[Carlos] sent us his project that uses an Arduino as a pH meter. In order to sense the acidity or alkalinity of a solution, a glass electrode is connected to the ADC of the Arduino through a fairly complicated calibration, amplification, and filtering circuit. Admittedly, it may not be cheaper or as accurate as some commercial models, but it is an open project and can be interfaced with a computer via USB.
arduinos on acid ;-)
the last time i checked, you need a pretty darn well designed analog input and careful design for high accuracy pH electrometers. the problem is that you have to have very, very low input bias current because of the very high output impedance of the pH electrometer–a tl072 is not the correct choice for this application (sure, it’s jfet input, but iirc plain old jfet input isn’t actually enough to do it right). for these applications, pcb layout and ensuring that the pcb is clean is also important.
Hi threepointone,
I know the electrometer OPA128/OPA129 (Burr-Brown/Texas). It is the right choice, but it is expensive. The input impedance of the TL072 is about 1E12 ohms and it is not a rail-to-rail OpAmp. The impedance of a glass electrode is about 1E10. I agree that is not the perfect choice, but It is enough a pH resolution of 0.02.
well what do you know, finally we have an arduino project that isn’t stupid. i like!
Does anybody have any idea what the cost to build this would be on an existing Arduino Duemilanove? Why may it ‘not be cheaper’?
Someone should invent a PH probe you don’t to take care of like a new born baby that never grows up.
In fact, there is a scientific article describing a pH glass electrode using glass Christmas balls.
Da Rocha, Rogerio T.; Gutz, Ivano G. R.; do Lago, Claudimir L., “From Christmas Ornament to Glass Electrode”, Journal of Chemical Education, 1995, 72, 1135-1136.
http://jchemed.chem.wisc.edu/Journal/Issues/1995/Dec/abs1135.html
https://www.noisebridge.net/wiki/BioBoard/Documentation/pH#Glass_electrode
What would be required to have it control the ph as well? Motor shield hooked up to peristaltic pump is what I’m thinking.
You are right. The peristaltic pump is the most import part to control the pH. In addiction, you will need a valve with three connections to change the solution. You need be able to control the pump flow (stop, fast, slow) and direction (forward and back). You could maintain the pH constant or make a titration. The follow link is about a pH-stat.
http://www.metrohmusa.com/products/titr_842_de.asp
There are some peristaltic pumps that you can control it by a serial port. Ismatec is a brand of pumps. Robust but expensive.
http://www.ismatec.com/
Construct one is a hard job. The system can not heat the solution, it can not permit reflow, it needs support long time operation, etc.
May be someone could construct one using a laser cutter. This is the basic idea of a peristaltic pump.
http://en.wikipedia.org/wiki/Peristaltic_pump
I believe that an open source peristaltic pump could be a very nice and useful project.
DIY pump: http://www.home.zonnet.nl/rsetteur/aquarium/karel/doseer_spuit/index_doseer_spuit.htm
you can find small peristaltic pumps in some inket printers (I think old epson, but I’m not sure).
Anyway, has anybody been able to download the pdf describing the creation of the glass electrode?
I’ve been figuring out ways to control pH levels in a project I’m working on. It’s a photobioreactor which will go open source by Feb 2012 hopefully.
I found an open source small peristaltic pump which most of the parts can be laser-cut out of acrylic. It’s Here:
http://blog.makezine.com/archive/2008/12/make-a-a-peristaltic-pump.html
These small and reliable peristaltic pumps could be the solution for you. With their special pump head mechanics even low cost silicone tubing can be used for long-lasting processes. They offer analog control (0-10V) but also control over RS-232 or RS-485 interface. You can find additional information on: http://www.peristaltic-pumps.eu
For openalgaefarm: Be aware that using peristaltic pumps of high quality in terms of gentle handling of the tubing (which means a longer lifetime of the given tubing) and also the possibility of a gradual speed adjustment (which allows a soft landing to the desired pH-value) will have a decisive impact on the quality of the pH regulation and thus on the results of your project…
An interesting option for your photobioreactor work could possibly be this very innovative laboratory fermenter-bioreactor: http://www.bioreactors.eu