WO1994027261A1

WO1994027261A1 - A transmitter-receiver set

Info

Publication number: WO1994027261A1
Application number: PCT/GB1994/001045
Authority: WO
Inventors: Graham Guymer
Original assignee: Graham Guymer
Priority date: 1993-05-14
Filing date: 1994-05-16
Publication date: 1994-11-24
Also published as: AU6655794A; GB9309960D0

Abstract

A transmitter-receiver set for use by a person charged with the responsability of looking after another individual. The receiver (11), which is to be carried by the other individual, is provided with an alarm (30) and a decoder (12). The decoder (12) enables the operation of the alarm (30) when in one state and prevents the operation when in another state. The transmitter (10) has an encoder (13) operable to send out a uniquely encoded signal which effects changes between said one state and said other state of the decoder (12) and an aerial (18) operable to transmit a radio signal which activates the alarm (30) in the receiver (11) when received thereby. The receiver (11) and transmitter (10) are adapted to be directly electrically connected to allow the uniquely encoded signal to be transferred directly from the transmitter (10) to the receiver (11).

Description

DESCRIPTION

A TRANSMITTER-RECEIVER SET

The present invention relates to a transmitter/receiver set suitable for use by a person charged with the responsibility of looking after another individual. Typically, although not exclusively the responsible person might be a parent in charge of a child.

An ever-increasing concern of parents is that their child might become the victim of an abduction. Whilst the most tangible benefit of any apparatus which militates against potential child-abductors will often be peace-of-mind, such apparatus must be effective in securing the child's safety if a potentially dangerous situation ever does arise. The situations imagined here are not limited to attempted abductions, but embrace any circumstance whether a parent might be caused to worry about the whereabouts of their child, for example, if they have lost visual contact with them in a crowded public place.

Although the child or other individual can carry his part of the set so that it is concealed or its appearance could be disguised, the effectiveness of the set is always vulnerable to the action of a potential abductor should he be able to find or recognise the part of the set that the child or other individual carries and render it .inoperative. An object of this invention is to arrange the transmitter-receiver set so that it is not easy for a third party to render it inoperative by interfering with the part of the set that is carried by the child or other individual.

According to this invention there is provided a transmitter-receiver set for use by a person charged with the responsibility of looking after another individual comprising one device to be carried by said other individual which is provided with a signal emitting means and multi-state means which enable operation of the signal emitting means when in one state and which render the signal emitting means inoperable when in another state, and another device to be carried by said responsible person, said other device including means operable to send out a signal which effects changes between said one state and said other state of said multi-state means, and means operable to transmit a radio signal which activates said signal emitting means in said one device when received thereby.

Preferably the signal which effects changes between the states is a uniquely encoded signal which may be a pulse position modulation coded signal. This allows, for example, a parent to activate their own child's alarm without setting off any similar alarm in the effective range of the transmitter.

In a preferred embodiment, the two devices of the set are adapted to be directly electrically connected to allow the uniquely coded signal to be transferred directly from said other device to said one device to effect the change of state in the multi-state means. Conveniently the radio signal uses the same unique coding as the signal which effects changes between the states in the multi-state device.

The signal emitting means may comprise an audio signal emitting means or a tracking signal emitting means.

In the circumstance of a child lost in a public place, the alarm will also alert passers by to the risk situation perceived by the parent.

In an alternative embodiment, the radio signal may be passed from the other device to said one device via a cellular network.

Either or both the devices may incorporate an LED indicator providing a flash light output when battery voltage of battery powered means for operating the respective device falls below a safe level.

Each of the devices may comprise a radio transmitter/ receiver which is tuned to complete a radiolink by one receiving a signal emitted by the other. Where the signal emitting means comprise an audio alarm signal emitting means, each of the devices may be provided with actuating means operable by the respective one of the other individual and the responsible person to initiate operation of the alarm means and only the other device that is to be carried by the responsible person is provided with means for deactivating the alarm means. The audible signal may be unpleasant so that a child will be disinclined to activate it unnecessarily. The other device that is to be carried by the responsible person may also include alarm means operable by operation of the tuned transmitter- receiver radio link to emit an alarm signal when the other individual operates the actuating means included in his unit.

One form of transmitter-receiver set for use by a parent to monitor the whereabouts of a child will be described now by way of example with reference to the accompanying drawing which is a circuit diagram of the transmitter and receiver devices of the set.

Referring to the drawing, the transmitter 10 uses pulse position modulation (PPM) to transmit a pre-programmed "word" or code at the carrier frequency. The receiver 11 for its part amplifies, de-modulates, and conditions the .incoming signal, which is then passed on to a pre-programmed decoder circuit 12. Provided the decoder 12 "recognises" the incoming signal as being the valid code, the receiver 11 then sets off an audible alarm. Such an arrangement of transmitter/receiver meeting DTI approvals typically has an rf power output in the range 250-350 μWatts and has a receiving range of some 100-200 metres under normal operating conditions.

To indicate to the user that the battery packs on both the transmitter 10 and the receiver 11 are at a safe level to guarantee satisfactory operation, the units 10 and 11 incorporate an LED indicator providing a flashing light output when the battery voltage falls below a safe level. At the heart of the transmitter 10 is a dedicated encoder integrated circuit 13 which has a built-in non-volatile memory, programmed at the time of manufacture/test with the unique word/code which remains "written" into the memory of the device for the whole period of its service life. When the encoder 13 is activated, it outputs a series of pulses which represent the unique word/code in the form of a series of 0s and Is at a rate determined by a rate oscillator 14. These encoded signals are passed to a modulator circuit 15, which modulates the output from the carrier frequency oscillator 16, in effect switching the carrier frequency on and off, producing pulses of radio frequency emissions which represent the unique word/code. The signal sequence timer 17 which is connected to the oscillator 16 allows the transmitter 10 to produce a given sequence of pulses at an aerial 18, before returning to a standby condition. This process is repeated for as long as an alarm switch 19 is in the "alarm" position.

Whilst the integrity of the transmitter/receiver apparatus is guaranteed by the detailed design of the encoder/decoder pre-programmed "differs", rf interference between similar transmitter/receiver sets is nevertheless a potential problem. ("Differs" here is defined as the number of different word codes which can be written into the non-volatile memory of the integrated circuits. Typically, this could be tens of thousands) . .Assuming that a cαrπmon carrier frequency were adopted and two independent operators initiated an "alarm" sequence in close proximity to each other, it is possible that unacceptable interference could arise. Since transmission on both transmitters is not continuous, thanks to the operation of the signal sequence timer 17, it would still be possible for both sets to receive and validate their separate word codes, but this would be more reliably achieved if the carrier frequencies were also different. This could be achieved by, for example, using different frequencies within the allocated band width. Since the above circumstance is statistically an unusual event, the number of different carrier frequencies need not be excessive.

Once an alarm sequence has been initiated, the transmitter 10 outputs a series of rf pulses via the aerial 18, as shown in the drawing. Initially, the PPM transmission provides a synchronizing pulse which sets a rate oscillator 21 in the receiver 11 to accept transmission. The receiver includes an aerial 22 which picks up the incoming radio signal and produces a sympathetic electrical signal, which is amplified by the signal amplifier 23, de-modulated by the de-modulator circuit 24, and then conditioned at the signal conditioner 25. Finally, the signal is fed into the decoder integrated circuit 12, via Port A. The decoder integrated circuit 12 processes the signal to validate the incoming code/word, and if the word is identical to that pre-programmed into its memory, then the decoder produces an output at Port C which is passed to an alarm circuit, which typically incorporates a piezoelectric-electric warning device. A latch circuit 29 ensures that the alarm can continue to sound when the output from Port C changes.

Bearing in mind that a potential child-abductor might take the trouble to acquaint him/herself with the operation of the apparatus described herein, it is iiπportant that the receiver cannot be easily rendered inoperative by an unauthorised third party. There is therefore provided an arming method whereby, once the receiver 11 has been armed by the responsible person, it remains in this active mode until such time as the responsible user decides that it should be deactivated. It is not desirable to just leave the apparatus permanently on, since the current drain would result in a service life which would be disadvantageously short. In this embodiment therefore the receiver 11 may be stored in a non-armed state with j-ftinimum drainage to the batteries, but can be easily armed for immediate use. The life of the transmitter's batteries is relatively long, since the transmitter 10 is only substantially active when being used to transmit an alarm signal: it does not transmit continuously. The arming method is an attempt to frustrate an .individual from prematurely de-activating the alarm mechanism, and is described below.

1. To initiate the receiver arming sequence, the receiver 11 and transmitter 10 are first connected electrically together by means of a coaxial cable 26.

2. A receiver arm switch 27 is closed to energize the receiver circuits and the transmitter alarm switch 19 is closed to enable the code word to be injected directly into the receiver decoder integrated circuit 12.

3. Assuming that the circuits are functioning correctly, and code word validation has been achieved, the decoder 12 produces an output at Port C. This signal is passed to an arm logic circuit 28 via the now closed coaxial link and Port D. The arm logic circuit 28 now produces an output at Port E, energizing a Mosfet transistor Tl which is connected in parallel with the arm switch 27. The arming sequence provides an alarm sounder 30 with a brief functional check, the alarm sounder being connected to the Port C of the decoder 12.

4. The receiver 11 is now armed, and for user convenience, the unit is provided with an LED to indicate that the receiver is in its active mode.

5. Once armed, the coaxial connection 26 is disengaged and the system is ready for use. The arm logic circuit 28 involves a logic flip/flop circuit in which the first signal received at Port D will cause an output at Port E. This potential remains until such time as another signal is applied at Port D, which then reverses the output at Port E.

The disarming of the receiver 11 would be necessary in the following circumstances: a) After an alarm sequence has been initiated and a risk condition has been perceived to have passed.

b) After a period of use where it has not been necessary to initiate an alarm sequence.

In both cases the procedure is idential; however in a) the alarm sounder is still operative, unless the battery pack has been exhausted. The procedure is as follows:

1. The transmitter/receiver are connected by means of the coaxial link 26.

2. The receiver arm switch 27 is positioned to "off" and the transmitter alarm switch 19 is positioned to "alarm".

3. The pre-prcxjrammed signal is now injected directly into the receiver decoder circuit 12 which, assuming the validated code word is received, produces an output at Port C.

4. Because in these conditions the latch circuit 29 is inhibited, the arm logic circuit 28 receives a feed at Port D, causing it to switch off the Mosfet transistor Tl.

5. Once disarmed, the coaxial link 26 is disconnected, and the apparatus can be set aside for future use without current drain.

Claims

1. A transmitter-receiver set for use by a person charged with the responsibility of looking after another individual comprising one device to be carried by said other individual which is provided with a signal emitting means and multi-state means which enable operation of the signal emitting means when in one state and which render the signal emitting means inoperable when in another state, and another device to be carried by said responsible person, said other device including means operable to send out a signal which effects changes between said one state and said other state of said multi-state means, and means operable to transmit a radio signal which activates said signal emitting means in said one device when received thereby.

2. A transmitter-receiver set according to claim 1, wherein said signal which effects changes between said states is a uniquely encoded signal.

3. The transmitter-receiver set according to claJL 1, wherein said uniquely encoded signal is a pulse position modulation coded signal.

4. A transmitter-receiver set according to either claim 2 or claim 3, wherein said one device and said - other device are adapted to be directly electrically connected, to allow said uniquely coded signal to be transferred directly from said other device to said one device, to effect said change of state in said multi-state means.

5. A transmitter-receiver set according to any of claims 2 to 4, wherein said radio signal uses the same unique coding as said signal which effects changes between said states in said multi-state device.

6. A transmitter-receiver set according to any of claims 1 to 5, wherein said signal emitting means comprises an audio alarm signal emitting means.

7. A transmitter-receiver set according to any of claiπis 1 to 6 wherein said signal emitting means comprises a tracking signal emitting means.

8. A transmitter-receiver set according to any of claims 1 to 7, wherein said radio signal is passed from said other device to said one device via a cellular network.

9. A transmitter-receiver set according to any of claims 1 to 8, wherein said one device and/or said other device incorporate an LED indicator providing a flash light output when battery voltage of battery powered means for operating the respective device falls below a safe level.

10. A transmitter-receiver set according to any one of clai.ms 1 to 9, wherein each of the devices comprises a radio transmitter/receiver and is tuned to complete a radio link by one receiving a signal emitted by the other.

11. A transmitter-receiver set according to cla 10 when appended to claim 6 wherein each of the devices is provided with actuating means operable by the respective one of the other individual and the responsible person to initiate operation of the alarm means and only the other device that is to be carried by the responsible person is provided with means for deactivating the alarm means.

12. A transmitter-receiver set according to clam 11, wherein the audible signal is unpleasant so that the other individual will be disinclined to activate it unnecessarily.

13. A transmitter-receiver set according to claim 11 or claim 12, wherein the other device that is to be carried by the responsible person also includes alarm means operable by operation of the tuned transmitter-receiver radio link to emit an alarm signal when the other individual operates the actuating means included in his unit.