#include <Keypad.h>
const byte ROWS = 4;
const byte COLUMNS = 4;
char keys [ROWS] [COLUMNS] = {
  {'1','2','3','A'},
  {'4','5','6','B'},
  {'7','8','9','C'},
  {'*','0','#','D'}
};
byte rowsPins [ROWS] = {9,8,7,6};
byte columnsPin [COLUMNS] = {5,4,3,2};
Keypad teclado = Keypad(makeKeymap(keys),rowsPins,columnsPin,ROWS,COLUMNS);
char key;

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

void loop() {
  key = teclado.getKey();
  Serial.println(key);
}