not only indicates the amount of water present in the
overhead tank but also gives an alarm when the tank
The circuit uses the widely available CD4066,
bilateral switch CMOS IC to indicate the water level
When the water is empty the wires
in the tank are open circuited and the 180K resistors
pulls the switch low hence opening the switch and LEDs
are OFF. As the water starts filling up, first the wire
in the tank connected to S1 and the + supply are shorted
by water. This closes the switch S1 and turns the LED1
ON. As the water continues to fill the tank, the LEDs2
, 3 and 4 light up gradually.
The no. of levels
of indication can be increased to 8 if 2 CD4066 ICs
are used in a similar fashion.
water is full, the base of the transistor BC148 is pulled
high by the water and this saturates the transistor,
turning the buzzer ON. The SPST switch has to be opened
to turn the buzzer OFF.
Remember to turn the switch
ON while pumping water otherwise the buzzer will not