As the top sensor goes low (water above level C), the CLR signal is activated and the output of the flipflop is low. This allows Q1 to turn on and activate a triac or relay for the pump.

By analyzing those patterns, an onboard Raspberry Pi microcomputer is able to determine the current water level to within an accuracy of plus or minus ~1.5 cm (0.6 in).

Some prebuilt sensor modules had some issues because of the 5V supply. In the end, he used a new sensor, a microcontroller, and then used the pump and valve from the blood pressure cuff.