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Contents Vol.31, No.5; May 2018 SILICON CHIP www.siliconchip.com.au Features & Reviews 14 Drone Air Taxis – Autonomous, Pilotless and Soon! Already trialling in several countries, you’ll soon be able to call up a pilotless drone taxi from your smartphone. Fares are projected to be not much more than street taxis but there will be no traffic hang-ups! – by David Maddison 24 Tiny capsule measures, radios your gut gas data Medical specialists need to know what gases are in your gut – but they are loathe to operate. Now researchers in Australia have come up with a capsule that measures gases and radios the info in real time – by Ross Tester 43 LTspice Simulation: Analysing/Optimising Audio Circuits Continuing our occasional tutorial series to help you understand the very versatile LTspice simulation software. It’s still available (free!) from new owners, Analog Devices – by Nicholas Vinen 82 El Cheapo Modules 16: 35-4400MHz frequency generator Based on the ADF4351 PLL, this <$30 module can produce a signal from 35MHz to 4.4GHz with crystal accuracy. It can even be used as a sweep generator – by Jim Rowe Constructional Projects 28 800W (+) Uninterruptible Power Supply (UPS) One of our most exciting projects ever: a build-it-yourself UPS which we believe isn’t as good as commercial models . . . it’s much better! And if you need even more grunt, this design allows it – by Duraid Madina and Tim Blythman 36 Multi-use Frequency Switch Some Drone “Taxis” are still figments of their proponents’ imagination – but some are already in testing phase – Page 14 Tiny capsules pass through the gut, reading and sending gas data as they go – Page 24 Suffer from blackouts in your office or home? You need a UPS to ensure you don’t lose valuable data. It’s also the answer to maintaining power after a disaster – Page 28 If you need something controlled when it exceeds a certain frequency – up or down – this superb circuit will do it. Anything that produces a frequency (or can have a sensor fitted) can be switched – by John Clarke 57 USB Port Protector – just in case! We thought we’d fried a laptop when something managed to drop onto the exposed USB port components. We were lucky – but made up this low cost, mini PCB to guard against “oopses” in the future! – by Nicholas Vinen 70 12V Battery Balancer 12V batteries in series need careful attention to charging if you’re expecting a long life. This little balancer does it automatically for you and you can even use them in parallel for extra power handling – by Nicholas Vinen Your Favourite Columns 63 Serviceman’s Log I reckon servicemen are cursed – by Dave Thompson 76 Circuit Notebook (1) 20V, 2.5A adjustable power supply with current limiting (2) A personal “speedometer” for joggers (3) Sunset switch to discourage possums and other night visitors! (4) Adjustable audio low-pass filter 90 Vintage Radio Zenith Royal 500 “Owl Eye” AM Radio – by Dr Hugo Holden Everything Else! 2 Editorial Viewpoint Feedback 88 Product Showcase 94 SILICON CHIP Online Shop 4 Mailbag – Your siliconchip.com.au   96    103    104    104 Ask SILICON CHIP Market Centre Advertising Index Notes and Errata Switch just about any device if its output frequency goes above or below limits which you set – Page 36. USB ports can be fried if you’re not careful (we know!!!). Be safe with this low-cost USB Port Protector – Page 57 You can’t simply charge 12V batteries in series as you would a single battery – you need a battery balancer to ensure they don’t get out of balance – Page 70 www.facebook.com/siliconchipmagazine