GSR / EDA measurement using EVAL-ADPD4000

Hello, I am trying to measure bioimpedance using EVAL-ADPD4000 but I keep failing.

If you look at the datasheet of EVAL-ADPD4000, there are IN5 and IN6 as impedance measurements.

I would like to use this to measure GSR or EDA, but there are no examples anywhere.

Please give me the example code or register value related to the above. I would very much like to solve this problem. Please help!

  • Hi GlenBu, 

    I follow your previous configuration file, but when I try to read the fifo buffer, I read only zeros or big values without sense. I use the oscilloscope to verify VC2, but I do not see any wave. Also if I change the register 0x0103 in order to have Vc2 no pulsing, it is always at ground voltage. Could you tell me anything? 

    BR

  • 0
    •  Analog Employees 
    on Feb 10, 2021 2:28 PM in reply to Gloi

    Hi Gloi,

    Which configuration did you use? If you used the one posted on Jan. 11, you need to remove the R11 from the board for IN5 as the receiving input. Please refer the directions posted on Jan. 14 for IN6 as the receiving if you don't want to remove R11.

    When you pulse VC2, you can see the bursts of 16 pulses on the oscilloscope. If you set VC2 to a DC value, the DC voltage will be blocked by the capacitor C9. 

    I cannot comment your FIFO readout as I don't know how you ran your test. If you are using the EVAL-ADPD4000Z-PPG with the Applications Wavetool software, you can log and check your data.

    Regards,

    Glen B. 

  • Thanks GlenBu for the answer,

    now it is ok. Another question, for the impedance measurements can i refer to the formula that you provided?(Changing the value in accord to the registers values). Where can I find that?  Because on the datasheet I found only the formula about TIA_ADC_Mode.

  • 0
    •  Analog Employees 
    on Feb 11, 2021 3:17 PM in reply to Gloi

    Hi Gloi,

    It is good to know you solved the problem. What was the cause of the issue?

    For calculating the current, please refer to the formula posted on Jan. 18 for TIA-BPF-INT-ADC mode. If you don't have the BPF in your signal path, you can remove the 0.81 factor, which is the BPF gain. You can then calculate your impedance using the excitation voltage (typically 250mV for ADPD4000).

    Regards,

    Glen B.

  • Hi GlenBu, 

    It was an hardware problem, but now  it is ok. Anyway, I still have the problem about the fifo buffer. I don't know it does not fill up. Do you know any idea about that? I used the example code I used the example code on the repository  on github. I created a new question about it, could you help me?