United States Patent (19)
`Chiu
`
`Patent Number:
`11
`45) Date of Patent:
`
`4,561,002
`Dec. 24, 1985
`
`56)
`
`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
`51) Int. Cl................................................. G08C 9/00
`52 U.S. C. ............................... 340/365 C; 200/5A;
`200/DIG. 1; 340/365 R
`58) Field of Search ........... 340/365 C, 365 E, 365 R,
`340/365 S, 365A; 400/479.1; 200/DIG. 1,5A;
`179/90 K; 219/10.77
`References Cited
`U.S. PATENT DOCUMENTS
`3,482,241 12/1969 Johnson .......................... 340/365 C
`3,653,038 3/1972 Webb .............................. 340/365 C
`3,668,47 6/1972 Sessler ............................. 340/365 C
`3,69,555 9/1972 Looschen ............................ 340/365
`3,750,149 7/1973 Sessler ............................. 340/365 C
`3,786,495 1/1974 Spence ............................ 340/365 C
`3,846,791 1/1974 Foster ............................. 340/365 C
`3,971,013 7/1976 Chaloner et al. .................. 340/337
`4,027,306 5/1977 Hackmeister ...
`340/365 C
`4,053,789 10/1977 Schultz ................................ 307/16
`4,125,783 1/1978 Sefton ................................. 307/116
`4,136,291 1/1979 Waldron ............................. 307/308
`4,145,748 3/1979 Eichelberger et al. ............. 364/862
`4,157,539 6/1979 Hunts et al.............
`... 340/365 C
`4,221,975 9/1980 Ledniczki ....................... 340/365 C
`4,233,522 11/1980 Grummer et al. .................. 307/116
`
`4,237,421 12/1980 Waldron ......................... 340/365 C
`4,288,786 9/1981 Ledniczki .
`... 340/365 C
`4,290,061 9/1981 Serrano ............................... 340/712
`4,394,643 7/1983 Williams ......
`... 340/365 C
`4,398,181 8/1983 Yamamoto ...
`... 340/365 C
`4,413,252 11/1983 Tyler ............
`... 340/365-C
`4,415,781 11/1983 Frame ......
`... 340/365 C
`4,441,097 4/1984 Anderson .....
`... 340/365A
`4,446,350 5/1984 Mizukawa ....................... 340/365 E
`Primary Examiner-John W. Caldwell, Sr.
`Assistant Examiner-Michael F. Hein
`Attorney, Agent, or Firm-H. Neil Houser; Radford M.
`Reams
`ABSTRACT
`57
`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
`coupling therebetween, which capacitive coupling is
`alterable by the human touching of or proximate to the
`touch pad. A scan signal is coupled from signal generat
`ing circuitry to the touch responsive pad by a separate
`transmitting capacitor. Signal detection circuitry senses
`the signal coupled to the receiver electrode to detect
`attenuation of the coupled signal signifying the touch
`ing of the touch pad. The use of a separate capacitor to
`provide the transmitting capacitance reduces the touch
`pad area requirement, thereby permitting closer spacing
`of touch switch cells for greater switch density on a
`control panel.
`
`10 Claims, 15 Drawing Figures
`
`
`
`
`
`
`
`
`
`
`
`Awaa
`Calify
`
`is
`
`SAGava.
`avacAoAv
`
`
`
`
`
`&
`
`

`

`U.S. Patent Dec. 24, 1985
`U.S. Patent Dec. 24, 1985
`
`Sheet 1 of 5
`Sheetlof5
`
`4,561,002
`4,561,002
`
`A 76. /
`F/G./
`
`
`
`
`
`if
`1|77 PF
`
`
`
`8n
`
` iENG
`
`y
`
`

`

`U.S. Patent Dec. 24, 1985
`
`Sheet 2 of5
`
`4,561,002
`
`
`
`
`
`
`PRIOR ART
`F/G. 2A
`
`0 TOCONTROLLER
`
`
`
`
`
`DETECT/ON
`L0G/C
`C/RPCUITRY
`
`0 TO CONTROLLER
`
`PRIOR ART
`F/G. 2B
`
`
`
`
`
`.
`
`/4'
`/
`~~ 32/
`
`20! !
`
`|
`
`/@;,
`
`carat
`
`|
`
`DETECTION
`22
`LOGIC.
`|
`
`
`C/RCU/TRY |.
`
`° TOCONTROLLER
`
`PRIOR ART
`FIG. GA
`
`0 TOCONTROLLER
`
`PRIOR ART
`F/G. 38
`
`

`

`U.S. Patent Dec.24,1985
`
` Sheet30f5
`
`4,561,002
`
`
`
`FIG. 4A
`
`
`
`S/GNAL
`DETECTION
`C/RCUITRY
`
`“SIGNAL
`
`DETECTION
`
`
`‘CIRCUITRY
`
`.
`
`-
`
`/
`/
`---+-+# 48
`| a, DETECTION|—o
`|
`aCc
`|
`C/RCUITRY
`So! Ll 91
`
`S/GNAL
`
`

`

`U.S. Patent Dec. 24, 1985
`
`Sheet 4 of 5
`
`4,561,002
`
`
`
`S/GMMA. AA7AC 7OAp
`/APCOM/7
`
`

`

`U.S. Patent Dec. 24, 1985
`
`Sheet5of5
`
`4,561,002
`
`F/G.6A
`
`90
`
`58
`
`2
`
`
`4 CIRCUITRY
`2 1976
`
`
`
`
`
`

`

`1.
`
`CAPACTIVE TOUCH SWITCH ARRANGEMENT
`
`BACKGROUND OF THE INVENTION
`The present invention relates to capacitive touch
`switch arrangements and more particularly to a novel
`touch switch arrangement employing only one elec
`trode on the opposing surface of a dielectric substrate.
`opposite each touch electrode to accommodate a
`greater number of touch electrodes in a given surface
`aca.
`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
`15
`ranges and microwave ovens, which have capacitive
`touch switches arranged in a keyboard array. With such
`touch panels, the user merely touches a touch area on
`the panel to initiate a switching action rather than mov
`ing a mechanical switch.
`20
`Capacitive touch systems can generally be classified
`in two types. In one, the switch cells each comprise a
`single capacitor formed of two conductive plates lo
`cated on a single surface of a dielectric material. The
`capacitor is energized from a pulsating signal source
`25
`and is coupled to a signal detection circuit, the detected
`signal being a function of the capacitance which is
`changed in response to touch. The switch cell of the
`other type of capacitive touch system each comprises
`one pair of series connected capacitors formed of three
`30
`conductive plates, two closely spaced on one surface of
`a dielectric material and the third plate on the opposing
`surface overlapping the other two plates. In this device,
`the series connected capacitors, which are energized by
`an AC signal source, form a voltage divider arrange
`ment with the stray capacitance at the input to the sig
`nal detector. Touching the third plate alters the capaci
`tive voltage divider arrangement, thereby changing the
`voltage level at the detection circuit as a function of
`touch.
`40
`This latter type of system is capable of good signal
`characteristics and an effective and reliable operation
`when sufficient signal is capacitively coupled through
`the series capacitor pair of each device. Satisfactory
`operation generally requires some minimum value of 45
`capacitance for the series capacitors, as well as rela
`tively small parasitic capacitive effects. Since, for a
`given dielectric material, the series capacitance is pro
`portional to the capacitor plate area, presently known
`switch devices of the capacitance attenuator type for
`50
`practical appliance control applications have minimum
`area requirements that tend to preclude their applica
`tion to switch arrays needing a relatively large number
`of switch cells within the constraint of a relatively small
`panel surface area.
`55
`A touch panel arrangement which provides the per
`formance capability and employs the well developed
`interfacing circuitry of the three-plate type of capaci
`tive touch system but which is applicable to switch
`array applications requiring a relatively large number of 60
`switch cells in a relatively small panel area would be
`highly desirable.
`OBJECTS OF THE INVENTION
`It is accordingly an object of the invention to provide
`a novel and improved capacitive touch switch arrange
`ment useful as a control panel for various devices re
`quiring control inputs from human users such as major
`
`4,561,002
`2
`home appliances, wherein switch cells can be relatively
`closely spaced.
`A further object of the invention is to provide a novel
`and improved capacitive touch switch arrangement as
`above described which retains the good signal transfer
`characteristics and reliable operation of the three plate
`device but wherein the touch cells have relatively small
`area touch electrodes that can be relatively closely
`spaced.
`A further object of the invention is to provide a novel
`and improved capacitive touch switch arrangement as
`above described which is compatible with interface
`circuitry used with the three-plate device.
`SUMMARY OF THE INVENTION
`The novel and improved capacitive attenuator type
`touch switch cell arrangement in accordance with one
`aspect of the present invention employs a touch respon
`sive pad or electrode and a receiver electrode of compa
`rable surface area on opposing surfaces of a dielectric
`substrate for capacitive coupling therebetween, which
`capacitive coupling is alterable by the human touching
`of or proximate to the touch pad. A scan signal is cou
`pled from signal generating circuitry to the touch re
`sponsive pad by a separate transmitting capacitor. Sig
`nal detection circuitry senses the signal coupled to the
`receiver electrode to detect attenuation of the coupled
`signal signifying the touching of the touch pad. The use
`of a separate capacitor to provide the transmitting ca
`pacitance reduces the touch pad area requirement,
`thereby permitting closer spacing of touch switch cells
`for greater switch density on a control panel.
`In accordance with a further aspect of the invention,
`a touch control panel comprising an array of touch
`switch cells of the above-described type is provided
`with a first plurality of conductive paths, each connect
`ing a transmitting capacitor to its associated touch pad
`fabricated on the outwardly facing surface of the sub
`strate. A second plurality of conductive paths is fabri
`cated, each extending relatively closely adjacent at least
`one of said first conductive paths such that the human
`touching of one of the first conductive paths ordinarily
`results in the touching of at least one of the second
`conductive paths. The second conductive paths are
`commonly connected to the junction of a pair of serially
`connected capacitors whereby the second paths act as a
`"psuedo' touch pad. A test signal is applied to the seri
`ally connected capacitors in concert with the applica
`tion of each scan signal to the touch pads. The touching
`of one or more of the second paths attenuates the test
`signal. The signal detection circuitry senses the coupled
`scan signal and the coupled test signal. Detection of
`attenuation of the test signal overrides the detection of
`attenuation of the scan signal to prevent an erroneous
`control input which might otherwise result from the
`inadvertent touching of the touch panel in the vicinity
`of the first conductive paths.
`In accordance with yet another aspect of the inven
`tion, the above-described touch switch cell arrange
`ment further includes an outer dielectric panel which
`overlays the dielectric substrate carrying the touch and
`receiver electrodes. Touch zones are depicted on the
`outer panel in register with the underlying touch pads.
`Such an arrangement permits the use of a thinner dielec
`tric substrate and less expensive circuit fabrication tech
`niques, in addition to greater flexibility in designing the
`appearance of the control panel.
`
`O
`
`35
`
`65
`
`

`

`3
`BRIEF DESCRIPTION OF THE DRAWINGS
`While the specification concludes with claims which
`particularly point out and distinctly claim that subject
`matter which is regarded as the invention, it is believed 5
`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 10
`control panel for a kitchen appliance;
`FIG. 2A is a sectional view of a capacitive attenuator
`type switch cell known in the prior art;
`FIG. 2B is a schematic circuit diagram representing
`the equivalent circuit for the touch switch cell of FIG. 15
`2A;
`FIG. 3A is a sectional view of another capacitive
`attenuator type touch switch cell known in the prior art;
`FIG. 3B is a schematic circuit diagram representing
`the equivalent circuit for the touch switch cell of FIG. 20
`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 25
`the equivalent circuit for the touch switch cell of FIG.
`4A;
`FIG. 5A is a plan view of the touch electrodes and
`associated circuitry carried on the front side of a dielec
`tric substrate for a touch control panel of the type illus- 30
`trated in FIG. 1, in accordance with one embodiment of
`the invention including a schematic diagram of the
`array of transmitting capacitors connected to the sub
`strate circuitry;
`FIG. 5B is a plan view of the receiver electrodes and 35
`associated circuitry carried on the rear side of the sub
`strate of FIG. 5A;
`FIG. 6A is a simplified schematic circuit diagram
`*illustrating the incorporation of a touch switch arrange
`"ment embodying the present invention in a control 40
`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 45
`employed in the circuit of FIG. 6;
`FIG. 8A is 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 50
`the equivalent circuit for the touch switch cell arrange
`ment of FIG. 8A; and
`W
`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 55
`arrangement of the invention.
`DETALEED DESCRIPTION OF THE
`INVENTION
`In FIG. 1, there is illustrated a capacitive touch panel 60
`10 for controlling the four surface units of an electric
`cooking range. In the example to follow, a capacitive
`touch panel of the type illustrated generally in FIG. 1,
`is connected to a microprocessor that controls the oper
`ation of a kitchen range appliance. It is to be under- 65
`stood, however, that the illustrative capacitive touch
`panel has application to many other appliances and
`equipment subject to user control.
`
`4,561,002
`4.
`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
`number of 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 power setting for each element.
`For ease of illustration, 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
`power level 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 number of control inputs.
`The description to this point, except for the relatively
`small closely spaced touch pads, is generally applicable
`to capacitive touch panel arrays well known in the art.
`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
`touchpad is 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 arrangement is 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 distanced, while each of
`electrodes 20 and 22 are separated from touchpad 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
`of the signal resulting from the body capacitance of the
`user being introduced into the circuit by a touch of
`touch pad 16.
`FIG.2B illustrates the equivalent electrical circuit for
`switch cell arrangement of FIG. 2A. In this circuit,
`capacitance CT 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 CTR 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 CB represent
`ing the body capacitance of the user which is switched
`into the circuit by touching to act as a shunt to ground
`
`

`

`10
`
`15
`
`20
`
`225 K X A
`C = --
`
`4,561,002
`6
`5
`the detection circuitry to operate effectively at the same
`which is effective to attentuate the signal at Point A. Cp
`sensitivity level.
`represents stray parasitic capacitance.
`When a large number of touch pads are desired in a
`In order to insure proper switch operation, the capac
`relatively small panel area, it is apparent that the mini
`itance of the series capacitors CT and CR formed by
`mum electrode and touch pad areas required to provide
`electrodes 20 and 22, respectively, in cooperation with
`the minimum capacitance presents a significant design
`touch pad 16, must be sufficient to reliably couple the
`limitation for conventional capacitive attenuator type
`pulsating signal from signal generator 28 to the detec
`tion circuitry 32. The larger the coupling capacitance,
`switch cells of either of the aforementioned type.
`Since in either arrangement, both receiver and trans
`the greater the current flow which in turn reduces the
`susceptibility to noise.
`mitter electrodes must share the touch pad, the touch
`pad area required to provide the minimum capacitance
`The capacitance of the capacitors CT and CR may be
`for each of the series capacitances CT and CR must be
`determined in accordance with the well known for
`more than twice that required for the transmitting or
`mula:
`receiving electrode alone.
`The capacitive touch switch cell arrangement con
`templated in the present invention allows the touchpad
`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 capacitor is
`the resultant flexibility 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 cell 40 in accordance
`with the invention comprises a conductive touch pad 42
`fabricated on the outward facing 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 touchpad 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 of the present invention is 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 (Crin FIG. 2B) is
`performed in this arrangement by discrete capacitor 52.
`As in FIG. 2B, the introduction of user body capaci
`tance by touching of touch pad 42 is represented by
`switch 34 and capacitor CB.
`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, touchpad 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.
`
`when
`C= capacitance (picofarads)
`K= dielectric constant of substrate
`A=common capacitor plate area (sq. in.)
`T=substrate thickness (in.)
`The total coupling capacitance should be on the
`order of 2-5 picofarads (pF). This means CT and CR
`should each be on the order of 4-10 pF. As an example
`25
`for coupling capacitance on the order of 3.5 pf, CT and
`CR would each be on the order of 7 pF. For a typical
`glass substrate having a thickness of 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
`30
`order to minimize the cross coupled capcitance CTR, a
`minimum spacing between electrodes 20 and 22 on the
`order of 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
`35
`each touch pad.
`An alternative touch switch cell arrangement in the
`prior art which may increase the capacitance somewhat
`for a given pad area is shown in FIG. 3A, designated
`14. In this arrangement an additional dielectric outer
`40
`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
`45
`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
`50
`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,
`55
`where outer panel 36 provides an additional capaci
`tance Co. in series with the body capacitance CB 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.
`60
`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
`65
`the touch on the coupling capacitance, thereby requir
`ing greater capacitance for capacitances CT and CR than
`that for the touch cell of the FIG. 2A type in order for
`
`

`

`10
`
`15
`
`4,561,002
`8
`7
`the signal generator circuitry 90 (FIG. 6A) and the
`FIG. 5A schematically illustrates the outer face 44 of
`signal detector circuitry 58. A scan or test pulse from
`a dielectric substrate 46 for a touch panel on which a
`the signal generator circuitry is applied to input 80 of
`4X6 array of conductive touch pads 42 are fabricated in
`network 74 simultaneously with each scan pulse applied
`a layout similar to that of the touch panel of FIG. 1. For
`clarity and simplicity, only two rows of the array are
`to one of the touch pad rows. The touching of any
`portion of conductive path 70 results in the attenuation
`shown in FIGS. 5A and SB. It is to be understood that
`of the signal coupled by capacitive network 74 to point
`each of the omitted rows is structurally identical to
`84 just as the touching of a touch pad attentuates the
`those shown. Each touch pad 42 has associated with it
`signal coupled to the associated receiver electrode for
`a conductive path or run 56 which is formed on surface
`44 extending substantially parallel to the horizontal
`that touch pad.
`As will be described in greater detail hereinafter, the
`rows of touch pads to an associated terminal point 60
`logic circuitry of detection circuitry 58 is arranged such
`near edge 62 of substrate 46. A plurality of separate
`discrete transmitter capacitors 52 are provided with one
`that detection of an attenuated signal at output terminal
`84 of capacitor network 74 takes priority over any other
`capacitor 52 associated with each touchpad. Capacitors
`input to the detection circuitry. The output of any other
`52 can be combined into an electrical circuit that can be
`signal to the control system signifying the touching of a
`located off of substrate 46, with a flex circuit connection
`touchpad is thus prevented. Since the relative position
`comprising silver conductor runs fabricated on a sub
`strate of Mylar (R) material coupling one plate 64 of each
`ing of conductive runs 56 and 70 is such that touching of
`one of runs 56 would ordinarily be accompanied by the
`capacitor 52 to terminal point 60 for its associated touch
`pad. The four capacitors 52 for each row of pads 42
`touching of runs 70 as well, the control system does not
`20
`respond to the inadvertent touching of any portion of
`each have their other plate 66 commonly connected to
`the panel except the touch pads.
`simultaneously receive the scan signal for their row
`from the external scan signal generating circuitry at
`In the illustrative embodiment of FIGS. 5A and 5B,
`the dielectric substrate 46 is a glass panel having a '
`input terminal 68.
`The opposite surface 50 of substrate 44 is schemati
`nominal thickness. A greater or lesser thickness could of
`25
`course be used with the understanding that coupling
`cally illustrated in FIG. S.B. Surface 50 has fabricated
`capacitance between pad 42 and electrode 48 is in
`thereon a 4x6 array of receiver electrodes or pads 48,
`versely proportional to thickness. Also, a thinner glass
`one for each of the touch pads 42. Each of receiver
`panel may not provide the desired structural rigidity.
`electrodes 48 are positioned in the area overlying and
`Top pads 42 and conductive paths 56 and 70 formed on
`bounded by the area of its associated touch pad 42 to
`surface 44 may be formed by depositing tin oxide on the
`form a 4x6 array of touch switch cells 40 of the type
`glass in the desired pattern. The glass plate would then
`illustrated in FIG. 4A. The receiver electrodes 48 in
`be baked at high temperature to passivate the tin oxide
`each column are serially connected by a conductive
`into the glass. The resultant passivated tin oxide pattern
`path 49 with each column of receiver electrodes being
`is resistant to cleaning and scouring of the panel. Re
`coupled to the signal detection circuitry 58.
`Referring again to FIG. 5A, since conductors 56 are
`ceiver electrodes 48 and conductors 49 and 73 formed
`on inner surface 50 may be inexpensively formed with
`formed on the outward surface 44 of substrate 46 along
`silver epoxy. To minimize stray capacitance effects, the
`with touch pads 42, it is possible for a user to inadver
`width of conductive paths 49, 56, 70, and 73 should be
`tently touch one or more of these conductive paths. The
`direct touching of one of conductors 56 would have an
`held to a minimum.
`attenuating effect similar to the touching of the pad
`Illustrative control circuitry for incorporating the
`touch panel of FIGS. 5A and 5B into a control system
`associated with the touched conductor. Thus, the
`for an appliance such as an electric cooking range is
`touching of a region of substrate surface 44 carrying
`illustrated schematically in FIG. 6A.
`conductors 56 would appear to detecting circuitry 58 as
`the touching of the pad associated with the touched
`In the illustrative control circuit of FIG. 6A, micro
`45
`processor 90 sequentially generates a scan pulse at each
`conductor.
`In order to prevent the control system from respond
`of outputs Ro-R5, which outputs are coupled to rows
`ing to the resulting erroneous signal, a second plurality
`a-f of the capacitive touch cell array 10 of FIGS. 5A
`and 5B via driver circuitry 92 and capacitor banks 94(a-
`of conductive paths or runs 70 are formed on surface 44
`)-94(f), respectively. A test signal is generated at Ko
`of substrate 46 such that each of the first conductive
`50
`simultaneously with each scan pulse which is coupled
`paths 56 has at least one of these second paths 70 closely
`adjacent to it. The spacing between adjacent sections of
`by driver circuit 92 to capacitive network 74, to provide
`the hereinbefore described prevention of erroneous
`paths 56 and 70 is selected such that the human touching
`signals from touching conductive paths on the control
`of one path would also ordinarily result in the touching
`panel rather than the touch pads.
`of the other path as well. Each of the paths 70 is con
`55
`Columns g-j of the touch cell array are coupled to
`nected at one end to a terminal point 72 which is electri
`inputs C5-C2, respectively, of detection circuitry 58 via
`cally connected through substrate 46 to terminal points
`limiting resistors 114. The output of capacitive network
`71 formed on opposite surface 50 of substrate 46.
`74 is similarly coupled to input C1 of detection circuitry
`A capacitor network 74, comprising a pair of serially
`58. A BCD coded output signal from circuitry 58 is
`connected discrete capacitors 75 and 76, which may be
`coupled to inputs K1, K2, K4 and K8 of microprocessor -
`mounted on surface 50 of substrate 44 or separately
`from substrate 44, is coupled to conductive paths 70 by
`90.
`Circuitry 58 senses the scan signal coupled by each of
`conductive runs 73 formed on surface 50 joining termi
`nal points 71. All conductive paths 70 are commonly
`the touch cells in the row being scanned to their respec
`connected via paths 73 to the junction 82 of serially
`tive column output lines 49 to detect an attenuation of
`65
`the column output line signal, signifying that a touch
`connected capacitors 75 and 76. This arrangement ena
`pad in a particular column has been touched. If a touch
`bles conductors 70 to function as a "psuedo touchpad.'
`pad in the row being scanned is touched, the signal
`Capacitive network 74 is serially connected between
`
`30
`
`35
`
`

`

`O
`
`15
`
`30
`
`25
`
`4,561,002
`10
`assigned the highest priority and C9 the lowest. The
`detector circuit will detect the attenuation of the
`input received having the highest priority is encoded as
`scanned signal for that column containing the touched
`pad. The BCD coded output signal coupled to micro
`a 4-bit BCD word and transmitted to an internal multi
`plexer.
`processor 90 indicates which column, if any, contains a
`touched pad. In this fashion, a touched pad is identified
`The output function of chip 58 is controlled by the
`by row and column.
`input designated ISR. When ISR is low, the BCD word
`In the illustrative embodiment, microprocessor 90 is a
`is transferred to outputs Y1-Y4. A high level at