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USB HID Keyboard Bridge Using UART -- STM32

This project implements a USB HID Keyboard emulator on an STM32 microcontroller.
Data received over UART is converted into USB keyboard keystrokes and sent to the connected PC.
It effectively works as a UART-to-Keyboard bridge, useful for automation, scripts, debugging tools, or custom input devices.

✨ Features

  • 📥 UART RX with Interrupts
    Receives characters one byte at a time using HAL_UART_RxCpltCallback.

  • ⌨️ USB HID Keyboard Output
    Sends received text to the PC as keystrokes using the HID interface (KeyBoardPrint).

  • 🔄 Line-Based Processing
    UART data is buffered until a newline (\n or \r) is received.

  • 🛡️ Robust Buffer Handling
    Prevents buffer overflow by limiting characters to a defined size.

  • 🔌 Plug-and-Play USB HID
    Works without installing drivers on Windows/Mac/Linux.

📂 Project Structure

.
├── Core/
│   ├── Src/
│   │   ├── main.c      <-- Main program logic
│   └── Inc/
├── USB_Device/
│   └── HID implementation
└── README.md

🛠️ How It Works

1. UART Reception

  • UART2 is initialized at 115200 baud.
  • Interrupt-based single-byte receive is enabled using:
HAL_UART_Receive_IT(&huart2, &uart_rx_byte, 1);
  • A line is considered complete when \n or \r is received.

2. HID Keyboard Output

Once uart_line_ready = true, the buffer content is sent to the computer:

KeyBoardPrint(uart_rx_buffer, uart_rx_index - 1);

3. Main Loop

  • Continuously checks if a full line is received.
  • Sends keystrokes and resets buffer.

🚀 Getting Started

Hardware Required

  • STM32 board with USB Device support (e.g., STM32F1/F4 series)
  • USB cable
  • UART sender (PC terminal, external module, another MCU)

Software Requirements

  • STM32CubeMX or STM32CubeIDE
  • HAL drivers for UART + USB HID
  • USB Device middleware (HID)

⚙️ Configuration Summary

UART Settings

Parameter Value

Baud Rate 115200 Word Length 8 bits Parity None Stop Bits 1 Mode RX/TX

USB

  • Class: HID Keyboard
  • Endpoint: IN
  • Polling interval: Firmware default (1ms typical)

📡 Example Usage

Send the following over UART:

Hello World\n

The PC will receive keyboard input as if typed:

Hello World

🔧 Customization

Change UART buffer size:

#define UART_RX_BUFFER_SIZE 64

Change keyboard behavior

Modify KeyBoardPrint() implementation inside USB HID source.

📜 License

This project follows the default STM32Cube license as included in ST's generated files.

🤝 Contributions

PRs, suggestions, and improvements are welcome!