Arduino “having11” Guy
Published © GPL3+

Open Source Pulse Oximeter for COVID-19

An easily constructed USB-powered pulse oximeter device that can be built for around $25 and features an OLED display.

IntermediateFull instructions provided5 hours38,098

Things used in this project

Hardware components

Arduino Nano R3
Arduino Nano R3
×1
Maxim Integrated MAX30102 Pulse and Heartrate Sensor
×1
Gravity I2C OLED-2864 Display
DFRobot Gravity I2C OLED-2864 Display
×1

Software apps and online services

Arduino IDE
Arduino IDE
Fusion 360
Autodesk Fusion 360

Hand tools and fabrication machines

3D Printer (generic)
3D Printer (generic)
Soldering iron (generic)
Soldering iron (generic)

Story

Read more

Custom parts and enclosures

Bottom Shell

Front + Bed

Top Piece

Schematics

Schematic

Code

Pulse Oximeter Code

C/C++
/*
  Hardware Connections (Breakoutboard to Arduino):
  -5V = 5V (3.3V is allowed)
  -GND = GND
  -SDA = A4 (or SDA)
  -SCL = A5 (or SCL)
  -INT = Not connected
 
  The MAX30105 Breakout can handle 5V or 3.3V I2C logic. We recommend powering the board with 5V
  but it will also run at 3.3V.
*/

#include <Wire.h>
#include "MAX30105.h"
#include "spo2_algorithm.h"
#include "SSD1306Ascii.h"
#include "SSD1306AsciiWire.h"

MAX30105 particleSensor;
SSD1306AsciiWire oled;

#define MAX_BRIGHTNESS 255

#if defined(__AVR_ATmega328P__) || defined(__AVR_ATmega168__)
//Arduino Uno doesn't have enough SRAM to store 50 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[50]; //infrared LED sensor data
uint16_t redBuffer[50];  //red LED sensor data
#else
uint32_t irBuffer[50]; //infrared LED sensor data
uint32_t redBuffer[50];  //red LED sensor data
#endif

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()
{
  Serial.begin(115200); // initialize serial communication at 115200 bits per second:

  oled.begin(&Adafruit128x64, 0x3C);
  oled.setFont(Arial14);

  // 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(55, 4, 2, 200, 411, 4096); //Configure sensor with these settings
}

void loop()
{

  //read the first 50 samples, and determine the signal range
  for (byte i = 0 ; i < 50 ; 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 50 samples (first 4 seconds of samples)
  maxim_heart_rate_and_oxygen_saturation(irBuffer, 50, 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 25 sets of samples to the top
    for (byte i = 25; i < 50; i++)
    {
      redBuffer[i - 25] = redBuffer[i];
      irBuffer[i - 25] = irBuffer[i];
    }

    //take 25 sets of samples before calculating the heart rate.
    for (byte i = 25; i < 50; 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.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, 50, redBuffer, &spo2, &validSPO2, &heartRate, &validHeartRate);
    printToScreen();
  }
}

void printToScreen() {
  oled.clear();
  oled.setCursor(0,0);
  if(validSPO2 && validHeartRate) {
    oled.print(F("HR: ")); oled.println(heartRate, DEC);
    oled.print(F("SPO2: ")); oled.println(spo2, DEC);
  } else {
    oled.print(F("Not valid"));
  }
}

Credits

Arduino “having11” Guy

Arduino “having11” Guy

81 projects • 538 followers
18 year-old IoT and embedded systems enthusiast. Also an intern at Hackster.io who loves working on projects and sharing knowledge.

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