File content as of revision 1:8b001f936bb0:

//This program displays heart rate and time between heart beats on LCD, serial port and on a USB mass storage device.
//The program has two interrupt routines: 1.Every 1ms a counter is increased with one, 2. On every heart beat the counter is value copied.
//In the main loop the beats per minute are calculated.
//Ext.Modules: -Polar RMCM-01 heart rate module connected to pin8.
//             -2x16 LCD

#include "mbed.h"
#include "TextLCD.h"
#include "MSCFileSystem.h"
#define FSNAME "msc"
MSCFileSystem msc(FSNAME);

Timer t;                // counts the time from beginning of main loop
TextLCD lcd(p10, p12, p15, p16, p29, p30); // rs, e, d0-d3
InterruptIn beat(p8);   // beat is the name for a inteerupt on pin 8 
DigitalOut led(LED1);   // this led is toggled on every heart beat
Ticker mscnt;           // this is used to create a ms counter

//initialize
int count, CNT,displayBPMFlag ;

void ms_counter() {         //this interrupt routine starts every ms
    count++;                //the counter is increased with 1
    if (count>1999) {       //when no heart beat is detected for >2ms, then display "-" in the main loop
        CNT=count;          // copy counter value to CNT
        displayBPMFlag = 1; // set flag that the BPM can be put to LCD in the main loop
        count=0;            // reset counter value
    }
}

void flip() { //this interrupt routine starts on every heart beat
    CNT = count;        // copy counter value to CNT
    count = 0 ;         // reset counter value
    displayBPMFlag = 1; // set flag that the BPM can be put to LCD in the main loop
    led = !led;         // toggle the led on/off
}

int main() {
    t.start();                          // The ti
    int BPM;                            //initialize BPM
    lcd.cls();                          //clear the lcd display
    mscnt.attach_us(&ms_counter, 1000); // the address of the function to be attached (ms_counter) and the interval (1ms)
    beat.rise(&flip);                   // attach the address of the flip function to the rising edge
    while (1) {
        if (displayBPMFlag == 1) {  // program loops around in here
            displayBPMFlag = 0;     // clear displayBPMflag
            if (CNT>250&CNT<2000) { //when heart rate is within 30-240BPM
                BPM = 60000/CNT;            //calculate BPM
                lcd.cls();                  //clear the lcd display
                lcd.locate(0,0);            //set cursor to first character and first line
                lcd.printf("%i ms", CNT);   //display the time in ms on the lcd
                lcd.locate(0,1);            //set cursor to first character and second line
                lcd.printf("%i BPM",BPM);   //display the beats per minute on the lcd
                printf("%i\r\n",CNT);       //print time between heart beats to the serial port
                FILE *fp = fopen( "/msc/HR.txt", "a+");//Open file on USB Mass Storage device, 8.3 filesystem, open for write and append 
                if ( fp == NULL )error("Could not open file for write\n"); // error code
                fprintf(fp, "%f %i\r\n",t.read(),BPM);//write time-since-start-main-loop and BPM to file
                fclose(fp);     // close file
            } else {//when heart rate is NOT within 30-240BPM
                lcd.cls();                  //clear the lcd display
                lcd.locate(0,0);            //set cursor to first character and first line
                lcd.printf("- ms");         //display empty time in ms on the lcd
                lcd.locate(0,1);            //set cursor to first character and second line
                lcd.printf("- BPM");        //display empty beats per minute on the lcd
                printf("- \r\n", CNT);      //print the time in ms to the serial port
            }

        }

    }
    
}