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Notes & Errata USB SuperCodec, August-October 2020: in the Fig.13 circuit diagram on page 88 of the September 2020 issue, pin 12 of IC7 (SDOUT) should not be shown connected to pin 9 of IC6. Instead, it goes to the I2S_ADC1 connection at the right edge of Fig.12 on p86. Car Altimeter, May 2020: the design is missing one schottky diode (D8) which connects from the cathode of ZD1 (schottky anode) to the positive terminal of the battery (schottky cathode). This is needed to charge the battery. It can be added to the underside of the PCB, as shown in the accompanying photograph. Advertising Index Altronics..................17, CATALOG Ampec Technologies................. 20 Analog Devices..................... OBC Dave Thompson...................... 111 Digi-Key Electronics.................... 3 Emona Instruments................. IBC Jaycar............................ IFC,53-60 Keith Rippon Kit Assembly...... 111 LD Electronics......................... 111 LEDsales................................. 111 Microchip Technology.................. 5 Mouser Electronics...................... 7 Ocean Controls......................... 19 SC Colour Maximite 2............... 71 Silicon Chip Binders............... 111 Silicon Chip Shop...............98-99 6GHz Touchscreen Frequency Counter, October-December 2017: in the circuit diagram on pages 30 & 31 of the October 2017 issue, a 1µF bypass capacitor is missing between the anode and cathode of REF1. Also, in the overlay diagram (Fig.3) on p86 of the November 2017 issue, the board shown is RevA; the final (RevB) board adds a 100µF capacitor just to the left of REG2, with its positive lead towards the regulator. The April 2021 issue is due on sale in newsagents by Thursday, March 25th. Expect postal delivery of subscription copies in Australia between March 23rd and April 9th. hardly any mention in that article of how the circuit works! Disconnecting the charger on full battery Some time ago, you advised me how to modify the “Add-On Regulator for 12 Volt Battery Chargers” published in Electronics Australia, June 1997, to charge a 24V SLA battery. I have used it for several years, but I am now planning to upgrade to a 24V Lithiumion battery. If I set the charge voltage to 28.5V, will I need to add extra circuitry to disconnect the battery at this point? Will one of the cut-out modules, as available from eBay, be suitable for this? (B. C., Dungog, NSW) • Yes, you would need to switch off the charger when the Lithium-ion 112 Silicon Chip battery is charged. You could use our Threshold Voltage Switch (July 2014; siliconchip.com.au/Article/7924), sold as a kit by Altronics (Cat K4005) and Jaycar (Cat KC5528). Any other similar device should also work. Graphic Equaliser level matching problem I have been using an Electronics Australia Graphic Analyser for many years, even though it spends most of its life in the cupboard. I drive it with an electret mic which is switchable between 600W and 50kW. The problem is that to get a decent level on the LED display, I must have the sound level in the room extremely high, to the point that I must wear ear protection and only do it when nobody else is at home. Australia’s electronics magazine Silicon Chip PDFs on USB....... 91 Switchmode Power Supplies..... 29 The Loudspeaker Kit.com........... 9 Tronixlabs................................ 111 Vintage Radio Repairs............ 111 Wagner Electronics................... 64 It has always been that way, but it seems that it would be best to do the process at a normal listening level. Is there something I can do to increase the mic preamp gain, or might there be some other problem? The original build did have problems with many dead or partially-dead quad op amps. Might there be more remaining undetected? (R. A., Hunter’s Hill, NSW) • We suggest that you use a preamplifier to boost the microphone signal. Then you won’t need to have the volume so loud. You could use our Multi-Role Champion Preamplifier published in the June 2015 issue (siliconchip.com.au/ Article/8609). It is inexpensive and easy to build, and its gain can be adjusted to suit your needs. We can supply the PCB for that project. SC siliconchip.com.au