MXPA98006544A

MXPA98006544A - System and method for locating the position of a superfi

Info

Publication number: MXPA98006544A
Application number: MXPA/A/1998/006544A
Authority: MX
Inventors: Conroy David; Flowers Mark
Original assignee: Explore Technologies Inc
Priority date: 1996-02-15
Filing date: 1998-08-12
Publication date: 1999-10-14

Abstract

An electrographic detection unit includes a layer of conductive material having an electrical resistivity and a surface, at least three separate contact points (12, 14, 16) electrically interconnected with a layer of conductive material, a processor (30) connected to the contacts separated and arranged to selectively apply a signal to each of the contact points, a stylet (20) coupled to the processor to receive the signals from the layer when the contact points have been selectively applied signal

Description

SYSTEM AND METHOD TO LOCATE THE. POSITION OF A SURFACE Field of the Invention The present invention relates to a system and method for determining a location selected by a user on a surface and providing the user with the information that has been determined in relation to that location. In particular, the present invention relates to position detection devices that are capable of detecting positions on a surface of two and three dimensional objects having complex shapes. Additionally, it relates to position detection devices in which the object can be rotated, rotated or otherwise manipulated in relation to the rest of the position detection system.

BACKGROUND OF THE INVENTION There are a variety of technologies for determining the position of a stylet, or a finger, placed on a surface. A technology is a mesh of horizontal and vertical wires, which are placed under the surface of a flat splint or on the surface of a visual display device and emit signals indicating the position, which are detected by a stylus. Two devices that use this type of technology are described in U.S. Patents 5,149,919 and 4,686,332 to Greanias, et al. The applications that use these devices are tablets in a drawing (or digitizers) of computer input, and devices for visual representation of touch screen. In another technology, surface acoustic waves are measured at the edges of a glass plate and used to calculate the position on the plate, which 'was 1' - selected 'by a finger or a stylet. include the use of touch screen iosco display devices / where a conductive coating technology could be used. Other technologies still include "the use of photosensitive pencils as optical detectors.

A frame may be used around a flat display device, with an array of light emitters and detectors around the edge of the frame, to detect when the finger or stylus is near the display surface. These technologies are limited to visual or flat surfaces. Position detectors such as the devices described in the Greanias patents, which use many conductors arranged in a mesh, are not very suitable for a surface of complex shape, either bi or three-dimensional. There are, at least, difficulties in the placement and conformation of drivers to adjust the contours in a complex way. Another similar device is a mesh of horizontal and vertical wires placed above and below the surface of a flat visualization device, which utilizes the capacitive coupling of a stylus or finger. In this device, the capacitive coupling transfers signals that indicate the position of one wire to another, which can be used to calculate the position of the coupling. The computer input slats, as well as the mouse replacement plates that point the finger, use this technology. In another technology, a transparent, homogeneous, rectangular conductor is placed on the surface of a visual representation device and plate contacts on the edges of the transparent conductor load the conductor. The capacitive coupling of a stylus or a finger to the transparent conductor causes the conductor to discharge while the sensors attached to the plate contacts measure the amount of current drawn through each of the contacts. The analysis of the relationships of the currents extracted from the pairs of contacts on the opposite sides of the rectangle provides a position XY on the panel that was selected by the user. A device of this type is described in the United States Patent 4, 853,498 to Meadows, et al. An application of this device is a touch-screen visual representation device. A similar technology uses a rectangular piece of extremely uniform resistive material with a series of discrete resistors along the edge and which is mounted on a flat surface. A voltage difference is applied to the row of resistors on the opposite sides of the rectangle / and a voltage difference is applied as a time division to the row of resistors on the other two opposite sides. The signals indicating the position are received by a stylus, or by a conductive coating, which can be pressed to contact the surface of the resistive material. A variety of these devices are described in the United States Patent 3,798,370 to Hurst. The devices described in U.S. Patents 4,853,498 (Meadows et al.) And 3,798,370 (Hurst) lead to a homogeneous, rectangular, resistive coating with plate contacts on a chain of resistors along each edge. These methods depend on the rectangular shape of a rectangle to work with. The shape and placement of the contacts provide the means to the detection portions of the surface within a rectangular sub-section of the resistive material of the surface. Other simple forms with plate contacts and resistor chains are also feasible, but of complex shapes that can create areas that can not be distinguished (for example, shapes with concave edges such as a circle or an ellipse can not be accommodated by any of - Meadows or Hurst methods). The use of plate contacts or chains of resistors substantially along the entire edge of an object limits its usefulness to objects where the position must be detected over the entire surface. The locations directly below each plate electrode and between each plate electrode or point and the edge of the object are not detectable in those devices. The devices described in the U.S. Patent 4,853,499 (Meadows et al.) And 3,798,370 fifteen - . fifteen -. (Hurst) do not take into account the effects of contact resistance. The resistance between the contacts and the homogeneous resistive material can be substantial in relation to the strength of the homogeneous material. Additionally, contact resistance may vary from electrode to electrode or change due to mechanical or environmental stresses. Meadows and Hurst devices rely on contacts of known or constant resistance, which restricts the use of materials and contact methods. Any variation in contact resistance or changes in contact resistance due to environmental factors is taken into account by and results in detection errors. In addition, Meadows charges the surface with a capacitively coupled stylus and determines the position by measuring the current drawn from the exciter circuits. The Meadows device requires four receiver circuits to accomplish this. The Meadows device is susceptible to the effects of coupling undesirable phantom stilettos to the surface. Ghost stilettos, such as rings or fingers, can be attached to the reactive surface instead of, or in addition to, the actual stylet. Those phantom stilettos can cause detection errors because the changes they also produce cause changes in the exciter circuit. In applications, where the object contains the mesh that needs to be rotated, or the electronic devices and the object are physically separated from each other, a large number of conductors must be coupled to the system, or between the elements of the systems, through mechanisms of connection that can allow rotation or other movements. Such cables for the systems of the prior art could also be large and embarrassing. In addition, connectors with a large number of contacts are expensive and reduce the total reliability of any system that requires them. Contacts that allow rotation, such as slideable connector rings, become prohibitively complex and expensive, since the number of connections rises above a small number. Additionally, the multiple circuits required to have the mesh arrays are complex and costly to manufacture. Acoustic wave detectors provide a robust position detection mechanism, but their implementation is expensive. The detection mechanisms of light waves are limited to flat surfaces and are susceptible to dust and insects that block the paths of light. It is believed, however, that the present invention solves those problems.

Brief Description of the Invention The present invention includes various apparatuses and methods for determining a position selected by a user on an electrographic detection unit. More generally, the electrographic detection unit of the present invention includes a layer of a conductive material having an electrical resistivity with K separated contact points, electrically interconnected therewith, a processor connected to the K separate contact points and arranged to selectively apply a signal to N of the K contact points, where N has an integer value of 3 to K, and a probe assembly, which includes a stylet or a flexible conductive layer placed on the layer, coupled to the processor, the stylet is arranged to be positioned by a user in the vicinity of the position selected by the user on the layer selected by the user, or the user to point a finger at the flexible conductive layer. In turn, the stylus, or the flexible conductive layer, receives the signals from the layer when the contact points have signals selectively applied to them by the processor, with the position selected by the user being determinable by the processor from the signals received from the stylet, or the flexible layer, each in relation to a similar excitation of (NJ) pairs different from the K points of contact under the processor control, where J is an integer of 2 a (Nl). Additionally, where the electrographic detector includes more than one conductive layer, which is each electrically isolated from each other, in the most general sense, M conductive layers, the present invention is also capable of determining which of those layers contains the selected position. by the user. Here, each layer has K points of contact separated, electrically interconnected with the layer of corresponding conductive material, where N of the K points of contact on each layer are used to locate the position selected * by the user, and where N has an integer value of three to K. The processor is also arranged to selectively apply a signal to each of the N contact points of each of the M layers and to determine which 5 of the M layers and position coordinates of the position selected by the user, on one of the corresponding M layers, cooperates with it to determine and release a signal of the position selected by the user on the * Selected layer of the electrographic detection unit to the processor. The identification of the selected layer is effected by sequentially applying the first selected signal of all the K contact points on each of the M layers in turn, inhibiting a first signal measured in the position selected by the user for each of the M '§ layers individually with the first measurement, corresponding to each of the M layers that are the signal received by the means for detection and release, when all the contact points on that layer have the first selected signal applied to those point of contact of the layer. Next, a second signal measured at the position selected by the user on the layer selected by the user is measured, for each one of the M layers with each of the K points of contact on each of the M's. layers in open circuit, followed by the subtraction of the second measured signal of the first signal measured by each of the M layers to form M values of the difference. Those M values of the difference are then each compared against a preselected threshold value to determine which of those M values of the difference i are greater than the selected threshold: and which exceed this by a greater value. The layer associated with the value of the difference cpie satisfies those conditions, is then identified "as the layer containing the position selected by the user. Then, once the determination has been made, the coordinates of the position selected by the user on that layer can be determined as discussed above. The present invention also includes the techniques to compensate for the resistance of the contact at each contact point on the conductive layer, as well as the formation of the conductive layer in a bi-or three-dimensional form, which can be opened or closed. In addition, the present invention includes the placement of a Conductive coating on the outer surface of the layer, which coating has a graphic representation thereon and the present invention has the ability to convert the position coordinates of the position selected by the user to the coordinates of the layer driver, to those of the graphic representation. Such a graphic representation can be that of a map or a globe, or even a mythical map or one of a star or another planet. By carrying out this additional step, those graphical coordinates can also be used to electronically provide information that has been pre-stored in the memory, in relation to the graphic coordinates selected to the user. In a real application, the present invention can take many forms, from a conductive layer with or without a non-conductive layer on it and a stylus to be used by the user, to select a position on the layer, up to a multi-layer structure with a conductive lower layer, a compressible, non-conductive inner layer and a conductive, flexible upper layer, wherein the user presses the upper layer towards the lower layer and the point at which the upper and lower layers approach, is determined as the position selected by the user. In addition, several designs are proposed in which the drive and measurement signals are AC of a selected frequency or CD. Thus, to fully explain the scope of the present invention, a detailed discussion of the different modalities is offered in the Description of the Preferred Modalities below. However, it should be kept in mind that this discussion is not an exhaustive discussion * and variations on the main / presented themes were also considered as part of the present invention.

Brief Description of the Figures Figure 1 is a simplified block diagram of a generalized embodiment of the system of the present invention. Figure 2 is an illustration of the location location algorithm of the present invention, for a two-dimensional surface shape. Figure 3 is similar to Figure 2, however, the illustration is for a three-dimensional shape. Figure 4 is a block diagram of a first embodiment of the present invention. Figure 5 is a block diagram of a second embodiment of the present invention. Figure 6 is a block diagram of a third embodiment of the present invention. '_ 20 Figure 7 is a block diagram of a fourth embodiment of the present invention. Figure 8 illustrates the restrictions on the placement of the contact points that allow to determine the position with only three contacts.

Figure 9 illustrates three contact points that can not be used to determine the position on the surface. Figure 10 is a partial embodiment, _e_n where a multi-layer compressible contact surface is described instead of the use of a stylet, for example, in Figure 4. Figure 11 is a schematic representation of one embodiment of the present invention. , adapted to be an interactive balloon that incorporates a spherical conductive surface. Figure 12 is a schematic representation of one embodiment of the present invention, adapted to be an interactive balloon incorporating two semi-spherical conductive surfaces.

Description of Preferred Modes The present invention relates to a system and method for determining a location on a bi or three-dimensional surface of any shape selected by a user, as well as to provide access to data storage locations or information stored therein. and that is related to that location. More specifically, the present invention determines the location information in the form of coordinates on a system of predefined coordinates. That location information then serves as a location address within the memory of an associated microprocessor subsystem. That location, or address can be used in turn to retrieve previously stored data belonging to the corresponding location on the surface, to store the data belonging to the corresponding location on the surface, to modify the behavior of the system that incorporates the present invention, or to be presented to the user on a conventional visualization device or printing device. In surfaces of simple form, such as a rectangle, a minimum of three contacts are necessary small electric, mounted on the edge of the surface.

^ On surfaces of more complex shape, the minimum number of electrical contacts can be increased to allow the system to determine between multiple locations on the surface, such as the one the user is indicating. In each surface configuration, the contacts need to be placed so that all locations on the surface can be identified individually. Through the use of small contacts and actuator / receiver techniques, the present invention is also able to compensate differences in the contact resistance ^ P of each of the contacts. Differences that can be compensated include differences between contacts on the same surface, differences between contacts on one surface versus those on another surface ^ 5 using the same electronic devices, as well as changes in contact resistance of individual contacts during the time due to mechanical and environmental efforts. * T The present invention determines a position selected by a user on the surface by measuring the unique position, indicating the signals with a receiver as discussed below. For two- or three-dimensional objects, the present invention only requires a single receiver circuit. 15 In the different modalities of this In the invention, the stylus does not charge with or negligibly charge the transmitters and a signal level is measured at the point on the surface that is touched by the stylet in place of the changes in the driver circuit. as in the Meadows device. Additionally, potential ghost stilettos, such as fingers and rings, that have a dramatic effect on the prior art operation, have only a negligible load effect on the transmitter of the present invention. In this way, The present invention is immune to phantom stylets.

In the present invention, the active surface can be made of a conductive polymer composition (conductive plastic), or a conductive coating or a non-conductive material. This has substantial cost advantages over the prior art, since coated or lined wires are not necessary, and since the surface itself provides the necessary structural support. The devices embodying the present invention could typically include a surface of a molded or vacuum formed conductive polymer composition that does not require any additional structure, thereby resulting in an additional cost only to the carbon-polymer material, or the applied conductive coating. In addition, the formation of the sensitive surface by injection molding makes it possible to easily create complex shapes that are sensitive to touch. The use of a carbon-polymer composite material as an element in the positioning system and structural support, provide a robust and reliable system. The carbon-polymer composites are inherently robust, and the system of the present invention employs a single layer of such material, rather than a multi-layer system, where the bonding of the layers can deteriorate and the layers separate.

# A minimum of three contacts are necessary to drive an entire surface of a single object (for example, a rectangle, circle or ellipsoid). Additional contacts can be used for complex objects or to provide higher resolution for simpler ways ^ instead of increasing the sensitivity of the circuit. The low number of contacts and therefore the number of wires, leads to a low cost, ease of manufacture, and allows f remote or mobile surface applications (for example, a rotating globe). An advantage of using a conductive polymer material for the surface is that it allows the contacts to be mounted on the back or inside the surface, and thus achieve a front surface or external 100% active. • 1M Additionally, the present invention includes unique surface drive techniques that can compensate for unknown and variable contact resistance. The various types of contact and mechanisms The mechanical connection creates contact resistances, which can vary substantially between contacts, and vary over time with mechanical and environmental stresses such as movement, temperature and aging. Other technologies depend on contact resistance contacts known or constant, without any change not compensated in the # resistance to contact that results in errors in the detection of the position. The present invention allows the use of various mechanisms to compensate for differences and variations in the resistance to contact. Each of these mechanisms can be used and provides its own advantages. A ~ Possible mechanism, involves using two electrodes as - ^ each contact, with those electrodes being very close and electrically interconnected, but not touching each other. He The first of these electrodes in this configuration is attached to the source of the signal drive, and the second of those electrodes provides a high impedance feedback path. In this configuration, the signal drive source is t adjusted, so that The signal level at the second electrode is of a desired value ijtt, thereby providing a known signal level at a point on the surface, independently of contact resistance. The drive method here also provides automatic adjustment of changes in the resistive material with time and temperature, as well as variations in contact resistance. A second possible mechanism has only one electrode per contact and measures the resistance value of each contact for the resistive material of the surface.

In such a system, which has three points of contact, A, B and C, is a measurement of the level of 'signal e? point C through a high impedance path, while a signal of a known level is applied between point A and point B. Next, similar measurements are made at point 5 with the signal applied between point C and point A, and at point A with the signal applied between point B and point C. In this way, knowing the positions of the contacts on the surface and the resistivity of the material * from the surface, contact resistance can be calculated between points A, B and C and the surface material as discussed below with respect to Figure 6. Additionally, the present invention incorporates the use of a multi-state excitation drive sequence to provide rapid measurement Y on-the-fly calibration to improve accuracy. The stylus is used to make several measurements of the signal in a # point on the surface of the object selected by the user. A first measurement is made without signals applied to the contacts to determine a baseline CD deviation, and the level of ambient noise for the surface, the. which, for purposes of discussion here, is the so-called CD DEVIATION. A second measurement is made with a signal applied to all contacts to determine the value of the full-scale signal, which, for discussion purposes here, is the called COMPLETE SCALE. Then another "measurement" is made by applying a signal to a pair of contacts to create a gradient of signal level across the surface between those two points, which, for discussion purposes here, is called the X-axis and the measured value of X. Then a signal is applied to another pair of contacts to create a signal level gradient in another direction, which, for discussion purposes here, was called the Y axis and the measured value of Y. Next, the following calculations are made by a system to determine the selected location along the X and Y axes defined on the surface. Px = (X - CD DEVIATION) / (COMPLETE SCALE - CD DEFLECTION) (1) P? = (Y - DEVIATION OF CD) / (COMPLETE SCALE - DEVIATION DE CD) (2) ¡fj The current position on the surface can then be determined from Px and P ?, using a mathematical model, or empirically determined, of the signal level gradients for the surface material. In the present invention, the basic points required (that is, the algorithm and the conductive material) have been around for some time. The bases for the algorithm date back centuries. Materials similar to those suggested for the surface material here, which have electrical properties similar, have also existed for decades.

The basis of the algorithm of the present invention is the use of triangulation to determine the location of the point on the surface of the object. The triangulation is defined as - "The location of an unknown point, as in navigation, by forming a triangle that has the unknown point and two points known as vertices." (The American Heritage Dictionary of the English Language, Third Edition). Triangulation is a basic principle of trigonometry and its use to find the location of a point on the surface of an object has been used for centuries. This is used in applications such as celestial navigation, surveying, global positioning system (GPS), and seismology. In the present invention, as in the case of triangulation, the position is determined by measuring the relationship at a point of interest with two known points. The ratio is determined from the signal level received in the stylus by injecting signals of known levels at the first two fixed points at the same time. All the points on the surface that could have that level of signal create a line of possible positions. Another relationship is determined using two other fixed points (a different pair of contacts, however, one contact may be one of those that was included in the first pair of contacts) and another level of signal received from the stylus. The intersection of two lines of possible positions of the two measurements tells us in this way where the stylus touched the surface. For some surfaces, this can be unique, such as a two-dimensional surface or a hemisphere with the contacts mounted on the edge or at the equator. In theory, any position in three-dimensional space can be uniquely identified by its distance from four known non-coplanar points, while the required number of known points can be reduced in some cases if possible positions in three-dimensional space are restricted. For the purposes of the present invention, the position of interest is restricted to that which is on the surface of the known shape of the surface. For a shape such as a rectangle or circle, a position on the surface can be defined by its distance from three known points on that surface, provided that the known points are all at the edge of the surface shape or are not collinear. For the shapes of spheres or ellipsoids of continuous surfaces, a position on the surface of the form can be defined by its distance from three known points, provided that the plane defined by the three known points does not include the central point of the shape. For a cylindrical shape, a position on the surface can be defined by its distance from three known points, provided that the plane defined by the three known points does not cross the central line of the cylinder. For a relationship to be determined between a contact and a point on the surface, the point must be in the field of view of a pair of contacts. That is, as shown in Figure 8, for any point, X that is in the field of view for a pair of contacts A and B, the included angle, Ai, between the vectors drawn between A and B, and A and X , as well as the included angle, Bi, formed by the vectors drawn between B and A, and B and X, must both be less than 90 °. Additionally, the surface must contain electrically conductive material between points A and X and between X and B. Figure 9 illustrates a situation where point X is not in the visual field of points A and B, since the included angle B ± is greater than 90 °, even when the included angle ± ± is less than 90 °. In practice, more contact points can be used due to the finite resolution of the actual measurement devices. Another factor that can increase the number of contacts is the cost. A relationship can be constructed between the resolution of the receiver and transmitter circuits, and the number of contacts between which the signal is applied to the surface for measurements. If more contacts are used that are closer, then the resolution of the transmitter / receiver circuit can be reduced. The use of resistivity in materials to measure distance or position has been common for some years. A first example is the use of rotating or sliding potentiometers to determine the position of a button or slider. The conducting polymers that could be employed by the present invention have been known since at least 1974, when CMI, a first producer of conductive polymeric compounds, was acquired by 3M Company. At least, the materials and algorithms used by the present invention have been available for 20 years, and probably more in total. However, the literature does not teach or suggest the combination of those elements to produce a device similar to that of the present invention, in fact,? all the teachings of 1-as known references are far from this technique. In Figure 1, the basic components of the location location system selected by the user of the present invention are shown. They include two or three dimensional conductive surfaces 10 (e.g., plastic with carbon charge or a conductive coating applied to a non-conductive surface) having a resistivity selected with three conductive contacts 12, 14 and 16 fixed thereon. Each of the contacts 12, 14 and 16 are connected via the connectors 24, 26 and 28, respectively, to the processor 30. Also connected to the processor 30, is the conductor 18 with a stylet 20 having a tip 22 fixed to the other end thereof for the user to use to indicate a position on the surface 10 that is of interest to that user. Next, as in Figure 2, when a user selects a point on the surface 10 with the stylet 20, a series of measurements are made as generally described above. First, without any signal applied to the contacts 12, 14 and 16, the processor 30 measures the value of the CD DEFLECTION of the system with the stylus 20.; Next, a signal of equal amplitude is applied to the three contacts 12, 14 and 16, and the processor 30 measures the value of the COMPLETE SCALE signal with the stylet 20; The third measurement is made by applying a signal of the amplitude used in the scale measurement will complete und of the three contacts, say the contact 12, with a second contact connected to ground, that is, contact 14, and the measurement of the signal it is done with the stylet 20, which will be somewhere along an equipotential line between those two contacts (ie, the X line in the Figure 2); A fourth measurement is made by applying the signal to, and connecting to ground, a pair of different contacts, say 12 and 16, and the measurement of the signal is made with the stylet 20, which will be somewhere along the an equipotential line between those two contacts (i.e., the line Y in Figure 2), with the position of the stylet 20 being the intersection of the lines X and Y; and The values of Px and P? they are then calculated as in equations 1 and 2 above. In the actual operation, each of these steps can be automated by the processor 30, without requiring the user to initiate the specific measurements or to switch the signals. The values of Px and Py can then be used as an address for a memory inside the processor 30, from which information relative to the position indicated with the stylet can be obtained. This same technique can also be used to determine the address in memory, where the data should be stored initially for later retrieval, or as an address on a remote visual representation device that can be activated for any purpose.

? Each unique position on the surface is defined by a unique combination of values of ~ PX and P ?. From the series of measurements described above, the position of the stylus on the surface can be expressed in terms of 5 Px and P ?, which were the so-called equipotential coordinates. Additional calculations can also be made to convert the position of the equipotential coordinates to another coordinate system, if desired. The conversion requires the trace of a known map of the coordinates equipotentials to the desired coordinate system. The map trace can be determined mathematically for an object made of a homogeneous conductive material, or one in which the distribution of the resistivity is known. For objects in which the distribution of resistivity is unknown, the outline of the map of the equipotential coordinates to the desired coordinates can be determined empirically. In any case, the trace of the map can be stored in the memory of the microprocessors and the conversion calculations carried out by the microprocessor. 20 Figure 3 illustrates the same method to determine the values of Px and P? on the surface that has a definition equation that is continuous over the entire surface, for example, a hemisphere as shown. The surface 10 of the present invention uses materials such as carbon-charged polymers or conductive coatings (for example, Velostat 1840 or 1801 of 3M), which can be easily molded into, or applied to, bi-or three-dimensional surfaces, including surfaces having complex shapes. A minimum number of circuits 5 exciters and connections between that surface and the electronic detection devices will further reduce the complexity in the electronic and mechanical aspects of the surface coupling to electronic devices. More specifically, the different embodiments of the present invention are described in the following paragraphs and are illustrated beginning with Figure 4. The embodiment, shown in Figure 4, includes a rectangular piece of conductive material such as sheet 100 (for example, For example, a 30.48 cm x 30.48 cm x 0.3175 cm (12 inches x 12 inches x 0.125 inches) sheet of a carbon loaded polymer, such as Velostat 1801 of 3M). The conductive material may also be composed of a non-conductive material with a conductive coating such as the Model 599Y1249 of Spraylat Corp. Fixed near the edge of the sheet 100, and making electrical contact between them, are the contacts 102, 104 and 106. Connected between the contacts 102, 104 and 106 on the sheet 100 and the contacts 126, 128 and 130 of? signal generator 122, respectively, are the electrically conductive cables 108, 110 and 112. The signal generator 122 includes an AC (alternating current) signal generator of 60 KHz, 124 which supplies the amplifier 134 with the terminal of non-inverting output of the amplifier 134 connected to three separate terminals (one corresponding to each of the contacts 102, 104 and 106) of the switch 132, and the inverting output terminal of the amplifier 134, connected to three terminals (one corresponding to each of the contacts 102, 104 and 106) of the switch 136. Next, each of the contacts 126, 128 and 130 are each connected to different terminals of each of the switches 132 and 136. In the Figure 4, each of the switches 132 and 136 are shown in the open position (ie, no signal applied to any of the contacts 126, 128 and 130). In turn, the position of each of the switches 132 and 136 is controlled via wires 138 and 140, respectively, of the microprocessor 142 to allow to the microprocessor 142 to select which of the contacts 102, 104 and 106 receives a signal of 60 KHz through the switch 132 via the associated control cable ,, and which of the contacts 102, 104 and 106 receives an inverted signal of 60 KHz through the switch 136 via the associated control cable.

# When the 60 KHz AC signal is connected to one or more contacts 102, 104 and 106 that radiate the signal through the conductive material of the sheet 100, and the stylet 116 acts as an antenna when it is brought near the surface 100. A signal detected by the stylet 116 is in turn driven to the measurement stage of the signal 120 via the sheathed cable 118. In this embodiment, the stylet 116 is completely passive and could be manufactured simply * consisting of a plastic liner surrounding the end of the cable 118 with 0.3175 cm (1/8 inch) end of the cable 118, at the distal end of the stylet 116, which has the liner removed to allow the center conductor of the cable 118 to be exposed to receive the radiated signals. In this way, when the tip of the stylet is close to the surface of the conductive material 100, the radiated signal is received by the stylus antenna, and provides it as an input signal to the measurement step of the signal 120. The measurement step of the signal 120 includes a demodulator 144 which is connected to cable 118, where the The signal received by the stylus 116 is demodulated and the demodulated signal is in turn presented as a signal level to an analog-to-digital (CAD) converter 146. The CAD 146 then digitizes that signal level and presents it to the microprocessor. 142 The use of an AC signal in this mode makes * it is possible for the stylet 116 to receive the radiated signals from the conductive material of the sheet 100 without being in direct contact with the conductive material of the sheet 100. This allows the conductive material of the sheet 100 to be covered. with a layer of non-conductive material for protection against impacts on the surface, unavoidable, of the i. .. . -,. .. - sheet 100 with stylet 116, or for the placement of? specific graphics of application on the surface of contact, and still allow the stylet 116 to act as an antenna to receive a signal from the sheet 100 at a selected point that must be measured by the measurement step of the signal 120. The microprocessor 142 has the codes for directing the operation of a series of t measurements with different contact sets 102, 104 and 106 connected to receive the 60 KHz signal, or the inverted 60 KHz signal. Once a user has selected a point of interest on the sheet 100, the system of the present invention, performs a series of measurements in rapid succession (e.g. time division multiplexing) to determine the location to which the stylus 116 is pointing and to provide the user with the information that is looking.

The first measurement, as explained above, is the so-called "SignalSpeak" and "N" and involves placing the switches 132 and 136 in the fully open positions. The microprocessor 142 then reads the signal level of the signal measurement stage 120 and assigns that value to the SignalDEsviAc? ON and stores that value in the RAM (random access memory) 144. The second measurement, as explained above, is the so-called "SignalCQMPLETA /" which involves connecting a 60 KHz AC signal to all the contacts 102, 104 and 106 at the same time, closing all three sets of contacts on the switch 132. The microprocessor 142 reads then the level of the signal of the measurement step of the signal 120 and assigns that value to the COMPLETE Signal and stores the value in the RAM 144. Next, the microprocessor 142 selects a pair of contacts, say 102 and 104, to use them in the next measurement. The contact 102, for this discussion, is a point A and is connected to receive the AC signal of 60 KHz via the switch 132. The other of those two contacts, the contact 104, which, for this discussion is a point B , is connected to receive the 60 KHz AC signal inverted via the switch 136. The third contact 106 is simply connected to the open positions of the switch on both switches 132 and 136. The microprocessor 142 then stores the signal level of * measuring step 120 in RAM 144 and assigning that value to the so-called RECTIFY-AB command. Between energized contacts 102 and 104, an equipotential map of signal level 114A could be drawn due to the effect of the resistance distributed in the material conductor of sheet 100. Equipotential maps of signals such as 114A, 114B and 114C, including the shape and values of the equipotential signal level lines, are stored in the ROM _ (memory of only reading) 146. As discussed in Electromagnetics, by John D. Kraus and Keith R. Carver, McGraw-Hill, 1973, pp. 266-278, these equipotential signal maps are created by finding the unique solution to the Laplace equation ( s2V = 0) that satisfies the limit conditions of the sheet 100 and each pair of contacts There are many methods to find the solution to the Laplace equation for an object, including, but not limited to, direct mathematical solutions, point-to-point computer modeling, and empirical determinations. For homogeneous conductive material and shapes simple, a direct mathematical solution can be easily obtained. For materials, whose homogeneity, form or placement of the contact does not lend itself to other methods, the empirical determination can be used. In the method of empirical determination, one chooses and places a coordinate system on the device. To determine the map for a specific pair of contacts, such * like 102 and 104, the contacts are energized in the same way to measure the previous RECTIFY-AB Signal. At each crossing point on the chosen coordinate system, the value of the RECÍFICAR-AB SEND ™ is measured. If the granularity of the chosen crossing point is sufficiently fine, the equipotential map can be obtained directly by finding the points containing the same measured value. In other circumstances, the equipotential lines can be calculated interpolating between the measured points. For the third embodiment, the microprocessor 142 selects another pair of contacts, such as 102 and 106. The contact 102, which, as discussed above, will again be referred to as point A, is connected to receive the AC signal of 60 KHz via the switch 132 and is V the only one of the contacts so connected. The other contact 106, which, for this discussion is referred to as a point C, is connected to the inverse signal of 60 KHz via the switch 136. The microprocessor 142 then registers the signal level of the measurement stage of the signal 120 and assigns that value to the so-called RECTIFYING-AC signal. The two signals, SIGNAL? N RECTIFY-AB and SIGNAL? N RECTIFY-AC- are affected not only by the resistance of the material between contacts, but also by numerous other factors, including the altitude of the stylet 116 from the surface of the conductive material of the sheet 100, to the attitude or angle of the stylet 116, and changes in the circuits due to environmental changes, aging or other factors. The signal, SignalMPLETA / - are also affected by the altitude, attitude and changes of the circuit, although they have an equipotential map of constant signals, so that the value of the SignalMPLETA can be used to normalize the values of the RECTIFYING AB and the RECALS-AC-RECEIVER to remove the effects of altitude, attitude and changes in the circuit using the following formula. NORM = Signal ™ RECTI FICAR / SeñalcoMPLE A (3) The RECTIFY and SeñalcoMPETA signals are affected by certain changes in the circuits that produce a deviation from CD to the final values. Equation 3, if desired, can be modified to remove those effects as shown in equation 4 below. SignalNORM = (Dies ™ RECTIFY - SIGNALISED) / SignpostMPLETA - Signal DIVIDED) (4) Applying any of the formulas of equations 3 and 4 to each of the RECAL-AB and RECAL-ACI signals, the normalized signals can be derived, Signal-AB and Signal No. M-Ac - For example, using the predetermined signal map 114A and the value Signal-0RM-AB / the position of the stylus 116 can be resolved to a single signal level line, such as 115, between contacts 102 and 104. Using the predetermined signal map 114B and the value of the N0RM-Ac-Signal, another line of 5 signal level can be determined on the signal map 114B between the contacts 102 and 106. The position of the stylet 116 is then solve the point, P, where the signal level line selected by the NORM-AB Signal at 114A crosses the signal level line selected by the N0RM-Ac Signal at 114B. The use of the resolved point, P, is qualified by the microprocessor 142 by comparing the value of the PICTURE Signal with a predetermined threshold level to determine whether the received signal is valid. This threshold is determined in a general empirical way to satisfy the requirements of resolution of the application or the user. When the altitude of the stylet 116 from the surface of the conductive material of the sheet 100 is reduced, the received signal is stronger and the resolution of the position is more accurate. Some applications such as scribble tablets may wish a specific amplitude threshold to adjust to the user's operating expectations. In those applications, users do not expect the system to recognize the position of the stylus until the tip is in contact with the surface. Other applications may want a greater or lower degree of resolution. The application can select the altitude threshold that best suits your requirements. When a threshold of the HANDBOOK signal for a particular application is satisfied, the resolved point, P, is considered valid. The measurements outlined above are done in succession, and each measurement can typically be done within 4 msec, so that the entire sequence is completed in 12-16 msec. This is important, since the measurement sequence needs to be completed quickly, so that Any changes in the position of the stylus between the measurements should be minimized. Substantially faster sampling times may be used, provided that the capabilities of the signal measuring device are appropriately selected. To support an application that requires a series of locations of the stylet to be measured in rapid succession, a sampling time that is substantially faster than the movement of the stylet needs to be chosen. An application that could require successive detection of the location of the stiletto, could be an electronic trace tablet, where the succession of points could form a line. An application of this type may require sampling times of the order of 200 microseconds. In the modality discussed above, the The signal generator 122 produces an AC signal of 60 KHz, however, a voltage level of GD could alternatively be used. With a CD signal level instead of the 60 KHz signal, the ability to detect the position of the stylus without making contact between the stylet 116 and the conductive material of the sheet 100 is eliminated. Since the direct contact is made between the stylet and the material, the effects of the altitude and posture of the stylet do not contribute more to the Measurement of the Lens ™ RECTIFY since the altitude and posture of the stylet are the dominant source of variation in the Measurement of the RECAL. The elimination of the altitude and posture of the stylet by measurement, reduces, or • eliminates, the need to normalize the RECTIFY SIGN with the SignalMPLETA • Further measurements can also be made (contacts 104 to 106, ie, B to C) to refine / co-sign the point at which the stylus 116 should be pointed with a minimum number of measurements. The microprocessor 142 could also be programmed to filter the measurements to dampen the changes made by the movement of the stylet 116 and to increase the resolution. The synchronous detection techniques in the receiver demodulator substantially improve the noise immunity. The received signal is multiplied by the signal transmitted with a FET switch (for example, DG441). The resulting multiplied signal is then integrated to determine the CD component. It is this integrated signal that is presented to the CAD for the conversion. The net effect of multiplication and integration is that only the signals received from the same frequency and 5 phase of the transmitted signal are observed. It is considered that such signals are synchronous with the transmitter, and hence the name of synchronous demodulation. Effective noise immunity is achieved, since, in general, noise sources will not synchronize with the transmitter, and therefore, will not be observed after multiplying and integrating. Only the desired position of the transmitted signal that has been detected by the receiving stylus will be measured. Special techniques can be used to improve accuracy near the edges of a surface driver. On surfaces of certain shapes, the equipotential lines can be almost parallel near the edges, which tends to reduce the positional accuracy. The distance to the edge can be estimated from the SignalMPET only, since the SignalMPETA tends to fall somewhat close to the edge. Applying an estimate of the edge distance to the point determined by the intersection of the two equipotential lines near the edge can help improve positional accuracy in some cases. In cases where two surfaces electrically isolated end up along the same edge, such as the equator in a globe made of isolated northern and southern hemispheres, improved techniques can be used to improve positional accuracy near the edge. In such cases, the distance from the edge can be estimated by comparing the SignalMPET of both surfaces, and using the relationship of the SignalMPLETA-A to the SignalCoMPLETA-B to help eliminate the effects of altitude and posture. Once the position indicated by the user is determined, the system could be used in an application where the information relating to that position has been pre-stored, or will be stored, in the total system. To allow that application, the RAM 144, ROM 146, audio / video card 150 and ROM unit of DC 156 are shown interconnected with the microprocessor 142 via a driver collective of data. For example, if the surface 100 has a superimposed map drawing, there may be pre-stored information in the ROM 146 or in a DC (compact disc) in the DC ROM unit 156 which may be provided to the user in the form of audio or visual, via the card audio / video 150 and the speaker 154 or monitor 152. The contact resistance of the connections between the contacts 102, 104 and 106 and the conductive material of the sheet 100 can play a significant role in defining the absolute levels of the Signal in the signal maps (114A, 114B and 114C). That resistance to contact affects the absolute value of the signal level, but has only a minor effect on the shape or distribution of the signal lines. In some cases, the contact resistance between a contact and the conductive material of the sheet 100 may be of a similar or higher value to that of the resistance through the conductive material between different contacts. The resistance between a single contact and the conductive material is also subject to changes over time, due to chemical or mechanical factors. The contact resistance of the conductive material can also differ from unit to unit in a manufactured product. To automatically compensate for differences in contact resistance of the conductive material, which is solved in the embodiment of Figure 4, by means of a calculation; in Figure 5 another embodiment of the present invention is shown. As can be seen, by comparison of Figures 4 and 5, many of the elements of the two circuit modes are the same and are connected in the same way, in particular the sheet 100, the signal measuring step 120, the microprocessor 142 and associated components, signal generator 124, amplifier 134, and switches 132 and 136. Additional elements in Figure 5, which are described below, have been added to provide automatic compensation for differences of resistance mentioned above.

- * The first difference between the two figures is found in the structure of the contacts fixed to the sheet 100. In Figure 5, said in simple terms, a single contact was replaced as shown in Figure 4 with a pair of 5 contacts connected. A first contact of each connected pair was used as the point at which the signal generator connection was made, while the second contact of the connected pair was used as the point at which the connection was made. * which measurements were made of the signal level, and in which made the adjustments of the level of the signal, which was injected to the first contact in that reconnected pair, so that the level of the signal at the measured point is a known level. For example, contact 102 in Figure 4 was replaced with connected pair 202a and 202b in Figure 5.

In this embodiment, the contact 202a could be a 0.16 cm (0.0625 inch) diameter contact placed at the same point on the sheet 100, as the contact 102 in Figure 4, and was used as the injection point of a signal to the conductor material of the sheet 100. Similarly, the contact 202b, could be a 0.16 cm (0.0625 inch) diameter contact placed 0.635 cm (0.25 inches) from contact 202a and used as the point at which the level of the signal at the associated point on the sheet 100. The second difference of the modality of the Figure 4, is the connection of the output terminal of each of two * amplifiers of the input terminal 220, 224 and 228 (e.g., MC4558) to the contacts 202a, 204a and 206a, respectively. Each of the amplifiers 220, 224 and 228 has the input terminal connected to a different output terminal of the switches 132 and 136. Each of the amplifiers 220, 224 and 228 has the negative input terminal connected to a different one. of the contacts "b" of each connected pair attached to the sheet 100 (ie, the * contacts 202b, 204b and 206b). 10 When the input signal passes through the contact resistance, the signal level decreases. If the contact resistance changes, the level of the signal changes inversely proportional to the change in contact resistance. Therefore, if such a change in the level of The input signal is inversely compensated in another way, any change in the level of the signal resulting from a change in the resistance of a contact is negated. Those skilled in the closed circuit feedback theory art will recognize that contacts wb "of the sheet 100, provide feedback to the contact drive amplifier "a" 202A, 204a and 206a, so that those amplifiers can detect any decrease in the level of the signal due to contact resistance, and provide the necessary reinforcement to the signal to compensate the losses.

An alternative mechanism to compensate for contact resistance is to determine the current value of the contact resistance and to adjust the absolute values in the signal map based on any change in the value of contact resistance. The modality shown in Figure 6 performs that function. Comparing again the embodiments of Figures 4 and 6, several similarities can be noted, which include sheet 100 with contacts 102, 104 and 106, the stylet 116 and the sheathed cable 118, the signal measurement stage 120, the microprocessor 142, and the associated components, and the signal generator 122. The new component here is the four position switch 301, which provides the capacity to select which signal should be fed to the input terminal of the demodulator 144 of the signal measurement stage 120, under the control of the # microprocessor 142 via line 302. The four potential sources of signal input are stylus 116 and any of contacts 102, 104 and 106 on sheet 100.

For any position in the signal map between two points, any change in the resistance of any contact through which current flows, will modify the value of the signal observed. For example, for a predetermined, or calculated, signal map, such as 114A between contacts 102 and 104 in Figure 4, a change in contact resistance, at contact 102 will change the absolute values on the signal map, but not the distribution or shape of the signal map. If the contact resistance at 104 had to change to a new measured contact resistance, the microprocessor could adjust the predetermined or calculated signal map to compensate for the change in contact resistance. To measure and calculate changes in contact resistance in the three contacts 102, 104 and 106 in Figure 6, three additional measurements are made. These measurements can be added to the sequence of measurements of the SignalCMPLETA SIGNAL / SIGNAL ™ RECTIFY-ABA SIGNALS ™ RECTIFY-AC-For this discussion, the contacts will be given the designation A, B and C for contacts 102, 104 and 106. For the first additional measurement, the microprocessor selects the contact 102 to be connected to the 60 KHz AC signal via the switch 132, and the contact 104 to be connected to the inverted 60 KHz AC signal via the switch 136 The signal measuring device is connected to a fixed location, the contact 106 via the switch 301. The microprocessor then stores the level of the signal of the measurement stage of the signal in RAM as Signal. The second additional measurement is made with the contact 102 connected to the AC signal of 60 KHz and the contact 106 connected to the inverted AC signal of 60 KHz.

The fixed point, contact 104, is connected to the signal measuring device. The microprocessor then stores the level of the signal from the signal measurement stage in the RAM as signal. The third measurement is made with the contact 5 104 connected to the 60 KHz AC signal and the contact 106 connected to the terminal. the 60 KHz inverted AC signal of the amplifier 134. The fixed point, contact 102, is connected to the signal measuring device. The microprocessor then stores the level of the signal in the signal measurement step in RAM as SignA. In this way, the measured signal levels can be defined by equations 5a-5c: Signal = Signal ™ [(X-RAB + RA) / (RA + RAB + RB)] (5a) Signals = Signal ™ [( Y-RAC + RA) / (RA + RAC + RC)] (5b) 15 SignalA = Signal ™ [(Z-RBC + RB) / (RB + RBC + RC)] (5c) where: The Signal ™ is the signal level injected between two contacts; RABA RAC and RBC are the volumetric resistances of the material between contacts A and B, A and C, and B and C, respectively; X, Y and Z define the distribution of the volumetric resistance as observed at the measurement point, between the two actuation or excitation contacts; and RA / - RB and Rc are contact resistances at contacts A, B and C, respectively. The values of Signal ™, X, Y, Z, RAB / RAC and RBC are constant values that can be measured and / or calculated by a particular device and stored in the microprocessor's memory. This gives rise to a series of three simultaneous equations with three variables, that is, RA / RB and Re- The microprocessor can then solve those simultaneous equations for the values of RA, RB and Rc / and then The microprocessor can adjust the value tables of the signals based on new values of RA, RB and Rc. An alternative mechanism to excite or drive a pair of contacts and detect a receiver connected to the stylet, is to use the stylus and one of the contacts as drive mechanism and perform the detection with one of the other contacts. A measurement sequence could be made, where the other contact is selected as the actuation contact and the other contact is selected as the selection contact. 20 An alternative excitation and measurement method is provided by the use of frequency division multiplexing. The methods discussed above include a series of separate measurement steps over time. In a multiplex method of division by frequency, they are excited ' pairs of contact points simultaneously with signals of different frequency. Therefore, the signal received by the stylus is a composite signal of those signals of different frequency and is thus distributed to the independent multiple signal measuring devices (i.e., that they are stored by frequency) each of the which measure the corresponding signal simultaneously. Multiple measurement devices in this mode are designed to measure signals within narrow frequency bands. This measurement method offers the possibility of measuring the position in less time, however, with a more complicated detection, excitation and signal measurement system. Various designs related to the implementation of the present invention can be made to be used in a specific device. To improve the resolution you can use a signal generation and measurement scheme of? M. higher resolution Alternatively, the number of contact points can be increased and a better algorithm using subsets of the contact points can be implemented to resolve the contacts of the stylus on the different areas of the surface. Another alternative could be the selection of a conductive material and a manufacturing method that would provide a more homogeneous surface resistivity. This increases the resolution and allows maps of calculated signals, rather than measurements. If the material used is not homogeneous, another way of raising the resolution can be carried out by measuring a more extensive signal map that is stored in the memory of the microprocessor. The embodiments described in Figures 4, 5, 6, and 7 include a stylet that is captive of the rest of the detection system due to conductor 118. This conductor can be replaced with a communication link that does not require capturing the stylet to the system with a driver. A low-power FR (Radio Frequency) transmitter could be included or connected to the stylus and connected to a compatible FR receiver to the signal measurement means. The FR transmitter and receiver could then implement the communication link provided by the conductor 118. The present invention can be extended to include other di-or three-dimensional shapes, both with a surface shape whose slope changes uniformly (e.g., a sphere or a saddle shape) and shapes with sharp edges (eg, a cube or pyramid) as long as the resistive surface is continuous through those changes of slope and around the edges of the shape. In another embodiment, as shown in Figure 7, the position of stylet 116 on a sphere can be detected. In this embodiment a sphere 400, molded of a conductive material of the same type discussed for each of the other embodiments, has four contacts 401, 402, 403 and 404 connected thereto. To be able to individually distinguish each point on the surface of a closed three-dimensional shape (for example a sphere) the contacts must be placed so that each plane defined by each possible combination of any three of those points, contact does not pass to through the center of the sphere. How close these imaginary planes can be to the center of the sphere (ie, the location of the contacts) is * determined by the resolution of the measuring device signals and the accuracy of the predetermined or calculated equipotential signal map that determines the point at which the stylus is pointing. The calculation of the position is therefore substantially the same as that discussed with respect to a pair of contacts, so that this discussion and the claims also include this variation. # To solve the position of the stylet 116 on the two-dimensional area of the rectangular sheet 100 in the embodiment of Figure 4, three measurements are required, SignalMPLETA / ESSAYS ™ RECTIFY-AB / and ESSALTM ™ RECTIFY-AC / since, as described above with respect to Figure 2, the equipotential lines for each of the AB and AC measurements can be crossed only at one point. For a sphere like in Figure 7, however, four are required measurements to completely resolve the position. For example, if contact 401 is point A, contact 402 is point B, contact 403 is point C and contact 404 is point D, a measurement of the SignalMPET with the four points excited, "simultaneously it is measurement one, and three measurements of the six possible pair combinations of the four contacts must be made, namely three of the possible measurements: RECALIFF-AB / and RECAL-AC / RECAL-AC, RECAL-D / RECTIFY-D ™ RECTIFY-BC / SEND ™ RECTIFY-BD / O Seña ™ RECTIFY-CD- Calculating the three values of the N0RM Signal as in equation (3) above, and plotting those values on the applicable signal maps, all the points on the sphere will be solved in a unique way. When two values of the NORM Signal are plotted, the equipotential lines intersect in two places on the opposite sides of the sphere. The value of the third SignalN0RM is used to determine which of the two points of intersection is to which the stylus is being pointed. Specifically / if the signal measured at the fourth point was used with the signal from one of the other two points that were used to To locate the first two alternative points, that combination could also result in two possible points on the sphere, however, one of those two points could correspond to one of the two points previously determined and is the point that corresponds to the actual point of interest on the sphere.

An alternative to the use of the stylus as a signaling device or indication is the use of a finger as a pointing device or indication. To enable this, a multi-layer material 5 constructed with an inner layer similar to the conductive material discussed in the above embodiments can be used. Such a surface is illustrated in Figure 10 with the conductive layer 100 on the bottom, and a conductive layer 501 on the part # higher (for example, a metal sheet or a thin layer of a conductive polymer), and a non-conductive, compressible layer, 502 (e.g., silicone rubber or plastic foam) between layers 100 and 501. Outer layer 501 may be metal, or some conductive material. In this configuration, the external conductive layer 501 replaces the connected stylet 116 as in Figure 4 with the outer layer 501 connected to the signal measurement device by the conductor 118 (for example, see Figure 4). In this way, when the user touches the outer layer 501, it is compressed and the conductive outer layer 501 is closer of the conductive inner layer 502. In that situation, the level of the signal received by the outer layer 501 of the irradiated signal ls, on the inner layer 100 is increased in the same way as the level of the signal received by the stiletto 116 is increased when the height of stylet 116 decreases in relation to the surface 100 in Figure 4. In the # modality using the multi-layer surface, the position of the user's finger could be calculated in the same way as the location of the stylet with a chosen threshold value for the SignalMPLETA in the determination step of the valid signal 5 corresponding to the fully compressed outer layer. As mentioned briefly above with respect to Figure 4, an application of the present # invention could be an interactive globe of the earth, the moon, one of the planets, one of the stars, or even an artificial body or planet for an interactive game. Two potential implementations of such a balloon are illustrated in Figures 11 and 12. The main differences between the modalities of those figures is that in Figure 11 the The conductive surface is a sphere, and in Figure 12 the conductive surface is implemented with two hemispheres. Figure 11 illustrates the system described above with respect to Figure 7 being modified to be a terrestrial globe. In this way, the devices The electronics in the lower portion of Figure 11 have the same reference numbers as, and operate in the same manner as described, in Figure 7. In Figure 11 there is a conductive sphere 603 with four contact points 604, 605, 606 and 607 on the inner side of the 603 sphere, with each one of the contact points connected, respectively, to one of the four insulated conductors of the cable 608 at one end of those conductors. The cable 608 exits the sphere 603 through a small hole in the bottom of the sphere 603, with the other end of the cable conductors 608 5 interconnecting with the corresponding sections of the switches 422 and 432. To provide the geographical details of the balloon, two coatings were placed on the sphere 603 * 601 and 602 vinyl, shown here representing the northern and southern hemispheres of the earth. In this way when a user uses the stylus 116 to point or point to a location on the globe, the electronic devices determine the coordinates of the selected location as described above in the discussion with respect to Figure 7, since the electronic devices here are as described there. The only location on the surface of the globe is defined in this way by the equipotential coordinates, which can then be traced by the microprocessor 142 (for example, example, by means of a look-up table) within the coordinates of the globe (for example, longitude and latitude) corresponding to the selected position on the globe. A database that contains the features of interest in the world, such as locations and names of countries, capitals and populations can be pre-stored in RAM 144 in relation to any coordinate system desired. Thus, when a user selects a point on the globe with the stylus 116, the microprocessor 142 determines the coordinates of that position and allows the retrieval of the information in relation to that position of the database to be presented to the user via , for example, the audio / video card 150 and the speaker 154. An alternative implementation of the globe * is illustrated in Figure 12, wherein the conductive hemispheres 10, 701 and 702, which are electrically isolated from each other, provide the conductive surfaces for the balloon. Here, the hemispheres 701 and 702 are joined with their edges very close to each other with continuous non-conductive spacers, or several rigid spacers (for example, three) fixed to F, 15 the edges of each of the hemispheres 701 and 702 to maintain fc ß the separation ratio and electrical insulation. Alternatively a non-conductive adhesive may be used between the edges of the hemispheres 701 and 702. Vinyl coatings 601 and 602 are then mounted with the geographic information on the two hemispheres as discussed above with respect to Figure 11. In FIG. this mode each hemisphere has three fixed contact points on each internal edge, with the hemisphere 701 having the contact points 710, 711 and 712, and the 25 hemisphere 702 having the contact points 740, 741 and 742. Here, each hemisphere it is shown with a small hole through the polar cap to allow three insulated conductor wires 730 and 750 to pass through and have one end of each insulated conductor connected to the three points on the inner edge of the corresponding hemisphere. The other end of each of the cables 730 and 750 is, in turn, connected to a separate pair of switches in the signal generator 722. The upper hemisphere 701 has the cable 730 connected to the switches 770 and 771, while the lower hemisphere 702 has cable 750 connected to switches 772 and 773. Comparing Figure 12 with Figure 4, it can be seen that while the embodiment of Figure 4 is for a single surface and Figure 12 is for a pair of surfaces, the only change in the wiring between the signal generator of each mode is the addition of a second pair of switches for the second surface for the mode of Figure 12. The rest "of the signal generator in each case is the same, with the amplifier 134 connected to both pairs of switches 770 and 771, and 772 and 773. This is possible because there is only one stylus 116 and only one point on the globe can be selected at a time (ie, that the pu selected can only be found on a hemisphere at a time).

In this way, each hemisphere is treated as an independent location sensing surface. To make the determination of which of the hemispheres 701 and 702 the user has pointed the stylus 116, the microprocessor 142 is programmed to make a series of measurements. First, as in many of the modalities discussed above, with the stylus 116 pointing to the selected point on one of the hemispheres, the ACCOMPLETE Signal and the SIGNALED Signal are measured for each hemisphere of independently, and the difference between these measured values is determined for each hemisphere (ie, Signal8MPLETA- 701 SignalSlide-7oi / and SignalMPLETA-702 / SignalSlide-702) and is stored in the BRANCH 144. In summary, the Signal8MPLETA measured by applying the 60 KHz AC signal to all points of contact on the surface, and the SignalSAVED will be measured in AND? all the contacts of the corresponding switches in the signal generator 722 for that open surface. Once those values of the difference are determined, each of those values of the difference is compared with a value of pre-selected threshold. The threshold value is determined empirically and typically are the measured values when the tip of the stylus is about 0.254 cm (0.10 inches) from the surface. It is then noticed in which, if any, those values of the difference exceed the threshold and if it is within the greater range of the corresponding hemisphere that is being identified as that to which the stylet 116 is being pointed. Once the hemisphere of interest has been determined, the microprocessor 142 calculates the position 5 selected by the sequence of calculations explained above with respect to Figure 4. In this way, four selections are made, SignalPET / DESTROYED signal / LADIES ™ RECTIFY- AB / y Señáis ™ RECTIFY-AC over the hemisphere and calculate the values of the N0RM-AB and the NoRM-Ac Signals as in equation 4 with those values that define a unique location on that hemisphere. The unique location provided by the NORM-AB and the NORM-Ac / Signal values together with the threshold test results to determine which hemisphere is of If the user is interested, they can then be plotted on a location on the globe by means of a look-up table for the selected hemisphere, if necessary, to obtain the longitude and latitude of the selected point, in a standard spherical coordinate system. Then, As discussed, with respect to Figure 11, the microprocessor 142 can present to the user information related to the memory via the audio / video card 150 and the horn 154, or by any other means desired (e.g. printer, monitor, etc.) or combinations of media.

Additionally, it is well known to those skilled in the art how point-related data could be stored on any surface that could be employed with the present invention, such as look-up tables for converting a coordinate system for one surface to another system. of coordinates. Although the discussion of the different embodiments of the present invention presented above deals with a variety of forms and applications for the present invention, the forms and applications discussed do not, of course, constitute an exhaustive list. It could easily extend such a list to many other forms and applications and the techniques discussed above could easily be extended to each of them. Thus, the present invention is not limited solely to the aspects discussed above, but is limited only by the scope of the claims appended hereto.

Claims

CHAPTER CLAIMEDICATORÍO Having described the invention, it is considered as a novelty and, therefore, the content is claimed in the following: CLAIMS

1. An electrographic detection unit for use in determining the position of a selected point, characterized in that it comprises: a layer of a conductive material having an electrical resistivity and a surface; three separate contact points, electrically interconnected with the layer of conductive material; a processor connected to the three separate contacts and arranged to selectively apply a signal to each of the three contact points; and a probe assembly, including a stylet, coupled to the processor, the stylet is arranged to be placed by a user in the vicinity of a point selected by the user on the surface of the layer and to receive signals from the layer when the contact points have signals applied selectively on them; wherein the position of the stylet in relation to the surface of the layer is determinable by the processor from the signals received from the stylus, each in relation to a similar excitation of two different pairs of three contact points under the control of the processor .

2. The electrographic detection unit according to claim 1, characterized in that it also includes an insulating layer placed on an exposed surface of the layer of conductive material.

3. The electrographic detection unit according to claim 1, characterized in that the layer of conductive material is a carbon-polymer composite material.

4. The electrographic detection unit according to claim 3, characterized in that the layer is in the form of a bi-or three-dimensional shape.

5. The electrographic detection unit according to claim 1, characterized in that the layer of conductive material has a defined edge and is formed in a bi-or three-dimensional manner.

6. The electrographic detection unit according to claim 5, characterized in that the three separate contact points are placed on the layer of conductive material, so that all the points of interest to a user that can be designated * indicating them with the stylet, so that each point of interest is in the visual field of two different pairs of the three points of contact.

7. The electrographic detection unit according to claim 6, characterized in that the angle included in each contact point of each pair ¡* of contact points is less than 90 °, with the included angle f being that defined angle. by the vectors between the pair of ^ points of contact, and the point of contact corresponding to 10 angle included and the point of interest towards which the stylus is being pointed by the user.

8. The electrographic detection unit according to claim 7, characterized in that it also includes an insulating layer placed on a 15 exposed surface of the conductive material layer. rjtfft

9. The electrographic detection unit according to claim 7, characterized in that the layer of conductive material is a carbon-polymer composite material that was formed in a bi-directional form. 20 three-dimensional. 10. The electrographic detection unit according to claim 7, characterized in that: each of the three contact points includes a pair of contacts in cascade with a first pair of contacts in 25 cascade connected to the processor to receive the signals to be applied to the layer and a second pair of cascade contacts connected to the processor from which the measurements of the signals will be made; and the processor includes three amplifiers, each 5 associated with a different one of the three contact points and each having an output terminal and two input terminals, the output terminal is coupled to the first of fJL the pairs of contacts in cascade of one of the associated contact points, one of the input terminals is

10 connected to the second of the cascaded contact pairs of one of the associated contact points, and the second input terminal is connected to receive the signals that are selectively applied by the processor to one of the three corresponding contact points . 15

11. The electrographic detection unit of ? According to claim 7, characterized in that: the processor includes a four-position switch connected to receive the signals that must be measured by the processor individually from the 20 probe and each of the three contact points, the signal measures the signals from each of the three contact points when the other two contact points are fed by the processor to allow the processor to determine the contact resistance, and changes in resistance to 25 contact, from each of the contact points; and «• 64 the processor calculates the contact resistance of each of the contact points by first injecting a known signal between each pair of the three contact points and measuring a resulting signal at the third contact point and then solving the following simultaneous equations for the contacts. resistance values of the contact point, Signal = Signal ™ [(X-RAB + RB) / (RAB + RB + RA)]; SignalB = Signal ™ [(Y-RAC + Rc) / (RAC + Rc + RA)]; and 10 Signal = Signal ™ [(Z-RBC + Rc) / (RBC + c + RB)]; where: the three points of contact were identified in those equations as A, B, and C; the Signal ™ is the signal injected by the processor 15 between each pair of contact points; RAB / RAC and RBC are the values of the volumetric resistance of the conductive material layer between the corresponding contact points of the resistors; X, Y and Z are the fractions of the values of the volumetric resistance between the respective contact points given the point selected by the user between each pair of contact points AB, AC and BC; and RA / RB and Re are the contact resistance values at those respective contact points.

12. The electrographic detection unit according to claim 7, characterized in that the position of the stylet is determined by the processor by having selected signals applied to various combinations of the contact points, and a measured signal received by the stylus in response to each Application of signals that are used by the processor to calculate the position towards which the stylus is being pointed by the user, a first measurement is made by putting each of the contact points in open circuit and measuring a deviation signal, DSD signal? ADA / with the stylet; a second measurement is made by applying the same signal at each of the contact points and measuring a complete signal, SignalMPLETA / with the stylet; a third measurement is made by applying a signal between the first two of the three contact points with the other contact point without connecting, the value of the signal applied between the first two contact points has a fixed relation with the value of the signal used to make the second measurement, and measuring an uncorrected signal between the first two points of contact, signal SIN-RECTIFY-FIRST-DOS / with the stylus; a fourth measurement is made by applying a signal between the second two points of the three points of contact with the other point of contact without connecting, the value of the signal applied between the second two contact points has a fixed relation with the value of the signal used to make the second measurement, and measuring an uncorrected signal between the second two contact points, Señais ™ RECTIFY-SECONDS-DOS / with the stylus; calculate the relative position towards which the stylus is being pointed by the user in relation to the first two points of contact and the second two points of contact using the following equations, the values of those equations are the coordinates on an equipotential map of the point selected by the user towards whom the user is pointing the stylus with the axes of those coordinates, with imaginary lines between each of the first two contact points and the second two contact points: PPRIMEROS-DOS - (RECAL) -FRIENDS-TWO ~ IAD Signals?) / (SeñalcoMP ETA - ES ESVIVI) / and PSEGUNDOS-DOS = (S? ÑalsiN RECTIFY-SECONDS-TWO - SIGNAL-SENT) / (SeñalcoMP ETA - EnsaloEsviADA) / a predetermined signal map of the conductive material layer is pre-stored in the processor; and the calculated values of PPRIMEROS-DOS and PSEGUNDOS-DOS are used by the processor in conjunction with the signal map to translate the calculated values into a physical position on the surface to which the user is pointing with the stylus.

13. The electrographic detection unit according to claim 7, characterized in that: the layer of conductive material is formed in a closed three-dimensional form; the electrographic detector further includes a fourth contact point separated from the three contact points, and electrically interconnected with the layer of conductive material; the position of the stylus is determined by the processor by having selected signals applied to various combinations of contact points and a measured signal received by the stylus in response to each application of signals that are used by the processor to calculate the position to which the stylus is being pointed by the user, a first measurement is made by placing an open circuit of each one of the contact points and measuring a deviated signal, FLOSS signal / with the stylet; a second measurement is made by applying the same signal at each of the contact points and measuring the complete signal, SignalMPLETA / with the stylus; a third measurement is made by applying a signal between the first two of four contact points with the other two contact points without connecting, the value of the signal applied between the first two contact points has a fixed relation with the value of the signal used to make the second measurement, and measuring an uncorrected signal between the first two points of contact, Señals ™ RECTIFY-FIRST-DOS / with the stylus; a fourth measurement is made by applying a signal between the second two points of the four contact points with the other two contact points without connecting, the value of the signal applied between the second two contact points has a fixed relationship with the value of the signal used to make the second measurement, and measuring an uncorrected signal between the second two contact points, RECAL-SECONDS-TWO / with the stylus; a fifth measurement is made by applying a signal between the third two points of the four contact points with the other two points of contact without connecting, the value of the signal applied between the third two contact points has a fixed relation with the value of the signal used to make the second measurement, and measuring a signal without rectifying between those third parties two points of contact, Señals ™ RECTIFYING-THIRD-TWO / with the stylus; and calculate the relative position towards which the stylus is being pointed by the user in relation to the first two points of contact, the second two points of contact and the third two points of contact using the following equations, the values of those equations are the coordinates on an equipotential map of the point selected by the user towards which the user is pointing the stylus with the axes of those coordinates, being imaginary lines between each of the first two points of contact, the second two points of contact and the third two points of contact: PpRIMEROS-DOS = (SßnalsiN RECTIFY-FIRST-TWO - SIGNED) / (SeñalcoMP ETA - SeñalpEsviADA); TWO-GETTINGS = (SßñalsiN RECTIFYING-SECONDS-TWO ~ SÍÑALÍESVIADA) / (SeñalcoMP ETA - Señaldesvi DA); and PTERCEROS-DOS = (Dice ™ RECTI FICAR-THIRD-TWO ~ ESTIMATED SIGN) / (SeñalcoMPLETA - SeñaLesviADA); a predetermined signal map of the conductive material is pre-stored in the processor; and the calculated values of PPRIMEROS-DOS / FSEGUNDOS-DOS / and PTERCEROS-DOS are used by the processor in conjunction with the signal map to translate the calculated values into a physical position on the surface to which the 'user is pointing with the stylus.

14. The electrographic detection unit according to claim 7, characterized in that the processor includes: a microprocessor having a collective data conductor associated therewith; a memory system interconnected with the collective data conductor; a signal generating stage coupled to the microprocessor for generating (and applying several signals to several of them, and various combinations, of the contact points under microprocessor control, and a signal measurement stage coupled to the microprocessor and the probe assembly for capturing and conditioning the signals received from the probe system under the control of the microprocessor

15. The electrographic detection unit according to claim 14, characterized in that the signal generating stage includes: a signal generator, and a switching system. coupled between the signal generator and the contact points on the layer to selectively apply a signal from the signal generator to the selected contact points under the direction of the microprocessor.

16. The electrographic detection unit according to claim 15, characterized in that: the memory includes pre-stored information related to the different coordinates on the layer; and the processor further includes: an electronic delivery system for providing information of the memory to the user in relation to the points selected with the stylus.

17. The electrographic detection unit according to claim 1, characterized in that the three contact points are not collinear.

18. The electrographic detection unit according to claim 1, characterized in that: the stylet includes an electrically conductive portion; and the probe assembly further includes: an electrically conductive cable connected between the electrically conductive portion of the processor.

19. The electrographic detection unit according to claim 18, characterized in that: the processor selectively applies AC signals to the selected ones of three contact points; and the electrically conductive portion of the stylet detects the signals radiated from the conductive layer as an antenna without making physical contact with the layer.

* 20. The electrographic detection unit according to claim 18, characterized in that: the processor selectively applies CD signals to those selected from three contact points; and the electrically conductive portion of the stylet detects the signals from the conductive material layer by making physical contact with the layer. 21. The electrographic detection unit of # according to claim 1, characterized in that: the stylet includes an electrically conductive portion; and the probe assembly further includes: a transmitter mounted on the stylet connected to the electrically conductive portion for 15 transmit an encoded signal with the information

, ^ Hf proportional to a value of a signal detected by the electrically conductive portion when it is brought to the vicinity of the conductive layer; and a receiver coupled to the processor for receiving signals from the transmitter and for displaying the encoded information in the signal transmitted by the transmitter in a signal compatible with the processor.

22. The electrographic detection unit according to claim 21, characterized in that: "the processor selectively applies AC signals to select one of the three contact points; and the electrically conductive portion of the stylet detects signals radiated from the layer of conductive materials such as an antenna without making physical contact with the layer.

23. The electrographic detection unit according to claim 21, characterized in that: the processor selectively applies DC signals to the selected ones of the three contact points; and the electrically conductive portion of the stylet detects the signals from the layer of the conductive material by making physical contact with the layer.

24. The electrographic detection unit according to claim 1, characterized in that: each of the three contact points includes a pair of contacts in cascade with a first pair of contacts in 1 cascade connected! to the processor to receive the signals that must be applied to the layer in a second of the pairs of 20 contacts in cascade connected to the processor from which the measurements of the signals will be made; and the processor includes three! amplifiers, each one associated with a different one of the three points of contact and each one has an output terminal and two terminals In the case of an input terminal, the output terminal is coupled to the first pair of contacts in cascade of one of the pairs of associated contacts, one of the input terminals is connected to the second pair of contacts in cascade of one of the associated contact points, and the second input terminal is connected to receive the signals that are selectively applied by the processor to the corresponding one of the three contact points.

25. The electrographic detection unit according to claim 1, characterized in that the processor includes a four-position switch connected to receive the signals to be measured by the processor, individually from the probe assembly and each of the three points. of contact, measuring the signals of each of the three points of L 15 contact, when the other two contact points are energized by the processor allows the processor to determine the contact resistance, and changes in contact resistance, of each of the contact points.

26. The electrographic detection unit according to claim 25, characterized in that the processor calculates the contact resistance of each of the contact points by first injecting a known signal between each pair of the three contact points and measuring the resulting signal at the third point of contact and * continuation solving. the following simultaneous equations for the resistance values of the contact point, Signal = Signal ™ [(X-RAB + RB) / (RAB + RB + RA)]; i SignalB = Signal ™ [(Y-RAC + RC) / (RAC + R + RA) 1; Y SignalA = Signal ™ [(Z-RBC + RC) / (RBC + RC + RB)]; where: the three points of contact are identified in those equations as A, B and C; 10 Signal ™ is the signal injected by the processor between each pair of contact points; RAB / RAC and BC are the values of the volumetric resistance of the layer of conductive material between the points 'of contact corresponding to such resistances; X, Y and Z are the fractions of the values of the m volumetric resistance between the respective contact points given the point selected by the user between each pair of contact points AB, AC and BC; and RA / RB and Rc are the contact resistance values at those respective contact points.

27. The electrographic detection unit according to claim 1, characterized in that the position of the stylus is determined by the processor causing selected signals to be applied to several. 25 combinations of contact points, and a measured signal received by the stylus in response to each application of signals that are used by the processor to calculate the position toward which the stylus is being pointed by the user, 5 is made a first measurement placing each of the contact points in open circuit and measuring a deflection signal, DEFLECTED / with the stylus; a second measurement is made applying the same # signal at each of the contact points and measuring one 10 complete signal, SignalMPLEA / with the stylus; a third measurement is made by applying a signal between the first two of the three points of contact with the other contact point without connecting, the value of the signal applied between the first two points of contact has a 15 fixed relation to the value of the signal used to make the second measurement, and measuring an uncorrected signal between the first two points of contact, Señáis ™ RECTIFY- FIRST-TWO / with the stylus; a fourth measurement is made by applying a signal 20 between the second two points of the three contact points with the other contact point, the value of the signal applied between the second two contact points has a fixed relationship with the value of the signal used to make the second measurement, and measuring an uncorrected signal between the second two contact points, RECAL-SECONDS-TWO / with the stylus; and calculate the relative position towards which the stylus is being pointed by the user in relation to the first two points of contact and the second two points of contact using the following equations, the values of those equations are the coordinates on an equipotential map of the point selected by the user to which the user is pointing the stylus with the axes of those coordinates, being imaginary lines between each of the first two points of contact and the second two points of contact: PpRIMEROS-DOS = (SßñalsiN RECTIFY- FIRST-TWO - SßnalüESVIADA.) / (SeñalcoMPLETA - SeñalDEsviADA); and TWO-SPREADS = (S? ñalsiN RECTIF CAR-SECONDS-TWO - SIGNPOSTED) / (SeñalcoMPLETA - ESIGNED ESTE) •

28. The electrographic detection unit, according to claim 27, characterized in that: a predetermined signal map of the conductive material layer is pre-stored in the processor; and the calculated values of PPRIMEROS-DOS and PSEGUNDOS-DOS are used by the processor in conjunction with the signal map to translate the calculated values to a physical position * on the surface to which the user is pointing with the stylus.

29. The electrographic detection unit according to claim 1, characterized in that: the layer of conductive material is formed in a closed three-dimensional shape; and the electrographic detector further includes a fourth contact point separated from the three contact points, and * Electrically interconnected with the layer of conductive material.

30. The electrographic detection unit, according to claim 29, characterized in that each plane defined by each combination of three of the four contact points does not pass through the central point. 15 of the closed three-dimensional shape.

31. The electrographic detection unit according to claim 29, characterized in that the position of the stylus is determined by the processor causing selected signals to be applied to several. 20 combinations of the contact points, and a measured signal received by the stylus in response to each application of signals that are used by the processor to calculate the position toward which the stylus is being pointed by the user, becomes a first measuring by placing each of the contact points in open circuit and measuring a deviated signal, DSS signal? ADA / with the stylus; a second measurement is made by applying the same signal at each of the contact points and measuring the complete signal, SignalMPLETA / with the stylus; a third measurement is made by applying a signal between the first two of four contact points with the other two contact points without connecting, the value of the signal applied between the first two contact points has a fixed relation with the value of the signal used to make the second measurement, and measuring an uncorrected signal between the first two contact points, RECTI FI CAR- PRIMEROS-DOS / COU? L is useful; a fourth measurement is made by applying a signal between the second two points of the four contact points with the other two contact points without connecting, the value of the signal applied between the second two contact points has a fixed relationship with the value of the signal used to make the second measurement, and measuring an uncorrected signal between the second two contact points, RECALIFY-SECONDS-TWO Signal / with the stylus; a fifth measurement is made by applying a signal between the third two points of the four contact points with the other two points of contact without connecting, the value of the signal applied between the third two contact points has a fixed relation with the value of the signal used to make the second measurement, and measuring a signal without rectifying between those third parties two points of contact, Señals ™ RECTIFYING-THIRD-TWO / with the stylus; and calculate the relative position towards which the stylus is being pointed by the user in relation to the first two points of contact, the second two points of contact and the third two points of contact using the following equations, the values of those equations are the coordinates on an equipotential map of the point selected by the user towards which the user is pointing the stylus with the axes of those coordinates, being imaginary lines between each of the first two points of contact, the second two points of contact and the third two points of contact: PpRIMEROS-DOS = (Sßñals ™ RECTIFY-FIRST-TWO ~ "SIGNAL FORWARDED) / (Signal P ETA ~ SignalSSEAD) PAGE-TWO - (Checks ™ RECTI FICAR-SECONDS-TWO ~ Sign them OUT) / (Signpost - SignalSAVED) / And PTERCEROS-DOS = (SenalsiN RECTIFYING-THIRD-TWO ~ SßnaloESVIADA) / (ESTERFULNESS ~ ESTIMATED SIGNAL) •

32. The electrographic detection unit, according to claim 31, characterized in that: a predetermined signal map of the conductor material layer is pre-stored in the processor; and the calculated values of PPRIMEROS-DOS and PSEGUNDOS-DOS and PTERCEROS-DOS are used by the processor in conjunction with the signal map to translate the calculated values to, • a physical position on the surface to which the user is pointing with the stylus.

33. The electrographic detection unit according to claim 1, characterized in that the processor includes: a microprocessor having a collective data conductor associated therewith; a memory system interconnected with the collective data conductor; a signal generating stage coupled to the microprocessor to generate and apply several signals to several of them, and various combinations, of the contact points under the control of the microprocessor; and a signal measurement stage coupled to the microprocessor and probe assembly for capturing and conditioning the signals received from the probe system under the control of the microprocessor.

34. The electrographic detection unit according to claim 33, characterized in that the signal generating stage includes: a signal generator; and a switching system coupled between the signal generator and the contact points on the layer to selectively apply a signal from the generator of 5 signals for the selected contact points under the direction of the microprocessor.

35. The electrographic detection unit of J according to claim 34, characterized in that: the memory includes pre-stored information related to the different coordinates on the layer; and the processor further includes: an electronic delivery system for providing information of the memory to the user in relation to the points selected with the stylus.

36. An electrographic detection unit for use in determining the position of a point selected by a user on the surface of the same, characterized in that it comprises: an indicator board having: a lower layer of a conductive material with an electrical resistivity; an upper layer of a flexible conductive material; and "" "" 'an inner layer between the upper and lower layers, wherein the inner layer is a non-conductive, compressible material; three separate contact points, electrically interconnected with the conductive material of the lower layer; a processor connected to the three separate contacts c and arranged to selectively apply a signal to each of the three contact points; and an electrical conductor coupled between the processor and the upper layer of the indicator board for transmitting the signals received by the upper layer of the lower layer when the user presses a point on the upper layer towards the lower layer in the vicinity of a point. 15 selected by a user on the upper layer; jfW wherein the position of the user's finger in relation to the lower layer is determinable from two signals received from the upper layer by the processor, each in relation to a similar excitation of two pairs 20 different from the three points of contact interconnected with the lower layer.

37. The electrographic detection unit according to claim 36, characterized in that: the layer of conductive material has a defined edge 25 and is formed in a bi-or three-dimensional form; and the three separate points of contact are placed on the layer of conductive material, so that all points of interest to the user can be "designated by placing a finger on them., so that each point of interest is in the field of view of two different pairs of the three points of contact with the included angle at each contact point of each pair of contact points being less than 90 °, with the included angle being the angle defined by the vectors between the pair of contact points, and the point of contact corresponding to the included angle and the point of interest to which the user is pointing.

38. The electrographic detection unit according to claim 36, characterized in that: each of the three contact points includes a pair of contacts in cascade with a first of the pairs of contacts in cascade connected to the processor to receive the signals that they must be applied to the layer and a second of the contact pairs in cascade connected to the processor from which the measurements of the signals are going to be made; and the processor includes: three feedback compensation circuits, each associated with a different one of the three contact points and each having an input terminal and an output terminal, the input terminal is coupled to the second of the contact pairs in cascade of one of the associated contact points; and three amplifiers, each associated with a different one of the three contact points and each having an output terminal and two input terminals, the output terminal is coupled to the first of the contact pairs in cascade of one of the points associated contact, one of the input terminals is connected to the output terminal of the feedback compensation circuit associated with it of the contact points, and the second input terminal is connected to receive the signals that are selectively applied by the processor to one of the three corresponding contact points.

39. The electrographic detection unit according to claim 36, characterized in that the position of the user's finger is determined by the processor causing selected signals to be applied to various combinations of contact points and a measured signal received by the upper layer in response to each application of signals that are used by the processor to calculate the position to which the user is pointing, a first measurement is made by open circuit each contact point and measuring a deviation signal, DEFENDED / with the upper layer; a second measurement is made by applying the same signal to each of the contact points and measuring a complete signal, SignalMPLETA / with the upper layer; a third measurement is made by applying a signal 5 between the first two of three contact points with the other contact point without connecting, the value of the signal applied between the first two contact points has a fixed relationship with the value of the signal used to make the second measurement, and measuring an uncorrected signal between the 10 first two contact points, Señals ™ RECTIFY-FIRST TWO / with the top layer; a fourth measurement is made by applying a signal between the two seconds of the three points of contact with the other point of contact without connecting, the value of the signal 15 applied between the second two contact points has a m t fixed relation to the value 'of the signal used to make the second measurement, and measuring a signal without rectifying between the second two points of contact, SEND ™ RECTIFY-SECONDS TWO / with the top layer; and calculating the relative position to which the user's finger is pointing in relation to the first two points of contact and the second two points of contact using the following equations, the values of those equations are coordinates on an equipotential map of the point 25 selected by the user to which the user is pointing with the axes of those coordinates being imaginary lines between each of the two contact points of the second two points of contact: PPRIMEROS DOS = (S? ÑalsiN RECTI ICAR- PRIMEROS DOS - SIGNAL DEVIATED) / (SIGNALFULNAME ~ SIGNALED SIGNAL) TWO = (S? ÑalsiN RECTIFYING-SECONDS TWO ~ SIGNAL DEVIATED) / (SIGNALFUL _ SIGNAL) / a predetermined signal map of the conductive material layer is pre-stored in the processor; and the calculated values of PPRIMEROS DOS and PSEGUNDOS DOS are used by the processor in conjunction with the signal map to translate the calculated values, 'a't a physical position on the surface to which the user is pointing.

40. The electrographic detection unit according to claim 36, characterized in that the processor includes: a microprocessor having a collective data conductor associated therewith; a memory system interconnected with the collective data conductor; a signal generating stage coupled to the microprocessor to generate and apply several signals to several of the contact points, and various combinations of these, under the control of the microprocessor; and a signal measurement stage coupled to the microprocessor and the electrical conductor to capture and condition the signals received from the upper layer under the control of the microprocessor.

41. The electrographic detection unit according to claim 40, characterized in that the signal generating stage includes: a signal generator; and a switching system coupled between the 10 signal generator and contact points on the lower layer to selectively apply a signal from the signal generator to the selected contact points under the direction of the microprocessor.

42. The electrographic detection unit according to claim 41, characterized in that: the memory includes pre-stored information * related to the various coordinates on the lower layer; and the processor further includes: an electronic delivery system for providing information of the memory to the user in relation to the position of the user's finger.

43. An electrographic detection unit in the form of a balloon for use in determining the position of a point selected by a user on the surface of the same, characterized in that it comprises: a sphere formed of a layer of a conductive material having a substantially uniform electrical resistivity and an external surface; a set of four separate contact points, electrically connected to the layer of the conductive material of the sphere; a processor connected to the set of four separate contacts and arranged to selectively apply a signal to each of the four contact points; and a probe assembly, including a stylet, coupled to the processor, the stylet is arranged to be placed by a user in the vicinity of a point selected by a user on the surface of the sphere and to receive signals from the layer when the contact points have signals selectively applied to them by the processor; wherein the position of the stylus in relation to the surface of the sphere is determinable from three signals received from the stylus and by the processor, each in relation to a similar excitation of three different pairs of four contacts on the sphere by the processor.

# 44. The electrographic detection unit according to claim 43, characterized in that it further includes: a non-conductive coating placed on the 5 sphere with the coating presenting on it, the geographical characteristics of a star, planet or other celestial body, 'selected. 45. The electrographic detection unit of * according to claim 44, characterized in that the

The processor determines the coordinates of the position of the stylus selected by the user in terms of the standard coordinates of the geographical features displayed on the coating.

46. The electrographic detection unit according to claim 45, characterized in that the processor includes: a memory in which information relating to the geographical characteristics for several coordinates on the coating was pre-stored; and an electronic delivery system for providing information of the memory to the user in relation to the position of the stylus selected by the user.

47. The electrographic detection unit according to claim 43, characterized in that: the four separate contact points are placed on the layer of conductive material, so that all the points of interest for a user that can be designated by pointing the stylus over them, so that each point of interest in the visual field of two different pairs of the three contact points with the included angle at each contact point of each pair of contact points is less than 90 °, with the included angle the angle defined by the vectors being between the pair of contact points, and the point of contact that corresponds to the included angle and the point of interest to which the stylus is being pointed by the user; the position of the stylus is determined by the processor by having selected signals applied to various combinations of the contact points, and a measured signal received by the stylus in response to each application of signals that are used by the processor, to calculate the position towards which the "stiletto" is being pointed out by the user, a first measurement is made by placing each of the contact points in an open circuit and measuring a deviated signal, "FLASH" / with the stylus, a second measurement is made applying the same signal at each of the contact points and measuring the complete signal, cuecoMPLETA with the stylus; * a third measurement is made by applying a signal between the first two of four contact points with the other two contact points without connecting, the value of the signal applied between the first two contact points 5 has a fixed relationship with the value of the signal used to make the second measurement, and measuring an uncorrected signal between the first two contact points, Señáis ™ RECTI FICAR-FIRST-TWO / COn? L ßStiletß; a fourth measurement is made by applying a signal 10 between the second two points of the four points of contact with the other two contact points without connecting, the value of the signal applied between the second two points of contact has a fixed relationship with the value of the signal used to make the second measurement, and measuring an uncorrected signal between the second two contact points, RECALD-SECONDS-TWO / with the stylus; a fifth measurement is made by applying a signal between the third two points of the four contact points, with the other two points of contact not connected, 20 the value of the signal applied between the third two contact points has a fixed relationship with the value of the signal used to make the second measurement, and measuring a signal without rectifying between those third parties two contact points, Sigals ™ RECTI ICAR-THIRD-TWO / with the stylus; and calculate the relative position towards which the stylus is being pointed by the user in relation to the first two points of contact, the second two points of contact and the third two points of contact using the following equations, the values of those equations are the coordinates on an equipotential map of the point selected by the user towards which the user is pointing the stylus with the axes of These coordinates, being imaginary lines between each of the first two points of contact, the second two points of contact and the third two points of contact: PPRIMEROS-DOS = (SßñalsiN RECTIFY-FIRST-TWO - SIGNALDEV) / (SeñalcoMP ETA - SeñalüEsviADA); TWO-GETTINGS = (SßñalsiN RECTIF CAR-SECONDS-TWO ~ GIVEN-SIGNED) / (Signal-Signal ~ Signals IADA) and PTERCEROS-DOS = (Drawers ™ RECTI FICAR-THIRD-TWO - LADIES IADA) / (SignalMPLETA - SignalSafe) • a predetermined signal map of the conductive material layer is pre-stored in the processor; and the calculated values of PPRIMEROS-DOS / PSEGUNDOS-DOS and PTERCEROS-DOS are used by the processor in conjunction with the signal map to translate the calculated values into a physical position on the surface to which the user is pointing with the stylus.

48. The electrographic detection unit according to claim 43, characterized in that the processor includes: a microprocessor having a collective data bus 5 associated therewith; a memory system interconnected with the collective data conductor; a signal generating stage coupled to the * microprocessor to generate and apply several signals to 10 various contact points, and various combinations of these, under the control of the microprocessor; and a signal measurement stage coupled to the microprocessor and the electrical conductor to capture and condition the signals received from the upper layer under the control of the microprocessor.

49. The electrographic detection unit according to claim 48, characterized in that the signal generating stage includes: a signal generator; and a switching system coupled between the signal generator and the contact points on the layer to selectively apply a signal from the signal generator to the selected contact points under the direction of the microprocessor.

* 50. The electrographic detection unit according to claim 34, characterized in that: the memory includes pre-stored information 5 related to the different coordinates on the layer; and the processor further includes: an electronic delivery system for providing information of the memory to the user in relation to the points selected with the stylus. 51. An electrographic detection unit for use in determining the position of a selected point, characterized in that it comprises: a first layer of a conductive material having an electrical resistivity and a first surface; 15 a first set of three contact points

[W separated, electrically interconnected with the first layer of conductive material; a second layer of a conductive material having an electrical resistivity and a second surface; 20 a second set of three separate contact points, electrically interconnected with the second layer of conductive material; a processor connected to each of the first and second sets of three separate contacts and arranged 25 to selectively apply a signal to each of the three contact points in each of the first and second sets thereof; and a probe assembly, including a stylet, coupled to the microprocessor, the stylet is arranged to be placed by a user in the vicinity of a point selected by the user on the first and second surface of the first and second layers, and to receive the signals of the layer associated with the point selected by the user when the corresponding set of points of

The contact has signals selectively applied to it; wherein the identification of which of the first and second surfaces of the stylet is adjacent is effected by the processor by independently measuring two signals from each of the first and second layers received by the 15 stylet, combining the signals of the same independent layer of the signals received from the other layer to form a first and second comparative values, with each of the comparative values associated with a different one of the first and second layers, independently comparing each 20 one of the first and second comparative values with a preselected threshold value with the layer associated with one of the first and second comparison values, which is larger and greater than the threshold, with the stylet layer being closest to, and therefore, an identifiable layer of the 25 first and second layers; and - ** - * - * 97 wherein the position of the stylus in relation to one of the first and second layers identified is determinable by the processor from the signals received from each of the stylets in relation to a similar excitation of all three contact points on a of the first and second layers identified, and two different pairs of the three points of contact on one of the first and second layers identified under the control of the processor. 52. The electrographic detection unit according to claim 51, characterized in that: the first and second layers are in the form of a first and a second hemisphere; and the electrographic detection unit further includes an electrically insulating separator between the first and second hemispheres to hold them in the form of a sphere while not making electrical contact with each other.

53. The electrographic detection unit according to claim 52, characterized in that it also includes: a non-conductive coating placed on the first and second hemispheres with the coating presented on it, the geographical characteristics of a star, planet or other celestial body selected.

54. The electrographic detection unit according to claim 53, characterized in that the 98 * processor determines the position coordinate selected by the stylus user, in terms of the standard coordinates of the geographical features presented on the coating.

55. The electrographic detection unit according to claim 54, characterized in that the processor includes: a memory in which pre-stored information related to the geographical characteristics is stored. 10 for the different coordinates on the coating; and an electronic delivery system for providing information of the memory to the user in relation to the position selected by the user of the "stylet."

56. The electrographic detection unit of 15 according to claim 51, characterized in that: the three separate contact points are placed on the layer of conductive material, so that all the points of interest for a user that can be designated by pointing the stylus on them, so that 20 each point of interest in the visual field (from two different pairs of the three points of contact with the angle included in each contact point of each pair of contact points is less than 90 °, with the included angle being the defined angle by the vectors between the pair of points of 25 contact, and the point of contact that corresponds to the included angle and the point of interest to which the stylus is being pointed by the user; the position of the stylet is determined by the processor by having selected signals applied to different combinations of contact points, and a measured signal received by the stylus in response to each application of signals that are used by the processor to calculate the position towards which is a stylus is being pointed by the user, 10 a first measurement is made by placing each of the contact points in an open circuit and measuring a deviated signal, DSS signal? ADA / with the stylus; a second measurement is made by applying the same signal at each of the contact points and measuring the entire signal, SeñalcoMPETA / with the stylet; a third measurement is made by applying a signal '• # between the first two of the three points of contact with the other point of contact without connecting, the value of the signal applied between the first two contact points has a fixed relation to the value of the signal used to make the second measurement, and measuring an uncorrected signal between the first two points of contact, Señals ™ RECTIFY- FIRST-TWO / with the stylus; • a fourth measurement is made by applying a signal 25 between the second two points of the three points of contact with the other point of contact without connecting, the value of the signal applied between the second two contact points has a fixed relation with the value of the signal used to make the second measurement, and measuring a signal without rectifying between the second two points of contact, signal SIN-RECTIFY-SECONDS-TWO / with the stylus; and calculate the relative position towards which the stylus is being pointed by the user in relation to the first two contact points and the second two contact points, using the following equations, the values of those equations are the coordinates of a map equipotential of the point selected by the user to which the user is pointing the stylus, with the axes of those coordinates, being imaginary lines between each of the first two points of contact and the second two points of contact: PPRIMEROS-DOS = ( SßñalsiN RECTI FICAR-FIRST-TWO - SßñalüESVIADA) / (SeñalcoMPLETA - SeñalDEsviADA); AND TWO-SPECKS = (SenalsiN RECTIFYING-SECONDS-TWO - IATA LADIES) / (SignalMPLETA - SignalSide) / a predetermined signal map of the conductive material layer is pre-stored in the processor; and the calculated values of PPRIMEROS-DOS and PSEGUNDOS-DOS are used by the processor in conjunction with the map of ~~ 101 signals to translate the calculated values into a physical position on the surface to which the user is pointing with the stylus.

57. The electrographic detection unit according to claim 51, characterized in that the processor includes: a microprocessor having a collective data conductor ^^ associated with it; a memory system interconnected with the collective data bus; a signal generating stage coupled to the microprocessor to generate and apply several signals to various contact points and various combinations thereof, under the control of the microprocessor; and 15 a signal measurement stage coupled to? microprocessor, and probe assembly to capture and condition signals received from probe system under the control of the microprocessor.

58. The electrographic detection unit according to claim 57, characterized in that the signal generating stage includes: a signal generator; and a switching system coupled between the signal generator and the contact points on the layer, to selectively apply a signal from the generator of and signals to the selected contact points under the direction of the microprocessor.

59. The electrographic detection unit according to claim 58, characterized in that: 5 the memory includes pre-stored information related to several coordinates on the layer; and the processor further includes: an electronic delivery system for providing memory information to the user in relation to the selected position of the stylus.

60. A method for locating a position selected by a user on an electrographic detection unit having a layer of a conductive material having an electrical resistivity with K separated contact points 5, electrically interconnected with the layer of conductive material, where N of the K contact points are used to locate the position selected by the user, and where N has an integer value of three to K, a processor arranged to selectively apply a signal to 0 each of the N points of contact and to determine the position coordinates of the position selected by the user, and means for detecting and releasing a signal from the position selected by the user of the electrographic detection unit to the processor, the method is characterized in that it includes the steps of: to. apply a first selected signal to all K contact points; b. measure a first signal measured at the position selected by the user with the first measurement corresponding to the application of the signal from step a .; c. sequentially applying a second signal selected from J different pairs of contact points with the second signal having a selected relation with the first signal, where J is an integer value between 2 and (N-1); d. sequentially measuring J second signals measured at the position selected by the user with each of those signal measurements corresponding to a different J of the second signal applications of step c.; and e. calculate a value proportional to a position coordinate between each pair of the J pairs of contact points in step c. which is proportional to a ratio of each of the second measured signals of step d. and the first measured signal from step b. to define the position selected by the user with J coordinates in relation to the contact points used in the second signal measurements.

61. The method for locating a position selected by a user on an electrographic detection unit according to claim 60, characterized in that: the method further includes the steps of: f. measure a third signal measured at the position selected by the user with all N contact points in open circuit before step e .; and »step e., also includes the steps of: 10 g. subtracting the third signal measured individually from each of the other measured signals to form J values of the difference; and h. calculate a value proportional to a position coordinate between each pair of the J pairs of 15 contact points of step c, which is proportional to a ratio of each of the J values of the difference in step g., and the first signal measured from step h., to define the position selected by the user with J coordinates related to the contact points used in the second 20 signal measurements.

62. The method for locating a position selected by a user on an electrographic detection unit according to claim 61, characterized in that: a predetermined signal map of the layer of conductive material is pre-stored in the processor; and the method also includes the step of: i. translate the J proportional values to a coordinate system of position of step h. using the pre-stored signal map in the physical position of the layer that the user has selected.

63. The method for locating a position selected by a user on an electrographic detection unit according to claim 62, characterized in that: the electrographic detection unit further includes a non-conductive coating placed on the layer with the coating presenting on he graphic characteristics; and the method also includes the steps of: j. translate the physical position of step i. in a set of coordinates related to the graphic features displayed on the coating.

64. The method for locating a position selected by a user on an electrographic detection unit according to claim 63, characterized in that: the processor further includes: r-> g. '106 a memory in which information relating to the graphic characteristics for several coordinates on the coating was pre-stored; and an electronic delivery system for providing information of the memory to the user in relation to the position selected by the user: and the method also includes the step of:. use the coordinates of step j. as an indicator for the memory to recover information relative to 0 the graphic characteristics on the coating in such coordinates; and 1. apply the information retrieved from step k., to the electronic delivery system to present it to the user.

65. The method for locating a position selected by a user on an electrographic detection unit according to claim 60, characterized in that the method, before step a., Further includes the step of: 0 m. select locations on the layer to N contact points, so that all potential positions that can be selected by the user are in the visual field of J pairs different from N contact points.

66. The method for locating a position selected by a user on an electrographic detection unit according to claim 65, characterized in that as in step m. a potential position can be selected by a user in the field of view of a pair of contact points, when an angle included in each point of contact of the pair of contact points is less than 90 °, with the included angle being less than angle defined by the vectors between the pair of contact points, and the point of contact that corresponds to the included angle and the potential position that can be selected by a user.

67. The method for locating a position selected by a user on an electrographic detection unit according to claim 60, characterized in that: each of the N contact points includes a pair of contacts in cascade with a first contact for receive signals, and a second contact, in which signals are measured; the electrographic detection unit further includes: N amplifiers with two input terminals, one input terminal) with one of the input terminals coupled to the processor and the output terminal connected to the first contact of one of the N corresponding contact points; and N feedback compensation circuits, each of which has an input terminal and an output terminal, each of the N feedback compensation circuits associated with one of the N contact points, corresponding to the terminal of input connected to the second contact of the contact point • from one of the N contact points, and the 10 output terminal connected to the other input terminal of the corresponding amplifier; in step a. the selected signal is applied to the first contact of each of the N contact points of the corresponding N amplifiers; 15 in step c. each of the second signal, applied sequentially, is applied between the first * contact of each of the (N-l) different pairs of contact points of the output terminal of the corresponding N amplifiers; and the method further includes the step of: n. individually compensating for the contact resistance of each of the N contact points by adjusting an output signal level of each of the N amplifiers in response to an output signal from one of the corresponding N feedback compensation circuits.

68. The method for locating a position selected by a user on an electrographic detection unit according to claim 60, characterized in that: the processor includes a switch (N + l) positions, connected to receive the signals that must be measured by the processor individually of the means for detecting and releasing a signal from the position selected by the user of the electrographic detection unit and each of the N contact points; The method also includes the steps of: o. injecting a third known signal between each pair of the N contact points; p. measure a third resulting signal at a point of contact different from any of the points of each of the pairs of N contact points; and q. solve N simultaneous equations for the resistance values of each of the N contact points, where each of the simultaneous equations was generalized as follows for each of the N contact points, where for the purposes of that equation, the third known signal of step o. is injected between contact points A and B and the third measured signal from step p. is measured at the contact point C: Signal = Signal ™ [(X-RAB + RB) / (RAB + RB + RA)] i where: Signal ™ is the signal injected by the processor between each pair of contact points; R? B is the value of the volumetric resistance of the layer of conductive material between contact points A and B; X is the fraction of the value of the volumetric resistance between contact points A and B; and RA and RB are the values of contact resistance at contact points A and B.

69. The method for the location selected by a user on an electrographic detection unit, according to claim 60, characterized in that the first and second selected signals are AC signals of a selected frequency that can be detected by the detection and release means.

70. The method for location selected by the user on an electrographic detection unit, according to claim 60, characterized in that: the first and second signals selected are CD signals; and the detection and release means make electrical contact with the layer to detect the second measured signal.

71. A method for locating a position selected by a user on an electrographic detection unit having M layers of a conductive material, each electrically isolated from the other and having an electrical resistivity with K points of contact separated, interconnected electrically with the corresponding conductive material layer, where N of K contact points are used to locate the position selected by the user, and where N has an integer value of three to K, a processor placed to selectively apply a signal to each of the N contact points of each of the M layers and to determine which of the M layers and the position coordinates of the position selected by the user on one of the corresponding M layers, and means to detect and release a signal of the position selected by the user on the electrographic detection unit to the processor, with the user having selected the position, the method is characterized because it includes the steps of: a. sequentially apply a first selected signal to all K contact points on each of the M layers at the same time; b. measure a first signal measured at the position selected by the user for each of the M layers, with the first measurement corresponding to the application of the signal from step a. for each of the M layers; c. measuring a second signal measured at the position selected by the user on the layer selected by the user with each of the K contact points on each of the M layers in open circuit; d. subtract the second measured signal from step c. of the first measured signal of the M layers of step b. to form M difference values; and. compare each of the M values of the difference of step d. against a preselected threshold value; and f. identify one of the M layers on which the position selected by the user is located as the layer associated with the value of the difference that is greater than the threshold value and that exceeds the threshold value by a greater amount.

72. The method for locating a position selected by a user on an electrographic detection unit according to claim 71, characterized in that it also includes the steps of: g. sequentially apply a third signal selected from J different pairs of contact points of the layer identified in step f., with the third signal having a selected relation with the first signal, where J has an integer value between 2 and (Nl ); h. sequentially measuring J third measured signals of the position selected by the user with each of those signal measurements corresponding to a different one of the second second applications of step g.; and i. calculate a value proportional to a position coordinate between each pair of the J pairs of contact points of step g., which is proportional to a ratio of each of the second measured signals of step h. and the first measured signal from step b. to define the position selected by the user with J coordinates in relation to the contact points used in the J second signal measurements on one of the M identified layers.

73. An electrographic detection unit for use in determining the position of a selected point, characterized in that it comprises: a layer of a conductive material having an electrical sensitivity and a surface; K separate contact points, electrically interconnected with the layer of conductive material; a processor connected to the K separate contacts and arranged to selectively apply a signal N of the K contact points, where N has an integer value of 3 to K; 114 a probe assembly, including a stylet, coupled to the processor, the stylet is arranged to be connected by a user in the vicinity of a point selected by a user on the surface of the layer and to receive signals from the layer when the contact points have signals selectively applied to them; wherein the position of the stylet in relation to the surface of the layer is determinable by the processor from two signals received from the stylet, each in relation to a similar excitation of J different pairs of the K points of contact under the control of the processor, where J is an integer between 2 and (Nl). \ * 115 SUMMARY OF THE INVENTION An electrographic detection unit includes a layer of conductive material having an electrical resistivity 5 and a surface, at least three separate contact points (12, 14, 16) electrically interconnected with a layer of a conductive material, a processor (30) connected to the separate contacts and arranged to selectively apply a signal to each of the contact points, a stylet (20) coupled to the processor to receive the signals from the layer when signals have been selectively applied to the contact points.