How do I access the Wii Nunchuck using WiringPi

Question

The Wii nunchuck is an I2C accessible device and can be wired to the I2C pins of a Pi. How do I read the data from a Wii nunchuck in C using the WiringPi library?

Answer 1

WiringPi is a C language interface to the GPIO pins including I2C. It can be used to access the Wii nunchuck.

First of all, the nunchuck is an I2C device on address 0x52. It expects to be initialized with a write of the value 0x00 to register 0x40.

Following that, sending a write request (without a register) of value 0x00 causes the nunchuck to return a simply encoded sequence of data which includes:

• Joystick position (x and y)
• Orientation (x, y and z)
• Two button states (called c and z)

The encoding protocol can be found by googling "nunchuck protocol".

A sample application for reading the nunchuck is shown next:

#include <stdio.h>
#include <unistd.h>
#include <stdlib.h>
#include <wiringPi.h>
#include <wiringPiI2C.h>
#include <errno.h>

int main(void) {
    int NUNCHUCK_DEVICE = 0x52;

    printf("Testing the nunchuck through I2C\n");
    wiringPiSetup();
    int fd = wiringPiI2CSetup(NUNCHUCK_DEVICE);
    if (fd < 0) {
        printf("Error setting up I2C: %d\n", errno);
        exit(0);
    }
    wiringPiI2CWriteReg8(fd, 0x40, 0x00);
    delayMicroseconds(500);

    int bytes[6];
    int i;
    while(1) {
        wiringPiI2CWrite(fd, 0x00);
        delayMicroseconds(500);
        for (i=0; i<6; i++) {
            bytes[i] = wiringPiI2CRead(fd);
        }

        int joyX = bytes[0];
        int joyY = bytes[1];
        int accelX = (bytes[2] << 2) | ((bytes[5] & 0xc0) >> 6);
        int accelY = (bytes[3] << 2) | ((bytes[5] & 0x30) >> 4);
        int accelZ = (bytes[4] << 2) | ((bytes[5] & 0x0c) >> 2);
        int c = (bytes[5] & 0x02) >> 1;
        int z = bytes[5] & 0x01;

        printf("data: joyX=%x joyY=%x accelX=%x accelY=%x accelZ=%x c=%x z=%x\n", joyX, joyY, accelX, accelY, accelZ, c, z);
    }
    return 0;
}