EP0161545B1 - Apparatus for locating persons for an electronic timepiece - Google Patents

Abstract

A pager is described for use in an electronic watch. The pager comprises a frame (1) for picking up a magnetic signal and a piezoelectric transducer (11) having a static capacitance on its terminals, for producing a sound. 11 To improve sensitivity of reception, a switching circuit (15) connects the transducer (11) in parallel with the frame (1) to tune it by means of the static capacitance to the frequency of the magnetic signal carrier wave. To increase the performance of the transducer (11 ) when it operates as a sound transmitter, the switching circuit (15) connects the frame (1) in series with the transducer (11).

Description

The present invention relates to people search devices. It relates, more particularly, to a miniaturized research apparatus capable of taking place in a watch.

People finders are well known. They include a frame or coil constituting an antenna capable of detecting a coded magnetic field coming from a transmitter located at a relatively short distance (a few tens of meters). If the code received corresponds to the device code, stored in a memory, a transducer produces an acoustic signal, possibly accompanied by an optical signal, warning the wearer of the device that he must, for example, dial a number phone.

These devices are in the form of small boxes that can easily take place in a pocket. They contain, in addition to the frame and the transducer, various electronic circuits and batteries ensuring their supply. A research device will be all the more interesting as it will have small dimensions, it will be able to detect a weak magnetic field, that it will emit a powerful acoustic signal, that it will consume little energy and finally that its price cost will be low.

To obtain maximum sensitivity of the frame vis-à-vis a sinusoidal magnetic field, it is known to tune the frame self on the frequency of this field using a capacitor. It is also known to place a self in series with the transducer so as to tune the latter on the frequency of the acoustic signal to increase the power of the sound emitted and improve the efficiency of the transducer which is the main energy consumer in such a device. .

These improvements are therefore obtained using two components, a capacity and a choke, which have the disadvantage, especially the second, of taking up space and increasing the price of the device. This becomes especially annoying if you try to reduce the size of the device until you can put it in an electronic watch.

The idea of pairing a people finder with a watch is not new in itself. For example, the patent CH 533 332, or the corresponding patent DE 2 149 535, mentions the possibility of including in a electronic watch a search device for people without however describing an embodiment thereof. US Pat. No. 3,937,004 describes a watch provided with a person search device, operating intermittently to save current. In this US patent, the means for picking up the external electromagnetic wave and those necessary for producing the sound signal are however not described in detail. Mention is simply made of an antenna and a sound transmitter, without specifying their nature. Finally, application CH 639 816 describes an analog watch in which the motor coil is used between the driving pulses as a magnetic field detector. However, these are parasitic magnetic fields which can occur at different frequencies, making the tuning of the coil uninteresting.

In none of the documents cited relating to watchmaking achievements, there is no mention of a frame tuned by a capacitance and of a piezoelectric transducer tuned by a self, let alone the possibility of totally or partially eliminating the capacitance and the self which have the disadvantage, already mentioned, of taking up space and being expensive.

The main object of the present invention is to avoid these drawbacks by eliminating the tuning capacity of the frame and the tuning inductor of the piezoelectric transducer without reducing the performance of the people search device.

• - une antenne pour capter un signal électromagnétique variable;
• - un transducteur capable de produire un son et ayant deux bornes;
• - une source ayant deux bornes et fournissant un signal électrique de fréquence acoustique;
• - des moyens pour produire un signal logique de commande en réponse au signal électromagnétique; et
• - un circuit de commutation répondant à un premier et à un second état du signal logique, est particulièrement remarquable en ce que:
• - l'antenne est un cadre présentant une self et ayant deux bornes;
• - le transducteur est un transducteur piézoélectrique ayant deux bornes entre lesquelles il présente une capacité statique; et en ce que:
• - le circuit de commutation est agencé pour connecter, en réponse au premier état du signal logique, le cadre et le transducteur en parallèle, et, en réponse au second état du signal logique, le cadre et le transducteur en série et aux bornes de la source. D'autre caractéristiques de l'invention ressortiront de la description qui va suivre, faite en regard des dessins annexés et donnant, à titre explicatif mais nullement limitatif, une forme de réalisation d'une telle pièce d'horlogerie. Sur ces dessins, où les mêmes références désignent les mêmes éléments:
• - la figure 1 représente un exemple de schéma bloc d'un appareil récepteur de recherche de personnes connu;
• - la figure 2 montre une forme possible du signal codé reçu par le cadre d'un appareil de recherche et le signal logique correspondant à ce code;
• - la figure 3 montre la forme des signaux apparaissant aux endroits principaux du schéma de la figure 1;
• - la figure 4 représente le schéma équivalent d'un transducteur piézoélectrique connecté en série avec une self d'accord; et
• - la figure 5 représente le schéma bloc d'une montre pourvue d'un dispositif de recherche de personnes selon l'invention.

To achieve this goal, the miniaturized person search apparatus according to the invention, comprising:

• - an antenna for picking up a variable electromagnetic signal;
• - a transducer capable of producing a sound and having two terminals;
• - a source having two terminals and providing an electrical signal of acoustic frequency;
• - means for producing a logic control signal in response to the electromagnetic signal; and
• - a switching circuit responding to a first and to a second state of the logic signal, is particularly remarkable in that:
• - The antenna is a frame having a choke and having two terminals;
• - The transducer is a piezoelectric transducer having two terminals between which it has a static capacitance; and in that:
• the switching circuit is arranged to connect, in response to the first state of the logic signal, the frame and the transducer in parallel, and, in response to the second state of the logic signal, the frame and the transducer in series and across the terminals of the source. Other characteristics of the invention will emerge from the description which follows, given with reference to the appended drawings and giving, by way of explanation but in no way limiting, an embodiment of such a timepiece. In these drawings, where the same references designate the same elements:
• - Figure 1 shows an example of a block diagram of a known paging receiver apparatus;
• - Figure 2 shows a possible form of the coded signal received by the frame of a research apparatus and the logic signal corresponding to this code;
• - Figure 3 shows the shape of the signals appearing in the main places of the diagram in Figure 1;
• - Figure 4 shows the equivalent diagram of a piezoelectric transducer connected in series with a choke choke; and
• - Figure 5 shows the block diagram of a watch provided with a person search device according to the invention.

A research facility includes a transmitter and a series of receiver devices carried by people. The transmitter radiates a sine magnetic field or carrier wave, coded for example by an amplitude modulation, having a well-defined carrier frequency and sufficient power to reach the receivers within a given radius. All the receiving devices are tuned to the same carrier frequency, but a device responds to the transmitted wave, for example by an acoustic signal, only if the wave code corresponds to the device code, written in a memory. . Each device responds to a different code. If several groups of devices are to operate in neighboring regions, each group will be assigned a different carrier frequency.

Typically, the frequency f _o of the carrier wave is between 28 and 55 kHz, while the frequency f ₁ of the acoustic signal is between 1 and 2 kHz.

Figure 1 shows the block diagram of a known pager. It includes a frame or coil 1, of self induction Le, acting as an antenna to pick up the magnetic field. The voltage induced in the frame by the field can be increased, in a known manner, by tuning the carrier frequency f _o the self Le of the frame using a capacitor 2 of capacitance Ce connected across its terminals. This voltage, then multiplied by the quality facor Q _c of the frame measured at the frequency f _o , is applied to the input of a very selective high frequency amplifier 3, tuned to this same frequency f _o using, by example, a ceramic or quartz filter. The output of amplifier 3 is connected to the input of a demodulator 4 which provides on its output a signal 4S formed of a series of pulses, corresponding to the positive half-envelope of the modulated carrier wave. Each arrangement of the pulses of signal 45 corresponds to a particular code.

The signal 4S is applied to the input of a decoder circuit 5. This includes a memory in which the code of the device is written and means making it possible to compare this code with that transmitted by the signal 4S. If the comparison shows that these two codes are identical, the signal 5S at the output of the decoder 5, normally being in the low logic state, passes for a short time to the high logic state. A flip-flop 6 receives on its input S the signal 5S state, which has the effect of putting the output Q of this flip-flop in the high logic state if the output of the decoder 5 is in the same state . The signal 5S is also applied to the input of a monostable flip-flop 7 the output of which is normally in the low logic state. This output goes briefly to the high logic state t ₂₁ seconds after each transition of the signal 5S from the low logic state to the high logic state. The signal taken from the output of the monostable 7 is applied to the reset input R of the flip-flop 6, the output Q of which is thus brought to the low logic state after each pulse of this signal. The output Q of this flip-flop, on which the signal 60 appears, is connected to an input of an AND gate 9 with two inputs, the other input of this gate being connected to the output of a generator 8 providing a signal acoustic frequency f _l . The output of the AND gate 9 is connected to the input of a power amplifier 10, equivalent to a source of electrical energy having two output terminals S, and S _z . Between these output terminals is connected a circuit formed by the series connection of an inductor 12 with inductance L _o and a piezoelectric transducer 11.

The operation of the circuit of FIG. 1 will now be explained using the signals shown in FIGS. 2 and 3.

An example of a coded magnetic field emitted by the transmitter of the paging system is represented as a function of time by the E wave in FIG. 2. It comprises a carrier wave modulated in amplitude by all or nothing, forming a series of programs of equal duration, distributed over time in accordance with a rule which defines the different codes of the coding system.

The magnetic field emitted by the emitter induces in frame 1 of FIG. 1 a voltage of the same shape as the E wave. If the frame 1 is tuned by the capacitor 2, the voltage obtained is of the order of a few tens of microvolts. After amplification and demodulation by circuits 3 and 4, the voltage induced in frame 1 takes the form of the signal 4S shown in FIG. 2. The same signal is also shown in FIG. 3 over a longer period. It consists of a series of pulse trains, each train defining the transmitted code. The first pulse train begins at an instant T ₀ and ends at an instant T ₁ . Likewise, the second train begins at an instant T ₀ 'and ends at an instant T ₁ ' Finally, the third train of pulses shown begins and ends respectively at instant T ₀ "and T ₁ ". The duration T ₁ - T ₀ , T ₁ '- T ₀ ' of each pulse train is constant, as well as the duration T ₀ '- T ₀ , T ₀ "T ₀ ' separating two consecutive trains. pulses follow one another until the person sought has replied or the broadcast stops after a predetermined time.

If the code of the pulse train starting at time T ₀ and ending at time T ₁ corresponds to that stored in the decoder 5, this circuit will deliver a short pulse at a time which immediately follows time T _l , as indicated by the signal 5S represented in FIG. 3. This pulse, applied simultaneously to the inputs of flip-flops 6 and 7, will put the output Q of the first one in the state logic high, as signal 6Q shows, and the output of the second in logic low. The AND gate 9, receiving on one input the signal 6Q, will pass the signal produced by the generator 8, applied to the other input, to the input of the amplifier 10.

The piezoelectric transducer 11, excited through the inductor 12 by the amplifier 10, then produces an acoustic signal from time T ₁ . This signal will last t ₂₁ seconds, up to an instant T ₂ time necessary for the output of the monostable flip-flop 7 to pass a brief instant from the low logic state to the high logic state in order to return to the low logic state. the output Q of the flip-flop 6. An input of the AND gate 9 being from the instant T ₂ in the low logic state, the signal from the acoustic generator 8 is blocked and can no longer excite the transducer 11.

The acoustic signal definitively ceases at time T ₂ if the person called takes the necessary steps before this time, for example by dialing a telephone number, to stop the transmission. Otherwise, a second pulse train, identical to the first, is emitted from time T _o ', triggering, at time T ₁ ', a second acoustic call which lasts until an instant T ₂ '.

The circuit of FIG. 4, having two terminals A and B, shows the equivalent diagram of the piezoelectric transducer 11 and the chord inductor 12 of value L _o , connected in series. This diagram includes a static capacitance co at the terminals of which is connected a motional branch composed of a self L ₁ , of a resistance R ₁ and of a capacitance C _l . The static capacitance C _o is equal to the capacitance existing between the electrodes of the transducer, while the vibratory properties of the transducer are represented by the parameters L ₁ , R ₁ , C ₁ of the motional branch.

The motional capacitance C ₁ is approximately 1000 times lower than the static capacitance C _o , the value of which can vary, depending on the form of metallizations, between 1 nF and 50 nF in a watch transducer. The frame 1, for its part, produced in horological dimensions, can typically be circular in shape, have a diameter of the order of 25 mm and contain a thousand turns of a wire of around 50 micrometers in diameter. The self L _c of such a frame is then between 10 mH and 50 mH.

The capacitance C ₀ can therefore be very suitable for granting the self Le of the frame. Indeed, with the limit values that these two components can take, it is possible to cover a frequency range from 3 kHz to 50 kHz, containing that used in people search installations. One of the aims of the present invention being to remove the tuning capacitor 2 from the frame, it can be seen that it can be achieved by using the capacitance C ₀ of the transducer 11 for this function.

We will now examine the operation of the transducer 11 as an acoustic transmitter. It is well known that the sound emitted will be all the stronger as the current passing through the motional branch L ₁ , R ₁ , C ₁ , shown in FIG. 4, is high. To best achieve this condition, the voltage across the capacitance C _{0 must} be as high as possible and the frequency of the current corresponds to the resonant frequency f, = (2 π ^-1 (L ₁ C ₁ ) ^-1/2 of the motional branch. If V is the alternating voltage of frequency f ₁ , supplied by the amplifier 10 at the terminals A, B of the circuit of FIG. 4, if the motional branch is assumed to be open and if the value L ₀ of the choke 12 is such that L ₀ C ₀ = L ₁ C ₁ , the voltage across the capacitors C ₀ will be equal to Q ₀ V, Q ₀ being the quality factor of the choke 12 at the frequency f ₁ .

At acoustic frequencies, the value of Q _o can vary between 3 and 10. The voltage across the capacitance C _o , even charged by the motional branch whose impedance is high compared to that of C _o , will therefore remain significantly higher to V.

In order to avoid a bulky and expensive component, in accordance with another object of the present invention, the choke 12 can be replaced by the frame 1. However if the choke Le of the frame 1 and the capacitance C _o of the transducer 11 are granted on the frequency f ₀ of the carrier wave, the efficiency of the frame at the acoustic frequency f ₁ , which is about twenty times lower than f ₀ , cannot be good while providing some improvement compared to a direct attack on the transducer 11 by amplifier 10.

To tune the self Le on the frequency f ₁ , an additional capacitor 13 of capacitance C _o 'can be connected in parallel on C _o , as shown in FIG. 4. The tuning will be carried out if the value of C _o ' satisfies the relation (C _o '+ C _o ) Le = L ₁ C ₁ . The use of such a capacitor at the terminals of the transducer 11 represents a complication which is however largely compensated by the possibility of eliminating the capacitor 2 and the inductor 12 from the diagram of FIG. 1. The additional capacitor 13 can be a second piezoelectric transducer having a static capacity C _o '. It is possible to produce the two transducers in the form of a single element having two faces and having a common electrode on one face and two electrodes on the other face, each of these latter electrodes defining one of the transducers.

The use of frame 1 either as a magnetic wave sensor or as a chord inductor of the transducer 11 and the use of this transducer either as an acoustic emitter or as a chord capacitor of frame 1 is only possible if a switching circuit is used to connect the frame and the transducer adequately to fulfill these various functions.

FIG. 5 represents the block diagram of a watch, for example digital, provided with a people search circuit according to the invention. The watch part, of classic design, includes a quartz 20 serving as time base, a maintenance circuit 21, a counter 22, a driving circuit 24 and a digital display 25. The quartz 20 is connected to the maintenance circuit 21, the assembly forming an oscillator. The signal at the output of the maintenance circuit is applied to the input of the counter 22 which has a main output Si and two auxiliary outputs S ₂ and S ₃ . On these last two outputs appear respectively a high frequency signal formed by pulses and an acoustic frequency signal. The output S ₁ provides, for its part, a signal containing the time information. It is applied to the input of the driving circuit 24 which generates the signals necessary for indicating the time by the display 25 to which it is connected.

The people search part of figure 5 includes elements 1, 3, 4, 5, 6, 9 and 10, already described in connection with figure 1 and connected in the same way in the two figures. The monostable lever 7 of FIG. 1 has been replaced, in FIG. 5, by a counter 23 of simpler construction. This counter 23 receives, on one input, the pulses coming from the output S ₂ of the counter 22 of the watch and, on another input, the signal 5S. Each pulse of signal 5S resets counter 23 to zero and then starts counting. Once the counter 23 is filled, it produces a pulse on its output, which is connected to the input R of the flip-flop 6. The time required to fill this counter corresponds to the time interval t ₂₁ , previously determined by the monostable rocker 7. The input of the AND gate 9 which was connected in FIG. 1 to the output of the acoustic frequency generator 8, is connected in the circuit of FIG. 5 to the output S ₃ of the counter 22 which supplies a signal of the same frequency.

The circuit for switching the frame 1 and the transducer 11 already mentioned, is represented by block 15 in FIG. 5. This circuit has three inputs E ₁ , E ₂ , E ₃ and three outputs S ₁ , S ₂ , S ₃ . The inputs E ₁ and E ₂ are respectively connected to the outputs S ₁ and S ₂ of the amplifier 10. The input E ₃ receives the signal 6Q coming from the output of the flip-flop 6. The output S ₁ of circuit 15 is connected to a terminal of frame 1. The output S ₂ of this same circuit is connected to a terminal of a capacitor 14 having a capacity equal to the capacity C _o 'of the capacitor 13 of FIG. 4. The other terminal of this capacitor is connected to one terminal of the transducer 11 and to the other terminal of the frame 1. The frame 1, the transducer 11 and the capacitor 14 thus have a common terminal. Finally, the output S ₃ , the input E ₁ and the other terminal of the transducer are connected together.

The circuit 15 essentially comprises two switches A and B actuated by relays not shown. The first switch is connected to the output S ₁ and the second to the output S ₂ . Switch A can occupy two positions a, and a ₂ . In position a ₁ , the switch closes a contact which links the output S ₁ with the input E _l . In position a ₂ , this output is connected to input E _Z. Switch B can also occupy two positions b, and b ₂ . In position b ₁ , the switch does not close any contact and the output S ₂ remains floating, while in position b ₂ , this output is connected to input E ₁ .

The relays, not shown, actuating the switches A and B are controlled by the signal 6Q shown in FIG. 3. This signal is applied to the input E ₃ of the circuit 15. It will be assumed that at a low logic state of the signal 6Q correspond the positions a ₁ and b ₁ of switches A and B and that at a high logic state of this signal correspond the positions a ₂ and b ₂ of these same switches.

The operation of the people search part of the circuit of FIG. 5 is as follows. In the absence of any coded search signal E, the signals 4S, 5S, and 6Q of FIGS. 2 and 3 all remain in the low logic state. This has the effect of putting the switches A and B respectively in the positions a ₁ and b ₁ . The two terminals of the transducer 11 are then connected to the two terminals of the frame 1 and one terminal of the capacitor 14 is made floating. The frame is tuned, under these conditions, by the static capacitance of the transducer on the carrier frequency f _o of the signal E, making unnecessary the tuning capacitor 2 shown in FIG. 1.

The circuit 15 remains in this state until a coded signal received by the frame 1 is recognized by the decoder 5. The output Q of the flip-flop 6 then goes to the high logic state at the instant T ₁ causing the switching of switches A and B respectively in positions a ₂ and b ₂ . The outputs S ₁ and S ₂ of the amplifier 10, which acts as a source producing an acoustic frequency signal, are then connected, by the switch A, to the terminals of the transducer 11 through the frame 1, making the choke 12 unnecessary. of FIG. 1. The capacitor 14 of capacity C _o "is connected, for its part, directly to the terminals of the transducer by the switch B. Under these conditions, the transducer being excited by the amplifier 10, it will emit an acoustic signal d call in the best performance conditions. This call signal will be transmitted for t ₂₁ seconds. Then, at time T ₂ , the output Q of the flip-flop 6 passing to the low logic state, the transducer 11 will be again connected to the terminals of frame 1, as at the start of the cycle If the call signal has remained unanswered, a new cycle, identical to the previous one, will be triggered from time T ₀ '.

The present invention is not limited to the single embodiment of a person search device which has just been described, but the scope of this patent also extends to the variants of the various circuits remaining within the framework of equivalences. For example. the operation of the circuit 15 in FIG. 5 has been described using contacts to facilitate understanding. Of course, without departing from the scope of the invention, the contacts can be replaced in a known manner by electronic switching devices such as transistors and transmission gates.

Claims (4)

1. A miniaturized pager, in particular for a watchomprising:

- an antenna (1) for picking up a variable electromagnetic signal;

- a transducer (11) able to produce a sound and having a pair of terminals;

- a source (10) having a pair of terminals and able to provide an electric signal of acoustic frequency;

- means (5, 6, 22, 23) for generating a logic control signal (6Q) in response to said electromagnetic signal; and

- a switching circuit (15) responsive to first and second states of said logic signal; characterised in that:

- said antenna (1) is a frame having an inductance and a pair of terminals;

- said transducer (11) is a piezoelectric transducer having a pair of terminals between which is provided a static capacitance; and in that:

- said switching circuit (15) is arranged to connect, in response to said first state of the logic signal, the frame and the transducer in parallel, and, in response to said second state of the logic signal, the frame and the transducer in series and to the terminals of said source.

2. A pager as in claim 1, characterized in that the inductance of said frame is tuned by the static capacitance of said transducer to the frequency of said magnetic field.

3. A pager as in claim 1 and 2, characterized in that it further comprises an additional capacitor (14) connected to the terminals of said transducer via said switching circuit when said logic control signal is in said second state.

4. A pager as in claim 3, wherein the inductance of said frame is tunde by said static capacitance augmented by the capacitance of said additional capacitor to said acoustic frequency.

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