This circuit is used to indicate level of water in three steps.It is used to avoid wastage of water.  The heart of the circuit is the transistors BC 547. There are total 3 transistors in the circuit and each one will be sensing the level of water present in the overhead water tank. Three different LEDs are used to indicate two different levels. Red LED is used to indicate a level which informs us that water tank is empty.  When you switch on your unit if you see only one Red LED lighting up then there is  no water present in the tank. Yellow led is used to indicate that tank contains moderate water and Green shows the tank is full.

Circuit Diagram:

Component Values:

  • Resistor: R1,R6,R9 =470 Ohm
  • Color code for 470 Ohm: Yellow-Violet-Brown-Golden
  • R2,R4,R7=330 Ohm
  • Color code for330 Ohm: Orange-Orange-Brown-Golden
  • R3,R5,R8= 470 Kilo Ohm
  • Color code for470 Kilo Ohm: Yellow-Violet-Yellow-Golden
  • Transistor :Q1,Q2,Q3 = BC 547
  • Battery: 9 Volts

Circuit Building Steps:

Step 1:

Mount N-P-N transistor Q1 BC 547 on Bread Board.

Step 2:

Connect resistor R2 of 330 Ohm to the base of transistor Q1.

Step 3:

Connect one terminal resistor R3 which is of 470 Kilo Ohm to the base of  Q1.

Step 4:

Connect second terminal of R3 to Collector terminal of transistor.

Step 5:

Connect Black wire between Ground terminal and Resistor R3.

Step 6:

Put one end of Yellow wire in second terminal of R2 and keep another end of wire open.

Step 7:

Connect one end of resistor R1 of 470 Ohm to emitter terminal of Q1.

Step 8:

Connect Cathode of LED to the resistor R1.

Step 9:

Connect one end of wire to the Anode of LED and keep second end of wire open.

Step 10:

Similarly mount transistors Q2 and Q3 on bread board and connect  resistors and LEDs to it.

Step 11:

Connect battery of 9 Volts to the Bread Board and insert wires A,B,C,D,E,F,G in the water at different levels along with positive terminal Red wire of Battery.

When level of water touches to the respective wires which are dip in the water it will turn ON the respective LED. Make sure each wire should be placed at different level and Red wire of Battery should be at the bottom of the tank.