Fully Digital Cosine Signal Driven Pulse Oximeter Without Bandpass Filter Based on Microcontroller

Abstract

ABSTRACT In this research, almost fully digital microcontroller pulse oximeter processing by two frequencies of cosine wave-driven red and infrared light sources as well as direct recovering photoplethysmography (PPG) signals from FDM signal without bandpass filter with coherent amplitude demodulation is proposed. An ESP32 microcontroller is employed to generate two cosine waves with two difference equation algorithms instead of using the function of cosine from Arduino or C library language. Two frequency digital cosine wave signals are generated and converted to analog signals with D/A to drive two light sources while two digital cosine signals as mentioned above are recognized in order to use to be as two local oscillator cosine wave signals for recovery of two PPG signals with synchronous demodulation. The RED and IR PPG signals are later used to estimate blood oxygen saturation (SpO2). The experimental result shows that it works well with accuracy and precision of 99.4448% and 0.5551, respectively.