Keypad ESL

///////////////////////////////////////////////////////////////////////////////
// Author: RSP @KMUTNB
// Date: 23-Oct-2013
// Target Board: Arduino Uno (ATmega328P, 5V, 16MHz)
// Arduino IDE: version 1.0.5
// This sketch demonstrates how to do a keypad scan (a 4x4 keypad used)
// (without use of the Keypad library).

// uncomment this line if you use Arduino Leonardo.
//#define USE_LEONARDO

// constant values
const byte BUZZER_PIN = 13;
const byte ROWS = 4;
const byte COLS = 4;

char keys[ROWS][COLS] = {
  {'1','2','3','A'},
  {'4','5','6','B'},
  {'7','8','9','C'},
  {'*','0','#','D'}
};

byte rowPins[ROWS] = {2,3,4,5};   // connect D2,D3,D4,D5 to Rows 1-4 (the left four pins)
byte colPins[COLS] = {8,9,10,11}; // connect D8,D9,D10,D11 to Column 1-4 (the right four pins)

void setup(){
  Serial.begin( 115200 );
  for (int i=0; i < ROWS; i++) {
     pinMode( rowPins[i], OUTPUT );
  }
  for (int i=0; i < COLS; i++) {
     pinMode( colPins[i], INPUT );
     digitalWrite( colPins[i], HIGH ); // enable internal pull-up
  }
  pinMode( BUZZER_PIN, OUTPUT );
  digitalWrite( BUZZER_PIN, LOW );

#ifdef USE_LEONARDO
  delay(1000);
  Keyboard.begin();
#endif
}

char getKey( ) {
  char key_pressed = 0;
  for (int j=0; j < ROWS; j++) { // scan the j-th row (j=0,1,2,3)
    for (int i=0; i < ROWS; i++) {
      // output HIGH to all rows, except the j-th row
      digitalWrite( rowPins[i], (i==j) ? LOW : HIGH );
    }
    for (int i=0; i < COLS; i++) {
      if ( digitalRead( colPins[i] ) == LOW ) { // Button at (R,C)=(j,i) is pressed
         // wait until the button is released.
         while ( digitalRead( colPins[i] ) != HIGH ) ; // blocking
         key_pressed = keys[j][i]; // get the associated key for that button
         break;
      }
    }
    digitalWrite( rowPins[j], HIGH );
    if ( key_pressed != 0 ) {
      return key_pressed;
    }
  }
  return 0; // no key pressed
}

void loop(){
  char key = getKey();
  if ( key != 0 ) {
     digitalWrite( BUZZER_PIN, HIGH );

#ifdef USE_LEONARDO
     Keyboard.press( key );
     delayMicroseconds( 10 );
     Keyboard.releaseAll();
#endif

     Serial.println( key );
     delay(50);
     digitalWrite( BUZZER_PIN, LOW);
  }
  delay(10);
}