GB2151116A - Signalling over power lines - Google Patents

Abstract

This is an electronic system designed to provide a measure of personal security to the aged or infirm. It is a semi-portable system where a transmitter can be plugged into any domestic mains power outlet and by superimposing a high frequency signal onto the mains, activate a receiver unit which is plugged into the mains somewhere in the near neighbourhood. The receiver would normally be situated facing out of a window or in some prominent place and upon activation would flash a bright red light, illuminating the word "HELP", while simultaneously operating an audible buzzer. Thus, the push of a bedside button can summon rapid help and since the system is not hard wired, it can be moved about within the home, or a neighbours home at will. <IMAGE>

Description

SPECIFICATION Aidalert This invention relates to an electronic system for use as an aid to personal security, primarilyforthe aged or infirm.

This system is intended to fill a gap in readily available, conventional security systems which are normally expensive, inflexible and in most cases, hard wired and non-portable. It is not intended as an automatic burglar alarm but rather as an inexpensive, moveable system to provide what can be described as "an electronic cryfor help". All conventional ideas in thefield of personal securityforthe elderly tend to be intheform of a hard wired system providing a bedside "panic button" orswitch operating a fixed outside light or in the case of the warden controlled sheltered housing, operating an alarm in the warden's premises.The system as described here is much more flexible, and while it would lead itself very easily to the sheltered housing situation it is primarily intended to provide a measure of security and peace of mind to infirm people who prefer to retain their independence and live in their own homes, quite often on their own.

The system comprises basically: two units, a transmitter (to provide a signal which will operate an alarm) and a receiver (to detectthissignal and display an alarm condition). These take the following formats: Thetransmitter is a small, easily hand-held box connected by conventional three core cable and three pin plug, into the domestic mains electricity supply.

Mounted on the box is a large push operated switch and two small indicator neon lights. One indicator glows whenever the unit is plugged into a live supply; afterthe push switch is operated, both flash in turn.

Thus, one indicator is used as an aid to finding the switch in the dark, and the second to confirm when the transmitter is operating i.e. the button has been pushed. All circuitryforthe transmitter is contained within this small box. The signal which is transmitted upon operation ofthe push switch is oftheform of a high frequency signal superimposed on top of the mains 240v 50 hz supply. This means that radiated electro-magnetic energy (i.e. radio or television interference) is minimal and no aerials etc. are required.

the he receiver is a larger box with a large illuminated red sign upon its front. This is positioned in an easily overlooked window, or other prominent position in the same, or closely adjoining house. It is connected also into the domestic mains supply, but has no external switch. This unit is left plugged in at all times.

In its normal quiescent condition only a small indicator light shows that power is on to the receiver. The receiver contains a simple amplifier and a frequency detector circuit (a phase-locked loop) so that if a nearby transmitter is activated, the receiver will pick its signal offthe mains supply, amplify it and if it is the correctfrequency, lock on to it. After a short delay (approximately one second) to eliminate the possibility of a spurious response, the front panel sign is brilliantly illuminated. This containsthe legend'HELP' in black letters. This flashes on and off at approximate- ly 0.5he all the time the transmitter is activated. A penetrating audible buzzer operates on and off simultaneously.The receiver unit also incorporates a lamp failure indicator which will glow even if the receiver is quiescent, in the event ofthe main lamp failing i.e. the bulb goes open-circuit.

The above description is intended as an operating description ofthe system. In practice variations in the circuitry of both transmitter and receiver can be used to providethefollowing options: 1. LOWCOSTUNIT A simple high stability, square wave output trans- mitter, operating between 40 khz and 100 khz (preset at manufacture) with single stage phase-lock loop receiver, operating illuminated sign and buzzer.

2. FOR MINIMUM INTERFERENCE A high stability, low distortion sine wave output transmitter, frequency range as above, operating an identical receiver.

Either ofthe above would be ideal in the private housing situation where the density of transmitter/ receivr pairs would be low and enough frequencies available to prevent confusion. For high density situations i.e. sheltered housing a third option would be possible.: 3. HIGH DENSITY OPTION Sine or square wave transmitter basically as above but frequency modulated by a second oscillator, driving a two phase-locked loop receiver. This would give a very high number of carrierimodulatorfrequen- cy permutations.

Afourth and lowest cost option would also be of use when intended to raise the alarm only within the house, such as the case of the ill child in bed wishing to signal its mother below: 4. BUZZER ONLY Option 1 or 2transmitter driving a low cost receiver of option 1 type, butwithoutthe illuminated sign. This would then operate only the audible warning at any point in the house.

In all cases, transmitter and receiver pairs are unconnected exceptthroughtheexisting mains wiring circuit, which also provides powerforthe devices. Furthermore, any number of receivers can be operated by one transmitter of the correct frequency, and vice versa.

The system is explained in more detail by means of the enclosed illustrations and circuits.

FIG. 1. Operation of the basic system.

FIG. 2. Circuit diagram-transmitter (square wave output).

FIG. 3. Circuit diagram-single phase-lock loop receiver.

Thesedescribethesystem in whatwould bethe normal form for domestic use. Prototypes have been operated satisfactorily. As previously stated, further options would include sine wave output transmitters, and a modulatedtransmitterwith matching receiver using two phase-lock loops. Inevitably, many different electronic circuits could be constructed, differing in some small detail, which would achieve the same aim, i.e. to operate an alarm using a mains carried signal.

Therefore, in the interests of simplicity, ci rcuits for one version only are included.

CIRCUIT DESCRIPTIONS FIG. 2. This shows a square wave output transmitter. Power is derived directly from the mains supply via a rectifier diode and dropper resister. This is then smoothed and zenerstabilised. i.c.l. is a 555 timer, used in the free-running astable mode giving a precise square wave output. This is then buffered by a transistor, to prevent inductive latch-up of the 555, and fed to a signal transformer. The signal is thus isolated bythetransformer, and then superimposed back onto the mains supply by a high quality isolating capacitor.

Asimple flasher circuit, comprising of: two miniature neon lamps, two resistors and a capacitor operates to showthe unit is switched on.

FIG. 3. Shows a single stage receiver. Power is again derived from the mains, this time via a transformer and bridge rectifier. A signal transformer identical with the one used in thetransmitter is used to filter and high frequencies off the mains supply. A 'CR'filter then removesanyunwanted harmonics and two diodes are used as an amplitude limiter. The signal is then fed to a 748 operational amplifier with a gain of ten, and then to a 567 phase-lock loop integrated circuit. If the signal frequency is within the bandwidth ofthe p.l.l. it will lock to it and pin 8 wiz be pulled down to ov. The 555 is again used in astable mode, at approximately 0.5 hz. When the 555 output is high, and the p.l.l. output low (i.e. locked) then the lamp and buzzer are operated via the three transistors in the drive circuit. Asmall light emitting diode is wired with a resistoracrossthe lamp, and will therefore illuminate via the resistor in parallel with the outputtransistor ifthe lamp should go open circuit.

Claims (15)

CLAIMS 1. This system comprises an inexpensive personal security aid which, whilst mains power dependant is not hard wired and is therefore semi-portable within the domestic environment. 2. The alarm is given by a brightly illuminated flashing sign plus an audibletoneemittedfrom a receiver which maybe positioned in such a manner that it is easily overlooked from the street, so thatthe word 'HELP' can be easily seen by passers-by. 3. Both transmitter and receiver are entirely self contained otherthan mains power, and require no external wiring or rials and no professional installation or settling up. 4. The alarm system is triggered by the operation, within the receiver, of a phase-lock loop decoder recognising a high frequency signal superimposed upon the mains supply bythe transmitter. This high frequency signal may be in the frequency range of 40 khzto 100 khz, sine, triangle or square wave, modulated or unmodulated. 5. The transmitter has a pair of indicator lights mounted in it, which flash upon activation, to give assurance to the person in need of help thatthe sytem has been activated. In the unactivated condition, one indicator glows steadily as an aid to being found in the dark. 6. The system istotallyindependantof,and unaffected by, ultrasonics, infrared and radio frequen cy radiations. New claims or amendments to claims filed on 25 September1984, superseding all claims New Claims:

1. An alarm system based on transmitting an electrical signal along domestic mains supply wiring, involving connecting transmitting and receiving devices in different physical locations between the live and neutral wires ofthe mains supply.

2. A system as claimed in Claim 1 where the electrical signal is at afrequencyof between 40 Khz and 100 Khz.

3. AsystemasinClalmsl and2wherethe electrical signal is of Sine wave, Square wave or Triangularwaveform.

4. A system where transmitters, operating at independant, fixed frequerraeswithirkthe range 40 Khz to 100 Khz may be switched on to transmit signals along the mains supply wiring

5. A system as in Claim 4where independant,fixed frequency receivers connected to the mains supply wiring come into operation independantly of one another upon receiving a signal transmitted at the correct frequency.

6. Asystem as in Claims 4 and 5 where a receiver is left plugged into the domestic mains, permanently switched on awaiting a signal from a transmitter of matching frequency.

7. A system as in Claims 4,5 and 6 where the transmitter is a small device easily moved from power pointto power point, plugged in and can then be operated by pressing a switch.

8. A system whereby an elderly or infirm person in distress can switch on a local transmitter, causing a remote receiverto operate an alarm for help.

9. Asystem as in Claim 8 where the receiver can be positioned in a prominent and easily seen place.

10. Asystem as in Claims 8 and 9 where the receiver, upon operation of a remote transmitter emits a loud noise and flashes on and off a brightly illuminated sign.

11. A system as in Claims 8,9 and 1 Owherethe receiverwill continue to give audible and visible alarms for as long as the remotetransmitter is left switched on.

12. Asystem wheretransmitter and receiver transmit and receive signals overthe mains supply, but are each isolated from the mains voltage by a capacitor and signal transformer.

13. A system whereby accurate operation ofthe receiver under adverse conditions is ensured by the use of a phase-lock loop detector system, driven by a high gain signal amplifierwith a signalfilterto remove unwanted harmonics.

14. Asystem wherethetransrnittergivesavisual assurance by means of flashing lights, that it has been activated.

15. A system where the receiver continuously monitorsthe condition of the visual alarm lamp and operates an indicator if the lamp should fail.