GB2098431A

GB2098431A - Apparatus for the contactless transmission of a numerical value

Info

Publication number: GB2098431A
Application number: GB8203728A
Authority: GB
Original assignee: Mannesmann VDO AG
Current assignee: Mannesmann VDO AG
Priority date: 1981-03-02
Filing date: 1982-02-09
Publication date: 1982-11-17
Also published as: DE3107928A1; FR2500944B1; GB2098431B; JPS57157667A; FR2500944A1

Abstract

Apparatus for transmitting a numerical value from a displaceable object such as a tyre to a stationary object such as the chassis of a vehicle, with the aid of a transmitter-receiver oscillator circuit (7) and a coupled oscillator circuit (9). The apparatus associated with the vehicle includes a transmitter (2) and a receiver (3) controlled from a control circuit (1). The apparatus associated with the wheel includes a D.C. voltage generator (17) energized from the oscillator circuit (9), a pulse extracting circuit (16), a transmission circuit control means (14), an electronic switch (12) and an information store (15). Under the control of the extraction circuit (16), the data stored in the information store (15), is scanned and transmitted back to the transmitter-receiver oscillator circuit (7) via the electronic switch (12) so that the numerical value stored in the store (15) is displayed by an evaluation circuit (5) having been demodulated in a circuit (4) of the receiver stage (3). <IMAGE>

Description

SPECIFICATION Apparatus for the contactless transmission of a numerical value The present invention relates to apparatus for the contactless transmission of a numerical value, in particular a measurand.

In a known form of apparatus, the coupled oscillator circuit is associated with a transponder having a switch, which in the event of the air pressure monitoring a vehicle wheel can be opened and closed depending on the pressure of air in the tyre, and either leaves the coupled oscillator circuit in the undamped condition or short-circuits it. Accordingly, with part of the apparatus arranged on the vehicle chassis it can be ascertained whether the air pressure has fallen below a present value. Initially, the transmission stage is effectively switched in such manner that it radiates via the transmitter-receiver oscillator circuit a frequency signal which is received by the couple oscillator circuit if the latter is located in the vicinity of the transmitter-receiver oscillator circuit.The energy of the frequency signal is magnetically coupled-in by a coil of the coupled oscillator circuit and energizes the coupled oscillation circuit into oscillation at its intrinsic frequency if the switch is open. In the event of a closed switch, no oscillation will occur in the coupled oscillation circuit. The transmitter-receiver oscillator circuit can now be damped by a control arrangement, so that the oscillation still occurring therein after switching-off the transmission stage very rapidly decays. Thereupon, the transmitter receiver oscillator circuit is also effectively connected with the transmitter stage by the control circuit arrangement.In the event in which the switch of the transponder is open and consequently a decaying oscillation occurs in the coupled oscillation circuit, the frequency signal is received by the transmitter-receiver oscillator circuit during the receiving phase if the latter is located in the vicinity of the coupled oscillator circuit. On the other hand, in the event of a closed circuit in this receiving phase no signal is received by the transmitter-receiver osciallator circuit. For evaluation of the received frequency signal, the receiver stage may have an electronic meter the metering input of which receives converted metering pulses during a pre-set time interval formed from the frequency signal received.The meter condition therefore indicates that the switch of the transponder is opened if a pre-set meter content is reached within the time duration whereas in the other case, if the switch in the transponder is closed, no metering pulses will be received by the meter and a display stage will indicate an excessively low pressure.

The above described apparatus has the disadvantage that only two discrete values of a measurand can be transmitted in contactless fashion, depending on whether the switch bridging the coupled oscillator circuit is opened or closed.

It is an object of the present invention to overcome the above referred to disadvantage by providing apparatus which is suitable for contactless transmission of a multi-digit numerical value in the form of a binary code.

According to the present invention there is provided apparatus for the contactless transmission of a numerical value from a displaceable object to an object which is stationary relative thereto, said apparatus including: a transmitter stage for transmitting a reference frequency signal; a receiver stage comprising a demodulator and means for evaluating and displaying the numerical value transmitted; a transmitter receiver oscillator circuit; means for connecting the transmitter stage and the receiver stage alternately with the transmitter-receiver oscillator circuit; an oscillator circuit arranged on the displaceable object which during at least part of its movement is coupled to the transmitter-receiver oscillator circuit; a switch means for short-circuiting said oscillator circuit; means for storing a numerical value in digital coded form, said value representing a measurand of a parameter to be monitored; means for extracting from the induced voltage at the coupled oscillator circuit, a rhythm pulse; and circuit means for transmission control having inputs associated with the rhythm pulse extraction means and the numerical value storing means and an output for controlling the switch means whereby said circuit means under the control of the rhythm pulse can scan the stored code representing the numerical value and transmit it via the couple oscillator circuits to the receiver stage where it is decoded in the modulator and displayed as a numerical value in the evaluating means.

It is thus possible to transmit a numerical value present as a statically binary bit sequence, for example a measurand, from the information carrier secured to a displaceable object to a stationary central unit with a high degree of accuracy and reliability. With this arrangement, the transmission of one bit in each particular instance takes place during a pulse time assembled from the transmission phase, the damping phase and the receiving phase of the central unit. The bit sequence thus transmitted is de-coded in the receiver stage of the central unit with a demodulator as bit sequence.

Despite the high transmission reliablity, if there is a minimum spacing between the coupled oscillator circuit and the transmitter-receiver oscillator circuit, the apparatus is relatively cheap to manufacture.

The apparatus may include a store, preferably a capacitor, which is connected with the coupled osciilated circuit via a rectifier in order to generate a D.C. supply voltage for the circuits associated with the coupled oscillator. In this form the operation of the information carrier unit be achieved without an energy source, so that it may be called a passive information carrier. The functions of the passive information carrier can be carried into effect relatively simply with one or more electronic assemblies.

The switch for short-circuiting the coupled oscillator circuit may be an electronically controlled switch which, to correspond to the bit sequence to be transmitted, can be quickly actuated with minimum energy.

The means for sequential transmission may comprise a counter supplied with the extracted rhythm pulses; and a data selector having the meter address inputs connected to respective outputs of the meter, data inputs for receiving the numerical valve to be transmitted, and an output connected to the electronic switch. The counter which controls a data selector which in turn selects the bits of the numerical value to be transmitted one after another and conveys them for controlling the electronic switch, enables the apparatus to function reliably, if it is controlled by rhythm pulses obtained from the frequency signal received.

The counter and the data selector may be fed in the passive information carrier unit with a supply voltage obtained from the frequency signal.

The present invention will now be described in greater detail by way of example with reference to the accompanying drawings, wherein: Figure 1 is a block circuit diagram of a preferred form of apparatus for the contactless transmission of digitally coded numerical values; Figure 2 shows waveform diagram to illustrate the operation of the apparatus; Figure 3 is a circuit diagram showing the passive information carrier unit; and Figure 4 is a diagram illustrating the information and signal sequences of the apparatus having the passive information carrier unit.

Referring first to Figure 1, a central unit of the apparatus comprises a control circuit 1, a transmitter stage 2, a receiver stage 3, a damping stage 6 and a transmitter-receiver oscillator circuit 7. The control circuit 1 supplies the transmitter stage 2, the receiver stage 3 and the damping stage 6 with control signals. The receiver stage 3 comprises an amplifier-demodulator 4 and an evuluation circuit 5.

The transmitter stage 2, the damping stage 6 and the amplifier-demodulator 4 are all connected to a transmitter-receiver oscillator circuit 7 which is formed as a parallel oscillator circuit having a coil 8 and a capacitor 9'.

The central unit is arranged on a stationary object such as the chassis of a vehicle, whereas the passive information carrier unit described hereinafter is arranged on an object displaceable relative thereto such as the wheel of the vehicle.

The information carrier unit comprises a coupled oscillator circuit 9 consisting of a coil 10 and a capacitor 11, also arranged in parallel. The coupled oscillator circuit is arranged to be shortcircuited by an electronically controllable switch 12.

A control input 13 of the electronically controlled switch 12 is supplied by circuit means 14 for transmission control. The circuit means 1 4 for transmission control is connected via parallel lines to an information store 1 5. The numerical value to be transmitted is stored in the information store as a binary bit sequence. The circuit means 14 for transmission control is supplied by circuit means 1 6 for pulse winning-back which is connected to the coupled oscillator circuit 9.

Also connected to the coupled oscillator circuit 9 are circuit means 1 7 for generating a supply voltage which, from a frequency signal supplied from or by the coupled oscillator circuit 9, supplies a D.C. voltage to the circuit means 1 6 for pulse winning-back and to the circuit means 14 for transmission control.

The operation of the apparatus shown in Figure 1 will now be described in greater detail with reference to the waveforms shown in Figure 2.

The signals supplied by the control circuit 1 during a transmission phase are shown by the waveform a. During the transmission phase the transmitted stage 2 is energized to supply a highfrequency oscillation to the transmitter-receiver oscillator circuit 7, in the form of a transmission burst. Due to this transmission burst, the coupled oscillator circuit 9 is energized as shown in waveform c, to an initially amplitude-increasing intrinsic oscillation, since the coils 8 and 10 are magnetically coupled with each other if the information carrier unit is located in the vicinity of the central unit.In the damping phase following the transmission phase, the transmitter-receiver oscillator circuit 7 is short-circuited by the damping stage 6, whilst the voltage in the coupled oscillator circuit 9 can further oscillate as shown by the waveform c if the electronically controlled switch 12 is open. Individually, the signal behaviour of the voltage in the coupled oscillator circuit 9 (as will be shown later) depends on whether a logic "0" or a logic "1" is to be transferred by the information carrier unit. It will be noted that in the left-hand part of the waveform c a logic "1" is transmitted and in the right-hand part of the waveform ca logic "0" is transmitted.

In each case, from the voltage induced in the coupled oscillator circuit 9 a DC voltage is generated by the supply voltage generator as shown by the waveform d. Additionally, there is extracted from the induced voltage at the coupled oscillator circuit 9 at the commencement of the amplitude-increasing voltage in waveform c at rhythm pulse which is not shown in Fig. 2. The rhythm pulse is supplied to the circuit means 14 for transmission control which, in the event of each rhythm or pulse, scans a bit of the binarystored numerical value out of the information store.

In the left-hand part of the waveforms shown in Figure 2 there is scanned a logic "1" in which the circuit means 14 for transmission control is in the inoperative state, so that the electronically controlled switch 12 remains open. Waveform e shows the input to the circuit means 14 and waveform fthe control signal for the electronic switch 12 output from the circuit means 14.

When the electronic switch 1 2 is open, the voltage at the coupled oscillator circuit 9 decays only slowly to correspond to the left-hand part of the waveform c and can during the receiving phase, as shown in the second part of the lefthand portion of the waveform g induce in the energized transmitter receiver oscillator circuit 7 a voltage whose amplitude initially increases and then decays.

The voltage induced in the transmitter receiver oscillator circuit is during the receiving phase demodulated in the amplifier-demodulator 4 and generates an output signal to correspond to waveform h and which is fed to the evaluation circuit 5.

If, during a period following thereon and comprising a transmission phase, a damping phase and a receiving phase, as shown in the right-hand part of the waveforms shown in Figure 2, by the circuit means 14 for transmission control of logic "0" is scanned as the next bit from the information store, then the signal at the output of the circuit means 1 4 for transmission control - as shown in waveform e is varied and supplied a control signal as shown in waveform f, to the electronic controlled switch 12 which closes the switch.Consequently, the voltage at the coupled oscillator circuit as shown in waveform c at the right-hand part thereof decays very rapidly subsequently to the transmission phase or the damping phase and can, during the receiving phase following thereon, induce practically no voltage in the transmitter/receiver oscillator circuit 7, as shown in the second part of the right-hand portion of waveform g. Consequently, there occurs at the output of the amplifier-demodulator 4 a signal containing a logic "0".

At the output of the amplifier-demodulator 4 there is therefore obtained a chronological bit sequence in receiving phases following one upon the other, corresponding precisely to the stationary bit sequence in the information store 15.

The bit sequence can be further-processed in the evaluation circuit 5, being in particular compared with a bit sequence stored therein of a numerical value so as to ascertain correspondence with the numerical value in the information store 1 5. This is the transmission principal of contactless "electronic key", for which the invention can advantageously be employed, since the information carrier unit can be designed in extremely compact manner and requires no energy source of its own.

To this end, the electronic system in the information carrier unit can be designed with discrete assemblies, in hybrid or integrated manner. The coding of the numerical value can, in this connection, be located directly in the circuit means 1 4 for transmission control, if this circuit is designed as a ROM.

A preferred form of the information carrier unit which is designed as an electronic key is shown in Figure 3.

There corresponds between Figures 1 and 3 the coupled oscillator circuit 9 having the coil 10 and the capacitor 11 and also the electronically controlled switch 1 2 connected parallel thereto and having the control input 13.

Associated with the coupled oscillator circuit 9 is a diode 1 8 for rectification of the frequency signal, so that there is formed therefrom a supply voltage which is smoothed by means of a capacitor 19'.

Furthermore, a rhythm pulse is obtained from the frequency signal induced in the coupled oscillator circuit via a further diode 1 9 connected to a parallel resistor-capacitor circuit 20. A DC voltage obtained from the diode 1 8 and the capacitor 19 is supplied to a counter 21 and to a data selector 22. A pulse line from the diode 19 is connected to a pulse input of the counter 21 and also to an AND circuit 23. The other input to the AND circuit 23 is from the data selector 22. The output of the AND circuit 23 is applied to the control input 1 3 of the electronically controlled switch 12.

Outputs 24,25 and 26 of the counter 21 are connected to address inputs 27, 28 and 29 respectiveiy of the data selector 22. Further inputs 34, 35 and 36 are connected to one of the number of bits of a bit sequence corresponding to switches 30,31 to 33.

The number stored in the information carrier unit, i.e. the binary bit sequency of this number, is therefore represented by the opened or closed switches, whereof each is associated with one bit.

The opened or closed switches 30, 31 to 33 determine a voltage value at the data inputs 34,35,36 of the data selector 22. Depending on the condition of the address inputs 27,28 and 29 determined by the meter, the "OUT" output of the data selector 22 assumes the condition of one of the data inputs of the data selector 22 are, during counting-up of the counter 21 with rhythm pulses, scanned one after the other and, via the AND circuit 23, transmitted to the control input 13 of the switch 1 2.

Referring to Figure 4, the logic conditions are shown at varying positions of the information carrier unit according to Figure 3 and the remaining device according to Figure 1, i.e. some characteristic signal behaviours: Referring to line a in Figure 4, a binary number obtaining according to the position of switches 30,31 to 33 at the data input 34,35 to 36 or XO-X7, is to be transferred.

For this purpose, there is obtained subsequent to each transmission phase a rhythm pulse counting-up the meter according to line b. In this way, there arises during the first appearing "0" of the meter condition in line b, at the negated output "OUT" of the data selector 22, a logic "0", since the corresponding input of the data selector is fed with a logic "1". Consequently, the voltage at the coupled oscillator circuit 9, indicated by the envelope in line d, can gradually decay during the receiving phase, as shown more precisely in the left-hand portion of the waveform c shown in Figure 2.

There therefore results, in consequence of the frequency signal fed-back in the transmitter/receiver oscillator circuit 7, at the output of the amplifier-demodulator 4, a voltage pulse corresponding to waveform h in Figure 2, and which melts itself in waveform e of Figure 4, with a corresponding voltage pulse in the preceding pulse time. The said voltage pulse signifies at logic "1" once again at the output of the amplifier-demodulator 4. In the pulse time following thereon, the time between two transmission phases is designated the pulse time, there is scanned from the data input of the data selector 22 a logic "0" which appears at the negated output of the data selector as a logic "1 ".

Thereby, the electronically controlled switch 12 is short-circuited and the voltage in the coupled oscillator circuit 9 immediately decays subsequent to the end of the transmission phase and the damping of the transmitter oscillator circuit 7. This is indicated diagrammatically by the waveform d in Figure 4 and more precisely the right-hand portion of the waveform c in Figure 2.

Consequently, no frequency signal is transmittedback from the coupled oscillator circuit 9 to the transmitter-receiver oscillator circuit 7. This condition of the transmitter-receiver oscillator circuit produces at the output of the amplifierdemodulator 4 a low signal level which contains a logic "0" as information, as shown in waveform f of Figure 4.

The above-discussed procedures are repeated during in each particular instance one pulse time, until the entire binary-coded number is transmitted from the information carrier to the central unit. Since following threon a renewed transmission commences, there is to be determined in the information carrier unit a special bit which signifies the end of the transmission of a numerical value.

Claims

1. Apparatus for the contractless transmission of a numerical value from a displaceable object to an object which is stationary relative thereto, said apparatus including: a transmitter stage for transmitting a reference frequency signal; a receiver stage comprising a demodulator and means for evaluating and displaying the numerical valve transmitted; a transmitter receiver oscillator circuit; means for connecting the transmitter stage and the receiver stage alternately with the transmitter-receiver oscillator circuit; an oscillator circuit arranged on the displaceable object which during at least part of its movement is coupled to the transmitter-receiver oscillator circuit; switch means for short-circuiting said oscillator circuit, means for storing a numerical value in digital coded form, said value representing a measurand of a parameter to be monitored; means for extracting from the induced voltage at the coupled oscillator circuit, a rhythm pulse; and circuit means for transmission control having inputs associated with the rhythm pulse extraction means and the numerical value storing means an output for controlling the switch means whereby said circuit means under the control of the rhythm pulse can scan the stored code representing the numerical value and transmit it via the coupled oscillator circuits to the receiver stage where it is decoded in the modulator and displayed as a numerical value in the evaluating means.

2. Apparatus according to Claim 1, wherein a capacitor is connected to the coupled oscillated circuit via a rectifier in order to generate a D.C.

supply voltage for the circuits associated with the coupled oscillator.

3. Apparatus according to Claim 1 or 2, wherein the switch means for short-circuiting the coupled oscillator circuit is an electronically controlled switch.

4. Apparatus according to Claim 3, wherein the sequential transmission control means comprises: a meter supplied with the extracted rhythm pulses; and a data selector having the meter address inputs connected to respective outputs of the meter data inputs for receiving the numerical value to be transmitted, and an output connected to the electronic switch.

5. Apparatus according to Claim 4, wherein the output from the data selector and an output from the meter are connected to the electronic switch via an AND gate.

6. Apparatus according to any one of the preceding claims, including means for damping the transmitter-receiver oscillator circuit.

7. Apparatus for the contractless transmission of a numerical value from a displaceable object to an object which is stationary relative thereto, constructed and arranged to operate substantially as herein described with reference to and as illustrated in the accompanying drawings.