Sinchai, Ananta

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Sinchai, Ananta
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ananta.sin@kmitl.ac.th

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    Pulse Oximetry Based on Quadrature Multiplexing of the Amplitude Modulated Photoplethysmographic Signals
    (2023-07-01)
    Koseeyaporn, Jeerasuda
    ;
    Wardkein, Paramote
    ;
    Sinchai, Ananta
    ;
    Kainan, Pattana
    ;
    Tuwanut, Panwit
    In this research, a pulse oximeter based on quadrature multiplexing of AM-PPG signals is proposed. The oximeter is operated by a microcontroller and employs a simple amplitude modulation technique to mitigate noise interference during SpO<inf>2</inf> measurement. The two AM-PPG signals (RED and IR) are quadrature multiplexed using carrier signals with equal frequencies but a 90-degree phase difference. The study focused on noise interference caused by light intensity and hand movement. The experiment was conducted under three different levels of light intensity: 200 Lux, 950 Lux, and 2200 Lux. For each light intensity level, the SpO<inf>2</inf> level was measured under three scenarios: hand still, shadow movement over the hand, and hand shaking. A comparison between the proposed technique and the conventional method reveals that the proposed technique offers a superior performance. The relative error of the measured SpO<inf>2</inf> level using the proposed technique was less than 3.1% overall. Based on the study, the proposed technique is less affected by noise interference caused by light intensity and hand movement compared to the conventional method. In addition, the proposed technique has an advantage over contemporary methods in terms of computational complexity. Consequently, the proposed technique can be applied to wearable devices that include SpO<inf>2</inf> measurement functionality.
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    New pulse oximetry detection based on the light absorbance ratio as determined from amplitude modulation indexes in the time and frequency domains
    (2022-05-01)
    Kainan, Pattana
    ;
    Sinchai, Ananta
    ;
    Tuwanut, Panwit
    ;
    Wardkein, Paramote
    The Pandemic COVID-19 situation, a pulse Oximetry is significant to detect a varying blood oxygen saturation of a patient who needed the device to operate with continuous, rapid, high accuracy, and immune of moving artifacts. In this article, three main schemes for low-complexity pulse oximetry detection are proposed. In the first scheme, the light absorbance ratio (R) is obtained by separating the red and infrared photoplethysmography (PPG) amplitude modulation (AM) signals from the frequency-division multiplexing (FDM) signal with two different bandpass filters (BPFs), determining the ratio of modulation index of red and infrared PPG AM signals. In the second scheme, the output PPG AM signals for the red and infrared light wavelengths from the BPFs are transformed into the frequency domain such that the AC components of both PPG AM signals are the magnitudes of the highest peaks in their respective sidebands, while the DC components are the magnitude of their carrier frequencies; then, the AC/DC ratio of the red PPG AM signal is divided by the AC/DC ratio of the infrared PPG AM signal is R. In the last scheme, the FDM signal is transformed into the frequency domain without being passed through any BPF, and R is obtained in the same way as in the same second scheme. Experimental results obtained by using the first scheme have an average error of about 0.7138%, for the second and the last scheme have an average error of about 1%, and all the methods agree with the corresponding mathematical model.
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    A Practical Circuit of Cyclic Chirp Spread Spectrum Modulation for Long Range Communication
    (2022-01-01)
    Sinchai, Ananta
    ;
    Saelim, Nopparut
    ;
    Pornavalai, Chotipat
    ;
    Wardkein, Paramote
    ;
    Tuwanut, Panwit
    Various technologies have been utilized in long range communication to satisfy increasing usage of the internet of things in a wide large area. Recently, a modulating technique called cyclic chirp spread spectrum (CSS) modulation has attracted attention due to its low power usage and long-range coverage. However, a cyclic CSS circuit is complex to build. Hence, the objective of the work is to propose a practical circuit of cyclic CSS modulation. The proposed circuit is designed to complicated-free creation. To prove that the presented circuit is pragmatic, a simulation test is performed. The simulation results have illustrated that the designed circuit well generates a chirp modulating signal. Also, the proposed circuit is flexibly configurable.
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    Simplified Derivative-Based Carrierless PPM Using VCO and Monostable Multivibrator
    (2025-06-01)
    Koseeyaporn, Jeerasuda
    ;
    Wardkein, Paramote
    ;
    Sinchai, Ananta
    ;
    Kaew-in, Chanapat
    ;
    Tuwanut, Panwit
    This study proposes a derivative-based, carrierless pulse position modulation (PPM) scheme utilizing a voltage-controlled oscillator (VCO) and a monostable multivibrator. In contrast to conventional PPM systems that rely on reference carriers or complex demodulation methods, the proposed architecture simplifies signal generation by directly modulating the time derivative of the message signal. The modulated signal, when processed through standard analog demodulators, inherently yields the derivative of the original message. This behavior is first established through theoretical derivations and then confirmed by simulations and circuit-level experiments. The proposed method includes a differentiator feeding into a VCO, followed by a monostable multivibrator to generate a carrierless PPM waveform. Experimental validation confirms that, under all tested demodulation approaches—integrator-based, PLL-based, and quasi-FM—the recovered output aligns with the differentiated message signal. The integration of this output to retrieve the original message was not performed to maintain focus on verifying the modulation principle. Additionally, the study aimed to ensure the consistency of derivative recovery. Signal-to-noise ratio (SNR) expressions for each demodulator type are presented and discussed in the context of their relevance to the proposed system. Limitations and directions for further study are also identified.