
A unusual keyboard key switch - redshirt
https://twitter.com/TubeTimeUS/status/1260688848104771586
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DavidVoid
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](https://youtu.be/AvszDsr1js8?t=6361)

[2] Slides:
[https://docs.google.com/presentation/d/1jfWpf8cABnH54yVjPIU3...](https://docs.google.com/presentation/d/1jfWpf8cABnH54yVjPIU3iECoH0aguMo6QFYJJptRous/edit?usp=sharing)

~~~
snori74
Once dealt with a 2d digitising pad that worked off the audio click of a spark
in a similar way. Wild.

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nick238
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!

~~~
DavidVoid
Realforce did this a few years ago with Topre switches (which are capacitive).
Here's a video demonstration of someone using a keyboard like that as a piano
[1].

[1] [https://www.youtube.com/watch?v=mhCSIy-
Qt0M](https://www.youtube.com/watch?v=mhCSIy-Qt0M)

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Exmoor
Slightly more readable version:
[https://threadreaderapp.com/thread/1260688848104771586.html](https://threadreaderapp.com/thread/1260688848104771586.html)

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whywhywhywhy
Shocked Twitter has chosen to make their reading experience even worse. Now I
get linked to a tweet thread, Twitter knows it's a tweet thread of one user
but what does it choose to show?

Just the single tweet, a small "Show this thread" link and then 5 random other
tweets from other people not connected or related to this tweet at all.

~~~
edjrage
It's almost like they don't want you to spend time reading but "engaging"...

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kabdib
This glorious hunk of junk

[https://oldcomputers.net/compucolor-8001.html](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.

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ComputerGuru
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.

~~~
tubetime
dome switches are definitely cheaper, but i was comparing this design to
mechanical switches. the magnetic switch has far fewer moving parts and the
tolerances don't have to be very tight.

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GuB-42
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...](https://en.wikipedia.org/wiki/Linear_variable_differential_transformer)

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akssri
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/](https://www.keychatter.com/topre-
switches/)

~~~
thesmok
You can also get Topre switches in Leopold keyboards, models ending with
letter C (for capacitive).

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alibert
Another unusual key switch is the opto-mechanical like the one used in
[https://wooting.io/wootingone](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.

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

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pjc50
Sound is determined by the springs and mechanical action. This design could
potentially be made silent. More interestingly, it could give you pressure-
sensitive switches ...

~~~
alibert
You might want to take a look at this :
[https://wooting.io/wootingone](https://wooting.io/wootingone) (not
affiliated)

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

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falcolas
Probably something like a U curve, with no explicit tactile bump, since the
magnets would be attracted to the ferrite core, and when that force falls off,
the spring force would pick back up.

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

~~~
bjoli
Hall effect switches are coming. Some manufacturers have already started. The
cool part is that you can set the actuation point in software on them.

~~~
DavidVoid
Hall effect switches have existed in keyboards for a long time [1]. I don't
think there are many of them being produced nowadays though, but there's at
least one new Chinese Hall effect keyboard that came out a few years ago [2].

Wooting also has a Hall effect switch [3]. You can't buy any keyboards with it
yet but you can pre-order one at least [4].

[1]
[https://deskthority.net/wiki/Keystroke_sensing#Hall_effect](https://deskthority.net/wiki/Keystroke_sensing#Hall_effect)

[2]
[https://geekhack.org/index.php?topic=84525.0](https://geekhack.org/index.php?topic=84525.0)

[3] [https://blog.wooting.nl/introducing-the-lekker-
switch/](https://blog.wooting.nl/introducing-the-lekker-switch/)

[4]
[https://wooting.io/wooting_two_lekker_pre_order](https://wooting.io/wooting_two_lekker_pre_order)

~~~
bjoli
Oh yes, I should have written "coming back". I have one from the 70s in my
posession somewhere. I am more a clicky kind of guy (or at least proper
tactile, not mx brown mush), but for linear switches I would love to be able
to set the actuation point!

