Since the non-inverting reference frequency is higher than the inverting input voltage, the IC ouput value is ’1'. Transistor in ‘ON’ state, relay is also ‘ON’, thus the AC light will be close and the light turns on.
When it’s bright or the resistor value of LDR is low, the current is high. Since the inverting input voltage is higher than the non inverting reference voltage, the IC output is ’0', transistor in ‘OFF’ state, thus the AC open and the light turns off.
Components List :
Resistor R1,R2,R3 : 10k ohm
Resistor R4 : 270k ohm
Resistor R5 : 4k7 ohm
Resistor R6 : 1k ohm
R8 : LDR
Resistor variable R7 : 1M ohm
IC UA741
Diode D1 : 1N4007
5mm LED
Transistor Q1 : BC109
Light bulb
9V relay
9V battery
