Ticket #475 (closed defect: fixed)
Touchpads are too "noisy" / Writing input doesn't work
|Reported by:||mfoster||Owned by:||mfoster|
|Deployments affected:||Blocked By:|
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.