Sound activated relay

Posted on May 15, 2012

The device remains dormat (in an off condition) until some sound causes it to tum on. The input stage is a 741 operational amplifier connected as a noninverting follower audio amplifier. Gain is approximately 100. To increase gain raise the value of R2

Sound activated relay
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The amplified signal is rectified and filtered to a dc level by R4. Then R5 is set to the audio level desired to activate the relay.

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