AFE4400 LED1 DATA analysis

Hello Hwang,

The mechanical setup, ambient light, distance between LED and PD in addition to other factors like plays a major role in getting good PPG signals from reflective sensors.

Could you send the PPG waveform?

Did you try the AFE TIA, 2nd stage gain settings to increase the DC and AC amplitude?

You may also try increasing the LED current.


Regards
Praveen.

hi Praveen,

Thanks for the reply,here is the PPG waveform

the green one is LED1 red one is LED1 - ALED1 quite flat .... I can't see any thing from this PPG waveform ,

also the voltage is pretty low, LED1 is only -0.009v,

after writing  0x4406 to TIA_AMB_GAIN (which is 12db gain plus Rf = 1M)

Regards
Whang wen-fu.

I figure out where might be the problem

After plotting six different var, in the middle of the graph ,i put my finger on the sensor 

red //LED2

blue //ALED2

green //LED1

lightpink //ALED1

lightskyblue //LED2-ALED2

lightsteelblue //LED1-ALED1

It seems that LED1 and LED2 never change!!

but because the change of ambient light, the LED1-ALED1 still change.

What happened to LED1 and LED2 ?

Hi Whang,

It looks like the LED1 and LED2 signal is saturated at the TIA output. This is because any change in the ambient light affects all the channels equally. But in your case, you do not see any change in the LED1 and LED2 channels.

You may have to reduce the TIA gain to avoid saturating the signal.

Could you check reducing the TIA gain?

Also it would help to analyze better if you could provide waveforms that have the X and Y axis labels marked.

Regards
Praveen.

Hi Praveen,

Thanks for the answer, the data seems to be good now

after ave for 10 data point:

and sorry that it still no labels, because the program I use doesn't have the option,

I need to write my own plotting program to do that.

I still have one last question, I'm using Arduino to calculate the data,

and is this ADC DATA to voltage function is right?

 int32_t longdata = (rawspidata<<10);

double voltage = longdata/1024/2097152*1.2;

rawspidata is the accumulation of the 3 byte with 

temp_byte = SPI.transfer(0x00);
reg_value |= temp_byte << 16;

// get second byte
temp_byte = SPI.transfer(0x00);
reg_value |= temp_byte << 8;

// get last byte
temp_byte = SPI.transfer(0x00);
reg_value |= temp_byte;

Thank you very much.

Regards
Whang.