How to Send SMS with 3G Modem in C#

AT commands are instructions used to control a modem. Every command line starts with "AT" or "at"

Open your Visual Studio, then click New Project, then select Visual C# on the left, then Windows and then select Windows Forms Application. Name your project "SendSMS" and then click OK button.

How to Send SMS Message via GSM Modem in C#

Sending SMS messages via a GSM modem in C# involves interacting with the modem using AT commands through a serial port.

Here's a basic outline of how you can achieve this

Drag and drop the Label, TextBox, Button controls from the Visual Studio toolbox onto your form designer, then you can design a simple UI that allows you to send sms message in c# as shown below.

Add a click event handler to the Send button allows you to send an sms in c#

private void btnSend_Click(object sender, EventArgs e)
{
    try
    {
        //Configure serial port, using serial port to send sms message
        SerialPort sp = new SerialPort();
        // Change this to the appropriate COM port for your GSM modem
        sp.PortName = txtPort.Text;
        // Open the serial port
        sp.Open();
        // Set up GSM modem for SMS mode, using AT command to send sms
        sp.WriteLine("AT" + Environment.NewLine);
        Thread.Sleep(100);
        sp.WriteLine("AT+CMGF=1" + Environment.NewLine);
        Thread.Sleep(100);
        sp.WriteLine("AT+CSCS=\"GSM\"" + Environment.NewLine);
        Thread.Sleep(100);
        sp.WriteLine("AT+CMGS=\"" + txtPhoneNumber.Text + "\"" + Environment.NewLine);//Set phone number
        Thread.Sleep(100);
        sp.WriteLine(txtMessage.Text + Environment.NewLine);//Set messages
        Thread.Sleep(100);
        // Send Ctrl+Z to indicate the end of the message
        sp.Write(new byte[] { 26 }, 0, 1);
        // Wait for the modem to send the message
        Thread.Sleep(100);
        // Read the response from the modem
        var response = sp.ReadExisting();
        if (response.Contains("ERROR"))
            MessageBox.Show("Send failed !", "Message", MessageBoxButtons.OK, MessageBoxIcon.Information);
        else
            MessageBox.Show("SMS Sent !", "Message", MessageBoxButtons.OK, MessageBoxIcon.Information);
        sp.Close();
    }
    catch (Exception ex)
    {
        MessageBox.Show(ex.Message, "Message", MessageBoxButtons.OK, MessageBoxIcon.Error);
    }
}

First, We will connect to the GSM modem by opening a serial port connection to communicate with the GSM modem, then send AT commands to the modem to configure it for sending SMS messages.

After successful connection of the GSM/GPRS modem with your PC, you can send sms message from this application

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