Waveforms from AFE4490 SPO2EVM

Hello Simi,

It looks like the 50Hz power line noise is getting coupled to the PPG signal.

Are you using the AFE4490SPO2EVM or your own evaluation board?

If you are using your own evaluation board, it would be helpful if you can provide the schematics and layout for review.

Also it seems like the register settings may not be the same between the two captures since the number of peaks for 700 samples are different between the two captures. Can you provide the register settings?

What is the Pulse Repetition Frequency (PRF) that you are using?

Regards

Praveen.

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Hi Praveen,

I am using AFE4490SPO2EVM. I have 2 boards of AFE4490SPO2EVM. One have the original firmware and the other have my own code. Initially I used the TI GUI and the board with the original firmware and set up all the settings I wanted. Then I used that register settings shown in the GUI in my own code. So both register settings are same. But I did not get a clean signal that time. 

On Wednesday I downloaded the source code provided by you in the forum. First I ran the source code and used it the same way with the TI GUI. So it works. Then I edited the source code to continuously send the red value only  as I wanted with my original software. This time the output is good. So I guess there is something wrong with my code. I tried using the same register settings provided with the source code. It still didn't work. Also when I read a register value say red value. I first give the address and then do 3 dummy reads to get the data. But in your code it first have 4 dummy reads and then the 4 original read and then again 4 dummy reads. I tried it the same way but still didn't work. 

About the wave forms, I guess did not plot it properly that's why you are seeing different no: of samples. I wanted to take the data for second time and attach it but I am having trouble programming with FET. So I am not able to do it at this point. I will do that later.

Thanks & Regards

Simi

Hello Simi,

Any AFE4490/AFE4400 register can be read only when the SPI_READ bit is enabled. SPI_READ bit is bit 0 of CONTROL0 Reg (addr: 0).

Also CONTROL0 register is a write-only register.

In the EVM Src. code, for any single register read, first the SPI_READ bit is enabled, followed by actual register read and then the SPI_READ bit is disabled. This is the reason why you notice those 3 accesses. They are not dummy reads. The first access is a register write (addr: 0, data: 1) to enable SPI_READ, the second access is the actual register read and the third access is a register write (addr: 0, data: 0) to disable SPI_READ.

So for multiple read access, the EVM SRC code may not be optimized since there are overheads associated because of enabling the SPI_READ bit before the actual read and then disabling the SPI_READ bit for every register read.

You can obviously optimize this by enabling the SPI_READ bit at the beginning of the multi-read and disabling the SPI_READ at the end of the multi-read.

Hope this helps.

Regards

Praveen.

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 green LED can be used as a reflective pulse detector design of the afe4400???

Hello Yan,

I have already replied to this query in the following post:

http://e2e.ti.com/support/applications/high_reliability/f/30/p/276162/963656.aspx#963656

Regards

Praveen.

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Dear Simi and Praven,

Inidicated in your post that some source code was posted in the fórum, but I´m unbale to found any link.

I´m developping an application based on the AFE4490, and any reference and guidance material will be very helpful no matter the target MCU.

Thanks in advance, best regards:

Eric

Hi Eric,

Please find the below link.

http://e2e.ti.com/support/applications/high_reliability/f/30/t/273490.aspx

Thanks & Regards

Simi

Dear Simi,

Thank you so much for your rapid answer, this is brilliant :-)!

I missed that post, thank you again!

Best regards:

Eric

Dear Praveen,

I have a question regarding LED2VAL or value of any ADC data.

The register is 24 bit but I understand the ADC value is 22 bit. So I want to confirm whether the actual data is a 22 bit signed value and I can ignore the 2 MSB bits.

Thanks & Regards

Simi

Hello Praveen,

Please see the following configuration for AFE4400:

  writeRegister(CONTROL1,0x000101);
  writeRegister(TIAGAIN,0x000000);
  writeRegister(TIA_AMB_GAIN,0x000000);
 
  writeRegister(LEDCNTRL,0x011414);  // LED current = 5.85
   
   writeRegister(CONTROL2,0x000000);
  writeRegister(MODE,0x000000);

I just wanted to confirm that the way I am calculating current is correct. According to me this will give 5.85mA of LED current to both IR and RED.  Please let me know if this is correct.

Thanks

Simi

writeRegister(LEDCNTRL,0x011414);  should give you 5.85mA of current for both LEDs. That is correct.

Example using Equation 6 of the datasheet.  Where Full-Scale Current= 75mA

LED1[7:0]/256*Full Scale Current

(20/256)*75=5.859mA

Thanks Amy...

Hi Amy,

I was checking on these today once again and I realized that this calculation is good for AFE4490 but not for AFE4400. For AFE 4400, with the same settings, I will get a current setting of 3.9mA since Full Scale Current of AFE4400 is 50mA. Please confirm whether this is right.

Thanks & Regards

Simi

IF the full scale current changes, then yes the LED currents will change as well. Both equations should work the same as long as the values used are correct.

How are you taking this data and where on the body is the data taken from. The waveforms are very suseptable to movement.