#include <Key.h>
#include <Keypad.h>

#define PIN_BUZZER 10

const byte ROWS = 4;
const byte COLS = 4;

byte rowPins[ROWS] = {5, 4, 3, 2};
byte colPins[COLS] = {6, 7, 8, 9};

char buttons[ROWS][COLS] = {
     {'1', '2', '3', 'A'}, // 1st row
     {'4', '5', '6', 'B'}, // 2nd row
     {'7', '8', '9', 'C'}, // 3rd row
     {'*', '0', '#', 'D'} // 4th row
}; // 2D array of character type variables.

Keypad pad = Keypad(makeKeymap(buttons), rowPins, colPins, ROWS, COLS);

int tones[ROWS][COLS] = { // a frequency tone for each button
     {31, 93, 147, 208},
     {247, 311, 370, 440},
     {523, 587, 698, 880},
     {1397, 2637, 3729, 4978}
};

void setup() {
// runs initially once, when Arduino is turned on.
     Serial.begin(9600);
}


void loop () {
// runs repeatedly, while Arduino is turned on.
    
     int toneFreq = 0;
     char result = pad.getKey();

     if (result) {      // if a button is pressed

          for (byte j=0; j<ROWS; j++) {
               for (byte i=0; i<COLS; i++) {
                    if (result == buttons[j][i]) {  // if found button, get the corresponding tone
                         toneFreq = tones[j][i];
                    }

                } // end i loop
          } // end j loop

          Serial.print("Key: ");
          Serial.println(result);
          Serial.print("     Freq:     ");
          Serial.println(toneFreq);

          tone(PIN_BUZZER, toneFreq, 500); // play tone for half a second.
          delay(500);
          noTone(PIN_BUZZER);

     }
}