130: PCB Enclosure

I really thought that when I got around to laser cutting and assembling my first PCB enclosure, it’d be for an Arduino or a Raspberry Pi. Y’know, something you can emulate retro games on. Hell, I’d 3D printed about a dozen different PCB enclosures for people making DIY emulator hardware back in the Aurora Public Library makerspace, but I just never got around to making one for myself. Oh well.

But then! Earlier this year, Chris of Windy Gaming got in touch about making a laser-cut enclosure. His project was more complicated than just wrapping acrylic around one PCB. This enclosure was meant to hold two adapters together:

  • A DB-15 to USB decoder (in its own black plastic enclosure)
  • A custom PCB, “UD2ATP,”  to connect that to an ATP-300 Supergun

Furthermore, because the finished assembly would be for arcade game setups involving two players, we’d be fitting two sets in there! I knew it’d be fun reconciling my obsession with designing things on a 1/16″ grid with the reality that the existing hardware wouldn’t quite fit that grid. Or would it?

I love dot grid paper.

I started out taking measurements of the PCB and decoder, scribbling on some dot grid paper. I’m not really certain that amateur technical drawing on paper is anything more than affectation at this point, but I still enjoy it, so there! This physical step was when I first realized I might be able to get away with my 1/16″ grid after all—many of the measurements fit very nicely in those increments, but I still had a feeling there’d be some nudging to do.

With total width, length, and height ascertained, I recreated the enclosure’s floor in Illustrator and threw some shapes together to represent the two pieces of hardware inside. Then I drew up the sides of the enclosure and added box joints. Box jointing is another situation where I often have to deviate from my 1/16″ grid: your joints shouldn’t be any thicker than the material itself. Conveniently for me, all of the acrylic we’d be using measures .120″ thick—a difference of five thousandths of an inch just wasn’t significant in the end.

The first prototype, with labeled sides and many small mistakes.

The first prototype exposed several small mistakes. My connector cutouts weren’t big enough. I placed the PCB mounting holes where the decoder would sit and the decoder button hole where the PCBs would sit. I even made the box exactly 1/8″ too long after counting the total length of the DB15 female connector rather than half. While these problems obviously needed fixing, they felt relatively small compared to the success I had in keeping to my 1/16″ grid! It also confirmed that the kerf settings I used—offset paths meant to account for the width of the laser when making precision cuts—kept the pieces tightly together, but not so tight that they couldn’t be disassembled.

The pieces are cut such that the enclosure can be opened if necessary, but will stay together through normal use

The second prototype fixed all of those problems, but it also confirmed one big problem we kind of saw coming. Chris had mentioned that we’d probably need to mount the PCB to the enclosure, so I did measure where the holes would need to be to line up properly. I was secretly hoping we wouldn’t need them, though, based on a misunderstanding of the DB15 female connector and the acrylic it’d be sitting inside. Unlike the decoder side (the face of which rests on the cutout edge) the DB15 female connector can’t rest on its cutout because it has to fit inside the male connector. Without something holding the PCB up from the bottom of the enclosure, it’d remain loose and floppy inside. Worse, the tiny needle-like points of the PCB’s contacts would be resting directly on the acrylic, which is us just asking for that burnt-plastic smell.

The DB15 side of the second prototype

The second prototype is also where I incorporated Chris’s excellent idea to add a blue accent to the box via the side pieces. We’d always planned on something transparent and also something blue, but I figured that we’d just end up using fluorescent blue acrylic for the whole piece and that’d be the end of it. I think the translucent blue is an excellent contrast to the clear cast acrylic used on the rest of the piece.

The almost-final enclosure stands tall

We went through a few different screw and spacer types, and landed on an all-nylon solution. Two 1/16″ washers filled just the right amount of space between the PCB and the enclosure, and it didn’t even require an adjustment to the total height of the enclosure! Now we just have a few small issues to work out—one being that our nuts are just a bit bigger than our feet. Huh!

The final product will be available on Windy Gaming.



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