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Advertising Index Altium............................................ 7 Altronics.................................45-48 Dave Thompson........................ 103 DigiKey Electronics....................... 3 Electronex................................... 21 Emona Instruments.................. IBC Hare & Forbes............................. 13 Jaycar..................IFC, 10-11, 15, 17 ................................... 19, 87, 89, 95 Keith Rippon Kit Assembly....... 103 Lazer Security........................... 103 LD Electronics........................... 103 LEDsales................................... 103 Microchip Technology.............OBC Mouser Electronics....................... 4 PCBWay......................................... 9 PMD Way................................... 103 Quest Semiconductors................. 8 SC GPS Analog Clock............... 101 SC Ideal Bridge Rectifiers........... 77 SC Keyboard Adaptor................. 57 SC PDFs on USB......................... 71 Silicon Chip Back Issues........... 93 Silicon Chip Binders................ 103 Silicon Chip Shop.................96-97 Silicon Chip Subscriptions........ 98 The Loudspeaker Kit.com.......... 83 Wagner Electronics..................... 14 Notes and Errata Microphone Preamplifier, February 2024: in Fig.8, the 150Ω resistor next to CON10 should be 330Ω and the two 3.9kΩ resistors above L2 should both be 3.0kΩ as described in the text on p33. Arduino DCC Controller, January 2020: transistor Q1 on the RevF DCC Power Shield PCB (09207181) has the connections to its collector and emitter reversed. To fix this, rotate the transistor 180° relative to the PCB silkscreen markings, swapping the collector and emitter. It might work with the original (incorrect) orientation, but it is not guaranteed. Next Issue: the May 2024 issue is due on sale in newsagents by Monday, April 29th. Expect postal delivery of subscription copies in Australia between April 26th and May 15th. 104 Silicon Chip LED Battery Voltage Indicator kit wanted Do you sell the KA1778 LED Battery Voltage Indicator kit? It was advertised as being sold by Jaycar in Electronics Australia magazine, September 1995 (pages 76-77). (S. W., Yungaburra, Qld) ● We have not made any kits for Jaycar. When they sell kits based on our designs, they make the kits themselves. Therefore, we do not have any Jaycar kits to sell, only our own kits. According to their website, that kit has been discontinued and is unavailable (www.jaycar.com.au/p/KA1778). You might be interested in our 10-LED Bargraph project from the February 2018 issue, which could be used for similar purposes (siliconchip. au/Article/10970). We don’t have a kit, but we can supply the PCB(s), as listed on our website at siliconchip. au/Shop/?article=10970 Tracing underground power lines I just bought a long property, and the power box is near the gate, while the shed is at the opposite end of the block. I don’t have dial-before-you-dig info and wish to avoid an accident. Have you published any articles on locating power lines underground? (S. B., Booval, Qld) ● We published a Magnetic Field Strength Meter that could be used to find the vicinity of powered mains wires in the October 1991 issue (see siliconchip.au/Article/5849). The LCD screen and driver chip (ICL7106) are not strictly necessary as a multimeter set for measuring DC volts could be used to monitor voltage after the full wave rectifier in the circuit. Essentially, you would need to walk around the area and use it to monitor the magnetic field strength, looking for a maximum reading. You would then be over the underground power lines. The best sensitivity would be when considerable power is drawn through the wiring. Detectors are commercially available but can be expensive. Building a low-power inverter I want to build a low-power AC inverter for electric toothbrushes and razors that do not have 12V charging capabilities. The 15W 240V Inverter in Australia's electronics magazine the June 1992 issue caught my eye, so I bought the magazine (siliconchip.au/ Article/5549). However, I need help as the main Mosfets (MTP3055E) are no longer made, and the article explicitly says not to substitute. Is there a modern equivalent? The dual transformers are pretty expensive at the moment ($15.75 each), so I thought element14 Cat 1214612 (16VA, 230V to 2 × 9V) might be a suitable replacement. I know it won’t fit the circuit board, but I will be designing a new (double-sided) one as you do not sell the old one anymore, and I want it to fit an existing case anyway. Before I start building it, do you have a newer version? Is there a pure sinewave version? Obviously, square wave drive is not suitable for many devices. Would switch-mode power supplies (shaver) and Braun Oral-B toothbrushes cope with the square wave output? (D. M., Hawthorn West, Vic) ● That design is somewhat outdated, although it would work for your purpose. The MTP3055E Mosfets can easily be replaced by many others. They were rated at 12A and 60V, and many better Mosfets are now available. The article said not to use alternatives because it utilised the avalanche rating of the Mosfet to clamp transients from the transformer windings when switched, and avalanche-rated Mosfets were rare then. The common IRF540(N) would be a suitable substitute. Yes, the element14 transformer would be appropriate. Although a square-wave inverter, the transformer will round off the squareness somewhat. A sinewave inverter would be better overall than a square wave type, but how much it matters depends on the charger’s design. Typically, a square wave inverter produces a 230V AC waveform with a 230V peak. A modified square wave inverter is better as it produces 230V AC with a 325V peak on the waveform, more like a sinewave inverter but with squarer edges. If you are after a small sinewave inverter, see our May 2016 project: the 230/115V AC, 50/60Hz Precision Turntable Driver (siliconchip.au/ Article/9930). The parts to build that should all still be available, although the transformer is now pretty expensive at over $60! SC siliconchip.com.au