Apparatus for determining planar coordinates
First Claim
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1. Apparatus for determining planar coordinates comprising:
- a pair of normally spaced overlapping conductive sheets having sufficient flexibility between them to permit electrical contact when touched;
first and second spaced approximately parallel electrodes extending across one sheet;
first and second spaced approximately parallel electrodes extending across the other sheet transversely to the first and second electrodes extending across the one sheet;
means for generating electrical power;
means for alternatively connecting the power across the first and second electrodes, respectively, of one sheet to the exclusion of the first and second electrodes of the other sheet;
a signal processing circuit having a high input impedance and first and second differential input terminals; and
meams for connecting the second electrodes of the sheets to the respective input terminals of the signal processing circuit to alternatively indicate across such input terminals the planar coordinates of a point of electrical contact between the sheets.
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Abstract
A pair of overlapping, normally spaced conductive sheets (16,18) have sufficient flexibility between them to permit electrical contact when touched. One sheet has spaced, approximately parallel electrodes (20,21). The other sheet has spaced approximately parallel electrodes (22,23) transverse to the electrodes of the one sheet. A source of electrical power (10,12) is alternatively connected across the electrodes of one sheet to the exclusion of the other sheet. One electrode of each sheet is coupled to a signal processing circuit (32) having a high impedance differential input.
16 Citations
12 Claims
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1. Apparatus for determining planar coordinates comprising:
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a pair of normally spaced overlapping conductive sheets having sufficient flexibility between them to permit electrical contact when touched; first and second spaced approximately parallel electrodes extending across one sheet; first and second spaced approximately parallel electrodes extending across the other sheet transversely to the first and second electrodes extending across the one sheet; means for generating electrical power; means for alternatively connecting the power across the first and second electrodes, respectively, of one sheet to the exclusion of the first and second electrodes of the other sheet; a signal processing circuit having a high input impedance and first and second differential input terminals; and meams for connecting the second electrodes of the sheets to the respective input terminals of the signal processing circuit to alternatively indicate across such input terminals the planar coordinates of a point of electrical contact between the sheets. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. Apparatus for determining planar coordinates comprising:
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a pair of normally spaced overlapping conductive sheets having sufficient flexibility between them to permit electrical contact when touched; first and second spaced approximately parallel electrodes extending across one sheet; first and second spaced approximately parallel electrodes extending across the other sheet transverse to the first and second electrodes extending across the one sheet; means for applying electrical power to the first and second electrodes of each sheet to generate a first signal and a second signal representative of the planar coordinates of a point of electrical contact between the sheets; signal processing means having an input; means for applying the coordinate representative signals to the input of the signal processing means; first output terminal means for the first coordinate representative signal; second output terminal means for the second coordinate representative signal; a first normally open switch coupling the first coordinate representative signal from the signal processing means to the first output terminal means; a second normally open switch coupling the second coordinate representative signal from the signal processing means to the second output terminal means; means in the absence of electrical contact between the sheets for injecting into the input of the signal processing means a no-touch representative signal; and means responsive to the absence of the no-touch representative signal in the signal processing means for closing the first and second switches, thereby transmitting the coordinate representative signals from the signal processing means to the respective output terminal means.
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Specification