1:3 Scale VT100 with working keyboard

I've made many retrocomputer miniatures but this is the most complex.

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The DEC VT100 is an iconic computer terminal from the 1970s and many influential software applications like VI were written on them.

So, to continue my smol retrocomputer series I decided to make this project a bit hard by giving it a working keyboard that looks, feels, and sounds as much like the original as I can manage.

I also post regular build updates on Mastodon:

I'm using FreeCAD to model the case parts and then 3D print them in Polylite PLA or PLA+.

I'm using KiCAD to make the custom circuit board for the small keyboard. I wish I had a LumenPNP to fab the boards but until I get one I'm using a Chinese fab house.

The case is sized to fit a single board computer like the RPi 4 or similar.

I've ordered but not yet tested a 3.5" diagonal TFT display that is 640x480 pixels and takes HDMI input. That would give it enough resolution to display the orginals' 80x24 character mode.

There are a few good emulators for the VT100 so I'm hoping that with the working keyboard and a serial port on the back it can be a handy portable terminal to use with old big iron like an IBM System/360 or the excellent PiDP/11.

  • PCBs arrived, mechanical assembly in progress

    Trevor Flowers05/20/2024 at 01:06 1 comment

    The prototype boards from PCBWay arrived and they look exactly as I spec'ed them. The components that their engineer helped choose look like they'll nicely work as expected, too. I really appreciate that they sponsored this first order.

    I've refined the mechanical assembly of the 1:3 scale keyboard switches quite a bit, trying out various materials and tolerances to find a great feel when pressing a key.

    One new material I'm working with is polymer clay. The curing temperature of polymer clay is lower than the melting point of PLA so it's possible to print molds and bake the clay in the molds. This is helpful because some of the parts for these switches are tiny, not much bigger than a couple of grains of sticky rice together, so they would be hard to remove from molds if they clay was still soft.

    Polymer clay can also be shaped after it is hard using machine tools like small milling machines and lathes. I have watchmakers tools including a mill and lathe so I can cut and turn precision features on molded and baked parts.

    If you've ever touched some of the polymer clay art from artists on Etsy or other platforms then you know it can be good to touch, feeling nicer than 3D prints and warmer than metal.

  • PCBs on their way

    Trevor Flowers05/02/2024 at 02:23 0 comments

    PCBWay is sponsoring a round of PCBs for the 1:3 scale VT100 keyboard! 🎉

    Their assembly engineer (who didn't know about the sponsorship) gave me advice about the design and component choice which is a level of service that I haven't received from other fab houses. The order is in so we'll see how they look in a week.

    In the meantime I'll to make a handful of switch parts so that when the boards arrive I can validate the entire assembly and code before making a bigger board order.

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svofski wrote 05/02/2024 at 16:31 point

I'm a huge fan of mini versions of working keyboards. Would love to see more about your VT100 variant.

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Trevor Flowers wrote 05/03/2024 at 22:28 point

Once the PCBs are here and I have a chance to validate the mechanical assemble of the switches I'll post more details. The short story is that I'm using a combination of printed mechanical parts, a bit of springy material, and an epoxy wiped into the keycap glyph indents to provide visual contrast.

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