Reading the Nintendo nunchuck

This example demonstrates how to read a Nintendo nunchuck.

#include <TwoWire.h>

uint8_t outbuf[6];  // array to store wiring output
int cnt = 0;
int ledPin = 13;

void setup ()
{
  Serial.begin (115200);
  Serial.print ("Finished setup\n");
  Wire.begin ();     // join i2c bus with address 0x52
  nunchuck_init ();  // send the initilization handshake
}

void nunchuck_init ()
{
  Wire.beginTransmission (0x52); // transmit to device 0x52
  Wire.send (0x40);		 // sends memory address
  Wire.send (0x00);		 // sends sent a zero.  
  Wire.endTransmission ();	 // stop transmitting
}

void send_zero ()
{
  Wire.beginTransmission (0x52); // transmit to device 0x52
  Wire.send (0x00);		 // sends one byte
  Wire.endTransmission ();	 // stop transmitting
}

void loop ()
{
  Wire.requestFrom (0x52, 6);	 // request data from nunchuck
  while (Wire.available ())
  {
    outbuf[cnt] = nunchuk_decode_byte (Wire.receive ()); // receive byte as an integer
    digitalWrite (ledPin, HIGH); // sets the LED on
    cnt++;
  }

  // If we recieved the 6 bytes, then go print them
  if (cnt >= 5)
  {
    print ();
  }

  cnt = 0;
  send_zero ();  // send the request for next bytes
  delay (100);
}

// Print the input data we have recieved
// accel data is 10 bits long
// so we read 8 bits, then we have to add
// on the last 2 bits.  That is why I
// multiply them by 2 * 2
void print ()
{
  int joy_x_axis = outbuf[0];
  int joy_y_axis = outbuf[1];
  int accel_x_axis = outbuf[2] * 2 * 2; 
  int accel_y_axis = outbuf[3] * 2 * 2;
  int accel_z_axis = outbuf[4] * 2 * 2;

  int z_button = 0;
  int c_button = 0;

  // byte outbuf[5] contains bits for z and c buttons
  // it also contains the least significant bits for the accelerometer data
  // so we have to check each bit of byte outbuf[5]
  if ((outbuf[5] >> 0) & 1)
  {
    z_button = 1;
  }
  if ((outbuf[5] >> 1) & 1)
  {
    c_button = 1;
  }

  if ((outbuf[5] >> 2) & 1)
  {
    accel_x_axis += 2;
  }
  if ((outbuf[5] >> 3) & 1)
  {
    accel_x_axis += 1;
  }

  if ((outbuf[5] >> 4) & 1)
  {
    accel_y_axis += 2;
  }
  if ((outbuf[5] >> 5) & 1)
  {
    accel_y_axis += 1;
  }

  if ((outbuf[5] >> 6) & 1)
  {
    accel_z_axis += 2;
  }
  if ((outbuf[5] >> 7) & 1)
  {
    accel_z_axis += 1;
  }

  Serial.print ("joy_x ");
  Serial.print (joy_x_axis, DEC);
  Serial.print ("  ");
  Serial.print ("joy_y ");
  Serial.print (joy_y_axis, DEC);
  Serial.print ("\r\n");

  Serial.print ("accel_x ");
  Serial.print (accel_x_axis, DEC);
  Serial.print ("  ");
  Serial.print ("accel_y ");
  Serial.print (accel_y_axis, DEC);
  Serial.print ("  ");
  Serial.print ("accel_z ");
  Serial.print (accel_z_axis, DEC);
  Serial.print ("\r\n");

  Serial.print ("z_button ");
  Serial.print (z_button, DEC);
  Serial.print ("  ");
  Serial.print ("c_button ");
  Serial.print (c_button, DEC);
  Serial.print ("\r\n");

  delay(1000);
}

// Encode data to format that most wiimote drivers except
// only needed if you use one of the regular wiimote drivers
char nunchuk_decode_byte (char x)
{
  x = (x ^ 0x17) + 0x17;
  return x;
}