Because this camera is for my rear window, I wanted a way to be able to turn it on and off from the driver's seat. I also wanted a method that defaults to "On" when the car starts, which ruled out a normal switch.
This simple circuit does the job with two cheap switches and a mini 5 amp relay. The switches are momentary, push-button types, with S1 having "normally open" contacts and S2 having "normally closed" contacts.
The power being supplied to the camera is 12V, because I am running it using a 12V to 5V converter that is widely used for dashcams.
When the car is started, 12V is fed to the circuit. The relay (K1) will remain off, because S1 is blocking power to its coil. The "normally closed" relay contact (K1A) then feeds that 12V to the converter, powering on the camera.
When S1 is pushed, K1 is activated, and the relay contacts switch to the "normally open" position. This keeps the relay on when you release S1. It also removes power to the converter, shutting down the camera.
Pressing S2 will deactivate K1, returning the circuit to its default state, and powering on the camera. Releasing S2 will not reactivate K1 because S1 is again blocking power to its coil.
Pressing either S1 or S2 multiple times will have no effect, so there is no problem with "switch bounce". When the ignition is turned off, the circuit will return to its default state.
You could use a circuit with only one switch, but it would need two relays, diodes and a resistor, which is not only more work but more cost.
If you wish to be able to control your rear window camera from the driver's seat, I hope this circuit is of some use to you.
This simple circuit does the job with two cheap switches and a mini 5 amp relay. The switches are momentary, push-button types, with S1 having "normally open" contacts and S2 having "normally closed" contacts.
The power being supplied to the camera is 12V, because I am running it using a 12V to 5V converter that is widely used for dashcams.
When the car is started, 12V is fed to the circuit. The relay (K1) will remain off, because S1 is blocking power to its coil. The "normally closed" relay contact (K1A) then feeds that 12V to the converter, powering on the camera.
When S1 is pushed, K1 is activated, and the relay contacts switch to the "normally open" position. This keeps the relay on when you release S1. It also removes power to the converter, shutting down the camera.
Pressing S2 will deactivate K1, returning the circuit to its default state, and powering on the camera. Releasing S2 will not reactivate K1 because S1 is again blocking power to its coil.
Pressing either S1 or S2 multiple times will have no effect, so there is no problem with "switch bounce". When the ignition is turned off, the circuit will return to its default state.
You could use a circuit with only one switch, but it would need two relays, diodes and a resistor, which is not only more work but more cost.
If you wish to be able to control your rear window camera from the driver's seat, I hope this circuit is of some use to you.
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