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Small-Scale Question Sunday for July 14, 2024

Do you have a dumb question that you're kind of embarrassed to ask in the main thread? Is there something you're just not sure about?

This is your opportunity to ask questions. No question too simple or too silly.

Culture war topics are accepted, and proposals for a better intro post are appreciated.

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If you wanted to make a foldable keyboard which merely stored keystrokes (the text you type) and nothing more, with no screen attached, in other words genuinely just a foldable keyboard, how thin could you make this? Could you make it so thin that it folds in your pocket?

As thin as a decent mechanical design allows you to. The electronics won’t take essentially any space and a small molded lithium battery won’t take much either. You could even make it wireless for dual use as a regular keyboard and for transferring any stored data out.

Yes. Variants that plug into small computer have been around for a while: early generation Palm Pilots rather famously had a pretty slick full-size TLK keyboard in the late 90s early 00s, and they're clever enough people make adapters for them today. No onboard storage without the Palm Pilot, though.

In terms of the smallest possible device that only had storage and operated without interacting with anything else, you're mostly going to be limited by your mechanicals and the software. If you're willing to deal with momentary switches, you don't even have to make it a folding device, though in turn it will absolute suck to use.

If you want conventional switches and keycaps, you're pretty much stuck with a pretty specific layout given your target number of keys, and mechanical switches are very hard to find slimmer than a half-inch (meaning you get one fold at most before it looks like you're smuggling the world's most awkward hardon). Scissor-style switches exist that about half that, but gfl finding 'em. For conventional cherry-MX and a 70% layout, expect a minimum size of 4" by 6" by 2" -- probably more cargo pant-pocket sized. The scissor-style switches can drop that down to less than an inch thick -- still bigger than a cell phone, but not as bad.

In the middle is... well, the membrane and lever approach from the Palm Keyboard, or membrane-and-contact. This only really saves vertical height, but it can be pretty huge in that dimension: membrane-and-contact keyboards can be literally a couple millimeters thick, or even rollable. Downside is that they're expensive and difficult in small sizes to get from major builders; DIY variants are usually based on flexPCBs that can be janky to work with or assemble.

The headless part is pretty trivial from a hardware perspective. You can get cheap tiny SOCs for a headless nix setup at sub 5 USD per chip at unit 1, and microcontrollers in the sub-1 USD range. The former will be easier to work with if you're trying to store data forever (who wants to write their own file system!), while the latter will be more energy-efficient.

Batteries are trivial, these days.

Super informative!