前言

光體積變化描記圖法

（Photoplethysmography，簡稱PPG）

當一定波長的光束照射到指端皮膚表面，每次心跳時，血管的收縮和擴張都會影響光的透射或是光的反射。當光線透過皮膚組織然后再反射到光敏傳感器時，光照會有一定的衰減。像肌肉、骨骼、靜脈和其他連接組織對光的吸收是基本不變的 (前提是測量部位沒有大幅度的運動)，但是動脈會不同，由于動脈里有血液的脈動，那么對光的吸收自然也會有所變化。當我們把光轉換成電信號時，正是由于動脈對光的吸收有變化而其他組織對光的吸收基本不變，得到的信號就可以分為直流DC信號和交流AC信號。提取其中的AC信號，就能反應出血液流動的特點。

提示：以下是本篇文章正文內容，下面案例可供參考

一、產品描述

1.產品特性

EM7028 is a low-power I2C interface module includes Heart Rate Sensor(HRS) and internal LED Current Drivers with 2 Green LED. It can work in both continuous mode and pulse mode. It is designed for applications of Heart Beat Rate detection esp. such as smart watch etc. Heart Rate Sensor in continuous mode is designed to monitor heart rate by optical detection. A 16-bit ADC detects the result constantly with adjustable gain and resolution. Heart Rate Sensor in pulse mode is designed to monitor heart rate by optical detection in low-power. It also acts as a proximity sensor with rejection of ambient light noise. In order to removing component variations and eliminate offset caused by IR reflection, 2 registers were specially defined for compensation and high dynamic range of detection. HRS in continuous mode stores ADC output result into HRS1 registers, while HRS in pulse mode stores ADC output result into HRS2 registers. All pixels are controlled by analog-MUX in different modes.

2.技術規格

二、應用領域

示例：

? 工業控制領域：工業、控制設備美。

? 智能交通設備：收費站、停車場、車內語音提示；

? 廣告宣傳行業：廣告語播報；

三、應用電路圖

示例：