Connected wristband with Arduino

We made a connected wrsitband using an arduino Nano 33 BLE and a PPG sensor MAX30100 form Mikroe to measure Hear Rate, HRV and SPO2 values

IntermediateShowcase (no instructions)Over 1 day668

Things used in this project

Hardware components

Arduino Nano 33 BLE Sense

MIKROE MAX 30100

pololu

Chargeur LiPo mini-USB MR1012

Li-Ion Battery 1000mAh

Software apps and online services

Arduino IDE

Nordic Semiconductor nRF Connect SDK

Hand tools and fabrication machines

3D Printer (generic)

Specifically a laser engraver

Soldering iron (generic)

Breadboard, 170 Pin

Wire Stripper & Cutter, 18-10 AWG / 0.75-4mm² Capacity Wires

10 Pc. Jumper Wire Kit, 5 cm Long

Story

Hello everyone !

We are students in an engineering school and for one of our project, we were asked to propose a connected wristband to measure in real time and for long period multiple signals thanks to a PPG sensor (HR, HRV, SPO2, body temperature, detect is the band is worn). In order to do that, we fisrtly made a FAST diagramm of our project to see all the things that needed to be done and how to get it done.

Then we got the Arduino Nano 33 BLE Sense and the MAX 30 100 PPG Sensor. Thanks to multiple links, mainly the one form the Last Minute Engineers, we recovered a simple code and a library to use the PPG sensor. With this code, we could retrieve the Heart Rate and the SPO2 values. The problem was that the value retrieved were not very precise with some abnormal values (less than 40 bpm or more than 150 bpm measured in a calm situation).

So we decided to change the way we would measure the heart rate and the variability of the heart rate. We used one of the available function, OnBeatDetected, to update the time at which the last Hear Beat was detected. This way, we could add the number of heart beat measured and add the time to a counter. When this counter reached 30 seconds, we would multiply the number of heart beat by 2, giving us the number of heart beat for a minute, so the heart beat measure. We would also read every 5 seconds the time between the last 2 heart beat, giving us the HRV mesaure.

Once this was done, we enabled the BLE of the arduino and send the data collected to NRF Connect for Mobile. This was the easiest way to retrieve the datas and see the updated value directly on our smartphone. The following images show you the result we obtained on NRF Connect.

After checking that our values were correct, we continue our prototype to ensure it could work autonomously. We needed to supply the Arduino with a constant 3.3V Voltage. We were given a 1000mAh battery, whcih delivers between 3V and 4.7V. We connectred this battery to a mini-USB battery charge to allow it to be charged when needed. The one thing that was needed to be done was to allow the arduino to be supply with a constant voltage of 3.3V. That is why we added between the Vout of the charge battery and the Vin (3.3V) of the arduino a 3.3V Voltage Regulator (pololu). You can see the result right here (for the measure shown, you have firstly the HR, then the HRV, then the skin temperature and finally the SpO2).

We also changed a little bit the first code to write a CSV file when the arduino was connected. We used puTTY to wrtie the CSV file as soon as it was connected to the arduino using the serial port.

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To ensure that our wristband could be worn, we had to optimize the space in order to get a wearable product in the end. We designed the PCB to allow space optimisation

1 / 2

Due to a lack of time and problems with the PCB, we couldn't get our final prototype to work correctly like the previous one. Nevertheless, we decided to use the time remaining to try and make the wristband the way we wanted it to look, given our client a proper look at the solution we designed.

#include <Wire.h>
#include "MAX30100_PulseOximeter.h"
#include <ArduinoBLE.h>           // Bluetooth Library

#define REPORTING_PERIOD_MS     1000

// Initalizing global variables for sensor data to pass onto BLE
String h, t, v, s;
// Create a PulseOximeter object
PulseOximeter pox;
MAX30100 sensor;

// Time at which the last beat occurred
uint32_t tsLastReport = 0;
uint32_t tsLastReport_av = 0;

//Hear rate
uint32_t calcul_HR=0;
float time_HR=0;

//HRV
uint32_t HRV=0;

void onBeatDetected() {
    //Serial.println("♥ Beat!");
    tsLastReport=millis();
}

// BLE Service Name
BLEService customService("180C");

// BLE Characteristics
// Syntax: BLE<DATATYPE>Characteristic <NAME>(<UUID>, <PROPERTIES>, <DATA LENGTH>)
BLEStringCharacteristic ble_heartrate("0xFC", BLERead | BLENotify, 30);
BLEStringCharacteristic ble_temperature("0x0C", BLERead | BLENotify, 13);
BLEStringCharacteristic ble_HRV("0xFC", BLERead | BLENotify, 13);
BLEStringCharacteristic ble_spo("0x02", BLERead | BLENotify, 13);

// Function prototype
void readValues();

void setup() {
  
  //Initializing all the sensors
  //Serial.begin(9600);
  //while (!Serial);
  if (!BLE.begin())
  {
      //Serial.println("BLE failed to Initiate");
      //delay(500);
      while (1);
  }

  // Setting BLE Name
  BLE.setLocalName("Arduino Environment Sensor");
  
  // Setting BLE Service Advertisment
  BLE.setAdvertisedService(customService);
  
  // Adding characteristics to BLE Service Advertisment
  customService.addCharacteristic(ble_heartrate);
  customService.addCharacteristic(ble_temperature);
  customService.addCharacteristic(ble_HRV);
  customService.addCharacteristic(ble_spo);

  // Adding the service to the BLE stack
  BLE.addService(customService);

  // Start advertising
  BLE.advertise();
  Serial.println("Bluetooth device is now active, waiting for connections...");

  digitalWrite(LED_PWR, LOW);

  //Serial.print("Initializing pulse oximeter..");
  // Initialize sensor
  if (!pox.begin() || !sensor.begin()){   //PULSEOXIMETER_DEBUGGINGMODE_PULSEDETECT
      //Serial.println("FAILED");
      for(;;);
  }else{
      //Serial.println("SUCCESS");
  }

  // Configure sensor to use 7.6mA for LED drive
  //pox.setIRLedCurrent(MAX30100_LED_CURR_7_6MA);
  //sensor.setLedsCurrent(MAX30100_LED_CURR_7_6MA, MAX30100_LED_CURR_0MA);
  configureMax30100();

  pox.setOnBeatDetectedCallback(onBeatDetected);
}

void loop(){

  pox.update();
  // Variable to check if cetral device is connected
  BLEDevice central = BLE.central();
  if (central){
    //Serial.print("Connected to central: ");
    //Serial.println(central.address());
    while (central.connected()){
      
      // Read values from sensors
      readValues();

      // Writing sensor values to the characteristic
      ble_heartrate.writeValue(h);
      ble_temperature.writeValue(t);
      ble_HRV.writeValue(v);
      ble_spo.writeValue(s);

      // Displaying the sensor values on the Serial Monitor
      //Serial.println("Reading Sensors");
      //Serial.println(h);
      //Serial.println(t);
      //Serial.println(v);
      //delay(1000);
    }
    //Serial.print("Disconnected from central: ");
    //Serial.println(central.address());
  }
}

void readValues(){

  // Read from the sensor
  pox.update();
  // Grab the updated heart rate and SpO2 levels
  
  if(tsLastReport != tsLastReport_av){
    time_HR += tsLastReport-tsLastReport_av;
    calcul_HR++;
    HRV=2.7*(tsLastReport-tsLastReport_av);
  }

  float SP=pox.getSpO2();
  if(SP != 0){
   if (time_HR >= 5000){
    time_HR=0;
    uint32_t final_HR = calcul_HR/2.95*12;
    //h = String(final_HR) + " BPM";
    calcul_HR = 0;
    if(final_HR>60 && final_HR<140){
      h = String(final_HR) + " BPM";
      v = String(HRV) + "ms";
    }else{
      h="0 BPM : not worn";
      v = "Not worn";
    }
  }
 }else{
  h="0 BPM : not worn";
  v = "Not worn";
 }

  sensor.startTemperatureSampling();
  //Serial.print("Temperature:");
  //Serial.println(temp);

  // Saving sensor values into a user presentable way with units
  t = String(sensor.retrieveTemperature()) + " C";
  s = String(SP) + "%";
  tsLastReport_av = tsLastReport;
}

void configureMax30100() {
  sensor.setMode(MAX30100_MODE_SPO2_HR);
  sensor.setLedsCurrent(MAX30100_LED_CURR_7_6MA, MAX30100_LED_CURR_27_1MA);
  sensor.setLedsPulseWidth(MAX30100_SPC_PW_1600US_16BITS);
  sensor.setSamplingRate(MAX30100_SAMPRATE_100HZ);
  sensor.setHighresModeEnabled(true);
}

#include <Wire.h>
#include "MAX30100_PulseOximeter.h"

#define REPORTING_PERIOD_MS     1000

// Create a PulseOximeter object
PulseOximeter pox;

// Time at which the last beat occurred
uint32_t tsLastReport = 0;
uint32_t HR=0;
uint32_t cpt=0;

// Callback routine is executed when a pulse is detected
void onBeatDetected() {
    Serial.println("♥ Beat!");
    tsLastReport = millis();
}

void setup() {
    Serial.begin(9600);

    //Serial.print("Initializing pulse oximeter..");

    // Initialize sensor
    if (!pox.begin()) {
        Serial.println("FAILED");
        for(;;);
    } else {
        Serial.println("SUCCESS");
    }

    // Configure sensor to use 7.6mA for LED drive
    pox.setIRLedCurrent(MAX30100_LED_CURR_7_6MA);

    // Register a callback routine
    pox.setOnBeatDetectedCallback(onBeatDetected);
}

void loop() {
    // Read from the sensor
    pox.update();

    // Grab the updated heart rate and SpO2 levels
    if (millis() - tsLastReport > REPORTING_PERIOD_MS) {
        cpt++;
        HR+=pox.getHeartRate();
        if(cpt==10){
          HR=HR/10;
          cpt=0;
          if(pox.getSpO2() ==0){
            HR=0;
          }else{
            if(HR<50 && HR>10){
              HR=HR*1.75;
            }
          }
          Serial.print("Heart rate:");
          Serial.print(HR);
          Serial.print("bpm");
          Serial.print(" / SpO2:");
          Serial.println(pox.getSpO2());
        }
   }
}

#include <Wire.h>
#include "MAX30100_PulseOximeter.h"
#include <ArduinoBLE.h>           // Bluetooth Library

#define REPORTING_PERIOD_MS     1000

// Initalizing global variables for sensor data to pass onto BLE
String h, t, v, s;
// Create a PulseOximeter object
PulseOximeter pox;
MAX30100 sensor;

// Time at which the last beat occurred
uint32_t tsLastReport = 0;
uint32_t tsLastReport_av = 0;

//Hear rate
uint32_t calcul_HR=0;
float time_HR=0;
uint32_t last_HR=0;
uint32_t HRV=0;

void onBeatDetected() {
    //Serial.println("♥ Beat!");
    tsLastReport=millis();
}

// BLE Service Name
BLEService customService("180C");

// BLE Characteristics
// Syntax: BLE<DATATYPE>Characteristic <NAME>(<UUID>, <PROPERTIES>, <DATA LENGTH>)
BLEStringCharacteristic ble_heartrate("0xFC", BLERead | BLENotify, 30);
BLEStringCharacteristic ble_temperature("0x0C", BLERead | BLENotify, 13);
BLEStringCharacteristic ble_HRV("0xFC", BLERead | BLENotify, 13);
BLEStringCharacteristic ble_spo("0x02", BLERead | BLENotify, 13);

// Function prototype
void readValues();

void setup() {
  
  //Initializing all the sensors
  Serial.begin(9600);
  while (!Serial);
  if (!BLE.begin())
  {
      //Serial.println("BLE failed to Initiate");
      //delay(500);
      while (1);
  }

  // Setting BLE Name
  BLE.setLocalName("Arduino Environment Sensor");
  
  // Setting BLE Service Advertisment
  BLE.setAdvertisedService(customService);
  
  // Adding characteristics to BLE Service Advertisment
  customService.addCharacteristic(ble_heartrate);
  customService.addCharacteristic(ble_temperature);
  customService.addCharacteristic(ble_HRV);
  customService.addCharacteristic(ble_spo);

  // Adding the service to the BLE stack
  BLE.addService(customService);

  // Start advertising
  BLE.advertise();
  Serial.println("Bluetooth device is now active, waiting for connections...");

  digitalWrite(LED_PWR, LOW);

  //Serial.print("Initializing pulse oximeter..");
  // Initialize sensor
  if (!pox.begin() || !sensor.begin()){   //PULSEOXIMETER_DEBUGGINGMODE_PULSEDETECT
      //Serial.println("FAILED");
      for(;;);
  }else{
      //Serial.println("SUCCESS");
  }

  // Configure sensor to use 7.6mA for LED drive
  //pox.setIRLedCurrent(MAX30100_LED_CURR_7_6MA);
  //sensor.setLedsCurrent(MAX30100_LED_CURR_7_6MA, MAX30100_LED_CURR_0MA);
  configureMax30100();

  pox.setOnBeatDetectedCallback(onBeatDetected);

  Serial.println("HR, HRV, temp, SpO2");
}

void loop(){

  pox.update();
  // Variable to check if cetral device is connected
  BLEDevice central = BLE.central();
  if (central){
    //Serial.print("Connected to central: ");
    //Serial.println(central.address());
    while (central.connected()){
      
      // Read values from sensors
      readValues();

      // Writing sensor values to the characteristic
      ble_heartrate.writeValue(h);
      ble_temperature.writeValue(t);
      ble_HRV.writeValue(v);
      ble_spo.writeValue(s);
    }
    //Serial.print("Disconnected from central: ");
    //Serial.println(central.address());
  }
}

void readValues(){

  // Read from the sensor
  pox.update();
  // Grab the updated heart rate and SpO2 levels
  
  if(tsLastReport != tsLastReport_av){
    time_HR += tsLastReport-tsLastReport_av;
    calcul_HR++;
    HRV=2.7*(tsLastReport-tsLastReport_av);
  }

  float SP=pox.getSpO2();
  if(SP != 0){
   if (time_HR >= 5000){
    time_HR=0;
    uint32_t final_HR = calcul_HR/2.95*12;
    calcul_HR = 0;
    if(final_HR>60 && final_HR<140){
      h = String(final_HR) + " BPM";
      v = String(HRV) + "ms";
      last_HR = final_HR;
    }else{
      h="0 BPM : not worn";
      v = "Not worn";
    }
  }
  Serial.print(last_HR);
  Serial.print(", ");
  Serial.print(HRV);
  Serial.print(", ");
 }else{
  h="0 BPM : not worn";
  v = "Not worn";
  Serial.print("0, 0, ");
 }
  sensor.startTemperatureSampling();
  //Serial.print("Temperature:");
  //Serial.println(temp);

  // Saving sensor values into a user presentable way with units
  t = String(sensor.retrieveTemperature()) + " C";
  s = String(SP) + "%";
  Serial.print(sensor.retrieveTemperature());
  Serial.print(", ");
  Serial.println(SP);
  tsLastReport_av = tsLastReport;
}

void configureMax30100() {
  sensor.setMode(MAX30100_MODE_SPO2_HR);
  sensor.setLedsCurrent(MAX30100_LED_CURR_7_6MA, MAX30100_LED_CURR_27_1MA);
  sensor.setLedsPulseWidth(MAX30100_SPC_PW_1600US_16BITS);
  sensor.setSamplingRate(MAX30100_SAMPRATE_100HZ);
  sensor.setHighresModeEnabled(true);
}