What are those things that turn on other things when power is detected?

[yuji]

So I bought a multi input LCD to run my existing backup camera as well as a camera mounted to the passenger side rack / potentially a $15 disposable on the undercarriage (for sharts and giggles).

Is there a way I can wire the camera so it is only enabled when the LCD is drawing current?

So I turn off the LCD and the cameras stop?

Some kind of relay? The LCD draws 5w

 

[rusty_tlc]

A relay would do it

 

[PAToyota]

A standard relay will only provide power to the accessory when power is applied to the relay - so if you had a switch that turned on the LCD you could run the power from that switch to the LCD and also to the relay, which would turn on the camera.

Current sensing relays are a bit different. They pass the power supply going to an item through a toroid. A current is created in the secondary winding when current is passing through the main winding. This secondary current is what activates the relay. So there isn't a "direct" power source like in a regular relay.

So, if the power switch is built into the LCD (which I think you are saying), you wouldn't have to open up the LCD to get power after the switch to send to the relay. You'd run the wire providing power to the LCD through the current sensing relay and it would sense the "movement" of power when the LCD was turned on.