#include <Keypad.h>

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

uint8_t colPins[COLS] = { 10, 9, 8, 7, 6 }; // Pins connected to C1, C2, C3, C4, C5
uint8_t rowPins[ROWS] = { 2, 3, 4, 5 };     // Pins connected to R1, R2, R3, R4

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);
  }
}