SpO2: Determine calibration factors for MAX86150
!414 (merged) introduced a demo app for SpO2 estimation using the MAX86150. It's results for SpO2 are not reliable though.
https://git.card10.badge.events.ccc.de/card10/firmware/-/issues/196 discusses details of how SpO2 is estimated using these algorithms. We currently implement an algorithm from Maxim based on the code for their RD117 reference design. What we are missing at the moment are the calibration values for the MAX86150 to at least get somehow reasonable results.
The estimated SpO2 values are generally too high. Heart rate seems to work if the finger is pressed on "correctly". I can imagine that it might be necessary to design a (printed) spacer around the sensor to have repeatable results.