Water tank overflow liquid level sensor alarm circuit

Water tank overflow liquid level sensor alarm circuit is a simple electronics project for school students. In the previous articles we had discussed about numeric water level indicator and water level controller circuit ,but those circuits are much complex and are advanced projects for engineering students. The circuit schematic for water tank over flow alarm is shown below. It produces a beep sound when the water tank  is completely filled by water.The advantage of this project circuit is that it saves water from accidental over flow. The circuit simply consists of a liquid (water) level sensor or water level detector with BC547 transistors. Any electronics hobbyist can implement this circuit at your home or work places at a cheap rate ($0.5). The heart of this water over flow circuit is  the transistor switching part. So this circuit always prevents the wastage of water when you forget to switch OFF the motor pump set after switch ON.

Circuit Diagram of water tank level alarm

Water+tank+overflow+liquid+level+sensor+alarm+circuit+liquid+level+sensor+for+school+electronics+project Water tank overflow liquid level sensor alarm circuit

Components required

  1. Power supply
  2. Resistors ¼ Watt (1kΩ x1, 100Ω x2)
  3. Transistors (BC 547 x 2)
  4. 6V Buzzer


  • Water over flow from a tank or reservoir is detected using this simple project circuit. Firstly close the switch SW to turn ON the device.
  • Initially the potential at point A in the circuit is Vcc, so the transistor Q1 remains in ON state (Read transistor act as a digital switch) and its collector voltage at Vce sat (0.02V).
  • The collector voltage of Q1 is fed to the base terminal of transistor Q2 via100Ω resistor.
  • 0.02V is not sufficient to turn ON the transistor Q2, hence it remains in OFF state and the buzzer will not produce any sound.
  • A connection from ground is dipped in the water reservoir. When water level rises, the ground comes in contact with the base terminal of transistor Q1. Thus it changes to OFF state and the collector voltage rises to Vcc.
  • The high voltage at the collector of Q1 turns ON the transistor Q2 since this high voltage is connected to the base of transistor Q2, then a current flow occur though the buzzer circuit and it produces beep alarm sound. (Read transistor act as a load switch)
  • See the simulation window below, here instead of buzzer circuit we have used a LED for simulation. The switch ON is similar to water touching the point A.
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Simulation of water tank level sensor alarm

Water+tank+overflow+liquid+level+sensor+alarm+circuit+liquid+level+sensor+for+school+electronics+project Water tank overflow liquid level sensor alarm circuit

BC 547 transistor pin out

BC547 Water tank overflow liquid level sensor alarm circuit

20 thoughts on “Water tank overflow liquid level sensor alarm circuit

  1. as per given above the circuit of water tank over flow ,i made it but its not working in the water ,can u please help me to how to worked proper

    • Hi Noble george,
      Did you connect ground in the water? What is the ampere rating of your transformer used in the power supply? Please use 1A transformer.

      • can u please modify the circuit so that the pump which is working on 220v ac supply can automatically be stopped.

  2. sir this project is not working please tell me how to check weather circuit is correct or not .
    when i touch both wire bellow and above in the water bugger rings please reply soon.

    • Hi shamshad ansari,
      Your problem seems to be insufficient current from the power supply. Please use 1A transformer to build power supply circuit

  3. This circuit works, however the sensor does not. The resistor above point A drops the voltage at point A to around 1 volt. This is insufficient voltage to conduct through the water. If the lead from point A is grounded, the circuit works fine. However placing the two leads in the water does nothing.

  4. I am a learner in this field though I am Electrical engineer I never worked with electricity but work on chemical plant setting and turnkey project. I am 76 years old and have keen interst in this field will you help me .If you send me the emil I will feel that you have noted my wish and give me reply

    Regards Ramesh K Phadke

  5. He I sir circuit is not working wen the two leads of water tank touch together buzer rings but in the water not working kindly give replay

  6. please send simulation execution clearly and are we use 3 led lights in this simulation.and tell simulation results in matlab please please

  7. great. But with this the dc current pass through water which causes lose of energy and ionise the water. Can u give me idea in which the current do not pass through directly water.

  8. in this project how you connected alarm and controller as same time may be the user of this device u
    se other water tanks ? second question how you use two circuit one is push water from tank controller and the other fill the water to the tanks automatically? thanks!

  9. hi,
    I tried using 2amp but still its not working in water, at the same time when I connect both the probes directly it is working. please suggest soon.

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