摘要： This paper presents the design and implementation of a robust heart rate monitor (HRM) based on photoplethysmography (PPG). This optical method is non-invasive and provides a convenient means of implementing a low-cost wearable HRM for eHealth applications. Our novel design consists of a light source that emits a modulated or unmodulated light signal through the finger tissue and measures the changes in the reflected light from the arterial blood. These reflections correspond well with the blood volume changes in synchrony with the heartbeat. Here we aim to provide a detailed description of how to design and implement an HRM device based on two approaches: 1) PPG using an unmodulated light source; 2) PPG using a modulated light source. Noise analysis in these devices enabled us to conceptualize and compare their performance and infer which one offers a better choice for optical heart rate monitoring. Based on the measurement results, the latter approach offers superior performance due to better noise cancellation and higher Signal-to-Noise Ratio (SNR) and is therefore robust against movement artefacts, power line noise, flicker noise of electronic components, as well as background environmental light interference.