This is one of the simplest water level indicator that can give up to 7 indications – Full, Half and Low water levels in the overhead tank through LED indications. The circuit is simple and uses a single IC and a few components.
IC = ULN2004
7 = LEDs (Red)
7 = Resistors 180 ohm
The main part of the water level circuit is the 7 channel Darlington array IC ULN2004. Its seven inputs are connected to seven probes to sense the water level and the corresponding outputs are connected to three LEDs through current limiting resistors. A common probe (common) is connected to the positive rail. When this probe gets electrical continuity through water with the other probes the corresponding LEDs light.