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I am experimenting at home with the idea of making an optical ph sensor that can read the colour of ph indicator using photodiodes.

I am wondering if there is some kind of ion permeable membrane that could be used to contain the indicator solution, so it can 'read' the ph of the solution being tested, without mixing with it.

I would like something that is fairly easily obtainable to me as a home experimenter.

The sensor could possibly be used make an automated ph corrector for my local aquaponics farm.

I looked into commercially available ph sensors. The glass bulb type and ISFET type suffer from drift and need regular calibration. There are optical types available, but they are too expensive for me.

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  • $\begingroup$ In terms of a membrane material, did you think about something like Nafion (en.wikipedia.org/wiki/Nafion)? This polymer already finds deployment as membrane material for fuel cells, for example. $\endgroup$ – Buttonwood Mar 29 '17 at 22:15
  • $\begingroup$ Ok, I might give it a go. I will need to work out a way to make a sealed pocket to contain the ph indicator. Maybe clamp the Nafion between solid frames. $\endgroup$ – John Spence Mar 30 '17 at 7:09

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