I was looking for different ideas for measuring water depth for my espresso machine and thought maybe the easiest way to measure water would be to measure the water pressure at the bottom of the water tank. Anyways, I came across this site: http://www.practicalarduino.com/projects/water-tank-depth-sensor
The schematic for the circuit is:
I have some generally understanding of the circuit, but I'm wondering if someone would be willing to take a few minutes and explain how the circuit works. I really can't figure out U1/4 is doing (maybe part of calibration), why the circuits go through the op-amp again at U1/3, etc.