Making high-resistance voltmeter is not easy, as such devices are much more sensitive to temperature changes and electromagnetic noise, as well as to electrostatic charges. However, with electronic elements available today it is not very difficult to create an ...
Gravity: Analog pH Sensor/Meter Kit V2 - DFRobot
Isolated pH Monitor with Temperature Compensation | Analog Devices
Small and simple pH-meter
Tiny pH-meter
DIY Arduino pH Meter using Gravity pH Sensor
OWL2/BASIC Stamp interface to pH sensor
Electronic circuit used for the pH sensor. | Download Scientific Diagram