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PICList Thread
'[EE]: DIY membrane keypads'
2004\09\07@184919 by Philip Pemberton

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Hi,
 I've been experimenting with the idea of DIYing a membrane keypad. So far,
this is what I've come up with:

1) Top layer: 0.05mm fiberglass PCB laminate, 2x 1/2oz copper.
2) Spacer: Acetate OHP sheet
3) Base: 0.8mm fiberglass PCB laminate, 2x 1oz copper

The top layer is the bit that gets subjected to the wrath of the heavy-handed
(or not) user. It consists of one round pad for each switch. All the pads
are connected horizontally, then each row is connected to a 4-way pad-block
at the bottom of the board. You'll see why in a minute.
The spacer has only one purpose - to stop the top layer from shorting out the
tracks on the base (and to stop the switches activating without having been
pressed).
Finally, there's the base layer. It has the same sort of layout as the top
layer, except instead of having the pads connected horizontally, they're
connected vertically. In addition, there's a set of solder pads on the
bottom of the board - one for each row or column. There's a pad-block above
the output connector, which connects to the top layer.

I still haven't sorted out what glue to use, but I'm leaning towards 3M
PhotoMount spray adhesive, assuming it's capable of sticking fiberglass and
plastic together. The only remaining question is conductivity - obviously
it's no good if it provides the effect of a dead short at 5V. Has anyone done
any testing of this nature on Photomount (red label) adhesive?

When I've got my final prototype working, I'll post a message to the list and
include some photos and design drawings. ATM I've got a 3x4 pad that "sort
of" works, except it takes far too much pressure to get it to activate :-/

Thanks.
--
Phil.                              | Acorn Risc PC600 Mk3, SA202, 64MB, 6GB,
spam_OUTphilpemTakeThisOuTspamdsl.pipex.com              | ViewFinder, 10BaseT Ethernet, 2-slice,
http://www.philpem.dsl.pipex.com/  | 48xCD, ARCINv6c IDE, SCSI
.... Oh no, not another learning experience!
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2004\09\07@202958 by hilip Stortz

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