Video Activated Relay


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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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Comments

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Colin Mitchell
Faulty Circuit
Sunday, November 20, 2011 12:07:28 AM
This circuit will not work. The diode will never remove the voltage on the electro.
anonymous
Video Activated Relay
Sunday, February 28, 2010 2:01:06 PM
if use this as a voice activated relay what should the value of R1 to be replace. do i use mic instead of rca jack? tnx
alain
Video Activated Relay
Thursday, January 17, 2008 2:42:02 PM
Simple, efficace, permet de multiples utilisations, par exemple dans la video HF... Merci pour ce petit montage.
anonymous
Video Activated Relay
Tuesday, January 08, 2008 12:24:17 AM
what is the function of the video activated relay?
adeyinkaq
Video Activated Relay
Saturday, November 17, 2007 7:35:14 PM
hello,plz i need circuit for my project can you kindly give me comphrensive note about it.
anonymous
Video Activated Relay
Thursday, May 24, 2007 8:04:36 PM
works great... but you have to use a 2n2222 for Q1... if you use a 2n3904 then you have to replace R1 with a smaller value(51 ohms worked... but it made the video going to the tv get slightly white-washed)... using the 2n2222 saturated the transistor and didnt make the video any different...
ruben
Video Activated Relay
Wednesday, May 23, 2007 8:14:58 PM
I think the D1 will cause a LOAD on the video signal, and maybe also R1 since it is only 10K.
anonymous
Video Activated Relay
Saturday, March 03, 2007 6:57:40 PM
This seems like a very good circuit. The only thing I see wrong is that it operates on 9V instead of 12V. Since most of the applications will normally be with a 12V video camera.
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