Due to popular demand, here is the source code for my blog entry, “PC to Arduino to LED Control.”

First the Processing Source code:

// ButtonProc
// Make a button on the screen that can be clicked
// and cause an LED to turn on and off in synch on 
// the Arduino.  Used in conjunction with ButtonArd.
// 

import processing.serial.*;

Serial myPort;  // Create object from Serial class
int val;        // Data sent to the serial port


  // set ButtonValueY = 0
    int ButtonValueY = 0;
    int ButtonValueR = 0;
    int ButtonValueG = 0;
    int ButtonValueB = 0;
    
  // set clickflag = 0
    int clickflag = 0;
    
void setup() {
  size(480, 500);
  smooth();
 
 String portName = Serial.list()[0];
  myPort = new Serial(this, portName, 9600);
  
 fill(150,150,0);
  rect(100, 100, 50, 50);
  fill(150,0,0);
   rect(100,200, 50,50);
   fill(0,150,0);
  rect(100,300,50,50);
  fill(0,0,150);
  rect(100,400,50,50);

    }

void draw() {

  // IF the mouse not pressed
  // THEN clickflag = 0 and return
  
     if (mousePressed) {
       clickflag = 0;
     return;
     }

  
  //for when the mouse is pressed:
  // IF clickflag = 1 
  // THEN return
  
    if (clickflag == 1) 
    {
      return;
    }
    
   // for the first time that we read the button is pressed:
   // clickflag = 1
   
   clickflag = 1;
   

  // Yellow LED:  Is MouseX and MouseY within boundaries?  
        if ((mouseX > 100) && (mouseX < 150) && (mouseY > 100) && (mouseY < 150)) 
       {
           // Is ButtonValueY = 0?
          if (ButtonValueY == 0) {
              ButtonValueY = 1;
              fill(255,255,0);
              myPort.write('A');
              rect(100, 100, 50, 50);
          } else {  
             fill(150,150,0);
             ButtonValueY = 0;
             myPort.write('B');
             rect(100, 100, 50, 50);           
          } // end of ButtonValueY check
          
          }
         
          
  // Red LED:  Is MouseX and MouseY within boundaries?  
        if ((mouseX > 100) && (mouseX < 150) && (mouseY > 200) && (mouseY < 250)) 
       {
           // Is ButtonValueR = 0?
          if (ButtonValueR == 0) {
              ButtonValueR = 1;
              fill(255,0,0);
              myPort.write('C');
              rect(100, 200, 50, 50);
          } else {  
             fill(150,0,0);
             ButtonValueR = 0;
             myPort.write('D');
             rect(100, 200, 50, 50);           
          } // end of ButtonValueR check  
          }  
    
  // Green LED:  Is MouseX and MouseY within boundaries?  
        if ((mouseX > 100) && (mouseX < 150) && (mouseY > 300) && (mouseY < 350)) 
       {
           // Is ButtonValueG = 0?
          if (ButtonValueG == 0) {
              ButtonValueG = 1;
              fill(0,255,0);
              myPort.write('E');
              rect(100, 300, 50, 50);
          } else {  
             fill(0,150,0);
             ButtonValueG = 0;
             myPort.write('F');
             rect(100, 300, 50, 50);           
          } // end of ButtonValueG check  
          }       
     
      // Blue LED:  Is MouseX and MouseY within boundaries?  
        if ((mouseX > 100) && (mouseX < 150) && (mouseY > 400) && (mouseY < 450)) 
       {
           // Is ButtonValueB = 0?
          if (ButtonValueB == 0) {
              ButtonValueB = 1;
              fill(0,0,255);
              myPort.write('G');
              rect(100, 400, 50, 50);
          } else {  
             fill(0,0,150);
             ButtonValueB = 0;
             myPort.write('H');
             rect(100, 400, 50, 50);           
          } // end of ButtonValueG check  
          }          
          
         


 
        
  
}

And here is the Arduino source code:

int incomingByte = 0;	// for incoming serial data

void setup() {
	Serial.begin(9600);	// opens serial port, sets data rate to 9600 bps
        // initialize the digital pin as an output.
        pinMode(13, OUTPUT);
        pinMode(12, OUTPUT);
        pinMode(11, OUTPUT);
        pinMode(10,OUTPUT);
        
}

void loop() {

	// act on data only when you receive data:
	if (Serial.available() < 1) {
          return;
          }
        
	// read the incoming byte:
	incomingByte = Serial.read();

        //yellow LED   
	if (incomingByte == 65){
          digitalWrite(13, HIGH);   // set the LED on
          }               
        if (incomingByte == 66) {
          digitalWrite(13, LOW);   // set the LED off
        }  
          

        //red LED           
	if (incomingByte == 67) {
          digitalWrite(12, HIGH);   // set the LED on
          } 
              
        if (incomingByte == 68) {
          digitalWrite(12, LOW);   // set the LED off
          } 

        //green LED           
	if (incomingByte == 69) {
          digitalWrite(11, HIGH);   // set the LED on
          } 
              
        if (incomingByte == 70) {
          digitalWrite(11, LOW);   // set the LED off
          }  
          
        //blue LED           
	if (incomingByte == 71) {
          digitalWrite(10, HIGH);   // set the LED on
          } 
              
        if (incomingByte == 72) {
          digitalWrite(10, LOW);   // set the LED off
          }            

	
}

You should be able to copy and paste this into the Processing and Arduino IDEs without any trouble. I’ll try to provide support, but I apologize in advance for being distracted with other stuff at the moment.