How to convert ADC results code to voltage?

Stella Laksono

Hey, all...
I just tried my AFE44902SPOEVM board and save the log data.
So, i just obtained the Codes data and the Volts data,
but i lost from here...
I am trying to approach the SpO2 measurement by making an algorithm from the ADC codes ->Volts data ->SpO2 percentage.

so for example, the ADC codes for RED LED is 114847,

and finally in volts data it becomes 0.065715981,

but i don't understand how the ADC codes converted to voltages data...
Is there anyone here can explain something about this?
Or maybe my approach is not proper?

Please for your advice and explanation.

Thank you!

Stella

over 12 years ago

0 Praveen Aroul over 12 years ago

TI__Guru 50036 points

Stella,

The ADC volts to codes conversion formula is:

ADC data (volts) = (ADC codes in two's complement format * Vref ) / 2^21

where Vref = 1.2V

0 Stella Laksono over 12 years ago in reply to Praveen Aroul

Intellectual 580 points

Thanks, Praveen!

this is maybe a novice question that anyone should already know it.

But your reply leads me to a bigger progress, so thank you!

0 Stella Laksono over 12 years ago in reply to Stella Laksono

Intellectual 580 points

Hey!

I also have another question,
So the following attachment is the Device_Analysis data that I obtained after saving the generated pulse oximetry.

how do you actually got the Vrms and the Vpeak?
It seems that two of them are not relating...
If I calculate, for example the RED LED,
Vrms = 0.707 X Vpeak.
In this case, Vpeak = Vpp/2 = (3.25X10^3)/2 = 1625 V,
Then using the formula above, the Vrms = 0.707 X Vpeak = 0.707 X 1625 = 1148.875 V,
but it shows the Vrms on the obtained file, is not similar as I expected.

So...I confused, where did I make the mistake?
Please help...

Best Regards,

Stella

0 Guilherme Borba over 12 years ago in reply to Stella Laksono

TI__Intellectual 1910 points

Hi Stella,

The formula below is how you calculate the RMS for a sinusoid. The signal you are looking at is most likely not a perfect sinusoid, so the formula does not apply.

Vrms = Vpeak/sqrt(2) ~= 0.707 * Vpeak

Regards,

Gui

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How to convert ADC results code to voltage?