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

Parts

Part	Total Qty.	Description	Substitutions
R1, R2	2	10K 1/4 W Resistor
R3	1	1K 1/4 W Resistor
R4	1	33K 1/4 W Resistor
C1	1	1uF Electrolytic Capacitor
Q1, Q2, Q3	3	2N2222 NPN Transistor	2N3904 NPN Transistor
D1, D2, D3	4	1N4148 Diode
K1	1	9V Relay
J1	1	RCA Jack
MISC	1	Case, wire, board

Notes

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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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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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.