This just reminded me of the most unusual switch I've ever heard of: Smith-Corona's acoustic switch from the 80s.

There's no per-switch sensor at all!

Instead, each key-press just results in one wide metal bar being hit. And to figure out which key was pressed, there's a sensor on the right and the left side which are used to calculate what key was pressed based on how long it took for the signal (i.e. vibration in the bar) to reach the left and right sensor.

It's so clever and so ridiculous at the same time!

[1] Video presentation (Talk about acoustic switches starts at 1:46:00): https://youtu.be/AvszDsr1js8?t=6361

[2] Slides: https://docs.google.com/presentation/d/1jfWpf8cABnH54yVjPIU3...

A flip-flop would work to convert the analog to 1-bit digital, but you could also tweak the magnetics and with a better ADC get velocity measurements! Add some software and you can type ANGRY MESSAGES by just pounding on your keyboard, no shift/cruise control needed!

Slightly more readable version: https://threadreaderapp.com/thread/1260688848104771586.html

This glorious hunk of junk

https://oldcomputers.net/compucolor-8001.html

had a keyboard that was optical, it ran beams of light through masks attached to the keys, and looked at the beam interruptions as keys were pressed.

The keyboarding experience was absolutely miserable; you had to COMPLETELY release a key before pressing another. Ghosting and mangled keystrokes were almost impossible to avoid. I'd rather type on a card punch than one of those . . . well, no. But it's darned close.

The claim that it was patents that prevented it from seeing widespread use doesn’t seem legitimate, especially as the list of cons doesn’t mention the high production and component costs of such a mechanism. The reason why crappy dome switches won out despite their really long list of cons is extreme price superiority. The linked design is simply far too expensive and complicated by comparison.

It looks a like a binary LVDT [1] sensor.

These are linear sensors that work by measuring the output of a transformer with a movable core. They have a reputation for being extremely reliable, even under harsh conditions. Therefore they are commonly used in aircraft, turbines, nuclear reactors, etc...

[1] https://en.wikipedia.org/wiki/Linear_variable_differential_t...

Very cool! Old keyboards and key-switches are an endless source of fun trivia.

I think Topre is the only one that manufactures keyboards with contactless key switches today. Topre key-switches measure the change in capacitance instead, and their keyboards (of the HHKB fame) sell for greater than $200.

https://www.keychatter.com/topre-switches/

Another unusual key switch is the opto-mechanical like the one used in https://wooting.io/wootingone (not affiliated).

They use infrared and they are also analog. You can bind different event based on the actuation force you put on the switch.

Interesting! I'm curious how this would sound on a built board compared to the other unique mechanical switches out there.

So, how's the tactile feel on this switch?

I wonder if this will make it into a modern mechanical keyboard.