The circuit is using two ICs, the IC1 is an ULN2803, that is an eight darlington array IC and IC2 is a famous NE555 timer IC. Working of the circuit is as follow.
The IC1 detects the level of the water through its eight probes, therefore when the water level reaches to any probe, the associated LED with that probe light's up and in the opposite conditions when the water level decreases from any probe the LED associated with the probe will goes off.
The IC2 is working as a relay driver, when the water level decreases below the last probe the output of the IC2 goes low due to which the relay will become activated, and when the water level reaches at the top probe the output of the IC2 goes high due to which the relay will become deactivated.
Here is a very interesting and useful project of a water level indicator with pump controller. The has 8 water level sensing points and it will automatically switch on the water pump motor when the water level reached below the last sensor point, and automatically close the water pump motor when
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