Water level indicator using 7-segment display

Using this schematic electronic project can be designed a very simple water level indicator electronic circuit that uses a 7-segment display to indicate the water level (low, half and full)in the tank. This water level indicator electronic circuit shows the water level by displaying L, H and F for low, half and full, respectively.
This water level indicator electronic circuit is based on the 7408 quad two inputs and gates IC (that contains four input independent gates) and a 7404 hex inverting gates IC.
When the tank is full a buzzer is used to alert you of water overflowing from the tank.
The circuit uses five level sensors to sense the different water levels ( one for common GND, one for low, one for high one for half and one for overflow ) .
A high voltage at the input pin of the NOT gate, it outputs a low voltage . For a low voltage at the input pin of the NOT gate, it outputs a high voltage.
When the tank is empty, the input pins of IC 7404 are pulled high via a 1-mega-ohm resistor.
When the water is at the low sensor the common cathode 7 segments DISP3 shows ‘L’ indicating low level of water in the tank.
When the water is at the half sensor the common cathode 7 segments DISP2 shows ‘H’ indicating half level of water in the tank.
When the water is at the low sensor the common cathode 7 segments DISP1 shows ‘F’ indicating that the tank is full.
When water is at the overflow sensor ( buzzer sensor ) the pin 13 of gate N6 goes
low to make output pin 12 and the buzzer will sound .
All water sensors must be constructed from noncorrosive material .