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USB to GameCube Adapter

Build a USB/Bluetooth-to-GameCube adapter on an RP2040 board. The wiring is identical across the supported boards — only the build target and a couple of pad labels change.

Supported Boards

Board Build Target 5V Pin Label Notes
Adafruit KB2040 usb2gc_kb2040 RAW Bridge USB power pads (see Controller Input)
Raspberry Pi Pico usb2gc_kb2040 VBUS No onboard NeoPixel — controller status only via flash
Waveshare RP2040-Zero usb2gc_rp2040zero 5V NeoPixel on GPIO 16; I2C remapped to GPIO 14/15

The Pi Pico runs the same firmware as the KB2040 — same RP2040 chip, same default GPIO map.

Parts Needed

  • One of the boards above
  • GameCube controller extension cable (cut to expose the five wires inside)
  • USB-A female to USB-C male adapter (KB2040) or USB-A to micro-USB OTG adapter (Pi Pico) so USB controllers can plug into the board's host port
  • Soldering iron and solder

Wiring

GameCube Connector

The GameCube controller port uses a proprietary connector. Cut a GC extension cable and wire the console-end plug to your board.

GameCube connector pinout — female socket and male plug, pin numbers and signal labels

GC Pin Signal RP2040 GPIO Notes
1 5V RAW (KB2040) / VBUS (Pico) / 5V (RP2040-Zero) Powers the board from the console
6 3.3V GPIO 6 Console-presence sense — distinguishes "plugged into a GameCube" from "powered over USB only"
2 Data GPIO 7 Bidirectional joybus data line
3, 4 GND GND Tie both GC ground wires to the board's GND
5 (unused) — Leave disconnected

Cable wire colors vary by manufacturer — verify with a multimeter against the GameCube Pinout reference before soldering.

When no console is detected (USB-only power), the adapter boots into USB device + CDC config mode so you can plug it into a computer for setup. With the console connected and powering the 3.3V sense line, the adapter runs in play mode as a GameCube controller.

Don't power the adapter from both ends at once

The GameCube cable's 5V wire connects to the board's 5V/RAW/VBUS rail, which is the same rail as USB-C/microUSB VBUS through the board's protection diode. Plugging the adapter into a console and a computer's USB port at the same time ties two 5V supplies together — you can backfeed one into the other and stress the regulators on either side. Use the console's power for play mode, or USB power for config mode, never both.

Controller Input

The board's native USB port is the host. Plug your USB controller into it through a USB-A female adapter (USB-C for KB2040, micro-USB OTG for Pi Pico, USB-C for RP2040-Zero) — no GPIO wiring is needed for the host side. The joybus PIO program would clash with PIO-USB on RP2040, so this build deliberately uses the native USB controller for input and reserves PIO entirely for the GameCube data line.

KB2040: bridge the USB power jumper

On the KB2040, bridge the solder pads on the underside next to the USB-C port to enable full USB host power. Without the bridge, attached controllers may not get enough current to enumerate or run rumble. Pi Pico and RP2040-Zero have this routed by default and need no jumper.

For Bluetooth controllers, none of these boards have an onboard radio — plug a compatible USB BT dongle into the host port (use a USB hub if you also need a wired controller alongside).

Reference Builds

KB2040

A finished KB2040 + GC cable build — five wires from the cable land on RAW (5V), GPIO 6 (3.3V sense), GPIO 7 (data), and a pair of GND pads:

Reference KB2040 build with GameCube extension cable soldered to RAW, GPIO 6, GPIO 7, and GND pads

RP2040-Zero

Same wiring on a Waveshare RP2040-Zero — only the physical pad locations and the NeoPixel/I2C settings change, the GC pins are identical:

Reference RP2040-Zero wiring for usb2gc — GPIO 6/7 on the joybus side, RAW for 5V, GND tied together

Build and Flash

# KB2040 (also use this target on Pi Pico)
make usb2gc_kb2040
make flash-usb2gc_kb2040

# RP2040-Zero
make usb2gc_rp2040zero
make flash-usb2gc_rp2040zero

Flash by holding the BOOT button while connecting USB (or double-tap reset on boards that support it) to mount the RPI-RP2 drive, then drag-and-drop the .uf2. Output files:

  • releases/joypad_<commit>_usb2gc_kb2040.uf2
  • releases/joypad_<commit>_usb2gc_rp2040zero.uf2

Testing

  1. Connect the GC cable to a GameCube or Wii console
  2. Plug a USB controller into the board's host port (through your USB-A adapter)
  3. The NeoPixel LED should turn solid purple (1 controller connected) — Pi Pico has no NeoPixel, so skip this step
  4. Press a button on the controller — the GameCube should register input
  5. Verify analog sticks, triggers, and rumble feedback

Important Notes

  • The RP2040 runs at 130 MHz (overclocked from 125 MHz) for precise joybus timing
  • All USB inputs are merged to a single GC output (MERGE_BLEND mode)
  • Profile cycling: hold SELECT + D-pad Up/Down for 2 seconds
  • See usb2gc app docs for profiles, keyboard mode, and feature details