This circuit switches a relay ON or OFF according the brightness of light shining on the photo sensitive resistor CDS.
CDS (made of cadmium sulphide), or so called LDR (light dependent resistor) has resistance that changes inversely proportional to intensity of light.
i.e. the brighter the light, the lower the resistance
The circuit can
operate in 2 different modes :
(you can select the mode by setting the slide switch S1)
1) LIGHT detection mode : In this mode, relay turns ON or actuates (LED lights up) when the light shining on the CDS is sufficiently BRIGHT.
2) DARK detection mode : In this mode, relay turns on (LED lights up) when the light shining on the CDS is sufficiently DARK
Applications : automatic corridor or porch light control, "chop-beam" intrusion alarm, . . .
The above project is available in DIY kit . Click here to view price list.