Precision Light Alarm With Hysteresis Circuit

Posted on Dec 17, 2012

The TL081 is used as a comparator in a Wheatstone bridge circuit. When the CDS cell resistance decreases due to exposure to light, the output from IC2 cause the low-frequency oscillator (a) and (b) to generate a 10-Hz square wave, gating the 1000 Hz oscillator (c) and (d) on and off. This signal drives an amplifier.

Precision Light Alarm With Hysteresis Circuit
Click here to download the full size of the above Circuit.

R3 controls hysteresis, which reduces on-off triggering near the threshold set by R4.

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