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Contents Vol.35, No.4 April 2022 14 Geiger Counters and Radiation 14 Radioactivity is everywhere! But since you can’t see it, how do you tell how much, if any, is present? This article investigates ways to measure radioactivity electronically plus some of the basics of radioactivity. By Dr David Maddison Science 38 The History of Transistors, Pt2 Transistor technology progressed rapidly in the ~20 years between the first commercial transistor being produced and the development of manufacturing techniques that are still in use today. By Ian Batty Semiconductors 50 80 New 8-bit PICs from Microchip When updating our SMD Test Tweezers we found out the micro used in it wasn’t in stock, so we had to pivot to using the newer PIC16F15214. So what does it offer over the previous 8-bit micro we were using? By Tim Blythman Microcontrollers 82 Dick Smith Contest Results We received some great submissions for the Noughts & Crosses competition. This article summarises the entries of the five winners (with one special prize awarded) and four runners-up. By Nicholas Vinen Competition 27 500W Power Amplifier, Part 1 Big, clear sound with low noise and distortion are just some of the aspects of our gigantic Amplifier module. It can deliver 500W RMS into a 4W load, or 270W into 8W. Two of them can also be bridged together to deliver 1000W! By John Clarke Audio project 50 Railway Semaphore Signal This realistic-looking OO gauge semaphore is modelled on a real British semaphore. It has a ‘flag’ that is driven by a servo and a bicolour LED to indicate to a train whether to pass or stop. By Les Kerr Model railway project 72 Update: SMD Test Tweezers The Improved SMD Test Tweezers are an in-place upgrade. All you need to do is slot in the new PIC to enable a swathe of extra features. The display can also be rotated 180° to help those who are left-handed. By Tim Blythman Test equipment project 100 Capacitor Discharge Welder, Pt2 After following the steps in this article you will have built your own Capacitor Discharge Welder, which forms a neat package. It is customisable and we also provide some tips on using it. By Phil Prosser Tool project in Sydney on the 5-6th 65 Back of April at Rosehill Gardens, ElectroneX returns with a plethora of companies and workshops to visit. 2 Editorial Viewpoint 4 Mailbag 37 Subscriptions 89 Circuit Notebook 92 Serviceman’s Log 98 Online Shop 1. Very simple adjustable electronic load 2. Three games that test reaction times 3. NBN battery backup 110 Vintage Radio 116 Ask Silicon Chip Monopole D225 radio by Graham Parslow 119 Market Centre 120 Advertising Index