Printing multi-key touch interfaces

Abstract

We present a technique for creating multi-key conductive ink touch user interfaces that can be printed on paper in a single pass. While 3D printing and open-source electronics platforms have led to enormous creativity in creating smart objects, the means for user interaction with such objects are often limited and require remote interaction through a smartphone app. Paper-based touch circuits are a convenient medium for exploring custom touch sensors that can be attached to numerous objects in our environment. The challenge lies in creating a reliable and customizable touch circuit that is easy to produce. Specifically, it should not require assembly of multiple layers and it should support multiple touch points without needing separate connections to a microcontroller for each touch point. We address this through a resistive touch sensor that exploits the inherently high resistance of printed traces to create multiple detectable touch points. The finger closes the circuit when in contact with the touch point and the sensor uses a polarity-switching technique to cancel out the effect of the unknown skin resistance. We evaluated the touch sensor using keypads with 10, 15 and 20 touch points and achieved 99.6%, 93.5%, and 91% touch detection accuracy, respectively. We also observed touch detection rates of up to 154 touches per minute.