File content as of revision 0:3309d940c502:

#include "mbed.h"
#include "USBKeyboard.h"
 
//LED1: NUM_LOCK, LED2: CAPS_LOCK, LED3: SCROLL_LOCK
BusOut leds(LED1, LED2, LED3);            //keyboard on/off set
DigitalIn start(PTC1);               // Configure SW2 pin as input function is start
DigitalIn stop(PTB17);               // Configure SW3 pin as input function is stop
USBKeyboard keyboard;

//user input key
#define user_button_key_1 'S'  
#define user_button_key_2 'D'  
#define user_button_key_3 'F' 
#define user_button_key_4 'E' 
#define user_button_key_5 'B' 
#define user_button_key_6 'C' 

//user input key delay time
#define user_button_delay_1 5   
#define user_button_delay_2 3
#define user_button_delay_3 4
#define user_button_delay_4 2
#define user_button_delay_5 8
#define user_button_delay_6 3    

char user_button_key[]={
    user_button_key_1,
    user_button_key_2,
    user_button_key_3,
    user_button_key_4,
    user_button_key_5,
    user_button_key_6
};

int user_button_delay[]={
    user_button_delay_1,
    user_button_delay_2,
    user_button_delay_3,
    user_button_delay_4,
    user_button_delay_5,
    user_button_delay_6
};

void user_button_content(char [],int []);

long int timer = 0;

int main() {

    while (!keyboard.configured()) {    // wait until keyboard is configured
    }
    
    while (1) {
        leds = keyboard.lockStatus();         //open keyboard 
                              
        if(start.read() == 0){                    //wait SW2 button press   
            while(stop.read() != 0){                    //wait SW3 button press
                user_button_content(user_button_key,user_button_delay);
                timer++;
                for(double i=0;i<1;i=i+0.1){                    //count 1 second time and wait SW3 button press
                    if(stop.read() == 0) break;
                    wait(0.1);
                }
            }
            timer = 0;
        }   
    }
}

void user_button_content(char key[],int delay[]){
    for(int i=0;i<strlen(key);i++){
        if((timer%delay[i]) == 0)
            keyboard._putc(key[i]);   
    }
}