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Video Activated Relay

2016-09-12 20:39  
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This simple circuit from the May 1996Think Tankcolumn of Popular Electronics activates a relay when it senses a composite video signal. This allows you to use the tuner built into your VCR to turn on and off older TVs that are not equipped with a remote. It can also be used to activate surround sound equipment, turn off the room lights, turn on video game consoles, etc. For such a simple circuit, it is very versatile.



Schematic for Video Activated Relay



Total Qty.
R1, R2210K 1/4 W Resistor 
R311K 1/4 W Resistor 
R4133K 1/4 W Resistor 
C111uF Electrolytic Capacitor 
Q1, Q2, Q332N2222 NPN Transistor2N3904 NPN Transistor
D1, D2, D341N4148 Diode 
K119V Relay 
J11RCA Jack 
MISC1Case, wire, board 



Since you may be using this circuit to switch mains voltage, it should be enclosed in a case.The circuit will also work with most line level audio, although you may have to adjust the value of R1.


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