Serial Duplex using an Arduino

Note: you might get an error message when trying to use the Processing Serial Library for the first time. Here are instructions on what to do if this happens.

boolean firstContact = false; // Whether we've heard from the microcontroller (:sourceend:)

Then modify the serialEvent(). Until that firstContact is true, the serialEvent() will look for the "hello" message from the microcontroller. When it gets the initial message, it will send out a byte to request data. From then on, it will read in the string, parse it, and send a byte to request more data when it's done.

(:source lang=processing tabwidth=4 :)

(:source lang=arduino tabwidth=4 :) void establishContact() {

 while (Serial.available() <= 0) {
      Serial.println("hello");   // send a starting message
      delay(300);
   }
 }

(:sourceend:)

To call this, add a line at the end of the setup() method:

establishContact();

Now, modify the loop() by adding an if() statement to look for incoming serial data and read it.

(:toggle question12 init=hide show='I give up, how do I do that?' hide='Let me figure it out':)

void loop() {

  if (Serial.available() > 0) {
     // read the incoming byte:
    int inByte =Serial.read();
   // read the sensor:
   sensorValue =analogRead(analogOne);
   // print the results:
  Serial.print(sensorValue, DEC);
  Serial.print(",");

   // read the sensor:
   sensorValue =analogRead(analogTwo);
   // print the results:
  Serial.print(sensorValue, DEC);
  Serial.print(",");

   // read the sensor:
   sensorValue =digitalRead(digitalOne);
   // print the last sensor value with a println() so that
   // each set of four readings prints on a line by itself:
  Serial.println(sensorValue, DEC);

Next modify the Processing program. Add a new global variable called firstContact before the setup():

Then modify the serialEvent(). Until that firstContact is true, the serialEvent() will look for the "hello" message from the microcontroller. When it gets the initial message, it will send out a byte to request data. From then on, it will read in the string, parse it, and send a byte to request more data when it's done.

(:toggle question2 init=hide show='I give up, what is going on?' hide='Let me figure it out':)

(:toggle question2 init=hide show='I don\'t know, what is going on?' hide='Let me figure it out':)

(:source lang=arduino tabwidth=4 :)

(:source lang=arduino tabwidth=4 :)

(:source lang=arduino tabwidth=4 :)

 void setup() {
   // open serial communications at 9600 bps
   Serial.begin(9600);

 void loop() {
   // read the analog input, divide by 4:
   int analogValue = analogRead(A0) /4;

   // print in many formats:
   Serial.write(analogValue);     // Print the raw binary value analogValue
   Serial.print('\t');                  // print a tab
   Serial.print(analogValue, BIN);      // print the ASCII encoded binary analogValue
   Serial.print('\t');                  // print a tab
   Serial.print(analogValue, DEC);      // print the ASCII encoded decimal analogValue
   Serial.print('\t');                  // print a tab
   Serial.print(analogValue, HEX);      // print the ASCII encoded hexadecimal analogValue
   Serial.print('\t');                  // print a tab
   Serial.print(analogValue, OCT);      // print the ASCII encoded octal analogValue
   Serial.println();                    // print a linefeed and carriage return

(:sourceend:)

[@

@]

(:source lang=arduino tabwidth=4 :) void loop() {

    for (int thisSensor = 0; thisSensor < 3; thisSensor++) {
       int sensorValue = analogRead(thisSensor);
       Serial.print(sensorValue);
       Serial.print(",");

 } 

(:sourceend:)

(:toggle question4 init=hide show='How can you tell which value corresponds to which sensor?' hide='Let me figure it out':)

There are two ways to get your sensor values in order. You can use punctuation or you can use a call-and-response or handshaking method. Use whichever makes the most sense to you.

One way to send the data such that it can be interpreted clearly is to punctuate each set of data uniquely. Just as a sentence ends with a period, you can end your data with a carriage return and a newline. Change the for loop above so that a carriage return and newline are printed at the end of each string of three values.

(:toggle question5 init=hide show='I give up, how do I do that?' hide='Let me figure it out':)

  void loop() {
    for (int thisSensor = 0; thisSensor < 3; thisSensor++) {
       int sensorValue = analogRead(thisSensor);
       Serial.print(sensorValue, DEC);

       // if this is the last sensor value, end with a println().
       // otherwise, print a comma:
       if (thisSensor == 2) {
          Serial.println();
       } else {
          Serial.print(",");

(:sourceend:)

[@

@]

This is much better. Whenever you get a newline, you know that the next value is the first sensor.

Write a program that reads the two analog sensors on your board and the one digital switch, and prints them out in this format:

analog1, analog2, switch
analog1, analog2, switch
analog1, analog2, switch

Start by setting up a constant for the switch pin's number. Then in the setup, initialize serial communications at 9600bps, and declare the switch pin as an input.

(:toggle question6 init=hide show='I give up, how do I do that?' hide='Let me figure it out':)

 void setup() {
   // configure the serial connection:
   Serial.begin(9600);
   // configure the digital input:
   pinMode(switchPin, INPUT);
 }
 (:sourceend:)
 >><<

In the main loop, use a local variable called sensorValue to read each input. Read the two analog inputs first, and print them with a comma after each one. Then read the digital input, and print it with a carriage return and linefeed at the end.

(:toggle question7 init=hide show='I give up, how do I do that?' hide='Let me figure it out':)

 void loop() {
   // read the sensor:
   int sensorValue = analogRead(A0);
   // print the results:
   Serial.print(sensorValue);
   Serial.print(",");

   // read the sensor:
   sensorValue = analogRead(A1);
   // print the results:
   Serial.print(sensorValue);
   Serial.print(",");

   // read the sensor:
   sensorValue = digitalRead(switchPin);
   // print the last reading with a println() so that
   // each set of three readings prints on a line by itself:
   Serial.println(sensorValue);
 }

 >><<

Once you've got a data format, all you have to do is read it in the receiving program. Now write a Processing sketch that reads the data as formatted by the Arduino program above.

First, set up the beginning of your program as you did in the first serial lab, to import the serial library and make a global variable to hold an instance of it. Then in the setup(), print out a list of serial ports, and put the one you want in a string. Then instantiate the serial library in the global variable you made.

(:toggle question8 init=hide show='I give up, how do I do that?' hide='Let me figure it out':)

  String portName = Serial.list()[0];
  myPort = new Serial(this, portName, 9600);

Now your serialEvent() method only occurs when you get a newline, so you can assume that the entire string that came before the newline is in the serial buffer. Read the string, and check to see if it's null. If it isn't, print it out. This way, you'll be sure you've got a full string before you do anything with it.

(:toggle question9 init=hide show='I give up, how do I do that?' hide='Let me figure it out':)

  if (myString != null) {
    println(myString);
  }

}

The Serial.println() in Arduino attaches a newline and a carriage return. Newlines, carriage returns, spaces, and tabs are often called whitespace and there's a command that removed whitespace from a string, called trim(). Replace the println() with the following two lines. The first trims the whitespace characters off. The second splits the string into three separate strings at the commas, the converts those strings to integers:

    myString = trim(myString);

    // split the string at the commas
    // and convert the sections into integers:
    int sensors[] = int(split(myString, ','));

Next, print out those three integers using a for() loop, like so:

(:toggle question10 init=hide show='I give up, how do I do that?' hide='Let me figure it out':)

size(800, 600);

Put the following lines in the draw method. These will draw the circle using the variables you just declared:

 background(bgcolor);
  fill(fgcolor);
  // Draw the shape
  ellipse(xpos, ypos, 20, 20);

(:sourceend:)

In order to see anything happen, you need to assign the sensor values to these variables. Do this at the end of the serialEvent():

(:source lang=processing tabwidth=4 :)

If your analog values are greater than 800 or 600, the ball will be offscreen, so you may have to map your sensor range to the screen size. For example, the accelerometer sensor ranges are approximately 430 to 580. Since the screen is 0 to 800 (horizontal) and 0 to 600 (vertical), map the ranges of the sensors to fill the screeen.

(:toggle question11 init=hide show='I give up, how do I do that?' hide='Let me figure it out':)

Call and Response (Handshaking) Method

Another way to keep multiple bytes of serial data in order is to send one set of values at a time, rather than sending repeatedly. If you use this method, the receiving program has to request new data every time it finishes reading what it's got.

You can convert the punctuation method shown above to a call-and-response method fairly simply. First, modify the Arduino code. Add a new method at the end of the sketch called establishContact(). This method sends out a message on startup until it gets a byte of data from Processing. Later you'll modify the Processing sketch to look for this message and send a response:

(:source lang=arduino tabwidth=4 :)

 void establishContact() {
  while (Serial.available() <= 0) {
       Serial.println("hello");   // send a starting message
       delay(300);
   }
 }

(:sourceend:)

To call this, add a line at the end of the setup() method:

establishContact();

Now, modify the loop() by adding an if() statement to look for incoming serial data and read it:

(:source lang=arduino tabwidth=4 :)

 void loop() {
   if (Serial.available() > 0) {
     // read the incoming byte:
     int inByte = Serial.read();
   // read the sensor:
   sensorValue = analogRead(analogOne);
   // print the results:
   Serial.print(sensorValue, DEC);
   Serial.print(",");

   // read the sensor:
   sensorValue = analogRead(analogTwo);
   // print the results:
   Serial.print(sensorValue, DEC);
   Serial.print(",");

   // read the sensor:
   sensorValue = digitalRead(digitalOne);
   // print the last sensor value with a println() so that
   // each set of four readings prints on a line by itself:
   Serial.println(sensorValue, DEC);
   }
 }

(:toggle question3 init=hide show='How many bytes does Serial.println(analogValue) send when analogValue = 32?' hide='Let me figure it out':)

(Diagram made with Fritzing

• Serial.println(analogValue) results in "32" with a linefeed and carriage return

• (:source lang=processing tabwidth=4 :)Serial.println(analogValue)(:sourceend:) results in "32" with a linefeed and carriage return

• Serial.write(analogValue) results in " ", the space character, which has the ASCII value 32.

Accelerometer and switch on an Arduino

[--(Diagram made with Fritzing

To begin with, just send the value from one sensor, the first analog sensor (the first axis of the accelerometer in the photos) and divide the output to give a maximum value of 255:

(:toggle question1 init=hide show='I give up, how do I do that?' hide='Let me figure it out':)

 void setup()

   // start serial port at 9600 bps:
   Serial.begin(9600);

 void loop()

   // read analog input, divide by 4 to make the range 0-255:
   int analogValue = analogRead(A0)/4; 
   Serial.println(analogValue);          

(:sourceend:)

When you open the serial monitor, you should see a number between 0 and 255 scrolling down the window. That's because Serial.println() formats the value it prints as an ASCII-encoded DECimal value, with a linefeed at a carriage return at the end. Also, the serial monitor assumes it should show you the ASCII character corresponding to each byte it receives. Try changing the Serial.println to a Serial.write().

(:source lang=processing tabwidth=4 :)

   Serial.write(analogValue);          

(:sourceend:)

Now you get a range of garbage characters. What's going on?

(:toggle question2 init=hide show='I don't know, what is going on?' hide='Let me figure it out':)

For example, imagine that analogValue = 32:

• Serial.println(analogValue) results in "32" with a linefeed and carriage return
• Serial.write(analogValue) results in "@nbsp;", the space character, which has the ASCII value 32.

Here's the tricky part: Serial.println(analogValue, DEC) actually sent FOUR bytes! It sent a byte to represent the 3, a byte to represent the 2, a byte to tell the Monitor to move the cursor down a line(newline), and a byte to move the cursor all the way to the left (carriage return). The raw binary values of those four bytes are 51 (ASCII for "3"), 50 (ASCII for "2"), 10 (ASCII for "newline"), and 13 (ASCII for "carriage return"). Check the ASCII table and you'll see for yourself.

Send the data in many formats

Try this program and view the results in the Serial Monitor:

(:div class=code :)

(:source lang=processing tabwidth=4 :)

(:sourceend:)

(:source lang=processing tabwidth=4 :)

(:sourceend:)

(:source lang=processing tabwidth=4 :)

(:sourceend:)

(:source lang=processing tabwidth=4 :)

(:sourceend:)

(:source lang=processing tabwidth=4 :)

(:sourceend:)

(:source lang=processing tabwidth=4 :)

(:sourceend:)

(:source lang=processing tabwidth=4 :)

(:sourceend:)

(:source lang=processing tabwidth=4 :)

(:sourceend:)

(:source lang=processing tabwidth=4 :)

(:sourceend:)

(:source lang=processing tabwidth=4 :)

(:sourceend:)

(:source lang=processing tabwidth=4 :)

(:sourceend:)

(:source lang=processing tabwidth=4 :)

(:sourceend:)

(:source lang=processing tabwidth=4 :)

(:sourceend:)

(:source lang=processing tabwidth=4 :)

(:sourceend:)

(:source lang=processing tabwidth=4 :)

(:sourceend:)

(:source lang=processing tabwidth=4 :)

(:sourceend:)

(:source lang=processing tabwidth=4 :)

(:sourceend:)

(:source lang=processing tabwidth=4 :)

(:sourceend:)

(Diagram made with Fritzing - download) (:cell:)

This is just a suggestion for a short project. Apply these principles to your media controller or final project, you don't have to do this exact application.

This is a suggestion for the Stupid Pet Trick assignment. You can do any project you wish as long as it demonstrates your mastery of the lab exercises and good physical interaction. This is just one suggestion.

 }

• Serial.println(analogValue, BYTE) results in " ", the space character, which has the ASCII value 32.

Here's the tricky part: Serial.println(analogValue, DEC) actually sent FOUR bytes! It sent a byte to represent the 3, a byte to represent the 2, a byte to tell the Monitor to move the cursor down a line(newline), and a byte to move the cursor all the way to the left (carriage return). The raw binary values of those four bytes are 51 (ASCII for "3"), 50 (ASCII for "2"), 10 (ASCII for "newline"), and 13 (ASCII for "carriage return"). Check the ASCII table and you'll see for yourself.

(:div class=code :)

 int analogPin = 0;
 int analogValue = 0;                // integer to print

 void setup() {
   // open serial communications at 9600 bps
   Serial.begin(9600);
 }

 void loop() {
   // read the analog input, divide by 4:
   analogValue = analogRead(analogPin) /4;

   // print in many formats:
   Serial.print(analogValue, BYTE);     // Print the raw binary value analogValue
   Serial.print('\t');                  // print a tab
   Serial.print(analogValue, BIN);      // print the ASCII encoded binary analogValue
   Serial.print('\t');                  // print a tab
   Serial.print(analogValue, DEC);      // print the ASCII encoded decimal analogValue
   Serial.print('\t');                  // print a tab
   Serial.print(analogValue, HEX);      // print the ASCII encoded hexadecimal analogValue
   Serial.print('\t');                  // print a tab
   Serial.print(analogValue, OCT);      // print the ASCII encoded octal analogValue
   Serial.println();                    // print a linefeed and carriage return

   delay(10);
 }

(:divend:)

You should get output like this:

(:div class=code :)

 void loop() {
    for (int thisSensor = 0; thisSensor < 3; thisSensor++) {
       int sensorValue = analogRead(thisSensor);
       Serial.print(sensorValue, DEC);
       Serial.print(",");
    }
 }

(:divend:)

(:div class=code :)

 void loop() {
    for (int thisSensor = 0; thisSensor < 3; thisSensor++) {
       int sensorValue = analogRead(thisSensor);
       Serial.print(sensorValue, DEC);

       // if this is the last sensor value, end the line.
       // otherwise, print a comma:
       if (thisSensor == 2) {
          Serial.println();
       } else {
          Serial.print(",");
       }
    }
 }

(:divend:)

From this loop, you'd get output like this:

452,345,416 234,534,417 325,452,231

(:div class=code :)

 /*
   Sensor Reader
  Language: Wiring/Arduino
  
  Reads two analog inputs and one digital input
  and outputs their values.
  Connections:  
  analog sensors on analog input pins 0 and 1
  switch on digital I/O pin 2
 */

 int analogOne = 0;       // analog input 
 int analogTwo = 1;       // analog input 
 int digitalOne = 2;      // digital input 

 int sensorValue = 0;     // reading from the sensor

 void setup() {
   // configure the serial connection:
   Serial.begin(9600);
   // configure the digital input:
   pinMode(digitalOne, INPUT);
 }

 void loop() {
   // read the sensor:
   sensorValue = analogRead(analogOne);
   // print the results:
   Serial.print(sensorValue, DEC);
   Serial.print(",");

   // read the sensor:
   sensorValue = analogRead(analogTwo);
   // print the results:
   Serial.print(sensorValue, DEC);
   Serial.print(",");

   // read the sensor:
   sensorValue = digitalRead(digitalOne);
   // print the last sensor value with a println() so that
   // each set of four readings prints on a line by itself:
   Serial.println(sensorValue, DEC);
 }

(:divend:)

Once you've got a data format, all you have to do is read it in the receiving program. Here's a Processing sketch that reads the data as formatted by the Arduino program above. First, set up the beginning of your program as you did in the first serial lab:

[@

import processing.serial.*; // import the Processing serial library Serial myPort; // The serial port

  // 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 module, so I open Serial.list()[0].
  // Change the 0 to the appropriate number of the serial port
  // that your microcontroller is attached to.
  myPort = new Serial(this, Serial.list()[0], 9600);

Add one extra line at the end of the setup() method. This line tells the sketch not to call serialEvent() unless an ASCII newline byte (value 10) comes in the serial port. It will save any other bytes it gets in the serial buffer, so you can read them all at once when the newline arrives:

// read bytes into a buffer until you get a linefeed (ASCII 10):

  myPort.bufferUntil('\n');

The draw() method doesn't do anything, just like the first serial lab:

void draw() {

  // twiddle your thumbs

}

The serialEvent() method is a bit different. Since it only occurs when you get a newline, you can assume that the entire string that came before the newline is in the serial buffer. So you start out by reading that string:

void serialEvent(Serial myPort) {

  // read the serial buffer:
  String myString = myPort.readStringUntil('\n');
  println(myString);

If you run this, you'll see the serial data print out just like it did in the arduino serial monitor. You'll also see a lot of null values. To clear those out, add an if statement around the println():

if (myString != null) {

   println(myString);

}

That makes sure you've got a full string before you do anything with it.

The Serial.println() in Arduino attaches a newline and a carriage return. Newlines, carriage returns, spaces, and tabs are often called whitespace and there's a command that removed whitespace from a string, called trim(). Replace the println() with the following two lines. The first trims the whitespace characters off. The second splits the string into three separate strings at the commas, the converts those strings to integers:

    myString = trim(myString);

    // split the string at the commas
    // and convert the sections into integers:
    int sensors[] = int(split(myString, ','));

Next, print out those three integers using a for() loop, like so:

(:div class=code :)

 void establishContact() {
  while (Serial.available() <= 0) {
       Serial.println("hello");   // send a starting message
       delay(300);
   }
 }C

(:divend:)

(:div class=code :)

 void loop() {
   if (Serial.available() > 0) {
     // read the incoming byte:
     int inByte = Serial.read();
   // read the sensor:
   sensorValue = analogRead(analogOne);
   // print the results:
   Serial.print(sensorValue, DEC);
   Serial.print(",");

   // read the sensor:
   sensorValue = analogRead(analogTwo);
   // print the results:
   Serial.print(sensorValue, DEC);
   Serial.print(",");

   // read the sensor:
   sensorValue = digitalRead(digitalOne);
   // print the last sensor value with a println() so that
   // each set of four readings prints on a line by itself:
   Serial.println(sensorValue, DEC);
   }
 }

(:divend:)

The rest of the Arduino sketch remains the same. When you run this and open the serial monitor, you'll see:

hello hello hello hello

Type any character in the output box and click Send. You'll get a string of sensor values at the end of your hellos:

510,497,0

• Serial.println(analogValue, DEC) results in "32"

• Serial.println(analogValue, DEC) results in "32"
• Serial.println(analogValue, BYTE) results in " ", the space character, which has the ASCII value 32.

(:div class=code :)

 int analogPin = 0;
 int analogValue = 0;            // outgoing ADC value

 void setup()
 {
   // start serial port at 9600 bps:
   Serial.begin(9600);
 }

 void loop()
 {
   // read analog input, divide by 4 to make the range 0-255:
   analogValue = analogRead(analogPin); 
   Serial.println(analogValue, DEC);
   // pause for 10 milliseconds:
   delay(10);                 
 }

(:divend:)

When you open the serial monitor, you should see a number between 0 and 1023 scrolling down the debugger pane. That's because the DEC modifier to Serial.println() formats the value it prints as an ASCII-encoded DECimal value. Also, the serial monitor assumes it should show you the ASCII character corresponding to each byte it receives. Try changing the Serial.println like so:

(:div class=code :)

 Serial.println(analogValue, BYTE);

(:divend:)

Now you get a range of garbage characters. What's going on? The BYTE modifier doesn't format the bytes. It sends out the raw binary value of the byte. The Serial Monitor receives that binary value and assumes it should show you the ASCII character corresponding to that value again. The garbage characters are characters corresponding to the ASCII values the Monitor is receiving.

• @@Serial.println(analogValue, DEC) results in "32"
• @@Serial.println(analogValue, BYTE) results in " ", the space character, which has the ASCII value 32.

Here's the tricky part: Serial.println(analogValue, DEC) actually sent FOUR bytes! It sent a byte to represent the 3, a byte to represent the 2, a byte to tell the Monitor to move the cursor down a line(newline), and a byte to move the cursor all the way to the left (carriage return). The raw binary values of those four bytes are 51 (ASCII for "3"), 50 (ASCII for "2"), 10 (ASCII for "newline"), and 13 (ASCII for "carriage return"). Check the ASCII table and you'll see for yourself.

Send the data in many formats

Try this program and view the results in the Serial Monitor:

int analogValue = 0; // integer to print

void setup() {

  // open serial communications at 9600 bps

void loop() {

  // read the analog input, divide by 4:
  analogValue = analogRead(analogPin) /4;

  // print in many formats:
  Serial.print(analogValue, BYTE);     // Print the raw binary value analogValue
  Serial.print('\t');                  // print a tab
  Serial.print(analogValue, BIN);      // print the ASCII encoded binary analogValue
  Serial.print('\t');                  // print a tab
  Serial.print(analogValue, DEC);      // print the ASCII encoded decimal analogValue
  Serial.print('\t');                  // print a tab
  Serial.print(analogValue, HEX);      // print the ASCII encoded hexadecimal analogValue
  Serial.print('\t');                  // print a tab
  Serial.print(analogValue, OCT);      // print the ASCII encoded octal analogValue
  Serial.println();                    // print a linefeed and carriage return

  delay(10);

You should get output like this:

â 11100010 226 E2 342 á 11100001 225 E1 341 á 11100001 225 E1 341 á 11100001 225 E1 341 à 11100000 224 E0 340 à 11100000 224 E0 340 ß 11011111 223 DF 337 ß 11011111 223 DF 337 ß 11011111 223 DF 337 @]

It's printing the raw binary value, then the ASCII-encoded binary value, then the ASCII-encoded decimal, hexadecimal, and octal values. You may never need all of these differnt formats, but you'll likely need at least the decimal and the raw binary versions at some point.

Send the values for all three sensors

In the first serial lab, you sent one byte representing one sensor's value, over and over. When you're sending multiple sensor values, it gets a little more complicated. You need to a way to know which value represents which sensor. For example, imagine if you used the following loop to send your sensor values:

[@

   for (int thisSensor = 0; thisSensor < 3; thisSensor++) {
      int sensorValue = analogRead(thisSensor);
      Serial.print(sensorValue, DEC);
      Serial.print(",");
   }

you'd get a string like this:

452,345,416,234,534,417,325,452,231

You don't know which sensor is which. You could assume that if you start listening when the microcontroller starts sending that the first reading corresponds to the first sensor, but you can't know that for sure. There are two ways to address this. You can use punctuation or you can use a call-and-response or handshaking method. Use whichever makes the most sense to you.

Punctuation Method

One way to send the data such that it can be interpreted clearly is to punctuate each set of data uniquely. Just as a sentence ends with a period, you can end your data with a carriage return and a newline. Here's a modification of the code above that does that:

      // if this is the last sensor value, end the line.
      // otherwise, print a comma:
      if (thisSensor == 2) {
         Serial.println();
      } else {
         Serial.print(",");
      }

From this loop, you'd get output like this:

452,345,416 234,534,417 325,452,231

This is much better. Whenever you get a newline, you know that the next value is the first sensor. Here's a program that reads the two analog sensors on your board and the one digital switch, and prints them out in this format:

Overview

(:title Serial Duplex using an Arduino:)

(:toc Table of Contents:)

Parts

(or two other analog sensors)-]

You just duplicated the basic functionality of a mouse; that is, a device with two analog sensors that affect X and Y, and a digital sensor (mouse button). What applications can you think of that could use a better physical interface for a mouse? A video editor that scrubs forward and back when you tilt a wand? An action game that reacts to how hard you hit a punching bag? An instructional presentation that speeds up if you shift in your chair too much? A music program driven by a custom musical instrument that you design?

Create a prototype in Arduino and Processing, or whatever programming environment you choose. Come up with a physical interface that makes it clear what actions map to what movements and actions. Figure out which actions can and should be possible at the same time. Present a working software and hardware model of your idea.

Then modify the serialEvent() as follows:

    myString = trim(myString);

That makes sure you've got a full string before you do anything with it.

The Serial.println() in Arduino attaches a newline and a carriage return. Newlines, carriage returns, spaces, and tabs are often called whitespace and there's a command that removed whitespace from a string, called trim(). Replace the println() with the following two lines. The first trims the whitespace characters off. The second splits the string into three separate strings at the commas, the converts those strings to integers:

Once you've got a data format, all you have to do is read it in the receiving program. Here's a Processing sketch that reads the data as formatted by the Arduino program above. First, set up the beginning of your program as you did in the first serial lab:

http://itp.nyu.edu/physcomp/images/labs/accelerometer.jpg | accelerometer (or two other analog sensors

Advantages of Raw Binary vs. ASCII

All the examples shown here sent the sensor values as ASCII-encoded strings. As mentioned above, that means you sent three bytes to send a three-digit value. If that same value was less than 255, you could send it in one raw binary byte. So ASCII is definitely less efficient. However, it's more readable for debugging purposes, and if the receiving program is well-suited to convert strings to numbers, then ASCII is a good way to go. If the receiver's not so good at converting strings to numbers (for example, it's more challenging to read a multiple byte string in Arduino than in Processing) then you may want to send your data as binary values.

The punctuation method for sending multiple serial values may seem simpler, but it has its limitations. You can't easily use it to send binary values, because you need to have a byte with a unique value for the punctuation. In the example above, you're using the value 10 (ASCII newline) as punctuation, so if you were sending your sensor values as raw bytes, you'd be in trouble when the sensor's value is 10. The receiver would interpret the 10 as punctuation, not as a sensor value. In contrast, call-and-response can be used whether you're sending data as raw binary values or as ASCII-encoded values.

Sometimes the receiver reads serial data slower than the sender sends it. For example, if you have a program that does a lot of graphic work, it may only read serial data every few milliseconds. The serial buffer will get full in that case, you'll notice a lag in response time. This is when it's good to switch to a call-and-response method.

Next modify the Processing program. You'll add a new global variable called firstContact. Until that variable is true, the serialEvent() will look for the "hello" message from the microcontroller. When it gets the initial message, it will send out a byte to request data. From then on, it will read in the string, parse it, and send a byte to request more data when it's done.

Add the following global variable before the setup():

boolean firstContact = false; // Whether we've heard from the microcontroller

Then modify the @@serialEvent() as follows:

void serialEvent(Serial myPort) {

  // read the serial buffer:
  String myString = myPort.readStringUntil('\n');
  // if you got any bytes other than the linefeed:
  if (myString != null) {

    myString = trim(myString);

    // if you haven't heard from the microncontroller yet, listen:
    if (firstContact == false) {
      if (myString.equals("hello")) { 
        myPort.clear();          // clear the serial port buffer
        firstContact = true;     // you've had first contact from the microcontroller
        myPort.write('A');       // ask for more
      } 

    // if you have heard from the microcontroller, proceed:
    else {
      // split the string at the commas
      // and convert the sections into integers:
      int sensors[] = int(split(myString, ','));

      // print out the values you got:
      for (int sensorNum = 0; sensorNum < sensors.length; sensorNum++) {
        print("Sensor " + sensorNum + ": " + sensors[sensorNum] + "\t"); 
      }
      // add a linefeed after all the sensor values are printed:
      println();
      if (sensors.length > 1) {
        xpos = map(sensors[0], 430,580,0,width);
        ypos = map(sensors[1], 430,580,0,height);
        fgcolor = sensors[2] * 255;
      }

    // when you've parsed the data you have, ask for more:
    myPort.write("A");

Once you've got the serial port open in your terminal program, type any character. You should get three bytes back, representing the three bytes sent out by the microcontroller. They won't be readable as numbers, though. If you want to see them as numbers, change BYTE above to DEC in each print statement.

What's happening here is that the computer is calling for a set of sensor readings by sending out a byte. The Arduino doesn't do anything unless it's received a byte (if (Serial.available() > 0)). When it gets a byte, it reads all three sensors and sends them. This method of communication between computers is called a call-and-response method, or handshaking. It's a good way to make sure you get only the data you need, and no more. In the next step, you'll write a Processing program to read those bytes.

  if (Serial.available() > 0) {

    int inByte = Serial.read();

  }

The rest of the Arduino sketch remains the same. When you run this and open the serial monitor, you'll see:

hello
hello
hello
hello

Type any character in the output box and click Send. You'll get a string of sensor values at the end of your hellos:

510,497,0

Type another character and click Send. It doesn't matter what character you send, but the loop will always wait for an incoming byte before sending a new set of sensor values.

Next, modify the Processing

This program will send a single character, "A", then it'll do nothing, because it's then waiting for data to arrive in the serial port before it sends. To make this work, you'll need to type characters back to the Arduino in the serial monitor. For every character you type, it'll send you three sensor readings.

Once you've got a data format, all you have to do is read it in the receiving program. Here's a Processing sketch that reads the data as formatted by the Arduino program above. First, set things up as you did in the first serial lab:

Another way to keep multiple bytes of serial data in order is to send one set of values at a time, rather than sending repeatedly. If you use this method, the receiving program has to request new data every time it finishes reading what it's got.

You can convert the punctuation method shown above to a call-and-response method fairly simply. First, modify the Arduino code. Add a new method at the end of the sketch called establishContact(). This method sends out a message on startup until it gets a byte of data from Processing. Later you'll modify the Processing sketch to look for this message and send a response:

void establishContact() {

 while (Serial.available() <= 0) {
      Serial.println("hello");   // send a starting message
      delay(300);
  }

To call this, add a line at the end of the setup() method:

establishContact();

Now, modify the loop() by adding an if() statement to look for incoming serial data and read it:

void loop() {

  '''if (Serial.available() > 0) {
    // read the incoming byte:
    int inByte = Serial.read();'''
  // read the sensor:
  sensorValue = analogRead(analogOne);
  // print the results:
  Serial.print(sensorValue, DEC);
  Serial.print(",");

  // read the sensor:
  sensorValue = analogRead(analogTwo);
  // print the results:
  Serial.print(sensorValue, DEC);
  Serial.print(",");

  // read the sensor:
  sensorValue = digitalRead(digitalOne);
  // print the last sensor value with a println() so that
  // each set of four readings prints on a line by itself:
  Serial.println(sensorValue, DEC);
  }

This program will send a single character, "A", then it'll do nothing, because it's then waiting for data to arrive in the serial port before it sends. To make this work, you'll needto type characters back to the Arduino in the serial monitor. For every character you type, it'll send you three sensor readings.

You can use other programs besides serial monitor to see the serial communication, as described below:

Windows: Hyperterminal can be found in the Start Menu, under All Programs, Accessories, Communications, Hyperterminal. To configure Hyperterminal for serial communication, open the program and click on the File, Properties menu item. Choose the serial port you want to open from the popup menu in the Configuration tab. Click on Configure to bring up the Port Settings tab. Set the properties as needed for the device you’re talking to. For many of the projects that follow, you’ll set the port settings to 9600 bits per second, 8 data bits, no parity, one stop bit, and no hardware flow control. Once you’ve applied those settings, click the Call button on the toolbar to open the serial port. Any bytes you type in the window will be sent out the serial port you opened. They won't show up on the screen, however. Any bytes received in the serial port will be displayed in the window. Click the Disconnect button to close the serial port.

OSX: To configure Terminal for serial communication in OSX, open the program and type ls /dev/tty.* This will give you a list of available serial ports. The names of the serial port in OSX are more unique than the names that Windows uses. Pick your serial port and type screen portname datarate. For example, to open the serial pot on an Arduino board at 9600 bits per second, you might type screen /dev/tty.usbserial-5B1 9600. The screen will cleared, and any bytes you type will be sent out the serial port you opened. They won't show up on the screen, however. Any bytes received in the serial port will be displayed in the window. To close the serial port, type control-A followed by control-\.

NOTE: only one program can control a serial port at a time. When you're not using a given program, remember to close the serial port. You won't be able to re-program the Arduino module if you don't, because the serial terminal program will have control of the serial port.

Once you've got the serial port open in your terminal program, type any character. You should get three bytes back, representing the three bytes sent out by the microcontroller. They won't be readable as numbers, though. If you want to see them as numbers, change BYTE above to DEC in each print statement.

What's happening here is that the computer is calling for a set of sensor readings by sending out a byte. The Arduino doesn't do anything unless it's received a byte (if (Serial.available() > 0)). When it gets a byte, it reads all three sensors and sends them. This method of communication between computers is called a call-and-response method, or handshaking. It's a good way to make sure you get only the data you need, and no more. In the next step, you'll write a Processing program to read those bytes.

Write a program to read those bytes

For this step, you'll need a programming environment that runs on the personal computer itslf, not on the microcontroller. Any environment that can open and close a serial port will do. For example, Java, Processing, Director, RealBASIC, Visual BASIC, and Max/MSP can all access the serial ports. JavaScript and Flash/Actionscript cannot, as of this writing.

The example below is in Processing. It listens for incoming serial bytes. IF it hasn't gotten any bytes, it looks for "A", which is the first thing that the Arduino sends. If it's gotten an A, it reads bytes until it gets three of them. Then it sets the foreground color, x position, and y position of a ball on the screen using those values. When there's no incoming bytes available, it sends a byte out to call for more bytes. Read through it line by line, including comments, for the details. Then run it with your Arduino module attached to the serial port it's listening to.

import processing.serial.*;

int bgcolor;			     // Background color
int fgcolor;			     // Fill color
Serial port;                         // The serial port
int[] serialInArray = new int[3];    // Where we'll put what we receive
int serialCount = 0;                 // A count of how many bytes we receive
int xpos, ypos;		             // Starting position of the ball
boolean firstContact = false;        // Whether we've heard from the microcontroller

void setup() {
  size(256, 256);  // Stage size
  noStroke();      // No border on the next thing drawn

  // Set the starting position of the ball (middle of the stage)
  xpos = width/2;
  ypos = height/2;

  // Print a list of the serial ports, for debugging purposes:
  println(Serial.list());

  // I know that the first port in the serial list on my mac
  // is always my  Keyspan adaptor, so I open Serial.list()[0].
  // On Windows machines, this generally opens COM1.
  // Open whatever port is the one you're using.
  port = new Serial(this, Serial.list()[0], 9600);
}

void draw() {
  background(bgcolor);
  fill(fgcolor);
  // Draw the shape
  ellipse(xpos, ypos, 20, 20);
}

void serialEvent(Serial port) {
  // read a byte from the serial port:
  int inByte = port.read();
  // if this is the first byte received, 
  // take note of that fact. Otherwise, add it to the array:
  if (firstContact == false) {
    if (inByte == 'A') { 
      port.clear();          // clear the serial port buffer
      firstContact = true;
      port.write('A');
    } 
  } 
  else {
    // Add the latest byte from the serial port to array:
    serialInArray[serialCount] = inByte;
    serialCount++;

    // If we have 3 bytes:
    if (serialCount > 2 ) {
      xpos = serialInArray[0];
      ypos = serialInArray[1];
      fgcolor = serialInArray[2];

      // print the values (for debugging purposes only):
      println(xpos + "\t" + ypos + "\t" + fgcolor);

      // Send a capital A to request new sensor readings:
      port.write('A');
      // Reset serialCount:
      serialCount = 0;
    }
  }
}

Advantages of Punctuation or Call-and-Response

452,345,416,234,534,417,325,452,231

Once you've got a data format, all you have to do is read it in the receiving program. Here's a Processing sketch that reads the data as formatted by the Arduino program above. First things up as you did in the first serial lab:

You don't know which sensor is which. You could assume that if you start listening when the microcontroller starts sending that the first reading corresponds to the first sensor, but you can't know that for sure. There are two ways to address this. You can use punctuation or you can use a call-and-response or handshaking method. Use whichever makes the most sense to you.

If your analog values are greater than 640 or 480, the ball will be offscreen, so you may have to map your sensor range to the screen size. For example, the accelerometer sensor ranges are approximately 430 to 580. Since the screen is 0 to 640 (horizontal) and o tp 480 (vertical), you'd map the ranges like this:

Here's the Processing sketch in its entirety:

/*

 Serial String Reader
 Language: Processing

 Reads in a string of characters from a serial port until 
 it gets a linefeed (ASCII 10).  Then splits the string into 
 sections separated by commas. Then converts the sections to ints, 
 and prints them out.

 created 2 Jun 2005
 modified 6 Aug 2008
 by Tom Igoe
 */

import processing.serial.*; // import the Processing serial library Serial myPort; // The serial port

float bgcolor; // Background color float fgcolor; // Fill color float xpos, ypos; // Starting position of the ball

void setup() {

  size(640,480);

  // 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 module, so I open Serial.list()[0].
  // Change the 0 to the appropriate number of the serial port
  // that your microcontroller is attached to.
  myPort = new Serial(this, Serial.list()[0], 9600);

  // read bytes into a buffer until you get a linefeed (ASCII 10):
  myPort.bufferUntil('\n');

void draw() {

  background(bgcolor);
  fill(fgcolor);
  // Draw the shape
  ellipse(xpos, ypos, 20, 20);

// serialEvent method is run automatically by the Processing applet // whenever the buffer reaches the byte value set in the bufferUntil() // method in the setup():

void serialEvent(Serial myPort) {

  // read the serial buffer:
  String myString = myPort.readStringUntil('\n');
  // if you got any bytes other than the linefeed:
  if (myString != null) {

    myString = trim(myString);

    // split the string at the commas
    // and convert the sections into integers:
    int sensors[] = int(split(myString, ','));

    // print out the values you got:
    for (int sensorNum = 0; sensorNum < sensors.length; sensorNum++) {
      print("Sensor " + sensorNum + ": " + sensors[sensorNum] + "\t"); 
    }
    // add a linefeed after all the sensor values are printed:
    println();
    if (sensors.length > 1) {
      xpos = map(sensors[0], 430,580,0,width);
      ypos = map(sensors[1], 430,580,0,height);
      fgcolor = sensors[2] * 255;
    }

Call and Response (Handshaking) Method

Now send the values for all three sensors as binary values, like so:

int firstSensor = 0; // first analog sensor int secondSensor = 0; // second analog sensor int thirdSensor = 0; // digital sensor int inByte = 0; // incoming serial byte

void setup() {

  // start serial port at 9600 bps:
  Serial.begin(9600);
  pinMode(2, INPUT);   // digital sensor is on digital pin 2
  establishContact();  // send a byte to establish contact until Processing responds 

void loop() {

  // if we get a valid byte, read analog ins:
  if (Serial.available() > 0) {
    // get incoming byte:
    inByte = Serial.read();
    // read first analog input, divide by 4 to make the range 0-255:
    firstSensor = analogRead(0)/4;
    // delay 10ms to let the ADC recover:
    delay(10);
    // read second analog input, divide by 4 to make the range 0-255:
    secondSensor = analogRead(1)/4;
    // read  switch, multiply by 255
    // so that you're sending 100 or 255:
    thirdSensor = 100 + (155 * digitalRead(2));
    // send sensor values:
    Serial.print(firstSensor, BYTE);
    Serial.print(secondSensor, BYTE);
    Serial.print(thirdSensor, BYTE);               
  }

void establishContact() {

 while (Serial.available() <= 0) {
      Serial.print('A', BYTE);   // send a capital A
      delay(300);

This program will send a single character, "A", then it'll do nothing, because it's then waiting for data to arrive in the serial port before it sends. To make this work, you'll needto type characters back to the Arduino in the serial monitor. For every character you type, it'll send you three sensor readings.

You can use other programs besides serial monitor to see the serial communication, as described below:

Windows: Hyperterminal can be found in the Start Menu, under All Programs, Accessories, Communications, Hyperterminal. To configure Hyperterminal for serial communication, open the program and click on the File, Properties menu item. Choose the serial port you want to open from the popup menu in the Configuration tab. Click on Configure to bring up the Port Settings tab. Set the properties as needed for the device you’re talking to. For many of the projects that follow, you’ll set the port settings to 9600 bits per second, 8 data bits, no parity, one stop bit, and no hardware flow control. Once you’ve applied those settings, click the Call button on the toolbar to open the serial port. Any bytes you type in the window will be sent out the serial port you opened. They won't show up on the screen, however. Any bytes received in the serial port will be displayed in the window. Click the Disconnect button to close the serial port.

OSX: To configure Terminal for serial communication in OSX, open the program and type ls /dev/tty.* This will give you a list of available serial ports. The names of the serial port in OSX are more unique than the names that Windows uses. Pick your serial port and type screen portname datarate. For example, to open the serial pot on an Arduino board at 9600 bits per second, you might type screen /dev/tty.usbserial-5B1 9600. The screen will cleared, and any bytes you type will be sent out the serial port you opened. They won't show up on the screen, however. Any bytes received in the serial port will be displayed in the window. To close the serial port, type control-A followed by control-\.

NOTE: only one program can control a serial port at a time. When you're not using a given program, remember to close the serial port. You won't be able to re-program the Arduino module if you don't, because the serial terminal program will have control of the serial port.

Once you've got the serial port open in your terminal program, type any character. You should get three bytes back, representing the three bytes sent out by the microcontroller. They won't be readable as numbers, though. If you want to see them as numbers, change BYTE above to DEC in each print statement.

What's happening here is that the computer is calling for a set of sensor readings by sending out a byte. The Arduino doesn't do anything unless it's received a byte (if (Serial.available() > 0)). When it gets a byte, it reads all three sensors and sends them. This method of communication between computers is called a call-and-response method, or handshaking. It's a good way to make sure you get only the data you need, and no more. In the next step, you'll write a Processing program to read those bytes.

Write a program to read those bytes

For this step, you'll need a programming environment that runs on the personal computer itslf, not on the microcontroller. Any environment that can open and close a serial port will do. For example, Java, Processing, Director, RealBASIC, Visual BASIC, and Max/MSP can all access the serial ports. JavaScript and Flash/Actionscript cannot, as of this writing.

The example below is in Processing. It listens for incoming serial bytes. IF it hasn't gotten any bytes, it looks for "A", which is the first thing that the Arduino sends. If it's gotten an A, it reads bytes until it gets three of them. Then it sets the foreground color, x position, and y position of a ball on the screen using those values. When there's no incoming bytes available, it sends a byte out to call for more bytes. Read through it line by line, including comments, for the details. Then run it with your Arduino module attached to the serial port it's listening to.

import processing.serial.*;

int bgcolor;			     // Background color
int fgcolor;			     // Fill color
Serial port;                         // The serial port
int[] serialInArray = new int[3];    // Where we'll put what we receive
int serialCount = 0;                 // A count of how many bytes we receive
int xpos, ypos;		             // Starting position of the ball
boolean firstContact = false;        // Whether we've heard from the microcontroller

void setup() {
  size(256, 256);  // Stage size
  noStroke();      // No border on the next thing drawn

  // Set the starting position of the ball (middle of the stage)
  xpos = width/2;
  ypos = height/2;

  // Print a list of the serial ports, for debugging purposes:
  println(Serial.list());

  // I know that the first port in the serial list on my mac
  // is always my  Keyspan adaptor, so I open Serial.list()[0].
  // On Windows machines, this generally opens COM1.
  // Open whatever port is the one you're using.
  port = new Serial(this, Serial.list()[0], 9600);
}

void draw() {
  background(bgcolor);
  fill(fgcolor);
  // Draw the shape
  ellipse(xpos, ypos, 20, 20);
}

void serialEvent(Serial port) {
  // read a byte from the serial port:
  int inByte = port.read();
  // if this is the first byte received, 
  // take note of that fact. Otherwise, add it to the array:
  if (firstContact == false) {
    if (inByte == 'A') { 
      port.clear();          // clear the serial port buffer
      firstContact = true;
      port.write('A');
    } 
  } 
  else {
    // Add the latest byte from the serial port to array:
    serialInArray[serialCount] = inByte;
    serialCount++;

    // If we have 3 bytes:
    if (serialCount > 2 ) {
      xpos = serialInArray[0];
      ypos = serialInArray[1];
      fgcolor = serialInArray[2];

      // print the values (for debugging purposes only):
      println(xpos + "\t" + ypos + "\t" + fgcolor);

      // Send a capital A to request new sensor readings:
      port.write('A');
      // Reset serialCount:
      serialCount = 0;
    }
  }
}

If you run this, you'll see the serial data print out just like it did in the arduino serial monitor. You'll also see a lot of null values. To clear those out, add an if statement around the println():

if (myString != null) {

   println(myString);

That makes sure you've got a full string before you do anything with it. The Serial.println() in Arduino attaches a newline and a carriage return. Newlines, carriage returns, spaces, and tabs are often called whitespace and there's a command that removed whitespace from a string, called trim(). Replace the println() with the following two lines. The first trims the whitespace characters off. The second splits the string into three separate strings at the commas, the converts those strings to integers:

 myString = trim(myString);

    // split the string at the commas
    // and convert the sections into integers:
    int sensors[] = int(split(myString, ','));

Next, print out those three integers using a for() loop, like so:

 // print out the values you got:
    for (int sensorNum = 0; sensorNum < sensors.length; sensorNum++) {
      print("Sensor " + sensorNum + ": " + sensors[sensorNum] + "\t"); 
    }
    // add a linefeed after all the sensor values are printed:
    println();

Run the sketch now and you should get output like this:

Sensor 0: 510	Sensor 1: 499	Sensor 2: 0	
Sensor 0: 510	Sensor 1: 498	Sensor 2: 0	
Sensor 0: 510	Sensor 1: 498	Sensor 2: 0	
Sensor 0: 510	Sensor 1: 497	Sensor 2: 0	
Sensor 0: 509	Sensor 1: 498	Sensor 2: 0	
Sensor 0: 510	Sensor 1: 497	Sensor 2: 0	

Now you've got all the sensor values as integers, and you can do whatever you want with them. Use them to move a circle on the screen.

To do that, you'll need a few global variables at the beginning of the sketch:

float bgcolor;			     // Background color
float fgcolor;			     // Fill color
float xpos, ypos;		     // Starting position of the ball

Add a line at the beginning of the setup() to set the window size:

size(640,480);

Put the following lines in the draw method. These will draw the circle using the variables you just declared:

 background(bgcolor);
  fill(fgcolor);
  // Draw the shape
  ellipse(xpos, ypos, 20, 20);

In order to see anything happen, you need to assign the sensor values to these variables. Do this at the end of the serialEvent():

// make sure there are three values before you use them:
 if (sensors.length > 1) {
      xpos = sensors[0];
      ypos = sensors[1];
      // the switch values are 0 and 1.  This makes them 0 and 255:
      fgcolor = sensors[2] * 255;
    }

If you run this, you should see the ball moving onscreen whenever you press the switch and move the analog sensors.

If your analog values are greater than 640 or 480, the ball will be offscreen, so you may have to map your sensor range to the screen size. For example, the accelerometer sensor ranges are approximately 430 to 580. Since the screen is 0 to 640 (horizontal) and o tp 480 (vertical), you' map the ranges like this:

xpos = map(sensors[0], 430,580,0,width);
ypos = map(sensors[1], 430,580,0,height);

Now send the values for all three sensors as binary values, like so:

int firstSensor = 0;    // first analog sensor
int secondSensor = 0;   // second analog sensor
int thirdSensor = 0;    // digital sensor
int inByte = 0;         // incoming serial byte

void setup()
{
  // start serial port at 9600 bps:
  Serial.begin(9600);
  pinMode(2, INPUT);   // digital sensor is on digital pin 2
  establishContact();  // send a byte to establish contact until Processing responds 
}

void loop()
{
  // if we get a valid byte, read analog ins:
  if (Serial.available() > 0) {
    // get incoming byte:
    inByte = Serial.read();
    // read first analog input, divide by 4 to make the range 0-255:
    firstSensor = analogRead(0)/4;
    // delay 10ms to let the ADC recover:
    delay(10);
    // read second analog input, divide by 4 to make the range 0-255:
    secondSensor = analogRead(1)/4;
    // read  switch, multiply by 255
    // so that you're sending 100 or 255:
    thirdSensor = 100 + (155 * digitalRead(2));
    // send sensor values:
    Serial.print(firstSensor, BYTE);
    Serial.print(secondSensor, BYTE);
    Serial.print(thirdSensor, BYTE);               
  }
}

void establishContact() {
 while (Serial.available() <= 0) {
      Serial.print('A', BYTE);   // send a capital A
      delay(300);
  }
}

This program will send a single character, "A", then it'll do nothing, because it's then waiting for data to arrive in the serial port before it sends. To make this work, you'll needto type characters back to the Arduino in the serial monitor. For every character you type, it'll send you three sensor readings.

You can use other programs besides serial monitor to see the serial communication, as described below:

Windows: Hyperterminal can be found in the Start Menu, under All Programs, Accessories, Communications, Hyperterminal. To configure Hyperterminal for serial communication, open the program and click on the File, Properties menu item. Choose the serial port you want to open from the popup menu in the Configuration tab. Click on Configure to bring up the Port Settings tab. Set the properties as needed for the device you’re talking to. For many of the projects that follow, you’ll set the port settings to 9600 bits per second, 8 data bits, no parity, one stop bit, and no hardware flow control. Once you’ve applied those settings, click the Call button on the toolbar to open the serial port. Any bytes you type in the window will be sent out the serial port you opened. They won't show up on the screen, however. Any bytes received in the serial port will be displayed in the window. Click the Disconnect button to close the serial port.

OSX: To configure Terminal for serial communication in OSX, open the program and type ls /dev/tty.* This will give you a list of available serial ports. The names of the serial port in OSX are more unique than the names that Windows uses. Pick your serial port and type screen portname datarate. For example, to open the serial pot on an Arduino board at 9600 bits per second, you might type screen /dev/tty.usbserial-5B1 9600. The screen will cleared, and any bytes you type will be sent out the serial port you opened. They won't show up on the screen, however. Any bytes received in the serial port will be displayed in the window. To close the serial port, type control-A followed by control-\.

NOTE: only one program can control a serial port at a time. When you're not using a given program, remember to close the serial port. You won't be able to re-program the Arduino module if you don't, because the serial terminal program will have control of the serial port.

Once you've got the serial port open in your terminal program, type any character. You should get three bytes back, representing the three bytes sent out by the microcontroller. They won't be readable as numbers, though. If you want to see them as numbers, change BYTE above to DEC in each print statement.

What's happening here is that the computer is calling for a set of sensor readings by sending out a byte. The Arduino doesn't do anything unless it's received a byte (if (Serial.available() > 0)). When it gets a byte, it reads all three sensors and sends them. This method of communication between computers is called a call-and-response method, or handshaking. It's a good way to make sure you get only the data you need, and no more. In the next step, you'll write a Processing program to read those bytes.

Write a program to read those bytes

For this step, you'll need a programming environment that runs on the personal computer itslf, not on the microcontroller. Any environment that can open and close a serial port will do. For example, Java, Processing, Director, RealBASIC, Visual BASIC, and Max/MSP can all access the serial ports. JavaScript and Flash/Actionscript cannot, as of this writing.

The example below is in Processing. It listens for incoming serial bytes. IF it hasn't gotten any bytes, it looks for "A", which is the first thing that the Arduino sends. If it's gotten an A, it reads bytes until it gets three of them. Then it sets the foreground color, x position, and y position of a ball on the screen using those values. When there's no incoming bytes available, it sends a byte out to call for more bytes. Read through it line by line, including comments, for the details. Then run it with your Arduino module attached to the serial port it's listening to.

import processing.serial.*;

int bgcolor;			     // Background color
int fgcolor;			     // Fill color
Serial port;                         // The serial port
int[] serialInArray = new int[3];    // Where we'll put what we receive
int serialCount = 0;                 // A count of how many bytes we receive
int xpos, ypos;		             // Starting position of the ball
boolean firstContact = false;        // Whether we've heard from the microcontroller

void setup() {
  size(256, 256);  // Stage size
  noStroke();      // No border on the next thing drawn

  // Set the starting position of the ball (middle of the stage)
  xpos = width/2;
  ypos = height/2;

  // Print a list of the serial ports, for debugging purposes:
  println(Serial.list());

  // I know that the first port in the serial list on my mac
  // is always my  Keyspan adaptor, so I open Serial.list()[0].
  // On Windows machines, this generally opens COM1.
  // Open whatever port is the one you're using.
  port = new Serial(this, Serial.list()[0], 9600);
}

void draw() {
  background(bgcolor);
  fill(fgcolor);
  // Draw the shape
  ellipse(xpos, ypos, 20, 20);
}

void serialEvent(Serial port) {
  // read a byte from the serial port:
  int inByte = port.read();
  // if this is the first byte received, 
  // take note of that fact. Otherwise, add it to the array:
  if (firstContact == false) {
    if (inByte == 'A') { 
      port.clear();          // clear the serial port buffer
      firstContact = true;
      port.write('A');
    } 
  } 
  else {
    // Add the latest byte from the serial port to array:
    serialInArray[serialCount] = inByte;
    serialCount++;

    // If we have 3 bytes:
    if (serialCount > 2 ) {
      xpos = serialInArray[0];
      ypos = serialInArray[1];
      fgcolor = serialInArray[2];

      // print the values (for debugging purposes only):
      println(xpos + "\t" + ypos + "\t" + fgcolor);

      // Send a capital A to request new sensor readings:
      port.write('A');
      // Reset serialCount:
      serialCount = 0;
    }
  }
}

Add one extra line at the end of the setup() method. This line tells the sketch not to call serialEvent() unless an ASCII newline byte (value 10) comes in the serial port. It will save any other bytes it gets in the serial buffer, so you can read them all at once when the newline arrives:

The draw() method doesn't do anything, just like the first serial lab:

void draw() {

  // twiddle your thumbs

@]

The serialEvent() method is a bit different. Since it only occurs when you get a newline, you can assume that the entire string that came before the newline is in the serial buffer. So you start out by reading that string:

void serialEvent(Serial myPort) { 
  // read the serial buffer:
  String myString = myPort.readStringUntil('\n');
  println(myString);

If you run this, you'll see the serial data print out just like it did in the arduino serial monitor.

Now send the values for all three sensors as binary values, like so:

[@ int firstSensor = 0; // first analog sensor int secondSensor = 0; // second analog sensor int thirdSensor = 0; // digital sensor int inByte = 0; // incoming serial byte

void setup()

  // start serial port at 9600 bps:
  Serial.begin(9600);
  pinMode(2, INPUT);   // digital sensor is on digital pin 2
  establishContact();  // send a byte to establish contact until Processing responds 

}

void loop() {

Once you've got a data format, all you have to do is read it in the receiving program. Here's a Processing sketch that reads the data as formatted by the Arduino program above. First things up as you did in the first serial lab?:

import processing.serial.*; // import the Processing serial library Serial myPort; // The serial port

void setup() {

  // 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 module, so I open Serial.list()[0].
  // Change the 0 to the appropriate number of the serial port
  // that your microcontroller is attached to.
  myPort = new Serial(this, Serial.list()[0], 9600);

}

Add one extra line at the end of the setup() method. This line tells the sketch not to call serialEvent() unless an ASCII newline byte (value 10) comes in the serial port:

// read bytes into a buffer until you get a linefeed (ASCII 10):

  myPort.bufferUntil('\n');

@]

Now send the values for all three sensors as binary values, like so:

[@

Here's the tricky part: Serial.println(analogValue, DEC) actually sent FOUR bytes! It sent a byte to represent the 3, a byte to represent the 2, a byte to tell the Monitor to move the cursor down a line(newline), and a byte to move the cursor all the way to the left (carriage return). The raw binary values of those four bytes are 51 (ASCII for "3"), 50 (ASCII for "2"), 10 (ASCII for "newline"), and 13 (ASCII for "carriage return"). Check the ASCII table and you'll see for yourself.

  // read the analog input, divide by 4:

452,345,416,234,534,417,325,452,231@

You don't know which sensor is which. You could assume that if you start listening when the microcontroller starts sending that the first reading corresponds to the first sensor, but you can't know that for sure. There are two ways to address this. You can use punctuation or you can use a call-and-response or handshaking method.

Punctuation Method

One way to send the data such that it can be interpreted clearly is to punctuate each set of data uniquely. Just as a sentence ends with a period, you can end your data with a carriage return and a newline. Here's a modification of the code above that does that:

void loop() {

   for (int thisSensor = 0; thisSensor < 3; thisSensor++) {
      int sensorValue = analogRead(thisSensor);
      Serial.print(sensorValue, DEC);

      // if this is the last sensor value, end the line.
      // otherwise, print a comma:
      if (thisSensor == 2) {
         Serial.println();
      } else {
         Serial.print(",");
      }
   }

From this loop, you'd get output like this:

452,345,416 234,534,417 325,452,231 @]

This is much better. Whenever you get a newline, you know that the next value is the first sensor. Here's a program that reads the two analog sensors on your board and the one digital switch, and prints them out in this format:

[@ /*

  Sensor Reader
 Language: Wiring/Arduino

 Reads two analog inputs and one digital input
 and outputs their values.
 Connections:  
 analog sensors on analog input pins 0 and 1
 switch on digital I/O pin 2

• /

int analogOne = 0; // analog input int analogTwo = 1; // analog input int digitalOne = 2; // digital input

int sensorValue = 0; // reading from the sensor

  // configure the serial connection:
  Serial.begin(9600);
  // configure the digital input:
  pinMode(digitalOne, INPUT);

void loop() {

  // read the sensor:
  sensorValue = analogRead(analogOne);
  // print the results:
  Serial.print(sensorValue, DEC);
  Serial.print(",");

  // read the sensor:
  sensorValue = analogRead(analogTwo);
  // print the results:
  Serial.print(sensorValue, DEC);
  Serial.print(",");

  // read the sensor:
  sensorValue = digitalRead(digitalOne);
  // print the last sensor value with a println() so that
  // each set of four readings prints on a line by itself:
  Serial.println(sensorValue, DEC);

Once you've got a data format, all you have to do is read it in the receiving program. Here's a Processing sketch that reads the data as formatted by the Arduino program above:

Now send the values for all three sensors as binary values, like so:

int firstSensor = 0;    // first analog sensor
int secondSensor = 0;   // second analog sensor
int thirdSensor = 0;    // digital sensor
int inByte = 0;         // incoming serial byte

void setup()
{
  // start serial port at 9600 bps:
  Serial.begin(9600);
  pinMode(2, INPUT);   // digital sensor is on digital pin 2
  establishContact();  // send a byte to establish contact until Processing responds 
}

void loop()
{
  // if we get a valid byte, read analog ins:
  if (Serial.available() > 0) {
    // get incoming byte:
    inByte = Serial.read();
    // read first analog input, divide by 4 to make the range 0-255:
    firstSensor = analogRead(0)/4;
    // delay 10ms to let the ADC recover:
    delay(10);
    // read second analog input, divide by 4 to make the range 0-255:
    secondSensor = analogRead(1)/4;
    // read  switch, multiply by 255
    // so that you're sending 100 or 255:
    thirdSensor = 100 + (155 * digitalRead(2));
    // send sensor values:
    Serial.print(firstSensor, BYTE);
    Serial.print(secondSensor, BYTE);
    Serial.print(thirdSensor, BYTE);               
  }
}

void establishContact() {
 while (Serial.available() <= 0) {
      Serial.print('A', BYTE);   // send a capital A
      delay(300);
  }
}

This program will send a single character, "A", then it'll do nothing, because it's then waiting for data to arrive in the serial port before it sends. To make this work, you'll needto type characters back to the Arduino in the serial monitor. For every character you type, it'll send you three sensor readings.

You can use other programs besides serial monitor to see the serial communication, as described below:

Windows: Hyperterminal can be found in the Start Menu, under All Programs, Accessories, Communications, Hyperterminal. To configure Hyperterminal for serial communication, open the program and click on the File, Properties menu item. Choose the serial port you want to open from the popup menu in the Configuration tab. Click on Configure to bring up the Port Settings tab. Set the properties as needed for the device you’re talking to. For many of the projects that follow, you’ll set the port settings to 9600 bits per second, 8 data bits, no parity, one stop bit, and no hardware flow control. Once you’ve applied those settings, click the Call button on the toolbar to open the serial port. Any bytes you type in the window will be sent out the serial port you opened. They won't show up on the screen, however. Any bytes received in the serial port will be displayed in the window. Click the Disconnect button to close the serial port.

OSX: To configure Terminal for serial communication in OSX, open the program and type ls /dev/tty.* This will give you a list of available serial ports. The names of the serial port in OSX are more unique than the names that Windows uses. Pick your serial port and type screen portname datarate. For example, to open the serial pot on an Arduino board at 9600 bits per second, you might type screen /dev/tty.usbserial-5B1 9600. The screen will cleared, and any bytes you type will be sent out the serial port you opened. They won't show up on the screen, however. Any bytes received in the serial port will be displayed in the window. To close the serial port, type control-A followed by control-\.

NOTE: only one program can control a serial port at a time. When you're not using a given program, remember to close the serial port. You won't be able to re-program the Arduino module if you don't, because the serial terminal program will have control of the serial port.

Once you've got the serial port open in your terminal program, type any character. You should get three bytes back, representing the three bytes sent out by the microcontroller. They won't be readable as numbers, though. If you want to see them as numbers, change BYTE above to DEC in each print statement.

What's happening here is that the computer is calling for a set of sensor readings by sending out a byte. The Arduino doesn't do anything unless it's received a byte (if (Serial.available() > 0)). When it gets a byte, it reads all three sensors and sends them. This method of communication between computers is called a call-and-response method, or handshaking. It's a good way to make sure you get only the data you need, and no more. In the next step, you'll write a Processing program to read those bytes.

Write a program to read those bytes

For this step, you'll need a programming environment that runs on the personal computer itslf, not on the microcontroller. Any environment that can open and close a serial port will do. For example, Java, Processing, Director, RealBASIC, Visual BASIC, and Max/MSP can all access the serial ports. JavaScript and Flash/Actionscript cannot, as of this writing.

The example below is in Processing. It listens for incoming serial bytes. IF it hasn't gotten any bytes, it looks for "A", which is the first thing that the Arduino sends. If it's gotten an A, it reads bytes until it gets three of them. Then it sets the foreground color, x position, and y position of a ball on the screen using those values. When there's no incoming bytes available, it sends a byte out to call for more bytes. Read through it line by line, including comments, for the details. Then run it with your Arduino module attached to the serial port it's listening to.

import processing.serial.*;

int bgcolor;			     // Background color
int fgcolor;			     // Fill color
Serial port;                         // The serial port
int[] serialInArray = new int[3];    // Where we'll put what we receive
int serialCount = 0;                 // A count of how many bytes we receive
int xpos, ypos;		             // Starting position of the ball
boolean firstContact = false;        // Whether we've heard from the microcontroller

void setup() {
  size(256, 256);  // Stage size
  noStroke();      // No border on the next thing drawn

  // Set the starting position of the ball (middle of the stage)
  xpos = width/2;
  ypos = height/2;

  // Print a list of the serial ports, for debugging purposes:
  println(Serial.list());

  // I know that the first port in the serial list on my mac
  // is always my  Keyspan adaptor, so I open Serial.list()[0].
  // On Windows machines, this generally opens COM1.
  // Open whatever port is the one you're using.
  port = new Serial(this, Serial.list()[0], 9600);
}

void draw() {
  background(bgcolor);
  fill(fgcolor);
  // Draw the shape
  ellipse(xpos, ypos, 20, 20);
}

void serialEvent(Serial port) {
  // read a byte from the serial port:
  int inByte = port.read();
  // if this is the first byte received, 
  // take note of that fact. Otherwise, add it to the array:
  if (firstContact == false) {
    if (inByte == 'A') { 
      port.clear();          // clear the serial port buffer
      firstContact = true;
      port.write('A');
    } 
  } 
  else {
    // Add the latest byte from the serial port to array:
    serialInArray[serialCount] = inByte;
    serialCount++;

    // If we have 3 bytes:
    if (serialCount > 2 ) {
      xpos = serialInArray[0];
      ypos = serialInArray[1];
      fgcolor = serialInArray[2];

      // print the values (for debugging purposes only):
      println(xpos + "\t" + ypos + "\t" + fgcolor);

      // Send a capital A to request new sensor readings:
      port.write('A');
      // Reset serialCount:
      serialCount = 0;
    }
  }
}

To begin with, just send the value from one sensor, the first analog sensor (the first axis of the accelerometer in the photos):

When you open the serial monitor, you should see a number between 0 and 1023 scrolling down the debugger pane. That's because the DEC modifier to Serial.println() formats the value it prints as an ASCII-encoded DECimal value. Also, the serial monitor assumes it should show you the ASCII character corresponding to each byte it receives. Try changing the Serial.println like so:

Now you get a range of garbage characters. What's going on? The BYTE modifier doesn't format the bytes. It sends out the raw binary value of the byte. The Serial Monitor receives that binary value and assumes it should show you the ASCII character corresponding to that value again. The garbage characters are characters corresponding to the ASCII values the Monitor is receiving.

In the first serial lab, you sent one byte representing one sensor's value, over and over. When you're sending multiple sensor values, it gets a little more complicated. You need to a way to know which value represents which sensor. For example, imagine if you used the following loop to send your sensor values:

void loop() {

   for (int thisSensor = 0; thisSensor < 3; thisSensor++) {
      int sensorValue = analogRead(thisSensor);
      Serial.print(sensorValue, DEC);
      Serial.print(",");
   }

@]

you'd get a string like this:

452,345,416,234,534,417,325,452,

The problem is that you don't know which sensor is which. You could assume that if you start listening when the microcontroller starts sending that the first reading corresponds to the first sensor, but you can't know that for sure. There are two ways to address this. You can use punctuation or you can use a call-and-response or handshaking method.

Now send the values for all three sensors as binary values, like so:

[@ int firstSensor = 0; // first analog sensor int secondSensor = 0; // second analog sensor int thirdSensor = 0; // digital sensor int inByte = 0; // incoming serial byte

void setup()

  // start serial port at 9600 bps:
  Serial.begin(9600);
  pinMode(2, INPUT);   // digital sensor is on digital pin 2
  establishContact();  // send a byte to establish contact until Processing responds 

}

void loop() {

http://itp.nyu.edu/physcomp/images/labs/accelerometer.jpg | accelerometer

The photos and schematic in this lab show an accelerometer and a pushbutton. You don't have to use these, though. Use whatever sensors are appropriate to your final application. While you're figuring what sensors to use, use the most convenient sensors you've got in hand; perhaps two potentiometers for the analog sensors and a pushbutton?

(:cellnr:)

The photos and schematic in this lab show a force-sensitive resistor, an infrared ranger, and a pushbutton. You don't have to use these, though. Use whatever sensors are appropriate to your final application. While you're figuring what sensors to use, use the most convenient sensors you've got in hand; perhaps two potentiometers for the analog sensors and a pushbutton?

(:cellnr )

(:cell:)

In the first serial lab, you sent data from one sensor to a personal computer. In this lab, you'll send data from multiple sensors to a program on a personal computer. You'll use the data from the sensors to create a pointing-and-selecting device (i.e. a mouse).

In this lab, you'll send data from sensors to a program on a personal computer. You'll use the data from the sensors to create a pointing-and-selecting device (i.e. a mouse).

For this lab you'll need:

http://itp.nyu.edu/physcomp/images/labs/breadboard.jpg | Solderless breadboard http://itp.nyu.edu/physcomp/images/labs/hookup_wire.jpg | 22-AWG hookup wire http://itp.nyu.edu/physcomp/images/labs/arduino.jpg | Arduino Microcontroller
module

http://itp.nyu.edu/physcomp/images/labs/resistors.jpg | 10Kohm resistors

http://itp.nyu.edu/physcomp/images/labs/flex_sensors.jpg | Flex sensors
(or a different
form of variable resistor) http://itp.nyu.edu/physcomp/images/labs/switch.jpg | switch

Prepare the breadboard

Connect power and ground on the breadboard to power and ground from the microcontroller. On the Arduino module, use the 5V and any of the ground connections:

http://itp.nyu.edu/physcomp/images/labs/arduino_bboard_power.jpg

If you're using an Arduino breadboard shield, there is a row of sockets connected to 5V on the analog in side of the breadboard, and a row connected to ground on the digital in side of the board:

http://itp.nyu.edu/physcomp/images/labs/breadboard_shield.jpg

Connect the sensors

Connect two analog sensors to analog pins 0 and 1 like you did in the analog lab. Connect a switch to digital pin 2 like you did in the digital lab.

For the photos in this lab, we used a force-sensitive resistor, an infrared ranger, and a pushbutton. The schematic and images are below. Use whatever sensors are appropriate to your final application. Whle you're figuring what sensors to use, use the most convenient sensors you've got in hand; perhaps two pots for the analog sensors and a pushbutton?

(:table:) (:cellnr colspan=2:) http://itp.nyu.edu/physcomp/images/labs/arduino_2_analog_1_dig_schem.png (:cellnr:) Breadboard version http://itp.nyu.edu/physcomp/images/labs/bboard_3_sensors.JPG (:cell:) Breadboard shield version http://itp.nyu.edu/physcomp/images/labs/bboard_shield_3_sensors.JPG (:tableend:)

Read and send the serial data

The goal of this section is to understand how the microcontroller formats data when you send it serially. You'll only use one analog sensor for it. Program the following into the module:

int analogPin = 0;
int analogValue = 0;            // outgoing ADC value

void setup()
{
  // start serial port at 9600 bps:
  Serial.begin(9600);
}

void loop()
{
  // read analog input, divide by 4 to make the range 0-255:
  analogValue = analogRead(analogPin); 
  analogValue = analogValue / 4;
  Serial.println(analogValue, DEC);
  // pause for 10 milliseconds:
  delay(10);                 
}

When you open the Serial Monitor, you should see a number between 0 and 255 scrolling down the debugger pane. That's because the DEC modifier to Serial.println() formats the value it prints as an ASCII-encoded DECimal value. Also, the Serial Monitor assumes it should show you the ASCII character corresponding to each byte it receives. Try changing the Serial.println like so:

Serial.println(analogValue, BYTE);

Now you get a range of garbage characters. What's going on? The BYTE modifier doesn't format the bytes. It sends out the raw binary value of the byte. The Serial Monitor receives that binary value and assumes it should show you the ASCII character corresponding to that value again. The garbage characters are characters correspinding to the ASCII values the Monitor is receiving.

For example, imagine the sensor's value is 128. Divided by four, it becomes 32.

• Serial.println(analogValue, DEC) results in "32"
• Serial.println(analogValue, BYTE) results in " ", the space character, which has the ASCII value 32.

Here's the tricky part: Serial.println(analogValue, DEC) actually sent FOUR bytes! It sent a byte to represent the 3, a byte to represent the 2, a byte to tell the Monitor to move the cursor down a line(newline), and a byte to move the cursor all the way to the left (carriage return). The raw binary values of those four bytes are 51 (ASCII for "3"), 50 (ASCII for "2"), 10 (ASCII for "newline), and 13 (ASCII for "carriage return"). Check the ASCII table and you'll see for yourself.

Send the data in many formats

Try this program and view the results in the Serial Monitor:

int analogPin = 0;
int analogValue = 0;                // integer to print

void setup() {
  // open serial communications at 9600 bps
  Serial.begin(9600);
}

void loop() {
  // read the analog inoput, divide by 4:
  analogValue = analogRead(analogPin) /4;

  // print in many formats:
  Serial.print(analogValue, BYTE);     // Print the raw binary value analogValue
  Serial.print('\t');                  // print a tab
  Serial.print(analogValue, BIN);      // print the ASCII encoded binary analogValue
  Serial.print('\t');                  // print a tab
  Serial.print(analogValue, DEC);      // print the ASCII encoded decimal analogValue
  Serial.print('\t');                  // print a tab
  Serial.print(analogValue, HEX);      // print the ASCII encoded hexadecimal analogValue
  Serial.print('\t');                  // print a tab
  Serial.print(analogValue, OCT);      // print the ASCII encoded octal analogValue
  Serial.println();                    // print a linefeed and carriage return

  delay(10);
}

You should get output like this:

â	11100010	226	E2	342
á	11100001	225	E1	341
á	11100001	225	E1	341
á	11100001	225	E1	341
à	11100000	224	E0	340
à	11100000	224	E0	340
ß	11011111	223	DF	337
ß	11011111	223	DF	337
ß	11011111	223	DF	337

It's printing the raw binary value, then the ASCII-encoded binary value, then the ASCII-encoded decimal, hexadecimal, and octal values. You may never need all of these differnt formats, but you'll likely need at least the decimal and the raw binary versions at some point.

Send the values for all three sensors

Now send the values for all three sensors as binary values, like so:

int firstSensor = 0;    // first analog sensor
int secondSensor = 0;   // second analog sensor
int thirdSensor = 0;    // digital sensor
int inByte = 0;         // incoming serial byte

void setup()
{
  // start serial port at 9600 bps:
  Serial.begin(9600);
  pinMode(2, INPUT);   // digital sensor is on digital pin 2
  establishContact();  // send a byte to establish contact until Processing responds 
}

void loop()
{
  // if we get a valid byte, read analog ins:
  if (Serial.available() > 0) {
    // get incoming byte:
    inByte = Serial.read();
    // read first analog input, divide by 4 to make the range 0-255:
    firstSensor = analogRead(0)/4;
    // delay 10ms to let the ADC recover:
    delay(10);
    // read second analog input, divide by 4 to make the range 0-255:
    secondSensor = analogRead(1)/4;
    // read  switch, multiply by 255
    // so that you're sending 100 or 255:
    thirdSensor = 100 + (155 * digitalRead(2));
    // send sensor values:
    Serial.print(firstSensor, BYTE);
    Serial.print(secondSensor, BYTE);
    Serial.print(thirdSensor, BYTE);               
  }
}

void establishContact() {
 while (Serial.available() <= 0) {
      Serial.print('A', BYTE);   // send a capital A
      delay(300);
  }
}

This program will send a single character, "A", then it'll do nothing, because it's then waiting for data to arrive in the serial port before it sends. To make this work, you'll needto type characters back to the Arduino in the serial monitor. For every character you type, it'll send you three sensor readings.

You can use other programs besides serial monitor to see the serial communication, as described below:

Windows: Hyperterminal can be found in the Start Menu, under All Programs, Accessories, Communications, Hyperterminal. To configure Hyperterminal for serial communication, open the program and click on the File, Properties menu item. Choose the serial port you want to open from the popup menu in the Configuration tab. Click on Configure to bring up the Port Settings tab. Set the properties as needed for the device you’re talking to. For many of the projects that follow, you’ll set the port settings to 9600 bits per second, 8 data bits, no parity, one stop bit, and no hardware flow control. Once you’ve applied those settings, click the Call button on the toolbar to open the serial port. Any bytes you type in the window will be sent out the serial port you opened. They won't show up on the screen, however. Any bytes received in the serial port will be displayed in the window. Click the Disconnect button to close the serial port.

OSX: To configure Terminal for serial communication in OSX, open the program and type ls /dev/tty.* This will give you a list of available serial ports. The names of the serial port in OSX are more unique than the names that Windows uses. Pick your serial port and type screen portname datarate. For example, to open the serial pot on an Arduino board at 9600 bits per second, you might type screen /dev/tty.usbserial-5B1 9600. The screen will cleared, and any bytes you type will be sent out the serial port you opened. They won't show up on the screen, however. Any bytes received in the serial port will be displayed in the window. To close the serial port, type control-A followed by control-\.

NOTE: only one program can control a serial port at a time. When you're not using a given program, remember to close the serial port. You won't be able to re-program the Arduino module if you don't, because the serial terminal program will have control of the serial port.

Once you've got the serial port open in your terminal program, type any character. You should get three bytes back, representing the three bytes sent out by the microcontroller. They won't be readable as numbers, though. If you want to see them as numbers, change BYTE above to DEC in each print statement.

What's happening here is that the computer is calling for a set of sensor readings by sending out a byte. The Arduino doesn't do anything unless it's received a byte (if (Serial.available() > 0)). When it gets a byte, it reads all three sensors and sends them. This method of communication between computers is called a call-and-response method, or handshaking. It's a good way to make sure you get only the data you need, and no more. In the next step, you'll write a Processing program to read those bytes.

Write a program to read those bytes

For this step, you'll need a programming environment that runs on the personal computer itslf, not on the microcontroller. Any environment that can open and close a serial port will do. For example, Java, Processing, Director, RealBASIC, Visual BASIC, and Max/MSP can all access the serial ports. JavaScript and Flash/Actionscript cannot, as of this writing.

The example below is in Processing. It listens for incoming serial bytes. IF it hasn't gotten any bytes, it looks for "A", which is the first thing that the Arduino sends. If it's gotten an A, it reads bytes until it gets three of them. Then it sets the foreground color, x position, and y position of a ball on the screen using those values. When there's no incoming bytes available, it sends a byte out to call for more bytes. Read through it line by line, including comments, for the details. Then run it with your Arduino module attached to the serial port it's listening to.

import processing.serial.*;

int bgcolor;			     // Background color
int fgcolor;			     // Fill color
Serial port;                         // The serial port
int[] serialInArray = new int[3];    // Where we'll put what we receive
int serialCount = 0;                 // A count of how many bytes we receive
int xpos, ypos;		             // Starting position of the ball
boolean firstContact = false;        // Whether we've heard from the microcontroller

void setup() {
  size(256, 256);  // Stage size
  noStroke();      // No border on the next thing drawn

  // Set the starting position of the ball (middle of the stage)
  xpos = width/2;
  ypos = height/2;

  // Print a list of the serial ports, for debugging purposes:
  println(Serial.list());

  // I know that the first port in the serial list on my mac
  // is always my  Keyspan adaptor, so I open Serial.list()[0].
  // On Windows machines, this generally opens COM1.
  // Open whatever port is the one you're using.
  port = new Serial(this, Serial.list()[0], 9600);
}

void draw() {
  background(bgcolor);
  fill(fgcolor);
  // Draw the shape
  ellipse(xpos, ypos, 20, 20);
}

void serialEvent(Serial port) {
  // read a byte from the serial port:
  int inByte = port.read();
  // if this is the first byte received, 
  // take note of that fact. Otherwise, add it to the array:
  if (firstContact == false) {
    if (inByte == 'A') { 
      port.clear();          // clear the serial port buffer
      firstContact = true;
      port.write('A');
    } 
  } 
  else {
    // Add the latest byte from the serial port to array:
    serialInArray[serialCount] = inByte;
    serialCount++;

    // If we have 3 bytes:
    if (serialCount > 2 ) {
      xpos = serialInArray[0];
      ypos = serialInArray[1];
      fgcolor = serialInArray[2];

      // print the values (for debugging purposes only):
      println(xpos + "\t" + ypos + "\t" + fgcolor);

      // Send a capital A to request new sensor readings:
      port.write('A');
      // Reset serialCount:
      serialCount = 0;
    }
  }
}

If you did everything right, the ball should move in response to the analog sensors, and appear or disappear when you press the button.

Get creative

You just duplicated the basic functionality of a mouse; that is, a device with two analog sensors that affect X and Y, and a digital sensor (mouse button). What applications can you think of that could use a better physical interface for a mouse? Create a prototype in Arduino and Processing, or whatever programming environment you choose. Come up with a physical interface that makes it clear what actions map to what movements and actions. Figure out which actions can and should be possible at the same time (e.g. moving x and y to make a diagonal path). Think about what actions should be exclusive, if any (e.g. pressing two mouse buttons at once?). Present a working software and hardware model of your idea.