On Thu, 28 Jun 2018 15:27:37 -0400, Dennis Lee Bieber wrote:

> When I Googled the devices I seem to recall something that mentioned
> light transmission in deep (visible) red vs transmission of infra-red.
> Those measurements are done sequentially (the sensors can't quite
> differentiate the light source so it needs vr/pause/ir/pause...

My googling a while back (when curiosity got the better of me) came
up with the two different wavelength IR sources but I have no
recollection of anything to do with time as far as the Sp02 was
concerned. My recollection is of a reference/measurement type system.

Quick google, early hit,
https://www.howequipmentworks.com/pulse_oximeter/

Bit "primary school" but seems to cover how a pulse oximeter works
pretty well. Explains the problem(s) and then gives the solution(s).
That link explains a reference/measurement system all be it with the
"reference" at 950 nm moving about a bit but a lot less than the
"measurement" at 650 nm.

--
Cheers
Dave.

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