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Notes & Errata Frequency Meter, October 2003: VR2 on both the circuit and overlay should be 10kΩ. The parts list is correct. PC Infrared Remote Control, August 2003: Some constructors have reported that the remote power-up function stops working after switching power on and off a number of times. The problem was traced to EEPROM corruption during brownout of the +5V supply to the microcontroller (IC1). To fix the problem, mount an MC34064P-5 undervoltage sensing IC on the bottom (copper) side of the PC board as shown in Fig.1. If you’ve yet to assemble your board, then this should be done after all other components have been installed. Slip a short length of heatshrink tubing over the GND lead of the IC before soldering it. dual-ganged potentiometer. Short of purchasing a much higher quality dual pot with guaranteed tracking, there is nothing you can do about it. Power meter for audio amplifiers I have some queries regarding the usage of the Audio Power Meter (April 1993) with the 175W Power Amplifier from the April 1996 issue and the Altronics 200 watt Mosfet Amplifier. I have used the Audio Power Meter with the Playmaster 200/300 watt amplifier (EA) and set up the unit to suit the resistance setting for trimpot VR1 that was quoted in a reply to “Ask Silicon Chip” in an earlier edition of Fig.1: this diagram shows how to modify existing boards. This ensures that the GND and +5V leads can’t short together. The MC34064P-5 is available from Altronics (cat. Z-7252) and Farnell (cat.703-709). the magazine. I am wondering if the APM can be used with these amplifiers and if so, what would the resistance be for both 8-ohm and 4-ohm loads? I am also building the DiscoLight project from the July & August 1988 issues. I generally have used IC sockets with the majority of the projects that I have built because of the ease of inserting and removal of the ICs. Is it advisable to use IC sockets for this project as my main concern is the high voltage that is present on the PC board and that is required to drive the light system? (D. W., via email). • You can use sockets for the Discolight ICs except for the optocouplers which are best soldered directly to the PC board. Fig.2: this new PC board design includes the extra IC. Note that you only need to do this modification if you’re using the remote power-up function. The power meter can be used for 175W amplifiers and 200/300W amplifiers. Values for VR1 are as follows: 175W into 8Ω, VR1= 57.6kΩ; 175W into 4Ω, VR1= 37.9kΩ; 200W into 8Ω, VR1= 62.5kΩ; 200W into 4Ω, VR1= 41.2kΩ; 300W into 8Ω, VR1= 78.5kΩ; 300W into 4Ω, VR1= 52.9kΩ. For powers in between these figures, you can estimate the resistance value required; eg, for 190W into 8Ω, VR1 should be between the 175W and 200W values of 57.6kΩ and 62.5kΩ. A value of 60kΩ for VR1 should be suitable. Generally, it is best to use a smaller value for VR1 than that calculated so the maximum power will be shown on the meter before the amplifier clips. WARNING! SILICON CHIP magazine regularly describes projects which employ a mains power supply or produce high voltage. All such projects should be considered dangerous or even lethal if not used safely. Readers are warned that high voltage wiring should be carried out according to the instructions in the articles. When working on these projects use extreme care to ensure that you do not accidentally come into contact with mains AC voltages or high voltage DC. If you are not confident about working with projects employing mains voltages or other high voltages, you are advised not to attempt work on them. Silicon Chip Publications Pty Ltd disclaims any liability for damages should anyone be killed or injured while working on a project or circuit described in any issue of SILICON CHIP magazine. Devices or circuits described in SILICON CHIP may be covered by patents. SILICON CHIP disclaims any liability for the infringement of such patents by the manufacturing or selling of any such equipment. SILICON CHIP also disclaims any liability for projects which are used in such a way as to infringe relevant government regulations and by-laws. Advertisers are warned that they are responsible for the content of all advertisements and that they must conform to the Trade Practices Act 1974 or as subsequently amended and to any governmental regulations which are applicable. 98  Silicon Chip www.siliconchip.com.au