Connecting a 4 X 4 Membrane Keypad to an Arduino

There are a lot of instructions and examples of how to connect a 4 x 3 membrane keypad but I couldn't find instructions on how to connect a 4 x 4 Membrane Keypad to an Arduino.

All that is needed for this Instructable is:

• An Arduino compatible board with 8 free digital pins
• A 4 x 4 Membrane Keypad

This library is available via the Arduino IDE library manager. If you are using a modern IDE (1.6.2 or above), you can simply use the menu:

Sketch->Include Library->Manage Libraries... Then search for Keypad.

Once found, click on its entry and the install button will appear.

The full instructions for the Keypad library can be found here.

In Example-->Keypad the default sketch "HelloKeypad" is set up for a 4 x 3 matrix.

Here is the modified code for the 4 x 4 Keypad:

#include <Keypad.h>

const byte ROWS = 4; //four rows
const byte COLS = 4; //four columns
char keys[ROWS][COLS] = {
  {'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 pinouts of the keypad
byte colPins[COLS] = {9, 8, 7, 6}; //connect to the column pinouts of the keypad

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

void setup(){
   Serial.begin(9600);
}
  
void loop(){
  char key = keypad.getKey();
  
  if (key){
    Serial.println(key);
  }
}

Using the diagram above as a reference the leftmost pin is pin 8 on the keypad and the rightmost is pin 1.

Pins 8, 7, 6, 5 on the keypad should be connected to digital pins 5, 4, 3, 2 on the Arduino respectively.

Pins 4, 3, 2, 1 on the keypad should be connected to digital pins 9, 8, 7, 6 on the Arduino respectively.

byte rowPins[ROWS] = {5, 4, 3, 2}; //connect to the row pinouts of the keypad
byte colPins[COLS] = {9, 8, 7, 6}; //connect to the column pinouts of the keypad

Upload the sketch to your Arduino and open the Serial Monitor.

The pressed keys should be displayed as in the window above.

In Examples-->Keypad there are several examples. All the example sketches can be made to function with the 4 x 4 matrix by changing the following lines of code:

const byte ROWS = 4; //four rows<br>const byte COLS = 4; //three columns
char keys[ROWS][COLS] = {
  {'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 pinouts of the keypad
byte colPins[COLS] = {9, 8, 7, 6}; //connect to the column pinouts of the keypad