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I'm installing a rear camera in my 2004 Jeep TJ with a new radio head unit with a large display. The head unit I'm using automatically switches to the backup camera when the camera video feed is enabled. The camera video is enabled when it receives power.

Typically, the rear camera is wired into the backup light circuit so that it automatically comes on when the car is put into reverse. I would also like to optionally view the camera using a (new) switch installed in the dashboard. Logically, I'm looking for an "or gate" arrangement to power the camera from either the backup light circuit or the switch circuit.

enter image description here

It's pretty straightforward, but I'm not a car guy and can't find an "automotive OR gate". So I'm looking for some quick guidance on what part will work best for this situation.

Pᴀᴜʟsᴛᴇʀ2
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PeterT
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2 Answers2

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I think what you are planning on doing is the way to go (per your diagram) with one small addition. You need to insert a diode between backup light power source and the junction (upside down Star Trek looking symbol) of the power where the goes to the backup camera.

enter image description here

If you don't have a diode in there, you'll feed power out to the backup lights every time you switch the backup cameral on. Other than that, I think your solution should work just fine.

Pᴀᴜʟsᴛᴇʀ2
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If the Aux Power is always available, you can simply use a relay that is controlled by the Backup Light Power. Then you wire the relay and Enable Backup Camera switches in parallel, so that either the relay being on, or the Enable Backup Camera switch being on, will let power to the backup camera.

Diode is a poor solution. Diode loses about 0.5-1.0 volts of voltage depending on the type of diode and the current going through the diode. This is 4-7% of the energy going to the backup camera. If the backup camera uses significant energy, the diode can generate significant heat, and in excessive cases it could even burn out unless you use a diode rated for a high current which is very expensive and usually needs a heatsink.

You don't need a diode or an OR gate.

An alternative to a relay could be a MOSFET, but MOSFET on the positive wire would need zero voltage signal to turn on and +12V signal to turn off, which is exactly the inverse of the Backup Light Power logic, so you actually need two MOSFETs, one for converting the logic to an inverse, and another for supplying power.

juhist
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