🚀 go-pugleaf

Sorry I lost the post from the person that requested information about pH 
meters. Here's my contribution.

I'm also interested in building a pH measuring circuit  (eventually).  I'd like 
to interface it into a microprocessor. Recently I found two circuits in:
 
Rudolf F. Graf, "The encyclopedia of electronic circuits", vol. 1, p. 399, 
(1985), ISBN 0-8306-1938-0, library of congress catalog no. TK7867.G66. Your 
public or academic library probably has the book. 

The low cost circuit looks particularly simple (+/- 15v supply, a probe, two op 
amps and a handfull of resistors), The output is 0.1 volts per pH increment. 
The more complicated circuit is temperature compensated. 

I can't image that the electronic parts cost more than $10. The costly items 
will be the probe, the power supply and the voltmeter (for reading the output 
voltage). From FAMA I see that the retail cost of probes is < $70. You can 
probably get them for less from other manufacturers (see below). Depending on 
how much of all this stuff you already have around the house you can  probably 
make a meter for not much more than the cost of the probe!

Graf suggest an "Ingold Electrodes" probe #465-35. I don't know anything about 
Ingold Electrodes, however, A good place to get information about any 
manufacturer in the United States is to look in the Thomas Register of Products 
and Services. Its a mammoth (>20 volumes) yellow-pages like index where 
manufacturers of everything are listed. Again this can probably be found in the 
reference section of your public library. Let me know what you turn up.

Good luck. If anyone tries this, let me know how it turns out. -- Fernando



Fernando Pineda (fernando@aplcomm.jhuapl.edu)