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startup problems with AFE4404EVM

theo van lieshout
Prodigy 30 points
Other Parts Discussed in Thread: AFE4404EVM, AFE4404

Hello all,

As a starter with the AFE4404EVM, I expected a heartbeat signal like in the documentation when the sensor is placed on my wrist. Instead I got a lot of noise with some small sign of a heartbeat. The board seems to work but my impression is that the configuration is totally wrong.  I am using the SFA7050.

Some tests I've done: placing the sensor above 3 different colour papers resulting in DC outputs of the sensor. led 1 sensor gives max at the green paper, led 2 max at the red paper and led 3 is high at white. Adjusting the current through  the leds has the expected effect. All logical for me so far.

Using autoconfiguration is switching off led 2 and led 3 (set to 0 mA).

I know, I can adjust all registers but I expect that the configuration as delivered is ok. So I assume something is wrong.

I am using Windows10 pro

The end application is measuring heartbeat and if possible saturation at birds (preferably small birds while flying). The first step is measuring my own heartbeat and so on. The next step is a sensor interface.

Any suggestions and help is very much appreciated.

Kind regards,

Theo van Lieshout

  • 0
    TI__Mastermind 49956 points

    Hello Theo,

    We have received your inquiry regarding the AFE4404 device and hope to have some answers back to you shortly.

  • 0
    TI__Genius 12575 points

    Hi Theo,

    Could you please share screenshot of data as well as register setting(configuration file). This will help us understand the situation.
    Meanwhile there are couple of things to try to get good heartbeat signal:
    1) Try to avoid any 50/60 Hz pick up: Run EVM form battery source (i.e. laptop unplugged from AC mains).
    2) Make sure that while placing sensor on wrist there is no electrical path between body and EVM. You can cover the sensor board with black tape as shown in Figure 6 in EVM's user guide.
    3) You should look at "LED1 - LED1 Ambient" data. This is to avoid any noise due to ambient light.
    4) Can you please try this measurements on few more people.

    Regards,
    Prabin

  • 0 in reply to Prabin Yadav
    Prodigy 30 points

    Hi Prabin,

     

    The things you mentioned I have noticed already. Indeed it is a matter of interference with the mains frequency.

    It is clear that using an unplugged laptop the problem disappeared for the most (first I was using a desktop model)

     

    1                    there is indeed an interference with the 50Hz. When I set the sample rate to 99.5Hz, I see a very low product frequency. Changing this frequency, the interference changes accordingly.

    I expected that using the 50Hz notch filter would solve this. The filter is too small (bandwidth)  I think.

    2                    I have wrapped the sensor PCB into black isolation tape to avoid leak currents or electrical contact with the body.

    3                    Using the laptop free from mains solved the problem.

     

    Using the difference led1 – led1 ambient gives a much better picture (this is not done in the user guide page 10)

     

    Anyway, my problem is solved for now.

     

     

    As I mentioned already, I like to measure heartbeat rate at birds.

    Can you tell me the upper limit for the heartbeat rate measured by the AFE4404?

    In case of birds this can be up to 600 bpm or even more.

     

    Thank you very much for your help and suggestions.

     

     

     

    Kind regards

     

    Theo van Lieshout

  • 0 in reply to theo van lieshout
    TI__Genius 12575 points

    Theo,

    Upper limit for heartrate measurement depends on many factors such as:
    1) Input signal as well as sampling frequency.
    2) Input signal quality i.e. SNR requirements of your algorithm (post processing of data).

    With all this being said, heart rate of 600bpm( 10 Hz input signal ) can be measured by AFE4404 as long as signal quality is accepted.

    Regards,
    Prabin

  • 0 in reply to Prabin Yadav
    Prodigy 30 points

    Hi Prabin,

    Many thanks, We will give it a try.

    kind regards,

    Theo