Turn a Raspberry Pi into a Serial Dial-up Modem to connect to ethernet or the Internet
Do you remember the early days of Internet and dial-up connectivity? We used to be connected to the Internet using a modem connected to a telephone network, and the only thing computers needed was a serial port for communication, which virtually every computer had. Nowadays every computer sold has some sort of Wi-fi or Ethernet connectivity, but our vintage computers are left to rot offline! I plan to change that. Nowadays, there are many ways you can get a PC online, including getting a 3com 3C503 or 3C509 network adapter, but sometimes an old PC just doesn't have expansion for a network card expansion, or maybe you're not even trying to connect with a PC. Well, whatever piece of technological equipment it may be, as long as it has at least one serial port, a keyboard and a display, you're in luck! Get to experience connecting to the Internet just like in the good old days.
In this four-part tutorial we will build a Raspberry Pi that will act as a serial modem to a legacy computer which will enable a straightforward connection to Internet using a pre-existing serial port on any computer with support for PPP, this includes all Windows computers starting from Windows 3.0 and early Macintosh classics. But PPP support is not strictly required, and even simple serial terminals can connect to the Internet using Linux as a login host. In other words we'll use a Raspberry to convert a serial connection to an Ethernet connection. When all is said and done, your legacy computer will think it's calling a real Internet Service Provider and establishing an Internet link with them! Your Raspberry Pi will just be telling your computer what it wants to hear, and is actually the one 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, or any other network, as long as there is a way to use dial-up PPP. Windows 3.0, 3.1 and 3.11 will need an extra program called Trumpet Winsock, but Windows 95 and later operating systems have built-in Dial-up networking.
There are probably better ways to accomplish some tasks. If you have any improvement suggestions, I'd love to hear from you! Especially if you have ideas how to improve the documentation, or the Virtual Modem scriptlet itself. Also a little disclaimer: I do not take any responsibility direct or otherwise for any damages that may could be caused using the material provided in this site. That being said, I've taken reasonable steps to ensure everything works as intended.
On to the next chapter!
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!
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.