This water level sensor (detector) circuit uses a standard NAND logic gate to produce oscillation and to detect the water level. Oscillation is included inside this circuit to provide alternating current (AC) source for probe electrodes, to achieve a corrosion free operation. With AC source, the process of electrolysis is done in both direction, neutralizing the process of ionic transfer from one side of electrode to the other side.
The D1 and D2 diodes rectify the detected AC current leakages through the liquid (water), produce a DC voltage that is needed by the logic gate to trigger high or low condition. This high or low condition is then appear on the gate’s output, driving an opto-coupler that can be used to drive remote circuits further. The probe can be a copper wires, stainless steel rods, or other conductor materials.