Design and Implementation of a Calibration - Free Pulse Oximeter

Abstract

Oxygen saturation in human beings is measured as the ratio of the amount of oxygen carried by hemoglobin to the maximum amount it could carry. A pulse oximeter is a device which measures this saturated oxygen content using the technique of photoplethysmography. Generally, the device consists of two LEDs (Red and IR) as light sources, and a photo diode as the detector. Depending on the intensity of light transmitted or reflected to the detector, oxygen saturation is computed. Commercially available pulse oximeters require calibration, since the device is dependent on sensor and patient-dependent parameters like skin color and thickness of the digit. This is normally done by acquiring data from volunteers, after which the necessary coefficients are extracted, for computing the saturated oxygen content. Such a calibration technique is dependent on the sample population, and hence is undesirable. The work presented here, makes use of a calibration-free algorithm published earlier, incorporating it into a micro-controller, leading to a compact, power-efficient, pulse oximeter. Moreover, present day pulse oximeters do not give access to the raw PPG data, which could be used for extracting important cardiovascular parameters. The preliminary design presented here provides a serial port interface in order to acquire and communicate the PPG signal to a PC, for further offline analysis.