Add an LED

Connect the LED and resistor to digital I/O pin 5 of the module:

Potentiometer and LED circuit

Arduino with LED circuit	Same circuit on a breadboard

Program the Microcontroller

Program your Arduino to read the analog input as follows:

void setup() {
 Serial.begin(9600);           // initialize serial communications
}

void loop() {
 if (Serial.available() > 0) { // if there's serial data available
 int inByte = Serial.read();   // read it
 Serial.write(inByte);         // send it back out as raw binary data
 analogWrite(5, inByte);       // use it to set the LED brightness
 }
}

The P5.js serialport library

To communicate with your microcontroller serially, you’re going to use the P5.js serialport library and the P5.serialserver (command line version) or p5.serialcontrol (GUI version). The P5.js serialport library can’t access your serial ports directly when a sketch is running in a browser because the browser doesn’t have direct access to the serial port. But it can communicate with a server program on your computer that can exchange data with the serialport.P5.serialserver (or p5.serialcontrol) is  the server that connects your sketch, running in a browser, with the serial ports on your computer as shown below:

Once you gain an understanding of serial communication, you can use any program that can connect with your computer’s serial ports to communicate with a microcontroller. Processing, Max/MSP, and OpenFrameworks are three other popular multimedia programming environments that can communicate via the serial ports.

Install the P5.serialcontrol App

Download the latest version of the P5.serialcontrol application and save it in your Applications folder. When you run it, it will check serial ports on your machine. Click “list ports” to refresh the list, and you should see the serial port of your Arduino board show up. You can now move onto using the P5.js editor making sure that the p5.serialport.js file is inside your project folder. You can skip the next section unless you want to run p5.serialserver from the command line instead from the p5.serialcontol app.

sudo npm install -g p5.serialserver

p5serial

p5.serialserver is running

You’ll need to know the name of your serial port to get started. If you’re not sure how to get this, see the Serial Input to P5.js lab for how to get a list of ports.

The P5.js Sketch

The sketch you’re going to write will control the microcontroller’s LED from P5.js. Dragging the mouse up and down the canvas will dim or brighten the LED, and typing 0 through 9 will set the LED’s brightness in increments from off (0) through almost full brightness (9). The sketch will also receive serial input from the microcontroller just as in the Serial Input to P5.js lab, so that you can see that the microcontroller is getting the same values you’re sending.

Program P5.js For Serial Communication

function draw() {
 // black background, white text:
 background(0);
 fill(255);
 // display the incoming serial data as a string:
 text("incoming value: " + inData, 30, 30);
}

To read the mouse and keyboard, you’ll need to write functions to respond to the ‘mouseDragged’ and ‘keyPressed’ events. ‘MouseDragged’ will happen whenever you click and drag the mouse on the canvas. When that happens, read the mouseY, and map its position on the canvas to a value from 0 to 255. Convert the result to a number using the int() function. Then send it out the serial port using the serial.write() function:

function mouseDragged() {
 // map the mouseY to a range from 0 to 255:
 outByte = int(map(mouseY, 0, height, 0, 255));
 // send it out the serial port:
 serial.write(outByte);
}

The serial.write() function is versatile. If you give it a variable or literal that’s a numeric data type, it will send it as its raw binary value. In the code above, note how you’re converting the output of the map() function to a number using the int() function.  If you give it a string, however, it will send out that ASCII string. So be aware of the difference, and make sure you know whether your serial receiving device wants raw binary or ASCII-encoded data.

function keyPressed() {
 if (key >=0 && key <=9) { // if the user presses 0 through 9
 outByte = byte(key * 25); // map the key to a range from 0 to 225
 }
 serial.write(outByte); // send it out the serial port
}

That’s all you want your sketch to do, so try running it now. You should see that the initial incoming serial value is undefined, but when you drag the mouse up and down, or type 0 through 9, it will update when the Arduino program returns what it received. The LED will also change with these actions.

Sending ASCII-Encoded Serial Data

If you want to send ASCII-encoded serial data from P5.js, all you have to do is to serial.write() your string. Sending strings is the P5.serialport’s default behavior. On the Arduino side, you can read single characters one byte at a time simply as well. However, if you want to convert multi-byte number strings to numeric values, you’ll need a new function to read ASCII encoded numeric strings called parseInt().

Program the  Microcontroller Again

To start off with, load a sketch from the Arduino examples called PhysicalPixel. You can find it in the File Menu -> Examples -> Communication -> PhysicalPixel. Here’s what it looks like. Change the LED pin number to pin 5 as follows:

const int ledPin = 5; // the pin that the LED is attached to
int incomingByte;     // a variable to read incoming serial data into

void setup() {
 Serial.begin(9600);             // initialize serial communication
 pinMode(ledPin, OUTPUT);        // initialize the LED pin as an output
}

void loop() {
 if (Serial.available() > 0) {   // see if there's incoming serial data
   incomingByte = Serial.read(); // read it
   if (incomingByte == 'H') {    // if it's a capital H (ASCII 72),
     digitalWrite(ledPin, HIGH); // turn on the LED
   }
   if (incomingByte == 'L') {    // if it's an L (ASCII 76)
     digitalWrite(ledPin, LOW);  // turn off the LED
   }
 }
}

When you run this, open the serial monitor and type H or L, and the LED will go on or off.  Try typing h or l instead. The LED won’t change, because H and h have different ASCII values, as do L and l. But you can see from this that you don’t need to memorize the ASCII chart to check for character values in your code. Put the character you want to read in single quotes, and the Arduino compiler will automatically convert the character to its ASCII value for you. It only works for single characters, though.

It is also possible to read and interpret ASCII-encoded strings in Arduino. The String.parseInt() function reads an incoming string until it finds a non-numeric character, then converts the numeric string that it read into a long integer. This is a blocking function, meaning that String.parseInt() stops the program and does nothing until it sees a non-numeric character, or until a timeout passes. The timeout is normally one second (or 1000 milliseconds), but you can set it to a lower number of milliseconds using Serial.setTimeout(). Here’s a variation on the original Arduino sketch from above, using Serial.parseInt() this time:

void setup() {
 Serial.begin(9600);    // initialize serial communications
 Serial.setTimeout(10); // set the timeout for parseInt
}

void loop() {
 if (Serial.available() > 0) {   // if there's serial data available
 int inByte = Serial.parseInt(); // read it
   if (inByte > 0) {
      Serial.write(inByte);      // send it back out as raw binary data
      analogWrite(5, inByte);    // use it to set the LED brightness
   }
 }
}

Upload this to your microcontroller, then open the Serial Monitor and send in some ASCII numeric strings. You’ll see the character that’s represented by the string’s value. For example, 65 will return A, 34 will return “, and so forth.

Notice that this version of the sketch has a conditional statement to check if the incoming byte is 0. This is because of a quirk of the parseInt() function. It returns 0 if the timeout is hit, or if the string is legitimately 0. This means you can’t really parse for a string like this: "0\n".