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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