#include <Keypad.h>
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' },
  { '*', '0', '#', 'D' }
};

uint8_t colPins [COLS] = { 5, 4, 3, 2};
uint8_t rowPins [ROWS] = { 9, 8, 7, 6};

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

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

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

  if (key != NO_KEY) {
    Serial.println(key); 
  }
}