Connect old DEC VT520 terminal to Raspberry Pi

A computer terminal is a hardware device that is used for entering data into a computing system via keyboard and for displaying data from a computing system using monitor. The first VT terminals were introduced by Digital Equipment Corporation (DEC) during late 70s, with model VT100. During 80s they were very popular, especially VT3xx series. During early 90s, the price of PC siginificantly droped and the terminal market began to crash. The last series VT520 and VT525 apperared during 1993 after whole DEC terminal divison was sold in 1995.

The primary purpose of these devices were to act as an ANSI standard terminal. Most terminals were connected to minicomputers or mainframe computers and often had a green or amber screen. The usual connection of the terminal and the computer was established over serial conneciton, using null modem cable (well known RS232).

I found some of these terminals recently and got the idea to use the terminal for managing mine Raspberry Pi which I use for different tasks like print server, webserver, mqtt broker and so on. First terminal is VT320 but unfortunately I didn't find its keyboard so I can't use it (these terminals used LK201 or LK401 keyboard, with 4 pins modular connector, so if you have one and you don't need it, please let me know). The other terminal is VT520 with the keyboard and, after plugging it to the main supply, it successfully booted its main screen. VT320 and VT520 terminals are shown in pictures below.

The terminal can be connected to Raspberry Pi in two ways. One way is to connect terminal output (COM port) to serial lines available on Raspberry Pi GPIO. The other way is to use usb to serial converter such that terminal COM port is connected to USB port of Raspberry Pi. Since I had one of these usb to serial cables, I decided to connect it to USB port of Raspberry Pi. As it can be seen from the picture of terminal backside, the computer can be connected to DB25 connector. My USB to serial converter has DB9 male connector so I have to make null modem cable with DB9 female connector on one side and DB25 female connector on the other side. Below you can see pin connection on DB9 and DB25 cable connectors:

DB9 DB25

RxD Receive Data 2 <-- 2 TxD Transmit Data

TxD Transmit Data 3 --> 3 RxD Receive Data

SG Signal Ground 5 --- 7 SG Signal Ground

CTS Clear To Send 8 <--20 DTR Data Terminal Ready

RTS Request To Send 7 --> 6 DSR Data Set Ready

Here is the picture of the USB to serial converter and serial cable that I made from some old DB connectors and a piece of cable with 6 wires .

After connecting the USB to serial converter to Raspberry Pi USB port, it was successfully recognized by Raspbian. I checked it with the following command:

lsusb

and I found it in dev directory using the following command:

ls -la /dev/tty*

To enable login over USB port, I added the following line to /etc/inittab (here you can find some additional information about this configuration file):

T1:23:respawn:/sbin/getty -L ttyUSB0 19200 vt520

To make changes to the /etc/inittab effective without a reboot, I ran the following command:

init q

On terminal I chose the same baudrate (19200 for COM1) and woohooo it is working. Below you can see some pictures from the action! I really like this amber color and the sound of old rusty keyboard.