Heart Rate Measurement with ESP32 and Pulse Oximeter Module using FFT

 Code listing used in video:

// Tinker Foundry

// Heart Rate Measurement with the MAX30102 breakout board using FFT

// Connections from WEMOS D1 R32 board to MAX30102 Breakout Board as follows:

//  SCL (ESP32) to SCL (breakout board)

//  SDA (ESP32) to SDA (breakout board)

//  3V3 (ESP32) to VIN (breakout board)

//  GND (ESP32) to GND (breakout board)

#include <Wire.h>

#include "MAX30105.h"    // sparkfun MAX3010X library

MAX30105 particleSensor;

#include "arduinoFFT.h"

arduinoFFT FFT;

double avered       = 0;

double aveir        = 0;

double sumirrms     = 0;

double sumredrms    = 0;

int    i            = 0;

int    Num          = 100;  // calculate SpO2 by this sampling interval

int    Temperature;

int    temp;

float  ESpO2;               // initial value of estimated SpO2

double FSpO2        = 0.7;  // filter factor for estimated SpO2

double frate        = 0.95; // low pass filter for IR/red LED value to eliminate AC component

#define TIMETOBOOT    3000  // wait for this time(msec) to output SpO2

#define SCALE         88.0  // adjust to display heart beat and SpO2 in the same scale

#define SAMPLING      100   //25 //5     // if you want to see heart beat more precisely, set SAMPLING to 1

#define FINGER_ON     30000 // if red signal is lower than this, it indicates your finger is not on the sensor

#define USEFIFO

#define PULSE_SAMPLES 256

#define SAMPLE_FREQ   50

// --- For Heart Rate ---

byte   rateSpot         = 0;

long   lastBeat         = 0;  // Time at which the last beat occurred

int    beatAvg          = 0;

bool   detect_high      = 0;

// ----------------------

double redArray[PULSE_SAMPLES]; // array to store samples from the sensor

double vReal[PULSE_SAMPLES];

double vImag[PULSE_SAMPLES];

double beatsPerMinute = 0;

void setup()

{

   Serial.begin(115200);

   Serial.setDebugOutput(true);

   Serial.println();

   Serial.println("Running...");

   delay(3000);

   // Initialize sensor

   while (!particleSensor.begin(Wire, I2C_SPEED_FAST)) //Use default I2C port, 400kHz speed

   {

      Serial.println("MAX30102 was not found. Please check wiring/power/solder jumper at MH-ET LIVE MAX30102 board. ");

      //while (1);

   }

   //Setup to sense a nice looking saw tooth on the plotter

   byte ledBrightness = 0x7F;  // 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

   //Options: 1 = IR only, 2 = Red + IR on MH-ET LIVE MAX30102 board

   int sampleRate     = 200;   // Options: 50, 100, 200, 400, 800, 1000, 1600, 3200

   int pulseWidth     = 411;   // Options: 69, 118, 215, 411

   int adcRange       = 16384; // Options: 2048, 4096, 8192, 16384

 

   // Set up the wanted parameters

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

   particleSensor.enableDIETEMPRDY();

}

void loop()

{

   uint32_t ir, red, green;

   double fred, fir;

   double SpO2 = 0; //raw SpO2 before low pass filtered

   float red_beat = 0;

   

#ifdef USEFIFO

   particleSensor.check();               // Check the sensor, read up to 3 samples

   while (particleSensor.available())

   {  // Do we have new data

#ifdef MAX30105

      red = particleSensor.getFIFORed(); // Sparkfun's MAX30105

      ir  = particleSensor.getFIFOIR();  // Sparkfun's MAX30105

#else

      red = particleSensor.getFIFOIR();  // why getFOFOIR output Red data by MAX30102 on MH-ET LIVE breakout board

      ir  = particleSensor.getFIFORed(); // why getFIFORed output IR data by MAX30102 on MH-ET LIVE breakout board

#endif

      i++;

      i = i % PULSE_SAMPLES; // wrap around every 256 samples

      fred = (double)red;

      redArray[i] = fred; // populate the array

      particleSensor.nextSample(); // We're finished with this sample so move to next sample

      if (i == 0) // execute every PULSE_SAMPLES

      {

         Serial.print("Time: ");

         Serial.println(millis()); // can use this to determine time it takes to collect 256 samples (sample rate)

         for (int idx=0; idx < PULSE_SAMPLES; idx++)

         {

            vReal[idx] = redArray[idx];

            vImag[idx] = 0.0;

            //Serial.println(redArray[idx]);

         }

         FFT = arduinoFFT(vReal, vImag, PULSE_SAMPLES, SAMPLE_FREQ); /* Create FFT object */

         FFT.Windowing(FFT_WIN_TYP_HAMMING, FFT_FORWARD); /* Weigh data */

         FFT.Compute(FFT_FORWARD); /* Compute FFT */

         FFT.ComplexToMagnitude(); /* Compute magnitudes */

         double peak = FFT.MajorPeak();

         //Serial.println(peak, 6);

         // print in beats per minute

         beatsPerMinute = peak * 60;

         Serial.print("BPM: ");

         Serial.println(beatsPerMinute);

      }

  }

#endif

  //Serial.println(i);

}