NumPad Emulator

An Arduino sketch that turns a 4×4 matrix keypad into a USB numeric keypad. The Arduino appears to the computer as a standard HID keyboard — no drivers needed.

Hardware

• Arduino Leonardo, Micro, or any board with native USB (required for Keyboard.h)
• 4×4 matrix keypad

Wiring

Keypad rows  → Arduino pins 6, 7, 8, 9
Keypad cols  → Arduino pins 2, 3, 4, 5

Key Mapping

┌───┬───┬───┬───┐
│ 1 │ 2 │ 3 │ - │  ← A = KP Minus
├───┼───┼───┼───┤
│ 4 │ 5 │ 6 │ + │  ← B = KP Plus
├───┼───┼───┼───┤
│ 7 │ 8 │ 9 │ / │  ← C = KP Slash
├───┼───┼───┼───┤
│ * │ 0 │ . │ ↵ │  ← # = KP Dot, D = KP Enter
└───┴───┴───┴───┘

Dependencies

Install via Arduino Library Manager:

• Keypad by Mark Stanley, Alexander Brevig
• Keyboard (built-in, part of Arduino IDE)