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AFE4403: Can the AFE4403 drive both SPH7050's red and green LED at the same time?

David__
Genius 3585 points
Part Number: AFE4403
Other Parts Discussed in Thread: CC3220SF-LAUNCHXL, ,

Hi, while reading the datasheet, looks like the green LED is used for measuring the heart rate. Whereas the red LED is used for measuring the SpO2 application.

I use CC3220SF-LAUNCHXL and a custom AFE4403 module that uses the SPH7050. These are my questions.

1. Is it not possible to turn on both green and red LEDs from SPH7050?

In other words, I cannot measure both the heart rate and the SpO2 at the same time?

2. Is the green LED is mandatory for HRM (Heart Rate Monitoring) application?

In the datasheet, it doesn't say that I must use the green LED for HRM.

I'm curious whether I can calculate both the heart rate and the SpO2 at the same time with a single LED (green or red, if I can only use one LED).

Although, TI's SLAA655 says that "The periodicity of the PPG signal corresponds to the heart rate.", I wanted to check this part since I think the green LED can give better HRM results if this guess is correct.

3. I read about the AFE4403EVM source code.

The AFE4403EVM_FW_SRCv2.3 doesn't calculate the heart rate or SpO2; it sends the LED values to the computer via USB.

Is the MPS430F5529 not fast enough to calculate the heart rate or the SpO2?

Although showing these with GUI is great, I was curious if there were any attempts to calculate these values with an MSP430 series or CC32xx MCU series.

4. Lastly, TI's SLAA655 doesn't go into the details of the SpO2 calculation.

Are there resources available for heart rate/SpO2 calculation from TI or other sources?

Thanks for your time.

  • 0
    TI__Genius 12575 points
    Hi David,

    As timing control signal of LED2 is shared between Green and Red LED, only one can be switched ON at a time.
    Also there is only one convert phase for Green and Red LED so it doesn't make sense to fire them simultaneously.

    Choice of Green LED for the HRM is based on some studies that suggest that Green wavelength is not effected by the skin factors. As for AFE4403 is considered, we don't have any restriction, it completely depends on the application as well as the post processing involved.

    Yes, you are correct then EVM sends the raw data to the PC where it gets displayed. The MSP430 can be programmed to calculate the heart rate or SpO2 but we leave this to the customer as different customer might have different approach to calculate this.

    Following is the link for the reference design that talks about SpO2 calculations.
    www.ti.com/.../tidu475.pdf

    Regards,
    Prabin
  • 0 in reply to Prabin Yadav
    Genius 3585 points

    Prabin Yadav said:
    Green wavelength is not effected by the skin factors.

    Thanks, Prabin. I found from "Comparison of green, blue and infrared light in wrist and forehead photoplethysmography, V. Vizbara et al" that

    It is known that light of short wavelengths (blue and green) penetrates less than light of longer wavelengths (infrared).
    Therefore, PPG using shorter wavelength optical signals is less influenced by the deeper tissue movements.

    Then, 

    Prabin Yadav said:
    Following is the link for the reference design that talks about SpO2 calculations.
    www.ti.com/.../tidu475.pdf

    are there reference materials for heart rate calculation using SPH7050's green LED with the AFE44xx series?

  • 0 in reply to David__
    TI__Genius 12575 points
    Hi David,

    Choice of the wavelength purely depends on the application , body location , skin factors, etc. Basically it is governed by biological parameters and I am no expert in this field.

    One simple way of calculating heart rate is to count the number of peaks in the given time frame and convert that to beats per minute. We don't have any reference materials that talks about the algorithm to find heart rate as this is customer dependent.

    Regards,
    Prabin
  • 0 in reply to Prabin Yadav
    Genius 3585 points

    Hello, Prabin.

    Prabin Yadav said:
    I am no expert in this field.

    I see. I tried to ask this in the TI's Medical Forum.

    However, when I type AFE4403 in the "Part number" blank, the question is automatically posted at TI's Optical Forum and I can only choose the Optical Forum.

    Then can you help me to post a question about the algorithm when using the Green LED? I hope the Medical Forum team can help me.

    Lastly, suppose I sample 256 LED values.

    Prabin Yadav said:
    One simple way of calculating heart rate is to count the number of peaks in the given time frame and convert that to beats per minute.

    After configuring AFE4403's TX3_MODE (in the CONTROL3 register),

    you mean that I can apply frequency calculations to the "LED2-ALED2VAL" samples such as FFT to obtain the heart rate, right?

  • 0 in reply to David__
    TI__Genius 12575 points
    Hi David,

    Let me check if I can move this post to Medical forum.
    Yes, you can looks for the peak in the FFT spectrum to find the heart rate frequency .

    Regards,
    Prabin
  • 0 in reply to Prabin Yadav
    Genius 3585 points
    Thanks, Prabin. I think this thread can be closed due to your hard work.

    Can you leave me an answer here whether it is possible to post questions to the Medical forum to ask about the HRM algorithm with the green LED?