TOUCH SENSING SYSTEMS

摘要

We describe a touch sensing system comprising a light source to project light defining a touch sheet above a surface; a camera directed to capture a touch sense image from the touch sheet, comprising light scattered by an object; and a signal processor to process the touch sense image to identify a lateral location of the object on the surface. A brightness of the projected light is modulated to define bright, touch detecting intervals and dark intervals. The camera and the light projection are synchronised such that the camera selectively captures scattered light during the touch detecting intervals and rejects ambient light during the dark intervals. The system further comprises a pen. The pen comprises a photodetector to detect the projected light, a first light source detectable by the camera, and a controller coupled to control the first light source such that it is selectively illuminated during touch detecting intervals in synchronism with modulated projected light of the touch sheet.