On Sunday 4. September 2016 18.50.53 Joseph Honold wrote:
My idea is to use snap domes attached to a sticker and placed directly on the pcb which has exposed copper pads for contacts (keyboard matrix). The sticker could be laser (or hand) cut to any shape and snap domes hand placed (for prototype). The snap dome method is how most phones (and Zipit Z2, see my post https://mozzwald.com/articles/zipit-soft-keypad-mod) do it these days. The snap domes are available and I actually got a sample kit from Snaptron (http://www.snaptron.com). There are some far east manufacturers of snap domes also.
For reference, here are some pictures of the originally-planned successor to the Ben NanoNote that show what you're talking about:
http://en.qi-hardware.com/wiki/File:AVT2_RC1_keys.jpg
(The circuit boards, employing fairly simple contacts for domes as opposed to the oft-seen elaborate patterns that are potentially more suitable for coated- silicone keymats/overlays, as far as I can tell.)
http://en.qi-hardware.com/wiki/File:AVT2_v1.0_works.jpg
(The "dome sheet" applied to the board.)
Somewhere on that site is a picture of the "dome sheets" being applied by assembly line workers, but I can't find it at the moment.
The difficult part (IMO) is creating the rubber/silicone overlay. A prototype could be made by either 3D printing a mold and casting a silicone keypad, or just 3D print the keys in plastic (or some other preferably soft material). Both these methods should work but I don't expect backlight to work well if at all (need translucent material). The labeling of keys might be difficult to achieve with 3d printng.
Overlay/keymat production seems quite specialised, but maybe people here know a bit more about it.
Before I found out about EOMA68 I was intending to make a raspi handheld using this keypad layout https://mozzwald.com/public/images/misc/keypad.png
Are there any preferred keypad layouts?
That's asking for trouble! One thing I wouldn't mind knowing is how decent space bars are done using domes. Do they really involve multiple domes, or are there elongated ones that do this job?
Paul