Arduinoセンサーキットに、Heart rate sensorある。

血中ヘモグロビンの近赤外線吸収の性質を利用して脈拍パルス検出するらしい。

Arduinoとの接続は３線（GND、VCC、アナログ入力）のみ。

「参考１」をみて、まず簡単の試す。ただA0の値を表示。

// Pulse Monitor Test Script
int sensorPin = 0;
void setup() {
   Serial.begin(9600);
}
void loop ()
{
   while(1)
   {
     Serial.print(analogRead(sensorPin));
     Serial.print('\n');
   }
}

指先センサー装着

シリアルプロッターに見える上昇カーブ

安定した状態これはなにもわからない

指はセンサーから離れる時の下降カーブ。

「参考１」を参考して、Smoothingしても、同じ判別不能。困った。

#define samp_siz 4
#define rise_threshold 5
// Pulse Monitor Test Script
int sensorPin = 0;
void setup() {
   Serial.begin(9600);
}
void loop ()
{
   float reads[samp_siz], sum;
   long int now, ptr;
   float last, reader, start;
   float first, second, third, before, print_value;
   bool rising;
   int rise_count;
   int n;
   long int last_beat;
   for (int i = 0; i < samp_siz; i++)
     reads[i] = 0;
   sum = 0;
   ptr = 0;
   while(1)
   {
     // calculate an average of the sensor
     // during a 20 ms period (this will eliminate
     // the 50 Hz noise caused by electric light
     n = 0;
     start = millis();
     reader = 0.;
     do
     {
       reader += analogRead (sensorPin);
       n++;
       now = millis();
     }
     while (now < start + 20);  
     reader /= n;  // we got an average
     // Add the newest measurement to an array
     // and subtract the oldest measurement from the array
     // to maintain a sum of last measurements
     sum -= reads[ptr];
     sum += reader;
     reads[ptr] = reader;
     last = sum / samp_siz;
     // now last holds the average of the values in the array
     // check for a rising curve (= a heart beat)
     if (last > before)
     {
       rise_count++;
       if (!rising && rise_count > rise_threshold)
       {
         // Ok, we have detected a rising curve, which implies a heartbeat.
         // Record the time since last beat, keep track of the two previous
         // times (first, second, third) to get a weighed average.
         // The rising flag prevents us from detecting the same rise 
         // more than once.
         rising = true;
         first = millis() - last_beat;
         last_beat = millis();
         // Calculate the weighed average of heartbeat rate
         // according to the three last beats
         print_value = 60000. / (0.4 * first + 0.3 * second + 0.3 * third);
         Serial.print(print_value);
         Serial.print('\n');
         third = second;
         second = first;
       }
     }
     else
     {
       // Ok, the curve is falling
       rising = false;
       rise_count = 0;
     }
     before = last;
     ptr++;
     ptr %= samp_siz;
   }
}

こんな図形になって、周囲の雑音とか酷いかな？

参考：

1. https://www.hackster.io/Johan_Ha/from-ky-039-to-heart-rate-0abfca

試み

MAX30102 というPulse Ox Sensorを利用して、脈拍と酸素濃度を測る試み。

MAX30100の実例が多いが、MAX30102の実例が少ない。

プログラム

「参考１」のSparkFunのライブラリを利用する。そのライブラリはMAX30105（R,G,IR LED）用だが、MAX30102（欠Green LED）でも利用できる。

OLED表示するため、「参考２」の表示部分を合体した。なんとなく、バグがある様な気がする。

// Sample implementation of the MAX30100 PulseOximeter
// Using the following module
// http://www.ebay.com/itm/-/391709438817?ssPageName=STRK:MESE:IT
// can not gaurantee if the app will work with other implementations of the module. 

//#include "MAX30100_PulseOximeter.h"
#include <U8g2lib.h>
#include <Wire.h>
#include "MAX30105.h"
#include "heartRate.h"

#define REPORTING_PERIOD_MS     500

 U8G2_SSD1306_128X32_UNIVISION_F_HW_I2C u8g2(U8G2_R0);

// PulseOximeter is the higher level interface to the sensor
// it offers:
//  * beat detection reporting
//  * heart rate calculation
//  * SpO2 (oxidation level) calculation
//PulseOximeter pox;
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;

//byte pulseLED = 13; //Must be on PWM pin
//byte readLED = 11; //Blinks with each data read
//
bool calculation_complete=false;
bool calculating=false;
bool initialized=false;
byte beat=0;

void show_beat() 
{
  u8g2.setFont(u8g2_font_cursor_tf);
  u8g2.setCursor(8,10);
  if (beat==0) {
    u8g2.print("_");
    beat=1;
  } 
  else
  {
    u8g2.print("^");
    beat=0;
  }
  u8g2.sendBuffer();
}

void initial_display() 
{
  if (not initialized) 
  {
    u8g2.clearBuffer();
    show_beat();
    u8g2.setCursor(24,12);
    u8g2.setFont(u8g2_font_profont15_mr);
    u8g2.print("Place finger");  
    u8g2.setCursor(0,30);
    u8g2.print("on the sensor");
    u8g2.sendBuffer(); 
    initialized=true;
  }
}

void display_calculating(int j)
{
  if (not calculating) {
    u8g2.clearBuffer();
    calculating=true;
    initialized=false;
  }
  show_beat();
  u8g2.setCursor(24,12);
  u8g2.setFont(u8g2_font_profont15_mr);
  u8g2.print("Measuring..."); 
  u8g2.setCursor(0,30);
  u8g2.print(beatsPerMinute);
  u8g2.print(" Bpm");
  u8g2.sendBuffer();
}

void display_values()
{
  u8g2.clearBuffer();
  u8g2.setFont(u8g2_font_profont15_mr);
 
  u8g2.setCursor(0,30);
  u8g2.print(beatsPerMinute);
  u8g2.print(" Bpm _ ");
  u8g2.setCursor(65,30);  
  u8g2.print(beatAvg);
  u8g2.sendBuffer();
}

void setup()
{
    Serial.begin(115200);
    
//    pinMode(pulseLED, OUTPUT);
//    pinMode(readLED, OUTPUT);

    u8g2.begin();

    // 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);
    }    

    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
    
    initial_display();
}


void loop()
{

  long irValue = particleSensor.getIR();
  float temperature = particleSensor.readTemperature();
//  digitalWrite(readLED, !digitalRead(readLED)); //Blink onboard LED with every data read

  if (checkForBeat(irValue) == true)
  {
    calculation_complete=true;
    calculating=false;
    initialized=false;

//    digitalWrite(pulseLED, !digitalRead(pulseLED)); //Blink onboard LED with every Beat
    //We sensed a beat!
    long delta = millis() - lastBeat;
    lastBeat = millis();

    if (delta < 10000) {
      beatsPerMinute = 60 / (delta / 1000.0);
    } else {
      calculation_complete=false;
      beatsPerMinute=0;
      initial_display();
    }
    
    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;
      display_values();
    }
  } else {
    if (irValue < 50000) {
      calculating=false;
      initial_display();
    } else {
      display_calculating(5);
    }
  }

  Serial.print("IR=");
  Serial.print(irValue);
  Serial.print(", BPM=");
  Serial.print(beatsPerMinute);
  Serial.print(", Avg BPM=");
  Serial.print(beatAvg);
  Serial.print(", initialized=");
  Serial.print(initialized);
  Serial.print(", calculating=");
  Serial.print(calculating);
  Serial.print(", calculation_complete=");
  Serial.print(calculation_complete);
  Serial.println();



}

実験

かなり不安定の感じがする。

一応、形はできたが、

しかし、脈拍捉えるのは稀て、今回も失敗して。。。

参考

1. https://learn.sparkfun.com/tutorials/max30105-particle-and-pulse-ox-sensor-hookup-guide
2. https://www.hackster.io/umar-sear/arduino-heart-rate-monitor-a8e9e1
3. https://www.hackster.io/AAKS/max30100-and-blynk-0f58f4