Abstract A system is disclosed for transmitting and receiving either graphic or aural information over a telephone quality communications link. A manually operated writing pen senses a composite electrostatic field representing instantaneous X and Y dimension position information on a writing surface. The field components are generated by the wires of a grid beneath the writing surface, the wires of each dimension being driven in a predetermined phase distributed pattern. A phase locked loop for each dimension channel is resolved to minimum phase shift such that its frequency of operation directly represents position information in the dimension. The phase locked loops operate at sufficiently diverse frequencies as to avoid crosstalk and also permit derivation of a single composite signal by frequency modulating the higher frequency signal with the lower frequency signal which, itself, may be shifting in frequency. In the receive mode, the incoming signal is frequency and/or phase compared in the higher frequency phase locked loop to develop a signal having a d-c level representative of pen position in that dimension and also an a-c component representative of pen position in the lower frequency dimension. The latter signal is frequency and/or phase compared in the lower frequency phase locked loop to develop a signal having a d-c level representative of pen position in that dimension. The two d-c signals drive X and Y servo amplifiers which determine the position of a reproducing pen on the writing surface. Logic means provide for the establishment of a master/slave relationship in which, once one system has assumed the transmit mode, all others are locked in a receive mode. If none of the linked systems are in either the transmit or receive mode, normal aural communication may be carried out over the link.
Inventors
👤 J Rodgers
Bibliographic Details
Application Number—
JurisdictionUS
Data Sourcegoogle_patents
Last Synchronized2026-10-26 22:05
CPC Classifications
G; G08; G08C; G08C21/00
Claims Analysis
Total Claims: 6
Claim 1
Independent Claim
165 words
Apparatus for encoding graphic information into a single signal comprising: A. a writing pen; B. a writing surface; C. first variable frequency means coupled to said pen and responsive to the position of said pen in a first dimension to assume a first operating frequency corresponding thereto, said first variable frequency means having a first predetermined range about a first center frequency; D. second variable frequency means coupled to said pen and responsive to the position of said pen in a second dimension to assume a second operating frequency corresponding thereto, said second variable frequency means having a second predetermined range about a second center frequency differing from said first center frequency; E. a first frequency divider coupled to the output of said first variable frequency means for deriving a subharmonic of said first operating frequency; and F. means coupling said first frequency divider to said second variable frequency means for frequency modulating said second operating frequency with said sub-harmonic of said first operating frequency.
Claim 2
Dependent Claim
165 words
Apparatus for encoding graphic information into a single signal comprising: A. a writing pen; B. a writing surface; C. first variable frequency means coupled to said pen and responsive to the position of said pen in a first dimension to assume a first operating frequency corresponding thereto, said first variable frequency means having a first predetermined range about a first center frequency; D. second variable frequency means coupled to said pen and responsive to the position of said pen in a second dimension to assume a second operating frequency corresponding thereto, said second variable frequency means having a second predetermined range about a second center frequency differing from said first center frequency; E. a first frequency divider coupled to the output of said first variable frequency means for deriving a subharmonic of said first operating frequency; and F. means coupling said first frequency divider to said second variable frequency means for frequency modulating said second operating frequency with said sub-harmonic of said first operating frequency.
Claim 3
Dependent Claim
52 words
The apparatus of claim 1 which further includes gain changer means responsive to contact between said writing pen and said writing surface to increase the amplitude of said sub-harmonic of said first operating frequency whereby the modulation index of said second operating frequency is increased to provide an indication of pen drop.
Claim 4
Dependent Claim
31 words
The apparatus of claim 1 which further includes a second frequency divider coupled to the output of said second variable frequency means for deriving a sub-harmonic of said Second operating frequency.
Claim 5
Dependent Claim
31 words
The apparatus of claim 2 which further includes a second frequency divider coupled to the output of said second variable frequency means for deriving a sub-harmonic of said second operating frequency.
Claim 6
Dependent Claim
51 words
The apparatus of claim 1 in which said first and second variable frequency means include, respectively: A. a first phase locked loop having a first variable frequency oscillator and a first phase detector; and B. a second phase locked loop having a second variable frequency oscillator and a second phase detector.