#12114 NORM 4-firmw: Touchscreen on XO-4 B1 sometimes misregisters one touch as two touches

Zarro Boogs per Child bugtracker at laptop.org
Wed Sep 19 00:49:20 EDT 2012

#12114: Touchscreen on XO-4 B1 sometimes misregisters one touch as two touches
 Reporter:  wad                |                 Owner:            
     Type:  defect             |                Status:  new       
 Priority:  normal             |             Milestone:  4-firmware
Component:  touchscreen        |               Version:  4-B1      
 Keywords:  XO-4, touchscreen  |           Next_action:  diagnose  
 Verified:  0                  |   Deployment_affected:            
Blockedby:                     |              Blocking:            
 On an XO-4 B1, occasionally one can see confusion in the touchscreen
 firmware about the number of touches present.

 This happens when LED drive currents are especially low, and when using a
 thin (7.5mm) stylus.   I've seen it on a touchscreen with a tinted
 lightguide and v0.0.2 of Neonode firmware, and also with a clear light
 guide and v0.0.3 of Neonode firmware.   It is hard to reproduce with
 v0.0.4 of Neonode firmware and a clear light guide, and never seen with
 v0.0.2 of firmware and a clear light guide.

 Using a 10mm finger, the problem is also much less likely to happen.

 The pictures illustrate the problem.   They were generated running the
 Open Firmware  test /touchscreen command, which identifies the first touch
 with yellow dots, and a second reported touch with purple dots.   In
 generating those pictures, the stylus was always moved in a diagonal
 direction (relative to the display frame).  You can see how a second touch
 is detected and is tracked vertically (purple) as the stylus continues to
 move diagonally (yellow).

Ticket URL: <http://dev.laptop.org/ticket/12114>
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