Automatic Water Level Controller


People generally switch on the pump when their taps go dry and switch off the pump when the overhead tank starts overflowing. This results in the unnecessary wastage and sometimes non-availability of water in the case of emergency. The circuit here makes this system automatic, i.e. it switches on the pump when the water level in the overhead tank goes low and switches it off as soon as the water level reaches a pre-determined level. It also prevents ‘dry run’ of the pump in case the level in the tank goes below the suction level.

The project aims at automatically switch ON and OFF the domestic water pump set depending on the tank water level. It can be implement at  home or college using less costly components. The main advantage of this water level controller circuit is that it automatically controls the water pump without any user interaction. The heart pump controller circuit is a NE 555 IC; This project consists of three water level sensors, one fixed at the top and other at the bottom.

1. Power supply (12v)
2. NE 555 timer IC
3. Resistors (100Ωx2, 10kΩ,1kΩ)
4. Relay (12V, 30A)
5. SL 100 transistor
6. 1N4007 Diode



We know that output of 555 timer goes HIGH when voltage at its second pin(trigger pin) is less than 1/3 Vcc.  Also the IC can be reset back by applying a LOW voltage at the 4th pin (Reset pin).  In this project 3 wires are dipped in water tank.

Let us define two water levels- Bottom (L) level and Top (H) level. One of the wire or probe is from Vcc, which can be called as middle level (M).


The probes can be arranged as shown in the diagram above. Insulated Aluminium wires can be used as the probes. The probes can be binded on a plastic rod and should be erected vertically inside the tank. The length of the probes wires and the supporting plastic rod must be chosen according to the depth of the tank. 

The probe from bottom level is connected to the trigger (2nd) pin of 555 IC. So the voltage at 2nd pin is Vcc when it is covered by water. When water level goes down, the 2nd pin gets disconnected(untouched) from water i.e. voltage at the trigger pin becomes less than Vcc. Then the output of 555 becomes high. The output of 555 is fed to a SL 100 transistor, it energizes the relay coil and the water pump set is turned ON. 

While the water level rises, the top level probe is covered by water and the transistor becomes ON. Its collector voltage goes to Vce(sat) =0.2V. The low voltage at the 4th pin resets the IC. So the output of 555 becomes 0V. Hence the motor will turn OFF automatically. Rating of relay is chosen according to the load (Motor). 32 Ampere relay is best suited for domestic applications.





hi,I have build the circuit with a little modification.I want to use the circuit as semi automatic water level controller(i.e. it will only turn off automatically, but one should have to press a switch for turn on).So i just short H & M in this circuit and connect a press switch between 2 and ground through resistor.It works fine.But when power cut occurs simultaneously the circuit turn on automatically.So plz help.

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