Abstract: The disclosure is directed to a microprocessor-based apparatus and method for determining the distance between an object and a reference position. An embodiment of a graphical digitizer is set forth in which a microprocessor system is adapted to generate and store a count that depends upon the number of instruction cycles that the microprocessor system performs during a time interval that is a function of the travel time of acoustic wave energy traveling between the object and the reference position. In a disclosed embodiment, acoustic receivers are mounted with their axes parallel, and each receiver has a generally circular receptivity pattern.

Abstract: The disclosure is directed to an apparatus for position determination in a data space, the position determination preferably being in the form of rectangular coordinates. First and second orthogonally oriented elongated microphones are provided. The microphones approximately define adjacent edges of a substantially rectangular data space. A passive movable element, such as a stylus or puck, is provided as being movable in the data space. Means are provided for periodically generating sound waves at a source position spaced from the movable element. Preferably, the source of sound waves is located such that the sound waves emanate from about the corner of the data space defined by the intersection of said adjacent edges. Timing means, coupled to the microphones and synchronized with the generation of the sound waves, are provided for measuring the transit times of the sound waves reflected off the movable element to the microphones.

Abstract: An apparatus for determining the position of a movable element or stylus which is movable in a data space. In accordance with the invention there are provided first and second spaced receivers, each receiver comprising a hollow shell of piezoelectric material, which may be cylindrical or spherical in shape, and resilient conductive means coupled across the inner and outer surfaces of the shell. Means are provided for periodically generating a source of sound waves for travel between the stylus and the first and second receivers. Timing means are coupled to the receivers and synchronized with the generation of the sound waves for measuring transit time of the sound waves between the source and receivers. Computing means are employed to determine the positional coordinates of the stylus in a desired coordinate system, such as rectangular coordinates. In an embodiment of the invention the first and second receivers have conductive mesh loaded within the shell and in contact with the inner surface of the shell.