In this tutorial-based article, we are going to learn about pH meters using pH sensors and Arduino.

Hardware Required

Software Required


What is pH?

  • pH is a scale that is used to measure the acidity or basicity of an aqueous solution. The pH scale ranges from 0 to 14. 0 being the most acidic and 14 being the most basic. Pure water is neutral and thus has a PH of 7. 

  • pH is the logarithmic scale and it inversely indicates the concentration of hydrogen ions in an aqueous solution.


  • The above mentioned is the formula to calculate the pH of an aqueous solution. 

pH meter construction and working principle

  • The pH sensor is a cylindrical glass structure that has a bulb situated at the bottom. This bulb is specifically designed to measure hydrogen-ion concentration when dipped in any solution. 

  • The hydrogen ions exchange the positively charged ions which are already situated inside the bulb, creating an electrochemical difference. 

  • This difference is interpreted by the electronic amplifier situated on the top. It further converts this difference into pH units. 

  • The pH meter sends the final pH values to the Arduino board.

  • The Arduino receives those signals and sends the appropriate data to be displayed on the OLED screen. 

  • The values at first might not be accurate as the pH meter needs to be in the solution for a while to have the proper pH values. 

Circuit Diagram

  • The pin connections for the circuit diagram are mentioned in the table below:

Pins on Arduino

Pins on pH sensor






Signal pin

Pins on Arduino

Pins on OLED Display









Arduino Code

  • Copy the Arduino code and upload it to your board via Arduino IDE.

Testing the code

  • We took 4 different solutions and tested the pH meter with them

  • Testing it with highly acidic lemon water. 

Your pH meter is ready to use.