NanoNotes and electronic dictionaries

Werner Almesberger werner at
Sun Aug 25 04:04:28 EDT 2013

Paul Boddie wrote:
> It's perhaps a wake-up call that a lot of open hardware sits at number 7 on 
> that list, really.

My assumption is to use a "friendly" CPU, like the i.MX283.

Of course, if you're trying to build an Ubuntu Edge, things will
get a bit more complicated :-)

> I couldn't find very much information about the nature of the dome
> switches

Here's the data sheet of a similar array:$file/B3DA_1110.pdf

> it looks like a 
> lot of devices settle for silicone rubber keypads/keymats with all the keys 
> provided on the same silicone rubber moulding and with the domes being 
> provided as part of the moulding.

Yes, that's what the Ben uses as well. It also has a metal sheet
between rubber sheet and keycaps, for structure.

> Meanwhile, here's what the OpenPandora device uses:

Interesting, a flat sheet. So it doesn't participate much in the
vertical movement of the keys. Do they use domes as well ?

> says 3.0" (60mm x 45 mm),

That's the active area. I used the module size. You typically have
three specified sizes, from largest to smallest:

- module: that's how much room you need at least,
- bezel: that's the maximum opening you want to have, and
- active area: that's where the pixels area.

For the total size of the display, add the thickness of the shell's
sidewalls, any spaces you choose to reserve (e.g., for RF, cameras,
etc.), any space you need for interfacing (e.g., for a clamshell,
you're likely to need a cable adapter - the FPC of the display
module will probably not be mechanically suitable and may face the
wrong way), and tolerances.

> but I suppose it is closer to 3.1".

That would be the bezel, 62.6 x 47.6 mm, 3.096" diagonal.
The active area is 60 x 45 mm, 2.953" diagonal.

> I don't think it is too unusual for smaller displays to have 
> their own framebuffer:

Yes, all the SPI-based ones have no other choice :)

> so we end up with the Arduino communicating with something that is 
> probably more powerful (an ARM7-based controller, I think).

Yeah, a lot of Arduino projects seem to aim to outdo Frankenstein
by performing the equivalent of transplanting a flea's brain into
a fully functioning human body :)

> For some odd reason, the "module dimensions" of these things seem to exceed 
> 100mm in width,

That includes the rather large cable assembly. For a small device,
I'd try to fold the cable under the display, then have a thin adapter
board there. And pick a display that comes with a bit less stuff
hanging off it :)

> Has anyone done anything with CAD software for the Ben's case?

Well, there's the counterweight, which I scripted with HeeksCAD:

> I see that there are DXF files as well as others,

Do you mean the (partical) case scans ?

They can be useful as a basis for own designs, e.g., by
calculating the difference between scan and design. (I used that
when making the counterweight.)

> it appeared 
> that the more useful technology emerging in their scene was in fact computer-
> controlled laser cutting.

I suppose that would be for inner structures (i.e., the skeleton),
with outer surfaces made by some other means (or maybe by wrapping
something around a skeleton) ?

- Werner

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