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This question already has an answer here:

I have designed a Pulse Oximeter with IR and red LED.
I need to calculate SpO2. How to calibrate the Sp02?

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marked as duplicate by Martin, PlasmaHH, Brian Drummond, Bence Kaulics, Olin Lathrop Sep 8 '16 at 11:06

This question has been asked before and already has an answer. If those answers do not fully address your question, please ask a new question.

  • \$\begingroup\$ a little bit late to think about calibration after designing it... \$\endgroup\$ – PlasmaHH Sep 8 '16 at 9:15
  • \$\begingroup\$ As @PlasmaHH suggests, if you don't know how to calibrate it, you haven't designed it yet. \$\endgroup\$ – Brian Drummond Sep 8 '16 at 9:31
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    \$\begingroup\$ @BrianDrummond + PlasmaHH -> You apparently would find reading up on the arcane magic behind pulse oximeters educational. BUILDING one is easy [tm]. Massaging the data is where the art takes over. As all (AFAIK) are by inference and proxy the results between products can vary widely between implementatins for the same subject. . \$\endgroup\$ – Russell McMahon Sep 8 '16 at 9:37
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Due to approximate duplication of question I accidentally answered this question here rather than on the still active question.

PLEASE IGNORE THIS ANSWER :-)

PLEASE REFER TO THIS ANSWER AND QUESTION.


I'LL LEAVE THIS ANSWER HERE AS IS FOR NOW BUT AN EXTENDED VERSION IS NOW AVAILABLE VIA THE LINK ABOVE:

I'll try to add to this later.

SPO2 calculations are a "black art".
While they are based on the optical characteristics of haemoglobin at two wavelengths, there are a range of other parameters which make a simple calculation impractical.

You say that you have referred to many papers that discussed calibration - which is an essential starting point. You now need to make your own decisions based on what others have done and applying some practical reasoning. Depending on the purpose of your device (student project or commercial product or ....) you may be able to get a 'good enough' result by simple means.

You may be able to get access to a commercial machine either on a loan basis or perhaps by persuading a local clinic or hospital to come in and "play" with one in an unused treatment room when they are not busy. All you then need is your machine, their machine , a means of measuring the output of your machine AND, importantly, a source of varyingly exygenated blood inside a finger or whatever target you are using. The last requirement is both the hardest and easiest.
I personally can reduce my SpO2 level to the point where a monitoring alarm will sound. From memory this is oftem about 80% but whatevber figure it is, it's not too hard = by breathing slowly and retaining air as long as possible and controlling breath size you can lower SpO2 to alarm level in perhaps (from memory) 20-30 seconds. Return to high levels (95% +?) is rapid when breathing normally.

SO if you have the two machines you can vary the SpO2 levels easily and widely, and record data output by your machine plus recorded Sp)2% from the commercial machine under various conditions. Being able to do this with several brands of commercial equipment would be even better. Doing this with different users, different fingers, varying conditions (temperature, user mild inebriation, fasting and post glucose 'spike', .... ) would allow you to see what if any difference these things make.

If you are using an Arduino or similar it would be easy to log your results - and not quite so easy to record the commercial machines SpO2 values. If it has a USB or serial output that can be logged. If not you may need to use manual keyboard input of displayed SpO2 levels.

Long ago (10-20 years) I read an utterly superb Hewlett Packard Journal with a number of related articles. It covered equipment and sensor design and decisions and more. Should be findable.


Possible use:

HP1997

Volunteer Study for Sensor Calibration

HPJ 1997 A New Family of Sensors for Pulse Oximetry

Neonatal Sensor Clinical Validation

HPJ 1976 Haha wow !!!

http://www.ncbi.nlm.nih.gov/pubmed/9635666

Philips 22 pages !!! Understanding Pulse Oximetry SpO2 Concepts

Maybe

http://www.iosrjournals.org/iosr-jeee/Papers/Vol8-issue1/D0812226.pdf?id=7592

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