This paper specifically describes the design of hardware and software of a digital pulse oximeter based on ARM core embedded system and light-frequency converter. In this study, a light-frequency converter instead of a photodiode was adopted to receive the light transmitting, which greatly simplified the design of hardware. Besides, traditional methods of calculate frequency of rectangle signal were improved and an algorithm with stable sampling rate and high resolution was proposed. Based on the filtering and detecting methods of the pulse signal, the baseline drift and the noise on high frequency were successfully removed by applying integer coefficient filter. A detecting algorithm based on difference and threshold was proposed, and the future points of the signal can be extracted effectively. The result shows that this oximeter can overcome usual noise, the software is very flexible and simple in structure.Keywords-pulse oxygen saturation, ARM core embedded system, light to frequency converter, baseline drift, integer coefficient filter, method of difference and threshold 1)
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