Minitel serial adapter - Mar 2026
A USB type C port for the Minitel !
DESCRIPTION
A while ago (2018) I made multiple experiments on the Minitel, time to get back to business.
Talking to the minitel from the computer always was a pain to wire due to the 5 pin DIN connector.
In my first experiments I used 1.5mm2 (+/-16AWG) solid core cable that I stuffed shamelessly into the female port of the Minitel.
This was a sad moment in history.
CONNECTOR
More recently a guy from the hackerspace got himself a Minitel and asked for advice in order to make it talk through standard serial.
I needed a solution and buying a connector was still out of the question.
At first I considered 3D printing a connector.
Instead I “borrowed” a MIDI cable from a musician friend SNS.
TTL to RS232
Salvaged cable in hand, I started designing a PCB.
I saw a handful of tutorials using 2 transistors in order to level shift the TTL to RS232.
After considering this hack I decided that I would do it the “proper” way by putting the mountain of ewaste I call my office to good use.
Finding a used MAX232 (datasheet) was surprisingly easy, this is an IC designed for TTL to RS232 and this enables a standard UART port to speak RS232.
Please note that RS232 is inverted logic compared to TTL, -15v indicates a logical 1 and +15v indicates a logical 0 whereas in TTL +5v is a logical 1 and 0v is a logical 0. Thus the signal is reversed. For this reason I decided to use the 2nd channel of the MAX232 to invert once more :)
The datasheet tells us that we can use 1µF capacitors but I had none that were polarized, so instead of desoldering 20 years old caps I put some 10µF which works fine in this application.
Also you have to keep in mind that the Minitel logic is floating unless pulled up, see documentation for open-collector / open-drain. So this is the reason for R1, I put 10k but anything between 4k7 and 47k should be fine.
SCHEMATIC
Here is the schematic for my TTL to RS232
USB TO MINITEL PCB
I plugged a off the shelf USB to serial converter based on the CH340G chip but anything that supports the target speed and parity of the Minitel is fine.
I also swapped the type A plug to a type C plug because it makes the adapter more practical to use.
Here is the final PCB
Here is the final PCB
SERIAL CONFIG
Here are the parameters used in Putty
