Water level indicator Using NPN Transistor BC547

Circuit Description:

1. Water Level Probes:
   • The water level probes are placed at different levels in the tank. These can be wires or sensors that come in contact with the water at different heights.
2. NPN Transistor (BC547):
   • The NPN transistor is used as a switch. When water completes the circuit between the probes, 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 base of the NPN transistor. It helps limit the current flowing into the base.
5. Resistor (R3):
   • R3 is connected in series with each LED. It limits the current flowing through the LEDs.
6. LEDs:
   • Multiple LEDs are connected in parallel with R3, each corresponding to a different water level. When the water reaches a specific level, the corresponding LED lights up.

How It Works:

1. When the water level completes the circuit between the water level probes, it allows current to flow through the base of the NPN transistor.
2. The completed circuit biases the NPN transistor, turning it on.
3. The activated transistor allows current to flow from the positive voltage rail through the resistor (R3) and the corresponding LED, lighting it up.
4. Each LED corresponds to a different water level, providing a visual indication of the water level.
5. As the water level changes, different LEDs light up accordingly.