• State
  • Locked Locked
  • Replies 2 replies
  • Subscribers 46 subscribers
  • Views 1160 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

AFE4300EVM: FWR Calibration Help

Matt Attok
Prodigy 40 points
Other Parts Discussed in Thread: AFE4300

End-application is to use AFE4300 to measure bioimpedance values using two pairs of tetra-polar electrodes.

We are attempting to do the FWR calibration, but we are unsure of how to get the ADC codes that corresponds with reference resistors.  Is the ADC code the peak value of the periodic waveform in the ADC capture window?  Are the reference resistors external resistors that are connected to the AFE through V_Sense0/V_Sense1 and OUT0/OUT1 and should both reference resistors be used in series?

  • 0
    TI__Genius 12575 points
    Hi Matt,

    There are four reference resistors on the AFE4300EVM board. These are R56, R57, R58 and R59 ( see pg. no 42 of AFE4300 EVM user guide).
    To get the ADC output for the reference resistor , you have to select the corresponding bits in "ISW_MUX" and "VSENSE_MUX" registers.
    For e.g. If you want the output for R58:
    1) Set RP0 (D8) and RN0 (D0) if ISW_MUX register
    2) Set VSENSEP_R0 (D8) and VSENSEM_R0 (D0) of VSENSE_MUX register
    3) Now if you read the ADC data ( Average of few samples) you will get output corresponding to R58.

    If you want to measure other reference register , just change the bits in ISW_MUX and VSENSE_MUX and capture the ADC data.
    You can even set the bits of "ISW_MUX" and "VSENSE_MUX" registers using the GUI as shown in Figure 25 of AFE4300EVM's user guide.
    IOUT and VSENSE terminals are used for electrodes, whereas RN0, RN1, RP0, RP1, VSENSEP_R0, VSENSEP_R1, VSENSEM_R0 and VSENSEM_R1 are used for calibration using reference resistors.

    Regards,
    Prabin
  • 0 in reply to Prabin Yadav
    Prodigy 40 points

    Thanks Prabin.  We got the calibration to work.

    We are trying to read correct impedance values through a localized area of the body using the FWR measure, however the impedance readings maxes out at 2388.59 ohms.  This seems very small for a bioimpedance value.  What can we do to get accurate readings above 2388.59 ohms?  What electrodes do you use to attach to the skin?