AFE4404EVM: AFE4404

Hi Prabin,

By running EVM from battery powered laptop did smooth the wave a lot. The snapshot of the waveform I sent was taken through finger tip. I am not able to get the same waveform from wrist.

Hi Prabin,

Does LED1 Ambient represents the current of photodiode? To estimate the DC current do I have to take average output of LED1 or LED1 Ambient?

Hi Prabin,

Thanks for all your responses. I need to ask that where can I find the wrist wrap that is shown in the picture below. I know its not the right question to ask here but I am unable to find it. So If you can help me out, I would be very thankful to you. 

Hi Prabin,

I used other ordinary elastic band but they are efficient in holding the sensor as well as blocking the ambient light. That's why I wanted to buy the similar one.

Hi Qasim,

That band was made in house, so we don't have the part number.
You can search for ESD wrist strap and use only the band part of it.

Regards,
Prabin

Hi Prabin,

I think that I need your help again. I have acquired a good PPG signal using green led only. The estimated heart rate from the signal was same as ground truth heart rate.

Now I am trying to estimate SpO2 level using red and IR led. Green led is off. By tuning the parameters as

LED 2 current = 30mA

LED 3 current  = 20.8mA

TIA Cf x TIA Gain = 5pF x 10K

I get the following waveform. LED 3 is a typical ppg signal but I am not getting the write waveform on LED2

Please guide me how can I get a typical ppg signal on LED 2 as well.

Hi Qasim,

Is LED2 a Red LED?
Can you first try at finger tip? This will make sure register settings are correct.
You can also try to filter out the high frequency noise by doing moving average of few samples.

Regards,
PRabin

Hi Prabin,

I got the following response at finger tip with parameter set as follow

LED 2 current = 19.2mA

LED 3 current  = 14.4mA

TIA Cf x TIA Gain = 2.5pF x 100K

TIA Cf_SEP x TIA Gain_SEP =2. 5pF x 10K

OFFDAC LED2 = 6uA

OFFDAC LED3 = 6uA

After that I tried to get the waveform at wrist. I had to increase the LED2 Current to 25mA with other parameters same. I import the data on MATLAB and applied moving average filter. The results are shown below. Plots are from the MATLAB

Still the signal is not fine. You can observe that the AC level of the signal is very low and signal is noisy also. Please what should I do further to get a good PPG signal as I got at finger tip.

Hi Qasim,

Amount of the PPG signal being received totally depends on sensor location on the body ( due to obvious biological factors).
That being said, following are my observation after seeing the waveform.
1) DC level of the signal is ~0.73V. Are you setting the OFFSET DAC to negative -6uA or 6uA? Try to cancel as much DC as you can.
2) Increase the LED current, so that more light can penetrate inside the skin.
3) Can you look at the frequency spectrum of the signal. This is to find the noise source, hope you are not picking AC mains.
4) Can you use LED-Ambient instead of just LED phase.

Regards,
Prabin.

Hi Prabin,

Thanks for your response. Answer to your questions are as follows
1) OFFSET DAC is set to -6uA.
2) I will increase the LED current and check whether the results are better or not
3) I don't think so I am getting the AC mains because during reading I operate my Laptop through battery by disconnecting the charger.
4) Actually I am using your GUI for evaluation, so Is there any way that I can access LED 2 and LED 3 ambients. Becuase the log data contains only LED 1 ambient and other are LED phase only.

Hi Qasim,

Out of 4 phases available, the phase where LED is off has the ambient information.
You can save all 4 phase data using the data and subtract the Ambient in the excel sheet yourself.

Regards,
Prabin

Hi Prabin,

As you can see the channels that are available. Is LED 1 Ambient represents the ambient data for all LEDs? Like I have to do this LED2 - LED1 Ambient and LED3 - LED1 ambient. Is that right?

Furthermore, why the TIA_SEP_GAIN affects the DC level of LED3, as mentioned in the GUI TIA_SEP_GAIN is for LED2.

Hi Prabin,

I am able to estiamte the heart rate and spo2 through finger and wrist as well but there is one thing i need to ask. During testing I found that sometimes LED2 and LED3 saturates at 0.6. Why is that so? If it were to saturate then it should saturate at 1.2

Hi Qasim,

Can you please read the output registers ( i.e 42d to 47d ) at those stuck state?
What exactly causes this? Do you change some registers that puts the AFE in this state?
Also do you see such saturation when running the EVM default register settings?

Regards,
Prabin

Hi Qasim,

I'm closing this thread since there hasn't been any followup in a while. If you have further questions feel free to post them and the thread will automatically reopen.