Hi Rodrigo,
There is definitely something funny going on in that first result. . I'm not sure what is causing it. I doubt that it was the firmware update. I would start with the usual things - make sure all the connections are OK and that the electrodes are connected correctly. Also, If you want to the send rodeostat back to I could have a look at. Send me an email (will@iorodeo.com) if this is the case.
On the cheapstat there aren't reallly any spare digital IOs which are conveniently available on a header or any thing like that. There are spare digital IOs on the ATXMega, e.g. PB0, PB1, PC0, PC1, etc., but the trick would be accessing them. You would have to solder a to the microcontroller pin/pad. Another option might be to the IO lines used for the SPI signals to IC4. This is a flash memory which isn't used by the current firmware. You could remove this chip and you would have four IO lines available at IC4 - CS (PD4), SI (PD5), SO (PD6) and SCK (PD7). Again you would have to solder to the pads - a pain, but at IC4 they are a bit bigger at least.
Another option might be the Rodeostat which has 2 expansions headers P13 and P14. Between them you have 16 digital IO lines you could use plus SPI and i2c bues. Both P13 and P14 use 5x2 shrouded headers which you can connect to with a standard IDC connector.
Unfortunately, it isn't possible to do a true linear ramp with the Rodeostat. It uses a Digital to Analog Converter (DAC) to set the analog output value and so the output will always be in discrete steps where the minimum possible step value set by the resolution of the DAC.
Yes, the current is measured as the test is run. The figure is showing the applied potential in order to illustrate the various test parameters e.g. quietTime, duration, etc.
The worked example in the link below shows a plot of the current vs time when using the constant voltage test and a dummy cell.
http://stuff.iorodeo.com/docs/potentiostat/examples.html#constant-voltage-voltammetry
@cylsky said in Amperometric i-t Curve:
Amperometric i-t Curve
Yes, you could use the "constant voltage" test for this.
http://stuff.iorodeo.com/docs/potentiostat/tests.html#constant-voltage
It looks like you are using Python 3.5. This issue you are seeing is due to the differences between the Python 2 and Python 3. The colorimeter software is not yet compatible with Python 3. So in order to run it you will need to install Python 2.7 and then reinstall the colorimeter software and its dependencies.
The standard dummy cell which comes with the Rodeostat consists of a single 50K Ohm resistor. When the dummy cell is attached with the cable to the Rodeostat one end of this resistor will be connected to both the counter and reference electrodes and the other end will be connected to the working electrode. The results you should get when using this dummy cell should follow Ohm's law i.e. the measured current should be I = V/R. In your images it looks like you are sweeping the voltages from about -0.6V to 1.5V - using the cyclic test?. So your measured currents should sweep from -12uA to 30uA and back again according to Ohms law. Looking at your results this seems to be what you are getting - so I would say this first test checks out. Note, when using the +/-1uA and +/-10uA current ranges some of the currents you are trying to measure during the sweep are outside of the measurement range. Thus you are seeing saturation in the measured currents i.e. the measure values can't go above or below the limits of the ranges.
From your results with the dummy cell it looks like the Rodeostat is working correctly.
I'm not sure what is happening with the drop sense electrodes and the Malonic/Lactic Acid. We haven't worked with the AuNP electrodes or with either of these Acids.
A couple of things to check.
Make sure you are getting a good electrical connection between the screen printed electrode and the adapter. Sometimes you might need to put a thin spacer on the back of the screen electrode in order press it against the electrical connections.
Make sure the screen printed electrode is connected correctly - so that the counter, reference and working electrodes are connected to the proper connections.
Hi Annie,
A couple of quick questions:
Do you get reasonable values when running a test using the dummy cell?
Have you tried to replicate the results using ascorbate?
The light sensor used by the colorimeter is a light to frequency converter which returns the squarewave with frequency directly proportional to the light intensity. The number of samples setting (for example 500) sets the number of pulses which will used in order to measure the frequency. The period of all the pulses sampled is then averaged in order to determine the frequency (light intensity).
The software and firmware for the colorimeter can be found in our online repository here https://bitbucket.org/iorodeo/colorimeter/src The firmware for the Arduino is in the "firmware" sub-directory of the project. This will be what you want to modify to add you LCD display. Beyond that it is really up to you add the display you want and modify the firmware correctly.
It looks like the nokia 5110 is 3.3V so you may require a level shifter.
You might look at using the Adafruit PCD8544 Nokia 5110 LCD-library https://github.com/adafruit/Adafruit-PCD8544-Nokia-5110-LCD-library
There is a tutorial here https://learn.adafruit.com/nokia-5110-3310-monochrome-lcd/testing
As a test try calibrating with no cuvette the device and with the slider open so that light sensor is exposed to the room light. Does the calibration/blanking procedure run? Do the you see the LEDs flash?
That is good to know. I'm not sure what is happening, but maybe there is some compatibility issue with the surface pro3? At the moment I don't have access to a surface pro3 which I can use for testing, however I will try to locate one.
Are all the ports on the surface pro USB 3 or are some USB 2? The Rodeostat/teensy 3.2 is USB 2, but should work fine on in USB 3 ports as they should be backwards compatible ... but you never know.
Another thing you could try is maybe putting a USB hub (maybe even a powered hub) between the surface pro and the Rodeostat.
Best,
Will
It looks like the device is correct - i.e, the vendor and product IDs for teensy are right (vid=16C0 and pid=0483) However, for some reason it looks like the software is unable to open USB/serial connection to the teensy. The "success": false part of the message is saying that the software is unable to open the device. I'm not sure why this is. Is it possible that some other software already has a connection open to the devices e.g. the Arduino IDE or a program using the Rodeostat's python library?
Hi, we are currently out of the office but we are back on Monday. We will take a look at your questions and get back to you asap next week.
Thanks for your patience !
For the LED transilluminator adjusting either voltage or current should work for reducing the intensity. However, I think adjusting the current would be the most effective approach and would give you a bit better control of the intensity. Be careful not to overcurrent the LEDs and they can be damaged.
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.".
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.
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.
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
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?