Patent Publication Number: US-2013229828-A1

Title: Display device of electrical apparatus

Description:
FIELD OF THE INVENTION 
     The present invention relates to a display device, and more particularly to a display device capable of displaying various patterns. 
     BACKGROUND OF THE INVENTION 
     Nowadays, a casing of an electrical apparatus is usually equipped with a display device to provide a prompt function. According to the patterns shown on the display device, the user may realize the current operating status of the electrical apparatus. Generally, the display device comprises a light-emitting element and a display panel. The light-emitting element is used for emitting a light beam and directing the light beam into the display panel. When the light beam is transmitted through the display panel, a corresponding luminous pattern is visible. 
     Hereinafter, the structure of a conventional display device will be illustrated with reference to  FIG. 1 .  FIG. 1  is a schematic exploded view illustrating the internal structure of a conventional display device. The conventional display device  1  comprises a backlight module  10  and a display panel  11 . The backlight module  10  is disposed under the display panel  11 . As shown in  FIG. 1 , the backlight module  10  is located at the right side of the display panel  11 . The display panel  11  is a twisted nematic (TN) liquid crystal display panel. The backlight module  10  comprises at least one light-emitting element (not shown) and a light guide plate  101 . The at least one light-emitting element is used for emitting at least one light beam and directing the at least one light beam to the light guide plate  101 . The light guide plate  101  is used for guiding the at least one light beam to the display panel  11 . 
     The display panel  11  comprises a first polarizing filter  111 , a first glass plate  112 , a plurality of liquid crystal molecules  113 , a second glass plate  114 , and a second polarizing filter  115 . The first polarizing filter  111  is disposed over the first glass plate  112 . As shown in  FIG. 1 , the first polarizing filter  111  is located at the left side of the first glass plate  112 . The first polarizing filter  111  is a vertical filter for filtering the light beam incident into the display panel  1  and only allowing the vertically polarized light to go through. The first glass plate  112  is arranged between the first polarizing filter  111  and the liquid crystal molecules  113 . In addition, a first transparent conductive film  1121  is coated on a surface of the first glass plate  112  to be used as an electrode. The first transparent conductive film  1121  is arranged in a shape of a number “8”. The second glass plate  114  is arranged between the liquid crystal molecules  113  and the second polarizing filter  115 . In addition, a second transparent conductive film (not shown) is coated on a surface of the second glass plate  114  to be used as an electrode. The first transparent conductive film  1121  and the second transparent conductive film are both made of indium tin oxide (ITO). Moreover, the first transparent conductive film  1121  and the second transparent conductive film are connected to a control circuit (not shown). 
     The liquid crystal molecules  113  are arranged between the first glass plate  112  and the second glass plate  114 . Depending on the arrangement of the liquid crystal molecules  113 , the incident light is rotated at a twist angle of from 0 to 90 degrees. In addition, the twist angle is changed according to the arrangement of the liquid crystal molecules  113 . 
     The surface of the first glass plate  112  is further plated with a first surface alignment layer (not shown). Due to the first surface alignment layer, the liquid crystal molecules  113  are arranged along the vertical direction and parallel with the surface of the first glass plate  112 . Moreover, the surface of the second glass plate  114  is plated with a second surface alignment layer (not shown). Due to the second surface alignment layer, the liquid crystal molecules  113  are arranged along the horizontal direction and parallel with the surface of the second glass plate  114 . The second polarizing filter  115  is disposed under the second glass plate  114 . As shown in  FIG. 1 , the second polarizing filter  115  is located at the right side of the second glass plate  114 . The second polarizing filter  115  is a horizontal filter for filtering the light beam incident into the display panel  1  and only allowing the horizontally polarized light to go through. 
     In a case that the backlight module  10  emits at least one light beam and directs the at least one light beam to the display panel  11 , the at least one light beam is incident into the second polarizing filter  115 . The horizontally-polarized portion of the at least one light beam is transmitted through the second polarizing filter  115 , but the other portions of the at least one light beam are blocked by the second polarizing filter  115 . The horizontally-polarized portion of the at least one light beam is then introduced into the second glass plate  114 , and partially transmitted through the gaps between the horizontally-arranged liquid crystal molecules  113  which are disposed on the second glass plate  114 . According to the arrangement of the liquid crystal molecules  113 , a portion of the light beam is rotated by 90 degrees. The rotated portion of the light beam is transmitted through the gaps between the vertically-arranged liquid crystal molecules  113  along the vertical direction, and then left from the liquid crystal molecules  113 . Next, the light beam is sequentially transmitted through the first glass plate  112  and the first polarizing filter  111 . Since the portion of the light beam is propagated along the vertical direction, the portion of the light beam is transmissible through the first polarizing filter  111 . If the light beam is transmitted through the first transparent conductive film  1121  of the first glass plate  112 , the first transparent conductive film  1121  exhibits a bright color. Whereas, if the light beam is not transmitted through the first transparent conductive film  1121 , the first transparent conductive film  1121  exhibits a dark color. In such way, the number can be shown on the display panel  11 . 
     Moreover, as the electric field is changed, the arrangement of the liquid crystal molecules  113  is correspondingly changed. The change of the electric field is controlled by the control circuit, which is connected with the first transparent conductive film  1121  and the second transparent conductive film. That is, the control circuit may change the electric field in order to adjust the arrangement of the liquid crystal molecules  113 . Since the arrangement of the liquid crystal molecules  113  is changed, the light beam is transmitted through different positions of the first transparent conductive film  1121 . In such way, a different number may be shown on the display panel  11 . The conventional display device  1  may be designed to display different numbers. Alternatively, the first transparent conductive film  1121  of the first glass plate  112  may be designed to have different shapes, so that the conventional display device  1  may display a number or an English letter. 
     However, since the display panel  11  of the conventional display device  1  is produced by stacking a plurality of plates or filters, the thickness is very large. Since the display panel  11  occupies a lot of layout space of the conventional display device  1 , it is difficult to reduce the overall thickness of the conventional display device  1 . Moreover, the conventional display device  1  should have the control circuit to control the arrangement of the liquid crystal molecules  113  in order to display different patterns. Since the control circuit is necessary and the display panel is complicated, the fabricating cost of the conventional display device  1  is high. In addition, the high-tech display device for displaying different patterns does not always meet the requirements of all users. In some occasions, a simple display device for displaying a simple pattern or a simple character is feasible to some users. Therefore, there is a need of providing a simply display device capable of displaying different patterns. 
     SUMMARY OF THE INVENTION 
     The present invention provides a slim-type display device of an electrical apparatus. 
     The present invention also provides a display device of an electrical apparatus with a simple displaying function. 
     In accordance with an aspect of the present invention, there is provided a display device of an electrical apparatus. The electrical apparatus has a casing. The display device is installed on the casing. The display device includes a first illumination module, a second illumination module, and a circuit board. The first illumination module is used for emitting a first light beam. The first illumination module includes at least one first luminous pattern. The at least one first luminous pattern is visible in response to the first light beam. The second illumination module is for emitting a second light beam. The second illumination module is disposed under the first illumination module and includes at least one second luminous pattern. The at least one second luminous pattern is visible in response to the second light beam. The circuit board is arranged between the first illumination module and the second illumination module. A first edge of the circuit board is inserted into a gap between the first illumination module and the second illumination module for blocking the first light beam or the second light beam. 
     In an embodiment, the casing further includes a protective layer, which is disposed over the first illumination module for protecting the first illumination module. The protective layer includes a light-transmissible zone and a light-shading zone. The light-shading zone is located around the light-transmissible zone for shading the first light beam or the second light beam. The at least one first luminous pattern or the at least one second luminous pattern is visible through the light-transmissible zone in response to the first light beam or the second light beam. In addition, the light-transmissible zone has a preset light-shading percentage. f the first light beam or the second light beam is not generated, the at least first luminous pattern of the first illumination module or the at least one second luminous pattern of the second illumination module is invisible according to the preset light-shading percentage. 
     In an embodiment, if the first light beam or the second light beam is not generated, an external light beam from surroundings of the display device is blocked by the light-shading zone according to the preset light-shading percentage, so that the at least one first luminous pattern or the at least one second luminous pattern is invisible, wherein the preset light-shading percentage is in a range between 75% and 80%. 
     In an embodiment, the first illumination module includes a first light-emitting element and a first light-guiding plate. The first light-emitting element is disposed on a first surface of the circuit board for emitting the first light beam. The first light-guiding plate is stacked on the first surface of the circuit board and located at a first side of the first light-emitting element for guiding the first light beam. The second illumination module includes a second light-emitting element and a second light-guiding plate. The second light-emitting element is disposed on a second surface of the circuit board for emitting the second light beam. The second light-guiding plate is stacked on the second surface of the circuit board and located at a first side of the second light-emitting element for guiding the second light beam. 
     In an embodiment, the first light guide plate further includes at least one first opening, and the second light guide plate further includes at least one second opening corresponding to the at least one first opening. The at least one second opening is aligned with the at least one first opening. The casing further includes at least one positioning post corresponding to the at least one first opening and the at least one second opening The at least one positioning post is penetrated through the at least one first opening and the at least one second opening for fixing the first light guide plate and the second light guide plate on the casing. 
     In an embodiment, the first light-emitting element and the second light-emitting element are both side-view light emitting diodes. In addition, the circuit board is parallel with the first light-guiding plate and the second light-guiding plate. 
     In an embodiment, the first light guide plate is made of polycarbonate or polymethyl methacrylate, and the at least one first luminous pattern is disposed on a top surface or a bottom surface of the first light guide plate. The second light guide plate is made of polycarbonate or polymethyl methacrylate, and the at least one second luminous pattern is disposed on a top surface or a bottom surface of the second light guide plate. In addition, each of the at least one first luminous pattern and the at least one second luminous pattern includes a plurality of closely packed light-guiding microstructures. 
     In an embodiment, if the top surface of the first light guide plate and the top surface of the second light guide plate are both flat surfaces, the first light guide plate and the second light guide plate are made of hard and non-flexible polycarbonate or hard polymethyl methacrylate, and each of the first light guide plate and the second light guide plate has a thickness of about 1 mm. Alternatively, if the top surface of the first light guide plate and the top surface of the second light guide plate are both curvy surfaces, the first light guide plate and the second light guide plate are made of soft flexible polycarbonate or soft polymethyl methacrylate, and each of the first light guide plate and the second light guide plate has a thickness of about 0.2˜0.4 mm. 
     In an embodiment, a white glossy solder-proof ink layer is further formed on the circuit board for reflecting the first light beam or the second light beam, wherein the white glossy solder-proof ink layer is printed on a first surface and a second surface of the circuit board. 
     In an embodiment, the electrical apparatus is a mouse, a charger, a paper shredder, a Bluetooth earphone or a wireless keyboard. 
     In accordance with another aspect of the present invention, there is provided a display device of an electrical apparatus. The electrical apparatus has a casing. The display device is installed on the casing. The display device includes a first illumination module, a second illumination module, a circuit board, and a light-shading structure. The first illumination module is used for emitting a first light beam. The first illumination module includes at least one first luminous pattern. The at least one first luminous pattern is visible in response to the first light beam. The second illumination module is for emitting a second light beam. The second illumination module is disposed under the first illumination module and includes at least one second luminous pattern. The at least one second luminous pattern is visible in response to the second light beam. The circuit board is arranged between the first illumination module and the second illumination module. The light-shading structure is located at a first side of the circuit board and arranged between the first illumination module and the second illumination module for blocking the first light beam or the second light beam. 
     In an embodiment, the casing further includes a protective layer, which is disposed over the first illumination module for protecting the first illumination module. The protective layer includes a light-transmissible zone and a light-shading zone. The light-shading zone is located around the light-transmissible zone for shading the first light beam or the second light beam. The at least one first luminous pattern or the at least one second luminous pattern is visible through the light-transmissible zone in response to the first light beam or the second light beam. In addition, the light-transmissible zone has a preset light-shading percentage. f the first light beam or the second light beam is not generated, the at least first luminous pattern of the first illumination module or the at least one second luminous pattern of the second illumination module is invisible according to the preset light-shading percentage. 
     In an embodiment, if the first light beam or the second light beam is not generated, an external light beam from surroundings of the display device is blocked by the light-shading zone according to the preset light-shading percentage, so that the at least one first luminous pattern or the at least one second luminous pattern is invisible, wherein the preset light-shading percentage is in a range between 75% and 80%. 
     In an embodiment, the first illumination module includes a first light-emitting element and a first light-guiding plate. The first light-emitting element is disposed on a first surface of the circuit board for emitting the first light beam. The first light-guiding plate is stacked on the first surface of the circuit board and located at a first side of the first light-emitting element for guiding the first light beam. The second illumination module includes a second light-emitting element and a second light-guiding plate. The second light-emitting element is disposed on a second surface of the circuit board for emitting the second light beam. The second light-guiding plate is stacked on the second surface of the circuit board and located at a first side of the second light-emitting element for guiding the second light beam. 
     In an embodiment, the first light guide plate further includes at least one first opening, and the second light guide plate further includes at least one second opening corresponding to the at least one first opening. The at least one second opening is aligned with the at least one first opening. The casing further includes at least one positioning post corresponding to the at least one first opening and the at least one second opening. The at least one positioning post is penetrated through the at least one first opening and the at least one second opening for fixing the first light guide plate and the second light guide plate on the casing. 
     In an embodiment, the first light-emitting element and the second light-emitting element are both side-view light emitting diodes. In addition, the circuit board is parallel with the first light-guiding plate and the second light-guiding plate. 
     In an embodiment, the first light guide plate is made of polycarbonate or polymethyl methacrylate, and the at least one first luminous pattern is disposed on a top surface or a bottom surface of the first light guide plate. The second light guide plate is made of polycarbonate or polymethyl methacrylate, and the at least one second luminous pattern is disposed on a top surface or a bottom surface of the second light guide plate. In addition, each of the at least one first luminous pattern and the at least one second luminous pattern includes a plurality of closely packed light-guiding microstructures. 
     In an embodiment, if the top surface of the first light guide plate and the top surface of the second light guide plate are both flat surfaces, the first light guide plate and the second light guide plate are made of hard and non-flexible polycarbonate or hard polymethyl methacrylate, and each of the first light guide plate and the second light guide plate has a thickness of about 1 mm. Alternatively, if the top surface of the first light guide plate and the top surface of the second light guide plate are both curvy surfaces, the first light guide plate and the second light guide plate are made of soft flexible polycarbonate or soft polymethyl methacrylate, and each of the first light guide plate and the second light guide plate has a thickness of about 0.2˜0.4 mm. 
     In an embodiment, the light-shading structure is disposed on a bottom surface of the first light-guiding plate or a top surface of the second light-guiding plate. Moreover, the light-shading structure is formed by painting, spraying, printing or bonding a light-shading material on the bottom surface of the first light-guiding plate or the top surface of the second light-guiding plate. 
     In an embodiment, the light-shading structure is a plastic sheet, a sponge structure or a light-shading plate. The light-guiding structure is disposed within a gap between the first light-guiding plate and the second light-guiding plate and located at a first side of the circuit board. 
     In an embodiment, a white glossy solder-proof ink layer is further formed on the circuit board for reflecting the first light beam or the second light beam, wherein the white glossy solder-proof ink layer is printed on a first surface and a second surface of the circuit board. 
     In an embodiment, the electrical apparatus is a mouse, a charger, a paper shredder, a Bluetooth earphone or a wireless keyboard. 
     The above objects and advantages of the present invention will become more readily apparent to those ordinarily skilled in the art after reviewing the following detailed description and accompanying drawings, in which: 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic exploded view illustrating the internal structure of a conventional display device; 
         FIG. 2  is a schematic perspective view illustrating the outward appearance of a display device of an electrical apparatus according to a first embodiment of the present invention; 
         FIG. 3  is a schematic side view illustrating the display device of the electrical apparatus according to the first embodiment of the present invention; 
         FIG. 4  is a schematic side view illustrating the display device of the electrical apparatus according to the first embodiment of the present invention and taken along another viewpoint; 
         FIG. 5  is a schematic side view illustrating the first light-emitting element and the second light-emitting element of the display device according to the first embodiment of the present invention and taken along another viewpoint; 
         FIG. 6  is a schematic perspective view illustrating the display device of the electrical apparatus according to the first embodiment of the present invention, in which the first luminous patterns are visible; 
         FIG. 7  is a schematic perspective view illustrating the display device of the electrical apparatus according to the first embodiment of the present invention, in which the second luminous patterns are visible; 
         FIG. 8  is a schematic perspective view illustrating the outward appearance of a display device of an electrical apparatus according to a second embodiment of the present invention; 
         FIG. 9  is a schematic perspective view illustrating the outward appearance of a display device of an electrical apparatus according to a third embodiment of the present invention; 
         FIG. 10  is a schematic side view illustrating the display device of the electrical apparatus according to the third embodiment of the present invention; 
         FIG. 11  is a schematic perspective view illustrating the outward appearance of a display device of an electrical apparatus according to a fourth embodiment of the present invention; 
         FIG. 12  is a schematic side view illustrating the display device of the electrical apparatus according to the fourth embodiment of the present invention; and 
         FIG. 13  is a schematic perspective view illustrating the outward appearance of a display device of an electrical apparatus according to a fifth embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     For eliminating the drawbacks encountered from the prior art, the present invention provides a display device of an electrical apparatus.  FIG. 2  is a schematic perspective view illustrating the outward appearance of a display device of an electrical apparatus according to a first embodiment of the present invention.  FIG. 3  is a schematic side view illustrating the display device of the electrical apparatus according to the first embodiment of the present invention. 
     As shown in  FIG. 2 , the electrical apparatus  2  comprises a casing  20  and a display device  21 . The casing  20  comprises a protective layer  201 . In this embodiment, the electrical apparatus  2  is a paper shredder. The protective layer  201  is integrally formed with the casing  20 . As shown in  FIG. 3 , the display device  21  comprises a first illumination module  212 , a second illumination module  213 , and a circuit board  214 . From bottom to top, the second illumination module  213 , the circuit board  214 , the first illumination module  212  and the protective layer  201  are sequentially shown. 
     The first illumination module  212  of the display device  21  comprises a first light-emitting element  2121  and a first light guide plate  2122 . The first light-emitting element  2121  is disposed on a first surface  2141  of the circuit board  214  for emitting a first light beam (not shown). The first light guide plate  2122  is stacked on the first surface  2141  of the circuit board  214 , and located at a first side of the first light-emitting element  2121  for guiding the first light beam. In addition, the first light guide plate  2122  has a plurality of first luminous patterns  2122 A. The first luminous patterns  2122 A are disposed on a bottom surface  2122 B of the first light guide plate  2122 . That is, when the first light beam is emitted by the first light-emitting element  2121 , the first luminous patterns  2122 A of the first light guide plate  2122  are illuminated and become visible. 
     Furthermore, the second illumination module  213  comprises a second light-emitting element  2131  and a second light guide plate  2132 . The second light-emitting element  2131  is disposed on a second surface  2142  of the circuit board  214  for emitting a second light beam (not shown). The second light guide plate  2132  is disposed on the second surface  2142  of the circuit board  214 , located at a first side of the second light-emitting element  2131  for guiding the second light beam. In addition, the second light guide plate  2132  has a plurality of second luminous patterns  2132 A. The second luminous patterns  2132 A are disposed on a bottom surface  2132 B of the second light guide plate  2132 . That is, when the second light beam is emitted by the second light-emitting element  2131 , the second luminous patterns  2132 A of the second light guide plate  2132  are illuminated and become visible. 
     In this embodiment, the first luminous patterns  2122 A and the second luminous patterns  2132 A are closely packed light-guiding microstructures. The light-guiding microstructures are for example closely packed microstructures (e.g. micro lenses or V-shaped notches) or closely packed dots. The light-guiding microstructures that constitute the luminous patterns may change the incidence angles of a portion of the light beam within the first light-emitting element  2121  or the second light guide plate  2132 . Since the uses of the light-guiding microstructures can destroy the total internal reflection path, the light beam is refracted and transmitted through the first light-emitting element  2121  or the second light guide plate  2132 . That is, the light beam is transmitted through the regions over the light-guiding microstructures, so that the first luminous patterns  2122 A or the second luminous patterns  2132 A are visible. 
     In an embodiment, the first light guide plate  2122  and the second light guide plate  2132  are both made of polycarbonate (PC), the first luminous patterns  2122 A are disposed on the bottom surface  2132 B of the second light guide plate  2132 , and the second luminous patterns  2132 A are disposed on a bottom surface  2132 B of the second light guide plate  2132 . Alternatively, in some other embodiments, the first light guide plate  2122  and the second light guide plate  2132  are both made of polymethyl methacrylate (PMMA). Moreover, the first luminous patterns  2122 A are disposed on a top surface of the second light guide plate  2132 , and the second luminous patterns  2132 A are disposed on a top surface of the second light guide plate  2132 . 
     Please refer to  FIG. 3  again. The protective layer  201  is disposed over the first illumination module  212  for protecting the first illumination module  212 . In addition, the protective layer  201  comprises a light-transmissible zone  2011  and a light-shading zone  2012 . The light-shading zone  2012  is located around the light-transmissible zone  2012 . The light-shading zone  2012  is used for shading the first light beam, the second light beam or other external light beams. In response to the first light beam or the second light beam, the first luminous patterns  2122 A or the second luminous patterns  2132 A are visible through the light-transmissible zone  2011 . Moreover, the light-transmissible zone  2011  has a preset light-shading percentage. For example, the preset light-shading percentage is in the range between 75% and 80%. The circuit board  214  is located beside the first illumination module  212  and the second illumination module  213 . In addition, the circuit board  214  is parallel with the first light guide plate  2122  and the second light guide plate  2132 . 
       FIG. 4  is a schematic side view illustrating the display device of the electrical apparatus according to the first embodiment of the present invention and taken along another viewpoint. The first light guide plate  2122  further comprises at least one first opening  2122 C. Corresponding to the first opening  2122 C, the second light guide plate  2132  further comprises at least one second opening  2132 C. In an embodiment, the first light guide plate  2122  comprises a plurality of first openings  2122 C, and the second light guide plate  2132  comprises a plurality of second openings  2132 C. The first openings  2122 C are aligned with respective second openings  2132 C. Moreover, the casing  20  further comprises at least one positioning post  202  corresponding to the at least one first opening  2122 C and the at least one second opening  2132 C. The positioning post  202  is penetrated through the corresponding first opening  2122 C and the corresponding second opening  2132 C, thereby fixing the first light guide plate  2122  and the second light guide plate  2132  on the casing  20 . 
     In some other embodiments, a double-sided adhesive tape (not shown) is arranged between the first light guide plate  2122  and the casing  20 . Through the double-sided adhesive tape, the first light guide plate  2122  is attached on the casing  20 . Consequently, the first light guide plate  2122  is securely fixed on the casing  20 , and the structural connection between the first light guide plate  2122  and the casing  20  is enhanced. 
       FIG. 5  is a schematic side view illustrating the first light-emitting element and the second light-emitting element of the display device according to the first embodiment of the present invention and taken along another viewpoint. The circuit board  214  has a first metallic contact  2143  and a second metallic contact  2144 . The first metallic contact  2143  is disposed on the first surface  2141  of the circuit board  214 . The second metallic contact  2144  is disposed on the second surface  2142  of the circuit board  214 . The first light-emitting element  2121  is disposed on the first surface  2141  of the circuit board  214 . In addition, the first light-emitting element  2121  is connected to the first metallic contact  2143  on the first surface  2141  through a welding material  215  by welding. In this embodiment, the welding material  215  is metallic tin. The second light-emitting element  2131  is disposed on the second surface  2142  of the circuit board  214 . Similarly, the second light-emitting element  2131  is connected to the second metallic contact  2144  on the second surface  2142  through the welding material  215  by welding. As shown in  FIG. 5 , both of the first light-emitting element  2121  and the second light-emitting element  2131  are side-view light emitting diodes. Moreover, the circuit board  214  further comprises a white glossy solder-proof ink layer  2146 . The first light beams and the second beams may be reflected by the white glossy solder-proof ink layer  2146 . In an embodiment, the white glossy solder-proof ink layer  2146  is formed on the first surface  2141  and the second surface  2142  of the circuit board  214  by a printing technology. 
     Please refer to  FIG. 3  again. The first illumination module  212  and the second illumination module  213  are separated from each other by a gap G. A first edge  2145  of the circuit board  214  is inserted into the gap G. Consequently, the first light beam from the first light-emitting element  2121  is blocked by the first edge  2145  of the circuit board  214 . Under this circumstance, the first light beam is not transmitted through the gap G to influence the second illumination module  213 . Similarly, the second light beam from the second light-emitting element  2131  is also blocked by the first edge  2145  of the circuit board  214 . Consequently, the second light beam is not transmitted through the gap G to influence the first illumination module  212 . 
     In a case that the first illumination module  212  and the second illumination module  213  of the display device  21  are disabled and the first light beam and the second light beam are not generated, the first luminous patterns  2122 A and the second luminous patterns  2132 A are not shown on the display device  21 . Although no light beams are emitted by the first light-emitting element  2121  and the second light-emitting element  2131 , the weak external light beams from the surroundings are possibly incident into the light-transmissible zone  2011  of the protective layer  201 . Since the preset light-shading percentage of the light-transmissible zone  2011  is in the range between 75% and 80%, about 75%-80% of the light beams incident into the light-transmissible zone  2011  are absorbed by the light-transmissible zone  2011 . That is, the rest (i.e. 20˜25%) of the light beams are transmitted through the first light-guiding plate  2122 . After the light-guiding microstructures on the bottom surface  2122 B of the first light-guiding plate  2122  are hit by the rest (i.e. 20˜25%) of the light beams, about a half of these light beams are refracted and continuously directed toward the region under the first light-guiding plate  2122  because the incidence angles of the light beams projected on the light-guiding microstructures are different. That is, only about 10% of the light beams are reflected by the light-guiding microstructures and directed toward the protective layer  201 . After the light beams are reflected to the protective layer  201 , portions of the light beams are absorbed by the light-transmissible zone  2011  again. Consequently, only about 2% of the light beams are transmitted through the light-transmissible zone  2011 . Since the light beam intensity is too weak, the first luminous patterns  2122 A and the second luminous patterns  2132 A are invisible. Under this circumstance, the first luminous patterns  2122 A and the second luminous patterns  2132 A fail to be viewed by the user. 
       FIG. 6  is a schematic perspective view illustrating the display device of the electrical apparatus according to the first embodiment of the present invention, in which the first luminous patterns are visible. After the first illumination module  212  is enabled and the first light-emitting element  2121  is turned on, a great portion of the first light beam is laterally incident into the first light-guiding plate  2122 . Moreover, a portion of the first light beam is blocked by the first edge  2145  of the circuit board  214  and reflected by the white glossy solder-proof ink layer  2146  on the surface of the circuit board  214 . Consequently, the portion of the first light beam is directed into the first light-guiding plate  2122  again. When the first light beam within the first light-guiding plate  2122  is directed to the first luminous patterns  2122 A that are constructed by the light-guiding microstructures, the first light beam is directed toward the region over the first light-guiding plate  2122  because the total internal reflection path is destroyed by the light-guiding microstructures. When the first light beam is directed to the light-transmissible zone  2011  of the protective zone  201 , transmitted through the protective layer  201  and about 75%˜80% of the first light beam is absorbed by the light-transmissible zone  2011 . That is, about 20˜25% of the first light beam is allowed to be transmitted through the light-transmissible zone  2011 , and the first luminous patterns  2122 A are visible through the light-transmissible zone  2011  and viewable by the user (see  FIG. 6 ). 
     The operations of enabling the second illumination module  213  of the display device  21  are similar to those of the first illumination module  212 , and are not redundantly described herein. That is, after the second illumination module  213  is enabled, the second luminous patterns  2132 A are viewable by the user (see  FIG. 7 ). 
     As shown in  FIGS. 6 and 7 , the first luminous patterns  2122 A are arranged in a brand logo (e.g. “PRIMAX”), and the second luminous patterns  2132 A are arranged in a specified character (e.g. “PAPER JAM”). For example, in a case that the first luminous patterns  2122 A are shown on the casing  20 , the electrical apparatus  2  is in a use status. Whereas, in a case that the second luminous patterns  2132 A are shown on the casing  20 , the electrical apparatus  2  is in a paper-jam status. On the other hand, if the first luminous patterns  2122 A and the second luminous patterns  2132 A are not shown on the casing  20 , the electrical apparatus  2  is in an off status or a sleep status. That is, the operating status the electrical apparatus  2  may be realized according to the kinds of the luminous patterns. 
     In this embodiment, the display device  21  is installed on a flat surface of the casing  20  of the electrical apparatus  2 . Correspondingly, as shown in  FIG. 3 , the first light guide plate  2122  and the second light guide plate  2132  have flat surfaces. In an embodiment, the first light guide plate  2122  and the second light guide plate  2132  are made of hard and non-flexible polycarbonate. In addition, the thickness of each of the first light guide plate  2122  and the second light guide plate  2132  is about 1 mm. 
     From the above discussions, the overall thickness of the display device  21  of the electrical apparatus  2  is the sum of the thicknesses of the circuit board  214 , the first light guide plate  2122  and the second light guide plate  2132 . The thickness of the first light guide plate  2122  is substantially identical to the thickness of the light guide plate  101  of the conventional backlight module  10 . In comparison with the overall thickness of the conventional display device  1  (including the display panel  11 ), the thickness of the display device  21  of the electrical apparatus  2  according to the present invention is largely reduced. Consequently, the display device  21  of the electrical apparatus  2  of the present invention is slim. Furthermore, it is not necessary to install an additional control circuit in the display device of the present invention to control the luminous patterns. As a consequence, the display device  21  of the electrical apparatus  2  of the present invention is more cost-effective. 
     The present invention further provides a second embodiment.  FIG. 8  is a schematic perspective view illustrating the outward appearance of a display device of an electrical apparatus according to a second embodiment of the present invention. As shown in  FIG. 8 , the electrical apparatus  3  comprises a casing  30  and a display device  31 . In this embodiment, the electrical apparatus  3  is a wireless keyboard. The display device  31  is installed on a flat surface of the casing  30  of the electrical apparatus  3 . The configurations of the display device  31  are similar to those of the display device  21  of the first embodiment, and are not redundantly described herein. The display device  31  is used for displaying the brand logo of the wireless keyboard  3  or the pairing status of the wireless signal receiver (not shown) of the wireless keyboard  3 . For example, the first luminous patterns are arranged in a brand logo (e.g. “PRIMAX”), and the second luminous patterns are arranged in a specified character (e.g. “PAIRING”) to denote that the pairing operation of the wireless signal receiver of the wireless keyboard  3  is being performed. On the other hand, if the first luminous patterns and the second luminous patterns are not shown, the electrical apparatus  3  is in an off status. 
     The present invention further provides a third embodiment.  FIG. 9  is a schematic perspective view illustrating the outward appearance of a display device of an electrical apparatus according to a third embodiment of the present invention.  FIG. 10  is a schematic side view illustrating the display device of the electrical apparatus according to the third embodiment of the present invention. The electrical apparatus  4  comprises a casing  40  and a display device  41 . The casing  40  comprises a protective layer  401 . In this embodiment, the electrical apparatus  4  is a Bluetooth earphone. As shown in  FIG. 9 , the display device  41  comprises a first illumination module  412 , a second illumination module  413 , a circuit board  414 , a first light-shading structure  415 , and a second light-shading structure  416 . From bottom to top, the second illumination module  413 , the second light-shading structure  416 , the circuit board  414 , the first light-shading structure  415 , the first illumination module  412  and the protective layer  401  are sequentially shown. 
     The first illumination module  412  comprises a first light-emitting element  4121  and a first light guide plate  4122 . The first light guide plate  4122  has a plurality of first luminous patterns  4122 A. The second illumination module  413  comprises a second light-emitting element  4131  and a second light guide plate  4132 . The second light guide plate  4132  has a plurality of second luminous patterns  4132 A. The protective layer  401  is disposed over the first illumination module  412  for protecting the first illumination module  412 . In addition, the protective layer  401  comprises a light-transmissible zone  4011  and a light-shading zone  4012 . 
     Except for the following three items, the configurations and functions of the display device  41  of this embodiment are similar to those of the first embodiment, and are not redundantly described herein. Firstly, the first edge  4145  of the circuit board  414  is not inserted into the gap G′ between the first illumination module  412  and the second illumination module  413 . Secondly, the display device  41  of this embodiment is additionally equipped with the first light-shading structure  415  and the second light-shading structure  416 . The first light beam from the first light-emitting element  4121  is blocked by the first light-shading structure  415 . Consequently, the first light beam is not transmitted through the gap G′ to influence the second illumination module  413 . Moreover, the second light beam from the second light-emitting element  4131  is blocked by the second light-shading structure  416 . Consequently, the second light beam is not transmitted through the gap G′ to influence the first illumination module  412 . Thirdly, the display device  41  is installed on a curvy surface of the casing  40  of the electrical apparatus  4 . Correspondingly, as shown in  FIG. 10 , the first light guide plate  4122  and the second light guide plate  4132  have curvy surfaces. In an embodiment, the first light guide plate  4122  and the second light guide plate  4132  are made of soft and flexible polycarbonate. In addition, the thickness of each of the first light guide plate  4122  and the second light guide plate  4132  is about 0.2˜0.4 mm. 
     Please refer to  FIG. 10  again. The first light-shading structure  415  is disposed on a bottom surface  4122 B of the first light-guiding plate  4122 . Moreover, the first light-shading structure  415  is formed by painting, spraying, printing or bonding a light-shading material on the bottom surface  4122 B of the first light-guiding plate  4122 . The second light-shading structure  416  is disposed on a top surface  4132 C of the second light-guiding plate  4132 . Moreover, the second light-shading structure  416  is formed by painting, spraying, printing or bonding a light-shading material on the  4132 C of the second light-guiding plate  4132 . In this embodiment, the first light-shading structure  415  is a light-shading layer, which is formed by coating the bottom surface  4122 B of the first light-guiding plate  4122  with light-shading ink. In addition, the second light-shading structure  416  is a light-shading tape, which is boned on the top surface  4132 C of the second light-guiding plate  4132 . 
     In this embodiment, the electrical apparatus  4  is a Bluetooth earphone. The display device  41  is used for displaying the brand logo of the Bluetooth earphone  4  or the playing status of an audio-generating device (e.g. a walkman, a CD player or any other song player) which is in communication with the Bluetooth earphone  4 . For example, the first luminous patterns  4122 A are arranged in a brand logo (e.g. “PRIMAX”), and the second luminous patterns  4132 A are arranged in a specified character or symbol (e.g. “PLAYING”) to denote that the audio-generating device is playing. 
     The present invention further provides a fourth embodiment.  FIG. 11  is a schematic perspective view illustrating the outward appearance of a display device of an electrical apparatus according to a fourth embodiment of the present invention.  FIG. 12  is a schematic side view illustrating the display device of the electrical apparatus according to the fourth embodiment of the present invention. As shown in  FIG. 11 , the electrical apparatus  5  comprises a casing  50  and a display device  51 . The casing  50  comprises a protective layer  501 . In this embodiment, the electrical apparatus  5  is a wireless mouse. In addition, the bottom surface of the casing  50  is a flat surface. As shown in  FIG. 12 , the display device  51  comprises a first illumination module  512 , a second illumination module  513 , a circuit board  514 , and a light-shading structure  515 . From bottom to top, the second illumination module  513 , the circuit board  514  (or the light-shading structure  515 ), the first illumination module  512  and the protective layer  501  are sequentially shown. 
     The first illumination module  512  comprises a first light-emitting element  5121  and a first light guide plate  5122 . The first light guide plate  5122  has a plurality of first luminous patterns  5122 A. The second illumination module  513  comprises a second light-emitting element  5131  and a second light guide plate  5132 . The second light guide plate  5132  has a plurality of second luminous patterns  5132 A. The protective layer  501  is disposed over the first illumination module  512  for protecting the first illumination module  512 . In addition, the protective layer  501  comprises a light-transmissible zone  5011  and a light-shading zone  5012 . 
     In this embodiment, the light-shading structure  515  is disposed within a gap G* between the first light-guiding plate  5122  and the second light-guiding plate  5132 . In addition, the light-shading structure  515  is located at a first side  5145  of the circuit board  514 . The configurations and functions of other components of the display device  51  of this embodiment are similar to those of the third embodiment, and are not redundantly described herein. An example of the light-shading structure  515  includes but is not limited to a plastic sheet, a sponge structure or a light-shading plate. 
     In an embodiment, the light-shading structure  515  is a plastic sheet. In addition, the light-shading structure  515  comprises another light-transmissible zone  5151  and another light-shading zone  5152 . The light-transmissible zone  5151  is aligned with the first luminous patterns  5122 A and the second luminous patterns  5132 A. Consequently, the first luminous patterns  5122 A and the second luminous patterns  5132 A are visible through the light-transmissible zone  5151 . The light-shading zone  5151  is located at the first side  5145  of the circuit board  514  for blocking the first light beam and the second light beam that are emitted by the first light-emitting element  5121  and the second light-emitting element  5131 . Consequently, the first light beam and the second light beam are not transmitted through the gap G* to influence the second illumination module  513  and the first illumination module  512 . The display device  51  is used for displaying the resolution status of a displacement sensor  52  of the wireless mouse  5 . For example, the first luminous patterns are arranged in a character “HIGH” to denote that the displacement sensor  52  has a high resolution, and the second luminous patterns are arranged in a character “LOW” to denote that the displacement sensor  52  has a low resolution. 
     The present invention further provides a fifth embodiment.  FIG. 13  is a schematic perspective view illustrating the outward appearance of a display device of an electrical apparatus according to a fifth embodiment of the present invention. As shown in  FIG. 13 , the electrical apparatus  6  comprises a casing  60  and a display device  61 . In this embodiment, the electrical apparatus  6  is a charger. In addition, the display device  61  is installed on a curvy surface of the casing  60 . The configurations and functions of the display device  61  of this embodiment are similar to those of the second embodiment, and are not redundantly described herein. The display device  61  is used for displaying the brand logo of the charger  6  or the charging status of the charger  6 . For example, the first luminous patterns are arranged in a brand logo (e.g. “PRIMAX”), and the second luminous patterns are arranged in a specified character symbol (e.g. “CHARGING”) to denote that the charging operation of the electrical apparatus  6  is being done. On the other hand, if the first luminous patterns and the second luminous patterns are not shown, the charging operation of the electrical apparatus  6  is stopped or has been completed. 
     The configurations of the display device  21  of the first embodiment may be applied to the display device  31  of the second embodiment. Alternatively, the configurations of the display device  41  of the third embodiment may be applied to the display device  31  of the second embodiment. Similarly, the configurations of the display device  51  of the fourth embodiment may be applied to the display device  31  of the second embodiment. Alternatively, the configurations of the display device  51  of the fourth embodiment may be applied to the display device  21  of the first embodiment. Similarly, the configurations of the display device  61  of the fifth embodiment may be applied to the display device  31  of the second embodiment. Alternatively, the configurations of the display device  61  of the fifth embodiment may be applied to the display device  21  of the first embodiment. 
     From the above description, the present invention provides a display device of an electrical apparatus. The display device utilizes only the light-emitting elements and at least two light guide plates to selectively display at least two luminous patterns without the need of installing a LCD panel and a control circuit therein. Consequently, the display device of the present invention not only has smaller thickness but also has lower fabricating cost. Moreover, for preventing the interference between the luminous patterns of two light guide plates, the display device of the present invention uses a circuit board or a light-shading structure to block the light beam from the adjacent light-emitting element, so that the luminous pattern of each light guide plate can be clearly viewed. Moreover, in a case that the first edge of the circuit board is inserted into the gap between the first light-guiding plate and the second light-guiding plate, the first light beam and the second light beam can be blocked by the first edge of the circuit board. Since no additional light-shading element is required, the fabricating cost can be further reduced. 
     While the invention has been described in terms of what is presently considered to be the most practical and preferred embodiments, it is to be understood that the invention needs not be limited to the disclosed embodiment. On the contrary, it is intended to cover various modifications and similar arrangements included within the spirit and scope of the appended claims which are to be accorded with the broadest interpretation so as to encompass all such modifications and similar structures.