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PSoC 5, 3 & 1 MCU

KaGa_3938861
New Contributor II

Hi,

I am working on the PSoC 5LP CY8C5888TPI-097 MCU galvanostat project, The project consists of a 3 Electrode system, to which

  • The constant current source is applied between the Working Electrode and the Counter Electrode.
  • The resultant voltage is measured between the Woking electrode and the Reference Electrode as shown in the figure.

pastedImage_1.png

Fig 1. Schematic diagram showing the three-electrode connection scheme between the electrochemical cell.

pastedImage_3.png

Fig 2 PSOC IDAC

For providing the constant current I am using IDAC and I am not finding a suitable example project on how the current source can be used between the two terminal devices with the PSoC examples. It will be really helpful if someone can guide me with how to deal with a current source in PSoC.

I came up with the following circuit connections, Is it the right way or any changes needed?

pastedImage_0.png
Figure. 3. one approach for the galvanostat

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Len_CONSULTRON
Honored Contributor

KaGa,

Can you show how the "System under test" is connected in your schematic?

Len

Len
"Engineering is an Art. The Art of Compromise."
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KaGa_3938861
New Contributor II

Len,

System under test is the 3 Electrode sensor dipped in the electrolyte, The terminals of the electrodes are connected to PSOC board pins,

Karthik

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odissey1
Honored Contributor II

Karthik,

I googled the "galvanostat" and it is quite developed area. I don't think I will be able to contribute much here. I would recommend to follow some of the original publications for techniques used in that area. I know that H2O conductivity is used in microcapillary electrophoresis using a couple of tiny interdigitated electrodes (similar to my previous project), but that's pretty much it.

Please note that PSoC opamps are not rail-to-rail, and not able to handle 0V at it terminals. Neither they can produce 0V output.

/odissey1

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KaGa_3938861
New Contributor II

Odessey1,

Thank you for your input,

Karthik

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Len_CONSULTRON
Honored Contributor

Karthik,

I read some of the theory of the galvanostat.  The details for your specific application are vague.

What's the minimum and maximum stimulus current you are trying to control?

What is the minimum and maximum resultant feedback voltage to are expecting to control your stimulus?

Len

Len
"Engineering is an Art. The Art of Compromise."
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KaGa_3938861
New Contributor II

Hi Len,

For Now, I am going with the specifications available in the PSoC 5LP CY8C5888TPI-097 MCU. I know the current source (IDAC8) can generate from 0 to 2mA max current, I am trying to provide this as input and read the result from the electrode system correspond to this,

Thanks,

Karthik

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Len_CONSULTRON
Honored Contributor

Karthik,

What are the needs of your electrolyte system?  Will up to 2mA suffice?

Len

Len
"Engineering is an Art. The Art of Compromise."
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KaGa_3938861
New Contributor II

Hi Len,

Currently, the electrochemical system (Potentiostat) I have(created) with the MCU works with the specifications current range 0 to 100uA and the Voltage +1.5 volt to -1.5 volt, I  want the galvanostat to be tested with the same specifications,

since IDAC generates up to 2mA, I don't mind extending it up to the 2mA current range.

Thanks,

Karthik

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Len_CONSULTRON
Honored Contributor

Evgeniy,

Looks like you found someone who's already implemented it on a PsoC5.  Bravo!.

Len

Len
"Engineering is an Art. The Art of Compromise."
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KaGa_3938861
New Contributor II

Hi Evgeniy,

Thank you for your input, The links you provided are potentiostat, They will provide voltage as an input to WE and RE and will measure resultant current between the WE and CE,

I am working on the Galvanostat which will provide current between the WE and CE and will measure voltage between The RE and WE, For this implementation I need to use current source to provide input, I was asking how I can do that,

Thanks,

Karthik

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odissey1
Honored Contributor II

Karthik,

I think this AN will also be useful:

an58827-psoc-3-and-psoc-5lp-internal-analog-routing-considerations

/odissey1

Fig 5_IDAC-DelSig-ADC.png

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Len_CONSULTRON
Honored Contributor

Karthik,

I'm a novice at Potentiostats and Galvanostats but from the info available to change from a Potentiostat to a Galvanostat you just need to place a low-value reference resistance in the path of the current stimulus with a differential voltage measurement across the resistance.

You CAN NOT trust the set value of the IDAC to be your feedback.  The IDAC should be able to source the current desired IF the load sinks it.  There is no guarantee that the load will sink the setpoint current.  Besides, even though the PSoC5 is an awesome part and the load uses all the current proved, there is an tolerance for the IDAC to achieve the set current.

As I said, I'm a novice at P or G applications.  Would a CCR (Constant Current Regulator) suffice for your application?  The CCR will adjust the current stimulus to always try to achieve the current setpoint.  The only reason it might not is if the internal source resistance of the load goes too high for the voltage bias proved.  In this case, the stim current will always be lower than the setpoint.

Len

Len
"Engineering is an Art. The Art of Compromise."
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EvPa_264126
Valued Contributor II

Sorry, I think I gave a link to your development)))

I am familiar with the design of the galvanostat / potentiostat is very superficial, so only assumptions:

IDAC will provide stable currentБ Or use voltage to current converter.

But it seems that the positive potential is being applied to CE, so I give two options.

An OpAmp high impedance input is required for the RE electrode.

voltage to current converter

5LP as constant current sink controller

p1.jpg
Evgeniy

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