GB2201819A - Intruder detection system - Google Patents

Abstract

The detection system comprises a microphone 15 for detecting predetermined sound characteristics such as breaking glass. When the sounds are detected, a monostable 18 is triggered into supplying a trigger signal to an alarm 20. The trigger signal also activates a transmitter 19, in the form of an astable, which supplies an enabling signal to remotely located alarms linked to an ac power supply line. The detection system also includes detector means which are remotely located and linked to the supply line. The detector means include transmitters 19 for transmitting an enabling signal in response to characteristic sounds detected at the remote location. The enabling signal is transmitted down the ac power supply line where it is received at a receiver 26. Receipt of the enabling signal at the receiver 26 causes the monostable 18 to generate the trigger signal, which in turn activates locally and remotely located alarms 20. Transmission of the enabling signal may be arranged to take place only during zero crossover of the current of the ac power supply (Figs 2 and 5, not shown). A sound discriminator may be provided for enhancing discrimination of detected sounds so that the chance of false alarm can be minimised, (Figs 1 and 4, not shown). <IMAGE>

Description

DETECTION SYSTEMS This invention relates to detection systems, and in particular to detection systems suitable for home security.

A known type of detection system for home security comprises a detector for detecting sounds which may be made by an unauthorised intruder, an alarm and a control unit for controlling the alarm in dependence upon signals generated by the detector. In such a system, a number of detectors may be linked by a specially installed cable to a central control unit which is situated at one location. This system has the disadvantage that the cable must be specially installed in the premises in which the security system is used.

It is possible that radio communication can be made between the detectors, the control unit and the alarms.

This is disadvantageous because it leads to increased costs in terms of hardware.

It is an aim of the present invention to provide a detection system which alleviates the aforementioned disadvantages by being relatively more simple to install while minimising hardware involved.

According to the present invention, there is provided a detection system comprising a detector means for detecting predetermined sound characteristics, alarm means, and control means for generating an enabling signal for activating the alarm means, in response to the predetermined sound detected by the detector means, wherein communication means is provided for enabling communication of the enabling signal between the control means and the detector means and/or the alarm means via an alternating current (ac) power supply line when the detector means and/or the alarm means are located remotely from the control means.

The detector means may comprise a plurality of detectors and the alarm means may comprise a plurality of alarms, wherein one of the detector means and/or alarm means is/are located at the control means. In the case where one of the detector means and/or the alarm means are located at the control means, the other detector means and/or alarm means are provide for remote location from the control means. Communication between the other detector means and/or alarm means exists via the ac power supply lines.

One or more of the detector means and alarm means, which are located remotely from the control means, may be in pairs to form unitary detector/alarm devices.

The alarm means may be in the form of an interface unit which is operative for connecting an electrical appliance to an ac supply, which electrical appliance is connected when the interface unit receives the enabling signal or a signal dependent thereon.

Alternatively, the alarm means may include a sounder, such as a bell, either alone or in addition to the interface unit.

The communication means preferably comprises a transmitter means for transmitting the enabling signal indicative of detection of predetermined sound characteristics, coupling means for coupling the transmitter to the ac power supply line so that the enabling signal can be transmitted down the supply line, and a receiver means for receiving the enabling signal transmitted down the supply line thereby to enable triggering of the alarm means.

The control means preferably comprises the transmitter means and the coupling means, for communicating detection of predetermined sound characteristics to a remote alarm means by way of the enabling signal, and the receiver means for receiving the enabling signal if supplied from one of the remotely located detector means.

According to the present invention, there is further provided a sound discriminator comprising a transducer for receiving sound signals and for producing electrical signals representative of the sound signals, conversion means for providing respective signals indicative of the amplitude and of the frequency of the received sound signals, and gating means for producing an indicator signal, in response to the respective signals, when the amplitude and frequeny of the received sound signals are each at one or more pre-selected frequencies and amplitudes.

The discriminator may include an amplifier means for amplifiying the electrical signals.

The conversion means preferably includes a frequency to voltage converter for generating a voltage representative of the frequency of the electrical signals, a voltage comparator or LED bar graph driver for providing respective output signals when the voltage lies between respective voltage ranges. and a second voltage comparator or LED bar graph driver for providing respective output signals when the frequency lies between respective frequency ranges.

The gating means may comprise a NAND gate having two inputs one of which is connected to one or more outputs of the first voltage comparator and the other one to one or more outputs of the second voltage comparator.

The gating means may comprise a plurality of NAND or AND gates in parallel so that the indicator signal can be produced when the amplitude and frequency are at more than one pre-selected amplitude and frequency.

The sound discriminator may be included in the detector means of the detection system so that by connecting the gating means to the outputs of the voltage comparators, which produce signals indicative of sound characteristics such as breaking glass or the like, the detector means can be used for generating an alarm trigger signal in, for example, a home security device.

According to the present invention, there is further provided apparatus for detecting zero crossover of an alternating current, thereby to enable signalling down an alternating current (ac) power supply line during the zero crossover, wherein zero crossover is defined by when the voltage of the ac supply is substantially equal to zero or within a predetermined range of zero, the apparatus comprising detection means responsive to the ac supply, when outside zero crossover to produce a signal, and switching means for switching between voltage levels in dependence upon the absence or presence of the signal thereby to indicate zero crossover.

The detection means preferably comprises a light-emitting diode (LED) for producing light signals when the ac supply is outside zero crossover. The switching means preferably comprises a light sensitive transistor device which is switched on (ie made to conduct) when light is received from the LED, and is switched off when no light is received from the LED.

The LED and transistor device are preferably coupled to form an opto-coupler device. The transistor device is preferably coupled between a voltage supply, so that a two voltage level output is provided at an output of the apparatus. In this case, one of the voltage levels corresponds to zero crossover and the other to non zero crossover.

The transmitter is preferably arranged to transmit the enabling signal during the time the output of the apparatus is at the voltage level corresponding to zero crossover.

The apparatus may be used in the control means and/or in one or more of the detectors of the detection system so that the communication, via the ac supply line, takes place during the zero crossover.

The invention will now be further described by way of example, with reference to the accompanying drawings, in which: Figure 1 is a block diagram of a sound discriminator according to one aspect of the present invention; Figure 2 shows a circuit diagram of an apparatus for detecting zero crossover of the voltage on an ac power supply line; Figure 3 shows a block diagram of a control means for a detection system according to another aspect of the present invention Figure 4 shows a circuit diagram of the control means of Figure 3; Figure 5 is a block diagram of a modified version of the control means of Figure 3; Figure 6 shows an alarm means for the detection system embodying the present invention; Figure 7 shows a circuit diagram of the alarm means of Figure 6; and Figure 8 shows a detector means for a detection system embodying the present invention.

Figure 1 shows a sound discriminator which comprises a microphone 1 which is sensitive to sound and is connected to an audio amplifier 2. The audio amplifier 2 provides an amplified electrical signal corresponding to sounds detected by the microphone 1, and feeds it to a frequency to voltage converter 3 and a LED bar graph driver 4. The LED bar graph driver has ten output stages and is operative for providing outputs at respective output stages, which correspond to the amplitude of the electrical signals received at the input of the driver 4.

The frequency to voltage converter 3 provides an output voltage which is dependent upon the frequency of the electrical signal amplified by the audio amplifier 2. This voltage is fed into a second LED bar graph driver 5 which also has ten output stages. A signal is provided at respective output stages when the input voltage lies between respective ranges.

The sound discriminator includes a gating means which, in this case, comprises a two input NAND gate 6.

One of the inputs of the NAND gate 6 is connected to an output of the driver 4 and the other input is connected to one of the outputs of the driver 5. By selecting the outputs to which the inputs of the NAND gate are connected, the NAND gate can be arranged to provide an output signal at an output terminal 7 when the sound sensed by the microphone 1 contains frequency components having a predetermined value and when the sound signals are of a predetermined amplitude.

The gating means may include further NAND sates or AND gates which may be connected in parallel with the NAND gate 6. In this way the sound discriminator can be arranged to produce an output at the output terminal 7 when the amplitude and frequency of the detected sound signals are at one of several predetermined levels.

Alternatively, the gating means may include a combination of gates such that an output signal is produced at the terminal 7 when the detected sound has desired predetermined characteristics.

Figure 2 shows a circuit diagram of an apparatus for detecting zero crossover of voltage on an alternating current (ac) power supply line. The apparatus is arranged for detecting when the voltage of the ac supply is substantially equal to or within a predetermined range of zero voltage and for generating a signal during the zero crossover thereby to indicate zero crossover.

In the example shown in Figure 2, a pair of opto-couplers 8 and 9 are connected across the live L and neutral N lines of an ac power supply line, and the outputs of the opto-couplers 8 and 9 are coupled between an output terminal 10 and a negative terminal 11 of a voltage supply. The output terminal 10 is connected to the positive terminal of the voltage supply via a resistor Roc.

The opto-couplers 8 and 9 each comprise a light-emitting diode (LED) optically coupled to a transistor device. The transistor is operative to switch on (ie become conducting) when light is produced by the LED during the time when the ac supply is not at zero crossover, and is operative to switch off (ie become non-conducting) when the LED produces no light during zero crossover. The ac supply gives rise to a pulsed waveform at the output terminal 10. The pulsed waveform has high level voltage VH when the transistor devices are switched on, thereby indicating non zero crossover. The waveform has a low level voltage VL, which may be zero volts, when the transistor devices are switched off thereby indicating zero crossover. Hence, zero crossover is indicated when the waveform at the output terminal 10 is at VL or zero volts.At normal mains frequency of 50 Hz, the output at the terminal 10 is in the form of a pulsed waveform having a period of 20 ms.

The output pulsed waveform of the apparatus can be used to trigger a transmitter or a receiver to transmit or receive enabling signals down an ac power supply line during the zero crossover range. In the present example, when the voltage at the output terminal 10 is VL, then this low voltage or zero voltage may be used to trigger an astable, so that the pulses produced by the astable can be transmitted down an ac power supply line. These pulses produced by the astable constitute the enabling signals in the detector system described below.

Figure 3 shows a block diagram of a control means for a detection system embodying the present invention.

The control means comprises a microphone 15 which is operative for sensing sound and for providing an electrical signal which is fed to an amplifier 16. The inherent circuit characteristics of the microphone 15 and the amplifier 16 may be adjusted by a selection of component values so that they may together perform sound discrimination. That is to say, so that the amplifier 16 provides an amplified output signal when the sound received by the microphone 15 has predetermined frequencies and amplitude.

The output of the amplifier 16 is fed to a delay 17 which is operative for delaying the progress of the amplified signal to a monostable 18 so that the alarm system is not activated during the short period of time from which the authorised alarm user sets the system and leaves the premises.

The amplified signal is then fed to the monostable 18 which is operative for providing a trigger signal on receipt of the amplified signal. The trigger signal is fed to a transmitter 19 which is coupled to the neutral N and earth E lines of an ac power supply line. The transmitter 19 comprises an astable which is operative for generating an enabling signal and for transmitting this signal down the ac supply line so that remotely situated alarm devices (not shown) can be activated.

The trigger signal is also fed to a local alarm 20, which may be in the form of a sounder, and to an isolating unit 21 which is operative for energising a local ac power supply socket 22. Any electrical appliance connected to the local ac power supply socket 22 can therefore be energised when the monostable 18 provides the trigger signal in response to sounds detected by the microphone 15.

A receiver 26 is provided in the control means for receiving enabling signals from an ac power supply line. The receiver 26 coupled to the neutral N and earth E of the power supply line and is operative for demodulating the enabling signals from the ac supply and feeding a trigger signal to the delay 17 in response to receipt of the enabling signals. The enabling signals received by the receiver 26 are sent from a remotely situated detector means. The alarm 20 and the isolating unit 21 can therefore be activated by sounds detected by the remotely situated detector means.

Figure 4 shows a circuit diagram of the control unit of Figure 3. The microphone 15 is coupled to an operational amplifier IC1 via a capacitor C1. The operational amplifier forms part of the amplifier 16.

The output of the operational amplifier IC1 is fed to the delay 17, which comprises a capacitor C3 and a resistor R5, via a capacitor C2.

When sound is sensed by the microphone 15, the electrical signals generated by the microphone are amplified by the operational amplifier IC1 to produce an amplified output. The values of the resistors R1, R2, R3 and R4, and capacitors C1 and C2 of the amplifier 16 may be adjusted so that a significant output is produced from the amplifier IC1 only when sounds of predetermined amplitude and frequency (ie sounds of breaking glass and the like) are sensed by the microphone 15.

When such predetermined sounds are sensed by the microphone 15, the output signal of the amplifier 16 is fed to the monostable 18.

The monostable 18, comprises gates Gl, G2 and G3 and is triggered when the amplified signal is received at one of the inputs of the gate G1. The monostable 18 is triggered for a period which is determined by the values of a capacitor C4 and a resistor R6 connected between the gates G2 and G3, and the low voltage rail 24 of the control means. When the monostable 18 has been triggered, further amplified signals from the operational amplifier IC1 are prevented from reaching the monostable by virtue of a field effector transistor Q1 which is switched off as the capacitor C5 is charged by the triggering of the monostable 18. This prevents the alarm from being re-triggered for a period dependent on the capacitance of the capacitor C5.

The trigger signal produced by the monostable 18 then activates an alarm in the form of a sounder 20, which is coupled to the output of the monostable 18 via a field effect transistor Q3 and a 3 input NAND gate G4. The trigger signal is also fed to a transistor T1 via a resister R10. This switches on the transistor T1 which in turn activates an opto-coupler triac IC4. The triac IC4 includes an LED which is coupled between the transistor T1 and the voltage supply rail Vcc of the control means. The switching on of the transistor T1 allows a current to flow from the voltage supply rail V to the low voltage rail 24 via the LED of the ce triac IC4, an alarm indicator L1 and a resistor Rill.

The alarm indicator L1 is in the form of an LED which emits light when current pauses therethrough.

Since current flows through the LED of the triac IC4, the LED emits light which switches on the triac of the triac IC4. This in turn switches on a triac TR1 which connects terminals 26 to the neutral N and live L terminals of a power supply. The opto-coupler triac IC4, the resistor R14 and the triac TR1 form the interface unit 21 of the control means. Hence, any electrical appliance connected across the socket 26 will be energised and will act as an alarm in addition to the sounder 20.

The control means also includes a power supply unit 25 for supplying power to the control means from the mains ac power supply. The power supply unit 25 comprises a mains transformer T2 to which is coupled a full wave bridge rectifier BR1 for providing a DC voltage supply to the supply rail Vcc The power supply unit 25 also includes smoothing capacitors C13, C14 and CiS and a regulator REG for regulating the voltage supply Vce The power supply unit 25 is connected between the Vcc rail and low voltage rail 24 of the control means.

The control unit is also provided with a power on indicator L2 which is connected across the supply voltage rail Vcc and the low voltage rail 24.

The transmitter 19 of the control means is also triggered by the trigger signal generated by the monostable 18. The trigger signal switches on a field effect transistor Q4 which triggers an astable comprising an integrated circuit IC3, resistor R12 and capacitors C7, C8 and C9. The astable is operative for providing a pulsed waveform of 150 KHz and for launching the waveform down the neutral N and earth E wires of an ac power supply line via capacitors C6 and C7. The capacitors C6 and C7 operate as isolation capacitors so as to protect the control means from the ac power supply. The frequency of the waveform generated by the astable is controlled by the values of the resistor R12 and the capacitor C6. The purpose of transmitting the waveform generated by the astable is to trigger any remotely located alarms by communicating with them via the ac power supply line.

The monostable 18 is triggered not only by the amplified electrical signals from the operational amplifier ICi. but also by signals received from the ac power supply line via the receiver 26. A remotely located detector (to be described below) may generate a waveform and launch the waveform down the ac supply line so that an alarm may be triggered when the waveform is received and demodulated by a control means. The receiver 26 of the control means is coupled to the ac supply line via an IF transformer T1 which comprises an internal capacitor for tuning the transformer. When the receiver 26 receives a waveform from a remotely located detector, the waveform is demodulated to provide a trigger signal which is fed to the field effect transistor Q1. The receiver 26 comprises a demodulator which has a pair of diodes D2 and D3, a capacitor Cli and C12, a resistor R15 and a zener diode Z1 connected as shown in Figure 4.

Figure 5 shows an alternative control means for a detection system embodying the present invention. This embodiment makes use of the sounds discriminator and the zero crossover apparatus described with reference to Figures 1 and 2. The sound discriminator 27 is inserted between the amplifier 16 and the delay 17 of the control means. Utilisation of the sound discriminator 27 has the advantage that the types of sound for which the detection system will respond can be adjusted for the desired purpose of the system. Additionally, the system can be more discriminating so that it responds to desired sounds and is less likely to create false alarms.

In this embodiment, the transmitter 19 and the receiver 26 are coupled to the ac supply line via a zero crossover unit 28 which is constructed in accordance with the embodiment described with reference to Figure 2. The use of the zero crossover 28 has the advantage that communication between remote detector means, alarm means and the control means can be effected over ac power supply lines with the minimum of interference.

Figure 6 shows an example of an alarm means which may be coupled to an ac power supply line at a location remote from the control means. The alarm can be coupled to the neutral N and earth E, or the live L and the neutral N terminals of an ac power supply line via terminals 30. A demodulator 31 receives pulses generated by the astable of the control means and demodulates them to generate a trigger signal which is fed to an isolating unit 32. In response to the received signals, the isolating unit switches on a power socket 33 which connects the mains ac power supply to any appliance connected thereto (not shown). The alarm shown in Figure 6 may be coupled to the mains terminals 30 via a zero crossover apparatus (not shown).

Figure 7 is a circuit diagram of the alarm device of Figure 6. The demodulator 31 is coupled across the neutral and earth terminals of the ac power supply so that when the waveform is received from the astable (that is, the transmitter 19) of the control means, a signal is generated by the demodulator circuit so as to switch on a field effect transistor Q10. The demodulator circuit comprises a transformer T10 which comprises a internal capacitor for tuning the transformer. The demodulator circuit also comprises a diode D10, capacitors C10 and Cli and resistors R10 and R11. The alarm derives power from the mains supply via a capacitor C12 which is in parallel with a resistor R12, and a resistor R13, a zener diode Z10, a diode D10 and capacitor C13.When the field effect transistor Q10 is switched on due to receipt by the alarm of the waveform transmitted by the astable of the control means, an opto-coupler triac IC5 is switched on, which in turn switches on the power supply across a load 35 which may be across the terminals of the power socket 33. The alarm is enabled for a time period lasting for the duration of receipt of the waveform from the astable. This duration may be, for example, two minutes and the duration is set by the values of resistor C6 and capacitor C4 of the monostable 18 of the control means.

Figure 8 shows a detector means for remote location of a detection system according to the present invention. The detector comprises a microphone 40 sensitive to sounds, and an amplifier 41 which produces an amplified electrical signal in response to sounds received by the microphone 40. A sounds discriminator 42 receives the amplified electrical signal and provides a trigger signal in response to characteristic sounds being sensed by the microphone 40. The trigger signal is then fed to a transmitter 43 which corresponds to the transmitter 19 of the control means. The transmitter 43, which may comprise an astable, is operative for generating a waveform for transmission down an ac power supply line via terminals 44.The detector means may be interfaced with the ac power supply line via a zero crossover unit (not shown) so that the waveform is transmitted during the zero crossover of the ac power supply.

A power supply 45, which may be similar in construction to the power supply 25, is included in the detector means for providing the transmitter 43 with power.

In an alternative embodiment of the present invention, the alarm means of Figure 6 may be combined with the detector means of Figure 8 to form a unitary detector/alarm device for location remote from the control means.

Various modifications may be made to the embodiments of the present invention without departing from the scope thereof. For example, the control means may only have a sounder alarm 20 and not a socket which is energised for energising an electrical appliance. In addition, the detection system may include only one sensor which is located with the control means and only remote alarms coupled to the control unit via the ac supply line. It is envisaged that various combinations of alarms and detectors may be used in conjunction with the control means, these combinations depending upon the desired working conditions of the detector system.

Claims (20)

1. A detection system comprising a detector means for detecting predetermined sound characteristics, alarm means, and control means for generating an enabling signal for activating the alarm means, in response to the predetermined sound detected by the detector means, wherein communication means is provided for enabling communication of the enabling signal between the control means and the detector means and/or the alarm means via an alternating current (ac) power supply line when the detector means and/or the alarm means are located remotely from the control means.

2. A detection system according to Claim 1, wherein the detector means comprises a plurality of detectors, and the alarm means comprises a plurality of alarms, wherein one of the detector means and/or alarm means is/are located at the control means, remaining detector means and/or alarm means being provided for remote location from the control means, communication between the control means and the remotely located detector means and/or alarm means existing via the ac power supply line.

3. A detection system according to Claim 1 or Claim 2, wherein one or more of the detector means and alarm means, which are located remotely from the control means, are arrange in pairs to form unitary detector/alarm devices.

4. A detection system according to Claim 1, Claim 2 or Claim 3, wherein the alarm means is in the form of an interface unit which is operative for connecting an electrical appliance to an ac supply, which electrical appliance is connected when the interface unit receives the enabling signal or a signal dependent thereon.

5. A detection system according to any one of the preceding Claims, wherein the alarm system includes a sounder.

6. A detection system according to any one of the preceding Claims, wherein the communication means comprises a transmitter means for transmitting the enabling signal, coupling means for coupling the transmitter to the ac power supply line so that the enabling signal can be transmitted down the supply line, and a receiver means for receiving the enabling signal transmitted down the supply line thereby to enable triggering of the alarm means.

7. A detection system according to Claim 6, wherein the control means comprises the transmitter means and the coupling means, for communicating detection of the predetermined sound characteristics to a locally and remotely located alarm means by way of the enabling signal, and the receiving means for receiving the enabling signal if supplied from one of the remotely located detector means.

8. A sound discriminator comprising a transducer for receiving sound signals and for producing electrical signals representative of the sound signals, conversion means for providing respective signals indicative of the amplitude and of the frequency of the received sound signals, and gating means for producing an indicator signal, in response to the respective signals, when the amplitude and frequency of the received sound signals are each at one or more pre-selected frequencies and amplitudes.

9. A sound discriminator according to Claim 8, wherein the discriminator includes an amplifier means for amplifying received signals.

10. A sound discriminator according to Claim 8 or Claim 9, wherein the conversion means includes a frequency voltage converter for generating a voltage representative of the frequency of the electrical signals, a voltage comparator or LED bar graph driver for providing respective output signals when the voltage lies between respective voltage ranges, and a second voltage comparater or LED bar graph driver for providing respective output signals when the frequency lies between respective frequency ranges.

11. A sound discriminator according to Claim 8, Claim 9 or Claim 10, wherein the gating means comprises a NAND gate having first and second inputs one of which is connected to one or more outputs of the first voltage comparator, and the other input being connected to one or more outputs of the second voltage comparator.

12. A sound discriminator according to Claim 8, Claim 9 or Claim 10, wherein the gating means comprises a plurality of NAND or AND gates in parallel so that the indicator signal can be produced when the amplitude and frequency are at more than one pre-selected amplitude and frequency.

13. A detection system according to any one of Claims 1 to 7, wherein the detector means includes a sound discriminator according to any one of Claims 8 to 12.

14. An apparatus for detecting zero crossover of an alternating current, thereby to enable signalling down an alternating current (ac) power supply line during the zero crossover, wherein zero crossover is defined by when the voltage of the ac supply is substantially equal to zero or within a predetermined range of zero, the apparatus comprising detection means responsive to the ac current when outside zero crossover, to produce a signal, and switching means for switching between voltage levels in dependence upon the absence or presence of the signal thereby to indicate zero crossover.

is. An apparatus according to Claim 14, wherein the detection means comprises a light-emitting diode (LED), and the switching means comprises a light sensitive transistor device, wherein when the ac supply in outside zero crossover, the LED produces light which causes the transistor device to switch on, and causes the transistor device to switch off when no light is received from the LED thereby indicating zero crossover.

16. An apparatus according to Claim 15, wherein the transistor device is coupled between a voltage supply so that a two voltage level output is provided at an output of the apparatus, whereby one voltage level indicates zero crossover and the other voltage level indicates non zero crossover.

17. A detection system according to any one of Claims 1 to 7, or Claim 13, wherein an apparatus according to Claim 14, Claim 15 or Claim 16 is included for enabling communication of the enabling signal to take place via the alternating current power supply line during zero crossover over.

18. A detection system substantially as herein described with reference to Figures 3, 4, or Figure 5 of the accompanying drawings.

19. A sound discriminator substantially as herein described with reference to Figure 1 of the accompanying drawings.

20. An apparatus for detecting zero crossover, substantially as herein described with reference to Figure 2 of the accompanying drawings.