I wanted a circuit to power on and off the front parking sensors of a car with a single button. After searching the internet for a bit I came across a soft latch circuit by eevblog and after changing the resistor values for 13V I re-created it on a breadboard which worked fine. This is the circuit I built.
Push button switch (SW) was already in the car (one end connected to ground) so in order to use that I had to use RLY1 relay.
When connected to the car it functioned as normal but when the circuit was in off state (when sensor is off) and I turned on my turn signal or low beam, the circuit got auto-triggered and moved to the on state turning on the sensor automatically and it kept on until I press the SW to switch it off again.
I thought this was because of the voltage fluctuations when the lights were turning on so tried putting 0.1uF, 4.7uF, 100uF capacitors parallel to the power lines but this didn't solve the problem.
Can I know why this happens and if it is happening because of the sudden voltage drop, why does the circuit gets auto-triggered when a sudden voltage drop happens and what can I do to prevent this?
(Please note that my car has incandescent turn signal lights and HID low beam lights)
PS : I found another circuit which consist of CD4017 IC and it rarely (about 1/10 times) gets auto triggered and it only happens when turning on the HID low beams. I am also inserting the schematic of that here in case someone wants to have a look on it.