Can't connect to Arduino from C# WIndows host on first try

Projects Programming
1

Hi all,

I am using C# 2010, Windows 7 and an Arduino Nano CH340G (serial USB interface) as a serial data source.

The Arduino is configured such that when I send it an asterisk it will respond with a plus sign. This code works and I tested it using the Arduino IDE Serial monitor and Putty.

In the form load event of the Windows Forms app I get a list of comm ports and then I traverse this list looking for the one corresponding to the Arduino test device. The odd behavior that I am experiencing is that when I first connect the serial device and run my app the program does not detect the Arduino. However, if I run the app again it locates it without any problems.

I got it to work by "polling" the comm port twice. The first time around it fails; the second time around it succeeds. Here is the working C# code:

private void frmMain_Load(object sender, EventArgs e)
{

      int iCboIdx;
      int iLoop = 0;

      //Get serial ports into list.
      List<String> lsPorts = new List<String>(System.IO.Ports.SerialPort.GetPortNames());

      lsPorts.Sort();
      
      foreach (string sPort in lsPorts){

        //Add the COM id to the dropdown list, get the list index.
        iCboIdx = cboPort.Items.Add(sPort);

        //Test whether the Arduino reader is connected to this port. Return True if so
        //or False if not.

        iLoop = 0;

        //I need to do this loop because for some unknown reason the software does not locate
        //the reader on the first attempt right after the reader has been connected to the PC.
        //It always seems to work on the second attempt though.
        do
          if (comTest4Reader(sPort))
          {
            //Yes, set selected index for this item.
            cboPort.SelectedIndex = iCboIdx;

            lblStatus.Text = "Reader found on " + sPort;
            break;
          }
          else
          {
            iLoop++;
            Thread.Sleep(500);
          }
        while(iLoop<2);

        }
}

I found that this code does not work if the Sleep statement is removed or too low. This gives me a suspicion that the issue is time based, but I am unable to see how.

The C# code for the function follows:

    Boolean comTest4Reader(string sCOMPort)
    {
      //Routine that tests to see whether the COM port corresponds to the Arduino Reader.
      
      //Use a local serial port object.
      SerialPort serRdr = new SerialPort(sCOMPort, 9600);

      try
      {

        if (!serRdr.IsOpen)
        {
          string sRetMsg = "";
          serRdr.ReadTimeout = 1000;

          //bad serRdr.DtrEnable = true;

          serRdr.Open();

          serRdr.Write("*");
          Thread.Sleep(1000);

          if (serRdr.BytesToRead > 0)
          {
            byte[] buffer = new byte[3];

            // There is no accurate method for checking how many bytes are read
            // unless you check the return from the Read method.
            int iBytesRead = serRdr.Read(buffer, 0, buffer.Length);

            sRetMsg = System.Text.Encoding.Default.GetString(buffer);
          }

          serRdr.Close();

          return sRetMsg.Contains("+");

        }
        else
        {
          //Port already open, can't do test.

          return false;
        }
      }
      catch (Exception ex)
      {
        MessageBox.Show(ex.Message);
        return false;
      }
    }

I can't seem to figure out what effect the above function has on the serial port leaving it functional on the second run. Before putting in the loop I would simply run the app, let it fail, exit and run it again, succeeding on the second try. It seems it initializes the serial port in some way that I am not able to determine. I will be testing with a different Arduino just to discard the possibility of it being the CH340G serial/USB interface. I can also test it on a different computer.

I am aware of the issue surrounding this USB/serial interface chip, but so far have been able to make this Arduino (technically it is called a DCcduino) work with the Ardiuno IDE and aside from this odd glitch the app works fine.

Has any one experienced this behavior? Any suggestions on what sort of initialization procedure I can follow with each comm port? I would like to remove the loop that performs each test twice as this slows down the start of the app. Thanks all for your help and orientation. Saga

2

What happens if you close the Arduino Serial port, send a message from Visual Studio, and then open the Arduino com port. Do you see anything?

3

Thanks econjack.

I changed the code, removed the Sleep function from the main Do loop and instead put in a MessageBox.Show() that displays a message. The code ran dine, but it still took two tries to locate the Arduino port. Saga

4

I wrote this some time ago, but see if it sheds any light for you:

using System;
using System.Threading;
using System.IO.Ports;
using System.IO;
using System.Windows.Forms;


public class frmMain : Form
{
  SerialPort currentPort;
  bool portFound;

  #region Windows-generated code

  private void InitializeComponent()
  {

  }
  #endregion

  public frmMain()
  {
    InitializeComponent();
    SetComPort();
  }
  [STAThread]
  public static void Main()
  {
    frmMain main = new frmMain();
    Application.Run(main);
  }

  private void SetComPort()
  {
    try
    {
      string[] ports = SerialPort.GetPortNames();
      foreach (string port in ports)
      {
        currentPort = new SerialPort(port, 9600);
        currentPort.Parity = Parity.None;
        currentPort.DataBits = 8;
        currentPort.StopBits =  (StopBits) 1;

        if (DetectArduino())
        {
          portFound = true;
          break;
        }
        else
        {
          portFound = false;
        }
      }
    }
    catch (Exception e)
    {
    }
  }
  private bool DetectArduino()
  {
    try
    {
      //The below setting are for the Hello handshake
      byte[] buffer = new byte[5];
      buffer[0] = Convert.ToByte(16);
      buffer[1] = Convert.ToByte(128);
      buffer[2] = Convert.ToByte(0);
      buffer[3] = Convert.ToByte(0);
      buffer[4] = Convert.ToByte(4);
      int intReturnASCII = 0;
      char charReturnValue = (char)intReturnASCII;
      currentPort.Open();
      currentPort.Write(buffer, 0, 5);
      Thread.Sleep(1000);
      int count = currentPort.BytesToRead;
      string returnMessage = "";
      while (count > 0)
      {
        intReturnASCII = currentPort.ReadByte();
        returnMessage = returnMessage + Convert.ToChar(intReturnASCII);
        count--;
      }
      
      //ComPort.name = returnMessage;
      currentPort.Close();
      if (returnMessage.Contains("HELLO FROM ARDUINO"))
      {
        return true;
      }
      else
      {
        return false;
      }
    }
    catch (Exception e)
    {
      return false;
    }
  }
}
5

Thanks again econjack,

I recognized the code that you posted. When looking how to recognize the Arduino found the page that lists that code. In fact, if you'll notice, the code that I posted is a derivative of that original code. It was very helpful!

Update: I tested my C# app using an original Arduino Uno and the codes works perfectly, so now I begin to suspect that it is some idiosyncratic detail that I am missing dealing specifically with the CH340G chip. Saga