Making a pulse oximeter using MAX30102

COVID-19 and pulse oximeter

A good way to know the severity of Covid-19 is to use a passel oximeter. However, there is a global shortage of pulse oximeters. I have built a pulse oximeter using the MAX30102 sensor. This could be helpful if my family member gets infected.

How to connect the ESP8266 to MAX3012

Arduino Project Hub

Measure Heart Rate and SpO2 with MAX30102

https://create.arduino.cc/projecthub/SurtrTech/measure-heart-rate-and-spo2-with-max30102-c2b4d8

Interfacing MAX30102 with Arduino + BPM measure project with OLED + buzzer. By SurtrTech.

MAX80102 sensor connects to ESP8366 using the I2C interface. The connection was made by referring to the following figure. 3.3k Ohm resistance is also available at 3.3-10k ohms

You have to remember to do the i2c setup with the Wire library.

Wire.begin(0,2);

The sensor I purchased was the following

<br />

In order to use MAX30102, you need to install Sparkfun’s library.

GitHub

GitHub - sparkfun/SparkFun_MAX3010x_Sensor_Library: An Arduino Library for th...

https://github.com/sparkfun/SparkFun_MAX3010x_Sensor_Library

An Arduino Library for the MAX3015 particle sensor and MAX30102 Pulse Ox sensor - GitHub - sparkfun/SparkFun_MAX3010x_Sensor_Library: An Arduino Library for the MAX3015 particle sensor and MAX30102...

I tried to run a sample program (Example8_SPO2).

GitHub

SparkFun_MAX3010x_Sensor_Library/Example8_SPO2.ino at master · sparkfun/Spark...

https://github.com/sparkfun/SparkFun_MAX3010x_Sensor_Library/blob/master/examples/Example8_SPO2/Example8_SPO2.ino

An Arduino Library for the MAX3015 particle sensor and MAX30102 Pulse Ox sensor - SparkFun_MAX3010x_Sensor_Library/Example8_SPO2.ino at master · sparkfun/SparkFun_MAX3010x_Sensor_Library

HR=166… SPO2=76-89…

This vital sign is a dead man!!

I scrutinized the content of the program. The code to find SPO2 is included in spo2_algorithm.cpp.

GitHub

SparkFun_MAX3010x_Sensor_Library/spo2_algorithm.cpp at master · sparkfun/Spar...

https://github.com/sparkfun/SparkFun_MAX3010x_Sensor_Library/blob/master/src/spo2_algorithm.cpp

An Arduino Library for the MAX3015 particle sensor and MAX30102 Pulse Ox sensor - SparkFun_MAX3010x_Sensor_Library/spo2_algorithm.cpp at master · sparkfun/SparkFun_MAX3010x_Sensor_Library

It’s too difficult for me to understand !!

However, direct observation of the sensor values appears to be coming in exactly the get. The code below is a test sketch to get the sensor data.

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

MAX30105 particleSensor;

void setup()
{
  Wire.begin(0,2);                       // I2Cのピン設定
  Serial.begin(115200);
  
  Serial.println("");
  Serial.println("Initializing...");

  // Initialize sensor
  while(!particleSensor.begin(Wire, I2C_SPEED_FAST)){
    Serial.print(".");
  }
  Serial.println("OK!");
  

  //Setup to sense a nice looking saw tooth on the plotter
  byte ledBrightness = 0x1F; //Options: 0=Off to 255=50mA
  byte sampleAverage = 8; //Options: 1, 2, 4, 8, 16, 32
  byte ledMode = 2; //Options: 1 = Red only, 2 = Red + IR, 3 = Red + IR + Green
  int sampleRate = 400; //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

  Serial.println("ir,red");  
}


void loop()
{
  uint32_t ir_v = particleSensor.getIR();
  uint32_t red_v = particleSensor.getRed();

  Serial.print(ir_v);
  Serial.print(",");
  Serial.println(red_v);
}

#include <Wire.h>

#include "MAX30105.h"

MAX30105 particleSensor;

void setup()

{

Wire.begin(0,2); // I2Cのピン設定

Serial.begin(115200);

Serial.println("");

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

// Initialize sensor

while(!particleSensor.begin(Wire, I2C_SPEED_FAST)){

Serial.print(".");

}

Serial.println("OK!");

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

byte ledBrightness = 0x1F; //Options: 0=Off to 255=50mA

byte sampleAverage = 8; //Options: 1, 2, 4, 8, 16, 32

byte ledMode = 2; //Options: 1 = Red only, 2 = Red + IR, 3 = Red + IR + Green

int sampleRate = 400; //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

Serial.println("ir,red");

}

void loop()

{

uint32_t ir_v = particleSensor.getIR();

uint32_t red_v = particleSensor.getRed();

Serial.print(ir_v);

Serial.print(",");

Serial.println(red_v);

}

The RED and IR pulses need to be analyzed to obtain SPO2. So I’ve been gathering information from net.

core.ac.uk

https://core.ac.uk/download/pdf/81961664.pdf

~~https://core.ac.uk/download/pdf/81961664.pdf~~

https://arxiv.org/ftp/arxiv/papers/1907/1907.11989.pdf

Qiita

Raspberry Piと心拍センサ(MAX30102)で脈を見てみよう - Qiita

https://qiita.com/vrn/items/1ac58c61194b23af1d8c

(2019.05.02 追記: github側で「redとirの読み出しがごっちゃだよ」と指摘があったので修正しました．影響範囲はmax30102.pyのread_fifo()部分と，「グラフ表示してみる」全般です．)健康，...

(抜粋)

It is necessary to obtain the values of Red_AC and Red_DC and IR_AC and IR_DC.
The formula for calculating SPO2 is as follows

$$R=\frac{Red_{AC} \div Red_{DC}}{IR_{AC} \div IR_{DC}}$$

$$SPO_{2}[\%]=-45.060R^2+30.354R+94.845$$

Normal SPO2 is 97-99%.

$$98=-45.060R^2+30.354R+94.845$$

In other words, the normal R value is about 0.54.

However, when calculated using the sensor values, the R value is 1.782

Isn’t this sensor already broken?

Just when I was about to give up, the reciprocal of 1.782 was…

$$\frac{1}{1.782}=0.561$$

Are the RED and IR values reversed?

In RED Value only mode(ledMode = 1), the red LED is not lit.
No…

I tried shooting it with an IR camera.

Oh… The sensor’s infrared light is glowing.

I need to reverse the IR value and Red value when programming

Assembly and Code

I used a 3D printer to make a sensor mounter. I put a band on my finger to hold it.

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

#include <movingAvg.h>   

MAX30105 particleSensor;

//------ 定数定義
const uint32_t TH_FIN = 7000;   //指が置いてあるかどうかの閾値
const int32_t  TH_AMOUNT = 300; //パルスの起点となる検出変化量

const int32_t MIN_INIT = 9999999; //最小値の初期値
const int32_t MAX_INIT = 0;       //最大値の初期値

//表示する心拍数とSpO2の範囲(用途により適宜変更)
const uint32_t DISP_MIN_HR   = 30;
const uint32_t DISP_MAX_HR   = 180;
const uint32_t DISP_MIN_SPO2 = 70;
const uint32_t DISP_MAX_SPO2 = 100;

//パルス検出保持変数
long l_time = millis();    //最後のパルス検出時間の保持
int32_t before_ir_v = 0;   //最後のir_v値保持
int32_t b_diff = 0;        // 最後の差の保持
long pulse_interval = -1;  // パルス間隔時間

//1パルス中の生データの最大・最小値の保持
int32_t min_ir_v = MIN_INIT ,max_ir_v  = MAX_INIT;
int32_t min_red_v= MIN_INIT ,max_red_v = MAX_INIT;

//移動平均値(IR_DC、RED_DC)　30(20～50)サンプル
movingAvg avgIr_v(30);
movingAvg avgRed_v(30);

//移動平均値(心拍数は直近3ビート、SPO2は5ビートの平均)
movingAvg avgHR(3);
movingAvg avgSPO2(5);

void setup()
{
  Wire.begin(0,2);                       // I2Cのピン設定
  Serial.begin(115200);
  
  Serial.println("");
  Serial.println("Initializing...");

  // センサー初期化
  while(!particleSensor.begin(Wire, I2C_SPEED_FAST)){
    Serial.print(".");
  }
  Serial.println("OK!");
  
  byte ledBrightness = 0x1F; //Options: 0=Off to 255=50mA
  byte diffmpleAverage = 8; //Options: 1, 2, 4, 8, 16, 32
  byte ledMode = 2; //Options: 1 = Red only, 2 = Red + IR, 3 = Red + IR + Green
  int diffmpleRate = 400; //Options: 50, 100, 200, 400, 800, 1000, 1600, 3200
  int pulse_intervalWidth = 411; //Options: 69, 118, 215, 411
  int adcRange = 4096; //Options: 2048, 4096, 8192, 16384

  particleSensor.setup(ledBrightness, diffmpleAverage, ledMode, diffmpleRate, pulse_intervalWidth, adcRange); //Configure sensor with these settings

  //初期値として一回読んでおく(ir_vをパルス計測に用いる)
  before_ir_v =  particleSensor.getRed();
  
  //パルス最終取得時間の初期化
  l_time = millis();

  //移動平均ライブラリの初期化
  avgIr_v.begin();
  avgRed_v.begin();
  avgHR.begin();
  avgSPO2.begin();
}

void loop()
{
  //逆になっている。センサーが逆を返しているので各自チェック
  uint32_t red_v = particleSensor.getIR();
  uint32_t ir_v = particleSensor.getRed();

  //指を置いているか
  if(red_v< TH_FIN || ir_v < TH_FIN) return;

  //移動平均値(IR_DC RED_DCの算出)
  double ir_v_dc = avgIr_v.reading(ir_v);
  double red_v_dc = avgRed_v.reading(red_v);
  
  //IRとREDのACを求める為に最大値・最初値の更新
  if(ir_v<min_ir_v) min_ir_v = ir_v; if(ir_v>max_ir_v) max_ir_v = ir_v;

  if(red_v<min_red_v) min_red_v = red_v; if(red_v>max_red_v) max_red_v = red_v;

  //パルス検出にはir_vを利用。前回との差分(変化値)を求める
  int32_t diff =  before_ir_v - ir_v;
  
  //TH_AMOUNT以上の変化がある場合、パルス起点とする
  if(b_diff < TH_AMOUNT && diff > TH_AMOUNT){
    
    //1パルスの時間を計算
    pulse_interval = millis() - l_time;
    l_time = millis();

    //1パルスの時間より心拍数の計算。avgHRは整数のみなので1000倍して1000で割り少数保持
    double hr =  (double)avgHR.reading(60000*1000/pulse_interval) / 1000.0;

    //SPO2の計算
    //IR・REDのACを求める(振幅最大-振幅最小)
    int32_t ir_v_ac = max_ir_v-min_ir_v;
    int32_t red_v_ac = max_red_v-min_red_v;

    // R = (AC_RED / DC_RED) / (AC_IR / DC_IR)の計算式より
    double red_div = double(red_v_ac)/red_v_dc;
    double ir_div = double(ir_v_ac)/ir_v_dc;
    double R = red_div / ir_div;
    
    // SPO2 = -45.060*R^2 + 30.354*R + 94.845 これはspo2_algorithm.cppにあったのを準用
    // 乗除1000は少数保持のため
    double spo2 = (double)avgSPO2.reading((-45.060*R*R + 30.354*R + 94.845)*1000.0) / 1000.0;

    //最大値・最小値の初期化
    min_ir_v = MIN_INIT;
    max_ir_v = MAX_INIT;
    min_red_v = MIN_INIT;
    max_red_v = MAX_INIT;

    //心拍数とSPO2の表示(範囲は定義で変更可)
    if(hr <= DISP_MAX_HR && hr >= DISP_MIN_HR && spo2 <= DISP_MAX_SPO2 && spo2 >= DISP_MIN_SPO2){    
      Serial.print(hr);
      Serial.print(",");
      Serial.println(spo2);
    }
  }

  //パルス検出用値の保持
  before_ir_v = ir_v;
  b_diff = diff;
}

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#include <Wire.h>

#include "MAX30105.h"

#include <movingAvg.h>

MAX30105 particleSensor;

//------ 定数定義

const uint32_t TH_FIN = 7000; //指が置いてあるかどうかの閾値

const int32_t TH_AMOUNT = 300; //パルスの起点となる検出変化量

const int32_t MIN_INIT = 9999999; //最小値の初期値

const int32_t MAX_INIT = 0; //最大値の初期値

//表示する心拍数とSpO2の範囲(用途により適宜変更)

const uint32_t DISP_MIN_HR = 30;

const uint32_t DISP_MAX_HR = 180;

const uint32_t DISP_MIN_SPO2 = 70;

const uint32_t DISP_MAX_SPO2 = 100;

//パルス検出保持変数

long l_time = millis(); //最後のパルス検出時間の保持

int32_t before_ir_v = 0; //最後のir_v値保持

int32_t b_diff = 0; // 最後の差の保持

long pulse_interval = -1; // パルス間隔時間

//1パルス中の生データの最大・最小値の保持

int32_t min_ir_v = MIN_INIT ,max_ir_v = MAX_INIT;

int32_t min_red_v= MIN_INIT ,max_red_v = MAX_INIT;

//移動平均値(IR_DC、RED_DC)　30(20～50)サンプル

movingAvg avgIr_v(30);

movingAvg avgRed_v(30);

//移動平均値(心拍数は直近3ビート、SPO2は5ビートの平均)

movingAvg avgHR(3);

movingAvg avgSPO2(5);

void setup()

{

Wire.begin(0,2); // I2Cのピン設定

Serial.begin(115200);

Serial.println("");

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

// センサー初期化

while(!particleSensor.begin(Wire, I2C_SPEED_FAST)){

Serial.print(".");

}

Serial.println("OK!");

byte ledBrightness = 0x1F; //Options: 0=Off to 255=50mA

byte diffmpleAverage = 8; //Options: 1, 2, 4, 8, 16, 32

byte ledMode = 2; //Options: 1 = Red only, 2 = Red + IR, 3 = Red + IR + Green

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

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

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

particleSensor.setup(ledBrightness, diffmpleAverage, ledMode, diffmpleRate, pulse_intervalWidth, adcRange); //Configure sensor with these settings

//初期値として一回読んでおく(ir_vをパルス計測に用いる)

before_ir_v = particleSensor.getRed();

//パルス最終取得時間の初期化

l_time = millis();

//移動平均ライブラリの初期化

avgIr_v.begin();

avgRed_v.begin();

avgHR.begin();

avgSPO2.begin();

}

void loop()

{

//逆になっている。センサーが逆を返しているので各自チェック

uint32_t red_v = particleSensor.getIR();

uint32_t ir_v = particleSensor.getRed();

//指を置いているか

if(red_v< TH_FIN || ir_v < TH_FIN) return;

//移動平均値(IR_DC RED_DCの算出)

double ir_v_dc = avgIr_v.reading(ir_v);

double red_v_dc = avgRed_v.reading(red_v);

//IRとREDのACを求める為に最大値・最初値の更新

if(ir_v<min_ir_v) min_ir_v = ir_v; if(ir_v>max_ir_v) max_ir_v = ir_v;

if(red_v<min_red_v) min_red_v = red_v; if(red_v>max_red_v) max_red_v = red_v;

//パルス検出にはir_vを利用。前回との差分(変化値)を求める

int32_t diff = before_ir_v - ir_v;

//TH_AMOUNT以上の変化がある場合、パルス起点とする

if(b_diff < TH_AMOUNT && diff > TH_AMOUNT){

//1パルスの時間を計算

pulse_interval = millis() - l_time;

l_time = millis();

//1パルスの時間より心拍数の計算。avgHRは整数のみなので1000倍して1000で割り少数保持

double hr = (double)avgHR.reading(60000*1000/pulse_interval) / 1000.0;

//SPO2の計算

//IR・REDのACを求める(振幅最大-振幅最小)

int32_t ir_v_ac = max_ir_v-min_ir_v;

int32_t red_v_ac = max_red_v-min_red_v;

// R = (AC_RED / DC_RED) / (AC_IR / DC_IR)の計算式より

double red_div = double(red_v_ac)/red_v_dc;

double ir_div = double(ir_v_ac)/ir_v_dc;

double R = red_div / ir_div;

// SPO2 = -45.060*R^2 + 30.354*R + 94.845 これはspo2_algorithm.cppにあったのを準用

// 乗除1000は少数保持のため

double spo2 = (double)avgSPO2.reading((-45.060*R*R + 30.354*R + 94.845)*1000.0) / 1000.0;

//最大値・最小値の初期化

min_ir_v = MIN_INIT;

max_ir_v = MAX_INIT;

min_red_v = MIN_INIT;

max_red_v = MAX_INIT;

//心拍数とSPO2の表示(範囲は定義で変更可)

if(hr <= DISP_MAX_HR && hr >= DISP_MIN_HR && spo2 <= DISP_MAX_SPO2 && spo2 >= DISP_MIN_SPO2){

Serial.print(hr);

Serial.print(",");

Serial.println(spo2);

}

//パルス検出用値の保持

before_ir_v = ir_v;

b_diff = diff;

}

The chart below shows the heart rate and SPO2 graph and each moving averages

I have a moving average library to thank.

GitHub

GitHub - JChristensen/movingAvg: A simple Arduino library for calculating mov...

https://github.com/JChristensen/movingAvg

A simple Arduino library for calculating moving averages. - GitHub - JChristensen/movingAvg: A simple Arduino library for calculating moving averages.

The red line is SPO2.
The blue line is heart rate.

When I held my breath, my SPO2 was dropping.
My heart rate is also a representation of my breathing.

NIKKEI STYLE

心拍の揺らぎを知ろう　飛ぶ脈・極端に遅い脈は要注意｜ヘルスＵＰ｜NIKKEI STYLE

https://style.nikkei.com/article/DGXKZO96409530S6A120C1W13001/

昼も夜も動き続ける心臓。生涯の心拍数は20億回にも上るという。時計のように規則正しいリズムを刻んでいると思うかもしれないが、心拍のリズムは、実は微妙に揺らいでいる。よく揺らぐのは、むしろ健康なあかしだという。なぜ心拍は揺らぐのだろう？心臓の…

RED and IR values should be checked !!

It’s important!!

[2020/05]

Display SPO2 and heart rate on a real-time graph

ANDROIPHONE

[ESP8266][MAX30102] パルスオキシメーターをリアルタイムでモニターする

https://androiphone.uvs.jp/?p=3099

MAX30102で作ったパルスオキシメーター以前の記事でパルスオキシメーターまで製作したけど、せっかくESP8266にやらせているんだからグラフでモニタリングできたらなと思った。そんな中こんなサイトを見つけた。Highchartsっていうグラフ描画用のライブラリを使って、BME280からリアルタイムでセンシングした温度・気圧・湿度を表示している様子。とりあえず、手元にBME280があったのでチュートリアルに沿って動かしてみたら結構良さそうなので心拍数、SPO2のリアルタイム表示をしてみようと思った。Youtubeで検索すると似たようなこと...

[2020/05/20]

GitHub

Wrong activation of R and IR in MAX30102? · Issue #25 · sparkfun/SparkFun_MAX...

https://github.com/sparkfun/SparkFun_MAX3010x_Sensor_Library/issues/25

Hi, I'm playing with a MAX30102 sensor using this library on Arduino Nano board. Trying to configure the code I came across with some guy who used this sensor in a research project. And he comm...

The official library has reported the same problem. I’m publishing this article on 5/4-5. I’m hoping that maybe the questioner has seen this article.
I’m praying for a resolution.

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