Public Class Form1
 
    Dim inputData As String
    Dim Empfangen As String
 
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button1.Click
        Try
            SerialPort1.PortName = ComboBox1.SelectedItem
            SerialPort1.BaudRate = ComboBox2.SelectedItem
            SerialPort1.Open()
            MsgBox("Ausgewählter Com-Port erfolgreich geöffnet!")
            Label1.Text = ""
            Label2.Text = "Geöffnet"
 
        Catch ex As Exception
            If SerialPort1.IsOpen = True Then
                MsgBox("Der ausgewählte Port ist bereits geöffnet!")
            Else
                MsgBox("Stellen Sie sicher, dass der ausgewählte Port verfügbar" & _
                  "ist!")
            End If
 
        End Try
    End Sub
 
    Private Sub Form1_FormClosed(ByVal sender As Object, ByVal e As _
      System.Windows.Forms.FormClosedEventArgs) Handles Me.FormClosed
        If SerialPort1.IsOpen = True Then
            SerialPort1.Close()
        End If
    End Sub
 
    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button2.Click
        If SerialPort1.IsOpen = False Then
            MsgBox("Der ausgewählte Port ist bereits geschlossen!")
        End If
        If SerialPort1.IsOpen = True Then
            SerialPort1.Close()
            MsgBox("Ausgewählter Com-Port erfolgreich geschlossen!")
            Label2.Text = "Geschlossen"
            Label1.Text = ""
        End If
 
    End Sub
 
    Private Sub SerialPort1_DataReceived(ByVal sender As Object, ByVal e As _
      System.IO.Ports.SerialDataReceivedEventArgs) Handles _
      SerialPort1.DataReceived
        inputData = SerialPort1.ReadExisting '//oder SerialPort1.ReadLine
        Me.Invoke(New EventHandler(AddressOf DoUpdate))
    End Sub
 
    Public Sub DoUpdate()
        Label1.Text = CStr(inputData) + " Volt"
    End Sub
End Class