Hier der Code (den habe ich einfach vom Video übernommen) :

Code:
Public Class Form1

    Private Sub COM1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles TextBox1.TextChanged
        Try
            SerialPort1.PortName = TextBox1.Text
            SerialPort1.BaudRate = TextBox2.Text
            SerialPort1.Open()
            Button1.Enabled = False
            Button2.Enabled = True
            Button3.Enabled = True

        Catch ex As Exception
            MsgBox("Verbindung konnte nicht hergestellt werden")
        End Try
    End Sub

    Private Sub Form1_FormClosing(ByVal sender As Object, ByVal e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing
        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
        SerialPort1.Write("1" & vbCr)

    End Sub

    Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
        SerialPort1.Write("0" & vbCr)
    End Sub
End Class
Zu DanielSan: Wie hast du das mit dem Com Port vorher schließen gemacht???