Electrochemistry
Update, March 26, 2024:
Our new WheeStat hardware is now available!
This instrument incorporates the Raspberry Pi Pico microcontroller board and a number of hardware changes that will give it a greater current capacity, lower noise, and greater voltage accuracy.
The WheeStat is a computer driven three electrode potentiostat, an instrument that measures electric current exchanged between electrodes and chemicals in solution.
It was designed for teaching electrochemistry and quantitative analysis. It supports a variety of experiments including cyclic voltammetry and differential pulse voltammetry.
What's it do?
The WheeStat is capable of measuring concentrations of trace metal ions in water, including lead, arsenic and mercury.
For more information, visit the WheeStat user's manual at the link below
How will the new instrument differ from older WheeStats?
To start with, we plan to abandon the Texas Instruments microcontroller environment that we have been using in favor of the Arduino compatible Raspberry Pi Pico. We are doing this to make the instrument amenable to hacking by the larger Arduino using community. The instrument will also employ a digital to analog converter (DAC) rather than relying on pwm signals to generate voltages.
This is the WheeStat. We offer the WheeStat fully assembled with software installed and a Windows compatible graphic user interface provided on a usb memory stick. The 40 mA potentiostat is powered from your computer over usb. We are also developing a 240 mA instrument that will be powered by an external AC to DC adapter.
Supported Experiments:
Cyclic Voltammetry (CV)
Linear Sweep Voltammetry
Differential Pulse Voltammetry (DPV)
Anodic and Cathodic Stripping Voltammetry
Chronoamperommetry (one and two step)
Repetitive CV and DPV experiments
Cyclic Square Wave Voltammetry
Normal Pulse Voltammetry
Electrical Attributes:
Working electrode voltage range: +4.10 volts to -4.10 volts
Counter electrode voltage range: +12 to -12 volts
Standard voltage step: 10 mV
Theoretical minimum voltage step: 2 uV
Standard current limits: +40 to -40 mA
Extended current limits (requires hardware upgrade): +240 to -240 mA
Maximum measurement rate: 120 data points / s
Standard measurement precision: 12 bits (1/4095)
Prices:
40 mA version: $200 USD plus shipping
240 mA version: $260 USD plus shipping
Our most frequent request from potential customers has been for an instrument capable of sourcing larger electric currents. The previous version of our potentiostat (Model 7) is limited to +/- 7 mA. While the lower current of the Model 7 is appropriate for teaching and for many analytical applications, other applications, such as electrochemical synthesis require greater currents.
Our most recent model is designed to source at least +/- 40 mA. We are working on a high current module to source up to 240 mA. The photo on the upper right shows an early prototype of the high current model. Notice the six-watt DC/DC converter on the perfboard in the back and the socket for a 1 Amp power connector in the front. Both models will run +/- 4.1 volts on the working electrode with a compliance voltage of +/-12 volts. The image to the lower right is a screenshot showing a recent test of the first prototype. In this test, the instrument was able to establish ~+/- 4 volts across a 20 ohm test resistor. While the power supply in this instrument was rated to supply 42 mA of current at +/- 12 volts, this data shows the instrument sourcing up to ~+/- 75 mA.
Availability
We have just received our first batch of professionally manufactured circuit boards. Final assembly and quality assurance is underway finalize software, fit the circuit board to boxes, etc.
Software.
The microcontroller that drives the new WheeStat is a Raspberry Pi Pico and comes loaded with software written in Arduino.
The WheeStat comes with our Graphic User Interface loaded on a USB flash drive. The GUI comes as an executable program for Windows 32 and 64 bit computers as well as source code written in the program Processing. At this point, we do not have the GUI application for Mac. We believe that the Mac App for OSX can be generated relatively easily (see this video). All experimental parameters are adjusted from your computer using our GUI. Data are displayed in real time on the GUI chart. Sequential experiments can be overlayed on the GUI chart. Once collected, data can be saved as CSV files and opened in excel (or another spreadsheet program).
All software is open source. Future updates can be downloaded for free from our GitHub site.
Hacking the WheeStat.
Want additional functionality? Have some unique experiment that you want to run? No problem. The programming languages are simple to learn and you will have the source code.
Electrodes.
The WheeStat does not come with electrodes. These need to be supplied from another source. We note that graphite pencil lead may be used for the working and counter electrodes (black and red leads, respectively) and a Ag/AgCl electrode is recommended for the reference (green lead). Here is a link to a page that will tell you how to make a low cost Ag/AgCl electrode.
