Minimal p5.js code to communicate with Arduino 

using handshaking. Arduino code is below

*/

​

let serial; // variable to hold an instance of the serialport library

let portName = "/dev/ttyACM0";

​

let outgoingData = 0;

​

function setup() {

  createCanvas(200, 50);

  serial = new p5.SerialPort(); // make a new instance of the serialport library

  serial.on("list", printList); // set a callback function for the serialport list event

  serial.on("connected", serverConnected); // callback for connecting to the server

  serial.on("open", portOpen); // callback for the port opening

  serial.on("data", serialEvent); // callback for when new data arrives

  serial.on("error", serialError); // callback for errors

  serial.on("close", portClose); // callback for the port closing

​

  serial.list(); // list the serial ports

  serial.open(portName); // open a serial port

  background(200);

}

​

function draw() {

  if (mouseIsPressed) {

    if (mouseX <= width / 2) 

    {

      outgoingData = 0;

    } else {

      outgoingData = 1;

    }

  }

}

​

// get the list of ports:

function printList(portList) {

  // portList is an array of serial port names

  for (let i = 0; i < portList.length; i++) {

    // Display the list the console:

    print(i + " " + portList[i]);

  }

}

​

function serverConnected() {

  print("connected to server.");

}

​

function portOpen() {

  print("the serial port opened.");

}

​

function serialEvent() {

  // read a string from the serial port

  // until you get carriage return and newline:

  let incomingData = serial.readLine();

  //check to see that there's actually a string there:

  if (incomingData.length > 0) {

    print("incoming: " + incomingData + " outgoing: " + outgoingData);

  }

​

  // this implements the handshaking: Only

  // send data if we received something

  serial.write(outgoingData);

}

​

function serialError(err) {

  print("Something went wrong with the serial port. " + err);

}

​

function portClose() {

  print("The serial port closed.");

}

​

​

/***********************************************

//

//   Arduino code for minimal communication 

//   with a P5.js sketch using handshaking

//

​

const int LED_PIN = 13;

const int SWITCH_PIN = 7;

​

void setup() {

  Serial.begin(9600);

  pinMode(SWITCH_PIN, INPUT);

  pinMode(LED_PIN, OUTPUT);

​

  // wait until the other side responds

  while (Serial.available() <= 0) {

    Serial.println("1"); // send a starting message

    delay(300);

  }

}

​

void loop() {

  while (Serial.available() > 0) {

​

    int inByte = Serial.read();

    digitalWrite(LED_PIN, inByte);

​

    int switchValue = digitalRead(SWITCH_PIN);

    Serial.println(switchValue);

  }

}

***************************************************/