑ ☑ control on the front panel or universal IR remote control Mute function (remote control only) Soft start at power-up ‘Clickless’ design Controlled by a PIC16F15214 microcontroller and TSOP4136 IR receiver Operates from a preamp power supply from ±8V to ±30V Optional LED indicator showing IR and volume change activity The SMD version of the Digital Potentiometer is a little larger than a dollar coin and just wide enough for the rotary encoder and IR receiver to fit. And for those who don’t want to squint while building it, there’s the larger through-hole version shown below. Specifications ☑ Gain and attenuation range: +31.5dB to -95.5dB in 0.5dB steps ☑ Channel gain match typically within ±0.05dB ☑ 0.0002% distortion ☑ ☑ ☑ ☑ ☑ at 1kHz (using the -UA version of the IC) – see Fig.1 Frequency response: essentially flat from 20Hz to 20kHz Able to drive 600W W loads Input resistance: 10kW W Signal handling: 2.5V RMS maximum input level Output level: up to 2.5V RMS (7.5V peak-to-peak) Australia's electronics magazine This prototype used a TSOP2136, instead of the recommended TSOP4136, which is why the IR receiver is shown mounted on the outer set of pads. Refer to the text on page 36. March 2023  31 Fig.1: THD and THD+N vs frequency plots for the Digital Pot for both channels – nothing to see here, folks! Move along! You’ll get similar or better performance from this design compared to a regular, passive potentiometer. even in these times of IC shortages. The PGA2311 contains a resistor network and analog switch along with switched resistors in the feedback network of the output buffer amplifier, as shown in Fig.2. This allows the device not only to attenuate but also to provide up to 31.5dB gain. Pay attention to this; turning it up too high when you don’t have an input signal leads to a loud surprise! This IC is very quiet, so do not expect to hear hiss or noise to warn you that the volume level is high. While these ICs can provide up to 31.5dB gain, we limited the Electronic Volume Control gain to +10dB. An alternative firmware allows you to run up to +31.5dB, but be warned that this is an awful lot of gain. Circuit details Fig.2: this shows what is inside the PGA2311 (and PGA2310, PGA2320) ICs. The switched resistive attenuator and switched feedback in the output amplifier allow for a wide range of gain and attenuation settings. with a through-hole equivalent design, so that is what I did. I checked its performance and found it to be close enough to the SMD version that nobody would notice an audible difference. So if you have room to fit a larger board, it is certainly an option. Its circuit is identical; it just uses physically larger components on a different PCB that measures 79mm wide and 57mm deep. Performance & IC choice The specifications panel and Fig.1 show the performance of the prototypes. There’s so little noise and distortion that it certainly won’t be audible and will not affect the audio quality of even the best amplifiers. We measured the distortion of five prototypes, and all were in the 0.00020.0003% distortion region, which is 32 Silicon Chip close to the measurement limit of our test equipment. The heart of the project is the PGA2311 Volume Control IC from Texas Instruments. The PGA2320 or PGA2310 can also be used with identical performance, but those versions are much more expensive for reasons we cannot explain, other than they can operate from higher ±15V supply rails compared to ±5V. You need to use one of the PGA2311 chips with a UA suffix to get the specified performance. The obsolete CS3310 will also work just fine, and they are still reasonably easy to find on the grey market (eBay, AliExpress etc). Still, all of those options will give acceptable performance. In short, we are confident that you will find one volume IC or another to fit on your board, Australia's electronics magazine The Digital Pot circuit is shown in Fig.3; there is not much to it. There are a couple of things on the board beyond IC2, the PGA2311 (or equivalent), PIC microcontroller IC1, rotary encoder RE1, IR receiver IRR1 and some power supply components. The audio performance of this project is almost entirely determined by the PGA2311, as there is nothing else in the signal path. The left channel signal is fed in via pin 1 of CON2, goes straight into IC2’s input pin 16, out of its output pin 14 to pin 2 of CON2, for feeding to the amplifier (or whatever is downstream). The other channel is routed similarly, via CON1. We have included input protection with a BAT54S dual schottky diode (or a pair of BAT85s on the through-hole version) from each input pin to the supply rails. This way, if the input is over-driven, the diodes will conduct and help to protect the PGA2311 from damage. We decided not to include DC-­ blocking capacitors on either the input or output. The reason is that four bipolar capacitors would have added probably 20% to the PCB size. We expect these will be in your signal chain already (after all, if you’re replacing a mechanical pot, you won’t be applying DC to it) and the output offset voltage of the PGA2311 is only 0.25mV at 0dB gain. If you have DC in your signal chain, you will need to include a blocking capacitor in series with the Digital Pot – we recommend a 10μF 25V bipolar electrolytic capacitor. You can also siliconchip.com.au use two regular 10μF 25V electrolytics connected in series, negative-to-­ negative or positive-to-positive. Both options will have no noticeable effect on the audio. With the outputs, we are assuming that the Digital Pot will drive short cables to your amplifier or follow on circuitry. The PGA2311 can drive 600W loads and has a short-­circuit current of 50mA, so it is unlikely to misbehave if presented with an unusual load. Still, if you intend to drive long cables with this, add a 100W resistor in series with each output. A convenient place for this would be at your output socket. Controller Power supply If the PGA2311 is the heart of this design, the 8-pin PIC16F15214 is the brain. We discussed the capabilities of this chip in April 2022 (siliconchip. au/Article/15277). The main job of the software running on this PIC is to monitor the rotary encoder and, if it is turned, send a signal to IC2 to adjust the volume appropriately. It also looks for signals from the infrared receiver and, if it receives a valid signal from a remote control, also figures out what command to send to IC2 in response. We’ll have more details on how the software works later. IC2 operates from ±5V supply rails. To allow a wide variety of amplifier/ preamplifier supply rails to be used to run this board, we have onboard 78(L)05 or 79(L)05 regulators. This means you can power the Digital Pot from split supply rails from ±8V to ±30V, which should suit most applications. A typical preamp will have such rails available, and some smaller amplifiers without preamps might too. In keeping with the design concept, the power supply is very simple. The PGA2311 has a typical power supply rejection ratio (PSRR) of 100dB at 250Hz, so any noise that the basic Fig.3: the complete circuit for the Digital Pot; this applies to both the SMD and through-hole versions. Just note that D1a/D1b and D2a/D2b are two dual diodes in the SMD version or four individual diodes in the other. The only extra part not shown here is the optional LED indicator that plugs into CON4. siliconchip.com.au Australia's electronics magazine March 2023  33 linear regulators let through will not realistically affect performance. Of course, you could ‘roll your own’ lownoise ±5V DC supply and delete the regulators as an upgrade. Suppose you want to fit the Digital Pot into a power amplifier with only split supply rails above ±30V. In that case, you could connect 5W zener diodes in series with the two supply rails to drop them into the Digital Pot’s acceptable range. It only draws a few tens of milliamps, so that should work for just about any amplifier. Just ensure the zener polarities are correct (anode to pin 1 of CON3; other cathode to pin 3). If you use the PGA2310 or PGA2320 devices, you also have the option of increasing the analog supply rails as high as ±15V. This will make no difference in the vast majority of applications, but the choice is there. The simplest way of doing this is to drop in 78(L)15 and 79(L)15 regulators for REG2 and REG3, respectively. Don’t change REG1 to a higher voltage type. Firmware The source code and HEX file for this project are available for download from the Silicon Chip website. We can also supply microcontrollers already loaded with the appropriate HEX file. On boot-up, the software configures several registers to set the processor clock speed to 4MHz, much lower than the maximum, and starts a timer for measuring IR signals. It then loads the saved volume level and remote control configuration from flash memory, checks to see if the user wants to change the remote code and, if not, ramps the volume from zero to the last used value over a couple of seconds. It then monitors the rotary encoder and IR input ports for action, and if anything happens, decides if the rotary encoder is being turned up or down or reads the IR stream to see what code was transmitted. The software writes a new volume level value to the PGA2311 IC if required. Then, if there are no changes for about 10 seconds, it saves the new volume level to flash memory. Modulated infrared signals are received by the TSOP4136, which includes an IR detector, 36kHz bandpass filter and output driver. The result is a digital serial stream including intentional signals from your remote control and also ambient light noise. 34 Silicon Chip IR Signal Decoding With Manchester encoding, a logic one is transmitted as a high-to-low transition, while a “0” is a low-to-high transition – see Fig.4. As transmission starts with a one bit, we know that there is a high level, then a low level, at the start of every transmission. Fig.4: the Manchester Encoding scheme used by the RC-5 remote control scheme. This encoding results in no DC component, a well-defined frequency range, and the ability of a receiver to work out the clock rate from the serial data stream. The decoder described here works well and is a good example of a simple state machine. Let’s start by listing what we know: ● A one is encoded as a period of no IR signal for 890μs (nominally), followed by an IR signal for the same time; zero is the reverse. We need to allow for some variation in the transmitter’s clock and thus periods (say ±10%). ● The IR level will never remain the same for much less than the nominally 890μs period, or much more than 1780μs if a zero follows a one or a one follows a zero. ● We are looking for 14 bits of data. The state machine states, shown in Fig.5, are as follows. A Clear any stored value and wait for an IR signal to be present. Set the first bit to one (we know this is true if it is a valid signal) and go to state B. B We are receiving a one. Measure the time until the IR signal stops. If this was too short (say, less than 890μs minus 10%), this is noise; go to state A. if the time was short (closer to 890μs than 1780μs), we have just received another one. Store this and go to state C. if the time was long (closer to 1780μs than 890μs), then we are receiving a zero. Store this and go to state D. if the time was far too long (more than 1780μs plus 10%), this is noise, so go to state A. C We just received an IR pulse starting with a one after having already received a one (there is no IR signal just now). Measure the time until we see an IR signal again. if we see it too soon, this is noise; go to state A. if the time was short, that is to be expected; store the bit and go to state B. if the time was longer than that, this is noise; go to state A. D We just received a zero; there is no IR signal now. Wait until the IR signal starts again. if we see no IR for too short a time, this is noise; go to state A. if we see no IR for a short time, we have just received another zero. Store this and go to state E. if we see no IR for a long time, we are receiving a one. Store this and go to state C. if there was no IR for longer than that, this is noise; go to state A. E We just received an IR pulse for a zero after a zero (there is an IR signal present now). Measure the time until we see no IR signal again. if this is less than a short pulse, this is noise; go to state A. if we see no IR for a short time, that is to be expected; go to state D. if we see no IR for longer than that, this is noise; go to state A. If the software receives all 14 valid bits using the above method, it is considered a valid command and processed, then it returns to state A, ready to receive another command. Otherwise, it throws the data away as it is considered noise. Fig.5 overleaf shows this as a “state diagram”. ↪ ↪ ↪ ↪ ↪ ↪ ↪ ↪ ↪ ↪ ↪ ↪ ↪ Australia's electronics magazine siliconchip.com.au Fig.5: the IR decoder state machine built into the software. This demonstrates how complex logic can be decomposed into a (relatively) simple flow chart and then implemented in logic or software. Writing software can become difficult without breaking the logic down like this. Noise will include ‘signals’ from lights, the sun and other IR remotes in the room. The IR receiver’s internal bandpass filter is not 100% effective at blocking this noise, but it helps a lot by reducing it to a manageable level. While a little old now, Philips RC-5 IR codes are prevalent, and virtually all universal remote controls can generate them. RC-5 IR transmissions each contain 14 bits of data. That’s broken down into five address bits (32 possible values for TV, VCR, DVD, receiver etc) and six command bits (64 possible values). The stream commences with two start bits and a ‘toggle’ bit that inverts with each subsequent command. The data is ‘Manchester encoded’, a clever way of sending a string of ones and zeros on a serial line while embedding a clock signal into it. Our PIC reverses this scheme to decode the serial stream of data from the TSOP4136; more detail on this is provided in the “IR Signal Decoding” panel. The PIC microcontroller untangles all this to extract commands from our remote and change the volume or toggle the mute status. PCB design method We thought it might be interesting to show what we do when designing such a tightly packed board and how we are sure it will all fit. Fig.6 is a 3D rendering of the PCB from Altium during the design phase. Compare this to the actual prototype; it’s pretty close. This depends on us entering the right models for every component, but you only need to do this once. After Note: the headers are swapped in the final version compared to the photos to make it easier to use shielded cable for the audio. Enlarged views of the SMD version of the Digital Volume Control Potentiometer. Note the different IR receiver, as we tested a few common types. siliconchip.com.au Fig.6: this is the 3D rendering we produced using Altium to verify that everything was going to fit. The final result looks remarkably similar. that, we can run interference checks and even get a rendering of what it will look like once assembled. We can spin it around to ensure there are no component collisions (and Altium can warn us if there are). Construction First, you need to choose which board you want to build. The SMD version is suitable for relative beginners as it has a handful of surface mount parts but no really fine pitch components. That said, if you have room for the full-size board, it might save you some squinting to build that. This especially applies to those of us with a few extra ‘miles on the clock’. SMD version The SMD version is built on a double-­ sided PCB coded 01101231 that measures 25.5 × 36.5mm, with the components placed as shown in Fig.7. Components are mounted on both sides to keep the final result compact. You might want to use a small vice or some Blu-Tack to stop the PCB from slipping around on the bench while you work on it. Start by soldering the 10kW resistor on the back of the board. Next, fit the 100nF capacitors. Four are on the board’s back, and two are on the front. Next, fit the PGA2311 IC (or similar) and the PIC16F15124 microcontroller. In both cases, ensure you have identified pin 1 and orientated it as shown in Fig.7 and the PCB silkscreen before tacking one pin. Then check the alignment of the other pins before soldering March 2023  35 them. If they are off, remelt the first solder joint and gently nudge the IC into position. Adding a bit of flux paste along the rows of pins before applying solder is recommended, as it makes the solder flow much better, to form good joints. With flux paste on the pins, you just need to load a little solder on your iron and then touch it to the junction of the pin and pad, and it should flow onto them and form a good joint. With practice, you can even drag the iron down the pins to solder them in rapid succession. After soldering, check carefully to ensure all the joints are good and no pins are bridged to adjacent pins with solder. If they are, add a bit more flux paste and then apply some solder wick to suck up the excess solder and clear the bridge. Now flip the board and solder the two dual BAT54S schottky diodes. These are SOT-23 package devices and the smallest parts you will need to deal with, but luckily, the pins are relatively widely spaced. Once you have these on the board, it is all downhill from there. Next, fit all five 10µF 35V SMD electrolytic capacitors (or, even better, 10µF 35V/50V SMD ceramics). If using electrolytics, orientate them as shown; the base has a chamfer at the positive end. You can use a small amount of solder to wet one pad and tack the capacitor lead to hold it in place before properly soldering both pins. Leave that fine tip on your soldering iron, as while the remaining parts are through-hole types, many of these parts use smaller pads to fit the tracks onto the PCB. Solder in the three voltage regulators next. Be careful to get Fig.8: the through-hole PCB is electrically identical to the SMD version but somewhat larger. For both IC1 and IC2, you can fit a part in a DIP (through-hole) or SOIC SMD package. Be careful which way around you install the regulators and ICs, and note the extra pad next to CON4 so that multiple units can be ‘ganged up’ for four or more channels. the 78(L)05 and 79(L)05 devices in the right spots. Next, mount the power and output connectors. We have chosen different types for these to make it less likely that the power will be inadvertently plugged into the audio connector. It is possible to solder wires directly to the PCB, but connectors provide a more professional finish and make for easier assembly and maintenance. A two-pin header is used as a jumper to isolate the IR receiver in case IC1 needs to be reprogrammed. If you need to program your PIC, install this header but not fit the jumper until after the PIC is programmed. If you are using a pre-programmed PIC, you can insert the jumper before or immediately after soldering it. The final part to install is the IR receiver. There are many similar types on the market, but they have annoying pinout differences. Some have the + and – power supply pins swapped! Check the ones you buy carefully; the specified TSOP4136 devices have GND on the middle pin and fit the inner set of holes on the PCB. TSOP2136 devices have GND on an outer pin, matching the pads nearest the PCB edge. Through-hole version The through-hole version is built on a double-sided PCB that’s coded 01101232 and measures 78.5 × 57mm. The parts layout on this board is shown in Fig.8. This board allows the use of all through-hole parts or, alternatively, you can use the surface-mounting versions of the PIC microcontroller and/ or PGA2311 IC. This makes sourcing parts easier. All the remaining through-hole parts are very common, so we do not envisage any difficulties in sourcing them. The assembly order is essentially the same as for the SMD version, listed above, with a few minor differences besides the different component packages. The main one is that the two dual SMD diodes are replaced with four individual leaded diodes. Also note that the through-hole electrolytics have their positive sides indicated using longer leads, which go towards Fig.7: the SMD version is very compact but is identical in performance and function to the larger through-hole version. If using 10μF ceramic capacitors instead of electrolytic (which we would recommend), they will fit on the same pads but are not polarised. You can use the same type of connector for CON3 as CON1 & CON2 but then there is a risk of accidentally plugging the power cable into the wrong header and doing damage. Choosing an infrared remote control We tested several remotes during development, including the Altronics A1012A. We programmed this for TV codes 0088, 0154, 0169 and others and AUX codes 0734, 0846, 0727 and others. We also tested a “One For All” remote and found it worked with TV code 0556 and RCVR/AMP code 1269. The easiest way to set this up for your remote is to plug the IR activity LED into the program port and watch for the LED lighting when you press buttons on the remote. Flashing indicates that valid IR codes are being received. It’s then just a matter of trying different codes (starting with Philips TVs) until you find one that works. You only need the volume up/down and mute button codes to be correct. 36 Silicon Chip Australia's electronics magazine siliconchip.com.au the + symbols on the board. For the regulators, you might as well use the same 78L05 and 79L05 devices as used on the SMD version; orientate them as per the smaller semi-­cylindrical footprints shown in Fig.8. However, you can also use the 7805/7905 or equivalent TO-220 regulators if you happen to have them on hand; the required orientation of those devices is also shown in Fig.8. Otherwise, follow the same order of assembly as the SMD version, referring to the section above. After that, you can install the four “feet” comprising tapped spacers held into the corner mounting holes with machine screws. These are not only handy during testing; you can use them to mount the more hefty through-hole board to the chassis later. Activity LED An activity LED is a useful thing to have; one that flashes at power-up, when valid infrared commands are received and when the encoder is rotated. To provide for this, the firmware stretches the length of the CS ‘chip select’ signal to the PGA2311 IC. By connecting our LED and resistor between this line and the 5V rail, it will light up whenever commands are sent to that IC. This is a bit cheeky, as we are using the chip select line for two purposes: while the CS line is low to enable the PGA2311’s digital interface, it also drives current through the activity LED to light it. To make the flash visible, we need to extend these pulses from what is required (just a few microseconds) to tens of milliseconds. The wiring for the optional activity LED is shown in Fig.9. It is done by soldering the light-duty figure-up cable to two pins on a female header with three to five pins. You can cut this from a longer header strip. It then plugs onto CON4 and allows you to mount the LED in a visible location, eg, on the front panel of your amplifier using a bezel. Try to keep this lead to a modest length (~10cm), as it helps to prevent noise getting on the CS line. Programming IC1 If you got IC1 from Silicon Chip, it should be pre-programmed and ready to go. If using a blank microcontroller, you will have to program it in-circuit for the SMD version (unless you have an SOIC programming socket). With siliconchip.com.au Parts List – Digital Volume Control ‘Potentiometer’ 1 universal remote control [Altronics A1012A] 1 rotary encoder (RE1) [Altronics S3350 or EN11-VNM1BF15 (Mouser)] 2 3-pin vertical polarised headers, 2.54mm pitch (CON1, CON2) [Altronics P5493] 2 3-way polarised header plugs with pins (for audio signals via CON1, CON2) [Altronics P5473 + 3 x P5470A] 1 3-pin JST style header, 2.54mm pitch (CON3) [Altronics P5743] 1 3-pin JST style plug, 2.54mm pitch (for power via CON3) [2 x Altronics P5743 + 6 x Altronics P5750] 1 2-pin vertical header, 2.54mm pitch, plus jumper shunt (JP1) 1 TSOP4136 or similar IR receiver, SIL-3 (IRR1) [Altronics Z1611A, Jaycar ZD1953, Mouser 782-TSOP4136] Additional components for the SMD version 1 double-sided PCB coded 01101231, 25.5 × 36.5mm 1 6-pin SMD vertical header, 2.54mm pitch (CON4) (optional; for ICSP, activity LED and/or multi-channel use) [Altronics P5435]  1 PIC16F15214-I/SN 8-bit microcontroller programmed with 0110123A.HEX, SOIC-8 (IC1) 1 PGA2311, PGA2310, PGA2320 or CS3310 digital volume control IC, wide SOIC-16 (IC2) 2 78L05 +5V 100mA linear regulators, TO-92 (REG1, REG2) 1 79L05 -5V 100mA linear regulator, TO-92 (REG3) 2 BAT54S 25V 200mA dual series SMD schottky diodes, SOT-23 (D1, D2) [Altronics Y0075] 5 10μF 35V SMD electrolytic capacitors, 5.3×5.3mm [Altronics R9442] OR 5 10μF 35V/50V SMD ceramic capacitors, X5R or X7R, M3216/1206 size 6 100nF 50V X7R SMD ceramic capacitors, M3216 size [Altronics R9935] 1 10kW SMD resistor, M2012/0805 size [Altronics R1148] Additional components for the through-hole version 1 double-sided PCB coded 01101232, 78.5 × 57mm 1 6-pin vertical header, 2.54mm pitch (CON4) (optional; for ICSP, activity LED and/or multi-channel use) 1 8-pin DIL IC socket (optional; for IC1 if DIP version used) 1 PIC16F15214 8-bit microcontroller programmed with 0110123A.HEX, DIP-8 or SOIC-8 (IC1) 1 PGA2311, PGA2310, PGA2320 or CS3310 digital volume control IC, DIP-16 or wide SOIC-16 (IC2) 2 78L05 or 7805 +5V 100mA/1A linear regulators, TO-92 or TO-220 (REG1, REG2) 1 79L05 or 7905 -5V 100mA/1A linear regulator, TO-92 or TO-220 (REG3) 4 BAT85 30V 200mA schottky diodes (D1a/b, D2a/b) [Altronics Z0044] 5 10μF 50V low-ESR radial electrolytic capacitors, 5mm diameter [Altronics R6067] 6 100nF 50V X7R multi-layer ceramic capacitors, 5mm pitch [Altronics R2931] 1 10kW ¼W resistor 4 M3-tapped spacers (for mounting PCB) 8 M3 × 6mm panhead machine screws (for mounting PCB) 4 M3 shakeproof washers (for mounting PCB) Optional parts for activity LED (suits either version) 1 LED with bezel and series current-limiting resistor 1 length of light-duty figure-8 wire, to suit installation 1 3-pin, 4-pin or 5-pin female header, 2.54mm pitch  Most SMD headers, including Altronics Cat P5435, have the pins staggered on either side of the header. The PCB requires the pins to all be on one side. This can generally be achieved by snapping or cutting off a 5-pin or 6-pin length of the header and rotating the even-numbered pins by 180°. Australia's electronics magazine March 2023  37 Fig.9: this circuit shows how to add an IR activity LED. We piggyback off the CS line for the PG2311 IC, which itself re-purposes the incircuit serial programming data line. It can be a 3-, 4- or 5-pin header as long as it’s plugged into CON4 so the correct connections are made; you can adjust the resistor value to suit the LED used. the through-hole version, you can program it in-circuit or off-board before fitting it (or even afterwards if you’re using an IC socket). For programming it in-circuit, remove JP1 and plug a programmer like a PICkit 4 or Snap programmer into CON4 with its pin 1 in the correct position. With the PICkit 4, you can get the programmer to deliver power during programming. For the Snap programmer, it’s probably easiest to apply 12V DC between the +VE and GND pins of power header CON3 during programming. Using MPLAB IPE, select the correct device (PIC16F15214), load the HEX file (available for download from the Silicon Chip website), enable power from the programmer if necessary, then connect to the chip and press the program button. It should only take a couple of seconds to load the firmware, and you will see a success For multi-channel use, a ‘slave’ version of either the through-hole or SMD version can be built using less components. See the panel overleaf for more details. message (or an error message if something goes wrong). Remember to re-fit the shorting block to JP1 after disconnecting the programmer. Changing remote control code The software can decode RC5 signals with any valid TV or “Receiver” address. The software defaults to the TV on first power-up, and if you do not need to change this, there is nothing to do. If you have another Philips TV remote in the room and need to use an alternative code, here is how to set the Digital Pot to use the Philips Receiver codes: To set the remote using a TV code: 1 Remove power from the Digital Pot. 2 Short pins 3 & 5 of CON4. 3 Apply power to the Digital Pot. 4 Wait a couple of seconds Are AliExpress PGA2311 ICs any good? We bought some PGA2311 chips from AliExpress (www.aliexpress.com/ item/1005003043805799.html). We built and measured the performance of a Digital Pot using one of these, and it worked just fine – see Fig.10. At $20.73 for five ICs, this is a rather attractive option! 5 Remove power from the Digital Pot. 6 Remove the short between pins 3 & 5 of CON4. To set it to accept a Philips Receiver remote control code, go through the steps above but instead, put the jumper between pins 3 & 4 of CON4. This procedure is the same for the through-hole or SMD versions, but if you haven’t fitted CON4, you will need to do so. Note that pin 1 of this header on the SMD board is nearest to the PIC microcontroller. Troubleshooting If it isn’t working as expected, check the following: 1 Is there 5V DC ±0.25V on the +5VD (IC2 pins 1, 4 and 8) and +5VA (IC2 pin 12) rails? If not, check for any parts getting hot. Verify that you are providing a minimum of 7V DC to the PCB positive input. Do you have the right parts for REG1 & REG2, in the correct orientations? 2 Are IC1 and IC2 soldered properly? Take a close-up photo if your phone has this function; it is surprising how zoomed-in you can get with some phones. 3 Is there activity on the encoder lines (pins 2 & 3 of IC1)? If you have a ‘scope, probe pins 2 and 3 of IC1 and see if they are at more than 3V, pulsing low as you rotate the encoder. If not, check that you have used a suitable encoder – there are a bewildering variety of rotary encoders; the recommended Altronics and Mouser parts have been tested to work. ↪ ↪ ↪ ↪ Fig.10: despite costing just over $4 each, the board built with the PGA2311UAs we got from AliExpress gave extremely low THD readings, just like the boards built with chips from more reputable vendors. 38 Silicon Chip Australia's electronics magazine siliconchip.com.au 4 Power up the board and monitor the CS line with an oscilloscope (IC1 pin 7). On power-up, the micro writes data to the PGA2311 for a couple of seconds to ramp the volume. If this signal is present, the PIC is running and programmed correctly. If you don’t have an oscilloscope, watch the LED very closely in a darkened room on power-up. After power is applied, you should see the LED light dimly for a second or two. If there is no activity on the CS line, go back and check power and check that your micro is programmed. You can also monitor the SDI and SCLK lines (IC1 pins 5 and 6) for activity. These should be active for the first second or so after power-up and when the encoder is rotated. 5 If the IR remote does not work: Have you installed the shunt on JP1? Have you put the TSOP4136 in the right location? Check the signal on JP1 or pin 2 of the TSOP4136 with an oscilloscope; there should be clear activity when the remote buttons are pressed. Have you programmed the remote with the right code? If using a universal remote, you will likely need to try a few of the configuration numbers for your remote to get it working. Install the activity LED and watch for the LED to flash; this will tell you that the remote is transmitting codes that work. Note that if you need to program your PIC on the board, you will need to remove the shunt from JP1. Many TSOP4136 devices otherwise stop the PIC from being programmed. Remember to reinstall the shunt SC after programming. ↪ ↪ ↪ ↪ ↪ ↪ ↪ ↪ Volume Control Pot Kit There are two kits for this project: • SMD version: SC6623 ($60) • Through-hole: SC6624 ($70) Note that the latter may be supplied with IC2 (the PGA2311) in the wide SOIC-16 package due to the limited availability of through-hole equivalents. The kits include all relevant parts in the parts list except the universal remote control and extra parts for the activity LED. siliconchip.com.au Ganging up multiple boards for more than two channels One really useful feature of this Digital Pot design is that it is easy to run one as a master and one or more as slaves. This allows one volume control or remote to set the level on four, six or more channels. This is great if you are making a home theatre system and want to use your own amplifiers. It is also handy if you want to control multiple channel levels in a multi-room system or need to adjust the level of multiple channels from one control. You can use either the through-hole or SMD versions to do this. The master is fitted with all the parts, while the slave(s) have the microcontroller, rotary encoder, infrared receiver, REG1 and associated parts left off. You need to have the programming header fitted to all the boards, and importantly, it must have six pins rather than five. The extra pin goes into or onto a pad labelled SCLK, right at the end of the programming header, allowing you to extend it by an extra pin. You then run a cable to join all the six-pin programming headers in parallel. That’s all you have to do! But remember to leave off the PIC microcontroller, REG1, IR receiver and encoder on each slave board. Otherwise, they will interfere with the master. To make a six-way ribbon cable that can join the boards, you can use two Altronics P5380 header sockets (or cut two 6-pin sections from a P5390 or similar strip). Wire pins 1-1 through 6-6 together using ribbon cable and insulate the soldered connections using 3mm diameter heatshrink tubing. Mark pin 1 at each end so you don’t accidentally swap them! That could cause damage to one or more boards. We tested this using 200mm of ribbon cable with no problems. This interface does not have fast data, so we expect you can stretch this a little if needed. You could also use a 12-way ribbon cable with IDC connectors as long as you were careful to plug the six-pin header into the same subset of the 12 pins on each connector. That might be easier since crimping IDC headers onto a ribbon cable only takes a few seconds with the right tool. Note that you still need to provide power to all boards (master and slave) since only the 5V digital power rail is carried on the connecting cable. They will generate independent split analog supplies. With the power connections made and the programming headers joined, you just need to connect the audio inputs and outputs to your various channels, ensure JP1 is fitted only on the master board, then power it up and go through the regular testing procedure. Note that the SCLK pin is at opposite ends of programming header CON4 on the SMD and through-hole boards, so you can’t mix the different board types (at least not without re-routing that signal between them). Also note that if you want to connect an IR activity LED to multiple ganged Digital Pots, you will need to split out those two wires from the harness to go to the LED and series resistor. This simple cable allows the master & slave Digital Pot boards to be ganged up to make a four-channel volume control. It can be extended to three boards for six channels and so on. Australia's electronics magazine March 2023  39 Make amazing prints with our wide range of Resin & Filament for 3D Printers 0 OV E R 2 I N S RE S CK & IN S TO G! 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It allows you to turn a locomotive around at the end of a track and automatically reverses power to the rails, so they aren’t shorted out. The electronics are easy to build, while the other parts can be made with moderate machining skills. R ailway turntables have been around since 1830. Some early engines could only run in one direction, so there needed to be a way to turn them around. The solution was to lay rails on a bridge and then mount the whole assembly on a bearing. To reduce sag as the engine moved onto the ‘table’, four wheels on the bridge extremities transferred the weight to a circular rail that ran around the perimeter. Initially, the turntables were rotated by hand, but later on, they were motorised. I can remember as a young lad being fascinated that the driver and fireman could push a massive steam 42 Silicon Chip engine through 180° with little effort. In Australia, most major country towns on the railways had one. Still, once the steam era ended, they fell into decline as the diesel engines were double-ended; ie, they could be driven from both ends. As I run Peckett-style tank engines on my OO gauge model railway, I searched the internet for a suitably-­ sized turntable and found one at Swanage in the UK. I based my design on that, and you can see it operating in the video at siliconchip.au/Videos/ Model+Railway+Turntable If you have larger engines, the design can be used by increasing its Australia's electronics magazine dimensions. The only restriction is the maximum diameter that your lathe can turn. I am using a bipolar 200-step stepper motor to rotate the train deck. As you need to line up the moving rails with the stationary rails precisely, the motor is driven using eight micro steps. This means the motor moves through ⅛th of a step for each controller input pulse. To rotate it 180°, you need to pulse the motor 800 times, giving better accuracy than in single-step mode. The other challenge is that you need to provide power to the rotating rails and need to reverse the rail polarity once the turntable has rotated through siliconchip.com.au Fig.1: this diagram shows the order in which the major parts are assembled in the stack. The Spring Tension Spacer may not be required, or it might need to be thicker; that can be determined during final assembly. siliconchip.com.au Australia's electronics magazine March 2023  43 SPRING LOADED CONNECTOR PINS (ONE FOR EACH RAIL) ROTATING RAIL PLATFORM WHEEL ASS’Y RAILS WHEEL ASS’Y GIRDER INSULATOR SPRING TENSION SPACER STATIONARY RAIL PLATE CENTRING INSERT BOTTOM PCB (SEE BELOW) HEIGHT ADJUSTMENT SPACER STEPPER MOTOR (NEMA 17) TRAIN CONTROLLER NEGATIVE SUPPLY PCB HELD IN PLACE ON STATIONARY RAIL PLATE BY PINS THROUGH THESE HOLES TRAIN CONTROLLER POSITIVE SUPPLY BOTTOM PCB, VIEWED FROM THE PIN CONNECTION SIDE Fig.2: this ‘cutaway’ overview of the Turntable doesn’t include all the parts and details, but it shows how most of the parts go together. Fig.3: the Centring Insert fits inside the Housing and keeps the stepper motor and Turntable aligned. 44 Silicon Chip Australia's electronics magazine 180°. To achieve this, I used two goldplated spring-loaded pins (shown in Fig.2), one connected to each moving rail. The spring-loaded parts of the pin make contact with the tracks on the stationary gold-plated PCB below. Initially, the first pin is connected to the positive terminal of the controller and the second pin is connected to the negative pin. When the rails rotate through 180°, the connections are swapped. You will need a lathe and a milling machine to make the various parts. The rails must line up in both the vertical and horizontal planes, so it is essential that you use the dials (without backlash) on your milling machine to set the distance between holes and centre lines. Where possible, you should do all operations to the part in one session. To help align the rails in the vertical direction on the Turntable, I placed a grub screw near the end of each rail. By rotating the grub screws clockwise, I could jack up the rail and reduce the height by turning them in the opposite direction. Fig.1 shows the various parts that make up the Turntable. I will go through each one in detail. The materials needed are all shown in the parts list. #1 Centring Insert Photo 1 shows the Centring Insert (Fig.3) fitted into the Housing, made from a piece of 65mm diameter aluminium round bar. Its purpose is to hold the stepper motor axis precisely in line with the axis of the base, ie, on-centre. The critical dimension is the 22mm hole through its centre, which must match the size of the locating boss on the top of the stepper motor assembly. In boring the hole, when I was just below the 22mm diameter, I made 1/1000th of an inch (25-micron) passes until the stepper motor just slid into place. To do this, mount the bar in a three-jaw lathe chuck so that at least 8mm protrudes. Face the end and reduce the outer diameter to 64mm. Drill a hole 8mm deep in the centre using a centre drill, followed by a 5mm diameter drill. Transfer the chuck to the milling machine. Using a centre finder, locate the centre of the 5mm hole. Drill the eight holes, tapping the outer four for M3 and countersinking the inner four holes. Return to the lathe and use a boring tool to enlarge the 5mm hole siliconchip.com.au Photo 1: the Timber Housing (base) with the Centring Insert and stepper motor already inside it. Photo 2: the timber Housing in the process of being turned. Note how the raw timber has been cut into a roughly octagonal shape to make turning it a bit easier. to 22mm, as described above. Part off and face the other side to a thickness of 4mm #2 Timber Housing The critical dimensions of the Timber Housing are the diameter and depth of the 64mm hole into which the Centring Insert fits (see Fig.4). It should fit tightly, and the top surface should be a few thousandths of an inch (about 0.1mm) below the bottom of the 120mm diameter hole. Start with a 140 × 140 × 45mm pine off-cut. To save time, cut off the corners to make it roughly octagonal, with the inscribed circle having a diameter of about 140mm. Use six wood screws and washers to mount the timber central on the lathe face plate (see Photo 2). Turn the outside diameter to 135mm for a length of 35mm. Drill a hole in the centre 35mm deep using a centre drill, followed by a 13mm drill. Fit a boring tool and cut the 120mm diameter hole to 18.6mm deep (see Photo 3). Next, bore out the hole for the Centring Insert as described above. Use a 400-grit emery cloth to smooth the surfaces. Fit the Centring Insert (shown in Photo 1) and, using a 2.5mm diameter drill and the centring piece as a template, drill the four holes that hold it in place. Next, enlarge the four holes in the Housing to 3mm diameter. Align the x/y coordinates of the milling machine with the four mounting holes. Using a 3/8in or 10mm end mill, cut out the rectangular clearance hole for the stepper motor to a depth of 12mm. Check that the stepper motor clears the cutout. siliconchip.com.au Fig.4: the Timber Housing forms the base of the Turntable with the stepper motor inside. The stationary Rail Plate fits inside it and the Turntable part rides on that. This diagram is shown at 75% of actual size. All cutting diagrams will be available for download on the Silicon Chip website. Australia's electronics magazine March 2023  45 Photo 3: at this stage of the turning, the timber Housing is almost complete. Fig.5: the Height Adjustment Spacer fits between the Centring Insert and Stationary Rail Plate. Its purpose is to allow you to adjust the height of the top of the Rail Platform to match the height of the top edge of the Housing. Photo 4: this shows the semi-rectangular recess in the Housing underside, where the stepper motor is mounted. While there, drill the 3.5mm clearance hole for the Rail Plate mounting and the two ¼in (or 6.5mm) holes for the rail power exit holes for the wires. The latter two are elongated at an angle using a round file. This makes it easier to get the wires through in the assembly process. Returning to the lathe, the next step is to machine the rear of the Housing, so it is the correct depth. Use a three-jaw chuck fitted with reverse jaws to hold the machined side against the chuck face, so it runs true. To prevent the timber from splitting when the jaws are expanded, fit a pipe clamp around the perimeter of the Housing (see Photo 4). Use a wood saw to reduce the thickness to about 30mm. Face the end to the finished thickness and clean up all the holes. Using four M3 × 10mm screws and shake-proof washers, fit the Centring Insert into the Housing. Attach the stepper motor using four M3 × 6mm countersunk head screws – refer to Fig.1. #3 Height Adjustment Spacer Photo 5: the Rail Plate inside the Timber Housing. Note that this was taken before all the holes were drilled. 46 Silicon Chip The purpose of the Spacer (Fig.5) is to allow you to adjust the height of the Rail Platform relative to the top edge of the Housing. I made mine from a piece of scrap PCB material 1.6mm thick. The Spacer is to eliminate any variation in material thickness and machining tolerances. You may have to experiment with its thickness or make it out of several pieces to get the correct height. You won’t know this until after the final assembly. #4 Rail Plate The Rail Plate (Fig.6) is a slide fit Australia's electronics magazine into the Housing and, as the name suggests, it has a circular rail on its perimeter for the four support wheels to run on – see Photo 5. These take the weight of the locomotive as it moves onto the Platform. It has grooves cut into the underside for the rail power wires. It is made from a piece of ¼in (6.35mm) thick aluminium plate. To save machining time, I used a hacksaw to cut out a hexagonal piece inscribed on a circle of about 124mm diameter. To enable it to be mounted on the face plate of the lathe for machining, drill and tap four holes marked A as shown in Fig.6. Depending on your face plate size and shape, you may have to move the position of these holes. Drill a further 3mm hole in the centre to centre the workpiece. Mount it to the lathe using M4 machine screws and washers with a piece of Masonite between the faceplate and workpiece, so it runs true. Face the surface, then turn the outside diameter (approximately 120mm) so that it is a slide fit in the Housing. Enlarge the centre hole to 10mm and then use a boring tool to reduce the inside to a depth of 2.7mm and a diameter of 109.6mm. Change over to an RH tool and reduce the outside depth by 2.7mm so that you end up with a rail width of 1.2mm. Using emery cloth, slightly round the top edges of the rail and smooth the Rail Plate surface. The rear of the Rail Plate now has to be machined to size. Remove the plate from the face-plate and remount it so its rear is facing away from the chuck. As you are only facing the surface, it is not essential to set it running true. siliconchip.com.au Fig.6: the Rail Plate fits inside the Timber Housing and is the stationary part, with the Turntable assembly riding on it by the Wheel Assemblies. Holes A are temporary holes used to fix the job to the face plate when machining. They are 3.3mm diameter tapped to M4 and spaced 30° from horizontal on a 40mm radius from centre. Fig.7: the Locating Pins keep the Contact PCB stationary, locked to the Rail Plate while the Turntable rotates above it. Reduce the plate width so that the dimension between the bottom of the rail and the back of the plate is 3.3mm. Remove the job and transfer it to the milling machine to drill the holes and cut the grooves for the wires on the bottom. To centre the job, I turned a piece of scrap aluminium into a disc that was a slide fit in the 10mm hole in the centre of the Rail Plate. I drilled a 5mm hole in the centre of the disc. I then clamped the job down and using precision drilling, bored and tapped holes as shown in the drawing. I loosely clamped the job onto the base of the milling machine and, with a centre finder in the drill chuck, moved the job until the centre finder moved true. I then clamped the job down and, using precision drilling, bored out the holes. Finally, I used a 1/8in (3.2mm) diameter slot drill to cut the grooves for the wires. Now make and fit the Locating Pins siliconchip.com.au for the PCB – see Fig.7. Cut two 4.6mm lengths of 1.5mm diameter brass rod. Clean the ends up using the lathe, then use Loctite 620 to glue them in place into the Rail Plate, in the holes marked F. The last job is to fill the four 4mm holes that were used to mount the job in the machining process. I made a piece of threaded M4 aluminium rod and chopped it up into four 3.5mm lengths. I applied Loctite 620, fitted them in the holes and ground off the excess material. #5 Spring Tension Spacer This is a small washer made of 0.25mm card that is placed under the PCB (see Fig.2). This increases the height of the PCB and hence the tension in the contact. #6 Contact PCB This will be available as a gold-plated Australia's electronics magazine Fig.8: the gold-plated Contact PCB is responsible for transferring power from the stationary Housing to the rotating Turntable above. The springloaded pins moving on its tracks reverse the polarity of the power to the rails as it passes through 90°. March 2023  47 Photo 6 (below): the Contact PCB used in the prototype is not gold-plated like the commercial version we’re making available, but it does the same job of transferring power to the rails. Photo 7 (right): this photo shows the Girder and Wheels attached to the Rail Platform along with the Insulator, springloaded pins and wires connecting the rails to those pins. You can also see where the Fence Posts are glued into holes along either side of the Rail Platform. PCB coded 09103232 (see Fig.8). It is held in place by the brass pins in the Rail Plate and the tension of the springloaded pins. #7 Girder This is made from a 118mm length of rectangular aluminium extrusion, 30 × 15 × 2mm (see Photo 7). You can purchase this from Bunnings in one-metre lengths. Take some time to locate the exact centre, then use a centre drill to drill a hole there, followed by the hole sizes shown in Fig.9. Precision drill all the holes on the top surface. Next, tap the two 1.4mm holes at the ends with 10BA threads. Note that two of the 2.3mm diameter holes are countersunk. The next step is to mill the sloping sides. To save milling time, use a hack saw to remove as much material as possible. Mount the 15mm sides between the jaws of the vice on the milling machine. Rotate the vice 3° and, using a long series end mill, cut the taper at one end until the desired thickness is reached. Repeat for the other end. Mill the thickness to the correct size. #8 Centring Bush As this part is a slide fit into the Girder, you should make it after the Girder is completed. Chuck a piece of 12mm diameter brass rod and reduce the outside diameter to 10mm for an 8mm length. For 1.9mm from the end, further reduce the outer diameter so that it is a slide fit into the 7.5mm hole in the centre of the Girder (see Fig.10). Using a centre drill, followed by a 5mm drill, bore a hole into the end for Fig.9: the Girder sits under the Rail Platform, strengthening it so that it doesn’t flex when the locomotive is driven onto the rails above. 48 Silicon Chip Australia's electronics magazine 8mm. Part off the piece to a finished length of 7.9mm. Transfer the part to the drill press, then drill and tap the hole for the 2.5 × 3mm grub screw. After that, fit the grub screw. The last operation is to glue the Bush into the Girder using Loctite 620 in the 7.5mm hole and drill the Allen key access hole for the grub screw. From the drawing, mark where the Allen key access hole should be. Insert the Bush in place and check that the tapped hole in its side lines up with the marked hole. When correct, drill the 1.8mm hole. When gluing it in place, make sure that the Bush is in the correct location by inserting an Allen key into the hole so that it fits into the grub screw and is at right angles to the side of the Girder. #9 Insulator This is made from a 38 × 25mm piece of blank PCB material (see Fig.11; FR4 fibreglass laminate). Locate the centre of the PCB and use precision drilling to drill the seven holes. Start each hole with a centre drill. The imperial drill size for the 3.97mm hole is 5/32in; the spring-loaded pins are a push-fit Fig.10: the Centring Bush ensures that the Rail Platform rotates evenly about its centre on the stepper motor shaft. siliconchip.com.au Photo 8: this shows how the Wheel Assemblies are mounted to the bottom of the Rail Platform. Ensure they’re angled correctly so the platform rotates smoothly about its centre. Fig.11: the Insulator prevents the pins carrying current to the train tracks from shorting onto the Rail Platform. into them (4mm is close enough if you don’t have a 5/32in drill). (1.6mm) thick sheet of aluminium (see Fig.13). Cut out a piece 50 × 118mm. Find the centre and inscribe a 59mm radius. Using a linisher, cut out the inscribed curved ends. Precision-drill all the holes, remembering that, except for the 2mm diameter holes, they must align with the Girder holes as shown in Fig.9. Countersink the six marked holes and clean off any burrs using emery cloth. #10 Wheel Assemblies The four wheels each consist of three parts: the wheel, the axle and the Housing (see Fig.12 & Photo 8). The wheels are made from ½in brass round bar stock. Face the end and turn the outside diameter to 7.9mm for 3mm. Use a centre drill followed by a 1mm drill to bore out the hole for the axle. Part off for a length of 2mm. Repeat for the other three wheels. For the axles, cut off four 7mm lengths of 1mm diameter brass rod. Clean up the ends in the lathe. The wheel housings are a bit more complicated. As I had to make four of these to the same accurate size, I first milled out a 70mm length of 5 × 7.5mm rectangular aluminium bar. I then mounted it in the vice with the 7.5mm side horizontal and then, using a 3/32in (2.4mm) slitting saw mounted in the chuck, cut the wheel slot 6.7mm deep. Next, I drilled the hole for the axle using a centre drill followed by a 1mm drill. I rotated the job so that the 5mm side was horizontal, then drilled and tapped the 1.8mm hole with an 8BA thread. The distance between this hole and the axle hole should be precisely 6.4mm. Cut off to length and create the 2.5mm radius using a linisher. Repeat for the other three housings. Fit the wheels and axles and, using a dob of Loctite Extreme Glue Gel (available from Bunnings), lock the axles in place. #11 Rail Platform The Platform is made from a 1/16in #12 Fence First, you need to cut 14 Posts 17.8mm in length from hollow 1/16in (1.6mm) square rod, as shown in Fig.14. Once cut, clean any burrs from the ends. Next, use the drilling machine at high speed to drill the holes for the wires to go through (see Fig.15). Again, clean off any burrs. Fig.12: these pieces make up the Wheel Assemblies that allow the rotating Rail Platform to ride on the Rail Plate. Fig.13: the Rail Platform is the rotating part of the Turntable that the train tracks are mounted to. Fences are fitted on either side to make it look realistic. siliconchip.com.au Australia's electronics magazine March 2023  49 Fig.14: these Posts are the vertical parts of the fences on either side of the train tracks. To make the rails for the Fence, cut four 100mm lengths of 0.5mm diameter brass rod. Insert the Posts into the Rail Plate and thread the 0.5mm rails through the Posts on both sides. Use Loctite Extreme Glue Gel to set the Posts and wires. #13 Rails/Tracks The locomotive rails are made from a length of R600 Hornby rail. Reduce the rail length by removing an equal amount from each end so the final length, as shown in the drawing, is 117mm. Clean up the cuts with emery cloth. Check that the existing 1.4mm holes are 90.4mm apart, then enlarge them to 1.8mm. As mentioned earlier, four 2.5mm grub screws should be inserted in the ends of the rail sleepers to adjust their final height. So drill four 2mm diameter holes in the sleepers, as shown in Fig.16, and tap them 2.5mm. Finally, to enable electrical contact Photo 9: The painted top side of the Rail Platform with the rails and Fences attached. Everything is painted matte black except for the rails, so that power can be transferred to the model locomotive. to be made to the rails, carefully remove the plastic shown in red in Fig.16. #14 Painting I sprayed the Rail Platform with two coats of black Rust-oleum Ultra Matte (available from Bunnings). At the same time, I sprayed the heads of six of the 8BA × ¼in screws and the sides of the Girder. I sprayed the top and inside edge of the timber Housing with rust-­coloured paint. Mask the edge of the Rail Plate and spray its top with a couple of coats of Riviera Grey Dulux Duramax Chalky Finish. When dry, use emery cloth Fig.15: here’s how the Fences are mounted on either side of the Rail Platform. Fig.16: the rails/tracks come pre-made but you need to make some modifications. After cutting them to length, some holes need to be added, others enlarged and a couple of pieces of the plastic insulation cut away so the springloaded pins can make contact with the conductive tracks. 50 Silicon Chip Australia's electronics magazine to remove the paint from the top of the rail. #15 Control electronics The chosen stepper motor is a bipolar type rated at 1A per phase and 200 steps. As mentioned earlier, we need to operate it in 1/8th step mode to achieve sufficient accuracy. The Allegro A3967 IC is ideal for the task and provides additional inputs to reverse the motor, regulate the motor drive current and has a 5V DC regulated output to power the driver microprocessor. When I went to purchase the A3967 IC, I found it much cheaper to buy it mounted on a small module named “Easy Driver stepper motor driver”. This also has the advantage that you don’t have to solder surface-mount components. The circuit diagram, Fig.17, shows that the module has four outputs to connect the two windings of the stepper motor. Two other inputs, MS1 and MS2, determine the number of steps per positive going pulse on the step input according to Table 1. As we want 1/8th steps, we leave those terminals unconnected and allow the internal pull-up resistors to keep them high. An enable input turns the driver on when low and off when it is high. Finally, if you ground the direction input, the motor will turn in the opposite direction. To turn the motor through 360° with the Full Step setting, we need to apply 200 pulses. In our case, we only want it to rotate through 180°, but as we are using it in the 1/8th step setting, we will need to apply 800 pulses on the step input. siliconchip.com.au Fig.17: most of the circuitry in the control module is within the Easy Driver stepper motor driving module (yellow shaded box). IC1 sends it signals when pushbutton S1 is pressed to rotate the platform by 180°. The pulse width and the delay between each pulse determine the Turntable rotation time. We are using a PIC12F675 microcontroller to generate the pulses. Its GP2 input (pin 5) is set to interrupt the microprocessor when it goes low, ie, when you press pushbutton S1. The 100nF capacitor from that pin to ground eliminates any contact bounce. The interrupt routine causes digital output GP1 (pin 6) to go low, enabling the motor, and produces 800 positive siliconchip.com.au pulses from the GP0 digital output (pin 7) that step the motor through 180°. At the end of the routine, GP1 goes high again, disabling the stepper motor. #16 PCB assembly The circuit is built on a 56 × 51mm PCB coded 09103231 that the Easy Driver module is mounted on, shown in Fig.18. Header pins are used to make the wire connections to the power supply, pushbutton and stepper motor. Start by fitting the male header pins Australia's electronics magazine (not the ones for the Easy Driver), the 8-pin IC socket, and the capacitors. Of the capacitors, only the 100µF type is polarised; its longer lead must Table 1 – steps per input pulse MS1 MS2 Resolution low low Full Step (two-phase) high low Half step low high Quarter step high high Eighth step March 2023  51 be soldered to the right-hand pad labelled “+”. The IC socket should also be installed the right way around, with its notch to the left. The reason for the IC socket is so that, if we wish to change the program, we can remove the microcontroller and reprogram it. Now add the resistors; they are mounted vertically. The wire link can be made from a leftover resistor wire off-cut; however, if you purchase the PCB from Silicon Chip, it will be a double-sided board, so the wire link is not needed. Fit the PIC12F675 microprocessor in the socket. If you have purchased this from the Silicon Chip Online Shop, it will already have the firmware loaded. If you wish to do this yourself, you can download the files from the Silicon Chip website. To enable the Easy Driver module to be removed, it is socketed. Cut apart the socket strip into five pairs of pins, one three-pin strip and one four-pin strip and solder them to the positions that will be under the Easy Driver. Insert matching male header pins into the sockets, drop the Easy Driver module on top, ensuring all the pins go into its pads, then solder them in place. #17 wiring & testing Check the PCB for solder bridges and dry joints, then wire up the 12V DC socket, stepper motor and the normally-­open pushbutton switch, as shown in Fig.18. The other connections are not used. Before switching on the power, double-­check the power supply polarity connections. The Easy Driver and PIC could be destroyed if they are the wrong way around. Temporarily remove IC1 from its socket. Switch on the power, and the LED on the Easy Driver module should glow. Use a voltmeter to check that you have 5V between pins 1 & 8 of IC1. If it’s OK, switch off the power, wait for the capacitors to discharge, then plug IC1 back into its socket. Next, set the current limit by powering it back up and adjusting the trimpot on the Easy Driver so that there is +4.2V between TP1 and ground. Then press the pushbutton, and you should see the stepper motor shaft rotated through 180°. Press it again, and the shaft should return to its original position. The Easy Driver board has two pairs of shorting pads on it. The first, if closed, reduces the output voltage to 3.3V, while the second enables the 5V output. When supplied, the first link is usually open but the second is closed. If you aren’t getting 5V out of it, check that both are set correctly. The circuit diagram and documentation for the Easy Driver are available at www.schmalzhaus.com/EasyDriver/ #18 mechanical assembly Attach the Insulator with the spring-loaded pins to the underside of the Girder using two unpainted 8BA x ¼in screws and nuts. Next, place the Rail Platform on top of the Girder. Use two painted 8BA × ¼in screws and nuts to join them together. Solder 50mm lengths of hook-up wire to the bottom of each rail (where you removed the plastic), ensuring that the wire insulation goes all the way up to the solder joints. Place the rail over the Rail Platform assembly and insert the wires through the holes marked “D” in the Rail Platform and the Girder. Fit the two 10BA × 3/8in screws, but leave them finger-tight at this stage. Solder the wires to the spring-loaded pins, leaving slack, as shown in Photo 7. Attach the Wheel Assemblies to the Rail Platform using the four remaining painted 8BA screws. The stepper motor, Centring Bush and Housing can now all be assembled as in Photo 1. Fit the Spacer over the stepper motor shaft, followed by the Rail Plate. Use 16mm M3 screws plus extra washers to fit the Rail Plate so that the end of the screws are flush with the plate. The next task is to get power to the Contact PCB. Cut two 300mm lengths of good-quality hook-up wire of different colours and strip away about 3mm of insulation from one end of each wire. Tin the ends and insert the wires into the board from the component side and solder them in place. Use as little solder as possible, as we don’t want any solder on the springloaded contact pins tracks on the PCB. Hold the PCB with the copper side up and feed the wires through the grooves and holes until they exit from the bottom of the Housing. Using a marking pen, place a mark on the edge of the Rail Plate that can be seen from the top, as shown in Fig.6. This mark Fig.18: both the PCB assembly and wiring are straightforward, as shown here. IC1 and the Easy Driver module are both socketed to make replacement and reprogramming (of IC1) simpler. 52 Silicon Chip Australia's electronics magazine siliconchip.com.au will be used later in positioning the Turntable in the final layout. The PCB should now be flat on the Rail Plate and held in place by the two Locating Pins. Strip the ends of the wires and, using an ohmmeter, check that there aren’t any shorts to the Rail Plate. Loosen the grub screw in the Rail Plate assembly and slide it over the stepper motor shaft. Loosen the screws on the Wheel Assembly to adjust their angles so that the wheels align with the track on the Rail Plate. Re-tighten the screws. Push it all the way down until the wheels make contact with the Rail Plate and note how much the springloaded contact pins compress. Ideally, this should be about 1mm. If it is less than 1mm, this can be increased by adding the Spring Tension Spacer, a small washer about 20mm in diameter with an 8mm hole in the centre made from 0.25mm card. It is placed under the Contact PCB. Next, check the level of the bottom of the rails in relation to the Housing side. If it is too low, you can adjust the height by increasing the thickness of the Height Adjustment Spacer. If all is well, tighten the 2.5mm grub screw in the Bush. You should now be able to rotate the Rail Plate assembly freely using your fingers. Connect an ohmmeter to one rail and the other end to one of the wires protruding from the base. Now rotate the Rail Plate assembly; depending on its position, it will either be a short circuit or open-circuit. Do the same for the other rail. #19 homing the stepper motor When you apply power to the circuit (with S1 not pressed), the motor windings receive power for a short time, causing the stepper (rail bridge assembly) to lock in one position. If you rotate the rail bridge less than 7.2° in either direction, on switching the power off and on, the rail bridge will return to the original position. There are 50 positions 7.2° apart at which the motor will lock in place. We need to pick one of these for the point at which the Turntable track and the train entry tracks align. This way, the bridge and entry tracks will be aligned when you switch the power on. #20 final set-up My layout is built on polyurethane siliconchip.com.au Parts List – Model Railway Turntable 1 12V DC 500mA+ plugpack 1 17HS08-1004S 1A 16Ncm stepper motor [eBay] 1 gold-plated Contact PCB coded 09103232, 29 × 29mm 1 assembled control module (see Fig.18) 1 chassis-mounting DC barrel socket (to suit plugpack) various lengths and colours of medium-duty hook-up wire Fasteners 2 M3 × 16mm Phillips panhead machine screws 4 M3 × 10mm Phillips head machine screws 4 M3 × 6mm countersunk head machine screws 6 M3 shakeproof washers 5 M2.5 × 3mm grub screws 8 8BA × ¼in countersunk screws [E & J Winter ] 4 8BA nuts [E & J Winter ] 2 10BA × ⅜in hex head bolts [E & J Winter ] Other hardware 2 Mill Max 0861015208214110 spring-loaded contacts [element14 2751176] 1 70 × 70mm × 1.6mm piece of copper-laminated FR4 (unetched clad PCB) 1 25 × 28mm × 1.6mm blank FR4 laminate (unclad PCB) 1 Hornby R600 rail [K&S Metals] 1 round aluminium bar, 65mm diameter, 15mm long 1 140mm × 140mm × 45mm piece of pine 1 125mm × 125mm × 6.35mm aluminium plate 1 120mm length of 30mm × 15mm × 2mm hollow rectangular extruded aluminium tube [Bunnings 1130544] 1 30mm length of ½in diameter brass round bar 1 35mm length of 1mm diameter brass round bar [K&S Metals] 1 10mm length of 1.5mm diameter brass round bar [K&S Metals] 1 70mm length of 12mm × 12mm square aluminium bar 1 300mm length of hollow 1/16in square brass bar [K&S Metals] 1 400mm length of 0.5mm diameter brass round bar [K&S Metals] 1 20 × 20mm piece of 0.25mm-thick card 1 small container of Loctite Extreme Glue No Drip Gel [Bunnings 0273717] 1 small container of Loctite 620 retaining compound [AIMS Industrial A0116625] 1 spray can of Rust-oleum Ultra Matte black paint [Bunnings 0197886] 1 spray can of Duramax Rust Effect Spray Paint or similar [Bunnings 0195384] 1 spray can of Dulux Duramax Chalky Finish Riviera Grey paint [Bunnings 1400964]  or another specialised fastener supplier Control module parts 1 single-sided or double-sided PCB coded 09103231, 56 × 51mm 1 Easy Driver stepper motor driver [Core Electronics ROB-12779] 1 PIC12F675-I/P 8-bit microcontroller programmed with 0910323A.HEX, DIP-8 (IC1) 1 8-pin DIL IC socket 1 SPST miniature pushbutton switch [Jaycar SP0710] 1 40-pin header, 2.54mm pitch [Jaycar HM3212] 1 40-pin female header, 2.54mm pitch [Jaycar HM3230] 1 100μF 16V radial electrolytic capacitor 2 100nF 50V ceramic, MKT or multi-layer ceramic capacitors 2 10kW 1% ¼W axial resistors 3 6.8kW 1% ¼W axial resistors Australia's electronics magazine March 2023  53 Fig.19: you need to ensure the tracks are aligned vertically and horizontally between the fixed and rotating sections before using the Turntable and that the wiring polarity is correct, so there is no voltage between the co-linear track sections. sheets, so all I had to do was cut a hole the same diameter as the Housing for the Turntable to fit in. The same would apply to layouts built of other materials. The centre of the hole should lie on the projection of the centre line of the entry track at a distance of 59.6mm from the end of the entry track. Fit the Turntable so that the top of the Housing is flush with the surface of the layout and the middle of the external track entry is roughly in line with the mark you previously placed on the Rail Plate. Switch the power on and off to find the homing position of the Turntable track. Once found, rotate the Turntable so the entry track lines up with the Turntable track. Switch the power on and press the rotate push button. If all is well, the other end of the Turntable track should align with the entry track. If not, the Turntable track isn’t aligned exactly in the centre of rotation. You can correct this by elongating the 1.8mm holes for the 10BA screws, allowing you to slightly move the position of the Turntable track on the rail bridge. The last job before tightening the 10BA screws is to adjust the height of the ends of the Turntable track to match those of the entry track. We now need to connect the train controller power to the Turntable track. If it is the wrong way around, the power supply will be shorted out when the engine wheels hit the Turntable track. With no engine on the track, connect the Turntable to the power supply so that there isn’t any voltage between the connecting tracks, as shown in Fig.19. #21 operation Switch the power on and use your train controller to shunt the engine slowly onto the Turntable. Press the rotate button, and when the table stops rotating, back the engine out. SC 54 Silicon Chip Australia's electronics magazine siliconchip.com.au PRODUCT SHOWCASE Electronex arrives in Melbourne this May Electronex, the electronics design and assembly expo returns to the Melbourne Convention and Exhibition Centre on the 10-11th of May 2023. Electronex is Australia’s pre-­ eminent exhibition for companies using electronics in design, assembly, manufacture and service in Australia. The SMCBA Electronics Design and Manufacture Conference will also be held, featuring technical workshops from international and local experts. In an exciting new development, Electronex will be co-located with Australian Manufacturing Week, with trade visitors now able to visit both events on Wednesday or Thursday. This allows visitors to see the entire spectrum of the latest products, technology and turnkey solutions for the electronics and manufacturing sectors. Attending this event is a must for designers, engineers, managers and other decision-­ makers involved in designing or manufacturing products that utilise electronics. The expo will showcase a wide range of electronic components, surface mount and inspection equipment, test and measurement and other products and services. Companies can also discuss their specific requirements with contract manufacturers that can design and produce turnkey solutions. Register to attend for free at www.electronex. com.au Australasian Exhibitions and Events Pty Ltd Suite 11, Pier 35-263 Lorimer St Port Melbourne VIC 3207 Tel: (03) 9676 2133 mail: ngray<at>auexhibitions.com.au Web: www.auexhibitions.com.au Nordic Semiconductors new nRF7002 companion IC for WiFi 6 The nRF7002 is a low-power WiFi 6 companion IC providing seamless dual-band connectivity (2.4 & 5GHz). The nRF7002 can be used together with Nordic’s nRF52 & nRF53 series multi-protocol SoCs and the nRF9160 cellular IoT SiP (LTE-M/NB-IoT) . But it also can be used in conjunction with non-Nordic host devices. The nRF7002 brings low power and secure WiFi to the IoT sphere. The dual-band IC complies with Station (STA), Soft Access Point (AP), and WiFi direct operation, and meets the IEEE 802.11b, a, g, n (“Wi-Fi 4”), ac (“5”), and ax (“6”) standards. It also works with Bluetooth LE, Thread, and Zigbee. The nRF7002 supports Target Wake Time (TWT), a key WiFi 6 power saving feature. Interfacing with a host processor is done via SPI or Quad SPI. The IC offers a single spatial stream, 20MHz channel bandwidth, 64 QAM (MCS7), OFDMA, up to 86Mbps PHY throughput, and BSS coloring. The nRF7002 is the ideal choice for implementing low power SSID-based WiFi locationing when used together with the nRF9160 and nRF Cloud Location Services. This is all supported by the devel- opment kit. The dev kit includes an nRF7002 IC and features an nRF5340 multi-protocol SoC as a host processor. The nRF5340 embeds a 128MHz Arm Cortex-M33 application processor and a 64MHz network processor. The dev kit includes: Arduino connectors; two programmable buttons; a WiFi dual-band antenna and a Bluetooth LE antenna, and current measurement pins. The nRF7002 companion IC and dev kit are available now from Nordic’s distribution partners. Nordic Semiconductors www.nordicsemi.com High current inductor for automotive applications Würth Elektronik introduces another AEC-Q200 certified SMD inductor: the WE-XHMA. It features an extremely high current capability of up to 50.6A saturation current and the ability to handle high current transient peaks. Its design with a flat wire coil and composite core material ensures low copper losses and stable behavior under temperature fluctuations. siliconchip.com.au The WE-XHMA is particularly suitable for use in DC/DC converters for high current supply and FPGAs, as well as filter applications. In contrast to conventional core materials, the compact coil shows hardly any temperature-­dependent fluctuations in terms of inductance and saturation current. The higher energy density and the compact design make it useful for switch-mode power supplies. Furthermore, it shows a lower skin effect at higher frequencies and the heat dissipation towards the circuit board is also Australia's electronics magazine better than round wire. The compact molded magnetically shielded coils have an operating temperature range of -40°C to +125°C. The WE-XHMA is available in SMT styles: 6030, 6060, 8080, 1090 and 1510. You can also choose between saturation currents from 9.3 to 50.6A. Free samples for developers are provided. Würth Elektronik Max-Eyth-Straße 1 74638 Waldenburg Germany www.we-online.com March 2023  55 Altium Designer 23 Review by Tim Blythman Altium Designer 23 is the latest version of Altium’s EDA (electronics design automation) software, released in December 2022. Since we use Altium Designer practically daily to draw circuit diagrams and lay out PCBs, we were keen to see what new features have been added. W e have used Altium Designer to create PCBs for projects for many years, counting back around 30 years if you include its predecessor, Protel Autotrax. You can still download Autotrax from the Altium website (www.altium. com/documentation/other_installers), although you will likely need a DOS emulator such as DOSBox to run it. Of course, it has evolved a lot since then. Sometimes the yearly updates are ‘revolutionary’ while others are ‘evolutionary’. While the latest updates are more in the latter category, several of the new features are very handy, and we will certainly be using them. Other changes streamline the workflow for existing features, which is always welcome. Previous versions of Altium Designer have seen substantial improvements, including complete code rewrites of the Schematic Editor (AD20) and PCB Editor (AD18), as well as integration with the Altium 365 cloud tool. Our last ECAD review was of Altium Designer 22 in the June issue last year (siliconchip.au/Article/15348). That built on our review of Altium 365 and Altium Designer 21 from January 2021 (siliconchip.au/Article/14705). Altium 365 is Altium’s ‘cloud’ tool which can be used on its own through a browser and is also integrated into versions of Altium Designer from Altium Designer 20 onward. Most of the features of Altium Designer are only available to paid subscribers, but this review also mentions some free online tools. For example, Altium 365 has a free online file viewer at www.altium.com/ viewer/ and you can register for a free Altium account to access the features of Altium 365 Basic. Altium Designer is used widely in industry by companies who design much more complex and exacting designs than us; many new features, past and present, are aimed at such companies. Still, some new features are just as valuable for small organisations like Silicon Chip. This review is of Altium Designer version 23.0.01; you might see even more updates and features if you use a later version. A minor version update appears about once per month. We shall now look at some of the improvements in AD23, describing them one by one. Gerber export Screen 1: the new Gerber Setup page places all the essential settings on a single tab. It is much simpler to use than the older version, which has five different tabs. 56 Silicon Chip Australia's electronics magazine Gerber files (also known as RS-274X) are sent to PCB manufacturers for making the actual PCBs. So the correct specifications and units (!) must be used when generating these files. A new version of Altium Designer’s Gerber file generation dialog box is now available, shown in Screen 1. This was enabled by default on our installation of Altium Designer 23, but appears to siliconchip.com.au have become available earlier in 2022. This is a much simpler and more succinct view than the older dialog box, which had five tabs and many selections we used sparingly, if at all. From now on, we will be using the newer dialog box for our Gerber file exports. If it is not enabled, you can change that by ticking the UI.Unification.GerberDialog setting under Advanced options on the System → General page of the Preferences dialog box. Screen 2: file comparisons can be made from this window by selecting two different files, including schematic, PCB, Gerber and BOM files. Here we chose two different versions of the same project PCB. File comparison Altium Designer 23 introduces a File Comparison tool that can work with schematics, PCBs, Gerber files and BOMs (bills of materials). Since we occasionally need to update designs to account for errors, improvements and even alternative parts, seeing the differences between file versions can be extremely useful. In the past, we often had to resort to a ‘flicker test’, rapidly switching between the two files so that our eyes could pick out the differences. That relies on aligning them properly and fast switching, and is error-prone, so thank goodness we won’t have to do that anymore! The option is found under the Project → Show Differences menu item and the dialog box, seen in Screen 2, allows two files to be chosen for comparison. Screen 3 shows two versions of our Advanced SMD Test Tweezers PCB with the differences listed at left and highlighted on the right. In this case, we moved a header slightly between the two versions. Clicking on the listed items highlights them in the PCB view. Besides comparing different revisions, such a tool could also be handy for reverse-­ engineering or recreating a design. If you have online access to projects via Altium 365, you can perform a file comparison via a project’s History in the browser interface, as shown in Screen 4. There’s even a version of the tool that does not require an Altium account, although it only works for Gerber files. It can be found on the web at www.altium.com/gerber-compare/ (output shown in Screen 5). Screen 3: when two files are compared, their differences are listed on the left and shown graphically at right, by highlighting the component or track that varies. Design Reuse Blocks A Reuse Block is a circuit snippet that can be added as though it were a component. At first glance, a Reuse Block seems like a module, and in siliconchip.com.au Screen 4: Altium 365 also allows projects to be compared over their history. A commit (file version) can be selected, and individual files can be compared with other versions, as seen here. Australia's electronics magazine March 2023  57 Screen 5: Gerber files can be compared with the free online tool at www.altium. com/gerber-compare/ This shows two versions of the Advanced SMD Test Tweezers, with red and green colour coding for the differences. Screen 6: to try out the Design Reuse Blocks feature, we created this block consisting of a microcontroller and a handful of passive components. The circuit snippet can now be placed in either a schematic or PCB file and added as needed. many cases, could be interchangeable. Reuse Blocks can be accessed from the Design Reuse panel (from the Panels button). Crucially, it can consist of a schematic document and a PCB document, but it doesn’t need to have both. As the name suggests, it is a document snippet that could be used in multiple projects. The standard workflow is to lay out the schematic, including wiring, then lay out and route the PCB block. It can then be placed as a ‘component’ from the Design Reuse panel. One scenario where this would come in handy is if a part of a circuit is subject to specific routing requirements due to speed or RF emissions. This routing becomes part of the Reuse Block. Or you may want to build a six-channel amplifier, in which case you can design one channel and then place it six times. Updating the original will affect all six channels. Once you have created and used a block, you can easily drop it into other designs where the remainder of the circuit can be routed around the existing embedded routing. This is also a way to reuse known-good designs with minimal testing and validation. The schematic module can be placed as a group of components, as it would appear on the schematic, or as a ‘black box’ module, where connections can be made to named ports. 58 Silicon Chip Such a block can be created by copying and pasting part of an existing design (schematic, PCB file or both) or made from scratch. Screen 6 shows a Reuse Block that we created. This consists of a microcontroller and its essential passive devices; the routing creates a compact unit that can be built on. This feature would be convenient if you are doing a lot of similar designs with common building blocks. It also simplifies using a common inventory, as the same components are guaranteed to be used in the blocks. A Reuse Block can also be saved into the Altium 365 cloud to be made accessible across larger teams. Pin functionality This feature will be especially handy for those who often work with microcontrollers but could apply to other components too. As you might realise from our recent microcontroller reviews, such as in the October 2022 issue (siliconchip.au/Article/15505), those parts are becoming more powerful and versatile. In particular, more peripheral features are being added, and these features are often available on many pins. Conversely, each pin on a microcontroller usually has many possible functions. Parts like the PIC16F18146 allow any of the many digital peripherals to Australia's electronics magazine ◀ be mapped to any of a group of 17 pins. You’ll often see on our schematics the numerous roles assigned to various pins, which may include multiple functions. For example, one of the pins used for programming may have a different function during regular operation, when a programmer is not connected. Depending on the chip, it can be quite an art to juggle the available peripherals between the pins that are available for multiplexing, especially when considering the PCB routing. The Pin Functionality feature of Altium Designer 23 allows the pins to be labelled with the function that is actually used in a particular application. This can be helpful in several ways. Firstly, each pin can be associated with a list of functions it can provide. This will allow those involved with ‘schematic capture’ (drawing up circuit diagrams) to ensure that the correct pins are used for the correct purpose. For example, if the list included the ‘SDA’ function, you would know that the pin could be used for the data line of an I2C bus. If there is a pin on that data bus lacking this function, that could indicate a mistake. Screen 7 shows how you can edit the pin functions. This dialog box can be found using the Edit option on the siliconchip.com.au Screen 7: pin functionality can now be edited from the Pins tab of a component’s Properties in the schematic editor. Multiple functions can be added to each pin of a device. ◀ Pins tab of a component’s Properties panel. This can be done from within the schematic document itself and does not require making changes to the schematic library, although you can do it that way too. Secondly, the functions that are actually displayed on the schematic can be selected from a drop-down menu. Any number of the functions can be chosen for display, matching the specific use in that project. This can also be handy for some ‘bitbanged’ peripherals, where a peripheral feature (for example, I2C or SPI) is performed by general-purpose I/O operations in software instead of via a dedicated hardware peripheral. Just about any pin can be used in such a case, and the function will not be fixed to that pin, so it would not usually be labelled with that function. Still, it can easily be added. Once a schematic has been ‘wired up’, the functions in use (of the many available) are selected for display. This will make it apparent to those writing the firmware what pin peripheral siliconchip.com.au Screen 8: once added, Pin functions can be selected in a schematic from a drop-down menu. This means that only the specific pin functions that are used are displayed. configuration is needed. Notably, only a small number of functions usually need to be displayed, meaning the schematic is less cluttered. Screen 8 shows the drop-down menu that alters the displayed pin functions. Some or all of the functions of that pin can be chosen as needed. PCB Health Check Altium Designer 23 also adds the ability to run a PCB Health Check. This is distinct from the Design Rules, which dictate whether the PCB is consistent with the fabrication rules set in accordance with (among other things) the PCB manufacturer’s requirements. The PCB Health Check is more aligned with aspects that may pass a design check but are functionally impractical or incorrect. For example, a component rotation of 360° is usually indistinguishable from one with a 0° rotation, but this might cause problems for an external MCAD (mechanical computer-aided design) program – see below. Other examples include zero-width Australia's electronics magazine Screen 9: PCB Health Check is found in the Properties panel when no objects are selected in the PCB Editor. It will highlight issues that might cause problems beyond those specified by Design Rules. March 2023  59 lines and zero-area regions, which may not be interpreted correctly after being exported into Gerber files. Such objects can be hard to find manually, since they are essentially invisible. The PCB Health Check is available from the Properties panel within the PCB editor anytime there is no object selected. You can see a typical report in Screen 9. From the top, there is a summary of all checks, a list of reported issues for each category and a brief explanation of the nature of the issue and how it might be fixed. Some can even be corrected automatically. We don’t think we’ve ever run into these sorts of defects. Still, those working with large designs (especially if created by a team) will undoubtedly want to ensure they don’t have any of these problems before ordering thousands of boards! If you experience unexplained slowdowns, crashes or strange PCB manufacturing problems, especially when working in collaboration with MCAD software, it might be worth performing a PCB Health Check. MCAD Mechanical CAD is often closely tied with EDA/ECAD since most electronic designs also require mechanical components, such as a case, front panel etc. A custom case is typically designed with dedicated MCAD software. Importantly, the electronic components must work with mechanical parts, eg, to ensure that the electronics will fit in the case and that the controls and displays line up correctly with cut-outs. Our Altium Designer 21 review noted the ability to integrate with MCAD programs such as SolidWorks, AutoDesk Inventor and PTC Creo. This requires the MCAD CoDesigner extension. This is not a feature we use as we do not have subscriptions to these programs, although we have dabbled with using 3D models of enclosures to generate renders of finished designs. Protel Autotrax is still available for download and can be run on modern operating systems under a DOS emulator. We only recommend doing this if you want to see how we did things 30 years ago! AD23 now supports integration with Autodesk Fusion 360 and Siemens NX MCAD software. This is done via the Altium 365 server, with both Altium Designer and the MCAD tool communicating with Altium 365. Webinars Altium’s ‘webinars’ are a great resource for finding out about new features in Altium Designer, as well as existing features that might not be immediately obvious. Apart from the Gerber export dialog box, we probably would have been unaware of many of the newer features. With ongoing software updates between major versions, sometimes they will add a new feature, and you won’t necessarily know until it’s mentioned in a webinar! The webinars also hint at new and upcoming features, many of which can be accessed via the beta program. The beta program gives access to upcoming software versions before its general release. One future feature we expect will be handy is the upcoming wiring harness designer, which will involve a new file type. Harnesses will have a BOM (bill of materials), wiring and layout, and they can be standalone projects or be part of a multi-board assembly. The harness designer will also work with Draftsman and allow manufacturing drawings to be created. Altium Designer 23 can now integrate with numerous MCAD tools. There is no need for manual file conversion, as Altium Designer works seamlessly with the various native MCAD file formats. 60 Silicon Chip Australia's electronics magazine Other planned features mentioned in the webinar included sectional views, an update to the variant manager and parameterised footprints. MCAD integration will also be updated to allow integration with multi-board assemblies. Summary Altium Designer 23 adds quite a few incremental features, many of which we think will come in handy. We’re already using the new Gerber expert dialog box. In particular, the pin functionality feature will allow us to better annotate and document our schematic diagrams. The PCB health check will come in handy as well. Even if you don’t use Altium Designer, you might like to try the free online tools that Altium provides. Availability Altium Designer 23 can be downloaded by those with a paid subscription; the latest software versions are included with a subscription. See www.altium.com/altium-designer/ If you haven’t used Altium Designer before and you’d like to try it out, take a look at www.altium.com/altium-­ designer/free-trial/ Altium also offers CircuitMaker (see our review in the January 2019 issue; siliconchip.au/Article/11378), an EDA tool targeted at hobbyists. It has a similar feel to Altium Designer, although designs are available for others to view online. You can also visit https://circuitmaker.com/ And as we mentioned earlier, Altium offers numerous free online tools, such as the Gerber viewer and Gerber compare. There is also Altium Basic, which can be accessed by simply creating a free account. SC siliconchip.com.au Fast and reliable temperature measurement. Digital Thermometers We stock a GREAT RANGE of thermometers, at GREAT VALUE, for domestic or commercial applications. MEASURE TEMPERATURES IN HOT, HAZARDOUS OR HARD TO REACH PLACES HELPS YOU AVOID FOOD FROM SPOILING FRIDGE/FREEZER THERMOMETER • -50°C to 70°C range • Min and max alarm function QM7209 JUST 29 $ 95 Non-Contact Thermometer • -50°C to 500°C range • 12:1 distance to spot ratio • Built-in laser pointer • Max, min, & auto data hold QM7410 JUST 5495 $ WATCH OVER THE TEMPS IN DIFFERENT ROOMS SUITABLE FOR THE LAB, WORKSHOP OR IN THE FIELD WIRELESS IN/OUT THERMOMETER/HYGROMETER • -45°C to 65°C (Outdoor), 0°C to 60°C (Indoor) range • 1% to 99% relative humidity range • Connect up to 3 sensors XC0322 JUST 4295 $ • -50°C to 750°C range • Built-in temperature sensor • K-type thermocouple input QM1602 RECORD AND STUDY TEMPS OVER TIME TEMPERATURE & HUMIDITY DATA LOGGER • -40°C to 70°C temp / 0-100% relative humidity range • 32,000 sample memory • Records at prescribed intervals • Easy USB interface QP6013 Shop at Jaycar for: Thermometer with K-Type Thermocouple • Thermometers & Thermocouples • Non-contact Thermometers • Probe/Stem Thermometers ONLY 129 $ JUST 4995 $ Includes Thermocouple • Digital Multimeters with Temperature • Desktop Temperature/Hygrometers • Weather Stations Explore our wide range of temperature measurement products, in stock at over 110 stores and 130 resellers or on our website. jaycar.com.au/thermometers 1800 022 888 Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. Using Electronic Modules with Jim Rowe ZPB30A1 Module - 60W Programmable DC Load - Battery Capacity Tester This programmable constantcurrent DC load can be used for testing power supplies or checking the capacity of storage batteries. It is essentially self-contained and delivers good value for the money. T he ZPB30A1 module carries the brand name Zhiyu, but it seems to be made in China by a firm called AoSong ELE Co Ltd. As you can see from the photos, it has two PCBs, with the smaller one (69 × 36mm) mounted above the larger main PCB that measures 100 × 69mm. The 50 × 50 × 23mm heatsink is at the rear of the larger PCB, along with its associated cooling fan on the finned side, for cooling the main load transistor. The fan extends past the rear of the main PCB by about 11mm. Mounted on the flat front of the heatsink is the power Mosfet that acts as the controlled load (in the centre), with a thermistor to its left used for sensing its temperature. To its right is a dual schottky diode that protects the power transistor from damage due to reversed voltage polarity. The smaller PCB is the control and display board, or the main ‘user interface’. Its four-digit 7-segment LED displays the voltage, battery capacity or various control and error messages. In contrast, the three-digit LED display below it is mainly used to show the current flow. Six additional green 3mm LEDs indicate which parameter is being Features & Specifications ∎ Test modes: programmable constant-current DC load (“Fun1”) or battery capacity tester (“Fun2”) ∎ Maximum dissipation: 60W ∎ Operating voltage range: 1-30V (separate 12V 500mA supply required) ∎ Operating current range: 0.1-9.99A in steps of 0.01A (10mA) ∎ Rated current measurement accuracy: ±(0.7% + 10mA) ∎ Test termination voltage range: 1-25V ∎ Voltage measurement: directly at the P+ and P− terminals or remotely for four-terminal measurements ∎ Voltage measurement accuracy: ±(1% + 0.02V) ∎ Battery capacity maximum values: 999.9Ah, 9999Wh ∎ Battery capacity test accuracy: 2.5% <at> 0.5A, 1.5% <at> 2A or 1.2% <at> 5A+ ∎ Protection: over-temperature (“otP”), transient over-power (“oPP”), overvoltage (“ouP”), reverse polarity (“Err3”) and abnormal voltage (“Err6”) ∎ Fan control: automatic, temperature-controlled ∎ Size: 69 × 111 × 57mm ∎ Weight: 270g 62 Silicon Chip Australia's electronics magazine displayed or which 7-segment digit is being adjusted, while a red 3mm LED indicates when the module is running. The function of the 3mm yellow LED function is not explained; it is labelled “L-4” and seems to be a recent addition to the latest (V3.3) version of the module. On the right of the smaller PCB are the two controls. The first is a rotary encoder, which changes modes and adjusts current and voltage values. The second is a small pushbutton used to confirm the module’s current and termination voltage settings and as an on/off control. Currently, the ZPB30A1 module is available from several sources on the internet, including Banggood (www. banggood.com/search/1146280.html) and many suppliers on AliExpress and eBay, ranging from $14.91 plus $7.37 for delivery to $37.53 plus $4.48 for delivery. I ordered one from Banggood at a price near the high end, and after the usual wait, it arrived safely – even though it was only wrapped in bubble wrap inside a plastic bag. What it does The module has two modes of operation. One is to serve as a programmable constant-current DC load, while the other is to test the capacity of storage batteries like Li-ion, Nicad or lead-acid batteries. The basic specifications are shown in the sidebar. The module’s internal circuitry is siliconchip.com.au Fig.1: a simplified block diagram of the ZPB30A1 module. powered by a 12V DC supply that must be separate from the measurement current source. The supply voltage must be between 11V and 13V, delivering at least 500mA. Power is applied to the module via a standard barrel-type DC connector (5.5mm outer diameter, 2.1mm inner diameter) on the left side of the main PCB. When power is applied, the module powers up in whichever of its two operating modes was last used. This mode is displayed in the upper fourdigit 7-segment LED display as either “Fun1” for programmable load mode or “Fun2” for battery capacity mode. The module defaults initially to the Fun1 mode. If you want to switch it to the other mode, you need to switch off the power, wait a few seconds and then hold down the on/off pushbutton while re-applying power. The module then allows you to switch modes using the rotary encoder, after which you press the on/off button again to lock the module into that mode. The module’s testing inputs are on the right-hand side of the main PCB. The small two-way screw terminal block is the main test input connector, with its inputs labelled “P+” and “P−”. The smaller two-pin socket is siliconchip.com.au used for the optional remote voltage sensing, to avoid errors due to voltage drops in the connecting wires. Its pins are labelled “V+” and “V−”. How it works Fig.1 shows a simplified block diagram of the ZPB30A1. I would have liked to show a complete schematic, but all I could find online was a partial circuit (at www.voltlog.com) that had been ‘reverse engineered’ and didn’t cover everything on the main PCB, let alone any of the circuitry on the display/control PCB. Still, all the most important details are shown in Fig.1. The ‘brains’ of the device is an STM8S105K4 microcontroller unit (MCU), shown at lower left. This The rotary encoder on the display PCB is used for changing modes and adjusting the current & voltage values. Australia's electronics magazine responds to the controls on the display and control board shown at upper left and shows the parameter values and testing status on the same board. The load current control circuit is shown at upper right. This uses the W60N10 power Mosfet (Q2) to maintain the load current between the test terminals P+ and P−, under the control of the MCU via the I_SET line. The current is monitored using a 10mW shunt resistor in Q2’s source connection; op amp IC4b compares the voltage drop across the shunt with the control voltage from the MCU. You can see a simplified version of the remote differential voltage sensing input below the current control circuit, using op amp IC4a. Its output is taken to the AIN2 analog input of the MCU. The thermistor mounted next to the Mosfet on the heatsink is shown below the remote voltage sensing input in Fig.1. The TEMP SENSING line from the thermistor goes to the MCU’s AIN0 analog input. Note that the micro doesn’t have a way to monitor the actual load current – there is no connection from the 10mW shunt to the micro. The actual load current will equal the set current almost all the time; if the source cannot March 2023  63 The “main” PCB measures 100 x 69mm and has the heatsink mounted on it. It’s also where the majority of the components and power socket are located. supply enough current to meet the target, the voltage will drop to near-zero, triggering the under-voltage alarm. So it is a safe assumption. The cooling fan’s driver Mosfet, Q3, is controlled by a PWM (pulse-width modulated) signal from the PD0 digital output pin of the MCU. This allows the MCU to turn on the fan as soon as the thermistor reports that the heatsink temperature has risen significantly, and to increase the fan’s speed as necessary to keep the temperature under control. If the temperature keeps rising beyond a safe level, the MCU turns off the load current and stops the test. The piezo sounder is driven by the MCU’s PD4 digital output pin. This allows the MCU to attract your attention whenever it needs to do so; for example, when a test comes to an end, or it detects an error condition. The module I received did not have the 6-pin header fitted (shown above the piezo sounder); there was just a set of pads and holes labelled G, R, T, L, F and Vc. While there was no mention of these in the sketchy data provided on the Banggood website, when I searched the internet, I found a couple of suggestions that the G, R and T pins could be used for serial communication with the MCU, at a rate of 115,200 baud and with the standard 8N1 protocol. The information I found said that the module only transmitted serial data in programmable current mode (Fun1), containing three-byte messages with the first two bytes representing the voltage while the third byte indicated testing status (1 = OK, 0 = undervoltage alarm). Trying it out The information on using the module provided on just about all of the supplier websites is very vague and quite hard to follow. As a result, you are largely ‘on your own’ when it comes to using it. It’s a matter of trial and error, not made easy by the multiple functions of the module’s controls and LED displays. That is a pity, since it performs surprisingly well when you manage to get it doing what you want. The first thing I did was ensure that my module was set to constant-­ current load mode (Fun1). Then I used the rotary encoder to set the load current for the test. This can be any value between 0.1A (100mA) and 9.99A, in steps of 0.01A (10mA). After this, I connected the module’s P+ and P− terminals to a 0-30V/5A programmable power supply, with one high-resolution bench DMM (digital multimeter) monitoring the current and another monitoring the actual voltage at the P+ and P− terminals. Then I pressed the module’s on/off button to begin testing. I set the power supply to a range of voltage levels (3.30V, 5.00V, 9.00V, 12.00V, 15.00V, 20.00V, 25.00V and 30.00V), and at each voltage level, I set the module to draw a series of current levels. At every current level, I used the bench DMM to set the voltage to precisely the desired level and used the other DMM to check the exact current. The results of these tests are shown in Fig.2. As you can see, in each case, the applied voltage remained constant over a wide range of current levels. That remained true to a point where either the module stopped the test Fig.2: I tested the load on constant-current load mode (Fun1) at a range of different voltage levels. This figure shows the current drawn by the module at those voltages. 64 Silicon Chip Australia's electronics magazine siliconchip.com.au due to the temperature rising above the limit (plots ending in an “X”), or my programmable power supply could provide no more current at that voltage (plots ending in a dot). Just to make sure, I undertook one further test using a different power supply capable of supplying 13.8V at up to 12A. This resulted in the brown plot in Fig.2. This showed that the module could maintain a current just below 5A at this voltage, corresponding to around 68W dissipation – not bad considering that it is rated to handle a maximum of 60W. During these tests, I monitored the difference between the module’s voltage and current readings and those of the two reference DMMs, to get an idea of the module’s measurement accuracy. Its current readings turned out to be less than 0.3% low for currents of 2.0A and above, rising to 1.0% low at 0.5A and 4% down at the lowest current level of 100mA. These figures compare pretty well with the module’s rated accuracy of ±(0.7% + 0.01A). The voltage readings turned out to be less than 0.4% low over the entire range, which is significantly better than the rated accuracy of ±(1% + 0.02V). So the ZPB30A1 module performs well in programmable current load (Fun1) mode. I moved on to checking out its battery capacity/Fun2 mode. Battery capacity testing I fully charged an 18650 Li-ion cell, then set up the ZPB30A1 module in Fun2 mode with a discharge current of 1.0A and a minimum voltage of 3.00V. After connecting the Li-ion cell to the P+ and P− inputs, I pressed the module’s on/off button to begin testing. Since the module doesn’t seem to have any serial output in this mode, I had to record the time and battery voltage the old-fashioned way, using a pen and paper while reading a stopwatch. The results of this first test are shown in Fig.3 (red plot). As you can see, the cell didn’t last all that long at the 1A discharge rate, with its voltage dropping below 3V after only 41 minutes. The module then displayed its capacity as 0.679Ah, close to my calculated figure of 683mAh (1A × 41 minutes ÷ 60 minutes). So its measurement was only about 0.58% low. I recharged the same 18650 cell overnight and set the ZPB30A1 to perform a second test at 500mA. I then spent the next few hours recording the battery voltage every five minutes, again in the old-fashioned way. The results of this second test are shown in the blue plot in Fig.3. It lasted a lot longer this time, with its voltage only reaching just below the test cutoff voltage of 3V after 228 minutes, corresponding to a capacity of 1900mAh. So it’s pretty clear that this particular 18650 battery is only capable of delivering its rated capacity at load currents of 500mA or less. It’s also apparent that the ZPB30A1 is well suited to performing the battery capacity testing role, despite a few minor drawbacks. Summary The ZPB30A1 module performs both its main functions – a programmable constant current load and battery capacity tester – very well indeed, especially considering its modest price. But it does have a few failings, including the lack of good instructions. It’s also pretty disappointing that its serial communications are so limited. Having an adequately documented serial connector that worked in all modes and provided a complete set of information would make it much easier to monitor the load voltage and time for each measurement. Adding a serial port header and supporting MCU firmware should be straightforward and would make things a lot easier, especially when testing a battery’s capacity. Hopefully, the module makers will add this serial port feature to it soon, making it a really handy piece of test gear. Despite that, given its low cost, I still think it is worth getting if you think SC you will use it. Fig.3: battery capacity testing was performed with a fully-charged 18650 Li-ion cell and the module in Fun2 mode. The test was done with a discharge current of 1A (and later at 0.5A) and battery voltage above 3V. siliconchip.com.au Australia's electronics magazine March 2023  65 Explore our GREAT RANGE of Filament 3D Printers Create amazing 3D prints with our great selection of 3D printers. 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Jaycar reserves the right to change prices if and when required. Active Mains Soft Starter Part Two by John Clarke Our Active Mains Soft Starter, introduced last month, is ideal for eliminating the switch-on kick from power tools rated up to 750W. You can also use it to avoid high inrush currents for stationary equipment that can trip circuit breakers or wear out switches. This article covers the assembly, testing, adjustment and calibration of this new Soft Starter. T he Active Mains Soft Starter uses a combination of an NTC thermistor and a Mosfet to provide an adjustable soft-starting period. Notably, the Mosfet means that the thermistor experiences little heating, so repeated starts (within reason) do not degrade the effectiveness of the Soft Starter. Both the Mosfet and the thermistor are bypassed by a relay after soft starting so that there is very little power loss or heating within the Soft Starter, even with a high load current draw. It is housed in a conveniently compact 17.1 × 12.1 × 5.5cm plastic enclosure with an IEC mains input socket, GPO output and three optional neon indicators to show what it is doing. Because it monitors the load current, it is automatically activated whenever the load appliance is switched on, even if the Soft Starter is already powered. That means you can use the trigger or switch on power tools to activate them. Or, you can simply switch it on at the wall, which is handy if you have multiple devices connected to the output (eg, via a power board). Having described what it does and how it works, let’s move on to building it. Construction Most of the parts mount on a double-­ sided, plated-through PCB coded 10110221 that measures 159 × 109mm. Once assembled, it is housed within a polycarbonate or ABS enclosure measuring 171 × 121 × 55mm. The only off-board parts are the IEC mains input socket, GPO mains output socket and three neon indicators. Fig.7 shows the parts layout on the PCB. Begin by installing the surface-­ mounting dual op amp (IC2). You will need a soldering iron with a fine tip (or a regular tip and some flux paste), a magnifier (if you do not have excellent Warning: Mains Voltage The entire circuit of the Active Soft Starter floats at mains potential and could be lethal should you make contact with it. Don’t assume that because we use isolation between different parts of the circuit that some parts are safe to touch – they are not! The isolation between parts of the circuit is to allow for the differing voltage potentials in parts of the circuit rather than for safety. 68 Silicon Chip Australia's electronics magazine vision) and good lighting. Solder the IC to its PCB pads by firstly placing it with the pin 1 locating dot to the top left and aligning the IC leads to the corresponding pads. Then solder a corner pin and check that it is still aligned correctly. If it needs to be realigned, re-melt the soldered connection and gently nudge the IC into alignment. When you’re sure it’s correct, solder all the IC pins. Any solder that runs between and bridges two pins can be removed with solder wicking braid (adding extra flux paste is recommended). Note that pins 6 and 7 are joined on the PCB, so a bridge between them won’t matter. Fit the resistors next. They have colour-coded bands indicating the values (see Table 1), but it’s best to use a digital multimeter (DMM) to check each resistor before soldering it in place. Three resistor types are used; one is a 1kW 5W wirewound, six are 1W types, and the remainder are smaller 1/2W resistors. Mount the 5W resistor with a gap of about 1mm from the PCB to allow air to circulate. Diodes D1-D3 and zener diodes ZD1-ZD3 are next on the list. Ensure they are orientated correctly and the siliconchip.com.au Fig.7: assembly is straightforward, with most parts mounting on the PCB, as shown here. Q1 has no mounting hole and is adhered to the PCB using double-sided adhesive thermal tape. Because of supply constraints, we have designed the board to accept two different types of current transformer, with either two or three pins. Note that the three TVSs are bidirectional, so their orientations are not critical. types are not mixed up before soldering their leads. TVS1-TVS3 can also be installed now. These are bi-directional (AC) devices, so they can be installed either way around on the PCB. Make sure the correct type number for each TVS is inserted in the specified location. Mount the remaining ICs, taking care to get the correct IC in each place and with the proper orientation. We used a socket for IC1, although you could solder it directly to the PCB, assuming it has already been programmed. IC3 and IC4 both have six pins, so don’t get them mixed up. On the PCB, pin 5 of IC4 has only a tiny pad to provide an increased creepage distance between pins 4 and 6. You can fit the capacitors next, of which there are four types: the mains X2-rated capacitors, electrolytic capacitors, MKT polyester and a multi-layer ceramic. The electrolytic capacitors need to be orientated correctly since they are polarised, while the others can be installed either way around. Note that the 100nF capacitors could be labelled as 104 (10pF × 104), while the 4.7nF capacitor could be labelled 472 (47pF × 102) and the 1μF ceramic siliconchip.com.au capacitor could be labelled as 105 (10pF × 105). Next, install potentiometer VR1 and thermistor NTC1. Bridge rectifier BR1 is next; its positive lead is spaced wider than the remaining leads, so it will only fit in one way. Mosfet Q1 can also be fitted now. Bend its leads by 90° about 5mm from the package and secure the metal tab to the PCB using double-sided thermal transfer tape before soldering the leads. Because the tracks are thin near the pads for the Mosfet leads, build up their exposed copper tracks on the underside of the PCB with solder. Install CON1 to CON4 next, as well as the current transformer, T1. Depending on which type of transformer you have, it might have two or three leads. The PCB will accommodate either type. The next step is to install relay RLY1 with its coil terminals toward CON4. The relay is secured using 15mm-long M3 screws and nuts, with each screw inserted from the underside of the PCB. Winding transformer T2 The windings on the toroidal ferrite core for T2 are made with 0.25mm Australia's electronics magazine diameter enamelled copper wire, as shown in Fig.8. The primary has 10 turns, while the secondary has 48 turns. Cut a 125mm length for the primary and 1m for the secondary and wind on each side-by-side; the winding directions are unimportant. The windings must be separated at least 3mm at each end. Mount the finished transformer on the PCB with two cable ties that both secure the toroid and keep the primary and secondary windings separated, so make sure they go between the windings. The third cable tie holds down the toroid in the middle of the secondary winding. Fig.8: wind T2 as shown here, keeping the windings neat and close together and ensuring at least 3mm of separation between the primary and secondary at either end. March 2023  69 Table 1: Resistor Colour Codes Fig.9: these are the required cut-outs in the side of the case and the lid. You can download this diagram as a PDF from the Silicon Chip website and print it to use as a template. Be careful making the IEC cut-out and neon holes as if they are too large, the parts will fall out. Try to avoid the GPO cut-out coming too close to the separate hole as, if the plastic in between is thin, it could break. Pass the primary and secondary wires through the PCB pads and strip off the insulation at all four ends to allow the wires to be soldered. The insulation can be burnt off with a hot soldering iron, by holding a blob of hot solder over the wire ends for a few seconds. Otherwise, you can scrape the insulation off with a sharp hobby or craft knife. Final assembly The soft starter PCB is secured to the base of the enclosure using 6mm-long M3 machine screws that screw into the integral brass inserts. But before 70 Silicon Chip attaching the PCB, the IEC connector cut-out will need to be made in the side of the enclosure. You will also need to drill holes in the lid for the GPO socket and neon indicators. Fig.9 is a template for the required cut-outs. You can photocopy it from the magazine at 1:1 scale or download a PDF from the Silicon Chip website and print it out (make sure to print it at “actual size”). The large cut-outs for the mains GPO socket and IEC connector can be made by drilling a series of small holes around the inside perimeter, knocking out the centre piece and filing the Australia's electronics magazine outline to a smooth finish. If you use Jaycar neon indicators, the holes must be sized so that they stay clipped in place when inserted into the cut-out. So take care with the hole size; the inside of the hole will need a slight chamfer to reduce the panel thickness so that the clips can spring outward to secure each neon. The Altronics neon indicators are secured with a nut threaded onto the plastic housing instead of clips. Once the drilling and filing are complete, install the IEC connector. The PCB can then be placed inside the case, but don’t secure it just yet. siliconchip.com.au Fig.10: there are two different versions of the front panel artwork that you can download, either with the neon holes marked (as shown here) or without, if you’d prefer not to fit them. First, the IEC connector must be secured using countersunk Nylon M3 × 10mm screws, although you can use metal nuts. You may need to cut away some of the internal ribs in the case to allow the nuts to fit as we had to for the prototype (you can just see this in the photo overleaf). The Nylon screws are essential as they avoid the possibility of the screws becoming live (at mains voltage) should a mains wire inside the enclosure come adrift and contact a screw holding the IEC connector. Before attaching the mains GPO and neon indicators, you can print out the front panel label shown in Fig.10. You can also download it as a PDF from our website. Details on making a front panel label can be found at siliconchip. au/Help/FrontPanels The download includes two versions of the front panel. One does not have the three neon indicator holes, and is included if you prefer not to use them. The wiring is also simplified when not utilising neon indicators. All wiring must be run as shown in Fig.11, using mains-rated cable. Be sure to use 10A cable for the thicker wires shown in Fig.11; brown wire must be used for the Active wiring while the blue wire is used for Neutral. Green/yellow-striped wire is used siliconchip.com.au for the Earth wiring only, and the Earth lead from the IEC socket must go straight to the GPO. The thinner wires shown (without a red asterisk) can use lighter-duty 7.5A mains wire, or use 10A wiring throughout if you prefer. Be sure to insulate all the connections with heatshrink tubing for safety and cable tie the wires as shown, to prevent any wire breakages coming adrift. Use 10mm diameter heatshrink around the bodies of the neon indicators, 5mm for the wires to the IEC connector (red or brown for Active, blue or black for Neutral and green for Earth) and 3mm for the wires to the relay (similar colour coding). Note how the relay contact connections are made using 4.8mm spade The relay wires are cabletied to other mains wires after installation in the case. Australia's electronics magazine 71 Fig.11: be very careful to run all the wiring as shown here, including using the colours shown, adding all the required insulation and the cable ties as indicated. All wires can be run using 10A mains-rated cable, or you can use 7.5A-rated cable for the thinner wires shown (without the red asterisks) if desired. crimp lugs while the relay coil wires are soldered. Try to avoid melting the surrounding relay plastic housing while doing that, and be sure to insulate the joints afterwards with heatshrink tubing. The wires to the IEC socket are also soldered and then insulated. Secure the Active and Neutral leads to the GPO using cable ties that pass through the holes in its moulding. 72 Silicon Chip Also, use neutral-cure silicone (eg, roof & gutter silicone) to cover the Active bus piece that connects the Active pin to the fuse at the rear of the IEC connector as it is live, and there is no good reason for it to be exposed. Take great care when making the connections to the mains socket (GPO). In particular, be sure to run the leads to their correct terminals (the GPO has the A, N and E clearly labelled) and do Australia's electronics magazine the screws up tightly so that the leads are held securely. Similarly, ensure that the wires to the screw terminals are firmly secured. Testing Always attach the lid using at least two screws at diagonal locations before switching on the power. Before applying power, check your wiring carefully and make sure that siliconchip.com.au setting only needs to be done if the soft start circuit does not correctly detect when the appliance is off. To set this offset, with the power off and unplugged from the wall, rotate VR1 fully clockwise. No appliance should be plugged into the Soft Starter’s GPO outlet. Attach the lid, power it up and wait a few seconds before switching it off. This will let it store the DC voltage produced by IC2 when no current is measured. Unplug it, remove the lid and rotate VR1 back from fully clockwise to the desired soft-start period. As mentioned earlier, somewhere mid-way will give a suitable soft-start duration of one or two seconds for most situations. However, other periods are available depending on the appliance requirements. Choosing the soft-start period The completed unit just before the lid is attached. The numerous cable ties mean that even if a wire breaks off, it can’t make contact and damage other parts of the circuit or create a shock hazard. all mains connections are covered in heatshrink tubing, and the wiring is cable tied. Then install the 10A fuse inside the fuse holder and verify that IC1 is plugged into its socket and correctly orientated. Should you forget to install IC1 before powering up, the 4.7nF capacitor at the pin 4 connection could be left with a remnant voltage when you switch off the power. This can destroy IC1 when it is plugged in. So if you power it up without IC1 plugged in, wait for a few minutes with power off and check that the voltage between pins 4 and 8 is less than 1V before plugging in the IC. Typically, VR1 would be set to midtravel for a nominal one-second softstart period. If set full anti-clockwise, VR1 gives a 9.5s soft-start period while near full-clockwise gives a half-second soft start period. Calibration Rotating VR1 fully clockwise has the soft starter enter another mode. This is used to measure the voltage from the precision rectifier when no appliance is connected. This is the offset voltage siliconchip.com.au that needs to be taken into consideration when detecting whether there is current flow or not when an appliance is detected. Typically, the output of IC2a (the full-wave rectified current waveform) will not sit at the negative supply at pin 4 with no load, but will be slightly positive. This offset can be measured and taken into account by IC1. This The available periods are 9.5, 5.5, 2.0, 1.0, 0.625 or 0.5 seconds, adjusted using VR1. You can use the slower rates for soft-starting capacitive loads if you are not concerned about how long it will take to power up the load. The 9.5s startup period is probably too long for most cases, but a 5.5s period is a good option. For power tools, the best period depends on the time the tool takes to get up to full speed and the acceptable amount of movement the tool makes during starting. A shorter duration will produce more tool movement than a longer duration but will let you get to work faster. If the period is longer than necessary, you will need to wait longer for SC the tool to be ready to use. The finished Active Mains Soft Starter is easy to use, just plug your desired appliance into the GPO on the front panel and then connect the Soft Starter to mains power via the IEC plug on its side. Australia's electronics magazine March 2023  73 73 ADVANCED TEST SMD T EEZERS Part 2 by Tim Blythman This new design, introduced last month, adds many features to the SMD Test Tweezers concept. No longer only for testing passive components, the new Tweezers can also act as a voltmeter, logic probe, basic oscilloscope, square wave generator and serial protocol analyser. This final article has all the construction and usage details. T he Advanced Test Tweezers circuit is simple and the PCB compact. The new functions are provided by the substantially larger firmware hosted in a 16-bit PIC24 rather than an 8-bit PIC12 or PIC16. That’s due to the PIC's hugely increased flash memory size, up from 7kiB to 256kiB, for only a couple of dollars more! This has allowed us to fit so many new modes, and enhance the existing ones, that a substantial part of this article will explain how to use them all. But before we get to that, we need to assemble the Tweezers. You can gather the parts yourself and program the blank PIC using software downloaded from our website, or you can buy a complete kit with the PIC already programmed. The design uses an SSOP-28 package microcontroller and M2012/0805 passive components, so the pin spacings are a bit tighter than the SOIC-8 and M3216/1206 parts that we used previously. Still, it’s eminently doable with patience and a fine-tipped soldering iron (or even a larger tip, if you know how to use it; flux paste is your friend). Start by assembling the main PCB and solder the microcontroller first. It’s easily the part with the finest pitch pins and is best dealt with if no other components get in the way. Apply flux to the pads on the PCB, then rest the IC in place, making sure pin 1 is aligned with the dot. Clean the tip of the iron and add some fresh solder, then carefully tack one pin and check with a magnifier that the pins are aligned on their pads and flat against the PCB. If necessary, adjust its position by remelting the solder and gently nudging it. Your life will be much easier if you get all the pins close to perfectly lined up with the pads now. Then, carefully solder each pin in turn, keeping the iron low on the pads, cleaning the tip and adding solder to it as necessary. You can apply more flux to the pins too. You can also drag-solder them if you know how. Check that the pins are soldered and that there are no bridges. If there are bridges, add more flux and use some solder wick to draw out the extra Construction Like the earlier Tweezers variants, we’re mainly using surface-mounting parts to keep it compact. The main change from the earlier versions is that the 28-pin micro has more closely-­ spaced pins than the 8-pin micros used before, but some passives are slightly smaller too. So you will need tweezers, flux paste, solder-wicking braid and a magnifier to complete this build. Use solder fume extraction or work outside if you don’t have one. Refer to Figs.5 & 6 (the PCB overlays) and photos as you go, which show where the components are mounted. 74 Silicon Chip The Advanced SMD Test Tweezers consists of the Main PCB (top and underside shown enlarged) and one of the Arm PCBs shown below (actual size). Australia's electronics magazine siliconchip.com.au solder. Surface tension should leave a small but sufficient amount of solder attached to the pin and pad. If you haven’t previously done any work with parts this small, you might like to clean the excess flux away to make it easier to inspect your work as you go. Even if you’re experienced, it’s best to clean it up when you’re done and use a magnifier to verify that all the solder joints have adhered to the pins and pads, and that there are no hard-to-see bridges. The remaining 14 passive components on the top of the PCB are all M2012/ 0805 size (2 × 1.2mm); none are polarised. The resistors should be marked with codes representing their values, but the capacitors will probably not be. If in doubt, the 10µF part is likely the thicker or larger capacitor. Apply flux to the pads for all the parts and solder the 10µF capacitor first. Like the IC, tack one lead, check that it is flat and aligned within its pads, then solder the other lead. Apply more flux and touch the iron to the first pad to refresh the joint. Use the same technique to solder the two 100nF capacitors, then the resistors, in the locations shown in Fig.5. There are only a few parts on the reverse of the PCB: two diodes and the cell holder, as shown in Fig.6. Solder in the two diodes now. Though small, the SOT-23 parts are pretty easy to work with and should only fit in the correct orientation. Then solder the cell holder. Make sure that the opening faces the edge of the PCB, as shown in Fig.6 and the photos. Use a generous amount of solder to ensure the connection is mechanically sound. It’s a good idea to clean any flux residue off the PCB now. Doing so at this stage means that the entire PCB can be immersed in a solvent before the switches are fitted, so it won’t get into their mechanisms. Your flux’s data sheet should recommend a solvent, but we find that isopropyl alcohol works well in most cases. Allow the PCB to dry thoroughly. The Advanced Tweezers can measure relatively high resistances, and traces of flux residue could affect readings. Now is a good time to thoroughly inspect the soldering of the smaller surface-mounted parts, as it will be tricky to make any repairs once the OLED has been fitted. Look closely for solder bridges and check that IC1 is in the correct orientation. Solder the three tactile pushbuttons in place next. That should be easy, as they have relatively large pads. You can carefully wipe away any flux residue left behind with a cotton tip dipped in solvent. Pre-calibration The standard 1% resistors used give the Advanced Tweezers a useful degree of accuracy. Still, if you have access to an accurate multimeter, you can measure the exact value of the six ‘probing’ resistors to improve its accuracy. They are marked in red in Fig.5. These are the 1kW, 10kW and 100kW resistors along the side near the top of IC1. The four lower 1kW resistors also affect measurements in the Scope and Meter modes, but we’ve provided an automatic calibration for them that does not depend on their exact values. Measure and separately note the exact values of the six resistors. It’s much easier to do this now, before the OLED is fitted over the top. A menu will allow these values to be loaded into the Tweezers during the calibration stage. Programming IC1 If you don’t have a pre-programmed chip (we sell a programmed micro individually and as part of a kit), you will need to program it using a programmer such as a PICkit 3, PICkit 4 or Snap. If you need to provide power to the chip (likely if you are using the Snap), you can temporarily insert a coin cell into the holder. The ICSP header, CON1, can be soldered in place for programming. However, we find it’s sufficient to insert a five-way header pin strip into the PCB pads, so you might like to try that. This way, the header does not get in the way when the arms are fitted. Gentle sideways pressure on the header during programming should keep the pins in contact with the plated holes. We recommend programming using the free MPLAB X IPE software. Select the correct part (PIC24FJ256GA702) and open the 0410622A.HEX file. Use the Program button to upload the HEX file to the device. The only indication that programming was successful will be a message like “Program/verify complete” in the Figs.5 & 6: remember to measure the resistances of the resistors marked in red and thoroughly check the soldering for bridges before fitting the OLED. It will take a lot of work to get to the top of this PCB (shown at left) after the OLED is fitted. You can use the large pad at top right (light grey) to support the OLED module by soldering a short piece of stiff wire between the two. The cell holder and two dual diodes are on the reverse side of the PCB (shown at right). The diodes should only fit one way, but the cell holder can be reversed. Fit it in the orientation shown so a cell can be inserted from the side near the edge of the PCB. Both overlays are shown enlarged at 150% of actual size. siliconchip.com.au Australia's electronics magazine March 2023  75 Fig.7: this shows how the two arms attach to the main PCB. It is easier to solder and align the tips to the arms after the arms are fitted to the main PCB. The arms are shown parallel here, but it's better to angle them as shown opposite. bottom window of the IPE. If you have fitted a cell, remove it now to complete the assembly. Fitting the arms and tips The arms must be fitted before the display to ensure that the OLED is spaced clear above the main PCB and clear of the arms. For the tips, we use the same arm design as the Updated Tweezers from April 2022, including the gold-plated header pins. Fig.7 shows the arrangement. The gold-plated header pins are easy to source, and as a bonus, they can also plug directly into prototyping gear like jumper wire sockets and breadboards. Fit the arms to the main PCB, then solder the tips, making it easier to align the tips to be the same length and parallel. Place the arms as seen in the photos. They connect to the CON+ and CON− pads and should have their copper tracks on the inside of the arms to reduce stray capacitance while being handled. They should only extend past the CON+ or CON− pads where they leave the PCB. This will keep the arms clear of other connections on the PCB, especially those for the OLED screen. Angle the arms slightly inward to achieve about 15mm of tip separation when at rest. This will allow the Advanced Tweezers to be used with axial leaded components too. You could set them closer if you only use them on surface-mounting parts. Use a small amount of solder to take the arms and adjust their positions as necessary. Then use a generous amount of solder on both sides of the arms and main PCB to ensure a good mechanical connection between them. Keep the pin headers side-by-side in their plastic holder until they are soldered, as this will keep them aligned. Use a generous amount of solder and ensure it flows into the holes on the arm PCB, giving more strength. Test the action of the arms and if necessary, use your iron to melt the solder and adjust them. OLED installation The final step is to fit the OLED module, MOD1. If the OLED does not have a header strip fitted, attach that first, ensuring that the pins are perpendicular to its PCB. The OLED needs to be fitted such that it cannot flex and touch any other part of the Tweezers, so space it about 1mm above the arms. You can use BluTack or similar to locate it squarely in place, and tack one lead to confirm. Check that there is clearance all around between the PCB and OLED. Then solder the remaining leads to their PCB pads. Take care when operating the Advanced Test Tweezers The Advanced Tweezers make use of a coin cell. Even though we have added protections such as the locking screw, there is no reason for this device to be left anywhere that children could get hold of it. Also, the tips are pretty sharp and might cause injury if not used with care. Avoid applying voltages across the Tweezers test tips when it is actively driving them. While this obviously includes the Tone mode, remember that the pins are also driven in the I/V, Auto, Res, Cap and Diode modes. So be sure that the Tweezers are set to the Meter, Scope, UART or Logic mode before connecting to an external voltage source. If a glitch causes the Tweezers to reset, they restart in Meter mode to avoid further damage. 76 Silicon Chip Australia's electronics magazine Removal of the coin cell is stopped by a Nylon screw and two nuts. siliconchip.com.au The arrangement of the arms and tips is much the same as that for the Updated Tweezers, using the same arm PCBs (blue this time) and gold-plated pins as simple, practical tips. This photo shows operation in left-handed mode. Initial testing At this stage, the Tweezers are complete enough to do a quick functional test. Insert the cell into the holder, and the OLED should light up in Meter mode, with a reading under 1V. Pressing S1 should cause the counter at bottom right to start flashing, and S2 will cause it to stop flashing. Pressing S3 will switch to the next mode (Scope). If something else happens, your Tweezers probably have a problem, so you should remove the cell and check the assembly. If the displayed voltage is wrong, check that the resistors all have the correct values and are in the right locations. Any of the switches not working could point to that switch not being soldered correctly. Any problem you spot might also be due to a soldering problem with IC1, particularly bridged pins or a solder joint that doesn’t contact both the pin and pad. If all is well, the assembly can be completed after removing the cell. The top-right mounting hole of the OLED is designed to be soldered to the main PCB using a header pin or similar. This will prevent the OLED from flexing at this end and coming into contact with the arms. You can now apply heatshrink tubing to the arms, taking care not to Fig.8: this sticker is for protecting the rear of the Advanced Tweezers PCB. Alternatively, you can print the artwork, laminate it, cut it out and glue it to the back of the cell holder. siliconchip.com.au direct heat towards the OLED screen. Cover as much of the arms as possible from the main PCB to just before the tips. The back of the Tweezers is protected by a small sticker that will be supplied with the kit or PCB set, shown in Fig.8. You can also download the artwork from siliconchip.au/ Shop/11/128 If printing it yourself, it’s a good idea to laminate it. Cut along the border to make a shape to match the main PCB. For more advice on making labels, see siliconchip.au/Help/FrontPanels Then use clear neutral-cure silicone or a similar adhesive to secure it to the back of the Tweezers. A small amount of glue on each of the arms and the back of the cell holder should be sufficient to hold it in place. Finally, fit the cell and secure it using the Nylon screw and two nuts. Put the head of the screw at the front, on the same side as the switches, so the extra height of the thread at the back blocks the cell from being removed. Before using the Tweezers, we recommend performing some calibration steps, explained just below. We’ll also explain all the various modes and how to use them. In general, pressing S3 cycles between the various modes and S1 and S2 have different functions depending on the mode. A long press (more than one second) of S3 changes between Settings and the normal operating modes. In Settings mode, pressing S3 cycles between the different settings, while S1 and S2 adjust the particular setting, as described on the screen. Calibration__________________ The calibration procedure has a few steps but is fairly logical. To enter the Settings mode, hold S3 for more than a second and release. Australia's electronics magazine #1 Handedness Screen 1: being configured for right- or left-handed operation doesn’t change the polarity of the CON+ or CON− connections, but the diode polarity icons will appear relative to the arms. The first page allows the display orientation to be set to suit either lefthanded or right-handed operation – see Screen 1. The setting is toggled by pressing either S1 and S2, and the change occurs immediately. All settings like this take effect immediately, so you can test them before being saved to non-volatile flash memory. There is also a Restore option to reload the initial defaults in case of a problem. Pressing S3 cycles to the next page. #2 Six resistor values Screen 2: while it will provide reasonably accurate readings without calibration, it is better to enter the exact values of the six most critical resistors (see Fig.5; as measured by a multimeter) on these screens. The following six pages set the values of the probing resistors you measured earlier, as shown in Screen 2. After the resistor value is an “L” or “R”, indicating whether you are setting the March 2023  77 value of the corresponding resistor on the left or right side of the main PCB. The values are adjusted in steps of 0.1%, ie, 1W for the 1kW resistors, 10W for the 10kW resistors and 100W for the 100kW resistors. Use S1 and S2 to adjust these values, and then press S3 to step to the next. On all pages like this, S1 will increase the displayed value and S2 will decrease it. Brief presses will make single steps, but holding the button in will cause it to increment or decrement about ten times per second. #3 Internal reference voltage Screen 3: diode and capacitor measurements will be most accurate if the internal bandgap reference is calibrated. Adjust it using S1 and S2 until the displayed cell voltage is correct. The BAT page (Screen 3) calibrates the internal reference, which is nominally 1200mV and is shown at the page's bottom. The value on the second line is the calculated cell voltage based on the reference setting. Trimming this parameter is best done with a multimeter. Measure the actual cell voltage (which can be measured at pins 2 and 3 of the ICSP header) and adjust the displayed cell voltage until it matches. The voltage shown in Screen 3 is higher than might be expected from a coin cell, as we were using a 3.3V supply for testing. In this case, the reference voltage has been trimmed upwards by about 3%, from 1200mV to 1237mV. #4 Lead/tip resistance Screen 4: the lead resistance was close to 0Ω in our prototype, but this setting might be handy if you are working with breadboards and jumper wires with significant resistance. The next page (Screen 4) sets the lead resistance, which defaults to 0W. Our prototypes had less than 1W of lead resistance and so were accurate enough; thus, you probably do not need to change this. You can test this by pressing the tips together on a mode that displays resistance. If you are connecting extra leads or jumper wires and breadboards, you can account for the higher resistance with this setting. #5 Auto calibration Silicon Chip #6 Stray capacitance Screen 6: stray capacitance can be tuned automatically or entered manually; it should be around 100pF. You can check it varies by setting it to 0pF and watching the value on the Cap screen. The stray capacitance of our prototype is around 100pF; check that you have a similar value, as seen in Screen 6. A vastly different value might indicate a problem, like a resistor in the wrong location. #7 Meter offset Screen 5: the AUTO SET tunes three calibration parameters by performing internal measurements with the tips open. It depends on the previous calibration settings being entered and correct. The next page (Screen 5) provides the option to AUTO SET several parameters, namely stray capacitance, Meter offset and CTMU trim. These require the tips to be left open and not As shown last month, a header pin is used to act as a reinforcing spacer at one corner of the OLED. This prevents the assembly flexing and causing a short between the two PCBs. 78 connected to anything, and are only accurate when the previous settings (test resistances and internal reference voltage) have been calibrated. Hold the Tweezers as you usually would to take into account the stray capacitance of your hand. Then press S1 to start this process. It takes less than a second and you can review the values on the subsequent pages by pressing S3. Australia's electronics magazine Screen 7: Meter offset adjusts for any difference in the two 1kΩ/1kΩ dividers and is set by the AUTO SET page. The 16mV error is noise in the ADC measurement, being a single ADC step. The Meter offset adjusts the relative value of the four lower 1kW resistors; it is effectively the difference between the midpoints of the two voltage dividers shown in Fig.4 last month. The value at the bottom is the number of ADC steps used to adjust the reading. In Screen 7, you can see the actual Meter reading at top right. You can validate this by verifying that the reading hovers close to 0mV when the tips are open. The -16mV seen corresponds to a single ADC step, and thus the resolution in this mode. siliconchip.com.au #8 Current source trimming #10 Screen blanking timeout Screen 8: the CTMU’s current source is also trimmed by the AUTO SET page but has very coarse trimming, with 2% steps. You can observe this by manually adjusting the trim value on this page. Screen 10: with an option to disable the timeout in all modes, the timeout value is less critical than on the earlier Tweezers. The default is 30s, but it can be set from 3s to 99s to suit your needs. The CTMU current source, used for capacitance measurements, can be trimmed on Screen 8. The lower value is the degree of trimming, with each step being a delta of about 2%. This is a hardware limitation and is a significant factor in limiting the accuracy of capacitance measurements. The value shown at upper right is the deviation of the measured current from its nominal value on the 550µA scale, while the lower number indicates the amount of trimming, with zero being the default. With a 2% deviation, the steps are around 11µA apart, so a setting within about 5µA of zero is optimal. Note that the Meter reading depends on the internal bandgap reference voltage being set correctly, as does the CTMU trim. The CTMU trimming procedure uses one of the 1kW resistors and thus depends on its actual resistance too. So ensure these values are set before running the AUTO SET process. Screen 10 sets the display Timeout and is the countdown (in seconds) before the Tweezers enter their lowpower sleep mode after the last button press. This value can be set between 3 and 99 seconds with a default value of 30s. Note that the operating screens all have the option to freeze the timer so that the Tweezers can be used continuously when required. #9 OLED brightness #11 Save settings to flash Screen 11: all calibration and operation parameters are live as soon as they are set. On this page, you can press S1, then S2 to save them to flash memory so you won’t have to repeat the calibration. Screen 11 gives the option to Save the calibration settings to flash memory. On this page, press and release S1 and then S2 to save the data. You should do this once the Tweezers are set up to your liking. #12 Restore settings from flash Screen 9: the OLED is one of the major drains on the coin cell, so a low brightness setting increases the cell life. We had no trouble using the Tweezers with the OLED set to quite a low brightness. On Screen 9, the display brightness can be set between 32 and 255, with 64 being the default. This setting is a compromise between display visibility and cell life. You should set this to the lowest level at which you can still read the screen clearly. siliconchip.com.au Screen 12: if the settings become corrupt, the Restore option will load defaults from a backup location. You can also load flash defaults by holding S3 while powering on the Tweezers. Australia's electronics magazine The Restore page (Screen 12) can be used to reload the default settings from a backup copy. These settings are put into use straight away. Although it would be very unusual, it’s possible for the saved settings in flash to be corrupted. This might happen if, for example, power is lost while writing to flash. Such corruption can be detected by the micro and trapped to avoid improper settings being used. If you get a “Flash Error” message when powering up the Tweezers, remove the cell and hold S3 in while reinserting it (giving a “No Flash” message). This bypasses the loading of the settings from flash, after which you can use the Restore and Save pages to reload and rewrite the flash memory with uncorrupted data. You should then treat the Tweezers as if they have not been calibrated and repeat the calibration procedure. #13 Exit settings Screen 13: besides this screen, you can also leave the Settings pages at any time by pressing and holding S3 for more than a second. A brief press of S3 will take you back to the first Setting. Screen 13 shows the final Exit page that allows you to press S1 or S2 to return to operating mode, while S3 will return to the first Settings page. A long press on S3 at any time will also exit Settings mode. Operation___________________ During operation, the bottom line in all modes shows data that always has the same format. From left to right, it shows the current mode, the cell voltage and a countdown timer. If the timer is flashing, it has been paused and does not count down, allowing continuous operation. When the timer counts down to zero, the Tweezers will enter the lowpower sleep mode with a blank display. Pressing any of S1, S2 or S3 will reset the timer and resume normal operation. March 2023  79 #1 Meter mode Screen 14: the initial Meter display mode, which can read up to 30V with both negative and positive polarities (with respect to CON+ and CON−). The resolution is 10mV to 9.99V and 0.1V above that. The Tweezers start on the Meter screen, which displays the measured voltage between the probe tips. Screen 14 shows the Tweezers in Meter mode, connected to a fresh 9V battery. Pressing S1 in this mode will pause the sleep counter and pressing S2 will resume it. As is typical, any button press will also reset the sleep counter. Pressing S3 cycles to the next mode. #2 Scope mode time division, which is marked by a more solid vertical graticule. Thus, one time division is displayed before the trigger point and three after. A tiny arrowhead also marks the trigger voltage level to the left of the grid area. Due to the slow update speed of the OLED display, the trace is not displayed live. Instead, a sample set is taken, spanning around two full screen widths. It is checked for trigger conditions and an appropriate portion is displayed. If no trigger is found (or AUTO trigger mode is selected), the first screenful of samples taken is displayed, along with a “WAIT” message. If a trigger is found, then the trigger point is aligned with the graticule and “TRIG” is displayed. Since a complete sample set at some of the longer time divisions can take several seconds, it can be a while before data is displayed. #3 UART serial decoding Screen 15: Scope mode is handy, even though there are only 100 horizontal and 48 vertical pixels in the trace area. It samples at up to 25kHz, is suitable for audio use, and has adjustable trigger settings. Screen 16: we find the UART Serial Decoder indispensable at times. Like the Scope mode, it is highly configurable in terms of baud rates, bit depth and data polarity. This shows the TXT view. Scope mode is shown in Screen 15, with a nominally 100Hz 6V peak-topeak waveform fed to the Tweezers by a second set of Advanced Tweezers in the Tone mode. This has various parameters to set; pressing S1 cycles between the parameters, while S2 adjusts the selected parameter by cycling between the available options. You can see which parameter is selected as it will be flashing. These include the vertical axis maximum (voltage), trigger mode (RISE, FALL, BOTH or AUTO), trigger level in volts, timebase per division and whether the vertical axis minimum is 0V or the negative of the maximum. Pressing S1 also cycles through the countdown timer; while it is selected, the countdown timer is paused. The trigger point is fixed at the first The next mode is the Serial Decoder, labelled “UART” (see Screen 16). The bottom text shows the current settings, which are similar to those in Scope mode. S1 cycles between the parameters (including the sleep timer) while S2 adjusts the selected, flashing parameter. The first setting is the baud rate, which includes standard rates from 110 to 115,200 baud. The second setting is the format, which can be eight bits with odd, even or no parity or nine bits with no parity. These are shown as 8O, 8E, 8N or 9N and are followed by a choice of one or two stop bits. The idle logic level is next and can be HI or LO, followed by a choice of text or hexadecimal (“TXT” or “HEX”) display output. Screen 16 shows TXT mode, which 80 Silicon Chip Australia's electronics magazine works much like a serial terminal and will handle line feed, carriage return and tab characters. The text will scroll up as lines are filled at the bottom of the screen. The text seen here is actually a decoded square wave; hence, the same character is repeated. HEX mode does not handle any control characters but displays both ASCII and HEX representations, also scrolling up as needed. Only HEX mode can display the full range of 9-bit data, and it also indicates parity (“P”) and framing (“F”) errors. Screen 17 shows the same data as Screen 16 but in HEX mode. The decoding depends on the PIC24FJ256GA702’s hardware UART and logic levels, but since the I/O pins are behind the protective resistors, this will work fine with any logic levels of around 3V or higher. Even non-TTL voltage levels, such as legacy RS-232 (which can swing between -15V to +15V) should be successfully decoded by choosing a LO idle level, since -15V is the idle level. Screen 17: the Serial Decoder also offers a hexadecimal mode, useful for seeing binary data and control codes. Framing or parity errors are shown, which can help to determine the data format. #4 I/V plotter Screen 18: while Diode mode cannot report dual diodes such as bicolour LEDs, the I/V Plotter shows both polarities. The current and voltage scales can be zoomed in for more detail. Screen 18 shows the I/V (current vs voltage) plotter, designed to characterise passive components. This uses much the same scheme as Meter mode, applying a voltage via different resistor combinations to probe the component at different operating points. siliconchip.com.au Six readings are taken, including the voltage and current at each point. This is limited to about ±3V due to the cell supplying the test current; the current can be no more than around 1.5mA due to the minimum 2kW resistance. Like in Scope mode, the vertical and horizontal scales can be adjusted by using S1 to cycle between current (vertical), voltage (horizontal) and the timeout counter. S2 cycles between the available values. The horizontal scale can be set to 1V, 0.5V, 0.25V, 0.1V or 0.05V per division, while the vertical scale can be 1mA, 500µA, 200µA, 100µA or 50µA per division. The values are displayed in mV and µA, respectively. The 0V/0A origin is always at the centre of the display, and the I/V display updates continuously, so it is well-suited to sorting through piles of unmarked parts. Screen 18 shows what it indicates for a yellow LED with a forward voltage of around 1.7V. #5 Logic Analyser Screen 19: the Logic Analyser shows whether it detects a high, low or high impedance logic level. A scrolling chart also shows a brief history, making it easier to see transients and repeating patterns. Pressing S3 again switches to the Logic Analyser, as shown above in Screen 19. Sensing is done by alternately probing with high and low voltage levels via one of the 100kW resistors. A voltage that follows the probing voltage is assumed to be high impedance. It shows 1, 0 or Z at the left of the screen to indicate a logical high, low or high impedance level. A horizontal scrolling display also shows about a second’s worth of history to allow brief transients or waveforms to be discerned. Here, we see a high-level signal that is interrupted by brief low pulses. Like in the Scope and Meter modes, S1 and S2 will pause and resume the countdown timer, respectively. siliconchip.com.au #6 Tone Generator an audio signal via a series capacitor (in the circuit, or added), which will remove the DC offset. #7 Component measurements Screen 20: like Scope mode, the Tone Generator is handy at audio frequencies or as a simple clock generator. It can produce square waves at five different frequencies and four different amplitudes. Screen 20 shows the Tone Generator. Unlike most of the other mode settings, which are retained between uses, the tone is turned off when it is not being used to avoid interfering with other modes. It can be toggled on and off by pressing S2 when the ON/ OFF indicator is flashing. There are choices of 50Hz, 60Hz, 100Hz, 440Hz and 1kHz. Only square waves are produced. There are four output (peak-to-peak) levels, which are nominally 300mV, 600mV, 3V and 6V. The 300mV waveform is produced by toggling one output via a 10kW resistor and dividing that with a 1kW resistor to ground. The 600mV selection drives two outputs similarly, but with opposing phases, to achieve the necessary swing. The 3V and 6V outputs are fed to the tips directly from one or two pins respectively, without the divider. The level selections assume that the supply is at 3V and the load resistance is relatively high. Under other conditions, the voltages could be different. Because of the way they are generated, the 300mV and 3V outputs also have a DC offset that the other two modes do not. So, you can use the 3V mode to drive a clock signal into 3.3V logic (or 5V logic, if it accepts a 3V signal swing), or you can use the 300mV and 3V modes to feed in Screen 21: the Auto screen is only one of ten pages but encompasses and surpasses the abilities of its predecessors. It shows resistance, capacitance, diode polarity and forward voltage. Finally, we come to the modes that can be used directly read off the values of passive components. These are similar to the older Tweezers variants but have wider measurement ranges. The Auto mode performs readings for resistors, capacitors and diodes and displays the readings for all three. You might get readings for more than one component type, as there is no algorithm that will always correctly determine what has been connected. Screen 21 shows Auto mode with no components connected. A high resistance and low capacitance are displayed. In Auto mode, pressing S1 will pause the countdown timer while S2 will resume it. The subsequent Res, Cap and Diode modes concentrate on just the one component type and display it in a larger font. These are seen on Screens 22-24, respectively. The maximum resistance that can be displayed depends mostly on leakage currents in the circuit. However, above 40MW, it will not achieve the stated 1% accuracy due to there being insufficient resolution at this end of the scale. We have specified much the same range for capacitor testing as the The underside of the Advanced SMD Test Tweezers (shown at actual size) is mostly empty, with only the battery holder and two diodes present. Australia's electronics magazine March 2023  81 Screen 22: the Res screen provides the same resistance information as the Auto screen but in a larger font, which is handy for checking and sorting through different resistor values. Screen 23: the Cap screen works similarly, displaying just the measured capacitance in large text. It’s perfect for working out which part is which amongst a pile of unmarked SMD capacitors. Screen 24: the Diode screen is similar to the diode display on the Auto screen but a bias is applied from CON+ to CON− between tests. This lets you quickly check the polarity and operation of LEDs. Improved Test Tweezers. Above these ranges, leakage and other factors make it difficult to achieve the stated accuracy, especially for electrolytic capacitors. The Advanced Tweezers will report up to 2000µF, but you should not rely on readings above 150µF. Since this is well above the typical range for the MLCC (multi-layer ceramic capacitor) types that we typically use for SMD designs, we don’t expect this will be much of a concern. Remember that many capacitors are manufactured to tolerances as wide as ±20% (and sometimes even +80,-20%). The diode test current is higher than the earlier Tweezers due to the 1kW test resistors. In the standalone diode mode, the forward test current (CON+ positive and CON− negative) is supplied between samples, so LEDs should be seen to light up when connected in the forward direction. passive component measurement and many new modes. The PIC24FJ256GA702 is a substantial upgrade over the tiny 8-bit, 8-pin parts we previously used; we are not even using half of its resources or features in this design. These new Test Tweezers can replace a basic voltmeter, logic probe and even oscilloscope in some situations, making them an indispensible general-purpose test instrument. We expect that the Advanced SMD Test Tweezers will be both popular and useful, not just for the numerous test and measure modes, but also as a SC tool during SMD assembly. Conclusion The original SMD Test Tweezers and the subsequent Updated SMD Test Tweezers are compact and handy devices. By adding a more powerful and better-provisioned microcontroller, we have added numerous extra features in creating the Advanced SMD Test Tweezers, including improved TEST MANY COMPONENTS WITH 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). 82 Silicon Chip Australia's electronics magazine siliconchip.com.au SERVICEMAN’S LOG Carpet vacuums suck, too Dave Thompson I don’t know what it is with vacuum cleaners and this household lately; if it isn’t one thing, it’s another. The symptom this time was a lot like the last – pull the trigger and nothing happens – but as it turned out, the cause was altogether different. After my previous repair of the Bissell AirRam, detailed last month, everything seemed fine. However, we ran into problems with another of our cleaning appliances. While the ‘repair’ was simple enough, it wasn’t an overly simple process, especially once we discovered what the problem was. Me! Let me explain in my usual roundabout fashion... Once a year, during the height of the summer months, we usually do a complete wet carpet clean throughout the house, just to spruce things up a bit. This year was no different. The problem is, last summer, we had some very unpredictable and inclement weather. We prefer to have a few nice consecutive sunny days to open all the windows and thoroughly dry the carpets out after cleaning them. As we felt we wouldn’t have that opportunity, we ended up not doing it at all that year. However, this year, we had to do a proper shampoo as the carpets were starting to show their true colours! Even this year, summer has been grey and unseasonably damp, with very few decent spells of warm weather. We’ve seen some extreme weather in other cities around the country (and indeed, other countries, as many of you know all too well). As it turned out, we were quite lucky not to have the severe storms, rain and floods that other towns and cities here were subjected to (and still are). We have had bursts of finer days, though, with the ‘mercury’ in the high twenties and low thirties, so we decided to take the opportunity to break out our wet vacuum/carpet cleaner and finally get our carpet clean. Once again, the machine is a Bissell appliance – we’ve had several Bissell vacuums of different types over the years, and all have been pretty good machines. Even though this one is getting on a bit now, it hasn’t done a tremendous amount of work because we only shampoo the carpets once a year (or thereabouts). Items Covered This Month • • • A carpet vacuum magic trick Remembering core memory Daikin three-phase aircon 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 siliconchip.com.au We try to keep the carpets clean regardless, with a ‘no shoes in the house’ policy and only the odd pet accident to clean up, meaning it is probably not essential they are done every year. Still, we try to keep to that schedule. Which brings me to my point; this machine does a lot of sitting around doing nothing. That also means that when we go to use it, we have to relearn how to operate it all over again. What’s the old saying? Use it or lose it? Well, that applies here, because the machine is relatively tricky to use and, to get the best results, it needs to be operated while taking all those quirks into account. Fortunately, we keep all the user manuals (they are also available for download on the web anyway). Since this was the first time we’d had problems when we fired up the machine, we had to find and dig the user manual out. To begin with, this is a very typical carpet shampoo vacuum cleaner. They are usually quite bulky devices and relatively hard to manoeuvre, especially around corners or in tight spaces. Ours is no different, although, to offset this and make it more appealing to the home user, our model boasts a removable motor assembly. That assembly has a smaller nozzle attached so it can be more easily used to shampoo and clean the likes of stairs and upholstery, where the original machine would not have a hope of reaching. Australia's electronics magazine March 2023  83 When the removable unit is ‘unplugged’ from the main body of the cleaner, a mechanically-operated valve diverts the water and shampoo mixture and vacuum to the small hand-held nozzle instead of the main head unit. This machine overall does a very good job for a domestic cleaner and has given us good service over the years. Rinse, lather, repeat In these devices, a specifically measured water/shampoo mixture is loaded into one of the two onboard tanks and pumped down through the head assembly onto the carpet (or upholstery) when a trigger is pressed on the operating handle. This mixture is driven deep into the pile of the carpet in a swirling motion, due to the head’s water-jet placement and the water pump pressure. When the carpet is well-shampooed, the trigger is released. The mixture stops pumping out, and the machine then essentially becomes a regular wet vacuum that pulls all the dirty water back out of the carpets, leaving them as dry and as clean as possible. Multiple passes are usually required for both the shampooing and vacuuming phases of the process. The dirty water (usually astonishingly dark and filthy looking) is collected and dumped into a clear plastic reservoir, which sits adjacent to the water and shampoo tank on our particular model. Both these tanks are removable for filling and emptying by means of clever locking levers. Therein lies the rub My wife got our shampooer out of the cupboard, installed all the hoses and bits and bobs and set it all up. She filled the tank with the correct shampoo/water mixture, plugged it in and switched it on. The problem she encountered was that nothing happened when she pulled the trigger. There was none of the usual water pump start-up noise from this machine when the trigger was pulled, but there was still plenty of suction at the cleaning head. Evidently, the vacuum part was working fine, but something was not quite right. This didn’t bode well, and was all I needed after the last vacuum-cleaner-related fiasco. 84 Silicon Chip The first thing I did was pull both the tanks off and check all the filters underneath. All are removable, but some only with screwdrivers, so I went to the workshop and tooled up for the coming disassembly. Like all our other Bissell vacuums, this one is also as over-engineered as a Bugatti Veyron. Everything removable is held on with many screws or bolts, making it quite a substantial and hard-to-disassemble unit. I hit the internet for a service manual but, as usual, found nothing (except those for sale on some manual sites). Still, I did find a couple of service videos on YouTube that vaguely included this model, though not in any great detail. It did get me up to speed on the filter checks and removals, however, so naturally, that’s where I started. Once I got them out, I could see the filters in question were relatively clean, with a little fine dust in some and a few pet hairs in others, but not enough to stop it from working. Regardless, I fired up the air compressor and gave them all a good clean-out before refitting them. I didn’t expect that solution to work, but I tried it anyway; still nothing. I hoped the pump hadn’t failed, because I wasn’t sure I’d be able to get another one, at least at a reasonable price. A pump failure could make the whole thing redundant, and it would then be just landfill fodder, a very unpalatable option. Time to take it apart The only thing for it was to strip the machine down to the pump and see what was happening. As I had no service manual, I was going in blind. That is not unusual in my line of work, but I would rather have at least some diagrams to follow, especially if it all springs apart somewhere and bits go flying. I’ve been there before, trying to reassemble something without any direction or idea of how it goes back together. It is incredibly time-consuming and frustrating; potentially, it might never go back together the same way. If that were the case, I’d also have to discard it. No pressure, then. I began by removing all the outer panels that could be removed; by past experiences, that might not have any real benefit, but I thought I might be able to see what was going on underneath them and find a way to burrow down to the pump. As is typical, the screws were very tight and some were hard to access, but I managed to get the panels off using several of my dozens of screwdrivers. Fortunately, there were no security-type fasteners, as seems to be the Bissell way, because that makes things so much harder. Underneath, I found two other sections I needed to remove to get to the pump, or at least where I thought the pump was. One was particularly difficult as it seemed to be interlocked with clips to the part next to it, but I finally finagled it off with much blue language and gnashing of teeth. There were also a couple of smaller filters in this area that I could remove and check. Both were a bit grubby but still relatively clear. I cleaned them with an old toothbrush in a bit of water and used compressed air to blow them out anyway. I finally found the pump, a compact self-enclosed unit, and removed the three screws holding the assembly in place. It spun freely, but without a service manual, I had no idea what voltage it ran on, and as it had no visible Australia's electronics magazine siliconchip.com.au markings on it, I had no way of finding out exactly what it was. Another Google search showed up similar items that looked like it, but with no specs available; I wasn’t about to just throw power at it to test it. Frustrating! At least it hadn’t jammed up, and while I had access, I carefully blew the water lines going to and from the pump through with low-pressure air to ensure everything was clear. It all seemed as expected, so I left it at that. Testing the trigger At this point, I considered that the trigger mechanism itself might be where the fault lay, and that it simply wasn’t switching the pump in and out, so I set about disassembling the handle assembly. This was an act in itself, with several screws holding it together that were quite challenging to get to, even with all my screwdrivers. I got it apart, though, and could see all the wires and the switch inside the handle. I used my trusty multimeter to ring the leads out, all the way down as far as I could see, and all seemed to be connected correctly. The trigger was working and switching, according to the meter. I tried ringing out the circuit all the way down to the pump motor leads, and while I got no reading, I wasn’t too surprised, as I knew there must be other sensors that controlled pump operation, such as the water tank being empty or the waste tank being full. I know this because the user manual mentions these as safety features. I couldn’t see these sensors in any part I had taken apart, and I guessed they’d be situated in the pipe assemblies somewhere beneath the tanks. Since the water tank was full and the waste tank empty, I didn’t think it would be one of those sensors preventing the pump from working. In my mind, it was still looking like the pump. I found what appeared to be a replacement unit on the web; the model of the cleaner matched, and the picture of it looked very similar, but I’d have to import it as there was nothing I could find locally. What a pain! And there was still the risk that replacing the pump assembly wouldn’t fix the problem anyway, so I held off going down that particular route for the time being. I still had niggling doubts about the whole deal – something seemed off about it. The cleaner had worked perfectly the last time we’d used it, and the pump wasn’t jammed by build-up or any foreign objects. The lines were all clear and the wiring was intact; it just didn’t make sense that it would stop working while sitting in the cupboard doing nothing. In the end, I reassembled the machine. The last thing I wanted was to have to wait for a new pump and then forget how it all went back together! At this point, there wasn’t much else I could do except try to find a service manual, or perhaps post in some online forums I had found, to find out what the experts had to say. 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. everything back together for what I knew would be a futile test of whether what I had done had made any difference, she suddenly said something that made perfect sense. She said, and I quote: “I think I put the shampoo and water in the wrong tank.” That did make good sense – as I mentioned, when that waste tank is full, the pump won’t switch on, and when the water tank is empty, the pump will not operate either. If I’d had even an ounce of sense, I would have figured this out before wasting all that time and expending so much bad language chasing a ghost. It transpired that she had forgotten how to use this machine as much as I had, and just filled the waste tank with the shampoo and water mixture, thinking that was the water tank. To be fair, the water tank system is a little unintuitive; just looking at it, anyone would think the waste tank is for water and shampoo. Still, at the end of the day, I was the one who went all repairman on it without looking for obvious solutions first. We poured the mixture from the waste tank into a jug and filled the water tank with it (pouring directly between them was not going to work due to the design), then put them both back in place. This time, well, you know what happened; everything worked perfectly. ...continued on page 88 Eureka! While I’d been doing all this, my wife was also hitting the web, trying to find anything relevant that might help. This is not uncommon; she often looks at things I wouldn’t think of, and vice versa, so between us, we can usually get to the bottom of something if we look long and hard enough. As I was turning the last few screws in and putting siliconchip.com.au Australia's electronics magazine March 2023  85 Don't pay 2-3 times as much for similar brand name models when you don't have to. 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Range 100-450°C 150-450°C 150-450°C 160-480°C 50-480°C Soldering 100-500°C Hot Air 200-480°C Display Digital Digital Digital ESD Safe • • • $189 $299 $339 Price $39.95 $74.95 $129 *Temperature rating is set by the soldering iron tip. ESD means Electro Static Discharge Shop Jaycar for your soldering essentials: • 6 Soldering stations • 12 Electric handheld irons • Over 12 gas powered irons • Classic 60/40, lead-free, silver & paste solder options • Multiple desolder braid and tools • Wide range of stands, cleaners and PCB holders Prices correct at time of publication but are subject to change. Jaycar reserves the right to change prices if and when required. I was kicking myself. I’m always banging on about hearing hoof beats and looking for horses, not zebras, but in this case, I just assumed that everything was right and there must be a fault if it wasn’t working. Thus, it is a very cautionary tale, then, and one I’ll (hopefully) learn a lot from. We’ll see! Remembering core memory R. E. of Freshwater, NSW enjoyed the article on “The History of Computer Memory” (January 2023; siliconchip. au/Series/393), particularly the section on magnetic core memory. It made me laugh, as the Australian Navy was still using core memory as ROM in 1990 and even later. In fact, I was informed that the bootstrap loader for the ROM was a punched paper tape. How embarrassing! 26 years earlier, I was introduced to the obsolete technology of saturable core reactors and magnetic amplifiers in my “Industrial and Automation Electronics” course at a college in Toronto. We learned that if you saturate a transformer or other magnetic material, it will no longer pass a signal from primary to secondary, but rather leave the secondary at 0V AC. In 1990, I was working for Bellinger Instrument Pty Ltd, a small defence contractor in Rydalmere, Sydney. The policy of the company was that we would repair and refurbish anything that the three defence arms could throw at us. “If it is small enough to fit in the building, we will fix it” was the motto. In came six boards of unknown function or use, with absolutely no documentation and most likely security restrictions on the system it came from. I must have been standing in the line of fire, as I got the job of determining what they were, their use and reverse engineering, writing a test, and repairing any faulty boards. I deduced that these were 32-bit core memories of unknown capacity. With my introductions to the saturable core reactors, I deduced that a core memory can be used to store data. A core that has been forced into saturation with 88 Silicon Chip an excessive current will not pass any voltage transients to the secondary, but it will retain the received energy once the energising current is removed. This energy is transferred to the secondary as back-EMF and can be measured as a several-millisecond-long pulse in the secondary, and a shoulder in the primary voltage directly after removing of the saturating current. The ROM boards I had were a three-wire system, where each toroid had three wires affecting its function. One was a biasing wire that energised each toroid with a direct current to just below the saturation point. The second was an address line for the 32-bit memory (or primary winding of the toroids). The third line was the read wire or secondary winding. By applying a pulse to the address line with enough current to put the toroids into saturation, the read line received a several-millisecond-long back-EMF pulse after the address pulse was removed. The bias and read wires are fed through the centre of the toroids, but the address wires were fed through the centre only for a ‘one’ bit and fed around the outside of the toroid where they did not send it into saturation, with no backEMF pulse, for a ‘zero’ bit. With this in mind, I developed a system to send pulses through the all addresses, then read the ROM contents with a sample-and-hold circuit timed to the back-EMF pulse, and present the result to a 32-bit logic analyser as a waveform pattern. The analyser had the capacity to recall previously stored memory maps and compare them to new data coming in from my ROM reader, thereby highlighting any errors. Errors could have been caused by a broken toroid, or one no longer able to be saturated. We found several faulty boards and were able to get replacement toroids from the Navy. Then came the task of removing three wires from a 32-toroid strip and any faulty toroids, noting the in/out sequence of the address line and rethreading three new wires through all 32 good toroids in the noted sequence with a needle and fine wire. Not easy task for a technician with fat fingers, as the toroids were less than 5mm in diameter! Without a memory map from the manufacturer, we relied on the principle that if five boards were exactly the same, and one was different, we had found one faulty board. This principle had served us well in the past without any consequences. As a technician with limited design experience, I found the process quite challenging, but I was able to continue the company policy of “we can fix anything”. Unfortunately, the company was unable to continue providing these services due to changes in government policy, resulting in insufficient work from the defence force for small contractors. Daikin three-phase aircon repair K. W., of Craigburn Farm, SA found that sometimes faults in seemingly complicated devices can be simple enough to find and fix with just a bit of investigation. It sure beats having to buy a whole new control board... On a hot Sunday, my Daikin FDY “F series” three-phase air conditioner started playing up. It gave me Error E3, which an internet search revealed was likely due to a compressor over-pressure condition. To survive the day (and Australia's electronics magazine siliconchip.com.au keep SWMBO [she who must be obeyed] happy), I periodically sprayed the compressor cooling fins with water and powered the unit off and then on again. The problem was that one fan of two wasn’t running, so the compressor was overheating. Direct sunlight on the unit and the wall behind it didn’t help either. My wife wanted me to call in a pro (oh, she of little faith!). After removing a bunch of screws from the outside unit, the top and a small front panel came off easily, exposing the electronics for inspection and probing. I made some measurements, then phoned an electrician mate who has a refrigeration ticket. He came over and had a look, but went away with the model number, expecting to get the price of a new controller board for me. I thought I’d investigate further. First, I went next door, where there is an identical unit and got my neighbour to start his air conditioner to see if both fans ran at startup. They did. I’d already unplugged the fans and swapped them over. The fault didn’t follow the leads, so the fan motor was OK, even though the winding resistances on one were a bit higher than the other. I then swapped the leads to the two start capacitors. No change, so they were both good. The circuit diagram inside the cover showed that the wire into each motor (excluding the capacitor connections) was fed from a relay. I prised the control board out and measured the coil resistances on all those PCB-mounted relays and the (I think) 1kW resistors going to them. All were roughly the same. I thought maybe a relay had crook contacts. I’d had to pull leads off a couple of connectors to move the PCB, and I noticed one was very wobbly. It definitely needed resoldering, thanks to my rough handling. That made me wonder if any other connector solder joints were dry/broken. One lead to the non-working fan was near zero volts, while on the working fan, that same lead was at 240V AC. Between those connector pins was a copper trace. So out with the magnifier and torch; sure enough, I found a broken-­off solder joint on one of those pins. After scraping the nearby tracks with a small cutting tool to expose the copper, I repaired the bad joints I could see and then touched up a few others for good measure. Both fans were running with the power back on and the air conditioner set to cool. Success! I put the covers back on, and SMS’d my mate so he didn’t have to chase up a new controller board. The moral of the story is: if you have experience with mains-powered equipment, have a go. The fault might be trivial, even where a microprocessor is involved. I felt a bit silly not suspecting a dry or broken joint in the first place. A PCB, connector pins, and vibration are a recipe for eventual failure. A few years back, I fixed our front-loading washing machine with the same type of problem. The controller board was mounted on top of the drum! The symptoms were intermittent wash operation. I couldn’t see the dry joint except with a powerful magnifier; resoldering the high-current joints fixed it. The ordinary repairman (not Dave, of course) simply replaces controller boards at great expense and waste. When your time is free, a deeper investigation is warranted. SC siliconchip.com.au Australia's electronics magazine March 2023  89 Vintage Radio Three “kindred” radios from STC By Assoc. Prof. Graham Parslow The BGE Dapper (green), STC Pixie (grey) and STC Bantam (red). The sales motto for STC was “for tone it stands alone”. The STC parent company in the UK was the primary supplier of English telephone systems, and STC was the first to use fibre optic cable for telephone transmission. STC also partnered with several US companies under the ITT umbrella to share technology. STC merged with BGE in the UK after World War 2. STC eventually failed globally in 1991 due to losses from computer manufacturing. The history of BGE Standard Telephones and Cables’ name was chosen to imply that STC was the standard by which others would be judged. That is probably a bit of a stretch, but you can at least say that the three Australian-made radios covered in this article from the mid-1950s have striking appearances that are definitely of their era. S TC started out in London as International Western Electric in 1883. It became STC in 1925 when it was taken over by ITT (International Telephone & Telegraph) of the USA. STC’s high points were supplying the entire radio systems for the liners Queen Mary and Queen Elizabeth (1936-39) and patenting pulse code modulation (1938). 90 Silicon Chip Their Australian operations date from 1923, when Western Electric set up a subsidiary in Sydney. Local manufacturing expanded significantly in 1936 with a new factory in Botany Road, Sydney, employing 700 people. Domestic radios were a minor part of STC operations, with commercial transmitters and military equipment being their major activities. Australia's electronics magazine BGE is British General Electric, a name created for Australian operations. The General Electric Company (GEC) rose to be a major UK-based industrial conglomerate producing consumer and defence products. From a small retail company in 1886, the company prospered through two world wars and amalgamation with Marconi. GEC merged with English Electric in 1968, a company famous for making jet aircraft like the Canberra and Lightning. GEC operations were broken into subsidiary companies after 2001. In 1999, GEC was renamed Marconi. That same year, Marconi Electronic Systems was sold to British Aerospace to become BAE Systems. Telecommunications giant Ericsson acquired the bulk of the remainder of the company in 2005. HRSA member Peter Hughes posted the following information about Australian operations at siliconchip.au/ link/abhi The British General Electric Co. started importing British-made sets into Australia under the name Gecophone from 1924 (a portmanteau of GEC-o-phone). The Gecophone radios sent to Australia were manufactured at the Coventry works (UK), which was “equipped with the most up to date machinery in the world”. Australian siliconchip.com.au A close-up of the dial used in the 1933 Genalex Dapper-5. The chassis of the STC model A5140 ► Bantam radio with the valves marked. models were “minutely adapted to suit Australian regulations and conditions”. A complete Gecophone two-valve radio with headphones cost £35 in 1924. Evan Murfett has described and illustrated many of the beautifully-­ presented Gecophone receivers of 1922-25 in the HRSA magazine “Radio Waves”, in a five-part series commencing in issue 146, September 2018. In 1929, the Australian government imposed a high tariff on imported radios. After 1930, BGE sets were manufactured in Sydney by Thom and Smith Ltd (Tasma) under the name of Genalex. The dial of a 1933 Genalex Dapper-5 from the author’s collection is pictured above. Also in 1933, the company made an agreement with Amalgamated Wireless Valve Co. Ltd. (AWV) for valves to be made with the Osram brand. The Osram boxes were marked “Made in Australia for the British General Electric Co. Ltd.”. The brand used for radios was changed from Genalex to BGE in 1953. Between 1956 and 1962, BGE-branded products were manufactured by STC in Australia, reflecting the amalgamation of STC and BGE in the UK. At no time was GEC (UK) affiliated with the General Electric Company of America. General Electric (US) had an association with AWA in Australia, marketing badge-engineered AGE radios that were clones of AWA radios. by using contemporary dual-colour plastic cases with the speaker grille moulded into the face. However, they are much the same internally, with the Dapper and Bantam being identical. The case design of the BGE Dapper is from the UK, while the Pixie is a reproduction of an ITT design from the USA. The Bantam & Dapper circuit An identical STC model 5140 chassis is used for both the Bantam and the Dapper radios. The original circuit is shown in Fig.1. Although ferrite antennas were becoming common in the mid-1950s, these radios have a conventional aerial coil with standard circuitry around the 12AH8 mixer valve. The local oscillator is the Armstrong type with a discrete coil to generate positive feedback to sustain oscillation (the 12AH8 triode oscillator couples internally to the heptode grid number three). The 9-pin 12AH8 valve is a rarity in Australian sets. It was designed by STC in the UK and released in 1953 under the brand Brimar, an STC An advert from 1955 showing off the STC Bantam model A5140. It has a plastic case and was sold with more colour options that those listed in the advertisement. The three featured radios The green BGE Dapper, the grey STC Pixie and the red STC Bantam were all current in the mid-1950s. Stylistically, they appear to be linked only siliconchip.com.au Australia's electronics magazine March 2023  91 Fig.1: the circuit diagram for the STC model 5140 radio. Note that while the circuit has been relabelled, there might be mistakes in the values due to the poor legibility of the original diagram. Power switch S1 is ganged to potentiometer P2 and is shown in the off position. C4 & C6 are ganged (15-450pF). C9, C10, C12 & C13 are all 75pF. subsidiary. The 12 prefix indicated that the heater requires a 12V supply, but this is a centre-tapped filament to allow two 6.3V connections to heat the cathode. The 12AH8 found application in UK and US sets with no mains transformer, using a valve series with heater voltages that add up to the mains voltage. In this radio, the 12AH8 recommends itself for the high stability of the local oscillator and high sensitivity provided. The STC service notes for this Bantam claim that only 10µV of signal is required for adequate reception. The intermediate frequency signal at 455kHz is passed to a 6BA6 valve for amplification. The 6BA6 was released by RCA in 1946 and became a popular RF amplifier globally. STC manufactured the 6BA6 under the Brimar brand. The resulting amplified IF signal passes to a 6AT6 double diode-­triode, also released by RCA in 1946 and commonly partnered with a 6BA6 IF amplifier. The volume control (500kW) is designated P1 and determines the audio level fed to the 6AT6 audio preamplifier grid. The ground return is via R14 (200W), which in theory should not prevent the volume control from achieving null volume. Still, in practice, most of these radios have some small residual audio output with the control at minimum. The junction of R13 and R14 provides negative audio feedback from the speaker to minimise distortion and improve frequency response. The sound is rather strident unless the topcut tone control (P2) is used to dampen higher frequencies. The 6CH6 output pentode operates with an anode voltage of 235V, allowing it to deliver 6W or more audio output. This valve is an STC UK design released in 1952 under the Brimar brand and intended for video amplification rather than audio. However, at higher volume levels, these radios rapidly enter into distortion because the Rola 5C speaker cannot handle much more than 2W (2.5W in the specifications). Another limitation to output power is the small Rola 5kW:3.5W output transformer that just fits in the limited space above the speaker. It is unfortunately common for these An aluminium dial version of the STC Bantam radio. The chassis underside of the STC model 5140 (Bantam series). 92 Silicon Chip Australia's electronics magazine siliconchip.com.au Fig.2: the circuit diagram for the STC model 5162 (used in the STC Pixie) which is mostly identical in design to the model 5140 apart from some component changes. small transformers to have open primaries. Replacing them with a larger standard transformer (which is generally the only realistic option) requires some creativity in the mounting. The dial stringing diagram for the Bantam and Dapper reflects a simple solution to driving a dial at the left-hand side by a knob at the righthand side. A long shaft across the top avoids complex runs of string threaded around guide pulleys. An unsophisticated timber bobbin redirects the string movement through 90°. The Pixie circuit The Pixie uses an STC model 5162 chassis. Although the case design makes this radio stand out, it is otherwise a conventional radio using readily-­available components. At a glance, the STC 5140 and 5162 circuits (see Fig.2) are similar. The first difference to observe is the use of a 6BE6 mixer in the 5162 (released by RCA in 1946), a valve choice that is common to many Australian radios. This valve also achieves a sensitivity of 10μV for effective reception. The 6BE6 sustains local oscillation The chassis underside of the STC ► Pixie. Compared to the STC Bantam, it’s a lot more spacious. siliconchip.com.au Australia's electronics magazine using a Hartley circuit (compared to the Armstrong circuit in the Bantam). The volume control is 1MW rather than 500kW in the Bantam. Other visible differences are mainly due to drafting choices in the circuit diagram rather than circuit differences. The Bantam-Dapper chassis Thermoplastics allowed any concept to become a reality, cheaply and in great quantity. The fifties was a time when plastic was fantastic and atomic energy was about to transform Shown from left-to-right, top-to-bottom are the Bantam series of STC radios from 1946, 1948, 1950 & 1952. Despite being part of the same series, the chassis varied wildly between them. Right: an example of a STC Dapper sporting a red case rather than the green shown in the lead image. Below: the rear interior view of the STC Pixie (also known as the STC model 5162). A clock version of this radio was also available (called the STC Radiotym). the planet. It was the period that gave us extravagant Cadillacs and radios in every colour of the rainbow. In one respect, it was a time like any other, in which stylists trumped the practical requirements of engineers. The mid-1950s STC Bantam was created on the stylist’s drawing board. After that, the engineers needed to make compromises to bring the concept to reality. The large capacitors of the day made for a cluttered layout that is difficult to troubleshoot. The hottest spot in the radio is above the 6CH6 output valve, followed closely by the 6X4 rectifier, and this commonly cooked the plastic above the valves. The hot spots are exacerbated by the closed design of the back panel. In later production, an aluminium sheet was fitted internally as a heat shield across the top, which did a reasonable job of protecting the plastic case. The Pixie is easier to work on, but it is still cluttered. The Bantam family of five After the second world war, STC catered to the market for a second radio in the home, and the first Bantam was a four-valve radio for the entrylevel market. The picture of the first four Bantams shows how style and taste changed in a decade. The 1950 model (called the ‘caravan’) and the 1952 model (called the ‘Eiffel Tower’ or ‘waterfall’) are particularly valued by collectors. A bit of nostalgia Every radio can be a TARDIS (for those Doctor Who fans) that transports us to another time and place. A red STC Bantam from 1957 transports me to my favourite aunt’s kitchen, where the Bantam radio resided on top of the fridge. That small modern kitchen was my aunt’s pride and joy because it was part of a bright new cream brick house. My uncle was a kind but stern man who exercised his right as head of the family to demand complete silence as he listened to Dossier on Demetrius and other favourites on the radio. This was Adelaide before television, when the radio was the entertainment and information hub of the house. I grew up in country SA, and it was exciting to go to the city and see that red STC Bantam on the fridge. SC 94 Silicon Chip siliconchip.com.au 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. Regenerative BFO (beat frequency oscillator) metal detector This circuit may represent a new concept in BFO metal detecting. It applies a well-known principle of radio receivers, regeneration, to a BFO, doubling its detection range and quadrupling its sensitivity. Where a BFO metal detector typically picks up an old English penny at about 100mm, this circuit will do so at about 200mm. Since inductor L1 and the two 1nF capacitors resist rapid changes in voltage (called reactance), any change in the logic level at IC1e’s pin 10 is delayed during the transfer back to input pin 1. Propagation delays within IC1 add further delays. The net result is oscillation at around 170kHz, which can be picked up by an AM radio. Any change to the inductance of L1, through the presence of nearby metal, shifts the oscillator frequency. The vital twist lies in positive feedback (regeneration) through VR1, which I adjusted to about 170kW. A lead from IC1b and IC1c pins 4 and 5 needs to be attached to an AM radio aerial. If the radio has a BFO switch, switch it on. Due to changes in voltage and temperature (in the circuit and radio), the tone will drift over time, so VR1 needs to be readjusted periodically. Almost any coil will do. The prototype used 50 turns of 30 SWG/22 AWG (0.315mm diameter) enamelled copper wire, wound on a 120mm/4.7-inch former. This was then tightly wrapped in insulation tape. This coil requires a Faraday shield, which is connected to 0V. This is a wrapping of aluminium foil around the coil, leaving a small gap, so the foil does not complete the entire circumference of the coil. The shield is again wrapped in insulation tape. You can make a connection to the Faraday shield by wrapping a bare piece of stiff wire around it before adding the tape. Ideally, the search coil will be wired to the circuit by a twin-core microphone cable, with the screen joined to the Faraday shield. The metal detector is set up by tuning the AM radio to pick up a whistle, a harmonic of the detector's (roughly) 170kHz. Not every harmonic works well, so the most suitable one needs to be found; tuning the radio to about 9MHz (shortwave) produced a good result for me. One should expect to pick up an old English penny at 170mm as a minimum. The Regenerative BFO metal detector will also discriminate between ferrous and non-ferrous metals through a rise or fall in tone. The 40106 chip used can affect performance. I used a CD40106BE (TI) initially; with a CD40106BCN (Fairchild), the performance was just average. Thomas Scarborough, Capetown, South Africa. ($100) Circuit Ideas Wanted Got an interesting original circuit that you have cleverly devised? We will pay good money to feature it in Circuit Notebook. We can pay you by electronic funds transfer, cheque or direct to your PayPal account. Or you can use the funds to purchase anything from the Silicon Chip Online Store. Email your circuit and descriptive text to editor<at> siliconchip.com.au siliconchip.com.au Australia's electronics magazine March 2023  95 3D-printed Robotic Arm You can teach this Robotic Arm a range of tasks. It has two joysticks and a colour TFT that acts as a touchbased control panel and also shows what's going on. The Robotic Arm can be operated directly through Manual Mode or taught new tasks through Automated Mode. The robot then repeats those tasks forever in a loop, until you tell it to stop! It has three degrees of freedom (DOF) and a gripper, so four MG90S metal gear servo motors are required. You can see a video of it operating at https://youtu.be/m7aQCT_xI4s An Arduino Mega is used for the controller as it has many I/O pins that are needed to drive the display and control the Arm simultaneously. Gerber files are available for the custom interface PCB I designed to prevent a mess of wires; you can also download them from the Silicon Chip website. The only specialised components you will need are the MG90S servos, an Arduino touchscreen shield (MCUFriend compatible; eg, Jaycar Cat XC4630) and an Arduino Dual PS2 Joystick Breakout Module (eg, www.ebay. com.au/itm/403015727271). As well as the Arm being 3D printed, I’ve designed a control panel box to host the electronics using Tinkercad that can also be printed. The Robotic Arm has two modes: Manual Mode and Automated Mode. In Manual Mode, the Arm is directly controlled using the two joysticks on the control panel. In Automated Mode, you can either record a sequence of actions or play back an already-recorded sequence. When you hit the record button, you can manoeuvre the Arm using the joysticks and save checkpoints (or ‘savepoints’) which the Arm will later repeat when in playback mode. Navigation takes place using the TFT touch display. I have made a responsive GUI (graphical user interface), so the Robotic Arm performs smoothly. Since I was mainly concerned with the logic behind the functioning of the Arm, I used an already-available opensource robotic arm, the EEZYbotARM. You can download the STL files for this Arm from www.thingiverse.com/ thing:1015238, print them on a 3D printer, and assemble them, including the four MG90S servos. See the assembly instructions at www.instructables. com/EEZYbotARM/ We are then ready to move on to the electronics. We just need to connect the servos, the joysticks and the display to the Arduino Mega board. The display can be directly plugged into the Arduino, but the other two cannot. So I designed a custom interface PCB with headers to make the servo connections, plus others for connecting the jumper wire ribbon from the joysticks can be downloaded from the Silicon Chip website. The resulting Arduino shield can be directly plugged into the Arduino Mega board, with the touchscreen plugged into the top. I added two LEDs, one indicating power, while the other can be controlled by the Arduino as needed. You could build the Robotic Arm without my PCB by connecting everything to the Mega using flying leads if you prefer. I designed the control panel box in Tinkercad, and the STL files are available to download from siliconchip. com.au/Shop/6/132 Note that it’s designed to suit a 2.4inch touchscreen; if using a larger one (eg, 2.8-inch), you would need to enlarge and possibly move the screen cutout. I used a single module with two joysticks for convenience, although it would be possible to use two separate joystick modules (they are more widely available). I have made an elevated pedestal with four screw holes in the 3D-printed enclosure, so you just need to screw the joystick module into the box using the pedestals. The box also has two cutouts for the two ports of the Arduino Mega. The Robotic Arm is powered using an AC/ DC adaptor; one port is for that, and the other is the USB port to upload code to the Arduino Mega. We need to attach the display to the bottom of the top lid. I used hot glue. Now, we just need to wire up the components. Connect the servos and joysticks to the control module (via the custom PCB shield, if you’re using it) as shown in the circuit diagram. Plug the touchscreen on top. There is a small rectangular opening at the front of the control panel box for the wires going to the servos. Note that at least six points need to be wired to the single +5V output on the Arduino, and also six grounds. So if you aren’t using the custom shield PCB, you will need to devise a method to split out the power pins on the Arduino to go to all those modules and servos. For example, you could use a pin header strip with all the pins soldered together using a wire across the base. After completing the wiring, close the top lid of the control panel box The Joystick module for the Robotic Arm is shown above, with the adjacent photo showing it fitted into an enclosure and connected to the Arm. 96 Silicon Chip Australia's electronics magazine siliconchip.com.au using some screws. Then you can download the control sketch from the Silicon Chip website and upload it to the Arduino Mega using the Arduino siliconchip.com.au IDE and the usual procedure. The code spans a few thousand lines and would be hard to comprehend, so I have added comments to provide Australia's electronics magazine adequate context and help you understand the code better. Aarav Garg, Hyderabad, India. ($120) March 2023  97 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. 03/23 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 24LC32A-I/SN ATmega328P ATmega328P-AUR ATtiny85V-10PU ATtiny816 PIC10F202-E/OT PIC10LF322-I/OT PIC12F1572-I/SN PIC12F617-I/P Digital FX Unit (Apr21) Si473x FM/AM/SW Digital Radio (Jul21), 110dB RF Attenuator (Jul22) RGB Stackable LED Christmas Star (Nov20) Shirt Pocket Audio Oscillator (Sep20) ATtiny816 Development/Breakout Board (Jan19) Ultrabrite LED Driver (with free TC6502P095VCT IC, Sep19) Range Extender IR-to-UHF (Jan22) LED Christmas Ornaments (Nov20; versions), Nano TV Pong (Aug21) Model Railway Level Crossing (two required – $15/pair) (Jul21) Range Extender UHF-to-IR (Jan22), Active Mains Soft Starter (Feb23) PIC12F617-I/SN Model Railway Carriage Lights (Nov21) PIC12F675-I/P Train Chuff Sound Generator (Oct22) PIC12F675-I/SN Tiny LED Xmas Tree (Nov19) PIC16F1455-I/P Digital Lighting Controller Slave (Dec20), Auto Train Controller (Oct22) PIC16F1455-I/SL Ol’ Timer II (Jul20), Battery Multi Logger (Feb21) PIC16LF1455-I/P New GPS-Synchronised Analog Clock (Sep22) PIC16F1459-I/P Cooling Fan Controller (Feb22), Remote Mains Switch Receiver (Jul22) PIC16F1459-I/SO Multimeter Calibrator (Jul22), Buck/Boost Charger Adaptor (Oct22) PIC16F15214-I/SN Tiny LED Icicle (Nov22), Digital Volume Control Pot (SMD; Mar23) PIC16F15214-I/P Digital Volume Control Pot (TH; Mar23) PIC16F1705-I/P Flexible Digital Lighting Controller (Oct20) Digital Lighting Controller Translator (Dec21) PIC16F18146-I/SO Digital Boost Regulator (Dec22) PIC16LF15323-I/SL Remote Mains Switch Transmitter (Jul22) W27C020 Noughts & Crosses Computer (Jan23) ATSAML10E16A-AUT PIC16F18877-I/P PIC16F18877-I/PT PIC16F88-I/P High-Current Battery Balancer (Mar21) USB Cable Tester (Nov21) Dual-Channel Breadboard PSU Display Adaptor (Dec22) Battery Charge Controller (Dec19 / Jun22) Railway Semaphore (Apr22) PIC24FJ256GA702-I/SS Ohmmeter (Aug22), Advanced SMD Test Tweezers (Feb23) PIC32MM0256GPM028-I/SS Super Digital Sound Effects (Aug18) PIC32MX170F256D-501P/T 44-pin Micromite Mk2 (Aug14), 4DoF Simulation Seat (Sep19) PIC32MX170F256B-50I/SP Micromite LCD BackPack V1-V3 (Feb16 / May17 / Aug19) RCL Box (Jun20), Digital Lighting Controller Micromite Master (Nov20) Advanced GPS Computer (Jun21), Touchscreen Digital Preamp (Sep21) PIC32MX170F256B-I/SO Battery Multi Logger (Feb21), Battery Manager BackPack (Aug21) PIC32MX270F256B-50I/SP ASCII Video Terminal (Jul14), USB M&K Adaptor (Feb19) $20 MICROS ATmega644PA-AU AM-FM DDS Signal Generator (May22) dsPIC33FJ64MC802-E/SP dsPIC33FJ128GP306-I/PT PIC32MX470F512H-I/PT PIC32MX470F512H-120/PT PIC32MX470F512L-120/PT 1.5kW Induction Motor Speed Controller (Aug13) CLASSiC DAC (Feb13) Stereo Echo/Reverb (Feb 14), Digital Effects Unit (Oct14) Micromite Explore 64 (Aug 16), Micromite Plus (Nov16) Micromite Explore 100 (Sep16) $25 MICROS $30 MICROS PIC32MX695F512H-80I/PT Touchscreen Audio Recorder (Jun14) PIC32MZ2048EFH064-I/PT DSP Crossover/Equaliser (May19), Low-Distortion DDS (Feb20) DIY Reflow Oven Controller (Apr20), Dual Hybrid Supply (Feb22) KITS, SPECIALISED COMPONENTS ETC DIGITAL VOLUME CONTROL POTENTIOMETER (MAR 23) SMD version kit: includes all relevant parts except the universal remote control and activity LED (Cat SC6623) $60.00 Through-hole version kit: includes all relevant parts (with SMD PGA2311) except the universal remote control and activity LED (Cat SC6624) $70.00 ACTIVE MAINS SOFT STARTER (FEB 23) Hard-to-get parts: includes the PCB, transformer, relay, thermistor, programmed micro and all other semiconductors (Cat SC6575; see page 41, February 2023) $100.00 ADVANCED SMD TEST TWEEZERS KIT (CAT SC6631) (FEB 23) RASPBERRY PI PICO W BACKPACK (JAN 23) Includes all parts (except coin cell and CON1) (see page 51, February 2023) Complete kit: includes all parts in the parts list, except the DS3231 real-time clock IC (Cat SC6625; see page 56, January 2023) - DS3231 real-time clock SOIC-16 IC (Cat SC5103) - DS3231MZ real-time clock SOIC-8 IC (Cat SC5779) Q METER SHORT-FORM KIT (CAT SC6585) $45.00 $85.00 $7.50 $10.00 (JAN 23) Includes the PCB, all required onboard parts (excluding optional debug interface) and the front panel. Just add a signal source, case, power supply and wiring $100.00 DUAL-CHANNEL BREADBOARD PSU (DEC 22) Power Supply kit: complete kit with a choice of red + green, yellow + cyan or orange + white knob colours (Cat SC6571; see page 38, December 2022) Display Adaptor kit: complete kit (Cat SC6572; see page 45, December 2022) $40.00 $50.00 DIGITAL BOOST REGULATOR KIT (CAT SC6597) (DEC 22) LC METER MK3 (NOV 22) NEW GPS(/WIFI)-SYNCHRONISED ANALOG CLOCK (SEP & NOV 22) Complete kit that also includes all optional components (see page 87, Dec22) Short Form Kit: includes the PCB and all non-optional onboard parts, except the case, front panel label and power supply (Cat SC6544) $30.00 $65.00 GPS-version kit: includes everything in the parts list with the VK2828 GPS module (Cat SC6472; see September 2022 p63) $55.00 WiFi-version kit: includes everything in the parts list with the D1 Mini module instead (Cat SC6472; D1 Mini is supplied not programmed, see November 2022 p76) $55.00 siliconchip.com.au/Shop/ - VK2828U7G5LF GPS module with antenna and cable (Cat SC3362) $25.00 BUCK/BOOST CHARGER ADAPTOR KIT (CAT SC6512) (OCT 22) MINI LED DRIVER (CAT SC6405) (SEP 22) WiFi PROGRAMMABLE DC LOAD (SEP 22) Includes everything in the parts list (see page 64, October 2022) except the Buck/Boost LED Driver (see adjacent; Cat SC6292) Complete Kit: includes everything in the parts list $40.00 Short Form Kit: includes all SMDs, the power Mosfets, four 0.02W 3W resistors and the VXO7805 regulator module (Cat SC6399) - laser-cut 3mm clear acrylic side panel (SC6514) - 3.5-inch TFT LCD touchscreen (Cat SC5062) $25.00 $85.00 $7.50 $35.00 WIDE-RANGE OHMMETER (CAT SC4663) (AUG 22) VGA PICOMITE KIT (CAT SC6417) (JUL 22) MULTIMETER CALIBRATOR KIT (CAT SC6406) (JUL 22) BUCK-BOOST LED DRIVER KIT (CAT SC6292) (JUN 22) SPECTRAL SOUND MIDI SYNTH KIT (CAT SC6261) (JUN 22) 500W AMPLIFIER HARD-TO-GET PARTS (CAT SC6019) (APR 22) HUMMINGBIRD AMPLIFIER (CAT SC6021) (DEC 21) Partial Kit: includes the PCB, programmed micro, all SMDs, most semiconductors, PPS capacitors and calibration resistors $75.00 - 16x2 alphanumeric LCD with blue backlighting (Cat 5759) $10.00 Complete kit with everything needed to assemble the board, you just require a few external parts such as a power supply, keyboard and monitor $35.00 Complete kit with everything needed to assemble the board Complete kit with everything needed to assemble the board Complete kit including all programmed PICs (no case or power supply) $45.00 $80.00 $200.00 All the parts marked with a red dot in the parts list, including the 12 output transistors, driver transistors, VAS transistors, input pair (2SA1312), BAV21 & UF4003 diodes, TL431 ICs, 75pF capacitor, E96 series resistors and 10kW 1W resistor $180.00 Hard-to-get parts includes: two 0.22W 5W resistors; plus one each of an MJE15034G, MJE15035G, KSC3503DS & 220pF 250V C0G ceramic capacitor *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. $15.00 PRINTED CIRCUIT BOARDS & CASE PIECES PRINTED CIRCUIT BOARD TO SUIT PROJECT THERMAL REGULATOR INTERFACE SHIELD ↳ PELTIER DRIVER SHIELD DIY REFLOW OVEN CONTROLLER (SET OF 3 PCBS) 7-BAND MONO EQUALISER ↳ STEREO EQUALISER REFERENCE SIGNAL DISTRIBUTOR H-FIELD TRANSANALYSER CAR ALTIMETER RCL BOX RESISTOR BOARD ↳ CAPACITOR / INDUCTOR BOARD ROADIES’ TEST GENERATOR SMD VERSION ↳ THROUGH-HOLE VERSION COLOUR MAXIMITE 2 PCB (BLUE) ↳ FRONT & REAR PANELS (BLACK) OL’ TIMER II PCB (RED, BLUE OR BLACK) ↳ ACRYLIC CASE PIECES / SPACER (BLACK) IR REMOTE CONTROL ASSISTANT PCB (JAYCAR) ↳ ALTRONICS VERSION USB SUPERCODEC ↳ BALANCED ATTENUATOR SWITCHMODE 78XX REPLACEMENT WIDEBAND DIGITAL RF POWER METER ULTRASONIC CLEANER MAIN PCB ↳ FRONT PANEL NIGHT KEEPER LIGHTHOUSE SHIRT POCKET AUDIO OSCILLATOR ↳ 8-PIN ATtiny PROGRAMMING ADAPTOR D1 MINI LCD WIFI BACKPACK FLEXIBLE DIGITAL LIGHTING CONTROLLER SLAVE ↳ FRONT PANEL (BLACK) LED XMAS ORNAMENTS 30 LED STACKABLE STAR ↳ RGB VERSION (BLACK) DIGITAL LIGHTING MICROMITE MASTER ↳ CP2102 ADAPTOR BATTERY VINTAGE RADIO POWER SUPPLY DUAL BATTERY LIFESAVER DIGITAL LIGHTING CONTROLLER LED SLAVE BK1198 AM/FM/SW RADIO MINIHEART HEARTBEAT SIMULATOR I’M BUSY GO AWAY (DOOR WARNING) BATTERY MULTI LOGGER ELECTRONIC WIND CHIMES ARDUINO 0-14V POWER SUPPLY SHIELD HIGH-CURRENT BATTERY BALANCER (4-LAYERS) MINI ISOLATED SERIAL LINK REFINED FULL-WAVE MOTOR SPEED CONTROLLER DIGITAL FX UNIT PCB (POTENTIOMETER-BASED) ↳ SWITCH-BASED ARDUINO MIDI SHIELD ↳ 8X8 TACTILE PUSHBUTTON SWITCH MATRIX HYBRID LAB POWER SUPPLY CONTROL PCB ↳ REGULATOR PCB VARIAC MAINS VOLTAGE REGULATION ADVANCED GPS COMPUTER PIC PROGRAMMING HELPER 8-PIN PCB ↳ 8/14/20-PIN PCB ARCADE MINI PONG Si473x FM/AM/SW DIGITAL RADIO 20A DC MOTOR SPEED CONTROLLER MODEL RAILWAY LEVEL CROSSING COLOUR MAXIMITE 2 GEN2 (4 LAYERS) BATTERY MANAGER SWITCH MODULE ↳ I/O EXPANDER NANO TV PONG LINEAR MIDI KEYBOARD (8 KEYS) + 2 JOINERS ↳ JOINER ONLY (1pc) TOUCHSCREEN DIGITAL PREAMP ↳ RIBBON CABLE / IR ADAPTOR 2-/3-WAY ACTIVE CROSSOVER TELE-COM INTERCOM SMD TEST TWEEZERS (3 PCB SET) USB CABLE TESTER MAIN PCB DATE MAR20 MAR20 APR20 APR20 APR20 APR20 MAY20 MAY20 JUN20 JUN20 JUN20 JUN20 JUL20 JUL20 JUL20 JUL20 JUL20 JUL20 AUG20 NOV20 AUG20 AUG20 SEP20 SEP20 SEP20 SEP20 SEP20 OCT20 OCT20 OCT20 NOV20 NOV20 NOV20 NOV20 NOV20 DEC20 DEC20 DEC20 JAN21 JAN21 JAN21 FEB21 FEB21 FEB21 MAR21 MAR21 APR21 APR21 APR21 APR21 APR21 MAY21 MAY21 MAY21 JUN21 JUN21 JUN21 JUN21 JUL21 JUL21 JUL21 AUG21 AUG21 AUG21 AUG21 AUG21 AUG21 SEP21 SEP21 OCT21 OCT21 OCT21 NOV21 PCB CODE Price 21109181 $5.00 21109182 $5.00 01106193/5/6 $12.50 01104201 $7.50 01104202 $7.50 CSE200103 $7.50 06102201 $10.00 05105201 $5.00 04104201 $7.50 04104202 $7.50 01005201 $2.50 01005202 $5.00 07107201 $10.00 SC5500 $10.00 19104201 $5.00 SC5448 $7.50 15005201 $5.00 15005202 $5.00 01106201 $12.50 01106202 $7.50 18105201 $2.50 04106201 $5.00 04105201 $7.50 04105202 $5.00 08110201 $5.00 01110201 $2.50 01110202 $1.50 24106121 $5.00 16110202 $20.00 16110203 $20.00 16111191-9 $3.00 16109201 $12.50 16109202 $12.50 16110201 $5.00 16110204 $2.50 11111201 $7.50 11111202 $2.50 16110205 $5.00 CSE200902A $10.00 01109201 $5.00 16112201 $2.50 11106201 $5.00 23011201 $10.00 18106201 $5.00 14102211 $12.50 24102211 $2.50 10102211 $7.50 01102211 $7.50 01102212 $7.50 23101211 $5.00 23101212 $10.00 18104211 $10.00 18104212 $7.50 10103211 $7.50 05102211 $7.50 24106211 $5.00 24106212 $7.50 08105211 $35.00 CSE210301C $7.50 11006211 $7.50 09108211 $5.00 07108211 $15.00 11104211 $5.00 11104212 $2.50 08105212 $2.50 23101213 $5.00 23101214 $1.00 01103191 $12.50 01103192 $2.50 01109211 $15.00 12110121 $30.00 04106211/2 $10.00 04108211 $7.50 For a complete list, go to siliconchip.com.au/Shop/8 PRINTED CIRCUIT BOARD TO SUIT PROJECT ↳ FRONT PANEL (GREEN) MODEL RAILWAY CARRIAGE LIGHTS HUMMINGBIRD AMPLIFIER DIGITAL LIGHTING CONTROLLER TRANSLATOR SMD TRAINER 8-LED METRONOME 10-LED METRONOME REMOTE CONTROL RANGE EXTENDER UHF-TO-IR ↳ IR-TO-UHF 6-CHANNEL LOUDSPEAKER PROTECTOR ↳ 4-CHANNEL FAN CONTROLLER & LOUDSPEAKER PROTECTOR SOLID STATE TESLA COIL (SET OF 2 PCBs) REMOTE GATE CONTROLLER DUAL HYBRID POWER SUPPLY SET (2 REGULATORS) ↳ REGULATOR ↳ FRONT PANEL ↳ CPU ↳ LCD ADAPTOR ↳ ACRYLIC LCD BEZEL RASPBERRY PI PICO BACKPACK AMPLIFIER CLIPPING DETECTOR CAPACITOR DISCHARGE WELDER POWER SUPPLY ↳ CONTROL PCB ↳ ENERGY STORAGE MODULE (ESM) PCB 500W AMPLIFIER MODEL RAILWAY SEMAPHORE CONTROL PCB ↳ SIGNAL FLAG (RED) AM-FM DDS SIGNAL GENERATOR SLOT MACHINE HIGH-POWER BUCK-BOOST LED DRIVER ARDUINO PROGRAMMABLE LOAD SPECTRAL SOUND MIDI SYNTHESISER REV. UNIVERSAL BATTERY CHARGE CONTROLLER VGA PICOMITE SECURE REMOTE MAINS SWITCH RECEIVER ↳ TRANSMITTER (1.0MM THICKNESS) MULTIMETER CALIBRATOR 110dB RF ATTENUATOR WIDE-RANGE OHMMETER WiFi PROGRAMMABLE DC LOAD MAIN PCB ↳ DAUGHTER BOARD ↳ CONTROL BOARD MINI LED DRIVER NEW GPS-SYNCHRONISED ANALOG CLOCK BUCK/BOOST CHARGER ADAPTOR 30V 2A BENCH SUPPLY MAIN PCB ↳ FRONT PANEL CONTROL PCB AUTO TRAIN CONTROLLER ↳ TRAIN CHUFF SOUND GENERATOR PIC16F18xxx BREAKOUT BOARD (DIP-VERSION) ↳ SOIC-VERSION AVR64DD32 BREAKOUT BOARD LC METER MK3 ↳ ADAPTOR BOARD DC TRANSIENT SUPPLY FILTER 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 DATE NOV21 NOV21 DEC21 DEC21 DEC21 JAN22 JAN22 JAN22 JAN22 JAN22 JAN22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 FEB22 MAR22 MAR22 MAR22 MAR22 MAR22 APR22 APR22 APR22 MAY22 MAY22 JUN22 JUN22 JUN22 JUN22 JUL22 JUL22 JUL22 JUL22 JUL22 AUG22 SEP22 SEP22 SEP22 SEP22 SEP22 OCT22 OCT22 OCT22 OCT22 OCT22 OCT22 OCT22 OCT22 NOV22 NOV22 NOV22 NOV22 DEC22 DEC22 DEC22 DEC22 JAN23 JAN23 JAN23 JAN23 JAN23 FEB23 FEB23 PCB CODE 04108212 09109211 01111211 16110206 29106211 23111211 23111212 15109211 15109212 01101221 01101222 01102221 26112211/2 11009121 SC6204 18107211 18107212 01106193 01106196 SC6309 07101221 01112211 29103221 29103222 29103223 01107021 09103221 09103222 CSE211002 08105221 16103221 04105221 01106221 04107192 07107221 10109211 10109212 04107221 CSE211003 04109221 04108221 04108222 18104212 16106221 19109221 14108221 04105221 04105222 09109221 09109222 24110222 24110225 24110223 CSE220503C CSE200603 08108221 16111192 04112221 04112222 24110224 01112221 07101221 CSE220701 CSE220704 08111221 08111222 10110221 04106221/2 Price $5.00 $2.50 $5.00 $5.00 $5.00 $5.00 $7.50 $2.50 $2.50 $7.50 $5.00 $5.00 $7.50 $20.00 $25.00 $7.50 $2.50 $5.00 $2.50 $5.00 $5.00 $2.50 $5.00 $5.00 $5.00 $25.00 $2.50 $2.50 $7.50 $5.00 $5.00 $5.00 $7.50 $7.50 $5.00 $7.50 $2.50 $5.00 $5.00 $7.50 $7.50 $5.00 $10.00 $2.50 $5.00 $5.00 $7.50 $2.50 $2.50 $2.50 $2.50 $2.50 $2.50 $7.50 $2.50 $5.00 $2.50 $5.00 $5.00 $5.00 $10.00 $5.00 $5.00 $5.00 $12.50 $12.50 $10.00 $10.00 DIGITAL VOLUME CONTROL POT (SMD VERSION) ↳ THROUGH-HOLE VERSION MODEL RAILWAY TURNTABLE CONTROL PCB ↳ CONTACT PCB (GOLD-PLATED) MAR23 MAR23 MAR23 MAR23 01101231 01101232 09103231 09103232 $2.50 $5.00 $5.00 $10.00 NEW PCBs We also sell the Silicon Chip PDFs on USB, RTV&H USB, Vintage Radio USB and more at siliconchip.com.au/Shop/3 ASK SILICON CHIP Got a technical problem? Can’t understand a piece of jargon or some technical principle? Drop us a line and we’ll answer your question. Send your email to silicon<at>siliconchip.com.au Changing active loudspeakers to passive Can your Active Monitor Loudspeakers (November & December 2022; siliconchip.au/Series/390) be built as a passive system with the addition of an appropriate crossover, to be driven by a 60W amplifier while the rest of the electronics is built? Can you suggest a design for the crossover? (P. K., Merewether, NSW) ● The monitors could possibly be built and set to work with a passive crossover. The question is how much effort and money you want to put into making the crossover as a stopgap while you build the Active Crossover Amplifier. The active crossover design removes a lot of complexity and expense in the crossover and allows you to tweak the balance of the drivers. It also provides superb control over the drivers. Designing an optimal passive crossover is not trivial; outside the simple job of choosing the parts to get the desired crossover frequency, there is invariably quite a process in tweaking the response. Also, one would often take a different approach in designing speakers to use a passive crossover rather than an active one. For example, selecting drivers with a large overlap in their operating frequency ranges to avoid needing a steep and, thus, a more complicated crossover network. So it isn’t just a simple matter of substituting one for the other. You could use a “cookbook” to build a first- or second-order crossover as a temporary measure, but we are confident you will get a sub-optimal result. The drivers in this project are very high quality and quite expensive. We think you will want to get the best from them. We would be inclined to get on with building the Active Crossover Amplifier; it isn’t all that hard once you’ve gathered the parts. If you really want to experiment, the following is a starting point. Aim for a crossover point of about 2.7kHz. We used a fourth-order crossover, but 100 Silicon Chip we strongly advise against building a fourth-order passive crossover as that would be very complex and expensive. A second-order crossover is a more reasonable starting point. The tweeter attenuation would need to be in the region of 4-5dB. Bridging Hummingbird Amps and transformers I have a 30-0-30V AC 300VA toroidal transformer. I expected to get ±45V DC rails, but when I measure them with a DMM, I get approximately ±42V with one bridge rectifier. I plan to run dual rectifiers giving a proper 100Hz supply with a star Earth point. Which components do I need to change for this to power Hummingbird amplifiers (December 2021; siliconchip.au/ Article/15126)? I plan to run four modules with pairs of modules bridged to give stereo outputs. What values and parts need adjusting? Should I change the biasing? (B. C., Albion, Vic) ● Phil Prosser responds: We have a few things in the question to tease out. With a 2 × 30V AC transformer, you will get rails of 30V × √2 minus a diode drop, ie, 30V × 1.414 − 0.6V unloaded, or 41.8V in an ideal world. Given the Australian mains tolerance of -6% to +10%, your measured 42V is well within the expected range. That +10% on mains voltages means we need to design all our circuits to handle those times when you have high voltages. This can present a real design constraint. As recommended in the Active Monitor Speaker article (December 2022; siliconchip.au/Article/15585), a bridge rectifier driven by your 30 + 30V AC transformer will full-wave rectify the transformer output, resulting in the reservoir capacitors being charged at 100Hz intervals. There is no significant need for two rectifiers; indeed, the design presented in that issue uses one rectifier for four (or six) modules. The most important things to worry about are: Australia's electronics magazine • Getting the Earthing right. That article shows how to do this. Pay attention to the wiring instructions and note that the power supply board has a massive ground plane and a very low impedance star point. • Sufficient filter bank capacity. Our power supply board has room for three large electrolytic capacitors per rail. As noted in the article, a minimum of 6800μF per capacitor seems reasonable. You can run Hummingbird amplifiers in bridge mode. Use a 25 + 25V AC transformer, giving ±35V rails. You can only run this configuration into 8W speakers in bridge mode. If you have a very good power supply with good filtering, you will be able to deliver close to 200W (double the rated 4W output power) into those 8W speakers. Say you only have a 2 × 30V AC transformer, and your speakers are not very low impedance (4W or more). In that case, I recommend you use one Hummingbird Amplifier per channel with plenty of power supply filtering capacitors. That will deliver close to 100W into each channel, more than enough for domestic use. That would be safer and cheaper than bridging, with less cost and only a minor impact on the actual power delivery. I would not change the biasing of the amplifier from that recommended in the article. If you follow the above advice, you should not need to change any components on the amplifier modules. Modified bench supply dropping its bundle I have built a single-channel version of the Hybrid Power Supply (February & March 2022; siliconchip.au/ Series/377) with potentiometer controls for voltage and amperage, rather than the digital controls of the published design. Unfortunately, it sees a load of anything less than about 10W as a dead short and invokes the safety cutout. siliconchip.com.au For example, I cannot light a 12V automotive globe as the cold filament resistance is too low. This makes the power supply less useful. Ideally, the cutout resistance should be adjustable or more precisely controllable. I want to avoid the complexity of complete digital control. Can you assist? (C. D., Adelaide, SA) ● From what we can make out, there is a problem in the current sense part of what you have built. We’re assuming that the voltage regulation part works and you can control output voltage into no load from zero volts upwards using a potentiometer on CON5 (with the clockwise end of the track to pin 1 and wiper to pin 2). Note that you must have a similarly connected pot on CON6, and this must be set to provide a reasonable voltage to the current limit set input at pin 2. Otherwise, the current limit will be zero (or, depending on the input offset of IC3a, it could even shut down). The current limit circuit is very conventional and operates as a limiter, not a cutout. This functions by the INA282 sensing the output current and presenting this to pin 3 of IC3a. IC3a acts as a comparator, so if your current limit set is greater than the current sensed by the INA282, IC3a’s output switches off Q5, and the power supply operates in voltage-control mode. If the current drawn exceeds the limit, the comparator starts to bias Q5 on. After that, at some point, the sensed output current falls below the set current, and Q5 begins to turn off. This implements a current-­ control mode. So if you have set the current limit to, say, 5A, then connect a 1W resistor, you will get 5V across it. It does not ‘shut down’. Assuming you have normal voltage regulation, check that you have a linear potentiometer of, say, 1kW (this is not that critical) on the “Iset” header, then check that pin 2 of IC3a has a positive voltage that is controlled by your potentiometer. Pin 1 of IC3a should have a negative voltage, close to -4.5V. Measure the voltage on pin 3 of IC3a. This is the output of the INA282 and is the sensed current. With no load on the PSU, this should be close to 0V and will go positive at higher output currents. If there is no current limiting happening, the base of Q5 should be very close to the -4.5V rail. During current limiting, this will increase until Q5 turns on at about -3.9V. If all the above checks are OK, the current limit on this power supply should be operating normally. We don’t know how large of a 12V bulb you are testing on. If you are using a very high-wattage bulb, your cold resistance may be a fraction of an ohm. When hot, the resistance could be over 2W, so cold, it will be well under 1W. If you have set the current limit to 5A, you should see the power supply deliver this current, initially at 1V or so, increasing as the bulb heats. If your current limit is set too low, the bulb temperature could stabilise at a low output voltage. If you dial that current limit voltage to 5V, the current limit will be way over 5A, and the power supply will try to deliver a substantial current. However, the MC33167/MC34167 has cycle-by-cycle current limiting that will kick in at a bit over 5A. Material entering the public domain I would like to know when the older publications you hold copyright on will enter the public domain according to Australian Copyright Law. Do you retain the copyright for all of your authors? Are they surviving within the 70-year limit? 1955 appears to be the cutoff date as a maximum. As a result of changes to the rules in 2005, copyright has expired for works where the creator died before 1 January 1955 and the work was made public before 1 January 1955. Before 2005, the general period of copyright was the life of the author plus 50 years. In January 2005, the Australian law relating to the duration of copyright in works was amended as part of Australia’s Free Trade Agreement with the USA, to extend the general period of copyright from the life of the author plus 50 years to the life of the author plus 70 years. This extended term of copyright applied to material still in copyright on 1 January 2005. However, if the copyright had expired by 1 January 2005, copyright was not revived (unlike in the UK) – see siliconchip.au/link/abjl (J. W., Berwick, Vic) ● This is a good question but difficult to answer. If you want to reproduce part or all of one of our publications without permission, to be sure to avoid infringing our copyright, you would need to perform extensive research to determine if it is in the public domain. This is one of the (many) disadvantages of how copyright law is written. An alternative would be to ask us for permission if you have a specific use in mind. As you point out, works published before 1955 might be in the public domain, but it is not guaranteed. For articles by a specific author, you need to find out when they died and add 50 Raspberry Pi Pico W BackPack The new Raspberry Pi Pico W provides WiFi functionality, adding to the long list of features. This easy-to-build device includes a 3.5-inch touchscreen LCD and is programmable in BASIC, C or MicroPython, making it a good general-purpose controller. This kit comes with everything needed to build a Pico W BackPack module, including components for the optional microSD card, IR receiver and stereo audio output. $85 + Postage ∎ Complete Kit (SC6625) siliconchip.com.au/Shop/20/6625 The circuit and assembly instructions were published in the January 2023 issue: siliconchip.au/Article/15616 siliconchip.com.au Australia's electronics magazine March 2023  101 years to that date. If the resulting date is in the past, the work is in the public domain. You have to be careful as one author’s work may contain the work of another (eg, photos, diagrams etc). For pages without a specific or known author, we think it is reasonable to assume they are in the public domain if published before 1955. Since magazines have numerous authors, it seems they would not enter the public domain all at once because the copyright obtained from the author by the magazine for each article is linked to that author’s lifespan. Some pages might have entered the public domain, while others remain copyrighted. 50-70 years after all authors have died, the entire work enters the public domain. Making matters even more confusing, we do not know if all the authors published in early magazines transferred their copyright over to the publication. If they still hold the copyright on their work, even if we decided to say that a particular issue was now in the public domain (or that we wouldn’t enforce copyright), those authors could still possibly take legal action. It’s a real can of worms! Many early magazines do not have a very good masthead or contents page, and you have to go through all the pages to see who wrote the articles. Many of the articles do not even have a byline. Radio, TV & Hobbies ran from April 1939 to March 1965, so there was nearly 16 years’ worth of issues before January 1955. If the authors of articles in those issues died before 1955, their articles would be in the public domain. It is unlikely that all the authors of the articles in the April 1939 issue died before January 1955, so we doubt that any single issue is in the public domain in its entirety yet. For example, John Moyle was the technical editor of Radio, TV & Hobbies from the first issue (April 1939) until the 1960s. We suspect he was also involved before April 1939, when the magazine had a different name. He passed away in 1960, so any articles with his name attached will not be in the public domain yet. We are sorry we can’t help more. The fact is that even we do not fully know the exact copyright status of many of ‘our’ publications, mainly those that came before Silicon Chip. We would prefer that copyright laws were better 102 Silicon Chip defined (eg, based on a fixed period since publication rather than the lifespan of the authors), but that is out of our control. Using 2.2kW pot in Bench Supply Can I use a 2.2kW multi-turn pot instead of the much more expensive 2.5kW potentiometer in the 30V 2A Bench Supply design (October & November 2022; siliconchip.au/ Series/389)? I could include a 300W 1W resistor in series and switch it in or out to retain the range. (D. R., Dianella, WA) ● Yes, you could do that, but it would not be as convenient as using a 2.5kW potentiometer. A better way around the voltage range problem when using a 2.2kW potentiometer is to reduce the resistance between the adjust and output pins of the LM317 regulator. Reduce it sufficiently to get the full 30V when the potentiometer is set at maximum resistance. A 1.1kW resistor in parallel with the original 100W should work, and the series 300W resistor would not be required. Building the DAB+/FM/ AM Tuner I am keen to know if an updated version of the DAB+/FM/AM tuner has been developed (January-March 2019; siliconchip.au/Series/330). How do I purchase the kit? (T. L., South Africa) ● That is the latest DAB+ radio we’ve published and the only one that can still be built. The first article in the January 2019 issue has the circuit diagram and explains how it works and what it does. Part two in the February 2019 issue has the parts list and PCB assembly instructions, while part three in the March 2019 issue includes final assembly, software set-up and use. We think you would need the February & March 2019 issues to build it; otherwise, there would be too much guesswork. They are available via our website. The design is quite complicated, so you should read the article(s) before going too much further. It involves building the Explore 100 microcontroller module, attaching a five-inch touchscreen, then building the DAB+ custom PCB and putting it all together in the optional case. Australia's electronics magazine We can supply many of the parts, but not all of them (siliconchip.au/ Shop/?article=11444). Parts we sell include a kit for the Explore 100 with everything except the touchscreen, the DAB+/FM/AM radio PCB, two sets of parts for that PCB (one with radio chip IC1 and its surrounding components, the other with all the remaining SMDs), plus some bits and pieces like the antenna, antenna connectors and RCA sockets. Building both boards (Explore 100 and DAB+/FM/AM) involves soldering some SMDs, including a QFN IC and fairly small passives, so you should be confident in your SMD soldering skills before tackling this project. Multi-Spark CDI crossfire prevention I have skimmed the High-Energy Multi-Spark CDI articles (December 2014 & January 2015; siliconchip.au/ Series/279) and saw comments that there is some potential problem with 6- and 8-cylinder engines cross-firing. I plan to install one on an old 1986 6-cylinder engine. I appreciate that it is a precautionary comment but is there anything I should consider to avoid this? (R. L., Robina, Qld) ● That wording is to inform you know that the high-tension (spark plug) leads need to be spaced apart to prevent cross-fire between cylinders due to capacitive coupling if they are too close. Take care with routing the spark plug leads and you should not have any cross-fire problems. Multi-Spark CDI draws too much current I have built your Multi-Spark CDI but have encountered some problems. When I plug the CDI in, it immediately draws 4A but will not spark. I measured 300V across the 1μF capacitor and noticed that Q3 gets extremely hot, and even appears to spark. There is no excess solder around Q3; I did check that. What could be causing this? I have attached some pictures. (J. M., New Haven, CT, USA) ● Is D4 actually a UF4007? It looks like a 1N4148, but the photo is a little too blurry for us to be sure. Q3 will get hot if the 1μF X2 capacitor is shorted or if it breaks down at 300V. There may continued on page 104 siliconchip.com.au MARKET CENTRE Advertise your product or services here in Silicon Chip KIT ASSEMBLY & REPAIR FOR SALE DAVE THOMPSON (the Serviceman from Silicon Chip) is available to help you with kit assembly, project troubleshooting, general electronics and custom design work. No job too small. Based in Christchurch, New Zealand, but service available Australia/NZ wide. Email dave<at>davethompson.co.nz LEDsales KEITH RIPPON KIT ASSEMBLY & REPAIR: * Australia & New Zealand; * Small production runs. Phone Keith: 0409 662 794 keith.rippon<at>gmail.com LEDs and accessories for the DIY enthusiast LEDs, BRAND NAME AND GENERIC LEDs. Heatsinks, LED drivers, power supplies, LED ribbon, kits, components, hardware – www.ledsales.com.au 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 OATLEY ELECTRONICS www.oatleyelectronics.com GET A TDA7297 STEREO IC MODULE + 4 x FORSTER 50mm 4R speakers + a used 12V/3A power supply for a total of $29 including P+P. OR Get two of these packs for $39 inc. P+P. www.oatleyelectronics.com Phone: 0428600036 SILICON CHIP VISIT THE NEW TRONIXLABS parts clearance store for real savings on new parts at clearance prices, with flat rate express delivery Australia-wide – go to https://tronixlabs.com Lazer Security PCB PRODUCTION FOR SALE For Quality That Counts... QUALITY COMPONENTS + MORE The parts clearance sale continues, but stock is limited, this month check out the freebies – go to lazer.com.au ASSORTED BOOKS FOR $5 EACH Electronics and other related subjects – condition varies. Some of the books may have already been sold. See all books at: siliconchip.com.au/link/aawx Email for a quote (bulk discount available), state the number directly below the photo when referring to a book: silicon<at>siliconchip.com.au BUSINESS FOR SALE Well known Australian electronics company for a bargain price. GENUINE BUYERS ONLY Phone: 0410600330 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 Glyn (02) 9939 3295 or 0431 792 293. 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 March 2023  103 be a short to ground elsewhere. The capacitor you used does not appear to be an X2-rated type. Check all the component values, especially around IC3. Suitable material for speaker cabinets I am interested in building the Senator loudspeakers (September 2015; siliconchip.au/Series/291). The author suggests making the walls of the cabinets from furniture boards available in Australia, but in Poland, it is difficult to find such material. Is it possible to build the columns simply from MDF or beech timber, keeping the dimensions? Also, three sides of the cabinet (front, top and side) have double thickness. Is this only for aesthetic reasons, or does it have acoustic significance? If it has an acoustical significance, can I simply use thicker material for these walls? (B. K., Poland) ● It is OK to use MDF or beech; our construction was based on locally available materials. The double sides are for both aesthetic reasons and superior acoustics, so please use the same Advertising Index Altronics.................................27-30 Dave Thompson........................ 103 Digi-Key Electronics...................... 3 ElectroneX..................................... 7 Emona Instruments.................. IBC Hare & Forbes............................. 11 Jaycar.........................IFC, 9, 40-41, ...............................61, 66-67, 86-87 Keith Rippon Kit Assembly....... 103 Lazer Security........................... 103 LD Electronics........................... 103 LEDsales................................... 103 dimensions if possible. You could use thicker MDF rather than doubling it up if you prefer. Currawong transistor equivalents Regarding the Currawong 2 × 10W Stereo Valve Amplifier (November 2014 – January 2015; siliconchip.au/ Series/277), the STX0560 transistors have been discontinued and are no longer available. Unfortunately, there don’t seem to be any 600V TO-92 transistors anywhere. The highest rating I can find is either 400V or 500V, and there is no stock until October 2023. I know the rail is only supposed to be 310V, but 400V is still too close for comfort to my mind. Do you know of any suitable equivalents, or are you confident that a 400V transistor like the PHE13003A,412 (currently in stock at Mouser) will be OK? (T. S., Balcatta, WA) ● We think a 400V collector-emitter rating is sufficient. That’s still a safety margin of more than 25%. However, the gain of those transistors is pretty poor compared to the originals (30 vs 100 <at> 100mA). Therefore, we recommend also changing Q1 to a transistor like the BUJ302A,127. Its higher hfe of about 70, compared to 30 of the original KSC5603D, will partially compensate for the lower gains of Q2 & Q3. They appear to be pin-compatible and the BUJ302A has a more-than-adequate 1050V, 4A collector-emitter rating. In fact, the BUJ302A is a great transistor when a high-voltage NPN BJT is required. It avoids the poor gain problem of most other transistors with similarly high voltage ratings. It is available in both through-hole (TO-220) and SMD (DPAK) packages, although the SMD version is currently scarce. Microchip Technology.............OBC Oatley Electronics..................... 103 SC Advanced Test Tweezers...... 82 SC Pico W BackPack................ 101 Silicon Chip Shop.................98-99 Silicon Chip Subscriptions........ 13 The Loudspeaker Kit.com............ 6 Tronixlabs.................................. 103 Wagner Electronics..................... 89 104 Silicon Chip Errata and Next Issue Mouser Electronics....................... 4 Getting back to the topic of the discontinued STX0560 transistors, we’ve noticed that high-gain, high-voltage NPN transistors have gone extinct for reasons we don’t understand. It isn’t just the high-voltage types; even the ‘garden variety’ BC846C & BC856C are now unavailable from most vendors. We wonder if the silicon fabs that used to make these parts have changed their processes. Boost Controller troubleshooting I have built the Independent Electronic Boost Controller (siliconchip. au/link/abhk). The 10W resistor burns out as soon as 12V is applied to the board. I have not connected any inputs. What can be causing this? (L. N., Johannesburg, South Africa) ● Most likely zener diode ZD2, just below the 10W resistor, is shorted. Perhaps it is the wrong voltage type or has been installed the wrong way around. Trouble locating pin 1 of an IC I have been unable to locate pin 1 of the supplied INA282 IC. I checked the Texas Instruments data sheet, and my markings don’t correspond, so I have included a photo of the device for your opinion. My device has a white bar at one end; is that indicating the pin 1 end? (B. R., Eaglemont, Vic) ● We checked the TI data sheet, and all it shows is a chamfered edge on the pin 1 side and an “ID” in the pin 1 quadrant. Unfortunately, it doesn’t say what the ID marking is. That bar must indicate the pin 1 end, but we suggest you also check for a chamfer on the expected side. It’s hard to see the champfer if you are looking at the IC top-down. SC Heart Rate Sensor Module review, February 2023: for safety reasons, the module should be used with a battery-powered computer that is not connected to the mains, or any other equipment, during use. We also advise that the ‘patient’ avoids contact with any other equipment while the ECG probes are connected. 45V 8A Linear Bench Supply, October-December 2019: the circuit diagram (Fig.3) on p27 of the October 2019 issue shows the cathode of D5 connecting to the wrong location. It should instead connect to the VCC rail, which includes the positive ends of the 4700µF capacitors and the collectors of Q4-Q7. Next Issue: the April 2023 issue is due on sale in newsagents by Monday, March 27th. Expect postal delivery of subscription copies in Australia between March 24th and April 14th. Australia's electronics magazine siliconchip.com.au “Rigol Offer Australia’s Best Value Test Instruments” Oscilloscopes NEW 200MHz $649! New Product! 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