Weapon detector for security systems - has search oscillator with coils in collector and emitter circuits of transistor

摘要

The metal detector can be used in security systems for the detection of arms, explosives etc. The circuit comprises a search oscillator running at between 17 and 25 kHz. The oscillator is formed from a transistor with coils in the collector and the emitter circuits. Temp. and voltage stability are provided by a zener diode and resistor in the base circuit. The frequency and amplitude of the oscillator are chosen so that heart pacemakers are unaffected by the circuit. A bistable circuit using two transistors with a 1.e.d. forms a monitor for the operating voltage supplied from the battery and provides an indication of low battery voltage. Audible output via loudspeaker is provided by a self-regulating tone converter circuit.