Diagram Diagosis

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. An alternative  use is burglar protection — if someone  wants to open the door or break some-thing the light will come on, suggesting  that someone’s at home. The circuit can work from any 5– 12 VDC regulated power supply pro-vided a relay with the suitable coil voltage is used.

 

Sound Activated Switch Circuit Diagram

When you first connect the supply  voltage to the circuit, the relay will  be energised because of the effect of capacitor C2. Allow a few seconds for  the relay to be switched off. You can  increase or decrease the ‘on’ period  by changing the value of C2. A higher  value results in a longer ‘on’ period,  and vice versa. Do not use a value  greater than 47 µF. Biasing resistor R1 determines to a  large extent the microphone sensitivity. An electret microphone usually has  one internal FET inside which requires  a bias voltage to operate. The optimum  bias level for response to sound has to  be found by trial and error.

http://streampowers.blogspot.com/2012/06/simple-sound-activated-switch.html