115
`United States Patent
`[11] Patent Number:
`4,561,002
`
`Chiu—itss—‘éCSDateofPatent:Dec.24,1985
`[45]
`Dec. 24, 1985
`Chiu
`
`[54] CAPACITIVE TOUCH SWITCH
`ARRANGEMENT
`
`[75]
`
`Inventor: Norman H.Chiu, Louisville, Ky.
`
`[73] Assignee: General Electric Company,
`Louisville, Ky.
`
`[21] Appl. No.: 412,737
`
`[22] Filed:
`Aug. 30, 1982
`[S51]
`Tint, C14 oe eescseneeeeeseneneeesenenes GO8C 9/00
`[52] U.S. Ch. eee eeeeeeeeeeeeteeeeee 340/365 C; 200/5 A;
`200/DIG. 1; 340/365 R
`[58] Field of Search........... 340/365 C, 365 E, 365 R,
`340/365 S, 365 A; 400/479.1; 200/DIG. 1,5 A;
`179/90 K; 219/10.77
`
`4,237,421 12/1980 Waldron ......... ec ceeeeeeee 340/365 C
`4,288,786
`9/1981 Ledniczki .... ee 340/365 C
`cceesseseeseenees 340/712
`4,290,061
`9/1981 Serrano ou...
`
`7/1983 Williams......
`.» 3407365 C
`4,394,643
`8/1983 Yamamoto...
`w 340/365 C
`4,398,181
`
`.. 340/365-G
`4,413,252 11/1983 Tyler ........
`
`4,415,781 11/1983 Frame...
`we 340/365 C
`
`4,441,097 4/1984 Anderson.....
`.. 340/365 A
`5/1984 Mizukawa.......eee 340/365 E
`4,446,350
`
`Primary Examiner—John W. Caldwell, Sr.
`Assistant Examiner—Michael F. Heim
`Attorney, Agent, or Firm-—H. Neil Houser; Radford M.
`Reams
`
`[57]
`
`ABSTRACT
`
`A capacitive attenuator type touch switch cell arrange-
`ment employs a touch responsive pad or electrode and
`a receiver electrode of comparable surface area on op-
`posing surfaces of a dielectric substrate for capacitive
`3,482,241 12/1969 JOHNSON .........ee eeeeeeeeeee 340/365 C
`coupling therebetween, which capacitive coupling is
`3,653,038
`3/1972 Webb 20.0...
`ceeseseeeereees 340/365 C
`alterable by the human touching of or proximate to the
`3,668,417
`6/1972 Sessler ........ecseetesseeee 340/365 C
`touch pad. A scansignal is coupled from signal generat-
`3,691,555
`9/1972 Looschen ..........csccsseseenees 340/365
`ing circuitry to the touch responsive pad by a separate
`
`3,750,149 7/1973 Sessler ........seescsseseeees 340/365 C
`transmitting capacitor. Signal detection circuitry senses
`3,786,495
`1/1974 Spence
`........cscsseseeeeees 340/365 C
`the signal coupled to the receiver electrode to detect
`3,846,791 11/1974 Foster 2...eeseseseseeee 340/365 C
`3,971,013
`7/1976 Challoneret al.
`.............. 340/337
`attenuation of the coupled signal signifying the touch-
`4,027,306
`5/1977 Hackmeister...
`340/365 C
`ing of the touch pad. The use of a separate capacitor to
`4,053,789 10/1977 Schultz oe
`eeeseteeeeeeeee 307/116
`provide the transmitting capacitance reduces the touch
`4,125,783 11/1978 Sefton oo...
`ceeenesecssereees 307/116
`pad area requirement, thereby permitting closer spacing
`4,136,291
`1/1979 Waldron...ee eeeeeeeceeees 307/308
`of touch switch cells for greater switch density on a
`4,145,748
`3/1979 Eichelbergeret al.
`............. 364/862
`control panel.
`4,157,539
`6/1979 Hunts et al. ............
`340/365 C
`4,221,975
`9/1980 Ledniczki ................0 340/365 C
`4,233,522 11/1980 Grummeretal. .................. 307/116
`
`[56]
`
`References Cited
`U.S. PATENT DOCUMENTS
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`10 Claims, 15 Drawing Figures
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`zs S/GNAL
`OETECTION
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`U.S. Patent Dec. 24, 1985
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`FIG./
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`U.S. Patent Dec. 24, 1985
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`Sheet20f5
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`PRIOR ART
`FIG. 2A
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`0 TOCONTROLLER
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`DETECTION
`LOG/C
`CIPCUITRY
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`PRIOR ART
`F/C.28B
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`to! on l4 36
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`PRIOR ART
`FIG.3A
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`DETECTION
`LOGIC.
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`CIRCUITRY
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`U.S. Patent Dee. 24, 1985
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`Sheet3 of5
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`DETECT/ON
`CIRCUITRY
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`TOUCH ZONE
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`SIGNAL
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`DETECTION
`CIRCUITRY
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`U.S. Patent Dec. 24, 1985
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`Sheet4of5
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`U.S. Patent Dec. 24, 1985
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`Sheet5of5
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`4,561,002
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`DETECTION
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`FIGC.68 —--~-3357
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`1
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`4,561,002
`
`CAPACITIVE TOUCH SWITCH ARRANGEMENT
`
`BACKGROUNDOF THE INVENTION
`
`5
`
`2
`home appliances, wherein switch cells can berelatively
`closely spaced.
`A further object of the invention is to provide a novel
`and improved capacitive touch switch arrangement as
`above described whichretains the good signal transfer
`invention relates to capacitive touch
`The present
`characteristics and reliable operation of the three plate
`switch arrangements and moreparticularly to a novel
`device but wherein the touch cells have relatively small
`touch switch arrangement employing only one elec-
`__area_ touch electrodes that can be relatively closely
`trode on the opposing surface of a dielectric substrate....-
`spaced.
`.
`opposite each touch electrode to accommodate a
`10.
`A further object of the inventionis to provide a novel
`greater number of touch electrodes in a given surface
`area.
`and improved capacitive touch switch arrangement as
`above described which is compatible with interface
`circuitry used with the three-plate device.
`SUMMARYOF THE INVENTION
`
`fs)
`
`Capacitive touch control panels are a well known
`means for providing user control inputs to various de-
`vices, including major home appliances such as cooking
`tanges and microwave ovens, which have capacitive
`The novel and improved capacitive attenuator type
`touch switches arranged in a keyboard array. With such
`touch switch cell arrangement in accordance with one
`touch panels, the user merely touches a touch area on
`aspect of the present invention employs a touch respon-
`the panelto initiate a switching action rather than mov-
`sive pad or electrode and a receiver electrode of compa-
`ing a mechanical switch.
`rable surface area on opposing surfaces of a dielectric
`Capacitive touch systems can generally be classified
`substrate for capacitive coupling therebetween, which
`in two types. In one, the switch cells each comprise a
`capacitive coupling is alterable by the human touching
`single capacitor formed of two conductive plates lo-
`of or proximate to the touch pad. A scan signal is cou-
`cated on a single surface of a dielectric material. The
`pled from signal generating circuitry to the touch re-
`capacitor is energized from a pulsating signal source
`sponsive pad by a separate transmitting capacitor. Sig-
`and is coupled to a signal detection circuit, the detected
`nal detection circuitry senses the signal coupled to the
`signal being a function of the capacitance which is
`receiver electrode to detect attenuation of the coupled
`changed in response to touch. The switch cell of the
`signal signifying the touching of the touch pad. The use
`other type of capacitive touch system each comprises
`of a separate capacitor to provide the transmitting ca-
`one pair of series connected capacitors formed of three ,
`pacitance reduces the touch pad area requirement,
`conductive plates, two closely spaced on one surface of
`thereby permitting closer spacing of touch switch cells
`a dielectric material and the third plate on the opposing
`for greater switch density on a control panel.
`surface overlapping the other twoplates. In this device,
`In accordance with a further aspect of the invention,
`the series connected capacitors, which are energized by
`a touch control panel comprising an array of touch
`an AC signal source, form a voltage divider arrange-
`switch cells of the above-described type is provided
`ment with the stray capacitance at the input to the sig-
`withafirst plurality of conductive paths, each connect-
`nal detector. Touching the third plate alters the capaci-
`ing a transmitting capacitorto its associated touch pad
`tive voltage divider arrangement, thereby changing the
`voltage level at the detection circuit as a function of
`fabricated on the outwardly facing surface of the sub-
`touch.
`strate. A second plurality of conductive paths is fabri-
`cated, each extending relatively closely adjacentat least
`This latter type of system is capable of good signal
`one ofsaid first conductive paths such that the human
`characteristics and an effective and reliable operation
`touching of one ofthe first conductive paths ordinarily
`when sufficient signal is capacitively coupled through
`results in the touching of at least one of the second
`the series capacitor pair of each device. Satisfactory
`operation generally requires some minimum value of
`conductive paths. The second conductive paths are
`commonly connectedto the junctionofa pair ofserially
`capacitance for the series capacitors, as well as rela-
`connected capacitors whereby the second paths actas a
`tively small parasitic capacitive effects. Since, for a
`“psuedo” touch pad. A test signal is applied to the seri-
`given dielectric material, the series capacitance is pro-
`ally connected capacitors in concert with the applica-
`portional to the capacitor plate area, presently known
`tion of each scan signal to the touch pads. The touching
`switch devices of the capacitance attenuator type for
`of one or more of the second paths attenuates the test
`practical appliance control applications have minimum
`signal. The signal detection circuitry senses the coupled
`area requirements that tend to preclude their applica-
`scan signal and the coupled test signal. Detection of
`tion to switch arrays needing a relatively large number
`of switch cells within the constraint ofa relatively small
`attenuation of the test signal overrides the detection of
`attenuation of the scan signal to prevent an erroneous
`panel surface area.
`control input which might otherwise result from the
`A touch panel arrangement which provides the per-
`inadvertent touching of the touch panel in the vicinity
`formance capability and employs the well developed
`of the first conductive paths.
`interfacing circuitry of the three-plate type of capaci-
`In accordance with yet another aspect of the inven-
`tive touch system but which is applicable to switch
`tion, the above-described touch switch cell arrange-
`array applications requiring a relatively large numberof
`ment further includes an outer dielectric panel which
`switch cells in a relatively small panel area would be
`highly desirable.
`overlays the dielectric substrate carrying the touch and
`receiver electrodes. Touch zones are depicted on the
`OBJECTS OF THE INVENTION
`outer panel in register with the underlying touch pads.
`Such an arrangement permits the use ofa thinner dielec-
`tric substrate and jess expensive circuit fabrication tech-
`niques, in addition to greater flexibility in designing the
`appearance of the control panel.
`
`It is accordingly an object of the invention to provide
`a novel and improvedcapacitive touch switch arrange-
`ment useful as a control panel for various devices re-
`quiring control inputs from human users such as major
`
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`3
`BRIEF DESCRIPTION OF THE DRAWINGS
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`4,561,002
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`While the specification concludes with claims which
`particularly point out and distinctly claim that subject
`matter whichis regarded as the invention,it is believed
`that the invention will be better understood and appre-
`ciated when considering the following detailed descrip-
`tion taken in conjunction with the accompanying draw-
`ings in which:
`FIG. 1 is a perspective view of a capacitive touch
`contro] panel for a kitchen appliance;
`FIG. 2Ais a sectional view of a capacitive attenuator
`type switch cell known in the priorart;
`FIG.2B is a schematic circuit diagram representing
`the equivalent circuit for the touch switch cell of FIG.
`2A;
`FIG. 3A is a sectional view of another capacitive
`attenuator type touch switch cell knownin the priorart;
`FIG.3B is a schematic circuit diagram representing
`the equivalent circuit for the touch switch cell of FIG.
`3A;
`FIG. 4A is a sectional view of a capacitive touch
`switch cell illustratively emboding the touch switch
`arrangement of the invention;
`FIG. 4B is a schematic circuit diagram representing
`the equivalent circuit for the touch switch cell of FIG.
`aA;
`FIG. 5A is a plan view of the touch electrodes and
`‘~ associated circuitry carried on the front side ofa dielec-
`tric substrate for a touch control panel of the type illus-
`trated in FIG. 1, in accordance with one embodimentof
`“the invention including a schematic diagram of the
`array of transmitting capacitors connected to the sub-
`strate circuitry;
`/
`FIG.5Bis a plan view of the receiver electrodes and
`associated circuitry carried on the rear side of the sub-
`strate of FIG. 5A;
`>". FIG. 6A is a simplified schematic circuit diagram
`“Gilustrating the incorporation of a touch switch arrange-
`“ment embodying the present invention in a control
`~ system for an appliance;
`* “FIG. 6B is a schematic circuit diagram illustrating
`certain details of a portion of the circuit diagram of
`FIG. 6A;
`FIG.7 is a timing diagram illustrating the scan signals
`employed in the circuit of FIG. 6;
`FIG.8Ais a sectional view of another embodiment of
`a capacitive touch switch arrangement in accordance
`with the invention;
`FIG. 8B is a schematic circuit diagram representing
`the equivalent circuit for the touch switch cell arrange-
`ment of FIG. 8A; and
`FIG. 9 is a partial perspective view of an alternate
`capacitive touch control panel for a kitchen appliance
`incorporating an illustrative embodiment of the switch
`arrangement of the invention.
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`'
`
`In FIG.1, there is illustrated a capacitive touch panel
`10 for controlling the four surface units of an electric
`cooking range. In the example to follow, a capacitive
`touch panel of the typeillustrated generally in FIG.1,
`is connected to a microprocessorthat controls the oper-
`ation of a kitchen range appliance. It is to be under-
`stood, however, that the illustrative capacitive touch
`panel has application to many other appliances and
`equipment subject to user control.
`
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`Capacitive touch panel 10 comprises an array of
`touch sensitive switch cells 12 responsive to the human
`touch which in accordance with the invention include
`relatively small area touch pads 13 which can be located
`on closely spaced centers providing the relatively high
`numberof switches in a relatively small panel area. In
`the illustrative example the touch pads enable the appli-
`ance user to select one or more surface heating elements
`and a powersettingforeach element.
`Forease ofillustration, the switch array is shown as
`a 4X6 matrix of six rows and four columns of touch
`sensitive switch cells 12 to provide ON, OFF and four
`powerlevel settings for each of four heating elements.
`It will be readily apparent that the switch array could
`be made larger or smaller as desired, depending upon
`the desired numberof control inputs.
`Thedescription to this point, except for the relatively
`small closely spaced touch pads, is generally applicable
`to capacitive touch panel arrays well known in theart.
`The switch cell arrangement commonly used in such
`prior art arrays is of the type referred to as a capacitive
`attenuator switch type in which the body capacitance of
`the user, which is added to the switch circuit when a
`touch padis touched, attenuates a scan signal, signifying
`to the associated control circuitry that the pad has been
`touched.
`Referring to FIG.2A,a prior art capacitive attenua-
`tor type switch cell arrangementis illustrated. The prior
`art switch cell designated 14 comprises a touch elec-
`trode 16 of conductive or semi-conductive material
`which is fabricated on the front or outwardly facing
`surface 17 of a dielectric substrate 18. A pair of elec-
`trodes or pads 20 and 22, commonly referred to as a
`transmitting electrode and a receiving electrode, re-
`spectively, are fabricated of a conductive or semi-con-
`ductive material upon the remaining inwardly facing
`surface 24 of substrate 18. Both transmitting and receiv-
`ing electrodes are typically of substantially smaller area
`than and are positioned substantially within the bound-
`aries of the area of touch pad 16. The closest points
`between transmitting and receiving electrodes 20 and 22
`are separated by a preselected distance d, while each of
`electrodes 20 and 22 are separated from touch pad 16 by
`a preselected dielectric thickness T derived in accor-
`dance with the insulating and structural characteristics
`to be achieved. Transmitting electrode 20 has an associ-
`ated conductor 26 coupled to a point thereon for con--
`nection of electrode 20 to a signal generator 28 config-
`ured to drive transmitting electrode 20 with a pulsating
`waveform. Receiver electrode 22 has an associated
`conductor 30 coupled to a point thereon for connection
`of electrode 22 to signal detection circuitry 32, which
`circuitry senses the signal coupled from electrode 20 to
`electrode 22 and detects the decrease in the magnitude
`ofthe signal resuliing from the body capacitance of the
`user being introduced into the circuit by a touch of
`touch pad 16.
`FIG.2Billustrates the equivalentelectrical circuit for
`switch cell arrangement of FIG. 2A. In this circuit,
`capacitance Cr represents the capacitance between
`electrode 20 and touch pad 16; capacitance Cr repre-
`sents the capacitance between touch pad 16 and elec-
`trode 22; and capacitance Crp represents the cross cou-
`pled capacitance between electrode 20 and electrode
`22. The human touching of pad 16 is represented sche-
`matically as the closing of switch 34, with Cg represent-
`ing the body capacitance of the user which is switched
`into the circuit by touching to act as a shunt to ground
`
`8
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`

`5
`whichis effective to attentuate the signal at Point A. Cp
`represents stray parasitic capacitance.
`In order to insure proper switch operation, the capac-
`itance of the series capacitors C7 and Cr formed by
`electrodes 20 and 22, respectively, in cooperation with
`touch pad 16, must be sufficient to reliably couple the
`pulsating signal from signal generator 28 to the detec-
`tion circuitry 32. The larger the coupling capacitance,
`the greater the current flow which in turn reduces the
`susceptibility to noise.
`The capacitance of the capacitors Cr and Cr may be
`determined in accordance with the well known for-
`mula:
`
`_ 25KXA
`c=
`r
`
`when
`C=capacitance (picofarads)
`K =dielectric constant of substrate
`A=commoncapacitor plate area (sq. in.)
`T=substrate thickness (in.)
`|
`The total coupling capacitance should be on the
`order of 2-5 picofarads (pF). This means Cr and Cr
`should each be on the order of 4-10 pF. As an example
`for coupling capacitance on the orderof 3.5 pF, Cand
`Cr would each be on the order of 7 pF. For a typical
`glass substrate having a thickness of4 inch, and a dielec-
`tric constant of 8, the minimum area for each of elec-
`trodes 20 and 22 would be on the order of 0.5 in2. In
`order to minimize the cross coupled capcitance Crp, a
`minimum spacing between electrodes 20 and 22 on the
`order of 3 inch is recommended. Since touch pad 16
`must substantially cover both electrodes, a touch pad
`area in excess of 1 square inch would be required for
`each touch pad.
`An alternative touch switch cell arrangement in the
`prior art which mayincrease the capacitance somewhat
`for a given pad area is shown in FIG. 3A, designated
`14’. In this arrangement an additional dielectric outer
`panel 36 overlies the substrate carrying the touch pad
`and electrodes. Because of the additional rigidity of
`outer panel 36, the dielectric substrate 18’ carrying the
`touch pad 16’ and electrodes 20’ and 22’ may be of
`reduced thickness which in accordance with the above-
`described formula provides increased capacitance for
`the same plate areas. Those elements of FIGS. 3A and
`3B carrying the (‘) designator function in the same man-
`ner as their counterparts in FIGS. 2A and 2B having the
`same numerical designators. Touch pad 16’ and the
`transmitter and receiver electrodes 20’ and 22’, respec-
`tively, are driven by signal generator 28’ and the cou-
`pled signal is sensed by detection circuitry 32'. The
`major difference functionally is illustrated in the equiva-
`lent circuit schematically represented in FIG. 3B,
`where outer panel 36 provides an additional capaci-
`tance Cg in series with the body capacitance Cz of the
`user in the short path to ground when pad 16’
`is
`touched, as represented in FIG. 2B by the closure of
`switch 34’.
`While the reduced thickness for substrate 18’ enabled
`by the additional structural rigidity provided by outer
`panel 36, provides greater capacitance for the same pad
`and electrode areas, the additional capacitance effect of
`the glass outer panel 36 reduces the attenuative effect of
`the touch on the coupling capacitance, thereby requir-
`ing greater capacitance for capacitances Crand Cr than
`that for the touch cell of the FIG. 2A type in order for
`
`4,561,002
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`6
`the detection circuitry to operate effectively at the same
`sensitivity level.
`When a large number of touch pads are desired in a
`relatively small panel area, it is apparent that the mini-
`mum electrode and touch pad areas required to provide
`the minimum capacitance presents a significant design
`limitation for conventional capacitive attenuator type
`switch cells of either of the aforementioned type.
`Since in either arrangement, both receiver and trans-
`mitter electrodes must share the touch pad, the touch
`pad area required to provide the minimum capacitance
`for each of the series capacitances C7 and Cr must be
`more than twice that required for the transmitting or
`receiving electrode alone.
`The capacitive touch switch cell arrangement con-
`templated in the present invention allows the touch pad
`size to be reduced by more than 50 percent without
`sacrificing coupling capacitance and also eliminates any
`problems presented by the cross-coupling capacitance
`between transmitter and receiver electrodes. This im-
`provement is achieved by removing the transmitter
`electrode from the substrate and replacing it with a
`discrete capacitor separate from the touch pad and the
`receiver electrode. By this arrangement, the required
`touch pad area can be reduced to the area of the re-
`ceiver electrode alone without reducing the capaci-
`tance of the resulting receiver capacitance. An addi-
`tional advantage of the discrete transmitter capacitoris
`the resultantflexibility to choose any capacitance value
`during the keyboard tuning and trimming process.
`Referring now to FIGS. 4A and 4B,an illustrative
`embodiment of a touch switch cel] 40 in accordance
`with the invention comprises a conductive touch pad 42
`fabricated on the outwardfacing surface 44 of dielectric
`substrate 46, and a conductive receiver electrode 48
`formed on the opposite surface 50 of substrate 46 in an
`area overlying and bounded by the area of touch pad 42
`to enable the capacitive coupling of a signal from pad 42
`to receiver electrode 48. A discrete capacitor 52 capaci-
`tively couples the pulsating signal from signal generator
`54 to pad 42 via conductor 56 a substantial portion of
`which is formed on surface 44 of substrate 46. Receiv-
`ing electrode 48 has an associated. conductor 49 coupled
`to a point thereon for connection of electrode 48 to
`detection circuitry 58. Detection circuitry 58 senses the
`signal at point A as in FIG. 2A to detect the change in
`the signal at A resulting from the human touching of
`pad 42.
`The equivalent circuit for the touch switch cell ar-
`rangement ofthe present inventionis illustrated in FIG.
`4B. In this circuit receiver capacitor Cr is formed by
`touch pad 42 and receiver electrode 48. However, the
`function of the transmitter capacitor (Cryin FIG. 2B)is
`performed in this arrangement by discrete capacitor 52.
`Asin FIG. 2B, the introduction of user body capaci-
`tance by touching of touch pad 42 is represented by
`switch 34 and capacitor Cp.
`Since only the receiver capacitor Cr uses pad 42 as a
`plate thereof, pad 42 need only be large enough to cover
`electrode 48. For the same glass substrate and minimum
`capacitance requirements described with reference to
`FIG.2A, touch pad 42 need be only on the order of 0.5
`square inch rather than the 1.0 square inch of the con-
`ventional arrangement.
`Having described an illustrative embodiment of an
`individual touch switch cell, reference is now made to
`FIGS. 5A and 5B to describe an array of such cells 40
`such as might be used for a touch panel 10 of FIG.1.
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`4,561,002
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`FIG.5A schematically illustrates the outer face 44 of
`a dielectric substrate 46 for a touch panel on which a
`4 6 array of conductive touch pads 42 are fabricated in
`a layoutsimilar to that of the touch panel of FIG. 1. For
`clarity and simplicity, only two rows of the array are
`shownin FIGS. 5A and 5B.It is to be understood that
`each of the omitted rows is structurally identical to
`those shown. Each touch pad 42 has associated with it
`a conductive path or run 56 which is formed on surface
`44 extending substantially parallel
`to the horizontal
`rows of touch pads to an associated terminal point 60
`near edge 62 of substrate 46. A plurality of separate
`discrete transmitter capacitors 52 are provided with one
`capacitor 52 associated with each touch pad. Capacitors
`52 can be combinedinto anelectrical circuit that can be
`located off of substrate 46, with a flex circuit connection
`comprising silver conductor runs fabricated on a sub-
`strate of Mylar ® material coupling one plate 64 of each
`capacitor 52 to terminal point 60 for its associated touch
`pad. The four capacitors 52 for each row of pads 42
`each havetheir other plate 66 commonly connected to
`simultaneously receive the scan signal for their row
`from the external scan signal generating circuitry at
`input terminal 68.
`The opposite surface 50 of substrate 44 is schemati-
`cally illustrated in FIG. 5B. Surface 50 has fabricated
`thereon a 4x6 array of receiver electrodes or pads 48,
`one for each of the touch pads 42. Each of receiver
`- electrodes 48 are positioned in the area overlying and
`bounded by the area ofits associated touch pad 42 to
`form a 4x6 array of touch switch celis 40 of the type
`illustrated in FIG. 4A. The receiver electrodes 48 in
`~gach column are serially connected by a conductive
`' path 49 with each column of receiver electrodes being
`coupled to the signal detection circuitry 58.
`Referring again to FIG. 5A, since conductors 56 are
`formed on the outward surface 44 of substrate 46 along
`.. with touch pads 42, it is possible for a user to inadver-
`*
`tently touch one or moreof these conductive paths. The
`direct touching of one of conductors 56 would have an
`attenuating effect similar to the touching of the pad
`-associated with the touched conductor. Thus,
`the
`touching of a region of substrate surface 44 carrying
`conductors 56 would appear to detecting circuitry 58 as
`the touching of the pad associated with the touched
`conductor.
`In order to prevent the control system from respond-
`ing to the resulting erroneous signal, a second plurality
`of conductive paths or runs 70 are formed on surface 44
`of substrate 46 such that each of the first conductive
`paths 56 hasat least one of these second paths 70 closely
`adjacent to it. The spacing between adjacentsections of
`paths 56 and 70 is selected such that the human touching
`of one path would also ordinarily result in the touching
`of the other path as well. Each of the paths 70 is con-
`nected at one end to a terminal point 72 whichis electri-
`cally connected through substrate 46 to terminal points
`71 formed on opposite surface 50 of substrate 46.
`A capacitor network 74, comprising a pair of serially
`connected discrete capacitors 75 and 76, which may be
`mounted on surface 50 of substrate 44 or separately
`from substrate 44, is coupled to conductive paths 70 by
`conductive runs 73 formed on surface 50 joining termi-
`nal points 71. All conductive paths 70 are commonly
`connected via paths 73 to the junction 82 ofserially
`connected capacitors 75 and 76. This arrangement ena-
`bles conductors 70 to function asa “‘psuedo touch pad.”
`Capacitive network 74 is serially connected between
`
`“
`
`8
`the signal generator circuitry 90 (FIG. 6A) and the
`signal detector circuitry 58. A scan or test pulse from
`the signal generator circuitry is applied to input 80 of
`network 74 simultaneously with each scan pulse applied
`to one of the touch pad rows. The touching of any
`portion of conductive path 70 results in the attenuation
`of the signal coupled by capacitive network 74 to point
`84 just as the touching of a touch pad attentuates the
`signal coupled to the associated receiver electrode for
`that touch pad.
`Aswill be described in greater detail hereinafter, the
`logic circuitry of detection circuitry 58 is arranged such
`that detection of an attenuated signal at output terminal
`84 of capacitor network 74takes priority over any other
`input to the detection circuitry. The output of any other
`signal to the control system signifying the touching of a
`touch padis thus prevented. Since the relative position-
`ing of conductive runs 56 and 70 is such that touching of
`one of runs 56 would ordinarily be accompanied by the
`touching of runs'70 as well, the control system does not
`respond to the inadvertent touching of any portion of
`the panel except the touch pads.
`In the illustrative embodiment of FIGS. 5A and 5B,
`the dielectric substrate 46 is a glass panel having a 4"
`nominal thickness. A greater or lesser thickness could of
`course be used with the understanding that coupling
`capacitance between pad 42 and electrode 48 is in-
`versely proportional to thickness. Also, a thinner glass
`pane] may not provide the desired structural rigidity.
`Top pads 42 and conductive paths 56 and 70 formed on
`surface 44 may be formed by depositing tin oxide on the
`glass in the desired pattern. The glass plate would then
`be baked at high temperature to passivate the tin oxide
`into the glass. The resultant passivated tin oxide pattern
`is resistant to cleaning and scouring of the panel. Re-
`ceiver electrodes 48 and conductors 49 and 73 formed
`on inner surface 50 may be inexpensively formed with
`silver epoxy. To minimize stray capacitanceeffects, the
`width of conductive paths 49, 56, 70, and 73 should be
`held to a minimum.
`Illustrative control circuitry for incorporating the
`touch panel of FIGS. 5A and 5B into a control system
`for an appliance such as an electric cooking rangeis
`illustrated schematically in FIG. 6A.
`In theillustrative control circuit of FIG. 6A, micro-
`processor 90 sequentially generates a scan pulse at each
`of outputs Ro-Rs, which outputs are coupled to rows
`a-f of the capacitive touch cell array 10 of FIGS. 5A
`and 5B via driver circuitry 92 and capacitor banks 94(a-
`)-94(/), respectively. A test signal is generated at Ko
`simultaneously with each scan pulse which is coupled
`by driver circuit 92 to capacitive network 74, to provide
`the hereinbefore described prevention of erroneous
`signals from touching conductive paths on the control
`panel rather than the touch pads.
`Columns g-j of the touch cell array are coupled to
`inputs Cs~C3, respectively, of detection circuitry 58 via
`limiting resistors 114. The output of capacitive network
`74 is similarly coupled to input Ci of detection circuitry
`58. A BCD coded output signal from circuitry 58 is
`coupled to inputs Kj, K2, K4and Kg of microprocessor
`
`Circuitry 58 senses the scan signal coupled by each of
`the touch cells in the row being scanned to their respec-
`tive column output lines 49 to detect an attenuation of
`the column output line signal, signifying that a touch
`pad in a particular column has been touched.If a touch
`pad in the row being scanned is touched, the signal
`
`— 0
`
`5
`
`40
`
`45
`
`60
`
`65
`
`-
`
`10
`
`10
`
`

`

`_ 5
`
`20
`
`25
`
`35
`
`40
`
`45
`
`9
`the attenuation of the
`detector circuit will detect
`scanned signal for that column containing the touched
`pad. The BCD coded output signal coupled to micro-
`processor 90 indicates which column,if any, contains a
`touched pad. In this fashion, a touched padis identified
`by row and column.
`In theillustrative embodiment, microprocessor 90 is a
`TMS1670 microprocessor commercially available from
`Texas Instruments Incorporated, which can be custom-
`ized by permanently configuring its read only memory
`(ROM) to implement
`the desired appliance control
`scheme. A portion of the ROM of microprocessor 90 is
`configured in a conventional manner to generate the
`capacitive touch keyboard drive signals and to receive
`keyboard output signals from conventional detection
`circuitry. The keyboard drive signals in this arrange-
`ment are scan pulses provided sequentially at outputs
`Ro-Rs of microprocessor 90. A test pulse is generated at
`output Kp of microprocessor 90 simultaneously with
`each scan pulse. These pulses are coupled to conven-
`tional keyboard driver circuitry 92 which inverts and
`amplifies the outputs from Ro-Rs to shape well defined
`negative going 30 volt scan pulses. Driver circuitry 92
`also serves as a buffer to isolate the keyboard from the
`electronic circuitry.
`A representative portion of typical driver circuitry is
`shown in FIG. 6B for coupling output Ro to the touch
`panel. Output Ro