DETECTING METHOD FOR COORDINATE POSITION OF ULTRASONIC TABLET

摘要

PURPOSE:To attain compensation of temperature without complicating constitution by using the count value ratio of a counter for counting the propagation time of ultrasonic waves in order to calculate the coordinate position of an input pen. CONSTITUTION:An input pen 3 produced the ultrasonic waves by the pulse voltage given from a pulser 4 and at the same time a time counting circuit 7 of a signal control part 12 starts via the pulser 4. The elastic wave produced by the ultrasonic wave is transmitted through an input flat plate 1 and are detected by piezoelectric elements 2a-2d set at four corners of the plate 1. Then the circuit 7 calculates the propagation time of the ultrasonic waves in response to the distance from each of four corners. A microcomputer 8 of the part 12 decides the coordinates of the pen 3 from a time ration free from the dependence on temperatures. In such a way, the compensation of temperatures is secured without using a temperature compensating circuit, etc. nor complicating the constitution. This attains the detection of coordinates with high accuracy.