Water level controller is one of the most popular circuits in household and industrial applications. Usually household water level controller is either mechanical controller or based on digital electronics.

Controller described here is extremely simple and provide service as efficiently as expensive controller. The circuit uses only two transistors and few other components. Metal rod is used as level sensor and is placed inside the tank and for better operation and long life aluminum rod is preferred.

Transistors are used as switch and are always switched on unless the sensor probe is connected to ground with water as a conducting medium.

Initially when tank is empty both transistor are switched on due to base voltage obtained form resistor R3 and R5, which switches on the relay (DPDT relay). As relay is switched on, one of its contact (P1) switches on water tank while another contact (P2) sorts the collector and emitter terminal of transistor (T1) because of which transistor (T1) is bypassed. Now when water level reaches bottom level transistor (T1) is switched off but as it was bypassed by relay the relay continues to stay in ON state. Ultimately when water level reaches top level transistor (T2) is switched off causing both relay and water pump to switch off. Now when water is used and level drops below top level motor is not switched on because at this instant transistor (T1) is in off state.

Circuit described here is extremely simple, cost effective and can be constructed by any one easily.

   Schematic

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