We are trying to build an automatic titrator for didactic purposes. We have been successful in controlling titration, but there are problems with electronic amplification of the glass electrode signal, so that we couldn't generate the digital signal that is necessary to record it. The processor is an Arduino uno board.
A glass electrode output spans from -0.7 V to 0.1 V [https://en.wikipedia.org/wiki/Glass_electrode], while plain Arduino input is 0-5V - one need to deal with that.
The proper way would be to implement dual supply op-amp with to get level-shift and amplification. You may check this link for schematics and resistor value calculator:
http://www.daycounter.com/Calculators/Op-Amp/NonInverting-Op-Amp-Resistor-Calculator.phtml
Simpler - yet less accurate (lower resolution) solution is to use voltage divider. Please refer to case 4 described here:
http://www.skillbank.co.uk/arduino/measure1.htm
If you are interested in making a data collecting interface for you - please do not hesitate to send me a private message
There are pH sensors available with embedded electronic amplification (for process sensors this is called "embedded transmitter"). Communication with the sensor can be purely digital, such as RS-485/Modbus. Make sure to select a sensor whose communication is based on public and not on proprietary standards.
This way you don't have to worry about amplification and proper shielding of the sensor signals.
Dear Peter,
I have the feeling that these pH sensors with embedded amplification are much more expensive than the old ones. Is it right? Anyway, I will also tell my students of your suggestion and ask them to see what are their costs here in Brazil. This project aims at low price equipments for didactic purposes. Thank you.
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