Automatic Night Lamp( L.D.R Based)
Automatic night light is a device with turns on light when there is darkness in the surrounding. Its a portable version of automatic street lights. In this I used LDR (Light Dependent Resistor) which varies resistance with respect to light intensity.
circuit diagram#https://drive.google.com/file/d/1We8W...
How the Night Lamp Circuit works
The L.D.R and the resistor 5.6k makeup a voltage divider network.
when there is lots of light , the L.D.R will have low resistance( lower than 5.6 k) which
makes the divider a low out put to the base of the transistor ( Emitter to base voltage around .3v)
which is not enough to turn on the NPN transistor
so the transistor is off and cuts off the current to LED .
when it's dark , the L.D.R will have high resistance(about 1.M ohm)
which makes the divider network a high out put to the base of the transistor.(Emitter to base voltage around .7v)
which turn on the NPN transistor and turn on the LED.
Resistor R2( 100 ohm) is using for LED current limiting purpose.