# Programming a custom pH controller



## timphiz (Oct 23, 2010)

Hi, I'm trying to make a custom pH controller out of a micro-controller. I'm using this pH probe. The problem is, when I emailed the merchant they weren't able to tell me how to interpret the output from the probe, just that it would work with standard commercial aquarium controllers. Does anyone know where I could find formula for calculating the pH or a good method for figuring it out myself? Thanks!


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## ObiQuiet (Oct 9, 2009)

I'm sure someone here knows the exact answer to your question.

All _I_ can say is that your project interests me, and maybe these links to circuit diagrams from similar projects will help in some way:
http://www.electro-tech-online.com/...hat/9419-ph-probe-op-amp-circuit-problem.html
http://damien.douxchamps.net/elec/ph_meter/

In the write-up of the 2nd link, note especially the Circuit Calibration and More Details sections near the bottom of the page.

Cheers!


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## ObiQuiet (Oct 9, 2009)

Found some more:
http://www.allaboutcircuits.com/vol_1/chpt_9/6.html
According to this, you should expect about 59 mV for each 1 pH, with 0V at pH=7. However note the points re: the high impedance getting in the way of the measurement.

Also, on this very forum, there is this great thread:
http://www.aquaticplantcentral.com/forumapc/diy-aquarium-projects/58487-diy-ph-controller.html

Which leads to a good answer to your question, here:
http://www.66pacific.com/ph/ph_2.htm


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## timphiz (Oct 23, 2010)

Thanks, that stuff helps a lot.


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