Vehicle lighting monitoring system - uses bulb failure voltage difference to activate warning circuit

摘要

The head lamp dipper, the side light, tail light and brake light circuits have separate test circuits. Each test circuit is connected to the emitter of a transistor whose collector is in contact with the vehicle battery via a fuse. The four transistors have a common switch, their bases being connected via resistances whose values correspond to the respective lamp filaments to the contacts of a time switch. The lamp voltage drop is passed by individual trim potentiometers to an OR-gate input and adjusted to give a tension below the normal value of that when the lamps are functioning correctly, and above when one or more filaments fails.