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Contents Vol.29, No.1; January 2016 SILICON CHIP www.siliconchip.com.au Features 12 Blood Pulse Oximeters: How They Work Ever visited someone in hospital and noticed a small sensor clipped over one of their fingers? That’s the business end of a blood pulse oximeter, used to monitor the oxygen level in a patient’s blood. Here’s a quick run-down on exactly what they do and how they work – by Jim Rowe 76 Versatile Technology: An Aussie Innovator Who said the Australian electronics industry was dead? One innovative company, Versatile Technology (Melbourne), has become a world leader in making equipment for testing metal soft-drink/beer cans and other containers such as PET plastic bottles – by Ross Tester Raspberry Pi Temperature, Humidity & Pressure Monitor – Page 18 88 Handy Reactance Wallchart This handy wallchart lets you easily check the -3dB rolloff point of a simple RC or RL network or find the resonant frequency of an LC network Pro jects To Build 18 Raspberry Pi Temperature/Humidity/Pressure Monitor Pt.1 Want to monitor temperature, humidity and pressure using a web browser from a remote location? Here’s how to do it using a Raspberry Pi 2 Model B computer, a Sense HAT module and a Wi-Pi WiFi dongle – by Greg Swain Valve Stereo Preamplifier For HiFi Systems – Page 28. 28 Valve Stereo Preamplifier For HiFi Systems This stand-alone stereo valve preamplifier offers good performance, with low distortion and a very high signal-to-noise ratio of -105dB. It’s easy to build too, with the preamp and power supply all on one PCB – by Nicholas Vinen 36 High Visibility 6-Digit LED GPS Clock, Pt.2 Our new GPS high-visibility 6-digit LED clock automatically changes time zones as you travel around the country or even between countries. This second article has all the information you need to complete and use it – by Nicholas Vinen 54 Reduce Rear-End Collision Risk With The QuickBrake High-Visibility 6-Digit LED GPS Clock, Pt.2 – Page 36. Reduce the risk of rear-end collisions by automatically switching on the brake lights each time you rapidly lift off the accelerator – by John Clarke Special Columns 62 Circuit Notebook (1) USB Power Injector; (2) Bi-Directional 8-Bit Digital Interface; (3) Audio Generator Has Triangle & Square Waveforms 66 Serviceman’s Log Tools, old scopes & my hoarding habit – by Dave Thompson 82 Vintage Radio Sony’s TR-63 shirt-pocket transistor radio – by Ian Batty Departments 2   4 53 86 Publisher’s Letter Mailbag Product Showcase SC Online Shop siliconchip.com.au 91 95 96 96 Ask Silicon Chip Market Centre Advertising Index Notes & Errata Reduce Rear-End Collision Risk With The QuickBrake – Page 54. January 2016  1