I'm actually looking for a fast&cheap circuit to interface a standard pH probe.
Details about the pH probes :
- pH 7 = 0v @ 25°C
- 1 pH level is = 0.05916v
- min probe value (pH = 0) = -0.41412v
- max probe value (pH = 14) = 0.41412v
I need the circuit output to be directly connected to an analog pin of an Arduino (or whatever ADC // µC), so levels should be between "0v and +5v"
I know that the pH probes has a few Tohms (//Tera-Ohms) of resistance and that the first stage Op Amp on which it is directly connected needs to has, idealy, a few fA (femto-Amperes // 10^-15 Amperes).
I found some ICs that could do the trick but i need someone to explain some things to me :
- CA3140 (max : 10>50pA)
- CA3140A (max : 10>40pA)
- LMC6001AI (25fA)
It could be really fine to realise this circuit and sharing with other people that needs the same.
I faced problems with the circuit explained inside the datasheets because they uses non-standard values resistances.
Thanks for the ones who will help me/us !
PS : i already have the pH probes, bought from eBay for some $ (cheap)