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This example is for Wiring version 1.0 build 0100+. If you have a previous version, use the examples included with your software. If you see any errors or have comments, please let us know.

Serial RGB controller by Tom Igoe
Reads a serial input string looking for three comma-separated integers with a newline at the end. Values should be between 0 and 255. The sketch uses those values to set the color of an RGB LED attached to pins 4 - 6. The circuit: Common-anode RGB LED cathodes attached to pins 4 - 6 LED anode connected to pin 13 To turn on any given channel, set the pin LOW. To turn off, set the pin HIGH. The higher the analogWrite level, the lower the brightness.

    String inString = "";    // string to hold input
    int currentColor = 0;
    int red, green, blue = 0;

    void setup()
    {
      // Initialize serial communications:
      Serial.begin(9600);
      // set LED cathode pins as outputs:
      pinMode(4, OUTPUT);
      pinMode(5, OUTPUT);
      pinMode(6, OUTPUT);
      // turn on pin 13 to power the LEDs:
      pinMode(13, OUTPUT);
      digitalWrite(13, HIGH);
    }

    void loop()
    {
      int inChar;

      // Read serial input:
      if (Serial.available() > 0)
      {
        inChar = Serial.read();
      }

      if (isDigit(inChar))
      {
        // convert the incoming byte to a char
        // and add it to the string:
        inString += (char)inChar;
      }

      // if you get a comma, convert to a number,
      // set the appropriate color, and increment
      // the color counter:
      if (inChar == ',')
      {
        // do something different for each value of currentColor:
        switch (currentColor)
        {
        case 0:    // 0 = red
          red = inString.toInt();
          // clear the string for new input:
          inString = "";
          break;
        case 1:    // 1 = green:
          green = inString.toInt();
          // clear the string for new input:
          inString = "";
          break;
        }
        currentColor++;
      }
      // if you get a newline, you know you've got
      // the last color, i.e. blue:
      if (inChar == '\n')
      {
        blue = inString.toInt();

        // set the levels of the LED.
        // subtract value from 255 because a higher
        // analogWrite level means a dimmer LED, since
        // you're raising the level on the anode:
        analogWrite(4, 255 - red);
        analogWrite(5, 255 - green);
        analogWrite(6, 255 - blue);

        // print the colors:
        Serial.print("Red: ");
        Serial.print(red);
        Serial.print(", Green: ");
        Serial.print(green);
        Serial.print(", Blue: ");
        Serial.println(blue);

        // clear the string for new input:
        inString = "";
        // reset the color counter:
        currentColor = 0;

      }

    }

    /*
    Here's a Processing sketch that will draw a color wheel and send a serial
    string with the color you click on:

    // Subtractive Color Wheel with Serial
    // Based on a Processing example by Ira Greenberg.
    // Serial output added by Tom Igoe
    //
    // The primaries are red, yellow, and blue. The secondaries are green,
    // purple, and orange. The tertiaries are  yellow-orange, red-orange,
    // red-purple, blue-purple, blue-green, and yellow-green.
    //
    // Create a shade or tint of the subtractive color wheel using
    // SHADE or TINT parameters.

    // Updated 29 November 2010.

    import processing.serial.*;

    int segs = 12;
    int steps = 6;
    float rotAdjust = TWO_PI / segs / 2;
    float radius;
    float segWidth;
    float interval = TWO_PI / segs;

    Serial myPort;

    void setup() {
      size(200, 200);
      background(127);
      smooth();
      ellipseMode(RADIUS);
      noStroke();
      // make the diameter 90% of the sketch area
      radius = min(width, height) * 0.45;
      segWidth = radius / steps;

      // swap which line is commented out to draw the other version
      // drawTintWheel();
      drawShadeWheel();
      // open the first serial port in your computer's list
      myPort = new Serial(this, Serial.list()[0], 9600);
    }

    void drawShadeWheel() {
      for (int j = 0; j < steps; j++) {
        color[] cols = {
          color(255-(255/steps)*j, 255-(255/steps)*j, 0),
          color(255-(255/steps)*j, (255/1.5)-((255/1.5)/steps)*j, 0),
          color(255-(255/steps)*j, (255/2)-((255/2)/steps)*j, 0),
          color(255-(255/steps)*j, (255/2.5)-((255/2.5)/steps)*j, 0),
          color(255-(255/steps)*j, 0, 0),
          color(255-(255/steps)*j, 0, (255/2)-((255/2)/steps)*j),
          color(255-(255/steps)*j, 0, 255-(255/steps)*j),
          color((255/2)-((255/2)/steps)*j, 0, 255-(255/steps)*j),
          color(0, 0, 255-(255/steps)*j),
          color(0, 255-(255/steps)*j, (255/2.5)-((255/2.5)/steps)*j),
          color(0, 255-(255/steps)*j, 0),
          color((255/2)-((255/2)/steps)*j, 255-(255/steps)*j, 0)
        };
        for (int i = 0; i < segs; i++) {
          fill(cols[i]);
          arc(width/2, height/2, radius, radius,
          interval*i+rotAdjust, interval*(i+1)+rotAdjust);
        }
        radius -= segWidth;
      }
    }

    void drawTintWheel() {
      for (int j = 0; j < steps; j++) {
        color[] cols = {
          color((255/steps)*j, (255/steps)*j, 0),
          color((255/steps)*j, ((255/1.5)/steps)*j, 0),
          color((255/steps)*j, ((255/2)/steps)*j, 0),
          color((255/steps)*j, ((255/2.5)/steps)*j, 0),
          color((255/steps)*j, 0, 0),
          color((255/steps)*j, 0, ((255/2)/steps)*j),
          color((255/steps)*j, 0, (255/steps)*j),
          color(((255/2)/steps)*j, 0, (255/steps)*j),
          color(0, 0, (255/steps)*j),
          color(0, (255/steps)*j, ((255/2.5)/steps)*j),
          color(0, (255/steps)*j, 0),
          color(((255/2)/steps)*j, (255/steps)*j, 0)
        };
        for (int i = 0; i < segs; i++) {
          fill(cols[i]);
          arc(width/2, height/2, radius, radius,
          interval*i+rotAdjust, interval*(i+1)+rotAdjust);
        }
        radius -= segWidth;
      }
    }

    void draw() {
      // nothing happens here
    }

    void mouseReleased() {
      // get the color of the mouse position's pixel:
      color targetColor = get(mouseX, mouseY);
      // get the component values:
      int r = int(red(targetColor));
      int g = int(green(targetColor));
      int b = int(blue(targetColor));
      // make a comma-separated string:
      String colorString = r + "," + g + "," + b + "\n";
      // send it out the serial port:
      myPort.write(colorString );
    }

    */