Posts made by Will Dickson

@brad

Q1.) I tried to run multiple sensors within a single experiment cell (shared buffer solution), but have observed what I think is cross-talk between the devices (particularly when running 2 electrodes for electrodeposition). Are there any issues I'll need to consider here?

Running multiple Rodeostats in a single cell (shared buffer) would be problematic. This issue is that the Rodeostat (and potentiostats in general) actively control the potential between the working and references electrodes using feedback. So when you have multiple Rodeostats in the same cell these feedback control systems can interfere with each other e.g. when the first Rodeostat adjusts the current sourced by its counter electrode in order to maintain the correct WE to RE potential this will effect the WE to RE potential of the second Rodeostat, and vice versa, etc. I think your best option here would be to isolate the test cells if you can.

Q2.) I sometimes experience more noise in my experiments. I was thinking about just swapping in larger caps on the TIA but it doesn't seem to happen all the time. Another thought was that the power being supplied by my USB hub might be contributing. Any reason to worry? What's the best way to power the rodeostat externally while using USB for serial comm?

You might try adding a USB isolator - not too expensive (~$35). Maybe something like this
https://www.amazon.com/SMAKN-Isolator-Digital-Isolation-Industrial/dp/B00XXPO4UG

Q3.) I see the P15, P16 (5/3.3V jumpers) next to the expansion headers as one option. However, I assume I would need to somehow physically disable the USB-provided +5V power away from the board?

It is possible to externally power the Rodeostat, but doing so requires requires cutting a small trace on the underside of the teensy 3.2. This documented on the PJRC website https://www.pjrc.com/teensy/teensy31.html See the images (further down the page) showing the underside of the teensy 3.0, 3.1 and 3.2. In the upper right corner of the board there is the trace which needs to be cut - there is an arrow which points to the trace and callout the describes cutting in e.g. "Cut to separate VIN from VUSB ... etc.".

@KarlHaxthausen

Yes the Rodeostat (and teensy 3.2) should work with windows 7. However, with windows 7 you will need to install a driver for the teensy 3.2. There are two ways to do this.

1.) You can directly install the serial driver which can be download from here https://www.pjrc.com/teensy/serial_install.exe

This would be the option you want if you just wish to access the device from the windows 7 computer.

2.) You can download/install the Arduino IDE and then install the Teensyduino add-on. Instructions for doing this can be found here https://www.pjrc.com/teensy/td_download.html

This will give you a development environment which will allow you to program the firmware on the teensy and would be the option you want if you wish to customize the firmware on the teensy in some way.

@mariana

Hi Mariana,

In response to your questions.

Q. Is Rodeostat ready for use? Do I have to do something to make it operational?

It is ready to use. The teensy 3.2 on the Rodeostat comes pre-programmed with the potentiostat firmware. Software is available for the host PC in the form of a Python library and a web app.

Q. What accessories (if any) does one need to work with Rodeostat? (Assume I have reference electrode and some ugly, home made three-electrode cell).

That should be sufficient. The Rodeostat comes with cables for connecting to the electrodes. It also in includes a 50k dummy cell for testing the device.

Q. Is the software for Rodeostat paid or free?

The Rodeostat firmware and software are both open source and free. The source for the firmware and software are available in projects repository on bitbucket here https://bitbucket.org/iorodeo/potentiostat/src The teensy 3.2 comes pre-programmed with the device firmware.

Q Is this software available for Linux (Debian or Ubuntu/Xubuntu)?

Yes. There is a Python library and a web app. Both will work on linux

Python library: http://stuff.iorodeo.com/docs/potentiostat/
Web App: https://blog.iorodeo.com/rodeostat-software/

Q. What are Rodeostat current ranges?

The Rodeostat has four current ranges +/- 1uA, +/-10uA, +/-100uA and +/-1000uA

Q. What will be the price for delivery of Rodeostat from your store location to my country?

You can get the price + shipping costs from our online store during the checkout procedure https://iorodeo.com/collections/cheapstat-open-source-potentiostat/products/potentiostat-shield

Q. If I buy Rodeostat, do I have to pay VAT and customs?

Yes.

@xilophant

You should get the best current measurement by selecting the smallest current range which will encompass your data.

In this case the sample rate just determines the rate at which samples are collected and sent to the host PC i.e. the time step between samples. So the scan rate (V/s) is independent from the sample rate. The scan rate is set via the 'amplitude' and the 'period' parameters as follows scan rate = 4 x amplitude/period.

You might be able to reduce the noise by taking advantage of signal averaging. You could do this by sampling at a higher rate (while maintaining the same scan rate) and then lowpass filtering the data. For example you could collect data sampling at 100 - 200Hz. And then after collecting the data lowpass filter the data to reduce the noise - maybe using a zero-phase forward-backward such as filtfilt
https://docs.scipy.org/doc/scipy-0.18.1/reference/generated/scipy.signal.filtfilt.html
https://www.mathworks.com/help/signal/ref/filtfilt.html

@xilophant

I'm wondering if it is possible that the CE and RE are being swapped? This could happen if the card orientation is not correct. Could you upload an image or two of your setup including an image card inserted into the electrode adapter?

@jbrenner

This is a very interesting idea - thanks for sending me a link to the paper. I think this would be a great way to expand the capabilities of the Rodeostat. Perhaps the quickest and cheapest way to try this with the Rodeostat would be be make a little external expansion board which implements the make-before-break multiplexing. The expansion board could connect the Rodeostat's K1 header for the working, counter and reference electrode connections and to the DIO header "P14" for power, ground and digital control signals. I think this would be a pretty easy expansion board to make as there are only a few components required. This way we could test the idea without too much new hardware. I think I will definitely have a go at designing this expansion board. I will send you a schematic when I have something ready.

@AnandSingh

Unfortunately, I don't know of any easy way to do this. There is a little flash chip (IC4) which is there to provide external memory which isn't actually used at all. It uses an SPI interface - like and SD card. If you don't include this chip you might be able to hack in and SD card in its place. Connecting wires to the pads maybe - it would be a bit dicey though. You would also have to modify the firmware to read/write to the SD card.

@Rodeo_First

The basic configuration for the dummy cell is just uses a single resistor. The PCB was designed to accommodate additional configurations e.g. a capacitor can be added to create dummy cells with different (dynamic) behavior.

@AheliGhosh

The Cheapstat is a feedback device - running a control loop - so it won't really work correctly without something connected to it. In general it is trying to control the voltage between the working and reference electrodes via the counter electrode.

You might start by using a simple dummy cell consisting of a single resistor. Connect both the reference and counter electrodes to one end of the resistor and working electrode to the other end of the resistor. Then maybe try a simple test such as a linear sweep or cyclic voltammetry. Select the resistor so that the currents are with the measurement range e.g. 50K might be a good choice for the +/- 50uA range. Measure the voltage across the resistor. If you are using a single ended input on the DAQ card (or oscilloscope) make sure to connect the ground to the working electrode and the probe to the counter/reference electrode.

In general the Cheapstat is not capable of a full -1.5V to 1.5V swing. The actual range is more like -0.8 Vto 1.6V. Below -0.8V the output is nonlinear.

@Will-Dickson

If you want to install the software from source you can get some prebuilt wheel packages for windows here https://www.lfd.uci.edu/~gohlke/pythonlibs/#pyqt4

Note, the colorimeter software only supports python 2.7 at this time. So you will want to have python 2.7 installed and you will want a version of PyQt4 with cp=27 in the name.

@liliagwc

You can download the colorimeter python software as a single executable (packaged using pyinstaller) from here https://bitbucket.org/iorodeo/colorimeter/downloads/colorimeter-v05.exe

@AheliGhosh

I haven't used these programmers - so I can't really recommend one over the other. However, if they work as advertised either should work.

@xilophant I've put a brief note regarding square wave voltammetry in the documentation here http://stuff.iorodeo.com/docs/potentiostat/tests.html#squarewave-voltammetry

You can find a blog post on metal testing using the Rodeostat and a commercial bismuth screen printed electrode here
https://blog.iorodeo.com/square-wave-anodic-stripping-voltammetry-and-metal-testing/

@xilophant

Actually, we have added a square wave voltammetry test to the Rodeostat. Sorry, it hasn't made it into the main documentation yet. However, there is an example in the project repository https://bitbucket.org/iorodeo/potentiostat/src See the run_squarewave.py example in the "software/python/potentiostat/examples" sub-directory.

@Will-Dickson

You could use the following to use the resulting files to program another device

avrdude -c avrispmkII -p x32a4 -U flash:w:cheapstat_flash.hex -U eeprom:w:cheapstat_eeprom.hex

I tested it out with the AVR ISP MKII and seems to work fine with the Cheapstat that I have. Again you may need to change the "-c" option for your programmer.

@Will-Dickson

The following avrdude command should read the flash and eeprom to .hex files

avrdude -c avrispmkII -p x32a4 -U flash:r:cheapstat_flash.hex:i -U eeprom:r:cheapstat_eeprom.hex:i

Again you may need to modify the -c option for your programmer.

@AheliGhosh

Sorry here is the link to the repository https://bitbucket.org/iorodeo/cheapstat_firmware/src

@AheliGhosh

The mcu on the cheapstat is ATXMEGA32A4 which is on the supported list for the model : RKI-1043 programmer in your first link. I haven't used that programmer - so I can't really give you any advice on using it. However, it does look like it is compatible with avrdude. I do have repository online with modified version of the cheapstat firmware which is set up so that you can build/flash the firmware from the linux command line (using avrdude) as follows

make hex - builds software and creates .hex and .eep files.
make flash - flashs firmware to cheapstat using the avrispmkII programmer
make clean - clean source directory

Note, you may need to modify the "-c" option in the call to avrdude in the Makefile in order to specify your programmer.

@Rodeo_First

Yes. However for chronoamperometry you will probably want to change the plot so that it displays current vs time rather than current vs voltage as the voltages are just stepped in chronoamperometry. Even better you could have two real-time plots - one showing the voltage vs time and the other showing the current vs time. This way you could see when the voltages are stepped.

@AheliGhosh

No lock bits have been set. Note, not all AVR programmers can program xmega chips - they don’t use the AVR ISP method for interacting with the chip and burning new firmware like the atmegas. The xmegas use PDI–a different pin layout and protocol–and you need a compatible programmer. Do you have the make and model of your programmer - I can check whether or not it is capable of programming xmegas. The AVR ISP MKII programmers can program xmegas however some other programmers e.g. STK500, cannot.