Abstract:
Techniques for displaying messages on top of a vehicle are disclosed. Although useful in many other areas, the techniques are particularly suitable for taxicab. According to one aspect of these techniques, a display unit is mounted on top of a vehicle. The display unit includes at least two display panels facing outward respectively. The display unit is controlled by a computing device to display various messages. In one embodiment, the vehicle is provided a Global Positioning System (GPS) that determines a location of the vehicle. Coupled to the GPS, the computing device sends the location information of the vehicle to a base station and receives returned information from the base station in accordance with the location information. The returned information, at least some of which are location based, is locally processed for suitable messages on the display panels. In another aspect, illumination of the display messages varies by a light sensor in response to intensity of ambient lights.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation-in-part of co-pending U.S. patent application Ser. No. 11/033,252 filed on Jan. 7, 2005. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to the area of presenting information for advertising or other purposes, and more specifically to a method and system for displaying information on top of a moving vehicle, at least some of the displayed information, at the time of being displayed, pertaining to the location of the moving vehicle. 
         [0004]    2. Description of the Related Art 
         [0005]    Studies show that people notice words and pictures displayed on moving objects, such as trucks more than those on stationary billboards. That is why nearly all companies use their trucks to promote intended messages. For example, delivery trucks by United Parcel Service (UPS) are all in brown color and carry the company logo as well as service messages while moving trucks from U-haul are all in orange and white colors and imprinted with different sizes of available trucks and corresponding prices. The purpose of using trucks as moving billboards is to make a company stand out and get noticed in traffic areas. Similarly, advertisements or any commercial messages on moving vehicles create an eye level impact so as to increase awareness and overall positive impression for the advertiser (e.g., a company). 
         [0006]    The moving advertisements on moving vehicles have proven to be as an effective advertising medium. Innovations in making such moving advertisements include vehicles (e.g., buses) entirely wrapped in electrostatic marking film carrying advertising messages. However, the moving advertisements on vehicles are stationary and sometimes permanent. It is generally difficult to change any messages or contents on the advertisements from time to time. 
         [0007]    It is well known in the advertising industry that direct or relevant marketing is much more effective than the mass marketing, namely an advertisement pertaining to someone&#39;s interest or need would generate a response. For example, showing a pricy European-style furniture advertisement would make a lot of sense in a well established residential area than in a disadvantaged or crowded neighborhood. 
         [0008]    Accordingly, there is a great need for solutions conveying information dynamically from a moving vehicle to viewers, wherein the information is conveyed based on a location of the moving vehicle and more related to viewers in the location and/or the time at which the information is seen. 
       SUMMARY OF THE INVENTION 
       [0009]    This section is for the purpose of summarizing some aspects of the present invention and to briefly introduce some preferred embodiments. Simplifications or omissions in this section as well as in the abstract and the title may be made to avoid obscuring the purpose of this section, the abstract and the title. Such simplifications or omissions are not intended to limit the scope of the present invention. 
         [0010]    The invention pertains to a display system mounted on top of a vehicle (e.g., a taxi). The display system includes a display unit configured to display messages provided locally or remotely, wherein the messages may be in form of static or moving graphics, texts, animation or video, and include a set of advertising messages and location-based messages. The display system includes a Global Positioning System (GPS) to detect the current position of the vehicle. In accordance with the location information, messages may be retrieved locally from a storage device or remotely from a base station via a wireless network. As a result, relevant messages or commercial advertisements can be displayed in the display unit. 
         [0011]    According to one aspect of the present invention, the display unit includes at least two display panels and two display plates. The display panels are for displaying received or retrieved messages. In one embodiment, two display panels are mounted oppositely with the display side facing outwards such that the display panels may be readily seen when the vehicle goes around. In another embodiment, three display panels are positioned along the three sides of a triangle. When mounted on top of a vehicle, with one of three display panels facing the rear of the vehicle, all three display panels may be conveniently viewed by viewers in nearly all directions of the vehicle. Depending on implementation, the display panel in use may be of any commercially available display means, such as liquid crystal display (LCD), Plasma or light emitting diode (LED). The display plates are for displaying emergency messages when needed. In general, the display plates are smaller in size compared to that of the display panels. The display plates that normally display a default message may be triggered to display an emergency message. For cost consideration, the display plates are normally made based on LED. 
         [0012]    According to another aspect of the present invention, the display unit is encased entirely in an enclosure that can be mounted on top of a vehicle (e.g., an automobile). The enclosure is configured to allow messages displayed on the display unit viewable all lateral directions: front, rear, and two sides. The display unit includes a pair of video image display panels (e.g., LCD or LED). The display panels are located in either side of the two sides of the display unit. A pair of display plates is located perpendicular to the pair of the display panels, one facing the front end and the other the rear end. Front and rear end cover of the enclosure are made of clear or transparent material such that messages on the display plates can be seen by the viewers. The top of the enclosure comprises a canopy also made of clear or transparent material. In order to reduce drags and noises caused by air flow, both the front and rear end covers and the canopy are configured with an aerodynamic shape (e.g., smooth curvature). The bottom of the enclosure comprises a contoured base so shaped to fit roof curvature of the vehicle. To ensure the weight of the display unit to be distributed substantially even on the vehicle root, a set of anchors are configured to adjustably secure the display unit onto ribs under the vehicle roof. 
         [0013]    According to still another aspect of the present invention, the display system is configured to include a power management circuit board, which ensures the efficient usage of a primary and a secondary power sources (e.g., primary battery and secondary battery) of the display unit. The power management circuit board comprises various electronic controls to provide at least the following functions: 1) preserve the primary power source so that the engine of the vehicle can be restarted; 2) automatically switch to the secondary power source within a predetermined amount of time (e.g., 0-5 minutes) after the engine is turned off; 3) automatically turn off the display unit after a predetermined amount of time (e.g., 60 minutes); and 4) change illumination intensity of the display unit in response to ambient environment detected by a light sensor (e.g., a Cadmium Sulphide (CdS) photocell light sensor). 
         [0014]    According to still another aspect, the enclosure is configured to include a number of cooling air duct openings such that the ambient air can flow through the interior of the enclosure to cool down interior of the enclosure (i.e., display panels and display plates). A number of air filters are placed behind the air ducts to reduce dust to be accumulated or built up within the enclosure. Also included inside the enclosure is a number of water diverter configured to divert any water (e.g., rain got through the air ducts) away from electronic parts (e.g., circuit board, LCD, LED) and to drain out through a set of drain holes. 
         [0015]    The present invention may be implemented in different forms. According to one embodiment, the present invention is a display system for showing electronic messages, the display system comprises at least the following: a vehicle having at least a primary battery; a display unit, mounted on roof of the vehicle, configured for showing electronic messages that can be illuminated with variable intensity; and a power management device coupled to the at least one battery of the vehicle and the display unit, wherein the power management device is configured to determine an appropriate battery to energize the display unit. The system further comprises a light sensor coupled to the power management device, wherein the light sensor is configured to detect an ambient light condition, responding to which the illumination intensity of the electronic messages varies; a computer device configured for processing and controlling the electronic messages to be shown in the display unit; and a Global Position System (GPS) configured to determine a location of the vehicle, wherein the computing device, coupled to the GPS, communicates wirelessly with a base station to receive at least some of the electronic messages in accordance with the location of the vehicle. 
         [0016]    One of the objects, features, advantages, benefits of the present invention is to provide a solution for conveying media information to viewers, the solution employs a vehicle mounted with a display system. When the vehicle goes around in traffic areas, relevant information displayed in the display system may be readily seen by viewers. 
         [0017]    Other objects, features, advantages, benefits of the invention will become more apparent from the following detailed description of a preferred embodiment, which proceeds with reference to the accompanying drawings 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]    The present invention will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
           [0019]      FIG. 1A  is a perspective view showing an exemplary display unit suitable for being mounted on top of a moving vehicle such as a taxi, the display unit includes two display panels and two display plates in accordance with one embodiment of the present invention; 
           [0020]      FIG. 1B  is a perspective view showing another exemplary display unit according to another embodiment of the present invention; 
           [0021]      FIG. 1C  shows a side elevation view of the display unit of  FIG. 1B ; 
           [0022]      FIG. 1D  shows a front end elevation view of the display unit of  FIG. 1B ; 
           [0023]      FIG. 2A  shows a functional block diagram of a control system in the display system; 
           [0024]      FIG. 2B  shows an example of processing a media content in a media processor; 
           [0025]      FIG. 2C  shows that information to be displayed may be retrieved locally or remotely; 
           [0026]      FIG. 2D  shows a control of two display plates that in a normal condition are emulated with a switch in “off” position to show a default message; 
           [0027]      FIG. 3  shows a flowchart or process of displaying media information to viewers via a display system mounted on top of a vehicle; and 
           [0028]      FIG. 4  is a circuit diagram of an exemplary power management circuit board of either display unit of  FIG. 1A  or  FIG. 1B , in accordance with one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    The invention pertains to a display system mounted on top of a vehicle (e.g., a taxi). The display system includes a display unit configured to display messages provided locally or remotely, wherein the messages may be in form of static or moving graphics, texts, animation or video and include a set of advertising messages and location-based messages. The display system includes a Global Positioning System (GPS) to detect the current position of the vehicle. In accordance with the location information, messages may be retrieved locally from a storage device or remotely from a base station via a wireless network. As a result, relevant messages or commercial advertisements can be displayed in the display unit. 
         [0030]    The detailed description of the invention is presented largely in terms of procedures, steps, logic blocks, processing, and other symbolic representations that directly or indirectly resemble the operations of data processing devices coupled to networks. These process descriptions and representations are typically used by those skilled in the art to most effectively convey the substance of their work to others skilled in the art. Reference herein to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment, nor are separate or alternative embodiments mutually exclusive of other embodiments. Further, the order of blocks in process flowcharts or diagrams representing one or more embodiments of the invention do not inherently indicate any particular order nor imply any limitations in the invention. 
         [0031]    Referring now to the drawings, in which like numerals refer to like parts throughout the several views.  FIG. 1A  shows a display system  100  suitable for being mounted on top of a moving vehicle such as a taxi. The display system  100  includes two display panels  102  and  104  (not explicitly shown in the figure), and two display plates  106  and  108  (not explicitly shown in the figure). Preferably, the display panels  102  and  104  are identical. According to one embodiment, the display panel  102  or  104  is a commercially available display panel based upon, for example, LCD, LED, Plasma or other lighting sources. According to another embodiment, the display panel  102  or  104  includes a matrix of light emitting diodes (LED). The light emitting diodes in the matrix may be in at least three different colors (e.g., red, green and blue), surface mount diodes or tri-color diodes. To support weather proof, in one embodiment, each of the diodes is positioned and sealed on a silicon base and/or UV protected. Additionally, the display panels and/or display plates may be protected by a tinted or clear polycarbonate screen for protection from harmful UV rays and damages from vandalism or accident. 
         [0032]    The two display panels  102  and  104  are provided to display media information that may include, but may not be limited to, images, graphics, animations, video and texts. The media information may be provided locally or remotely. As will be further described below, locally provided media information is typically from a storage device integrated or enclosed in the display system  100  while remotely provided multimedia information is provided wirelessly from a base station. 
         [0033]    The two display plates  106  and  108  are configured to display fixed messages such as “Taxi” or “Help”. In a normal condition, a word “Taxi” or the like may be displayed. In an emergency situation in which, for example, a driver needs help, a switch in the vehicle may be activated to cause an eye-catching message (e.g., “Help”) to be displayed. In one embodiment, each of the two display plates  106  and  108  includes an array a matrix of light emitting diodes in at least one color. In a normal condition, the two display plates  106  and  108  are coupled to a fare meter and, when a taxi operates, are turned on to display a word or phrase in one color (e.g., green or yellow) to indicate that the taxi is for hire. In an emergency situation, a word or phrase is shown, perhaps in another color (e.g., red or amber), and/or flashed panically or periodically. As will be described below, the word or phrase in the emergency situation may be supplied by a base station via a network for applications of an amber alert. 
         [0034]    In one embodiment, spaces such as those above the display plates, referenced by  110  as an example, may be used for displaying static messages. Thus the display system  100  essentially provides means to display both media information that may be dynamic or static as well as to display pure static information in the traditional billboard style. 
         [0035]    In another embodiment, a perspective view of another exemplary display unit  120  is shown in  FIG. 1B . A side and a front end elevation view of the display unit  120  are shown in  FIG. 1C  and  FIG. 1D , respectively. Due to the symmetry in both directions, the view from other side is a mirror image of  FIG. 1C  and a rear end elevation view is a mirror image of  FIG. 1D . In particular,  FIG. 1D  shows that a LED panel is housed in a chamber with a transparent cover. The LED panel displays, for example, “HELP” if the driver/passenger needs help or in emergency, or “TAXI” if the taxicab is available for hire. The display unit  120  comprises two display panels  122  and  124 , and two display plates  126  and  128  similar to the embodiment of  FIG. 1A . The display panel  124  and the display plate  128  are not explicitly shown due to the viewing angle in  FIG. 1B  and  FIG. 1C . 
         [0036]    In one embodiment, the display unit  120  is encased in an enclosure made of clear or transparent material (e.g., acrylic glass) such that messages (static or dynamic) displayed on the display unit  120  can be seen through by viewers. In particular, the top cover or canopy  136  of the enclosure has a semi-circular cylindrical shape. Further, the top cover or canopy  136  is shaped to substantially reduce the drags and noises when the vehicle is in motion. Front end cover  132  and rear end cover  134  of the enclosure are similar. Each comprises a lower portion having a cut-off semi-conical shape and a top portion with a shape of rounded corner. Smooth aerodynamic curvature of the front end  132  and rear end covers  134 , and the canopy  136  is configured to reduce drags and noises caused by air flows due to speed of a traveling vehicle, on which the display unit is mounted. 
         [0037]    In one embodiment, as shown in  FIG. 1D , the front end  132  and rear end covers  134  is shown to have three parts, the bottom part  133  forms a chamber with a transparent cover. A display plate is positioned in the chamber and may be configured to display a default message “TAXI” when the vehicle is in service. The display plate may display “HIRE” when the vehicle is for hire. The display plate may display some other type of messages, for example, “HELP” when occupants in the vehicle need help. The middle part is used to display static messages. The top part  135  also forms a chamber. Depending on implementation, the top part  135  may be used to display an indicator or house another display plate. 
         [0038]    The bottom  138  of the display unit  120  is so shaped to fit roof curvature of a vehicle, on which the display unit is mounted. The bottom curvature may be custom made to fit different vehicle models. For example, due to popularity of using Ford Crown Victoria as taxicabs, the default bottom  138  may be configured to fit the roof shape of a Crown Victoria. The custom made bottom  138  not only provides better fit as good appearance, but also reduces wind drags and noises as the vehicle travels. In addition, a better bottom fit allows a pair of adjustable anchors, located inside the bottom  138  portion of the enclosure, to be securely locked onto ribs under the roof of the vehicle such that the weight of the display unit  120  can be distributed substantially even over the roof of the vehicle. 
         [0039]    In order to provide ventilation of the enclosure for the display unit  120 , a number of cooling air ducts  142  and  144  are included, for example, the front end cover  132  and the rear end cover  134 , respectively. The cooling air duct openings  142  and  144  are configured to allow relatively cooler ambient air to flow through the interior of the enclosure and the display unit  120  to reduce the heat generated by the display panels  122  and  124 , and/or by the display plates  126  and  128 . To prevent dust from dirty airs to be accumulated inside the enclosure, a number of air filters are placed behind the cooling air duct openings  142  and  144  to filter out the dust. Also included in the display unit  120  is a set of water diverters and drain holes, which are configured to divert any water (e.g., rain) getting through the air duct openings  142  and  144 . 
         [0040]    Referring to  FIG. 2A , there shows a functional block diagram  200  of a control system or computing device in the display system  100  of  FIG. 1A . According to one embodiment, the control system includes a network interface  202 , a controller  204 , a media processor  206 , a global positioning system (GPS)  208 , a storage device  209 , a display driver  210 , a power management device  212 , and a display plate controller  214 . It should be noted that not all of these components must be employed in order to practice the present invention. 
         [0041]    The network interface  202  facilitates data exchange between the system  100  and a base station. In one embodiment, the network interface  202  operates to facilitate the system  100  of  FIG. 1A  to exchange data over a wireless network. In one example, the network interface  202  operates in accordance with a commonly used protocol such as UDP, TCP/IP or a cellular protocol. The controller  204  controls operations of these and other components and causes the display driver  210  to output desired information in desired manners. 
         [0042]    The media processor  206  may be part of the controller  204  and is configured to perform processing of media information. One of the features in the present invention is that the display system  100  of  FIG. 1A  displays all types of information including static or moving graphics, texts, animations as well as motion images. Because the physical sizes of the display panels such as those panels  102  and  104  in  FIG. 1A  can be in sizes different from the original sizes of the content intended to be displayed, if displayed without preprocessing, cropping or other undesired effects may be seen. In some case, a retrieved movie or message is in compressed format, the media processor  206  is configured to decompress the movie or message. The media processor  206  is provided to ensure that contents to be displayed are processed accordingly so as to display the information correctly on the display panels. 
         [0043]      FIG. 2B  shows that an original content  222  is in a first size and the processed content  228  is in a second size. The original content  222  may be provided locally or remotely. The media processor  206  is configured to process the original content  222  in accordance with display parameters  224  pertaining to the display panels or other desired artistic effects. The display parameters  224  include at least information about width and height of the display panels. Subsequently, processed content is produced in a format  228  or  230 . According to one embodiment, the format  228  is simply a standard display. Like a television or computer display monitor, the standard display means herein to display the original content in fidelity. Conversely, the format  230  is a format that includes some artistic effects in the original content. For example, the height of the original content is bigger than that of the display panel, the processed content in format  230  is now in several frames that can be shown sequentially or in a rolling manner. Another example of the format  230  may include special artistic effects in the processed content, where these special artistic effects may be very suitable for a type of display panel. In an amber application, a special message is received. The message can be processed to be displayed on a display panel in a manner that readily draws attention from viewers (e.g., pedestrians). 
         [0044]    The GPS  208  is a device that, when operating in conjunction with the vehicle, detects the present location of the display system. When the display system is mounted on top of a taxi, the GPS  208  indicates the present location of the taxi. According to one embodiment, the GPS  208  outputs the location information that enables the display system  100  to display location-based information. An example of the location-based information is a special offering in a local department store. Together with a current time provided inherently in the display system  100 , the location-based information can be also time-sensitive. An example of the location-based information that is also time sensitive is an advertisement of a special offer valid from 11:00 AM to 2:00 PM from a local restaurant or a fast food chain store. 
         [0045]      FIG. 2C  shows that the location-based information that may be also time sensitive may be from a local storage device  232  or provided from a base station via a the display unit wireless network. In one embodiment, the storage device  232  in the display system  100  is loaded with a plurality of commercial advertisements, some of which are specifically requested to be displayed in a certain location during a certain time. When a taxi happens in the specified location detected by the GPS  208  and when the certain time arrives, such commercial advertisements are retrieved and may be processed by the media processor  206  for display on the display panels. When a taxi mounted with such display system is in a location other than the specified location, commercial advertisements pertaining to the location may be provided from a base station via the wireless network  234 . Regardless of the original source of the commercial advertisements, the GPS  208  and the media processor  206  (perhaps with other components) facilitate polling of relevant commercial advertisements and to display the advertisements properly on the display panels. 
         [0046]    The storage device  209  is provided to store code or software modules for various applications in addition to providing a storage space for media information. One of the modules is to facilitate the operations of many of the components in the control unit  200  of  FIG. 2A . Another one of the modules is to record time, duration or location when a particular piece of media information has been displayed. Still another one of the modules is a schedule that determines how, when and where a particular piece of media information needs to be displayed. In one application, the storage device  208  is scheduled to download media information from a base station along with a schedule. In another application, the storage device  208  is scheduled to receive certain media information from a base station when the vehicle is in a coverage area of the base station. 
         [0047]    According to one embodiment, one of the modules is configured to perform conversations of media information received for display. When a received media advertisement is in MPEG2 that is good for LCD display panels but nevertheless not suitable for display on LED display panels, the module converts the media advertisement in MPEG2 to MPEG4 or other format suitable for display on the LED display panels. 
         [0048]    The display driver  210  or the display plate controller  214  is a device that facilitates a proper display of any content on a corresponding display panel or plate. To distinguish the two types of functions of displays, the display  102  or  104  is referred to as a display panel while the display  106  or  108  is referred to as a display plate. Those skilled in the art would understand that it is not a limitation in the present invention that the two displays must be different. Both the displays  102  or  104  may be of the same type. In practice, according to one embodiment, the displays  106  and  108  are used for emergency messaging when needed, while the displays  102  and  104  are primarily used for conveying static or dynamic messaging to potential viewers (e.g., pedestrians). 
         [0049]    A display system (e.g.,  100  of  FIGS. 1A and 120  of  FIG. 1B ) operates on a power unit (e.g. battery) of the vehicle and may draw significant power from the power unit. The power management  212  is provided to ensure that the vehicle is not disabled from a drained power unit because of the display system. In one embodiment, the power management  212  is configured to regulate the use of the power by the display system to ensure that the display system operates with a least amount of power. In another embodiment, the power management  212  is configured to automatically turn off the display system in an event that the vehicle stops for an undesired lengthy period. In another embodiment, a back-up power unit is provided that is switched on to energize the display system when the vehicle stops for a predefined time to keep the vehicle power unit in good condition. When the vehicle starts to move again, the vehicle power unit is switched on to energize the display system and the back-up power unit gets charged. 
         [0050]    Referring now to  FIG. 2D , there shows a control of the display plate  106  and  108 . The display plate  106  and  108  in a normal condition emulated with a switch  250  in “off” position show a default message. When a driver needs immediate help from others, the switch  250  is in “on” position, causing the display plate controller  214  to display an emergency message on the display plates. Preferably the emergency message is displayed in a manner that readily draws attention from others. According to one embodiment, the switch  250  may be located conveniently near the driver. When, for example, the driver is being attached or in need for help, the driver may activate the switch that causes the display plates to show an emergency message to draw attentions from viewers. In any case, it should be understood to those skilled in the art that either the default message or the emergency message may be dynamically changed to a situation or electronically determined by the control unit  200  of  FIG. 2 . 
         [0051]    Referring now to  FIG. 3 , there shows a flowchart or process  300  of displaying media information to viewers via a display system mounted on top of a vehicle. The process  300  may be understood in conjunction with the previous figures and implemented as a method and a system to efficiently convey relevant information to viewers. At least some of the relevant information may be location-based and others may be time sensitive. The relevant information may come in a form of graphics, texts, animation or video. 
         [0052]    As described above, a display system, such as that  100  of  FIG. 1A , is preferably mounted on top of a car (e.g., a taxi). Accordingly, at  302 , the current location of the car is determined via a GPS. At  304 , the location information is transported to a base station via a wireless network (e.g., a cellular network). The base station may be operated by a service provider and provide various information to registered cars to display some of the information at relevant location at a predefined time. In one embodiment, the location information including longitude and altitude of the vehicle is transported to the base station in data format suitable for a commonly used communication protocol (e.g., UDP or TCP/IP). 
         [0053]    At  306 , the display system receives media information either locally or remotely. As described above, some of the media information may be pre-stored or loaded at a certain time in a storage device integrated or enclosed in the display system and others can be lively fed or retrieved from a base station. In one embodiment, a request including the location and time information is generated, the request is sent to the storage device to determine whether any preloaded information shall be displayed. If there is one commercial message that needs to be displayed, the message is retrieved from the storage device. The request may also be sent to the base station that determines any relevant information with criteria met by the parameters in the request. If there is one message that shall be displayed on the display system of the vehicle in the particular location at the specified time, the message is then transported in response to the request to the display system. 
         [0054]    Regardless where the message or media information is retrieved, at  308 , a decision is determined whether the retrieved media information needs to be processed. If there is no need to process the retrieved information, the process  300  goes to  312  that causes the display panels to display the retrieved information. If the retrieved information needs to be processed, the process  300  goes to  310 , where the retrieved information is processed in accordance with predefined requirements (e.g., resizing and rendering to add artistic effects). The processed information is then sent to the display panels for display at  312 . 
         [0055]    Other functions, not shown in  FIG. 3 , may include recording time, duration and location of a particular message that has been displayed. Such information may facilitate a service provider to determine billing information for its clients. 
         [0056]    Referring to  FIG. 4 , there shows an exemplary circuit of a power management unit  420  configured to control the power supply to a display unit  456  (e.g.,  100  of  FIG. 1A  or  120  of  FIG. 1B ). In one embodiment, a power source to energize the display unit  456  is provided by a battery of the vehicle. In another embodiment, there are two power sources: a primary battery  402  and a secondary battery  404 . The primary battery  402  is the main battery for the vehicle. The secondary battery  404  is a backup battery when the primary battery  402  needs to be preserved to start or restart the vehicle engine. The power management unit  420  is configured to select which one of the power sources to energize the display unit by detecting a state of the vehicle engine and states of the primary  402  and/or secondary battery  404 . In addition, the power management unit  420  is configured to automatically turn up or down the illumination intensity of the display system in response to detected ambient light conditions. It is desirable to avoid keeping the illumination low when the vehicle enters a neighborhood of low lighting condition, and bring up the illumination intensity when the vehicle is in the vicinity of bright areas. 
         [0057]    When the engine of the vehicle is started and running, the display unit  456  (e.g., LCD and/or LED display screen) receives power from the engine (i.e., alternator) of the vehicle, and both the primary  402  and the secondary  404  batteries are being charged. The primary battery voltage sampling  422  receives and detects a higher electric voltage (e.g., 13.5 Volts) than a benchmark voltage  424  (e.g., 5.1 Volts) from the primary battery  402 . The secondary battery voltage sampling  426  also receives and detects a higher voltage (e.g., 10 Volts) than the benchmark voltage  428  (5.1 Volts) from the secondary battery  404 . As a result, power with sufficient electric voltage is passed by a controller  423  to a first electric relay  442 , which closes or turns on a first switch  441  in providing power to the display unit  456 . The power with sufficient high voltage is passed by the controller  427  to an AND gate  448 . In addition, the power from the primary battery  402  is also sent through a timer  440  to the AND gate  448 . Then the power is sent to a second electric relay  444 , which closes or turns on a second switch  443  in providing power to the display unit  456 . 
         [0058]    Once the vehicle engine is turned off, the primary battery voltage sampling block  422  detects a lower voltage than the benchmark voltage  424 , the low voltage electric power triggers the first relay  442  to open or turn off the first switch  441 . The lower voltage also causes the timer  440  to start its clock for a pre-determined time (e.g., one hour) and the display unit  456  is powered by the secondary battery  404  for the duration of the pre-determined amount of time in the timer  440  before the second relay  444  is triggered to turn off or open the switch  443  to cut off the power to the display unit  456 . The exemplary logic of the power management board  420  is to preserve the primary battery  402  to restart the engine of the vehicle; and to prevent excessive draining of the secondary battery  404  with the timer  440 . The automated electronic logics can be overridden by a manual reset  412 , which may be activated by an operator of the vehicle (e.g., a driver). In one embodiment, the power is turned off as soon as the reset  412  is activated. In another embodiment, when the reset  412  (e.g., a hard or soft button) is activated, an electronic signal (e.g., a pulse) is sent to the computer device of the display unit  456  to initiate a power off operation (e.g., a power off operation performed by an operating system of a computer). 
         [0059]    Further included in the power management circuit board  420  are power management logics for back light  458  (e.g., LED back light) of static display in the front and rear end of the display unit  456 . A light sensor  414  (e.g., Cadmium Sulphide (CdS) photocell light sensor) is included to convert ambient lights to electrical signals or pulses. The light sensor voltage sampling  432  detects the voltage out of the light sensor  414  and compares to a benchmark voltage  434 . If a higher than benchmark voltage is detected, a signal is sent from block  433  to a third relay  446 . The third relay  446  turns on and off a third switch  445 , which controls the power to the back light  458 . For example, the back light  458  is turned on automatically in response to a darker ambient light condition (e.g., evening, early morning, foggy day, etc.) 
         [0060]    In another embodiment, illumination intensity of the display unit  456  is adjustable in response to the detected ambient light conditions by the light sensor  414 . The power management circuit board  420  may be configured to automatically dim the illumination of the display panels and display plates in a darker environment and brighten in a brighter environment. For example, local city ordnance may only allow a vehicle carrying a display sign in certain brightness level. In another example, a brighter sign is needed in a very bright ambient environment such as downtown or city center area. Changing illumination intensity of the displayed messages may be managed in conjunction with a GPS. For example, when the vehicle travels into a local area that prohibits displaying certain messages, the display unit computer device, basing on the location information determined by the GPS, will automatically change the display illumination to an acceptable level according to the local rules or regulations. 
         [0061]    The present invention has been described in sufficient detail with a certain degree of particularity. It is understood to those skilled in the art that the present disclosure of embodiments has been made by way of examples only and that numerous changes in the arrangement and combination of parts may be resorted without departing from the spirit and scope of the invention as claimed. While the embodiments discussed herein may appear to include some limitations as to the presentation of the information units, in terms of the format and arrangement, the invention has applicability well beyond such embodiment, which can be appreciated by those skilled in the art. Accordingly, the scope of the present invention is defined by the appended claims rather than the forgoing description of embodiments.