With the recent growth in projection technologies, interactive applications using portable projectors have received attention from research communities. However, almost all applications are limited to controller-centered interactions and few pay attention to the existence of other objects found in an environment. In this paper, we propose an object-centered interactive system using a single self-contained device. Physical objects are integrated into the system so virtual objects projected by a projector can respond to them in a realistic manner. The device consists of a portable projector, a FireWire camera, a motion sensor and a VGA splitter. A computational framework for the system is presented in the paper. We focus on the three fundamental requirements of the system and their solution. First, a projector and a camera were geometrically calibrated in real time using a motion sensor. Physical objects were then identified and tracked using particle filters. Finally, virtual information was projected using a nonintrusive projection technique. Two basic programs were implemented as proofs of concept, and experiments were conducted to evaluate the accuracy and speed of the proposed system.