Keyboard for GTA04

Al Johnson openmoko at
Thu Mar 15 17:28:40 CET 2012

On Thursday 15 March 2012 15:30:34 Dr. H. Nikolaus Schaller wrote:
> Am 15.03.2012 um 15:10 schrieb Al Johnson:
> > On Thursday 15 March 2012 12:57:23 Dr. H. Nikolaus Schaller wrote:
> >> During the "Openmoko Stammtisch Munich" yesterday, we
> >> have once again discussed options to build a special GTA04 keyboard.
> >> 
> >> And now I think we have found a way to really square the
> >> circle. The square being functionality and the circle being
> >> cost.
> >> 
> >> The idea is to use:
> >> * off-the shelf pushbutons (Panasonic has some nice and very
> >> 
> >>   flat SMD buttons readily available at DigiKey)
> >> 
> >> * a Shapeways made custom case
> >> * a not very sophisticated PCB with the buttons, a Bluetooth
> >> 
> >>   HCI module [1], a small LiIon battery and a microcontroller
> >>   scanning
> >>   the keyboard and supporting USB charging
> >> 
> >> Now comes the key idea: having a shapeways printed case makes
> >> it possible to think about a keyboard built into a replacement battery
> >> cover. It makes it a little thicker than normal, but you can detach it
> >> and use it as a keyboard.
> > 
> > I was with you up to the bluetooth + battery part. Why not use a slide
> > out keyboard with a TCA8418 and wired i2c connection to the main board?
> > The board should be cheaper and simpler, the plastics little different
> > to a sliding bluetooth device, and there'd be no messing about
> > remembering whether you'd charged the keyboard.
> Yes, there are contact points on the GTA04A4 board prepared for this.

Thanks to your fine documentation I could check that before I posted ;-) The 
power and unused i2c3 on the test pads looked good. Did I miss a better one? 
It looks like there's a reasonable bit of space above them in the case too.

> My main concern are that cables may break too often and connecting
> it to the main board plus getting it out of the device is a little fiddly.

I agree that's probably the trickiest bit. Any idea how sensitive the i2c is 
to the cable? Would a flexible headphone lead type work, or would it need 

> But this could be a cheaper (and easier to develop) option than BT+Battery.
> It just needs to place the TCA (plus some ESD-protection) on the board and
> a set of buttons like these:

With a thin cover of laser cut and etched stainless, or a plastic part to keep 
it all from shapeways? Either option would make changing the keymap relatively 

Also I thought the TCA included ESD protection, although that was just from a 
quick glance at the datasheet.

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