File content as of revision 11:d32f4f43161d:

#include "mbed.h"
#include <limits.h>

#ifdef __cplusplus
extern "C" {
#endif // __cplusplus

#define NEED_DEBUG 
#ifdef NEED_DEBUG
#define DEBUG(...) { printf(__VA_ARGS__); }
#else
#define DEBUG(...) /* nothing */
#endif 

#define N 10
#define DEFAULT_THRESHOLD 500
#define DEFAULT_AMP 100


volatile int BPM = 60;
volatile int IBI = 600;

volatile bool Pulse = false;
volatile bool QS = false;

volatile int Rate[N];
volatile int CurrentBeatTime = 0;
volatile int LastBeatTime = 0;

volatile uint16_t Signal;
volatile uint16_t P = DEFAULT_THRESHOLD;
volatile uint16_t T = DEFAULT_THRESHOLD;
volatile uint16_t Threshold = DEFAULT_THRESHOLD;

volatile int Amplifier = DEFAULT_AMP;

Timer timer;
AnalogIn ain(p5);

void initPulseSensor(void) {
    for (int i = 0; i < N; ++i) {
        Rate[i] = 0;
    }
    timer.start();
    LastBeatTime = timer.read_ms();
}

int getBPM(void) {
    return BPM;
}

bool isQS(void) {
    bool qs = QS;
    QS = false;
    return qs;
}


void reset() {
    Threshold = DEFAULT_THRESHOLD;
    Amplifier = DEFAULT_AMP;
    P = T = DEFAULT_THRESHOLD;
}

void calcHeartRate(void) {
    
    Signal = ain.read_u16();
    CurrentBeatTime = timer.read_ms();
    // DEBUG("%d\t%d\r\n", CurrentBeatTime, Signal);
    
    int interval = 0;
    if (CurrentBeatTime < LastBeatTime) {
        interval = INT_MAX - CurrentBeatTime + LastBeatTime;
    } else {
        interval = CurrentBeatTime - LastBeatTime;
    }
    
    if ((Signal < Threshold) && (interval > IBI * 3/5)) {
        if (Signal < T) {   // hold bottom 
            T = Signal;
            // DEBUG("T:%d\r\n", T);
        }
    } else if ((Signal > Threshold) && (Signal > P)) {
        P = Signal; // hold peak 
        // DEBUG("P:%d\r\n", P);
    }
    
    if (interval > 250 && interval < 2500) { // msec
    
        if ((Signal > Threshold) && !Pulse && (interval > IBI * 3/5)) {
            Pulse = true;
            IBI = interval;
            
            if (Rate[0] < 0) {  // first time
                Rate[0] = 0;
                LastBeatTime = timer.read_ms();
                return;
            } else if (Rate[0] == 0) { // second time
                for (int i = 0; i < N; ++i) {
                    Rate[i] = IBI;
                }
            }
            
            int running_total = 0;
            for (int i = 0; i < N-1; ++i) {
                Rate[i] = Rate[i+1];
                running_total += Rate[i];
            }
            
            Rate[N-1] = IBI;
            running_total += IBI;
            running_total /= N;
            BPM = 60000 / running_total;
            QS = true;
            LastBeatTime = timer.read_ms();
            // DEBUG("P:%d T:%d AMP:%d THR:%d BPM:%d\r\n"
            //        ,P ,T ,Amplifier ,Threshold ,BPM);
        }
    }
    
    // check if Signal is under Threshold
    // if (Pulse) {
    if ((Signal < Threshold) && Pulse) {
        Pulse = false;
        if (P >= T) {
            Amplifier = P - T;
            Threshold = Amplifier/2 + T;  // update Threshold
            P = T = Threshold;
            // DEBUG("Update Threshold:%d\r\n", Threshold);
        } else {
            // DEBUG("Error: T(%d) over P(%d)\r\n", T, P);
            reset();
        }
    }
    
    // check if no Signal is over 2.5 sec
    if (interval >= 2500) {
        DEBUG("No Signal over 2.5sec\r\n");
        reset();
        LastBeatTime = timer.read_ms();
        for (int i = 0; i < N; ++i) {
            Rate[i] = -1;
        }
    }
}

#ifdef __cplusplus
}
#endif