Sending And Receiving SMS From GSM modem - vb.net

Question

I am trying to send message from GSM modem. I can submit AT commands the response is OK without any ERRORS. But the problem is I can't send message or read message.
I have implemented 3 functions:
Connect to port
Read SMS
Send SMS
Handles
1. Connect To Port:
Private Sub BtnConnect_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles BtnConnect.Click
If SerialPort1.IsOpen Then
SerialPort1.Close()
BtnConnect.Text = "Connect"
Else
Try
With SerialPort1
.PortName = Trim(Mid(ComboBox1.Text, 1, 5))
.BaudRate = 9600
.Parity = IO.Ports.Parity.None
.DataBits = 8
.StopBits = Ports.StopBits.One
.Handshake = Ports.Handshake.None
.RtsEnable = True
.DtrEnable = True
.Open()
.WriteLine("AT+CNMI=1,2,0,0,0" & vbCrLf) 'send whatever data that it receives to serial port
End With
BtnConnect.Text = "Disconnect"
Catch ex As Exception
BtnConnect.Text = "Connect"
MsgBox(ex.Message)
End Try
End If
End Sub
2. Read SMS
Private Sub btn_read_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btn_read.Click
Try
SerialPort1.WriteLine("AT" & vbCrLf) 'is modem okay?
Thread.Sleep(1000)
SerialPort1.WriteLine("AT+CMGF=1" & vbCrLf) 'To format SMS as a TEXT message
Thread.Sleep(1000)
SerialPort1.WriteLine("AT+CPMS=""SM""" & vbCrLf) ' Select SIM storage
Threading.Thread.Sleep(1000)
SerialPort1.WriteLine("AT+CMGL=""REC UNREAD""" & vbCrLf) 'read unread messages
Threading.Thread.Sleep(1000)
SerialPort1.WriteLine("AT+CMGL=""ALL""" & vbCrLf) 'print all message
Threading.Thread.Sleep(1000)
Catch ex As Exception
MsgBox(ex.Message)
End Try
End Sub
3. Send SMS
Private Sub btn_send_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btn_send.Click
Try
With SerialPort1
.WriteLine("AT" & vbCrLf)
Threading.Thread.Sleep(1000)
.WriteLine("AT+CMGF=1" & vbCrLf) 'Instruct the GSM / GPRS modem to operate in SMS text mode
Threading.Thread.Sleep(1000)
.WriteLine("AT+CMGS=""9802100355""" & vbCr) 'sender ko no. rakhne ho tyo txtnumber ma
Threading.Thread.Sleep(1000) 'thapeko
.WriteLine("This is test message" & vbCrLf & Chr(26)) 'txtmessage automatic huna parchha haina?
End With
Catch ex As Exception
MsgBox(ex.Message)
End Try
End Sub
4. Handles for Data received in Serial Port
Private Sub serialport1_datareceived(ByVal sender As Object, ByVal e As System.IO.Ports.SerialDataReceivedEventArgs) Handles SerialPort1.DataReceived
'Pause while all data is read
System.Threading.Thread.Sleep(300)
rcvdata = SerialPort1.ReadExisting()
MsgBox(rcvdata, , "Response From AT")
rcvdata = ""
End Sub
Where did I miss anything? While sending SMS I get CMS 500 error. With the software from the modem I am able to read and send sms. But I need to implement my own in my software.

Answer 1

There may several cause of this error. First check your network. Second set Message service center number using AT commands and save this setting. Hope this will help you

Answer 2

In your second function, you can try declaring a string variable to receive the data, like this:
With serialport1
rcvdata=""
.Write(All AT commands)
Threading.Thread.Sleep(1000)
Msgbox(rcvdata.Tostring)
End With
You can add a handler to datareceived to read all the bytes:
Dim entrada As String = " "
Dim numeros As Integer = SerialPort1.BytesToRead
For i As Integer = 1 To numeros
entrada&= Chr(SerialPort1.ReadChar)
Next
chama(entrada)
Private Sub chama(ByVal dados As String)
rcvdata &= dados
End Sub

Answer 3

AT+CMGS=""9802100355"
Your Phone number is wrong thats why you getting error 500, you need to enter full phone number including 0 at the front.