Knock detector Using NPN Transistor BC547

Circuit Description:

1. NPN Transistor (BC547):
   • The NPN transistor is used as a switch. When a knock is detected, the transistor biases accordingly.
2. Piezoelectric Sensor:
   • The piezoelectric sensor generates a voltage in response to mechanical vibrations (knocks).
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 base of the NPN transistor. It helps limit the current flowing into the base.
5. Indicator (LED or Buzzer):
   • The indicator is connected to the collector of the NPN transistor. When a knock is detected, the transistor turns on, allowing current to flow through the indicator.

How It Works:

1. The piezoelectric sensor generates a voltage when subjected to mechanical vibrations or knocks.
2. When a knock is detected, the voltage from the piezoelectric sensor biases the base of the NPN transistor.
3. The biased NPN transistor turns on, allowing current to flow from the positive voltage rail through the indicator.
4. The indicator (LED or buzzer) is activated, providing a visual or audible alert in response to the detected knock.
5. When there is no knock, the transistor remains off, and the indicator stays inactive.