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SPO2 AND HR FROM AFE4400

Other Parts Discussed in Thread: AFE4400

Hi,

I am using AFE4400 in one of my project. My intention is to calculate SPO2 and HR. I am wondering how to use those ADC data and formulate them to extract the intended parameters(spo2 and HR)? Regards.

Nazrul

  • Nazrul,


    1. Question 18 in our FAQ explains how to get HR. e2e.ti.com/.../369445

    2. The AC and DC component can be found from the PPG signal on the GUI, which you use to calculate SPO2. Also, I have included this link to another e2e post that discusses how to calculate SPO2.

    e2e.ti.com/.../1099135

  • hi Amy,

    Thanks for the reply. I have still some dilemma regarding few terms and their meaning. These are:

    1. In FAQ(#18), a method is mentioned to calculate HR. In that it is said to detect the presence of beats by comparing the outputs against a set threshold - what is that threshold and it is based on what?

    2. The ADC has six output channels: RED, RED Ambient, IR, IR Ambient, RED - RED Ambient and IR - IR Ambient. What each channel data means? Specifically, say, RED Ambient or RED - RED Ambient. Also, How each channel contributes to ac/dc component calculation?


    I am bit confused with those terminology and their physical meaning. If you can put some light on those will greatly help me to understand the working principle of the device. Regards.

    Nazrul
  • Nazrul,

    1. This threshold will depend on the subject under test. Most people use a dynamic threshold depending on the subject it is calibrated for.

    2. Each of the channels are outputs from the ADC. For example RED are the ADC codes received from sampling the RED LED. RED-REDAmbient is the ADC codes from the RED LED minus the RED Ambient light. The AC and DC components is a ratio used to calculate SPO2. You can take this from the PPG signal of your RED and IR data as described in the link given in my previous post.
  • Hi,

    Thanks for your reply. With your reply and further reading the data sheet and the reference, I have some working understanding about the device. To further clarify, I have the following questions:


    1. To estimate SPO2, shall I consider the DC and AC component of RED and IR data pair or the RED - RED Ambient and IR - IR Ambient pair? Also, what is the usage of 2nd pair(say, RED - RED Ambient....)?

    2. Do I need to filter the raw data(output of ADC) further before estimating the SPO2?

    3. Once, I calculate the ratio, R, do I need to use look up tables( as seen in other implementations) to calculate the SPO2 %?


    Hope to hear from you soon. Regards.


    Nazrul
  • 1. We have used RED and IR, the purpose of the other data is to give the LED- LED ambient data. Sometime there is a large amount of ambient light and this math can be useful to some users.
    2. It depends on your application and if there is a need for it.
    3. You may use that implementation. We have used the equation %SPO2=110-25R

    Here is another app note that might be helpful. www.ti.com/.../slaa655.pdf