Electronic blackboard system marker and eraser therefor
First Claim
1. In combination, a coil, plural objects adapted to be selectively in proximity to the coil, each of the objects including a tuned circuit having a different resonant frequency, means for supplying AC energy at the different resonant frequencies to the coil, the tuned circuit on the particular object in proximity to the coil having substantially the same resonant frequency as the frequency of the AC energy supplied to the coil causing a change in the current flowing in the coil at said same resonant frequency, means for sensing the change in the current flowing in the coil at said same resonant frequency, and means responsive to the current change at said same resonant frequency for indicating the particular object having the tuned circuit with the same resonant frequency as the frequency of the applied AC energy, said indicating means including phase detector means responsive to the changed current flowing in the coil at said same resonant frequency and a reference wave at said same resonant frequency for:
- (a) deriving indications of the polarities of the phase of quadrature components of the change current relative to the reference wave, and (b) indicating the durations of the polarity indications relative to predetermined values therefor.
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Accused Products
Abstract
A determination is made as to which one of plural objects is proximate a region having a coil therein. Each object includes a tuned circuit having a different resonant frequency. AC energy at the different resonant frequencies is supplied to the coil. The tuned circuit on the particular object in the region having substantially the same resonant frequency as the AC energy supplied to the coil causes a change in the current flowing in the coil at the same resonant frequency. The change in the current flowing in the coil at the same resonant frequency is sensed. In response to the current change at the same resonant frequency the particular object having the tuned circuit with the same resonant frequency as the frequency of the applied AC energy is indicated with a phase detector arrangement responsive to the changed current flowing in the coil at the same resonant frequency and a reference wave at the same resonant frequency. The phase detector arrangement derives indications of the polarities of the phase of quadrature components of the changed current relative to the reference wave and indicates the durations of the polarities relative to predetermined values therefor.
100 Citations
38 Claims
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1. In combination, a coil, plural objects adapted to be selectively in proximity to the coil, each of the objects including a tuned circuit having a different resonant frequency, means for supplying AC energy at the different resonant frequencies to the coil, the tuned circuit on the particular object in proximity to the coil having substantially the same resonant frequency as the frequency of the AC energy supplied to the coil causing a change in the current flowing in the coil at said same resonant frequency, means for sensing the change in the current flowing in the coil at said same resonant frequency, and means responsive to the current change at said same resonant frequency for indicating the particular object having the tuned circuit with the same resonant frequency as the frequency of the applied AC energy, said indicating means including phase detector means responsive to the changed current flowing in the coil at said same resonant frequency and a reference wave at said same resonant frequency for:
- (a) deriving indications of the polarities of the phase of quadrature components of the change current relative to the reference wave, and (b) indicating the durations of the polarity indications relative to predetermined values therefor.
- View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28)
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29. Apparatus for determining which one of plural objects is in proximity to a region, each of the objects including a tuned circuit having a different resonant frequency, comprising a coil in the region, means for supplying AC energy at the different resonant frequencies to the coil, the tuned circuit on the particular object in the region having substantially the same resonant frequency as the AC energy supplied to the coil causing a change in the current flowing in the coil at said same resonant frequency, means for sensing the change in the current flowing in the coil at said same resonant frequency and responding to the current change at said same resonant frequency to indicate the particular object having the tuned circuit with the same resonant frequency as the frequency of the applied AC energy, said sensing means including phase detector means responsive to the changed current flowing in the coil at said same resonant frequency and a reference wave at said same resonant frequency for:
- (a) deriving indications of the polarities of the phase of quadrature components of the changed current relative to the reference wave, and (b) indicating the durations of the polarities relative to predetermined values therefor.
- View Dependent Claims (30, 31, 32, 33, 34, 35, 36, 37, 38)
Specification