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Notes: Pulse Oximeter



Pulse Oximeter

Nov 2, 01:34 PM

Biometric sensors that can detect pulse and oxygen content in the blood are called Pulse Oximeters.

Here are two great examples of do it yourself pulse oximeters-

Mike Szczys’ hack-a-day diy sensor
And an Arduino based sensor

The DIY uses a red LED and an infrared LED (for baseline light measurements), and it seems to work well. The initial info I was reading mentioned the wavelengths 650 nm and 805nm.

The secret sauce is in the ratio conversion. From

After the transmitted red and infrared (IR) signals pass through the measuring site and are received at the photodetector, the R/IR ratio is calculated. The Red/IR is compared to a “look-up” table (made up of empirical formulas) that convert the ratio to an SpO2 value. Most manufacturers have their own look-up tables based on calibration curves derived from healthy subjects at various SpO2 levels. Typically a R/IR ratio of 0.5 equates to approximately 100% SpO2, a ratio of 1.0 to approximately 82% SpO2, while a ratio of 2.0 equates to 0% SpO2