Light Operated Light Switch

Here is a light-operated, remote-controlled solidstate switch to operate a lamp. During darkness, the resistance of LDR shoots up to meg-ohm range. Thus, the triac does not get gate drive and hence it does not conduct.

Circuit diagram:

Light-Operated Light Switch Circuit Diagram

When LDR is illuminated by means of a torch-light beam, the resistance of LDR suddenly decreases (below 10-kilo-ohm). This causes the triac to conduct and switch ‘on’ the lamp. Light received from the lamp (not from the torch) keeps LDR’s resistance low. So, the lamp re-mains continuously ‘on’. Once the lamp is‘on’, it can be switched ‘off’ again by in-terrupting the light falling on LDR, by either waving hand in front of it or by interrupting power supply to the circuit for a moment.

RFC emplo-yed here can be made by winding about 15 turns of 18 SWG wire over an insulated ferrite rod.

Author : Pradeep G. - Copyright :electronicsforu

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