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Contents Vol.37, No.12 December 2024 14 Undersea Communications Undersea cables carry nearly all international internet traffic, making them one of the most important parts of the internet. As we explain, there is a lot more to them than you may realise! By Dr David Maddison, VK3DSM Communications technology 38 Precision Electronics, Part 2 This series covers the basics of precision electronics design. Building on from last month, we aim to improve the precision of our example circuit. In doing so, we investigate many features of precision op amps. By Andrew Levido Electronic design 62 Raspberry Pi Pico 2 The new Raspberry Pi Pico 2 is priced around $8 and uses an RP2350 micro. Compared to the previous iteration, it boasts double the RAM, faster clock speeds and other features like a hardware random number generator. Review by Tim Blythman Microcontroller board 98 MicroBee 256TC Restoration The MicroBee 256TC is a computer kit from 1987 and the last of the original MicroBee computers. This article details the work needed to restore one of these old devices. By Don Peterson Vintage computers UNDERSEA COMMUNICATIONS DATA TRANSMISSION & POWER CABLES Feature, Page 14 Project, Page 33 Capacitor Discharger Discharg er Precision Electronics Part 2 – Page 38 2 Editorial Viewpoint 5 Mailbag 13 Subscriptions 26 Circuit Notebook 52 Mini Projects 86 Online Shop 88 Serviceman’s Log 94 Vintage Electronics 109 Ask Silicon Chip 78 Variable Speed Drive Mk2, Part 2 111 Market Centre Our Variable Speed Drive can drive single-phase shaded pole or permanent split capacitor induction motors, as well as three-phase 230V induction motors, up to 1.5kW. We cover the construction, testing and how to use it. By Andrew Levido Motor speed control project 112 Advertising Index 112 Notes & Errata 33 Capacitor Discharger Safely discharge capacitors, both large and small, including capacitors used to store rectified mains (up to ~400V DC). It is especially helpful when servicing switch-mode power supplies and valve gear. By Andrew Levido Safety equipment project 44 Compact HiFi Headphone Amp Our new Headphone Amplifier is easy to build, fairly priced and most importantly, sounds great! It’s powered via a 9-12V AC plugpack and delivers up to 0.9W into 8Ω, 1W into 16Ω and 140mW into 600Ω. Part 1 by Nicholas Vinen Audio project 66 The Pico Computer Turn a Raspberry Pi Pico into a standalone computer with a USB keyboard and HDMI monitor. All the Pico’s I/O pins are broken out on a separate header, making it easy to use for controlling other circuitry. By Tim Blythman Computer project 1. Regulated negative supply with a 555 2. Four-cell voltage monitor 3. Over-temperature alarm 4. HT supply generator 1. Automatic night light 2. WiFi weather logger Dallas Arbiter Fuzz Face guitar pedal by Brandon Speedie