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    Fully Digital Cosine Signal Driven Pulse Oximeter Without Bandpass Filter Based on Microcontroller
    (2022-04-20)
    Kainan, Pattana
    ;
    Wiriyatanachit, Supatsara
    ;
    Rungkrae, Manussawee
    ;
    Wardkein, Paramote
    ;
    Maneerat, Noppadol
    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.
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    Fully Digital Pulse Oximeter Cosine Wave Driven Generate two PPG AMs and AM Synchronous Detector with Single Microcontroller
    (2022-01-01)
    Kainan, Pattana
    ;
    Rungkrae, Manussawee
    ;
    Wiriyatanachit, Supatsara
    ;
    Wardkein, Paramote
    ;
    Lertterada, Krittapas
    In this article, an embedded microcontroller ESP32 implement to be a pulse oximeter is proposed. The almost overall system operates on a microcontroller except for the analog front-end trans-impedance amplifier. The system works by generating two different frequency cosines with cosine function and converting them to be analog cosine signals to drive IR and Red-light sources. The two PPG AM signals are summed in FDM form at the output of the light detector, and it is amplified and converted to be digital signal by the microcontroller after that the digital signal as mentioned above is selected by two digital BPFs with different center frequencies and two PPG AMs are obtained. Two PPG AMs have been demodulated with AM synchronous detector therefore the PPG IR and PPG RED are obtained. They are employed to estimate oxygen saturated and display on OLED along with mobile devices android OS by Bluetooth communication channel. The experiment results show that the proposed system can well operate and have accuracy and precision are 98.1261% and 0.9031, respectively.