#include <Keypad.h>

const byte ROWS = 4;
const byte COLS = 4;
const byte LED_PIN = 13;

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};    

byte colPins[COLS] = {8, 9, 10, 11};  

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

void setup() {
  Serial.begin(115200);
  keypad.setDebounceTime(20);
  pinMode(LED_PIN, OUTPUT);
  digitalWrite(LED_PIN, LOW);
}

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

  if (key != NO_KEY) {
    digitalWrite(LED_PIN, HIGH);
    Serial.println(key);
    delay(20);
    digitalWrite(LED_PIN, LOW);
  }
}