SimPanel Button Box v1

A USB gamepad controller built with an Arduino Pro Micro, featuring 25 push buttons and 4 rotary encoders. Designed for sim racing and flight simulation, it is detected as a standard USB gamepad (HID joystick) with 33 buttons — no additional drivers required.

Supported Games

Tested and confirmed working with:

• Assetto Corsa / Assetto Corsa Competizione
• Microsoft Flight Simulator (2020 / 2024)
• Forza Horizon 4 / 5

Also compatible with any game or application that supports USB gamepad button mapping, including:

• iRacing
• Euro Truck Simulator 2 / American Truck Simulator
• Project CARS 2
• rFactor 2
• BeamNG.drive
• DCS World
• X-Plane
• And many more

Hardware Requirements

Component	Quantity	Notes
Arduino Pro Micro (ATmega32U4, 5V/16MHz)	1	Must be the ATmega32U4 variant for USB HID support
Momentary push buttons	25	Wired in a 5x5 matrix
Rotary encoders (with push button)	4	Standard quadrature encoders (e.g., KY-040)
Wires / PCB	—	For connecting the matrix and encoders
Enclosure	—	Optional, 3D printed or custom box

Pin Mapping

Button Matrix (5x5)

The 25 buttons are wired in a matrix with 5 row pins and 5 column pins:

Function	Pins
Row pins	21 (A3), 20 (A2), 19 (A1), 18 (A0), 15
Column pins	14, 16, 10, 9, 8

Rotary Encoders

Each rotary encoder uses 2 digital pins:

Encoder	Pin A	Pin B	CCW Button	CW Button
Encoder 1	0 (RX)	1 (TX)	Button 26	Button 27
Encoder 2	2 (SDA)	3 (SCL)	Button 28	Button 29
Encoder 3	4 (A6)	5	Button 30	Button 31
Encoder 4	6 (A7)	7	Button 32	Button 33

Note: Pins 0 and 1 are the hardware serial (TX/RX) pins. Using them for encoders means serial debugging via Serial.print() is not available. This is fine for normal operation.

Button Numbering (in Windows)

Button Index (code)	Windows Button #	Source
0 – 24	1 – 25	Push buttons (5x5 matrix)
25 – 26	26 – 27	Encoder 1 (CCW / CW)
27 – 28	28 – 29	Encoder 2 (CCW / CW)
29 – 30	30 – 31	Encoder 3 (CCW / CW)
31 – 32	32 – 33	Encoder 4 (CCW / CW)

Note: The Windows "Game Controllers" test dialog only displays up to 32 buttons. Button 33 still works in games — it just won't light up in the Windows test panel.

Wiring Diagram

Arduino Pro Micro
┌──────────────────────┐
│                      │
│  Pin 21 (A3) ────── Row 1    ┐
│  Pin 20 (A2) ────── Row 2    │
│  Pin 19 (A1) ────── Row 3    ├── 5x5 Button Matrix
│  Pin 18 (A0) ────── Row 4    │   (25 buttons)
│  Pin 15     ─────── Row 5    │
│                               │
│  Pin 14     ─────── Col 1    │
│  Pin 16     ─────── Col 2    │
│  Pin 10     ─────── Col 3    │
│  Pin 9      ─────── Col 4    │
│  Pin 8      ─────── Col 5    ┘
│                      │
│  Pin 0 (RX) ─────── Encoder 1A  ┐
│  Pin 1 (TX) ─────── Encoder 1B  │
│  Pin 2 (SDA) ────── Encoder 2A  ├── 4 Rotary Encoders
│  Pin 3 (SCL) ────── Encoder 2B  │   (8 virtual buttons)
│  Pin 4 (A6) ─────── Encoder 3A  │
│  Pin 5      ─────── Encoder 3B  │
│  Pin 6 (A7) ─────── Encoder 4A  │
│  Pin 7      ─────── Encoder 4B  ┘
│                      │
│  GND ────────────── Common ground for all buttons & encoders
│                      │
└──────────────────────┘

• Each button in the matrix connects one row pin to one column pin when pressed.
• Each encoder's common/ground pin connects to GND.
• Internal pull-up resistors are enabled in software — no external resistors needed.

Software Setup

Prerequisites

1. Arduino IDE (1.8.x or 2.x) — Download here
2. Board package: Arduino AVR Boards (included by default)
3. Required libraries (install via Library Manager):
   • Keypad by Mark Stanley & Alexander Brevig
   • Joystick by Matthew Heironimus

Installing Libraries

In Arduino IDE:

1. Go to Sketch > Include Library > Manage Libraries...
2. Search for Keypad and install it
3. Search for Joystick and install it

Note: The Joystick library may not appear in the Library Manager. You can install it manually:

1. Download from MHeironimus/ArduinoJoystickLibrary
2. Extract to your Arduino/libraries/ folder
3. Restart Arduino IDE

Uploading

1. Connect the Pro Micro via USB
2. In Arduino IDE, select:
   • Board: Arduino Leonardo (Pro Micro is Leonardo-compatible)
   • Port: Select the COM port that appears when you plug in the board
3. Open ButtonBox/ButtonBox.ino
4. Click Upload

Upload via Arduino CLI

arduino-cli compile --fqbn arduino:avr:leonardo ButtonBox/
arduino-cli upload --fqbn arduino:avr:leonardo --port COM10 ButtonBox/

Replace COM10 with your actual port.

Testing

Windows

1. Open Control Panel > Devices and Printers
2. Find Arduino Leonardo (it appears as a game controller)
3. Right-click > Game controller settings > Properties
4. Press buttons and turn encoders to verify they register

In-Game

1. Open your game's controller/input settings
2. The device should appear as Arduino Leonardo or Joystick
3. Map each button/encoder to your desired function

Troubleshooting

Issue	Solution
Board not detected	Try a different USB cable (some are charge-only). Ensure it's a data cable.
Wrong COM port	Unplug and replug the Pro Micro. Check Device Manager for the correct port.
Upload fails	Double-tap the reset button on the Pro Micro within 8 seconds, then upload immediately. The bootloader COM port appears briefly.
Buttons not registering	Check your wiring matches the pin mapping above. Verify solder joints.
Encoder skipping/jittery	Ensure encoder pins are connected correctly (A to pin1, B to pin2). Try adding 100nF capacitors across each encoder pin to GND.
Button 33 not visible in Windows test	This is a Windows limitation (max 32 shown). The button still works in games.

Project Structure

SimPanel-Button-Box-v1/
├── ButtonBox/
│   └── ButtonBox.ino    # Main Arduino sketch
├── LICENSE
└── README.md

License

This project is open source and available under the MIT License.

Credits

• Built for the sim racing and flight sim community
• Uses ArduinoJoystickLibrary by Matthew Heironimus
• Uses Keypad Library by Mark Stanley & Alexander Brevig