Compact Large-Area Graphic Digitizer for Personal Computers

Abstract
Accurate graphic position digitizers now require the use of a tablet. In rearprojection tablets the embedded wires or electrode structure tends to limit the optical quality of the image. The ultrasonic device described here avoids these limitations. It is wireless and uses any table or surface "tablet." Two small cylindrical transducers at the base station and a third as a hand-held positioncursor are used. Specially shaped inaudible pulses sense the position of the cursor, which is wireless and battery powered, and automatically switches off when not in use. Status and positional data are communicated to the base station with an infrared beam. Resolution is 0,1 mm over an area of approximately one square meter.The base station may be integrated with the keyboard of a personal computer. The device has the operational convenience of a wireless "mouse" because it uses any convenient surface as a tablet. The x and y coordinates are calculated by triangulation, using driver software of the personal computer or a microprocessor controller. Calibration for changes in ambient temperature is made, before using the equipment, by entering the required origin and one other known position. For an alternative to the wireless cursor, the controller may also be designed to accommodate a sparking ballpoint stylus.

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