MAX30102传感器接Arduino：读BPM与SpO2

手腕上的智能手表能测心率、测血氧，靠的大多是一颗指甲盖大小的光学传感器。这颗叫 MAX30102 的芯片来自 Analog Devices，是老款 MAX30100 的升级版，两颗 LED 加一个光电探测器，走 I2C 总线，接 Arduino 就能把 BPM 和 SpO2 数据读出来。这篇按接线、装库、逐级验证的顺序把流程理一遍，代码全部来自 SparkFun 官方库的例程，先摆数据再动手，新手照着做一遍就能跑通。

先认识模块：一颗芯片管两束光

MAX30102 内部有红色和红外两颗 LED，波长分别是 660nm 和 880nm，配合光电探测器把反射回来的光强转成数字量。芯片供电要 1.8V、LED 要 3.3V，模块上已经带了稳压器，所以只需要给模块一路 3.3V 到 5.5V 的电源。正常测量电流不到 600μA，待机只有 0.7μA，做电池供电的可穿戴实验很合适。

几个关键规格列一下：供电 3.3V 到 5.5V；红光 660nm、红外 880nm；板载温度传感器量程 -40°C 到 +85°C，精度 ±1°C；片上 ADC 是 18 位，共 262144 级；FIFO 缓存最多存 32 组测量数据，主控忙别的也不会丢样本。

通信是标准 I2C：写地址 0xAE，读地址 0xAF，固定不可改，所以一条总线上挂别的器件要注意地址冲突。芯片还支持 5 类中断（上电就绪、新数据就绪、环境光过强、温度就绪、FIFO 将满），都从 INT 引脚输出，平时高电平，触发时拉低。这篇的例程用轮询方式读数据，INT 可以先不接。

接线：只用四根线，SCL 对 A5、SDA 对 A4

模块引脚从电源到地一共 7 个，逐个说清楚：

1. VIN：电源输入，接 3.3V 或 5V，跟主控逻辑电平保持一致，Arduino Uno 这类 5V 板就接 5V；
2. GND：地，接 Arduino 的 GND；
3. SCL：I2C 时钟线，接 Uno 的 SCL（即 A5）；
4. SDA：I2C 数据线，接 Uno 的 SDA（即 A4）；
5. INT：中断输出，本篇例程不接；
6. IRD 和 RD：分别是红外 LED 和红光 LED 的内部接地端，芯片内部已经处理，悬空即可。

背面的焊接跳线默认选 3.3V 逻辑，接 Arduino 和 ESP32 都不用动；只有接 1.8V 逻辑的主控才需要改。上拉电阻模块已经带好，总线直接挂就行。

装库：认准 SparkFun 那一个

自己写寄存器配置太折腾，直接用 SparkFun Electronics 的官方库。打开 Arduino IDE，点左侧 Library Manager 图标，搜索框输入 MAX3010x，找到 SparkFun MAX3010x Pulse and Proximity Sensor Library，点 Install。装完就能跑下面的例程。另外说明一下：例程里的 #include "Wire.h" 原写法是尖括号包 Wire.h，两种写法在 Arduino 工具链下等价，这里统一用引号写法。

第一步：先读红光和红外的原始值

拿到传感器别急着测心率，先确认它活着、数据在动。下面这段把红光和红外两路原始值打到串口：

#include "Wire.h"
#include "MAX30105.h"

MAX30105 particleSensor;

void setup() {
  Serial.begin(9600);

  // Initialize sensor
  if (particleSensor.begin() == false) {
    Serial.println("MAX30102 was not found. Please check wiring/power.");
    while (1)
      ;
  }

  particleSensor.setup();  //Configure sensor. Use 6.4mA for LED drive
}

void loop() {
  Serial.print(" R[");
  Serial.print(particleSensor.getRed());
  Serial.print("] IR[");
  Serial.print(particleSensor.getIR());
  Serial.println("]");
}

上传后打开串口监视器，传感器朝上，手掌在上方晃动，两组数字会跟着变化；把指腹轻轻贴上去，数字会出现规律起伏。想看得更直观，把 loop() 换成下面两行，再用 Tools 菜单里的 Serial Plotter 画出来：

void loop() {
  Serial.print(particleSensor.getRed());
  Serial.print(", ");
  Serial.println(particleSensor.getIR());
}

绘图仪上会出现两条曲线，手指贴稳之后，红外那一路的波形就是你的脉搏波，一个波峰对应一次心跳。

第二步：算心率 BPM

确认波形正常后，用库自带的 heartRate.h 做峰值检测，滑动平均 4 次读数输出 BPM。代码原样贴上：

#include "Wire.h"
#include "MAX30105.h"
#include "heartRate.h"

MAX30105 particleSensor;

const byte RATE_SIZE = 4;  //Increase this for more averaging. 4 is good.
byte rates[RATE_SIZE];     //Array of heart rates
byte rateSpot = 0;
long lastBeat = 0;  //Time at which the last beat occurred

float beatsPerMinute;
int beatAvg;

void setup() {
  Serial.begin(9600);
  Serial.println("Initializing...");

  // Initialize sensor
  if (!particleSensor.begin(Wire, I2C_SPEED_FAST)) {
    Serial.println("MAX30102 was not found. Please check wiring/power. ");
    while (1)
      ;
  }
  Serial.println("Place your index finger on the sensor with steady pressure.");

  particleSensor.setup();                     //Configure sensor with default settings
  particleSensor.setPulseAmplitudeRed(0x0A);  //Turn Red LED to low to indicate sensor is running
  particleSensor.setPulseAmplitudeGreen(0);   //Turn off Green LED
}

void loop() {
  long irValue = particleSensor.getIR();

  if (checkForBeat(irValue) == true) {
    //We sensed a beat!
    long delta = millis() - lastBeat;
    lastBeat = millis();

    beatsPerMinute = 60 / (delta / 1000.0);

    if (beatsPerMinute < 255 && beatsPerMinute>  20) {
      rates[rateSpot++] = (byte)beatsPerMinute;  //Store this reading in the array
      rateSpot %= RATE_SIZE;                     //Wrap variable

      //Take average of readings
      beatAvg = 0;
      for (byte x = 0; x < RATE_SIZE; x++)
        beatAvg += rates[x];
      beatAvg /= RATE_SIZE;
    }
  }

  Serial.print("IR=");
  Serial.print(irValue);
  Serial.print(", BPM=");
  Serial.print(beatsPerMinute);
  Serial.print(", Avg BPM=");
  Serial.print(beatAvg);

  if (irValue < 50000)
    Serial.print(" No finger?");

  Serial.println();
}

手指轻贴传感器、保持不动，等几秒钟 Avg BPM 就会稳定下来。程序里还有个小细节：IR 值低于 50000 时提示 No finger?，这是判断有没有人把手指放上去的粗门槛，顺手就能改成检测手指离开自动暂停的功能。

放手指的姿势，决定读数能不能看

光学测量对接触方式很敏感，读数飘的时候按下面几条排查：

1. 不能按太重：指腹压太狠会掐断皮下血流，脉搏波直接变形；
2. 也不能太轻：漏进环境光会引入噪声，波形抖成毛刺；
3. 力度找个中间值，感觉像手指间轻轻捏着一枚硬币；
4. 手指容易酸的话，用橡皮筋或胶带把手指固定在传感器上，比悬空稳得多；
5. 换别的部位也行，耳垂、下唇这类皮肤薄、血流丰富的地方同样能测。

第三步：算血氧 SpO2

血氧的原理是把两束光的吸收差算成一个百分比：含氧血红蛋白吸收 880nm 红外更多，脱氧血红蛋白吸收 660nm 红光更多，对比两种光的吸收量就得到 SpO2。健康人一般在 95% 到 100% 之间。下面是库自带的 spo2_algorithm 例程，逻辑是先攒 100 个样本（约 4 秒），之后每秒滚动计算一次心率和血氧：

#include "Wire.h"
#include "MAX30105.h"
#include "spo2_algorithm.h"

MAX30105 particleSensor;

#define MAX_BRIGHTNESS 255

#if defined(__AVR_ATmega328P__) || defined(__AVR_ATmega168__)
//Arduino Uno doesn't have enough SRAM to store 100 samples of IR led data and red led data in 32-bit format
//To solve this problem, 16-bit MSB of the sampled data will be truncated. Samples become 16-bit data.
uint16_t irBuffer[100];   //infrared LED sensor data
uint16_t redBuffer[100];  //red LED sensor data
#else
uint32_t irBuffer[100];   //infrared LED sensor data
uint32_t redBuffer[100];  //red LED sensor data
#endif

int32_t bufferLength;   //data length
int32_t spo2;           //SPO2 value
int8_t validSPO2;       //indicator to show if the SPO2 calculation is valid
int32_t heartRate;      //heart rate value
int8_t validHeartRate;  //indicator to show if the heart rate calculation is valid

byte pulseLED = 11;  //Must be on PWM pin
byte readLED = 13;   //Blinks with each data read

void setup() {
  Serial.begin(9600);  // initialize serial communication at 9600 bits per second:

  pinMode(pulseLED, OUTPUT);
  pinMode(readLED, OUTPUT);

  // Initialize sensor
  if (!particleSensor.begin(Wire, I2C_SPEED_FAST))  //Use default I2C port, 400kHz speed
  {
    Serial.println(F("MAX30105 was not found. Please check wiring/power."));
    while (1)
      ;
  }

  Serial.println(F("Attach sensor to finger with rubber band. Press any key to start conversion"));
  while (Serial.available() == 0)
    ;  //wait until user presses a key
  Serial.read();

  byte ledBrightness = 60;  //Options: 0=Off to 255=50mA
  byte sampleAverage = 4;   //Options: 1, 2, 4, 8, 16, 32
  byte ledMode = 2;         //Options: 1 = Red only, 2 = Red + IR, 3 = Red + IR + Green
  byte sampleRate = 100;    //Options: 50, 100, 200, 400, 800, 1000, 1600, 3200
  int pulseWidth = 411;     //Options: 69, 118, 215, 411
  int adcRange = 4096;      //Options: 2048, 4096, 8192, 16384

  particleSensor.setup(ledBrightness, sampleAverage, ledMode, sampleRate, pulseWidth, adcRange);  //Configure sensor with these settings
}

void loop() {
  bufferLength = 100;  //buffer length of 100 stores 4 seconds of samples running at 25sps

  //read the first 100 samples, and determine the signal range
  for (byte i = 0; i < bufferLength; i++) {
    while (particleSensor.available() == false)  //do we have new data?
      particleSensor.check();                    //Check the sensor for new data

    redBuffer[i] = particleSensor.getRed();
    irBuffer[i] = particleSensor.getIR();
    particleSensor.nextSample();  //We're finished with this sample so move to next sample

    Serial.print(F("red="));
    Serial.print(redBuffer[i], DEC);
    Serial.print(F(", ir="));
    Serial.println(irBuffer[i], DEC);
  }

  //calculate heart rate and SpO2 after first 100 samples (first 4 seconds of samples)
  maxim_heart_rate_and_oxygen_saturation(irBuffer, bufferLength, redBuffer, &spo2, &validSPO2, &heartRate, &validHeartRate);

  //Continuously taking samples from MAX30102.  Heart rate and SpO2 are calculated every 1 second
  while (1) {
    //dumping the first 25 sets of samples in the memory and shift the last 75 sets of samples to the top
    for (byte i = 25; i < 100; i++) {
      redBuffer[i - 25] = redBuffer[i];
      irBuffer[i - 25] = irBuffer[i];
    }

    //take 25 sets of samples before calculating the heart rate.
    for (byte i = 75; i < 100; i++) {
      while (particleSensor.available() == false)  //do we have new data?
        particleSensor.check();                    //Check the sensor for new data

      digitalWrite(readLED, !digitalRead(readLED));  //Blink onboard LED with every data read

      redBuffer[i] = particleSensor.getRed();
      irBuffer[i] = particleSensor.getIR();
      particleSensor.nextSample();  //We're finished with this sample so move to next sample

      //send samples and calculation result to terminal program through UART
      Serial.print(F("red="));
      Serial.print(redBuffer[i], DEC);
      Serial.print(F(", ir="));
      Serial.print(irBuffer[i], DEC);

      Serial.print(F(", HR="));
      Serial.print(heartRate, DEC);

      Serial.print(F(", HRvalid="));
      Serial.print(validHeartRate, DEC);

      Serial.print(F(", SPO2="));
      Serial.print(spo2, DEC);

      Serial.print(F(", SPO2Valid="));
      Serial.println(validSPO2, DEC);
    }

    //After gathering 25 new samples recalculate HR and SP02
    maxim_heart_rate_and_oxygen_saturation(irBuffer, bufferLength, redBuffer, &spo2, &validSPO2, &heartRate, &validHeartRate);
  }
}

程序用橡皮筋把手指固定后按任意键开始，串口会输出 red、ir、HR、SPO2 和各自的 valid 标志位。注意两点：一是 Uno 的 SRAM 只有 2KB，例程里专门用条件编译把缓冲区降成 16 位才放得下，ESP32 这类大内存板走 32 位分支；二是看 SPO2Valid 位，为 0 的那轮数据说明信号质量不够，别当真值用。

把丑话说在前面：它不是医疗设备

MAX30102 靠光反射取脉搏，手指晃动、按压力度变化、环境光干扰、指甲油、低灌注状态都会把读数带偏，原厂定位就是学习和实验工具，官方文档也明确提醒它不适合医疗场景。这个模块适合做桌面监测实验、课程设计、给机器人加个人体存在检测，所有 BPM 和 SpO2 数据只能作实验参考，不能用于任何健康判断。

玩到后面还可以解锁两个附赠功能：芯片内置的温度传感器能当快速温度计用（读芯片结温），把 LED 全关后调用 readTemperature() 即可；另外把红外通道当接近传感器，开机先取 32 次平均值做基线，之后检测到偏差超过阈值就报"有东西"，手在上方挥一下就能触发，给桌面装置做无接触交互挺方便。18 位 ADC 的灵敏度摆在那，几十厘米内的小动作都逃得过。