Overhead Tank Controller

In many places such as hostels, apartments, school/colleges, hospitals, etc, overhead tanks are used for storing the water. As the requirement of water is large, controlling of tank is very important. Overhead Tank Controller is a specially designed circuit to overcome this problem. Overhead Tank Controller has two sensors named as HIGH and LOW immersed into the tank with reference, which is at positive potential. The motor is on until the tank is full. When it reaches to HIGH level, the motor automatically turns OFF and it remains OFF until water level goes below LOW sensor and then it becomes on again. Thus, Overhead Tank Controller prevents the overflow of water.
About the Circuit :

• The circuit is designed using IC1, which consists of four AND gates and IC2, which is used in bistable mode. The HIGH and LOW sensors are connected to one of the input of two AND gates at pin 8 and 12 respectively. Other inputs are connected to positive supply through resistors. The output of these two AND gates at pin10 and 11 are given to input of another AND gate at pin 5 and 6. The output of this AND gate at pin4 is given to threshold input pin6 of IC2. The trigger input pin2 of IC2 receives input from LOW sensor.
• When the tank is empty, logic of AND gate and input of LOW sensor make pin6 and pin2 of IC2 are low. IC2 gets set, output at pin3 goes high which in turn makes transistor T1 on, and relay energized. When water reaches to LOW level, output at pin3 of IC2 remains unchanged and relay remains on. When water reaches to HIGH level, pin6 of IC2 becomes high which resets IC2. Output at pin3 goes low and relay goes off. It remains off until water level goes below LOW sensor and then becomes on again.
• LED D2 gives the visual indication of relay on or off. When D2 glows indicates that the relay is on. When it turns off indicates that the relay is off.