• State
  • Locked Locked
  • Replies 4 replies
  • Subscribers 30 subscribers
  • Views 1494 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

AFE4405EVM: The EVM board doesn't show a valid waveform when tested using PC GUI app.

Konan Kim
Prodigy 210 points
Part Number: AFE4405EVM
Other Parts Discussed in Thread: AFE4405

Hi,

I've tried to capture the signal from wrist using the afe4405 EVM and 2 LED/PD boards(TI board with 2 green LEDs and 6 LEDs(green/red/IR) from Osram.

After trying several times during a few days, I failed to get a valid waveform for any of the LEDs. The result was a flat of 1.2V(Input Voltage) for LED1, LED2 and LED3.

Sometimes only green LED looked working. I guess the following causes:

1) the parameter settings are not correct.

2) I've tried on wrist and at finger. Maybe for finger the signal is too strong, for wrist the signal is too weak.

3) Or even though I pressed it with a reasonable pressure, the light of the LEDs transfered to the PD directly.

Could anybody let me know what's wrong with my settings or methods?

0) app: AFE4405 EVM version 1.0.0 build date 4 20, 2016

1) TX stage: The TX parameters are as follows: LED1 current 23.46mA, LED2 current 4.692mA, LED3 current 4.692mA.   8bit LED current control = 100mA

2) Timing control:  Duty cycle is 1%, pulse rate 100Hz (I've tried duty cycle to 10% but didn't work.)

3) RX stages:  ENSEPGAIN: checked(TIA_CF 5pF, TIA_GAIN 50k

4) LED probe 1: the TI probe board shipped with the EVM (2 green LED s + 1 PD)

5) LED probe 2: OSRAM LED/PD: Firefly and SFH 22xx for TI AFE4405 (6 G,R, IR LEDs + 1 PD)

Thanks,

Konan Kim

  • 0
    TI__Genius 12575 points
    Hi Konan,

    Are you getting PPG signal from the finger? Also did you try on some other people?
    Getting constant 1.2V means the AFE is saturated , you can try to reduce the LED currents or reduce the TIA gain (i.e. RF) or both.
    I would suggest to get everything working on finger then move on to wrist.

    Regards,
    Prabin
  • 0 in reply to Prabin Yadav
    Prodigy 210 points

    Hi Prabin,

    Thanks for your reply.

    I've tried both on writst and on finger. And tried only on two people including myself.

    So, to resolve the issue, 1) to reduce the LED currents 2) to reduce the TIA gain or both.

    I will try it but could you send me an example to do that ?

    The product will be on wrist, could you let me know a recommended electrical spec of the LEDs ?

    I am considering bigger LEDs than those used on OSRAM probe board which consists of:

    1) CH DELSS1.22 Hyper Red 660nm Firefly E1608

    2) CT DELSS1.21 True Green Firefly E1608

    3) SFH4043 IR 940nm Emitter

    4) SFH 2200 Photodiode

    Regards,

    Konan

  • 0 in reply to Konan Kim
    Prodigy 210 points

    Hi Prabin,

    I've tried capturing test by changing TX parameters according to your advice.

    The result was good. There was a progress. When it was tested on a finger, the waveform was very good.

    When it was tried on wrist, the waveform is as attached. It looks the envelope is changing rapidly and the shape of one period is not regular.

    Is it a right capture ? I've adjusted the current settings and duty cycle.(8 ~ 15 and 5% repectively)

    Thanks,

    Konan

  • 0 in reply to Konan Kim
    TI__Genius 12575 points
    Hi Konan,

    I think you might be picking 50/60 Hz noise from the AC mains.
    Can you try using battery operated Laptop also you can enable notch filter in the GUI for reject 50/60 Hz.
    You can also do post processing like filtering using LPF, DC removal etc.

    Regards,
    Prabin