High sensitivity alarm circuit

Published:2011/6/9 2:19:00 Author:Christina | Keyword: High sensitivity, alarm | From:SeekIC

The high sensitivity alarm circuit is as shown in the figure, the photoconductive resistance LDR is connected with three ordinary resistances. The alarm sensor circuit is as shown in the figure. In this circuit, the half of the CMOS integrated timer 7556 is connected as the self-excited oscillator, the IC2c constitutes the equivalent inverter, the oscillator is under the function of IC2c to complete the alternate connection. The IC2a and IC2b are the two-node switch. The input impedance if the IC2's control pin is very high, so the load is very light for the IC1a, the voltage dividing network is composed of the R3, R4, R5, R6, the photoconductive resistance and the LDR, this makes the X point has the required potential to charge the C4 and C5 through the double node switch.



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