In this article, I will show you how to use the SerialPort control in .NET 2.0 for your serial communication needs. In particular, I will build a chat application that allows two computers (connected using either a serial cable or a Bluetooth connection) to communicate. One interesting use of this chat application is in communicating with external serial devices. You will learn how to use the AT commands to programmatically control your mobile phones through a serial Bluetooth connection

Hardware Needed
Unless you have two computers, you won't be able to test serial communications. However, you can use a null modem cable to connect two serial ports on the same computer to simulate two computers communicating over serial ports. But most computers today come with at most one serial port (and some notebooks do not even have one).

One good solution is to use a USB-to-serial port adapter to convert an USB connection into a serial port. Hence, if you computer does not have any serial ports, you would need a pair of USB-to-serial port adapters, and a null modem cable 1

The USB-to-serial port adapter comes with its own drivers. After installing the drivers, right-click on My Computer on the Desktop and select Properties. In the System Properties window, click on the Hardware tab and click the Device Manager button. Expand the Ports (COM & LPT) item and locate the two newly added COM ports (see Figure 2).
On my computer, the two serial ports are COM28 and COM29. Write down the port names as you'll need these later