Emergency switch circuit for lighting or sound warning - has transistor controlled relay located in supply to emergency service

摘要

The safety device includes an output supplying lighting or a sound warning, powered by a self contained source of DC. Between source and output lies a relay controlled switch powered from the same source. The relay is supplied via a transistor with a biassing circuit to make it conducting. A further part of the circuit is arranged to short-circuit the base - emitter of the transistor to make it nonconducting when a push-button is operated. The push button switch may incorporate two flexible metal plates connected to base and emitter respectively. When deformed these make contact in order to activate the circuit.