Fail safe design for a stylus that is used with a touch sensor

The method as defined in step 3 wherein the method further comprises using the following algorithm when the inking switch may have failed open:

• 1) determining if the Z threshold has been reached;
• 2) tracking the location of the tethered stylus if the Z threshold has been crossed;
• 3) determining that the inking switch is open;
• 4) determining if the variable XTIME is less than the current time if the switch is still open, and repeating steps 1 through 4 until the variable XTIME is not less than the current time;
• and
• 5) activating the inking function.

A system for enabling a tethered stylus to activate an inking function even if an inking switch has failed in an open mode or a closed mode, said system comprised of:

• a touch sensor;
• a tethered stylus that is detectable by the touch sensor;
• touch sensor circuitry that receives input from the touch sensor and the tethered stylus and that determines a position of the tethered stylus in proximity of or in contact with the touch sensor;
• an inking switch in the tethered stylus that can activate or deactivate an inking function, wherein the inking function is activated when the inking switch is closed when the tethered stylus makes contact with the touch sensor, and wherein the inking function is deactivated when the tethered stylus is lifted off the touch sensor and the inking switch is opened, and wherein the inking function is activated when the inking switch has failed by detecting when the tethered stylus has closed to within a Z threshold of the touch sensor, and wherein the inking function is deactivated when the tethered stylus has moved beyond the Z threshold.