2

I'm trying to communicate with my Arduiono UNO via USB serial port, more precisely I'm trying to read a string like 125,0, I know it's full of article out there about this, but belive me I've tryied more or less everything, now I got a NODEJS server on a Raspberry Pi that looks like:

var express = require('express');
app = express();
server = require('http').createServer(app);
io = require('socket.io').listen(server);

var SerialPort = require("serialport")
var serialPort = new SerialPort("/dev/ttyACM1", { baudrate: 115200 });

server.listen(8080);
app.use(express.static('public'));      

var brightness1 = 0;
var brightness2 = 0;
var string;

io.sockets.on('connection', function (socket) {
    socket.on('led', function (data) {
        brightness1 = data.value1;
        brightness2 = data.value2;
        string = brightness1 +","+brightness2;
        var buf = new Buffer(1);
        buf.write(string);
        serialPort.write(buf);
        console.log(buf);
        console.log(string);
        io.sockets.emit('led', {value1: brightness1, value2: brightness2});

    });

So based on that, I'm sending a string over the serial and the console log showed above gives me that:

<Buffer 32>    //console.log(buf);
23,0           //console.log(string);

Wich I think it should be ok because I'm sending what I need a 32 and a 0, also if i don't know what it means the

Arduino side I used the sketch provided here and retouch it a bit based on my needs:

void setup()
{
  Serial.begin(115200);
}
void loop()
{
  while(!Serial.available());   //wait until a byte was received
      Serial.println(Serial.read());
      int a = Serial.parseInt();
      int b = Serial.parseInt();
      Serial.println(a);
      Serial.println(b);
      //analogWrite(3, a);
}

but the result of my Serial.print() are really incongruents, something like: 5--2224, which is totally nosense, my question so is WHY? Where I'm getting wrong? I read a lot around, am I missing something?

3
  • You sized your buffer with room for one single byte: it only gets the '2' of "23,0". The ASCII code for '2' is 0x32 (in hex). That's the meaning of <Buffer 32>. Oct 23, 2016 at 16:24
  • @Edgar thanks for your reply! So basically my problem is on server side, so I just need to increase the buffer size to 7? Arduino side is all good right?
    – FabioEnne
    Oct 23, 2016 at 16:55
  • There is a problem server side, but then I am not sure how well the Arduino side would perform, especially if you don't control the timing of the sent bytes. Oct 23, 2016 at 17:01

3 Answers 3

2

This is a common (and my favorite) approach:

  • Choose an “end of message” character. CR or LF can be good choices, especially if you want to test your program with a terminal emulator.
  • On the Arduino, buffer all the received bytes until you see the end of message.
  • When you see the end of message, handle the buffer to a function that will parse and process it.

I would avoid parseInt() for anything but the simplest tests, because it is both blocking and sensitive to the timing of the input.

For an example, you can take a look at this Simple Arduino command line interpreter (look at loop()). It's non blocking, so you can add background processing to perform while waiting for input characters.

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I fully agree here with edgar Bonet.
I only want to add a link to a library I have written that does a line by line (based on end message CR and/or LF)
SerialStringReader This library contains examples.
Note that for many reasons the library uses null terminated strinsg (also known as char arrays) and not the Arduino String class

0

How to correctly read a string from Arduino serial port?

You can use the function Serial.readString(). It will return a string that you typed from the serial monitor.

1
  • No, really. This way you will only get what is in the buffer now. If you read faster than the other end writes you will get just a piece Sep 8, 2018 at 8:13

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