แป้นปุ่มกดแบบตัวเลข Keypad 4x4

/* Keypad Membrane 4x4 Example
Connects to 8 pins defined below.  Can be changed to any digital pins as needed.
Uses Keypad.h library
*/
#include <Keypad.h>

const byte ROWS = 4; // Define the number of rows on the keypad
const byte COLS = 4; // Define the number of columns on the keypad
char keys[ROWS][COLS] = { // Matrix defining character to return for each key
 {'1','2','3','A'},
 {'4','5','6','B'},
 {'7','8','9','C'},
 {'*','0','#','D'}
};
byte rowPins[ROWS] = {5, 4, 3, 2}; //connect to the row pins (R0-R3) of the keypad
byte colPins[COLS] = {9, 8, 7, 6}; //connect to the column pins (C0-C3) of the keypad

//initialize an instance of class
Keypad keypad = Keypad( makeKeymap(keys), rowPins, colPins, ROWS, COLS );
//===============================================================================
//  Initialization
//===============================================================================
void setup(){
 Serial.begin(9600);
}
//===============================================================================
//  Main
//===============================================================================  
void loop(){
 char key = keypad.getKey();
 
 if (key){     // If key is pressed, send it to the Serial Monitor Window
   Serial.println(key);
 }
}