Attaching Objects to Smartphones Back Side for a Modular Interface

This paper proposes a new approach to enhancing interaction with general applications on smartphones. Physical objects held on back surface of the smartphone, which can be captured by the rear camera with a mirror, work as input devices or controllers. It does not require any additional electronic devices but offers tactile feedback. The occlusion problem does not occur when using smartphone's back side, in terms of both display and camera viewing. We implemented on an Android smartphone and confirmed that it provides richer interaction and low latency (100 ms).