Question

I’m developing a piece of software, which reads data sent through the COM port and display the value in a live graph and in a textbox (for debugging). It reads fine at first, but then suddenly one of the numbers is divided into two pieces. Like this:

63 – 64 – 65 – 66 – 67 – 6 – 8 – 69 – 70 – 80

It should say 68. This makes the graph all wrong!

What is the cause of this?

My code is as follows:

   private void DisplayText(object sender, EventArgs e)
    {
        textBox1.AppendText(RxString);
        textBox1.AppendText(" - ");

    }



    private void comPort_DataReceived_1(object sender, SerialDataReceivedEventArgs e)
    {
      RxString = comPort.ReadExisting();
      this.Invoke(new EventHandler(DisplayText));

      newRead = Convert.ToDouble(RxString);
      AddDataToGraph(zedGraph, howfar, newRead);
      howfar++;


    }

Thanks in advance.

Answer 1

There’s no guarantee in what size chunks you will get the data….

it could get them character at a time, or several characters at a time.

Generally, never depend on timing to work out the difference between logical “chunks” ( in your case, numbers). Instead create a protocol that you can interpret.

in your case if you have a VERY simple protocol where you send a number [space] number [space] number then you can parse out

eg…

RxString += comPort.ReadExisting();  // add to an existing string
if(RxString.Contains(" ") // ok, there is a space, so we can parse out a number
{
  // parse...
  newRead = Convert.ToDouble(RxString.Substring(0,RxString.IndexOf(" "));
  RxString = RxString.Remove(0,RxString.IndexOf(" ")+1;
  AddDataToGraph(zedGraph, howfar, newRead);
  howfar++;
}

and if you were using 123,123,234,123,343\n

    RxString += comPort.ReadExisting();  // add to an existing string
    if(RxString.Contains("\n")   // ok, there is a linefeed, so we can parse out all the numbers
    {
       // parse...
       var line = RxString.Substring(0, RxString.IndexOf("\n"));
       var values = line.Split(new char[] {','}, StringSplitOptions.None).ToList();
       values.ForEach(v =>  AddDataToGraph(zedGraph, howFar, Convert.ToDouble(v)));
       RxString = RxString.Remove(0, RxString.IndexOf("\n"));
       howfar++;
    }