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I don't know if anybody else will find this interesting, but... this is the latest version of my cap discharger.
Its basically a voltmeter that makes audio frequencies instead of numbers (kind of like a metal detector,) the idea being that you can know from the sound what the voltage is, which allows you to keep your eyes on your hands while you have them in a potentially lethal chassis.
On the left you can plug in any fluke or banana test leads, and depending on the white knob it can just measure, or discharge at two rates, 50K (10W) or 5K (100W.)
The audio part runs on a 9V and pulls about 8mA. The audio amp (far right) is a 386 amp that is kind of overkill, but they used to be available already made and cheap on ebay. The speaker came out of a casio keyboard I think. I built the breadboard in-between. It has a divider and limiter, then an absolute-value opamp, a level-shift gain-adjust opamp, and the last opamp and transistor is a clever VCO I wanted to try from Horowitz and Hill (which they got it off some app note or data sheet.) All the opamps are 358.
My setup is that 0V is about 200Hz, and the freq goes up linearly with voltage to +-500V where it peaks out at about 2kHz. You can easily hear variations as small as 1V.
Its basically a voltmeter that makes audio frequencies instead of numbers (kind of like a metal detector,) the idea being that you can know from the sound what the voltage is, which allows you to keep your eyes on your hands while you have them in a potentially lethal chassis.
On the left you can plug in any fluke or banana test leads, and depending on the white knob it can just measure, or discharge at two rates, 50K (10W) or 5K (100W.)
The audio part runs on a 9V and pulls about 8mA. The audio amp (far right) is a 386 amp that is kind of overkill, but they used to be available already made and cheap on ebay. The speaker came out of a casio keyboard I think. I built the breadboard in-between. It has a divider and limiter, then an absolute-value opamp, a level-shift gain-adjust opamp, and the last opamp and transistor is a clever VCO I wanted to try from Horowitz and Hill (which they got it off some app note or data sheet.) All the opamps are 358.
My setup is that 0V is about 200Hz, and the freq goes up linearly with voltage to +-500V where it peaks out at about 2kHz. You can easily hear variations as small as 1V.
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