Show HN: Threeboard – a full-size mechanical USB keyboard with only three keys (opens in new tab)

I've actually thought about creating something like this. It looks pretty good for combating RSI. Because it would allow you to have your arms in any position. However, I think it would be necessary to have two of them, one in each hand. And maybe a small trackball on one of them. It would probably also help to have straps on them that wrap around your hand, so you didn't need to grip them to keep them from falling to the floor.

Haven't I seen you in ai03's Discord channel? I would have gone by a different name in there (this was from before the name change of the server, I think), but your handle is very familiar.

I can't stand when I sit down at a co-workers desk to help them and they configured a DSA layout!

I tried to give a bit of an overview of this in the 'hardware design' section of the documentation [0]. It has some external links to further documentation and tutorials in it too. But the learning curve is very steep.

I'd maybe suggest looking for an electrical engineering intro book or course at a level you feel comfortable with, just to get an idea of the basics.

For the ErgoDox keyboard, the schematic is actually available on their own repo [1], but it's going to look quite intimidating initially. But I found a pretty great looking article explaining the electrical design of the ErgoDox that you might find useful [2]. The ErgoDox actually looks very similar electrically to the threeboard, it uses the same MCU (atmega32u4), but of course has the extra complexity of communicating with the other half of the keyboard over the 3.5mm connector.

[0]: https://github.com/taylorconor/threeboard/blob/master/docume... [1]: https://github.com/zsa/docs/blob/master/ErgoDox%20EZ%20Schem... [2]: https://kandepet.com/dissecting-the-ergodox-the-ergonomic-pr...

You don't need a PCB. The Ergodox uses two ICs. One is the microcontroller; it is a mini computer that reads the state of the keys (which ones are pressed right now) and emits the relevant USB messages so your computer interprets those as keystrokes. The other is an i2c i/o expander that reads the keys for the other hand exactly like the microcontroller does. (The microcontroller periodically asks it to scan the matrix on its behalf.) It exists so that only four wires need to span the gap between the two hands, instead of one wire for each row and column. You could, of course, just treat both halves as one keyboard and run the matrix wires between the two sides, and omit the i/o expander. It's basically an optimization for split keyboards. (I have built ergonomic keyboards before, and just make it one big thing instead of two halves. Simpler. But takes up more desk space and is less flexible.)

Each key also has a diode which might look like an IC. This is to prevent "ghosting", where pressing a certain combination of keys looks identical to pressing another combination of keys. The lowest of low-cost keyboards don't include this, because if you only press one key at a time, ghosting can't happen. (Most people don't press more than one key at once, except for modifiers like Shift + letter. They work around this by handling modifiers specifically, often not including them as part of the matrix.) Here's an explanation: https://deskthority.net/wiki/Rollover,_blocking_and_ghosting

The search term you want for building a keyboard without a PCB is "handwiring". Here are some guides: https://geekhack.org/index.php?topic=87689.0 https://matt3o.com/hand-wiring-a-custom-keyboard/

I thought I had some better resources in my bookmarks, but I don't.

Here's a keyboard PCB I designed a while ago: https://imgur.com/gallery/lZglox7

I followed the ai03 tutorials (https://wiki.ai03.com/books/pcb-design/page/pcb-guide-part-1...) to design the MCU area of this (The 32u4 and supporting hardware), but if you look at the traces, you can see that the switch matrix is dumb-as-bricks and can easily be replaced with some kind of handwiring.

Don't try to replicate the diode banks if you want sane wiring. The linked tutorial assumes someone is designing for function instead of form.

I actually built my first mechanical keyboard hand wired, it helped understand the basics of how it all worked.

I don't remember if it was this exact guide, but I'm pretty sure I was following Matt3o's guide when I did it: https://matt3o.com/hand-wiring-a-custom-keyboard/

edit: it may have actually been this one: https://deskthority.net/viewtopic.php?f=7&t=6050&start=

Search for a 6-key handwired tutorial, like this one: https://medium.com/cracked-the-code/a-complete-guide-to-buil...

The only parts you need are switches, wires, diodes, and a Pro Micro clone from eBay.

I recommend 6-key because they are supported out of the box by QMK and there are plenty of tutorials.

It looks like the tutorial I linked to above doesn’t actually explain how the matrix / diodes work, so you’ll want to google for an explainer.

Happy hacking!

That's essentially 5-bit Baudot code: https://en.wikipedia.org/wiki/Baudot_code

These kinds of things are distinctly different, assigning macros or keycodes to specific keys. The threeboard is not a macropad, it's a fully-functional keyboard that can type anything, it just requires specifying the keycode to type or programming in macros to type words/sentences.

It does just send ASCII codes (well, USB keycodes)! It's not supposed to be practical, just to be technically interesting and useful to learn from!

Simavr was fantastic to work with, it's a very impressive project!

SparkFun have some pretty good tutorials and resources for learning, e.g. this tutorial which guides you through using KiCad, a tool for designing schematics and PCBs: https://learn.sparkfun.com/tutorials/beginners-guide-to-kica....

haha, I have one too!

Yes the A key is the most frequently used, as it increments the USB keycode in all layers. An alternative would be a mode that allows setting individual bits in the keycode byte, but that's still quite arduous.

Put whatever switches you want on it and it can be!