Capacitive touch device

Abstract

A capacitive touch device is described. The device comprises a capacitive touch controller (19) which includes an input port (20) and a capacitive touch sensor (23). The input port is coupled to the capacitive touch sensor by a path (25) which includes at least one capacitive coupling (26).

Claims

1. A capacitive, touch device comprising: a capacitive touch controller including an input port; a module which includes the capacitive touch controller; and a capacitive touch sensor; wherein the input port is coupled to the capacitive touch sensor by a path which includes at least one capacitive coupling, wherein the module includes a module substrate supporting a first coupling region for forming the capacitive coupling, wherein the input port is coupled to the first coupling region by an unbroken conductive path, wherein the module substrate comprises first and second opposite faces, wherein the capacitive touch controller is supported on the first face, and wherein the first coupling region is supported on the first face; wherein the device further comprises; an opaque sheet comprising dielectric material which supports the capacitive touch sensor, the sheet including a first face and a second, opposite face; and a conductive track supported on the first face of the sheet, the track including a second coupling region for the capacitive coupling; wherein the capacitive coupling includes at least one dielectric region between the first and second coupling regions.

2. A capacitive touch device according to claim 1, wherein the conductive path includes at least one conductive track.

3. A capacitive touch device according to claim 2, wherein the at least one conductive track comprises a metal track.

4. A capacitive touch device according to claim 2, wherein the at least one conductive track comprises conductive ink.

5. A capacitive touch device according to claim 1, wherein the conductive track comprises conductive ink.

6. A capacitive touch device according to claim 1, wherein the conductive track comprises conductive foil.

7. A capacitive touch device according to claim 1, wherein the sheet comprises a fibre-based material.

8. A capacitive touch device according to claim 1, wherein the sheet comprises a plastics material.

9. A capacitive touch device according to claim 1, wherein the capacitive touch sensor comprises a conductive pad.

10. A capacitive touch device according to claim 9, wherein the conductive pad comprises conductive ink.

11. A capacitive touch device according to claim 9, wherein the conductive pad has an area of at least 1 mm.sup.2.

12. A capacitive touch device according to claim 1, wherein the at least one dielectric region includes glue and/or tape.

13. A capacitive touch device according to claim 1, wherein the at least one dielectric region includes a dielectric sheet.

14. A capacitive touch device according to claim 13, wherein the dielectric sheet comprises a fibre-based material.

15. A capacitive touch device according to claim 13, wherein the dielectric sheet comprises a plastics material.

16. A capacitive touch device according to claim 1, wherein the at least one dielectric region includes a module substrate which supports the capacitive touch controller.

17. A capacitive touch device according to claim 1, wherein the at least one dielectric region includes a substrate comprising dielectric material.

18. A capacitive touch device according to claim 17, wherein the substrate supports the capacitive touch sensor.

19. A capacitive touch device according to claim 17, wherein the substrate comprises a fibre-based material.

20. A capacitive touch device according to claim 17, wherein the substrate comprises a plastics material.

21. A capacitive touch device according to claim 1, wherein the path which includes at least two capacitive couplings in series having an effective capacitance.

22. A capacitive touch device according to claim 1, wherein the capacitive coupling has an area having a value between 0.001 mm.sup.2 and 100 mm.sup.2, optionally between 0.01 mm.sup.2 and 10 mm.sup.2.

23. A capacitive touch device according to claim 1, wherein the capacitive coupling(s) has (have) a (an effective) capacitance having a value between 0.1 to 100 pF, optionally between 1 and 10 pF.

24. A capacitive touch device according to claim 1, wherein the capacitive touch controller is configured to perform a resistor-based capacitive measurement.

25. A printed article comprising a capacitive touch device according to claim 1.

26. A printed article according to claim 25, comprising a substrate which supports printed indicia.

27. A printed article according to claim 25, comprising a book, game, greeting card, poster, product packaging, promotional item or point of sale display.

28. A capacitive touch device according to claim 1, wherein the at least one dielectric region comprises non-conductive ink.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Certain embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:

(2) FIG. 1 is a schematic diagram of a capacitive touch sensing arrangement;

(3) FIG. 1a is illustrates a conductive line coupling an input/output port and a capacitive touch sensor;

(4) FIG. 2 is a schematic diagram of an article which includes a capacitive touch sensing arrangement in accordance with the present invention;

(5) FIG. 2a is a side view of a portion of a module forming part of the article;

(6) FIG. 3 is a plan view of a capacitive coupling;

(7) FIG. 4 is a longitudinal side view of the capacitive coupling shown in FIG. 3;

(8) FIG. 5 is a longitudinal side view showing a module comprising a substrate having coupling regions provided on an underside of substrate;

(9) FIG. 6 is a schematic diagram of a circuit between a port of a capacitive sensing controller via a capacitive sensor and person to ground;

(10) FIG. 7 is a schematic diagram of an article which includes another capacitive touch sensing arrangement in accordance with the present invention;

(11) FIG. 8 illustrates multiple capacitive couplings between an input/output port and a capacitive touch sensor; and

(12) FIG. 9 is a schematic diagram of a poster with a clip-on module.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS

(13) Referring to FIG. 1, a capacitive touch sensing arrangement 1 is shown which may be regarded as useful for understanding the invention.

(14) The capacitive touch sensing arrangement 1 includes a capacitive touch controller 2 in the form of mixed-signal microcontroller, such as a Texas Instruments MSP 430, which includes first and second general-purpose input/output ports 3.sub.1, 3.sub.2 which are coupled by conductive lines 4.sub.1, 4.sub.2 to first and second capacitive touch sensors 5.sub.1, 5.sub.2. The first and second lines 4.sub.1, 4.sub.2 are connected by a resistor 6. The arrangement 1 can be used to sense touch using a resistor-based capacitive measurement as described, for example, in Zack Albus: PCB-Based Capacitive Touch Sensing With MSP430, Texas Instruments Application Report, SLAA363A (2007) (http://www.ti.com/lit/an/slaa363a/slaa363a.pdf).

(15) Referring also to FIG. 1a, each conductive line 4 provides a continuous conductive path (i.e. one that is unbroken) between a respective port 3 and a corresponding sensor 5. Each conductive line 4 consists of conductive sections 7.sub.1, 7.sub.2, . . . , 7.sub.n?1, 7.sub.n joined by conductive connections 8.sub.1, 8.sub.2, . . . , 8.sub.n+1. A conductive section 7.sub.1, 7.sub.2, . . . , 7.sub.n may take the form of, for example, a metal track on a printed circuit board (not shown), a wire, a piece of metal foil or a conductive ink track. Typically, a conductive line 4 includes at least two different types of conductive section. The conductive connections 8.sub.1, 8.sub.2, . . . , 8.sub.n+1 may take the form of, for example, a solder joint, a conductive glue joint, an abutting joint (that is, two conductors which are in contact but are not, for example, fused) or an integral joint (for example, between a track and a pad of conductive ink which provides a unitary structure).

(16) The capacitive touch sensing arrangement 1 can be embedded in a book, game, greeting card or other printed item (not shown) to form an interactive printed item (not shown). However, the controller 2 and the touch sensor 5 can be disposed in different parts of the printed item (not shown), for example, on different substrates (for example, the controller is disposed on a printed circuit board and the touch sensors 5 are disposed on a piece of card), on different sides of a common substrate and/or on different parts of a common substrate separated by a crease or fold. Thus, it can be difficult to form continuous conductive lines 4. Therefore, a simpler, but less desirable, layout may be needed to allow the arrangement 1 to be embedded in the printed item (not shown). Additionally or alternatively, it may be necessary to rely on electrical wires and/or connector ribbons to provide paths which may make the interactive printed product more expensive and/or difficult to make.

(17) The present invention is based, at least in part, on the insight that reliable capacitive touch sensing can still be achieved without a continuous conductive path between port and sensor.

(18) Referring to FIG. 2, an article 10, for example a printed item such as poster, greeting card or point of sale display, is shown which includes a capacitive touch sensing arrangement 11 in accordance with the present invention.

(19) The article 10 includes a substrate 12, for example formed of paper, card or other fibre-based material, plastic or a laminate. The substrate 12 supports an electronic module 13.

(20) Referring also to FIG. 2a, the module 13 includes a printed circuit board 14 comprising a dielectric substrate 15 having front and back surfaces 16, 17 and a set of conductive tracks 18 supported on the front surface 16 and/or on the back surface 17. The module 13 includes a capacitive touch controller 19, such as a Texas Instruments MSP 430, which includes general-purpose input/output ports 20. The ports 20 are accessed by respective pins 21.

(21) The printed circuit board 14 may be a traditional type comprising copper or metal tracks 18 formed on front and or back surfaces 16, 17 of a laminate substrate formed from, for example, cloth or paper and a thermoset resin. Solder (not shown) can be used to connect the conductive tracks 18 and pins 19.

(22) However, printed circuit board 14 may comnprise conductive ink or foil track 18 formed on front and or back surfaces 16, 17 of a substrate formed from, for example, paper, card or other fibre-based material or plastic. Conductive ink or glue (not shown) can be used to connect the conductive tracks 18 and pins 19. If conductive ink is used, then screen, flexography, offset lithography or gravure printing can be used.

(23) The capacitive touch controller 19 is used to sense touch using a resistor-based capacitive measurement. A timer (not shown) is clocked at a frequency of 8 MHz.

(24) Pairs of input/output ports 20 are connected by a resistor 22 having a value R. R may have a value which lies in the range between 500 k? and 5 M?. The resistor 22 effectively provides a resistor to ground when a port 20 is scanned (as shown in FIG. 5). Thus, for a sensor 23 which has a capacitance to ground of about 10 pF, then the discharge time of the sensor 23 is about 0.5 to about 50 ?s.

(25) The substrate 12 also supports at least one capacitive touch sensor 23 and at least one conductive track 24. Each touch sensor 23 is connected to a respective conductive track 24. In this case, the conductive track 24 comprises a single line. However, a conductive track may comprise more than one line and may include cross-linking lines.

(26) The capacitive touch sensor(s) 23 and conductive track(s) 24 comprise conductive ink and may be formed by printing the conductive ink onto the substrate 12. Printing may comprise screen, flexography, offset lithography or gravure forms of printing.

(27) As shown in FIG. 2, an input/output port 20 and a corresponding capacitive touch sensor 23 are coupled by a path 25. The path 25 includes first and second conductive sections 25.sub.1, 25.sub.2 provided mainly by a conductive track 18 (for example, formed of metal) and a conductive ink track 24 respectively. The resistance of the conductive ink 24 is R.sub.track. If the conductive track 18 comprises metal, then the resistance of the track can be assumed to relatively small. However, if the conductive track 18 on the printed circuit board comprises conductive ink, then the conductive track 18 may have an appreciable resistance, R.sub.track.

(28) The first and conductive second sections 25.sub.1, 25.sub.2 are coupled by a capacitive coupling 26. Thus, the path 25 is broken and is not a single continuous electrical path. Expressed differently, the port 20 of the controller 19 and the sensor 23 are connected by a path 25 which is not ohmic.

(29) Referring to FIGS. 2, 3 and 4, the first and second conductive sections 25.sub.1, 25.sub.2 comprise respective first and second coupling regions 27, 28 which are separated by at least one dielectric layer or region 29 (shown shaded). The first and second coupling regions 27, 28 take the form of conductive pads or parts of tracks 18, 24 which overlap.

(30) The first and second coupling regions 27, 28 have first and second areas A.sub.1, A.sub.2 respectively and are separated by a distance, d, of dielectric having a (or an average) relative dielectric constant ?.sub.r. Typically, the first and second areas A.sub.1, A.sub.2 have values which lie in a range between about 0.001 mm.sup.2 to about 100 mm.sup.2, for example, around 0.1 mm.sup.2 to about 10 mm.sup.2. The first and second areas A.sub.1, A.sub.2 may have the same value, i.e. A.sub.1=A.sub.2=A. In any case, the effective area of the capacitive coupling is limited by the area of overlap. The distance, d, may have a value which lies in a range between about 1 ?m to about 1 mm. The relative dielectric constant ?.sub.r lies in the range between about 2 and 10. As will be explained in more detail, combinations of values of first and/or second areas A.sub.1, A.sub.2, distance, d, and relative dielectric constant ?.sub.r can be found by experiment.

(31) In this example, the at least one dielectric layer 29 consists mainly of the printed circuit board substrate 15. However, this need not be the case.

(32) For example, the module 13 may be placed face down on the substrate 12. The at least one dielectric layer 29 may include the substrate 12. In other words, the module 13 is mounted on one side (i.e. face) of the substrate 12 and the sensor 23 and tracks 24 may be formed on the other, opposite side of the substrate 12. The at least one dielectric layer 29 may include air, glue and/or adhesive tape. The at least one dielectric layer 29 may include a dielectric sheet (not shown). The at least one dielectric layer 29 may include electrically non-conductive ink (not shown). A dielectric layer 29 may take the form of a pad, e.g. a patterned layer.

(33) In another example, the module 13 may still be placed face up on the substrate 12, but the at least one dielectric layer 29 is not provided by the printed circuit board substrate 15.

(34) Referring to FIG. 5, the dielectric substrate 15 supports conductive tracks 18 on the back surface 17. The dielectric substrate 16 includes through holes 31 between the front and back surfaces 16, 17 and a conductive via 32, for example solder or conductive ink, passes through the hole 31 to connect the tracks 18 on front and back surfaces 16, 17.

(35) A dielectric layer 33 separates the conductive track 18 on the back surface 17 from the conductive track 24 on the substrate 12. The dielectric layer 33 may be an adhesive, such as tape or glue. Alternatively, the dielectric layer 33 is not adhesive and additional adhesive material (e.g. glue) and/or an adhesive arrangement (e.g. adhesive tape applied over the module 13) can be used.

(36) This arrangement means that the printed circuit board substrate 15 does not provide the at least one dielectric layer 29. This can help to reduce the thickness, d, of the dielectric material and/or allow materials having a value of relative dielectric constant ?.sub.r which is different from that of the printed circuit board substrate 15, e.g. having a value which is greater than or equal to 5 (i.e. ?.sub.r?5) or greater than or equal to 10 (i.e. ?.sub.r?10) to be used.

(37) The capacitive touch controller 19 can be mounted directly or via a carrier (not shown) on the substrate 12, i.e. without being supported by printed circuit board. The capacitive touch controller 19 or carrier (not shown) supports first coupling regions 27 which capacitively couple with the second coupling regions 28 on the substrate 12. The capacitive touch controller 19 or carrier (not shown) may take the form of a surface mount package or chip carrier. The first coupling regions 27 may take the form of conductive pads on a surface (e.g. back surface) of the controller or carrier (not shown).

(38) Referring also to FIG. 6, the capacitive coupling 26 has a capacitance, C.sub.1. Thus, for a parallel plate arrangement, the capacitance of the capacitive coupling 26 is equal to about ?.sub.r?.sub.oA/D where ?.sub.o is the permittivity of free space, A is the area of overlap of the first and second coupling regions 27, 28 and d is the separation of the first and second coupling regions 27, 28. The capacitance between the sensor 23 and a person 34 when touching the sensor 23 is C.sub.2. Typically, C.sub.2 is about 1 to 10 pF, for example, around 3 pF. The capacitance between the person 34 and ground 35 is C.sub.3. Typically, C.sub.3 is about 100 pF.

(39) C.sub.1 may have a value which lies in a range of 0.1 pF to about 100 pF. The value of capacitance, C.sub.1, can be found by experiment. Generally, however, the value of capacitance, C.sub.1, is such that the capacitive touch controller 19 (FIG. 2) is able to detect that a person 34 has touched the sensor 23. For example, this may be achieved if an impedance, Z, between the sensor 23 and the person 30 (which comprises C.sub.2) dominates. This can occur C.sub.1<C.sub.2. For example, C.sub.1 may be no more than half of C.sub.2 or may be not more than a tenth of C.sub.2.

(40) Even though the capacitive touch controller port 20 and capacitive touch sensor 23 are connected by a path 25 which is not ohmic, effective capacitive sensing is still possible.

(41) This can help facilitate assembly of the item 10 and/or affords greater design freedom. This is because the module 13 can be attached to the substrate 12 using non-conductive glue or tape or held (temporarily) against the substrate 12 using, for example, a clip or frame.

(42) Referring to FIGS. 7 and 8, the path 25 may include more than one capacitive coupling 26.sub.1, . . . , 26.sub.n having respective capacitances, C.sub.n, . . . , C.sub.m. This can help facilitate routing of tracks around an item 10. In FIG. 7, track resistances, R.sub.track, . . . , R.sub.trackn, are not shown.

(43) For example, a further intermediate substrate 36 may be placed between the substrate 12. The intermediate substrate 36 includes conductive tracks 24.sub.1 and can be used to link the module 13 and the sensor 23. The intermediate substrate 32 may itself include one or more sensors 23.

(44) Thus, capacitive coupling can be used to route a path between a capacitive touch controller port 20 and a capacitive touch sensor 23.

(45) Capacitances, C.sub.11, . . . , C.sub.1n, of capacitive couplings 26.sub.1, . . . , 26.sub.n which are arranged in series can be combined to provide an equivalent capacitance, C.sub.1. Thus, values of capacitances, C.sub.11, . . . , C.sub.1n, can be found by experiment to provide an equivalent capacitance C.sub.1 having a value as hereinbefore described.

(46) The item 10 may be book. A module 13 embedded, for example, in a cover and a sensor 23 on a page of the book may be connected through a single coupling through more than one page. Alternatively, capacitive coupling can be achieved between the module 13 and the page through a series of couplings.

(47) The item 10 may be game which is formed by laminating several layers of card. Regions of the layers of card can be cut out and stacked to form cavities. A module 13 may be embedded within the game and sensors 23 may be disposed on a layer at or towards the top of the laminate. Like the book, the game may include a module 13 and the sensor 23 can be connected through a single coupling through more than one layer of card. Alternatively, capacitive coupling can be achieved between the module 13 and the sensor 23 through a series of couplings.

(48) Referring to FIG. 9, the item 10 may comprise two parts, such as a frame 37 providing a surround or edge which includes the module 13, and a sheet 12, such as a poster or card, which can be replaced with another, different sheet 12 and which includes one or more sensors 23 and tacks 24. In FIG. 9, the sensor 23 is on the reverse side which is not seen by the user. On the front side, images and text 38 are printed.

(49) A clamping arrangement, for example a sprung clip, may be used to hold the sheet 12 between two jaws (not shown). One of the jaws (not shown) may support terminals 27 for coupling to corresponding terminals 28 on the sheet 12. The terminals 27, 28 do not need to be direct contact. Instead, a reliable, capacitively coupling may be formed between the terminals 27, 28.

(50) It will be appreciated that many modifications may be made to the embodiments hereinbefore described.

(51) For example, the tracks on the substrate need not be printed but may comprise, for example, foil tracks.

(52) The substrate may be opaque or transparent.

(53) Other forms of capacitive measurement can be used.