building a ph tester

here's a good document pH meter principles

I have some old little test tubes from an old chemistry kit. it's a real thin glass. if I clean one really well, maybe try filling it with some general hydroponics ph down solution, stick in a wire electrode and see what I get. I don't expect it to work well, or be useable, but I'm interested to know if this will work. a little experiment to help learn how a ph probe works. 7 - (v / .06) a cheap volt meter should give me some kind of a reading, hopefully close to the actual ph of the solution being tested.

now that I understand how it works a little better, I know a probe can't be made, so I'll happily buy one and see if I can use it to build a digital meter for my computer

so at a pH of 7 the probe should be .06 volts?

If so, I'd run it through an op amp with a gain of 10, maybe even 100 depending on the full swing of the probe.

Cool idea.
You can do some glass blowing at home. Charcoal and a shop vac can create a lot of heat.

BigBudBalls said:

so at a pH of 7 the probe should be .06 volts?

If so, I'd run it through an op amp with a gain of 10, maybe even 100 depending on the full swing of the probe.

Cool idea.
You can do some glass blowing at home. Charcoal and a shop vac can create a lot of heat.

Click to expand...

I'm not exactly sure yet, but I'll figure it out. I've read 2 different descriptions online. one says it's inverted voltage with .06v per ph unit, and another said 7ph is 0 then .059 volts per ph unit either + or - in either direction from neutral. so a ph of 5.8 would either be 0.492 volts or 0.0708 volts coming from the probe. you then run it into an op amp like you said, then into a volt meter to get a reading. run that number into a calculator and you have your ph. to get it more accurate, you also have to take temperature into consideration.