Dark detector 2011-06-16

The dark detector circuit shown here can be used to produce an audible alarm when the light inside a room goes OFF. The circuit is build around timer IC NE555.A general purpose LDR is used for sensing the light. When proper light is falling on the LDR its resistance is very low. When there is no light the LDR resistance increases. At this time the IC is triggered and drives the buzzer to produce an alarm sound. If a transistor and relay is connected at the output (pin3) of IC1 instead of the...

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