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Sound activated relay

2017-08-16 02:16  
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This non-latching mini voice/sound activated relay switch can be used as a hands-free voice activation switch to operate tape recorders, lights, and a variety of other devices.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 audioamplifier. Gain is approximately 100. To increase gain raise the value of R2 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.With this sound activated switch, control by sound may be very useful, not just on a robot but also for a bit of home automation, for example a sound-activated light responding to a knock on the door or a hand clap. The light will be automatically switched off after a few seconds.
 

Sound activated relay