This project describes an open software open hardware pH meter using an Arduino/Freeduino board. In other words, this is an electronic circuit to be connected with a glass electrode pH sensor.

The pHduino can operate using a LCD to display the pH and the temperature data like a pH meter. Also, you can control it using a computer by USB port.

The signal gain (slope) and the signal offset are adjusted manually by trimpots. The signal is compensated by a temperature sensor.

It seems inferior and a little bit more expensive compared with a pH meter bench instrument. However, it is interfaceable, programmable, expansible, and, the more important, open and free!

Again, it is not intent to be a high resolution analytical instrument to compete with a commercial pH meter. It is to be simple, easy to understand, easy to modify, and different!