Arduino (any Arduino will do). Keypad (it can be 4x4 or 4x3. I have used a 4x4 keypad). Processing Software. Keypad library; Here are the links if you don't have the software. Arduino IDE, Processing.

Keypad Input: The code reads the input from a 4x4 keypad matrix.; Keyboard Emulation: Based on the pressed key, the Arduino sends corresponding keystrokes to the computer.; Keystroke Repetition: When ...