
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 oximetry.org:

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