Abstract: An array of sensitive pixel elements is configured to generate signals representative of sensed light that is associated with writing being done by a user, and an optical system concentrates light from a light source across a section of the array of sensitive pixel elements, the signals being useful to compute a subpixel measurement of a position of the light source.

Abstract: Among other things, a holder for an electronic stylus includes a cavity in which the stylus can be placed when not in use. The cavity includes a receptacle at one end for a writing end of the stylus and a stop at the other end. The stop has an opening into which an opposite end of the stylus can be placed. The receptacle has a resilient element to urge the stylus against the stop.

Abstract: A housing contains electronics used in determining locations of a writing instrument based on wireless signals, defines a chamber in which the writing instrument may be held when not in use, and includes a retention element to retain the writing instrument from falling out of the chamber. In general, in one aspect, a writing instrument includes an elongate pen body, an electrical contact on a surface of the pen body, and a light source disposed near an end of the pen body. The light source includes a light guide having an optically conductive portion and an optically reflective portion.

Abstract: A display is projected, information representing an image of the projected display and at least a portion of a pointing device in a vicinity of the projected display is optically captured, and the display is updated based on the captured image information.