As the water level touches the HIGH level probe, the pump must stop and should not start until the level of water reaches the low level probe. The circuit requires working at 12V battery or 230V AC mains using a 12V adaptor.
All the sensors used in water tank are built up from non- corrosive metal. They are fitted on the OHT and then connected to the circuit at appropriate terminals. At the bottom of the tank there is power supply terminal Vcc. Just above the bottom of the tank there is a sensor terminal L and at the highest point i.e. at the top of the tank there is a sensor terminal H. After the proper installation of the sensors and connection with the power supply, the circuit becomes ready for the use.
When the water level falls below the level of sensor L, the timer IC2 gets triggered at pin2 through inverters N1 and N2 and the output of IC2 goes HIGH. As the output goes high, the relay gets energized and the motor starts filling water in the tank. The motor remains ON even though the water level crosses sensor L.
As the water in the tank touches the sensor H, the timer IC2 gets retriggered at pin6 through inverters N3 and N4 due to this the output of IC2 goes LOW. The relay gets de-energized and the motor gets turned OFF. The motor remains OFF even though the water level goes below the sensor H. The motor again gets restarted only when the water level fall below sensor L. This cycle repeats every time. This process can also be handled manually by using the switch S1.
This water level indicator circuit is configured around a well known CMOS input- compatible 7-channel IC ULN2003. As soon as the water level rises, water comes in contact with the probe P1 via P3 thereby making pins 7, 2 and 1 HIGH is sequential manner. As a result the corresponding pins 10, 15 and 16 goes LOW is the sequence and the LEDs 1 and 3 lights up in sequence. When the water comes in contact with the last probe i.e. the top most, the piezo buzzer starts sounding which is connected to pin 16 along with the LED.