Touchscreen requirements

Wed Jun 9 18:32:50 EDT 2010

On Tue, Jun 8, 2010 at 2:23 PM, John Watlington <wad at laptop.org> wrote:

>
> On Jun 8, 2010, at 9:03 AM, Bert Freudenberg wrote:
>
> > Thanks for inviting discussion!
> >
> > I recently started testing Etoys on the Apple iPad - not the least to get
> an idea of what needs to be done to it for an XO tablet. Multi-touch is
> definitely "cool", e.g. you can move around multiple Etoys objects
> simultaneously. If you are interested, I can send you a test version (pm
> me).
> >
> > Etoys uses the Sugar tool bar on all platforms. That works very well, the
> buttons are large enough even for my fingers.
> >
> > However, many other Etoys UI elements are much too small for touching.
> They're finicky even on the XO screen, but with a pointer you can at least
> hit them. That's rather hard with a finger (though the Apple touch screen is
> amazingly precise). A stylus would be preferable, but then, two-finger
> gestures are awkward with a stylus.
>
> We aren't planning to provide a stylus (just something for the
> kids to loose), but with some touchscreens any pointed stick
> can be used as a stylus if needed.  The projected
> capacitance touchscreens becoming popular (iPhone, iPad), on
> the other hand, don't support just any old stylus, it has to have a
> special tip.
>
> > It would help if the tablet had a 4:3 ratio. Ideally 1200x900 pixels just
> like the XO, but at least preserve the ratio. The iPad has 1024x768 pixels
> and I made Etoys use a virtual 1200x900 screen hw-scaled to the actual
> screen size, looks very nice.
>
> The aspect ratio of a tablet device is the source of much debate
> these days.    16:9 displays are cheaper due to volume sales, but
> many (most ?) people around OLPC prefer 4:3.
>
>
iPad is 4:3, more could follow, so I guess you're referring to PixelQi's
current customers?

>  >> -----------------
> >> 1) Number of simultaneous touches:
> >> The number of simultaneous touches that can be tracked.
> >> For W7, this is two.   I believe OLPC is looking for more.
> >
> > IMHO multi-touch is almost essential on a tablet. Two would be enough
> IMHO, more are nice.
> >
> > What's "W7"?
>
> Windows 7
> I listed M$'s specifications as most vendors are trying to meet them.
>
> >> 2) Behavior when number of simultaneous touches is exceeded:
> >> If the number of simultaneous touches is exceeded, what happens ?
> >> I suggest that the "oldest" touch be forgotten and no longer tracked,
> >> but have seen other behaviors as well.
> >
> > I'd rather keep tracking the first touches and ignore additional ones.
> Then accidental touches wouldn't interrupt the current interaction.
>
> Interesting point.
>
> >> 3) Palm rejection:
> >> A number of vendors include "palm rejection" algorithms in their
> >> controllers.   I'm not sure how I feel about this --- I would prefer to
> >> push this information higher in the stack before discarding it...
> >>
>

I would love this on the touchpad of the 1.5 XO also. I keep having problems
of jumping cursor when I'm clicking on the pad's buttons.

>  >> 4) "Sensor size":
> >> This applies to multizone resistive touchscreens, which may be
> >> thought about as a number of small touchscreens, each capable of
> >> a single touch.    Two touches cannot be detected in any one zone,
> >> so this affects how close buttons which might be pressed simultaneously
> >> (think piano keys) can be placed to one another.   W7 specs 1 in. x1 in.
> max.
> >> I believe this needs to be closer to 1 cm x 1cm max.
> >
> > I'm imagining to use a two-finger tap to invoke meta operations, like the
> right touchpad button in Etoys on the XO. For this it would need to detect
> two kid's fingers form one ...
>
> Getting closer than 1 cm x 1 cm would probably rule out
> multi-zone resistive.   But a 1 cm^2 zone would probably work fine
> for two finger tap, even with kid's fingers.
>
> >> 5) Resolution:
> >> Do we need to have a touch resolution equal to the screen size ?
> >
> > I have no real experience with this yet, but it needs to be high enough
> to allow drawing.
>
> I didn't list W7's specs for this:
> 2.5mm accuracy for single touches, and 5mm accuracy for multiple touches
>
> An interesting effect I've noticed is that with some touchscreen, you get
> smooth
> lines when moving your finger at a "normal speed", say 8 cm/s, but when you
> slow
> down (1 cm/s) the line wiggles around.
>
> >> 6) Scan rate:
> >> The number of times a second that the touch controller
> >> can identify and report a touch.    W7 specifies 50 Hz minimum,
> >> which seems a little high.
> >>
> >> 7) Robustness:
> >> This is usually specified as the number of presses in one spot with a
> contact
> >> area of either 8mm (finger) or 0.8mm (stylus).   Industry standard for
> resistive
> >> (single or multizone) seems to be around 80K, which is too low for our
> needs
> >> (we try to reach a 2000 day lifetime).  But the one vendor supporting
> 250K
> >> touches was unusable by a bare finger (needed fingernail or stylus).
> >>
>

Not that the 250K touchscreen probably needs it... but will the other one be
replaceable, if necessary?

Best regards,
Tiago

 >> 8) UV resistance:
> >> Since this touchscreen is on top of a sunlight readable display, it will
> need
> >> to be UV resistant.   Our current standard (for the display) is no
> significant
> >> change (>5%) in optical properties after 4000 hours of full sunlight UV
> >> irradiation.
> >>
> >> 9) Humidity, temperature:
> >> Same as the XO:  operation from 0 to 50C, in RH up to 95%.
> >>
> >> Regards,
> >> wad
> >
> > No opinion on these issues, yet ...
>
> Keep experimenting!
>
> Thanks,
> wad
>
> _______________________________________________
> Devel mailing list
> Devel at lists.laptop.org
> http://lists.laptop.org/listinfo/devel
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.laptop.org/pipermail/devel/attachments/20100609/a10d23c8/attachment.html>