Hi Dickson, I am also interested in the Increasing current ranges. Please tell me how to swap out R8 ? I found the R8 resistor has been fixed in the board. Would I add another external trans impedance amplifier feed back path to increase the current range ?
The get_volt() method returns the current output voltage setting i.e., the value set by the user (perhaps with the set_volt method) for the voltage between the working and reference electrode. Whereas the get_ref_volt() method returns a measurement of the voltage between the working and reference electrode. There is no method to get the voltage between the working electrode and counter electrode.
I'm not sure the exact cause of the "hairyness" the CV's. I do know that it only seems to occur when using certain electrochemical setups. We don't see it with purely resistive loads such as dummy cells or even simple dummy cells with combined resistive and capacitive loads. You can do CV sweeps etc. and no hairiness . So it isn't really a matter of whether or not the potential is fixed - maybe it is some characteristic of the load in the cases where we see the hairiness. It would definitely be interesting to explore the issue. I've been considering designing some more general dummy cell PCBs for testing purposes and I would love some input on designs. It would be great to have a very general dummy cell design which could mimic all sorts of loading situations. In particular, could we find a dummy cell with the correct load characteristics to reproduce the issue? or is this really something to do with the electrochemical cell?
The capacitor in the feedback loop of capacitor of the control amplifier is a compensation capacitor used to improve stability. It is basically providing a high-frequency bypass. The load which the potentiostat is going to be hooked up to is essentially unknown (lots of different variations) so we wanted the control loop to stable under a broad range of conditions. Adding this compensation capacitor was found to help extend in stability over a broader range of conditions without causing a detrimental effect. I don't believe this capacitor is the cause of the hairiness you are seeing.
The compensation capacitors on the transimpedance amplifiers are also for stability. The values have been selected fairly conservatively. So we are probably getting a bit more lowpass filtering then absolutely necessary. For the most part this is more of an issue for the lower current ranges where the resistor in the feedback loop is larger. We've made some nA versions of the Rodeostat where we had to go to larger capacitor values in order to ensure stability. For example, for a +/- 60nA range with a 10MOhm resistor we needed a 100nF compensation capacitor for stability. Again I don't think these capacitors are the issue.
I would recommend running the cyclic voltammetry experiment from 0.1 V to 1.0 V, at 50 mV/s for a few cycles (3-4 should be plenty). That would be a direct comparison to the experiment I described.
Let me know how that experiment works and we can go from there.
Thank you so much! We tried rebooting it before with the potentiostat.ino file; however, we had set CPU speed to 96 MHz and Optimize to "FASTER". It is now working with the settings you specified. Thank you again.
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 (firstname.lastname@example.org) if this is the case.
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.