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Sound Operated Switch
   
This circuit can be used to switch something on and off by clapping your hands within a couple of metres of the microphone (a small loudspeaker works quite well as a mic).  
To be useful, you will have to connect it to a Relay Driver or similar.  
Be warned, it's a bit lacking in selectivity, so don't try to use it to switch on/off anything important... it might be activated by other, loud, high pitched sounds!
 
   
The sensitivity of the circuit can be adjusted using the variable potential divider connected to the inverting input of the comparator.  
To set the sensitivity to maximum, connect a voltmeter to the output of the second amplifier and adjust the variable potential divider to the point which just takes the voltmeter reading to its lowest figure (zero for CA3140, about 1.5V for TL081).  
   
Amplifier: TL081
Comparator: TL081 or CA3140
 
R can be almost any value greater than about 10k.  
Use a small (low impedance) loudspeaker as a microphone.  
This circuit must have a regulated supply; this is provided by the 7805 regulator.  
   
Vero board, copper side.  
   
 
   
Vero board, component side.  
 
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