Am Mi 5. März 2008 schrieb Marco Trevisan (Treviño): > joerg ha scritto: > > I'm investigating to squeeze some multi-touch properties out of the GTA02 > > 4wire-resistor touchscreen, by hacking the basics and probing the ts in a > > couple non-recommended completely different manners. There still is a > > little hope... > > What's your hope exactly? > Do you have some "secrets" to share? :P
Well, it's basically a 4wire (2 metal coated transparent plastic foils) design: you apply + and - at X+ X- which creates a linear voltage gradient over the one foil, and you messure the voltage at any of both Y of the point where the second foil touches the first. (and vice versa x<>y, for other coordinate). So much for the classics. However there are a couple of other permutations to apply + and minus and/or leave open and where to probe for voltage, given you have 4 wires and 3 states (+,-,probe+open) for each one of the 4 to choose from. Hard to explain without some graphics showing a simplified circuit diagram. And then, if all this fails, there still remains the dynamic approach (pulse-response), for there are two planes creating a R-C-R-C-R... network, resembling somewhat like e.g. a coax cable. You know you can analyze coax (10Base2 ethernet, even BaseT) for position of sharp bends with an analysis of pulse response. Somewhat like hitting a drum and telling from resulting sound where there are the 2 stones on the drum membrane. All this *VERY* theoretical anyway for now, for i got scope etc, but even don't have real hw to test with it :-( (who was the guy with a fried NEO and no idea what to do with it? I had a real use for it, even better when it's broken), and i was too lazy (or too poorly gifted) to do the math yet. What i expect/hope: At least i now got diagrams, so i know what _can_ or _must_not_ be done with given hw in GTA01/02. Just dreaming for now... ;-) But i'm quite sure it's feasible to get at least kinda force feedback for the single touch. Maybe more... Amazing what 12 formulae with 5 (10) unknown variables(R) can reveal (ok, this are just numbers for instance, didn't the math yet). When it comes to dynamic pulse response analysis - with all sorts of filters and the whole scary stuff (any volunteers?), we probably even get the weight of user-C touching the screen ;-) In an ideal world. A/D converters of CPU to sample the response are not _so_ bad. All this [patent pending, (C), smells like me etc]:jOERG ;-). At least mention me, and send me a beer each day, and this is prior art. Ehrrm. This week CeBIT, let's see what's my schedule for next week. cheers jOERG _______________________________________________ OpenMoko community mailing list [email protected] http://lists.openmoko.org/mailman/listinfo/community
