We present HaptiCoil, an embedded system and interaction method for prototyping low-cost, compact, and customizable wide bandwidth (1-500 Hz) soft haptic buttons. HaptiCoil devices are built using mass-produced,  waterproof planar micro-speakers which are adapted to direct energy to the skin using a novel hydraulic coupling mechanism. They can sense force input, using a measurement of self-inductance, and provide output in a single package, yielding a flexible all-in-one button solution. Our devices offer a wider perceptual range of tactile stimuli than industry standard approaches, while maintaining comparable power threshold levels (typical threshold under 40 mW). We detail the construction and underlying principles of our approach, as well as an extensive physical quantification of both input and output. We share psychophysical data on device bandwidth, and show three illustrative examples of how HaptiCoil buttons can implemented in use cases such as spatial computing, digital inking, and remote control.

Authors: Jung-Hwan Youn, Seung Heon Lee, Craig Shultz

Jung-Hwan Youn, Seung Heon Lee, and Craig Shultz. 2025. HaptiCoil: Soft Programmable Buttons with Hydraulically Coupled Haptic Feedback and Sensing. In CHI Conference on Human Factors in Computing Systems (CHI ’25), April 26–May 01, 2025, Yokohama, Japan. ACM, New York, NY, USA, 16 pages. https://doi.org/10.1145/3706598.3713175