Building A PH Meter
Because the circuitry of a basic pH meter is quite simple, it is possible to build a serviceable pH meter or pH controller with parts available at a neighborhood electronics retailer. (pH probes, however, are not so easily acquired and must usually be ordered from a scientific instrument supplier.) For a walkthrough of how to build the simplest possible pH meter or a detailed description of how to build a pH meter/pH controller, see The pH Pages. The application note for the LM6001 chip at the National Semiconductor web site also has a very simple demonstration circuit. Although the application note is for a specialty IC, serviceable pH meters can be built from any operational amplifier with a high input impedance, such as the common and inexpensive National Semiconductor TL082 or its equivalent.
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