Apple Inc.
STRAIN SENSING KEY MEMBRANE

Abstract:

An electronic device has a keyboard with an internal membrane. The membrane has a set of strain gauges configured to respond to a key press, such as when a collapsible dome collapses into contact with the membrane. The strain gauges are connected in a half Wheatstone bridge configuration and are positioned on the membrane in order to limit effects of temperature and subtle flexure of the membrane. The strain gauges are also configured to magnify detection of a resistance differential when a keycap is pressed with sufficient force.