Arduino Uno HID Keyboard

Unlike some other microcontrollers, the Arduino Uno does not natively support sending keystrokes over USB like an actual keyboard. However, with a bit of tinkering, it is possible to enable this feature. The Arduino Uno board features a USB-to-serial converter (ATmega16U2), which by default acts as a USB serial device. However, with a firmware update, this converter can be made to act as a USB keyboard.

To accomplish this, you can upload custom firmware onto the ATmega16U2 microcontroller. This new firmware replaces the default USB-to-serial firmware and allows the ATmega16U2 to send keystrokes and other input directly to your computer, just like a regular USB keyboard.

Important note: Flashing any firmware other than the stock one will lead to the loss of USB serial functionality and the board will no longer be programmable. So you should first upload your code to the board and then change the firmware. If you need to update or change your code later on, you will have to reflash the stock firmware and then upload the new code. Once you have uploaded the new code, you can proceed to flash the keyboard firmware again, if needed.

Getting Started

Prerequisites

Before starting, you'll need the following:

• An Arduino Uno board
• A computer running Windows, macOS, or Linux
• The Keyboard Firmware and Stock Firmware files
• The dfu-programmer tool

Installing dfu-programmer

dfu-programmer is a command-line tool for programming Atmel AVR microcontrollers.

To install it on Arch Linux run the following command:
sudo pacman -S dfu-programmer dfu-util

On other OS, you can download dfu-programmer from its GitHub repository.

Setting the Arduino Uno to DFU Mode

To flash any custom firmware onto the ATmega16U2 chip, you'll need to put the Arduino Uno into Device Firmware Update (DFU) mode. Follow the official Arduino guide to do this.

Flashing the Firmware

To flash the keyboard firmware onto the ATmega16U2 chip, follow these steps:

1. Connect the Arduino Uno board to your computer via USB and set it to DFU mode.

2. Open a terminal window and navigate to the directory where the firmware files are located.

3. Verify if the board is in DFU mode:
   sudo dfu-programmer atmega16u2 read

   If you receive a lengthy binary output, that indicates the board is in DFU mode.

4. Erase the ATmega16U2 chip by running the following command:
   sudo dfu-programmer atmega16u2 erase

5. Flash the keyboard firmware onto the ATmega16U2 chip by running the following command:
   sudo dfu-programmer atmega16u2 flash "keyboard-firmware.hex"

   Replace keyboard-firmware.hex with the actual name of the keyboard firmware file.

6. Reset the Arduino Uno by running the following command:
   sudo dfu-programmer atmega16u2 reset

   This will cause the ATmega16U2 chip to restart with the new firmware.

7. Unplug and replug the board.

   Now it should get connected to computer as a USB keyboard.

To restore the Arduino Uno to its original state and regain its full functionality, simply repeat the above steps, but flash the stock firmware file instead of the custom firmware file.