pH meter/controller prototype

Note that the connection from the pH electrode BNC connector to the input of the amplifier (yellow arrow) on this prototype is very short and direct . The reason for this is that this is an extremely high impedance point, and any extra wire length here will act as a very effective antenna,  picking up any electrical noise in the area. 

 

Photo of a pH controller built by a reader
When completed, this circuit reportedly worked fine, despite the fact that it was made by an inexperienced builder, on perf board, and with very long leads.

A pH meter adapted from the circuit described here, enhanced with a microcontroller, analog to digital converter, and additional circuitry. (Click image to view full size.)
 

More pH-related photos are available at The pH Pages.