Automatic street light Using NPN Transistor BC547 Full Making Project

Circuit Description:

1. Light-Dependent Resistor (LDR):
   • The LDR is used to detect ambient light levels. Its resistance changes with light intensity, providing a variable voltage to the base of the NPN transistor.
2. NPN Transistor (BC547):
   • The NPN transistor is used as a switch. When the ambient light decreases (during the evening or night), the resistance of the LDR increases, changing the biasing of the transistor.
3. Resistor (R1):
   • R1 is connected between the positive voltage rail and the base of the NPN transistor. It is used for biasing the transistor.
4. Resistor (R2):
   • R2 is connected in series with the LDR to create a voltage divider. It helps adjust the voltage level at the base of the transistor.
5. Relay Module:
   • A relay module is used to control the streetlight or LED module. The NPN transistor activates the relay, allowing it to switch the streetlight on and off.

How It Works:

1. During the day, when ambient light is sufficient, the resistance of the LDR decreases, resulting in a lower voltage at the base of the NPN transistor.
2. The lower voltage biases the transistor in a way that it remains in the off state, and the relay is not activated.
3. As it gets darker, the resistance of the LDR increases, causing the voltage at the base of the NPN transistor to rise.
4. The higher voltage biases the transistor in a way that it turns on, activating the relay.
5. The activated relay switches its contacts, allowing current to flow through the streetlight or LED module, turning it on.
6. When it gets bright again, the LDR resistance decreases, and the transistor turns off, deactivating the relay and turning off the streetlight.