Have there been any advances on a Propeller powered pH or TDS meter?
Brann Fenix
Posts: 57
Hi there [noparse]:)[/noparse]
I last attempted to work on these projects back in 2006 with a BS2 and received a single reply from the talented Tracy Allen:
Now the cost of those probes, lack of replies, lack of time and difficulty of the temperature compensation sorta put my whole project on hold. But, it is now the time of the propeller and it is a whole new world out there... [noparse]:)[/noparse] I have seen some amazing projects and ideas that I never thought possible in the microcontroller world and I think now is the time to get back into the mix.
So random babble aside... is there anyone out there working with pH or TDS sensors that work with the propeller? There are so many really nice low cost options now like network access and such. Please let me know if any of your projects have taken you near this part of the game.
Thanks in advance,
Brann
I last attempted to work on these projects back in 2006 with a BS2 and received a single reply from the talented Tracy Allen:
Tracy Allen said...
Try Vernier, very niice for educational and hobby use...
www.vernier.com/probes/index.html
The PH-BTA has a built in amplifier with an offset, so you can connect it directly to an ADC. Software would be easy, because the voltage is linear 0.25 volts per pH unit,
pH = (volts - 1.75) * 4
The harder part is the calibration and standardization and temperature compensation.
For long term deployments, I'd recommend Sensorex probes...
www.sensorex.com/
Now the cost of those probes, lack of replies, lack of time and difficulty of the temperature compensation sorta put my whole project on hold. But, it is now the time of the propeller and it is a whole new world out there... [noparse]:)[/noparse] I have seen some amazing projects and ideas that I never thought possible in the microcontroller world and I think now is the time to get back into the mix.
So random babble aside... is there anyone out there working with pH or TDS sensors that work with the propeller? There are so many really nice low cost options now like network access and such. Please let me know if any of your projects have taken you near this part of the game.
Thanks in advance,
Brann
Comments
What I found out:
- Electrodes are very high impedance > 100Mohm
- JFet Op-amps are the way to go. Two as followers, one in each electrode's lead to a third as amplifier, then an ADC.
- Electrodes give roughly +/- 1 V for the full range. They work for pH 1-2 to 12. beyond than range they are a bit unlinear.
- Temperature compensation has to be done with a curve
- You have to calibrate the electrode... they do not have an absolute scale. Standard pH solutions of pH 4, 7 and 10 can be obtained, or prepared by yourself. pH 4 is an acetate buffer, pH 7 is phosphate and pH 10.. I do not remember
I even have an electrode lying around.. but never attempted it again... well
have fun
Ale