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

DETAILED DESCRIPTION What is claimed is: 1.
A coordinate input device for use in indicating a location on a coordinate surface, said coordinate input device comprising: oscillation generating means for generating an oscillation signal; a capacitor connected to said oscillation generating means for producing said oscillation signal as an output oscillation signal; coordinate indicator which has a winding connected to said capacitor for inducing a magnetic field; a coordinate input unit which defines said coordinate surface, on which said coordinate indicator is movable, and which comprises a plurality of conductor loops, each conductor loop being for producing an electrical signal when magnetically coupled to said magnetic field; superposing means connected to said conductor loops and said capacitor for superposing said electrical signal on said output oscillation signal to produce a superposed signal; amplifying means connected to said superposing means for amplifying said superposed signal into an amplified signal; envelope detector means connected to said amplifying means for detecting an envelope of said amplified signal to produce an envelope signal indicative of said location; calculating means connected to said envelope detector means for using said envelope signal in calculating said location as a calculated location to produce a location signal representative of said calculated location; output oscillation detector means connected to said envelope detector means for detecting said output oscillation signal to produce a detection signal; and failure monitoring means connected to said output oscillation detector means for monitoring said detection signal to produce a fault signal when said detection signal is found faulty.
2.
A coordinate input device as claimed in claim 1, said detection signal having a signal level, wherein said failure monitoring means comprises: reference signal producing means for producing a reference signal having a reference level; comparing means connected to said output oscillation detection means and said reference signal producing means for comparing said signal level with said reference level to produce said fault signal when said signal level is lower than said reference level