Students collecting data on their own potentiostats

One of the problems I am trying to solve with the FeAtHEr-Cm platform is to eliminate the instrument bottleneck that we see in analytical chemistry courses. For example, a class of 12 students, even if paired up, will unlikely be able to perform an electrochemistry experiment simultaneously because there are few institutions that would be equipped with a half dozen potentiostats.

That is, unless your institution is equipped with FeAtHEr-Cm potentiostats that your students built.

OK, so my class only has 2 students, but each student is working on their own potentiostat (which they built).

Each student is using python on their own computer to communicate with the potentiostat they built. In a previous class, we calibrated the feedback resistor in the current-to-voltage converter to ensure that the current reported by the instrument is correct (both students obtained relative errors better than 0.1%).

Jarrod is collecting data on ferrocyanide using a 2 mm platinum disk electrode.

In this experiment, the students are collecting cyclic voltammograms at scan rates ranging from 1 V/s to 0.01 V/s. This range requires them to change the feedback resistor so that the current range is appropriate for the measurement. They also explore the impact of including a filtering capacitor in the feedback circuit.

Nate is using a 25 micrometer diameter platinum electrode with the FeAtHEr-Cm. The image is hard to see, but yes, that is a steady state voltammogram with a steady state current of 15 nA!

Nate is trying a slightly different experiment, using a 10 MOhm feedback resistor, he is determining whether or not the home-built potentiostat can measure nanoamp levels of current. Turns out, we can! Here, the filtering capacitor plays a very important role in the integrity of the voltammogram. The 0.1 uF capacitor used for microamp current ranges is much too large, and when Nate saw that the voltammogram was “too smoothed”, he broke out the Santana lyrics. For everyone’s benefit, we ended class at that point.

FeAtHEr-Cm spectrometer

If you’ve been following (and I know one or two of you are), then you know that FeAtHEr-Cm is my Adafruit Feather microcontroller-based approach to building scientific instrumentation for the chemistry teaching laboratory. Not only does the platform allow for inexpensive instruments to be distributed throughout a classroom (at under $50/unit, each student in an analytical chemistry lab could have their own potentiostat), but the instruments are designed so that students can understand what makes them tick.

The btm100-alpha version

Joining the team is the btm100 which is a spectroscopic instrument designed to perform turbidity and nephelometry experiments. These techniques help scientists explore heterogenous solutions by measuring their cloudiness, and the techniques are used widely in fields such as environmental analysis. As an added bonus, the response from turbidity/nephelometry measurements mimics that of absorption/fluorescence measurements which are commonly covered early in the chemistry curriculum, so we have a fine opportunity to build on fundamental concepts (Beer’s Law) while expanding the suite of tools students are exposed to.

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FeAtHEr-Cm meets Star Wars

I have this little Star Wars lunch box, and just noticed that it is big enough to fit the Adafruit Feather along with my potentiostat featherwing. What does that mean? I have the most awesome Faraday cage!

Mini metal Star Wars lunch box hanging out with the bob173 potentiostat.
And voila! A Faraday cage… if I’m willing to drill holes in the case.

FeAtHEr-Cm gamma tests

I received the PCBs for the gamma (3rd) version of the FeAtHEr-Cm potentiostat. I really like how this one comes together. Complete with 2 20kohm pots for adjusting virtual ground and iR compensation plus the passives all fit in a single 14-pin socket which allows students to explore how changing these components can influence the performance of the instrument (and to hack it to do things it’s not intended to do). Plus, it’s got buttons! This is the version that students will see this fall.

The bob173-gamma potentiostat.

FeAtHEr-Cm update

Previously, I announced my latest project in The start of FeAtHEr-Cm. Over the past several weeks, I’ve been iterating through the potentiostat design and I think I’m at a point that the design will stay more or less in place, allowing me to shift my focus to documentation, instrument use and lesson plans.

I’ve also spent some time building a website that contains the documentation for building the instrument, writing code and using the potentiostat in an educational setting. Rather than re-write all of that information here, head on over to this page for a summary of what’s been done and what’s in the pipeline.

Example CVs from 0.01 to 0.5 V/s of potassium ferrocyanide in 0.1 M KCl at a 2 mm diameter Pt electrode. Obtained using the gamma version of the bob173 potentiostat.