[Community] OpenPhoenux Prototype of GTA04 based 7 inch tablet

Dr. H. Nikolaus Schaller hns at goldelico.com
Wed Nov 7 13:14:43 CET 2012

Hi all,
some status update on this project.

Am 09.10.2012 um 12:51 schrieb Dr. H. Nikolaus Schaller:

> OpenPhoenux 7004 Prototype
> ========================
> We have finally assembled a prototype of a 7 inch
> tablet system based on the GTA04 mother board
> using the custom connector option.
> Contrary to other approaches (was it called Mozart
> or Beethoven?) we are proud that we already
> have solved the kernel adaptation problem and
> nobody can unexpectedly change the motherboard
> while we are developing software :)
> The price we have to pay is of course a higher
> price of the devices... In this case the high price
> is also coming from the Sharp display module
> (LQ070Y3DG3B) which is more expensive
> than a no-name display from the scrap heap :)
> Again, we have used a 3D printing service to build
> the prototype case (thanks to Lukas 'slyon' for the
> 3D design).
> So enjoy the Video showing the prototype and
> spread the word about this latest project progress:
> 	<http://youtu.be/MKUVtGp_AmY>
> (sorry for the Ads - this helps a tiny bit for financing
> the OpenPhoenux story).
> Another note: this device can be built as a really
> fully featured tablet with UMTS, WLAN, GPS, position
> sensors, FM radio, etc. almost everything available in the
> GTA04 when it is stuffed into a Freerunner case. It just
> differs in the *big* display and a bigger battery and
> availability of speakers.
> Software is also compatible, although writing a GUI that
> works on any dimension, orientation and resolution of the
> screen is quite a challenge. But it should be easy to adapt
> QtMoko, SHR, Replicant etc.
> The plan for the next step is to redesign the PCB and
> the case to fix some minor and major bugs in the
> electronics and mechanics.

Some minor bugs have been identified and one major bug:

	the display backlight draws too much power

The effect is that if you operate the device with the
standard USB power supply (even the 1 A Openmoko one)
this does not provide sufficient current to operate the GTA04
plus display plus backlight and leave some additional
current to charge the battery.

I.e. the device works, but if you use it heavily it will
discharge the battery even if connected to the wall socket...

As soon as the battery is empty, there is no way to come
out of the trap because the backlight is turned on during

So the only approach is to use a different display that
consumes less energy than the current one.

But the current one is already quite standard. The key
factor is that the energy required to operate a backlight
is proportional to the surface area. I.e. a 7 inch display
needs approx (7 / 2.8 ^2) = 6.25 as much energy as the
original Openmoko freerunner display. This fits quite well
to the measurements.

So does anyone know a really low power backlight display
module with these key features:

* 7 inch
* WVGA (or better)
* integrated touch (resistive or capacitive)
* can be bought @ some distributor (i.e. not by disassembling
   a Nexus 10 :)


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