Keypads constructed from fabric materials are the ideal input devices for smart clothing applications. However, multi-modal reaction problems have to be addressed before they can be of practical use on apparels, i.e., the fabric-based keypads need to distinguish between the legitimate actions by the fingertips and the illegitimate deformations and stresses caused by human movements. In this paper, we propose to use the humidity sensor functionalized from graphene oxide (GO)-coated polyester fibers to construct the e-textile keypads. As the moisture level in the proximity of human fingertips is much higher (over 70%) than other parts of the human body, humidity sensing has many advantages over other tactility mechanisms. Experiments have demonstrated that the GO-functionalized fabric keypad has a stable uni-modal tactility only to fingertip touches, and it is not sensitive to deformation, pressure, temperature variation, and other ambient interferences. With biasing and sensing circuits, the keypad exhibits a quick response and recovery time (around 0.1 s), comparable to mechanical keyboards. To demonstrate its application on smart clothing, the keypad was sewn on a sweater and embroidered conductive yarns were used to control an MP3 player in the pocket.
Keywords: fast switch; graphene oxide; humidity sensor; keypad; textile; uni-modal.