Ocean XPRIZE pH Sensor

Description

Electrochemical pH Sensor
The measurements and a real time clock reading are saved in nonvolatile memory and retrieved via a USB cable when the sensor is retrieved. These data can be converted to pH using a calibration table. We hope that Salinity and other properties might be extracted from the data using multivariate analysis.
Low Power Operation
The sensor uses a low power ATtiny85 microcontroller that is programmed using the Arduino IDE, to achieve very low power operation. The ATtiny85 can be put to sleep and in this state uses less than 200 uA of current when running through an efficient inverter from 12V batteries. The rest of the system is turned on and off by the ATtiny85, so the high power used by the Arduino and other devices only operates for as long as is necessary to take measurements of the electrochemical voltages and other readings (about 5 seconds).

Discussions

zakqwy wrote 03/04/2015 at 14:52

Hi--how do you handle probe calibration?

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Martin Brooke wrote 03/04/2015 at 14:58

Currently we calibrate like Silver Chloride pH sensors. We get pH adjusted seawater (using HCL and NaOH) and do an interpolation, using a Nernst equation to compensate for temperature. I think we might have to do a much better job and consider salinity and degradation over time due to fouling to really get the best out of this type of sensor. Its main advantage is it is very robust physically.

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zakqwy wrote 03/04/2015 at 15:10

Makes sense. I do a bit of work with process pH measurement, and hitting the right balance of durability, accuracy, and stability is a real challenge. You might want to look at retractable housing designs--there are a few out there that can pull the probe into a flushing chamber to clean out reference junctions. You could probably design your own that would extend the life of your sensor by a bit.

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Martin Brooke wrote 01/29/2015 at 13:35

We are Blue Devil Ocean Engineering. I Added the ATtiny85 code.

This MEGA code is actually older code, but it works fine. We have a new version that works on an UNO and on a Yun, still in debug.

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PointyOintment wrote 01/29/2015 at 03:51

Your ATtiny85 Code link seems to be missing the URL.

Also, which team are you?

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Ocean XPRIZE pH Sensor

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