|Publication number||WO2004025402 A2|
|Publication date||25 Mar 2004|
|Filing date||10 Sep 2003|
|Priority date||10 Sep 2002|
|Also published as||WO2004025402A3|
|Publication number||PCT/2003/28179, PCT/US/2003/028179, PCT/US/2003/28179, PCT/US/3/028179, PCT/US/3/28179, PCT/US2003/028179, PCT/US2003/28179, PCT/US2003028179, PCT/US200328179, PCT/US3/028179, PCT/US3/28179, PCT/US3028179, PCT/US328179, WO 2004/025402 A2, WO 2004025402 A2, WO 2004025402A2, WO-A2-2004025402, WO2004/025402A2, WO2004025402 A2, WO2004025402A2|
|Inventors||Roy J. Lahr|
|Applicant||Rast Associates, Llc|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (3), Classifications (3), Legal Events (6)|
|External Links: Patentscope, Espacenet|
RF ABSORPTION SWITCHING FOR KEYBOARD SIGNALING
CROSS-REFERENCE TO RELATED APPLICATIONS
This application claims the benefit of U.S. Provisional Patent Application No. 60/409,953, filed on
September 10, 2002, which is expressly incorporated herein in its entirety by reference thereto.
FIELD OF THE INVENTION
The present invention relates to a method of utilizing the selective absorption of radio frequency for signaling which keybuttons on a keyboard are depressed by the user.
This invention relates, generally, to ensembles of keybuttons, e.g., to keyboards used for typing of individual symbol, as in the formation of texts in documents.
A keyboard that is used for typing of individual symbols must signal which keybutton has been depressed by the user. In some cases, more than one keybutton may be depressed at once, so that essentially simultaneous signaling of several keybutton depressions must occur. The signal that indicates the depression of a keybutton operates through a matrix logic element that "labels" each observed keybutton depression with a corresponding symbol or symbol formation control operator function.
It is common to use a microprocessor for this matrix logic "tagging" function.
Commonly, the depression of a keybutton directly operates an electrical switch, which is connected by a connector wire to the matrix logic device. In a fixed size keyboard, the ensemble of wires connecting each keybutton to the logic device may be replaced by a thin insulative, flat surface on which copper traces are either etched or printed. In a keyboard that varies in size or shape, the insulative surface may be flexible, as polyamide plastic, and this allows some physical shifting of the keybuttons.
If the keybutton positions on a keyboard may be altered, as for compact storage and transport, followed by opening out into one or more use sizes, it can be difficult to arrange for electrical interconnection to the switches associated with each keybutton on the keyboard. In previous submissions, the use of a stretchable conductor cable has been proposed. U.S. Patent No. 6,092,944 is believed to describe festooning of flat flexible cable as the keyswitches alter position laterally. This festooning of a fixed size flat cable is a bit cumbersome, physically, and limits the designer in furnishing a keyboard which can be compressed to a small size for carrying.
U.S. Patent No. 4,677,600 is believed to describe a method of acoustic signaling, wherein each keybutton depression generates an acoustic "chirp", and a sensor array triangulates on the "chirp" to indicate just which keybutton has been depressed (differences in time of arrival at the sensor from the "chirping" keybutton emitter) . The acoustic signaling method is a means of replacing the standard switch circuitry, but this method could be used for keyboards which compress or expand in size. However, acoustic echoes and multiple bounces in a small keyboard sub-structure can give poor echo location results, since a keyboard that is designed to change its geometry between carrying and one or more use sizes has a lot of structural elements that can interfere with the "clean transmission" of an acoustic "chirp" signal. Without a clean acoustic signal, the sensor may not yield a clean electrical signal to the logic device.
Other alternative signaling systems for keybuttons have been presented.
Optics is a frequent theme of these alternatives to fixed wiring connecting electrical switches to a logic device. It is believed that over twenty optical keyboard proposals have been patented. In an optical keyboard, one or more light sources are coupled to one or more light sensitive receiver (s) , as by optical rods, fibers or other conducting channels. The flow of light from source to receiver is modulated by physical intersection, moving of the conducting channels, or moving shaped intersection plates within a channel. The modulation occurs when a keybutton is depressed. The selective modulation of light is designed to produce a particular output signal which represents which of the keybuttons has been depressed by the user. It is not known whether any of the presented optical methods have been in a commercially successful device to implement a keyboard signaling system.
Accordingly, it is an aspect of the present invention to provide a keyboard system which may signal a logic device which key, or keys, has been depressed by the user during typing operations.
More particularly, it is an aspect of the present invention to provide a keyboard whose keybuttons, when depressed, may signal a logic device as to that depression, and further, to provide a system in which the physical separation of said keybuttons may not be restricted by physical interwiring.
An aspect of the present invention is to construct a signaling system which may notify a logic matrix device that one or more keybuttons have been depressed by a typist during construction of a text.
A further aspect of the present invention is to construct a signaling system that may not depend on electrically conductive circuit wires between a keybutton location and the logic matrix device.
An example embodiment of the present invention may provide three elements in the signaling system.
(1) The signaling system may require a source of RF energy that is either at a particular frequency, or acts as an RF carrier wave having a modulation with chosen frequency characteristic .
(2) The signaling system may have a sensor which detects the particular energy emitted by the source .
(3) The signaling system may provide resonant elements attached or located at each keybutton location, said resonant elements being capable of absorbing a measurable portion of the emitted energy, such that the sensor will report that energy has been absorbed.
The source of RF energy in (1) above may be programmed to emit or modulate at many frequencies, in this application, one frequency per discrete keybutton to be monitored by the signaling system. The programming of the several frequencies provided thus constitute steps in a logic pattern. This pattern of discrete steps may normally operate at least several times per second, so as to monitor the momentary depression of one or more keybuttons.
The sensor, or sensors of (2) above, when used to received the RF energy may be pre-calibrated for each frequency step. The calibration begins by operating the emitter source is operating at the first frequency step, but with no resonant element of (3) is operating. The received energy is noted and recorded. Energy at frequency step two is emitted, and the energy at the sensor is measured. This procedure is repeated until all frequency steps have been emitted, one at a time. This pattern of received energy levels, one for each frequency step, may be stored, as in a logic memory device. This relieves the system of requiring that the received energy at all frequency steps is nominally equal energy emission at all step frequencies, and thus may only require that for a particular frequency step, a comparison of received sensor levels between the calibration value and the observed value is required. The storage of a table of received energy for each frequency step may be stored in a logic device, such as a programmable RAM memory attached to a microprocessor. The resonant element (3) above, may, when activated, absorb sufficient RF energy so that the sensor may unambiguously report (a) no significant change in energy observed for this frequency step, or (b) report that there is a significant change in received or sensed level so that this significant change may be reported and the cause interpreted as the activation of a particular energy absorber element. Since the energy absorber for each keybutton may be unique in energy absorption frequency, the system may signal that a particular keybutton has been operated. The reporting of the particular keybutton depression may then cause the matrix logic device to emit a signal which may be interpreted by an associated computer or other information processing device as a character or symbol in a text stream.
Note that the resonant element of (3) above may include discrete circuit components, as C (capacitor) , L (inductor) and R (resistor) , plus a switch in the case that the resonant circuit is switched "on", or completed by depressing a keybutton. When energy is absorbed by the RLC circuit, it is transformed into heat, largely in the resistive element, but also in the L and C components to the extent that they are electrically "lossy".
Alternately, the resonant circuit may be of a distributed nature, such as a strip line "antenna" of particular geometry so that it is resonant at a chosen frequency, and in this case, backing the strip line antenna with an RF energy absorber such as a layer of carbon "space cloth" so as to transform the absorbed RF signaling energy into heat. Again, most of the absorbed energy may pass into the resistive "space cloth" layer, but a minor portion of energy may be absorbed by the strip line antenna, as its component parts are also "lossy" .
The programming of the many frequency steps is easily accomplished, as by building a table of discrete voltage values in a RAM memory of a microprocessor. The logic in the microprocessor may access these voltage values several times per second. This set of discrete voltage steps may then be transformed into discrete frequency values, e.g., by using a VCO element, or voltage-controlled oscillator. The output of the VCO may then be used to directly or indirectly modulate the operation of an emitter element. For operation at microwave frequencies, a Gunn Diode may be a simple form of emitter.
Note that a several value table may be built so as to incorporate the calibration set of received energy values, so that there may be a corresponding set of sensor calibration values, one per frequency step, just as there is one stored voltage value per frequency step.
The sensor may be chosen to have satisfactory electrical sensitivity over the range of chosen frequency values. The sensor may be a "receiver" broadly tuned over the range of frequency values, or it may be a selectively tuned receiver, receiving the output of the VCO so that it is appropriately tuned to the individual frequency step being emitted. Thus, the output of the receiver may be an electrical signal of sufficient strength to be used in a logic comparison circuit that may compare the observed receiver output with the calibration output at each frequency ste .
A broadband RF sensor, such as one that converts received energy to heat and thereby generates a voltage may be used, but it may be unlikely that the sensitivity of such a sensor may be as great as in the case when a tuned receiver is used as a sensor of RF energy.
Note also that the RF absorber element associated with each keybutton may operate in at least two different modes.
Mode one may include a switch in the RLC resonant circuit, and when the keybutton was sufficiently depressed mechanically, the switch may operate to complete the RLC resonant circuit. A keyboard using Mode One operation may place all potentially resonant circuits in the path of RF energy as it flows from emitter source to receiver.
Mode two may utilize a resonant circuit that had no switch and may always absorb energy at a particular frequency step. When a Mode two absorber device is used, the absorber device is physically moved from a storage location that is not in the path of RF energy flowing between emitter source and receiver to a new location that now is in the path of RF energy flow, and thus absorbs a significant amount of energy at that step frequency. The downward motion of the keybutton may be coupled directly to the absorber element, moving it downwardly from a non-absorbing storage location to the new, energy absorbing location.
If the step frequencies used are in the microwave region, it is possible to form ducts which preferentially guide the flow of RF energy. These microwave guides or ducts are usually referred to as "microwave plumbing" .
If the storage location places the absorber element at' or just outside the walls of such microwave guides, the conducted RF energy may not impinge on the absorber element. However, when the keybutton is depressed, this down motion of the keybutton may shift the absorber element downwardly into the interior of the microwave duct, thus exposing it to the conducted energy. When pushed downwardly by keybutton action, the absorber element may be positioned to "absorption signal" the logic element that energy has been absorbed at the emitted source frequency, and thus that a particular keybutton has been depressed.
Note also that the RF ducting that couples the emitter to a particular row of keybuttons may be constructed of coaxial pipes, so that a trombone slide action may accommodate lateral changes in relative keybutton locations and still may assure good RF coupling or transmission between the RF source (1) , receiver (2) , and absorber element (3) .
According to an example embodiment of the present invention, a keyboard device includes a plurality of keybuttons, a resonant tank circuit corresponding to each of the plurality of keybuttons, each resonant tank circuit configured to absorb energy at a respective predetermined frequency, a sensor device configured to sense absorption of energy by the resonant tank circuits at the predetermined frequencies, an emitter device configured to emit energy in a path of the resonant tank circuits toward the sensor device, and a determination device configured to determine a depression state of the keybuttons in accordance with absorption, sensed by the sensor device, at the predetermined frequencies of the energy emitted by the emitter device .
Each resonant tank circuit may include a resistor, a capacitor and an inductor.
Each resonant circuit may include a switch, and the resonant tank circuit may be configured to sense the absorption of the energy in accordance with an operative state of the switch.
The keyboard device may include a memory device configured to store data representing each of the predetermined frequencies .
The keyboard device may include a comparison device configured to compare the absorption sensed by the sensor device to the data stored in the memory device .
The emitter device may be configured to emit the energy at least at each of the predetermined frequencies .
A device according to an example embodiment of the present invention includes a plurality of operative elements, a resonant tank circuit corresponding to each of the plurality of operative elements, each resonant tank circuit configured to absorb energy at a respective predetermined frequency, a sensor device configured to sense absorption of energy by the resonant tank circuits at the predetermined frequencies, an emitter device configured to emit energy in a path of the resonant tank circuits toward the sensor device, and a determination device configured to determine an operative state of the operative elements in accordance with absorption, sensed by the sensor device, at the predetermined frequencies of the energy emitted by the emitter device .
A keyboard device according to an example embodiment of the present invention may include a plurality of keybuttons, resonant tank circuitry means corresponding to each of the plurality of keybuttons, each resonant tank circuitry means for absorbing energy at a respective predetermined frequency, sensing means for sensing absorption of energy by the resonant tank circuitry means at the predetermined frequencies, emitting means for emitting energy in a path of the resonant tank circuitry means toward the sensing means, and determining means for determining a depression state of the keybuttons in accordance with absorption, sensed by the sensing means, at the predetermined frequencies of the energy emitted by the emitting means.
A method according to an example embodiment of the present invention includes emitting energy at a plurality of predetermined frequencies in a path, selectively operating at least one resonant tank circuit to absorb the energy at a respective one of the predetermined frequencies, and determining an operative state of the at least one resonant tank circuit in accordance with the absorption of the energy at the respective one of the predetermined frequencies.
The features which are considered characteristic for this invention are set forth in particular in the appended claims. The present invention itself, however, both in its construction and its method of operation, together with additional aspects thereof, will be best understood from the following description of the example embodiments when read in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1, entitled "Energy Flow" shows a keyboard 10, and its associated RF energy flows as the potentially resonant RLC circuit capsules are probed.
Figure 2, entitled "Individual R-L-C Circuit in Keytop Flat Capsule" illustrates an example embodiment in which a resonant absorber circuit element incorporates a switch "S" in the RLC circuit.
Figure 3, entitled "Data Flow: Probing the Individual R-L-C Circuits in Capsules", illustrates a partial information flow diagram showing how the microprocessor controls all aspects of RF energy generation and reception. Figure 4, entitled "Data Flow: Providing a Tuned Receiver Circuit and Logic Gate for Detecting Absorption Dips" shows the further logical elements necessary to provide a high sensitivity examination of output RF energy by using a frequency-tuned receiver.
Figure 5 is a cross-sectional view of a keybutton unit to which an unswitched RLC capsule is attached, and selective absorption occurs when that RLC capsule in inserted into the passing RF energy.
LIST OF REFERENCE NUMERALS
5 fingertip (of typist)
20 Resistor R
30 Capacitor C
40 Inductor L
50 Switch S (and associated switches SI, S2, S3, S4 , and S5) 70 RF source (emitter) 72 Emitted RF Energy 80 RF Energy sensor 90 Input energy coupler 100 Output energy coupler 110 Energy channel 120 RLC circuit in capsule
(switch able) 122 RLC circuit in capsule
(not switch able) 125 Test capsule, if used 140 Individual keybuttons 150 row of keybuttons
(rows 150a, 150b, 150c, 150d, and 150e for a five row keyboard) 200 microprocessor 210 RAM memory (holds data table) 220 Step voltage (from table) , digital 230 DAC (digital to analog voltage converter) 240 Step voltage, analog 250 VCO (voltage controlled oscillator) 260 secondary voltage output of VCO
(analog) 300 Injected RF energy 420 Energy absorption dip (observed) 500 frequency-tuned receiver 600 logic gate, detects presence of energy absorption dip 700 wave guide tunnel 720 wave guide tunnel wall
Figure 1, entitled "Energy Flow" shows a keyboard 10. In the top figure, the RLC encapsulated elements 120 are shown grouped into rows to form lateral energy channels . RF energy is produced at left in RF Emitter 70, which may be a Gunn Diode. An input energy coupler distributes the RF to all five channels (for a five row keyboard configuration) . The RF energy flows laterally rightwardly toward the output energy coupler 100, and thence to an RF sensor 80, such as a receiver.
The lower figure shows the physical arrangement of keybutton tops 140 in keybuttons rows 150 (the separate rows are labeled 150e, 150d, 150c, 150b, and 150 a) . The space bar 145 is constructed to be wider than other keybuttons as it is operated by the typist's thumbs.
Figure 2, entitled "Individual R-L-C Circuit in Keytop Flat Capsule" illustrates the case when an resonant absorber circuit element incorporates a switch "S" in the RLC circuit.
The inset figure at upper right is a circuit diagram for an individual RLC circuit placed in a flat capsule 120. This switch able resonant circuit contains four components, Resistor R 20, Capacitor C 30, Inductor L 40, and Switch S 50.
Since the space bar 145 is physically wide, that resonant circuit may contain several switches S 50, here labeled SI, S2, S3, S4 and S5. These switches 50 are distributed over the lateral extent of the spacebar, so that at least one will be actuated when the typist's thumb depresses the spacebar (the thumb may be placed anywhere on the space bar during typing, e.g., at left end, in the middle, or at the right end.
Figure 3, entitled "Data Flow: Probing the Individual R-L-C Circuits in Capsules", is a partial information flow diagram showing how the microprocessor 200 controls all aspects of RF energy generation and reception, and how that energy flow 70 is potentially modulated by the action of individual RLC circuits in capsules 120. When the RLC circuit is operated to create energy absorption at chosen frequencies f .
Since a microprocessor (as 200) may be used to matrix process the wired signals from individual keyswitches attached to each keybutton in a standard keyboard, extending the function of the microprocessor to control the operation of a resonant circuit keyboard may be a practical choice.
Here, the microprocessor generates time-based pulses, or steps, which may control "clocking" of the data stored in a RAM memory table 210. It may be common practice to construct microprocessors with integral RAM memory sections. In this application, the RAM memory is storing digital voltage values in a table as shown in the inset at upper left . The sequential steps 1, 2, 3, 4 . . . n correspond to an individual keybutton 120 position on keyboard 10, here shown as Q, W, E, R, T, Y, U and "n", wherein the stored digital voltage values may range from 0.05 to 3.01 volts.
As the microprocessor 200 "clocks out" each step 1, 2, 3 . . . "n", the output of the RAM memory table 210 sends the corresponding digital voltage value to a DAC 230. The DAC is a "digital to analog" converter, which produces analog voltages corresponding to the input digital voltage numbers . These individual step voltages 240 are sent to a VCO 250, which is a "voltage controlled oscillator", producing a frequency fl, f2, f3 , f4 to fn, corresponding to each step 1, 2, 3, 4 . . . n. The step frequencies 260 are introduced to a RF amplifier 280, which attempts to normalize the output voltage level of the generated frequency wave, as by clipping or use of a compressor circuit. The output of the RF amplifier 280 serves as input signal for an RF emitter 70, such as Gunn Diode. Note that this signal may serve to produce a carrier wave of frequency f, or alternately, a modulation frequency f for a carrier wave of another frequency.
The injected energy 300 from the RF emitter passes through the input energy coupler 90 of Figure 1, and thence into the individual energy channels 110, passing by the potentially absorptive RLC circuit capsules 120, thence through the output energy coupler 100 and into the RF sensor 80. If a keybutton 140 is depressed, the corresponding RLC circuit capsule 120 will then absorb energy from the passing RF wave, and the output level of energy observed at the RF sensor 80 will be lower than as if the absorptive capsule 120 were not activated.
Thus, this selective absorption of energy by the capsule 120 will result in energy dips 420. Note that only one frequency f is produced for each step output of the microprocessor 200, so that the absorption of each resonant capsule may be clearly observed to represent the depression of the corresponding keybutton.
When an absorptive dip 420 is noted at the microprocessor 200 (see also Figure 4) , the microprocessor will emit a signal to the associated information handling device (e.g., a computer, PDA, cell phone, etc.) that represents a particular character. The data handling capability of the "BIOS" (or basic input-output system) chip in the associated device translates that particular character-associated signal from the microprocessor 200 into a familiar character code, e.g., in an 7 or 8 bit ASCII format (American Standard for Communication and Information Interchange) .
Inset Figure 3b at lower left shows an observed energy waveform showing the absorption dips 420 which occur as frequency f is stepped from fl, f2, f3 . . . fn. Since each particular RF frequency fl, f2, f3 . . . fn is generated at time tl, t2, t3, tn by the microprocessor clock, the observed absorption dips will also occur at exactly these times .
Figure 4, entitled "Data Flow: Providing a Tuned Receiver Circuit and Logic Gate for Detecting Absorption Dips" shows the further logical elements necessary to provide a high sensitivity examination of output RF energy.
The VCO 150 (Voltage Controlled Oscillator) produces step frequency output waves 260 at frequency f, a new frequency f for each step. These frequency waves serve as input to the RF amplifier 280 which then drives RF emitter 70.
A secondary output of the step frequency 260 generated by the VCO 150 is used to control the receiver frequency of a tuned receiver 500. It may be necessary to use a fixed oscillator to "beat" with the step frequency 260. This mixing of the two frequency waves produces a beat frequency at both the sum and difference frequencies of linear mixing of the two different frequency waves, and then a standard RF filter removes the unwanted mixed output wave. This operation then "tunes" the receiver 500 to the step frequency f, making it highly sensitive to the dip 420 in RF energy 72 passing by the encapsulated RLC modules 120, in comparison to a broad band receiver which can receive all frequencies fl, f2 , f3 , £4 . . . fn.
The received energy sensor 80 (here being represented by tuned receiver 500) passes the observed RF absorption dips 410 to a logic gate which acts as a dip sensor 600. The logic gate is "clocked" to make a comparison of observed voltage at each time step produced by the microprocessor 200. If the input voltage 420 represents a dip in voltage that is significant compared to the unabsorptive voltage level for that frequency, a binary output of "dip observed" versus "no dip observed" is generated.
The reference level for this logic gate 600 may be stored in an associated memory cell, and it may be usual for one reference level to serve for all observed dip values 420, since a constant output amplifier 280 is used to normalize the RF level that is input to the RF emitter 70.
If the output level of the RF emitter 70 varied widely over the fl, f2, f3 . . . fn used, it may be possible to store the various individual reference values for fl, f2, f3... fn for comparison, with the individual value used for each step comparison being clocked out of memory under control of the microprocessor 200.
Since the microprocessor may rapidly step through all fl, f2, f3...fn in the RAM memory table 210, the keyboard's RLC circuit capsules 120 may be examined many times per second, e.g., much faster than the typist's finger can depress or release an individual keybutton.
And, since the examination for observed "dip" 420 or no dip is so fast, when the typist holds down more than one key at a time (e.g., "shift" plus a character keybutton), the system may be sufficiently fast to indicate both observations to the microprocessor so that a correct output signal is made (here, an upper case character is signaled) .
The foregoing discussions of Figures 1 to 4 utilized a switch able RLC circuit 120, whose switch S 50 was closed by depressing a keybutton 140.
It is also possible to employ a RLC circuit 122 which is permanently wired for energy absorption at frequency f , that is, it does not have a switch 50 incorporated in the capsule. This absorptive energy operation without a switch is shown in Figure 5.
The RLC circuit 122 without a switch is shown at upper right. Since there is no switch, this resonant tank circuit will always be operative if it is exposed to RF energy at its tuned frequency f .
At center of Figure 5 is shown a cross-sectional view of a keybutton unit 140. The center drawing shows the keybutton in the upper position under influence of spring 142 placed on keyboard support platform 146. With the keybutton 140 in the raised position, the keybutton stem 144 keeps the RLC capsule 122 in an upper position. The lower section of the capsule 122 also operates as a section of the wave guide tunnel 700 which channels the RF energy for each keyboard row 110. Thus, in the raised position, the RLC capsule 122 may have no absorptive affect on the passing RF energy 72.
In the lower figure, a fingertip 5 depresses the keybutton 140 against the upward force of spring 142, compressing the spring 142. This pushes keybutton step 144 downwardly, lowering the RLC capsule into the RF energy 72 passing by in wave guide tunnel 700. Now, the RLC capsule will absorb RF energy from the passing RF wave, and thus a resonant dip 420 will be observed at this frequency f. .
Note that a "reference test" capsule 125 may be included in keyboard 10. This capsule may be always active and may operate at a test frequency ft. When the microprocessor 200 accessed the test frequency ft, the energy absorption of the test capsule 125 may always produce a resonant energy dip 420, and this dip 420 may serve as a calibration value, e.g., for controlling the decision level of the logic gate 600.
While the foregoing description describes absorption switching for keyboard applications, it should be understood that the device and method according to the present invention may be provided for any other applications .
It should be understood that each of the elements described above, or two or more together, may also find application in other types of equipment than keyboards. And, while the description has been illustrated and described as embodied for keybutton depression sensing in a keyboard, it is not intended to be limited to the details shown, since it should be understood that various omissions, substitutions and changes in the forms and details of the device illustrated and its operation may be made by those skilled in the art without departing in any way from the spirit and scope of the present invention.
Without further analysis, the foregoing will so fully reveal aspects of the present invention that others may, by applying current knowledge, readily adapt it for various applications without omitting features that, from the standpoint of conventional devices, systems, methods, etc., fairly constitute essential characteristics of the generic or specific aspects of the present invention. What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims .
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|US3818472 *||26 May 1972||18 Jun 1974||K Mauk||R.f. system for detecting unauthorized travel of articles through a selected zone|
|US5378069 *||15 Dec 1993||3 Jan 1995||Product Engineering & Mfg., Inc.||Environmentally safe touch typing keyboard|
|US5677688 *||13 May 1992||14 Oct 1997||David Sarnoff Research Center, Inc.||Optomechanical information entry device|
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