Hi All,

Here's a little utility circuit designed to drive something (?) with sound. This can be used to flash lights for a lightning effect with a thunder sound track, as a single channel color organ or whatever you dream up. I guess if you were to use a latching relay, it could even be used as a Clapper.

The circuit started life as the first part of my audio/servo driver circuit, which has now been revised. Depending on the relay you choose, this circuit can be made for $10 or less.

Scary Terry


  Click on schematic for a PDF version  
  Circuit Description: This circuit will accept a wide range of input levels, which are compensated for by feedback resistor R3. OpAmp U1a amplifies the signal while U1b is used as a comparator whose sensitivity is set by R6. The output of U1b feeds the transistor Q1 which controlls relay K1 and optional LED D3. I find the LED useful in initial setup (without an audio signal, R6 is adjusted so that D3 just turns off) and confirms the circuit is working properly. Relay K1 should have a 5 volt coil and contacts rated for whatever you're driving with it. Capacitor C2 is used for smoothing the relay action, without it, relay action is very sharp, with a larger value, relay action becomes slower. You may want to experiment to see what value works best for your application. In operation, just adjust R6 for the desired level of sensitivity.  

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