Laser security alarm Using NPN Transistor BC547

Circuit Description:

1. Laser Module:
   • The laser module emits a laser beam. Ensure it is aligned with the photodiode so that the beam is incident on the photodiode’s surface.
2. Photodiode:
   • The photodiode detects the laser beam. When the beam is uninterrupted, the photodiode produces a voltage.
3. NPN Transistor (BC547):
   • The NPN transistor is used as a switch. When the laser beam is interrupted, the voltage at the base of the transistor changes, biasing the transistor accordingly.
4. Resistor (R1):
   • R1 is connected between the positive voltage rail and the base of the NPN transistor. It is used for biasing the transistor.
5. Resistor (R2):
   • R2 is connected in series with the photodiode to create a voltage divider. It helps adjust the voltage level at the base of the transistor.
6. Buzzer:
   • The buzzer is connected to the collector of the NPN transistor. When the laser beam is interrupted, the transistor turns on, allowing current to flow to the buzzer, activating

How It Works:

1. When the laser beam is uninterrupted, the photodiode produces a voltage.
2. The voltage at the base of the NPN transistor is determined by the voltage divider formed by R2 and the photodiode.
3. When the laser beam is interrupted (e.g., by an object passing between the laser module and the photodiode), the photodiode voltage decreases.
4. The decreased voltage biases the NPN transistor, turning it on.
5. When the transistor turns on, it allows current to flow from the collector to the emitter, activating the buzzer.
6. The buzzer produces an audible alarm, signaling the interruption of the laser beam.