Various electronic projects using LDR (Light Operated Resistor) is already posted in bestengineeringprojects.com. Now, here is one another simple project using LDR called light operated lamp switch using DIAC and TRIAC. This circuit utilizes very few components and so simple that anyone can understand.
Circuit Description of Light Operated Lamp Switch:
The circuit of light operated lamp switch utilizes a diac and a triac as semiconductor and LDR as sensor. LDR is a type of variable resistor and change its value according to intensity of light fall on its surface. At dark its resistance increases up to mega ohms, which does not exit triac and hence it does not conduct.
When LDR is illuminated by mean of any light source (like torch light), the resistance of LDR suddenly decreases and further drive triac as a result switch on the lamp. LDR is so adjusted that light received from the lamp keeps resistance low. So, the lamp remains continuously ‘ON’. Once lamp is ‘ON’ it can be switched ‘OFF’ again by interrupting the light falling on LDR, either by waving hand in front of it or by interrupting power supply to the circuit for a moment.
PARTS LIST OF LIGHT OPERATED LAMP SWITCH
Resistor (all ¼-watt, ± 5% Carbon)
R1 = 10 KΩ/1W
R2 = 470 Ω/1W
C1 – C3 = 0.1 µF/400V (POLY)
DIAC = D-84
TRIAC = 8T44A (4A,400V)
RFC = 15 turns of 18 SWG wire over an insulated ferrite rod.
BULB = 230V