Dec. 2, 1969
`
`Filed Aug. 2, 1966
`
`E, A. JOHNSON
`TOUCH DISPLAYS
`
`3,482,241
`
`3 Sheets—Sheet 1
`
`SEl
`
`ew
`
`TI
`
`PHASE
`SENSITIVE
`DETECTOR
`
`
`
`
`
`CONTROL
`
`FIG.2
`
`
`
`BIC PRTHORUOONNSON
`
`inventor
`JoboWoksCoohwe
`
`orneys’
`
`1
`
`CYPRESS 1022
`CYPRESS 1022
`
`1
`
`

`

`Dec. 2, 1969
`
`Filed Aug. 2, 1966
`
`3,482,241
`E. A. JOHNSON
`/
`TOUCH DISPLAYS
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`Dec. 2, 1969
`
`_
`
`£, A. JOHNSON
`TOUCH DISPLAYS
`
`3,482,241
`
`Filed Aug. 2, 1966
`
`3 Sheets-Sheet 3
`
`2 C
`
`OR
`
`19
`
`
`ONTROL OF PLANT
`
`
`REASSESSMENT
`
` DATA INPUT
`
`| 5
`FROM SENSORS
`
`
`REVALUATION
`|
`DATA INPUT FROM
`
`OTHER OPERATORS
`
`|
`
`7
`
`NEW DISPLAY
`OF CHOICES
`
` INDICATES|
`
`CHOICE
`
`|.
`
`FIG. 5,
`
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`3
`
`

`

`United States Patent Office
`
`3,482,241
`Patented Dec. 2, 1969
`
`1
`
`3,482,241
`TOUCH DISPLAYS
`Eric Arthur Johnson, Malvern, England, assignor to
`Minister of Aviation in Her Britannic Majesty’s
`Government of the United Kingdom of Great
`Britain and Northern Ireland, London, England
`Filed Aug. 2, 1966, Ser. No. 569,731
`Claimspriority, application Great Britain, Aug. 5, 1965,
`-
`.33,524/65; June 28, 1966, 28,883/66
`Int. CL. GO9b 13/00; HO5b 41/00; G061/00
`US. -Cl. 340-—337
`7 Claims
`
`
`ABSTRACT OF THE DISCLOSURE
`A plurality of touch-sensitive contacts, placed adjacent
`thescreen ‘of a cathode ray tube, which may be’ selec-
`tively actuated forindicating which portion of the image
`on the cathode ray-screen is to be exmained in further
`detail. The position of the actuated contact with Tespect
`to.
`the viewing screen indicates- which portion of the
`image. has been selected to an output means such as
`a data processing system. Either resistance change or
`capacitance change across the actuated contact may be
`sensed,
`
`2
`The means responsive to touch may include a transparent
`screen responsive to touch suitable for fixing in front of
`the meansfor displaying data.
`Preferably the means responsive to touch is connected
`to a data input of a data processing system. In such a
`case it is highly advantageous for the means for display-
`ing data to be connected to a data output of the: data
`processing system in such a manner that the data dis-
`played may be altered under the control of the data
`processing system.
`- A convenient means for displaying data is, of course,
`provided by the cathode ray tube, which may be con-
`trolled to write output information on its screen; the
`inventionprovides a method of feeding more information
`to the data processing system, so continuing the. pro-
`gramme. For example, the cathode ray tube may display
`a list of items and it may be desired io examine one of
`the items in further detail. It is frequently troublesome
`to indicate to the data processing system which item is
`the one to be examined. Under these circumstances it
`should be possible to provide sites on the cathode ray
`tube which are responsive to touching by the hand of
`the operator, The effect would be that
`the operator
`touches the place on the cathode ray tube screen where
`the item is displayed and this signals back to the data
`processing system that
`that particular item is selected
`The presnet ‘invention relates to touch displays.
`(for further examination, say).
`’ A very large number of so-called automatic data proc-
`Such a system may be arranged by embedding elec-
`essing systems require the co-operation of human opera-
`tric wires in the screen, one to each site on the cathode
`tors to achieve satisfactory operation. In many. of these
`ray tube, and using the operator’s natural capacitance
`systems it is necessary tO reduce operator reaction time
`to earth, whichis of the order of 100pf.
`to a minimum, which in turn demands an arrangement
`In an alternative arrangement a pair of wires may be
`where conimunciations between the operator and the
`arranged close to one another and the operator’s finger,
`system and vice versa is the best possible. This requires
`touching the two wires, would short them out via the
`that the methods of presenting information to and re-
`natural skin resistance of the finger plus the contact re-
`ceiving instructions from the operator should be rapid
`sistance, which is of the order of 500,000 ohms.
`and easy.
`Embodiments of the invention will be described by
`For the presentation of information to the operator,
`way of example with reference to the accompanying
`a method often used at the present time is some form
`drawings, in which:
`of printing, usually electromechanical. Although the
`FIGURE1 is a circuit diagram of a touch sensitive
`normal] teleprinter output is rather slow in relation to
`system;
`the speed with which an operator can absorb informa-
`FIGURE 2 is a more complete circuit diagram of
`tion, an extension of the technique to line printing cn
`part of a display incorporating a touch-sensitive system;
`overcomethis. Alternatively an electronic data display is
`FIGURE3 is a circuit diagram of part of an alter-
`sometimes used, and in the case of line printing or elec-
`45
`native display incorporating a touch sensitive system;
`tronic data display time required to produce a readable
`FIGURE4is a circuit diagram of part of a further
`output from the system does not really add significantly
`alternative display incorporating a touch sensitive sys-
`to the time required for an operator to accept informa-
`tem; and
`:
`;
`tion. There is also a considerable amount of flexibility
`FIGURE 5 is a diagrammatic representation of the
`of formatavailablé to easé understanding.
`logic steps taken in a process using a data processing
`The situation is not so satisfactory in the case of
`system andinput and outputfacilities.
`a
`accepting instructions
`from an operator. A current
`In FIGURE 1 the primary winding of a transformer
`method is to make use of some form of keyboard with
`TI is fed’ from a high frequency source S (say 3000
`either a standard set of alpha-numeric keys or some
`cycles per second) and the secondary winding is centre-
`spécial keys, usually called function keys; or both, The
`tapped. One half L1 of the secondary winding is con-
`function keys as their name implies, usually provide con-
`nected bteween the centre tap CT1 and a terminal con-
`trol instructions to the system whilst the alpha-numeric
`nected to earth via a variable capacitor C1 and a varia-
`keybord is used for information input,
`interpreted by
`ble resistor R1 in series and the other half L2 of the
`the system in acocrdance with the most recent control
`secondary winding is connected between the centre tap
`instructions. The process can be rather slow and clumsy
`CTI and a sensitive electrode SE1. The centre tap CT1
`especially when a fairly large system is involved with
`is connected to carth via the primary winding L3 of a
`several operators having a wide range of input possibili-
`transformer T2.
`ties in the interests offlexibility.
`The action of the circuit is as follows. The windings
`It is an object of the invention to provide means for
`L1 and L2,
`together with the capacitor C1 and the
`feeding data (instructions or information)
`to a system
`resistor R1, and the self capacity of the sensitive elec-
`by using a touch display by means of which means re-
`trode SE1 form a bridge circuit which is adjusted to
`sponsive to touch are associated with a display. The
`be balanced at the frequency fy of the source S. When
`means responsive to touch may be connected to a data
`the sensitive electrode SEL is touched by anoperator
`input of the system.
`the capacitance to earth presented to it
`is sufficient to
`According to the present invention there is provided,
`throw the bridge off balance and ‘an alternating ‘poten-
`for use with means for displaying data, means responsive
`tial appears across the winding L3 and hence a signal ap-
`to touch having an output indicative of the area touched,
`pears in the secondary winding of the transformer T2.
`
`on
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`

`

`3,482,241
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`or
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`30
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`In FIGURE 2 an electronic data display includes a
`FIGURE4is a circuit diagram of part of a further
`matrix M of sensitive electrodes SE1, SE2,..., two
`alternative display incorporating a touch sensitive system.
`This is an alternative way of using the skin resistance
`of which are connected (via screened cable) to the end
`terminals of the transformer T1. One of the end terminals
`of the operator’s finger to unbalance bridge circuits.
`A matrix of pairs of sensitive electrodes SP00, SPO1,
`(depending on the stray capacities) of the secondary
`SP02, SP03, SP10, SP11, SP12, SP13, SP20, SP21, SP22,
`winding of the transformer T1 is connected to earth via
`SP23, SP30, SP31, SP32 and P33 is connected in rows
`the capacitor C1 and the resistor R1 in series. The centre
`tap CTI of the secondary winding of the transformer
`to the secondary windings of two transformers T4 and
`TS in the following manner. One terminal of the second-
`T1 is connected to earth via the primary winding of
`the pulse transformer T2, as before. The secondary wind-
`ary winding of the transformer T4 is connected to the
`upper electrode of each of the pairs P00,.SP01, SP02
`ing of the transformer T2 is connected to a phase control
`unit P the output of which is connected to a phase sensi-
`and SP03 of sensitive electrodes in the. first row,
`the
`other terminal of the secondary winding of thetrans-
`tive detector PSD via an amplifier/limiter. The output
`former T4 is connected to the upper electrode of each
`of the phase sensitive detector PSD is applied to a com-
`of the pairs SP10, SP11, SP12 and SP13 of sensitive
`puter K which has an output applied to the display
`control DC.
`electrodes in the second row, one terminal of the second-
`The action of this circuit differs from that of the circuit
`ary winding of the transformer T5 is connected to the
`described with reference to FIGURE 1 in the fact that
`upper electrode of each of the pairs SP20, SP21,. SP22
`the bridge circuit RI-C1-T1 secondary—T2 primary may
`and SP23 of sensitive electrodes in the third row, and
`the other. terminal of the secondary winding of the. trans-
`be unbalanced by touching either of the sensitive elec-
`trodes SE1 or SE2. In each case the result will be an
`former TS is connected to the upper electrode of each
`output from the transformer T2 but the phase relation-
`of the pairs SP30, SP31, SP32 and SP33. of sensitive
`electrodes in the fourth row.
`ship of this output with the supply current S will be
`different for the two different electrodes SE1 and SE2.
`Similarly the matrix is connected in columns to the
`The function of the phase control P is to ensure that
`primary windings of two transformers T6 and T7 in
`the following manner. The lower electrode of each of
`the signal
`is in the correct phase to ensure a suitable
`the pairs SP00, SP10, SP20 and SP30 of sensitive elec-
`output from the phase sensitive detector after allowing
`trodes in the first column is connected to one terminal
`for stray phase shift throughout the system. The output
`of the primary winding of the transformer T6, the lower
`of the transformer T2 is applied from the phase control
`electrode of each of the pairs SP01, SP11, SP21 and
`P to the amplifier A and thence to the phase sensitive
`SP31 of sensitive electrodes in the second column is con-
`detector PSD where its phase is compared with that of
`the supply current S. The phase sensitive detector PSD
`nected to the other terminal of the primary winding of
`the transformer T6, the lower electrode of each of the
`has two outputs and these will therefore correspond sepa-
`rately to the two separate sensitive electrodes SE1
`pairs SP02, SP12, SP22 and SP32 of sensitive electrodes
`and SE2.
`in the third column is connected to one terminal of the
`Thus an output, indicating which sensitive electrode is
`primary winding of the transformer T7 and the lower
`touched, is applied to the computer K, where it is used
`electrode of each of the pairs SP03, SP13, SP23 and
`SP33 of sensitive electrodes in the fourth column is con-
`typically to set up a fresh display via the display con-
`trol DC.
`nected to the other terminal of the primary winding of
`the transformer T7.
`The remaining electrodes (SE3, etc.) are also con-
`nected in pairs to circuits similar to FIGURE 2 while
`The primary windings of the transformers T4 and T5
`for the sake of economy the amplifier A and phase sensi-
`are each excited by a high frequency source (say 3000
`tive detector may be time shared between the circuits.
`cycles per second). The primary winding of a transformer
`FIGURE3 is a circuit diagram of part of an alterna-
`T8 is connected between a centre tap on the secondary
`tive display incorporating a touch-sensitive system.
`In
`winding of the transformer T4 and earth and the primary
`this display a matrix M1 of pairs of sensitive electrodes
`winding of a transformer T9 is connected between a cen-
`such as SP1 is arranged on the display. All the upper
`tre tap on the secondary winding of the transformer TS :
`electrodes of each row are connected together to a posi-
`and earth. The secondary windings of the transformers
`tive voltage source via a commonresistor such as R11
`T8 and T9 are connected in series in a row interrogate
`wire RI.
`,
`and all the lower electrodes of each column are connected
`together to earth via a common resistor such as R21.
`The primary windings of the transformers T6 and T7
`The terminals remote from the positive voltage source of
`are each earth centre tapped. The secondary winding of
`the resistors (such as R11) associated with the upper
`the transformer T6 is connected across the primary wind-
`electrodes are connected to separate leads in a bundle
`ing of a transformer T10.and a switch SW1 is connected
`Li and the terminals remote from earth of the resistors
`across them both. The secondary winding: of the trans-
`(such as R21) associated with the lower electrodes are
`former T7 is ‘connected across the primary winding of a
`transformer T11 and a switch SW2 is connected across
`connected to separate leads in a bundle L2.
`When a pair of electrodes (such as the pair SP1) is
`them both. The secondary windings of the transformers
`T1060 and Til are connected in series in a column inter-
`touched by an operator a current will flow and this may
`be detected both by a voltage drop at the terminal remote
`rogate wire CI.
`is an extension of that de--
`The acion of the circuit
`from the positive voltage source of the corresponding
`resistor (such as R11) connected to the positive voltage
`scribed above with reference to FIGURE2; the touching
`source and a voltage rise at the terminal remote from
`of a pair of electrodes such as the pair SP12 will unbal-
`earth of the corresponding resistor (such as R21) con-
`ance two bridge circuits, namely in this case’the bridge
`nected to earth. This rise and fall in voltage may be
`circuit which includes the secondary winding of the trans-
`amplified,
`inverted and/or otherwise manipulated in a
`former T4 and the bridge circuit which includes the pri-
`_ known manner and a series of known gates connected
`mary winding of the transformer T7, the bridge circuits
`between pairs of wires of which one is from the bundle
`associated with the columns(i.e. the bridge circuits which
`L1 and one from the bundle L2. By this way which pair
`include the primary windings of the transformers T6 and
`of wires has been touched may be determined exactly.
`T7 respectively) being energised from the transformers
`Alternatively the rows of upper electrodes and the
`T4 and T5 via the capacitances between the electrodes of
`columns of lower electrodes may be connected to inde-
`the sensitive electrode paris SPO etc. The particular
`pendent systems each system being a set of circuits similar
`“row” and “column” bridges unbalanced and the direc-
`to FIGURE 2. An output simultaneously from row and
`tion of unbalance define exactly which pair of electrodes
`column system then indicates which pair of electrodes
`is touched. The result will be an A.C. signal having a
`has been touched.
`5
`given phase in the primary winding of one of the trans-
`
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`5
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`

`

`5
`formers T8 or T9 and an A.C. signal having a given
`phase in the primary winding of one of the transformers
`T10 or Til. In a time-shared system which bridge is un-
`balanced may be determined by shorting out the primary
`windings of the transformers T8 and T9 in turn and ob-
`serving when the signal in the row .interrogate wire RI
`disappears and similarly shorting out the primary wind-
`ings of the transformers T10 and T11 in turn and observ-
`ing when the signal in the. column interrogate wire CI
`disappears.
`This system may obviously be extended to a larger
`matrix of pairs of sensitive electrodes.
`FIGURE 5 is a diagrammatic representation of the
`logic steps taken in a processusing a data processing sys-
`tem and input and outputfacilities.
`In such a process the system may. be constantly: reas-
`sessing or revaluing a situation. (step 1) in the light of
`various data inputs. The result.of its. reassessment or re-
`valuation may be applied to the control of plant 3 (such as
`industrial plant) or.air traffic or some other situation.
`One data input. to the system may be from sensors or
`other automatic devices some of which.may be controlled
`by the plant 5. Another may be from other human opera-
`tors 7. Sooner or later the data process will reach a stage
`in which the system is programmed to ask: for human
`intervention and a display of choices is made 9.
`‘The
`human operator makes the choice 11 in the light of past
`experience 13 his senses (such as what he sees or hears)
`15 and so on. The choice is indicated to the system 17
`and becomes a further data input 19 and the process
`continues.
`It is obvious that the speed of such a process will de-
`pend upon the speed of the slowest step, that is, the step
`17. Gin a conventional system) and.
`the. invention is an
`attempt to overcomethis. speed limitation.
`The first idea underlying the design and operation of
`a touch display is that, no matter what the overall and
`complete range of possible signals from an operator might
`be, at any one time the signal actually sent by. the opera-
`tor to the data processing system will be one chosen
`from a strictly limited range. For example,
`the signal
`might be one of the ten numerical: digits. Possibly one of
`the widest range of choice ‘actually exercised would be
`to select one. from the twenty-six available: alphabetic
`characters. Secondly, in order that the system should be
`able to interpret the signal correctly, it must know from
`what range of possibilities it has: been chosen. and also
`what consequences must stem from that choice. This in-
`formation within the system .can therefore be used to
`restrict the range.of choice available to the operator at
`any given time to just those possibilities which are rele-
`vant to his present task.-Subsequent to any input signal
`being received the system can alter the range of choice
`as and when required. This control is, of course, exercised
`by the computer programmein the system and in conse-
`quence, the operation of the-touch display system can be
`described as programmed control.
`One consequence of this control is that the scope for
`operator errors, especially errors of omission, is signifi-
`cantly. reduced.
`Since the matter actually displayed on the electronic
`data display may be varied by the.system, the meaning
`of the touch wires (or the units of whatever touch sys-
`tem is in use)
`is variable. In other words, the display
`resembles an alpha-numeric keyboard in which the labels
`attached to the keys are not fixed but can be changed by
`the system computers in accordance with the required
`meaning at any time. The effect of this idea is far reach-
`ing. Not only does it allow the number of “keys” to be
`very limited whilst retaining a large measure of flexibility
`in their interpretation but also it allows the “meaning” of
`a key to be changed as a result of information previously
`fed to the system. A particular example is given below
`where one meaning attached to the keys is that of the
`“call signs” of theaircraft under control of a given opera-
`
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`3,482,241
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`6
`tor. These of course change quite often and normally con-
`sist of up to seven alpha-numeric symbols, By labelling
`“keys” in this way, communication with the system for a
`particular aircraft can be established in a single operation.
`The first requirement of a data input device based on
`the ideas outlined above. is a flexible display system, ca-
`pable of presenting the possible choices to an operator.
`Such a possibility is clearly available in an electronic
`data display for many applications. An extension to pro-
`vide some form of graphical display may be desirable
`in certain cases. The second requirement is to provide
`sensitive areas of the display screen which are capable of
`producing a signal when touched by a bare finger, Such
`an arrangement is described above.
`“,
`An example will be given of the use of the touch dis-
`play device in the amendment of flight plans in an Air
`Traffic Control system. In order to simplify the descrip-
`tion it will be assumed that the amendments. arise as a
`result of radio telephone reports from the aircraft.
`The sequence of events is as follows.
`Firstly, in the rest condition, ie., between. amendments
`the next action of the controller must logically be to refer
`to a particular aircraft, and the programmeof the data
`processing system is written to take this into account. The
`system already has the call signs of all the aircraft in
`the sector, and it therefore displays these call signs one
`against each touch wire.
`Secondly, when the aircraft calls and identifies itself
`by its call sign,
`the controller touches the wire against
`the call sign.
`This may be contrasted with the conventional present-
`day action in which the five to seven characters involved
`ate typed on a teleprinter, or the numberof the line on
`which the call sign is shown is read off and injected into
`an electronic data display.
`The computer has now been instructed as to which
`aircraft is involved and the computer programme is such
`that the controller must next specify which item of the
`flight plan is to be amended, The computer therefore
`displays on the top half of the touch-display the call
`sign selected followed by the items of the flight plan,
`each item consisting of its name and under the name the
`present value, Against
`the touch wires there are dis-
`played the namesof items, the pattern of the arrangement
`of the items being made the sameasin theflight plan dis-
`played above.
`The controller selects an item by touching the wire
`and the computer responds by marking the selected item
`and offering to the controller, against the touch wires,
`the list of possibilities for the first character of the value.
`If it is a numerical value the digits 0 to 9 may be offered
`but if the first digit is limited, as for a time in minutes
`to 5 then only 0 to 5 need be offered; on the other
`hand if the value is a symbol, then the appropriate sym-
`bols can be offered.
`The controller selects the character and the computer
`inserts this in the flight plan under the first character of
`the old value of the item and then, if the value consists
`of more than one character, the computer presents the
`possibilities for the next character and so on, until the new
`value of the item has been built up and displayed under
`the old value.
`The computer than asks the controller by words against
`the touch wires is this new value to be “executed” or
`“ignored”; the controller inspects the old and new values
`to see if the new value appears correct and credible and
`if so, by touching “execute,” instructs the computer, to in-
`corporate the new value.
`The computer then puts the display back to the initial
`reset condition to await the arrival of a new amendment.
`Various refinements can be added, for instance, “back-
`step” which cancels the previous input and restores the
`display to the previous condition; this gives a quick way
`of correcting input errors.
`
`6
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`

`

`3,482,241
`
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`has been actuated by determining in which of said rows
`and said columns said actuated contact meansis located.
`3. The apparatus defined in claim 1 wherein said
`means for generating visible images is a cathode ray
`tube and said viewing meansis a screen mounted on and
`responsive to said cathode ray tube.
`4. The apparatus defined in claim 1. wherein manual
`actuation of said touch sensitive contact means causes
`a capacitance charge across the actuated contact means
`andsaid sensing means comprises a means for detecting
`a capacitance change at each of said touch sensitive
`contacts.
`5. The apparatus defined in claim 4 wherein said means
`for detecting a capacitance change comprises a normally
`balanced alternating current bridge circuit adapted to
`be ‘unbalanced by a change in capacitance caused by
`actuation of one of said touch sensitive contacts.
`~
`6. The apparatus defined in claim 1 wherein each of
`said touch sensitive contact means incldue a first contact
`and a second contact and said sensing means comprises
`means for detecting a resistance change between said
`first and second contacts of the selected contact means.
`7. The apparatus defined in claim6 wherein said means
`for detecting a resistance change between said first and
`said second contacts of said selected contact means com-
`prises normally. balanced alternating current bridge means
`adapted to detect said resistance change.
`
`7
`the sequence
`According to the amendment required,
`can vary. One in particular with deserves special mention
`is the sequence for cancelling a flight plan.It is of course,
`very important that this does not happen by error and
`so when the controller uses the touch wire labelled
`“RRASE,” the computer is programmed to present the
`words “CONFIRM ERASURE OF KL104”for example.
`This illustrates the way in which the touch display can
`be used to alert the controller at critical phases in opera-
`tion.
`Of course other possible applications exist and if the
`display process has adequate flexibility to present solu-
`tions to a problem pictorially then by appropriate labelling
`of the touch wires corresponding to the. solution the
`choice can be indicated by a single operation. Again, an-
`other interesting possibility is the case of rarely used
`procedures, for example. EMERGENCY. Here the in-
`structions can be presented in plain language e.g., “alert
`fire brigade,” “you must now choose to do...
`. or to
`do
`.” and so on, The computer ensures that not
`only does thecontroller clearly understand what is to De
`done but ensures that no omissions occur.
`I claim:
`1. Apparatus for indicating to an output means which
`portion of a data-representing image on a viewing means
`has been selected for further processing comprising
`display means including means for generating visible
`images,
`input means connected to said means for
`generating visible images for altering said image on
`said display means and viewing means responsive to
`said generating means for displaying said visible
`10/1918 ~ Ghio.
`1,283,147
`images,
`7/1965 Diamond.
`3,194,975
`a plurality of touch sensitive contact means sensitive
`3,207,905.9/1965 Bray.
`to a change in impedance presented by touching by
`35
`3,307,071
`2/1967 Diamond.
`:
`the human body, said contact means being placed
`3,256,516 6/1966.Melia et al. .2-.--. 340—324.1
`
`adjacent said viewing means for indiacting which
`3,342,935
`9/1967 Leifer et al. -.--... 340-—324.1
`portion of the image on said viewing means has been
`3,399,401.
`8/1968 Ellis et al; _---__-__ 340—324.1
`selected, the position of said touch sensitive contact
`OTHER REFERENCES
`means selected with respect to said viewing means
`. Bezgin, Generation of X and Y Coordinate Informa-
`being related to the position of the selected portion
`of said image on said viewing means, and
`tion, IBM publication, vol. 1, No. 6, April 1959.
`sensing means for determining and indicating to said
`JOHNW. CALDWELL, Primary Examiner.
`output means which of said touch sensitive contacts
`has been activated.
`MARSHALL M. CURTIS, Assistant Examiner
`2. The apparatus defined in claim 1 wherein said plu-
`rality of touch sensitive contact means are arranged in
`US. Cl XR.
`rows and columns and said sensing means is adapted to
`determine which of said touch sensitive contact means
`
`References Cited
`UNITED STATES PATENTS
`
`25
`
`30
`
`40
`
`235—61.6; 340—365
`
`7
`
`