WO1992006454A1

WO1992006454A1 - Method and apparatus for price display

Info

Publication number: WO1992006454A1
Application number: PCT/US1991/007358
Authority: WO
Inventors: Larry A. Lincoln; Kent A. Fritz; Joseph S. Chan; Michael V. Nanevicz; Edward D. Olson; James W. Pfeiffer; Erno B. Lutz; Leland M. Farrer
Original assignee: Diablo Research Corporation
Priority date: 1990-10-05
Filing date: 1991-10-02
Publication date: 1992-04-16
Also published as: AU8876891A

Abstract

Improvements in price display system for a retail establishment which includes transmission of UPC price data from a central computer (18) to a large number of display modules via intermediary nodes (90, 92). Features of the system include various system architectures for connecting to a conventional point-of-sale store system (16), multiple radio transmitters (28) and receivers (30) for communication to the display modules, isolation of groups of display modules from their power sources to provide a more robust system, hard wiring (32) display modules to the store computer (18) and providing mains current to power the display modules, methods for ensuring that individual display modules are operating properly, improvements in the display module optical port (180) to be responsive to changes in ambient light level, an improved method for programming display modules directly via a light wand, and a display module which includes a heater element (200) with a protective circuit (204, 206).

Description

METHOD AND APPARATUS FOR PRICE DISPLAY

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to a system for display of prices associated with merchandise in a store, and in particular to improvements in an electronic system which allows the prices associated with any item in the store not only to be electronically displayed, but also to be changed from time to time.

Designer's Description of the Prior Art

A system relevant to this disclosure is described in copending U.S. patent application 07/348,355 filed May 5, 1989, entitled "System for Display of Prices and Related Method" invented by James . Pfeiffer et al., attorney docket number M-925 US, incorporated herein by reference. Improvements in the system described in the copending application are disclosed herein.

SUMMARY OF THE INVENTION

The system architecture and the system interface with the store computer and regional host computer are improved to provide greater flexibility in store installations, and to make the system compatible with various types of existing store computer systems.

In another improvement, instead of having only one transmitter and receiver in the store ceiling as in the copending application, multiple transmitter-receiver sets are provided, i.e. up to six sets in one embodiment, all of which are controlled by one module controller in the store, so as to provide better radio communications within the store. With the multiple receivers and transmitters, each receiver includes the capability to report the signal transmission strength of the other transmitters. Thus if one transmitter fails, it is possible to detect this failure and switch transmissions to another unit.

In another improvement, a "group node" providing communications and power to many display modules (such as all the display modules on one gondola) is substituted for several shelf nodes, thus economizing on the relatively costly radio communications circuitry in the shelf nodes. In another improvement, bidirectional data lines are provided between the shelf nodes and the display modules. This improves and simplifies data communication.

Also provided in conjunction with the bidirectional data lines is a five wire to four wire converter to convert the five signal lines (including power) to a four signal line system for connection to the display modules. Another improvement is hard wiring the shelves to provide external power, i.e. mains electrical current, to the system and thus avoid the use of batteries in the shelf nodes where desired. This eliminates the problem of replacing batteries in the shelf nodes and allows many modules to be powered by one shelf node.

Also provided is a method for indicating when a display module has failed or has lost contact with the store computer. This "orphan" process provides a visual indication on the display module (in the form of a dot or other symbol in a predetermined display location) that communications have been lost. Also provided is an improved method for a particular display module to rejoin the system after communications to that module have been lost.

An associated improvement in display module communications is a "bed check" which provides that periodically (such as every eight hours) each display module is checked by the store computer to ensure that the display modules are each capable of answering.

An improvement in the shelf nodes is circuitry to provide an indication of the condition of the shelf node batteries, i.e., being low or dead. This improvement includes a mode in which when the batteries are low, a report is provided; when the batteries are dead, the shelf node and connected display modules continue operating, but without the ability to transmit or receive by radio to maximize useful life of the shelf node battery set.

Another improvement associated with the shelf node batteries is a voltage doubler circuit so that when the battery voltage drops below a certain level, the voltage is doubled to ensure that sufficient voltage is provided to the shelf nodes.

An additional improvement with regard to the display modules is an adaptive threshold for the optical port in each display module, so that the optical port is not confused by varying levels of ambient light. This feature causes the display module to react only to significant changes in the level of received light in terms of receiving information by light input or by sensing a cutoff of ambient light. Another improvement associated with the display modules is the capability to write an image to be displayed into the module via the optical port, by using for instance a hand-held portable computer driving an optical wand. Thus the modules may be programmed without use of the central store computer.

Also provided is an indication in the display module to module controller communications protocol to distinguish the various types of modules, i.e., standard size or compact modules having different types of LCD's, to make sure that the proper display information is sent to each module as needed.

An additional improvement relating to the display modules is a heater in those modules located in a store freezer. This heater ensures that the display modules are kept warm enough to operate properly, and includes a feature so that these modules (which draw more current when heating than does a normal module) when connected to the system in places where adequate power is not avail¬ able, will not draw any heating current.

BRIEF DESCRIPTION OF THE DRAWINGS

Figures 1, 2 and 3 show various system configurations in accordance with the invention.

Figure 4 shows multiple transmitter-receiver units in accordance with the invention.

Figure 5 shows a ceiling receiver in accordance with the invention. Figure 6 shows bidirectional data transmission in accordance with the invention.

Figures 7 and 8 show five to four wire conversion in accordance with the invention.

Figure 9 shows the display module in accordance with the invention.

Figure 10 shows an orphan process in accordance with the invention.

Figure 11 shows a module joining a system in accord¬ ance with the invention. Figure 12 shows a battery condition indicator in accordance with the invention.

Figure 13 shows a voltage doubler in accordance with the invention.

Figure 14 shows the optical port adaptive threshold in accordance with the invention.

Figures 15 and 16 show a display module heater in accordance with the invention.

Similar reference numbers in various figures denote similar or identical structures. DETAILED DESCRIPTION OF THE INVENTION

Various store system architectures are available in accordance with the invention. One such architecture is shown in Figure 1. In this embodiment, the regional host computer 10 contains price change information and much of the data necessary for running the system. This regional host computer is connected via a conventional modem (not shown) over telephone lines 12 (i.e. "telco" lines) to a gateway computer 14 inside the particular store. Gateway computer 14 may be a personal computer or mini-computer. The gateway computer 14 accepts from the regional host computer information to be sent to either the POS (point of sale) δcontroller 16 in the store or to the module controller 18. The regional host 10, POS controller 16 and associated POS terminals (not shown) are conventional. The module controller 18 is connected to the ceiling node 22 which may be in one embodiment of the invention one of six nodes, as described below. The ceiling node 22 includes the ceiling digital circuitry 26 and the radio transmitter 28 and radio receiver 30 which contacts by radio the various group and shelf nodes (not shown) . In one embodiment, the ceiling digital circuitry 26 is connected directly by a five wire connection 32 to shelf wiring and to five wire to four wire converters (see below) .

In an alternate architecture shown in Figure 2, the regional host computer 10 is again connected via modem and telephone lines 12 to an IBM 4680 POS controller 34 which is commercially available from the IBM Corporation. Normally two such IBM 4680 POS controllers 34, 36 are present in a store and are conventionally in communication with each other via an IBM token ring LAN 38 (local area network) . In accordance with the invention, the module controller 18 is also connected to the LAN 38. Thus the module controller 18 receives the information necessary to operate the display modules (not shown) from the LAN 38. In another alternate architecture shown in Figure 3, the regional host computer 10 is in communication via modem and telephone lines 12 with first gateway computer 14 in the store. First gateway computer 14 is connected via a local area network 38 such as the IBM token ring network referred to above, with other computers in the store. As shown, these other computers may include an administration computer 44 for use by store management, a pharmacy computer 46 and the various point of sale terminals 48, as is conventional. In accordance with the invention, a second gateway computer 50 is also connected to the LAN 38. This second gateway computer 50 is responsible for accepting all information from the regional host 10 which has been placed on the LAN 38 by the first gateway computer 14 and which is relevant to operation of the electronic display system. In-store price changes are also made available to gateway computer 50 over LAN 38. The second gateway computer 50 is connected via an RS232 link 54 to the module controller 18. Downstream of the module controller 18 the system is as described above.

Figure 4 shows the module controller 18 in any one of the systems of Figures 1-3 connected by wires 60a, ..., 60f to a plurality of ceiling digital circuit boards 26a, ... , 26f each of which is in turn connected to a radio transmitter-radio receiver set 28a, 30a as described in the copending application. The plurality of ceiling nodes 22 ensures good radio communications throughout the store. Each ceiling node 22 as described above includes the ceiling digital board 26a and a radio transmitter 28a and a radio receiver 30a. Each ceiling digital board 26a also has the capability to connect via a multi (five) wire connection (as described below) to display modules (not shown) thus eliminating the need for radio communication with those particular five to four converters and display modules.

Thus multiple (six) channels 60a, ..., 60f of communication are provided, with unique information usually being transmitted via each channel 60a and the associated ceiling node 22 to a particular part of the store. At any one time, only one ceiling node 22 transmits. Any ceiling node 22 transmitter 28a may transmit to any group or shelf node. The module controller 18 determines which ceiling node 22 transmits to which group or shelf node.

Also provided in accordance with the invention as shown in Figure 5 is circuitry whereby each ceiling radio receiver 30 reports the strength of the transmitters associated with the other ceiling nodes. If the signal strength of any one transmitter changes, this change is reported and the system thereupon switches the transmissions intended for that particular transmitter to another transmitter unit. The receiver with the best signal strength upon reception from a particular shelf node or group node is preferred to communicate with that particular shelf node or group node. Thus each ceiling radio receiver has the capability to monitor the trans- mission of each one of the other transmitters, so as to indicate major changes in transmit power for any one transmitter. As shown in Figure 5, each receiver 30 has an associated antenna 62 with the strength of received signals reported to an analog-to-digital converter 64 and hence to a microcontroller 66 in the ceiling node digital board 26 and then reported to the module controller 18. The module controller 18 determines which alternate transmitter is to be used to replace the suspect transmitter. Figure 6 shows bidirectional data transmission in accordance with the invention. On the left side of Figure 6 two separate data lines 70, 72 provide respec¬ tively data in and data out. The data out and data in lines at the left side of the drawing are connected to the group node, or hard wired to a ceiling node. Each data line 72, 70 is connected to one terminal of, respectively, a transistor 76, 78. The data out line is connected by a resistor to the base of transistor 78 and the data in line is connected to the collector of transistor 76. The emitter of transistor 78 is connected to the bidirectional data line and through a resistor to the base of transistor 76. Thus on the right hand side of the drawing is a bidirectional data line 82. The single bidirectional data line 82 is connected to the shelf rails and thence to the display modules (not shown) . Thus the bidirectional data line 82 is used for communication both to and from the display modules.

When a display module transmits data to the group or ceiling node, the bidirectional data line 82 is high by switching on transistor 76 and sending a low level to the group or ceiling node. When the bidirectional data line 82 is allowed to be pulled low by resistor 80, transistor 76 is turned off, sending a high level to the group or ceiling node. Conversely, data directed from the shelf node to a display module turns on and off transistor 78 and thus transmits high and low levels on the bidirectional data line 82 to the display modules.

Also provided in accordance with the invention is a five to four wire (or line) converter, part of which is the bidirectional data line of Figure 6. Figure 7(a) shows the five to four wire conversion diagrammatically. As shown in Figure 7(b), this converter such as 90a, ..., 90d is located between' a group node 92 (or hard wiring to the ceiling node) and the display modules (not shown) . The five wires refers to the five lines i.e. power which is V+, ground which is GND, clock which is the clock timing signal, data out and data in. The 4 wires (which are the shelf rail conductors) are power, ground, clock and bidirectional data as described above in connection with Figure 6.

Groups of display modules are isolated from the associated group node 92. This solves a problem that occurs if a large number (such as 1,000) display modules are connected to one group node 92. Under these . circumstances the bidirectional data line might suffer from performance degradation. A five to four wire converter 90a, ..., 90d provided at each group of display module (such as 100 display modules) buffers the shelf node power supply from the display modules, by transistor switching. Thus effectively only a relatively small number (such as 100) display modules are connected to the bidirectional line at any one time, instead of the total number of 1,000 display modules. This isolation has a further advantage that if for instance shelf rail power is shorted out due to vandalism, the electrical short will only affect a group of display modules rather than all the display modules connected to the particular group node.

Figure 7(c) shows a portion of the five to four wire converter using a transistor switch 96 to current limit the power i.e. to +V on the four wire side of the five to four converter.

Figure 7(d) shows how the clock line is current limited (buffered) via similar transistor switching as in Figure 7(c) .

Figure 8 shows schematically the five to four wire converter including transistors 76 and 78 and transistors 96 and 100. Five wires are available at the connector J2 on the left side of the drawing and four wires are available on the connectors J3, J4 at the right side thus providing the five wire to four wire conversion. Two four wire connectors J3, J4 are provided for convenience. Normally, connector J2 provides the five wire connection and there is no connector Jl and the jumper is used. If the converter is used in a freezer with display modules including heaters (see below) then power for the heater and module is provided via connector Jl and the jumper is removed.

The five wire to four wire converter enables the use (as discussed above) of group nodes. A group node is a shelf node which services a large number of display modules. (Figure 9 shows schematically a display module. The circuitry inside the broken line rectangle in one embodiment is included in an application specific integrated circuit.) Such a group node is powered by mains current rather than by battery to deliver the large amounts of electric power required for such a large number of display modules. This configuration eliminates large numbers of shelf nodes. In one configuration, one such group node is located at each gondola in the store and services all of the display modules on that gondola. Also provided as an improvement in the system is an "orphan" process. The orphan process is a modification to the program in the microprocessor in each display module and addresses the problem of a particular display module not being in communication with the module controller for a given period (such as 30 hours) . If that occurs, then a visual indication appears on the display, which will be observable by a store employee. The store employee will know that that particular display module has a problem with its communications or operation, and that particular display module may be reprogrammed manually and/or replaced.

A flowchart for the orphan process software is shown in Figure 10. The program determines 110 if there is successful communication with the controller. If no, then a timer is decremented 112 until the timer is empty 114. When the timer is empty, then the orphan dot (which is a dot or other mark at a particular location in the display module) is illuminated 116 and the timer is reloaded 118 for an approximate period of time such as 30 hours in this example. Any variations in the time will not impact the orphan process usefulness. Then the display module attempts to carry out the "join system" process 120 (described below) to reprogram the module so as to be in communication with the controller module. If at the first step 110 the display module is in successful communication with the controller, then the timer is reloaded 122 with a particular time (such as 30 hours) and the orphan dot is cleared 124, i.e., no longer illuminated. As shown, illumination of the orphan dot is simultaneous 116 with the "join system" process 120 which is a reprogra ming of the display module in which the display module transmits its UPC code and its image type to the ceiling node.

In one embodiment the orphan dot is a single segment on the display, (segment 81) which is set if the display module has not communicated with the module controller for the given period such as approximately 30 hours. The orphan dot is in the same common-segment intersection on every display and as discussed above is set and cleared by the microcontroller in each display module.

Also provided (as discussed above) is a "join system" process shown in Figure 11. This process reprograms the display module. In the first step 130 a UPC (Uniform Product Code) or EAN (European Article Numbering) is read from a product or entered through a keypad into a display module programmer, then is programmed into the display module through the optical port. In the next step 132, the UPC or EAN and the image-type number of the particular display module accepted is transmitted to the module controller through the hard wired or wire and radio frequency link. The orphan process (Figure 10) in step 120 enters "Join System" at step 132. Alternatively, at the occurrence and anniversary of becoming an orphan (every 30 hours) , the display module remembers its UPC or EAN, looks up its image-type number and also sends 132. In step 134, bits are received from the module controller which are appropriate for the UPC or EAN and the image number associated with a particular display. The bits are then passed directly to the display module micro¬ processor's display driver and the display is then driven 136 accordingly. Also in accordance with the invention is a method for distinguishing amongst various types of display modules. The system may include standard width display modules and narrower display modules for use for instance in displaying prices associated with packaged spices. The narrower display needs different conversion of price, etc., to image data than does a standard size display. In accordance with the invention, the conversion routine from data such as price, etc., to a bit stream for the different display modules associated with the different size displays and variations of same size displays is located in the module controller rather than at the display module. Thus the module controller must be informed as to what type of image is required to be transmitted to each display module. The image type is three bits of information read from the printed circuit board (see Figure 9) in the display module which indicate the format for the LCD display of that particular display module. In one embodiment, a standard module and a narrow module have different display layouts and thus different maps between segments of digits and particular common- segment intersections. When terminal P03 on the Sanyo microprocessor

(Figure 9) is high, the three bond wires (dashed lines) attached to terminals Ml, M2, M3, and GND or P03 are read through terminals Ml, M2, M3 to form an image-type number. A small module might be 101, a large module might be 010 or any of the 8 possible values. The module announces its image-type number, then the module controller recognizes the number and creates the correct data stream to be used by that display module to drive its LCD.

In accordance with the invention, periodically (such as every eight hours) the module controller goes through the entire list of all of the display modules connected to the system (the "bed check") and ensures that each display module is able to answer. Thus each display module is addressed and responds by indicating its presence on the system, i.e., it has not been removed or damaged. Also in conjunction with the "bed check", the entire set of information to be displayed can be rewritten from the module controller to each display module, thus refreshing the entire set of display images.

Also provided in accordance with the invention is circuitry to indicate the condition of batteries in the shelf node. Upon detection of a low battery state

(defined by voltage levels) , this condition is reported to the module controller. Detection of a dead battery state (a significantly lower voltage output from the batteries than the low battery state) results in a cessation of radio frequency communications involving that shelf node and instead only use of the batteries for supporting the relatively low current drain display modules. Thus upon detection of a low battery, i.e., a low battery output voltage, a logic signal is provided from the low battery indicator circuitry to the shelf node microprocessor. The logic signal sets a bit in the communications protocol in the microprocessor, which information is transmitted back to the module controller. Thus any subsequent communication from that shelf node to the module controller informs the module controller of the low battery condition. The module controller then produces a low battery message on the display of the module controller (and/or a printed report) which directs a store employee to replace the batteries at the particular shelf node. The low battery indicator relies on the fact that the major drain on the' batteries is radio frequency communications, and so cessation of such radio frequency communications ensures an extended battery set useful life even though the battery is largely exhausted. Figure 12 shows one embodiment of the battery condition indication circuitry. The shelf node batteries 140 are connected to a voltage doubler 142 (described below) and to a voltage regulator 144 which in turn provides the output voltage VCC for powering the shelf node. Included in the shelf node circuitry are three comparators. The first comparator 148 is provided with a 3.2 volt reference. The second comparator 150 is provided with a 3.9 volt reference. The third comparator 152 is provided with a selectable 5.2 or 7.0 volt reference. When the output voltage of the battery 140 drops below 3.9 volts, the low battery indication is given by the second comparator 150 to the control logic 151 in the shelf node. If the voltage output drops below 3.2 volts, the dead battery indication is provided to the control logic by first comparator 148.

The third comparator 152, with the selectable references, is for use with the voltage doubler 142 as described below. This third comparator 152 provides an indication of whether the voltage output of the battery is below 7 volts during the radio transmit cycle and below 5.2 volts during the radio receive cycle. Thus the select line "SEL" selects between the transmit or receive states. Also as shown, a logic output 160 from the control logic 156 controls the regulator 144 to select between a 3.0 volt output or a 4.8 volt output. The lower voltage output is provided during the standby mode with the 4.8 voltage output provided during the active mode.

In the active mode, which takes place during trans¬ mission and receiving periods of the radio frequency circuitry, and during the decision making process as to what to transmit or receive, if the battery is indicated as being dead, then any activity is aborted. If the battery 140 is low, then this condition is stated in any transmission from the shelf node to the module controller so as to report the low battery.

During a receive cycle of the shelf node, at any time that the battery output at the output of doubler 142 is below 5.2 volts, the voltage doubler 142 is turned on. Once the regulator 144 input, i.e., the output of doubler 142, is greater than 5.2 volts, the regulator 144 is switched from the 3 volt output to the 4.8 volt output. Then the control logic 156 may safely increase the clock speed and turn on the radio frequency transmit and receive circuits. This ensures that the output voltage VCC is sufficient to operate the microprocessor in the shelf node at the desired speed.

The voltage doubler of Figure 12 is shown in detail in Figure 13. The shelf node batteries 144 are connected to transistors 170, 172, 174, and 176. Pins 1, 2, 3 and 4 are connected respectively to the bases of transistors 170, 172, 174, and 176 and are driven by output signals from the shelf node digital integrated circuitry in response to the program resident in the microprocessor. Transistors 174 and 176 are not on at the same time, to prevent excessive power drain from the battery. Transistor 176 is an NPN transistor and transistor 174 is a PNP transistor. Conventional current source 179 provides sufficient current to keep the 3.0 volt circuits operational. When transistors 170 and 176 are on, this is the charge phase. When all transistors are off, this is a gap phase. When transistors 172 and 174 are on, this is the pump phase. When all transistors are off, this is also a gap phase. The charge phase charges the capacitor 180 which is intermediate between the collectors of transistor 170 and 176. In the pump phase, the voltage at the collector of transistor 174 is increased to the top battery 140 voltage thereby pumping the voltage on the output capacitor 182 which is connected to the collector of transistor 172 to substantially above the battery 140 voltage. The on and off cycles are 40% on, and 10% off (as determined by the control logic 156) .

The duty cycle on the voltage doubler 142 thus increases as the battery 140 output declines with age. When the regulator 144 input is less than 5.2 volts, the doubler 142 is turned on thereby producing a voltage of at least 5.2 volts and allowing the regulator 144 to output 4.8 volts. The regulator 144 itself incurs an overhead of .3 volts. The voltage doubler circuit 142 as shown in Figure 13 advantageously substitutes transistors 170 and 172 in positions where in such circuitry diodes are normally used. The transistors advantageously substantially eliminate the voltage drop characteristic of diodes used in such circuitry and hence conserve power. During transmission, the 5.2 volts is raised to 7.0 volts to allow for more input capacitor 182 voltage sag before the output sags during the high current draw portion of the transmission.

Figure 14 shows schematically the adaptive threshold circuitry for the optical port in the display modules. The optical circuitry is substantially the same as in the copending application, with a modification to allow sensing of an adaptive threshold. The object is to com¬ pensate for changes in ambient light levels and to allow sensing of higher or lower ambient light levels so as to make the optical port resistant to malfunctioning due to unusually high or low ambient light levels.

The adaptive threshold cyclically compares the input light level to the photo sensor to an ambient level and then adjusting the ambient light level one step at each cycle. The input light level sensed by the photo sensor 180 and amplified by log amplifier 182 is compared to a brightness threshold by comparator 186. Thus the brightness threshold is the ambient light level plus n steps of additional light intensity. The input light level is also compared to a dark threshold which is the ambient light level less m steps of light intensity. The dark light level is generally when a finger is placed over the optical port (as described in the copending application for display module image switching) . The bright threshold level is typically that provided to the optical port when an optical wand is inserted therein for programming purposes.

In one embodiment, the programming light level provided from the optical wand is eight steps above the ambient light level. The DAC (digital-to-analog converter) 188 provides a reference level to comparator 186, which level is set by software in the microcontroller 190 in response to the detected light level from comparator 186. The circuitry of Figure 14 is shown in more detail in Figure 9 which shows schematically the display module. In Figure 9, the photo sensor 180 is phototransistor Ql. Also provided in accordance with the invention is a method for transmitting information (in addition to the UPC code) to the display module via the optical port. The capability is provided to send display information (images) in through the optical port. This is an improvement over the method described in the copending application whereby only the UPC code is transmitted through the optical port, and then the display module receives display information only through its wire-radio and/or hardwired connection to the module controller. In accordance with the present embodiment, images (i.e., price information) may also be sent directly into the display module via the optical port. The display also provides via the interface module its image-type number (described above) so that the programmer (typically a portable computer including an optical wand) , can distinguish between several types of LCD's (typically present in different sizes of displays) because this affects the configuration of the downloaded image data.

In one embodiment, the writing of images to a display module begins with an assignment of the UPC code, followed by a write of 5 checksums and an image of validity nibble, a write of each of the four images to the display module, and acknowledge of successful checksums, and a retry if required. The four images fit in five pages in memory in the display module microcontroller.

Also, in accordance with the invention, a heater is provided in those display modules located in store freezers. An unheated display module may not function properly at the low temperatures present in the freezer and even if it does function, condensation on the LCD will prevent observation thereof. While low temperature LCD's are available, they are expensive and would require use of a special LCD in those display modules intended for use in freezers.

The freezer module is an otherwise conventional display module which includes a heat sink (in one embodiment a thin sheet of copper) inside the display module housing and extending over the rear surface of the LCD display. The heat sink in this embodiment is approximately .010 to 0.15 inch thick and approximately the same dimensions as the LCD in the display module. As shown in Figure 15, the heat sink 200 is in thermal contact with the LCD 202. Provision of power (i.e. +V and -V) to the heat sink 200 is by a series-connected zener diode 204 and a resistor 206. Zener diode 204 has an on-resistance equal to the resistance of resistor 206. As shown in Figure 16, the resistor 206 is thermally attached to the heat sink 200 by one lead and inserted in a small hole provided in the heat sink 200. The zener diode 204 (not shown) is similarly thermally attached to the heat sink 200. Thus heating of the resistor 206 and zener diode 204 heats the heat sink 200.

The zener diode 204 prevents excessive power drain by a heater-equipped display module if such a module is accidentally used in a store area other than a freezer. The heater-equipped modules draw substantially more electric power than do conventional modules and cannot usefully be powered by the batteries in an ordinary shelf node. Thus the heater-equipped modules are connected to mains current to provide power thereto. The zener diode 204 ensures that no current flows in the heater circuit until the voltage provided is significantly higher than any voltage likely to be provided by batteries in an ordinary shelf node. Thus no current will be drawn by the heater unless it is connected to a higher voltage mains current source. However, the heater-equipped display module functions as an ordinary module when used connected to an ordinary shelf node; only the heater element will not operate in this situation. Thus if the provided voltage is above 13 volts, the heater will draw approxi¬ mately 1/2 watt. If the voltage supplied is below 6.5 volts, the heater will draw no current due to the voltage drop across the zener diode 204. Since the voltage sup- plied by the batteries is approximately 6 volts at most, a heater-equipped module will draw no heating current when connected to an ordinary battery-powered shelf node.

The above description of the invention is illustra¬ tive and not limiting; further modifications will be apparent in light of this disclosure to one skilled in the art.

Claims

CLAIMSWe claim:

1. A price display system comprising: a controller for providing price information; a plurality of receiver/transmitter sets each connected to the controller; and means at each receiver for measuring a transmission strength of signals transmitted from each transmitter.

2. The device of Claim 1, further comprising means for switching between transmitters in response to the measured transmission strength.

3. A price display system comprising: a node for providing price information; a display module for displaying the price information; wherein the node is connected to two data lines for providing respectively data in and data out to the node, and the display module is connected to a bidirectional data line for providing information to and from the module; and means for connecting the two data lines to the bidirectional data line.

4. A price display system comprising: a controller for providing price information; a plurality of nodes, each connected to the controller by conductors for receiving the price information from the controller; and a plurality of display modules for displaying the price information, each one of the plurality of display modules being connected in parallel to one of the nodes.

5. A method for determining the operability of a display in a price display system, wherein the display is in communication with a controller, comprising the steps of: determining if the module is in communication with the controller; if the display is not in such communication, determining the amount of elapsed time since such communication was last established; and after the expiration of a given amount of time, providing a visual indication on the display that communication is not established.

6. A method for connecting a display module in an electronic price display system to a controller which provides information to the display module, comprising the steps of: providing a product code to the display module through an optical port; sending the product code and an image-type number to the controller; and displaying on the display module information received in response thereto from the controller.

7. A battery condition indicator for a communications node connected to a power supply driven by a battery comprising: means for determining a voltage output by the battery; means for increasing the voltage provided by the battery; a voltage regulator which receives a voltage output from the means for increasing the /oltage; and means for controlling the regulator and the means for increasing the voltage, wherein when the voltage output by the battery is determined to be below a first threshold, the means for increasing voltage increases the voltage output by a predetermined multiple and when the voltage output by the battery is determined to be below a second threshold, the means for controlling inhibits communications by the node.

8. The device of Claim 7, wherein the voltage regulator changes the voltages provided in response to a signal from the means for controlling.

9. A voltage increasing device for connection to a battery comprising: a first transistor and a second transistor connected in series to a terminal of the battery; a third transistor and a fourth transistor connected in series to the terminal of the battery; a capacitor having a first terminal connected between the first transistor and the second transistor and a second terminal connected between the third transistor and the fourth transistor; and means for providing a signal to a control terminal of each of the transistors thereby charging the capacitor in a duty cycle which varies in response to an output voltage of the battery.

10. An adaptive threshold circuit for a light sens¬ ing device for adjusting ambient light levels comprising: an amplifier for amplifying an output of the light sensing device; a comparator having as its first input an output of the amplifier and having as its second input an output of a digital to analog converter; and means for detecting an output of the comparator and adaptably providing an output in response thereto to an input of a digital to analog converter.

11. A heater for a liquid crystal display comprising: a heat sink in contact with the liquid crystal display; means for limiting current; a resistor thermally in contact with the heat sink and connected electrically in series with the means for limiting current; and means for providing electric current to the means for limiting current and the resistor.

12. The device of Claim 11, wherein the means for limiting current is a zener diode.

13. The device of Claim 11, wherein the zener diode has an on-resistance equal to a resistance of the resistor.

14. The device of Claim 11, wherein the means for providing is connectable to a mains current supply and also to a battery.

15. A method for providing information to a price display module having an optical port for receiving and transmitting information comprising the steps of: providing signals comprising light pulses to the optical port; receiving the signals in the display module; converting the signals to digital data indicating a product code and price information relating to that product code; and displaying the price information on the display module.