Capacitive key switches in Compaq Portable1

[bettablue]

Hi everyone!  It's been quite some time since I've posted on these pages.  It's good to see that GH is back.  I didn't like the temporary pages that were setup.   Any way, I was given an all original and authentic Compaq Portable manufactured in 1983.  This is the 1st PC compatible PC manufactured by Compaq.  While the computer is in very good shape, there is a major issue with the keyboard.  In particular, the capacitive key switches.   I have never worked on this type of switch.  But I do understand the concept behind their construction. It seems as though the construction is pretty simple, and the design quite robust.  I am more worried about how to repair the individual padded disks than anything.

These padded disks themselves do not convey any electricity across the surface.  That was verified by testing the surface of some of the metallic faces with a multimeter to determine if they would cause a short circuit..  They do not.  That means there is another layer or coating over the metallic surface to keep them electrically neutral.  The issues I am having is the size of the disks.  Does it really matter if the end result leaves a smaller metallic surface than the original?  The originals are all 1cm in diameter.  I was actually thinking of using a hand held paper hole punch that would give me a perfect 1/4"circle.  (My hole punch will handle the thickness quite well.)  If I can use this method, I can crank out all of the padded disks I want by the dozens in only a few minutes, but if I have to make them the same size as the originals, then where can I get a 1cm single hole punch that will leave me with the circular "dot"? 

Only a few keys are left working at this time, so any ideas to simplify making 83 of these padded disks to replace all of them in the keyboard would be greatly appreciated.  As always, I would love your feedback, regardless of the news; good, bad, or ugly.

Thank You. 

Thomas

[pli]

Paper hole punches are probably quite standard in size, but you could check out a leather punch (http://commons.wikimedia.org/wiki/File:Leather_punch.jpg or http://commons.wikimedia.org/wiki/File:Lochzange.jpeg). Making one yourself by sharpening the edges of a pall point pen hull would probably just end in tears, but you can always try to look around for something to use.

In case you don't find an answer here (since judging from the thread view counts users of this board are far more interested in gaming backlights than DIY projects) you might have better luck on any hobbyist electricity/arduino/DIY board. The question seems to be more about general electrics and repair than keyboards -- unless of course there is someone here with that exact model and a technical understanding of it.

Good luck!

[fohat.digs]

Is this a "foam and foil" setup?

My experience with them is that it is almost always the foam that fails.

PS - my cousin had one of those Compaqs back in the day, and lugged it around for a couple of years. it weighs about the same as a medium-sized dog, doesn't it?

[Soarer]

Since capacitance varies with the area, I think they would need to be the same size as the originals.

[dorkvader]

I would be somewhat surprised if the shiny side conducted electricity. They likely have coated it with a clear polymer, to prevent shorts in their circuit. I am reasonably sure that the shiny area is indeed metal, but you can't conduct that much electricity across it because it is coated.

I would also agree that it's likely the foam has failed. Old foam wasn't really meant to last this many decades, so just replacing that would be your best bet.

Keep in mind the new foam will likely have some effect on your keypress and bottom out feel.

[bettablue]

All of the replies to this thread have proven to be true.  Unfortunately, my 1st attempt at rebuilding this keyboard failed miserably, so I'm looking for something else I can do.  If anyone here has any idea on how to make this keyboard work again, please send me your ideas.  Trust me, I need all the help I can get. 

Where's Ripster when you need him the most?  He may not have the answer, but at least he would tell me where to go, on more than one level!~  Hah!

Thanks everyone...

[asura]

Cypress have some decent datasheets on cap-sense if memory serves... http://www.cypress.com/?id=1932&source=home_products  It may be a bit of a trawl to find anything appropriate there, but there's a lot of information to be had.

[Bry]

Paper hole punches are probably quite standard in size, but you could check out a leather punch (http://commons.wikimedia.org/wiki/File:Leather_punch.jpg or http://commons.wikimedia.org/wiki/File:Lochzange.jpeg). Making one yourself by sharpening the edges of a pall point pen hull would probably just end in tears, but you can always try to look around for something to use.

In case you don't find an answer here (since judging from the thread view counts users of this board are far more interested in gaming backlights than DIY projects) you might have better luck on any hobbyist electricity/arduino/DIY board. The question seems to be more about general electrics and repair than keyboards -- unless of course there is someone here with that exact model and a technical understanding of it.

Good luck!

Ahh, yes. A few years ago I found an old leather punch in my father's toolbox and I can recall at least 2 occasions where I used it to punch holes in a belt. It came with many different sized punch blades like the one you linked. I actually wish I still had that thing, it was so useful. I'm sure something like this would be the best bet.