From KY-039 To Heart Rate

1#define samp_siz 4
2#define rise_threshold 4
3
4// Pulse Monitor  Test Script
5int sensorPin = 0;
6
7void setup() {
8    Serial.begin(9600);
9}
10
11void  loop ()
12{
13    float reads[samp_siz], sum;
14    long int now, ptr;
15    float  last, reader, start;
16    float first, second, third, before, print_value;
17    bool rising;
18    int rise_count;
19    int n;
20    long int last_beat;
21
22    for (int i = 0; i < samp_siz; i++)
23      reads[i] = 0;
24    sum = 0;
25    ptr = 0;
26
27    while(1)
28    {
29      // calculate an average of the  sensor
30      // during a 20 ms period (this will eliminate
31      // the 50  Hz noise caused by electric light
32      n = 0;
33      start = millis();
34      reader = 0.;
35      do
36      {
37        reader += analogRead (sensorPin);
38        n++;
39        now = millis();
40      }
41      while (now < start +  20);  
42      reader /= n;  // we got an average
43      
44      // Add the  newest measurement to an array
45      // and subtract the oldest measurement from  the array
46      // to maintain a sum of last measurements
47      sum -= reads[ptr];
48      sum += reader;
49      reads[ptr] = reader;
50      last = sum / samp_siz;
51      // now last holds the average of the values in the array
52
53      // check  for a rising curve (= a heart beat)
54      if (last > before)
55      {
56        rise_count++;
57        if (!rising && rise_count > rise_threshold)
58        {
59          //  Ok, we have detected a rising curve, which implies a heartbeat.
60          //  Record the time since last beat, keep track of the two previous
61          //  times (first, second, third) to get a weighed average.
62          // The rising  flag prevents us from detecting the same rise more than once.
63          rising  = true;
64          first = millis() - last_beat;
65          last_beat = millis();
66
67          // Calculate the weighed average of heartbeat rate
68          // according  to the three last beats
69          print_value = 60000. / (0.4 * first + 0.3 *  second + 0.3 * third);
70          
71          Serial.print(print_value);
72          Serial.print('\n');
73          
74          third = second;
75          second  = first;
76          
77        }
78      }
79      else
80      {
81        //  Ok, the curve is falling
82        rising = false;
83        rise_count = 0;
84      }
85      before = last;
86      
87      
88      ptr++;
89      ptr  %= samp_siz;
90
91    }
92}
93
94 
95