#include <Keypad.h>
const byte ROWS = 4;
const byte COLS = 4;

char customKey;

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

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

Keypad customKeypad = Keypad(makeKeymap(hexaKeys), rowPins, colPins, ROWS, COLS);

void setup() {
  Serial.begin(9600);

}

void loop() {
  customKey = customKeypad.getKey();

  if (customKey) {
    Serial.println(customKey);
  }
}