WO2018078175A1

WO2018078175A1 - Backlit capacitive control interface for motor vehicle

Info

Publication number: WO2018078175A1
Application number: PCT/EP2017/077834
Authority: WO
Inventors: Ciprian Musat; Henry Beraud; Martin Schmitt; Joachim Hentschel
Original assignee: Valeo Comfort And Driving Assistance
Priority date: 2016-10-28
Filing date: 2017-10-30
Publication date: 2018-05-03
Also published as: FR3058102A1; FR3058102B1

Abstract

The invention relates to a backlit capacitive control interface (100) for a motor vehicle, comprising: a decorative faceplate (102) with a front surface (104) intended for being turned towards a user and a rear surface (106) opposite the front surface (104), the decorative faceplate (102) having an area to be backlit (108); a printed circuit board (112) mounted separated from (G) and facing the rear surface (106) of the decorative faceplate (104); a light-emitting diode (114) mounted on the printed circuit board (112); a capacitive detection sensor (116); at least one capacitive detection electrode (118) connected electrically to the capacitive detection sensor (116), characterised in that the capacitive detection electrode (118) is arranged on the printed circuit board (112) and in that the control interface (100) also comprises a transparent or translucent optical guide (120), attached to the printed circuit board (112), and having a housing (121) of the light-emitting diode (114), the optical guide (120) being in contact with the capacitive detection electrode (118).

Description

CAPACITIVE AND RETROTECTIVE CONTROL INTERFACE FOR VEHICLE

AUTOMOBILE

The present invention relates to a capacitive and backlit control interface for a motor vehicle, in particular for the passenger compartment of a motor vehicle.

In a vehicle, there are many buttons to activate functions. Among these, there is for example the button to activate the hazard warning lights or the button for central locking of the passenger compartment. These control buttons are for example installed at the dashboard, for example at the height of the center console or at the armrests of the doors. They are and must be very visible to the users of the vehicle so that they can locate them quickly when it is necessary to activate them.

For this reason, we attach great importance to the appearance and style of these buttons. Thus, the trend in recent years promotes smooth surfaces at the dashboard, which has resulted in relegating pressure knobs achieving control by a movement of opening and / or closing of a mechanical switch to second plan.

New control interfaces have emerged and among these, we note more particularly capacitive control interfaces.

For the latter, it is known to install on a rear face of a style facade in which is integrated for example a symbol to backlight, a capacitive detection electrode, for example in the form of a circle under the symbol to backlight . In order not to hinder the backlight, it is necessary for the electrode to be conductive and transparent. It can then be manufactured for example in ITO (indium oxide - tin), but this is quite expensive. This capacitive detection electrode is connected to a capacitive sensor disposed on a printed circuit board (PCB for "printed circuit board" in English). The printed circuit board installed behind the style facade is thus invisible to a user, and is arranged at a distance from the style facade. The printed circuit board also carries one or more light-emitting diodes (LEDs) vis-à-vis the symbol to backlight. The distance between the light-emitting diode, and therefore the circuit board, and the style facade depends on emission cone of the light-emitting diode and the size of the symbol or symbols to be illuminated.

This gap between the style facade and the printed circuit board poses a problem for detecting the touch of a finger of a user.

Indeed, it is necessary to fix for example by gluing the detection electrode on the rear face of the styling facade, then to connect this electrode for example by a flexible circuit or a cable to the printed circuit board.

However, during assembly, sticking errors of the electrode and a poor connection of the detection electrode to the printed circuit board can lead to malfunctions requiring subsequent costly interventions.

An object of the present invention is to provide a capacitive and backlit control interface that is more robust, particularly in terms of mounting, while having a very good detection sensitivity at the level of the style facade at the location of the symbol to backlight.

For this purpose, the subject of the present invention is a capacitive and backlit control interface for a motor vehicle, comprising:

a facade of style with a front face intended to be turned towards a user and a rear face opposite to the front face, the style facade having a backlit area,

- a printed circuit board mounted remotely and vis-à-vis the back side of the facade style,

an electroluminescent diode mounted on the printed circuit board,

a capacitive detection sensor,

at least one capacitive detection electrode electrically connected to the capacitive detection sensor,

characterized in that the capacitive sensing electrode is disposed on the printed circuit board and the control interface further comprises a transparent or translucent optical guide having a housing of the light-emitting diode, the optical guide being in contact with the capacitive sensing electrode. The arrangement of the capacitive sensing electrode on the printed circuit board, reduces the overall cost, increases the reliability of the interface while ensuring good detection sensitivity at the level of the facade style because of the interposition of the optical guide in the gap between the style facade and the printed circuit board.

The capacitive and backlit control interface may have one or more of the following features taken alone or in combination:

In one aspect, the capacitive sensing electrode is formed by at least one conductive track of the printed circuit board.

In another aspect, the sensing electrode surrounds the light emitting diode. The optical guide extends for example from the printed circuit board to the rear face of the style facade.

The optical guide is formed in particular by a solid body. The optical guide may be transparent or translucent and is for example made of transparent polycarbonate, polymethylmethacrylate, or transparent silicone.

The optical guide can be fixed on the printed circuit board.

A portion of the face of the optical guide vis-à-vis the light emitting diode may be a curved diopter.

The material forming the optical guide may be according to one embodiment, electrically non-conductive, that is to say insulating.

The material forming the optical guide can be according to another mode of embodiment, electrically conductive, for example by having fillers or additives making the optical guide electrically conductive.

According to another embodiment, the material forming the optical guide has at least a portion of its periphery, a transparent conductive layer connecting the capacitive detection electrode to the facade style.

According to yet another aspect, the face of the optical guide vis-à-vis the rear face of the style facade is in contact with this rear face.

The area to be backlit for example has an engraved symbol.

The interface may include an active guard disposed on the printed circuit board, surrounding the light emitting diode being interposed between the light emitting diode and the capacitive sensing electrode.

An air gap may be provided between the light guide and the active guard. The active guard can extend into the printed circuit board by forming a "squirrel cage".

The active guard may have an inner member arranged in an inner layer of the printed circuit board, extending between the capacitive sensing electrode and the power conductors of the light emitting diode.

The capacitive detection sensor may comprise a first voltage generator, a second voltage generator and a follower circuit, the active guard being connected to the second voltage generator configured to generate a guard signal substantially identical to the excitation signals of the capacitive sensing electrode through a follower circuit connected to the output of the first voltage generator producing the excitation signal of the capacitive sensing electrode.

The interface may further include a pulse width modulated power supply configured to power the light emitting diode. SUMMARY DESCRIPTION OF THE DRAWINGS

Other advantages and characteristics will appear on reading the description of the invention, as well as on the appended figures which represent a non-limiting exemplary embodiment of the invention and in which:

FIG. 1 represents a diagram of a portion of the interior passenger compartment of a motor vehicle comprising a capacitive and backlit control interface which is installed as an example at the level of a ceiling lamp module,

FIG. 2 represents a simplified cross-sectional diagram of a first embodiment of the control interface,

FIG. 3 represents a simplified diagram of a top view of a printed circuit board of the control interface of FIG. 2,

FIG. 4 is an enlargement of detail IV of FIG. 2,

- Figure 5 is a top view on a facade style,

FIG. 6 represents a simplified cross-sectional diagram similar to FIG. 2 for a second embodiment of the control interface,

FIG. 7 represents a simplified cross-sectional diagram similar to FIG. 2 for a third embodiment of the control interface,

FIG. 8 shows a simplified cross-sectional diagram similar to FIG. 2 for a fourth embodiment of the control interface,

FIG. 9 shows a schematic view of an exemplary embodiment of an active guard of the control interface of FIG. 8,

FIG. 10 shows a simplified diagram of a partial top view of a printed circuit board of the control interface of FIG. 8.

In these figures, the identical elements bear the same reference numbers. The following achievements are examples. Although the description refers to one or more embodiments, this does not necessarily mean that each reference relates to the same embodiment, or that the features apply only to a single embodiment. Simple features of different embodiments may also be combined or interchanged to provide other embodiments.

The terms "upstream" and "downstream" are defined with reference to the direction of propagation of the light beams. By "upstream" is meant that one element is placed before another with respect to the direction of propagation of a light beam. On the other hand, "downstream" is understood to mean that one element is placed after another relative to the direction of propagation of the light beam. By upper, lower, upper and lower, reference is made to the arrangement of the elements in the figures, which generally corresponds to the arrangement of the elements in the assembled state in a motor vehicle.

The horizontal plane is designated by a reference (X, Y) and the vertical direction by the Z direction, the three directions forming a trihedron (X, Y, Z), fixed with respect to a control interface. These axes may correspond to the denomination of the axes in a motor vehicle, that is to say by convention, in a vehicle, the X axis corresponds to the longitudinal axis of the vehicle, Y corresponds to the transverse axis of the vehicle and the Z axis to the vertical axis of the vehicle. DETAILED DESCRIPTION

Figure ι shows schematically the front part of a passenger compartment ι of a motor vehicle seen from the rear part of the vehicle. The front part of the passenger compartment comprises a capacitive and backlit control interface 100 which is made in the present example in the form of a touch button for switching on the hazard warning lights.

The passenger compartment comprises in particular a driver's seat noted -C arranged behind a steering wheel 3 and a dashboard 5, a passenger seat noted -P-, a center console 7, an interior mirror 9 and a ceiling module 11 also called dome or dome-ceiling lamp in which is placed and mounted the capacitive control interface and backlit 100. The ceiling lamp module 11 is placed near the interior rearview mirror 9 in the upper central part of the front part of the passenger compartment 1.

Of course, the capacitive and backlit control interface 100 can also be placed at other places in the passenger compartment 1, for example on the control panel of an air conditioning control panel, at the center console. 7, at the dashboard 5 or any other suitable place. Such a control interface 100 may in particular be installed for other functions, for example for central locking of the passenger compartment, or for activating / deactivating, for example, passenger air bag functions or for controlling air conditioning functions in a switchboard. control.

The structure of the control interface 100 is more detailed in FIGS. 2 to 5.

The control interface 100 comprises a style facade 102. The style facade 102 may be a particular, distinct wall, installed in a larger assembly for example of the dashboard 5 or the ceiling module 11 or be a portion dashboard wall 5 or ceiling lamp module 11.

This style facade 102 has on the one hand a front face 104 which is oriented towards the interior of the passenger compartment 1 and thus intended to be turned towards a user, the driver or a passenger, and secondly a rear face 106 opposed to the front face 104.

The front face 104 is shown in a view from above in Figure 5 and comprises a backlit area 108 in which a symbol 110 for example engraved.

In this case, it is a triangle to indicate to the user the area to be touched to control the activation of the hazard warning lights.

At a distance G (see arrow in FIG. 2) of the style facade 102, and opposite the rear face 106 of the style facade 102, is a printed circuit board 112 (or PCB for "Printed circuit board"), with a gap between the rear face 106 and the printed circuit board 112.

As shown in Figures 2 and 3, the printed circuit board 112 carries a light emitting diode 114, such as CMS ("surface mounted components").

The control interface 100 further comprises a capacitive detection sensor 116 carried by the printed circuit board 112 and at least one capacitive sensing electrode 118 electrically connected to the capacitive sensing sensor 116.

In Figs. 2 and 3, the capacitive sensing sensor 116 is only shown schematically as a single component. Of course, it can be realized from several basic components and include for example capabilities or a processor or an integrated circuit.

The capacitive sensing electrode 118 is also arranged on the printed circuit board 112.

In the present case, it is for example a ring-shaped electrode 118 surrounding the light-emitting diode 114 and which is placed on the printed circuit board 112. Of course, it is also possible to have other forms of FIG. electrode surrounding the diode 114, such as rectangular, elliptical, or polygonal shapes.

The detection electrode 118 may be a metal piece fixed, for example by gluing, to the printed circuit board 112 or simply formed by one or more conductive tracks on the printed circuit board 112. It is therefore no longer necessary to fabricate the sensing electrode 118 with a transparent and conductive material, thereby reducing the cost of the control interface 100.

When using a single electrode 118, the electrode is both input and output.

According to one variant, the interface 100 comprises several electrodes 118, at least two of which, one of which is considered as transmitter and the other as a receiver.

The control interface 100 further comprises a transparent or translucent optical guide 120.

As seen in the figures, the optical guide 120 may be a solid body. This optical guide 120 is in direct contact with the capacitive detection electrode

118, for example by being placed on it and fixed against the detection electrode 118.

According to a variant not shown, the optical guide 120 can be integrated into the style facade 102.

The optical guide 120 extends for example from the printed circuit board 112 to the rear face 106 of the style facade 102 thus filling the gap (distance G) between the printed circuit board 112 and the rear face 106 of the facade of style 102.

The optical guide 120 may touch the rear face 106 of the style facade 102, but it is also possible to leave a thin air gap between the two to facilitate assembly and to overcome manufacturing tolerances and assembling games ( for example of the order of 0.21mm).

The optical guide 120 is transparent or translucent to diffuse the light. This is for example a parallelepipedal block which comprises on its face in contact with the detection electrode 118 a housing 121 for the light-emitting diode 114. It is thus clear that the optical guide 120 covers not only the light-emitting diode 114, but also the capacitive sensing electrode 118. This allows a direct illumination of the backlit area 108, which is more effective than indirect lighting and allows to choose a light-emitting diode 114 of lower power. In addition, a single light-emitting diode 114 is then sufficient for effective backlighting, which also avoids backlight homogenization problems that arise from the use of multiple light-emitting diodes.

The optical guide 120 is for example made of transparent polycarbonate, polymethyl methacrylate (PMMA), or transparent silicone.

According to one embodiment, the optical guide 120 is electrically non-conductive and guides the electric field lines between the detection electrode 118 and the front face 104. The approach of a user's finger, for example at the of the front face 104 causes modifications of the electric field and capacitances which are transmitted by the optical guide 120 to the detection electrode 118 and measured as variations of the self-capacitance of the sensor electrode 118 by the sensor capacitive sensing 116.

Thanks to the optical guide 120, it is possible to detect the touch of a user at the front face 104 of the style facade 102 by the variation of the electric field, while the detection electrode 118 is away from this front face. 104, on the printed circuit board 112.

The detection of touch is considered acquired, when for example the finger of a user is in physical contact with the control surface formed in this case by the front face 104 of the style facade 102. Due to the optical guide 120, it is also possible to reduce the sensitivity of the capacitive detection sensor 116, since the optical guide 120 makes it possible to increase the variation of the self-capacitance of the detection electrode 118, which makes it possible to reduce detection errors and therefore increase the detection accuracy.

As an indication, for the assembly of FIG. 2, the variation of the self-capacitance of the detection electrode 118 is measured when the finger is 3 mm from the front face 104 and when the finger touches this front face. 104, this for two cases: in the first case, the optical guide 120 is present and the mounting of the control interface 100 is in accordance with the assembly of Figures 2 to 5, and in a second case, the optical guide 120 is absent .

In the first case, a variation of the self-capacitance of the detection electrode of more than 25% was measured, while in the second case, the variation is only about 6%. It is therefore easy to understand that the control interface 100 according to FIGS. 2 to 5 makes it possible to obtain a good response amplitude and therefore an accurate detection of the touch of a user's finger on the front face 104.

According to a first possible mode of operation of the interface 100, the electrode 118 is both input and output (voltage excited and the current or the amount of electrical charge which passes through) is measured. At the approach of a conductor, the (clean) capacitance of the electrode 118 increases and the electric field intensifies.

According to a second possible mode of operation and alternative to the first mode of operation, there are at least two electrodes 118, one of which is considered as emitter and the other as a receiver, the two electrodes forming a capacitance by mutual coupling. At the approach of the hand of a user, the capacitance between the two electrodes 118 decreases and the electric field weakens.

In all cases, the optical guide 120 is made of a material with high permittivity, which makes it possible to better transmit the electric field, and more specifically the variations of the electric field of the style facade 102 towards the measurement electrode 118.

FIG. 6 is a second embodiment of the control interface 100. This embodiment differs from that of the preceding figures in that a portion 122 of the face of the optical guide 120 forming part of the housing 121, and -Lien vis-à-vis the light-emitting diode 114, is a curved diopter, in particular concave or convex, at least on a portion corresponding to the emission cone of the light-emitting diode 114.

Thus, by the curvature of the portion 122, one can further shape the light beam emitted by the light emitting diode 114 by the optical guide 120 to properly adapt the beam output of the light emitting diode 114 to the extent of the area to backlighting 108. This also allows to obtain a uniform backlight, by direct lighting, that is to say without multiple reflections.

It is therefore clear that the control interface 100 allows a simpler mounting of the interface 100, by mounting the detection electrode 118 on the printed circuit board 112 while ensuring a good detection of a user's finger at the level of the front face 104 of the style facade 102. Other variants are conceivable without departing from the scope of the present invention.

Thus, the optical guide 120 of Figures 2 to 6 is made by a solid body. However, it is also possible to envisage a hollow body with an internal cavity 140, for example in the form of a cube, and in particular made of polycarbonate with an opening 142 in the bottom wall for the light-emitting diode 114, as shown in FIG. this case, it is the solid portions of the electrically non-conductive optical guide 120 which guide the electric field lines between the detection electrode 118 and the front face 104.

According to another variant, the material forming the optical guide 120 may comprise charges or additives, for example conductive transparent particles or conductive polymers, making the optical guide 120 electrically conductive.

It is also conceivable that the material forming the optical guide 120 has at least a portion of its periphery or is completely surrounded by a conductive transparent layer, for example ITO (indium tin oxide), connecting the detection electrode capacitive 118 to the facade style 102.

According to an exemplary embodiment shown in FIG. 8, the capacitive and backlit control interface 100 includes an active guard 143 (or "active shield" in English) (also called "guard electrode" or "active shield"). protection against electromagnetic interference ") disposed on the printed circuit board 112. The active guard 143 is interposed between the light emitting diode 114 and the capacitive sensing electrode 118 and surrounds the light emitting diode 114.

The active guard 143 is made of conductive material, for example copper.

The active guard 143 is isolated from the diode 114 and from the capacitive detection electrode 118. The active guard 143 and the diode 114 are for example separated from the smallest distance possible, for example from a distance of between 0.2 and 0.5mm.

The active guard 143 has for example a ring shape or any other shape surrounding the diode 114, such as rectangular, elliptical or polygonal shapes.

According to an exemplary embodiment, the active guard 143 extends into the printed circuit board 112 forming a "squirrel cage" (FIG. 9). For this, two flat closed shapes such as rings 149 are deposited on the two opposite faces of the printed circuit board 112. These two rings 149 are interconnected by bars 150. The bars 150 are arranged so that they form a substantially cylinder shape. The bars 150 are formed by vias (or metallized bridges) formed in the thickness of the printed circuit board 112. The squirrel cage may further comprise one or more internal flat closed shapes, such as internal rings 151 when the printed circuit board 112 has one or more internal metal layers. The power supply tracks of the light-emitting diode 114 are deposited on the printed circuit board 112 and are connected by supply conductors 152 passing, for example, in the thickness of the printed circuit board 112, between the bars 150 of the squirrel cage, with a feed for example with pulse width modulation 147.

According to an exemplary embodiment, the capacitive detection sensor 116 comprises a first voltage generator 146, a second voltage generator 144 and a follower circuit 145 (FIG. 10). The active guard 143 is connected to the second voltage generator 144 generating a guard signal, that is to say an electrical excitation signal substantially identical to the excitation signals of the capacitive detection electrode 118. By substantially identical is meant for example that the excitation signals are identical to 100% or have deviations of amplitudes of less than 20% when they are not staggered temporarily. The guard signal can be produced by copying the excitation signal of the capacitive sensing electrode 118 through the follower circuit 145 connected for example to the output of the first voltage generator 146 producing the excitation signal of the electrode capacitive sensing 118 (Figure 10). The follower 145 and the second voltage generator 144 may be a single component. Connecting the follower 145 and the second voltage generator 144 on the output of the first voltage generator 146 makes it possible to copy the excitation signal actually sent to the capacitive detection electrode 118.

The active guard 143 then acts as a Faraday cage in which the internal electric field is canceled, forming a barrier around the light emitting diode 114 for spurious electromagnetic interference generated by the supply of the diode 114.

This type of disturbance can occur in particular when the power supply of the light-emitting diode 114 is modulated by pulse width modulation (PWM or PWM in English for "Pulse Width Modulation"). A pulse width modulation power supply 147 modulates the light intensity of the light emitting diode 114 with a good energy efficiency.

The active guard 143 may furthermore have an internal element arranged in an inner layer of the printed circuit board 112, extending between the capacitive detection electrode 118 and the supply conductors 152 of the light-emitting diode 114. This element internal may be formed by an inner flat closed form of the squirrel cage, such as the inner ring 151. The outer diameter of the inner ring 151 thus has for example the same dimension as the diameter of the detection electrode capacitive 118 and a dimension therefore greater than the dimensions of the ring 149 surrounded by the capacitive sensing electrode 118.

It is furthermore preferably provided that a gap 148 is provided between the optical guide 120 and the active guard 143 (FIG. 8). The gap 148 makes it possible not to isolate the capacitive detection electrode 118 from the field induced by the hand of the user through the front face 104. The useful signal can thus reach the capacitive detection electrode 118. The interstice 148 is for example formed by air, allowing the dielectric permittivity of the gap to be lower than that of the material of a guide optical 120 polycarbonate for example.

The active guard 143 thus makes it possible to attenuate or even eliminate any electrical (capacitive) coupling between the light-emitting diode 114 and the capacitive detection electrode 118. The capacitive detection electrode 118 is not disturbed by signals parasitic, which improves the signal-to-noise ratio and therefore the sensitivity of a user's touch detection at the front face 104 of the style facade 102.

Claims

CLAIMS l. A capacitive and backlit control interface (ιοο) for a motor vehicle, comprising:

- a style facade (102) with a front face (104) to be turned towards a user and a rear face (106) opposite the front face (104), the style facade (102) having a backlit area (108)

- a printed circuit board (112) mounted at a distance (G) and opposite the rear face (106) of the style facade (104),

an electroluminescent diode (114) mounted on the printed circuit board (112),

a capacitive detection sensor (116),

at least one capacitive sensing electrode (118) electrically connected to the capacitive sensing sensor (116),

characterized in that the capacitive sensing electrode (118) is disposed on the printed circuit board (112) and in that the control interface (100) further comprises a transparent or translucent optical guide (120) having a housing (121) of the light emitting diode (114), the optical guide (120) being in contact with the capacitive sensing electrode (118).

2. Interface according to claim 1, characterized in that the capacitive sensing electrode (118) is formed by at least one conductive track of the printed circuit board (112).

3. Interface according to claim 1 or 2, characterized in that the detection electrode (118) surrounds the light emitting diode (114).

4. Interface according to any one of claims 1 to 3, characterized in that the optical guide (120) extends from the printed circuit board (112) to the rear face (106) of the facade style (102).

5. Interface according to any one of claims 1 to 4, characterized in that the optical guide (120) is formed by a solid body.

6. Interface according to any one of claims 1 to 5, characterized in that the optical guide (120) is made of transparent polycarbonate.

7. Interface according to any one of claims 1 to 5, characterized in that the optical guide (120) is made of polymethyl methacrylate.

8. Interface according to any one of claims 1 to 5, characterized in that the optical guide (120) is made of transparent silicone.

9. Interface according to any one of claims 1 to 8, characterized in that the material forming the optical guide (120) is electrically non-conductive.

10. Interface according to any one of claims 1 to 8, characterized in that the material forming the optical guide (120) comprises charges or additives making the optical guide (120) electrically conductive.

11. Interface according to any one of claims 1 to 8, characterized in that the material forming the optical guide (120) has at least a portion of its periphery a transparent conductive layer connecting the capacitive sensing electrode (118). to the style facade (102).

12. Interface according to any one of claims 1 to 11, characterized in that the optical guide (120) is fixed on the printed circuit board (112).

13. Interface according to any one of claims 1 to 12, characterized in that a portion (122) of the face of the optical guide (120) vis-à-vis the light emitting diode (114) is a curved diopter .

14. Interface according to any one of claims 1 to 13, characterized in that the face of the optical guide (120) vis-à-vis the rear face (106) of the style facade (102) is in contact with this rear face (106).

15. Interface according to any one of claims 1 to 14, characterized in that the backlit area (108) has a symbol (110) etched.

16. Interface according to any one of the preceding claims, characterized in that it comprises an active guard (143) disposed on the printed circuit board (112), surrounding the light emitting diode (114) being interposed between the light emitting diode. (114) and the capacitive sensing electrode (118).

17. Interface according to the preceding claim, characterized in that a gap (148) of air is provided between the optical guide (120) and the active guard (143).

18. Interface according to one of claims 16 or 17, characterized in that the active guard (143) extends in the printed circuit board (112) forming a "squirrel cage".

19. Interface according to one of claims 16 to 18, characterized in that the active guard (143) has an inner member (151) arranged in an inner layer of the printed circuit board (112), extending between l capacitive sensing electrode (118) and power conductors (152) of the light emitting diode (114).

Interface according to one of Claims 16 to 19, characterized in that the capacitive detection sensor (116) comprises a first voltage generator (146), a second voltage generator (144) and a follower circuit (145). , the active guard (143) being connected to the second voltage generator (144) configured to generate a guard signal substantially identical to the signals energizing the capacitive sensing electrode (118) through a follower circuit (145) connected to the output of the first voltage generator (146) producing the excitation signal of the capacitive sensing electrode (118).

21. Interface according to one of the preceding claims, characterized in that it comprises a pulse width modulation power supply (147) configured to supply the light emitting diode (114).