Coordinate input device capable of indicating a failure in a coordinate indicator

摘要

In a coordinate input device including a coordinate input unit and a coordinate indicator which comprises a winding and is movable on the coordinate input unit, an oscillation generator generates an oscillation signal. Connected to the oscillation generator, a capacitor produces the oscillation signal as an output oscillation signal. When the output oscillation signal is supplied to the winding without failure, the coordinate input unit produces an electrical signal. A superposing circuit superposes the electrical signla on the output oscillation signal to produce a superposed signal. An envelope detector detects an envelope of the superposed signal to produce an envelope signal indicative of a location of the coordinate indicator on the coordinate input unit. A calculating circuit uses the envelope signal in calculating the location as a calculated location. An output oscillation detector detectes the output oscillation signal to produce a detection signal. A failure monitoring circuit monitors the detection signal to produce a fault signal when the detection signal is found faulty. Preferably, a failure announcer announces a failure of the coordinate indicator in response to the fault signal.