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Coming up in Silicon Chip Underground Mapping, Pipe Inspection and Leak Finding Dr David Maddison explains the numerous techniques and devices which can be used to find wires, pipes and other structures underground. In some cases, it is possible to build a complete map of everything near the surface. This is critical when digging in urban or suburban areas, to avoid damaging existing services or, in the worst case, starting a fire or a flood! 4G Remote Monitoring Station It’s often necessary to know what’s going on in a remote location, such as whether your boat battery is low, or if it is taking on water. Now that 2G is gone, and there’s talk of 3G being phased out, this is best done via 4G. Our new Arduino-based remote monitoring station can send updates over 4G mobile data or via SMS, and can even be used to switch things on and off at a distance. Micromite Air Quality Monitor An easy-to-build device which measures the concentration of Volatile Organic Compounds (VOCs) in the air and displays it on a colour LCD, both as a numeric reading (in parts-per-billion) and as a graph, showing how it changes over time. Use it to monitor your home, office, or anywhere else that you might experience poor air quality. Low-cost Hifi Bookshelf Speaker System, Pt.2 These medium-sized bookshelf speakers are made from a sheet of plywood and a couple of drivers from Altronics. While they are quite cheap to build, they certainly don’t sound cheap! And if you build the optional subwoofers, using a similar construction method, you get decent bass too, plus bonus speaker stands. Low-distortion Direct Digital Synthesiser This two-channel digital signal generator can produce very low distortion sinewaves across the audio frequency band (20Hz-20kHz), plus several other waveform shapes. The output levels are independently adjustable over a wide range, and the channels can also be phase-locked with a 0-360° phase offset. Note: these features are planned or are in preparation and should appear within the next few issues of Silicon Chip. The February 2020 issue is due on sale in newsagents by Thursday, January 30th. Expect postal delivery of subscription copies in Australia between January 28th and February 14th. Advertising Index Altronics...............................81-84 Ampec Technologies................. 19 Dave Thompson...................... 111 Digi-Key Electronics.................... 3 Emona Instruments................. IBC Jaycar............................ IFC,53-60 Keith Rippon Kit Assembly...... 111 LD Electronics......................... 111 LEACH PCB Assembly............... 5 LEDsales................................. 111 Microchip Technology................ 65 Ocean Controls........................... 6 RayMing PCB & Assembly.......... 8 Rohde & Schwarz.................. OBC SC Micromite BackPack............ 69 Silicon Chip Binders............... 111 Silicon Chip Shop...............90-91 Silicon Chip Subscriptions..... 109 Switchmode Power Supplies....... 7 The Loudspeaker Kit.com......... 67 Vintage Radio Repairs............ 111 Wagner Electronics..................... 9 Notes & Errata Discrete pump timer, Circuit Notebook, November 2019: the diodes are all shown correctly orientated, however the anode (“A”) and cathode (“K”) markings have all been swapped. Also note that the 12V version of the Cyclic Pump Timer was in the July 2017 issue, not July 2016. 45V 8A Linear Bench Supply, October-December 2019: in the PCB overlay diagram (Fig.6) on page 70 of the November issue, the types and labels for diodes D5 and D6 are swapped. D5 is on the left and should be a 1N5404 type, while D6 is closer to the edge of the board and should be an SB380. The PCBs supplied for this project have the same error on their silkscreen printing. The circuit will still function correctly if both diodes are SB380s. LoRa Chat Terminal, Circuit Notebook, August 2019: the connections from IC2 to the LCD12864 display module are incorrect. The correct connections are: 1) pins 1-8 on IC2 go to pins 7-14 on the LCD; 2) pins 23-25 on IC2 go to pins 15-17 on the LCD; 3) pins 26-28 on IC2 go to pins 4-6 on the LCD. 112 Silicon Chip Australia’s electronics magazine siliconchip.com.au