Question

So I am trying to talk to a gsm modem using AT commands, I’m trying to do a basic test to make sure the modem is ok by sending the command AT and receiving OK. The issue is that I’m receiving “AT Blank Line OK”, is there any way so when I send AT, I only read OK?

Imports System.IO.Ports

Public Class GUI
Dim Device As New System.IO.Ports.SerialPort()
Private Sub GUI_Load(ByVal sender As System.Object, ByVal e As System.EventArgs)         Handles MyBase.Load
    Port.Text = "Select Port"
    For Each item As String In IO.Ports.SerialPort.GetPortNames
        Port.Items.Add(item)
    Next
    Device.BaudRate = 9600
    Device.Parity = Parity.None
    Device.StopBits = StopBits.One
    Device.DataBits = 8
    Device.Handshake = Handshake.RequestToSend
    Device.DtrEnable = True
    Device.RtsEnable = True
    Device.NewLine = vbCrLf
    Device.WriteTimeout = 5000
End Sub

Private Sub Port_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Port.SelectedIndexChanged
    Device.PortName = Port.SelectedItem.ToString
End Sub

Private Sub Send_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Send.Click
    Try
        Device.Open()
        Dim msg As String
        msg = Message.Text
        Device.DiscardInBuffer()
        Device.DiscardOutBuffer()
        Device.Write("AT" & vbCrLf)
        MsgBox(Device.ReadExisting())
    Catch ex As Exception
        MsgBox("Error!")
    End Try
    Device.Close()
End Sub
End Class

Answer 1

Sounds like the modem is set to Echo commands. To turn this off try sending E0 first.

More info here