nunchuck sentry gun

so i’ve finally finished the hardware portion of my coil turret. i have a coil mounted on a servo, and it’s controlled by a wii nunchuck. i have the capacitor discharging through a relay using a transistor, and that works just fine. i’ve also got my servo responding to the nunchuck (albeit a little srewy, but hey, its nintendo). my problem now is that i’m totally stuck on how to program it, and that seems like a pretty huge problem to me. i think i can manage to get most of it coded by myself, but it’ll be tricky. i’m using the following code right now.

#include <Wire.h>

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

int servoPin = 2;      // Control pin for servo motor
int pulseWidth = 0;    // Amount to pulse the servo
long lastPulse = 0;    // the time in millisecs of the last pulse
int refreshTime = 20;  // the time in millisecs needed in between pulses
int minPulse = 700;   // minimum pulse width

#define pwbuffsize 4   
int pwbuff[pwbuffsize]; // buffer for smoothing pulseWidths
int pwbuffpos = 0;      // position in pwbuff

void setup()
  Wire.begin ();            // join i2c bus with address 0x52
  nunchuck_init (); // send the initilization handshake
  pinMode(servoPin, OUTPUT);  // Set servo pin as an output pin
  pulseWidth = minPulse;      // Set the motor position to the minimum
  Serial.print ("Finished setup\n");

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

int t = 0;  // when it gets to 25, read nunchuck
void loop()
  if( t == 25 ) {
    t = 0;
    Wire.requestFrom (0x52, 6);      // request data from nunchuck
    while (Wire.available ()) {
      // receive byte as an integer
      outbuf[cnt] = nunchuk_decode_byte (Wire.receive ());
      digitalWrite (ledPin, HIGH);      // sets the LED on
    // If we recieved the 6 bytes, then go print them
    if (cnt >= 5) {
    //  printNunchuckData();            // uncomment this for debug
      // update servo pulseWidth
      float tilt = outbuf[4];            // z-axis, in this case ranges from ~75 - ~185
      tilt = (tilt - 70) * 1.5;          // convert to degrees angle, approximately
      pulseWidth = (tilt * 9) + minPulse; // convert angle to microseconds
      pwbuff[pwbuffpos] = pulseWidth;    // save for averaging
      if( ++pwbuffpos == pwbuffsize ) pwbuffpos = 0;

      pulseWidth=0;                      // reset so we can  
      for( int p=0; p<pwbuffsize; p++ )  // do the smoothing
        pulseWidth += pwbuff[p];         // sum up them all
      pulseWidth /= pwbuffsize;          // divide to get average
      // uncomment this for debug
      //Serial.print("tilt: ");   Serial.print((int)tilt);
      //Serial.print(" pulseWidth: ");  Serial.println(pulseWidth);
    cnt = 0;
    send_zero(); // send the request for next bytes
  } // if(t==)

  updateServo();   // update servo position


// called every loop().
// uses global variables servoPin, pulsewidth, lastPulse, & refreshTime
void updateServo() {
  // pulse the servo again if rhe refresh time (20 ms) have passed:
  if (millis() - lastPulse >= refreshTime) {
    digitalWrite(servoPin, HIGH);   // Turn the motor on
    delayMicroseconds(pulseWidth);  // Length of the pulse sets the motor position
    digitalWrite(servoPin, LOW);    // Turn the motor off
    lastPulse = millis();           // save the time of the last pulse

// 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
int i=0;
void printNunchuckData()
  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 (i,DEC);
  Serial.print ("\t");

  Serial.print (joy_x_axis, DEC);
  Serial.print ("\t");
  Serial.print (joy_y_axis, DEC);
  Serial.print ("\t");

  Serial.print (accel_x_axis, DEC);
  Serial.print ("\t");
  Serial.print (accel_y_axis, DEC);
  Serial.print ("\t");
  Serial.print (accel_z_axis, DEC);
  Serial.print ("\t");

  Serial.print (z_button, DEC);
  Serial.print (" ");
  Serial.print (c_button, DEC);

  Serial.print ("\r\n");

// 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;

and i’d really like how to know how to use the c and z buttons. i’m going to make “z” fire the relay and “c” turn on a laser pointer. could someone tell me how to make this work, or even post some example code?

much thanks in advance!

edit: i just realized another problem =[ when i run it from usb, it works fine. but when i run it off a 9V battery, it stalls and the servo moves all the way left and stops. is my battery the culprit?

bump can anyone offer any words of advice here?

looks to me your code is missing the servo.h library to get the servo working?

You don't need the servo libraries, but they do make things a bit simpler.

Some comments on comments:

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

This is called "stating the obvious". We can see what value (and how many) you're sending to the device at address 0x52. The comments are superfluous. What you're not telling us is what that does.

code not work

it sounds like your servo might be drawing too much power for the arduino, causing the processor to stall and have it continue to issue a command to go all the way to the stop.

How to do it (i think):

-check the voltage of your servo; i'm pretty sure most are 5V -find a way to supply this amount of voltage for your servo -now, wire the negative terminal of the battery pack (or power source of your choice) to the negative terminals of the arduino and servo -wire the positive terminal of the battery pack to the servo -now connect the signal wire (usually yellow or white, double check the documentation for your servo) from your servo to the appropriate pin on the arduino.

this should allow the servo to draw power from the secondary power source, and still take the commands form the arduino.

good luck! i'm interested in seeing if this succeeds ;)