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Firmware

Firmware for the USB Business Card (CH552G), built with the ch55xduino core under Arduino IDE 2.x.

Full hardware, pinout and schematics: https://wiki.netrunsecurity.com/electronics/sao/business-card/

Folders

Folder What it does
rubber-ducky/ USB HID keystroke injection (opens a URL on plug-in)
touchpad-testing/ Capacitive Touch-Key + LED demo
ctf/ USB serial CLI with hidden flags
usb-uart-bridge/ USB ↔ UART bridge for debugging IoT targets

Toolchain setup (once)

  1. Install Arduino IDE 2.x : https://www.arduino.cc/en/software
  2. File → Preferences → Additional Boards Manager URLs, add: https://raw.githubusercontent.com/DeqingSun/ch55xduino/ch55xduino/package_ch55xduino_mcs51_index.json
  3. Tools → Board → Boards Manager → search ch55xduino → install.

Board settings (Tools menu)

Board         : CH552
Clock Source  : 16 MHz (internal)
Upload method : USB
USB Settings  : USER CODE w/ 148B USB ram

⚠️ USER CODE w/ 148B USB ram is mandatory. With any other USB setting, the HID / serial headers are not found and compilation fails. This is the #1 gotcha.

Compiling

HID / serial sketches (rubber-ducky, serial-ctf) need the USB source files that ship with the ch55xduino examples:

  1. File → Examples → CH55xDuino → HidKeyboard (or the matching USB example).
  2. Replace the sketch code with the .ino from this repo.
  3. Sketch → Verify/Compile.

Opening the example first is required, a blank sketch is missing the USB header sources and will not compile.

Plain sketches (touch-led-test): no example needed. Open the .ino and Verify/Compile directly.

Flashing

  1. Hold SW2 (BOOT), plug the card in, release after ~1 s.
  2. Device enumerates as VID_4348 PID_55E0.
  3. Sketch → Upload, or flash the built binary with WCHISPTool.
  4. Unplug / replug to run.