This is my first post here. I have an aftermarket backup sensor that needs to be disabled when I back a trailer. I want to be able to push a button to disable it, but have it be automatically re-enabled when the ignition is cycled. Right now the buzzer is powered by the reverse tail light, but I want the disable device to be controlled by the ignition. Reason being is when I've got a trailer, I may put it in R and D many times (cycling power to the unit), but I'll want the system to be silent until the next time I start the vehicle. So whatever controls it controls the power is NC until I press the button to open the circuit, but then it goes closed when ignition is OFF (or off then on).
I looked for a simple NC latching relay, but it doesn't seem to exist. All latching relays I found required a signal to toggle them between open and closed. The push button will give it the signal to open, but how can I give it a momentary signal to close once the ignition cuts off?
I suppose I can also use a timer relay, but I am hoping to do it the way I described.
Best Answer
simulate this circuit – Schematic created using CircuitLab
Probably easiest to use a SPDT relay with the NC contact for your sensor and the NO contact wired back into the relay coil. D1 depends on your coil rating, the 4148 is just the standard one the schematic editor puts in. V1 is an ignition controlled supply that can handle your sensor.
Edit: if it's important that the sensor only have power if you are in reverse, use a DPDT relay and hook up the reverse light and sensor to the other pole.