The present invention relates to public display devices and in particular to mobile public display devices.

Nowadays most public places such as train stations, bus stations, shopping centres, cinemas and so forth include means for displaying important information to the public, be that journey details, warnings, film details and other announcements. Until recently those display systems were mechanical and typically comprise an array of cells capable of representing an array of alphanumeric characters. Each cell may be defined by a plurality of cards each bearing a character and a drive mechanism is provided to scroll through those cards and present a single card bearing the required character. Such display systems have generally been phased out due to a combination of being too slow, too heavy and too cumbersome and advancements with LCD and LED display technologies.

Public display devices employing LCD and LED technologies are widely known and are commonly found above motorways, at train stations and in car parks, to name a few examples. Such devices are intended for permanent installation and are typically hard wired to an electricity supply and a data source so as to have a constant supply of electricity and a secure data link for updating the content to be displayed. Furthermore, such devices may be installed out of the public's reach so as to prevent theft and vandalism.

Although those devices are intended for permanent installation, they are neither suitable nor easily adaptable for temporary installation and are certainly not suitable for mobile applications. For instance, it may be necessary to locate a display device near the entrance of a station to advise the public about problems with certain routes. Alternatively it may be necessary to locate display devices at sporting and social events to assist with directing the public. Display devices suitable for such purposes must be operable for most of the day and must not rely on a mains power supply since one may not be available, but even if one were available the trailing cables would inevitably present a health and safety hazard.

It is an object of the present invention to overcome the above noted shortcomings apparent in existing display systems, by providing a display device that may be used up to 20 hours per day without requiring connection to a mains electricity supply and which may continually update the content being displayed.

It is a further object of the present invention to provide a display device that may be fully charged in less than four hours.

It is yet a further object of the present invention to provide a display device that may be easily manoeuvred while still being sufficiently stable to comply with health and safety requirements and being sufficiently secure to deter thieves and vandals.

According to the invention, there is provided a mobile public display device comprising:

- a wheeled base defining a housing;

- a screen for displaying content and being of sufficient size to enable the content to be viewed by passing public;

- a receiver for wirelessly receiving signals from an external transmitter, which signals include data representing the content to be displayed;

- a controller for processing the signals and causing the content to be displayed on the screen; and

- a battery located in the housing and adapted to power the controller. The term content is used herein to mean matter to be displayed to the public, which includes, but it not limited to, alphanumeric characters, symbols, words, images and videos.

Advantageously the display device may also comprise a data port through which the controller may communicate with an external data carrier holding data representing the content to be displayed. That way, if there is a problem with the external transmitter, or even the receiver, the display device is not rendered inoperable as data can be communicated to the controller via the data port. Preferably the data port comprises a universal serial bus (USB) port or a memory card reader and most preferably the data port is provided on a component stowed inside the housing so as to be inaccessible to the public.

There may also be provided a transmitter electrically connected to the controller for performing several functions. For example, the controller and the transmitter may be configured to relay to a central control station data relating to the content being displayed and also the display device's operational status such as power consumption, battery charge status, component functionality, temperature and so on. Furthermore, the controller and transmitter may be adapted to relay data signals to other display devices that may not be within the range of the external transmitter. Thus, the display device could be deployed at a location between the external transmitter and one of said other display devices and act as a repeater. In one arrangement the wireless receiver and transmitter may comprise a transceiver.

Advantageously the battery may have its own management system that may communicate to the controller via a data lead and may measure various parameters such as temperature, current and voltage levels during use and charging. That data may be used to isolate the battery in order to prevent it being damaged in the event that one of those parameters exceeds the battery's tolerance.

So as to avoid having to remove the battery for recharging there is also provided a battery charger connectable to a mains power supply and which may be installed inside the housing. Preferably the battery charger includes a voltage and current regulating circuit, an input connector electrically and mechanically connectable to the mains power supply and an output electrically connected to the battery. There may also be provided a display panel indicating the level of charge stored in the battery and the status of the battery charger.

Furthermore, the battery charger may include a cable interconnecting the regulating circuit and the input connector, said cable being moveable between an extended position whereat said cable at least partially extends from the housing and a retracted position whereat said cable locates wholly within the housing.

Preferably, the display device is provided with cable drive means for drawing the cable towards its retracted position and which most preferably comprises a drum around which the cable coils in its retracted position. The end of the cable connected to the regulating circuit may be fixed relative to the housing so that as the drum rotates in a predetermined direction the cable automatically winds around the peripheral face. The drum may be provided with spring means to effect automatic rotation in the predetermined direction when the tension in the cable is sufficiently low. Alternatively the drum may be fixed relative to the display device and a winding member may be provided that rotates relative to the drum to coil the cable therearound. Advantageously the drum may be enclosed in a housing having an opening through which the cable extends. Optionally the battery display panel mentioned above may be provided on the housing.

The screen unit may be any light-emitting device capable of displaying content and is most preferably a liquid crystal display screen, an LED display screen or a plasma display screen. The screen unit may be any shape, but is preferably rectangular and most preferably the distance between two opposite corners is at least 1 m (40 inches) so the content being displayed may be easily viewed by the passing public. The screen unit may include screens on its front and rear surfaces or just on one of those surfaces. The or each screen may be divided into a plurality of sub-screens for displaying a plurality of distinct images, videos or other content, and which division may be implemented by the controller. The screen may even include touch screen technology for use by the public or authorised personnel.

The display device may advantageously include an antenna through which the signals are transmitted and received. In a preferred arrangement the antennal is mounted on the top face of the screen so as to be at the highest point and not to be obscured by any other components.

The housing may comprise a base and at least one cover portion provided on the base so as to define an interior. For example, the cover portion may be integral to the base and include an opening through which the interior may be accessed. Alternatively, the base and the cover portion may comprise distinct components and the cover portion may be mounted to the base. Preferably the base comprises a rigid support member such as a plate suitable for bearing the weight of the display device, which may be in excess of 150 KG. Most preferably the base is made from metal.

To provide access in to the interior of the housing, at least one cover portion is moveable relative to the base between open and closed positions. For example, the at least one cover portion may be coupled to the base for relative sliding or pivoting movement between those positions or even fully detachable from the base. Furthermore, some cover portions may be secured to the base by bolts while other cover portions may be moveable for the purpose of access.

Advantageously a frame is mounted to the base and may be arranged at least partially to support the cover portions. First guide means may be fixed relative to the base and arranged to cooperate with second guide means provided on the at least one cover portion so as to facilitate relative sliding movement between the base and the cover portion. For instance, the guide means may be attached to the base, frame or even a fixed cover portion. In one arrangement, the first guide means may comprise a U-shaped channel carried on a support member secured to the base and the second guide means may comprise a bar extending from the cover portion and arranged to form a sliding fit with said U-shaped channel. Alternatively the cover portions may be hinged to the frame, the base or the fixed cover portions.

In a preferred embodiment, the housing includes a generally rectangular base, two opposed end cover portions, two opposed side cover portions and a top cover portion. Furthermore, the top and side cover portions may be fastened to the frame and the end cover portions may be adapted for sliding movement relative to the other cover portions. The top and side cover portions may even comprise one unit having a generally U-shaped cross-section.

Because the display device may be left unattended in public areas it is preferable to furnish the cover portions with locking means operable to prevent unauthorised access into the interior of the housing. Advantageously the locking means are configured to secure the or each moveable cover in its closed position and are releasable selectively to permit movement of the or each moveable cover portion towards its open position. Preferably the locking means include a primary lock accessible from the exterior of the housing selectively to permit movement of a first cover portion to its open position. The lock may include a lock body provided on one of the base and the cover portion and which includes a locking member configured for selective engagement with a keep provided on the other of the base and the cover portion. The primary lock may be mechanical and operable by inserting a key into the lock body or electromechanical and operable remotely by, for example, a radio frequency identification tag or even by a signal sent from the external transmitter and picked up by the receiver and the controller.

In a preferred embodiment the locking means include at least one secondary lock operable only from the interior of the housing selectively to permit movement of a second cover portion to its open position. The secondary lock may be adapted to control the movement of more than one cover portion. Alternatively, each cover portion may have its own secondary or primary lock.

Advantageously the interior of the housing may be divided into two or more compartments and each moveable cover portion provides access to only one of said compartments. For instance, one end of the base may define a primary compartment enclosed by a primary cover portion secured by a primary lock and the other end of the base may define a secondary compartment enclosed by a secondary cover portion secured by a secondary lock.

For example, the secondary lock may comprise a shaft extending between those compartments and arranged to rotate about its own axis relative to the cover portions. The end of the shaft located in the primary compartment may have an aperture formed in its end for receiving a correspondingly shaped secondary key and the other end of the shaft located in the secondary compartment may have a cam extending laterally from the shaft for selective engagement with an abutment provided on the secondary cover portion. By locating the secondary key in the aperture the shaft may be rotated about its axis to engage or disengage the cam and the abutment.

Thus a person in possession of the primary key for operating the primary lock may open the primary cover portion to access the primary compartment, which may house the cable, connector, status indicators and or any basic controls such as a display power switch and a computer reset switch. A person in possession of the primary key and the secondary key may access the primary compartment and then the secondary compartment. Advantageously, the secondary compartment may be furnished with two secondary locks disposed on opposed sides thereof. Once the secondary compartment is accessible a further compartment housing the battery and or battery charger may also be accessed.

The secondary compartment may house the controller, receiver and any other electrical components. The controller may comprise a computer electrically connected to the other components and may, for example, detect operation of the battery recharger and subsequently shut down the screen to conserve energy. While so doing, the computer may continue to receive, via the receiver, commands from the external transmitter and may continue to update the status indicators.

It is advantageous for the housing to accommodate the controller, the receiver, and any other components so as to lower the centre of mass and increase the stability of the display device. Preferably the screen unit may be mounted above the housing and most preferably spaced above the housing by struts extending upwardly from the base. For instance, there may be provided a pair of struts upstanding from the base and spaced laterally apart on opposed sides of the frame. The struts may even be fastened to the frame for increased stability. The screen unit may locate between the struts and bolts may extend through the struts and threadingly engage bores formed in the side faces of the screen unit.

The display device may be furnished with fascias adapted to overlie various components to increase the aesthetic appeal of the device and also to inhibit the ingress of dust and moisture. For example, the fascias may over lie the side and top faces of the screen unit so as to conceal the struts and may include fastening means which attach to suitably profiled formations provided on the struts.

Advantageously the wheeled base includes four castors so as to enable the display device to be easily manoeuvred and at least two of those may be rotatable about a generally vertical axis to allow the display device to turn. Preferably the base is stepped so as to include a lower portion to which most of the components may be mounted and two upper portions to which the castors are attached. This way, the castors may be sufficiently large to overcome irregularities and small steps in the floor while a portion of the base carrying the load is spaced close to the floor.

The screen is external to the housing. The screen is preferably supported above the base remote from the housing. The screen ideally is positioned at a fixed height with respect to the housing. The other components such as the battery in the housing may provide a sufficiently low centre of gravity to ensure stability of the display device in the event of movement or impact despite the raised position of the screen. The wheeled base advantageously is non- vehicular, by which it is meant that it is neither towed behind a vehicle, mounted on a vehicle nor is it self-propelled. Instead it is of a size and weight that it can easily be moved by an operator, for example by pushing it by hand.

The base may also be furnished with an immobiliser operable to prevent unauthorised movement of the display device. The immobiliser may comprise a foot arranged to engage the ground in its locked position and to be elevated above the ground when in its inactive position. Alternatively or additionally the immobiliser may include a brake provided on at least one of the wheels. Advantageously the cover portion extends below the base so as to shield the immobiliser from the public. Activation and deactivation of the immobiliser would thus be possible only by a person in possession of a key to unlock the necessary cover portion and move it to its open position.

For added security the display device may also be provided with location detection means, such as a GPS transmitter, so that its location may be tracked in the event of theft. The detection means may also be useful to monitor the location of all display devices deployed within a particular organisation so that they may be easily located for redeployment.

The temperature inside the display device is controlled so as to remain within a suitable range. Temperature sensing means are located within the housing and electrically connected to the controller for monitoring the temperature. The controller is configured to energise a fan arranged to circulate the air within the display device when the temperature exceeds a predetermine value.

Some embodiments of the invention may include additional features such as security cameras, thermal printers, two way audio communication systems, and even a wireless transmitter /receiver for public internet access.

By way of example only, one embodiment of the present invention will now be described in detail, with reference being made to the accompanying drawings, in which:

Figure 1 is a front perspective view of a display device according to the invention; Figure 2 is a support structure forming part of the display device;

Figure 3 is a base forming part of the support structure shown in Figure 2;

Figure 4 is a frame also forming part of the support structure of Figure 2;

Figure 5 is a perspective view of a locking mechanism and guide rail mountable to the base of Figure 2;

Figure 6 is a perspective view of the support structure shown in Figure 2, but provided with end cover portions;

Figure 7 is a front perspective view of the screen assembly forming part of the display device;

Figure 8 is a rear view of the screen assembly shown in Figure 7;

Figure 9 is a front view of the screen unit forming part of the screen assembly of Figures 7 and 8;

Figure 10 is an exploded view of the screen assembly of figure 7;

Figure 11 is a rear perspective view of the support assembly fitted with components;

Figure 12 is a front perspective view of the support assembly shown in Figure 11 ;

Figure 13 is another front view of the support assembly; and

Figure 14 shows the relationship between the electronic components of the display device.

Referring initially to Figure 1 there is shown a display device generally indicated 10 including a base assembly 11 and a screen assembly 12 mounted above the base assembly 11. The display device 10 is arranged for location in a train station, bus station, cinema or other public place and the screen assembly 12 may be configured to display text, images or videos to the passing public.

The base assembly 11 comprises a support structure 15 as best shown in Figures 2 to 4. The support structure 15 includes a base 16 made from a steel plate formed to define a generally rectangular central portion 17 lying in a substantially horizontal plane, two intermediate portions 18 extending at an angle of substantially 45 degrees from opposed side edges of the central portion 17, and two semicircular end portions 19 extending generally horizontally from the intermediate portions 18. The underside of each end portion 19 is furnished with two ground-engaging castors 21 , the size of the castors being selected to raise the central portion 17 of the base 16 several millimetres above the ground. The purpose of the stepped profile of the base 16 is to enable larger castors 21 to be fitted while maintaining a portion of the base in close proximity to the ground.

Furthermore, a mechanical immobiliser 23 is mounted to the underside 24 of the right-hand end portion 19 so as selectively to inhibit unauthorised removal of the display device 10. The immobiliser 23 comprises a foot 25 arranged for movement between an extended position whereat it engages the ground and an elevated position whereat it is spaced above the ground. The immobiliser 23 also includes two pedals 26,27 for controlling the position of the foot 25 and the front of the end portion 19 is cut back to provide access to those pedals.

Figure 4 shows a frame 30 that bolts to the base 16. In particular, the frame 30 includes a U-shaped lower section 31 , a set of four pillars 32 upstanding from each short side 33 of the lower section 31 , and a rectangular upper section 35 supported on the pillars 32 so as to overlie the lower section 31. The lower section 31 is wider than the upper section 35 thereby requiring the front and rear pillars 32 of each set to extend at an angle from the corners of the lower section 31 to the corners of the upper section 35, thus giving the frame 30 a tapered appearance. Each set of pillars 32 is provided with an A- section 36 extending outwardly in a generally horizontal plane spaced above the plane of the lower section 31. This arrangement allows the lower section 31 to rest on the central portion 17 of the base 16 and each A-section 36 to rest on a respective end portion 19 of the base 16.

Referring to Figure 2, the two sets of pillars 32 are furnished with panels 38 to enclose the ends of the frame 30, the lower front and rear portion of each panel 38 being provided with a cut-out 39, the purpose of which is discussed below. Each end of the frame 30 is provided with a strut 40 that extends upwardly from the base 16 and is secured to a respective panel 38 by bolts (not shown). The two struts 40 support the screen assembly 12 above the base assembly 11.

As shown in Figure 1 , the base assembly 11 includes front and rear cover portions 45,46, opposed side portions 47,48 and a top portion 49, all carried on the support structure 15. The top cover portion 49 is generally rectangular with rounded ends so as to correspond with the general shape of the base 16 and has a lower side 50 (see Figure 8) adapted to locate on the upper section 35 of the frame 30 and a domed upper side 51 provided with a pair of sleeves 52 through which the struts 40 extend. The domed upper side 51 includes a glass panel 53 for displaying indicia therebehind and which includes lighting means (not shown) such as incandescent bulbs, LEDS or the like for illuminating the indicia.

The side cover portions 47,48 are arranged to slide relative to the base 16 between open and closed positions and are supported by upper guide members 55 (see Figure 4) provided on the upper section 35 of the frame 30 and lower guide members 56 mounted on the central portion 17 of the base 16. Each end cover portion 47,48 comprises an arcuate wall that tapers towards the top and has a radius of curvature at its lower end that corresponds to that of the end portion 19 of the base 16 and a radius of curvature at its upper end that corresponds with that of the round end of the top cover portion 49.

The upper guide member 55 comprises front and rear sleeves 57 rigidly supported on the lower side of the top section 35 of the frame 30 and extend parallel to one another in a substantially horizontal plane. Front and rear parallel rods 58 extend laterally from the upper end of each side cover 47,48 and are arranged to form a sliding fit within the two sleeves 56, each sleeve having an opening at each end for receiving a rod from a respective side cover portion.

The lower guide members 56 are best described with reference to Figures 2, 5 and 6. The lower guide members 56 include front and rear T-shape supports 60 upstanding from the central portion 17 of the base 16 and arranged to rest against the cut-outs 39 in the front and rear of the panels 38. The ends of the cross-bar of each T-shape support are furnished with a U-shape rail with an outwardly facing opening 62. Each end cover portion 47,48 has front and rear bars 63 projecting laterally from its lower end and which slidably locate inside the opening 62 defined by each of the front and rear U-shaped channels 61 .

The right hand cover portion 48 may be secured in its closed position by a primary lock mechanism, which includes a lock body (not shown) having a bolt selectively engageable with a keep defined by a slot 66 formed in the right hand end portion 19 of the base 16. The bolt is controlled by a key which is inserted into the lock body through a keyhole 67 defined in the right hand cover portion 48. Thus, only a person in possession of an appropriate key can disengage the bolt from the keep 66 and slide the right hand end cover portion 48 towards its open position.

Two secondary lock mechanisms 70 are disposed on opposed sides of the frame 30 and arranged for securing the left end cover portion 47 in its closed position, each secondary lock mechanism 70 being operable only once the right end cover portion 48 is in its open position (as shown in Figure 6). Each secondary mechanism 70 includes a support member 71 comprising a flat strip of metal having upturned ends defining outer flanges 72 and an intermediate flange

73 stamped from the strip and bent upwardly. Each outer flange 72 has a plate

74 bolted to its outside face 75. The plates 74 are spaced apart by a distance equal to the distance between the panels 38 and are shaped to locate in the cut-outs 38 defined within the panels 38. The inside edge 76 of each plate is recessed to accommodate the respective cross-bar and U-shape channel 61 of the T-member 60 and the outside edge 77 is angled so as to be coextensive with the front edge of the respective panel 38. The upper portions of the outer flanges 72 are stepped inwardly so as to be spaced from the plates 74. The second locking mechanisms 70 are bolted to the central portion 17 of the base 16 and the T-shape supports are held in position by virtue of their crossbars being trapped within the recesses defined by the plates 74.

The plates 74 and flanges 72,73 are provided with openings arranged coaxially and sized to receive a control shaft 78 adapted for rotation about its axis. The right hand end of the control shaft is provided with a uniquely shaped aperture 80 and the left hand end of the control shaft 78 is provided with a cam 81. When the right hand end cover portion 48 is in its open position a special key (not shown) may be inserted into the uniquely shaped aperture 80 and turned so as to rotate the control shaft 78 about its axis so as to turn the cam 81 between first and second positions. In its first position (as shown in Figure 5) it is disengaged from an abutment (not shown) provided on the left hand cover portion 47, but in its second position it engages the abutment and the left hand end cover portion 47 is prevented from sliding to its open position. Front and rear cover portions 45,46 are fastened to the front and rear edges of the panels 38 by bolts (not shown) or the like so as to be easily removed once both end cover portions 47,48 are in their open positions.

With reference to Figures 7 to 10, there is shown the screen assembly 12 including a relatively flat rectangular LED screen unit 85 comprising a rectangular flat case provided with a glass window 86 on the front face 87. Behind the window 86 there is disposed an array of LED elements (not shown) for displaying content and inside the case is circuitry (not shown) for driving the LED elements. On the front and rear faces 87,88 of the case is a further area 89 on to which indicia may be printed, mounted, embossed or otherwise provided and lighting means (not shown) may be disposed within the case for illuminating that area.

Referring specifically to Figures 9 and 10, each side face 90 of the screen unit is provided with a row of six threaded holes (not shown) that align with a row of six holes 91 provided in each strut 40 upstanding from the base 16. The screen unit 85 rests on the sleeves 52 upstanding from the domed upper surface 51 of the top cover portion 49 and is secured to the struts 40 by bolts extending through the holes 91 in the struts 40 and threadingly engaging the threaded holes on the screen unit 85.

An antenna (not shown) is mounted in a cover 93 located midway along the upper face 94 of the screen unit 85 and which antenna is configured to receive and transmit data representing the content to be displayed on the screen 86. Cables (not shown) extend from the antenna and the drive circuitry through one or both of the sleeves 52 and into the base assembly 1 1 .

Fascias 95 are mounted to the upper and side faces 94,90 of the screen unit 85 and each has the shape of an inverted-L with a semi-circular cross- section sized to correspond with that of the antenna cover 93 and the sleeves 52 so as to provide a continuous profile around the periphery of the screen assembly 12. The upright member of each fascia 95 is provided with a row of five outwardly extending limbs 96 having a flange depending from its free end to define a hook. The struts 40 each have a row of 5 slots 97 into which the hooks locate as the fascias 95 are presented to the side faces 90 of the screen unit 85. The fascias 95 are lowered to engage the sleeves 52 and the upper face 94, which causes the flanges located in the slots 97 to slide lower inside the strut 40. With particular reference to figure 10, the upper end of each side face 90 is furnished with a rectangular tab 98 that locates inside a respective strut 40 as the screen unit 85 is lowered into position so as to prevent forward and rearward movement of the screen unit relative to the struts during assembly.

Referring now to Figures 1 1 to 13, inside the frame 30 there is disposed an enclosure 100 in which there is stowed a battery unit 101 and a charger 102. The battery unit includes two 24V sealed batteries encased in aluminium giving a combined output of 24V capable of supplying sufficient power to allow the display device 10 to run continuously for 20 hours. The charger 102 is standard in that it includes an AC to DC converter and means for regulating the supply current according to the requirements of the battery and the computer. The charger 102 is connected to the battery unit 101 by wires (not shown) and the charger is connectable to the mains power supply by a cable 103 having a connector 104 on its free end.

There is also provided a cable assembly 105 provided on the right panel 38 and accessible only when the right end cover portion 48 is in its open position. The cable assembly 105 includes a drum 106 rotatably mounted on the panel 38 and around which drum 106 the cable 103 is wound when not in use. A coil spring (not shown) is fitted to the drum 106 and is in a state of equilibrium when the cable is fully wound around the drum. The drum 106 and spring are disposed within a housing 107 mounted to the panel 38 and having an opening 108 through which the cable 103 and connector 104 extend, the connector being held in a receptacle 109 when the charger is not being used.

To use the charger 102 the cable 103 is pulled through the opening 108 which causes the drum 106 to rotate in the clockwise direction thereby energising the spring. When the tension in the cable 103 is reduced, the energy in the spring urges the drum 106 to rotate in the counter-clockwise direction so as to wind the cable 103 therearound.

Mounted to the left hand plate 38 is a power supply unit 1 10 electrically connected to the battery 101 and configured to supply three regulated voltages to power different components, those voltages being 5V, 12V and 24V. The left hand panel 38 also carries a computer 1 1 1 , a wireless modem 1 12 or other transmitter receiver device, an interface PCB and a display controller PCB. There is also provided a 5V, 12V and 24V power input connectors, a data port and an antenna connector. The base assembly is also furnished with temperature sensing means (not shown) that relay information to the interface PCB, which energises up to four electrical fans disposed within the display device when the temperature therein exceeds a predetermined value. Light sensing means (not shown) are provided for determining the ambient level of light and the display controller PCB is configured to adjust the screen brightness accordingly. The display device 10 has a modular design so that any one of the display module, battery-charging module and electronic control module may be replaced quickly and easily, typically in less than 20 minutes.

Figure 14 is a schematic illustration showing the electrical connections between the various electrical components of the display device 10. A data signal representing the content to be displayed on the screen 86 is generated by a computer 120 and transmitted through antenna 130. The antenna 160 of the display device 10 receives the data signal and sends it to the computer which uses it to generate a drive signal for driving the screen elements. It may be that the computer 120 and antenna 130 are used to control several display devices, each intended to display different content depending on their geographic location. For instance, each display device may be configured to receive signals of a particular frequency and the external computer 120 and transmitter 130 may be adapted to modulate the frequency of each signal to match that of the display device for which the signal is intended. Alternatively, each display device may have its own unique address stored in its memory and the signal may be encrypted with the address of the display device for which the signal is intended. Each display compares its own address with the address encrypted in the signal and responds only if those addresses match. Since this area of technology is so well known it is unnecessary to discuss it any further here.