Debouncer for 12 V Contacts

Usually some effort is required if it is desired to use the positive edge of a switched 12 V signal (for example from a 12 V horn relay in a car) in a digital system. Digital systems place particular requirements on the signals they use, and the RS flip-flop often used for debouncing purposes does not provide a complete guarantee against interference. If, furthermore, there is no auxiliary 5 V supply available for the debounce circuit, we must turn to a device such as the 555 timer IC to clean up the signal.