looks like a classical two op. amps circuit. You will have to calibrate first. The two (blue) variable resistors are for calibration. The output is analog so you will have to calibrate that voltage on Arduino as well. If is 0 - 5 V the pH=7 would be 2.5V, etc.hope it helps,MaLi
You need to connect a pH probe to the module.
I brought this ph module from ebay. But this gives me ghost outputs. They are not stable. I have no idea how to use this. Anyone have experience with this module? help me