Wire Loop Breaking Alarm System

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Model No: 214 The operation of the circuit depends on the astable mode of the 555 timer, which is driven by...
Model No: 214 The operation of the circuit depends on the astable mode of the 555 timer, which is driven by the emitter current coming from BC109C/ BC548 transistor, since this transistor has high gain. Being in astable mode the IC 555 functions as an oscillator or as a free running mode. To power the 555 oscillator in full operation of the series transistor, it needs to be enabled by a larger current that flows in the collector circuit. This is made possible when the transistor is switched ON by the small current that flows between the base and emitter because of the loop/moisture or wetness sensed by the probes at contact points. On the other hand, the transistor will remain OFF and without any bias during dry conditions. To control the conduction of the circuit, a switch for ON/OFF state is supplied. The probe contacts should be made of non-reactive metal so that there will be no capacitance or impedance present. It can be achieved by salvaging silver or gold plated contacts from old relays. A cheaper alternative is wiring alternate copper wires. Since the transistor is in emitter follower mode, the impedance at the emitter or the oscillator circuit acts as the current limit so placing a base resistor is no longer required. For more details visit www.efxkits**** or www.facebook****/edgefx
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