#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 }; // Pins connected to C1, C2, C3, C4
uint8_t rowPins[ROWS] = { 9, 8, 7, 6 }; // 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); 
 } 
}