This example may help you grasp the basics.
Code for Arduino:
void setup() {
Serial.begin(9600);
}
void loop() {
Serial.println(analogRead(A0));
delay(2);
}
Code for Processing:
import processing.serial.*;
Serial myPort; // The serial port
int xPos = 1; // horizontal position of the graph
void setup () {
// set the window size:
size(400, 300);
// List all the available serial ports
println(Serial.list());
// I know that the first port in the serial list on my mac
// is always my Arduino, so I open Serial.list()[0].
// Open whatever port is the one you're using.
myPort = new Serial(this, Serial.list()[0], 9600);
// don't generate a serialEvent() unless you get a newline character:
myPort.bufferUntil('\n');
// set inital background:
background(0);
}
void draw () {
// everything happens in the serialEvent()
}
void serialEvent (Serial myPort) {
// get the ASCII string:
String inString = myPort.readStringUntil('\n');
if (inString != null) {
// trim off any whitespace:
inString = trim(inString);
// convert to an int and map to the screen height:
float inByte = float(inString);
inByte = map(inByte, 0, 1023, 0, height);
// draw the line:
stroke(127,34,255);
line(xPos, height, xPos, height - inByte);
// at the edge of the screen, go back to the beginning:
if (xPos >= width) {
xPos = 0;
background(0);
}
else {
// increment the horizontal position:
xPos++;
}
}
}