Community Project Collection: How to Build a Cost-effective Pulse Oximeter with Wio Terminal and MAX30105 Sensor

This tutorial is translated by Seeed from Wio Terminal でパルスオキシメータを制作 written by homemadegarbage (twitter: @H0meMadeGarbage). Thank you for sharing this with us! Visit their homepage for more interesting projects: homemadegarbage.com.

This a simple tutorial about how to use Wio Terminal and MAX30105 sensor to make a pulse oximeter.

MAX30105 is a module equipped with red, green, and infrared LEDs and a high-sensitivity photon detector, and can be used for dust measurement or blood oxygen saturation measurement (SpO2).

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1. How to Connect MAX30105 to Wio Terminal

Connect the MAX30105 to the 4-pin Grove connector on the Wio Terminal.

2. Set Up the Pulse oximeter

You can check the library of the MAX30105 on Github. Other sample codes are listed below.

#include <Wire.h>
#include "MAX30105.h"

#include"seeed_line_chart.h" //include the library
#include "spo2_algorithm.h"

MAX30105 particleSensor;
TFT_eSPI tft;

long baseValue = 0;
long HB = 0, oldHB = 0;
int diffHB = 0;
int state = 0;
int th = -500;
 
#define max_size 50 //maximum size of data
doubles data; //Initilising a doubles type to store data
TFT_eSprite spr = TFT_eSprite(&tft);  // Sprite 


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

float beatsPerMinute;
int beatAvg;
long delta;


#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

void setup() {
  pinMode(WIO_BUZZER, OUTPUT);
  tft.begin();
  tft.setRotation(3);
  spr.createSprite(TFT_HEIGHT,TFT_WIDTH);

  Serial.begin(115200);
  Serial.println("Initializing...");

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

  particleSensor.setup(); //Configure sensor with default settings
  particleSensor.setPulseAmplitudeRed(20); //Turn Red LED to low to indicate sensor is running
  particleSensor.setPulseAmplitudeGreen(0); //Turn off Green LED
}
 
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];
      display();
    }

    //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

      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);

      display();
    }

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


void display() {
    spr.fillSprite(TFT_WHITE);
    if (data.size() == max_size) {
        data.pop();//this is used to remove the first read variable
    }
    HB = particleSensor.getIR();
    
    diffHB = HB - oldHB;
    data.push(diffHB); //read variables and store in data

    if(state == 0 && diffHB < th){
      delta = millis() - lastBeat;
      lastBeat = millis();
      beatsPerMinute = 60 / (delta / 1000.0);

      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.println(beatAvg);
      
      state = 1;
      analogWrite(WIO_BUZZER, 128);
      Serial.println("Beat!!!!!!!");
    }else if(state == 1 && diffHB > th){
      state = 0;
      analogWrite(WIO_BUZZER, 0);
    }

    
  //Settings for SpO2
    String stSpO2 = " SpO2:";
    if(validSPO2){
      stSpO2 += spo2;
    }else{
      stSpO2 += "-";
    }

    char charSpO2[20];
    stSpO2.toCharArray(charSpO2, 20);
  
    auto header =  text(0, 0)
                .value(charSpO2)
                .align(left)
                .valign(vcenter)
                .width(tft.width())
                .thickness(3);
                
    header.height(header.font_height() * 2);
    header.draw(); //Header height is the twice the height of the font


  //Settings for HeartRate
    String stHB = " HeartRate:";
    stHB += beatAvg;

    char charHB[20];
    stHB.toCharArray(charHB, 20);

    auto header2 =  text(0, header.height())
                .value(charHB)
                .align(left)
                .valign(vcenter)
                .width(tft.width())
                .thickness(3);
                
    header2.height(header.font_height() * 2);
    header2.draw(); //Header height is the twice the height of the font
    
 
  //Settings for the line graph
    auto content = line_chart(0, header.height() + header2.height()); //(x,y) where the line graph begins
         content
                .height(tft.height() - (header.height() + header2.height()) * 1.0) //actual height of the line chart
                .width(tft.width() - content.x() * 2) //actual width of the line chart
                .based_on(0.0) //Starting point of y-axis, must be a float
                .show_circle(false) //drawing a cirle at each point, default is on.
                .value(data) //passing through the data to line graph
                .color(TFT_PURPLE) //Setting the color for the line
                .draw();
 
    spr.pushSprite(0, 0);

    oldHB = HB;
}
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