This is a simple water level indicator circuit which can be used to indicate water at 3 stages EMPTY, LOW and FULL by three respsctive LEDs.
The heart of this circuit is a 4011 NAND IC. You have to supply 3 volts to this circuit possible from two AA battery and connect the -ve terminal to lowest level of tank by a wire, you can tie this to the metal pipe outlet of tank.
The L terminal will go from up to down upto the lowest allowed level of tank and the F terminal wire should hang with tank’s cap upto the full water level’s height.
A simulated prototype bellow, check the circuit diagram and working principle for more details about this project.
- When water is below low level, both terminal(TP1, TP2) goes high by 10K pullup resistors and thus LED-EMPTY glows only.
- When water level is above low level, but below high level then TP1 is low, and TP2 is high. This makes only LED-MID ghlow.
- When water level is above full,then TP1 and TP2 both comes to low, and every LED glows including LED-FULL indicating it’s time to turn off motor.
Note: Full water level could be shown in one LED only, but to make the circuit much simpler I used one logic IC and hence the result being all LEDs on at full water level. You can use 7400 IC too as replacement of 4011, but 7400 IC will require 5V supply and you need to add a series 100Ohm resistor to the LEDs to run them at 5V.