Introduction
Many NEC Litepad
TabletPCs have a 'crazy cursor' hardware bug which causes the
pen/cursor to move to and click at the top right hand corner of
the screen (in Portrait mode) or the button right hand corner of
the screen (in Landscape mode). This can cause the tablet
to randomly close windows or open up the Date and Time dialog box.
Very annoying!
All Tablet PCs use
electromagnetic digitizers for input (instead of touch panel
based input) and the source of this bug appears to be related to the lack of
sufficient electromagnetic shielding. Some users find that
the bug occurs at certain physical locations (like at work or at home) more
than at other locations.
If you are still under
warranty, a replacement motherboard from NEC may be able to fix
the issue but users have reported that after a period of time,
the problem reoccurs.
LitePadFix is a small
software based fix for the 'crazy cursor'. The program filters out
sudden cursor jumps to the top right hand corner of the screen
(in Portrait mode) and to the bottom right hand corner of the
screen (in Landscape mode). It should eliminate most, if
not all, unwanted 'crazy cursor' clicks and jumps.
Limitations
- Closing Windows
Pen based computing is different from mouse based computing
in that if you want to move your cursor from location A to
location B, you can do it instantly without the cursor
having to travel through points in the space between A and
B. If you try to close a maximized window by
instantaneously moving to the top right hand corner of the
screen (by raising your pen over 2cm above the screen when
moving) LitepadFix will detect this as a 'crazy cursor'
movement and filter it out. In order to close a
maximized window should move your pen above the screen (no
more than 1cm above so that the digitizer can detect it) and
move the cursor towards the top right hand corner of the
screen in a continuous motion as you would with a mouse.
Most people will find that this already is how they close
windows on a Tablet PC.
- Screen
Orientation.
Litepad displays can be (software) oriented in all four
directions. LitepadFix will only work in two
directions: Normal portrait mode (Litepad right side up) and
normal landscape mode (Litepad rotated clockwise 90
degrees). These are usually the only
orientations people work with as the other two orientations
aren't hardware accelerated and are *VERY* slow.
Besides, Litepads are so thin and light that it's faster to
just physically reorient a tablet when demonstrating to
people :-).
Update!
I may have discovered
the real hardware reason for this problem. I experienced
mild electric shocks from the case of my tablet PC. This
is usually caused by AC leakage from the power supply and sure
enough, when I measure the AC output from the power
adapter (which should be outputting only DC and very low amounts
of AC) it measured 80VAC output. That's 80VAC
that's going into my tablet PC. Not good at all and
undoubtedly the reason why the cursor jumps around all over the
place. 80VAC zooming around my tablet trying to
earth is probably generates quite a bit of EM interference which
screws around with the tablet digitizer. I should have
thought of this earlier as, now I think of it, my tablet tends
to exhibit crazy cursor syndrome almost exclusively when it is
plugged into the AC adapter.
At work we've
encountered many new computers that have power supplies that
output AC. This current degrades the components on the
motherboard and once we lost several motherboards because their
LAN ports which couldn't handle 120VAC trying to drain through
them (who wouldn't have guessed?). Come to think of it,
that could be part of the reason why our previous 1Gb switch
developed dead ports. All dodgy power supplies we've
encountered thus far seem to have been manufactured in China
which coincidentally also manufactured the NEC Litepad power
supplies :-|.
I'd be interested to
know if other Litepad users are measuring significant AC
output from their power adapters. If you do measure
significant amounts, I advise you to stop using your adapter as
it will eventually destroy components in your tablet.
Please email me at
tum@veridicus.com with details so I can get a general idea
of how widespread this issue is.
Update: Some people
have reported to me that changing power adapters has helped with
their cursor problems and also eliminates the minor electric
shocks that they too were getting.
Full
hardware fix
You can permanently fix
the problem by adding additional EM shielding to your tablet pc.
All you need are a screwdriver and some aluminium foil.
The fix was found by jonnyquest from
tabletpcbuzz.
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Remove the circled screws from the back of the
tablet. After you remove the battery using the
battery release (circled in green), you'll find a
small screw mounted laterally which you'll also need
to remove. |
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Turn the tablet over and remove the top part of the
case. To do this, you'll need to remove and
compact flash cards you have installed as well as
open the video port cover. You'll need to
fiddle a bit with the compact flash switch to get
the top part of the cover around it. After
opening the top cover, you'll need to unplug the
cables circled above. They're the LCD power
cable, case switch cables, and video data thin film
cables. Be extra careful with the video data
cables. The sockets have a release mechanism
which you'll need to lift to release the cable and
push down to lock the cables back into place.
You don't strictly need to remove
all the cables but it makes working a bit easier.
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Underneath the LCD you should find a foil shield.
You'll need to add additional aluminium to the
shield. I used a combination of normal
aluminium foil as well as thicker over liner and
attached them to the existing shield with
double-sided tape. The result should look
something like the diagram above.
Make sure your foil doesn't go outside the bounds of
the original cover or else you might end up with a
tablet sized paper weight. The bottom of the
shield should already be covered in plastic.
You might want to check and make sure the top side
of the shield doesn't short with the bottom of your
LCD. Most of the exposed circuits on the
bottom of my LCD were already covered with Mylar. |
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This is the tablet with the shield placed back on
top of the motherboard. |
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Put the cover back on and replace the screws. |
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You might have noticed some weird cabling on the
bottom right of the tablet in my pictures that your
tablet doesn't have. That was from my
not-so-successful attempt to embed a USB hub and USB
bluetooth adapter inside my tablet. The idea
was to use the hub to ensure that I still would have
3 useful USB ports after the hack.
Although I took care to ensure the USB wiring was
properly twisted and shielded, it still wasn't enough
to make the adapter detect (as a USB device) properly
with the tablet case back on.
It probably would have been fine had the tablet not
used a magnesium case. |
Installing
Download the
zip file then extract
and run the setup exe file inside. If you have anti-spyware software
installed, you may get a warning about LitepadFix installing
itself into the startup sequence of windows. Please allow
this action. If you block
the action then LitepadFix won't automatically start when you start
windows and you will have to manually run it every time you
login.
For those who want to know, LitepadFix adds itself to the
HKLM\Software\Microsoft\Windows\CurrentVersion\Run
registry key.
Using
LitepadFix starts
quietly in the background and adds an icon to
the system tray whenever you login. You can identify what
the icon looks like from the following
screenshot:
If for any reason you want to close LitepadFix, right click on the system tray icon and
select "Exit". If you don't want the LitePadFix icon
showing up on the system tray (this is usually the case since tablets have very limited taskbar
real-estate), use the taskbar "inactive icons" feature inbuilt
into XP.
You can test to see if LitepadFix is working by moving your
cursor to the bottom left hand corner of the screen, raising
your pen away from the screen and then bringing the pen
down onto the top right hand corner of the screen. If
LitepadFix is working then you will find that the cursor remains
at the bottom of the screen and won't move to the
top right hand corner of the screen. Try moving your pen
(hovering less than 1cm above the screen) in a steady continuous
motion from the bottom left of the screen to the top right.
You should find that, this time, the cursor will follow the pen
and move all the way to the top right hand corner of the screen.
Uninstalling
Go to Add/Remove
programs in Control Panel. LitepadFix will be listed under
the name "LitepadFix".
Requirements
- Windows XP Tablet PC edition
(.NET not required)
Donations
LitepadFix is freeware.
If like LitepadFix and you would like to make a donation, please use the following form:
Download links:
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