Here is a very useful project of an automatic water pump controller circuit. The circuit will automatically switch ON any water pump / motor when the level of water in a tank reaches below from the required level and automatically switch OFF the pump after filling the tank.
The circuit can be used for variety of purposes like filling pools, tanks, container, washing machines etc. and it can not only use for controlling water level but you can use it for many other liquids.
The three probes shown in the schematic will detect the high and low levels of water. The probe marked "Upper level probe" will detect the upper level of water or when the tank become full. Positioned the "Upper level probe" on the level on which you want to switch OFF the pump.
The two probes marked "Bottom level probes" will detect the bottom level of tank and should be positioned at the level where you want to switch ON the pump.
The circuit is built around a 555 timer IC. The sensitivity of the circuit can be controlled by increasing and decreasing the values of the two 390K resistors. For more sensitivity use higher value resistors and less sensitivity use lower value resistors. The operating voltage of the circuit is 9 to 12 volt DC. You can also operate it with lower voltages like 5 or 6 volt but make sure to use same voltage relay also.