Low battery indicator Using NPN Transistor BC547

How It Works:

1. The microphone or sound sensor module detects sudden sound changes, such as claps, and produces a voltage variation.
2. The voltage change biases the NPN transistor’s base, allowing current to flow from the collector to the emitter.
3. The transistor’s activation triggers the relay module, allowing it to switch the appliance on.
4. After a short delay, the appliance remains on until the next clap.
5. The circuit can be adjusted for sensitivity by tweaking resistor values and the microphone’s placement.

1. NPN Transistor (BC547):
   • The NPN transistor is used as a switch. When the microphone detects a clap sound, the resulting
   • voltage change biases the transistor accordingly.
2. Electret Microphone or Sound Sensor Module:
   • The microphone or sound sensor module is used to detect claps or sudden sound changes. It produces a voltage variation in response to sound.
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 between the base of the NPN transistor and the positive voltage rail. It is used for sensitivity adjustment.
5. Resistor (R3):
   • R3 is connected in parallel with C1 for further sensitivity adjustment.
6. Capacitor (C1):
   • C1 is connected in parallel with R3 for filtering out noise and stabilizing the circuit.
7. Relay Module:

A relay module is used to control the appliance. The NPN transistor activates the relay, allowing it to switch the appliance on and off.