#include <Keypad.h>

const byte ROWS = 4; 
const byte COLS = 4; 

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

byte rowPins[ROWS] = {19, 18, 5, 17}; 
byte colPins[COLS] = {33, 25, 26, 27}; 

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

void setup(){
  Serial.begin(9600);
}
  
void loop(){
  byte numKeys = customKeypad.getKeys();
  
  if (numKeys){
    Serial.println(numKeys);
  }
}