Wiimote Extension Code

C Library to Make DIY Wiimote Extensions with AVR Microcontrollers

This is a library that gives an AVR microcontroller the ability to act as a Wiimote extension controller (Nunchuk, Classic Controller, Guitar Hero 3 controller, Guitar Hero World Tour guitar controller, Guitar Hero World Tour drum controller, etc). The library has two parts: the I2C slave device and Wiimote protocol handling. It can be used with AVR-GCC, and it is possible to adapt it to work with Arduino if you know how to include the files into your sketch properly.


click here to download the code

wiimoteext.c and wiimoteext.h handles the interface between the application software and the I2C bus, it also handles the encryption of the data sent to the Wiimote. The encryption look-up tables are in wm_crypto.h .

wiimoteext.c has code to make the microcontroller a register based I2C slave device. It has 256 registers in an array, these registers are written to and read by the Wiimote via the I2C bus using a fairly standard method.

Using the Library

You need to connect the Wiimote’s extension port to your microcontroller’s I2C bus. There is also one pin on the extension port that is used to detect whether or not something is connected, this should be connected to Vcc, or if you want to control this detection, connect it to an I/O pin.

The pin-out of the extension port can be found on Wiibrew.org’s page on extension controllers

Define your hardware connections in wiimote.h like so:

#define twi_port PORTC
#define twi_ddr DDRC
#define twi_scl_pin 5
#define twi_sda_pin 4
#define dev_detect_port PORTD
#define dev_detect_ddr DDRD
#define dev_detect_pin 4

This depends on the chip you use and your circuit.

Calling wm_init will start up the I2C hardware and prepare the AVR for communication with the Wiimote. wm_init has 4 parameters: device ID, initial data, calibration data, and an application function. The device ID depends on what type of controller you want to make, it’s an array of 6 bytes. The initial data is the button press data that is sampled during game play, which should be set as a default state. The calibration data is an array of 32 bytes containing calibration data for the controller, this is composed of things like maximum/minimum joystick positions and things like that, I have no more details about this. The user application will link a function in the application, and it will be called every time the Wiimote requests a sample of button press data.

If you have the device detection pin of the extension port connected to an I/O on your microcontroller, then the wm_init function will simulate a disconnection and reconnection every time it is called. This is useful if you don’t want your microcontroller to be powered by the extension port of the Wiimote.

Once wm_init has been called, button press data can be set by calling wm_newaction. The parameter is an array of 6 bytes containing the button press data. You can continuously call this function in your main application loop, when the Wiimotes samples the data, the latest data sent to wm_newaction will be read.

For various controller IDs, and information on the button press data array, visit Wiibrew.org’s page on extension controllers

Thanks to Hector Martin for the decryption and encryption method. He wrote about it here, and his example code is here

Bonus: Drum Robot

I found out how to extract the track data from a copy of Rock Band 2. The data is in MIDI format. I wrote some C# code to translate the MIDI data into instructions for a robot. Then I used an AVR chip with a heavily modified version of my drum controller code to play back those instructions. The result should make the robot play any song in Rock Band automatically (cheating!!!). It worked to an extent, but super accurate timing became an issue. I learned a lot about making a good buffer system while doing this project. The instructions are transmitted via serial port from a computer, and the AVR reports back to the computer when it’s buffer is less than 33% full to enable the instruction stream, and disables the stream when the buffer is 66% full. This way, the computer can be hit with unexpected lag and the robot will still work.

One thought on “Wiimote Extension Code

  1. Paulo

    Im thinking on make a DIY wii rockband drumset with arduino. After a search, i found your work.
    Do you have code used in this vĂ­deo demo?


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