Abracadabra: Wireless, High-Precision, and Unpowered Finger Input for Very Small Mobile Devices

Advances in small and low power electronics have created new opportunities for mobile computing, leading to an explosion of new devices for the general public. Overall, these advances have allowed extremely powerful computing capabilities to be packaged in smaller and smaller form factors. These devices offer tremendous new potential due to e.g., their extreme mobility. However, with this potential come new challenges for interaction design.

In particular, while electronic devices have simultaneously increased in computational power and decreased in size, human factors have not changed dramatically, e.g., our fingers are the same size and our average visual acuity has not changed. As a result, for some devices, we are now bounded not by the size of the electronics or perhaps even battery size, but instead by the surface area needed to sup-port user I/O. In these cases, conventional input mecha-nisms such as buttons and touch screens cannot be scaled smaller because of the way they interact with e.g., fingers. This recently led Olsen to pose as a grand challenge question: "If I can fit my entire PC in a cubic inch, how will I interact with it?" The technique described in this paper attempts to address at least part of that question.

We developed Abracadabra, a magnetically driven input approach that makes use of the (larger) space around a (very small) device. Our technique provides robust, inexpensive, and wireless input from fingers, without requiring powered external components. By extending the input area to many times the size of the device’s screen, our approach is able to offer a high C-D gain, enabling fine motor control. Additionally, screen occlusion can be reduced by moving interaction off of the display and into unused space around the device.



Harrison, C. and Hudson, S. E. 2009. Abracadabra: Wireless, High-Precision, and Unpowered Finger Input for Very Small Mobile Devices. In Proceedings of the 22nd Annual ACM Symposium on User interface Software and Technology (Victoria, British Columbia, Canada, October 4 - 7, 2009). UIST '09. ACM, New York, NY. 121-124.

© Chris Harrison