FR2712408A1 - Keyboard for controlling an electric or electronic system, in particular for an anti-theft system for a motor vehicle. - Google Patents

Abstract

The present invention relates to a control keypad for an electrical or electronic system, in particular for a motor vehicle anti-theft system, characterized in that it comprises: a housing (100, 200) which houses: a printed circuit (500), a membrane of elastic material of the silicone type provided with conductive pads (328) for connecting, on command, associated conductive pads (528) provided on the printed circuit (500) and an optical prism plate (400) forming a diffuser suitable for providing illumination of the keyboard, in which the prism plate (400) and the printed circuit (500) are snapped into the housing (100, 200) and the silicone membrane (300) ensures both the wedging of the prism plate (300) and of the circuit printed (500).

Description

The present invention relates to the field of keyboards.

  control of electrical or electronic systems.

  The present invention finds particular application in the production of an anti-theft system for a motor vehicle, comprising a control keyboard, and a circuit capable of acting on at least one member.

  active vehicle, for example injection means, to invalidate it

  ci, failing to enter a predetermined code using the keyboard in

a predefined deadline.

  Many control keyboards have already been proposed.

  In particular, control keyboards are known today comprising: - a housing provided on its front face with several openings each capable of receiving a respective key, - a printed circuit housed fixed in the housing and - a silicone membrane interposed between the keys and the printed circuit and provided with conductive pads capable of connecting associated pads on the

  printed circuit when keys are pressed.

  Such keyboards are for example disclosed in documents FR-A2669462 and FR-A-2647588, according to which the keys are integrated into

the membrane.

  These known keyboards are not entirely satisfactory, however. The main object of the present invention is to improve the

existing keyboard systems.

  More specifically, auxiliary aims of the present invention are: to improve the tightness of keyboards to external agents, and in particular to dust, - to produce an economical keyboard, - to produce a keyboard which is easy to assemble, - to make an illuminated keyboard,

  - to create a compact keyboard.

  These various aims are achieved within the framework of the present invention by means of a control keyboard, in particular for an anti-theft system for a motor vehicle, of the type comprising: of conductive pads for connecting, on command, associated conductive pads provided on the printed circuit, and an optical prism board forming a diffuser adapted to provide lighting for the keyboard, in which the prism board and the printed circuit are snapped into the housing and the membrane silicone ensures both the timing of the plate

prism and printed circuit.

  Other features, purposes and advantages of this

  invention will appear on reading the detailed description which will

  follow, and with reference to the appended drawings given by way of non-limiting example and in which: - Figure 1 shows an exploded schematic perspective view of a keyboard according to a preferred embodiment of the present invention, - Figure 2 shows a partial perspective view of the same keyboard, - Figures 3A, 3B and 3C show, in a cross-sectional view, three alternative embodiments of a key for the keyboard according to the present invention, - Figure 4 shows a front perspective view of a keyboard cover according to the present invention, - Figure 5 shows a plan view of a printed front of the keyboard according to the present invention, - Figures 6 and 7 show two perspective views respectively front and rear of a membrane used in the keyboard according to the present invention, - Figure 8 shows a front perspective view of an optical prism plate ant diffuser according to the present invention, - Figure 9 shows a perspective view of an additional sealing membrane capable of being used in the context of the present invention, - Figures 10, 11 and 12 show three views in section of the cover according to the present invention according to the section planes referenced XX, XI-XI and XII, XII in FIG. 4, and - FIGS. 13 and 14 represent two views in orthogonal section between

  them of an assembled keyboard according to the present invention.

  As can be seen in the appended figures, the keyboard according to the present invention essentially comprises: - a housing formed by assembling a front cover 100 and a rear bottom 200, - a membrane 300 made of elastic material forming a keyboard, - an optical plate / prism forming a diffuser 400, and

- a printed circuit 500.

  Where appropriate, as will be explained below, the keyboard according to the present invention can be completed by a printed front 600 visible in FIG. 5 and an additional membrane

  seal 700, visible in FIG. 9.

  The cover 100 and the bottom 200 constituting the housing can be the subject of numerous variant embodiments. Preferably, they are

  made by plastic molding.

  Although the outline of the cover 100 and the bottom 200 can also be the subject of numerous variants, preferably, these have a rectangular outline, as can be seen in the appended figures. The cover 100 more precisely comprises a generally flat wall 110 forming the front face of the keyboard, surrounded by a skirt

  rectangular 150 projecting from its rear face.

  Preferably, the wall 110 is provided on its front face, with a peripheral framing rib 113 whose height is equal to

  the thickness of the printed facade 600.

  The front wall 110 is provided with several openings.

  First, the wall 110 is provided with several openings 120 intended to each receive an associated key 320 provided on the

membrane 300.

  Preferably these openings 120 are arranged regularly

  according to a matrix of rows and columns on the wall 110.

  More specifically, according to the particular and nonlimiting embodiment shown in the appended figures adapted to a twelve-key keyboard 320, the wall 110 has twelve openings 120 arranged according to

four columns of three rows.

  Of course, the section of the openings 120 must be complementary to the cross section of the keys 320. According to the particular nonlimiting embodiment shown in the appended figures,

  the openings 120 are of rounded oblong shape.

  Preferably, the wall 110 also has a second series of openings 122 designed to be placed opposite respectively associated symbols 622 formed on the printed facade 600. Preferably, a symbol 622 and consequently an opening 122 are associated respectively with each key 320. The geometry of the openings 122 can

  be the subject of numerous variant embodiments.

  It will also be noted on examining the appended figures, the presence in the front wall 110 of two additional cylindrical openings 124. These openings 124 are preferably placed laterally with respect to the opening matrix 120 receiving the keys 320. The openings 124 are designed to receive indicators carried by the printed circuit 500 for viewing the state of the control circuit. Preferably, these openings 124 are each surrounded by

  a cylindrical sheath 126 projecting from the rear face of the wall 110.

  The wall 110 is also advantageously provided, on its rear face with protruding pins 116, for example cylindrical, designed to ensure the centering of the plate 400. According to the particular embodiment shown in the appended figures, two are thus provided

  centering pins 116 on the rear face of the wall 110.

  The front cover 100 and the rear bottom 200 can be immobilized by any suitable known means, for example by gluing,

  ultrasonic welding, screwing, etc.

  However, preferably, in the context of the present invention, the cover 100 and the rear bottom 200 are snapped together. For this purpose, the front cover 100 is preferably provided, at the level of the skirt 150, with four elastic tabs 152 each provided with a toothing 154, capable of engaging with a respective housing 254 formed s

in the rear bottom 200.

  The front cover 100 also has, at its peripheral skirt 150, latching structures of the plate 400 and the

printed circuit 500.

  More specifically, according to the particular and nonlimiting embodiment shown in the appended figures, there are provided, in the wall of the peripheral skirt 150, four elastic snap teeth 160

  for immobilization of plate 400.

  More precisely still, a pair of snap teeth 160 is thus provided on each of the two long sides of the skirt 150. These snap teeth 160 are connected to the peripheral wall 150 in the vicinity of the rear edge thereof. and do

  protruding both forwards and inwards from the cover 100.

  Preferably, the peripheral skirt 150 is also provided with internal walls 162 making it possible to guide and position the plate.

  400. These walls 162 extend perpendicular to the wall 110.

  The peripheral skirt 150 also has snap teeth 170 for the printed circuit 500. There is thus preferably provided a tooth 170 on at least three sides of the skirt

device 150.

  Of course, the teeth 170 are located at a distance from the wall 110 greater than the distance separating this wall from the aforementioned teeth 160 designed to immobilize the plate 400. The teeth 170 are preferably molded on the internal face of the peripheral skirt.

  150, as can be seen in particular in FIG. 10 and FIG. 12.

  As can be seen in particular in FIGS. 10 to 12, the skirt can be provided on its internal face with various ribs 156 orthogonal to the wall 110. These ribs 156 can serve as a guide and

to support the printed circuit 500.

  The rear bottom 200 can be the subject of numerous variant embodiments. It has a complementary geometry of the front cover 100. Essentially, the rear bottom 200 comprises a generally flat rear wall 210 surrounded by a peripheral skirt 250 of

  same geometry as the peripheral skirt 150 of the front cover 100.

  The openings 254 intended to receive the elastic tabs

  152 are formed in the peripheral skirt 250.

  It will be noted that preferably, the rear bottom 200 has a housing 220 designed to receive a connector 520 carried by the circuit

printed 500.

  The membrane 300 is preferably made of silicone material or equivalent. More specifically, the membrane 300 is composed

  essentially of an electrically non-conductive elastic material.

  The membrane 300 performs three basic essential functions.

  The first function of the membrane 300 is to ensure contacting on the printed circuit 500 when a key 320 is pressed. The second function of the membrane 300 is to ensure the setting

  of board 400 and printed circuit 500.

  Finally, the third function of the membrane 300 is to ensure

tightness of the system.

  The membrane 300 essentially comprises a flat sheet 310 which carries a plurality of actuating keys 320 in a number equal to the number of openings 120 provided in the front face 110 of the housing. The keys 320 are thus placed on the sheet 310 according to an arrangement in

  matrix identical to that of the openings 120 in the wall 110.

  The keys 320 came from molding with the sheet 310.

  The keys 320 can be the subject of numerous variant embodiments known to those skilled in the art, as described for example

  in the documents of the state of the art FR-A-2669462 and FR-A2647588.

  Each key 320 mainly comprises a block 322 of rounded envelope, projecting from the front face of the sheet 310. The cross section, parallel to the sheet 310, of each block 322, is complementary to the cross section of the openings 120. Each block 322 is connected to the surrounding sheet 310 by means of a lip

blistering frustoconical 324.

  In a manner known per se, the function of this connecting lip 324 between the sheet 310 and each block 322 is to authorize an abrupt movement of each key 320 when the force exerted on it exceeds

a predetermined threshold.

  Generally the connecting lips 324 are, at rest, concave towards the rear of the membrane 300 so that the blistering effect of the keys

  320 is obtained by inverting the concavity of these connecting lips 324.

  In addition, each block 322 is extended by a central finger 326,

  for example cylindrical, projecting from the rear face of the membrane 300.

  The rear end of each finger 326 is thus placed opposite the printed circuit 500. This rear end of each finger 326 is provided with a pad 328 of electrically conductive material, for example carbon or any other electrically conductive material, such as for example a noble metal. The pellets 328 can be overmolded or screen printed, or else deposited by any equivalent means on

  the rear end of the fingers 326.

  It will be noted that the membrane 310 is provided on its front face with a network of grooves 330. These grooves 330 communicate, on the one hand between them, on the other hand communicate with the cavities 332 delimited

  around each block 322 by the blistering connecting lips 324.

  More precisely, according to the particular embodiment shown in FIG. 6, two series of orthogonal grooves 330 are provided, which surround each key 320. These grooves 330 are used in particular when the keyboard incorporates an additional sealing membrane 700 on the front of the keyboard membrane 300, to avoid the harmful suction effects which may result from the

  juxtaposition of two waterproof membranes.

  It will also be noted that, as seen in FIGS. 6 and 7, the sheet 310 is provided on its rear face with several candles

orthogonal 340 projecting.

  More specifically, according to the preferred embodiment shown in the appended figures, a candle 340 is provided near each of the four corners of the rear face of the membrane 300. More specifically, a first candle 341 is formed by a

  full pawn of square cross section.

  A second candle 342 is formed by a pawn full of section

rectangular right.

  In contrast, the other two candles 343, 344 are formed of hollow cylindrical chimneys. These cylindrical chimneys 343, 344 are placed opposite the openings 124 formed in the wall 110. They are

  designed to receive system status indicators.

  The candles 340 are intended to support, by their rear face, and consequently to wire, the printed circuit 500, when the latter is snapped into the teeth 170. The membrane 300 is also preferably provided with cylindrical barrels 350 intended to receive the centering pins 116 and seal thereon. The 350 barrels protrude from the rear face of the

membrane 300.

  As indicated above, a second membrane 700 improving the seal can be placed on the front of the keyboard membrane 300. This seal membrane 700 advantageously has a constant thickness. It essentially comprises a flat sheet 710 provided with a network of protrusions 720 of

  geometry and complementary arrangement of pavers 322.

  The waterproofing membrane 700 can have openings

  placed opposite the openings 122 of the wall 110.

  It also preferably has openings 724 placed opposite the openings 124 of the wall 110 and openings 716 receiving

the centering pins 116.

  762 cutouts formed around the periphery of the membrane 700

  are engaged on the walls 162 of the housing.

  The sealing membrane 700 is thus pinched between the face

  internal of the wall 110 and the membrane forming the keyboard 300.

  The waterproofing membrane 700 is advantageously formed from translucent silicone material, loaded where appropriate with colored pigments, for example black pigments, depending on the style and aesthetics sought. It will be noted that the presence of the waterproofing membrane 700 charged with pigment, on the front of the membrane forming the keyboard 300, makes it possible to improve the homogeneity of the lighting, despite the presence of

  discrete sources to provide this lighting, on the printed circuit 500.

  According to the embodiment shown in the figures, the production of the snap teeth 160, 170, by molding, on the peripheral skirt 150 of the front cover 100 results in the formation of openings

112 on the front of the housing.

  To avoid any light leakage at this level, preferably at least one of the two silicone membranes 300, 700 is provided with peripheral beads or lips adapted to close these openings.

112.

  Of course, those skilled in the art will also be able to adapt the molding technique in a manner known per se, teeth 160,170 in particular by the use of drawers, to avoid the formation of such openings 112, in order to perfect the sealing of the device. So is

  even for the openings 254 in the bottom 200.

  The plate 400 shown in Figure 8 is made of an optically transparent material, for example polycarbonate or poly (methacrylate) methyl. This part 400 is preferably produced by

molding.

It performs several functions.

  Its main role is to guide the light coming from light sources 580 carried by the printed circuit 500 towards the symbols 622 of

the printed facade 600.

  Another function of the plate 400 is to serve as a support and a support for the sheet 310 of the membrane forming the keyboard 300 thanks to

  the snap-fit on the teeth 160.

  Another function of the board 400 is to guide the keys 320

  in translation perpendicular to the wall 110.

  Another function of stage 400 is to guide the candles

  holding 340 provided on the rear face of the membrane 300.

  The plate 400 has a complementary contour of the internal volume of the housing. Thus, the plate 400 preferably has a rectangular outline. Plate 400 has at least one through bore 480

  intended to receive a light source carried by the printed circuit 500.

  This bore 480 is preferably cylindrical of revolution about an axis perpendicular to the mean plane of the plate 400 so that the light coming from the light source 580 penetrates into the plate 400 without

refraction or reflection.

  More specifically, according to the preferred embodiment shown in Figure 8 attached, the plate 400 has two bores 480. These two bores 480 are arranged substantially along a diagonal of the key matrix 320, that is to say more precisely in the center of two respective groups four 320 keys located on corners

  diagonally opposite of this matrix.

  To ensure the locking of the plate 400 on the elastic teeth 160, the plate 400 is preferably provided with projecting ears 460. It is thus preferably provided two ears 460 projecting respectively on each long side of the plate 400, designed for

  respectively engage with a toothing 160.

  Preferably, these ears 460 have edges

bevelled engagement 462.

  To guide the fingers 326 of each key 322, the plate 400 is provided with a matrix of through bores 426 of cross section complementary to said fingers 326. These bores 426 are provided in the center of cavities 422 opening out on the front plate 400. These cavities 422 have a cross section complementary to the blocks 322, to allow the

blistering displacement of these.

  Preferably, these cavities 422 are themselves surrounded by an annular recess 429 intended to receive a complementary rib 329 provided on the rear face of the membrane 300 on the

periphery of each key 320.

  The plate 400 also has openings 441, 442, 443 and 444 respectively complementary to the candles 341, 342, 343, 344 and intended to receive these. Finally, the plate 400 has through passages 416 intended to receive the complementary centering fingers 116. Preferably, these passages 416 and the pins 116

complementary are layered.

  To avoid the leakage of light introduced by the openings 480, on the periphery of the plate 400, the latter is preferably provided on its periphery with a roof prism. In other words, the edge 410 of the plate 400 is preferably formed of two facets 412, 414 symmetrical with respect to a median plane of the plate 400, inclined on the order of 45 'with respect to this median plane and forming a convex dihedral towards

the outside of plate 400.

  Preferably, there are provided near the cavities 422 intended to receive the keys 320 furthest from the passages 480 receiving the S light sources 580, reflection surfaces intended to reflect the light channeled by the plate 400 towards the blocks 322 forming the keys. These reflection surfaces can be formed of any suitable structure. These are for example simple frustoconical cavities made

  by molding, with concavity opening onto the rear face of the plate 400.

  The number and the arrangement of these reflection surfaces are determined according to the particular layout of the keys on the

platinum 400.

  The printed circuit 500 can be the subject of numerous variant embodiments. Its structure will therefore not be described in detail

thereafter.

  It is preferably a double-sided printed circuit.

  In FIG. 1 appended, apart from the aforementioned light sources 580 and the connector 520, there are various components 510 and a matrix of pairs of electrically conductive pads 528 placed respectively opposite the pads 328 of the keys 320. Thus, the pairs 528 of electrically conductive pads are short-circuited

  when an associated key 320 is actuated.

  The printed facade 600 shown in FIG. 5 can be the subject of numerous variant embodiments, depending on the style of keyboard sought. Preferably, the symbols 622 are produced by screen printing in a sheet of plastic material, for example based on the material

  marketed under the name 'LEXAN'.

  In addition to the symbols 622 mentioned above, the front panel 600 has openings 620 allowing the passage of the keys 320, as well as colored areas 624 placed respectively with regard to the indicator lights

  carried by circuit 500 and placed in chimneys 343, 344.

  The light sources 580 carried by the printed circuit 500 can be formed by any suitable known lighting means, such as

  for example light emitting diodes.

  However, in the context of the present invention, the sources

  580 luminaires are preferably formed from small filament lamps.

  These have the advantage of delivering white light. To ensure the assembly of the keyboard according to the present invention, the procedure is essentially as follows. The sealing membrane 700, when it is used, is placed on the front face of the membrane 300 forming the keyboard and the assembly

  thus formed is disposed inside the cover 100.

  The support plate 400 is then engaged in the cover 100, taking care to introduce the fingers 326 into the openings 426 and the candles 341, 342, 343, 344 in the complementary passages 441, 442, 443 and 444. The plate 400 is immobilized at the inside of the cover 100 as soon as the ears 460 pass through the latching teeth 160. The plate 400 is then cabled and free of any play thanks to the pinching of the membrane 300 obtained between the internal face of the wall 110 of the cover and the support plate 400, at the ribs 329 surrounding each key 320, in the

  respective offset 429 of plate 400.

  It should be noted that the height of the fingers 326 and of the candles 340 is greater than the thickness of the plate 400 so that the fingers 326 and

  the candles 340 protrude from the rear face of the plate 400.

  Thus, on the one hand the conductive pads 328 preferably formed of carbon are located on the rear of the plate 400 and in no way disturb the path of the light which passes from the plate 400 into the fingers 326 of the keys 320 to ensure the lighting

these.

  On the other hand the 340 candles serve as elastic support to the

printed circuit 500.

  To immobilize it, it suffices therefore to engage the printed circuit on the rear of the plate 400, until it clicks into place.

  printed circuit 500 on the elastic teeth 170.

  Of course, to ensure effective and free play of the plate 400 and the printed circuit 500, the thickness of the membrane 300 at the ribs 329 must be greater than L1-L2, relationship in which L1 represents the distance separating the snap face of the teeth 160 from the rear face of the wall 110 and L2 represents the thickness of

  the plate 400 at the level of the recesses 429.

  Furthermore, the sum of the thickness of the membrane 300 and the height of the candles 340 must be greater than L3-L4, a relationship in which L3 denotes the distance separating the snap face of the teeth 170 from the internal face of the wall 110 and L4 denotes the thickness of the circuit

printed 500.

  It then remains to snap the rear bottom 200 onto the hood.

  before 100 thanks to the snap-in tabs 152.

  Once the assembly thus produced, the structure comprises from the front to the rear of the system, the wall 110, the sealing membrane 700, the membrane forming the keyboard 300, the plate forming the prism 400 and the

printed circuit 500.

  The electrical connection between the pairs of conductive pads 528 resulting from the actuation of a key 320 is used in all

  technique known to those skilled in the art.

  The light from the light sources 580 is guided by the plate 400 to the respective keys 320 into which it penetrates the

finger level 326.

  Of course the present invention is not limited to the particular embodiment which has just been described but extends to any variant

conforms to his spirit.

  For example, the waterproofing membrane 700 provided with a colored pigment can be replaced with any equivalent coating or varnish deposited directly on the front face of the membrane 300

forming keyboard.

  Furthermore, the membrane 300 can also be adapted to ensure automatic take-up of the closing clearances, by elasticity,

  between the front cover 100 and the rear bottom 200. As shown in FIG. 2, the front face 110 of the cover 100 can be

  domed. Furthermore, as shown in FIGS. 3A, 3B and 3C, the keys 320 can be the subject of numerous variants of

  realization as for their geometry.

  Likewise, the style of the front panel of the system can be

many variations.

  Thus, the sealing membrane 700, or the coating deposited directly on the front face of the membrane forming the keyboard 300 can be adapted to define keys with black appearance by day and white by night, or even keys with black appearance. by day and surrounded by a white border

the night.

Claims (22)

  1. Keyboard for controlling an electrical or electronic system, in particular for an anti-theft system for a motor vehicle, characterized in that it comprises: - a housing (100, 200) which houses: a printed circuit (500) a membrane ( 300) made of elastic silicone-type material provided with conductive pads (328) for connecting, on command, associated conductive pads (528) provided on the printed circuit (500) and an optical prism plate (400) forming a diffuser suitable for lighting the keyboard, in which the prism board (400) and the printed circuit (500) are snapped into the housing (100, 200) and the silicone membrane (300) ensures   both the setting of the prism board (300) and the printed circuit (500).   2. Keyboard according to claim 1, characterized in that it further comprises a waterproof membrane (700), silicone type, on the front face of the membrane (300) provided with electrically pads conductive (328).   3. Keyboard according to one of claims 1 or 2, characterized by   the fact that the housing comprises a skirt (110) provided with teeth (160)   ensuring the locking of the plate (400).   4. Keyboard according to one of claims 1 to 3, characterized by the   the case (100) comprises a skirt (110) provided with teeth   (170) ensuring the locking of the printed circuit (500).   5. Keyboard according to one of claims 1 to 4, characterized by the   the fact that the housing (100) also has internal pins (116) ensuring the centering of the plate (400).   6. Keyboard according to one of claims 1 to 5, characterized by the   causes the membrane (300) to have a structure ensuring sealing on the centering pins (116).   7. Keyboard according to one of claims 1 to 6, characterized by the   causes the membrane (300) to have protruding candles (340) ensuring   the timing of the printed circuit (500).   8. Keyboard according to claim 7, characterized in that at least some of the candles (343, 344) are adapted to receive indicator lights.   9. Keyboard according to one of claims 1 to 8, characterized by the   the fact that the membrane (300, 700) has peripheral lips designed to close openings (112) formed on the front face of the housing, to   avoid any light leakage at this level.   10. Keyboard according to one of claims 1 to 9, characterized by   the fact that the plate (400) is provided with at least one cylindrical orifice   intended to receive a light source of lighting (580).   11. Keyboard according to one of claims 1 to 10, characterized by   the fact that the light sources are made up of small filament lamps.   12. Keyboard according to one of claims 1 to 11, characterized by   the fact that the plate (400) is provided with a roof prism (412, 414) on its periphery.   13. Keyboard according to one of claims 1 to 12, characterized by   the fact that the plate (400) is provided with projecting ears (460), on its periphery, adapted to engage with clipping teeth   complementary (160) provided on the housing (100).   14. Keyboard according to one of claims 1 to 13, characterized by   the fact that the plate (400) has through openings (426) intended to receive fingers (326) integral with each key (320) formed on the membrane (300).   15. Keyboard according to claim 14, characterized in that the height of the fingers (326) provided on each key (320) of the membrane (300) is greater than the thickness of the plate (300) so that the electrically conductive end (328) of each finger (326) makes   projection on the rear of the plate (400).   16. Keyboard according to one of claims 1 to 15, characterized by   the fact that the plate (400) is provided with through openings (440) intended to receive complementary candles (340) projecting from the front back of the membrane (300).   17. Keyboard according to one of claims 1 to 16, characterized by   the fact that the candles (340) are adapted to protrude rear face   of the plate (400) in order to support the printed circuit (500).   18. Keyboard according to one of claims 1 to 17, characterized by   the fact that the plate (400) has on the periphery of each opening (426) designed to receive a finger (326) keys (320), a cavity   annular (422) complementary to the cross section of the keys.   19. Keyboard according to claim 18, characterized in that each cavity (422) is surrounded by a recess (429) complementary   a rib (329) provided on the rear face of the membrane (300).   20. Keyboard according to claim 19, characterized in that the membrane (300) is pinched between the internal face of the housing (100) and the   plate (400), at the ribs (329).   21. Keyboard according to one of claims 1 to 20, characterized by   the fact that the membrane (300) provided with electrical pads   conductive (328) is provided with a pigmented coating on its front face.   22. Keyboard according to one of claims 1 to 21, characterized by   the fact that the membrane (300) provided with an electrically conductive pad also ensures automatic take-up of the play of   closure between a front cover and a rear bottom constituting the housing.