Johan_Ha
Published © CC BY-NC

From KY-039 To Heart Rate

Get your heart rate, not just an IR sensor reading.

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From KY-039 To Heart Rate

Things used in this project

Story

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Schematics

Circuit

Circuit ir06dqxo0k

Code

Final version

C/C++
The program reads the heartbeat and prints the rate in the serial window.
#define samp_siz 4
#define rise_threshold 4

// Pulse Monitor Test Script
int sensorPin = 0;

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

void loop ()
{
    float reads[samp_siz], sum;
    long int now, ptr;
    float last, reader, start;
    float first, second, third, before, print_value;
    bool rising;
    int rise_count;
    int n;
    long int last_beat;

    for (int i = 0; i < samp_siz; i++)
      reads[i] = 0;
    sum = 0;
    ptr = 0;

    while(1)
    {
      // calculate an average of the sensor
      // during a 20 ms period (this will eliminate
      // the 50 Hz noise caused by electric light
      n = 0;
      start = millis();
      reader = 0.;
      do
      {
        reader += analogRead (sensorPin);
        n++;
        now = millis();
      }
      while (now < start + 20);  
      reader /= n;  // we got an average
      
      // Add the newest measurement to an array
      // and subtract the oldest measurement from the array
      // to maintain a sum of last measurements
      sum -= reads[ptr];
      sum += reader;
      reads[ptr] = reader;
      last = sum / samp_siz;
      // now last holds the average of the values in the array

      // check for a rising curve (= a heart beat)
      if (last > before)
      {
        rise_count++;
        if (!rising && rise_count > rise_threshold)
        {
          // Ok, we have detected a rising curve, which implies a heartbeat.
          // Record the time since last beat, keep track of the two previous
          // times (first, second, third) to get a weighed average.
          // The rising flag prevents us from detecting the same rise more than once.
          rising = true;
          first = millis() - last_beat;
          last_beat = millis();

          // Calculate the weighed average of heartbeat rate
          // according to the three last beats
          print_value = 60000. / (0.4 * first + 0.3 * second + 0.3 * third);
          
          Serial.print(print_value);
          Serial.print('\n');
          
          third = second;
          second = first;
          
        }
      }
      else
      {
        // Ok, the curve is falling
        rising = false;
        rise_count = 0;
      }
      before = last;
      
      
      ptr++;
      ptr %= samp_siz;

    }
}

 

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Johan_Ha

Johan_Ha

2 projects • 9 followers

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