Serial Communication , a neat trick

[bachphi]

I came across this article with a neat trick, I thought I would share with you:
https://www.codemag.com/article/0611061/Fun-with-RFID


The RFID reader send 12-byte datagram with a format that looks like :
<LF>123456789A<CR>

Since serial devices send their datagram in more than one blocks, his neat trick was
using a TextBox control (with the Multiline property set to True), then append all data until
the last line is an empty string. then data( TagID) is in the second to the last line.
To check for this condition, he use the Text changed event.

Code: [Select]

Public Class Form1

    Private WithEvents serialPort As New IO.Ports.SerialPort
    Private tagID As String = String.Empty
    Private timeRecorded As DateTime = Now
    Const COM As String = "COM3"
    Const FILE_NAME As String = "C:\Attendance.csv"
    Const INTERVAL As Integer = 3

    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load

        Timer1.Interval = INTERVAL * 1000
        If serialPort.IsOpen Then
            serialPort.Close()
        End If
        Try
            With serialPort
                .PortName = COM
                .BaudRate = 2400
                .Parity = IO.Ports.Parity.None
                .DataBits = 8
                .StopBits = IO.Ports.StopBits.One
                .Handshake = IO.Ports.Handshake.None
            End With

            serialPort.Open()

        Catch ex As Exception
            MsgBox(ex.ToString)
        End Try
    End Sub

    Private Sub DataReceived(ByVal sender As Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles serialPort.DataReceived

        txtTagID.BeginInvoke(New myDelegate(AddressOf updateTextBox), New Object() {})

    End Sub

    Public Delegate Sub myDelegate()
    Public Sub updateTextBox()
        ' for receiving plain ASCII text
        With txtTagID
            .AppendText(serialPort.ReadExisting)
            .ScrollToCaret()
        End With
    End Sub

    Private Sub Timer1_Tick(sender As Object, e As EventArgs) Handles Timer1.Tick

    End Sub

    Private Sub txtTagID_TextChanged(sender As Object, e As EventArgs) Handles txtTagID.TextChanged
        If txtTagID.Lines(txtTagID.Lines.Length - 1) = String.Empty Then
            Dim temptagID As String = txtTagID.Lines(txtTagID.Lines.Length - 2)

            Dim tp As TimeSpan = Now.Subtract(timeRecorded)
            Dim timeInterval As Double = tp.Ticks / TimeSpan.TicksPerSecond

            If (temptagID = tagID) And timeInterval < INTERVAL Then
                Exit Sub
            End If

            tagID = temptagID

            timeRecorded = Now
        End If
    End Sub

    Private Sub Form1_FormClosing(sender As Object, e As FormClosingEventArgs) Handles MyBase.FormClosing
        serialPort.Close()
    End Sub
End Class



[larryhts]

bachphi,  Thanks this is will help with a project I have coming up next year.