#include <Keypad.h>
#define MAX_MESSAGE_LENGTH 64

const uint8_t ROWS = 4;
const uint8_t COLS = 4;
char keys[ROWS][COLS] = {
  { '1', '2', '3', 'A' },
  { '4', '5', '6', 'B' },
  { '7', '8', '9', 'C' },
  { 'E', '0', 'F', 'D' }
};

uint8_t colPins[COLS] = { 5, 4, 3, 2 }; // Pins connected to C1, C2, C3, C4
uint8_t rowPins[ROWS] = { 9, 8, 7, 6 }; // Pins connected to R1, R2, R3, R4

String messageString;
static char message[MAX_MESSAGE_LENGTH];
static unsigned int message_pos = 0;

Keypad keypad = Keypad(makeKeymap(keys), rowPins, colPins, ROWS, COLS);

void setup() {
  Serial.begin(9600);
  pinMode(13, INPUT_PULLUP);
  delay(10000);
  Serial.println("48");
  Serial.println("45");
  Serial.println("4C");
  Serial.println("4C");
  Serial.println("4F");
  Serial.println("20");
  Serial.println("57");
  Serial.println("4F");
  Serial.println("52");
  Serial.println("4C");
  Serial.println("44");
}

void loop() {
  char key = keypad.getKey();

  if (key != NO_KEY) {
    message[message_pos] = key;
    message_pos++;
  }
  if (digitalRead(13)==LOW){
    message[message_pos] = '\0'; 
    messageString = message;
    message_pos = 0;
    static char message[MAX_MESSAGE_LENGTH];
    Serial.println(messageString);
    delay(500);
  }
}