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Tangible objects on capacitive multi-touch surfaces are usually only detected while the user is touching them. When the user lets go of such a tangible, the system cannot distinguish whether the user just released the tangible, or picked it up and removed it from the surface. We introduce PERCs, persistent capacitive tangibles that ‘know’ whether they are currently on a capacitive touch surface or not. This is achieved by adding a small field sensor to the tangible to detect the touch screen’s own, weak electromagnetic touch detection probing signal. Thus, unlike previous designs, PERCs do not get filtered out over time by the adaptive signal filters of the touch screen. We provide a technical overview of the theory be- hind PERCs and our prototype construction, and we evaluate detection rates, timing performance, and positional and angular accuracy for PERCs on a variety of unmodified, commercially available multi-touch devices. Through their affordable circuitry and high accuracy, PERCs open up the potential for a variety of new applications that use tangibles on today’s ubiquitous multi-touch devices.

The Team

PERCs are a cooperative research project by Simon Voelker, Christian Cherek, Jan Thar, Dr. Thorsten Karrer, Prof. Jan Borchers from the Media Computing Group, as well as by Christian Thoresen and Kjell Ivar Øvergård from the Buskerud and Vestfold University College, Norway. It is funded in part through the MACS Project and the German B-IT Foundation. Special thanks to our student assistants Rene Linden and Florian Busch for their support.



  • Florian Busch. PERCbots: Actuated Tangibles on Capacitive Touch Screens. Bachelor's Thesis, RWTH Aachen University, Aachen, January 2016.
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  • 2015

  • Simon Voelker, Christian Cherek, Jan Thar, Thorsten Karrer, Christian Thoresen, Kjell Ivar Øvergård and Jan Borchers. PERCs: Persistently Trackable Tangibles on Capacitive Multi-Touch Displays.  In UIST '15: Proceedings of the 28th Annual ACM Symposium on User Interface Software and Technology, UIST '15, pages 6, ACM, New York, NY, USA, November 2015.
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  • Christian Cherek, Simon Voelker, Jan Thar, Rene Linden, Florian Busch and Jan Borchers. PERCs Demo: Persistently Trackable Tangibles on Capacitive Multi-Touch Displays.  In Proceedings of the 2015 International Conference on Interactive Tabletops and Surfaces, pages 389–392, ACM, New York, NY, USA, November 2015.
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  • Rene Linden. Multitouchkit: A Software Framework for Touch Input and Tangibles on Tabletops and Mobile Devices. Master's Thesis, RWTH Aachen University, Aachen, September 2015.
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  • Jan Thar. APUCS: Active Tangible Input Devices for Capacitive Multitouch Surface. Master's Thesis, RWTH Aachen University, Aachen, June 2015.
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Related Projects

PERCs are an extension and continuation of our PUCs, which were the first tangibles to be detectable on unmodified capacitive multi-touch displays without the user touching them.

Before moving to modern capacitive multi-touch surfaces, we worked on tangibles for vision-based multitouch tables, starting with our SLAP Widgets. We later actuated these widgets, leading to Madgets, and subsequently used the same technique to create haptic feedback above the surface in project FingerFlux.

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