Lights Warning

[angelo_f]

I have made up a little circuit to give a warning buzzer if the parking lights are on and the ignition (or rather accessories) is off (save running battery flat if I left light on). I have attached a picture and a circuit diagram. This is probably the cheapest way to do it and did not need a relay.

I use 2 x resistors in the circuit in parallel because it will generate about 0.7 W and I didn't want just one resistor to handle that. I had to keep the resistance low because the buzzer needs to draw at least 30ma. The purpose of the diodes in the circuit is to stop voltage from accessories going to light circuit and vice versa.

When the lights are on and accessories are off, current flows through buzzer. When accessories are on, the +12V goes through diode and prevents a potential difference across buzzer even when lights are on.