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bead which I found in my junk box. 20 turns of fine wire (about 0.2mm) and I had a choke which worked. The core was about 6mm OD, 6mm long with a centre hole about 3mm. I then purchased a pack of Jaycar LF-1250 ferrite suppression beads. These are 5mm long, 4mm in diameter and with a 1.5mm bore although some of the bores appear larger – nearly 2mm. I select­ed two with the larger bores, superglued them end to end and wound on about 20 turns. This also worked and I am now ready to tackle the miniature versions when I get some copies of the PC boards. This could help other readers complete this project. (B. L., via email). • Thanks to these readers for these tips. Dick Smith Electron­ics are about to release their kit for the torch as well. It will be supplied with a penlite torch for just $14.60 (Cat K-3018). VU meter needs auto level control I have constructed a LED VU level meter for my car stereo, which is purely for aesthetic purposes; ie, regardless of volume, the display should work over most of its displayable range. The only problem is that the stereo does not have a constant volume output and therefore the input sensitivity of the VU meter must be varied each time the volume of the stereo is varied. Is there a way to obtain a constant volume level from the stereo, so that I won’t have to turn two dials each time I change the volume? (J. P., via email). • Short of building our CD Compressor described in the July 2000 issue, the only way to avoid the need to change the LED VU setting is to take the signal from across the volume Using a different spring reverb module I have a large 3-spring reverb unit made by Belton Engi­neering, which I’d love to build into a home-brew valve guitar amp, using the circuitry from your Spring Reverb Module published in your January 2000 edition. The Belton unit has the following specifications (obtained from Belton’s website) and they differ considerably from the unit used in your design: input impedance 190Ω; output impedance 2.575MΩ. control; ie, you have to access the signal from inside the car stereo. Thorn Atlas B+W TV needs a good home I have an old valve TV set that I would like to go to an interested collector. It is an old large (59cm?) Thorn Atlas B+W valve TV set, part of a relative’s deceased estate. The cabinet, made of solid wood, is in Notes & Errata Audio/Video Transmitter, July 1999: the PC board overlay on page 38 shows the two regulators swapped. The circuit on page 37 is correct. Rain Gauge, June 2000: the software for this project has a prob­lem when used with the newer PIC16F84A version of the chip. The A suffix version has a faster EEPROM programming time and this interferes with the in- Could you please advise what modifications I would need to make to the circuit for this to work? (P. S., via email). • As far as the input side is concerned, you could use our circuit as is because Q1 & Q2 will quite happily drive a higher impedance. On the output side you need a higher input impedance for IC2a and this can simply be done by changing the 100kΩ resis­tor at pin 5 to say 1MΩ or higher. However, you haven’t quoted signal delay times or signal levels so the result may be a little hit or miss. excellent condition and I think that the internals are all there, although the circuit diagram is only half complete (pasted in the back of the set). It even has the original knobs intact and would make a fantastic restoration project (although most of the work would be internal as the externals are in such good nick). If anyone is interested, they can contact me at: p_sun<at>optusnet.com. au terrupt routine earlier than it does with the standard version of the PIC. It causes the daily rain read­ings to be randomly updated at 10 minute intervals into the next day rather than only once per day. A new version of the software solves the problem. RAINA.ASM and RAINA.HEX software must be used with the PIC16F84 A versions. This software will also run with the standard PIC16F84 and can be downloaded SC from our website. 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. FEBRUARY 2001  91