Opened 10 years ago

Closed 10 years ago

Last modified 20 months ago

#475 closed defect (fixed)

Touchpads are too "noisy" / Writing input doesn't work

Reported by: mfoster Owned by: mfoster
Priority: blocker Milestone:
Component: hardware Version:
Keywords: relnote Cc: smithbone
Blocked By: Blocking:
Deployments affected: Action Needed:
Verified: yes


The touchpad assembly on the B1 systems was built incorrectly by Alps, the manufacturer of the dual-mode touchpad. An internal ground layer was added in contrast to OLPC's guidance, causing insufficient capacitive sensing signal amplitude. As a result, the touchpad is far more noise sensitive than it should be.

The real fix is to remove the internal ground plane layer, which dramatically increases the available signal sensing voltage. In the interim, the decision was made to disconnect the resistive sensor and the ground plane in the B1 build, which is an effective workaround. However, the proper fix in the B2 systems will further improve touchpad accuracy and tracking, and will allow proper operation of both the capacitive and resistive sensors.

One consequence of this change is that elimination of the ground layer will have the positive outcome of reducing the force required for written input. As documented in Trac #474, the ESD ramifications of removing this ground plane will be avoided by introducing a new metal plate that underlies the touchpad sensor assembly.

Change History (6)

comment:1 Changed 10 years ago by mfoster

  • Status changed from new to assigned

comment:2 Changed 10 years ago by mfoster

  • Resolution set to fixed
  • Status changed from assigned to closed

The second iteration of the Alps touchpad looks really, really good. Though driver development hasn't yet caught up, the hardware was tested using diagnostics code written by Quanta, and the pads seem rock-solid, with no noise and no jitter. It's a vast improvement, and I think folks are going to like it!

comment:3 Changed 10 years ago by jg

  • Cc smithbone added
  • Keywords relnote added
  • Milestone changed from BTest-2 to BTest-3
  • Resolution fixed deleted
  • Status changed from closed to reopened

additionally, a mylar sheet was required to make it work (along with a ec work around to get up behavior to work properly).

This should get release noted (the mylar improves the B1 touchpads as well), along with how to recalibrate the touchpad, and that mylar sheets can be had to improve B1 units (all B2 units have the mylar).

Richard, close this one when we're sure the EC workaround for "UP" being reported reliably is implemented.

comment:4 Changed 10 years ago by cjb

Richard, can this be closed?

comment:5 Changed 10 years ago by jg

  • Resolution set to fixed
  • Status changed from reopened to closed

comment:6 Changed 20 months ago by Quozl

  • Milestone BTest-3 deleted

Milestone BTest-3 deleted

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