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geekhack Community => Keyboards => Topic started by: nakedninja on Fri, 20 February 2015, 10:53:34

Title: How does this typewriter keyboard work?
Post by: nakedninja on Fri, 20 February 2015, 10:53:34

I've been disassembling an old electronic typewriter in my spare time and as I took apart the keyboard (to see if I could repurpose it as a computer keyboard, don't think I can) the setup confused me.
It has rubber domes that press down onto two plastic (maybe silicon) sheets. I don't understand.
I have some pictures on my potato - perhaps they will tell the story better.
If you can, explain like I'm brand new, thanks.

Title: Re: How does this typewriter keyboard work?
Post by: Dihedral on Fri, 20 February 2015, 11:04:08

Quote from: nakedninja on Fri, 20 February 2015, 10:53:34

I've been disassembling an old electronic typewriter in my spare time and as I took apart the keyboard (to see if I could repurpose it as a computer keyboard, don't think I can) the setup confused me.
It has rubber domes that press down onto two plastic (maybe silicon) sheets. I don't understand.
I have some pictures on my potato - perhaps they will tell the story better.
If you can, explain like I'm brand new, thanks.

This is a very common type of design for membrane boards. I believe it works by pressing the two sheets together - cheaper than metal contacts.

Title: Re: How does this typewriter keyboard work?
Post by: nubbinator on Fri, 20 February 2015, 11:08:05

From the ones I've seen similar to that, there's three sheets, a top layer with traces, a mix layer with cutouts, and a bottom layer with traces.  When you depress the switch, the top sheet moves and makes contact with the bottom sheet, completing the circuit.

Title: Re: How does this typewriter keyboard work?
Post by: chyros on Fri, 20 February 2015, 11:27:25

It's a standard rubber dome over membrane keyboard, practically all modern keyboards have this. The plastic sheets and rubber mats are a fraction of the cost to manufacture compared to a PCB with individual, quality switches for each key. The downside of course is that it's about as ****ty as diarrhoea.

Title: Re: How does this typewriter keyboard work?
Post by: 0100010 on Fri, 20 February 2015, 13:22:51

You could convert that to USB.  Question is, with it being rubber dome - would you still want to?

Title: Re: How does this typewriter keyboard work?
Post by: FrostyToast on Fri, 20 February 2015, 13:25:32

Quote from: 0100010 on Fri, 20 February 2015, 13:22:51

You could convert that to USB.  Question is, with it being rubber dome - would you still want to?

Could be the next Topre.
Kek.

Title: Re: How does this typewriter keyboard work?
Post by: Daniel Beardsmore on Fri, 20 February 2015, 14:46:04

Interesting, looks like NMB sliders …

Title: Re: How does this typewriter keyboard work?
Post by: chyros on Fri, 20 February 2015, 17:33:07

Almost certainly, yes:

(http://deskthority.net/wiki/File:AppleDesign_Keyboard_with_sliders.jpg)

Title: Re: How does this typewriter keyboard work?
Post by: nakedninja on Sat, 21 February 2015, 08:43:43

Hey, thanks for all the replies. I probably can't be bothered to convert it to be honest, but am fascinated to learn how it works.
Now to find a use for it.

Title: Re: How does this typewriter keyboard work?
Post by: Daniel Beardsmore on Sat, 21 February 2015, 08:57:28

Just to be clear, do you understand it now, or are you still seeing further explanation?

You might find the exploded diagram here useful:

http://deskthority.net/wiki/Rubber_dome_over_membrane

Title: Re: How does this typewriter keyboard work?
Post by: nakedninja on Sun, 22 February 2015, 04:48:12

Thanks, I think I have it now.