[Fwd: Re: gta04 / MPU / JTAG]

joerg at openmoko.org joerg at openmoko.org
Thu Apr 17 18:17:09 CEST 2008

Am Do  17. April 2008 schrieb Graeme Gregory:
> On Thu, Apr 17, 2008 at 12:18:50PM +0100, Andy Green wrote:
> > | It can be good if we can run the touchscreen from MSP430 ADC.  Maybe see
> > | if you can think that through, we need to use GTA01 style external drive
> > | for X and Y when we measure.  Maybe internal DMA helps there.
> >
> > Forget DMA, AFAICS the A/D is running while cpu sleeping, and we even
> > have a
> > COMPARATOR! :-)) to irq when a certain analog level is detected! That's
> > plain
> > great! Resistive TS no issue at all.
> > OTOH I seen some capacitive TS around those GTA04 modells ?!? Have to ask
> > Allen what's the plan here...
> >
> This is actually a question I meant to bring up and keep forgetting.
> There are numerous complaints from the GUI guys about the gta01/02 TS
> varying from jitter to too low resolution.
> Someone should investigate the n800/n810 TS that works well with both
> finger and stylus. How did they do this trick? Is it just software or
> did they do something in hardware.

I suggested some tests longtime ago to run the 2foil-X/Y-R-ts in some modes 
that the inventors of this concept never even dreamt about - like (+)_on_top,
(-)_on_X, probe bottom and Y (and compare). This way you get a nice couple of 
additional info out of this simple thing, like pressure*area of touch (which 
determines R *between* the 2 foils).
Jitter OTOH might be a RF / LF noise issue which can be handled either by 
C/R-filters or by SW. Anyway with the tests we will get better insight there 
too. I'm planing to run these tests on some spare ts while I'm in .tw, only 
have to find a few hours time to get me the right equipment.


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