C# Reading data from a serial port - How to only get new/current data?

Question

I'm working on a project in ASP.NET and the code behind is in C#. I've been reading data from a scale that sends me "YES" or "NOT" if the weight displayed on the scale is within two numbers that you set on the actual scale. As far as I know those two strings are the only data the scale can send. Right now, A button on the page reads data and changes a label to "good job" or "wrong" (Pretty simply just working on functionality right now). But I've been getting older data when I click the button, for example I'll click it twice with nothing on the scale and get "NOT" and the label will change to "wrong" but once I put something on the scale that is within the limit instead of getting "YES" I'll get something like "NOTYES".

I've got a ReadTimeout on the serial port and I have a thread, but I'm not to familiar with threads this is my first time doing something like this. I added a DiscardInBuffer() to the serial port and it seemed to help a bit, but not too much, I also wasn't too sure where to put it.

I've also been printing to the console so I can see what data is actually getting read. It constantly sends data so I'll have a huge string that is somewhat unpredictable like "NOT\nNOT\nNot\n..." so that's why I cleaned the data.

The button has auto post back and the label is in an update panel, so it runs loadPage(), and then read() and then the buttonClick() - which is essentially useless at this point.

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.IO.Ports;
using System.Diagnostics;
using System.Threading;

namespace ScaleTest
{

    public partial class WebForm1 : System.Web.UI.Page
    {
        public SerialPort port;
        public string scaleData = "";

        protected void Page_Load(object sender, EventArgs e)
        {

            if (IsPostBack)
            {
                Thread readThread = new Thread(Read);
                port = new SerialPort("COM3", 9600, Parity.None, 8, StopBits.One);
                port.ReadTimeout = 1000;
                if (port.IsOpen == false)
                    try
                    {
                        port.Open();
                    }
                    catch (Exception oex)
                    {
                        Debug.WriteLine(oex);
                    }
                readThread.Start();
                readThread.Join();
                port.Close();
            }
        }

        public void Read()
        {
            try
            {
                string message;
                string scaleData = port.ReadLine();
                port.DiscardInBuffer();
                Debug.WriteLine(scaleData);
                scaleData = scaleData.Trim().Replace("\r", string.Empty).Replace("\n", string.Empty);
                scaleData = String.Join("", scaleData.Distinct());


                Debug.WriteLine(scaleData);


                if (scaleData == "YES")
                {
                    message = "Good Job!";
                }
                else if (scaleData == "NOT")
                {
                    message = "WRONG!";
                }
                else
                {
                    message = "Try Again.";
                }
                ScaleLabel.Text = message;

            }
            catch (TimeoutException) { }
        }

        protected void ButtonClick(object sender, EventArgs e)
        {
        }

    }
}

If I start with nothing on the scale, run the program and press the button, scaleData will be "NOT" and the label will change to wrong which is correct. But if I put something on the scale within the limit and press the button again, I'll usually have to press the button a few times to get "YES" because it is getting old data and giving me stuff like "NOTYES".

The data is buffered and you have to read until you clear the buffer. — jdweng, Jul 05 '19 at 22:06
Try using the `DataReceived` event. https://learn.microsoft.com/en-us/dotnet/api/system.io.ports.serialport.datareceived?view=netframework-4.8 — Baddack, Jul 08 '19 at 21:55

score 0 · Answer 1 · answered Aug 07 '21 at 16:40

You can try this sample code in this link, which use ReadLine() Method

public static void Main()
{
     _serialPort = new SerialPort();
     _serialPort.BaudRate = 115200;
     _serialPort.PortName = "COM7";
     _serialPort.DataReceived += new SerialDataReceivedEventHandler(DataReceivedHandler);
}

private void DataReceivedHandler(object sender, SerialDataReceivedEventArgs e)
{
    try
    {
        SerialPort sp = (SerialPort)sender;
        if (!sp.IsOpen) return;

        string indata = _serialPort.ReadLine();
        Console.WriteLine(indata);
    }
    catch (Exception) {};
}

C# Reading data from a serial port - How to only get new/current data?

1 Answers1