Thursday, April 4, 2013

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Night Security Light Circuit

This is a design simple circuit switches on a light around 2 hours after midnight, the time at which most of the robberies taking place. This circuit is work based on CMOS IC and LDR system. This is the figure of the circuit.

This is the explanation for the operation of the circuit. This simple circuit is build around a CMOS IC 4060 to obtain the required timing. During day time the LDR has low resistance and keeps the pin 12 of the IC1 high, preventing the IC1 from oscillating. When it is dark the LDR resistance becomes high and the pin 12 of IC1 becomes low and the IC starts oscillating, which indicated by the flashing of LED D3.

The values of the timing components R1, R2, C4 are so selected that the out put pin3 of IC1 goes high after 8 hours. That means the high output drives the triac to switch on the lamp around 2, 0 clock. At morning, the LDR resistance drops and the pin 12 of IC1 goes high and stops the oscillation, making the lamp OFF. The switch S1 can be used to manually ON the lamp. The capacitor C2 prevents false triggering. The LDR can be general purpose LDR. The light sensitivity can be adjusted using the preset R6. The IC1 must be mounted on an IC holder.

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