MULTIPLEXED_BURGLAR_ALARM

Published:2009/6/30 1:54:00 Author:May | From:SeekIC

Multiplexing technique provides for detection of state of up to 10 sensors, with immediate identification and location of activated sensor. Only one pair of wires runs from control unit to paralleled remote sensor circuits, one of which is shown at upper right. Each sensor location uses different output from one to zero. Multiplexor circuit is based on 4017 decade counter having 10 individual outputs, to give signals in 10 time slots. Power supply rail is used to reset counter. Clock line is eliminated by switching supply line as square wave. Sensor indication line is eliminated by detecting power supply current drain. Control unit uses oscillator and shift register to generate clocking waveforms. 3900 quad opamp converts sensorline current to logic levels for clocking by master 4017 to control 10 out-put latches and display driver. Two consecutive sensor-open signals are required to activate alarm, minimizing false alarms by interference pulses.-R. J. Chance, Multiplexed Alarm, Wireless World, Nov 1978, p 73-74.



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