pH determination is an essential experiment in many chemistry laboratories. It requires a potentiometric instrument with extremely low input bias current to accurately measure the voltage between a pH sensing electrode and a reference electrode. In this technology report, we propose an open-source potentiometric instrument for pH determination experiments with Bluetooth wireless connectivity. The hardware is built on a solderless breadboard and mainly composed of an Arduino Nano microcontroller, a 16-bit analog-to-digital converter, two electronic buffer amplifiers, a temperature sensor, and a Bluetooth module with a total cost around $50 (US dollars, including a portable power supply ~$10). The software is written in Arduino Sketch and the cross-platform Python language, both of which the students can access and modify freely. The instrument was demonstrated with a traditional glass electrode and a custom palladium/palladium oxide pH sensing electrode, and compared with a commercial pH meter. Results showed that both the accuracy and precision of the developed instrument are adequate for teaching purposes. Understanding the workings of electronics of the pH meter can inform the students of the mechanism of pH determination.