Water-level controllers are common nowadays. The one described here is built around timer NE555 and inverter buffer CMOS IC CD4049. It uses readily-available, low-cost components, and is easy to build and install on the over-head tank (OHT) to prevent wastage of water. The circuit works off a 12V battery or 230V AC mains using a 12V adaptor. Since Vcc terminal is at the bottom of the tank, when the water level falls below sensor L, timer IC2 is triggered at pin 2 via inverters N1 and N2 and its output goes high. As a result, the output of timer IC2 goes high. Relay RL1 energises and the motor starts filling water in the tank. The motor remains ‘on’ even when the water level crosses sensor L.

 

As water in the tank rises to touch sensor H, timer IC2 is retriggered at pin 6 via inverters N3 and N4 and as a result, its outputgoes low. The relay de-energises and

the motor stops filling water in the tank. The motor remains ‘off’ even when the water level falls below sensor H. As water is consumed and its level falls below sensor L, the motor restarts.Thereafter, the cycle repeats.