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Original question:

AFE4404: problem of the direction of AFE4404 PPG waveform

AFE4490: Inversion of PPG waveform

Harikrishnan k
Intellectual 455 points

Part Number: AFE4490
Other Parts Discussed in Thread: MSP430F2416

Hi all,

I have also faced the flip/inversion issue in PPG waveforms obtained from the AFE4490,and now I understand the reason for flip from the below thread

 e2e.ti.com/.../600556

but my question is 1. how can the waveform get inverted by subtracting a threshold value from raw data?

2. How to decide the threshold value to subtract?

3.we require a flip/inversion in x axis but the subtraction in threshold only reduce the amplitude isn't it ?

please help me to resolve this.

  • 0
    TI__Genius 12575 points

    Hi Hari,

    You can subtract the average value (i.e. DC) from the raw data to invert the PPG waveform. 

    You can think PPG as sine wave and subtracting each  point of the sine wave from the average value will result in inverted sine wave.

    If you are interested in hear rate's frequency then even inverted PPG waveform can be used without the need for inversion.

    Regards,

    Prabin.  

  • 0 in reply to Prabin Yadav
    Intellectual 455 points

    Hi Prabin,

    Thanks now I got the idea I am trying to extract heart rate and SPO2 readings.

    Now I am plotting the wave and extracting features in Matlab,I subtract the row datas with the maximum of values in matlab code itself and I got the PPG waveforms.

    PPGData = max(IRadc) - IRadc  this is how  I subtract the raw data from  some fixed threshold level.

    Is it possible to do the inversion in firmware itself (I am using MSP430f2416 with AFE4490).