Siemens S 22759 keyboard - Siemens STB 21 switche


04 Apr 2021, 00:26

Hello, a week ago I found a offer of a Siemens board that looked quite interesting so I started to lurk and find as much information about it as possible.
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(Sorry that it's so dirty, I didn't assemble it back yet but I did clean the case and keycaps already)
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Turns out that was harder than I anticipated, as the only info about the same model I could find was posted here, by user PlacaFromHell on this post;

The keyboard has a few different keycap sets in different languages from what I've gathered, this one is in a Polish layout, the one posted by PlacaFromHell was in spanish so I reckon there was quite a few layouts.
From what I understand they keyboard was used in telephonic communication with such buttons as "Connect 1-5", "Subscription type", "Break" or "Hang up", as well as all of the funny Polish letters such as "Ż", "Ń", and even "Ź, Ó" and "Ę, Ą" on the same button.

The switches are bit more interesting, as they are Siemens ST 21 tactile switches. They're really nice to be honest, although the tactlity is a bit light it still gives some nice feedback while typing. Problem being that some of them are a bit scratchy, possibly from dirt and dust. I'll see if I can desolder some and clean em, as the spacebar switch is especially bindy and scratchy.
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The resistor and metal leaf have two pins each, making up for four pins in total.

If you're wondering where are the pins, well, it's a funny story, as one of the switches came loose from the pcb while I was taking off the keycaps, while I was trying to shake off some dust from the pcb it just came off and left the pins soldered in. Too bad, but at least I got to take a few pictures of it.
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Sorry for the hardware gore haha.

The cable is quite bizarre, reminds me of the VGA cable, but has only 9 pins.
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And here's what it connects to, another 9 pin connector with what I believe is a ground connector as well.
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Now, I'll be honest, I'm no expert in electronics, but the thoughts of making a converter for this keyboard have been bugging me, I'd do it myself if I knew how to, but would it be possible to make a converter for this keyboard?

Anyhow, that's my find, got real lucky with it.

Thanks for reading and I'll upload some pics when I assemble the keyboard back together, peace!

User avatar

04 Apr 2021, 09:19

Very nice board! Well you could try to trace the keyboard matrix and solder it to a Teensy or just hand solder the whole thing altogether. I'm no expert on this but there are people who already did that if you search on deskthority :)

Jan Pospisil

04 Apr 2021, 09:45

I'd be curious to see someone convert these. I do have a Siemens, though not the exact same model, but it does have that kind of connector.

John Doe

04 Apr 2021, 16:20

Very impressive layout, wish to have one to get fun. :D

User avatar

04 Apr 2021, 17:37

Well has the plug.


Those caps are real pretty!

Here’s the switch.


Those aren’t resistors: they are diodes. Which means this keyboard ought to be NKRO, which is always a relief!

They do have a right direction and a wrong direction though. (Keep track of which side the stripe goes) So beware of that!


04 Apr 2021, 20:45

Muirium wrote:
04 Apr 2021, 17:37
Those aren’t resistors: they are diodes.
Ah, thank you for correcting me, sorry about that. At least the n-key rollover feature is presant haha, I'll be able to press more than two keys at once.

About that plug... That diagram barely tells me anything but thank you for sharing it with me, has pretty interesting content on vintage connectors!

Also I got the keycaps and case all nice and clean!
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