A RECEIVER AND TRANSMITTER ARRANGEMENT INTENDED PREFERABLY FOR AN ELECTRONIC PRICE INFORMATION SYSTEM

Abstract: The present invention relates to a receiver and transmitter arrangement for a price information system which includes a plurality of price information units in a shop or store, for instance. Each price information unit includes a loop (20) for receiving a signal (f1) from the control unit. When there is no communication with the price information unit, a voltage-controlled oscillator (50) is controlled by an incorporated crystal (46) via a phase locked loop. When communication is effected with the price information units, the voltage-controlled oscillator (50) is controlled in a manner such that the frequency and phase position of the oscillators in the control unit and the price information unit will coincide. This is achieved by activating a phase comparator (58) (with switch 60) which then receives the following input signals: a real value signal (f6) from the voltage-controlled oscillator (50), and two control value signals [(f3a), (f4a)] obtained by passing the signal (f) through two filter and demodulator circuits (30) and (32) and two comparators (34) and (36). The output signal obtained from the voltage-controlled oscillator (50) is passed directly to the filter and demodulator circuit (32) and indirectly to the filter and demodulator circuit (30), via a phase shift circuit (42).

Description: A RECEIVER AND TRANSMITTER ARRANGEMENT INTENDED PREFERABLY FOR AN ELECTRONIC PRICE INFORMATION SYSTEM The present invention relates generally to a receiver and transmitter arrangement and then in particular although not exclusively, to a receiver and transmitter arrangement for an electronic price information system comprising a plurality of price information units operative in displaying changeable information in a store or shop for instance. Electronic price information systems for displaying the price, article number and like changeable information on the edges of shelves or like places in stores, shops and goods-storage locations are known to the art. SE-441 477 teaches a computer-controlled electronic price information system which includes a plurality of displays arranged on shelves, such as to display the information desired, for instance the price, article number and like information relating to the goods on show. The information shown on the display unit is changed by transmitting the changed information from a control unit to a receiver in the display unit, over a cordless connection, either a radio connection or an IR-connection. Communication in this system takes place solely from the control unit to the receiver, i.e. unidirectional communication. US-4,521,677 teaches a computer-controlled electronic shelf marking system which includes a plurality of shelf displays for presenting changeable alphanumerical information. Changes are effected to the information presented by the display unit, by transmitting changed information from a computer-connected transmitter to a receiver connected to the shelf display, over a cord¬ less connection. EP-A2-0 337 283 teaches a goods marking arrangement which includes an output device placed on a particular goods item in order to show the price of said item, for instance. The transmission of information between the output devices and a central transmitter is effected in a cordless fashion, for instance with the aid of induc¬ tive or capactive coupling means. The receiver's pro¬ vided in the transmitter and the output device can be tuned to a variable receiver frequency, so that an article or item in a particular division or display compartment or of a particular type of goods can be called by frequency selection. One problem with the earlier known electronic price information systems is that the signal/noise ratio can differ very considerably between transmission and reception of signals, which limits the information that can be transmitted from the price information units to the control unit. The signal/noise ratio between trans¬ mission in respective directions can often vary by a factor of at least 500 times. As a result, the informa¬ tion transmitted from the price information unit to the control unit will often solely comprise one single response signal, often of long duration and which is filtered in a narrow filter in the control unit. An- other problem is that the frequency between the oscil¬ lators in the control unit and the price information units will deviate unless relatively expensive crystals are used for the oscillators in the control unit and the price information units respectively. The total cost of the price information system is influenced quite considerably by the price of the crystals used, since one crystal is required for each price informa¬ tion unit included in the system and the number of price information units in the system may often be very large. It is therefore desirable to use the cheapest crystals possible. These drawbacks are eliminated with the inventive receiver and transmitter arrangement having the charac- teristic features set forth in the characterizing clause of Claim 1. By controlling the voltage- controlled oscillator in the receiver and transmitter arrangement in a manner such that both the frequency and phase-position of the oscillators in the communica- tion unit and the price information units coincide, it is possible to use signals of longer duration and filters of narrower bandwidth. Furthermore, it is possible to transmit signals in a relatively compli¬ cated pattern while retaining the signal/noise ratio. This feature can also be utilized to reduce the effect of constant frequency disturbance sources. The invention will now be described in more detail with reference to an exemplifying embodiment thereof il- lustrated in the accompanying drawings, in which Figure 1 is a simplified block schematic of a price information system in which the present invention can be used; and Figure 2 is a circuit diagram of one embodiment of the inventive receiver and transmitter arrangement. The inventive price information system illustrated in Figure 1 is intended for use in a store, shop or storage location for instance, and includes a control computer unit 10, which may have the form of a personal computer or the like, for instance. The control com¬ puter unit 10 is connected to a communication unit 12, which is connected constantly to an inductively coupled loop-pair 14 installed in the shop or storage location. A loop pair implies two loops (a loop is an electric conductor having the same starting and finishing point) which are positioned in a manner such that when current flows therethrough the direction of the magnetic field will be changed to the greatest possible extent when the use of one loop is transferred to the other. Dis¬ posed in the shop or storage location is a plurality of price information units 18 which are placed, for in¬ stance, on the shelves adjacent those items of goods about which information is to be displayed. Each of the price information units 18 includes a display unit 28 (see Figure 2) which displays, for instance, the price of the goods concerned and/or other information. Com¬ munication between the communication unit 12 and the price information units 18 is effected in a cordless fashion, by inductive coupling. When transmitting to the price information unit 18, the communication unit 12 drives a sinusoidal current through one loop pair 14. A magnetic field proportional to the current is then generated in space (Biot-Savart's law) . By chang¬ ing the frequency of the sinusoidal shape, two states are produced, so-called frequency modulation, therewith enabling binary coded information to be transmitted. The "0"-state can correspond, for instance, to the frequency 48.96-0.64 kHz and the "l"-state can cor¬ respond, for instance, to the frequency 40.96+0.64 kHz. Each price information unit 18 includes a loop in which there occurs a voltage which is proportional to the derivative of the magnetic field (Faraday's induction law) . Each price information unit is also provided with two sampled filters which are responsive to the afore¬ said frequencies. The information corresponding to the two states is recreated in this way. If the shop or storage location is so large that the range of the communication unit 12 is insufficient for the purpose intended, one or more slave units 16 may be connected to the communication unit 12. Each slave unit 16 is equipped with two loop-pairs. When information is transmitted, all slave units 16 and the communication unit 12 transmit in parallel, i.e. currents of mutually the same size and mutually the same rotational direc- tion are generated in all connected loop pairs 14 simultaneously. Figure 2 is a circuit diagram of a receiver and trans¬ mitter arrangement constructed in accordance with the invention. The illustrated receiver and transmitter arrangement is intended to be included in a price information unit. The receiver and transmitter arrange¬ ment includeds a loop 20 which is intended to receive information from the communication unit and to transmit information to said communication unit. At those times when there is no communication with the price informa¬ tion unit, a switch 26 is switched to the illustrated position, in which no power is supplied from a power source 40 to a number of circuits, namely two filter and demodulator circuits 30, 32 of the so-called switched capacitor type, an amplifier 22 connected between the loop 1 and the two filter and demodulator circuits 30, 32, and two comparators 34, 36. When information is transmitted from the control unit to the price information unit, an activating message is recei- ved by a digital network 38, which in response thereto activates the switch 26 and causes said switch to take its other position, in which power is supplied con¬ tinuously to the amplifier 22, the filter and de odula- tor circuits 30 and 32 and the comparators 34, 36. The resonance frequency of the filter and demodulator circuits 30 and 32 is controlled by a voltage-control¬ led oscillator 50, which is in turn controlled by an incorporated crystal 46 via a so-called phase-locked loop 52, 54 and 56, when a switch 60 is in the position shown in Figure 2. The phase-locked loop includes two frequency dividing circuits 52 and 54 and a phase comparator 56 of the edge-triggered type. This con¬ figuration is quite usual in modern receivers, since it requires only one crystal for receiving on different frequencies and since adjustment of the received fre¬ quency can be achieved readily by changing the fre¬ quency dividing circuits 52 and 54. When information is transmitted to the price information unit, the voltage- controlled oscillator 50 is steered by the information received, so that both frequency and phase position of the oscillators in the control unit and the price information unit will coincide. When information is transmitted to the price information unit, the digital network 38 functions to steer the switch 60 to the position in which a second phase comparator 58 is connected to the voltage-controlled oscillator 50. The phase comparator 58 receives input signals from the frequency dividing circuit 52 and from the two com- parators 34 and 36. The receiver and transmitter arrangement also includes a phase shift circuit 42 [-90 ° ] which is connected to the filter and demodulator circuit 30. The illustrated receiver and transmitter arrangement can also be operated in the transmission mode, wherein a switch 62 is in either one of two positions when the receiver and transmitter arrangement is in the receiving mode. Assume that the control unit produces the output signal sine (Wref ± Wmod) t. This signal is designated (fl) and is received by the loop 1 in the price information unit. This change in the frequency of the sinusoidal signal produces two states, so-called frequency modula¬ tion, therewith enabling coded information to be trans- mitted. The state "1" can correspond, for instance, to the frequency Wref + Wmod whereas the state "0 "11 can correspond, for instance, to the frequency Wref - Wmod. Further assume that the phase angle of the output signal of the control unit is 0 at t=0. Also assume that the voltage-controlled oscillator 50 of the price information unit generates the signal sine (Wot + Vo) , where Vo is the phase angle at t=0. This signal is designated (f2) and is transmitted directly to the filter and demodulator circuit 32 or to the filter and demodulator circuit 30, or is transmitted thereto via the phase shift circuit 42. The signal (fl) received on the loop 20 is transmitted to the two filter and de¬ modulator circuits 30 and 32 via the amplifier 22. The output signal (f3) from the filter and demodulator circuit 30 can thus be described as the function sin (Wref ± Wmod) t-sin (Wot + Vo) and the output signal (f4) from the filter and demodu- lator circuit 32 can be described by the function sin (Wref ± Wmod) t-sin (Wot + Vo + π) 2 The function (f3) can be described in another way sin((Wref ± Wmod-Wo)t + Vo-37τ) + sin((Wref ± Wmod) 2 t + ) where the last term can be ignored, since a signal of such high frequency is effectively filtered out by the filter. The output signals (f3) and (f4) are amplified by the comparators 34 and 36, wherein the signals (f3a) and (f4a) received from these comparators constitute control value signals, or desired value signals, which are transmitted to the phase comparator 58. Subsequent to being divided by Wref/Wmod (frequency dividing circuit 52) and by the phase position V, i.e. sin(Wo(Wmod/Wref)t + V) the signal (f2) is transmitted to the phase comparator 58 as a real value signal. This signal is designated (f6). The output signal from the phase comparator 58 controls the voltage-controlled oscillator 50 in res¬ ponse to the input signals [(f6), (f3a) , (f4a)], such that the following relationship will apply sin ((Wref ± Wmod - Wo)t + Vo - 3J sin 2 (Wo(Wmod/Wref)t + V) The equation for the high frequency is calculated first Wref + Wmod - Wo =Wo(Wmod/Wref) and Vo - 3π = V 2 i . e . Wo= Wref and Vo = V + 3jr ( 1 ) 2 The phase position, however, cannot be related to the oscillator of the control unit with the aid of one frequency. The phase position obtained is dependent on the oscillator frequency. The following relationship applies in the case of the low frequency Wref - Wmod - Wo = - Wo(Wmod/Wref and Vo - 3π = π - V 2 i.e. Wo = Wref and Vo = STΓ - V (2) 2 If the phase position shall remain unchanged in the frequency change-over, there is obtained with relation¬ ships (1) and (2) V = π 2 Naturally, one condition for this is that each package of high and low frequency respectively has a length equal to n.2π/Wmod, i.e. the package includes Wref/Wmod ± n cycles. If a more general efforts is made, with view to the fact that the function is perio¬ dic, the solution V =π ± m π will be obtained. 2 Each of the signals according to (f3) and (f4) is an input signal to a respective comparator 34 and 36. The output signals from the comparator (f3a) and f4a) behave in the following manner. (f3a) (f4a) ! I I i [ i |~- .___ (fl) LLLLL LLLL HHHHHHHHHHHHHHH LLLLLLLLLLL The signs "LL." and "HH." designate periods of low and high frequency respectively. It might be more conven¬ ient, however, to lock the phase at another phase position: (f3a) ! I (f4a) ( fl ) LLLLLLLLLL HHHHHHHHHHHHHHH LLLLLLLLLLLL This results in a 90° phase shift of both (f3) and (f4), which reduces the extent to which the signals are blocked in the bandpass filters 30 and 32. The time lapse between the positive lanks of the control value signals [(f3a), (f4a)] and the real value signal (f6) controls the voltage-controlled oscillator 50 subsequent to receipt of the alarm message, i.e. when communication commences. The voltage-controlled oscillator 50 is controlled in a normal manner over those times periods in which no communication takes place, i.e. is controlled by the crystal 46 incorpora- ted in the price information unit, via the phase-locked loop 52, 54 and 56. Internal frequency (f6) <- 3a) (Ma) Jft flC ) Jt» *#!!.* • * ***** Output signal to VCO The frequency of the voltage-controlled oscillator 50 is changed between the markings "f". This change is proportional to the time between the edges. It is also important that the relationship Wref-Wmod <Wo<Wref + Wmod applies during the whole of this period, otherwise Wo would be changed in the "wrong direction". When the price information unit transmits to the con¬ trol unit, the output signal is modulated with the change-over switch 62. This modulation may conceivably be effected in the following manner: (f11) "+" designates a transmitted signal of frequency Wo and phase position 0 ° . "-" designates a transmitted signal of frequency Wo and phase position 180°. The following is obtained at the interface between 0 and -180° : <fll> l „.„i i -t~4-4-l- -r " τ-+.4-+--r- <f11) The embodiment of the invention described above is only one example of how the invention can be realized and does not therefore limit the scope of the invention, the true scope of which is defined in the following Claims.

Claims: CLAIMS 1. A receiver and transmitter arrangement intended preferably for a price information system which in- eludes a plurality of price information units for displaying changeable information, a control computer unit to which information is supplied and which com¬ municates with a communication unit connected thereto, wherein two-directional communication between the communication unit and the price information units is effected with cordless inductive coupling, said arrangement also including a voltage-controlled oscil¬ lator (50) which controls the resonance frequencies of two filter and demodulator circuits (30, 32) included in the arrangement, a crystal oscillator (46) which controls the voltage-controlled oscillator (50) with the aid of a phase locked loop (52, 54, 56), c h a r a c t e r i z e d in that the arrangement further includes a switch (60) which is controlled by a digital network (38) included in said arrangement and which switch (60) occupies a first position when no communication takes place when the voltage-controlled oscillator (50) is controlled via the phase locked loop (52, 54, 56) and a second position when communication takes place when the voltage-controlled oscillator (50) is controlled via a phase comparator (58) included in said arrangement such that frequency and phase position of the oscillators in the receiving and the transmitt¬ ing devices used coincide. 2. An arrangement according to Claim 1, c h a r a c ¬ t e r i z e d in that the two filters in the filter and demodulator circuit (30, 32) are so-called switch¬ ed capacitor filters, wherein the circuits function both as filters and demodulators and both of which are supplied with a signal which has been amplified in an amplifier (22) and which has been received in a cord¬ less fashion by a receiver/transmitter device (20) included in the arrangement. 3. An arrangement according to Claim 1 or 2, c h a r a c t e r i z e d in that it also includes a comparator (34, 36) which is connected to each filter and demodulator circuit (30, 32) for receiving two control value signals (f3a, f4a) which are delivered to the phase comparator (58) for the purpose of control¬ ling the voltage-controlled oscillator (50) when com¬ munication takes place. 4. An arrangement according to Claims 1-3, c h a r ¬ a c t e r i z e d in that the real value signal de¬ livered to the phase comparator (58) is an output signal (f2) from the voltage-controlled oscillator (50) which is transmitted to the phase comparator (58) via a frequency dividing circuit (52). 5. An arrangement according to Claims 1-4, c h a r ¬ a c t e r i z e d in that the amplifier (22), the two filter and demodulator circuits (30, 32) and the com- parators (34, 36) are either powered by a power source (40) via a switch (26) when communication takes place or intermittently. 6. An arrangement accordinng to Claims 1-5, c h a r - a c t e r i z e d in that the digital network (38) receives two input signals (f3a, f4a) from the com¬ parators (34, 36) for steering or controlling the two switches (60, 26), and a switch (62) having n posi¬ tions , wherein the switch is switched to a first posi- tion when the arrangement functions as a receiver and to the n-1 other positions when the arrangement func¬ tions as a phase modulating transmitter. 7. An arrangement according to Claims 1-6, c a r - a c t e r i z e d in that the phase-locked loop (52, 54, 56) includes the frequency dividing circuit (52) connected to the voltage-controlled oscillator (50), a frequency dividing circuit (54) connected to the crystal oscillator (46), and a phase comparator (56) of the flank-triggered type connected to the two frequency dividing circuits (52, 54). 8. An arrangement according to Claims 1-7, c h a r ¬ a c t e r i z e d in that the signal (f3) obtained from the filter and demodulator circuit (30) is phase shifted through a phase shifting circuit (42) which is connected between the voltage-controlled oscillator (50) and the filter and demodulator circuit (30), so as to obtain a phase difference of 90° between the signals (f3) and (f4).

Inventors: BRAENNSTROEM ROLAND, BRAENNSTROEM, ROLAND
Applicants: BRAENNSTROEM ROLAND, BRAENNSTROEM, ROLAND
Application year: 1991
Main classification: G06K7
IPC codes: G06K17, G06K19, H04B5