Sending a numerical variable from Processing to Arduino

edited December 2015 in Arduino

I'm new in this world, and I'd know how to send a numerial variable Processing-->Arduino (not Arduino-->Processing!!).

I've got the programme for send only a letter, but i don't know hoy to send a number (0-100).



  • Answer ✓

    I would just send the number as a String followed by a delimiter. Then on the arduino-side you can reconstruct the number from the characters that you receive.

    Here is an example-code for processing that sends random numbers when you click a mouse-button:

    // libraries
    import processing.serial.*;
    // serial connection
    Serial port;
    void setup() {
      // init serial-port
      port = new Serial(this, Serial.list()[2], 57600);
    void draw() {}
    void mousePressed() {
      // create random number
      int number = (int) random(100);
      // debug
      println("now sending number: "+number);
      // send number
      // write any charcter that marks the end of a number
    // this part is executed, when serial-data is received
    void serialEvent(Serial p) {
      try {
        // get message till line break (ASCII > 13)
        String message = p.readStringUntil(13);
        // just if there is data
        if (message != null) {
          println("message received: "+trim(message));
      catch (Exception e) {

    And here is the counter-part for the arduino, that reads the incoming serial-data and writes the number back to the serial-port when a delimiter is received:

    int c;
    int v=0;
    void setup() {
    void loop() {
      // read serial-data, if available
      while (Serial.available()) {
        c =;
        // handle digits
        if ((c >= '0') && (c <= '9')) {
          v = 10 * v + c - '0';
        // handle delimiter
        else if (c == 'e') {
          v = 0;

    I hope that helps to understand the principle.

  • If you only have a single value to send, you could as well just send a single byte. Would be easier on the arduino-side. Just saw this thread with an example code:

  • Thank you, you have fixed my problem!! Now I have another one, but I'll write a new discussion :D

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