Automatic drawer light Using NPN Transistor BC547

Circuit Description:

1. Magnetic Reed Switch:
   • The magnetic reed switch is used to detect the opening and closing of the drawer. When a magnet (attached to the drawer) is in proximity, the switch closes, and when the magnet is removed, the switch opens.
2. NPN Transistor (BC547):
   • The NPN transistor is used as a switch. When the reed switch is closed (drawer is opened), the biasing of the transistor changes.
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 LED to limit the current flowing through the LED.
5. LED:
   • The LED is connected to the collector of the NPN transistor. When the drawer is opened, the transistor turns on, allowing current to flow through the LED.

How It Works:

1. When the drawer is closed, the magnetic reed switch is open, and the NPN transistor is biased to remain in the off state.
2. When the drawer is opened, the magnet attached to the drawer comes close to the reed switch, closing the switch.
3. When the reed switch is closed, current flows from the positive voltage rail through R1 to the base of the NPN transistor.
4. The closed reed switch biases the NPN transistor, allowing current to flow from the collector to the emitter.
5. The activated transistor allows current to flow through the LED, turning it on and illuminating the drawer.
6. When the drawer is closed again, the reed switch opens, and the NPN transistor turns off, turning off the LED.