GB2053622A - Radio transmitter and alarm system - Google Patents

Abstract

A radio transmitter unit has a radio transmitter housed within an elongate, pen-like body. The radio transmitter is arranged to generate two dual tones, one selected from a plurality of low group frequencies suitably between 697 Hz and 941 Hz, and the other tone selected from high group frequencies between 1209 Hz and 1633 Hz. This enables a plurality of different radio transmitters to be coded differently so that a plurality of radio transmitters are individually identifiable in an anti-kidnap/security alarm system including a receiver operable to receive alarm signals from the transmitters.

Description

SPECIFICATION Radio transmitter and alarm system The invention relates to an improved radio transmitter unit and to a security alarm system incorporating such a unit.

Radio transmitter units per se are well known as for example exemplified by British Patent No.

1469509 which discloses a wristlet comprising a casing having a strap by which it may be mounted on the wrist of a user, the casing housing a radio transmitter having an actuator by which it may be operated and a removable timepiece.

Whilst such a wristlet unit is perfectly satisfactory for certain security alarm systems or distress signalling systems we believe there is a need for a radio transmitter unit more particularly suited for use by industrialists, bank officials and like persons for use as an anti-kidnap security alarm system or for use in remote control system applications.

According to the present invention a radio transmitter unit comprises a radio transmitter housed within a pen-like body, propelling pencil or pen torch. Preferably the pen-like body also includes operable writing means such as a replaceable ball point unit.

The power pack for the transmitter may be provided by a removable battery magazine receiving a plurality of mercury cells Preferably the radio transmitter comprises a tone generator, a radio frequency oscillator and an aerial, the output of the transmitter being matched to the impedance of the aerial by means of a stepup transformer. The aerial may be formed by the body of the pen.

In the preferred form of radio transmitter the step-up transformer includes a secondary winding of thinner wire than the primary winding, the primary winding being wound on top of the secondary winding.

The invention also includes an antikidnap/security alarm system comprising a radio transmitter and a receiver at a remote location operable to receive an alarm signal from the radio transmitter, the radio transmitter being housed within a pen-like body.

The radio transmitter preferably operates on 27.45 MHz, however, if desired, it may be arranged to operate on VHF.

The invention will now be described by way of example with reference to the accompanying drawings in which: Figure 1 is a side view of a preferred embodiment of radio transmitter unit in accordance with the invention; Figure 2 is an exploded view of the radio transmitter unit shown in Figure 1; and Figure 3 is a circuit diagram of the preferred circuitry.

In the drawings a radio transmitter unit is housed in a pen body 1, the pen body 1 also including a full length replaceable ball point refill 2. In this preferred embodiment the ball point is not retractable and therefore, when not in use, it is enclosed in a repiaceable tapered end cover 3 which frictionally fits over the corresponding tapered end 4 of the pen body 1.

At the other end of the pen body 1 there is a battery compartment 5 for the 9 volt power pack necessary for the operation of the radio transmitter. Preferably the power pack is in the form of a battery magazine 6 which holds seven mercury cells giving the required 9 volts. More specific details of a suitable battery magazine may be seen from our co-pending patent application No. 7906735.

The free end of the battery magazine has an activating switch button 7 by means of which the radio transmitter may be operated.

The pen body 1 constitutes the aerial for the transmitter package housed within and is provided with a L.E.D. transmission indicator 9. The pen body 1 preferably also includes a conventional clip 10 so that it may be readily retained in the user' pocket.

In Figure 3 the preferred circuitry of the transmitter is diagrammatically illustrated. The transmitter is an amplitude modulated micro miniature transmitter arranged to radiate two sequential dual frequency audio tones on a frequency of 27.45 Megahertz.

The circuit includes an integrated circuit dual tone multiple frequency tone generator AY--33-9410 the frequencies of which are determined by the 559.7 KHz nominal frequency MFO2 resonator and pre-programmed frequency dividers embodied within the AY-3-9410 device. The preferred nominal frequencies capable of being generated by such an arrangement are 697 Hz, 770 Hz, 852 Hz, 941 Hz, 1209 Hz, 1336 Hz, 1477 Hz and 1633 Hz. The actual frequencies selected are determined by the voltages impressed on pins 3, 4, 6, 7, 9, 10, 11 and 12 of the device. The device is normally arranged to generate two tones simultaneously, one selected from one of the four low group frequencies, i.e.

697 Hz to 941 Hz., the other selected from one of the four high group frequencies, i.e. 1209 Hz to 1 633 Hz. This dual tone output is applied to a conventional Sallen and Key unity gain low pass filter network comprising Q2, R3, R4, R5, R6, C5 and C6, this not only filters out unwanted harmonics and other spurii but acts Cs an amplitude modulated current source which in turn supplies audio frequency modulation to the 27.45 MHz 3rd overtone crystal oscillator comprising Q3, R7, R8, C7, L1, L2 and X1. L1 and L2 consist of a step up transformer which effectively matches the comparatively low output impedance of Q3 to the high impedance presented by the aerial AC which is principally capacitively reactive at 27.45 Megahertz.

A step-up transformer is used to obtain correct electrical matching since in a conventional transmitter the output has a higher impedance than the aerial whereas the reverse is the case in the present invention. In order to keep the dimensions of the transformer to a minimum one winding is made concentric to the other on a common former and by using thinner wire for the secondary winding the required step-up ratio can be obtained without increasing the former length beyond that required by the primary winding. In order to facilitate winding the secondary thin wire is wound on to the former first and the primary thicker wire is wound on top.

The circuit so far described with the exception of MFO2, X1, L1 and L2 is embodied within a custom built hybrid thick film integrated circuit.

The transmitter also includes a control circuit comprising IC1 and associated components whose function is to automatically generate three separate output control voltages after activation of the push switch SWl . These control voltages are sequenced to provide the necessary supply potential to power the tone generator, modulator and crystal oscillator previously described, and in addition provide a means of activating the AY-3-94l 0 such that it generates two sequential dual tone signals, the individuai frequencies of which have been previously determined by the position of the connecting links W1,2,3,4.

The operation of the control circuit is as follows - assume that prior to SW1 being depressed a 9 volt battery is connected as shown in the diagram, and a steady state condition has been established, then because of the low state potential existing on the inputs of the CMOS Norgate IC1A the output of this gate must be in its high state. It therefore follows that the outputs of Norgates IC 1 B, IC IC, 101 D are held in their low state and as a result Q1 is turned off and no potential is available to power IC2, Q2, Q3 etc.The oniy power of any consequence consumed by the entire circuit in this condition is that taken as a result of the small quiescent current required to operate 101, typically 1 uA. Because of this very low current drain the circuit can be left permanently connected to the battery without fear of any appreciable discharge occurring and hence there is no need for an additional switch to disconnect the battery.

if SW1 is now momentarily activated the impact of IC1A is forced into its high state and its output into its low state, as a result related inputs of IC1 B, IC1C and 101 D are now also in their low state and the output of 101 B is forced into its high state, thus turning on (21. This corresponding rise in emitter potential of Q1 is also temporarily impressed on the inputs of gate IT1 A via C1 and on the input of gate IC1C via C2.The corresponding outputs of gates IC1A and iC1C are thus respectively held and forced into their low states and hence subsequently the output potential of 101 D is forced into a high state. Due to the presence of R1 and R2 these input potentials decay exponentially with time. The time constant determined by Rl Cl is made approximately twice that of R2C2 such that the inputs of IC1A are held high for a period of time twice that of IC1 C.

When the input potential applied to gate IC1C can no longer sustain the output of IC1C in the low state the output of 1010 switches to its high state and the output of ICl D switches to its initial low state.Similarly when the input potential applied to gate IC1A can no longer sustain the output of IC1A in its low state the inputs to 101 B and IC1C are driven high and hence their corresponding outputs are forced low, this subsequently results in turning of (21. Any residual charge remaining on C1 and C2 is quickly dissipated in the load presented via D1 and D2 which momentarily conduct when the potential on Q1 falls to zero and the circuit returns to its initial steady state.

By routing the two sequential positive going pulses originating at the outputs of 101 D and 1010 during the above sequence via the appropriate pre-programmable links it is thus possible to generate two sequential dual tones from the eight available tone frequencies produced by the AY-3-941 0, providing a maximum capability of 256 combinations. This allows individual transmitters to be coded differently and thus several may be used without interaction on the same radio carrier frequency.

A LED indicator activated by the control circuit power output provides a means of indicating completion of the tone sequencers.

Although the circuit as described incorporates a mechanical initiating switch, if desired the circuit can be operated using a conductive or capacitive touch switch by separating the input gates of It 1 A as indicated. Alternatively the transmitter can be activated manually by disconnecting the positive electrodes of C1 and C2 from Q1 emitter and returning them to the positive supply, the circuit is then connected via SW1 to the battery. The switch SW1 is required to be kept depressed until the LED extinguishes. The latter arrangement may be preferred where it is desired to be able to release the activating button before completion of the alarm signal sequence and hence be able to abort an alarm call in the event of the button having been accidentally momentarily depressed.

A situation which would be irrevocable in the case of the automatic sequence being initiated as described in detail earlier.

l01,(21,Dl,D2,R4,R2,Rl0havebeen embodied in a custom built thick film integrated circuit, C1 and C2 having been purposely retained as discrete components to allow time of tone durations to be externally programmable if desired.

In an anti-kidnap or secuirty alarm system the radio transmitter unit would be used in conjunction with a radio receiver, adapted to give some form of visual or audible alarm when a signal is received from the transmitter or from one of a number of transmitters operating in the same system. The design of the receiver is conventional and therefore no details are provided herein.

Although the radio transmitter particularly described includes a ball point refill it is understood that the pen body may be inoperative or may include other writing means, such as felt tip or even a nib and ink.

We have therefore provided a radio transmitter unit comprising a radio transmitter housed within an elongate body, the radio transmitter being arranged to generate two sequential dual tones to allow identification of a particular transmitter.

The invention also includes an antikidnap/security alarm system comprising a plurality of separate radio transmitters, and a receiver at a remote location operable to receive alarm signals from said transmitters, the radio transmitters being operable to generate sequential tones of different frequencies from a plurality of available tone frequencies allowing respective transmitters to be coded differently for identification purposes.

The radio transmitter is preferably tubular so as to receive and surround a ball-point refill. Suitably the radio transmitter comprises an integrated circuit dual tone multiple frequency tone generator arranged to generate two sequential dual tones, a modulator, a radio frequency oscillator and an aerial, the output of the transmitter be matched to the high impedance presented by the aerial by means of a step-up transformer.

The transmitter may also include a control circuit operable an actuation of the transmitter to generate three separable output control voltages to provide the necessary supply potential to power the tone generator, modulator and oscillator.

Claims (12)

1. A radio transmitter unit comprising a body and a radio transmitter housed with the body, the radio transmitter being arranged to generate a plurality of different tones to allow identification of a particular transmitter.

2. A radio transmitter unit according to claim 1 wherein the radio transmitter is housed within a pen-like body.

3. A radio transmitter unit according to claim 2 wherein the pen-like body includes operable writing means.

4. A radio transmitter unit according to any one of the preceding claims wherein the transmitter is arranged to generate two sequential dual frequency audio tones.

5. A radio transmitter unit according to claim 4 wherein the tones are selected one from each of two different groups of a plurality of frequencies.

6. A radio transmitter unit according to claim 5 wherein one tone is selected from a plurality of low group frequencies between 697 Hz and 941 Hz, and the other tone is selected from a plurality of high group frequencies between 1209 Hz and 1633 hut.

7. A radio transmitter unit according to any of the preceding claims wherein the radio transmitter comprises a tone generator arranged to generate two sequential dual tones, a modulator, a radio frequency oscillator, and an aerial, the output of the transmitter being matched to the high impedance presented by the aerial by means of a step-up transformer.

8. A radio transmitter unit according to claim 7 wherein the aerial is formed by the unit body.

9. A radio transmitter unit according to claim 7 or 8 wherein the radio transmitter also includes a control circuit operable, on actuation of the transmitter to generate three separate output control voltages to provide the necessary supply potential to power the tone generator, modulator and oscillator.

10. A radio transmitter unit according to any one of the previous claims wherein the body is adapted to receive, as a power pack for the transmitter, a battery magazine including a plurality of mercury cells.

11. A radio transmitter unit according to any one of the preceding claims wherein the body is in the form of a pen and the radio transmitter is tubular so as to receive and surround a ball-point writing cartridge.

12. An anti-kidnap/security alarm system comprising a plurality of separate radio transmitters, and a receiver at a remote location operable to receive alarm signals from the transmitters, the radio transmitters being operable to generate sequential tones of different frequencies from a plurality of available frequencies allowing respective transmitters to be coded differently for identification purposes.

1 3. A radio transmitter unit substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.