A keypad device for a mobile telephone or other device utilizing a keypad or
keyboard
is comprised of a flexible substrate and a keypad cover. The flexible substrate
includes a plurality of keys affixed to the surface as well as a plurality first
conductive strips associated with each key. The keypad cover is attached to the
flexible substrate. The keypad cover typically includes holes that permit the plurality
of keys to protrude through the keypad cover. In addition, the keypad cover further
includes a plurality of second conductive strips that selectively contact a corresponding
first conductive strip on the flexible substrate. The plurality of first conductive
strips is coupled to ground and the plurality of second conductive strips is coupled
to logic circuitry. Or, in another embodiment, both sets of conductive strips are
coupled with the logic circuitry. The default position of the keypad device has
each of the first conductive strips in contact with each of the corresponding second
conductive strips. This creates a short circuit condition that prevents key signals
from being received by the logic circuitry. When a particular key is depressed
to the point where the first conductive strip associated with that particular key
is separated from the second conductive strip corresponding to the first conductive
strip, the short circuit condition is removed. This allows a signal to be transmitted
to and processed by the logic circuitry indicating that a particular key has been selected.
