United States Patent
`
`[19]
`
`[11] Patent Number:
`
`5,594,222
`
`Caldwell
`
`[45] Date of Patent:
`
`Jan. 14, 1997
`
`US005594222A
`
`[54] TOUCH SENSOR AND CONTROL CIRCUIT
`THEREFOR
`
`[75]
`
`Inventor: David w. Caldwell, Lapeer, Mich.
`v
`.
`-
`[73] Assrgnee.
`Integrated Controls, Lapeer, Mich.
`
`Appl. Na: 328.852
`Filed:
`on. 25, 1994
`Int. Cl.° .................................................. H03K 17/975
`
`........................................... 200/600; 341/33
`U.S. Cl.
`Field of Search ...............
`200/S A, 600;
`361/278, 280; 307/116, 99; 341/22, 33,
`26, 24; 345/ 173, 174; 400/479.1
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`8/1965 Atkins ct al.
`......
`5,1966
`9,1966
`9,1931
`4/1933
`4/1983
`7/ 1983
`3/1933
`9/1983
`9/1983
`7/1985
`
`.
`
`.
`
`3,200,305
`3,254,313
`$275,897
`4291303
`4,379,237
`4,380,040
`4.394.643
`4300-753
`4,405,917
`4,405,918
`4.529.968
`
`8/1985
`4.535.254
`4,550,310 10/1935
`4,552,315 1211985
`
`4/1986
`4»584»519
`3/1983
`4,731,548
`3/l988
`4,733,222
`4,740,781 M988
`4,855,550
`s/1939
`5,053,305
`11/1991
`
`5'239'152
`
`8,1993 Ca'dw°“°'a]'
`
`p,.,'ma,y Emm,',,e,._J_ R_ Sam
`Augmg}-_ Agent, or Firm—Young & Basile, P.C.
`
`157]
`
`A3STR-ACT
`
`A low impedance touch sensor detects manual contact of a
`dielectric substrate by a human user. The touch sensor
`includes a first conductive electrode pad having a closed,
`°°“d“"°".‘ g"'°“'°”i°.f°"“ am a ‘°°°“d °°“d“°"-"° °'°°'
`trode which substantially co-planarly surrounds the first
`electrode and is spaced from the first electrode by a channel.
`The first and second electrodes are disposed on the same
`surface of the substrate. An active electrical component,
`such as a transistor is located on the substrate proximate the
`first and second electrodes, and is electrically coupled to the
`first and second electrodes.
`
`..... 345/174
`_ 200/600
`. 200,600 X
`_ 345/"74
`_. 200/500 x
`...... 200/600
`400/479.1 X
`
`..
`
`32 Claims, 6 Drawing Sheets
`
`INITIALIZE
`VARIABLES
`
`GET PEAK
`DETECTOR LEVEL
`
`AVERAGE
`VALUES
`INITIALIIED ?
`
`DETERMINE DIFFERENCE
`BETWEEN PEAK DETECTOR
`LEVEL AND AVERAGE
`PEAK DETECTOR LEVEL
`
`NEGATWE
`CHANGE FROM
`AVERAGE ‘?
`
`CHANGE
`GREATER THAN
`SET POINT VALUE ?
`
`M3
`
`DECREMENT
`AVERAGE
`VALUE
`
`ser smus
`mncrwe
`
`ser swus
`*°""V5
`
`VALUE
`
`SH’ STATUS
`INACTNE
`
`Page 1 of 13
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`SAMSUNG EXHIBIT 1009
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`U.S. Patent
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`Jan. 14, 1997
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`Sheet 3 of 6
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`5,594,222
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`5,594,222
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`1
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`TOUCH SENSOR AND CONTROL CIRCUIT
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`THEREFOR
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`FIELD OF THE INVENTION
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`The present invention relates to a touch panel system, and
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`more particularly, a touch sensor attached to one side of a
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`substrate for detecting user contact of the opposite side of
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`the substrate.
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`BACKGROUND OF THE INVENTION
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`Touch panels are used in various applications to replace
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`conventional mechanical switches; e.g., kitchen stoves,
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`microwave ovens, and the like. Unlike mechanical switches,
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`touch panels contain no moving parts to break or wear out.
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`Mechanical switches used with a substrate require some type
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`of opening through the substrate for mounting the switch.
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`These openings, as well as openings in the switch itself,
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`allow dirt, water and other contaminants to pass through the
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`substrate or become trapped within the switch. Certain
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`environments contain a large number of contaminants which
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`can pass through substrate openings, causing electrical
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`shorting or damage to the components behind the substrate.
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`However, touch panels can be formed on a continuous
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`substrate sheet without any openings in the substrate. Also,
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`touch panels are easily cleaned due to the lack of openings
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`and cavities which collect dirt and other contaminants.
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`Existing touch panel designs provide touch pad electrodes
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`attached to both sides of the substrate; i.e., on both the
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`“front” surface of the substrate and the “back” surface of the
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`substrate. Typically, a tin antimony oxide (TAO) electrode is
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`attached to the front surface of the substrate and additional
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`electrodes are attached to the back surface. The touch pad is
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`activated when a user contacts the TAO electrode. Such a
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`design exposes the TAO electrode to damage by scratching,
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`cleaning solvents, and abrasive cleaning pads. Furthermore,
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`the TAO electrode adds cost and complexity to the touch
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`panel.
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`Known touch panels often use a high impedance design
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`which may cause the touch panel to malfunction when water
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`or other liquids are present on the substrate. This presents a
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`problem in areas where liquids are commonly found, such as
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`a kitchen. Since the pads have a higher impedance than the
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`water, the water acts as a conductor for the electric fields
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`created by the touch pads. Thus, the electric fields follow the
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`path of least resistance; i.e., the water. Also, due to the high
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`impedance design, static electricity can cause the touch
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`panel to malfunction. The static electricity is prevented from
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`quickly dissipating because of the high touch pad imped-
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`ance.
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`Existing touch panel designs also suffer from problems
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`associated with crosstalk between adjacent touch pads. The
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`crosstalk occurs when the electric field created by one touch
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`pad interferes with the field created by an adjacent touch
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`pad, resulting in an erroneous activation such as activating
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`the wrong touch pad or activating two pads simultaneously.
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`Known touch panel designs provide individual pads
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`which are passive. No active components are located in
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`close proximity to the touch pads. Instead, lead lines connect
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`each passive touch pad to the active detection circuitry. The
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`touch pad lead lines have different lengths depending on the
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`location of the touch pad with respect
`to the detection
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`circuitry. Also, the lead lines have different shapes depend-
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`ing on the routing path of the line. The differences in lead
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`line length and shape cause the signal level on each line to
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`be attenuated to a different level. For example, a long lead
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`2
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`line with many comers may attenuate the detection signal
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`significantly more than a short lead line with few comers.
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`Therefore,
`the signal received by the detection circuitry
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`varies considerably from one pad to the next Consequently,
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`the detection circuitry must be designed to compensate for
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`large differences in signal level.
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`Many existing touch panels use a grounding mechanism,
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`such as a grounding ring, in close proximity to each touch
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`pad. These grounding mechanisms represent additional ele-
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`ments which must be positioned and attached near each
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`touch pad, thereby adding complexity to the touch panel.
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`Furthermore, certain grounding mechanisms require a dif-
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`ferent configuration for each individual touch pad to mini-
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`mize the difference in signal levels presented to the detection
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`circuitry. Therefore, additional design time is required to
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`design the various grounding mechanisms.
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`SUMMARY OF THE INVENTION
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`The present invention solves the above-mentioned prob-
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`lems associated with existing touch panel designs by pro-
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`viding an active, low impedance touch sensor attached to
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`only one side of a dielectric substrate. The inventive touch
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`sensor has a first conductive electrode pad and a second
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`conductive electrode which substantially surrounds the first
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`electrode in a spaced apart relationship. The first electrode
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`pad has a closed, continuous geometric shape with an area
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`providing substantial contact coverage by a human append-
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`age. Both electrodes are attached to the same surface of the
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`substrate. An active electrical component is placed in close
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`proximity to the electrodes.
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`The inventive touch pad can be used in place of existing
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`touch pads or to replace conventional switches. The touch
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`pad is activated when a user contacts the substrate with a
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`human appendage, such as a fingertip. The touch pads can be
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`used to turn a device on or 011”, adjust temperature, set a clock
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`or timer, or any other function performed by a conventional
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`switch. In addition to solving problems associated with
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`existing touch pad designs, the present invention is espe-
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`cially useful in applications which presently use membrane-
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`type switches, such as photocopiers and fax machines. The
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`inventive touch pad design operates properly with liquids
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`present on the substrate and in the presence of static elec-
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`tricity. The touch pad is well-suited for use in a kitchen or
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`other environment where water, grease and other liquids are
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`common, such as control panels‘ for ranges, ovens and
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`built-in cooktops.
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`In the preferred form, touch pad electrodes are attached to
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`the back surface of a substrate. The back surface of the
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`substrate is opposite the front or “touched” surface, thereby
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`preventing contact of the electrodes by the user. Since the
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`touch pad is not located on the front surface of the substrate,
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`the pad is not damaged by scratching, cleaning solvents or
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`any other contaminants which contact the front surface of
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`the substrate. Furthermore, the cost and complexity of the
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`touch panel is reduced since a TAO pad is not required on
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`the front surface of the substrate.
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`In the preferred form, a strobe line is electrically con-
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`nected to the outer electrode and delivers a strobe signal to
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`the outer electrode. A strobe signal applied to the strobe line
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`creates an electric field between the outer electrode and the
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`center electrode. The electric field paths are in opposition to
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`one another, thereby reducing the possibility of crosstalk
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`between adjacent pads. The electric field path is are-shaped
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`and extends through the substrate and past the front surface.
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`A sense line is attached to the substrate proximate the touch
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`Page 8 of 13
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`5,594,222
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`3
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`pad and carries a detection signal from the touch pad to a
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`peak detector circuit. The detection signal level is altered
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`when the substrate is touched by a user.
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`In the preferred form, an active electrical component,
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`such as a surface mount transistor, is located at each touch
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`pad. Preferably,
`the transistor is connected between the
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`sense line, the center electrode and the outer electrode of
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`each pad. The transistor acts to amplify and buffer the
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`detection signal at the touch pad,
`thereby reducing the
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`difierence in signal level between individual touch pads due
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`to different lead lengths and lead routing paths. Therefore,
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`the difference in voltage levels from one pad to the next is
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`significantly reduced, providing a more uniform detection
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`voltage among all touch pads.
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`A plurality of touch pads may be arranged on the substrate
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`in a matrix. Using a matrix configuration, the strobe signal
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`is applied to a particular column of touch pads while the
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`sense line is monitored for a particularrow of touch pads. By
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`applying the strobe to a column of pads and monitoring the
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`sense line from a row of pads, a particular pad is selected.
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`4
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`glass and has a uniform thickness of approximately 3 mm.
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`The thickness of substrate 10 varies with the particular
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`application such that a thicker substrate is used where
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`additional strength is required. If substrate 10 is manufac-
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`tured from glass, the substrate can be as thin as approxi-
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`mately l.l mm and as thick as approximately 5 m. If
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`substrate 10 is manufactured from plastic, the substrate can
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`be less than 1mm thick, similar to the material used in plastic
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`membrane switches. A thin substrate 10 may permit the
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`touch pad to be operated by a user wearing a glove or mitten.
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`Substrate 10 has a front surface 12 and an opposite back
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`surface 14 (as shown in FIG. 2). A user activates the touch
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`pad by touching front surface 12 of substrate 10. The touch
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`pad includes a thin, conductive center electrode pad 16 and
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`a thin, conductive outer electrode 18 which substantially
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`surrounds the center electrode. A charmel 20 is located
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`between center electrode 16 and outer electrode 18. Elec-
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`trodes 16 and 18 are positioned such that channel 20 has a
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`substantially uniform width.
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`Preferably, center electrode 16 has dimensions such that
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`the electrode is substantially covered by a user’s fingertip or
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`other appendage when touched.
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`In the preferred embodiment, center electrode 16 is square
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`and outer electrode 18 has a square shape which conforms
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`to the shape of the center electrode. However, it will be
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`understood that various closed, continuous geometric shapes
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`may also be used for the center electrode including, but not
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`limited to, rectangles, trapezoids, circles, ellipses, triangles,
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`hexagons, and octagons. Regardless of the shape of center
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`electrode 16, outer electrode 18 substantially surrounds the
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`center electrode linearly in a spaced apart relationship, and
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`charmel 20 has a generally uniform width.
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`Preferably, center electrode 16 is a solid conductor. How-
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`ever, center electrode 16 may also have a plurality of
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`apertures or may have a mesh or grid pattern. It is important
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`that center electrode 16 have a plurality of electrical contact
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`points i.n substantially the same plane and having the same
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`electrical potential.
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`As shown in FIG. 1, a strobe line 22 is connected to outer
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`electrode 18. Strobe line 22 provides a strobe signal (shown
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`in FIG. 8) to outer electrode 18. In the preferred embodi-
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`ment, the strobe signal is a square wave oscillating between
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`0 and +5 volts at a frequency between 100 kHz and 200 kHz.
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`Alternatively, the strobe signal may have a frequency less
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`than 100 kHz 01' greater than 200 kHz, depending on the
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`detection circuitry used. Furthermore, the strobe signal may
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`oscillate between 0 and +3 volts, 0 and +12 volts, 0 and +24
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`volts, -5 volts and +5 volts, or any other voltage range,
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`depending on the voltage readily available from the device
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`being controlled.
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`The strobe signal has a sharp rising edge (shown in FIG.
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`8) which creates a difference in the electrical potential
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`between outer electrode 18 and inner electrode 16. This
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`difference in potential between electrodes 16 and 18 creates
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`an arc-shaped electric field between the electrodes, as shown
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`by the dashed lines in FIG. 2. The electric field extends
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`through substrate 10 and past front surface 12.
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`Although not shown in FIG. 2, the electric field between
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`electrodes 16 and 18 follows a similar arc-shaped path away
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`from substrate 10 rather than through the substrate. This path
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`is a mirror image of the dashed lines shown in FIG. 2,
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`extending downwardly rather than upwardly.
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`As shown in FIG. 2, the electric fields created are in
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`opposition to one another. For example, the two field paths
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`shown in FIG. 2 originate from electrode 18, at opposite
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`sides of the pad. Since the field paths each terminate at
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`BRIEF DESCRIPTION OF Tl-IE DRAWINGS
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`FIG. 1 illustrates an inventive touch pad as viewed from
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`the back surface of the substrate with the transistor and
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`resistor removed;
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`FIG. 2 is a side cross-sectional view of the touch pad and
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`substrate with the transistor and resistor removed;
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`FIG. 3 is the same view as that shown in FIG. 1, but with
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`the transistor and resistor attached;
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`FIG. 4 is the same view as that shown in FIG. 2, but with
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`the transistor and resistor attached;
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`FIG. 4A is the same view as that shown in FIG. 4, but with
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`the touch pad, transistor and resistor mounted on a carrier;
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`FIG. 5 is an electrical schematic representation of the
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`touch pad shown in FIG. 3;
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`FIG. 6 illustrates a matrix of touch pads according to the
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`present invention as viewed from the back surface of the
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`substrate with the transistors and resistors removed;
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`FIG. 7 is a side cross-sectional view of three adjacent
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`touch pads attached to a substrate;
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`FIG. 8 illustrates the strobe signal waveform;
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`FIG. 9 illustrates the waveform of the detection signal on
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`the sense line;
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`FIG. 10 shows the waveform of the peak detector output
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`signal when the touch pad is not being touched;
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`FIG. 11 shows the waveform of the peak detector output
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`signal when a user contacts the touch pad;
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`FIG. 12 is a block diagram of the control circuit for a
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`matrix of touch pads;
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`FIG. 13 is an electrical schematic representation of the
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`peak detector circuit shown in FIG. 11; and
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`FIGS. 14A and 14B illustrate a flowchart detailing the
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`operation of the microprocessor when monitoring a matrix
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`of touch pads.
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`DETAILED DESCRIPTION OF THE
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`PREFERRED EMBODIMENT
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`Referring to FIG. 1, a single touch pad is shown attached
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`to a dielectric substrate 10. Substrate 10 has a substantially
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`uniform thickness and can be manufactured from any type of
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`dielectric material, such as glass, ceramic or plastic. In the
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`preferred embodiment, substrate 10 is manufactured from
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`Page 9 of 13
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`

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`5,594,222
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`5
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`center electrode 16, the paths travel toward one another.
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`Thus, all field paths originate at outer electrode 18 and travel
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`inwardly toward center electrode 16.
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`Referring again to FIG. 1, a sense line 24 is attached to
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`substrate 10 adjacent outer electrode 18. Sense line 24
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`carries a detection signal from the touch pad to the remain-
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`der of the detection circuitry discussed below.
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`As shown in FIG. 3, a surface mount transistor 26 and a
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`surface mount resistor 28 are electrically connected to the
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`touch pad. Resistor 28 is connected between center electrode
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`16 and outer electrode 18. In the preferred embodiment,
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`resistor 28 has a value of 10 K ohms, thereby providing a
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`relatively low discharge input impedance for the touch pad.
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`Transistor 26 is connected between center electrode 16,
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`outer electrodc'18 and sense line 24. In the preferred
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`embodiment,
`transistor 26 is a PNP transistor, such as a
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`2N3086. The base of transistor 26 is connected to inner
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`electrode 16, the transistor emitter is connected to outer
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`electrode 18, and the transistor collector is connected to
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`sense line 24. Transistor 26 provides amplification and
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`buffering of the detection signal directly at the touch pad.
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`Alternatively, a NPN transistor, MOSFET, or other active
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`electrical component which is triggerable may be used in
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`place of a PNP transistor.
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`FIG. 5 illustrates schematically a model of the connection
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`of transistor 26 and resistor 28 to the touch pad. The
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`capacitive coupling between electrodes 16 and 18 is repre-
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`sented in FIG. 5 as a capacitor, with resistor 28 connected in
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`parallel with the capacitor. Resistor 28 acts to discharge the
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`capacitor formed by electrodes 16 and 18. Capacitor 27
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`represents the parasitic capacitance and the results of contact
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`by a user. Capacitor 21 represents the parasitic capacitance
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`on strobe line 22. Capacitor 23 represents the parasitic
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`capacitance on sense line 24. A resistor 25 can be used to
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`compensate for differences in beta values between different
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`transistors and to compensate for differences in transistor
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`operating characteristics based on temperature. However, in
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`the preferred form, resistor 25 has a value of 0 ohms; i.e., no
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`resistor 25 is used.
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`In the preferred embodiment shown in FIG. 4A, elec-
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`trodes 16 and 18, strobe line 22, and sense line 24 are
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`attached to a flexible carrier 25 manufactured from a poly-
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`ester material such as Consolidated Graphics No. HS-500,
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`Type 561, Level 2, 0.005 inches thick. Electrodes 16 and 18,
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`strobe line 22, and sense line 24 are formed using a
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`conductive silver ink such as Acheson No. 427 SS, 0.5 mills
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`thick. Transistor 26 and resistor 28 are then attached to the
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`electrodes and lines. A dielectric layer 27 is placed over the
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`electrodes and lines to protect the conducting surfaces.
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`Preferably, the dielectric 27 is Acheson No. ML25089, 1.5
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`mills thick. The flexible carrier 25 is then bonded to sub-
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`strate 10 using an adhesive 29 such as 3M No. 467. The
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`flexible carrier 25 can be curved and twisted to conform to
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`the shape of substrate 10.
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`Alternatively, electrodes 16 and 18, strobe line 22 and
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`sense line 24 can be attached directly to substrate 10.
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`Transistor 26 and resistor 28 are then attached to electrodes
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`16 and 18, and sense line 24.
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`Referring to FIG. 6, a matrix of touch pads are attached
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`to substrate 10. Each touch pad in the matrix has the same
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`configuration as the individual pad discussed above. Also,
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`each touch pad contains a transistor 26 and resistor 28, as
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`described earlier. The touch pads are arranged into rows and
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`columns and attached to substrate 10. Each touch pad in a
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`particular column is connected to a common strobe line 22.
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`Each touch pad in a particular row is connected to a common
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`6
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`sense line 24. Thus, no two touch pads are connected to the
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`same combination of strobe line 22 and sense line 24.
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`Although FIG. 6 illustrates a particular arrangement of a
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`touch pad matrix, it will be understood that any number of
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`touch pads can be arranged in any pattern depending on the
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`particular application. The touch pads need not be arranged
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`in rows and columns. Instead,
`the touch pads may be
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`randomly placed on the substrate or arranged in a circular or
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`diagonal manner. The number of touch pads which can be
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`attached to a substrate is limited only by the size of the
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`substrate.
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`Referring to FIG. 7, three adjacent touch pads are shown
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`attached to substrate 10. The electric field associated with
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`each touch pad is shown with dashed lines. As described
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`with the individual touch pad above, the electric field path
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`originates at outer electrode 18 and follows an arc—shaped
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`path outwardly through substrate 10 and back toward center
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`electrode 16. Since the electric field created by each touch
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`pad is directed toward the center of the pad, the electric
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`fields of adjacent pads are in opposition to one another; i.e.,
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`moving in opposite directions. Thus,
`there is a reduced
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`chance of crosstalk between adjacent pads.
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`In an alternate embodiment, outer electrode 18 does not
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`substantially surround center electrode 16. An important
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`feature of the arrangement of electrodes 16 and 18 is the
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`creation of opposing electric fields. Thus, an opposing
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`electric field is only needed where an adjacent touch pad
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`exists. For example, if three touch pads are positioned on a
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`substrate in a linear arrangement, outer electrodes 18 are
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`located between adjacent pads. If the middle pad in the
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`three-pad arrangement has adjacent pads to the left and right,
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`outer electrode 18 will be located on the left and right sides
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`of the middle pad. However, since no adj aeent pad is located
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`above or below the middle pad, there is no possibility of
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`crosstalk above or below the middle pad. Therefore, outer
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`electrode 18 is not required above or below the middle pad.
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`Similarly, the two end pads in the three-pad arrangement
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`have an adjacent touch pad on one side and therefore require
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`outer electrode 18 only on the single adjacent side.
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`Referring to FIG. 12, a block diagram of the control
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`circuit for a matrix of touch pads is shown. An oscillator 30
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`produces a square wave on line 32 which functions as the
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`strobe signal. A demultiplexer 34 receives the strobe signal
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`from oscillator 30. A microprocessor 36, such as Motorola
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`MC68HC05P9, generates a strobe address which is provided
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`to demultiplexer 34 on line 38. The strobe address causes
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`demultiplexer 34 to select one of several output lines which
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`receives the strobe signal. Each output line from demulti-
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`plexer 34 is connected to one strobe line 22 for a particular
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`column of touch pads. Thus, the output from oscillator 30 is
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`connected via demultiplexer 34 to strobe line 22 for a
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`particular colurtm of touch pads.
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`Microprocessor 36 also generates a sense address which
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`is provided to multiplexer 46 on line 48. The sense address
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`causes multiplexer 46 to select one of several input lines
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`which will be monitored as the sense line. Each input line
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`represents the sense line 24 for a particular row of touch
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`pads. Thus, a particular touch pad in the matrix can be
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`selectively monitored by “strobing” a colurrm of pads, and
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`“sensing” a row of pads. Alternatively, the matrix of touch
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`pads can be arranged such that monitoring is accomplished
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`by “strobing” arow of pads and “sensing” a colurrm of pads.
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`Sense line 24 selected by multiplexer 46 is connected to
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`a peak detector and amplifier circuit 52 using line 50. The
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`output of circuit 52 is provided to microprocessor 36 on line
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`54. Depending on the signal received from circuit 52, an
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`Page 10 of 13
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`

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`5 ,594,222
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`7
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`algorithm running on microprocessor 36 determines whether
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`a controlled device 58 should be activated, deactivated or
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`adjusted.
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`The peak detector and amplifier circuits shown in FIG. 13
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`are used in either a single touch pad design or a multiple
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`touch pad design; e.g., a matrix of touch pads. The left
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`portion of FIG. 13 represents the peak detector circuit and
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`the right portion of FIG. 13 represents the amplifier circuit.
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`The detection signal
`is carried by sense line 24 to the
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`non-inverting input of operational amplifier 64. A resistor 62
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`is connected between sense line 24 and ground. Preferably,
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`resistor 62 has a value of 10K ohms. A pull-up resistor 66 is
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`connected between +5 volts and the output of operational
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`amplifier 64. In the preferred embodiment, resistor 66 has a
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`value of 10K ohms. The output of operational amplifier 64
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`is connected through diode 67 to the inverting input of
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`operational amplifier 64. A resistor 68 and capacitor 70 are
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`connected in parallel between ground and the inverting input
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`of operational amplifier 64. Preferably, operational amplifi-
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`ers 64 and 72 are of the type LM339.
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`The non-inverting input of operational amplifier 72
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`receives the output signal from the peak detector circuit. A
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`pull-up resistor 74 is connected between +5 volts and output
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`82 of operational amplifi