Water Level Indicator
A water level indicator is used to show the level of water in an over head tank. This keeps the user informed about the water level at all times and avoids the situation of water running out when it is most needed. There are ton of water level indicator circuits on the web. But this one is unique because this water level indicator circuit also has an alarm feature. It not only indicates the amount of water present in the overhead tank but also gives an alarm when the tank is full.
The circuit uses the widely available CD4066, bilateral switch CMOS IC to indicate the water level through LEDs.
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 number of levels of indication can be easily increased to 8 if 2x CD4066 ICs are used in a similar fashion.
When the 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.
Since it uses CMOS switches the current flowing through the wires is very less and hence the corrosion of electrodes is very minimum.
Remember to turn the switch ON while pumping water otherwise the buzzer will not sound!
NOTE: You will need to power the circuit with a 6V DC supply which can provide 100mA or more current. The transistor BC148 maybe substituted with any general purpose transistor such as BC548, 2N2222, PN2222 etc.
Video of water level indicator
Here is a video showing someone building the above water level indicator circuit: