These two headlight reminder circuits are easy to install and operate on the KISS
(Keep It Simple Stupid) principle. The simple circuit involves adding
just a 12V piezo buzzer between the lights circuit and a door switch.
The buzzer sounds if the lights are left on and you open a door. The
disadvantage of this simple circuit is that it’s annoying to have the
buzzer sound continuously if you want to leave the door open while the
lights are on. The improved circuit overcomes that problem by adding a
1000µF capacitor and a parallel 100kO resistor in series with the
buzzer. Now, when a door is opened, the buzzer gives a brief burst of
sound only, while the 1000µF capacitor charges. The 100kO resistor
discharges the capacitor when the lights are switched off.
Author: Andrew Gibbs