Keep Talking Or The Microcontroller Explodes (KTOME)

The Physical Build Project based on the game Keep Talking And Nobody Explodes

Project maintained by bcorwen Hosted on GitHub Pages — Theme by mattgraham

Dev blog

I’m currently making short update videos on progress on my Youtube playlist. It’s certainly much quicker to film/narrate what’s new than type up a new blog post! Check there for more up-to-date info, meanwhile a more detailed write-up will appear here going into much more detail.

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2022/05/05 - Building The Button and Keypad

Yet more catch-up with prior progress - this post covers progress from August to September 2021.

The Button

This was a very tricky module to design and print. Although the components I needed to integrate are fairly simple (only the button and an RGB LED), copying the look of the game meant this would need a lot of complex parts.

For the LED, as I was used to using the chunky LEDs, it made sense to design a light box that the LED poked into. Similarly to a prior post describing how the transparent PLA used to make the module indicator bulb turning out diffuse and translucent, this same plastic could be printed on the front of the light box so as to catch the light and make a great diffuser.

The grey PLA I was using as the main module colour turned out to be slightly transparent itself however, so I covered the inside of the light box in aluminium tape to stop unwanted light leakage. This surprisingly made a big difference in the amount of light that made it to the front where it should be seen.

The last issue for the light box was how to attach it to the front of the module. The module fronts were printed laying on their inner face, so it could not be easily printed as part of the face. Instead this was separated into another part which would need to be bolted to the front face. Yet there is so little space between the light box and two sides of the module that it could not be bolted very securely. My solution was to move some of the material of the module box on to the light box to create a rim, and incorporate the bolts which held the module face to the box, sandwiching the light box.

Showing the light box with a rim

The light box sandwiched by the face and box

Sticking with the transparent plastic, the downside to the difficulty in very clear prints meant that the button cover ended up frosted. This isn’t ideal but not a deal-breaker. There’s certainly no off-the-shelf product that could hold the button given how large these buttons are…

The button cover, still able to squint and see the button inside

The hinge was very difficult to modle and also print, but I think I got quite lucky with this one. I’d started to dial in the tolerances so parts slotted together snuggly, and somehow lucked-out in that the hinge would stay in place so that buton cover won’t fall on your fingers when you’re holding the button.

For the button mechanism, I had originally thought of clamping it in place but decided to continue my trend of attempting difficult prints and wanted to use the threads of the button mechanism. There are a couple of threads I used: one to screw the main body of the button into the face of the module, and another screw for the button cap. I’d specifically tracked down a mechanism which had detachable button caps to make changing the button really easy between games, and although the thread seemed far too tiny to print, it actually worked very well (and my surprise was very great considering I was eye-balling the thread size with my calipers)! After a lot of trial and error to nail down the start of the thread, I could print buttons which would orient themselves correctly when screwed tightly in place!

Button bolts and screw thread

Then came a lot of printing! I needed 20 buttons for a set: 4 labels in 5 colours. The buttons were printed in two parts and bolted together, which was simply done to keep the print simple and efficient. I also had to spend a lot of time tweaking the font to be able to import it into Fusion 360, and more time to get a two-colour print with my single-extruder printer. Unless you get very close, the button labels look really nice.

Lots of buttons!

And after alllll of that design and printing work, this module was done!

The finished Button module

Keypads

Another tricky one. Again, the main components to integrate were the key switches and LED bulbs, but creating switchable, oversized keycaps involved a lot of attempts to get right.

The main issue with oversized keycaps is that if the caps are pressed near the side (rather than in the middle, above the switch), then this will cause a twisting force between the cap and switch, and the cap can jam or even break off the switch. To tackle this, I decided to increase the distance from the face of the cap to the switch, making the switches super tall, as well as adding in 4 rods to the cap thatwould act as stabilisers.

Switch holder and keycap

Switch and cap in place

So with the caps having such a large stand-off from the switch, the switches needed to be held at a good distance from the face of the module. This necessitated the use of a “cradle”, which hangs below the face and holds both the switches and the LEDs for the lighting effects.

The key cradle

Cradle attached to the module face

And lastly, another modification to make my life easier when the game is played: splitting the keycaps in two. As the keycaps are tall due to the guiding rods, as well as quite fragile while out of the cradle, all of the possible caps needed for the module would take up a lot of space and would have to be handled carefully. So after identifying this issue, I split the cap into a lower piece with the rods which would stay in place and an upper piece which would be thin and switchable to change symbols displayed.

Showing the key cap split in two, to aid in storage and easy of swapping symbols.

This photo above shows an initial version which was just held in place with a push-fit. However, after other builders pointed out there could be quick degredation of the fit after a few cycles, I have designed another version with a magnetic conncetor.

As for the symbols? I could print these into the plastic as I did with the Button’s buttons, but as this is supposed to be as keyboard keys, I thought it more thematic to use stickers. These haven’t been designed yet, and will probably be done when I’m sure there’ll be no more little changes.

Wrapping up

At this point, I’ve closed in the on case design, and have built 4 (pretty tricky) module boxes!

Showing the inner case and modules made so far at this point in time!

It’s starting to come together even more!

The outer case was still being worked on at this point, where the side panels and widgets needed to be designed…

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