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Wearable Heart Rate Monitoring Device

In this session, we will build a wearable Arduino heart rate monitor to measure the heart rate of a remote patient.

BeginnerFull instructions provided2,236
Wearable Heart Rate Monitoring Device

Things used in this project

Hardware components

Arduino nano R3
×1
nrf24 module
×1
NeoPixel Ring: WS2812 5050 RGB LED
Adafruit NeoPixel Ring: WS2812 5050 RGB LED
×1
Li-Po Battery
×1

Story

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Schematics

Arduino based Wearable Heartbeat Monitoring System Schematic

Code

Arduino based Wearable Heartbeat Monitoring System Source Code

C/C++
#include <Adafruit_NeoPixel.h>
#ifdef __AVR__
  #include <avr/power.h>
#endif

#include <SPI.h>
#include <RF24.h>
#include <RF24_config.h>
#include <nRF24L01.h>

int rf_cen = 9; //nRF24 chip enable pin
int rf_cs = 8; //nRF24 CS pin

RF24 rf(rf_cen, rf_cs);
//pipe address - hardcoded on uECG side
uint8_t pipe_rx[8] = {0x0E, 0xE6, 0x0D, 0xA7, 0, 0, 0, 0};

// Which pin on the Arduino is connected to the NeoPixels?
#define PIN            5
// How many NeoPixels are attached to the Arduino?
#define NUMPIXELS      16

Adafruit_NeoPixel pixels = Adafruit_NeoPixel(NUMPIXELS, PIN, NEO_GRB + NEO_KHZ800);

uint8_t  swapbits(uint8_t a){ //uECG pipe address uses swapped bits order
  // reverse the bit order in a single byte
    uint8_t v = 0;
    if(a & 0x80) v |= 0x01;
    if(a & 0x40) v |= 0x02;
    if(a & 0x20) v |= 0x04;
    if(a & 0x10) v |= 0x08;
    if(a & 0x08) v |= 0x10;
    if(a & 0x04) v |= 0x20;
    if(a & 0x02) v |= 0x40;
    if(a & 0x01) v |= 0x80;
    return v;
}

void setup() {
  pixels.begin(); // This initializes the NeoPixel library.

  for(int i=0;i<NUMPIXELS;i++){
     pixels.setPixelColor(i, pixels.Color(1,1,1));
  }
  pixels.show();

  //nRF24 requires relatively slow SPI, probably would work at 2MHz too
  SPI.begin();
  SPI.setBitOrder(MSBFIRST);
  SPI.beginTransaction(SPISettings(1000000, MSBFIRST, SPI_MODE0));

  for(int x = 0; x < 8; x++) //nRF24 and uECG have different bit order for pipe address
    pipe_rx[x] = swapbits(pipe_rx[x]);

  //configure radio parameters
  rf.begin();
  rf.setDataRate(RF24_1MBPS);
  rf.setAddressWidth(4);
  rf.setChannel(22);
  rf.setRetries(0, 0);
  rf.setAutoAck(0);
  rf.disableDynamicPayloads();
  rf.setPayloadSize(32);
  rf.openReadingPipe(0, pipe_rx);
  rf.setCRCLength(RF24_CRC_DISABLED);
  rf.disableCRC();
  rf.startListening(); //listen for uECG data
  //Note that uECG should be switched into raw data mode (via long button press)
  //in order to send compatible packets, by default it sends data in BLE mode
  //which cannot be received by nRF24
}

long last_pix_upd = 0;
byte in_pack[32];
int rf_bpm = 0;
int bpm_hist[5]; //since we disabled CRC, need to filter incoming data

void loop() 
{
  if(rf.available())
  {
    rf.read(in_pack, 32);
    int bb = in_pack[5]; //BPM is located at the 5th byte of the packet
    //detailed packet structure is in uECG docs

    //since we have no CRC for compatibility reasons, we need to filter
    //incoming data, radio channel could be noisy. We compare last 5
    //received BPM values and use one only if all 5 were the same.
    //Since uECG sends about 100 packets per second, it won't cause
    //any noticeable delay in displaying data
    for(int n = 0; n < 5-1; n++) //shift bpm history array by 1
      bpm_hist[n] = bpm_hist[n+1];
    bpm_hist[4] = bb; //add new bpm value
    for(int n = 0; n < 5; n++) //check if all are equal
      if(bpm_hist[n] != bb) bb = -1;
    if(bb > 0) //if yes - store it as new received BPM
      rf_bpm = bb;
  }  
  long ms = millis();
  if(ms - last_pix_upd > 10) //don't update pixels too often
  {
    int r, g, b;
    last_pix_upd = ms;
    int bpm = rf_bpm;
    int max_bright = 160; //value of maximum brightness, max 255. But you don't always want it at max :)
    float dd = 25; //change in BPM between color tones (blue->green->yellow->pink->red)
    float t1 = 90, t2, t3, t4; //t1 - "base" BPM, lower than t1 would be blue
    t2 = t1 + dd;
    t3 = t2 + dd;
    t4 = t3 + dd;
    //code for changing color depending in which t1...t4 range we are now
    if(bpm < t1){ r = 0; g = 0; b = max_bright; }
    else if(bpm < t2) { r = 0; g = max_bright * (bpm-t1)/dd; b = max_bright - g; }
    else if(bpm < t3) { r = max_bright * (bpm-t2)/dd; g = max_bright - r; b = r/4; }
    else if(bpm < t4) { r = max_bright; g = 0; b = max_bright/2 - max_bright * (bpm-t3)/(2*dd); }
    else {r = max_bright; g = 0; b = 0; }
    int on_pixels = (bpm-80)/8; //since it's intended for running, I'm not
    //showing anything less than 80 BPM, this way it's more sensitive in
    //high load area
    for(int i=0;i<NUMPIXELS;i++)
    {
      //pixels are set from last to first for no particular reason, would
      //work just as fine if set from first to last
      if(i < on_pixels) pixels.setPixelColor(NUMPIXELS-i-1, pixels.Color(r,g,b));
      else pixels.setPixelColor(NUMPIXELS-i-1, pixels.Color(0,0,0)); //turn off all other LEDs
    }
    pixels.show();
  }
}

Credits

ProjectsDIY
6 projects • 8 followers
Electronic projects, Arduino, Raspberry Pi, NodeMCU, Sensor, IoT based projects. Tutorial and instruction for all projects. DIY projects.

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Related channels and tags
  • Adafruit
  • Fitness
  • Fitness
  • Health & Medical Devices
  • Health & Medical Devices
  • Wearables
  • Wearables