GB2286073A - Display system - Google Patents

Abstract

A display system (1), particularly for hotel or restaurant use, allows graphical editing, updating and scheduling by a software program installed on a personal master computer (3). Signals to and from displays (2) are transmitted along the mains electricity supply (4). A given display message can be received by a plurality of the displays together, and any which do not receive the message properly, signal the fact to the computer together (using a common signal) to cause retransmission. <IMAGE>

Description

1 DISPLAY SYSTEM 2286073 The present invention relates to a display

system.

Traditionally, hotel personnel have displayed room locations and other messages such as promotional information to arriving guests or visitors on pin-boards erected on stands placed at key points in the foyer, or near the lifts on each floor of the hotel. Plastic moulded lettering is often used to display this information. A revision of the temporary information requires each notice board to be visited and to be updated manually at the time of the revision. Such updating is time-consuming and, when staff are busy, alterations to the displays are frequently delayed or not made, which can be inconvenient for guests and visitors. The choice of lettering styles and colours is also often limited and, where variation is possible, considerable ef fort is required to achieve attractive, eyecatching results. Where background lighting is reduced, for instance at the entrance to cocktail bars or in areas surrounding the lifts, it may be dif f icult to read the pinboard display or easy to miss the display altogether if the observer is in a hurry. In larger hotels, such manual displays may supplement teletext, video and 'Itickertapell information systems which describe the hotel's services in general, and which typically make use of cathode-ray tube or LED displays. The information displayed manually on pin-boards in these large hotels is typically too recent, short-lived, and guest-specific to allow or warrant inclusion in these other non-static electronic displays.

These other types of display are also usually fixed to mountings on walls or overhead, or are difficult to move from one location to another.

Many restaurants and public houses display their menus on blackboards, and particularly display special dishes which vary with the availability of ingredients and which cannot be included with standard dishes included in a written menu. As an alternative to a blackboard, a list of 9 -0 v 2 special dishes may be handwritten, typed or reproduced on an additional sheet of paper to be inserted in such a written menu. Typically, such blackboard displays or lists are updated twice a day: at lunchtime and for dinner.

Preparing the blackboard is time-consuming and especially messy if white or coloured chalks are used. Such blackboards are also used where dishes are prepared at reasonably frequent but unpredictable intervals. During busy lunchtime and evening periods, the displays are frequently not updated, which may lead to frustration on the part of customers who place orders for dishes which are no longer available. Where a restaurant owner wishes to modify details of the available dishes, for instance to reflect an alternative ingredient or change in price, it is impractical to modify the display. similarly, opportunities are lost to welcome important customers or parties and to mention special features such as entertainment or promotions taking place at some later date in the restaurant or public house. Where illumination is poor, the blackboard displays may be hard to read and there are limited technical possibilities to enliven the display frequently enough to avoid customer fatigue. In public houses and restaurants, electronic moving displays are seldom used on the grounds of expense and because of the likely detrimental effect on the ambience surrounding customers or clients.

Other systems have been proposed for updating electronic display signs. In particular, GB-A-2244359 discloses a system for updating supermarket pricing by flashing the store lighting. This prior art technique addresses a different and highly specific problem, namely updating of mass pricing. It would not be suitable for the application intended for the present invention, which requires the broadcast of much higher data volumes (100K bytes versus 100 bytes per broadcast event), nor is it likely that hotels and restaurants would want their 3 reception and public areas illuminated withflashing lights.

Various systems have been devised in the past f or mains borne signalling between devices spread over a building. GB-A-2174273 describes a method whereby a point to-point computer network can be implemented by the mains.

US-A-4429299 discloses a mains-borne system of communication between a central controller and a plurality of room control units in hotels. Neither of these systems is suitable f or a remote portable sign system, because neither provides f or message broadcasting but only f or point-to-point communication.

According to the present invention, there is provided a display system, the system comprising:

a plurality of displays, each display having means for connecting the display to a mains power supply; a master system having means f or connecting the master system to the mains power supply, the master system having transmission means f or broadcasting a display signal via the mains power supply to specified ones of the displays; each of the displays having means for detecting that the display signal has not been properly received and for transmitting an error signal via the mains power supply to the master system substantially simultaneously or in phase with corresponding error signals transmitted by any other of the specified ones of the displays when the display signal has not been properly received.

This invention provides a remote display system which can use illuminated portable electronic displays updated from a central computer. The central computer may serve as a station f or the design of messages, as a scheduler for assigning messages to remote displays around the building, and as the master station for broadcasting messages to the remote displays. The messages themselves, which may be either textual or graphical, are broadcast from the central computer over the mains electricity supply, avoiding the need for dedicated wiring. In order to make this mains- I,,- 4 borne transmission practical for high resolution messages, a broadcast protocol is used. With this system, a sign may be moved from one location to another just by unplugging it from the mains supply and reconnecting it in its new location.

The display system has application in many public places, such as restaurants, hotels, retail shops, offices, auditoria, etc.

The primary intended use for the present invention requires the transmission of relatively large quantities of data (on the order of 100K bytes for a complex graphical message) over a relatively slow (9600 baud) and error prone medium (Frequency Shift Key transmissions over the mains). A message of this size broadcast at 9600 baud will take in excess of 100 seconds to broadcast, with no allowance for retransmission. Alternative network protocols in common use, e.g. token passing or other point-to-point protocols, are not suitable for this application, because it would be necessary for the same message to be sent many times, once for each sign in the group destination address. A message transmission time of 100 seconds is practical for the hotel and restaurant environments envisaged, but would be impractical if a point-to-point protocol were required. For example, 15 slaves in the message destination group would take in excess of 1500 seconds or almost half an hour. The present invention permits broadcasting rather than point-to-point communications such as proposed in GB-A-2174273 and US-A-4429299 described above. In this way, one transmission can be used to update a whole group of signs and thus it is possible to shorten the time taken to execute a new or modified message.

A problem exists in that some signs in a group may receive corrupted messages. The normal network approach to this would be to have a receiver of a corrupted message transmit a "distress" signal which means "please send that message again". But the simultaneous broadcast of many such messages would generally create a confusion of noise on the network. The system of the present invention operates by arranging the "distress" signal so that, regardless of whether one node sends it or many nodes send it, the broadcaster hears the same signal. -In such a case, the broadcaster simply retransmits the signal until the distress signal is not received. The present invention makes use of what is termed herein a "concurrent veto" protocol, so that any distress signal will appear the same to the listener regardless of whether it is transmitted by a single node or by many nodes.

An example of the present invention will now be described with reference to the accompanying drawings, in which:

Figure 1 is a diagrammatic representation of a display system according to the present invention; Figure 2 shows a screen from a Message Manager program, used to identify a particular portable remote display by reference to a floor plan; Figure 3 shows the screen after the icon representing a particular portable display has been opened; Figure 4 illustrates the command menus available in the Message Manager program; Figure 5 is a diagrammatic circuit diagram of a Mains Signalling Interface; Figure 6 is a diagram of circuitry associated with a Frequency Shift Keying modulation/demodulation block; Figure 7 is a diagram of mains zero crossover detection circuitry, used to synchronise the concurrent veto signal broadcast by the slave MSIs; Figure 8 is a diagram of circuitry used to generate any-complaints and concurrent-veto signals; Figure 9 is a diagram of the circuitry used to detect the any-complaints and concurrent - veto signals; Figure 10 is a table showing communication to and from 35 the master and slaves; and, Figure 11 is a table showing the complete sequence of communication required to broadcast a new message.

le- 6 General Description of Hardware

The specific example of a system includes three main pieces of hardware:

(A) portable illuminated displays remotely operated by coded signals transmitted along the standard electricity mains power supply, which signals encode an addressing component, a command component, and a kernel of changeable information embedded in a variable image format which is modifiable and controllable; (B) a master system, comprising a personal computer and supporting peripherals and dedicated software and hardware instructions broadcast to specified sets of the portable remote displays by means of coded signals transmitted to each display along the cables providing mains electricity to the displays; (C) each of the displays and master system is connected to its own dedicated bi-directional Mains Signalling Interface (hereafter referred to as an MSI). This device contains a serial interface which permits the reception and transmission of data for a display or master system as well as providing mains power to this attached device. This device ensures the integrity of data sent and received using a broadcast protocol (the "Concurrent Veto" protocol, to be described in more detail below).

General Description of Software

All three hardware components are microprocessor driven. Four programs are used to operate the system, two running on the master, one on each of the slave remote display systems, and one on each of the MSIs. The programs are:

(1) a Message Manager program, which operates on the master system and provides the human user with an interface for:

k (i) designing, editing, saving and retrieving messages 7 (A) updating the allocation of remote displays into groups (iii) archiving and retrieving messages designed using other applications for display (iv) scheduling messages for display by time and by group (v) simulating the display screen of a given remote display (vi) network diagnostics and error correction (2) a Message Driver program which operates on the master system and which assembles messages to be displayed into packets of display information comprising an addressing component, a command component and the image data, and transmits them serially to the local MSI for broadcasting over the mains; (3) a Mains Protocol program which operates on each MSI and is responsible for managing the decoding and encoding of messages and the implementation of the Concurrent-veto protocol (4) a Message Display program which operates on the portable remote display systems which takes packets of information received from its local MSI and displays them as messages on the display.

General Description of System Operation

The following is the typical sequence of events f or creating and displaying a new message:

(1) The message is designed by the human operator, either using the Message Manager program or a third party product, and stored on disk on the master system.

(2) Using the scheduler function of the Message Manager, the human operator determines the location of the new message on the remote signs and certain display options (e.g. "flashing"), then assigns the message to a group destination address (e.g. "Reception") and schedules the message for display (e.g. from 7.30am to 10am).

8 (3) The Message Driver program polls the schedule of messages to be displayed. When a message is due f or display, the Message Driver retrieves the message data from disk and transmits it serially to its local MSI, including the group destination address, location and display options and the image data itself.

(4) The Mains Protocol program running on the local MSI breaks the received data up into packets and transmits them over the mains using the standard technique of Frequency Shift Keying (PSK), by which digital data is impressed on the mains signal. FSK is frequency modulation applied to the mains power supply. In the case of digital FSK, the zeros and ones are transmitted by modulating the carrier frequency by a fixed amount up or down. For example, if the carrier frequency is F, the Os are transmitted on frequency F+AF and the ls are transmitted on F-AF. The Mains Protocol program attaches the group destination address to the beginning of each packet and a data integrity indicator (either a simple checksum or Cyclic Redundancy Check) to the end of the packet.

(5) The Mains Protocol programming running on each slave MSI converts the incoming XSK signal into a string which it stores in its local random access memory (RAM).

(6) If the Mains Protocol program running on any slave recognizes both that (i) it is a member of the group destination address and that (ii) it has received a corrupt or incomplete packet (according to the checksum. or CRC check), then it broadcasts the concurrent - veto signal.

(7) On receiving a concurrent - veto signal, the Mains Protocol program running on the master MSI rebroadcasts the preceding packet; otherwise, it broadcasts the next packet.

(8) This process continues until either the complete message has been successfully transmitted or a prespecified number of failures has occurred; the status in either case is relayed to the Message Driver program running on the master for display to the human operator.

z 9 9 (9) On receiving a complete message, the MSI attached to each slave in the destination group relays the message serially to the Message Display program on its remote display.

(10) The Message Display program on each remote display program in the destination group updates its display with the new message.

Implementation of the Concurrent - veto protocol described above requires that the master MSI should receive the same concurrent - veto signal, regardless of whether one slave has transmitted it or many slave MSIs have transmitted it. In the particular implementation described in more detail below, this is achieved by making the slave MSIs impress the same frequency (tone) signal on the mains but synchronised using the 'mains alternating current crossover point (i.e. zero voltage point) as a trigger.

The concurrent - veto tone is chosen to be an exact integer multiple of double the mains frequency (i.e. typically an integer multiple of 100 or 120 Hz). In this way, the signal transmitted by all dissatisfied slave devices is synchronised, and the master will perceive the same signal regardless of whether one slave is transmitting or many slaves are transmitting. The significance of doubling the mains frequency is that the zero crossover detection circuitry is not required to distinguish between 00 crossover and 1800 crossover. At whichever point a given slave starts, its concurrent-veto signal will still be in phase with its fellows.

A number of variations and refinements on this basic technique can be used to provide for higher speed data transmission and more robust signalling in the case of dirty power. For example, a second concurrent veto (i.e.

a second frequency) tone may be used to indicate that a slave has previously vetoed a packet which was not retransmitted. The second concurrent - veto tone may be transmitted as before at the end of transmission of the packets from the master MSI. The appropriate action in M---, such a case would be f or the master to broadcast the preceding N packets, or the entire message from the beginning. Another alternative is the use of another frequency by the master to indicate that the packet currently broadcast is a retransmitted packet which should be decoded only by slaves which did not properly receive the previous broadcast of this packet.

Referring now to Figure 1, a portable remote display system 1 for a hotel or restaurant comprises one or more illuminated transparent portable remote liquid crystal displays 2, and a master personal computer 3, each of which is connected to the mains power supply 4 via its own MSI 5.

The illuminated transparent portable remote displays 2 may be free standing (as shown in Figure 1), wall mounted or tabletop, for example. Each display 2 may have a monochrome liquid crystal array sandwiched between two layers of glass. The LM type is positive transmissive. When a pixel in the display is turned on, a black dot or square appears to form on the surface between the two glass layers; when no pixels are turned on the display is completely transparent. The display is 640 x 480 pixels in format. An enclosed strip light source may run along the top of the liquid crystal display inside the housing of the display 2, illuminating the display from above to make the images stand out against the background and visible in poor lighting conditions. The static image display controller, associated random access memory and circuitry can be contained within the housing for the display 2.

For applications where higher quality resolution is required, an alternative embodiment could use a liquid crystal display of higher specification supporting 8, 16 or 64 grey scales or 16 colours.

For applications where lower production cost is combined with lower resolution, an alternative embodiment would use a light emitting diode (LED) display, either monochrome or colour.

1 11 Messages f or updating the contents of a particular display 2 are received by its MSI 5 (see Figure 1). DIP switches or a reprogrammable memory (not shown) to allow each display to be allocated an identity number are contained under a protective cover in the display housing. The portable remote displays 2 may be turned on and off by means of a switch, and may be carried from one location to another by means of a handle. Various ones of the displays 2 may be grouped as a subset. For example, all of the displays on a particular floor may form one group, or all of the displays in dining areas may form a group.

The portable remote hotel or restaurant display system preferably uses a personal computer as the master system with monitor, keyboard and mouse connected to the mains via an MSI. There are two interfaces between the master personal computer and the MSI: a mains electricity cable and a serial data cable, plugged into a serial port at the back of the computer.

The Message Manager program which operates on the master personal computer 3 allows the information on each portable remote display to be shown on the computer monitor in a WYSIWYG format ("what you see is what you get"). The image itself may be created using other computer programs (editors, graphics packages, etc) and imported into the Message Manager for scheduling. Technical features of this software program are: (a) a graphical user interface as exemplified by Microsoft Windows or Apple Macintosh System Seven supported by a mouse or electronic pen; (b) a graphical window where icons 6 represent individual portable remote displays 2, f or example as shown in Figure 2 (the icons 6 are here presented, as in the case of a hotel, on a series of f loor plans 7 indicating the precise position of the portable remote display 2 in the hotel); the icons 6 representing the displays 2 can be dragged and dropped into new positions on the floor plan 7 corresponding to changes made in the physical siting of the portable remote displays 2; (c) double clicking on the 12 icons 6 representing individual portable remote displays 2 to reveal the current information 8 held on the display in question, as shown in Figure 3; (d) a graphical editor permitting the creation and editing of simple drawings using standard paintbox software tools and menus and allowing a limited range of colours if the portable remote display 2 is capable of supporting colour; (e) a graphical input procedure allowing display information to be transferred from an archive of stored display information or from other software programmes by file transfer and object-linking techniques; (f) display scheduler allowing precise display instructions to be made in advance with regard to particular information and groups of remote portable displays; (g) an archive procedure to store particular display information for further use; (h) query and status -software procedures to access and control remotely and to manage the information on a particular remote portable display in conjunction with the graphical editor; and, (i) diagnostics and utility procedures to test and monitor the performance of the computer remote portable display system software and hardware, in particular the software and hardware including associated circuitry for the remote access and control of the portable displays. An example of the menu options available in the Message Manager program is shown in Figure 4.

In this embodiment, the MSIs 5 used by the master personal computer 3 and the slave remote displays 2 are identical, and run the same Message Protocol manager software. However, certain parts of the circuit are used only by the master or by the slaves, as indicated by [] or [] in Figure 5. For example, only the MSI attached to the master would generate an anycomplaints tone and only the MSIs attached to the slaves would listen for it, whereas with the con-veto tone, the reverse is true.

In this embodiment, communication through the mains takes place using four channels as shown in the Table 1 shown in Figure 10. Each tone represents an alternative A 13 signal of a particular and unique frequency impressed on the mains and having a particular meaning in the protocol. In addition to the con - veto tone broadcast by the slave MSIs, the master uses two additional tones, any-complaints to indicate that a transmission is finished, and rebroadcast to indicate that a transmission is in fact a re-transmission.

The complete sequence of communication required to broadcast a new message is given at the functional level in the sequence shown in Table 2 in Figure 11. For the purposes of illustration, it is assumed that the message to be broadcast fits into 2 packets, and that the second packet has to be repeated because two slave MSIs called Y and Z did not receive it correctly on the first transmission but do so on the second transmission.

The main functional components of the MSI are shown in Figure 5. As can be seen from the example of the communications between master and slave MSIs given in Tables 1 and 2 of Figures 10 and 11, the MSI circuitry is required to generate or detect certain signals. In particular, the MSIs need both to detect and generate Frequency Shift Keyed data signals; the MSIs need both to detect and generate tones (i.e. any-complaints, con veto, reb.roadcast); and the MSIs need to detect the mains cycle crossover, for synchronising tones. This is achieved by having a central microprocessor 25 which is linked to generation and detection circuitry 20,30,40 as shown in Figure 5. The detector circuits 40,20 for tones and the mains cycle zero crossover generate interrupts to the microprocessor 25. Data from the FSK circuitry is fed into the microprocessor circuitry 25 via a bi-directional serial port. Data to and from the display 2 or master system 3 attached to the MSI 5 also pass through this port. Schematic circuitry for each of the functional blocks shown in Figure 5 is shown in later diagrams: PSK decoding/encoding circuitry (Fig. 6), mains crossover detection (Fig. 7), a generic concurrent-veto and 14 any__complaints generation circuit (Fig. 8), and a generic concurrent veto and any_pomplaints detection circuit (Fig. 9).

The MSIs 5 may have an external appearance very much like that of a conventional mains plug, with pins f or connection to live, earth and neutral. The various circuits are held in a housing on the rear of the plug-like MSI 5. In an alternative embodiment, the MSI circuitry may be embedded in a housing of the displays and/or master computer 3, avoiding the need for an external unit for the MSIS 5.

The circuitry required for each detector or generator block 20,30,40 (as shown in Figure 5 above) requires its own transformer which converts the mains signal to a low voltage signal or, conversely. transforms a low voltage signal to impress it on the mains. These transformers are mounted in parallel in a transformer/mains coupling block 51 shown in Fig. 5.

Each of the tone and zero crossover detectors 20,40 requires a resonating LC filter to pick out the particular frequency it is listening for. In the case of the zero crossover detector 20, this is an active filter because the inductance required for a passive filter operating at 50Hz would be too large.

Referring now in detail to Fig. 5, the MSI 5 uses a commercially available mains signalling transceiver 21, the LM2893 manufactured by National Semiconductor Inc. The transceiver 21 acts both to transmit FSK modulated signals and provide demodulation of signals received. The transceiver 21 is fed the FSK signals as filtered out of the mains 4 by a resonant bandpass filter 22 as shown. The bandpass filter 22 passes signals received whose frequency is close to the carrier frequency F chosen, which includes both the Os signal (F+AF) and the ls signal (F-, &F).

The details of the circuitry associated with the FSK reception and transmission are shown in Fig. 6. Only the main lines into the transceiver 21 are shown. Information i 1 M flows in both directions between the microprocessor 25 of the MSI 5, through the modulating/ demodulating chip 21, through mains coupling circuitry and to the building mains wires (L, G and N).

A transformer T, inductance L and capacitor C constitute the resonant bandpass filter 22 which is centred on the carrier frequency F of the FSK encoding. The FSK signals which pass through the filter 22 from the mains 4 arrive for demodulation on Pin 10 of the transceiver 21.

Similarly, modulated signals created by the transceiver 21 are transmitted from Pin 10, and impressed on the mains 4 by a mains coupling transformer 23. Zener diodes 24 are provided as transient protection diodes for the 110 Pin 10. A transistor Q8 and resistor % constitute a transmission boost circuit 25 enabled by opening a switch Si. A variable resistor % is used to adjust the resonance frequency about F.

Referring to Figure 7, the mains crossover detection circuitry uses an active filter 26 to detect the 50Hz (or 60Hz) mains signal. This active filter 26 is fed by a transformer 27 which is in parallel with the transformer 23 driving the transceiver 20 (see Fig. 5). The output from the active filter 27 is fed into a standard LM311 comparator 28 powered between +5V and ground. A 10kn resistor 29 provides a pull-up for the open emitter of the comparator 28. The mains frequency square wave generatedby the comparator 28 is fed into an interrupt generator 31 (constituted by an exclusive-or gate and a low pass filter combination). The output from the generator 31 is a positive pulse every time there is a square wave transition, i.e. on a zero crossover point. This provides the microprocessor 25 of the MSI with an interrupt for synchronizing the fail tone (concurrent-Veto) signals with the mains crossover point.

Referring to Figure 8, this shows the details of the circuitry used in the specific embodiment to generate an any_questions or concurrent-veto tone. A voltage 16 controlled oscillator 32, such as a LMS66, is enabled by the microprocessor 25, thus forcing an output pin of the VCO 32 high and hence switching a simple WT switch 33 ON to allow current to flow into the supply pin. The output on Pin 4 of the WO 32 is a triangle wave. By passing this wave through a low pass filter 3 4, the higher harmonics are removed and the result is approximately sinusoidal. This signal is fed through a transformer 35 and thence impressed onto the mains supply.

Referring to Figure 9, this shows the details of the circuitry used in the detector 40 for detecting an any-complaints or concurrent - veto tone. It uses a commercially available tone decoder 41, the LM567. A transformer 42 of the same type and impedance as used for is tone generation (see Fig. 8) is run in parallel with the decoder 41. The transformer 42 feeds the mains signal into a resonant circuit 43 consisting of a resistor Rt and a capacitor Cf. A variable resistor 44 and a capacitor 45 on Pins 5 and 6 of the tone decoder 41 determine the frequency detected. When this frequency occurs, Pin 8 of the tone decoder 41 becomes low. A NOT gate 46 connected between Pin 8 of the tone decoder 41 and the microprocessor 25 instigates an interrupt to the microprocessor 25.

31 J 17

Claims (11)

1. A display system, the system comprising: a plurality of displays, each display having means for connecting the display to a mains power supply; a master system having means for connecting the master system to the mains power supply, the master system having transmission means f or broadcasting a display signal via the mains power supply to specified ones of the displays; each of the displays having means for detecting that the display signal has not been properly received and for transmitting an error signal via the mains power supply to the master system substantially simultaneously or in phase with corresponding error signals transmitted by any other of the specified ones of the displays when the display signal has not been properly received.

2. A display system according to claim 1, wherein the master system transmission means includes means for impressing the display signal on the mains by Frequency Shift Keying.

3. A display system according to claim 1 or claim 2, wherein each of the displays includes means for impressing the error signal as a monotone on the mains.

4. A display system according to claim 3, connected to a mains power supply having a frequency F, wherein the error signal is a tone having a frequency which is an integer 30 multiple of 2F.

5. A display system according to any of claims 1 to 4, wherein each display includes a zero crossover circuit for detecting the zero crossover points of the mains supply to that display, transmission of said error signals being synchronised with a zero crossover point of the mains power supply.

is

6. A display system according to any of claims 1 to 5, wherein at least one of the displays is a portable illuminated remote display.

1

7. A display system according to claim 6, wherein the portable illuminated remote display is a top-lit transparent LCD display.

8. A display system according to any of claims 1 to 7, wherein each display is identified by an address set by a series of microswitches or in a programmable memory.

9. A display system according to claim 8, wherein the displays are addressed in discrete groups.

10. A display system according to any of claims 1 to 9, wherein the master system includes a software programme providing a graphical user interface, a WYSIWYG environment for modifying the information to be displayed, and a scheduling procedure for organising the display of information.

11. A display system substantially as described herein with reference to the accompanying drawings.