Sound-operated trigger/switch – another Top-Tenner (beginner's) project.

A sound-operated trigger has many applications. This project shows how one can be used to switch on a low voltage lamp. The lamp might be a porch lamp, or a child’s bedside night-light, or a lamp on a dark stairway or corridor.

When the circuit is triggered by a sudden sound, the lamp comes on and stays on for about 50 seconds. This allows time for someone to negotiate the stairs or make their way along the corridor, or perhaps to find the switch of the usual lighting and turn it on. A lamp that comes on whenever a noise is heard in the vicinity is also an effective intruder deterrent. In general, the circuit is most sensitive to a sharp, crisp sound, such as a handclap. It is less likely to be triggered by ordinary conversation or passing traffic.