Automatic Turn-Off Alarm With Delay

In this circuit, IC1A and IC1B act as a monostable multivibrator. Any input from the sensors S1 through S5 forces IC1A to produce logic low, which causes IC1B to turn on Q1 until C3 changes through R6. This action resets the latch formed by IC1A and IC1B.
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Automatic Turn-Off Alarm With Delay - Circuitos de Electronica