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Monday, August 16, 2010

Video Activated Relay

This simple circuit from the May 1996 Think Tank column 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

Schematic for Video Activated Relay

Parts

Part
Total Qty.
Description
Substitutions
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

Notes

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

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