I used pH sensor circuit sold on Sparkfun to assemble Arduino UNO controlled pH sensor.
I already had BNC connector and pH sensor probe (Vernier Tris Compatible pH sensor probe).
I used this code found on sparkfun
https://www.atlas-scientific.com/_files/code/Arduino_pH_sample_code.pdf
The sensor worked perfectly until I tried to calibrate it for more precise measurement (it is being used to measure pH of water samples)
I followed their calibration instruction. Ever since I tried to calibrate the sensor with pH4.01 buffer solution, everything got messed up.
When I measured the pH of pH 7.01 buffer solution using the pH sensor I made, I got measures around pH 10.32 up and down.
When I measured the pH of pH 4.01 buffer solution, I got the same readings.
When I measured the pH of pH 10.01 buffer solution, I got "check your sensor".
I even reset the circuit by "x" code, but nothing changes when I measured pH4.01, pH7.01, and pH10.01 buffer solutions.
I cannot find any resources online regarding this problem, and I am also new to Arduino.
It would be fantastic if someone can help me out here.