Minitel screen for video synthesis
(composite video to minitel)

I previously got my hand on a Minitel, a popular computer like device in the late 80s in France. Its screen could only display text with some early graphic with ASCII art.

I used its keyboard for a MIDI keyboard project call Miditel and was left with the screen.

Without its keyboard, my Minitel was not really useful since its purpose is to display character and not any picture, video, etc…

But I found a project whose goal was to give a composite video input to a Minitel by cfp-radio : Recycler un ancien Minitel :adaptation moniteur TV.

On their webpage, they explain how to create a little adapter board that would allow converting a Minitel from a character displaying console to a true CRT monitor with a composite input. I really like the idea and wanted to re-create it to be able to use the Minitel screen for video synthesis in my synthesizer setup.

On the right you can find the original schematic from cfp-radio and my version updated with KiCad. The circuit is quite simple and runs arround the LM1881 a video sync separator. For more detail about the circuit, go check the description by cfp-radio (in French, but Google Translate can help you!).

My goal was to take their schematic, re-create it, make a small SMD board with all the components and make it fully open-source (MIT licence). Everything is available on GitHub. Thanks to Pierre from cfp-radio that allows me to re-create their circuit and share my version of their project freely.

The result is a small all SMD PCB (42x19mm). I decided to go with rounded tracks using the kicad-round-tracks plugin to give it an old school look that fit with the Minitel circuit style.

As per usual, the circuit was manufactured using PCBWay services.

One mistake I made is with the output connector of the PCB. The pitch between the pin to connect it to the Minitel mother board is too small (2.54mm pitch versus 5.08mm pitch).

In my case, I unsoldered the 5.08mm pin header from the original Minitel board I’m replacing, and made a custom adapter cable to fit the main mother board. See the below picture for more detail.

With that adapter I could connect my circuit to the Minitel, and it worked without any problem thanks to the previous work of cfp-radio!

The last step for me was to set up a video synthesis setup. I went for Auto Waaave by Andrei_Jay. Installed everything on a Raspberry Pi 3b, connected its composite signal via 3.5 mm CTIA style TRRS jack to my newly composite Minitel and voilà, I have a nice retro screen to display some video synthesis. See the video below for a simple demo.

Again, the whole KiCad project is open-source and available on GitHub.