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A Raspberry Pi Serial to Ethernet adapter

Turn a Raspberry Pi into a Dial-up Modem to act as a LAN interface for legacy computers and serial terminals.

Anyone remember the good old days of dial-up connectivity? Well, back in 80's and 90's, computers connected using a dial-up modem, and the only thing computers needed was a serial COM port for communication, which was included virtually with every computer (USB didn't exist back then!). Nowadays every computer sold has some sort of Wi-fi or Ethernet connectivity, and our old legacy computers are just left to rot! Well, I'm planning on changing that! Why? For fun, of course! :-D

In this four-part tutorial we will build a Raspberry Pi that will be able to present itself as a serial modem to a client computer which will enable easy connection to Internet using their pre-existing serial port on any Windows 3.1/95/98/Me and any other operating system with built-in support for PPP. In other words we'll use a Raspberry to convert a serial connection to an Ethernet connection. When all is said and done, your old legacy computer will be fooled to think that it's calling an actual Internet Service Provider and establishing an Internet connection with them! Your Raspberry Pi will just be telling your computer what it wants to hear, and is providing access to the Internet using your pre-existing Internet connection.

The Virtual Modem script will not only allow you to connect your old computer to the Internet, it will allow you to use the serial connection to login to the console of the Raspberry Pi or fake BBS phone calls for example. The VModem script was designed to be modular, and allows you to assign your own Linux scripts to specific phone numbers, accessed with standard Hayes “ATD12345”-style commands, and the scripts will be able to do whatever you would like them to do. I will be writing more specific tutorials about these functions at a later time, so stay tuned!

My goal is to have a Raspberry Pi simulate a Standard 56K modem. Your client computer will be able to communicate with it over serial, and through the Raspberry, connect to the Internet. The baud rate can be changed to your liking. I've tested the virtual modem at the following symbol rates: 9600, 19200, 38400 and 57600 baud.

This guide is useful for anyone who would like to do PPP networking experimentation or have a computer connect to the Internet without a network card. It could also be useful for anyone who would like to experiment with a Virtual Modem. Since pretty much every IBM compatible computer has a RS-232 serial port, technically you could connect any computer to the Internet, as long as there is a way to use PPP. Windows 3.1 will need an extra program called Trumpet Winsock, but Windows 95 and later operating systems have Dial-up networking built-in!

Before we start

There may be better ways to accomplish these tasks. This process has worked for me, however there are probably a plethora of ways this software could be improved. That's why I welcome improvement ideas and fixes to the guide and scripts provided. Also, obviously, I do not take any responsibility direct or otherwise for any damages that may be caused using the material provided in this site. This being said, I've taken every reasonable step to make sure everything works as intended.

On to the next chapter!


Questions? Comments?

I welcome any corrections, additions, files or any other handy resources you'd like to share. And if you'd like to become a contributor, I would be happy to hear from you!

About this site

Resources on this site are provided as-is. I cannot guarantee that the information is accurate and/or that the software will work as expected in your case. As such, I cannot be held responsible or liable for any damage(s) caused either directly or indirectly by using any of the resources on this site, or by relying on other information I have provided. That said, I've made every effort to make sure the information and resources provided on this site are as accurate as possible.

guides/virtual_modem.txt · Last modified: 2019-05-27 18:12 by omolini